A kind of yield strength 800MPa grade Cu-containing low alloy high-strength steel and its manufacturing method

Abstract

The invention relates to a Cu-containing low-alloy high-strength steel with a yield strength of 800 MPa. The chemical components of the steel are as follows by weight: C: 0.04%-0.07%, Si: 0.70%-0.85%, Mn: 0.15%-0.40%, P≤0.010%, S≤0.005%, Cr: 0.40%-0.55%, Ni: 1.50%-1.70%, Cu: 1.45%-1.65%, Zr: 0.090%-0.160%, Mo: 0.15%-0.25%, Alt: 0.090%-0.190%, Ni / Cu ratio is controlled at 1-1.2, and the remainder is Fe and impurities. Through the synergistic effect of elements such as Cu, Al, Mn, Ni, Si, Mo, and Zr, combined with the "offline quenching + high temperature tempering" process, Cu-containing nano-metastable phase dispersion precipitation and Zr and / or Mo carbide precipitation are formed, combined with solid solution strengthening, the finished steel plate has high strength, excellent low-temperature toughness, good welding performance and cold forming performance.

Description

Technical Field

[0001] The present invention relates to the technical field of low alloy high strength steel production, and in particular to a Cu-containing low alloy high strength steel with a yield strength of 800 MPa and a manufacturing method thereof. Background Art

[0002] Traditional high-strength steel mainly obtains a good match of strength and toughness by adding a large amount of alloy elements and increasing the carbon content, but high carbon content and alloy content will lead to serious deterioration of weldability. With the vigorous development of microalloying technology, the design concept and performance of low-alloy high-strength steel are also constantly developing and improving. The upgraded low-alloy high-strength steel is widely used in many fields such as oil pipelines, high-rise building structures, bridges, railway transportation and excavation equipment due to its relatively low cost, high strength, high toughness, easy welding and easy processing. It can not only increase the load capacity of components and improve safety performance, but also reduce its own weight, which meets the requirements of energy-saving and environmental protection development.

[0003] The Chinese patent application with publication number CN 113604736 A discloses "a high-strength medium and thick plate with a yield strength of 800 MPa and a preparation method thereof". A steel plate with a yield strength higher than 800 MPa is prepared by using Ti microalloying, a Cu content of less than 1.0%, and a TMCP+tempering process. However, the low-temperature toughness of the product is limited to -20°C, which cannot meet the use requirements of high-strength low-alloy steel.

[0004] The Chinese patent application with publication number CN 114164374 A discloses "a 5-60 mm thick 850 MPa grade high-strength, high-toughness, easy-to-weld nano steel and its preparation method", which uses Nb and Ti microalloying combined with Cu nano reinforcement to ensure strength and toughness, but its Ni and Mo element content is high and the production cost is relatively high.

[0005] The Chinese patent application with publication number CN 114086051 A discloses "a 60-120 mm thick 850 MPa grade high-strength, high-toughness, easy-to-weld nano steel and its preparation method". The steel plate is a super thick plate, which uses Nb and Ti microalloying combined with Cu nano reinforcement to ensure strength and toughness, but its Ni and Mo content is high and the production cost is relatively high.

[0006] The Chinese patent application with publication number CN 105177425 A discloses "a copper-containing nanophase reinforced low alloy steel and a preparation method thereof". The steel plate is an ultra-high-strength steel with a tensile strength of more than 1400 MPa, a high content of Ni, W, Mo, and Al, and a high production cost.

[0007] The Chinese patent application with publication number CN 106834942 A discloses "a copper-containing nanophase reinforced medium manganese steel and its preparation method". The steel plate belongs to medium manganese automobile steel, with a strength-plasticity product higher than 30GPa%, a tensile strength of more than 1400MPa, Mn>6%, and high Ni, W, Mo, and Al contents, and high production costs.

[0008] The steel types and production methods involved in the above-mentioned patent documents have certain defects and cannot fully meet the use requirements of high-strength steel in different fields. How to use suitable chemical composition and reasonable production process to produce a high-strength, excellent toughness and ductility Cu-containing low-alloy high-strength steel plate is one of the technical difficulties that need to be solved urgently in this field. Summary of the invention

[0009] The present invention provides a Cu-containing low-alloy high-strength steel with a yield strength of 800 MPa and a manufacturing method thereof. Through the synergistic effect of elements such as Cu, Al, Mn, Ni, Si, Mo, and Zr, combined with the "offline quenching + high-temperature tempering" process, Cu-containing nano-metastable phase dispersion precipitation and Zr and / or Mo carbide precipitation precipitation are formed, and combined with solid solution strengthening, the finished steel plate has high strength, excellent low-temperature toughness, good welding performance and cold forming performance; at the same time, it has cost advantages compared with traditional high-strength alloy steels.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A Cu-containing low-alloy high-strength steel with a yield strength of 800 MPa, wherein the chemical composition of the steel is C: 0.04%-0.07%, Si: 0.70%-0.85%, Mn: 0.15%-0.40%, P≤0.010%, S≤0.005%, Cr: 0.40%-0.55%, Ni: 1.50%-1.70%, Cu: 1.45%-1.65%, Zr: 0.090%-0.160%, Mo: 0.15%-0 .25%, Alt: 0.090%~0.190%; Ni / Cu ratio is controlled at 1~1.2; the balance is Fe and unavoidable impurities; in addition: carbon equivalent CEV≤0.48%, and CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; welding crack sensitivity index Pcm≤0.25%, and Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B.

[0012] Furthermore, the steel contains Cu nano-metastable phase dispersion precipitation and Zr and / or Mo carbide precipitation precipitation.

[0013] Furthermore, the yield strength of the finished steel plate is ≥800MPa, the tensile strength is ≥850MPa, the elongation after fracture is ≥19%, the cross-sectional shrinkage is ≥65%, and the longitudinal impact energy KV2 at -60°C is ≥200J.

[0014] A method for manufacturing Cu-containing low-alloy high-strength steel with a yield strength of 800 MPa, the production process includes smelting, continuous casting, heating, rolling and heat treatment; wherein the rolling and heat treatment processes are controlled as follows:

[0015] 1) Rolling;

[0016] Two-stage controlled rolling is adopted; the rough rolling and final rolling temperature is 1081~1121℃; the finishing rolling temperature is 840~940℃, and the finishing rolling temperature is 780℃~830℃; the finishing rolling reduction rate is controlled at 66%~72%;

[0017] 2) Heat treatment;

[0018] The offline quenching + high temperature tempering process is adopted; the quenching temperature is 880-900℃, and after keeping warm for 40-125min, it is water-cooled to room temperature; tempering is carried out at 560-580℃, the holding time is 80-150mm / min, and finally air-cooled to room temperature.

[0019] Furthermore, a method for manufacturing a Cu-containing low alloy high-strength steel with a yield strength of 800 MPa is provided, wherein the smelting, continuous casting and heating processes are controlled as follows:

[0020] 1) Smelting;

[0021] It includes hot metal pretreatment, converter smelting, LF refining and RH vacuum treatment process; among which, before LF refining, the ladle is purged with argon statically, the argon blowing time is greater than 15 minutes, and the RH cycle time is greater than 12 minutes;

[0022] 2) Continuous casting;

[0023] The superheat of the tundish is controlled at 21-24°C, and dynamic soft reduction and electromagnetic stirring are applied; the continuous casting billet is slowly cooled at a temperature of 470-500°C and a slow cooling time of 36-48h;

[0024] 3) heating;

[0025] The heating rate of the preheating section is 7-10°C / min; the heating rate of the heating section is 14-16°C / min, and the heating temperature is 1250-1280°C; the holding time of the soaking section is greater than 35 minutes; and the total heating time is 210-260 minutes.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1) Through the synergistic effect of elements such as Cu, Al, Mn, Ni, Si, Mo, and Zr, combined with the "offline quenching + high temperature tempering" process, the Cu-containing nano-metastable phase dispersion and Zr and / or Mo carbide precipitation are formed, combined with solid solution strengthening, so that the finished steel plate has high strength, excellent low-temperature toughness, and good welding performance;

[0028] 2) The yield strength of the finished steel plate shall be ≥800MPa, the tensile strength shall be ≥850MPa, the elongation after fracture shall be ≥19%, the cross-sectional shrinkage shall be ≥65%, and the longitudinal impact energy KV2 at -60℃ shall be ≥200J. DETAILED DESCRIPTION

[0029] The invention discloses a Cu-containing low-alloy high-strength steel with a yield strength of 800 MPa, wherein the chemical components of the steel are as follows by weight: C: 0.04%-0.07%, Si: 0.70%-0.85%, Mn: 0.15%-0.40%, P≤0.010%, S≤0.005%, Cr: 0.40%-0.55%, Ni: 1.50%-1.70%, Cu: 1.45%-1.65%, Zr: 0.090%-0.160%, Mo: 0.15 %~0.25%, Alt: 0.090%~0.190%; Ni / Cu ratio is controlled at 1~1.2; the balance is Fe and unavoidable impurities; in addition: carbon equivalent CEV≤0.48%, and CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; welding crack sensitivity index Pcm≤0.25%, and Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B.

[0030] Furthermore, the steel contains Cu nano-metastable phase dispersion precipitation and Zr and / or Mo carbide precipitation precipitation.

[0031] Furthermore, the yield strength of the finished steel plate is ≥800MPa, the tensile strength is ≥850MPa, the elongation after fracture is ≥19%, the cross-sectional shrinkage is ≥65%, and the longitudinal impact energy KV2 at -60°C is ≥200J.

[0032] The present invention discloses a method for manufacturing a Cu-containing low-alloy high-strength steel with a yield strength of 800 MPa. The production process includes smelting, continuous casting, heating, rolling and heat treatment. The rolling and heat treatment processes are controlled as follows:

[0033] 1) Rolling;

[0034] Two-stage controlled rolling is adopted; the rough rolling and final rolling temperature is 1081~1121℃; the finishing rolling temperature is 840~940℃, and the finishing rolling temperature is 780℃~830℃; the finishing rolling reduction rate is controlled at 66%~72%;

[0035] 2) Heat treatment;

[0036] The offline quenching + high temperature tempering process is adopted; the quenching temperature is 880-900℃, and after keeping warm for 40-125min, it is water-cooled to room temperature; tempering is carried out at 560-580℃, the holding time is 80-150mm / min, and finally air-cooled to room temperature.

[0037] Furthermore, a method for manufacturing a Cu-containing low alloy high-strength steel with a yield strength of 800 MPa is provided, wherein the smelting, continuous casting and heating processes are controlled as follows:

[0038] 1) Smelting;

[0039] It includes hot metal pretreatment, converter smelting, LF refining and RH vacuum treatment process; among which, before LF refining, the ladle is purged with argon statically, the argon blowing time is greater than 15 minutes, and the RH cycle time is greater than 12 minutes;

[0040] 2) Continuous casting;

[0041] The superheat of the tundish is controlled at 21-24°C, and dynamic soft reduction and electromagnetic stirring are applied; the continuous casting billet is slowly cooled at a temperature of 470-500°C and a slow cooling time of 36-48h;

[0042] 3) heating;

[0043] The heating rate of the preheating section is 7-10°C / min; the heating rate of the heating section is 14-16°C / min, and the heating temperature is 1250-1280°C; the holding time of the soaking section is greater than 35 minutes; and the total heating time is 210-260 minutes.

[0044] The working principle of each chemical component in the 800MPa-grade Cu-containing low-alloy high-strength steel of the present invention is as follows:

[0045] C is a major solid solution strengthening element. Too high a C content will deteriorate the welding performance and toughness and plasticity of the steel plate, and may form carbide precipitation with strong carbide alloy elements. The present invention controls the C content to be 0.04% to 0.07%.

[0046] Si is a ferrite-forming element, which can effectively reduce the austenite phase region and expand the ferrite phase region, and is an important solid solution strengthening element; too high Si content will reduce the toughness of the steel plate and form iron oxide scale that is difficult to remove during the rolling process; the present invention controls the Si content to 0.70% to 0.85%.

[0047] The main function of Mn in steel is solid solution strengthening. It is an austenite forming element. At the same time, Mn and Ni elements can be compositely precipitated in the Cu-containing nano-metastable phase, which can improve the strength and low-temperature toughness of the steel plate. However, excessive Mn content will seriously reduce the plasticity of the steel. The present invention controls the Mn content to be 0.15% to 0.40%.

[0048] P is an impurity element in steel, which can deteriorate the toughness, plasticity and welding performance of the steel. The P content is controlled below 0.010% in the present invention.

[0049] S is an impurity element in steel, which can significantly reduce the plasticity, toughness and welding performance of the steel. The present invention controls the S content to be below 0.005%.

[0050] Cr is a ferrite-forming element, which can effectively reduce the austenite phase area and expand the ferrite phase area, and can prevent the precipitation of Cu-containing nanophase during the cooling process after rolling or austenitization, as well as the nucleation and growth of Cu-containing nanophase, and significantly improve the hardenability of steel and the tempering stability after heat treatment; Cr is also an effective element for improving the weather resistance of steel. However, too high Cr content will deteriorate the welding performance of the steel plate. The present invention controls the Cr content to 0.40% to 0.55%.

[0051] Ni can significantly improve the low-temperature impact toughness and hardenability of steel plates, promote the Cu-Ni enriched phase in the steel to be retained in the oxide layer in a granular form, and improve the hot brittleness problem of Cu-containing steel; when the Ni / Cu ratio is above 1, liquid Cu will not appear; Ni in solid solution can improve the strength of ferrite; Ni can act as a nucleation particle to promote the precipitation of Cu nanometastable phase, and can also be compounded with Mn and Al in Cu-containing nanometastable phases to precipitate, optimizing the strength and low-temperature toughness of steel plates; in addition, Ni is an important element for improving the seawater corrosion resistance of steel. However, too high Ni content will cause residual austenite in the steel, resulting in uneven organization, increasing costs and affecting welding performance. The present invention controls the Ni content to be between 1.50% and 1.70%.

[0052] Cu is an important strengthening element in the steel of the present invention. The solid solubility of Cu in austenite and ferrite is very different. Under certain heat treatment conditions, the dispersion and precipitation of Cu-containing nanophases of different shapes, sizes, quantities and distribution positions can be controlled to effectively improve the strength of the steel, improve the low-temperature toughness of the steel, and improve the welding and seawater corrosion resistance of the steel. The present invention controls the Cu content to be 1.45% to 1.65%.

[0053] Zr is a ferrite forming element with excellent hardenability; it is a strong carbonitride forming element, and Zr carbonitride is precipitated during the tempering isothermal transformation process; Zr and Mo elements are precipitated in the form of second phase particles of (Zr, Mo) C, which improves the strength of steel by preventing grain boundary growth, refining grains, and pinning dislocations, while improving the low-temperature toughness of steel and the welding performance of steel. The present invention controls the Zr content to 0.090% to 0.160%.

[0054] Mo is a ferrite-forming element that can improve the hardenability and tempering stability of steel. MoC is formed during the isothermal transformation of steel, and precipitates with Zr in the form of (Zr, Mo)C to improve the strength and low-temperature toughness of steel. Mo acts together with Cr during tempering at different temperatures to ensure the stability of the tempered structure, including the nano-metastable phase of Cu contained in the precipitate, so that the steel plate obtains excellent comprehensive mechanical properties. However, when the Mo content is too high, the production cost will increase and the welding performance of the steel will be affected. In the present invention, the Mo content is controlled at 0.15% to 0.25%.

[0055] Al is a ferrite-forming element and a commonly used deoxidizer in steel. It can improve the corrosion resistance of steel and has a better effect when used in combination with Cr-Mo-Cu-Si. Al in Cu-containing steel can promote the precipitation of Cu-containing nanophases. Al can also be compound-precipitated with Mn or Ni in Cu-containing nanometastable phases to ensure the strength of the steel. Al first exists in steel as a deoxidizer, then combines with N to generate AlN, and finally compound-precipitates with Mn or Ni in Cu-containing nanometastable phases. However, too high Al content will affect the low-temperature toughness of steel, and oxides are easily formed during the smelting process, causing flocculation, which seriously affects production. The present invention controls the Alt content to be between 0.090% and 0.190%.

[0056] The manufacturing method of the Cu-containing low-alloy high-strength steel with a yield strength of 800 MPa described in the present invention has a typical production process flow of: molten iron pretreatment → converter smelting → refining outside the furnace (LF) → RH vacuum treatment → continuous casting (electromagnetic stirring) → slab continuous casting → slab stacking → slab cleaning → heating → rolling → flaw detection → heat treatment → inspection → storage. Among them:

[0057] 1. Smelting process: Before LF refining, ensure that the static argon blowing time of the ladle is greater than 15 minutes, and the RH cycle time is greater than 12 minutes; through LF+RH double refining, it can ensure that non-metallic inclusions are fully floated, greatly reduce the inclusion content in the molten steel, and at the same time ensure that the nitrogen, hydrogen and oxygen contents are at extremely low levels.

[0058] 2. Continuous casting process: The superheat of the tundish is controlled at 21-24°C, and dynamic light pressure and electromagnetic stirring are applied; the continuous casting billet enters the slow cooling pit for slow cooling, the slow cooling temperature is 470-500°C, and the slow cooling time is 36-48h. After leaving the slow cooling pit, it is cleaned in time. In conjunction with the continuous casting process, the qualified rate of steel plate flaw detection can be improved and the crack defects on the rolling edge can be reduced.

[0059] 3. Heating process: The heating rate of the preheating section is 7-10℃ / min, the heating rate of the heating section is 14-16℃ / min, the heating temperature is 1250-1280℃, the holding time of the soaking section is greater than 35min, and the total heating time is 210-260min. The heating speed should be slowed down in the preheating stage to prevent the continuous casting billet from cracking due to excessive heating. The heating rate in the heating section is increased to improve the heating efficiency. The higher heating temperature combined with sufficient soaking section holding time and total heating time can make the alloy elements fully dissolved and evenly distributed, and the segregated elements in the center of the billet are fully diffused to ensure the ideal billet heating organization state.

[0060] 4. Rolling: Two-stage controlled rolling is adopted, the rough rolling and final rolling temperature is 1081-1121℃, ensuring that the steel plate is rolled in a recrystallized state; the finishing rolling temperature is 840-940℃, the finishing rolling temperature is controlled at 780℃-830℃, and the finishing rolling reduction rate is controlled at 66%-72%; after two-stage rolling, a uniform rolled structure is obtained, preparing for heat treatment.

[0061] 5. Heat treatment: The "offline quenching + high temperature tempering" process is adopted, the quenching temperature is 880-900℃, and after keeping warm for 40-125min, it is water-cooled to room temperature, and the quenched structure is obtained by rapid cooling. Cu exists in the form of supersaturated solid solution, and the dislocation density in the steel is extremely high, which provides a large number of nucleation points for the precipitation of Cu-containing phases during the tempering process. The cooling rate can also make Zr, Cu, and Al in a solid solution state, which is convenient for obtaining nano-scale precipitation strengthening phases during subsequent tempering. The offline quenched steel plate has good uniformity and high comprehensive performance; the tempering temperature is 560-580℃. The tempering temperature is the most important process parameter to ensure the comprehensive performance of the steel plate. During the tempering process, the Cu-containing nano-metastable phase is in the ferrite matrix, dislocation lines, grain boundaries, phase The Cu nano-metastable phase continuously nucleates, precipitates and grows up, losing the coherence with the matrix, weakening the strengthening effect on the steel parts and greatly enhancing the toughness. It is in a semi-coherent or incoherent state with the ferrite matrix, with a size of about 10-30nm. At the same time, Zr or Mo carbides precipitate in the ferrite matrix and at dislocation lines to make up for the strength loss caused by the over-aging of the Cu nano-metastable phase due to tempering, ensuring that the steel plate has high strength and toughness. The tempering time is 80-150mm / min. Sufficient tempering time can ensure the uniformity and stability of the steel plate's organizational properties. Too long tempering time not only coarsens the precipitated phase but also reduces production efficiency and increases costs. Air cooling to room temperature after tempering saves furnace cooling time and increases production efficiency.

[0062] The following embodiments are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0063] [Example]

[0064] In this embodiment, the production process flow of Cu-containing low-alloy high-strength steel with a yield strength of 800 MPa is: molten iron pretreatment → converter smelting → refining outside the furnace (LF) → RH vacuum treatment → continuous casting (electromagnetic stirring) → slab continuous casting → slab stacking → slab cleaning → heating → rolling → flaw detection → heat treatment → inspection → warehousing.

[0065] The chemical composition of the steel in each embodiment is shown in Table 1, the smelting and continuous casting process parameters are shown in Table 2, the heating process parameters are shown in Table 3, the rolling and heat treatment process parameters are shown in Table 4, and the properties of the finished steel plate are shown in Table 5.

[0066] Table 1 Chemical composition of steel in each example (wt%)

[0067] Example C Si Mn P S Cr Ni Cu Zr Mo Alt Ni / Cu CEV <![CDATA[P cm ]]> 1 0.051 0.82 0.31 0.009 0.004 0.44 1.61 1.47 0.099 0.17 0.129 1.095 0.43 0.23 2 0.053 0.76 0.39 0.007 0.003 0.43 1.58 1.51 0.149 0.15 0.142 1.046 0.44 0.23 3 0.060 0.79 0.26 0.008 0.004 0.51 1.63 1.56 0.137 0.19 0.127 1.045 0.47 0.25 4 0.061 0.78 0.32 0.005 0.005 0.48 1.51 1.51 0.151 0.20 0.148 1.000 0.45 0.24 5 0.062 0.77 0.28 0.007 0.003 0.52 1.59 1.49 0.091 0.18 0.151 1.067 0.45 0.24 6 0.067 0.83 0.34 0.007 0.002 0.49 1.53 1.48 0.113 0.21 0.130 1.034 0.46 0.24 7 0.051 0.85 0.27 0.006 0.005 0.53 1.67 1.53 0.119 0.16 0.139 1.092 0.45 0.24 8 0.070 0.80 0.18 0.009 0.004 0.47 1.56 1.47 0.127 0.21 0.151 1.061 0.45 0.25 9 0.048 0.81 0.21 0.008 0.003 0.46 1.57 1.50 0.103 0.20 0.163 1.047 0.42 0.22 10 0.058 0.75 0.36 0.006 0.004 0.50 1.54 1.52 0.142 0.22 0.167 1.013 0.47 0.24 11 0.041 0.83 0.37 0.009 0.003 0.54 1.70 1.61 0.157 0.24 0.161 1.056 0.48 0.24 12 0.057 0.84 0.40 0.008 0.002 0.55 1.62 1.60 0.159 0.25 0.157 1.013 0.48 0.25

[0068] Table 2 Smelting and continuous casting process parameters of each example steel

[0069]

[0070]

[0071] Table 3 Heating process parameters of each example steel

[0072]

[0073] Table 4 Rolling and heat treatment process parameters of each example steel

[0074]

[0075] Table 5 Mechanical properties of finished steel plates of various embodiments

[0076]

[0077]

[0078] In Table 5, R eH is the upper yield strength, R m is the tensile strength, A is the elongation after fracture, and Z is the cross-sectional shrinkage.

[0079] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for manufacturing Cu-containing low alloy high-strength steel with a yield strength of 800 MPa, characterized in that: The chemical composition of the steel is C: 0.04% ~ 0.07%, Si: 0.70% ~ 0.85%, Mn: 0.15% ~ 0.40%, P ≤ 0.010%, S ≤ 0.005%, Cr: 0.40% ~ 0.55%, Ni: 1.50% ~ 1.70%, Cu: 1.45% ~ 1.65%, Zr: 0.090% ~ 0.160%, Mo: 0.15% ~ 0.25%, Alt: 0.090% ~ 0.190%; Ni / Cu ratio is controlled at 1 ~ 1.2; the balance is Fe and unavoidable impurities; in addition, the carbon equivalent is satisfied CEV≤0.48%, and CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; welding crack sensitivity index Pcm≤0.25%, and Pcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B; the steel contains Cu nanometastable phase dispersion precipitation and Zr and / or Mo carbide precipitation precipitation; the yield strength of the finished steel plate is ≥800MPa, the tensile strength is ≥850MPa, the elongation after fracture is ≥19%, the cross-sectional shrinkage is ≥65%, and the longitudinal impact energy KV2 at -60℃ is ≥200J; The production process includes smelting, continuous casting, heating, rolling and heat treatment; each process is controlled as follows: 1) Smelting; It includes hot metal pretreatment, converter smelting, LF refining and RH vacuum treatment process; among which, before LF refining, the ladle is purged with argon statically, the argon blowing time is greater than 15 minutes, and the RH cycle time is greater than 12 minutes; 2) Continuous casting; The superheat of the tundish is controlled at 21-24°C, and dynamic soft reduction and electromagnetic stirring are applied; the continuous casting billet is slowly cooled at a temperature of 470-500°C and a slow cooling time of 36-48h; 3) heating; The heating rate of the preheating section is 7-10°C / min; the heating rate of the heating section is 14-16°C / min, and the heating temperature is 1250-1280°C; the holding time of the soaking section is greater than 35 minutes; the total heating time is 210-260 minutes; 4) rolling; Two-stage controlled rolling is adopted; the rough rolling and final rolling temperature is 1081~1121℃; the finishing rolling temperature is 840~940℃, and the finishing rolling temperature is 780℃~830℃; the finishing rolling reduction rate is controlled at 66%~72%; 5) Heat treatment; The off-line quenching + high temperature tempering process is adopted; the quenching temperature is 880-890°C, and after keeping warm for 40-125 minutes, it is water-cooled to room temperature; tempering is carried out at 560-580°C, the holding time is 80-150mm / min, and finally air-cooled to room temperature.

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