Large-strain-resistant hydroelectric steel plate with tensile strength of 1000 MPa and preparation method

Abstract

The invention belongs to the technical field of steel production, and particularly relates to a large-strain-resistant hydroelectric steel plate with the tensile strength being 1000 MPa and a preparation method. The steel comprises the following chemical components in percentage by mass: less than or equal to 0.08% of C, 0.20%-0.30% of Si, 0.30%-0.70% of Mn, 0.30%-0.60% of Cr, 0.20%-0.40% of Mo, 2.50%-3.00% of Ni, 0.02%-0.03% of Al, 0.03%-0.06% of Nb, 0.03%-0.06% of V, 0.01%-0.02% of Ti, less than or equal to 0.004% of S, less than or equal to 0.015% of P and the balance of Fe and inevitable impurity elements. Through reasonable component design, rolling control and an on-line relaxation-rapid cooling structure regulation and control process, the obtained structure is ferrite, bainite and retained austenite, and the large-strain-resistant hydroelectric steel plate with the low yield ratio, high plasticity and high toughness is obtained by regulating and controlling the content of the retained austenite and the ferrite.

Description

Technical Field

[0001] The invention belongs to the technical field of steel production, and specifically relates to a 1000MPa-level high-strain resistant hydropower steel plate and a preparation method thereof. Background Art

[0002] As an important component of clean energy, hydropower is of great significance for building a modern energy system, promoting low-carbon and green transformation of energy, and achieving the strategic goal of "dual carbon". At present, the hydropower steel commonly used in my country is 800MPa grade. With the increasing installed capacity of hydropower stations, the maximum wall thickness of the pressure pipe has reached 90mm, and the thickness of the steel plate on the crescent rib has even reached 150mm. Continuing to increase the thickness will bring great difficulties to the subsequent preparation, welding and transportation of steel plates. Therefore, the research and development of 1000MPa hydropower steel is extremely important, which requires hydropower steel to develop in the direction of higher strength, energy saving, green and lightweight.

[0003] However, considering strength alone can no longer meet the safety needs in extreme environments, and operational safety under special geological conditions must also be considered. Hydropower steel is mainly used in water diversion pressure pipes, and its application scenarios have high requirements for the strength, plasticity, yield strength ratio and welding performance of the steel plate. Steel plates that are usually subjected to quenching and tempering treatment have good strength and toughness, but their yield strength ratio will be higher, the uniform elongation will be lower, and they do not have the ability to resist large deformation. Hydropower steel that resists large strains must not only meet the various performance requirements of conventional pipeline steel of the same steel grade, but also require that its longitudinal performance must have sufficient ability to resist large strains, that is, it requires a larger uniform elongation (UEL%), a lower yield strength ratio (Rt0.5 / Rm), and a dome-shaped tensile stress-strain curve (no yield platform), etc.

[0004] Some geological activities in some earthquake-prone areas may cause impact deformation to hydropower steel pressure pipes, which poses certain safety hazards to the subsequent use of steel plates. This requires that hydropower steel pressure pipes must have a greater ability to resist plastic deformation to withstand compression deformation, tensile deformation, and local torsional deformation. Moreover, after the pipeline is subjected to a large impact force, even if a certain degree of deformation occurs, the deformed pipeline can still operate safely. High yield strength ratio steel plates are difficult to apply to special environments such as frequent earthquakes. Therefore, there is a certain demand for large strain resistant hydropower steel plates, and their research and production are of great significance.

[0005] The patent publication number is CN 118374743A, a low yield ratio 960MPa grade high-strength steel and a production method thereof. The composition of the steel plate is calculated by mass percentage: C: 0.09% to 0.11%, Si: 0.2% to 0.6%, Mn: 1.3% to 2.5%, Cr: 0.5% to 1.0%, Ni: 0.7% to 1.5%, Mo: 0.2% to 0.5%, Nb: 0.04% to 0.08%, V: 0.004% to 0.08%, Ti: 0.01% to 0.03%, Al: 0.01% to 0.06%, Cu: 0.7% to 1.5%, and the balance is Fe and unavoidable impurities. The off-line two-phase zone quenching + low-temperature tempering heat treatment process is adopted, the quenching temperature is 800-840℃, water quenching to room temperature, tempering temperature is 200-300℃, and finally air cooling to room temperature. The yield strength of the obtained steel plate is ≥960MPa, the tensile strength is ≥1150MPa, the yield strength ratio is ≤0.85, the elongation is ≥13%, and the -40℃ impact energy is ≥69J. The steel plate obtained by this invention has low elongation and impact toughness, and its Pcm is 0.30-0.428%, which is not suitable for application in low temperature and high-cold areas, and it is difficult to weld later, and is not suitable for use in hydropower steel pressure pipelines.

[0006] The patent publication number is CN 118441225A. A low yield ratio 1000MPa grade high-strength steel and a production method thereof. The composition of the steel plate is calculated by mass percentage as follows: C: 0.09% to 0.1%, Si: 0.2% to 0.6%, Mn: 1.3% to 1.9%, Cr: 0.4% to 0.5%, Ni: 0.7% to 1.5%, Mo: 0.2% to 0.3%, Nb: 0.04% to 0.08%, V: 0.001% to 0.04%, Ti: 0.01% to 0.02%, Al: 0.01% to 0.03%, Cu: 0.7% to 0.8%, and the balance is Fe and impurities. The offline complete austenitization quenching + two-phase zone secondary quenching + low-temperature tempering heat treatment process is adopted: the primary quenching temperature is above 900℃, and then water quenching to room temperature; the secondary quenching temperature is 800-840℃, and then water quenching to room temperature; the tempering temperature is 200-300℃, and finally air cooling to room temperature. The maximum thickness of the steel plate obtained by this invention is only 20mm, and the subsequent thick-gauge steel plate is difficult to increase in thickness.

[0007] Patent publication number CN117821846A discloses a method for manufacturing an ultra-low temperature 1000MPa grade high-strength hydropower steel plate. The composition of the steel plate is calculated by mass percentage as follows: C: 0.085% to 0.115%, Si: 0.10% to 0.28%, Mn: 0.90% to 1.40%, Cr: 0.30% to 0.60%, Ni: 1.60% to 2.50%, Al: 0.02% to 0.08%, Mo: 0.30% to 0.60%, Nb≤0.05%, V: 0.03% to 0.06%, P≤0.015%, S≤0.003%, B: 0.001% to 0.002%, and the rest is Fe and impurities. The steel plate is put into the furnace for offline quenching + first long tempering + second rapid tempering heat treatment, wherein the quenching temperature is 880~930℃, the furnace time is 1.5~2.0 min / mm, the first tempering temperature is 500~540℃, the furnace time is 3.0~5.0 min / mm, the second tempering temperature is 600~640℃, and the furnace time is 1.5~2.0 min / mm. This invention adopts offline quenching and two tempering processes, and the production process is complex and the cycle is long, which increases the production cost.

[0008] The existing 1000MPa grade hydroelectric steel production technology usually uses a process of complete quenching + high temperature tempering to obtain tempered martensite hydroelectric steel, but the yield strength ratio of the steel plate is relatively large (> 0.9), and even the yield strength ratio of the steel plate in many process methods is close to 1, which does not have the ability to resist plastic deformation and cannot resist large stress deformation. In summary, although these patents provide different solutions, there are still some technical and economic challenges that need to be overcome. Summary of the invention

[0009] In view of the problems in the prior art, the present invention provides a hydropower steel plate with a tensile strength of 1000MPa and a preparation method thereof. The stability of austenite is improved by increasing the Ni element, and the increase in the Ni content is beneficial to the impact toughness, and more residual austenite structure is retained during the subsequent relaxation cooling process. The present invention adopts a controlled rolling and relaxation cooling process to generate a part of ferrite during the relaxation process, and then quickly water cools to the bainite phase region to obtain a bainite structure. Bainite has a higher elastic limit, which is beneficial to the resistance to large strain. The ferrite, bainite and residual austenite multiphase structures are comprehensively obtained by coordinated regulation, and a steel plate with low yield ratio, high plasticity and high toughness is obtained.

[0010] The technical solution of the present invention is: The invention discloses a 1000MPa tensile strength high strain resistant hydropower steel plate, the chemical composition and mass percentage of which are 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%, and the balance is Fe and unavoidable impurity elements.

[0011] As a traditional strengthening element in low-carbon steel, C 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 the ferrite in the steel and increase the brittle cementite, which will have a greater impact on plasticity and toughness. A higher C content will also increase the carbon equivalent and affect subsequent welding performance. Therefore, the low-carbon concept is adopted to limit the mass percentage of C element to 0.08%.

[0012] The Si element will be dissolved in the iron matrix to play a role of solid solution strengthening to improve the strength, and can increase the strain hardening rate of the alloy, generate a large number of slender deformation twins to improve the strength and plasticity of the material, so the mass percentage content of the Si element is controlled in the range of 0.20-0.30%.

[0013] The mass percentage content of Mn element is controlled in 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. In addition, Mn can also reduce the free energy of transformation of austenite to ferrite, shift the isothermal transformation curve of austenite to the right, and increase the hardenability of steel. Therefore, the mass percentage content of Mn element is controlled in the range of 0.3 to 0.7%.

[0014] The Cr element can improve the hardenability, increase the strength of the iron matrix through solid solution strengthening, and also increase the self-corrosion potential of the iron matrix, preferentially forming a continuous and dense passivation film on the steel surface. However, excessive Cr elements will increase the possibility of pitting corrosion of steel materials. Therefore, the mass percentage content of Cr elements is controlled in the range of 0.30-0.60%.

[0015] Mo is an element that reduces the austenite phase area, promotes the transformation of bainite structure, and obtains medium-temperature transformation structure in a wide temperature range. However, if the Mo content is too high, it will produce strong solid solution strengthening, cause lattice distortion, and reduce the impact toughness of the weld metal. Therefore, the mass percentage content of Mo is controlled within the range of 0.20-0.40%.

[0016] Ni is an austenite-forming element that can expand the austenite phase, stabilize the austenite structure, reduce the resistance to dislocation movement in steel, relax stress, significantly improve the low-temperature toughness of steel, and improve hardenability and toughness. However, if the Ni content is too high, the production cost will increase. Therefore, the mass percentage range of Ni is controlled within the range of 2.50-3.00%.

[0017] The mass percentage content of Al is controlled within the range of 0.02-0.03%. Al has a strong affinity with O and N, and is a deoxidizing and nitrogen fixing agent during steelmaking. However, too high an Al content will affect the hot working properties, welding properties, and cutting properties of the steel. Therefore, the mass percentage content of Al is controlled within the range of 0.02-0.03%.

[0018] Among the microalloying elements, Nb has the most significant precipitation strengthening effect. Nb can form very stable carbides or nitrides with C, N, and O, pinning the migration of grain boundaries and dislocations during recrystallization, hindering the growth of high-temperature deformed austenite recrystallization grains, and thus refining the grains. Therefore, in this composition design, its content is controlled within the range of 0.03-0.06%.

[0019] The V element can form fine carbides with C and N, refine the grain size, and thus improve the strength and toughness. Therefore, in this composition design, its content is controlled within the range of 0.03 to 0.06%.

[0020] Ti has a strong affinity with N, O and C. It is a good deoxidizing and degassing agent and an effective element for fixing nitrogen and carbon. The formation temperature and affinity of the compounds formed by Ti with N, O and C are higher than those of Nb. Therefore, it can effectively reduce the harmful effect of Nb (C, N) on the plasticity of steel and avoid the occurrence of surface cracks. Therefore, in this composition design, its content is controlled within the range of 0.01-0.02%.

[0021] The S element is considered as an impurity element in steel. It is easy to combine with Fe to form a brittle phase FeS with a low melting point of 989℃, which makes the steel hot brittle during processing and seriously reduces the plasticity and toughness of the steel. In addition, S also has a certain harmful effect on welding performance. Therefore, its content is controlled below 0.004% in this composition design.

[0022] If the P content is too high, it will easily combine with iron in the steel to form a hard and brittle Fe3P phase, resulting in the "cold brittleness" phenomenon, which seriously reduces the low-temperature toughness of the steel. In addition, P is prone to segregation at high temperatures, which is not conducive to welding. Therefore, this composition design strictly controls the P content within 0.015%.

[0023] The above-mentioned method for preparing a hydropower steel plate with a tensile strength of 1000MPa and high strain resistance includes smelting, continuous casting, heating, rough rolling, finishing rolling, relaxation and cooling, wherein: the continuous casting billet is heated to 1150-1250°C, and the heating coefficient is 8-12min / cm, so as to ensure that the carbides of the microalloying elements in the steel can be completely dissolved and play the role of solid solution strengthening; if the heating temperature is too high, the longer the holding time, the coarser the austenite grains, which has a great impact on the fine grain strengthening effect. After two stages of controlled rolling, rough rolling and finishing rolling, during the rough rolling process, the rough rolling final rolling temperature in the complete recrystallization zone is 980-1100°C, and the rolling in the partial recrystallization zone of austenite is avoided and the total reduction rate is ≥50%. The use of a multi-pass large reduction process in the rolling of the austenite fully recrystallized zone can reduce the austenite grain size, make the high-temperature austenite repeatedly undergo dynamic recovery and dynamic recrystallization behavior, and make the austenite grains fully refined by means of the micro-alloying elements Nb, Ti and their carbonitrides that inhibit recrystallization. Furthermore, in the above-mentioned method for preparing a 1000MPa tensile strength hydropower steel plate with high strain resistance, during the finishing rolling process, the finishing rolling temperature of the austenite non-recrystallization zone is 800~840℃, wherein the single-pass reduction rate of the last three passes is ≥10%, and the total reduction rate is ≥60%. When rolling in the austenite non-recrystallization zone before the phase transformation, since recovery and recrystallization behavior cannot occur, a large number of deformation bands are generated with the cumulative deformation of rolling, which increases the nucleation position and driving force of ferrite. Under the action of a lower finishing rolling temperature and a larger deformation rate in the last three passes, the grains can be refined.

[0024] Furthermore, in the above-mentioned method for preparing a hydropower steel plate with a tensile strength of 1000MPa and high strain resistance, the steel plate after final rolling is relaxed and air-cooled online. During the relaxation and air-cooling process, the relaxation temperature is 750-640°C, and the relaxation time is 15-25s. Part of ferrite is generated during the relaxation and cooling process. If the relaxation time is too long and the relaxation temperature is too low, there will be too much ferrite structure, which will have a great impact on the strength. After relaxation, rapid water cooling is used to 480-540°C, and the cooling rate is 15-25°C / s. After relaxation, rapid water cooling is used to the bainite phase region to obtain a bainite structure, which is beneficial to improving the elastic limit and plastic deformation capacity of the material, and is beneficial to the high strain resistance performance.

[0025] Furthermore, the above-mentioned large-strain resistant hydropower steel plate with a tensile strength of 1000 MPa has a maximum thickness of 50 mm.

[0026] Furthermore, the above-mentioned 1000MPa tensile strength large strain resistant hydropower steel plate has a microstructure of ferrite, bainite and retained austenite, the retained austenite content is 5-10%, and the retained austenite + ferrite content is ≤20%.

[0027] Furthermore, the above-mentioned 1000MPa-grade large-strain resistant hydropower steel plate has a yield strength Rt0.5 of 885-930MPa, and three cycles of tension and compression under 3% strain can ensure a yield strength greater than 900MPa, a tensile strength Rm≥1050MPa, a yield strength ratio Rt0.5 / Rm≤0.85, a uniform elongation UEL≥10%, and an average Charpy impact energy KV2≥150J at -60°C.

[0028] Advantages and beneficial effects of the present invention:

[0029] The "controlled rolling + relaxation cooling" process is adopted, and the structure is adjusted to a multi-phase structure of bainite and a small amount of ferrite and residual austenite through composition and process. The proportion of the organizational phases is strictly controlled. On the basis of maintaining high strength and high toughness, the steel plate's resistance to plastic deformation is synergistically improved, the steel plate's yield strength ratio is reduced, thereby improving the steel plate's ability to resist large strains.

[0030] Compared with the traditional modulation process, the present invention uses relaxation cooling after rolling, which does not require complicated heat treatment procedures. This innovative process not only simplifies the production process, but also significantly reduces manufacturing costs and improves production efficiency. By omitting the traditional heat treatment steps, enterprises can reduce energy consumption and time costs, while reducing the impact on the environment, achieving the dual goals of economic benefits and environmental friendliness, and also ensuring the service safety of hydropower steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The microstructure morphology of the finished steel plate of Example 1 of the present invention; Figure 2 The microstructure morphology of the finished steel plate of Example 2 of the present invention; Figure 3 The microstructure morphology of the finished steel plate of Example 3 of the present invention; Figure 4 The microstructure morphology of the finished steel plate of Example 4 of the present invention; Figure 5 The microstructure morphology of the finished steel plate of Example 5 of the present invention; DETAILED DESCRIPTION

[0032] In order to make the technical solutions and advantages of the present invention easier to understand, the specific implementation modes of the present invention are further described below in conjunction with examples. The following examples are used to illustrate the present invention, but cannot be used to limit the scope of the present invention in any way. Example 1

[0033] The present embodiment provides a high-strain hydropower steel plate with a tensile strength of 1000 MPa, whose chemical composition and mass percentage are 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%, and the remainder is Fe and unavoidable impurity elements.

[0034] The above-mentioned method for preparing a hydropower steel plate with a tensile strength of 1000 MPa and a large deformation resistance comprises a preparation process including smelting, continuous casting, heating, rough rolling, finish rolling, relaxation and cooling, wherein: The continuous casting slab was heated to 1200℃, with a heating coefficient of 10min / cm; the final rolling temperature of the rough rolling was 1045℃, with a total reduction rate of 66.67%; the final rolling temperature of the finishing rolling was 825℃, and the single-pass reduction rates of the last three passes were 13.81%, 12.93%, and 11.45%, respectively, with a total reduction rate of 66.31%; The temperature of the relaxation process was cooled to 650°C, and the relaxation time was 23s; after relaxation, rapid water cooling was used to 500°C, and the water cooling rate was 22°C / s, and then air cooling was used to room temperature.

[0035] like Figure 1 As shown, the microstructure of the finished steel plate of this embodiment is ferrite, bainite and retained austenite, the content of retained austenite is 7.63%, the content of ferrite is 10.64%, and the thickness of the finished steel plate is 50 mm.

[0036] The mechanical properties of the finished steel plate of 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 strength ratio Rt0.5 / Rm is 0.836, uniform elongation UEL is 11.1%, and average Charpy impact energy KV2 at -60°C is 152 J. Example 2

[0037] The present embodiment provides a high-strain hydropower steel plate with a tensile strength of 1000 MPa, whose chemical composition and mass percentage are 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%, and the remainder is Fe and unavoidable impurity elements.

[0038] The above-mentioned method for preparing a hydropower steel plate with a tensile strength of 1000 MPa and a large deformation resistance comprises a preparation process including smelting, continuous casting, heating, rough rolling, finish rolling, relaxation and cooling, wherein: The continuous casting slab was heated to 1200℃, with a heating coefficient of 10min / cm; the final rolling temperature of the rough rolling was 1034℃, with a total reduction rate of 65.81%; the final rolling temperature of the finishing rolling was 832℃, and the single-pass reduction rates of the last three passes were 13.42%, 11.06%, and 10.38%, respectively, with a total reduction rate of 66.31%; The temperature of the relaxation process was cooled to 670°C, and the relaxation time was 19s; after relaxation, rapid water cooling was used to 520°C, and the cooling rate was 18°C / s, and then air cooling was used to room temperature.

[0039] like Figure 2 As shown, the microstructure of the finished steel plate of this embodiment is ferrite, bainite and retained austenite, the content of retained austenite is 7.29%, the content of ferrite is 9.82%, and the thickness of the finished steel plate is 40 mm.

[0040] The mechanical properties of the finished steel plate of 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 strength ratio Rt0.5 / Rm is 0.839, uniform elongation UEL is 10.6%, and average Charpy impact energy KV2 at -60°C is 146 J. Example 3

[0041] The present embodiment provides a high-strain hydropower steel plate with a tensile strength of 1000 MPa, whose chemical composition and mass percentage are 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%, and the remainder is Fe and unavoidable impurity elements.

[0042] The above-mentioned method for preparing a hydropower steel plate with a tensile strength of 1000 MPa and a large deformation resistance comprises a preparation process including smelting, continuous casting, heating, rough rolling, finish rolling, relaxation and cooling, wherein: The continuous casting slab was heated to 1200℃, with a heating coefficient of 10min / cm; the final rolling temperature of the rough rolling was 1046℃, with a total reduction rate of 70.00%; the final rolling temperature of the finishing rolling was 815℃, and the single-pass reduction rates of the last three passes were 16.21%, 14.93%, and 11.54%, respectively, with a total reduction rate of 66.67%; The temperature of the relaxation process was cooled to 680°C, and the relaxation time was 21s; after relaxation, rapid water cooling was used to 480°C, and the cooling rate was 24°C / s, and then air cooling was used to room temperature.

[0043] like Figure 3 As shown, the microstructure of the finished steel plate of this embodiment is ferrite, bainite and retained austenite, the content of retained austenite is 8.29%, the content of ferrite is 10.22%, and the thickness of the finished steel plate is 30 mm.

[0044] The mechanical properties of the finished steel plate of 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 strength ratio Rt0.5 / Rm is 0.846, uniform elongation UEL is 11.4%, and average Charpy impact energy KV2 at -60°C is 156 J. Example 4

[0045] The present embodiment provides a high-strain hydropower steel plate with a tensile strength of 1000 MPa, whose chemical composition and mass percentage are 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%, and the remainder is Fe and unavoidable impurity elements.

[0046] The above-mentioned method for preparing a hydropower steel plate with a tensile strength of 1000 MPa and a large deformation resistance comprises a preparation process including smelting, continuous casting, heating, rough rolling, finish rolling, water cooling, quenching and tempering heat treatment, wherein: The continuous casting slab was heated to 1200℃, with a heating coefficient of 10min / cm; the final rolling temperature of the rough rolling was 1034℃, with a total reduction rate of 66.67%; the final rolling temperature of the finishing rolling was 806℃, and the single-pass reduction rates of the last three passes were 15.32%, 14.13%, and 10.59%, respectively, with a total reduction rate of 64.81%; The temperature of the relaxation process was cooled to 660°C, and the relaxation time was 22s; after relaxation, rapid water cooling was used to 490°C, and the cooling rate was 17°C / s, and then air cooling was used to room temperature.

[0047] like Figure 4 As shown, the microstructure of the finished steel plate of this embodiment is ferrite, bainite and retained austenite, the content of retained austenite is 6.78%, the content of ferrite is 11.03%, and the thickness of the finished steel plate is 20 mm.

[0048] The mechanical properties of the finished steel plate of 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 strength ratio Rt0.5 / Rm is 0.843, uniform elongation UEL is 10.3%, and average Charpy impact energy KV2 at -60°C is 141 J. Example 5

[0049] The present embodiment provides a high-strain hydropower steel plate with a tensile strength of 1000 MPa, whose chemical composition and mass percentage are 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%, and the remainder is Fe and unavoidable impurity elements.

[0050] The above-mentioned method for preparing a hydropower steel plate with a tensile strength of 1000 MPa and a large deformation resistance comprises a preparation process including smelting, continuous casting, heating, rough rolling, finish rolling, water cooling, quenching and tempering heat treatment, wherein: The continuous casting slab was heated to 1200℃, with a heating coefficient of 10min / cm; the final rolling temperature of the rough rolling was 1044℃, with a total reduction rate of 68.91%; the final rolling temperature of the finishing rolling was 835℃, and the single-pass reduction rates of the last three passes were 17.25%, 13.33%, and 11.84%, respectively, with a total reduction rate of 66.67%; The above-mentioned method for preparing a hydropower steel plate with a tensile strength of 1000 MPa and a large deformation resistance comprises a preparation process including smelting, continuous casting, heating, rough rolling, finish rolling, relaxation and cooling, wherein: The temperature of the relaxation process was cooled to 690°C, and the relaxation time was 17s; after relaxation, rapid water cooling was used to 510°C, and the cooling rate was 21°C / s, and then air cooling was used to room temperature.

[0051] like Figure 5 As shown, the microstructure of the finished steel plate of this embodiment is ferrite, bainite and retained austenite, the content of retained austenite is 5.94%, the content of ferrite is 10.78%, and the thickness of the finished steel plate is 50 mm.

[0052] The mechanical properties of the finished steel plate of 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 strength ratio Rt0.5 / Rm is 0.846, uniform elongation UEL is 10.7%, and average Charpy impact energy KV2 at -60°C is 132 J.

[0053] The above are only some embodiments, which are only for better explanation of the present invention, not for limitation. A person skilled in the art may modify some technical features of the above embodiments, but any modification made within the principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A hydropower steel plate with a tensile strength of 1000MPa and high strain resistance, characterized in that: Its chemical composition and mass percentage are 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%, and the balance is Fe and unavoidable impurity elements.

2. A method for preparing a hydropower steel plate with a tensile strength of 1000 MPa and high strain resistance as claimed in claim 1, characterized in that: The preparation process includes smelting, continuous casting, heating, rough rolling, finishing rolling, relaxation and cooling processes, wherein: the continuous casting billet is heated to 1150-1250°C, the heating coefficient is 8-12min / cm, and the rolling is controlled in two stages of rough rolling and finishing rolling. During the rough rolling process, the rough rolling final rolling temperature of the complete recrystallization zone is 980-1100°C, and the rolling is avoided in the partial recrystallization zone of austenite, and the total reduction rate is ≥50%; during the finishing rolling process, the finishing rolling final rolling temperature of the austenite non-recrystallization zone is 800-840°C, and the single pass reduction rate of the last three passes is ≥10%, and the total reduction rate is ≥60%.

3. The method for preparing a hydropower steel plate with a tensile strength of 1000 MPa and high strain resistance according to claim 2, characterized in that: The steel plate after final rolling is relaxed and air-cooled online, with a relaxation temperature of 750-640°C and a relaxation time of 15-25s. After relaxation, it is rapidly water-cooled to 480-540°C with a cooling rate of 15-25°C / s.

4. The hydropower steel plate with a tensile strength of 1000 MPa and high strain resistance according to claim 1, characterized in that: The steel plate microstructure is ferrite, bainite and retained austenite, the retained austenite content is 5-10%, and the retained austenite+ferrite content is ≤20%.

5. The hydropower steel plate with a tensile strength of 1000 MPa and high strain resistance according to claim 1, characterized in that: The maximum thickness of the steel plate is 50 mm.

6. The hydropower steel plate with a tensile strength of 1000 MPa and high strain resistance according to claim 1, characterized in that: The steel plate has a yield strength Rt0.5 of 885-930 MPa, and can ensure a yield strength of >900 MPa after three tension-compression cycles under 3% strain, a tensile strength Rm ≥1050 MPa, a yield strength ratio Rt0.5 / Rm ≤0.85, a uniform elongation UEL ≥10%, and an average Charpy impact energy KV2 ≥120 J at -60°C.

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