阅读说明：本技术 一种低温高韧性铈锆复合处理fh40船板钢及其制备方法 (Low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel and preparation method thereof ) 是由 李运刚 孟祥海 王哲 李孟星 马涛 李慧蓉 高建新 张士宪 于 2019-05-05 设计创作，主要内容包括：本发明公开了一种低温高韧性铈锆复合处理FH40船板钢,所述船板钢的原料化学成分质量百分比为：C 0.04～0.08％,Si 0.2～0.4％,Mn 1.4～1.7％,P≤0.012％,S≤0.005％,Nb 0.020～0.055％,Ti 0.01～0.02％,V 0.025～0.060％,Ni 0.20～0.35％,Al 0.01～0.04％,Ce 0.01～0.04％,Zr 0.01～0.03％以及余量的Fe和不可避免的杂质；其制备方法包括以下步骤：S1、准备原料熔炼成钢坯；S2锻造得到锻坯；S3轧制；S4冷却成钢。本发明通过采用控轧控冷技术,并且复合添加Ce、Zr合金元素,使晶粒细化,获得组织为铁素体和贝氏体；生产出的钢板强度高,屈服强度≥435MPa,抗拉强度≥530MPa,断后延展率≥22.4％,低温冲击韧性良好,-60℃纵向冲击功≥244J。(The invention discloses low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel, which comprises the following raw materials in percentage by mass: 0.04-0.08% of C, 0.2-0.4% of Si, 1.4-1.7% of Mn, less than or equal to 0.012% of P, less than or equal to 0.005% of S, 0.020-0.055% of Nb, 0.01-0.02% of Ti, 0.025-0.060% of V, 0.20-0.35% of Ni, 0.01-0.04% of Al, 0.01-0.04% of Ce, 0.01-0.03% of Zr and the balance of Fe and inevitable impurities; the preparation method comprises the following steps: s1, preparing raw materials and smelting the raw materials into a steel billet; s2 forging to obtain a forging stock; s3 rolling; s4 cooling to steel. The invention adopts the controlled rolling and controlled cooling technology and compositely adds Ce and Zr alloy elements to refine grains and obtain tissues of ferrite and bainite; the produced steel plate has high strength, yield strength of more than or equal to 435MPa, tensile strength of more than or equal to 530MPa, elongation after fracture of more than or equal to 22.4 percent, good low-temperature impact toughness and longitudinal impact energy of more than or equal to 244J at minus 60 ℃.)

1. The low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel is characterized in that the ship plate steel is prepared from the following raw materials in percentage by mass: 0.04-0.08% of C, 0.2-0.4% of Si, 1.4-1.7% of Mn, less than or equal to 0.012% of P, less than or equal to 0.005% of S, 0.020-0.055% of Nb, 0.01-0.02% of Ti, 0.025-0.060% of V, 0.20-0.35% of Ni, 0.01-0.04% of Al, 0.01-0.04% of Ce, 0.01-0.03% of Zr and the balance of Fe and inevitable impurities.

2. The low-temperature high-toughness FH40 ship plate steel recited in claim 1, wherein the ship plate steel structure is composed of ferrite and bainite, wherein the volume fraction of ferrite is 71-80%, the volume fraction of bainite is 20-29%, and the average grain size of ferrite is 9.0-10.8 μm.

3. The low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel and the preparation method thereof as claimed in claim 1, wherein the ship plate steel has a thickness of 16-26 mm, a yield strength of 435-480 MPa, a tensile strength of 530-599 MPa, a yield ratio of 0.76-0.83, a ballistic work at-60 ℃ of 244-275J, and an elongation after fracture of 22.4-24.2%.

4. The preparation method of the low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel recited in claim 1 comprises the following steps:

s1, preparing the raw materials of the chemical mass percentage, and finely adjusting the components of the raw materials by adopting metal manganese, ferrosilicon, ferroniobium, steel-cored aluminum, ferrotitanium, nickel plate alloy, ferromolybdenum, ferrovanadium, cerium powder and ferrozirconium; smelting cerium powder, wrapping the cerium powder by a metal sheet, adding the cerium powder to the bottom of a smelting furnace, smelting molten steel and casting the molten steel into a billet;

s2, forging: heating the billet prepared in the step S1 to 1160-1220 ℃, preserving heat for 0.5-1 h, forging, wherein the start forging temperature is 1130-1170 ℃, the finish forging temperature is 850-900 ℃, and then air cooling to obtain a forging stock;

s3, rolling:

(1) rough rolling: heating the forging stock prepared in the step S2 to 1200-1230 ℃, preserving heat for 1-2 h, then carrying out 2-4 times of rough rolling on the steel billet, wherein the initial rolling temperature is 1150-1180 ℃, the total accumulated reduction rate is 52.5-67.6%, obtaining an intermediate stock,

(2) finish rolling: carrying out 4-pass finish rolling on the intermediate blank, wherein the initial rolling temperature is 940-960 ℃, the total accumulated reduction rate is 24.6-64.6%, and the final rolling temperature is 860-880 ℃, so as to obtain a steel plate with the thickness of 16-26 mm;

s4: cooling to form steel: carrying out water cooling-air cooling-water cooling three-stage cooling on the steel plate: and (3) water cooling at the section I, cooling to 640-680 ℃, air cooling at the section II, water cooling at the section III, and slowly cooling to room temperature to obtain the low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel.

5. The low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel and the preparation method thereof of claim 4, wherein the thickness of the steel billet prepared in the step S1 is 110-135 mm.

6. The method for preparing the low-temperature high-toughness FH40 ship plate steel according to claim 4, wherein in step S2, the reduction rate in the forging stage is 20.8-25.0%, and the thickness of the forging stock is 95-105 mm.

7. The preparation method of the low-temperature high-toughness FH40 ship plate steel recited in claim 4, wherein in step S3, the single pass reduction of rough rolling is 16.3-23.5%, the single pass reduction of finish rolling is 20.2-25.4%, and the thickness of the intermediate billet is 34-64 mm.

8. The preparation method of the low-temperature high-toughness FH40 ship plate steel recited in claim 4, wherein in step S4, the water cooling rate in section I is 100-150 ℃/S, the air cooling time in section II is 3.3-5.0S, and the water cooling rate in section III is 28-44 ℃/S.

Technical Field

The invention relates to the technical field of metallurgy, in particular to low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel and a preparation method thereof.

Background

In recent years, the shipbuilding industry develops rapidly, and the ordinary strength shipbuilding steel plate cannot meet the development requirement of the shipbuilding industry. Such as in the context of polar resources and airline development, ships need to withstand low temperature climates at-60 ℃ and below, and therefore, high strength deck steel is required for components such as decks, gas turbines, bearings and connectors during the construction of polar transport vessels, resource exploration vessels, icebreakers, naval vessels. The ship plate is required to have good toughness matching and stability, and also has good low-temperature toughness, high heat input welding performance and seawater corrosion resistance. At present, researches on the alloying structure and the performance of AH, BH, DH and EH series high-strength steel are more at home and abroad, but the researches on the structure and the performance of FH series high-strength ship plate steel are few, especially, the research on the influence mechanism after the addition of rare earth composite elements is less, the large heat input welding performance is poorer, the toughness of a welding seam heat influence area is lower, and the actual production requirement cannot be met. Therefore, the development of the low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel has important significance for improving the safety of the ship working at the temperature of-60 ℃ and below.

In recent years, certain results are obtained in the preparation of FH40 grade ship plate steel, and related patents have published reports.

Such as: the patent with the publication number of CN 103695769B discloses a high-strength steel plate for FH40 ocean engineering and a production method thereof, wherein the yield strength is 420-440MPa, the tensile strength is only 530-580 MPa, and the elongation is only 22-24 percent; the V-shaped impact energy at the temperature of minus 60 ℃ is only 180 to 240J; and the structural characteristics of the steel sheet are not given.

The invention discloses a hot-rolled marine low-temperature ferrite LT-FH40 steel plate and a production method thereof, wherein the hot-rolled marine low-temperature ferrite LT-FH40 steel plate is prepared by low-carbon and niobium-titanium alloying component design, a low-phosphorus and sulfur smelting process and a reasonable rolling and cooling control technology, and is complex in process, long in production period and low in production efficiency.

The patent publication No. CN101876033A discloses a low-temperature high-toughness ship plate steel, which has high low-temperature impact toughness and low tensile strength of 480MPa, and the longitudinal impact energy at-60 ℃ can reach more than 250J. The requirements of modern large ships cannot be met.

Disclosure of Invention

The invention aims to solve the defects in the prior art, and provides low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel and a preparation method thereof.

In order to achieve the purpose, the invention adopts the following technical scheme:

the low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel comprises the following raw materials in percentage by mass: 0.04-0.08% of C, 0.2-0.4% of Si, 1.4-1.7% of Mn, less than or equal to 0.012% of P, less than or equal to 0.005% of S, 0.020-0.055% of Nb0.01-0.02% of Ti, 0.025-0.060% of V, 0.20-0.35% of Ni, 0.01-0.04% of Al, 0.01-0.04% of Ce, 0.01-0.03% of Zr and the balance of Fe and inevitable impurities.

C, Si, Mn, P, S, Nb, V, Al, Ti, Ni, Ce and Zr are added into the raw material components for fine adjustment of the components, wherein:

c: is a main strengthening element in the microalloy steel and is a main element for improving the hardenability of the steel plate; if the content is too low, the amount of carbide and the like produced decreases, and the effect of refining grains during rolling is impaired. When the content is too high, the low-temperature toughness and weldability of the steel sheet are adversely affected. The range of the C is controlled to be 0.04-0.08%.

Si: the steel plate can promote the deoxidation of molten steel and improve the strength of the steel plate, has strong solid solution capability in steel and can play a certain role in strengthening, but the low-temperature toughness and the welding performance of the steel plate are seriously damaged when the content is too high. Therefore, the invention controls the content of Si to be 0.05-0.2%.

Mn: the proper Mn can delay the transformation of steel ferrite and pearlite, greatly increase the hardenability of steel, reduce the brittle transformation temperature of steel and improve the impact toughness. The invention controls the range of Mn to be 1.4-1.7%.

Ti: ti can generate strong precipitation strengthening effect, improve the strength of steel and prevent austenite from recrystallizing; meanwhile, the grain refining effect can be generated, and the yield strength of the steel is improved. The range of Ti controlled by the invention is 0.01-0.02%.

Nb: one is that the high temperature region improves the austenite complete recrystallization temperature through the solute dragging effect of Nb on the austenite grain boundary, and prevents the recrystallized austenite grain from growing large; the other is that the carbon and the nitride of Nb pass through the lower temperature area to become nucleation particles of ferrite, thereby refining ferrite grains. The range of Nb controlled by the invention is 0.02-0.055%.

V: as well as Ti, are strong carbide formers. The carbon and nitride of V are separated out in large quantity at low temperature, which can refine crystal grains and strengthen crystal grains due to the precipitation of VC and V (CN), thereby improving the strength of the steel plate. Under the condition of coexistence of V, Nb and Ti, proper vanadium content has good effect on improving the toughness of the welding seam. The range of V controlled by the invention is 0.025-0.060%.

Al: is a strong oxide forming element and a strong nitride forming element, and generally requires that Al is more than or equal to 0.020%, so that fine austenite grains can be obtained when the steel plate is reheated in the welding and heat treatment processes. The invention controls the range of Al to be 0.01-0.04%.

Ni: is the only element capable of improving low temperature impact toughness (DWTT, NDT, CTOD and CVN). Copper-induced surface cracking during continuous casting and hot rolling can also be effectively prevented. The invention controls the range of Ni to be 0.2-0.35%.

Ce: oxides, sulfides or oxysulfides of Ce are high-melting-point inclusions with good thermal stability, and the high-melting-point inclusions cannot be dissolved in the large-heat-input welding process, can be effective nucleation particles of ferrite and are beneficial to improving HAZ toughness. The function of the method is also beneficial to purifying molten steel in the steelmaking process. The Ce content is controlled to be 0.01-0.04%.

Zr: the Zr-containing inclusions are precipitated in the solidification process and have very important influence on the toughness. The Zr controlling range of the invention is 0.01 percent to 0.03 percent.

Preferably, the ship plate steel structure is ferrite and bainite, wherein the volume fraction of the ferrite is 71-80%, the volume fraction of the bainite is 20-29%, and the average grain size of the ferrite is 9.0-10.8 μm.

Preferably, the thickness of the ship plate steel is 16-26 mm, the yield strength is 435-480 MPa, the tensile strength is 530-599 MPa, the yield ratio is 0.76-0.83, the impact energy at-60 ℃ is 244-275J, and the elongation after fracture is 22.4-24.2%.

A preparation method of low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel comprises the following steps:

s1, preparing the raw materials of the chemical mass percentage, and finely adjusting the components of the raw materials by adopting metal manganese, ferrosilicon, ferroniobium, steel-cored aluminum, ferrotitanium, nickel plate alloy, ferromolybdenum, ferrovanadium, cerium powder and ferrozirconium; smelting cerium powder, wrapping the cerium powder by a metal sheet, adding the cerium powder to the bottom of a smelting furnace, smelting molten steel and casting the molten steel into a billet;

s2, forging: heating the billet prepared in the step S1 to 1160-1220 ℃, preserving heat for 0.5-1 h, forging, wherein the start forging temperature is 1130-1170 ℃, the finish forging temperature is 850-900 ℃, and then air cooling to obtain a forging stock;

s3, rolling:

(3) rough rolling: heating the forging stock prepared in the step S2 to 1200-1230 ℃, preserving heat for 1-2 h, then carrying out 2-4 times of rough rolling on the steel billet, wherein the initial rolling temperature is 1150-1180 ℃, the total accumulated reduction rate is 52.5-67.6%, obtaining an intermediate stock,

(4) finish rolling: carrying out 4-pass finish rolling on the intermediate blank, wherein the initial rolling temperature is 940-960 ℃, the total accumulated reduction rate is 24.6-64.6%, and the final rolling temperature is 860-880 ℃, so as to obtain a steel plate with the thickness of 16-26 mm;

s4: cooling to form steel: carrying out water cooling-air cooling-water cooling three-stage cooling on the steel plate: and (3) cooling the steel plate by water in the section I to 640-680 ℃, cooling the steel plate by air in the section II, cooling the steel plate by water in the section III to the final cooling temperature of 480-550 ℃, and then slowly cooling the steel plate to the room temperature to obtain the low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel.

Preferably, the thickness of the steel billet prepared in the step S1 is 110-135 mm.

Preferably, the rolling reduction in the forging stage in the step S2 is 20.8 to 25.0%, and the thickness of the forging blank is 95 to 105 mm.

Preferably, the single-pass reduction rate of the rough rolling in the step S3 is 16.3 to 23.5%, the single-pass reduction rate of the finish rolling is 20.2 to 25.4%, and the thickness of the intermediate billet is 34 to 64 mm.

Preferably, in the step S4, the water cooling rate of the section I is 100-150 ℃/S, the air cooling time of the section II is 3.3-5.0S, and the water cooling rate of the section III is 28-44 ℃/S.

The invention has the beneficial effects that: according to the invention, Ce and Zr are added in a composite manner, and the as-cast structure is eutectoid ferrite, acicular ferrite and pearlite; the rolling structure is ferrite and bainite, and the control of the grain size of the ferrite after the gamma-alpha phase transformation is obviously refined; not only can improve the strength, but also can improve the low-temperature toughness. The ship plate steel ferrite volume fraction is 71-80%, the bainite volume fraction is 20-29%, the thickness is 16-26 mm, the yield strength is 435-495 MPa, the tensile strength is 530-599 MPa, the yield ratio is 0.76-0.83, the impact work at-60 ℃ is 244-275J, and the elongation after fracture is 22.4-24.2%. By forging the casting blank, the density of the casting can be improved, and the tendency of defects is reduced; by adopting a three-section type rapid cooling method, the finish rolling temperature can be properly increased, the high-temperature rolling of the ship plate steel is realized, and the load of a rolling mill is reduced. The low-temperature impact toughness value at minus 60 ℃ far meets the requirements of classification society, and the safety of the ship body in operation is improved in the aspect of service performance.

Drawings

FIG. 1 is a rolled metallographic structure photograph of low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel prepared in example 3 of the invention;

FIG. 2 is an as-cast metallographic structure photograph of the low-temperature high-toughness cerium-zirconium composite treated FH40 deck steel prepared in example 3 of the present invention;

fig. 3 is a stress-strain curve of the low-temperature high-toughness cerium-zirconium composite treated FH40 ship plate steel prepared in example 3 of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments.