阅读说明：本技术 超高强度耐候钢桩和结构底座 (Super-strength weather-resistant steel pile and structural base ) 是由 T.王 K.米什拉 B.H.博 于 2020-02-07 设计创作，主要内容包括：本文中公开在结构体例如诸如太阳能装置中作为钢底座使用的轻型超高强度耐候钢桩。该轻型超高强度耐候钢桩包括2.5mm或更小的厚度,其已经冷轧成形为具有多个侧壁的钢桩。该钢桩进一步包括700和1600MPa之间的屈服强度、1000和2100MPa之间的抗拉强度、以及1％和10％之间的伸长率。(Disclosed herein are lightweight ultra-high strength weathering steel piles for use as steel foundations in structures such as, for example, solar installations. The lightweight ultra-high strength weathering steel pile includes a thickness of 2.5mm or less that has been cold rolled into a steel pile having a plurality of sidewalls. The steel pile further comprises a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%.)

1. Super high strength resistant steel stake of waiting, it includes:

a plurality of sidewalls, each having a thickness of about 2.5mm or less and a composition comprising, by weight:

(i) between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and sedated for silicon containing less than 0.01% aluminum, and

(ii) the balance being iron and impurities resulting from the smelting;

the stake has a corrosion index of 6.0 or greater, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%.

2. The ultra-high strength, weathering-resistant steel pile of claim 1, wherein the thickness is about 2.0mm or less.

3. The ultra-high strength, weathering-resistant steel pile of claim 1, wherein the thickness is about 1.6mm or less.

4. The ultra-high strength, weathering steel pile of claim 1, cold formed from a steel strip, wherein the thickness is a hot rolled thickness with a reduction between 15% and 50% of the thickness.

5. The ultra-high strength, weathering steel pile of claim 4, wherein the hot rolled thickness is a high friction rolled thickness.

6. The ultra-high strength weathering steel stake of claim 1, being a hemmed C-channel shape, wherein the plurality of sidewalls are a web and one or more flanges.

7. The ultra-high strength, weathering steel pile of claim 1, which is corrugated C-channel shaped, wherein the plurality of sidewalls are webs and one or more flanges.

8. The ultra-high strength, weathering-resistant steel pile of claim 1, which is corrugated tube.

9. The ultra-high strength, weathering-resistant steel pile of claim 8, wherein the bellows is generally square.

10. The ultra-high strength, weathering-resistant steel pile of claim 8, wherein the bellows is generally rectangular.

11. The ultra-high strength, weathering steel pile of claim 1, wherein the plurality of sidewalls do not have a separately applied coating.

12. The ultra-high strength, weathering steel pile of claim 1, wherein the plurality of sidewalls are non-galvanized.

13. The ultra-high strength, weathering steel pile of claim 1, wherein at least one sidewall of the plurality of sidewalls includes one or more corrugations.

14. The ultra-high strength, weathering steel pile of claim 1, wherein each sidewall of the plurality of sidewalls includes one or more corrugations.

15. A solar device, comprising:

super high strength resistant steel stake of waiting, it includes:

a plurality of sidewalls, each having a thickness of about 2.5mm or less and a composition comprising:

(i) between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and sedated with silicon containing less than 0.01% aluminum, and

(ii) the balance being iron and impurities resulting from the smelting;

the ultra-high strength weathering steel stake has a corrosion index of 6.0 or greater, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%; and

wherein a portion of the length of the ultra-high strength weathering steel pile is forced into the ground and one or more solar cells are supported above the ground by the ultra-high strength weathering steel pile.

16. The solar device of claim 15, wherein the plurality of side walls are a web and one or more flanges and form a hemmed C-channel shape.

17. The solar device of claim 15, wherein the plurality of side walls are webs and one or more flanges and form a corrugated C-channel shape.

18. The solar device of claim 15, wherein the plurality of sidewalls form a bellows.

19. Super high strength resistant steel stake of waiting, it includes:

a plurality of sidewalls each having a thickness of about 2.5mm or less, a corrosion index of 6.0 or greater, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%.

20. The ultra-high strength, weathering steel pile of claim 19, having a composition comprising:

(i) between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, killed by silicon containing less than 0.01% aluminum, and an amount of nickel sufficient to shift the peritectic point away from the carbon region and/or to increase the transition temperature of the peritectic point to form a carbon alloy steel strip having a microstructure of at least 75% by volume martensite or martensite plus bainite, and

(ii) the balance being iron and impurities resulting from the smelting.

Technical Field

The present invention relates to a thin cast steel strip, a method for high friction rolling of a thin cast steel strip, and a steel product made from the thin cast steel strip and by the method.

Background

In a twin roll caster, molten metal is introduced between a pair of counter-rotating internally cooled casting rolls such that metal shells solidify on the moving roll surfaces and are brought together at the nip therebetween to produce a solidified strip product, which is delivered downwardly from the nip between the casting rolls. The term "nip" is used herein to refer to the general area: at this region, the casting rolls are closest together. Pouring molten metal from a ladle through a metal delivery system comprising a tundish and a core nozzle located above the nip to form a molten metal casting pool supported on the casting surfaces of the rolls above the nip and extending along the nip length. The casting pool is typically confined between refractory side plates or dams held in sliding engagement with the end surfaces of the rolls to dam the two ends of the casting pool against outflow.

To achieve the desired thickness, the thin steel strip may be passed through a rolling mill to hot roll the thin steel strip. When hot rolling, the thin steel strip is typically lubricated to reduce roll gap friction, which in turn reduces rolling load and roll wear, as well as providing a smoother surface finish. Lubrication is used to provide low friction conditions. The low friction condition is defined as a friction condition in which the friction coefficient (μ) of the roll gap is less than 0.20. After hot rolling, the thin steel strip undergoes a cooling process. Under low friction conditions, large prior austenite grain boundary pits have been observed on the hot rolled outer surface of the cooled thin steel strip after undergoing a pickling or acid etching process to remove the scale. Specifically, although thin steel strip tested using the dye penetrant technique appears defect-free, prior austenite grain boundaries are acid etched to form prior austenite grain boundary pits after acid pickling of the same thin steel strip. The etching may further cause defect phenomena to occur along the etched prior austenite grain boundaries and resulting pits. The resulting defects and spaces (which are more commonly referred to as spaces) can extend to a depth of at least 5 microns, and in some cases, to a depth of 5-10 microns.

Also suitable for use in the present disclosure is that the weathering steel is typically a high strength low alloy steel that is resistant to atmospheric corrosion. In the presence of moisture and air, low alloy steels oxidize at a rate that depends on the level of exposure to oxygen, moisture, and atmospheric contaminants for the metal surface. When steel oxidizes, it can form an oxide layer often referred to as rust. As the oxidation process proceeds, the oxide layer forms a barrier to the ingress of oxygen, moisture and contaminants, and the rate of rusting slows. In the case of weathering steels, the oxidation process is initiated in the same way, but the specific alloying elements in the steel produce a stable protective oxide layer that adheres to the base metal and is much less porous than oxide layers typically formed in non-weathering steels. The result is a much lower corrosion rate than would be found on ordinary non-weatherable structural steel.

Weathering steel is defined in ASTM A606High strength, low alloy, hot and cold rolled steel sheet with improved atmospheric corrosion resistance Standard Specification for Steel, plate and strip (Sheet) and Strip,High Strength,Low-Alloy,Hot Rolled and Cold Rolled with Improved Atmospheric Corrosion Resistance)。Weathering steels are supplied in two types: type 2, which contains at least 0.20% copper (minimum 0.18% Cu for product inspection) based on casting or melting analysis (heat analysis); and type 4, which contains additional alloying elements to provide a composition as provided by ASTM G101Standard for evaluating atmospheric corrosion resistance of low alloy steel South (Standard Guide for) Estimating the Atmospheric Corrosion Resistance of Low- Alloy Steels)A calculated corrosion index of at least 6.0 and provides a significantly better level of corrosion resistance than that of carbon steel with or without copper additions.

Prior to the present invention, weathering steels were typically limited to yield strengths less than 700MPa and tensile strengths less than 1000 MPa. Also, prior to the present invention, the strength properties of weathering steels were typically achieved by age hardening. U.S. patent No.10,174,398 (incorporated herein by reference) is an example of weathering steel achieved by age hardening.

Due to strength limitations and corrosion limitations, steels such as G100 or Gr70 steel are not well suited for many products such as piles or steel foundations forced into the ground such as used in solar installations and/or the highway industry such as support railings, signs, etc., for example. As used herein, a solar installation is a structure that supports solar cells on a solar farm (solar farm), such as a photovoltaic power plant designed to supply solar energy for use in an electrical grid or the like. The corrosive nature of groundwater and soil compositions requires material thicknesses of well over 2.5mm to maintain the required integrity for these structural components. Therefore, hot-dip galvanized steel is used in such applications instead. Hot dip galvanized steel is coated with zinc in order to improve the corrosion resistance of the underlying material properties. Therefore, it has been common practice in the solar industry for structural piles to rely on piles designed from galvanized 50ksi W6 or W8 i-beam steel. However, the zinc coating reacts negatively with groundwater and soil constituents, creating the potential for contamination thereof. The zinc coating also provides only a limited degree of protection. Once zinc oxidation degrades the zinc coating, metal oxidation still begins to degrade the structural integrity of the underlying material and/or requires increased material thickness to maintain the required integrity for these structural components.

Disclosure of Invention

Accordingly, the present disclosure sets out to provide a pile or steel base design made of lightweight ultra-high strength weathering steel that replaces the existing materials on which the pile or steel base relies. In particular, the present disclosure sets out to provide a lightweight pile or steel foundation having a shaped body (shape) made from thin cast metal strip. The shaped bodies of the present disclosure address increasing the strength and durability of the piles or steel foundations to withstand deformation from the force required to force the structural components into the ground and/or to act as external structures for the ground, e.g., structural components such as solar devices, guard rails, signs, and the like. In particular, the present disclosure addresses providing a pile or steel foundation cold rolled from a thin cast steel strip having a thickness of 2.5mm or less, 2.0mm or less, or 1.6mm or less or cast as a thin cast steel shape having a material thickness of 2.5mm or less, 2.0mm or less, or 1.6mm or less. The pile or steel foundation is manufactured from thin cast steel strip that has been cold rolled using one or more roll stands. In addition, through-holes, slots and/or spot welding heads may also be provided depending on the punch system, CNC plasma system and/or mill system, etc., as noted below. The present disclosure also addresses providing a pile or steel foundation cold rolled from thin cast steel strip that does not require a separately applied protective coating, such as a zinc coating for example, as provided on hot dip galvanized structural components. As used herein, a separately applied coating is a protective coating that is independent of the steel composition, which may be a surface protective agent. Examples of such separately applied protective coatings include zinc coatings, galvannealed coatings (e.g., hot-dip galvanized coatings), aluminum-silicon corrosion resistant coatings, and the like. More importantly, the pile or steel base of the present disclosure produces corrosion resistance without resorting to a separately applied coating, as set forth below. Inherently, by definition, the ultra-high strength weathering steels disclosed herein possess the requisite corrosion resistance that would otherwise be dependent on hot dip galvanization. Thus, the weathering steel of the present disclosure will not require or be provided with a zinc coating, a hot-dip galvanized coating, or the like, nor will it be applied with such a coating.

In one set of examples, the present disclosure sets forth providing a lightweight ultra-high strength weathering steel formed by shifting the peritectic point away from the carbon region and/or increasing the transition temperature of the peritectic point of the composition. Specifically, shifting the peritectic point away from the carbon region and/or increasing the transition temperature of the peritectic point of the composition appears to suppress defects and result in a high strength martensitic steel sheet that is defect free. In the present example, the addition of nickel is relied upon for this purpose, where the addition of nickel must be sufficient to shift the 'peritectic point' away from the carbon region that would otherwise be present in the same composition without the addition of nickel. Also disclosed are the following products made from the ultra-high strength weathering steel: it is of various shapes (as otherwise disclosed herein) and has improved strength properties not previously obtainable.

In another set of examples, the present disclosure addresses the elimination of prior austenite grain boundary pits, but maintains a smeared (smear) pattern. In this set of examples, the thin cast steel strip is subjected to high friction rolling conditions in which grain boundary pits form a floating pattern at least at the surface of the thin cast steel strip. In particular, the present example addresses the formation of a flattened pattern of prior austenite grain boundary pits when the prior austenite grain boundary pits are eliminated from the surface and the formability of the steel strip or steel product is improved. By improving the formability of the steel strip, previously unavailable products with various shapes (as otherwise disclosed herein) and with improved strength properties become available. This example is applicable not only to the aforementioned ultra-high strength weathering steels, but may additionally be applicable to martensitic steels, other weathering steels, and/or steel strips or products that exhibit prior austenite grain boundary pits.

In addition, however, in another set of examples, the present disclosure addresses the elimination of grain boundary pits and the smearing patterns formed therefrom. In this set of examples, the thin cast steel strip undergoes surface homogenization to eliminate the floating pattern. As a result, the thin cast steel strip has a surface that is free of not only prior austenite grain boundary pits, but also, in addition, a floating pattern produced as a result of the high friction rolling conditions to provide a thin cast steel strip surface having a surface roughness (Ra) of not more than 2.5 μm in some examples. This example is applicable not only to the aforementioned ultra-high strength weathering steels, but may additionally be applicable to martensitic steels, other weathering steels, and/or steel strips or products that exhibit prior austenite grain boundary pits.

Super-strength weather-resistant steel

First, a lightweight ultra-high strength weathering steel plate manufactured by the steps comprising: (a) preparing a molten steel melt comprising: (i) between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and sedated with silicon containing less than 0.01% aluminum, by weight, and (ii) the balance iron and impurities resulting from smelting; (b) at a molecular weight of more than 10.0MW/m²Is solidified into a steel sheet having a thickness of 2.5mm or less and is cooled to 1080 ℃ or less and Ar in a non-oxidizing atmosphere at a cooling rate of more than 15 ℃/s before rapid cooling and/or before hot rolling when hot rolling₃Above the temperature; and (c) rapidly cooling to form a steel sheet having a microstructure with at least 75% martensite by volume, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%.

Here and elsewhere in this disclosure, elongation means total elongation. By "rapid cooling" is meant cooling at a rate greater than 100 deg.c/s to between 100 and 200 deg.c. Rapid cooling of the nickel-added composition of the invention achieves steel strip up to more than 95% martensite phase. In one example, the rapid cooling forms a steel sheet having a microstructure with at least 95% martensite by volume. The addition of nickel must be sufficient to shift the 'peritectic point' away from the carbon region that would otherwise be present in the same composition without nickel added. Specifically, it is believed that the inclusion of nickel in the composition helps to shift the peritectic point away from the carbon region and/or increase the transition temperature of the peritectic point of the composition, which appears to suppress defects and results in a high strength martensitic steel sheet that is free of defects. In one example, the lightweight ultra-high strength weathering steel sheet may also be hot rolled to between 15% and 50% reduction before rapid cooling.

The carbon level in the steel sheet of the present invention is preferably not 0.20% or less to suppress peritectic cracking of the steel sheet. The addition of nickel is provided to further inhibit peritectic cracking of the steel sheet, but does so independent of relying on carbon composition alone. The effect of nickel on corrosion index is reflected in the following equation for determining the result of the corrosion index calculation: cu 26.01+ Ni 3.88+ Cr 1.2+ Si 1.49+ P17.28-Cu Ni 7.29-Ni P9.1-Cu 33.39 (wherein the elements are in weight percent).

The molten melt may be brought to a molecular weight of greater than 10.0MW/m²Is solidified into a steel sheet having a thickness of less than 2.5mm, and the sheet may be cooled to 1080 ℃ or below and Ar in a non-oxidizing atmosphere at a cooling rate of more than 15 ℃/s before rapid cooling and/or before hot rolling when hot rolling₃Above the temperature. The non-oxidizing atmosphere is an atmosphere of typically an inert gas such as nitrogen or argon or mixtures thereof, which contains less than about 5% by weight oxygen. In another example, the sheet may be cooled to below 1100 ℃ and Ar in a non-oxidizing atmosphere at a cooling rate of greater than 15 ℃/s prior to rapid cooling and/or prior to hot rolling when hot rolled₃Above the temperature.

In some examples, the martensite in the steel sheet may be formed from austenite having a grain size greater than 100 μm. In other examples, the martensite in the steel sheet may be formed of austenite having a grain size greater than 150 μm.

The steel sheet is rapidly cooled to form a steel sheet having a microstructure with at least 75% martensite, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%. In other examples, the steel sheet is rapidly cooled to form a steel sheet having a microstructure with at least 75% martensite plus bainite. In a particular example, the rapid cooling forms a steel sheet having a microstructure with at least 95% martensite plus bainite by volume.

In some examples, the steel sheet may be hot rolled to between 15% and 35% reduction before rapid cooling. In other examples, the steel sheet may be hot rolled to between 15% and 50% reduction before rapid cooling.

The molten steel used to make the ultra-high strength weathering steel plate is silicon killed (i.e., silicon deoxidized) comprising between 0.10% and 0.50% by weight silicon. The steel sheet may further include less than 0.008% aluminum or less than 0.006% aluminum by weight. The molten melt may have a free oxygen content of between 5 and 70ppm or between 5 and 60 ppm. The steel sheet may have a total oxygen content of greater than 50 ppm. The inclusions comprise MnOSiO typically with 50% of them being less than 5 μm in size₂And has the potential to enhance the microstructure evolution (evolution) and hence the mechanical properties of the tape.

Also discloses a manufacturing method of the light ultrahigh-strength weather-resistant steel plate, which comprises the following steps: (a) preparing a molten steel melt comprising: (i) between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and sedated with silicon containing less than 0.01% aluminum, by weight, and (ii) the balance iron and impurities resulting from smelting; (b) forming the molten melt into a casting pool supported on the casting surfaces of a pair of cooled casting rolls having a nip therebetween; (c) counter-rotating the casting rolls and at greater than 10.0MW/m²Is solidified, thereby producing a steel sheet having a thickness of less than 2.5mm, and the sheet is cooled to below 1080 ℃ and Ar before rapid cooling and/or when hot rolled in a non-oxidizing atmosphere before hot rolling at a cooling rate of more than 15 ℃/s₃Above temperature, and (d) rapidly cooling to form a composition having at least 75% horseMicrostructure of the matrix, yield strength between 700 and 1600MPa, tensile strength between 1000 and 2100MPa and elongation between 1% and 10%. In a particular example, the rapid cooling forms a steel sheet having a microstructure with at least 95% martensite plus bainite by volume. The sheet may be cooled to below 1100 ℃ and Ar before rapid cooling and/or when hot rolled in a non-oxidizing atmosphere prior to hot rolling at a cooling rate of greater than 15 ℃/s₃Above the temperature. The steel sheet composition cannot be made to have a carbon level below 0.20% because it does not contribute to peritectic cracking of the steel sheet. In one example, a lightweight ultra-high strength weathering steel sheet may be hot rolled to between 15% and 50% reduction before rapid cooling.

Further, the method for manufacturing the lightweight ultra-high strength weathering steel plate may include the step of tempering the steel plate at a temperature between 150 ℃ and 250 ℃ for 2-6 hours.

The molten melt may have a free oxygen content of between 5 and 70ppm or between 5 and 60 ppm. The steel sheet may have a total oxygen content of greater than 50 ppm. The molten melt may be brought to a molecular weight of greater than 10.0MW/m²Is solidified into a steel sheet having a thickness of less than 2.5mm, and is cooled to 1080 ℃ or less and Ar is reduced in a non-oxidizing atmosphere at a cooling rate of more than 15 ℃/s before rapid cooling and/or before hot rolling in a non-oxidizing atmosphere when hot rolling₃Above the temperature. In another example, the sheet may be cooled to below 1100 ℃ and Ar in a non-oxidizing atmosphere at a cooling rate of greater than 15 ℃/s prior to rapid cooling and/or prior to hot rolling when hot rolled₃Above the temperature.

In some embodiments, the martensite in the steel sheet may be derived from austenite having a grain size greater than 100 μm. In other embodiments, the martensite in the steel sheet may be derived from austenite having a grain size greater than 150 μm.

The method of manufacturing a light-weight ultra-high strength weathering steel sheet may further include hot rolling the steel sheet to a reduction ratio of between 15% and 35%, and then rapidly cooling to form a steel sheet having a microstructure with at least 75% by volume martensite, a yield strength of between 700 and 1600MPa, a tensile strength of between 1000 and 2100MPa, and an elongation of between 1% and 10%. In some embodiments, the method of manufacturing a light-weight ultra-high strength steel sheet may further comprise hot rolling the steel sheet to a reduction between 15% and 50%, and then rapidly cooling to form a steel sheet having a microstructure with at least 75% by volume martensite plus bainite, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%. Further, a method of manufacturing a hot rolled light ultra high strength steel sheet may include hot rolling the steel sheet to a reduction between 15% and 35% and then rapidly cooling to form a steel sheet having a microstructure with at least 75% by volume martensite plus bainite, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%. In the above specific example, the hot rolled steel sheet and then rapidly cooled forms a steel sheet having a microstructure having at least 95% martensite plus bainite by volume.

Also disclosed is a steel pile comprising one or more flanges (flanges) and a web (web) cold rolled from a carbon alloy steel sheet having the composition: which comprises, by weight, between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and is silicon killed containing less than 0.01% aluminum, wherein the carbon alloy steel sheet has a microstructure with at least 75% by volume martensite or martensite plus bainite, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, an elongation between 1% and 10%, and has a corrosion index of 6.0 or more.

High-friction rolled high-strength weathering steel

Second, in one set of examples, thin cast carbon alloy steel strip having an as cast thickness of less than or equal to 2.5mm is presently disclosed. These examples are applicable not only to the aforementioned ultra-high strength weathering steels, but may additionally be applicable to martensitic steels, other weathering steels, and/or steel strips or products that exhibit prior austenite grain boundary pits. The carbon alloy thin cast steel strip may include between 0.20% and 0.40% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and is silicon killed with less than 0.01% aluminum, and the balance iron and impurities resulting from smelting, by weight. After high friction hot rolling, the thickness of the carbon alloy thin cast steel strip is reduced by 15-50% of the as-cast thickness. The hot rolled steel strip includes a pair of opposed high friction hot rolled surfaces that are substantially free, or free of prior austenite grain boundary pits and have a troweled pattern. In some embodiments, the steel strip comprises a microstructure having at least 75% martensite or at least 75% martensite plus bainite by volume, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%. In some examples, the steel strip is a weathering steel having a corrosion index of 6.0 or greater.

In some examples, the pair of opposing high friction hot rolled surfaces are substantially free of prior austenite grain boundary pits. In some examples, the pair of opposing high friction hot rolled surfaces are substantially free of prior austenite grain boundary pits.

Also disclosed is a method of making a hot rolled carbon alloy steel strip comprising by weight between 0.20% and 0.40% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and killed by silicon containing less than 0.01% aluminum, with the balance being iron and impurities resulting from smelting, the method comprising the steps of:

(a) preparing a molten steel melt;

(b) forming the melt into a casting pool supported on the casting surfaces of a pair of cooled casting rolls having a nip therebetween;

(c) counter-rotating the casting rolls and melting the melt at greater than 10.0MW/m²Is solidified into a steel strip having a thickness of less than or equal to 2.5mm delivered downwardly from the nip, and the strip is subjected to a non-oxidizing atmosphere to a temperature greater than or equal toCooling to below 1080 ℃ at a cooling rate of 15 ℃/s and Ar₃Above the temperature;

(d) high friction hot rolling a thin cast steel strip to a hot rolled thickness at a reduction between 15% and 50% of the as-cast thickness produces a hot rolled steel strip that is substantially free, or free of prior austenite grain boundary pits and has a screeded pattern.

The high friction hot rolled thin cast steel strip having a smear pattern that is substantially free, or free of prior austenite grain boundary pits may be a weathering steel having a corrosion index of 6.0 or greater. Moreover, the high friction hot rolled steel strip may comprise a microstructure having at least 75% martensite or at least 75% martensite plus bainite by volume, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%.

High friction rolled high strength martensitic steel

Third, in yet another set of examples, a thin cast carbon alloy steel strip is presently disclosed that includes a pair of opposed high friction hot rolled surfaces that have been surface homogenized while having been high friction rolled. These inventive examples are applicable not only to the ultra-high strength weathering steels previously described, but may additionally be applicable to martensitic steels, other weathering steels, and/or steel strips or products that exhibit prior austenite grain boundary pits. The pair of opposing high friction hot rolled surfaces, when surface homogenized, are free of smoothed grain boundary pits previously formed as a result of the high friction rolling process. In some embodiments, the carbon alloy thin cast steel strip may further include a microstructure having at least 75% martensite or at least 75% martensite plus bainite by volume and a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%. In some embodiments, the steel strip includes a microstructure having at least 90% martensite or at least 90% martensite plus bainite by volume. In some embodiments, the steel strip of claim 1 comprises a microstructure having at least 95% martensite or at least 95% martensite plus bainite by volume.

Exemplary homogenized steel strip within the scope of the present disclosure may include, by weight, between 0.20% and 0.40% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and silicon killed with less than 0.01% aluminum, and the balance iron and impurities resulting from melting.

A method of making a hot rolled carbon alloy steel strip is also disclosed. The method may comprise the steps of:

(a) preparing a molten steel melt;

(b) forming the melt into a casting pool supported on the casting surfaces of a pair of cooled casting rolls having a nip therebetween;

(c) counter-rotating the casting rolls and melting the melt at greater than 10.0MW/m²Is solidified into a steel strip having a thickness of less than or equal to 2.5mm delivered downwards from the nip, and the strip is cooled to below 1080 ℃ and Ar in a non-oxidizing atmosphere at a cooling rate of greater than 15 ℃/s₃Above the temperature;

(d) high friction rolling the thin cast steel strip to a hot rolled thickness at a reduction between 15% and 50% of the as-cast thickness to produce a hot rolled steel strip free of prior austenite grain boundary pits and having a trowelled pattern; and

(e) the high friction hot rolled steel strip is surface homogenized to eliminate the floating pattern.

The high friction hot rolled homogenized thin cast steel strip may comprise a microstructure having at least 75% martensite or at least 75% martensite plus bainite by volume, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%, thereby providing a high strength martensitic steel. Further, the high friction hot rolled homogenized steel strip may include between 0.20% and 0.40% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and is silicon killed with less than 0.01% aluminum, and the balance iron and impurities resulting from smelting, by weight.

The present disclosure further sets forth how ultra-high strength weathering steel piles may rely on thin cast steel strip as described, each of the above compositions, and/or the above properties. Specifically, in one example, the ultra-high strength, weathering-resistant steel pile includes a plurality of sidewalls, each sidewall having a thickness of about 2.5mm or less, 2.0mm or less, or 1.6mm or less. The pile may be formed from steel strip. In particular, the pile may be formed from cast steel strip. The pile may be formed from hot rolled as-cast steel strip. Also, the stake may be cold rolled. The pile may have a composition comprising: between 0.20% and 0.35% by weight of carbon, less than 1.0% of chromium, between 0.7% and 2.0% of manganese, between 0.10% and 0.50% of silicon, between 0.1% and 1.0% of copper, less than or equal to 0.12% of niobium, less than 0.5% of molybdenum, between 0.5% and 1.5% of nickel, and sedated for silicon containing less than 0.01% of aluminium, and the balance being iron and impurities resulting from smelting. The stake may further include or have a corrosion index of 6.0 or greater, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and/or an elongation between 1% and 10%.

In some examples, the composition of the stakes includes an amount of nickel sufficient to shift the peritectic point away from the carbon region and/or increase the transformation temperature of the peritectic point to form a carbon alloy steel strip having a microstructure of at least 75% by volume martensite or martensite plus bainite. In some examples, the pile may be formed from a steel strip, wherein the as-cast thickness of the steel strip is hot rolled to a hot rolled thickness having a reduction between 15% and 50% of the as-cast thickness. The hot rolled material may be high friction rolled to provide a high friction rolled thickness.

Various features and shapes of the ultra-high strength weathering steel are further described herein. These features may be provided in combination or independently of each other. In some examples, the ultra-high strength weathering steel piles may be C-channel shaped with the plurality of side walls being webs and one or more flanges. More specifically, the ultra-high strength weathering steel piles may be hemmed C-channel shaped and/or corrugated C-channel shaped, with the plurality of sidewalls being webs and one or more flanges. In some examples, the ultra-high strength, weathering-resistant steel pile may be a tube, with a plurality of sidewalls forming the tube. More specifically, the ultra-high strength weathering steel pile may be a square tube or a rectangular tube. Further, the ultra-high strength, weathering-resistant steel pile may be a generally square or rectangular tube, wherein one or more of the plurality of sidewalls further includes one or more corrugations. The plurality of sidewalls do not include a separately applied coating. The plurality of sidewalls are non-galvanized. At least one of the plurality of sidewalls may be a bead. More specifically, one or more flanges of the hemmed C channel shape can be a single hemmed. The first and second layers of each single turn of the one or more flanges may be secured (fastened) together by one or more spot welding heads. The first layer of one or more flanges may be transferred to the second layer by a tear drop transfer. Additionally or alternatively, at least one of the plurality of sidewalls may include one or more corrugations. In some examples, the C-channel shaped web may include one or more corrugations. Additionally or alternatively, one or more flanges of the C-channel shape may include one or more corrugations.

In some examples, the ultra-high strength, weathering-resistant steel piles include a thickness of about 2.5mm or less, 2.0mm or less, or 1.6mm or less. The pile may be formed from thin cast steel strip that is cold rolled to form a steel pile having a plurality of sidewalls with a corrosion index of 6.0 or greater. The ultra-high strength weathering steel stake may further include a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%. The composition of the ultra-high strength weathering steel stake may include an amount of nickel sufficient to shift the peritectic point away from the carbon region and/or increase the transformation temperature of the peritectic point to form a carbon alloy steel strip having a microstructure of at least 75% by volume martensite or martensite plus bainite. In one example, an ultra-high strength, weathering-resistant steel pile has a material composition comprising: between 0.20% and 0.35% by weight of carbon, less than 1.0% of chromium, between 0.7% and 2.0% of manganese, between 0.10% and 0.50% of silicon, between 0.1% and 1.0% of copper, less than or equal to 0.12% of niobium, less than 0.5% of molybdenum, between 0.5% and 1.5% of nickel, and sedated for silicon containing less than 0.01% of aluminium, and the balance being iron and impurities resulting from smelting.

Solar energy devices are also discussed herein. The solar energy device may include an ultra-high strength, weathering-resistant steel pile including a plurality of sidewalls, each sidewall having a thickness of about 2.5mm or less, 2.0mm or less, or 1.6mm or less. An ultra-high strength weathering steel stake for a solar energy device may include, by weight, between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and sedated for silicon containing less than 0.01% aluminum, with the balance being iron and impurities resulting from melting. The ultra-high strength weathering steel stake of the solar device may include a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%. In this example, a partial length of the ultra-high strength weathering steel pile is forced into the ground and one or more solar cells are supported above the ground by the ultra-high strength weathering steel pile. Accordingly, the ultra-high strength weathering steel piles of solar devices may additionally or alternatively have many of the features as described above and in the remainder of this disclosure.

Drawings

The present invention may be more fully described and explained with reference to the accompanying drawings, in which:

FIG. 1 illustrates a strip casting plant with hot rolling mill and coiler on the lead-in line.

FIG. 2 illustrates details of a twin roll strip caster.

Fig. 3 is a photomicrograph of a steel sheet having a microstructure with at least 75% martensite.

Fig. 4 is a phase diagram illustrating the effect of nickel in shifting the peritectic point away from the carbon region.

Fig. 5 is a flow diagram of a process according to one or more aspects of the present disclosure.

Fig. 6 is an image showing the surface of a steel strip hot-rolled under high friction conditions after a surface uniformization process.

FIG. 7 is an image showing the surface of a hot rolled steel strip having a trowelled pattern subjected to high friction conditions that has not been homogenized.

Fig. 8 is a friction coefficient model chart created for measuring the friction coefficient for a specific pair of work rolls, the rolling mill specific force, and the corresponding reduction ratio.

Fig. 9 is a Continuous Cooling Transformation (CCT) diagram of steel.

Fig. 10 is a cross section of a hemmed C channel shaped body of a pile or steel foundation cold rolled from a thin cast steel strip according to one or more aspects of the present disclosure.

Fig. 11 is a perspective view of the pile or steel foundation of fig. 10 cold rolled from a thin cast steel strip according to one or more aspects of the present disclosure.

FIG. 12 is a cross-section of a corrugated C channel shaped body of a pile or steel foundation cold rolled from thin cast steel strip according to one or more aspects of the present disclosure.

FIG. 13 is a cross-section of a corrugated C channel shaped body of a pile or steel foundation cold rolled from thin cast steel strip according to one or more aspects of the present disclosure.

Fig. 14 is a cross-section of a square tube with rigid components of a steel pile or steel base cold rolled from thin cast steel strip according to one or more aspects of the present disclosure.

Fig. 15 is a cross-section of a rectangular tube with rigid components of a steel pile or steel foundation cold rolled from a thin cast steel strip according to one or more aspects of the present disclosure.

Fig. 16 is a graph illustrating test results of a prior art hot-dip galvanized (G324) steel material having a representative image thereof.

Fig. 17 is a graph illustrating the test results of the (G100) steel material of the related art having a representative image thereof.

Fig. 18 is a graph illustrating the test results of the (Gr70) steel material of the related art having a representative image thereof.

Fig. 19 is a graph illustrating test results of the lightweight ultra-high strength weathering steel pile material of the present disclosure.

Detailed Description

Lightweight ultra-high strength weathering steel panels are described herein in one example. The lightweight ultra-high strength weathering steel plate may be made from a molten melt. The molten melt may be cast by twin roll castingAnd (6) machining. In one example, the lightweight ultra-high strength weathering steel plate may be made by the steps comprising: (a) preparing a molten steel melt comprising: (i) between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and sedated with silicon containing less than 0.01% aluminum, and (ii) the balance iron and impurities resulting from smelting, by weight; (b) at a molecular weight of more than 10.0MW/m²Is solidified, thereby producing a steel sheet having a thickness of less than 2.5mm, and is cooled to 1080 ℃ or below and Ar in a non-oxidizing atmosphere at a cooling rate of more than 15 ℃/s before rapid cooling and/or before hot rolling when hot rolling₃Above the temperature; and (c) rapidly cooling to form a steel sheet having a microstructure possessing at least 75% by volume martensite or martensite plus bainite, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%. In one example, the lightweight ultra-high strength weathering steel sheet may also be hot rolled to between 15% and 50% reduction before rapid cooling. The sheet may be cooled to below 1100 ℃ and Ar before rapid cooling and/or when hot rolled in a non-oxidizing atmosphere before hot rolling at a cooling rate of greater than 15 ℃/s₃Above the temperature. Ar (Ar)₃The temperature is the temperature at which austenite begins to transform to ferrite during cooling. That is, Ar₃The temperature is the austenite transformation point. In various examples, the nickel shifts the peritectic point away from the carbon region and/or increases the transition temperature of the peritectic point of the steel sheet composition to provide a defect-free steel sheet. The effect of nickel on corrosion index is reflected in the following equation for determining the result of the corrosion index calculation: cu 26.01+ Ni 3.88+ Cr 1.2+ Si 1.49+ P17.28-Cu Ni 7.29-Ni P9.1-Cu 33.39 (wherein the elements are in weight percent).

Also described herein is a thin cast steel strip having a hot rolled exterior side surface as follows: the exterior side surface is characterized by being substantially free, or free of prior austenite grain boundary pits, but having a slick, or elongated surface structure, such as in the example of high friction rolled high strength martensitic steel. Methods or processes for making the same are also described herein. These examples are applicable not only to the aforementioned ultra-high strength weathering steels, but may additionally be applicable to martensitic steels, other weathering steels, and/or steel strips or products that exhibit prior austenite grain boundary pits.

Further described herein is a thin steel strip having a hot rolled outer side surface as follows: the exterior side surface is characterized by being substantially free, or free of prior austenite grain boundary pits and free of a slick, or elongated, surface structure, such as in the example of high friction rolled high strength weathering steel. Methods or processes for making the same are also described herein. These examples are applicable not only to the aforementioned ultra-high strength weathering steels, but may additionally be applicable to martensitic steels, other weathering steels, and/or steel strips or products having prior austenite grain boundary pits.

As used herein, predominantly free means that less than 50% of each opposing hot rolled exterior side surface contains prior austenite grain boundaries or prior austenite grain boundary pits after acid etching (pickling). By at least substantially free of all prior austenite grain boundaries or prior austenite grain boundary pits is meant that 10% or less of each opposing hot rolled exterior side surface contains prior austenite grain boundary pits or prior austenite grain boundary pits after acid etching (pickling). The pits form etched grain boundary pits after acid etching (also known as pickling) making the prior austenite grain boundaries visible at 250x magnification. In other cases, free means that each opposing hot rolled outer side surface is free (i.e., completely free) of prior austenite grain boundary pits, including being free of any prior austenite grain boundary pits after acid etching. It is emphasized that prior austenite grain boundaries may still be present within the material of the hot rolled strip, where grain boundary pits and spaces on the surface have been by the techniques described herein (e.g., where hot rolling is at a)_r3A temperature above the temperature occurs using a roll gap friction coefficient equal to or greater than 0.20).

Fig. 1 and 2 illustrate successive components of a strip casting machine for continuously casting steel strip or plate according to the invention. Twin roll caster 11 continuously produces cast steel strip 12 which is transported in a transport path 10 through a guide table 13 to a pinch roll stand 14 having pinch rolls 14A. The strip immediately after leaving the pinch roll stand 14 is passed to a hot rolling mill 16 having a pair of work rolls 16A and back rolls 16B, where the cast strip is hot rolled to a desired reduction thickness in the hot rolling mill 16. The hot rolled strip is conveyed onto a run-out table 17 where the strip enters an intensive cooling section via water jets 18 (or other suitable means). The rolled and cooled strip is then passed through a pinch roll stand 20 comprising a pair of pinch rolls 20A and then to a coiler 19.

As shown in FIG. 2, twin roll caster 11 comprises a main machine frame 21 which supports a pair of laterally positioned casting rolls 22 having casting surfaces 22A. Molten metal is supplied during a casting operation from a ladle (not shown) to a tundish 23, through a refractory brick sheath (shroud)24 to a distributor or removable tundish 25, and then from the distributor or removable tundish 25 through a metal delivery nozzle 26 to between the casting rolls 22 above a nip 27. The molten metal delivered between the casting rolls 22 forms a casting pool 30 supported on the casting rolls above the nip. The casting pool 30 is bounded at the ends of the casting rolls by a pair of side dams or plates 28, which side dams or plates 28 may be urged against the ends of the casting rolls by a pair of pushers (not shown) comprising hydraulic cylinder units (not shown) connected to side plate holders. The upper surface of the casting pool 30 (commonly referred to as the "meniscus" type level) is generally above the lower end of the delivery nozzle so that the lower end of the delivery nozzle is submerged within the casting pool 30. The casting rolls 22 are internally water cooled so that the shells solidify on the moving casting roll surfaces as they pass through the casting pool and are brought together between them at the nip 27 to produce the cast strip 12 which is delivered downwardly from the nip between the casting rolls.

The twin roll caster may be of the type illustrated and described in considerable detail in U.S. Pat. Nos. 5,184,668, 5,277,243, 5,488,988 and/or U.S. patent application No.12/050,987 published as U.S. publication No.2009/0236068A 1. For appropriate constructional details of twin roll casters that may be used in the present examples, reference is made to these patents and publications, which are incorporated by reference.

After the thin steel strip is formed (cast) using any desired process, such as the strip casting process described above in connection with fig. 1 and 2, the strip may be hot rolled and cooled to form the desired thin steel strip having opposing hot rolled exterior side surfaces that are at least predominantly free, substantially free, or free of prior austenite grain boundary pits. As illustrated in fig. 1, the in-line hot rolling mill 16 provides 15% to 50% reduction of the strip from the caster. On the run-out table 17, the cooling may include water cooling sections for controlling the cooling rate of the austenitic transformation to achieve the desired microstructure and material properties.

Fig. 3 shows a micrograph of a steel sheet having a microstructure with at least 75% martensite from prior austenite having a grain size of at least 100 μm. In some examples, the steel sheet is rapidly cooled to form a steel sheet having a microstructure with at least 90% by volume martensite or martensite and bainite. In another example, the steel sheet is rapidly cooled to form a steel sheet having a microstructure with at least 95% by volume martensite or martensite and bainite. In each of these examples, the steel sheet may additionally be hot rolled to between 15% and 50% reduction before rapid cooling.

Referring back to fig. 1, the hot box 15 is illustrated. After the strip has been formed, it may be transferred to an environmentally controlled box, referred to as hot box 15, where it continues to be passively cooled before being hot rolled to its final gauge by hot rolling mill 16, as shown in FIG. 1. An environmentally controlled box with a protective atmosphere is maintained until entry into the hot rolling mill 16. Within the hot box, the strip is moved on a guide table 13 to a pinch roll stand 14. In examples of the present disclosure, undesirable thermal etching may occur in the hot box 15. Based on whether the thermal etching has taken place in the hot box or not, the strip may be hot rolled under high friction rolling conditions based on parameters defined in more detail below.

In certain instances, the method of forming a thin steel strip further comprises hot rolling the thin steel strip using a pair of counter-rotating work rolls that produce an increased coefficient of friction (μ) sufficient to produce the following counter-hot rolled exterior side surfaces of the thin steel strip: the exterior side surface is characterized by being predominantly free, substantially free, or free of prior austenite grain boundary pits, and by having a cross-sectional area comparable to that of a cross-sectional area of a steel sheet passing under shearThe plastic deformation forms a surface smoothing pattern related to the elongated surface structures. In some cases, the pair of opposing work rolls is at A_r3A temperature above the temperature produces a coefficient of friction (μ) equal to or greater than 0.20, 0.25, 0.268, or 0.27, each with or without lubrication. It is recognized that the coefficient of friction may be increased by increasing the surface roughness of the work roll surface, eliminating the use of any lubrication, reducing the amount of lubrication used, and/or selecting the particular type of lubrication to be used. Other mechanisms for increasing the coefficient of friction, as may be known to one of ordinary skill, may be used in addition to or separately from the previously described mechanisms. The above process is generally referred to herein as high friction rolling.

As mentioned above, it is recognized that high friction rolling may be achieved by increasing the surface roughness of the surface of one or more work rolls. This is generally referred to herein as work roll surface texturing. The work roll surface texturing can be varied and measured by various parameters used in high friction rolling applications. For example, the average roughness (Ra) of the work roll profile may provide a reference point for generating the coefficient of friction necessary for the roll gap as noted above in the examples. To achieve high friction rolling by way of work roll surface texturing, in one example, the freshly ground and textured work roll may have an Ra between 2.5 μm and 7.0 μm. The newly ground and textured work roll is more generally referred to herein as a new work roll. In a specific example, the new work roll may have an Ra of between 3.18 μm and 4.0 μm. The roughness average of the new work roll may decrease during use or upon wear. Thus, the high friction rolling conditions described above can also be produced depending on the used work rolls, as long as the used work rolls have an Ra between 2.0 μm and 4.0 μm in one example. In a specific example, the used work rolls may have an Ra between 1.74 μm and 3.0 μm while still achieving the high friction rolling conditions described above.

Additionally or alternatively, the mean surface roughness depth (Rz) of the work roll profile may also be relied upon as an indicator to achieve the high friction rolling conditions described above. The new work roll may have an Rz of between 20 μm and 41 μm. In one particular example, the new work roll may have an Rz of between 21.90 μm and 28.32 μm. The high friction rolling conditions for the above may in one example be dependent on the used work rolls as long as they maintain an Rz of between 10 μm and 20 μm before out of service. In one particular example, the used work roll has an Rz of between 13.90 μm and 20.16 μm before out of service.

In addition, however, the above parameters may be further defined by the average spacing (Sm) between peaks throughout the profile. The new work rolls relied upon to create high friction rolling conditions may include between 90 μm and 150 μm of Sm. In one particular example, the new work rolls relied upon to produce high friction rolling conditions include Sm between 96 and 141 μm. The high friction rolling conditions for the above may in one example be dependent on the used work rolls as long as they maintain Sm between 115 μm and 165 μm.

Table 1 below illustrates test data measured as a function of position on the work rolls for work roll surface texturing to produce high friction rolling conditions and further provides a comparison between new work roll parameters and used work roll parameters before the used work rolls are going out of service:

"OS Qtr" is operator side quarter; and "Avg" is an average value

"Ctr" is the center of the band; and "Avg" is an average value

The DS Qtr is a drive side quarter; and "Avg" is an average value

Determining whether high friction rolling is suitable for use in examples of the present disclosure may depend on whether hot etching has occurred in the hot box. Hot etching is a side effect or consequence of the casting process that exposes prior austenite grain boundary pits at the surface of the steel strip. As noted above, prior austenite grain boundary pits may tend to cause the aforementioned defect phenomenon along etched prior austenite grain boundary pits upon further acid etching. Specifically, when the steel is exposed to high temperatures, such as a hot box, in an inert atmosphere, the hot etching reveals prior austenite grain boundary pits in the steel strip by forming grooves at the intersections between the prior austenite grain boundary pits and the surface. These grooves make the prior austenite grain boundary pits visible at the surface. Thus, the present examples of the process identify high friction rolling as the step that produces the desired steel properties when hot etched in a hot box. Regardless of the presence or absence of hot etching and evidence of prior austenite grain boundary pitting, high friction rolling can be provided to increase recrystallization of the thin steel strip.

FIG. 5 is a flow chart illustrating a process for applying high friction rolling and/or surface homogenization. In this example, determining whether a steel strip or steel product should undergo high friction rolling depends on whether undesirable thermal etching has occurred in the hot box 510. If hot etching has not occurred in the hot box, high friction rolling is not needed and not undertaken to (1) smooth out prior austenite grain boundary pits, (2) increase formability of steel products, such as ultra-high strength weathering steels, for example, and/or (3) improve hydrogen resistance (H)₂) Embrittlement. However, even if thermal etching has not occurred in the hot box, high friction rolling may still be pursued in order to achieve recrystallization 520 or to produce a microstructure as otherwise disclosed herein. If hot etching has occurred in hot box 510, high friction rolling 530 is performed to (1) smooth prior austenite grain boundary pits, (2) increase formability of the ultra-high strength weathering steel, and/or (3) improve hydrogen (H) resistance by removing prior austenite grain boundary pits and eliminating weak points formed as defects after 120 hours corrosion testing₂) Embrittlement. In one example of the present disclosure, an ultra-high strength weathering steel 550 having a trowelled pattern is produced. In another embodiment of the present disclosure, the trowel pattern is removed, thereby improving the pitting corrosion resistance 540, such as that required in automotive applications. Such an embodiment yields, for example, a high strength martensitic steel560. The floating pattern can be removed by means of a surface homogenization process. Fig. 5 additionally illustrates a surface homogenization process 540. The applicability of the surface homogenization process is discussed in more detail below with respect to the present disclosure. Representative examples are also discussed in more detail below.

Super-strength weather-resistant steel

In some embodiments, the lightweight ultra-high strength weathering steel sheet may be made from a molten melt. The molten melt may be processed through a twin roll caster. In one example, the lightweight ultra-high strength weathering steel plate may be made by the steps comprising: (a) preparing a molten steel melt comprising: (i) between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and sedated with silicon containing less than 0.01% aluminum, by weight, and (ii) the balance iron and impurities resulting from smelting; (b) at a molecular weight of more than 10.0MW/m²Is solidified, thereby producing a steel sheet having a thickness of less than 2.5mm and is cooled to 1080 ℃ or below and Ar in a non-oxidizing atmosphere at a cooling rate of more than 15 ℃/s before rapid cooling and/or before hot rolling when hot rolling₃Above the temperature; and (c) rapidly cooling to form a steel sheet having a microstructure possessing at least 75% by volume martensite or martensite plus bainite, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%. In one example, the lightweight ultra-high strength weathering steel sheet may also be hot rolled to between 15% and 50% reduction before rapid cooling. The sheet may be cooled to below 1100 ℃ and Ar before rapid cooling and/or when hot rolled in a non-oxidizing atmosphere prior to hot rolling at a cooling rate of greater than 15 ℃/s₃Above the temperature. Ar (Ar)₃The temperature is the temperature at which austenite begins to transform to ferrite during cooling. That is, Ar₃The temperature is the austenite transformation point. In various examples, the nickel shifts the peritectic point away from the carbon region and/or increases the transition temperature of the peritectic point of the steel sheet composition to provide a defect-free steel sheet. Shadow of nickel on corrosion indexThe response is in the following equation for determining the corrosion index calculation: cu 26.01+ Ni 3.88+ Cr 1.2+ Si 1.49+ P17.28-Cu Ni 7.29-Ni P9.1-Cu 33.39 (wherein the elements are in weight percent).

Examples of the steel sheet of the present invention provide for the addition of nickel to further prevent peritectic cracking while maintaining or improving hardenability. In particular, between 0.5% and 1.5% by weight of nickel is added. The addition of nickel is believed to prevent warping of the belt shell caused by the volume change of the peritectic zone during phase transformation on the casting rolls and thus enhance uniform heat transfer during belt solidification. It is believed that the addition of nickel shifts the peritectic point away from the carbon zone and/or raises the transition temperature of the peritectic point of the composition to form a defect free steel sheet. The phase diagram of fig. 4 illustrates this. Specifically, the phase diagram of fig. 4 illustrates the effect of each of 0.0 wt% nickel 100, 0.2 wt% nickel 110, and 0.4 wt% nickel 120. As illustrated in FIG. 4, the peritectic point P is found at the intersection of the liquid + delta phase 90, the delta + gamma phase 50, and the liquid + gamma phase 60₁₀₀、P₁₁₀And P₁₂₀A lower mass percentage of carbon (C) is transferred to a higher temperature with increasing nickel. Otherwise, the carbon content makes the steel strip susceptible to defects at lower temperatures in steel strips with high yield strength. The addition of nickel shifts the peritectic point away from the carbon zone and/or raises the transformation temperature of the peritectic point of the steel sheet to provide a defect-free martensitic steel strip with high yield strength.

The effect of nickel on corrosion index is reflected in the following equation for determining the result of the corrosion index calculation: cu 26.01+ Ni 3.88+ Cr 1.2+ Si 1.49+ P17.28-Cu Ni 7.29-Ni P9.1-Cu 33.39 (wherein the elements are in weight percent).

Table 2 below shows several composition examples of the lightweight ultra-high strength weathering steel sheet of the present disclosure.

TABLE 2

In Table 2, LecoN is the weight percent nitrogen (N) measured₂) And CEAWS isMeasured weight percent Carbon Equivalent (CE).

Other elements that are dependent on hardenability produce the opposite effect by moving the peritectic point closer to the carbon region. Such elements include chromium and molybdenum which are dependent for increased hardenability but ultimately lead to peritectic cracking. By the addition of nickel, hardenability is improved and peritectic cracking is reduced to provide a fully quenched martensitic grade steel strip with high strength.

In the compositions of the present invention, the addition of nickel may be combined with a limited amount of chromium and/or molybdenum, as described herein. As a result, nickel mitigates any effect these hardening elements may have in creating peritectic cracking. However, in one example, the additional nickel is not combined with the intentional addition of boron. Boron was intentionally added at 5ppm or more. That is, in one example, the addition of nickel will be used in combination with substantially no boron or less than 5ppm boron. In addition, the lightweight ultra-high strength weathering steel plate may be manufactured by further tempering the steel plate at a temperature between 150 ℃ and 250 ℃ for 2-6 hours. Tempering the steel sheet provides improved elongation with minimal loss of strength. For example, after tempering as described herein, a steel sheet having a yield strength of 1250MPa, a tensile strength of 1600MPa, and an elongation of 2% is improved to a yield strength of 1250MPa, a tensile strength of 1525MPa, and an elongation of 5%.

The lightweight ultra-high strength weathering steel plate may be silicon killed, containing less than 0.008% aluminum or less than 0.006% aluminum by weight. The molten melt may have a free oxygen content of between 5 and 70ppm or between 5 and 60 ppm. The steel sheet may have a total oxygen content of greater than 50 ppm. The inclusions comprise MnOSiO typically with 50% of them being less than 5 μm in size₂And has the potential to enhance the microstructure evolution and hence the mechanical properties of the strip.

The molten melt may be greater than 10.0MW/m²Is solidified into a steel sheet having a thickness of less than 2.5mm, and is cooled to 1080 ℃ or less and Ar in a non-oxidizing atmosphere at a cooling rate of more than 15 ℃/s₃Above the temperature. The non-oxidizing atmosphere is an atmosphere of typically an inert gas such as nitrogen or argon or mixtures thereof, which contains less than about 5% by weight oxygen.

In some embodiments, the martensite in the steel sheet may be formed of austenite having a grain size greater than 100 μm. In other embodiments, the martensite in the steel sheet may be formed of austenite having a grain size greater than 150 μm. At a power of more than 10MW/m²The rapid solidification of the heat flux enables the production of austenite grain sizes in response to controlled cooling to achieve defect-free sheet manufacture.

The steel sheet may additionally be hot rolled to between 15% and 50% reduction and then rapidly cooled to form a steel sheet having a microstructure with at least 75% martensite plus bainite, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%. Further, the steel sheet may be hot rolled to a reduction between 15% and 35% and then rapidly cooled to form a steel sheet having a microstructure with at least 75% martensite plus bainite, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%. In one example, a steel sheet is hot rolled to between 15% and 50% reduction and then rapidly cooled to form a steel sheet having a microstructure with at least 90% by volume martensite or martensite and bainite. In even yet another example, the steel sheet is hot rolled to a reduction of between 15% and 50% and then rapidly cooled to form a steel sheet having a microstructure with at least 95% by volume martensite or martensite and bainite.

Many products can be manufactured from light-weight ultra-high strength weathering ("UHSW") steel sheets of the type described herein. One example of a product that can be made from lightweight ultra-high strength weathering steel sheet includes steel piles. More specifically, the pile or foundation for a solar device is an example of the use of a product made of lightweight ultra-high strength weathering steel plate. As used herein, a solar device, as used herein, is a structure that supports solar cells on a solar farm, such as a photovoltaic power plant designed to supply solar energy for use in an electrical grid or the like. The highway industry has similar needs for example for bases such as those used to support guardrails, signs and the like. The pile or steel foundation may be manufactured from thin cast steel strip that has been cold rolled using one or more roll stands. In addition, through-hole, slotted, continuous, partial, and/or spot welding may also be provided depending on the punch system, CNC plasma system, and/or mill system, etc., as noted below.

In one example, the steel pile includes a web and one or more flanges cold rolled from the various carbon alloy steel strips described above. Fig. 10 and 12-15 illustrate cross-sectional examples of UHSW steel piles formed by cold rolling thin cast steel strip. In fig. 10, a UHSW piling 100 is C-channel shaped including a web 110, a first flange 120, and a second flange 130, and is an illustrative example referred to herein as a hemmed C-channel shaped or NXW piling. Height H of web 110 along steel pile 100₁₀₀Extends and is transitioned at a curved transition joint 140 into the first flange 120 at the first end 112 of the web 100. The web 110 is additionally transitioned into a second flange 130 at a second end 113 of the web 110 opposite the first end 112 of the web 110 at a curved transition joint 150. In this example, each curved adapter 140, 150 has a respective radius R₁₄₀、R₁₅₀Each forming an arc extending 90 degrees. Thus, each flange 120, 130 is perpendicular to the web 110. In fig. 10, the first flange 120 is parallel to and opposite the second flange 130. Both the first flange 120 and the second flange 130 are from the web 110 and in the same direction along the width W of the steel pile 100₁₀₀And (4) extending.

In fig. 10, the first flange 120 and the second flange 130 include a crimping structure. With particular reference to the first flange 120, the crimping structure is a single crimp comprising a first layer 122 and a second layer 124, wherein the first layer 122 is bent from the bend adapter 140 over the width W of the piling 100₁₀₀Extending in the direction of the tear drop adapter 160. The teardrop adapter 160 is an open bead that is adapted to a closed bead. Width W of teardrop adapter 160 in steel pile₁₀₀And height H₁₀₀Proceeding in both directions towards the opposite second flange 130 towards the interior of the steel pile 100. In one embodiment, the first layer 122 is formed to have a width W with respect to the steel pile width₁₀₀Angle lambda of 45 degrees in direction₁₆₀To the first leg 162 of the teardrop adapter 160. The tear-drop adapter 160 travels through an arc from the first leg 162 to the second tier 124. The second layer 124 is positioned to the secondThe outer side of one layer 122 at the closing bead. The second layer 124 abuts the first layer 122 and runs parallel to the first layer 122. In fig. 10, the second layer 124 is along the width W of the steel pile₁₀₀Extending to the curved adapter 140. In addition, the teardrop adapter 160 is maintained at a piling height H defined by the curled portions of the respective first and second flanges 120, 130₁₀₀And (4) the following steps.

Still referring to fig. 10, and similar to but opposite the first flange 120, the second flange 130 includes a crimping structure. The hemmed configuration of the second flange includes a first layer 132 and a second layer 134, wherein the first layer 132 extends from the bent adapter 150 across the width W of the piling 100₁₀₀Extending in a direction up to the teardrop adapter 170. The tear drop adapter 170 is an open bead that is adapted to a closed bead as follows. Width W of teardrop adapter 170 in steel pile₁₀₀And height H₁₀₀Proceeding in both directions towards the opposite first flange 120 towards the interior of the steel pile 100. In one embodiment, first layer 132 is formed to correspond to the width W of the steel pile₁₀₀The 45 degree angle of direction travels to the first leg 172 of the tear drop adapter 170. The teardrop adapter 170 travels through an arc from the first leg 172 to the second tier 134. The second layer 134 is positioned outboard of the first layer 132 at the closure bead. The second layer 134 abuts the first layer 132 and runs parallel to the first layer. In fig. 10, the second layer 134 is along the width W of the steel pile₁₀₀To curved adapter 150. The tear-drop adapter 170 is maintained at a piling height H defined by the curled portions of the respective first and second flanges 120, 130₁₀₀And (4) the following steps. In the example of fig. 10, the thickness T of the steel plate forming the steel pile 100 is 0.062 inches (") (1.575 mm). Thus, the bead portion was 0.124 "(3.15 mm). In some examples, the thickness of the steel sheet forming the steel pile 100 may be 2mm or less. In other examples, the thickness of the steel sheet forming the steel pile 100 may be 2.5mm or less.

Fig. 11 illustrates a perspective view of the steel pile 100 of fig. 10 at the first flange 120. The steel pile 100 has a length L₁₀₀Wherein the web 110, the first flange 120 and the second flange 130 are along the length L of the steel pile₁₀₀And (4) extending. One or more spot welding heads 180 may be disposed at the first flange 120 and the second flange 130 to maintain the first flange 120 and the second flange 130The abutting relationship of the layers 122, 132 with the second layers 124, 134, respectively (as illustrated in fig. 10). The spot welding head 180 may be along the length L of the steel pile₁₀₀Spaced 6 "to 24". The spot welding head 180 may also be positioned relative to the width W of the steel pile₁₀₀Centered or with respect to the width W of the pile₁₀₀And (4) biasing. Further, the spot welding heads 180 may be uniformly spaced or the spacing of the spot welding heads 180 may be along the length L of the steel pile₁₀₀And (4) changing. In one example, the first point welding head is 0.50 "from the first end 102 of the steel pile and along the remaining steel pile length L₁₀Evenly spaced at 13.22 ". The spot welding head 180 may also be positioned relative to the width W of the steel pile₁₀₀Centered or with respect to the width W of the pile₁₀₀An offset, or a combination thereof. In one example, the spot welds are positioned 2.68 "from the outermost tangent of the respective tear-drop adapters 160, 170.

Still referring to fig. 11, the first flange 120 and/or the second flange 130 may additionally include one or more through-holes 190 and/or one or more slots 192. The through-holes 190 and slots 192 may be provided for securing items to the steel piles, such as solar installations, highway guardrails, and the like, for example. One or more through-holes 190 and/or one or more slots 192 may additionally or alternatively be provided in the web 110. This perspective view also represents a perspective view of the profile of the steel pile of fig. 12-15.

In the example UHSW piling 100 of fig. 10-11, the UHSW piling includes a constant thickness T. The constant thickness may be less than or equal to 2.5mm, less than or equal to 2.0mm, or less than or equal to 1.6 mm. A constant thickness T is maintained by each of the features described above. More specifically, the constant thickness is the product of cold forming a UHSW piling from a steel sheet (result). In one example, the steel plate width is 50 ". The profile of the C-channel of fig. 11 results from a steel plate of the width and then has a total cross-sectional material length of 50 "or less. More specifically, the total cross-sectional material length may be one-half or one-third of the width of the steel sheet, at the hem flange, maintaining the material thickness T on each layer. However, by abutting the first and second layers 122, 132, 124, 134 and while the material thickness is maintained at T, the flange thickness has doubled, as shown by T in FIG. 10_X2And (4) reflecting. In FIG. 10, the flange thickness T is doubled_X2Extending from the tear-drop adapter 160To the curved adapter 140. In the example of fig. 10, the steel pile height H₁₀₀Is greater than the width W of the steel pile₁₀₀. In the example of fig. 10, the steel pile 100 has a height H with respect to bisecting the steel pile 100₁₀₀Is symmetrical about the axis. Typical UHSW piling of fig. 10 may be, for example, C-channel shapes (with or without corrugations) of 6x4, 6x6, 8x6, 8x8, 10x8, 10x10, 12x8, 12x10, 12x12, 14x10, 14x12, 14x14 (in inches), any value in between, and so forth.

Turning now to fig. 12, a C-channel UHSW piling 200 is illustrated. The C-channel shape includes a web 210, a first flange 220, and a second flange 230, and is an illustrative example of what is referred to herein as a corrugated C-channel shape or NCW pile. Web 210 is along the height H of the steel pile 200₂₀₀Extends and transitions at curved adapter 240 to first flange 220 at first end 211. The web 210 is also transitioned to a second flange 230 at the second end 212 at a curved transition joint 250. In this example, each curved adapter 240, 250 has a respective radius R₂₄₀、R₂₅₀. Each radius R₂₄₀、R₂₅₀Forming an arc of greater than 90 degrees. Also, each flange 220, 230 remains generally perpendicular to the web 210. The web 210 further includes one or more web corrugations. In fig. 12, the web 210 includes a first web corrugation 213 and a second web corrugation 214. To form the web corrugations, the outside surface 215 of the web 210 is at the pile width W₂₀₀Is directionally offset from one or more inboard surfaces 216 of web 210. Both the outside surface 215 and the inside surfaces 216 are at the pile height H₂₀₀In an orientation wherein the outer side surface 215 and each inner side surface 216 are perpendicular to the first flange 220 and/or the second flange 230. Outboard surface 215 and each inboard surface 216 form a majority of web 200 such that the web is said to remain generally perpendicular to first flange 220 and/or second flange 230. Each curved adapter 240, 250 extends from the respective first flange 220 or second flange 230 along a respective radius R₂₄₀、R₂₅₀The formed arc extends. As noted above, the arc of each curved adapter 240, 250 extends at greater than 90 degrees to form a web corrugation at the respective inboard surface 216, which is then transferred to the outboard surface 215. Outboard surface 215 is at a height H relative to the steel pile on web 210₂₀₀CenteringA bit. In FIG. 12, the radius R is shown₂₄₀Circular arc formed and with radius R₂₅₀The formed circular arcs are respectively further included in the height H of the steel pile₂₀₀A tangent line oriented in alignment with the outboard surface 215.

The web corrugations 213, 214 of the UHSW piling of fig. 12 each include a surface perpendicular to the first flange 220 and the second flange 230. From the respective curved joints 240, 250, the web 210 is recessed to form two web corrugations 213, 214. Each web corrugation then returns to full width W₂₀₀And are connected by an outer side surface 215 of web 210. In contrast, and as explained below by the flange corrugations 222, 232, the corrugations may be formed entirely of circular arcs.

Still referring to fig. 12, the first flange 220 may also include one or more corrugations. In the example of fig. 12, first flange 220 includes a width W along the steel pile₂₀₀A flange corrugation 222 is formed in the center. The flange corrugation 222 is a radius R extending inwardly from between a first outer side surface 224 and a second outer side surface 226 of the flange 220₂₂₂Forming an arc. Opposite web 210, a first leading edge 228 extends from first flange 220 at a curved adapter 260. The first front edge is at the height H of the steel pile₂₀₀Extend in a direction and parallel to the inboard surface 216 and the outboard surface 215 of the web 210. The first leading edge 228 may further include a curved transition 280 into the return portion 229. The return portion 229 extends inwardly from the first leading edge 228 toward the web 210. The return portion 229 is parallel to the first and second outer side surfaces 224, 226 of the flange 220.

Similar to the first flange 220, the second flange 230 may also include one or more corrugations. In the example of fig. 12, second flange 230 includes a width W along the steel pile₂₀₀A flange corrugation 232 is formed in the center. Flange corrugation 232 is a radius R extending inwardly from between first and second outer side surfaces 234, 236 of flange 230₂₃₂Forming an arc. Opposite web 210, a second leading edge 238 extends from second flange 230 at curved joint 270. Second front edge at height H of steel pile₂₀₀Extend in a direction and are parallel to the inboard surface 216 and the outboard surface 215 of the web 210. First, theThe leading edges 228 may further include a curved transition 290 into the return portion 239. The return portion 239 extends inwardly from the leading edge 228 toward the web 210. Return portion 239 is parallel to first and second outboard surfaces 234, 236 of second flange 230. In the example of fig. 12, the thickness T of the steel plate forming the steel pile 200 is 0.062 inches (") (1.575 mm). In some examples, the thickness of the steel plate forming the steel pile 200 may be 2mm or less. In other examples, the thickness of the steel plate forming the steel pile 200 may be 2.5mm or less. The first flange 220 and/or the second flange 230 of the UHSW piling 200 of fig. 12 may additionally include one or more through holes and/or one or more slotted holes. The through holes and slots may be provided for securing items to the steel piles, such as solar installations, highway guardrails, etc., for example. One or more through holes and/or one or more slots may additionally or alternatively be provided in the web 210.

In the example UHSW piling 200 of fig. 12, the UHSW piling includes a constant thickness T. The constant thickness may be less than or equal to 2.5mm, less than or equal to 2.0mm, or less than or equal to 1.6 mm. A constant thickness T is maintained by each of the features described above. More specifically, the constant thickness is the product of cold forming a UHSW piling from a steel sheet. In one example, the steel plate width is 50 ". The profile of the C-channel of fig. 11 results from a steel plate of the width and then has a total cross-sectional material length of 50 "or less. More specifically, the total cross-sectional material length may be one-half or one-third of the width of the steel plate. At the corrugations, the material thickness T remains constant at the layers and at the transition. In the example of fig. 12, the steel pile height H₂₀₀Is greater than the width W of the steel pile₂₀₀. In the example of fig. 12, the height H of the steel pile 200 with respect to bisecting the steel pile 200₂₀₀Is symmetrical about the axis. Typical UHSW piling of fig. 12 may be, for example, C-channel shapes (with or without corrugations) of 6x4, 6x6, 8x6, 8x8, 10x8, 10x10, 12x 812 x10, 12x12, 14x10, 14x12, 14x14 (in inches), any value in between, and the like.

Turning now to fig. 13, a UHSW piling 300, shown as a C-channel shape including a web 310, a first flange 320, and a second flange 330, is another example of a corrugated C-channel or NCW piling. Similar to the steel pile of fig. 12, the web of the steel pile 300 of fig. 13The height H of the plate 310 along the steel pile 300₃₀₀Extends and is joined at a curved joint 340 to a first flange 320 at a first end 311. Web 310 is also transitioned at curved transition 350 to second flange 330 at second end 312. Each curved adapter 340, 350 has a radius R₃₄₀、R₃₅₀. In fig. 13, web 310 includes single web corrugations 313. Single-web corrugation 313 relative to height H of steel pile₃₀₀Is positioned in the center. This is in contrast to fig. 12, where the web 210 includes a first web corrugation 213 and a second web corrugation 214. To form the web corrugations of FIG. 13, the outside surface 315 of the web 310 is at the pile width W₃₀₀Is offset in a direction from the inboard surface 316 of the web 310. Both outside surface 315 and inside surface 316 are at the piling height H₃₀₀Wherein the lateral side surface 315 and the medial side surface 316 are perpendicular to the first flange 320 and/or the second flange 330. Outboard surface 315 and each inboard surface 316 form a majority of web 300 such that the web is said to remain generally perpendicular to first flange 320 and/or second flange 330. Each curved adapter 340, 350 extends from the respective first flange 320 or second flange 330 along a respective radius R₃₄₀、R₃₅₀The formed arc extends. Also, in contrast to fig. 12, the arc of the curved joints 340, 350 of fig. 13 extends only 90 degrees, because the single web corrugation 313 is centrally located on the web 310 and is independent of the curved joints 340, 350.

The single web corrugation 313 of the UHSW piling of fig. 13 includes an inside surface 316 perpendicular to the first flange 320 and the second flange 330. Inboard surface 316 may additionally or alternatively be referred to as being recessed relative to web 310 or outboard surface 315 of web 310. In contrast, and as explained below by the flange corrugations 322, 332, the corrugations may be formed entirely of circular arcs.

Still referring to fig. 13, the first flange 320 may also include one or more corrugations. In the example of fig. 13, first flange 320 is included along steel pile width W₃₀₀A flange corrugation 322 formed in the center. The flange corrugation 322 is a radius R extending inwardly from between a first outer side surface 324 and a second outer side surface 326 of the flange 320₃₂₂Forming an arc. Opposite the web 310, a first leading edge 328 extends fromFirst flange 320 extends at curved adapter 360. The first front edge is at the height H of the steel pile₃₀₀Extend in a direction and are parallel to the inboard surface 316 and the outboard surface 315 of the web 310. The first leading edge 328 may further include a curved adapter 380 to the return portion 329. The return portion 329 extends inwardly from the first leading edge 328 toward the web 310. The return portion 329 is parallel to the first and second outer side surfaces 324, 326 of the flange 320.

Similar to the first flange 320, the second flange 330 may also include one or more corrugations. In the example of fig. 13, second flange 330 includes a width W along the steel pile₃₀₀A flange corrugation 332 is formed in the center. The flange corrugations 332 are formed to extend inwardly from between a first outer side surface 334 and a second outer side surface 336 of the flange 330 at a radius R₃₃₂Forming an arc. Opposite the web 310, a second leading edge 338 extends from the second flange 330 at a curved transition joint 370. Second front edge at height H of steel pile₃₀₀Extend in a direction and are parallel to the inboard surface 316 and the outboard surface 315 of the web 310. The second leading edge 328 may further include a curved transition 390 to the return portion 339. The return portion 339 extends inwardly from the leading edge 328 toward the web 310. The return portion 339 is parallel to the first and second outer side surfaces 334, 336 of the second flange 330. In the example of fig. 13, the thickness T of the steel plate forming steel pile 300 is 0.062 inches (") (1.575 mm). In some examples, the thickness of the steel plate forming the steel pile 300 may be 2mm or less. In other examples, the thickness of the steel sheet forming the steel pile 300 may be 2.5mm or less. The first flange 320 and/or the second flange 330 of the UHSW piling 300 of fig. 13 may additionally include one or more through holes and/or one or more slotted holes. The through holes and slots may be provided for securing items to the steel piles, such as solar installations, highway guardrails, etc., for example. One or more through holes and/or one or more slots may additionally or alternatively be provided in the web 310.

In the example UHSW piling 300 of fig. 13, the UHSW piling includes a constant thickness T. The constant thickness may be less than or equal to 2.5mm, less than or equal to 2.0mm, or less than or equal to 1.6 mm. A constant thickness T is maintained by each of the features described above. More specifically, constant thicknessThe UHSW steel pile is a product formed by cold forming of a steel plate. In one example, the steel plate width is 50 ". The C-channel shaped profile of fig. 11 results from a steel plate of the width and then has a total cross-sectional material length of 50 "or less. More specifically, the total cross-sectional material length may be one-half or one-third of the width of the steel plate. At the corrugation, the material thickness T remains constant at the layers and at the transition. In the example of fig. 13, the height H of the steel pile₃₀₀Is greater than the width W of the steel pile₃₀₀. In the example of fig. 13, the height H of the steel pile 300 with respect to bisecting the steel pile 300₃₀₀Is symmetrical about the axis. A typical UHSW piling of fig. 13 may be C-channel shaped (with or without corrugations) such as 6x4, 8x6, 10x8, 12x 812 x10, 14x10, 14x12 (in inches), and the like.

Turning now to fig. 14, a UHSW piling 400 having a tubular cross-section is illustrated. The steel pile 400 of fig. 14 has a square shape. The steel pile 400 includes a first sidewall 410, a second sidewall 420, a third sidewall 430, and a fourth sidewall 440. The first sidewall 410 is generally parallel to the third sidewall 430. The second sidewall 420 is generally parallel to the fourth sidewall 440. Also, the first sidewall 410 and the third sidewall 430 are generally perpendicular to the second sidewall 420 and the fourth sidewall 440. As used in this context, "generally" refers to the arrangement of the sidewalls except for the corrugations, as described further below. Height H of the steel pile 400 of FIG. 14₄₀₀And width W₄₀₀Likewise, a generally square cross-section is formed. Again, as used in this context, "generally" refers to the arrangement of walls other than corrugations. That is, the overall dimensions of the cross-section of each side wall of the steel pile 400 are the same. The bending adapter is arranged between the side walls. More specifically, first curved adapter 450 is disposed between first sidewall 410 and second sidewall 420; a second curved swivel 460 is disposed between second sidewall 420 and third sidewall 430; a third curved adapter 470 is disposed between third sidewall 430 and fourth sidewall 440; and a fourth flex joint 470 is disposed between fourth sidewall 440 and first sidewall 410. Each curved transition 450, 460, 470 and 480 is at a respective radius R₄₅₀、R₄₆₀、R₄₇₀And R₄₈₀Forming an arc.

One or more of the steel piles 400 of fig. 14The sidewalls may each include one or more corrugations. In the example of fig. 14, each sidewall 410, 420, 430, 440 includes a corrugation 412, 422, 432, 442, respectively. In fig. 14, the sidewalls and corrugations are of the same arrangement and size. Thus, the cross-section of FIG. 14 is taken along a longitudinal axis X_axisAny plane extending above is symmetrical. Similar to the web corrugations of fig. 12-13, each corrugation 412, 422, 432, 442 includes an inboard surface 413, 423, 433, 443, respectively, that is offset from and parallel to an outboard surface 411, 421, 431, 441, respectively, of the sidewall 410, 420, 430, 440. In the example of fig. 14, a sloped sidewall 480 is provided to transition from the medial surface to the lateral surface. In fig. 14, each inside surface includes opposing sloped sidewalls 414, 424, 434, 444. Arcs may be provided to transition between surfaces, between surfaces and sloped sidewalls, and the like. As indicated above, the corrugations act as a rigid body (stiff) of the steel pile. In FIG. 14, each corrugation 412, 422, 432, 442 extends inwardly. In other examples, the corrugations may each extend outward, alternate (alternate), or form opposing halves. In some examples, one or more of the sidewalls may include a plurality of corrugations, such as the web corrugations of fig. 10, for example. Additionally or alternatively, the corrugations may be formed entirely of circular arcs, such as the flange corrugations as illustrated in fig. 12-13. The corrugations may be a combination of the corrugations described with respect to fig. 14 and corrugations formed entirely from circular arcs.

In the example UHSW piling 400 of fig. 14, the UHSW piling includes a constant thickness T. The constant thickness may be less than or equal to 2.5mm, less than or equal to 2.0mm, or less than or equal to 1.6 mm. A constant thickness T is maintained by each of the features described above. More specifically, a constant thickness UHSW steel pile is cold formed from a steel sheet. In one example, the steel plate width is 50 ". The profile of the tube of fig. 14 is produced from a steel plate of the width and then has a total cross-sectional material length of 50 "or less. More specifically, the total cross-sectional material length is one-half or one-third of the width of the steel plate. Also, welds, rivets, lap joints and/or joints may be provided to close the tubular steel pile of fig. 14 when formed from sheet steel. The welding may be continuous welding, partial welding, and/or spot welding. The welds, rivets, overlap and/or joints may be located on arcs, on corrugations, on inside surfaces, on outside surfaces and/or on sloped side walls. Typical UHSW steel piles of fig. 14 may be steel pipes such as 4x4, 6x6, 8x8, 12x12 (in inches) with or without corrugations, and any values in between.

Turning now to fig. 15, a UHSW piling 500 having a tubular cross-section is illustrated. The steel pile 500 of fig. 15 is rectangular in comparison to the square steel pile of fig. 14. Similar to the steel pile of fig. 14, the steel pile 500 comprises a first side wall 510, a second side wall 520, a third side wall 530 and a fourth side wall 540. The first sidewall 510 is generally parallel to the third sidewall 530. The second sidewall 520 is generally parallel to the fourth sidewall 540. Also, the first sidewall 510 and the third sidewall 530 are generally perpendicular to the second sidewall 520 and the fourth sidewall 540. As used in this context, "generally" refers to the arrangement of the sidewalls except for the corrugations, as described further below. Height H of the steel pile 500 of fig. 15₅₀₀Is greater than width W₅₀₀Forming a generally rectangular tube. Again, as used in this context, "generally" refers to the arrangement of walls other than corrugations. That is, the overall dimensions of the first and third sidewalls 510 and 530 are the same as the overall dimensions of the second and fourth sidewalls 520 and 540. The bending adapter is arranged between the side walls. More specifically, first curved adapter 550 is disposed between first sidewall 510 and second sidewall 520; a second curved adapter 560 is disposed between the second sidewall 520 and the third sidewall 530; the third curved adapter 570 is disposed between the third sidewall 530 and the fourth sidewall 540; and a fourth curved transition joint 570 is disposed between the fourth sidewall 540 and the first sidewall 510. Each curved transition 550, 460, 570 and 580 is at a respective radius R₅₅₀、R₅₆₀、R₅₇₀And R₅₈₀Forming an arc.

The one or more side walls of the steel pile 500 of fig. 15 may each comprise one or more corrugations. In the example of fig. 15, each sidewall 510, 520, 530, 540 includes a corrugation 512, 522, 532, 542, respectively. In fig. 15, the corrugations of the first sidewall 510 and the third sidewall 530 are the same and the second sidewall 520 and the fourth sidewall 540 include the same corrugations different from the first and third sidewalls. Thus, the cross-section of FIG. 15 is taken along a longitudinal axis X_axisArbitrary plane angle of upper extensionIs diagonally symmetrical. Similar to the web corrugations of fig. 10, 12-13, each corrugation 512, 522, 532, 542 includes an inboard surface 513, 523, 533, 543, respectively, that is offset from and parallel to the outboard surface 511, 521, 531, 541, respectively, of the sidewall 510, 520, 530, 540. In the fig. 15 example, sloped sidewalls 514, 524, 534, 544 are provided to transition from the medial to lateral surfaces. In fig. 15, each of the inside surfaces includes opposing sloped sidewalls. Arcs may be provided to transition between surfaces, between surfaces and sloped sidewalls, and the like. As indicated above, the corrugations act as a rigid body of the steel pile. In fig. 15, each corrugation 512, 522, 532, 542 extends inwardly. In other examples, the corrugations may each extend outward, alternate, or form opposing halves. In some examples, one or more of the sidewalls may include a plurality of corrugations, such as the web corrugations of fig. 10, for example. Additionally or alternatively, the corrugations may be formed entirely from arcs of a circle, such as the flange corrugations illustrated in fig. 12-13. The corrugations may be a combination of the corrugations described above with respect to fig. 15 and corrugations formed entirely from circular arcs.

In the example UHSW piling 500 of fig. 15, the UHSW piling includes a constant thickness T. The constant thickness may be less than or equal to 2.5mm, less than or equal to 2.0mm, or less than or equal to 1.6 mm. A constant thickness T is maintained by each of the features described above. More specifically, a constant thickness UHSW steel pile is cold formed from a steel sheet. In one example, the steel plate width is 50 ". The profile of the tube of fig. 15 is produced from steel plate of the width or less and then has a total cross-sectional material length of 50 "or less. More specifically, the total cross-sectional material length may be one-half or one-third of the width of the steel plate. Also, welding, riveting, overlapping and/or joints may be provided to close the tubular steel pile of fig. 15 when formed from sheet steel. The welding may be continuous welding, partial welding, and/or spot welding. The welds, rivets, overlap and/or joints may be located on arcs, on corrugations, on inside surfaces, on outside surfaces and/or on sloped side walls. A typical UHSW piling of fig. 15 may be steel pipe (with corrugations) such as 6x4, 8x6, 10x8, 12x 812 x10, 14x10, 14x12 (in inches), any value in between, etc.

The above-described shape provides additional structural integrity to withstand the loads experienced by a pile or steel foundation as described further below. Further, by increasing the structural integrity in a form-wise manner, steel piles can be manufactured relying on much thinner materials than conventional galvanized i-beams. Thus, in order to force into the ground while maintaining the requisite strength and integrity, a much thinner material also requires less force, as the cross-section of the UHSW steel pile of the invention is reduced compared to previous piles and structural foundations.

In use, part of the length of the steel pile is forced into the ground or soil to provide a structural base. The steel piles are forced into the ground or soil using a ram such as a piston or hammer. The ram may be part of and driven by the pile driver. The ram impacts or impacts the steel pile, forcing the steel pile into the ground or soil. Due to the impact, the previous steel piles may warp or deform under the impact of the ram. To avoid buckling or damage to the previous steel pile, the RPM or force of the pile driver is maintained below a damage threshold. The present steel pile has demonstrated the ability to apply an increase in RPM or force to the steel pile without buckling or damaging the steel pile as compared to prior steel piles, as reflected by the strength properties of the steel pile. Specifically, as tested, prior art steel piles of comparable size characteristics were driven and structurally failed, with the steel pile of the present disclosure providing a 25% RPM increase. Furthermore, existing steel piles are additionally not weathering steel in the absence of a galvanized or zinc-coated surface. Thus, existing steel piles are susceptible to corrosion due to their placement in external conditions (including ground and soil conditions) or require additional treatment such as galvanization, for example. Again, the present invention piling provides the corrosion index required to withstand these conditions. For such products, the strength properties and corrosion properties of the present invention have not previously been seen in combination.

The crimped flange of the crimped C-channel shape as described and illustrated above by fig. 10, the corrugated web and flange of the corrugated C-channel shape as described and illustrated above by fig. 12-13, and the bellows as described and illustrated above by fig. 14-15 further increase the stiffness of the piling to prevent buckling and/or withstand driving forces, as noted above. By providing the features and shapes of the hemmed C-channel, corrugated C-channel, and corrugated tube, the material thickness of the thin cast steel strip forming the ultra-high strength weathering steel stake may additionally be maintained at 2.5mm or less, 2.0mm or less, or 1.6mm or less, as described herein. The reduction in material thickness further contributes to a reduction in the driving force required for driving the ultra-high strength weathering steel pile into the ground (e.g., the ground or soil) by reducing the cross-sectional resistance between the ultra-high strength weathering steel pile and the ground. Moreover, because the ultra-high strength, weathering-resistant steel piles do not have a separately applied corrosion-resistant coating, such coatings are not susceptible to being scraped off or removed when contacting the ground during the installation process and/or may otherwise be negatively affected by the effects of groundwater and/or soil conditions. As used herein, a separately applied coating is a protective coating that is a surface protective agent independent of the steel composition. Examples of such separately applied protective coatings include zinc coatings, galvanized coatings (e.g., hot-dip galvanized coatings), aluminum-silicon corrosion-resistant coatings, and the like. More importantly, the pile or steel base of the present disclosure produces corrosion resistance without the aid of a separately applied coating, as set forth below. Inherently, weathering steels, including the ultra-high strength weathering steels disclosed herein, possess the requisite corrosion resistance by definition, otherwise a separately applied hot dip galvanizing coating process would result. Thus, the weathering steel of the present disclosure would not require or be provided with a zinc coating, a hot dip galvanized coating, or the like.

Steel piles formed from the lightweight ultra-high strength weathering steel of the present disclosure have been tested in comparison to existing steel pile materials for operating life and corrosion resistance potential. Existing steel piling materials include hot-dip galvanized ("HDG") piling, such as, for example, G235 grade steel, and non-galvanized steel, such as, for example, G100, Gr70, and the like. In solar installations, it has been common practice in the solar industry for structural purposes to use stakes designed from galvanized 50ksi steel W6 i-beam steel. Often redox analysis is performed on the soil type to confirm the corrosion characteristics of the soil. These properties are then relied upon to determine the rate of corrosion of materials placed in the soil. Soil conditions may additionally or alternatively be analyzed for electrical resistance, pH, chloride and sulfate. The steel piles must be specified to withstand the load requirements regardless of corrosion. To compare the operating life and corrosion resistance potential of the inventive material for light-weight ultra-high strength weathering ("UHSW") steel piles, UHSW steel slabs were directly compared to steel slabs of different materials, such as G235, G100 and Gr70, using the salt-mist test. Specifically, the test was performed according to ASTM B117-18 standard specifications on four steel sheets of different materials: "G235", "G100", "Gr 70" and "UHSW". The test file specifies the use of a 1000-hour salt spray test at 250 hour check intervals. Random sheets from each material type (1 out of 4) were selected for examination and fig. 16-19 and table 3 below show the average of the thickness measurements, both quantitative and qualitative, taken at 250 hour intervals at each corner for G235, G100, Gr70 and UHSW. Thickness measurements are taken by calipers and therefore represent the thickness of the envelope (envelope). The preliminary measurement results deviate due to initial buildup of oxidized material; however, each sheet showed a relatively stable material loss rate after 250 hours. The color and approximate percent coverage of each sheet is described. White coloration indicates zinc oxidation and red coloration indicates steel oxidation. The comparative test results are reproduced in table 3 below. Fig. 16-19 illustrate the same test results in graphical format with representative images, wherein fig. 16 illustrates steel grade G325, fig. 17 illustrates steel grade G100, fig. 18 illustrates steel grade Gr70, and fig. 19 illustrates UHSW steel.

TABLE 3

Thickness values are the average of four readings taken at each corner of the sheet.

To compare the relative corrosion rates of the materials tested, the difference in material loss per hour was measured for each sample and the initial data reading was excluded as the oxidation appearance typically deviated the results. That is, the oxidized appearance increases the measured thickness. After 250 hours, the results were generally more linear. The average value of this run (exercise) shown in table 4 below was used to generate the relative relationship between the corrosion rates of UHSW steel and other sheets:

TABLE 4

Using this relationship alone, UHSW sheets perform better than galvanized sheets. It can be noted that the measurement results of UHSW outperform other steel sheets greatly. The ultra-high strength weathering steels of the present disclosure exhibit corrosion resistance that one of ordinary skill would otherwise rely on separately applied metallic coatings or galvanization to achieve. Thus, ultra-high strength weathering steels exhibit the requisite combination of strength and corrosion properties in combination with the benefits of the above shaped bodies (shapes) for use as piles or structural foundations, where a separately applied coating is otherwise required on the steel to achieve the same strength properties that are not otherwise present in existing weathering steels.

The following table 5 illustrates the steel grade and chemical composition of the UHSW steel sheet depending on the above results of tables 3 to 4.

TABLE 5

Additional tests were conducted to evaluate the corrosion rate of UHSW steel versus galvanized ("HDG") steel for different geometries, embedment duration and simulated aging. Tables 6-7 below illustrate the results from these tests. The material was tested in moderately saline low resistance soil, which may also be designed to be "very corrosive". The material geometries tested included small angle shaped posts (stabe) and full size cold rolled C-shaped stakes. The material labeled "applied current" received a voltage high enough to artificially induce approximately 24 hours of corrosion in an attempt to simulate longer term installation effects. In this comparative analysis, the measured rate of UHSW steel material varies from 77% to 99% of the measured rate of HDG steel material.

TABLE 6

TABLE 7

The above comparative tests and structural capability calculations show that steel piles made from thin cast steel strip outperform hot dip galvanized ("HDG") steel piles as well as existing steel piles. The UHSW piling of the present disclosure provides greater corrosion resistance and is provided with a much thinner material thickness. Maintaining these improvements while also maintaining desirable strength and elongation properties that allow UHSW steel piles to resist deformation when forced into the ground. As also illustrated by the material thickness, UHSW piling is made with much lower weight than existing piling. Specifically, the total cross-section equivalent UHSW hemmed C channel or NXW pile weighs 5 pounds per foot (lbs) and the cross-section equivalent UHSW corrugated C channel or NCW pile weighs 3.5 pounds per foot (lbs) compared to a steel pile constructed from a W6x7 i-beam weighing 7 pounds per foot (lbs) or from a W6x9 i-beam weighing 9 pounds per foot (lbs). A UHSW steel stake of the present disclosure is also provided without a hot dip galvanized coating or a zinc coating. The UHSW piling of the present disclosure then eliminates any undesirable interaction between the soil or groundwater and the zinc coating that would otherwise exist in the case of an HDG piling. The UHSW piling of the present disclosure significantly outperforms other alternatives to piling without a separately applied coating, such as the other non-galvanized piling tested herein.

Even with a galvanised coating, the structural capacity and service life of HDG steel piles do not outperform those of thinner UHSW steel piles. The time for the galvanized layer to completely corrode is estimated by using the thickness divided by the corrosion rate. The remaining time is then multiplied by the steel corrosion rate to determine the final material thickness. For example, consider a 0.124 "thick G235 plate metal assembly: if the standard ratio of corrosion rates between the zinc layer and the base metal in corrosive soil conditions is applied and the corrosion rate of the zinc coating of G235(2.1 mil/face) galvanized steel is estimated to be 0.0003 "/y, then the base steel corrosion rate should be about 0.0021"/y, with the total reduction per face calculated as follows for a 30 year service life:

0.0021'/year/side × 23 year × 2 side ═ 0.0966 ″

The total metal loss will be about 0.1008 "and this will leave a 0.0232" thick assembly at the end of the service life.

Assuming that UHSW material with a thickness of 0.062 "corrodes at the same rate as zinc, the final thickness is more simply calculated after the first two years as follows:

0.3 mil/year/face x 30 years x 2 faces-18 mils resulted in a material thickness of 0.0440 "at the end of 30 years. This mild corrosive situation demonstrates how the life of the material can outperform a zinc + carbon steel structure and the greatly increased strength compared to carbon steel enables significantly greater capacity in virtually any load scenario.

In some examples, the ultra-high strength, weathering-resistant steel piles include as-cast materials having a thickness of less than or equal to 2.5mm, less than or equal to 2.0mm, or less than or equal to 1.6 mm. The as-cast material thickness is a thin cast steel strip cold rolled into a steel pile having a web and one or more flanges with a corrosion index of 6.0 or greater. The ultra-high strength weathering steel stake may further include a material yield strength between 700 and 1600MPa, a material tensile strength between 1000 and 2100MPa, and a material elongation between 1% and 10%. The material composition of the ultra-high strength, weathering steel stake may include an amount of nickel sufficient to shift the peritectic point away from the carbon region and/or increase the transformation temperature of the peritectic point to form a carbon alloy steel strip having a microstructure of at least 75% martensite or martensite plus bainite by volume.

The UHSW piling may be a piling comprising a web and one or more flanges, or one of the above-described shaped bodies formed from a carbon alloy steel strip having a composition comprising: between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and silicon killed containing less than 0.01% aluminum by weight, wherein the carbon alloy steel strip has a microstructure with at least 75% by volume martensite or martensite plus bainite, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, an elongation between 1% and 10% and has a corrosion index of 6.0 or more. In one example, the steel pile may be cold rolled from a carbon alloy steel strip cast at a cast thickness of less than or equal to 2.5 mm. In another example, the steel pile may be cold rolled from a strip of less than or equal to 2.0mm or less than or equal to 1.6 mm. In even yet another example, the steel pile may be formed of a steel plate having a thickness of between 1.4mm and 1.5mm or 1.4mm or 1.5 mm. The steel piles may be channel-shaped such as C-channel, box channel, double channel, etc. The steel pile may additionally or alternatively be an i-shaped member, an angle, a structural T-shape, a hollow structural section (hollow structural section), a double angle, an S-shape, a tube, or the like. Also, many of these components may be joined together, for example welded together, to form a single steel pile. It is recognized herein that additional products can be made from lightweight ultra-high strength weathering steel sheets. Further, it is recognized herein that additional products may be made from ultra-high strength weathering steels that are not manufactured by a twin roll caster, but rather ultra-high strength products may be made by other methods.

Additional examples of ultra-high strength weathering steels are provided below:

a lightweight ultra-high strength steel sheet comprising: a carbon alloy steel strip cast at a casting thickness of less than or equal to 2.5mm having a composition comprising:

(i) between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and sedated with silicon containing less than 0.01% aluminum, and

(ii) the balance being iron and impurities resulting from the smelting;

wherein the nickel shifts the peritectic point away from the carbon region and/or raises the transition temperature of the peritectic point in the composition to form a defect free carbon alloy steel strip having a microstructure with at least 75% by volume martensite or martensite plus bainite, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%.

In one example above, the lightweight ultra-high strength steel sheet has a microstructure having at least 75% by volume martensite. In another example above, the lightweight ultra-high strength steel sheet has a microstructure having at least 90% by volume martensite. In yet another example of the above, the light-weight ultrahigh-strength steel sheet has a microstructure having at least 95% martensite.

In one example above, the lightweight ultra-high strength steel sheet includes less than 5ppm boron.

In one example above, the lightweight ultra-high strength steel sheet comprises between 0.05% and 0.12% niobium.

In one example of the above, the martensite in the steel sheet comes from austenite having a grain size of more than 100 μm.

In one example of the above, the martensite in the steel sheet comes from austenite having a grain size of more than 150 μm.

In one example above, the steel sheet may additionally be hot rolled to between 15% and 50% reduction before rapid cooling.

In one example above, a carbon alloy steel sheet is hot rolled to a hot rolled thickness at a reduction of between 15% and 35% of the cast thickness before rapid cooling.

In one example above, the steel sheet is a weathering steel having a corrosion index of 6.0 or greater.

The manufacturing method of the light ultrahigh-strength weather-resistant steel plate comprises the following steps:

(a) preparing a molten steel melt comprising:

(i) between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, silicon killed with less than 0.01% aluminum, and

(ii) the balance being iron and impurities resulting from the smelting;

(b) forming the melt into a casting pool supported on the casting surfaces of a pair of cooled casting rolls having a nip therebetween;

(c) counter-rotating the casting rolls and melting the melt at greater than 10.0MW/m²Solidifying the heat flux of (a) into a steel sheet having a thickness of less than 2.5mm conveyed downwardly from the nip and cooling the sheet in a non-oxidizing atmosphere to below 1100 ℃ and above the Ar3 temperature at a cooling rate of greater than 15 ℃/s; and

(d) rapidly cooling to form a steel sheet having a microstructure with at least 75% by volume martensite or martensite plus bainite, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%, wherein the nickel shifts the peritectic point away from the carbon region and/or raises the transition temperature of the peritectic point to inhibit crack or defect formation in the high strength martensitic steel sheet.

In one example above, the microstructure has at least 75% martensite by volume. In another example above, the microstructure has at least 90 volume% martensite. In yet another example above, the microstructure has at least 95 volume% martensite.

In one example above, a carbon alloy steel sheet is formed having less than 5ppm boron.

In one example above, the carbon alloy steel sheet includes between 0.05% and 0.12% niobium.

In one example of the above, the martensite in the steel sheet comes from austenite having a grain size of more than 100 μm.

In one example of the above, the martensite in the steel sheet comes from austenite having a grain size of more than 150 μm.

In one example above, the steel sheet is hot rolled to a hot rolled thickness at a reduction of between 15% and 50% of the cast thickness before rapid cooling.

In one example above, the steel sheet is hot rolled to a hot rolled thickness at a reduction of between 15% and 35% of the cast thickness before rapid cooling.

In one example above, the high strength steel sheet is defect free.

Also disclosed is a steel pile comprising a web cold rolled from a carbon alloy steel plate cast at a cast thickness of less than or equal to 2.5mm and one or more flanges, the carbon alloy steel plate having a composition comprising: between 0.20% and 0.35% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and silicon killed containing less than 0.01% aluminum, by weight, wherein the carbon alloy steel sheet has a microstructure possessing at least 75% by volume of martensite or martensite plus bainite, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, an elongation between 1% and 10% and is defect-free.

In one example above, the lightweight ultra-high strength steel sheet has a microstructure having at least 75% by volume martensite. In another example above, the lightweight ultra-high strength steel sheet has a microstructure having at least 90% by volume martensite. In yet another example of the above, the light-weight ultrahigh-strength steel sheet has a microstructure having at least 95% martensite.

In one example above, the carbon alloy steel sheet of the steel pile comprises less than 5ppm boron.

In one example above, the carbon alloy steel sheet of the steel pile comprises between 0.05% and 0.12% niobium.

In one example of the above, the martensite in the steel pile comes from austenite having a grain size greater than 100 μm.

In one example of the above, the martensite in the steel pile comes from austenite having a grain size greater than 150 μm.

In one example above, the steel sheet may additionally be hot rolled to between 15% and 50% reduction before rapid cooling.

In one example above, a carbon alloy steel sheet is hot rolled to a hot rolled thickness at a reduction of between 15% and 35% of the cast thickness before rapid cooling.

In one example above, the carbon alloy steel sheet is a weathering steel having a corrosion index of 6.0 or more.

High-friction rolled high-strength weathering steel

In the following examples, high friction rolled high strength weathering steel sheets are disclosed. An example of the ultra-high strength weathering steel plate is made by the steps comprising: (a) preparing a molten steel melt comprising: (i) between 0.20% and 0.40% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and sedated with silicon containing less than 0.01% aluminum, by weight, and (ii) the balance iron and impurities resulting from smelting; (b) at a molecular weight of more than 10.0MW/m²Is solidified into a steel sheet having a thickness of 2.5mm or less and the sheet is cooled to 1080 ℃ or less and Ar in a non-oxidizing atmosphere at a cooling rate of more than 15 ℃/s before rapid cooling₃Above the temperature; (c) high friction rolling the thin cast steel strip to a hot rolled thickness at a reduction of between 15% and 50% of the as-cast thickness to produce a hot rolled steel strip that is substantially free, or free of prior austenite grain boundary pits and has a screeded pattern; and (d) rapidly cooling to form a steel sheet having a microstructure possessing at least 75% martensite or at least 75% martensite plus bainite by volume, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%. Here and elsewhere in this disclosure, elongation means total elongation. By "rapid cooling" is meant cooling at a rate greater than 100 ℃/s to between 100 and 200 ℃. The rapid cooling of the composition according to the invention with the addition of nickel achieves up to more than 95% of the martensitic phase steel strip. In one example, rapid cooling forms micro-spheres having a volume of at least 95% martensite or at least 95% martensite plus bainiteStructural steel plate. The addition of nickel must be sufficient to shift the 'peritectic point' away from the carbon region that would otherwise be present in the same composition without nickel added. In particular, the nickel in the composition is believed to help shift the peritectic point away from the carbon region and/or increase the transition temperature of the peritectic point of the composition, which appears to suppress defects and produce ultra-high strength weathering steel sheets free of defects.

The formability of the ultrahigh-strength weathering steel is further improved by high-friction rolling of the ultrahigh-strength weathering steel. A measure of formability is set forth by ASTM a370 bend test standard. In embodiments, the ultra-high strength weathering steel of the present disclosure will pass the 3T 180 degree bend test and will do so consistently. In particular, high friction rolling produces screeding from prior austenite grain boundary pits by plastic deformation under shear. These elongated surface structures characterized by a trowelled pattern are desirable for the properties of ultra-high strength weathering steels. In particular, formability of ultra-high strength weathering steel is improved due to the floating pattern.

The steel strip may further comprise greater than 0.005% niobium or greater than 0.01% or 0.02% niobium by weight. The steel strip may comprise greater than 0.05% molybdenum or greater than 0.1% or 0.2% molybdenum by weight. The steel strip may be silicon killed, containing less than 0.008% aluminium or less than 0.006% aluminium by weight. The molten melt may have a free oxygen content of between 5 and 70 ppm. The steel strip may have a total oxygen content greater than 50 ppm. The inclusions comprise MnOSiO typically with 50% of them being less than 5 μm in size₂And has the potential to enhance the microstructure evolution and hence the mechanical properties of the strip.

The molten melt may be greater than 10.0MW/m²Is solidified into a steel strip having a thickness of less than 2.5mm and is cooled to 1080 ℃ or less and Ar in a non-oxidizing atmosphere at a cooling rate of more than 15 ℃/s₃Above the temperature. The non-oxidizing atmosphere is an atmosphere of typically an inert gas such as nitrogen or argon or mixtures thereof, which contains less than about 5% by weight oxygen.

In some embodiments, the martensite in the steel strip may be derived from austenite having a grain size greater than 100 μm. In other embodiments, in steel stripThe martensite may be derived from austenite having a grain size greater than 150 μm. At a power of more than 10MW/m²The rapid solidification of the heat flux enables the production of austenite grain sizes responsive to controlled cooling after subsequent hot rolling to achieve defect-free strip manufacture.

As noted above, the steel strip of this set of examples may include a microstructure having martensite or martensite plus bainite. Martensite is formed in carbon steel by rapid cooling or quenching of austenite. Austenite has a particular crystal structure known as Face Centered Cubic (FCC). If allowed to cool naturally, austenite transforms into ferrite and cementite. However, when austenite is rapidly cooled or quenched, face-centered cubic austenite transforms into a highly strained body-centered tetragonal (BCT) form of ferrite that is supersaturated with carbon. The resulting shear deformation produces a large number of dislocations, which is the main strengthening mechanism of the steel. The martensite reaction begins during cooling when the austenite reaches the martensite start temperature and the parent austenite becomes thermodynamically unstable. As the sample is quenched, an increasing percentage of the austenite transforms to martensite until a lower transformation temperature is reached, at which point the transformation is complete.

However, martensitic steels tend to produce large prior austenite grain boundary pits observed on the hot rolled outer surface of a cooled thin steel strip formed from a low friction condition rolled steel. The step of pickling or acid etching amplifies these defects which lead to defects and spaces. High friction rolling is now being introduced as an alternative to overcome the identified problems for low friction condition rolling of martensitic steels. High friction rolling produces a smoothed boundary (grain boundary) pattern. A flattened boundary pattern may be more generally referred to herein as a flattened pattern. Additionally, a flattened boundary pattern may alternatively be referred to as a fish scale pattern.

Just as relying on the above ultra-high strength weathering steels to produce product shapes and configurations such as the piles described above, many products can be produced from high friction rolled high strength weathering steel plates of the type described herein. As above, one example of a product that can be manufactured from high friction rolled high strength weathering steel sheet includes steel piles. In one example, the steel pile includes a web and one or more flanges cold rolled from the various carbon alloy steel strips described above. The steel pile may further comprise a length, wherein the web and the one or more flanges extend the length. In use, the length of the steel pile is forced into the ground or soil to provide a structural base. The steel piles are forced into the ground or soil using a ram such as a piston or hammer. The ram may be part of and driven by the pile driver. The ram impacts or impacts the steel pile, forcing the steel pile into the ground or soil. Due to the impact, the previous steel piles may warp or deform under the impact of the ram. To avoid buckling or damage to the previous steel pile, the RPM or force of the pile driver is maintained below a damage threshold. The present steel pile has demonstrated the ability to increase the RPM or force applied to the steel pile compared to previous steel piles without buckling or damaging the steel pile, as reflected by the strength properties of the steel pile. Specifically, as tested, prior steel piles of comparable dimensional characteristics were driven and structurally damaged, with the steel piles of the present disclosure providing 25% RPM amplification. Moreover, previous steel piles are not additionally weathering steel. Therefore, previous steel piles are susceptible to corrosion due to their placement in external conditions, including ground and soil conditions. Again, the present invention piling provides the corrosion index necessary to withstand these conditions. The strength properties and corrosion properties of the present invention have not previously been seen in combination for such products.

In one example, the steel pile may be formed from a carbon alloy steel strip casting of the present example cast at a casting thickness of less than or equal to 2.5 mm. In another example, the steel pile may be formed of the steel strip of this example of less than or equal to 2.0 mm. In even yet another example, the steel pile may be formed from a steel plate of the present example having a thickness of between 1.4mm and 1.5mm or 1.4mm or 1.5 mm. The steel piles may be channel-shaped such as C-channel, box channel, double channel, etc. The steel pile may additionally or alternatively be an i-shaped member, an angle, a structural T-shape, a hollow structural section, a double angle, an S-shape, a tube, or the like. Also, many of these components may be joined together, e.g., welded together, to form a single steel pile. It is recognized herein that additional products may be made from high friction rolled ultra high strength weathering steel plates.

High frictionFriction rolled high strength martensitic steel

In an embodiment of the present disclosure, a high strength martensitic steel sheet is also disclosed. The following examples of high strength martensitic steel sheets may additionally include weathering characteristics. Therefore, the high strength martensitic steel sheet example herein may also be referred to as ultra high strength weathering steel sheet due to such properties. Martensitic steels are increasingly used in applications requiring high strength, such as in the automotive industry. Martensitic steels provide the necessary strength for the automotive industry while reducing energy consumption and improving fuel economy. Martensite is formed in carbon steel by rapid cooling or quenching of austenite. Austenite has a particular crystal structure known as Face Centered Cubic (FCC). If allowed to cool naturally, austenite transforms into ferrite and cementite. However, when austenite is rapidly cooled or quenched, face-centered cubic austenite transforms into a highly strained body-centered tetragonal (BCT) form of ferrite that is supersaturated with carbon. The resulting shear deformation produces a large number of dislocations, which is the main strengthening mechanism of the steel. The martensite reaction begins during cooling when the austenite reaches the martensite start temperature and the parent austenite becomes thermodynamically unstable. As the sample is quenched, an increasing percentage of the austenite transforms to martensite until a lower transformation temperature is reached, at which point the transformation is complete.

However, martensitic steels tend to produce large prior austenite grain boundary pits observed on the hot rolled outer surface of a cooled thin steel strip formed from a low friction condition rolled steel. The pickling or acid etching step amplifies these defects leading to defects and spaces. High friction rolling is now being introduced as an alternative for overcoming the identified problems for rolling martensitic steels under low friction conditions, however, it has also been observed that high friction rolling produces an undesirable surface finish. In particular, high friction rolling produces a smoothed boundary pattern combined with a non-uniform surface finish. The smoothed boundary pattern may be more generally referred to herein as a troweled pattern. Additionally, a flattened boundary pattern may alternatively be referred to as a fish scale pattern. Then, uneven surface finishes with a trowelled pattern (e.g., when thin steel strip is subjected to subsequent acid etching) become prone to trapping acid and/or cause excessive corrosion, resulting in excessive pitting. In view of this, for some steel strips or products, such as martensitic steel sheets used in automotive applications, it is necessary to perform an additional surface treatment to provide the following surfaces: wherein a floating pattern and/or uneven surface finish is removed from the surface.

To reduce or eliminate the screeding pattern and/or uneven surface finish, the thin steel strip is subjected to a surface homogenization process after the hot rolling mill. Examples of surface homogenization processes include abrasive blasting, such as, for example, by using grinding wheels, shot blasting, sand blasting, wet blasting, pressurized application of other abrasives, and the like. One specific example of a surface homogenization process includes environmentally-friendly pickled (eco-pickled) surfaces (referred to herein as "EPS"). Other examples of surface homogenization processes include the forceful application of abrasive media to the steel strip surface to homogenize the steel strip surface. For a powerful application, it may also rely on a pressurized component (assembly). For example, the fluid may propel the abrasive medium. Fluids as used herein include liquids and air. Additionally or alternatively, the mechanical device may provide a forceful application. The surface homogenization process occurs after the thin cast steel strip reaches room temperature. That is, the surface homogenization process does not occur in an on-line process using a hot rolling mill. The surface homogenization process may occur at a location separate from the hot rolling mill and/or the twin casting mill or off-line therefrom. In some examples, the surface homogenization process may occur after coiling.

As used herein, a surface homogenization process changes the surface to be free of or eliminate a floating pattern. The thin steel strip surface that does not contain a troweling pattern or in which the troweling pattern has been eliminated is a surface that passes the 120 hour corrosion test without any surface pitting. The test piece not subjected to the surface homogenization process was cracked (fractured) due to surface corrosion after 24 hours during the 120-hour corrosion test. Fig. 6 is an image showing a high-friction hot-rolled steel strip whose surface is homogenized using EPS. By contrast, fig. 7 is an image showing the surface of a high friction hot rolled steel strip having a trowel pattern that has not been subjected to a surface uniformizing process. As noted above, a smeared pattern, unless it is removed by a surface homogenization process, may trap acid upon acid etching and thus be prone to excessive pitting and/or corrosion. In summary and as used herein, a surface that has undergone surface homogenization is a surface that is free of a previously formed floating pattern by high friction rolling conditions.

After hot rolling, the hot-rolled thin steel strip is cooled. In each embodiment, the steel strip undergoes a surface homogenization process after cooling. It is recognized that cooling may be achieved by any known means. In some cases, when cooling the thin steel strip, the thin steel strip is cooled to equal to or less than the martensite start temperature M_STo thereby form martensite from prior austenite in the thin steel strip.

One embodiment of a high strength martensitic steel sheet is made by the steps comprising: (a) preparing a molten steel melt comprising: (i) between 0.20% and 0.40% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and sedated with silicon containing less than 0.01% aluminum, by weight, and (ii) the balance iron and impurities resulting from smelting; (b) at a molecular weight of more than 10.0MW/m²Is solidified into a steel sheet having a thickness of 2.5mm or less and the sheet is cooled to 1080 ℃ or less and Ar in a non-oxidizing atmosphere at a cooling rate of more than 15 ℃/s before rapid cooling₃Above the temperature; (c) high friction rolling the thin cast strip to a hot rolled thickness at a reduction between 15% and 50% of the as-cast thickness to produce a hot rolled strip free of prior austenite grain boundary pits; (d) rapidly cooling to form a steel sheet having a microstructure with at least 75% martensite or at least 75% martensite plus bainite by volume, a yield strength between 700 and 1600MPa, a tensile strength between 1000 and 2100MPa, and an elongation between 1% and 10%; and surface homogenizing the high friction hot rolled steel strip to produce a high friction hot rolled steel strip having a pair of opposing high friction hot rolled homogenized surfaces free of a floating pattern. Here and elsewhere in this disclosure, elongation means total elongation. By "rapid cooling" is meant cooling at a rate greater than 100 ℃/s to between 100 and 200 ℃. Will be added withThe inventive composition of nickel rapidly cools steel strip achieving up to greater than 95% martensite phase. In one example, the rapid cooling forms a steel sheet having a microstructure with at least 95% martensite or at least 95% martensite plus bainite by volume. The addition of nickel must be sufficient to shift the 'peritectic point' away from the carbon region that would otherwise be present in the same composition without nickel added. In particular, the nickel in the composition is believed to help shift the peritectic point away from the carbon region and/or increase the transformation temperature of the peritectic point of the composition, which appears to suppress defects and results in a high strength martensitic steel sheet that is defect free.

Further variants of the examples of high friction rolled high strength martensitic steel are given below. In some examples, the steel strip may include a pair of opposing high friction hot rolled homogenized surfaces substantially free of prior austenite grain boundary pits and a troweling pattern. In yet another example, the steel strip may further comprise a pair of opposing high friction hot rolled homogenization surfaces that are substantially free of prior austenite grain boundary pits and a troweling pattern. In each of these examples, the surface may have a surface roughness (Ra) of no more than 2.5 μm.

In some examples, the thin steel strip may further be tempered at a temperature between 150 ℃ and 250 ℃ for 2-6 hours. Tempering the steel strip provides improved elongation with minimal loss of strength. For example, after tempering as described herein, a steel strip having a yield strength of 1250MPa, a tensile strength of 1600MPa and an elongation of 2% is improved to a yield strength of 1250MPa, a tensile strength of 1525MPa and an elongation of 5%.

The steel strip may further comprise greater than 0.005% niobium or greater than 0.01% or 0.02% niobium by weight. The steel strip may comprise greater than 0.05% molybdenum or greater than 0.1% or 0.2% molybdenum by weight. The steel strip may be silicon killed, containing less than 0.008% aluminium or less than 0.006% aluminium by weight. The molten melt may have a free oxygen content of 5-70 ppm. The steel strip may have a total oxygen content greater than 50 ppm. The inclusions comprise MnOSiO typically with 50% of them being less than 5 μm in size₂And has the potential to enhance the microstructure evolution and hence the mechanical properties of the strip.

Can melt the molten metalThe volume is more than 10.0MW/m²Is solidified into a steel strip having a thickness of less than 2.5mm and is cooled to 1080 ℃ or less and Ar in a non-oxidizing atmosphere at a cooling rate of more than 15 ℃/s₃Above the temperature. The non-oxidizing atmosphere is an atmosphere of typically an inert gas such as nitrogen or argon or mixtures thereof, which contains less than about 5% by weight oxygen.

In some embodiments, the martensite in the steel strip may be derived from austenite having a grain size greater than 100 μm. In other embodiments, the martensite in the steel strip may be derived from austenite having a grain size greater than 150 μm. At a power of more than 10MW/m²The rapid solidification of the heat flux enables the production of austenite grain sizes responsive to controlled cooling after subsequent hot rolling to achieve defect-free strip manufacture.

High friction rolled steel sheets may be provided for use in hot stamping applications. Typically, steel sheets relied upon for use in hot stamping applications are stainless steel compositions or require aluminum-silicon corrosion resistant coatings. In hot stamping applications, a corrosion resistant protective layer is desirable while maintaining high strength properties and favorable surface structure characteristics. The high friction rolling compositions of the present invention have achieved the desired properties without relying on stainless steel compositions or otherwise providing aluminum-silicon corrosion resistant coatings. In contrast, the high friction rolling compositions of the present invention rely on a mixture of nickel, chromium and copper as illustrated in the various examples above to improve corrosion resistance. In hot stamping applications, the high friction rolled steel sheet is subjected to austenitizing conditions between 900 ℃ and 930 ℃ for a period of time between 6 minutes and 10 minutes. In one example, a high friction rolled steel sheet is subjected to austenitizing conditions at 900 ℃ for a period of 6 minutes. In another example, a high friction rolled steel sheet is subjected to austenitizing conditions at 900 ℃ for a period of 10 minutes. In yet another example, the high friction rolled steel sheet is subjected to austenitizing conditions at 930 ℃ for a period of 6 minutes. In even yet another example, the high friction rolled steel sheet is subjected to austenitizing conditions at 930 ℃ for a period of 10 minutes. Table 8 below illustrates that the properties of the high friction rolled steel sheet are maintained above the minimum tensile strength of 1500MPa, the minimum yield strength of 1100MPa, and the minimum elongation of 3% for hot stamping applications.

TABLE 8

Austenitizing conditions	Tensile strength (MPa)	Yield strength (MPa)	Elongation (%)
				900 ℃ for 6 minutes	1546.98	1155.06	7.3
900 ℃ for 6 minutes	1576.65	1154.37	7.0
				900 ℃ for 10 minutes	1591.14	1168.86	6.4
900 ℃ for 10 minutes	1578.03	1152.30	6.6
				930 ℃ for 6 minutes	1566.30	1146.09	7.3
930 ℃ for 6 minutes	1566.99	1178.52	6.5
				930 ℃ for 10 minutes	1509.03	1109.52	6.6
930 ℃ for 10 minutes	1521.45	1129.53	6.4

In these examples, the steel sheet provided for use in hot stamping applications may include the composition of any of the examples of steel sheets disclosed above, but is a steel sheet that may remain unquenched. In particular, a steel sheet provided for use in hot stamping applications may be made by steps comprising: (a) preparing a molten steel melt comprising: (i) between 0.20% and 0.40% carbon, less than 1.0% chromium, between 0.7% and 2.0% manganese, between 0.10% and 0.50% silicon, between 0.1% and 1.0% copper, less than or equal to 0.12% niobium, less than 0.5% molybdenum, between 0.5% and 1.5% nickel, and sedated with silicon containing less than 0.01% aluminum, by weight, and (ii) the balance iron and impurities resulting from smelting; (b) at a molecular weight of more than 10.0MW/m²Is solidified into a steel sheet having a thickness of 2.5mm or less and the sheet is cooled to 1080 ℃ or less and Ar in a non-oxidizing atmosphere at a cooling rate of more than 15 ℃/s before rapid cooling₃Above the temperature; (c) high friction rolling of thin cast steel strip to a hot rolling thickness with a reduction between 15% and 50% of the as-cast thicknessProducing a hot rolled steel strip having a smeared pattern that is substantially free, or free of prior austenite grain boundary pits; and (d) cooling at less than 100 ℃/s to form a steel sheet having a predominantly bainitic microstructure. That is, the steel sheet provided for use in hot stamping applications may be any of the examples of steel sheets disclosed above except for: the steel sheet is not rapidly cooled and, therefore, a microstructure mainly or substantially having martensite or martensite plus bainite is not formed. In contrast, steel sheets provided for use in hot stamping applications are cooled at less than 100 ℃/s.

Hot rolling, including low friction hot rolling and high friction hot rolling

Hot rolling (and more specifically, low friction rolling and high friction rolling) as relied upon in the above examples of the present disclosure is described further below. The concepts described below can be applied to the examples provided above as needed to achieve the properties of each respective example. Generally, in each hot rolling example, the strip is passed through a hot rolling mill to reduce the as-cast thickness before being cooled, for example, in particular embodiments, to a temperature at which austenite in the steel transforms to martensite. In certain cases, the hot solidified strip (cast strip) may be conveyed through a hot rolling mill while at an entry temperature greater than 1050 ℃ and in some cases up to 1150 ℃. After the strip exits the hot rolling mill, the strip is cooled, for example in certain exemplary cases to a temperature at which austenite in the steel transforms to martensite, by cooling to a temperature equal to or less than the martensite start temperature Ms. In some cases, the temperature is 600 ℃ or less, wherein the martensite start temperature M_SDepending on the particular composition. Cooling may be achieved by any known method using any known mechanism, including the mechanisms described above. In some cases, the cooling is fast enough to avoid appreciable ferrite initiation, which is also affected by the composition. In such a case, for example, the cooling is configured to reduce the temperature of the belt at a rate of about 100 ℃ to 200 ℃ per second.

Hot rolling is performed using one or more pairs of counter-rotating work rolls. Work rolls are commonly used to reduce the thickness of a substrate such as a plate or belt. This is accomplished by passing the substrate through a gap disposed between the pair of work rolls, the gap being less than the thickness of the substrate. This gap is also referred to as the roll gap. During thermal processing, a force is applied to the substrate by the work rolls, thereby exerting a rolling force on the substrate to thereby achieve a desired reduction in the thickness of the substrate. In doing so, friction is generated between the substrate and each work roll as the substrate translates through the gap. This friction is called roll gap friction.

Conventionally, it is desirable to reduce the seam friction during hot rolling of steel sheets and strips. By reducing the slot friction (and therefore the coefficient of friction), rolling loads and roll wear are reduced and machine life is extended. Various techniques have been employed to reduce the roll gap friction and coefficient of friction. In certain exemplary cases, thin steel belts are lubricated to reduce roll gap friction. Lubrication may take the form of: oil applied to the rolls and/or the thin steel strip, or scale formed along the outside of the thin steel strip prior to hot rolling. By using lubrication, hot rolling can occur under low friction conditions, where the coefficient of friction (μ) of the roll gap is less than 0.20.

In one example, the coefficient of friction (μ) is determined based on a hot rolling model developed by the HATCH for a particular set of work rolls. The model is shown in FIG. 8, which provides the reduction in thickness of the thin steel strip in percent along the X-axis and the specific force "P" in kN/mm along the Y-axis. The specific force P is the normal (perpendicular) force applied to the substrate by the work roll. The model includes five (5) curves, each representing a coefficient of friction and providing a relationship between reduction and work roll force. For each coefficient of friction, the expected work roll force is obtained based on the measured reduction. In operation, during hot rolling, a target coefficient of friction is preset by adjusting the work roll lubrication, a target reduction is set by the desired strip thickness required at the mill exit to meet a particular customer order, and the actual work roll force will be adjusted to achieve the target reduction. FIG. 8 shows typical forces required to achieve a target reduction for a particular coefficient of friction.

In certain exemplary cases, the coefficient of friction is equal to or greater than 0.20. In other exemplary cases, the coefficient of friction is equal to or greater than 0.25, equal to or greater than 0.268, or equal to or greater than 0.27. It is recognized that these coefficients of friction are sufficient under certain conditions for austenitic steels (which are the steel alloys used in the examples shown in the figures) to at least predominantly or substantially eliminate prior austenite grain boundary pits from the hot rolled surface and to produce elongated surface features that are plastically formed by shear, wherein the steel is austenitic during hot rolling but forms martensite with prior austenite grains and prior austenite grain boundary pits present after cooling. As previously mentioned, various factors or parameters may be varied to achieve a desired coefficient of friction under certain conditions. It is noted that for the friction coefficient values previously described, for a substrate having a thickness of 5mm or less prior to hot rolling, the normal force applied to the substrate during hot rolling may be 600 to 2500 tons at a temperature of greater than 1050 ℃, and in some cases up to 1150 ℃, of the substrate entering the work rolls as the substrate enters the pair of work rolls and translates or advances at a rate of 45-75 meters per minute (m/min). For these coefficients of friction, the work rolls had diameters of 400-600 mm. Of course, variations outside each of these parameter ranges may be used as desired to achieve different coefficients of friction, as may be desired to achieve the surface characteristics of the hot rolling described herein.

In one example, hot rolling is conducted under high friction conditions with a coefficient of friction of 0.25 at 60 meters per minute (m/min) at a 22% reduction with a work roll force of approximately 820 tons. In another example, hot rolling is conducted under high friction conditions with a coefficient of friction of 0.27 at 60 meters per minute (m/min) at a 22% reduction rate with a work roll force of approximately 900 tons.

Hot rolling of thin steel strip as relied upon in the examples of the present disclosure when the thin steel strip is at A_r3At a temperature above the temperature. Ar (Ar)₃The temperature is the temperature at which austenite begins to transform to ferrite during cooling. That is, Ar₃The temperature is the austenite transformation point. Ar (Ar)₃Temperature in ratio A₃A position several degrees lower in temperature. At Ar₃Below the temperature, alpha ferrite is formed. These temperatures are shown in the exemplary CCT diagram in fig. 9. In FIG. 9, A₃170 represents the upper temperature at which ferrite stability ends at equilibriumAnd (4) degree. Ar (Ar)₃The upper limit temperature at which the ferrite stability ends during cooling. More specifically, Ar₃The temperature is the temperature at which austenite begins to transform to ferrite during cooling. That is, Ar₃The temperature is the austenite transformation point. For comparison, A₁180 denotes the lower limit temperature at which ferrite stability ends at equilibrium.

Referring also to fig. 9, a ferrite curve 220 represents a transformation temperature of a microstructure generating 1% ferrite, a pearlite curve 230 represents a transformation temperature of a microstructure generating 1% pearlite, an austenite curve 250 represents a transformation temperature of a microstructure generating 1% austenite, and a bainite curve (B)_s)240 denotes the transformation temperature resulting in a microstructure of 1% bainite. As described in greater detail previously, the martensite start temperature M_SRepresented by the martensite curve 190, where martensite begins to form from prior austenite in the thin steel strip. Further illustrated in fig. 9 is a 50% martensite curve 200 representing a microstructure having at least 50% martensite. Additionally, fig. 9 illustrates a 90% martensite curve 210 representing a microstructure having at least 90% martensite.

In the exemplary CCT plot shown in FIG. 9, the martensite start transition temperature M is shown_S190. The austenite in the strip transforms to martensite when passing through the cooler. In particular, in this case, cooling the strip to below 600 ℃ results in a transformation of coarse austenite, in which a distribution of fine iron carbides is precipitated within the martensite.

While the invention has been illustrated and described in the foregoing drawings and description, the same is to be considered as illustrative and not restrictive in character, it being understood that only illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention as described by the following claims are desired to be protected. Additional features of the invention will become apparent to those skilled in the art upon consideration of the description. Changes may be made without departing from the spirit and scope of the invention.