A large-strain-resistant hydroelectric steel plate with a tensile strength of 1000 MPa and a preparation method thereof

Abstract

This invention belongs to the field of steel production technology, specifically relating to a 1000MPa grade high-strain hydroelectric steel plate and its preparation method. Its chemical composition and mass percentage are as follows: C: ≤0.08%, Si: 0.20%–0.30%, Mn: 0.30%–0.70%, Cr: 0.30%–0.60%, Mo: 0.20%–0.40%, Ni: 2.50%–3.00%, Al: 0.02%–0.03%, Nb: 0.03–0.06%, V: 0.03–0.06%, Ti: 0.01–0.02%, S: ≤0.004%, P: ≤0.015%, with the balance being Fe and unavoidable impurity elements. This invention achieves a microstructure of ferrite, bainite, and retained austenite through rational composition design and control of rolling and online relaxation-rapid cooling processes. By controlling the content of retained austenite and ferrite, a hydroelectric steel plate with low yield strength ratio, high plasticity, and high toughness is obtained.

Description

Technical Field

[0001] This invention belongs to the field of steel production technology, specifically a high-strain hydroelectric steel plate with a tensile strength of 1000MPa and its preparation method. Background Technology

[0002] Hydropower, as an important component of clean energy, is of great significance for building a modern energy system, promoting the low-carbon and green transformation of energy, and achieving the "dual-carbon" strategic goal. Currently, the hydropower steel commonly used in my country is 800MPa grade. As the installed capacity of hydropower stations increases, the maximum wall thickness of pressure pipes has reached 90mm, and the thickness of steel plates on crescent ribs has even reached 150mm. Further increasing the thickness brings enormous difficulties to the subsequent steel plate preparation, welding, and transportation. Therefore, the research and development of 1000MPa grade hydropower steel is extremely important, which requires hydropower steel to develop towards higher strength, energy saving, greenness, and lightweight.

[0003] However, considering strength alone is insufficient to meet safety requirements in extreme environments; operational safety under special geological conditions must also be considered. Hydropower steel is mainly used in water intake pressure pipes, where the application demands high strength, toughness, plasticity, yield strength ratio, and weldability of the steel plates. Steel plates that undergo quenching and tempering typically possess good strength and toughness, but their yield strength ratio is high, uniform elongation is low, and they lack resistance to large deformations. Hydropower steel resistant to large strain must not only meet the performance requirements of conventional pipeline steel of the same grade, but also possess sufficient longitudinal resistance to large strains, requiring a large uniform elongation (UEL%), a low yield strength ratio (Rt0.5 / Rm), and a dome-shaped tensile stress-strain curve (without a yield plateau).

[0004] In areas prone to earthquakes, geological activities can cause impact deformation of hydroelectric steel pressure pipes, posing certain safety hazards to the subsequent use of steel plates. This necessitates that hydroelectric steel pressure pipes possess significant resistance to plastic deformation to withstand compression, tensile, and local torsional deformation. Moreover, even after being subjected to significant impact forces and undergoing a certain degree of deformation, the deformed pipeline should still be able to operate safely. However, high yield strength ratio steel plates are difficult to apply to special environments such as frequent earthquakes. Therefore, there is a certain demand for hydroelectric steel plates resistant to large strain, making their research and production of great significance.

[0005] Patent publication number CN 118374743A discloses a low yield strength ratio 960MPa grade high-strength steel and its production method. The composition of the steel plate, by mass percentage, is as follows: C: 0.09%~0.11%, Si: 0.2%~0.6%, Mn: 1.3%~2.5%, Cr: 0.5%~1.0%, Ni: 0.7%~1.5%, Mo: 0.2%~0.5%, Nb: 0.04%~0.08%, V: 0.004%~0.08%, Ti: 0.01%~0.03%, Al: 0.01%~0.06%, Cu: 0.7%~1.5%, with the balance being Fe and unavoidable impurities. The process employs offline two-phase quenching followed by low-temperature tempering heat treatment. The quenching temperature is 800–840℃, followed by water quenching to room temperature, and the tempering temperature is 200–300℃, with final air cooling to room temperature. The resulting steel plate exhibits a yield strength ≥960MPa, tensile strength ≥1150MPa, yield-to-tensile ratio ≤0.85, elongation ≥13%, and impact energy ≥69J at -40℃. However, the steel plate obtained by this invention has relatively low elongation and impact toughness, and its Pcm (partial crack diameter) is 0.30–0.428%, making it unsuitable for use in low-temperature and high-altitude regions. Furthermore, it is difficult to weld subsequently and is unsuitable for use in hydropower steel pressure pipelines.

[0006] Patent publication number CN 118441225A discloses a high-strength steel with a low yield strength ratio of 1000MPa and its production method. The composition of the steel plate, by mass percentage, is as follows: C: 0.09%–0.1%, Si: 0.2%–0.6%, Mn: 1.3%–1.9%, Cr: 0.4%–0.5%, Ni: 0.7%–1.5%, Mo: 0.2%–0.3%, Nb: 0.04%–0.08%, V: 0.001%–0.04%, Ti: 0.01%–0.02%, Al: 0.01%–0.03%, Cu: 0.7%–0.8%, with the balance being Fe and impurities. The invention employs an offline fully austenitizing quenching process followed by a two-phase region secondary quenching and low-temperature tempering heat treatment. The primary quenching temperature is above 900℃, followed by water quenching to room temperature. The secondary quenching temperature is 800–840℃, followed by water quenching to room temperature. The tempering temperature is 200–300℃, and finally, the steel plate is air-cooled to room temperature. The maximum thickness of the steel plate obtained by this invention is only 20mm, making it more challenging to produce thicker steel plates.

[0007] Patent publication number CN117821846A discloses a method for manufacturing a 1000MPa-grade high-strength hydroelectric steel plate at ultra-low temperature. The composition of the steel plate, by mass percentage, is as follows: C: 0.085%–0.115%, Si: 0.10%–0.28%, Mn: 0.90%–1.40%, Cr: 0.30%–0.60%, Ni: 1.60%–2.50%, Al: 0.02%–0.08%, Mo: 0.30%–0.60%, Nb≤0.05%, V: 0.03%–0.06%, P≤0.015%, S≤0.003%, B: 0.001%–0.002%, with the remainder being Fe and impurities. The steel plate undergoes offline quenching, a first long-time tempering, and a second rapid tempering heat treatment in a furnace. The quenching temperature is 880–930℃, with a furnace time of 1.5–2.0 min / mm; the first tempering temperature is 500–540℃, with a furnace time of 3.0–5.0 min / mm; and the second tempering temperature is 600–640℃, with a furnace time of 1.5–2.0 min / mm. This invention employs offline quenching and a two-stage tempering process, resulting in a complex and time-consuming production process, increasing production costs.

[0008] Existing technologies for producing 1000MPa grade hydroelectric steel typically employ a process of complete quenching followed by high-temperature tempering to obtain tempered sorbite microstructure. However, this results in steel plates with a high yield strength ratio (>0.9), and in many processes, the yield strength ratio approaches 1. Consequently, these steels lack resistance to plastic deformation and cannot withstand high-stress deformation. In summary, while these patents offer different solutions, several technical and economic challenges remain to be overcome. Summary of the Invention

[0009] To address the problems in existing technologies, this invention provides a hydroelectric steel plate with a tensile strength of 1000 MPa and a method for preparing it to withstand large strain. The method improves austenite stability by increasing the Ni content, and the increased Ni content also benefits impact toughness. Furthermore, it retains a significant amount of retained austenite during the subsequent relaxation cooling process. This invention employs controlled rolling and relaxation cooling processes, generating a portion of ferrite during relaxation. This ferrite is then rapidly water-cooled to the bainitic phase region to obtain a bainitic microstructure. Bainite has a high elastic limit, which is beneficial for resistance to large strain. By comprehensively controlling the multiphase microstructure of ferrite, bainite, and retained austenite, a steel plate with a low yield strength ratio, high plasticity, and high toughness is obtained.

[0010] The technical solution of this invention is as follows:

[0011] A type of hydroelectric steel plate with a tensile strength of 1000MPa and resistance to large strain has the following chemical composition and mass percentage: C: ≤0.08%, Si: 0.20%~0.30%, Mn: 0.30%~0.70%, Cr: 0.30%~0.60%, Mo: 0.20%~0.40%, Ni: 2.50%~3.00%, Al: 0.02%~0.03%, Nb: 0.03~0.06%, V: 0.03~0.06%, Ti: 0.01~0.02%, S: ≤0.004%, P: ≤0.015%, with the balance being Fe and unavoidable impurity elements.

[0012] Carbon (C) is a traditional strengthening element in low-carbon steel. It can expand the austenite phase region and form high-strength carbides, thereby improving the strength of the material. However, an increase in C content will reduce ferrite in the steel and increase brittle cementite, which will have a significant impact on plasticity and toughness. A higher C content will also increase the carbon equivalent, affecting subsequent welding performance. Therefore, the low-carbon concept is adopted, and the mass percentage content of C is limited to within the range of 0.08%.

[0013] Si can dissolve in the iron matrix to strengthen it and increase its strength. It can also increase the strain hardening rate of the alloy and generate a large number of slender deformation twins to improve the strength and plasticity of the material. Therefore, the mass percentage content of Si should be controlled in the range of 0.20% to 0.30%.

[0014] The mass percentage content of manganese (Mn) is controlled within the range of 1.30% to 1.60%. Mn is an austenite-forming element and can form an infinite solid solution with austenite, thereby improving the strength, hardness, and wear resistance of steel. Furthermore, Mn can lower the free energy of the austenite-to-ferrite transformation, shifting the isothermal transformation curve of austenite to the right and increasing the hardenability of steel. Therefore, the mass percentage content of Mn is controlled within the range of 0.3% to 0.7%.

[0015] Cr can improve hardenability, enhance the strength of the iron matrix through solid solution strengthening, and increase the self-corrosion potential of the iron matrix. It can also preferentially form a continuous and dense passivation film on the steel surface. However, excessive Cr will increase the possibility of pitting corrosion in steel materials. Therefore, the mass percentage content of Cr should be controlled within the range of 0.30% to 0.60%.

[0016] Mo (Mo) is an element that shrinks the austenite phase region, promotes bainite transformation, and achieves a medium-temperature transformation structure over a wide temperature range. However, excessive Mo content can lead to strong solid solution strengthening, causing lattice distortion and reducing the impact toughness of the weld metal. Therefore, the Mo content is controlled within the range of 0.20% to 0.40% by mass.

[0017] Ni is an austenite-forming element that expands the austenite phase region, stabilizes the austenite structure, reduces the resistance to dislocation movement in steel, relaxes stress, and significantly improves the low-temperature toughness and hardenability of steel. However, excessively high Ni content increases production costs. Therefore, the mass percentage of Ni is controlled within the range of 2.50% to 3.00%.

[0018] The Al content (by mass percentage) is controlled within the range of 0.02% to 0.03%. Al has a strong affinity for O and N, making it a deoxidizing and nitrogen-fixing agent during steelmaking. However, excessive Al content will affect the hot working properties, weldability, and machinability of the steel. Therefore, the Al content (by mass percentage) is controlled within the range of 0.02% to 0.03%.

[0019] Nitrogen (Nb) exhibits the most significant precipitation strengthening effect among microalloying elements. Nb can form very stable carbides or nitrides with C, N, and O, pinning grain boundaries and dislocation migration during recrystallization and hindering the growth of recrystallized austenite grains under high-temperature deformation, thus refining the grain size. Therefore, its content is controlled within the range of 0.03–0.06% in this composition design.

[0020] V can form fine carbides with C and N, refining the grain structure and thus improving strength and toughness. Therefore, its content is controlled within the range of 0.03% to 0.06% in this composition design.

[0021] Ti has a strong affinity for N, O, and C, making it an excellent deoxidizer and effective element for fixing nitrogen and carbon. Furthermore, the formation temperature and affinity of compounds formed by Ti with N, O, and C are higher than those with Nb, thus effectively reducing the harmful effects of Nb(C,N) on the plasticity of steel and preventing surface cracks. Therefore, its content is controlled within the range of 0.01–0.02% in this composition design.

[0022] Sulfur (S) is considered an impurity element in steel. It readily combines with iron (Fe) to form the brittle FeS phase, which has a low melting point of 989℃. This causes hot brittleness during processing and severely reduces the steel's ductility and toughness. Furthermore, S also negatively impacts weldability. Therefore, its content is controlled below 0.004% in this composition design.

[0023] Excessive phosphorus (P) content in steel easily combines with iron to form a hard and brittle Fe3P phase, leading to "cold brittleness" and severely reducing the steel's low-temperature toughness. Furthermore, P tends to segregate at high temperatures, which is detrimental to welding. Therefore, this composition design strictly controls the P content to below 0.015%.

[0024] The above-mentioned method for preparing a 1000MPa tensile strength grade hydroelectric steel plate for high strain includes smelting, continuous casting, heating, rough rolling, finish rolling, relaxation, and cooling processes. Specifically, the continuously cast billet is heated to 1150–1250℃ with a heating coefficient of 8–12 min / cm to ensure complete solid solution of the carbides of microalloying elements in the steel, thus maximizing solid solution strengthening. Excessive heating temperature and prolonged holding time result in coarser austenite grains, significantly impacting the fine-grain strengthening effect. The rolling process is controlled through two stages: rough rolling and finish rolling. During rough rolling, the final rolling temperature in the fully recrystallized zone is 980–1100℃, avoiding the partial recrystallization zone of austenite, and the total reduction rate is ≥50%. Rolling in the fully recrystallized austenite region using a multi-pass, high-reduction process can reduce the austenite grain size, allowing the high-temperature austenite to repeatedly undergo dynamic recovery and recrystallization. Furthermore, the inhibitory effect of microalloying elements Nb, Ti, and their carbonitrides on recrystallization further refines the austenite grains. In the aforementioned method for preparing a 1000MPa tensile strength, high-strain hydroelectric steel plate, the finishing rolling temperature in the non-recrystallized austenite region is 800-840℃, with a single-pass reduction rate of ≥10% and a total reduction rate of ≥60% in the last three passes. During rolling in the non-recrystallized austenite region before phase transformation, recovery and recrystallization cannot occur. With cumulative deformation during rolling, numerous deformation bands are generated, increasing the nucleation sites and driving force for ferrite. The relatively low finishing rolling temperature and the large deformation rate in the last three passes effectively refine the grains.

[0025] Furthermore, in the aforementioned method for preparing a 1000MPa tensile strength grade hydroelectric steel plate resistant to large strain, the final rolled steel plate undergoes online relaxation and air cooling. During the relaxation and air cooling process, the relaxation temperature is 750–640℃, and the relaxation time is 15–25s. Some ferrite is generated during the relaxation and cooling process. If the relaxation time is too long or the relaxation temperature is too low, excessive ferrite will occur, significantly impacting the strength. After relaxation, rapid water cooling to 480–540℃ is employed at a cooling rate of 15–25℃ / s. Rapid water cooling to the bainitic phase region after relaxation, resulting in a bainitic structure, is beneficial for improving the material's elastic limit and plastic deformation capacity, and is advantageous for its resistance to large strain.

[0026] Furthermore, the above-mentioned 1000MPa grade high strain hydroelectric steel plate has a maximum thickness of 50mm.

[0027] Furthermore, in the aforementioned 1000MPa grade hydroelectric steel plate for high strain resistance, the microstructure of the steel plate consists of ferrite, bainite and retained austenite, with a retained austenite content of 5-10%, and the content of retained austenite + ferrite ≤20%.

[0028] Furthermore, the aforementioned 1000MPa grade high-strain hydroelectric steel plate has a yield strength Rt0.5 of 885-930MPa, and can guarantee a yield strength greater than 900MPa after 3 cycles of tensile and compressive stress at 3% strain. It also has a tensile strength Rm ≥ 1050MPa, a yield-to-tensile ratio Rt0.5 / Rm ≤ 0.85, a uniform elongation UEL ≥ 10%, and an average Charpy impact energy KV2 ≥ 150J at -60℃.

[0029] Advantages and beneficial effects of the present invention:

[0030] By employing a "controlled rolling + relaxation cooling" process, the microstructure is adjusted through composition and process control to form a multiphase microstructure consisting of bainite, a small amount of ferrite, and retained austenite. The phase ratio of the microstructure is strictly controlled, which, while maintaining high strength and high toughness, synergistically improves the steel plate's resistance to plastic deformation and reduces the yield strength ratio, thereby enhancing the steel plate's resistance to large strain.

[0031] This invention utilizes post-rolling relaxation cooling, eliminating the need for complex heat treatment processes compared to traditional molding processes. This innovative process not only simplifies the production flow but also significantly reduces manufacturing costs and improves production efficiency. By omitting traditional heat treatment steps, companies can reduce energy consumption and time costs, while minimizing environmental impact, achieving the dual goals of economic benefits and environmental friendliness, and ensuring the safe operation of steel used in hydropower projects. Attached Figure Description

[0032] Figure 1 The microstructure morphology of the finished steel plate in Example 1 of the present invention;

[0033] Figure 2 The microstructure morphology of the finished steel plate in Example 2 of this invention;

[0034] Figure 3 The microstructure morphology of the finished steel plate in Example 3 of this invention;

[0035] Figure 4 The microstructure morphology of the finished steel plate in Example 4 of this invention;

[0036] Figure 5 The microstructure morphology of the finished steel plate in Example 5 of the present invention; Detailed Implementation

[0037] To make the technical solutions and advantages of the present invention easier to understand, the specific implementation of the present invention will be further described below with reference to the embodiments. The following embodiments are used to illustrate the present invention, but should not be used to limit the scope of the present invention in any way. Example 1

[0038] This embodiment provides a 1000MPa grade high-strain hydroelectric steel plate with the following chemical composition and mass percentage: C: 0.08%, Si: 0.29%, Mn: 0.68%, Cr: 0.59%, Mo: 0.40%, Ni: 2.95%, Al: 0.026%, Nb: 0.055%, V: 0.06%, Ti: 0.018%, S≤0.004%, P≤0.015%, with the balance being Fe and unavoidable impurity elements.

[0039] The above-mentioned method for preparing a 1000MPa grade hydroelectric steel plate resistant to large deformation includes smelting, continuous casting, heating, rough rolling, finish rolling, relaxation, and cooling processes, wherein:

[0040] The continuously cast billet was heated to 1200℃ with a heating coefficient of 10 min / cm; the roughing rolling temperature was 1045℃ with a total reduction of 66.67%; the finishing rolling temperature was 825℃, and the single-pass reduction rates for the last three passes were 13.81%, 12.93%, and 11.45%, respectively, with a total reduction of 66.31%.

[0041] The temperature was cooled to 650℃ during the relaxation process, and the relaxation time was 23s. After relaxation, the temperature was rapidly cooled to 500℃ with water at a rate of 22℃ / s, and then air-cooled to room temperature.

[0042] like Figure 1 As shown, the microstructure of the finished steel plate in this embodiment consists of ferrite, bainite and retained austenite, with a retained austenite content of 7.63% and a ferrite content of 10.64%. The thickness of the finished steel plate is 50 mm.

[0043] The mechanical properties of the finished steel plate in this embodiment are as follows: yield strength Rt0.5 is 892 MPa, yield strength Rt0.5 after 3 cycles of tension and compression at 3% strain is 912 MPa, tensile strength Rm is 1066 MPa, yield ratio Rt0.5 / Rm is 0.836, uniform elongation UEL is 11.1%, and average Charpy impact energy KV2 at -60℃ is 152 J. Example 2

[0044] This embodiment provides a 1000MPa grade hydroelectric steel plate with high strain resistance. Its chemical composition and mass percentage are as follows: C: 0.071%, Si: 0.26%, Mn: 0.58%, Cr: 0.49%, Mo: 0.31%, Ni: 2.86%, Al: 0.024%, Nb: 0.049%, V: 0.051%, Ti: 0.016%, S≤0.004%, P≤0.015%, with the balance being Fe and unavoidable impurity elements.

[0045] The above-mentioned method for preparing a 1000MPa grade hydroelectric steel plate resistant to large deformation includes smelting, continuous casting, heating, rough rolling, finish rolling, relaxation, and cooling processes, wherein:

[0046] The continuously cast billet was heated to 1200℃ with a heating coefficient of 10 min / cm; the roughing rolling temperature was 1034℃ with a total reduction of 65.81%; the finishing rolling temperature was 832℃, and the single-pass reduction rates for the last three passes were 13.42%, 11.06%, and 10.38%, respectively, with a total reduction of 66.31%.

[0047] The temperature was cooled to 670℃ during the relaxation process, and the relaxation time was 19s. After relaxation, the temperature was rapidly cooled to 520℃ with water at a rate of 18℃ / s, and then air-cooled to room temperature.

[0048] like Figure 2 As shown, the microstructure of the finished steel plate in this embodiment consists of ferrite, bainite and retained austenite, with a retained austenite content of 7.29% and a ferrite content of 9.82%. The thickness of the finished steel plate is 40 mm.

[0049] The mechanical properties of the finished steel plate in this embodiment are as follows: yield strength Rt0.5 is 901 MPa, yield strength Rt0.5 after 3 cycles of tension and compression at 3% strain is 919 MPa, tensile strength Rm is 1073 MPa, yield ratio Rt0.5 / Rm is 0.839, uniform elongation UEL is 10.6%, and average Charpy impact energy KV2 at -60℃ is 146 J. Example 3

[0050] This embodiment provides a 1000MPa grade hydroelectric steel plate with high strain resistance. Its chemical composition and mass percentage are as follows: C: 0.068%, Si: 0.24%, Mn: 0.46%, Cr: 0.41%, Mo: 0.32%, Ni: 2.69%, Al: 0.024%, Nb: 0.043%, V: 0.046%, Ti: 0.015%, S≤0.004%, P≤0.015%, with the balance being Fe and unavoidable impurity elements.

[0051] The above-mentioned method for preparing a 1000MPa grade hydroelectric steel plate resistant to large deformation includes smelting, continuous casting, heating, rough rolling, finish rolling, relaxation, and cooling processes, wherein:

[0052] The continuously cast billet was heated to 1200℃ with a heating coefficient of 10 min / cm; the roughing rolling temperature was 1046℃ with a total reduction of 70.00%; the finishing rolling temperature was 815℃, and the single-pass reduction rates for the last three passes were 16.21%, 14.93%, and 11.54%, respectively, with a total reduction of 66.67%.

[0053] The temperature was cooled to 680℃ during the relaxation process, and the relaxation time was 21s. After relaxation, the temperature was rapidly water-cooled to 480℃ at a cooling rate of 24℃ / s, and then air-cooled to room temperature.

[0054] like Figure 3 As shown, the microstructure of the finished steel plate in this embodiment consists of ferrite, bainite and retained austenite, with a retained austenite content of 8.29% and a ferrite content of 10.22%. The thickness of the finished steel plate is 30 mm.

[0055] The mechanical properties of the finished steel plate in this embodiment are as follows: yield strength Rt0.5 is 913 MPa, yield strength Rt0.5 after 3 cycles of tension and compression at 3% strain is 928 MPa, tensile strength Rm is 1079 MPa, yield ratio Rt0.5 / Rm is 0.846, uniform elongation UEL is 11.4%, and average Charpy impact energy KV2 at -60℃ is 156 J. Example 4

[0056] This embodiment provides a 1000MPa grade hydroelectric steel plate with high strain resistance. Its chemical composition and mass percentage are as follows: C: 0.062%, Si: 0.24%, Mn: 0.36%, Cr: 0.38%, Mo: 0.26%, Ni: 2.65%, Al: 0.028%, Nb: 0.036%, V: 0.039%, Ti: 0.014%, S≤0.004%, P≤0.015%, with the balance being Fe and unavoidable impurity elements.

[0057] The above-mentioned method for preparing a 1000MPa grade hydroelectric steel plate resistant to large deformation includes the following processes: smelting, continuous casting, heating, rough rolling, finish rolling, water cooling, quenching, and tempering heat treatment.

[0058] The continuously cast billet was heated to 1200℃ with a heating coefficient of 10 min / cm; the roughing rolling temperature was 1034℃ with a total reduction of 66.67%; the finishing rolling temperature was 806℃, and the single-pass reduction rates for the last three passes were 15.32%, 14.13%, and 10.59%, respectively, with a total reduction of 64.81%.

[0059] The temperature was cooled to 660℃ during the relaxation process, and the relaxation time was 22s. After relaxation, the temperature was rapidly water-cooled to 490℃ at a cooling rate of 17℃ / s, and then air-cooled to room temperature.

[0060] like Figure 4 As shown, the microstructure of the finished steel plate in this embodiment consists of ferrite, bainite and retained austenite, with a retained austenite content of 6.78% and a ferrite content of 11.03%. The thickness of the finished steel plate is 20 mm.

[0061] The mechanical properties of the finished steel plate in this embodiment are as follows: yield strength Rt0.5 is 899 MPa, yield strength Rt0.5 after 3 cycles of tension and compression at 3% strain is 915 MPa, tensile strength Rm is 1066 MPa, yield ratio Rt0.5 / Rm is 0.843, uniform elongation UEL is 10.3%, and average Charpy impact energy KV2 at -60℃ is 141 J. Example 5

[0062] This embodiment provides a 1000MPa grade hydroelectric steel plate with high strain resistance. Its chemical composition and mass percentage are as follows: C: 0.059%, Si: 0.25%, Mn: 0.35%, Cr: 0.33%, Mo: 0.24%, Ni: 3.55%, Al: 0.026%, Nb: 0.032%, V: 0.031%, Ti: 0.012%, S≤0.004%, P≤0.015%, with the balance being Fe and unavoidable impurity elements.

[0063] The above-mentioned method for preparing a 1000MPa grade hydroelectric steel plate resistant to large deformation includes the following processes: smelting, continuous casting, heating, rough rolling, finish rolling, water cooling, quenching, and tempering heat treatment.

[0064] The continuously cast billet was heated to 1200℃ with a heating coefficient of 10 min / cm; the roughing rolling temperature was 1044℃ with a total reduction of 68.91%; the finishing rolling temperature was 835℃, and the single-pass reduction rates for the last three passes were 17.25%, 13.33%, and 11.84%, respectively, with a total reduction of 66.67%.

[0065] The above-mentioned method for preparing a 1000MPa grade hydroelectric steel plate resistant to large deformation includes smelting, continuous casting, heating, rough rolling, finish rolling, relaxation, and cooling processes, wherein:

[0066] The temperature was cooled to 690℃ during the relaxation process, and the relaxation time was 17s. After relaxation, the temperature was rapidly water-cooled to 510℃ at a cooling rate of 21℃ / s, and then air-cooled to room temperature.

[0067] like Figure 5 As shown, the microstructure of the finished steel plate in this embodiment consists of ferrite, bainite and retained austenite, with a retained austenite content of 5.94% and a ferrite content of 10.78%. The thickness of the finished steel plate is 50 mm.

[0068] The mechanical properties of the finished steel plate in this embodiment are as follows: yield strength Rt0.5 is 894 MPa, yield strength Rt0.5 after 3 cycles of tension and compression at 3% strain is 911 MPa, tensile strength Rm is 1056 MPa, yield ratio Rt0.5 / Rm is 0.846, uniform elongation UEL is 10.7%, and average Charpy impact energy KV2 at -60℃ is 132 J.

[0069] The above descriptions are merely some embodiments, intended only to better explain the present invention, and are not intended to limit it. Those skilled in the art can modify some of the technical features of the above embodiments, but any modifications made within the principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A hydroelectric steel plate with a tensile strength of 1000MPa and resistance to large strain, characterized in that, Its chemical composition by mass percentage is as follows: C: ≤0.08%, Si: 0.20%–0.30%, Mn: 0.30%–0.70%, Cr: 0.30%–0.60%, Mo: 0.20%–0.40%, Ni: 2.50%–3.00%, Al: 0.02%–0.03%, Nb: 0.03–0.06%, V: 0.03–0.06%, Ti: 0.01–0.02%, S: ≤0.004%, P: ≤0.015%, with the balance being Fe and unavoidable impurity elements; The microstructure of the steel plate consists of ferrite, bainite, and retained austenite, with a retained austenite content of 5-10%, and the total content of retained austenite + ferrite ≤20%. The steel plate has a yield strength Rt0.5 of 885-930 MPa, and can guarantee a yield strength >900 MPa after 3 cycles of tensile and compressive stress at 3% strain. Its tensile strength Rm ≥1050 MPa, yield ratio Rt0.5 / Rm ≤0.85, uniform elongation UEL ≥10%, and average Charpy impact energy KV2 ≥120 J at -60℃.

2. The method for preparing a high-strain hydroelectric steel plate with a tensile strength of 1000 MPa according to claim 1, characterized in that, The preparation process includes smelting, continuous casting, heating, rough rolling, finish rolling, relaxation and cooling. Specifically, the continuously cast billet is heated to 1150-1250℃ with a heating coefficient of 8-12 min / cm. It undergoes two stages of controlled rolling: rough rolling and finish rolling. During rough rolling, the final rolling temperature in the fully recrystallized zone is 980-1100℃, avoiding the recrystallized austenite zone, and the total reduction is ≥50%. During finish rolling, the final rolling temperature in the non-recrystallized austenite zone is 800-840℃, with the single-pass reduction of the last three passes ≥10% and the total reduction ≥60%.

3. The method for preparing a high-strain hydroelectric steel plate with a tensile strength of 1000 MPa according to claim 2, characterized in that, After final rolling, the steel plate is relaxed and air-cooled online at a temperature of 750–640℃ for 15–25 seconds. After relaxation, it is rapidly water-cooled to 480–540℃ at a rate of 15–25℃ / s.

4. The 1000MPa tensile strength grade high strain hydroelectric steel plate according to claim 1, characterized in that, The maximum thickness of the steel plate is 50mm.

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