High toughness, layer tearing resistant steel sheet and method of production thereof

Abstract

The present application relates to a kind of high tough anti-laminated tearing steel plate and its production method, and the chemical composition of steel is C:0.17~0.20%, Si:1.00~1.10%, Mn:1.0~1.2%, Nb:0.015~0.03%, Cr:0.40~0.60%, Ni:0.30~0.40%, W:0.40~0.50%, Al:0.04~0.07%, B:0.0005~0.0020%, RE:0.0015~0.0035%, the balance is Fe and impurity;Steel is added W and cooperates Cr, Nb microalloying, adds rare earth RE, utilizes the original organization of the steel plate of controlled rolling and controlled cooling refinement and homogenization, improves the anti-laminated tearing performance;Using tempering heat treatment fully releases residual stress;Finally produces the yield strength 1100MPa level high tough anti-laminated tearing low alloy steel plate.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel plate production, and particularly relates to a high-strength and high-toughness anti-lamellar tearing steel plate with a thickness of 30-80 mm and a yield strength of 1100 MPa and a production method thereof. BACKGROUND

[0002] The yield strength 1100 MPa grade ultra-high strength low alloy steel plate is widely used in the fields of engineering machinery and mining machinery, and is used for manufacturing heavy load components. Generally, a heat treatment process of quenching and then tempering is adopted, and the structure is mainly low-carbon martensite.

[0003] When the high-strength steel plate with a thickness of more than 30 mm is welded or subjected to Z-direction stress, the lamellar tearing phenomenon often occurs due to the large residual stress in the thickness direction, which is manifested as the delamination cracking of the steel along the thickness direction, and seriously threatens the use safety of the components. In recent years, with the development of the fields of engineering machinery and the like, the requirements for the performance of high-strength steel plates are increasingly stringent. For example, the key parts of engineering machinery such as heavy-duty crane rotary tables not only need to achieve 1100 MPa grade ultra-high strength and toughness, but also need to have excellent anti-lamellar tearing performance when subjected to Z-direction stress.

[0004] A Chinese patent application with the application publication number CN115216701A discloses "a low compression ratio anti-lamellar tearing Q960 high-strength steel and a preparation method thereof". The steel includes the following chemical components by weight percentage: C: 0.12-0.15%, Si: 0.12-0.50%, Mn: 1.30-1.60%, P≤0.020%, S≤0.010%, Mo: 0.20-0.40%, Cr: 0.20-0.60%, Ni: 0.10-0.30%, V: 0.04-0.06%, Nb: 0.015%-0.060%, Alt: 0.010%-0.060%, Ti: 0.008%-0.035%, B≤0.005%, N≤0.0070%, O≤0.0030%, H≤0.0002%, and the balance is Fe and inevitable impurities. A cast blank with a thickness of 150 mm is used to produce a high-thickness and high-strength steel plate Q960D with a thickness of 60 mm, and the compression ratio is 2.5, which breaks through the technical difficulty of producing a high-strength steel plate with a compression ratio > 3. Only a small amount of Nb, Cr, Mo, Ni and V alloy elements are added, and the alloy cost is lower than that of the existing steel plate of the same strength grade and the same specification, thereby saving the cost. Through the high-temperature large reduction process + quenching and tempering process, the thickness direction structure is uniform, and the anti-lamellar tearing steel performance is good. When the yield strength of the steel plate is lower than 1100 MPa, high-temperature tempering heat treatment is needed.

[0005] A Chinese patent application with publication number CN116855835A discloses a production method of a large-thickness quenched and tempered high-strength steel plate resistant to lamellar tearing. The chemical composition of the steel by weight percentage is C=0.11-0.16, Si=0.15-0.35, Mn=0.80-1.30, P≤0.010, S≤0.002, Nb=0.015-0.025, V=0.02-0.06, Ti≤0.005, Al=0.07-0.09, Cr=0.30-0.80, Mo=0.35-0.65, Ni=0.30-1.20, B=0.001-0.002, CEV≤0.70, and the balance is Fe and inevitable impurities. The process route is BOF-LF-VD-continuous casting-billet heating-rolling-pile cooling-quenching and tempering heat treatment-performance test. The billet is heated to 1180-1230℃, and the soaking time is ≥60min; the rolling is two-stage rolling, the rough rolling stage rolling temperature is ≥1120℃, and the last 3 passes are controlled according to single pass reduction ≥35mm; the finish rolling stage rolling temperature is ≤900℃, and the rolled steel plate is cooled to 250-300℃ on the cooling bed before being discharged and stacked for slow cooling, and the stacking time is ≥48h; after slow cooling, the steel plate is subjected to quenching+tempering treatment in a continuous heat treatment furnace, the quenching temperature is 900-930℃, and the tempering temperature is 620-680℃. The matrix structure of the steel plate is tempered sorbite+lower bainite, and no TiN and MnS inclusions affecting the lamellar tearing resistance of the steel plate are detected in the core. It adopts Ti-free and Al-containing composition design, optimizes the Ca treatment process, eliminates the influence of TiN and MnS inclusions on the Z-direction performance of the steel plate; light reduction combined with convex roller reduction is used during continuous casting to improve the core porosity, and a reasonable steel plate pile cooling hydrogen removal process is developed; without adjusting other alloying elements and without affecting the steelmaking and rolling production rhythm, the qualified rate of the 100-150mm Q550 and Q690 grade high-strength steel resistant to lamellar tearing is stably above 98.0%. However, the strength of the steel plate does not reach the 1100MPa level, and the Al content in the steel is relatively high, which can easily cause continuous casting nozzle blockage and more inclusions, affecting the low temperature toughness.

[0006] A Chinese patent application with publication number CN115747657A discloses "a high-strength HY950CF steel plate for water and electricity engineering and a production method thereof", the thickness of the steel plate is 50-120 mm, and the steel plate contains the following chemical components (unit, wt%): C: 0.09-0.12, Si: 0.15-0.25, Mn: 0.30-0.60, P≤0.010, S≤0.003, Als: 0.020-0.040, Nb: 0.02-0.03, V: 0.04-0.1, Cr: 1.2-1.6, Ni: 2.4-2.8, Cu: 0.8-1.0, Mo: 0.2-0.3, Re: 0.0015-0.0025, the rest being Fe and residual elements, carbon equivalent Ceq<0.7, the microstructure is bainite tempering structure, and the longitudinal and transverse V-type impact energy at-60 ℃ is≥127 J. The production process is ingot casting, primary heating, breakdown rolling, secondary heating and rolling, and heat treatment, high temperature quenching + critical quenching + tempering heat treatment, quenching and then loading into a quenching furnace at 650±20 ℃ for tempering, and air cooling to room temperature. The process uses rolling instead of forging, and the heat treatment link quenches multiple times to ensure quenching and refine austenite grains, and the uniformity of the mechanical properties of the whole plate is improved through tempering. The finished steel plate has high strength, high toughness, fatigue resistance, lamellar tearing resistance, and good weldability and corrosion resistance, but it needs to be produced by using large thickness ingots, and the Cr and Ni contents in the steel are high, so it cannot be continuously cast and cannot be cold bent.

[0007] A Chinese patent application with publication number CN108642390A discloses "a high-strength thick steel plate with thickness direction performance Z of 35-50% and a production method thereof", the components and wt% of the thick steel plate are as follows: C: 0.10-0.18%, Si: 0.10-0.40%, Mn: 1.20-1.60%, P≤0.010%, S≤0.005%, Cr: 0.10-0.50%, Mo: 0.45-0.75%, Ni: 0.05-0.20%, the sum of Nb+Ti+V is 0.040-0.06%, B: 0.0008-0.0020%, and H≤2 ppm. The production steps include: after clean steel smelting, the cast blank is continuously cast; after the cast blank is heated, rough rolling is performed; finish rolling is performed; quenching is performed; tempering is performed; and natural cooling is performed to room temperature. It mainly solves the problem that high-strength steel is prone to lamellar tearing after welding or stress under 107 cycle fatigue conditions. The yield strength of the finished steel plate is 900-1000 MPa, the tensile strength is≥1000 MPa, the elongation A is≥15%, and the thickness direction performance Z value is 35%-50%; after welding or 107 cycle fatigue test, no lamellar tearing phenomenon occurs. However, the strength of the finished steel plate is lower than 1100 MPa, and high temperature tempering heat treatment is required.

[0008] Chinese patent application CN116583610A discloses a "very thick steel plate for steam drum with excellent surface quality and resistance to lamellar tearing and a method of manufacturing the same", the steel plate composition and structure: C: 0.2% to 0.3%, Si: 0.05% to 0.5%, Mn: 1.0% to 2.0%, Al: 0.005% to 0.1%, P: 0.01% or less, S: 0.015% or less, Nb: 0.001% to 0.02%, V: 0.001% to 0.03%, Ti: 0.001% to 0.03%, Cr: 0.01% to 0.3%, Mo: 0.01% to 0.12%, Cu: 0.01% to 0.4%, Ni: 0.05% to 0.4%, Ca: 0.0005% to 0.004%, the balance being Fe and other unavoidable impurities. Ceq satisfies the range of 0.5 to 0.6; the first heating is performed on the slab at a temperature of 1100°C to 1300°C; the second heating is performed on the first intermediate material at a temperature of 1000°C to 1200°C; the third heating is performed on the second intermediate material at a temperature of 1000°C to 1200°C; the normalizing heat treatment is performed after the hot rolling is completed. The thickness of the steel material is 133mm to 250mm. The tensile strength of the steel material is 550MPa to 690MPa. The reduction of area (ZRA) is 35% or more. However, the tensile strength of the steel material is only 550MPa to 690MPa, the reduction of area (ZRA) is 35% or more, and the steel plate needs to be heated and heat treated multiple times in the production process, and the production process is complex.

[0009] In summary, the existing high-strength lamellar tearing-resistant steel plate production has the following disadvantages: 1. The yield strength of the finished steel plate is less than 1100MPa; 2. The production process is complex; 3. The alloy content is high, and continuous casting is not possible; 4. The cold forming performance is poor. SUMMARY

[0010] The present application provides a high-strength and high-toughness lamellar tearing-resistant steel plate and a production method thereof. A new chemical composition and production process design are adopted, W is added to the steel and combined with Cr and Nb micro-alloying, the hardening depth is improved while the precipitation of harmful oxides at the grain boundary is inhibited; rare earth RE is added to purify the molten steel, modify the inclusions, and reduce the grain boundary segregation of P, S, and B, the original structure of the steel plate is refined and homogenized by controlled rolling and controlled cooling, and the lamellar tearing resistance is improved; a long-term tempering heat treatment is adopted to fully release the residual stress; the combination of the above technical means greatly reduces the risk of lamellar tearing cracking, and finally a high-strength and high-toughness lamellar tearing-resistant low-alloy steel plate with a thickness specification of 30-80mm and a yield strength of 1100MPa is produced.

[0011] In order to achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0012] A high-toughness and anti-laminated tearing steel plate, the chemical composition of the steel is as follows in terms of percentage by weight: C: 0.17% to 0.20%, Si: 1.00% to 1.10%, Mn: 1.0% to 1.2%, Nb: 0.015% to 0.03%, Cr: 0.40% to 0.60%, Ni: 0.30% to 0.40%, W: 0.40% to 0.50%, Al: 0.04% to 0.07%, B: 0.0005% to 0.0020%, RE: 0.0015% to 0.0035%, and 0.7% ≤ W+Cr ≤ 1.0%, the balance being Fe and inevitable impurities; the impurity elements in the steel are controlled as follows: P ≤ 0.009%, S ≤ 0.0015%, [N] ≤ 0.0040%, [H] ≤ 0.00015%, [O] ≤ 0.0010%, and the residual austenite content is 5% to 8%.

[0013] The yield strength of the finished steel plate is ≥ 1100 MPa, the tensile strength is ≥ 1300 MPa, the longitudinal impact energy Akv at -40 ℃ is ≥ 50 J, the elongation A is ≥ 12%, the 180° cold bending D = 6a is qualified, and the thickness direction Z is ≥ 25%.

[0014] The thickness of the finished steel plate is 30 to 80 mm.

[0015] A production method of a high-toughness and anti-laminated tearing steel plate, the production process flow comprises converter smelting, refining, continuous casting, slab heating and slow cooling, slab heating, controlled rolling, controlled cooling, stacking slow cooling / high temperature tempering, quenching and tempering heat treatment; and the following processes are controlled:

[0016] 1) Refining: LF+RH refining treatment is adopted, and the RH refining vacuum circulation time is ≥ 22 min; after the RH vacuum treatment, RE alloy is added through argon protection wire feeding;

[0017] 2) Continuous casting: the casting speed of the slab is 0.9 to 1.1 m / min, and the target superheat of the tundish is controlled to be below 20 ℃; the whole process is protected pouring, and electromagnetic stirring is adopted; the center segregation of the slab is controlled to be below C1.0 level;

[0018] 3) Slab heating and slow cooling: the slow cooling heating starting temperature is ≥ 550 ℃, the heating speed is ≤ 50 ℃ / h, and the temperature is heated to 600 to 700 ℃, and then the temperature is kept for 25 to 35 h, and then the temperature is slowly cooled to below 400 ℃ and discharged, and then air cooled to room temperature;

[0019] 4) Slab heating: the temperature of the soaking section is 1150 to 1200 ℃, and the soaking time is 1.5 to 2 h;

[0020] 5) Controlled rolling: two-stage controlled rolling is adopted, the compression ratio, i.e. the slab thickness / finished plate thickness, is ≥4; the speed ratio of the upper roller to the lower roller is 1.1:1-1.3:1; the rough rolling starting temperature is ≥1000℃, the rough rolling final rolling temperature is ≥960℃; the finish rolling starting temperature is 850-880℃, the finish rolling reduction is ≥50%, and the finish rolling final rolling temperature is 800-850℃;

[0021] 6) Controlled cooling: after rolling, super-fast cooling or laminar cooling is adopted, the starting cooling temperature is ≥760℃, and the final cooling temperature is 630-680℃;

[0022] 7) Piling and slow cooling or high-temperature tempering: when the slab off-line temperature is >450℃, piling and slow cooling is carried out, and the piling and slow cooling time is ≥24h; when the slab off-line temperature is ≤450℃, high-temperature tempering is carried out, the tempering heating temperature is 550-600℃, and the holding time is 2.5-3.5min / mm;

[0023] 8) Quenching and tempering heat treatment: the quenching temperature is 860-880℃, and the holding time is 3.0-3.5min / mm; the low-temperature stress relief tempering temperature is 180-220℃, and the holding time is 6-8min / mm.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] 1) A new chemical composition and production process design are adopted, tungsten is added in the steel and combined with Cr and Nb micro-alloying, the hard oxide precipitation at the grain boundary is inhibited while the hardenability is improved; rare earth RE is added to purify the molten steel, modify the inclusions, reduce the grain boundary segregation of P, S and B, and refine and homogenize the original structure of the steel plate by controlling rolling and cooling, so as to improve the lamellar tearing resistance; a long time tempering heat treatment is adopted to fully release the residual stress; the combination of the above technical means greatly reduces the risk of lamellar tearing cracking, and finally produces a low-alloy steel plate with a thickness of 30-80mm, a yield strength of 1100MPa, and high strength and toughness and lamellar tearing resistance.

[0026] 2) The yield strength of the finished steel plate is ≥1100MPa, the tensile strength is ≥1300MPa, the longitudinal impact energy Akv at-40℃ is ≥50J, the elongation A is ≥12%, the 180° cold bending D=6a is qualified, and the thickness direction Z is ≥25%.

[0027] 3) The chemical composition design of the steel plate is characterized by low carbon, tungsten, niobium, boron and rare earth synergistic micro-alloying, and the alloy content is relatively low, which is convenient for smelting and continuous casting, and the production process is simple. DETAILED DESCRIPTION

[0028] The high strength and toughness anti-laminated tearing steel plate provided by the application has the following chemical components in percentage by weight: C: 0.17% to 0.20%, Si: 1.00% to 1.10%, Mn: 1.0% to 1.2%, Nb: 0.015% to 0.03%, Cr: 0.40% to 0.60%, Ni: 0.30% to 0.40%, W: 0.40% to 0.50%, Al: 0.04% to 0.07%, B: 0.0005% to 0.0020%, RE: 0.0015% to 0.0035%, and 0.7%≤W+Cr≤1.0%, the rest being Fe and inevitable impurities; the impurity elements in the steel are controlled as follows: P≤0.009%, S≤0.0015%, [N]≤0.0040%, [H]≤0.00015%, [O]≤0.0010%, and the residual austenite content is 5% to 8%.

[0029] The high strength and toughness anti-laminated tearing steel plate provided by the application has the following chemical components in percentage by weight: C: 0.17% to 0.20%, Si: 1.00% to 1.10%, Mn: 1.0% to 1.2%, Nb: 0.015% to 0.03%, Cr: 0.40% to 0.60%, Ni: 0.30% to 0.40%, W: 0.40% to 0.50%, Al: 0.04% to 0.07%, B: 0.0005% to 0.0020%, RE: 0.0015% to 0.0035%, and 0.7%≤W+Cr≤1.0%, the rest being Fe and inevitable impurities; the impurity elements in the steel are controlled as follows: P≤0.009%, S≤0.0015%, [N]≤0.0040%, [H]≤0.00015%, [O]≤0.0010%, and the residual austenite content is 5% to 8%.

[0030] C: carbide forming element, which can ensure that the steel plate has a strength of 1100 Pa after quenching, and can improve the hardenability of the thick steel plate and ensure that the performance of the steel plate is uniform along the thickness direction. However, too high carbon content can reduce the plasticity and low-temperature toughness of the steel plate, and can easily cause center segregation of the continuously cast slab after high continuous casting, which can be a crack source to reduce the anti-laminated tearing capacity of the steel plate after rolling. Therefore, the C content is controlled to be 0.17% to 0.20% in the application.

[0031] Si: non-carbide forming element, which mainly functions to inhibit the precipitation of carbides and stabilize the residual austenite content in the steel. The residual austenite can inhibit the formation and expansion of laminated cracks as a soft phase when Z-direction tension is applied. However, too much Si can reduce the toughness and welding performance. Therefore, the Si content is controlled to be 1.00% to 1.10% in the application.

[0032] Mn: deoxidizing and solid solution strengthening element, which can ensure the strength of the steel plate and can delay the transformation of austenite to ferrite and pearlite and improve the hardenability. However, Mn can easily form center segregation in the steel, which can cause laminated cracks at the center of the steel plate. Therefore, the Mn content is controlled to be 1.0% to 1.2% in the application.

[0033] Nb: the most effective element for refining grains and realizing controlled rolling. In the two-stage rolling process, Nb can form carbonitride, inhibit austenite recrystallization, refine austenite grains, and form refined martensite lath bundles after quenching, thereby effectively preventing the occurrence of laminated cracks in the steel plate. Nb can also synergize with W to delay the diffusion of B to the grain boundary and avoid the formation of B2O3 brittle phase which can cause laminated cracks. However, too high Nb content can cause too much carbonitride to precipitate, which can affect the anti-laminated tearing capacity of the steel plate. Therefore, the addition amount of Nb is controlled to be 0.015% to 0.03% in the application.

[0034] Al: effective element for deoxidation and nitrogen fixation. By deoxidation, oxide inclusions in steel can be reduced and the steel can be purified. After deoxidation, nitrogen fixation can ensure that B element does not combine with N, so that B can play a role in improving the hardenability. When the content of Al is less than 0.03%, the effect is small; when the content of Al is too high, a large amount of Al2O3 inclusions will be formed in the steel, which is easy to become the source of layered tearing under the action of Z stress. Therefore, the content of Al is controlled to be 0.04% to 0.07% in the present application.

[0035] Cr: has the effect of significantly delaying the transformation of austenite to ferrite and pearlite, promoting the transformation of martensite, and improving the hardenability of the steel plate. However, too much Cr will increase the risk of layered cracking. Therefore, the content of Cr is controlled to be 0.40% to 0.60% in the present application.

[0036] W: can effectively inhibit the segregation of P at the grain boundary, thereby improving the Z-direction performance; W and Nb have a synergistic effect, which can delay the diffusion of B to the grain boundary, avoid the formation of B2O3 brittle phase, and WC and NbC are coherent precipitates, which are finer under the same process conditions, the pinning dislocation effect is doubled, and the ability to inhibit the segregation of P at the grain boundary is better; W also has the effects of solid solution strengthening and grain refinement. In addition, W can also significantly improve the hardenability and promote the transformation of martensite. Compared with Mo, the carbide of W is more stable, and the effect of improving the hardenability is better. Therefore, the content of W is controlled to be 0.30% to 0.40% in the present application. Since W and Cr both have the effect of improving the hardenability, too much addition will increase the risk of layered cracking, therefore, the present application additionally limits that 0.7%≤W+Cr≤1.0%.

[0037] Ni: can improve the low temperature toughness, hardenability and layered tearing resistance of the steel, can form FeNi compound with Fe, when the steel plate is subjected to low temperature impact load at a lower temperature, the solid solution Ni will improve the low temperature impact absorption energy; Ni and W, Cr have a synergistic effect, which can make the CCT curve move to the right and improve the hardenability. Ni can also reduce the segregation of impurity elements such as P and S at the grain boundary, and improve the layered tearing resistance; but the cost of Ni is high, therefore, the present application adds 0.3% to 0.4% of Ni, which can ensure the mechanical properties of the steel plate, especially the low temperature toughness at-40℃, and at the same time will not greatly increase the production cost, so that the product has market competitiveness.

[0038] RE: adding 0.0015% to 0.0035% of RE is mainly used for the shape control of inclusions in steel, which can modify the long strip sulfide Mns and oxide Al2O3 into spherical inclusions, avoiding them to become Z-direction crack source, thereby improving the Z-direction performance. At the same time, the RE atoms segregate at the austenite grain boundary, which can delay the precipitation of proeutectoid ferrite, inhibit the grain boundary adsorption of harmful elements such as P and S, and reduce the temper brittleness. When the content of RE is less than 0.0010%, there is no effect; when the content of RE is too high, coarse oxides will be formed, which will reduce the Z-direction performance.

[0039] B: trace amount of boron in steel can inhibit the formation of pro-eutectoid ferrite, greatly improve the hardenability. When the content of B is too much (≥0.0025%), it is easy to enrich at the grain boundary, reduce the grain boundary binding energy, and then form lamellar fracture under the action of Z stress. Therefore, the content of B is controlled in the present application at 0.0005% to 0.0020%.

[0040] Residual austenite: 5% to 8% of residual austenite as a soft phase can prevent the formation and expansion of lamellar tear, and too high content of residual austenite will reduce the strength of the steel plate.

[0041] Impurity elements: P and S are easy to segregate at the grain boundary or form segregation in the center of the steel plate, which seriously affects the low temperature toughness and Z-direction performance; H gathers at the metallurgical defects of the steel plate, which can become the crack source of lamellar tearing; in addition, the strip sulfide, oxide and sharp corner nitride in the steel can cause local stress concentration, which significantly reduces the crack arrest capability of the steel plate lamellar crack; in order to ensure good Z-direction performance, the present application controls P ≤ 0.009%, S ≤ 0.0015%, [H] ≤ 0.00015%, [O] ≤ 0.0010%, [N] ≤ 0.0040% in the steel.

[0042] The production method of the high strength and toughness anti-lamellar tearing steel plate provided by the present application, the production process flow includes converter smelting, refining, continuous casting, slab heating and slow cooling, slab heating, controlled rolling, controlled cooling, stacking slow cooling / high temperature tempering, quenching and tempering heat treatment; wherein the following processes are controlled:

[0043] 1) Refining: LF+RH refining treatment is adopted, and the RH refining vacuum circulation time is ≥22 min; through long time vacuum treatment, [N] ≤ 0.0040%, [O] ≤ 0.0010%, [H] ≤ 0.00015% in the molten steel are controlled. After RH vacuum treatment, RE alloy is added by argon protection wire feeding; the purpose is to prevent rare earth oxidation, improve the yield, and reduce the harm of sulfide and oxide inclusions by adding rare earth modification treatment.

[0044] 2) Continuous casting: the casting speed of the slab is 0.9 to 1.1 m / min, and the target superheat of the tundish is controlled below 20℃; the whole process is protected pouring to prevent oxidation of the molten steel and hydrogen entering the tundish; electromagnetic stirring is adopted during continuous casting; the center segregation of the slab is controlled below C1.0 level; the purpose is to reduce the center segregation (the crack initiation point of lamellar crack).

[0045] 3) slab heating and slow cooling: after the slab is discharged from the continuous caster, it is heated and slowly cooled in a slow cooling pit. The heating and slow cooling starts at a temperature of ≥550℃, and the heating is performed at a rate of ≤50℃ / h to a temperature of 600-700℃. After a holding time of 25-35h, the slab is slowly cooled to a temperature of ≤400℃ and then discharged from the pit. The slab is then air cooled to room temperature. The heating process reduces the segregation in the core of the slab and also reduces the hydrogen content and the casting internal stress in the slab.

[0046] 4) slab heating: in order to prevent the rare earth elements from being oxidized after a long time of heating in the soaking section, the temperature in the soaking section is 1150-1200℃, and the soaking time is 1.5-2h.

[0047] 5) controlled rolling: the rolling is performed in two stages, i.e. rough rolling and finish rolling, so as to sufficiently refine and homogenize the rolling structure. In order to ensure that the deformation in the core is deep and thorough, the compression ratio, i.e. the thickness of the slab / the thickness of the finished plate, is ≥4. Differential speed rolling, i.e. controlling the speed of the upper and lower rollers to be different, can introduce asymmetric deformation in the thickness direction, form a shear strain gradient, and improve the performance in the Z direction. The speed ratio of the upper and lower rollers in the present application is 1.1:1-1.3:1. The rough rolling start temperature is ≥1000℃, and the rough rolling finish temperature is ≥960℃. The finish rolling start temperature is 850-880℃, the finish rolling reduction is ≥50%, and the finish rolling finish temperature is 800-850℃.

[0048] 6) controlled cooling: after rolling, the slab is cooled at a super-fast cooling rate or a laminar flow cooling rate. The start cooling temperature is ≥760℃, and the finish cooling temperature is 630-680℃. The purpose of the controlled cooling is to prevent grain growth and to prevent the W carbide from precipitating too early.

[0049] 7) slow cooling by stacking or high temperature tempering: after the steel plate is hot rolled, it is discharged and slowly cooled by stacking or high temperature tempering. When the slab is discharged at a temperature of >450℃, it is slowly cooled by stacking. The slow cooling by stacking is performed for a time of ≥24h. When the slab is discharged at a temperature of ≤450℃, it is high temperature tempered. The high temperature tempering is performed at a temperature of 550-600℃, and the holding time is 2.5-3.5min / mm. The purpose of the slow cooling by stacking / high temperature tempering is to remove the hydrogen in the steel plate, diffuse the segregation elements, and remove the internal stress caused by uneven rolling and cooling.

[0050] 8) quenching and tempering heat treatment: the quenching temperature is 860-880℃, and the holding time is 3.0-3.5min / mm. The purpose of the quenching is to obtain a martensite structure and to ensure that the strength of the steel plate reaches 1100MPa. The low temperature stress relief tempering temperature is 180-220℃, and the holding time is 6-8min / mm. The purpose of the lower temperature and longer quenching time is to diffuse the segregation elements in the core without causing the grains to grow excessively. The long time low temperature tempering after quenching is performed to fully remove the internal stress caused by the quenching and to further improve the resistance to lamellar tearing.

[0051] The yield strength of the finished steel plate is ≥1100MPa, the tensile strength is ≥1300MPa, the longitudinal impact energy Akv at -40℃ is ≥50J, the elongation A is ≥12%, the 180° cold bending D=6a is qualified, and the Z-direction performance is ≥25%.

[0052] The thickness of the finished steel plate is 30-80mm.

[0053] In order to more intuitively embody the present application, the embodiments of the present application are further described in combination with examples. The following examples are only the preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any skilled person in the art can obtain the technical solutions which are obvious within the technical range disclosed by the present application, including simple changes or equivalent replacements, and all of them are within the protection scope of the present application.

[0054] Example:

[0055] The chemical components of the steel in each example are shown in Table 1, the smelting process parameters are shown in Table 2, the rolling process parameters are shown in Table 3, the slow cooling process parameters after rolling are shown in Table 4, the heat treatment process parameters are shown in Table 5, and the performance test results of the finished steel plate are shown in Table 6.

[0056] Table 1 Chemical components of the steel, wt%

[0057]

[0058] Table 2 Smelting process parameters

[0059]

[0060] Table 3 Rolling process parameters

[0061]

[0062] Table 4 Slow cooling process parameters after rolling

[0063]

[0064] Table 5 Heat treatment process parameters

[0065]

[0066] Table 6 Performance test results of the finished steel plate

[0067]

[0068] It can be seen that the steel plate produced in the present example has high strength, good plasticity and toughness, qualified cold bending, Z-direction performance ≥25%, and good resistance to lamellar tearing.

[0069] The above merely describes preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical solution and inventive concept of the present application, makes equivalent replacement or change within the technical range disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method of producing a high tough high resistance to lamellar tearing steel sheet, characterized in that, The chemical composition of the steel is as follows in terms of percentage by weight: C: 0.17% to 0.20%, Si: 1.00% to 1.10%, Mn: 1.0% to 1.2%, Nb: 0.015% to 0.03%, Cr: 0.40% to 0.60%, Ni: 0.30% to 0.40%, W: 0.40% to 0.50%, Al: 0.04% to 0.07%, B: 0.0005% to 0.0020%, RE: 0.0015% to 0.0035%, and 0.7%≤W+Cr≤1.0%, the balance being Fe and inevitable impurities; the impurity elements in the steel are controlled as follows: P≤0.009%, S≤0.0015%, [N]≤0.0040%, [H]≤0.00015%, [O]≤0.0010%, and the residual austenite content is 5% to 8%; The production process flow includes converter smelting, refining, continuous casting, slab heating and slow cooling, plate slab heating, controlled rolling, controlled cooling, stacking slow cooling / high temperature tempering, quenching and tempering heat treatment; and the following processes are controlled: 1) Refining: LF+RH refining treatment is adopted, and the RH refining vacuum circulation time is ≥22 min; after the RH vacuum treatment, RE alloy is added through argon protection wire feeding; 2) Continuous casting: the casting speed of the slab is 0.9 to 1.1 m / min, and the target superheat of the tundish is controlled to be below 20℃; the whole process is protected pouring, and electromagnetic stirring is adopted; the center segregation of the slab is controlled to be below C1.0 level; 3) Slab heating and slow cooling: the slow cooling heating starting temperature is ≥550℃, the heating speed is ≤50℃ / h to 600 to 700℃, after the heat preservation for 25 to 35 h, the furnace is slowly cooled to below 400℃ for discharging, and air cooling is performed to room temperature; 4) Plate slab heating: the soaking section temperature is 1150 to 1200℃, and the soaking time is 1.5 to 2 h; 5) Controlled rolling: two-stage controlled rolling is adopted, the controlled compression ratio, i.e. the thickness of the slab / the thickness of the finished plate, is ≥4; the control upper and lower roller speed ratio is 1.1:1 to 1.3:1; the rough rolling opening rolling temperature is ≥1000℃, and the rough rolling final rolling temperature is ≥960℃; the finish rolling opening rolling temperature is 850 to 880℃, the finish rolling reduction is ≥50%, and the finish rolling final rolling temperature is 800 to 850℃; 6) Controlled cooling: after rolling, super-fast cooling or laminar cooling is adopted, the opening cooling temperature is ≥760℃, and the final cooling temperature is 630 to 680℃; 7) Stacking slow cooling or high temperature tempering: when the slab offline temperature is >450℃, stacking slow cooling is performed, and the stacking slow cooling time is ≥24 h; when the slab offline temperature is ≤450℃, high temperature tempering is performed, the tempering heating temperature is 550 to 600℃, and the heat preservation time is 2.5 to 3.5 min / mm; 8) Quenching and tempering heat treatment: the quenching temperature is 860 to 880℃, and the heat preservation time is 3.0 to 3.5 min / mm; the low temperature stress relief tempering temperature is 180 to 220℃, and the heat preservation time is 6 to 8 min / mm; The finished steel plate has a yield strength of ≥ 1100 MPa, a tensile strength of ≥ 1300 MPa, a longitudinal impact energy Akv of ≥ 50 J at -40 ℃, an elongation A of ≥ 12%, a 180° cold bending D = 6a, and a thickness direction Z of ≥ 25%.

2. The method of producing a high tough and lamellar tear resistant steel sheet according to claim 1, characterized by, The finished steel plate has a thickness of 30-80 mm.

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