950 mpa-grade steel plate for hydropower, and preparation method therefor

Abstract

Disclosed in the present application are a 950 MPa-grade steel plate for hydropower, and a preparation method therefor. The steel plate comprises the following components: 0.08-0.13% of C, 0.05-0.15% of Si, 0.8-1.1% of Mn, 1.4-2.0% of Ni, 0.45-0.65% of Cr, 0.40-0.65% of Mo, 0.2-0.3% of Cu, 0.01-0.04% of Nb, 0.030-0.045% of V, 0.01-0.02% of Ti, 0.04-0.05% of Al, 0.0006-0.0016% of B, 0.003-0.004% of N, wherein the balance is Fe and impurities; and 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, and Ceq≤0.57.

Description

950mpa grade steel plate for hydropower and method for manufacturing the same

[0001] This application is based on and claims priority to Chinese patent application No. CN202411019508.6, filed on July 29, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to a 950MPa grade steel plate for hydropower and a method for manufacturing the same. BACKGROUND

[0003] Hydropower, as one of the main sources of electricity, has been widely used. With the development of hydropower stations and large-scale pumped storage power stations, the requirements for the wear resistance and impact resistance of steel plates for pressure pipes, ribbed plates, bifurcated pipes, volutes and other facilities are increasing, and thus the requirements for the strength grade and thickness specifications of the steel plates for hydropower are also increasing.

[0004] Currently, the commonly used steel plates for hydropower are mainly 610MPa and 780MPa grade steel plates. With the development of hydropower stations and large-scale pumped storage power stations, the strength and toughness of the 610MPa and 780MPa grade steel plates are difficult to meet the construction requirements when used for building large-scale hydropower projects.

[0005] Any prior art mentioned in the specification does not mean that it is recognized or suggested that the prior art constitutes part of the common general knowledge in any jurisdiction, or can be reasonably expected to be understood, considered relevant and / or combined with other prior art by those skilled in the art. SUMMARY

[0006] The purpose of the present application is to provide a 950MPa grade steel plate for hydropower and a method for manufacturing the same.

[0007] To achieve one of the above application purposes, an embodiment of the present application provides a preparation method of a 950MPa-grade steel plate for hydropower, the chemical composition of the steel plate includes, in terms of mass percentage, Cd 0.08-0.13%, Si 0.05-0.15%, Mn 0.8-1.1%, Ni 1.4-2.0%, Cr 0.45-0.65%, Mo 0.40-0.65%, Cu 0.2-0.3%, Nb 0.01-0.04%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the rest is Fe and inevitable impurities; and the following conditions are met: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, carbon equivalent Ceq=[C]+[Mn] / 6+[Si] / 24+[Ni] / 40+[Cr] / 5+[Mo] / 4+[V] / 14, and Ceq≤0.57.

[0008] The preparation method includes the following sequentially performed processes of molten steel smelting, continuous casting, heating, rolling, laminar cooling, and tempering heat treatment;

[0009] In the continuous casting process, electromagnetic stirring is adopted, and the end of continuous casting is controlled to be slightly pressed down, so as to obtain a continuous casting billet, which is then stacked and slowly cooled for 72 hours before being unpacked; the press-down rate of the end of continuous casting is 1.20±0.5mm / m, and the center segregation level of the obtained continuous casting billet is not higher than C0.5 level, and the levels of A, B, C, and D type inclusions are all not higher than level 1.

[0010] In the heating process, the heating temperature is 1200-1230℃, the heating coefficient a1 is 1.0-1.1min / mm, and the steel plate is descaled after heating.

[0011] In the rolling process, single-billet rolling is adopted, and the length of the continuous casting billet is controlled to be ≤4.5m; the finish rolling temperature of the rolling process is (Ar3+150)℃-(Ar3+180)℃, and the press-down rate of at least two passes is ≥20%, and the interval time between passes is <7s, wherein Ar3 is calculated by the following formula:

[0012] Ar3=910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo];

[0013] In the laminar cooling process, the steel plate obtained in the rolling process is relaxed for 40-60s before being subjected to laminar cooling, and the cooling water amount is 4000-5000m 3 / h, cooling water temperature ≤ 15-20℃, final cooling temperature ≤ 300℃;

[0014] In the tempering heat treatment process, the heating temperature for tempering is 600-660℃, the heating coefficient a2 is 2.5-3.0 min / mm, and the steel plate is air-cooled after tempering.

[0015] As a further improvement of the embodiment of the present application, the thickness of the continuous casting billet is 320mm.

[0016] When the thickness t of the steel plate obtained in the rolling process is less than 90mm, the rolling process adopts two-stage rolling, which includes recrystallization zone rolling and non-recrystallization zone rolling performed in sequence; the starting rolling temperature of the recrystallization zone rolling is 1150-1180℃, the final rolling temperature of the recrystallization zone rolling is 1010-1050℃, and the starting rolling temperature of the non-recrystallization zone rolling is less than or equal to 890℃.

[0017] As a further improvement of the embodiment of the present application, when t is less than or equal to 60mm, the thickness of the intermediate billet obtained in the recrystallization zone rolling is 150-170mm.

[0018] As a further improvement of the embodiment of the present application, the thickness t of the steel plate is less than or equal to 60mm, and the chemical composition of the steel plate includes, in mass percent: C 0.08-0.10%, Si 0.05-0.15%, Mn 1.0-1.1%, Ni 1.4-1.6%, Cr 0.45-0.55%, Mo 0.40-0.55%, Cu 0.2-0.3%, Nb 0.010-0.040%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P less than or equal to 0.010%, S less than or equal to 0.003%, O less than or equal to 0.002%, H less than or equal to 0.0015%, and the rest is Fe and inevitable impurities; and the following conditions are satisfied: 1.0%≤Cr+Mo≤1.1%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, and Ceq≤0.54.

[0019] As a further improvement of the embodiment of the present application, when 60mm

[0020] As a further improvement of the embodiment of the present application, the thickness t of the steel plate satisfies: 60mm < t < 90mm, the chemical composition of the steel plate includes, in mass percent: C 0.10-0.12%, Si 0.05-0.15%, Mn 0.9-1.0%, Ni 1.4-2.0%, Cr 0.45-0.65%, Mo 0.40-0.65%, Cu 0.2-0.3%, Nb 0.01-0.04%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the rest is Fe and inevitable impurities; and satisfies: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, Ceq≤0.56.

[0021] As a further improvement of the embodiment of the present application, the thickness of the continuously cast billet is 320mm.

[0022] When the thickness t of the steel plate obtained by the rolling process is 90-130mm, single-stage rolling is adopted, only non-recrystallization zone rolling is performed, the rolling-in temperature is ≤900℃, and the reduction of each pass of the non-recrystallization zone rolling is ≥20%.

[0023] As a further improvement of the embodiment of the present application, the thickness t of the steel plate satisfies: 90mm≤t≤130mm, the chemical composition of the steel plate includes, in mass percent: C 0.11-0.13%, Si 0.05-0.15%, Mn 0.8-0.9%, Ni 1.8-2.0%, Cr 0.45-0.65%, Mo 0.50-0.65%, Cu 0.2-0.3%, Nb 0.010-0.040%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the rest is Fe and inevitable impurities; and satisfies: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, Ceq≤0.57.

[0024] As a further improvement of the embodiment of the present application, the preparation method further comprises a spraying process performed before the heating process.

[0025] The spraying process is to spray the surface of the continuous casting billet to form an oxidation-resistant layer after the oxidation-resistant coating is configured into a solution, the thickness of the oxidation-resistant layer is 0.2-0.4 mm, and the chemical components of the oxidation-resistant coating include, in mass percentage, SiO2 55-65%, Al2O3 8-12%, ZrO2 7-12%, Na2SiO3 14-20%, and SiC 6-10%.

[0026] To achieve one of the above purposes, one embodiment of the present application provides a 950MPa-grade steel plate for hydroelectric power, the chemical components of the steel plate include, in mass percentage, C 0.08-0.13%, Si 0.05-0.15%, Mn 0.8-1.1%, Ni 1.4-2.0%, Cr 0.45-0.65%, Mo 0.40-0.65%, Cu 0.2-0.3%, Nb 0.01-0.04%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the rest is Fe and inevitable impurities; and satisfies 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, and Ceq=[C]+[Mn] / 6+[Si] / 24+[Ni] / 40+[Cr] / 5+[Mo] / 4+[V] / 14, Ceq≤0.57.

[0027] As a further improvement of one embodiment of the present application, the thickness of the steel plate is t≤60mm, the chemical components of the steel plate include, in mass percentage, C 0.08-0.10%, Si 0.05-0.15%, Mn 1.0-1.1%, Ni 1.4-1.6%, Cr 0.45-0.55%, Mo 0.40-0.55%, Cu 0.2-0.3%, Nb 0.010-0.040%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the rest is Fe and inevitable impurities; and satisfies 1.0%≤Cr+Mo≤1.1%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, and Ceq≤0.54.

[0028] As a further improvement of the embodiment of the present application, the thickness t of the steel plate satisfies: 60mm < t < 90mm, the chemical composition of the steel plate includes, in percentage by mass: C 0.10-0.12%, Si 0.05-0.15%, Mn 0.9-1.0%, Ni 1.4-2.0%, Cr 0.45-0.65%, Mo 0.40-0.65%, Cu 0.2-0.3%, Nb 0.01-0.04%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, the rest being Fe and inevitable impurities; and satisfies: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, Ceq≤0.56.

[0029] As a further improvement of the embodiment of the present application, the thickness t of the steel plate satisfies: 90mm≤t≤130mm, the chemical composition of the steel plate includes, in percentage by mass: C 0.11-0.13%, Si 0.05-0.15%, Mn 0.8-0.9%, Ni 1.8-2.0%, Cr 0.45-0.65%, Mo 0.50-0.65%, Cu 0.2-0.3%, Nb 0.010-0.040%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, the rest being Fe and inevitable impurities; and satisfies: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, Ceq≤0.57.

[0030] As a further improvement of the embodiment of the present application, the center segregation level of the steel plate is not higher than C0.5 level, the center porosity level is not higher than 0.5 level, the yield strength RP 0.2 ≥890MPa, the tensile strength is 950-1100MPa, the elongation after fracture is ≥16%, the yield strength ratio is ≤0.97, and the impact energy at -60℃ is ≥150J.

[0031] Compared with the prior art, the present application has the beneficial effects that:

[0032] (1) The steel plate of the present application, on the basis of the above chemical composition design scheme, by controlling the types and contents of chemical elements and the matching relationship of the contents of each element, fully plays the role of each chemical element and the synergistic effect between them while keeping the low carbon equivalent, reduces the adverse effects of harmful elements, and lays the foundation for the steel plate to obtain excellent performance matching such as high strength, high toughness, excellent surface quality and welding performance.

[0033] (2) On the basis of the above chemical composition design scheme, when the thickness of the steel plate is ≤ 130 mm, the center segregation level of the steel plate is not higher than C0.5 level, the center porosity level is not higher than 0.5 level, the yield strength RP 0.2 ≥ 890 MPa, the tensile strength is 950-1100 MPa, the elongation after fracture is ≥ 16%, the yield ratio is ≤ 0.97, and the impact energy at -60 ℃ is ≥ 150 J.

[0034] (3) On the basis of the above chemical composition optimization design, combined with the production process control scheme, the chemical composition of the steel plate is precisely controlled through molten steel smelting; through electromagnetic stirring and light pressing at the end of continuous casting in the continuous casting process, the flow of molten steel is promoted to fill the shrinkage hole to control the center segregation and center porosity, while preventing the formation of intermediate cracks and improving the low temperature impact performance of the continuous casting billet; by controlling the heating temperature and heating time in the heating process, it is ensured that the alloy is fully solid-solved and the grains do not grow too much; through high temperature large reduction in the rolling process and controlling the interval time between passes, the core grains are refined and deformation is ensured to penetrate to the core; through relaxation first and then cooling in the laminar cooling process, fine carbides and nitrides of elements such as Nb and Ti are formed, which strongly pin the dislocations generated in the non-recrystallization zone of austenite, inhibit grain growth, so that the cooled steel plate obtains a structure mainly composed of bainite, and then obtains a structure mainly composed of tempered bainite after tempering, thereby improving the low temperature impact performance, so that the finally prepared steel plate has high strength, toughness, excellent surface quality and welding performance, and is suitable for large-scale water and electricity projects such as diversion pressure pipes, ribbed plates, branch pipes, volute casings and other facilities.

[0035] The terms "comprise" and variations of the term, such as "comprises" and "comprised of", unless the context requires otherwise, do not exclude other features, ingredients, components, or steps. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a metallographic structure photograph of the steel plate in Example 1;

[0037] Figure 2 is a metallographic structure photograph of the steel plate in Example 2;

[0038] Fig. 3 is a metallographic structure photo of the steel plate in Example 3;

[0039] Fig. 4 is a metallographic structure photo of the steel plate in Example 4;

[0040] Fig. 5 is a metallographic structure photo of the steel plate in Example 5;

[0041] Fig. 6 is a metallographic structure photo of the steel plate in Example 6. DETAILED DESCRIPTION

[0042] The technical solutions of the present application will be further described in combination with specific embodiments, but the scope of protection is not limited to the description.

[0043] The present application provides a 950MPa grade steel plate for hydropower and a preparation method of the 950MPa grade steel plate for hydropower. The steel plate is suitable for manufacturing facilities such as diversion pressure pipe, ribbed plate, branch pipe, volute, etc. in the dam of a hydropower station.

[0044] In terms of chemical composition, in the present application, the chemical composition of the 950MPa grade steel plate for hydropower includes, in terms of mass percentage: C 0.08-0.13%, Si 0.05-0.15%, Mn 0.8-1.1%, Ni 1.4-2.0%, Cr 0.45-0.65%, Mo 0.40-0.65%, Cu 0.2-0.3%, Nb 0.01-0.04%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the rest is Fe and unavoidable impurities; and satisfies: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, carbon equivalent Ceq=[C]+[Mn] / 6+[Si] / 24+[Ni] / 40+[Cr] / 5+[Mo] / 4+[V] / 14, and Ceq≤0.57.

[0045] Wherein, the brackets "[]" represent the mass percentage value of the element, for example, [C] represents the mass percentage value of C, if the mass percentage of C is 0.10%, then [C]=0.10, and the other elements are similar.

[0046] The effects of the action and content control of each chemical composition are as follows:

[0047] C: is an important element for ensuring strength in high-strength steel plate for water and electricity, has the dual role of gap solid solution strengthening and increasing hardenability, and can also form carbides with alloying elements such as Mo, Nb, V, etc., increase high-temperature tempering resistance, and effectively avoid the strength decrease of the steel plate for water and electricity during post-weld heat treatment; but too high C content will increase the carbon equivalent and cold crack sensitivity coefficient, which is not conducive to welding. In the present application, the C content is controlled to be 0.08-0.13%.

[0048] Si: is the main deoxidizing element of the steel plate for water and electricity, but too much Si will cause difficulty in removing iron oxide scale. In the present application, the Si content is controlled to be 0.05-0.15%.

[0049] Mn: can effectively improve the strength of the steel plate by substitutional solid solution strengthening, and can also improve the hardenability of the steel plate, but the increase of Mn content will increase the cold crack sensitivity, which is not conducive to welding; in addition, Mn is an easy segregation element, which is easy to gather at the center of the thickness of the steel plate, resulting in a decrease in toughness at the center of the thickness of the steel plate. In the present application, the Mn content is controlled to be 0.8%-1.1%.

[0050] Ni: has a significant effect on reducing the cold brittle transition temperature, is an important alloying element in high-strength water and electricity steel, can improve the strength and toughness of the steel plate, but is easy to cause difficulty in descaling of high-strength water and electricity steel. In the present application, the Ni content is controlled to be 1.4-2.0%.

[0051] Cr, Mo: are important hardenability elements in the steel plate for water and electricity. Mo has a solid solution effect and can also improve the stability of carbides and the strength of the steel plate; Cr can partially replace Mo alloy, which is beneficial to reducing the formation of MA components while ensuring hardenability, but too high Cr content will increase the temper brittleness of the steel. In the present application, the Cr content is controlled to be 0.45-0.65%, the Mo content is controlled to be 0.40-0.65%, and at the same time, 1.0%≤Cr+Mo≤1.2%, which can effectively ensure the hardenability and strength of the steel plate without compromising the welding performance of the steel plate.

[0052] Cu: is an element that can expand the austenite phase region, can replace part of Ni, and is beneficial to reducing the alloy cost; Cu can be solid-solved in austenite, and produces precipitation strengthening and hardening during subsequent heat treatment, thereby effectively supplementing the strength of the core of thick plate; but too high Cu content will easily cause surface cracks and reduce the welding performance. In the present application, the Cu content is controlled to be 0.2-0.3%.

[0053] Nb, V, Ti: as micro-alloying elements, can combine with harmful elements N, O to form V2O3, TiN, etc., reduce the adverse effects of harmful elements, and inhibit the growth of austenite grains; in addition, the solid-solution micro-alloying elements will precipitate during the temperature reduction process, which will also play a role in refining the grains; but too much Nb will lead to the decline of welding performance, and too much Ti will lead to the growth of TiN particles, which will adversely affect the material; appropriate amount of V can stabilize carbide and play a role in precipitation strengthening during the heat treatment process. In the present application, the content of Nb is controlled to be 0.01-0.04%, the content of V is controlled to be 0.030-0.045%, the content of Ti is controlled to be 0.01-0.02%, and 0.06%≤Nb+V+Ti≤0.09% is satisfied, so that good performance matching can be obtained.

[0054] Al: has strong affinity for N and O, can refine the grains of steel as a deoxidizer and nitrogen fixing agent in the steelmaking process; but too low Al content can easily lead to insufficient deoxidation, and too high Al content can easily generate inclusions to block the water gap. In the present application, the content of Al is controlled to be 0.04-0.05%.

[0055] B: can be segregated on the austenite grain boundary to reduce the interfacial energy, increase the hardenability, and inhibit the growth of recrystallized grains, thereby achieving the effects of refining the grains and improving the toughness, and can partially replace Ni, Cr, and Mo; but too high B content can generate eutectic borides at the grain boundaries, reducing the mechanical properties. In the present application, the content of B is controlled to be 0.0006-0.0016%.

[0056] N: is usually a harmful element in steel, but can combine with Ti to form TiN, which is insoluble at high temperatures and can effectively inhibit the growth of austenite grains; when the content of N is too low, there are few TiN particles to inhibit the growth of austenite grains; when the content of N is too high, large TiN particles are easily generated, which can cut the matrix and reduce the performance of the material, and the excess N can react with B to generate BN and aggregate at the grain boundaries, reducing the effective B content. In the present application, the content of N is controlled to be 0.003%-0.004%, and Ti / N=3-3.4 is satisfied, i.e., the mass percentage ratio of Ti to N is 3-3.4.

[0057] P, S, O, H: as harmful elements in steel, the upper limits of their contents need to be limited.

[0058] In summary, on the basis of the above chemical composition design scheme, by controlling the types and contents of chemical elements and the matching relationship between the contents of the elements, the present application fully plays the role of each chemical element and the synergistic effect between them, reduces the adverse effects of harmful elements, and lays a foundation for the steel plate to obtain excellent performance matching such as high strength, high toughness, excellent surface quality, and excellent welding performance.

[0059] The steel plate of the present application, based on the above chemical composition design, has a center segregation level of no more than C0.5 level and a center porosity level of no more than 0.5 level, and a yield strength RP 0.2 ≥890MPa, a tensile strength of 950-1100MPa, an elongation after fracture of ≥16%, a yield strength ratio of ≤0.97, and an impact energy at -60℃ of ≥150J, when the thickness of the steel plate is ≤130mm.

[0060] The present application also provides a preparation method of the above-mentioned steel plate for water and electricity, which comprises sequentially performing the following steps: molten steel smelting, continuous casting, heating, rolling, laminar cooling, and tempering heat treatment, so that the steel plate product is obtained.

[0061] The preparation method, based on the above chemical composition, is improved in production technology, so that the obtained steel plate is comprehensively optimized in strength, toughness, welding performance, surface quality, and production efficiency.

[0062] Specifically, based on the above-mentioned chemical composition optimization design, the production process control scheme is combined, the chemical composition of the steel plate is accurately controlled through molten steel smelting, the molten steel flow is promoted to fill the shrinkage hole to control the center segregation and center porosity through electromagnetic stirring and light pressing at the end of continuous casting in the continuous casting process, while preventing the formation of intermediate cracks and improving the low-temperature impact performance of the continuous casting billet, the heating temperature and heating time of the heating process are controlled to ensure that the alloy is fully solid-solved and the grains do not grow too much, high-temperature large reduction is adopted in the rolling process and the interval time between passes is controlled to refine the core grains and ensure that the deformation penetrates to the core, the elements Nb, Ti, etc. are first relaxed and then cooled in the laminar cooling process to form fine carbides and nitrides, which strongly pin the deformation dislocations generated in the austenite non-recrystallization zone, inhibit grain growth, so that the cooled steel plate obtains a structure mainly composed of bainite, and further obtains a structure mainly composed of tempered bainite after tempering, thereby improving the low-temperature impact performance, so that the finally prepared steel plate has high strength, toughness, excellent surface quality and welding performance, and is suitable for diversion pressure pipes, ribbed plates, branch pipes, volute casings and other facilities of large-scale water and electricity projects.

[0063] The following will introduce the details of each process in the preparation method of the steel plate for water and electricity.

[0064] (1) Molten steel smelting process

[0065] The raw materials are smelted to obtain molten steel, and the chemical composition of the molten steel includes, in mass percent: C 0.08-0.13%, Si 0.05-0.15%, Mn 0.8-1.1%, Ni 1.4-2.0%, Cr 0.45-0.65%, Mo 0.40-0.65%, Cu 0.2-0.3%, Nb 0.01-0.04%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the balance being Fe and inevitable impurities; and satisfies: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, carbon equivalent Ceq=[C]+[Mn] / 6+[Si] / 24+[Ni] / 40+[Cr] / 5+[Mo] / 4+[V] / 14, and Ceq≤0.57.

[0066] It can be understood that the chemical composition of the molten steel obtained in the molten steel smelting process and the chemical composition of the continuous casting billet obtained in the continuous casting process are the same as the chemical composition of the final obtained steel plate, and both conform to the chemical composition described above, which will not be described here.

[0067] (2) Continuous casting process

[0068] The molten steel obtained in the molten steel smelting process is fully protected cast by using a continuous casting machine, electromagnetic stirring is used during casting, and the end of the continuous casting is controlled to be slightly pressed down, so as to obtain a continuous casting billet with a thickness of 320 mm, and then the continuous casting billet is stacked and slowly cooled for 72 hours before being unpacked.

[0069] Among them, the press-down rate of the end of the continuous casting is controlled to be 1.20±0.5 mm / m, the center segregation level of the obtained continuous casting billet is not higher than C0.5 level, and the levels of A, B, C and D type inclusions are all not higher than level 1.

[0070] In this way, by using electromagnetic stirring and slight press-down at the end of the continuous casting in the continuous casting process, the flow of the molten steel is promoted to fill the shrinkage holes, the center segregation and center porosity are controlled, and the formation of intermediate cracks is prevented, so that the flaw detection qualified rate of the steel plate product can be effectively improved, and the low temperature impact performance of the core of the steel plate can be improved.

[0071] (3) Heating process

[0072] The continuous casting billet is sent into a heating furnace for heating, the heating temperature is controlled to be 1200-1230°C, the heating coefficient a1 is 1.0-1.1 min / mm, and the continuous casting billet is descaled after heating.

[0073] wherein the heating coefficient a1 determines the heating time, the heating time = a1 x D, D is the thickness of the slab, in mm. In the heating process, the slab is the continuous casting slab, and the thickness of the slab is the thickness of the continuous casting slab, i.e. 320 mm.

[0074] Due to the high alloy content in the continuous casting slab, by controlling the heating temperature and the heating coefficient, the alloy can be fully solid-solved and the grain can not be excessively grown, and by immediately descaling after heating, the iron oxide scale on the surface of the continuous casting slab can be removed so as to prevent the iron oxide scale on the surface of the slab from being pressed into the steel plate during subsequent rolling.

[0075] (4) Rolling process

[0076] The continuous casting slab after descaling is rolled to obtain a steel plate.

[0077] wherein single slab rolling is adopted during rolling, i.e. one continuous casting slab is rolled into one steel plate, and the length of the continuous casting slab is controlled to be ≤ 4.5 m, the finish rolling temperature of the rolling process is (Ar3+150)℃-(Ar3+180)℃, the reduction rate of at least two passes is ≥ 20%, and the interval time between passes is < 7s.

[0078] By adopting single slab rolling and controlling the length of the continuous casting slab, the grain refinement effect in the recrystallization zone can be ensured; by adopting a higher rolling temperature and a large reduction rate, the core grain of the steel plate can be refined, the deformation can be ensured to penetrate into the core of the steel plate, and the stability of the cooled austenite can be ensured; by controlling the interval time between passes, the cumulative deformation effect can be ensured, and the temperature drop can be effectively controlled.

[0079] wherein the austenite transformation start temperature Ar3 is calculated by the following formula:

[0080] Ar3 = 910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo],

[0081] wherein the brackets "[]" represent the mass percentage value of the element, for example, [C] represents the mass percentage value of C, if the mass percentage of C is 0.10%, then [C] = 0.10, and the other elements are similar.

[0082] (5) Laminar cooling process

[0083] The steel plate obtained in the rolling process is relaxed for 40-60s and then subjected to laminar cooling, the cooling water amount is 4000-5000m 3 / h, the cooling water temperature is ≤ 15-20℃, and the final cooling temperature is ≤ 300℃.

[0084] By cooling after relaxing for 40-60s, carbides and nitrides of fine elements Nb, Ti, etc. can be formed, which strongly pin the deformation dislocations in the non-recrystallized austenite region, and inhibit the grain growth; if the relaxing time is too short, the carbides and nitrides of fine elements Nb, Ti, etc. are not fully precipitated, and if the relaxing time is too long, a small amount of ferrite is easily formed, which is not good for the strength and toughness of the steel plate; further combining the control of the cooling water amount, cooling water temperature and final cooling temperature, the steel plate after cooling can obtain a structure mainly of bainite, and then after subsequent tempering heat treatment, a structure mainly of tempered bainite is obtained, and the low temperature impact performance is improved.

[0085] (6) tempering heat treatment process

[0086] The heating temperature of tempering is 600-660℃, the heating coefficient a2 is 2.5-3.0 min / mm, and the steel plate product is obtained after air cooling after tempering.

[0087] The heating coefficient a2 determines the tempering time, and the tempering time=a2xD, where D is the thickness of the slab in mm. In the tempering heat treatment process, the slab is the steel plate, and the thickness of the slab is the thickness t of the steel plate.

[0088] In this way, the tempering time is limited according to the thickness of the steel plate, and the heating temperature of tempering is controlled, which, in combination with the previous processes, makes the steel plate obtain a structure mainly of tempered bainite, and improves the low temperature impact performance, so that the finally prepared steel plate has high strength, toughness, excellent surface quality and welding performance, and is suitable for the diversion pressure pipe, ribbed plate, bifurcated pipe, volute and other facilities of large-scale hydropower projects.

[0089] The steel plate after the tempering heat treatment process is tested for performance. The center segregation level of the steel plate is not higher than C0.5 level, the center porosity level is not higher than 0.5 level, the yield strength RP 0.2 ≥890MPa, the tensile strength is 950-1100MPa, the elongation after fracture is ≥16%, the yield strength ratio is ≤0.97, and the impact energy at -60℃ is ≥150J.

[0090] Further, the preparation method of the steel plate for hydropower projects further comprises a spraying process performed after the continuous casting process and before the heating process;

[0091] In the spraying process, the anti-oxidation coating is configured into a solution, and then the surface of the continuous casting slab obtained in the continuous casting process is sprayed to form an anti-oxidation layer, the thickness of the anti-oxidation layer is 0.2-0.4mm, and the chemical components of the anti-oxidation coating include, in mass percentage: SiO2 55-65%, Al2O3 8-12%, ZrO2 7-12%, Na2SiO3 14-20%, and SiC 6-10%.

[0092] By adopting the above anti-oxidation coating chemical component system, the anti-oxidation layer formed can be reasonably matched with the chemical components of the substrate formed by the continuous casting billet, which can not only reduce the oxidation of the substrate, but also can be self-stripped during subsequent heating descaling, on the one hand, reducing the difficulty of descaling, avoiding the problem of iron oxide scale pressing into the substrate due to incomplete descaling, saving labor and improving production efficiency, on the other hand, effectively avoiding the surface defect problem caused by descaling, and improving the yield.

[0093] Specifically, the control of each chemical component and its content in the anti-oxidation coating has the following effects:

[0094] SiO2 is the main substance of the anti-oxidation coating, and is also the main reason for forming a dense viscous glass film of the anti-oxidation layer at high temperature. The content of SiO2 determines the melting point and density of the anti-oxidation layer. In the present application, the content of SiO2 is controlled to be 55-65%.

[0095] Al2O3 can improve the viscosity of the anti-oxidation layer at high temperature, and can also improve the softening temperature of the anti-oxidation layer and adjust the thermal expansion coefficient of the anti-oxidation layer. Al2O3 can form a tetrahedral structure (i.e. Al 3+ ion and four oxygen atoms) to fill into the silicon-oxygen structure of the anti-oxidation layer, filling the cracks and gaps formed by the anti-oxidation layer at high temperature. In the present application, the content of Al2O3 is controlled to be 8-12%.

[0096] ZrO2 has a high melting point and is a high-temperature resistant filler. When the heating temperature reaches 1000°C, ZrO2 will undergo a crystal type conversion from monoclinic phase to tetragonal phase, which is accompanied by a change in volume, thus causing the volume of the anti-oxidation layer to expand, making the anti-oxidation layer easy to peel off from the surface of the substrate. In the present application, the content of ZrO2 is controlled to be 7-12%.

[0097] Na2SiO3 acts as a binder, which is beneficial to improve the coating performance and suspension performance of the anti-oxidation layer material, and affects the strength and density of the anti-oxidation layer. If the content of Na2SiO3 is too low, it will cause problems such as loose structure of the anti-oxidation layer, bubbles, pores, and incomplete wrapping of the substrate surface. If the content of Na2SiO3 is too high, it will cause the bonding force between the anti-oxidation layer and the substrate to increase, making it difficult to peel off during the cooling process of the anti-oxidation layer. In the present application, the content of Na2SiO3 is controlled to be 14-20%.

[0098] SiC: In the heating process, SiC will react with O2, thereby consuming the oxygen diffused to the oxidation-resistant layer, causing the surface of the substrate to be in an oxygen-deficient or oxygen-free state, reducing the oxidation of the substrate. In this application, the content of SiC is controlled to be 6-10%.

[0099] Specifically, the anti-oxidation coating and water are configured into a solution in a mass ratio of 1:1 using a spray machine, and then the solution is left to stand and age, and then sprayed onto the surface of the continuous casting billet to form an oxidation-resistant layer.

[0100] The following describes three preferred embodiments of the application.

[0101] <First embodiment>

[0102] The present embodiment provides a 950MPa grade steel plate for hydropower, and a preparation method of the 950MPa grade steel plate for hydropower.

[0103] In terms of chemical composition, the chemical composition of the 950MPa grade steel plate for hydropower includes, in terms of mass percentage: C 0.08-0.10%, Si 0.05-0.15%, Mn 1.0-1.1%, Ni 1.4-1.6%, Cr 0.45-0.55%, Mo 0.40-0.55%, Cu 0.2-0.3%, Nb 0.010-0.040%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the balance being Fe and unavoidable impurities; and satisfies: 1.0%≤Cr+Mo≤1.1%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, and Ceq≤0.54.

[0104] The steel plate of the present embodiment is based on the above chemical composition design scheme, and the thickness of the steel plate is controlled to be t≤60mm. The center segregation level of the obtained steel plate is not higher than C0.5 level, the center porosity level is not higher than 0.5 level, the yield strength RP 0.2 ≥960MPa, the tensile strength is 980-1100MPa, the elongation after fracture is ≥16%, the yield strength ratio is ≤0.97, and the impact energy at -60℃ is ≥150J.

[0105] The present embodiment also provides a preparation method of the above-mentioned steel plate for hydropower, which comprises sequentially performing the following processes: molten steel smelting, continuous casting, heating, rolling, laminar cooling, and tempering heat treatment, thereby obtaining a steel plate finished product.

[0106] The following describes each process in the preparation method of the steel plate for hydropower in detail.

[0107] (1) Molten steel smelting process

[0108] The raw materials are smelted to obtain molten steel, and the chemical composition of the molten steel includes, in mass percent: C 0.08-0.10%, Si 0.05-0.15%, Mn 1.0-1.1%, Ni 1.4-1.6%, Cr 0.45-0.55%, Mo 0.40-0.55%, Cu 0.2-0.3%, Nb 0.010-0.040%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the balance being Fe and unavoidable impurities; and satisfies: 1.0%≤Cr+Mo≤1.1%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, ≤Ceq≤0.54.

[0109] It can be understood that the chemical composition of the molten steel obtained by the molten steel smelting process and the chemical composition of the continuous casting billet obtained by the continuous casting process are the same as the chemical composition of the final obtained steel plate, and will not be described here.

[0110] (2) Continuous casting process

[0111] The molten steel obtained by the molten steel smelting process is fully protected cast by a continuous casting machine, electromagnetic stirring is used during casting, and the end of continuous casting is controlled to be slightly pressed down, to obtain a continuous casting billet with a thickness of 320 mm, and then the continuous casting billet is stacked and slowly cooled for 72 hours before being unpacked.

[0112] Among them, the press-down rate of the end of continuous casting is controlled to be 1.20±0.5 mm / m, the center segregation level of the obtained continuous casting billet is not higher than C0.5 level, and the levels of A, B, C and D type inclusions are all not higher than level 1.

[0113] (3) Heating process

[0114] The continuous casting billet is sent into a heating furnace for heating, the heating temperature is controlled to be 1200-1230°C, and the heating coefficient a1 is 1.0-1.1 min / mm. After heating, the continuous casting billet is descaled.

[0115] Among them, the heating coefficient a1 determines the heating time, and the heating time=a1×D, D is the thickness of the slab, unit: mm. In this heating process, the slab is the continuous casting billet, and the thickness of the slab is the thickness of the continuous casting billet, i.e. 320 mm.

[0116] (4) Rolling process

[0117] The descaled continuous casting billet is rolled to obtain a steel plate.

[0118] wherein, single slab rolling is adopted in the rolling process, that is, one continuous casting slab is rolled into one steel plate, and the length of the continuous casting slab is controlled to be ≤4.5 m, the finish rolling temperature of the rolling process is (Ar3+150)℃-(Ar3+180)℃, the reduction of at least two passes is ≥20%, and the interval time between passes is <7s.

[0119] wherein, the austenite transformation start temperature Ar3 is calculated by the following formula:

[0120] Ar3=910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo].

[0121] Preferably, in the present embodiment, the rolling process adopts two-stage rolling, which includes recrystallization zone rolling and non-recrystallization zone rolling performed in sequence, that is, the continuous casting slab after descaling is first subjected to recrystallization zone rolling to obtain an intermediate slab, and then the intermediate slab is subjected to non-recrystallization zone rolling to obtain a steel plate with a thickness t≤60mm. The starting rolling temperature of the recrystallization zone rolling is 1150-1180℃, and the finish rolling temperature of the recrystallization zone rolling is 1010-1050℃; the starting rolling temperature of the non-recrystallization zone rolling is ≤890℃, and the finish rolling temperature of the non-recrystallization zone rolling is the finish rolling temperature of the rolling process, that is, (Ar3+150)℃-(Ar3+180)℃.

[0122] wherein, the thickness of the intermediate slab obtained by the recrystallization zone rolling is 150-170mm.

[0123] By adopting two-stage rolling and controlling the rolling temperatures of the two stages and the thickness of the intermediate slab, the rolling reduction can be reasonably distributed to prepare a steel plate with a thickness t≤60mm; by high-temperature rolling in the recrystallization zone, the rolling force can be effectively reduced to ensure the refinement of the austenite grains in the core of the slab; by austenite flattening in the non-recrystallization zone rolling, the nucleation points in the phase transformation process can be effectively increased, and the steel plate structure can be refined. In this way, by the reasonable matching of the two-stage rolling, the grains can be maximally refined, and the performance of the product can be improved.

[0124] (5) laminar cooling process

[0125] The steel plate obtained by the rolling process is subjected to laminar cooling after relaxation for 40-60s, the cooling water amount is 4000-5000m 3 / h, the cooling water temperature is ≤15-20℃, and the finish cooling temperature is ≤300℃.

[0126] (6) tempering heat treatment process;

[0127] The tempering temperature is 600-660℃, the heating coefficient a2 is 2.5-3.0 min / mm, and after tempering, it is air-cooled to obtain a finished steel plate with a thickness t≤60mm.

[0128] Among them, the heating coefficient a2 determines the tempering time, and the tempering time = a2 × t, t ≤ 60 mm.

[0129] Furthermore, the method for preparing the steel plate for hydropower also includes a spraying process performed after the continuous casting process and before the heating process;

[0130] In the spraying process, after the anti-oxidation coating is prepared into a solution, it is sprayed onto the surface of the continuously cast billet obtained in the continuous casting process to form an anti-oxidation layer. The thickness of the anti-oxidation layer is 0.2-0.4 mm. The chemical composition of the anti-oxidation coating, by mass percentage, includes: SiO2 55-65%, Al2O3 8-12%, ZrO2 7-12%, Na2SiO3 14-20%, and SiC 6-10%.

[0131] Specifically, the anti-oxidation coating is prepared by mixing the anti-oxidation coating with water at a mass ratio of 1:1 using a spraying machine, and then allowed to stand and age before being sprayed onto the surface of the continuous casting billet to form an anti-oxidation layer.

[0132] The steel plate after tempering heat treatment was subjected to performance tests. The center segregation level of the steel plate was no higher than C0.5, the center porosity level was no higher than 0.5, and the yield strength RP... 0.2 ≥960MPa, tensile strength of 990~1100MPa, elongation after fracture ≥17%, yield strength ratio ≤0.97, impact energy at -60℃ ≥150J.

[0133] <Second Implementation Method>

[0134] This embodiment provides a 950MPa grade hydroelectric steel plate and a method for preparing the 950MPa grade hydroelectric steel plate. The main difference between this second embodiment and the aforementioned first embodiment is:

[0135] Regarding the chemical composition, the 950MPa grade hydropower steel plate comprises, by mass percentage: C 0.10–0.12%, Si 0.05–0.15%, Mn 0.9–1.0%, Ni 1.4–2.0%, Cr 0.45–0.65%, Mo 0.40–0.65%, Cu 0.2–0.3%, Nb 0.01–0.04%, V 0.030–0.045%, Ti 0.01–0.02%, Al 0.04–0.05%, B 0.0006–0.0016%, N 0.003~0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, the remainder being Fe and unavoidable impurities; and satisfying: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3~3.4, Ceq≤0.56.

[0136] Based on the above chemical composition design scheme, the thickness t of the steel plate in this embodiment is controlled to satisfy: 60mm < t < 90mm. The resulting steel plate has a center segregation level not higher than C0.5 grade, a center porosity level not higher than 0.5 grade, and a yield strength RP 0.2 ≥940MPa, tensile strength ≥970MPa, elongation after fracture ≥17%, yield strength ratio ≤0.97, impact energy at -60℃ ≥160J.

[0137] In terms of production process, the main difference between this second embodiment and the aforementioned first embodiment is:

[0138] The chemical composition of the molten steel obtained from the steelmaking process, by mass percentage, includes: C 0.10–0.12%, Si 0.05–0.15%, Mn 0.9–1.0%, Ni 1.4–2.0%, Cr 0.45–0.65%, Mo 0.40–0.65%, Cu 0.2–0.3%, Nb 0.01–0.04%, V 0.030–0.045%, Ti 0.01–0.02%, Al 0.04–0.05%, B 0.0006–0.0016%, N 0.003~0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, the remainder being Fe and unavoidable impurities; and satisfying: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3~3.4, Ceq≤0.56.

[0139] In the rolling process, a two-stage rolling process is adopted. First, the recrystallization zone is rolled to obtain an intermediate billet with a thickness of 180-200 mm. Then, the intermediate billet is rolled in the non-recrystallization zone to obtain a steel plate with a thickness of t, where 60 mm < t < 90 mm.

[0140] In the tempering heat treatment process, the tempering time = a2×t, where 60mm < t < 90mm.

[0141] The steel plate after tempering heat treatment was subjected to performance tests. The center segregation level of the steel plate was no higher than C0.5, the center porosity level was no higher than 0.5, and the yield strength RP... 0.2 ≥940MPa, tensile strength ≥970MPa, elongation after fracture ≥17%, yield strength ratio ≤0.97, impact energy at -60℃ ≥160J.

[0142] The second embodiment is identical to the first embodiment except for the differences mentioned above, and will not be repeated here.

[0143] <Third Implementation Method>

[0144] This embodiment provides a 950MPa grade hydroelectric steel plate and a method for preparing the 950MPa grade hydroelectric steel plate. The main difference between this third embodiment and the aforementioned first embodiment is:

[0145] Regarding the chemical composition, the 950MPa grade hydropower steel plate comprises, by mass percentage: C 0.11–0.13%, Si 0.05–0.15%, Mn 0.8–0.9%, Ni 1.8–2.0%, Cr 0.45–0.65%, Mo 0.50–0.65%, Cu 0.2–0.3%, Nb 0.010–0.040%, V 0.030–0.045%, Ti 0.01–0.02%, Al 0.04–0.05%, B 0.0006–0.0016%, N 0.003~0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, the remainder being Fe and unavoidable impurities; and satisfying: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3~3.4, Ceq≤0.57.

[0146] Based on the above chemical composition design scheme, the thickness t of the steel plate in this embodiment is controlled to satisfy: 90mm ≤ t ≤ 130mm. The resulting steel plate has a center segregation level not higher than C0.5 grade, a center porosity level not higher than 0.5 grade, and a yield strength RP 0.2It has a strength of 890-920 MPa, tensile strength ≥950 MPa, elongation after fracture ≥16%, yield strength ratio ≤0.94, and impact energy at -60℃ ≥150 J.

[0147] In terms of production process, the main difference between this third embodiment and the aforementioned first embodiment is:

[0148] The chemical composition of the molten steel obtained from the steelmaking process, by mass percentage, includes: C 0.11–0.13%, Si 0.05–0.15%, Mn 0.8–0.9%, Ni 1.8–2.0%, Cr 0.45–0.65%, Mo 0.50–0.65%, Cu 0.2–0.3%, Nb 0.010–0.040%, V 0.030–0.045%, Ti 0.01–0.02%, Al 0.04–0.05%, B 0.0006–0.0016%, N 0.003~0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, the remainder being Fe and unavoidable impurities; and satisfying: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3~3.4, Ceq≤0.57.

[0149] In the rolling process, a single-stage rolling process is adopted, which only rolls the non-recrystallized zone to obtain steel plates with a thickness t of 90-130 mm. The initial rolling temperature is ≤900℃, and the final rolling temperature is (Ar3+150)℃~(Ar3+180)℃, and the reduction in each pass of the non-recrystallized zone rolling is ≥20%.

[0150] By using single-stage rolling to obtain steel plates with a thickness of 90-130 mm, and by rationally arranging the rolling temperature and pass reduction, the cumulative deformation effect of the non-recrystallization zone can be maximized, thereby reducing the grain coarsening problem caused by rolling in the non-recrystallization zone.

[0151] In the tempering heat treatment process, the tempering time = a2×t, 90mm≤t≤130mm.

[0152] The steel plate after tempering heat treatment was subjected to performance tests. The center segregation level of the steel plate was no higher than C0.5, the center porosity level was no higher than 0.5, and the yield strength RP... 0.2 It has a strength of 890-920 MPa, tensile strength ≥950 MPa, elongation after fracture ≥16%, yield strength ratio ≤0.94, and impact energy at -60℃ ≥150 J.

[0153] The third embodiment is identical to the first embodiment except for the differences mentioned above, and will not be repeated here.

[0154] The following six specific embodiments are provided to further illustrate the technical solution of this application. Of course, these six embodiments are only a part of the many variations contained in this implementation method, and not all of them.

[0155] The six embodiments each provide a steel plate. The chemical composition of the steel plates of the six embodiments is shown in Table 1 by mass percentage. In addition to the chemical composition in Table 1, the N content is 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the remainder is iron and unavoidable impurities.

[0156] Table 1

[0157] The preparation method for the steel plate follows the method described above.

[0158] In Examples 1-3, the steel plates were prepared using the <First Embodiment>, in Example 4, the steel plates were prepared using the <Second Embodiment>, and in Examples 5-6, the steel plates were prepared using the <Third Embodiment>.

[0159] The heating temperature and heating time of the heating process, the rolling temperature and intermediate billet thickness of the rolling process, the final cooling temperature of the laminar flow cooling process, and the heating temperature and tempering time of the tempering heat treatment process are shown in Table 2.

[0160] Table 2

[0161] The tensile properties of the steel plates from the above six embodiments were tested according to GB / T 228.1-2021 standard, as follows:

[0162] The tensile strength and elongation after fracture of the steel plate were tested using a tensile testing machine. The test results are shown in Table 3.

[0163] The impact energy of the steel plate at -60℃ was tested using an impact testing machine. Three sampling test results are shown for each test location. The impact energy of the steel plate at -60℃ is the average of the three sampling test results. The test results are shown in Table 3.

[0164] In addition, the thickness of the steel plates in the six embodiments is shown in Table 3.

[0165] Table 3

[0166] As shown in Table 3, the tensile strength of the steel plates in Examples 1 to 6 is ≥950MPa, reaching the 950MPa level. Furthermore, these six examples all possess high strength, toughness, excellent surface quality, and weldability, making them suitable for facilities such as water diversion pressure pipelines, ribs, branch pipes, and spiral casings in large-scale hydropower projects.

[0167] The metallographic structure of the steel plates of Examples 1 to 6 was observed using a metallographic microscope, and the metallographic structure of the steel plates of Examples 1 to 6 is shown in Figures 1 to 6.

[0168] As can be seen from Figures 1 to 6, the microstructure of the steel plates in Examples 1 to 6 is tempered bainite.

[0169] As the steel plate thickness increases and the compression ratio decreases, the lath spacing increases and the retained austenite content increases, causing the austenite grain boundaries to gradually transform from a flattened state to an equiaxed state. The <First Embodiment>, <Second Embodiment>, and <Third Embodiment> increase the hardenability of the steel plate by increasing the content of C, Cr, and Mo, and correspondingly reduce the content of easily segregating element Mn. Simultaneously, by controlling the rolling process and heat treatment temperature, a balance of overall performance is achieved, avoiding the performance degradation of the steel plate caused by microstructure coarsening. In particular, the <Third Embodiment>, which only involves rolling in the non-recrystallized zone, does not show a significant increase in the width of the internal laths.

[0170] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0171] The detailed descriptions listed above are merely specific descriptions of feasible implementation methods of this application, and are not intended to limit the scope of protection of this application. All equivalent implementation methods or modifications made without departing from the spirit of the art of this application should be included within the scope of protection of this application.

Claims

1. A method of producing a steel sheet, characterized by, The chemical composition of the steel plate includes, in mass percent: C 0.08-0.13%, Si 0.05-0.15%, Mn 0.8-1.1%, Ni 1.4-2.0%, Cr 0.45-0.65%, Mo 0.40-0.65%, Cu 0.2-0.3%, Nb 0.01-0.04%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the balance of Fe and inevitable impurities; and satisfies: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, carbon equivalent Ceq=[C]+[Mn] / 6+[Si] / 24+[Ni] / 40+[Cr] / 5+[Mo] / 4+[V] / 14, Ceq≤0.57; The preparation method comprises sequentially performing the following steps: molten steel smelting, continuous casting, heating, rolling, laminar cooling, and tempering heat treatment processes; In the continuous casting process, electromagnetic stirring is adopted, and the end of continuous casting is controlled to be slightly pressed, so as to obtain a continuous casting billet, which is then stacked and slowly cooled for 72 hours before being unpacked; the press-down rate of the end of continuous casting is 1.20±0.5 mm / m, and the center segregation level of the obtained continuous casting billet is not higher than C0.5 level, and the levels of A, B, C and D type inclusions are all not higher than level 1; In the heating process, the heating temperature is 1200-1230℃, the heating coefficient a1 is 1.0-1.1 min / mm, and the scale is removed after heating; In the rolling process, single-billet rolling is adopted, the length of the continuous casting billet is controlled to be ≤4.5 m, the finish rolling temperature of the rolling process is (Ar3+150)℃-(Ar3+180)℃, the press-down rate of at least two passes is ≥20%, and the interval time between passes is <7 s, wherein Ar3 is calculated by the following formula: Ar3=910-310[C]-80[Mn]-20[Cu]-15[Cr]-55[Ni]-80[Mo]; In the laminar cooling process, the steel plate obtained in the rolling process is relaxed for 40-60 seconds and then subjected to laminar cooling, the cooling water amount is 4000-5000 m 3 / h, the cooling water temperature is ≤15-20°C, and the final cooling temperature is ≤300°C. In the tempering heat treatment process, the heating temperature of tempering is 600-660℃, the heating coefficient a2 is 2.5-3.0 min / mm, and the steel plate is air-cooled after tempering.

2. The method of producing a steel sheet according to claim 1, characterized by, The thickness of the continuous casting billet is 320 mm; When the thickness t of the steel plate obtained in the rolling process is <90 mm, the rolling process adopts two-stage rolling, which comprises sequentially performing recrystallization zone rolling and unrecrystallization zone rolling; the start rolling temperature of the recrystallization zone rolling is 1150-1180℃, and the finish rolling temperature of the recrystallization zone rolling is 1010-1050℃; the start rolling temperature of the unrecrystallization zone rolling is ≤890℃.

3. The method of producing a steel sheet according to claim 2, characterized by, When t≤60 mm, the thickness of the intermediate billet obtained by the recrystallization zone rolling is 150-170 mm.

4. The method of producing a steel sheet according to claim 3, characterized by, The thickness t of the steel plate is 60mm or less, the chemical composition of the steel plate comprises, in mass percent: C 0.08-0.10%, Si 0.05-0.15%, Mn 1.0-1.1%, Ni 1.4-1.6%, Cr 0.45-0.55%, Mo 0.40-0.55%, Cu 0.2-0.3%, Nb 0.010-0.040%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, the rest being Fe and inevitable impurities; and satisfies: 1.0%≤Cr+Mo≤1.1%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, Ceq≤0.

54.

5. The method of producing a steel sheet according to claim 2, characterized by, When 60mm 6. The method of producing a steel sheet according to claim 5, characterized by, The thickness t of the steel plate satisfies: 60mm 7. The method of producing a steel sheet according to claim 1, characterized by, The thickness t of the steel plate satisfies: 60mm The thickness of the continuous casting billet is 320mm; When the thickness t of the steel plate obtained by the rolling process is 90-130mm, single-stage rolling is adopted, only non-recrystallization zone rolling is performed, the rolling-in temperature is≤900℃, and the reduction of each pass of the non-recrystallization zone rolling is≥20%.

8. The method of producing a steel sheet according to claim 7, characterized by, The thickness t of the steel plate satisfies 90mm≤t≤130mm, and the chemical components of the steel plate include, in mass percent, C 0.11-0.13%, Si 0.05-0.15%, Mn 0.8-0.9%, Ni 1.8-2.0%, Cr 0.45-0.65%, Mo 0.50-0.65%, Cu 0.2-0.3%, Nb 0.010-0.040%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the rest Fe and inevitable impurities; and satisfies 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, and Ceq≤0.

57.

9. The method of producing a steel sheet according to claim 1, characterized by, The preparation method further comprises a spraying process performed before the heating process; In the spraying process, the anti-oxidation coating is configured into a solution, and then is sprayed on the surface of the continuous casting billet to form an anti-oxidation layer, the thickness of the anti-oxidation layer is 0.2-0.4mm, and the chemical components of the anti-oxidation coating include, in mass percent, SiO255-65%, Al2O38-12%, ZrO27-12%, Na2SiO314-20%, and SiC6-10%.

10. A steel sheet characterized by, The chemical components of the steel plate include, in mass percent, C 0.08-0.13%, Si 0.05-0.15%, Mn 0.8-1.1%, Ni 1.4-2.0%, Cr 0.45-0.65%, Mo 0.40-0.65%, Cu 0.2-0.3%, Nb 0.01-0.04%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, and the rest Fe and inevitable impurities; and satisfies 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, carbon equivalent Ceq=[C]+[Mn] / 6+[Si] / 24+[Ni] / 40+[Cr] / 5+[Mo] / 4+[V] / 14, and Ceq≤0.

57.

11. Steel sheet according to claim 10, characterized in that, The thickness t of the steel plate satisfies: 60mm < t < 90mm, the chemical composition of the steel plate includes, in mass percent: C 0.10-0.12%, Si 0.05-0.15%, Mn 0.9-1.0%, Ni 1.4-2.0%, Cr 0.45-0.65%, Mo 0.40-0.65%, Cu 0.2-0.3%, Nb 0.01-0.04%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, the rest being Fe and inevitable impurities; and satisfies: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, Ceq≤0.

56.

12. The steel sheet according to claim 10, characterized by The thickness t of the steel plate satisfies: 60mm < t < 90mm, the chemical composition of the steel plate includes, in mass percent: C 0.10-0.12%, Si 0.05-0.15%, Mn 0.9-1.0%, Ni 1.4-2.0%, Cr 0.45-0.65%, Mo 0.40-0.65%, Cu 0.2-0.3%, Nb 0.01-0.04%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, the rest being Fe and inevitable impurities; and satisfies: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, Ceq≤0.

56.

13. The steel sheet according to claim 10, characterized by The thickness t of the steel plate satisfies: 60mm < t < 90mm, the chemical composition of the steel plate includes, in mass percent: C 0.10-0.12%, Si 0.05-0.15%, Mn 0.9-1.0%, Ni 1.4-2.0%, Cr 0.45-0.65%, Mo 0.40-0.65%, Cu 0.2-0.3%, Nb 0.01-0.04%, V 0.030-0.045%, Ti 0.01-0.02%, Al 0.04-0.05%, B 0.0006-0.0016%, N 0.003-0.004%, P≤0.010%, S≤0.003%, O≤0.002%, H≤0.0015%, the rest being Fe and inevitable impurities; and satisfies: 1.0%≤Cr+Mo≤1.2%, 0.06%≤Nb+V+Ti≤0.09%, Ti / N=3-3.4, Ceq≤0.

56.

14. The steel sheet according to claim 10, characterized by The center segregation level of the steel plate is not higher than C0.5 level, the center porosity level is not higher than 0.5 level, the yield strength RP 0.2 ≥ 890 MPa, the tensile strength is 950-1100 MPa, the elongation after breaking is ≥ 16%, the yield strength ratio is ≤ 0.97, and the impact energy at -60 ℃ is ≥ 150 J.

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