阅读说明：本技术 一种无横折缺陷的300MPa级低碳热轧钢生产方法 (Production method of 300 MPa-grade low-carbon hot rolled steel without transverse fracture defect ) 是由 欧阳页先 陈潮 郑泽林 孙向阳 秦哲 陈良 朱经涛 陈统 陈传敬 季长恩 李立根 于 2020-10-31 设计创作，主要内容包括：本发明公开了一种无横折缺陷的300MPa级低碳热轧钢生产方法,属于钢铁生产领域,包括(1)钢水冶炼；(2)连铸,获得铸坯；(3)热轧：加热温度1150～1200℃；终轧温度控制在850～900℃；(4)冷却卷取：层流冷却采用分段式冷却,≥750℃,采用空冷,冷却速率＜15℃/s；＜750℃,采用激冷,冷却速率大于35℃/s；卷取温度620℃-680℃；(5)平整酸洗：采用先平整后酸洗工艺,控制平整压下量1.5-2.5％,平整速率≥200m/min,反弯辊采用恒包角控制,包角80-130°。本发明通过成分控制、热轧工艺、平整酸洗工艺的控制,可生产出低强度、无横折纹缺陷产品。(The invention discloses a production method of 300 MPa-grade low-carbon hot rolled steel without a transverse fracture defect, which belongs to the field of steel production and comprises the steps of (1) smelting molten steel; (2) continuously casting to obtain a casting blank; (3) hot rolling: heating at 1150-1200 ℃; the finishing temperature is controlled to be 850-900 ℃; (4) cooling and coiling: the laminar cooling adopts sectional cooling, the temperature is more than or equal to 750 ℃, air cooling is adopted, and the cooling rate is less than 15 ℃/s; chilling at the temperature of less than 750 ℃ at a cooling rate of more than 35 ℃/s; the coiling temperature is 620-680 ℃; (5) leveling and pickling: the flattening and pickling processes are adopted, the flattening rolling reduction is controlled to be 1.5-2.5%, the flattening speed is more than or equal to 200m/min, the reverse bending roller is controlled by a constant wrap angle, and the wrap angle is 80-130 degrees. The invention can produce the product with low strength and no transverse crease defect by controlling the components, the hot rolling process and the flattening pickling process.)

1. A production method of 300 MPa-grade low-carbon hot rolled steel without transverse fracture defects is characterized by comprising the following steps: the method comprises the following steps:

(1) smelting molten steel: performing converter smelting according to the component proportion;

(2) continuous casting: continuously casting qualified molten steel obtained by a ladle furnace to obtain a casting blank;

(3) hot rolling: heating at 1150-1200 ℃; the finishing temperature is controlled to be 850-900 ℃;

(4) cooling and coiling: the laminar cooling adopts sectional cooling, the temperature is more than or equal to 750 ℃, air cooling is adopted, and the cooling rate is less than 15 ℃/s; chilling at the temperature of less than 750 ℃ at a cooling rate of more than 35 ℃/s; the coiling temperature is 620-680 ℃;

(5) leveling and pickling: the flattening and pickling processes are adopted, the flattening rolling reduction is controlled to be 1.5-2.5%, the flattening speed is more than or equal to 200m/min, the reverse bending roller is controlled by a constant wrap angle, and the wrap angle is 80-130 degrees.

2. The method of claim 1, wherein the hot rolled pickled sheet band transverse fold control method comprises the steps of: the yield strength of the thin plate strip is 180-250 MPa, the tensile strength is 300-350 MPa, and the elongation A50 is more than or equal to 40%.

3. The method of claim 1, wherein the hot rolled pickled sheet band transverse fold control method comprises the steps of: the thickness specification of the thin plate strip is 0.80mm-2.0 mm.

Technical Field

The invention relates to the field of metallurgy, in particular to a production method of low-strength thin-specification low-carbon hot-rolled thin plate strip steel (less than or equal to 2.0 mm).

Background

The low-carbon steel sheet strip is widely applied to basic civil industries such as machinery, hardware, household appliances, electrical appliances and the like, and has huge market demand. With the progress of the hot continuous rolling technology, the low-carbon hot rolled steel with the thickness of less than or equal to 2.0mm tends to replace common cold rolled products.

However, low carbon steel has low strength and is prone to ' Luders ' band ' or transverse crease defects during pickling and leveling. In the traditional cold rolling annealing process, Ti and Nb are added to fix interstitial atoms C, N to avoid forming Cocker air mass and control the generation of transverse fold defects. In the other method, an overaging section is added after annealing, supersaturated solid solution C, N is fully precipitated, the appearance of Coriolis gas masses is delayed, and the transverse fold defect is reduced. The former has narrow application range, is effective only for ultra-low carbon (C is less than or equal to 0.0030 percent), has high C content and large required Ti and Nb content, and can precipitate fine C, N second phases to increase the strength and be not beneficial to cold working forming. The latter requires a longer aging period, greatly increases investment costs, and is less suitable for thin gauge pickling or leveling products that are hot to cold. At present, the patent of the transverse crease control method for the thin hot-rolled pickled plate strip is very few. The invention relates to a method for eliminating transverse crease lines of the head of a low-carbon steel hot-rolled pickled plate (application number 202010060659.1), which discloses the following steps: the method comprises the steps of controlling the laminar cooling speed of 26-28 ℃/s after hot rolling and finish rolling, coiling at low temperature of 560 +/-10 ℃, cooling to the temperature of less than or equal to 50 ℃ and then flattening, and controlling the internal transverse fold lines with the head and the tail of 30-50 m. The method mainly eliminates transverse fold lines by improving yield strength, and greatly deteriorates the cold-working formability of the steel plate strip. A suitable thickness range is 1.50mm-6.0 mm. The invention relates to a method for flattening the transverse folding defect of the surface of a hot-rolled pickled plate (application number 201510763550.3), which discloses the following steps: the hot rolling flattening unit adopts constant rolling force control, selects a flattening and straightening mode, adopts a deep bending roll subsection pressure control strategy, adjusts the pressure of a deep bending roll according to the cross section area of the strip steel, and controls the elongation of the strip steel to be 3-3.5%. The method has excessive elongation, causes work hardening, increases yield strength, and deteriorates workability. For the low-carbon steel thin strip, the rolling force is low, the rolling force is controlled constantly, and the thickness precision is difficult to ensure. The pressure of the deep bending roller is adjusted by the cross section area, the influence of the thickness of the steel coil on the transverse fold lines is only considered, and the influence of the coiling curvature on the transverse fold lines is not considered.

Therefore, the control of transverse fold defects under the condition of ensuring low strength and cold working performance of the hot-rolled thin pickled strip with hot instead of cold specifications becomes a key technical problem.

Disclosure of Invention

The technical task of the invention is to provide a control method of transverse fold of hot-rolled pickled sheet strip aiming at the defects of the prior art, and the invention can produce low-strength products without transverse fold defects by controlling components, hot-rolling process and flattening pickling process, and provides technical support for the application of low-carbon steel sheet strip products in hot-cooling instead of cold-cooling.

The technical scheme for solving the technical problem is as follows: a production method of low-carbon hot rolled steel without transverse fracture defects and with 300 MPa-level tensile strength is characterized by comprising the following steps: the method comprises the following steps:

(1) smelting molten steel: performing converter smelting according to the component proportion;

(2) continuous casting: continuously casting qualified molten steel obtained by a ladle furnace to obtain a casting blank;

(3) hot rolling: heating at 1150-1200 ℃; the finishing temperature is controlled to be 850-900 ℃;

(4) cooling and coiling: the laminar cooling adopts sectional cooling, the temperature is more than or equal to 750 ℃, air cooling is adopted, and the cooling rate is less than 15 ℃/s; chilling at the temperature of less than 750 ℃ at a cooling rate of more than 35 ℃/s; the coiling temperature is 620-680 ℃;

(5) leveling and pickling: adopting a process of flattening and then pickling, controlling the flattening rolling reduction to be 1.5-2.5%, the flattening speed to be more than or equal to 200m/min, and controlling the reverse bending roller to be at a constant wrap angle of 80-130 degrees;

the yield strength of the sheet band is 180-250 MPa, the tensile strength is 300-350 MPa, and the elongation A50 is more than or equal to 40%.

The thickness specification of the thin plate strip is 0.80mm-2.0 mm.

Compared with the prior art, the invention has the following outstanding beneficial effects:

1. according to the invention, through reasonable component design, the contents of Mn, Si, Al, N and C elements are controlled, meanwhile, trace B element is added, B/N is controlled, solid solution C and N are reduced, the generation of Coriolis gas clusters is reduced, the generation of transverse fold defects is controlled, meanwhile, the strength is reduced, the elongation is improved, and the cold processing performance is improved;

2. controlling the temperature of the hot rolling and the finish rolling, carrying out sectional cooling, and selecting a proper coiling temperature to obtain a uniform microstructure and a precipitated phase;

3. selecting a process arrangement of flattening and then pickling, and delaying the generation of Coriolis gas masses by controlling the flattening reduction rate and the flattening speed and adopting a constant wrap angle reverse roll application mode;

4. the product and the technology of the invention prepare the product with the yield strength Rel: 180-250 MPa, tensile strength Rm: 300-350 MPa, the elongation A50 is more than or equal to 40%, the thickness specification is 0.80-2.0mm, the application range of low-carbon steel products is promoted, and the technical support is provided for energy saving and cost reduction of a full supply chain.

Drawings

FIG. 1 is a photograph of the surface quality of example 1 of the present invention.

FIG. 2 is a photograph showing the surface quality of comparative example 1 of the present invention.

Detailed Description

The present invention will be further described with reference to the following embodiments.

The invention provides a hot-rolled pickled sheet strip with low strength and no transverse crease defect, which comprises the following components in percentage by mass: c: 0.010-0.050%, Si is less than or equal to 0.10%, Mn: 0.08-0.30%, Alt: 0.015-0.050%, N: less than or equal to 0.005 percent, B: 0.0010-0.0050, and the balance of iron and inevitable impurities; wherein, B/N: 0.7-1.2.

The component design of the hot-rolled pickled thin plate strip produced by the patent is detailed as follows:

c exists in the steel in the form of solid solution atoms and carbides, affecting the properties and microstructure of the steel, and is therefore one of the main controlling elements of the hot-rolled pickled sheet strip. The content of C is higher than 0.05%, the solid solution C of the finished product is increased, and fine cementite is precipitated in the rolling process to prevent the crystal grains from growing and improve the strength. The content of C is lower than 0.01 percent, deep decarburization is needed, the smelting cost is increased, less cementite is precipitated in the rolling and cooling process, and the solid solution C is increased;

si is a harmful element to improve strength, reduce elongation, and deteriorate cold-formability. In addition, the Si content is too high, and iron scale is difficult to remove, so that the surface quality is influenced.

Mn is a solid-solution strengthening element, and is an element for enlarging a gamma phase region and an alpha + gamma two-phase region. The phase change and the second phase precipitation in the rolling and cooling process can be controlled by adding a proper amount of Mn content. The Mn content is higher than 0.3%, the two-phase region is enlarged, and the high-temperature solid solution C/N is increased, which is not beneficial to precipitation. Mn is too low, less than 0.08%, resulting in hot brittleness of the cast slab and edge cracking.

Alt is a main alloy element for deoxidation, the bonding force with N is strong, and AlN is separated out in the casting blank cooling and rolling processes. Alt is too high, increasing the strength of the steel and increasing the cost. Too low, the deoxidation ability is weakened, and the N fixation effect is reduced, which is not favorable for controlling the reduction of the solid solution N.

N is an unavoidable harmful element in steel, is over high and is more than 50ppm, solid solution N is increased, Cocker gas masses are easily formed, the defect of transverse fold lines is caused, and the strength is increased.

B is a strong N element, and the BN precipitation temperature is high, so that coarse BN can be precipitated in the continuous casting process, and the effects of fixing N and reducing strength are achieved. Compared with the mode of adding Ti and Nb to fix the interstitial atoms C, N, the defects of large amount of Ti (C, N) precipitation, strength increase and inconvenience for cold forming processing are avoided. In addition, the content of C is 0.010-0.050% in the formula, the needed Ti and Nb are large in amount, the cost is high, and the defects are more obvious. The addition amount of B is in a proper range, is higher than 50ppm, the casting blank has cracks and even bleed-out, is too low and lower than 10ppm, and the effects of fixing N and reducing strength are not obvious. In addition, the addition of B is related to the content of N, and the B/N needs to be controlled to be 0.7-1.2, so that a better effect can be achieved.

In the optimization scheme, the B/C ratio is controlled to be 0.03-0.1 when the thickness specification is 0.80-1.2mm, and the B/C ratio is controlled to be 0.1-0.31 when the thickness specification is 1.2-2.0mm, so that the defect of cold forming processing is favorably overcome.

The process for producing the low-carbon hot-rolled pickled sheet strip comprises the following steps: converter → ladle furnace → continuous casting → hot rolling → cooling and coiling → leveling and pickling.

(1) Smelting of molten steel

According to the component proportion, converter smelting is carried out, a ladle furnace is used for desulfurization, and ferroboron is added for alloying.

(2) Continuous casting

And (4) continuously casting the qualified molten steel obtained by the ladle furnace to obtain a casting blank.

(3) Hot rolling

The hot rolling process adopts a proper heating temperature of 1150-1200 ℃, so that the second phase BN can be coarsely and fully separated out, and the nitrogen fixation and strength reduction effects are achieved. The temperature is over-high and is more than 1200 ℃ or less than 1150 ℃, and the BN precipitation of the second phase is insufficient. In the hot rolling process, fine second phase AlN is precipitated, and the strength of the steel is improved.

The finishing temperature is an important technical point in the hot rolling process and is also a key element for controlling transverse wrinkles. The final rolling temperature of the invention is controlled at 850-900 ℃, the final rolling temperature is lower than 850 ℃, the final frame is rolled in a two-phase region, the phenomenon of mixed crystals is easy to occur, the strength is increased, the extension is reduced, the precipitation of C/N and the micro-strength are uneven, and the defect of transverse wrinkles is easy to occur. Too high, more than 900 ℃, slow gamma-alpha phase transformation speed, and increased solid solution C/N in the cooling process, resulting in transverse fold defects.

(4) Cooled coiling

Laminar cooling and coiling temperature are important for diffusion and precipitation of solid solution C/N. The coiling temperature is 620-680 ℃, the coiling temperature is too low and is less than 620 ℃, the recrystallization is incomplete, and the strength is increased. And the crystal grain difference of the steel coil along the length direction and the width direction is large when the temperature is higher than 680 ℃, the internal stress is increased in the cooling and flattening process, and the transverse fold defect is easy to occur.

The laminar cooling of the invention adopts sectional cooling, the temperature is more than or equal to 750 ℃, air cooling is adopted, and the cooling rate is less than 15 ℃/s. When the temperature is less than 750 ℃, chilling is adopted, the cooling rate is more than 35 ℃/s, and the process controls the diffusion of solid solution C/N to achieve the effect of effectively controlling the transverse wrinkles.

(5) Temper rolling acid wash

The flattening and pickling processes are adopted, the flattening rolling reduction is controlled to be 1.5-2.5%, the flattening speed is more than or equal to 200m/min, the reverse bending roller is controlled by a constant wrap angle, and the wrap angle is 80-130 degrees. The C/N content of interstitial solid solution atoms is controlled, the proliferation of dislocation is reduced to form Coriolis air mass, and the generation of transverse wrinkles is avoided.

And (4) acid leveling, namely uncoiling and throwing a reverse bending roller, and controlling by adopting a constant wrap angle. The wrap angle is 80-100 degrees when the thickness specification is 0.80-1.2mm, and the wrap angle is 100-130 degrees when the thickness specification is 1.2-2.0 mm. According to different thickness specifications, different wrap angles are selected, the lowest residual stress of the inner surface and the outer surface can be obtained, and the occurrence of the transverse fold line defect is controlled.

The flattening reduction is controlled to be 1.5-2.5%, the yield platform is not completely eliminated when the flattening reduction is too low, and the yield platform is too high, so that the work hardening is caused, the yield strength is improved, and the cold processing performance is influenced.

The leveling rate is controlled to be more than or equal to 200m/min, the deformation rate is increased, the solid solution C/N aggregation and the pinning dislocation are delayed, and the occurrence of transverse wrinkles is controlled.

And finally preparing the yield strength Rel: 180-250 MPa, tensile strength Rm: 300-350 MPa, the elongation A50 is not less than 40%, the transverse fold defect is avoided, and the cold forming performance is excellent. The product is applied to the industries of door industry, fire fighting, automobile parts and the like, forms a brand replacing cold with heat, and promotes the reduction of the production cost of the whole industrial chain.

Smelting qualified molten steel according to target components, carrying out continuous casting and hot continuous rolling to obtain a hot-rolled substrate with the thickness of 0.80-2.0mm, carrying out acid pickling and leveling, and preparing the low-strength low-carbon steel hot-rolled pickled sheet strip without transverse wrinkles.

The smelting components of each group are shown in the table below, and the balance is iron and inevitable impurities;

the hot rolling process parameters of each group are shown in the following table:

the acid-washing and flattening process parameters of each group are shown in the following table:

the mechanical properties and surfaces of each group are shown in the following table:

as can be seen from the above table and the figures 1 and 2, the low-carbon steel hot-rolled pickled sheet strips produced by the components and the process in the examples 1 to 9 have excellent mechanical properties and surface quality (yield strength Rel: 180-250 MPa, tensile strength Rm: 300-350 MPa, elongation A50 being more than or equal to 40%), no transverse crease defect, plastic strain ratio being more than 1.0 and good cold processing performance. The production process is less, the common cold rolling and annealing process is saved, and the energy consumption and the cost are low.

The component B/N ratio of comparative example 1 is too low, resulting in unremoved solid solution N, obvious transverse fold defects in the flattening process of the steel strip, high strength, low extension and low r value, and being not beneficial to cold forming.

The components of comparative examples 2-3 control the B/N ratio, but the rolling and cooling control parameters are different, and the traditional acid leveling process control is adopted. The results show that the dense transverse wrinkles are generated due to the failure of effective control of solid solution C/N and internal stress of the steel strip.

It should be noted that while the invention has been described in detail with respect to specific embodiments thereof, it will be apparent to those skilled in the art that various obvious changes can be made therein without departing from the spirit and scope of the invention.