Low-carbon-equivalent 1000MPa-grade ultrahigh-toughness hydroelectric steel plate and preparation method thereof

Abstract

The thickness of the produced steel plate is 40-108 mm, the lowest carbon equivalent of the produced steel plate is 0.42, a trace element B can enable an austenite isothermal transformation curve to move rightwards, a transformation starting curve is delayed within the pearlite forming temperature range, then upper bainite is formed easily, and the strength of the steel plate is improved. The Ti element is supplemented to increase the content of effective B in the steel, so that the hardenability of the hydroelectric steel plate is greatly improved; according to material characteristics, proper preparation modes of hot rolling, sectional quenching, thermal refining and the like are selected, the grain size of the steel plate before quenching can be greatly reduced, and grain refinement of the finished steel plate is further facilitated; according to the method, the problem that the strength of the steel plate produced through off-line quenching is low is solved, and the technical problem that the plate shape is poor due to a conventional on-line rolling and tempering preparation mode is solved at the same time.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgy, and in particular relates to a low-carbon equivalent 1000MPa grade ultra-high strength and toughness hydropower steel plate and a preparation method thereof. Background Art

[0002] As a clean energy, hydropower has become the first choice for people to obtain energy due to its advantages of high efficiency, cleanliness and sustainability. Hydropower generators are developing in the direction of high head, high speed and large capacity. In order to meet the layout of power stations, reduce the weight and wall thickness of pressure steel pipes, and reduce the overall cost of the project, high-strength steel plates are constantly being updated. 2 ) and Kamiryu River (HD value is 4238m 2 ) Pumped-storage power stations all use 1000MPa ultra-high strength and high toughness steel plates, with maximum thicknesses of 66mm and 62mm respectively. The Fengning, Wendeng, Wuhuangping Secondary, Jixi, Tiantai, Yajiang and other pumped-storage power stations under design in China all need to use 1000MPa ultra-high strength and high toughness steel plates according to their HD values. They are mainly used in important components such as turbines, volutes, and steel bifurcated pipes of large hydropower units. However, the 1000MPa ultra-high strength and high toughness steel for domestic hydropower is still in the research and development stage, with no engineering application cases, and is almost completely dependent on imports, which is a "stuck neck" material.

[0003] The yield strength of 1000MPa ultra-high strength and high toughness steel is ≥870MPa, and the tensile strength is ≥920MPa. The -60℃ impact energy requirement for this ultra-high strength and high toughness steel is ≥70MPa. This strength-toughness match is rare in steel materials. Generally speaking, there is a certain contradiction between strength and low-temperature impact toughness, that is, high strength will inevitably lead to a loss of plasticity. Ordinary steel materials sacrifice strength in exchange for improved plasticity, and ultimately obtain the optimal match between strength and plasticity. However, there is a great contradiction between the ultra-high strength and extremely high low-temperature impact toughness indicators of 1000MPa ultra-high strength and high toughness hydropower steel. In addition, in order to ensure the welding quality of 1000MPa ultra-high strength and high toughness steel plates, users have also double-strictened the carbon equivalent and welding crack sensitivity of the steel plates. The lower carbon equivalent and crack sensitivity index limit the addition of C elements and alloy elements such as Ni and Mo. The above restrictions have brought great difficulties and challenges to the development of 1000MPa ultra-high strength and high toughness hydropower steel.

[0004] In the prior art, systematic research has been conducted on the preparation process of 1000MPa ultra-high strength and high toughness hydroelectric steel, but its composition design and preparation process are not yet sufficient, and there are many defects. For example, in Patent CN117248157A, "A Steel Plate for Hydropower Station with a Strength Level of 1000MPa and Its Preparation Method", it adopts a composition design idea of low Ceq and low Pcm, and through the solid solution strengthening and fine grain strengthening means exerted by the added alloying elements, and at the same time uses a large reduction ratio rolling process for 400mm extra-thick continuous casting slabs and a quenching + tempering heat treatment process to produce a steel plate for hydropower station with good performance indicators at 1000Mpa, but its carbon equivalent is 0.62, exceeding the technical index requirements. In Patent CN117385280A, "A 1000MPa Ultra-High Strength Steel and Its Preparation Method", the chemical composition adopts a high carbon, high manganese, and high chromium design, and its mechanical properties meet the technical requirements, but neither the carbon equivalent nor the steel plate thickness is introduced, and based on the published chemical composition, its carbon equivalent far exceeds the technical index requirements. Summary of the Invention

[0005] In order to overcome the defects existing in the above prior art, the purpose of the present invention is to provide a 1000MPa ultra-high strength and toughness hydroelectric steel plate with a steel plate thickness of 40 - 108mm and a minimum carbon equivalent of 0.42, and its preparation method, which can fundamentally solve the problem of insufficient strength of low carbon equivalent high strength and toughness hydroelectric steel plates.

[0006] In order to achieve the above invention purpose, the present invention provides a low carbon equivalent 1000MPa ultra-high strength and toughness hydroelectric steel plate. The components and mass percentages of the hydroelectric steel plate are as follows: C: 0.08% - 0.12%; Si: 0.05% - 0.30%; Mn: 0.60% - 1.05%; P ≤ 0.006%; S ≤ 0.002%; Cr: 0.40% - 0.60%; Mo: 0.45% - 0.70%; Ni: 1.65% - 3.00%; B: 0.0007% - 0.0013%; Ti: 0.005% - 0.017%; Nb: 0.01% - 0.03%; Al: 0.020% - 0.055%; Cu ≤ 0.30%; the balance is iron and unavoidable impurities.

[0007] The thickness of the low carbon equivalent 1000MPa ultra-high strength and toughness hydroelectric steel plate is 40 - 108mm, the minimum carbon equivalent Ceq is 0.42, and the hardenability index DI ≥ 0.65 × plate thickness;

[0008] Among them, the carbon equivalent Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14; in the formula, each element symbol represents the mass percentage of the corresponding element.

[0009] The functions of key elements are as follows:

[0010] Element C: The most effective strengthening element in steel. When dissolved in the matrix, it plays a solution strengthening role and can improve the hardenability of the steel plate. During the heat treatment process, it can form carbides with strong carbide-forming elements to play a precipitation strengthening role. However, for 1000 MPa grade hydroelectric steel, the carbon content is required to be significantly reduced. Therefore, the C content in this invention is controlled to be 0.08% - 0.12%.

[0011] Element Mn: An austenite stabilizing element, which can significantly improve the hardenability of the steel plate, slow down the decomposition and transformation rate of the structure during the heat treatment process, and increase the tempering resistance. To a certain extent, it can hinder the formation of MC-type carbides inside the structure and reduce the consumption of elements such as Ti and Nb. However, if its content is too high, it will be unfavorable for the weldability and toughness of the steel plate. Therefore, in this invention, the Mn content is 0.60% - 1.05%.

[0012] Element Cr: It can improve the hardenability of the steel plate. Although the effect is not as good as that of Mn and Mo elements, the cost-effectiveness is better. It can significantly improve the corrosion resistance and oxidation resistance of the steel plate. In this invention, the Cr content is controlled to be 0.40% - 0.60%.

[0013] Element Mo: A strong hardenability element, which helps to improve the hardenability in the thickness direction of the steel plate and the later tempering stability. It can enable the steel plate to be tempered at a higher temperature, thereby improving the plasticity and toughness of the steel plate. It can increase the solubility of microalloying elements in austenite, reduce the precipitation of carbonitrides of microalloying elements, and make the microalloying elements precipitate from ferrite at a lower temperature, enhancing the precipitation strengthening effect. Therefore, in this invention, the Mo content is controlled to be 0.45% - 0.70%.

[0014] Element Ni: A good solution strengthening and hardenability enhancing element in steel. It can expand the austenite phase region, lower the austenite transformation temperature, prevent the transformation of austenite to pearlite, and thus reduce the critical transformation temperature of the steel. Ni and Fe elements exist in a mutually soluble form, which can effectively improve the toughness of the steel plate, especially suitable for improving the plasticity and toughness of the core of extra-thick plates. However, its cost is relatively high. Therefore, in this invention, the Ni content is 1.65% - 3.00%.

[0015] Element B: A strong hardenability improving element. It is easy to adsorb on the grain boundaries to reduce the grain boundary energy, making it difficult for proeutectoid ferrite to nucleate, extending the incubation period of the proeutectoid ferrite and upper bainite transformation, suppressing and delaying the ferrite transformation, thereby improving the hardenability, especially suitable for improving the hardenability of extra-thick plates. However, its solubility in steel is relatively low, and affected by its existing form, it is easy to form B embrittlement, which is not conducive to the plasticity of the steel. Therefore, in this invention, its content is 0.0007% - 0.0013%.

[0016] In the above technical solution, the minimum carbon equivalent of the 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate is 0.42. On this basis, the functions of trace B (7-13 ppm) and other microalloying elements are fully exerted. The B element can shift the austenite isothermal transformation curve to the right and delay the transformation start curve within the pearlite formation temperature range, which is conducive to the formation of upper bainite. In addition, the addition of Ti (0.005%-0.017%) can increase the effective B content in the steel. Through this composition ratio, the key element B can exist in the form of effective B, thereby greatly improving the hardenability of the 1000 MPa grade hydroelectric steel. At the same time, the steel plate is strengthened by the combined strengthening effect of Cr and Mo elements.

[0017] In the above technical solution, further, the yield strength of the 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate is ≥870 MPa, the tensile strength is ≥920 MPa, and the impact energy requirement at -60 °C is ≥70 MPa.

[0018] A preparation method of the above low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate adopts the process of deep desulfurization of hot metal + converter smelting + secondary refining + vacuum treatment + continuous casting. The continuous casting billet is prepared strictly according to the target chemical composition. Online rolling + sectional quenching + tempering treatment are selected to prepare low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plates with different thicknesses. The preparation method includes processes such as smelting, casting, online rolling, sectional quenching, and tempering heat treatment. The specific steps are as follows:

[0019] ① Smelting

[0020] During the smelting process, high-purity hot metal is used and the double slag method is adopted for operation. Deep desulfurization treatment and slag skimming are required to be clean. LF and RH are used for secondary refining of the molten steel to ensure that the LF furnace makes white slag, ensure that [S] in the steel is ≤0.001%, strictly control the gas content such as H, O, and N in the steel, require that the net circulation of RH is not less than 10 min, the standing time before casting is not less than 15 min, keep the slag surface in the ladle in a surging state without exposing the molten steel surface, and at the same time modify the inclusions in the steel through the treatment of the composite deoxidizer to maximize the purity of the steel quality.

[0021] ② Casting

[0022] During the whole process of continuous casting, protective casting is adopted to avoid secondary oxidation of the molten steel. Control the superheat of the molten steel below 30 °C to minimize the generation of defects such as central porosity and central segregation. To ensure the internal quality of the continuous casting billet, control the casting speed of the continuous casting billet at 0.8-1.2 m / min, and adopt the soft reduction (1-3 mm) technology at the end of continuous casting to fully improve the internal quality of the billet.

[0023] ③ Rolling and sectional quenching

[0024] Send a continuous casting billet with an appropriate thickness into a heating furnace, with a heating temperature of 1100°C to 1200°C and a net holding time of 8.5 to 10 hours. Adopt a two-stage rolling method of rough rolling and finish rolling, and set different rolling passes according to the finished plate thickness. The rough rolling starting temperature is 1050°C to 1150°C, and the finishing temperature is 1000°C to 1050°C; the finish rolling starting temperature is 960°C to 980°C, and the finishing temperature is above 900°C, with a total reduction ratio of 64% to 82%, ensuring that the reduction ratio in at least three passes is ≥20%. Immediately after finish rolling, use laminar cooling to perform section quenching on the steel plate, with a cooling temperature range of 60°C to 150°C. This operation can effectively reduce the initial grain size of the steel plate, provide more nucleation sites during the later tempering treatment process, and is beneficial to further refining the steel plate grains.

[0025] ④ Heat treatment

[0026] To ensure excellent comprehensive mechanical properties of the finished steel plate along the thickness direction, the corresponding heat treatment process of the steel plate is as follows, giving full play to the roles of key elements such as B, Ni, Ti, etc. in the steel, so that excellent strength and toughness matching can also be obtained at the 1 / 4 position of the new 1000MPa grade hydroelectric steel plate. The specific process is as follows:

[0027] Quenching process: temperature 890°C to 930°C, net holding time 0.5 to 3.5 min / mm;

[0028] Tempering process: temperature 540°C to 600°C, net holding time 1.0 to 4.0 min / mm.

[0029] According to the material characteristics of the above-mentioned low carbon equivalent 1000MPa grade ultra-high strength and toughness hydroelectric steel plate, select an appropriate preparation method of hot rolling + section quenching + tempering treatment. Section quenching can significantly reduce the grain size of the steel plate before quenching, and thus is beneficial to the grain refinement of the finished steel plate, solving the problem of insufficient strength.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] ① The lowest carbon equivalent of the low carbon equivalent 1000MPa grade ultra-high strength and toughness hydroelectric steel plate in the present invention is 0.42. On this basis, give full play to the roles of trace B (7 to 13 ppm) and other microalloying elements. The B element can shift the austenite isothermal transformation curve to the right and delay the transformation start curve within the pearlite formation temperature range, which is beneficial to the formation of upper bainite; in addition, with the synergistic effect of Ti (0.005% to 0.017%) element, the effective B content in the steel can be increased. Through this composition ratio, the key element B can exist in the form of effective B, thereby greatly improving the hardenability of the 1000MPa grade hydroelectric steel, and at the same time using the composite strengthening effect of Cr and Mo elements to strengthen the steel plate.

[0032] ② Based on the material properties of the 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent, an appropriate preparation method of hot rolling + step quenching + tempering treatment is selected. Step quenching can significantly reduce the grain size of the steel plate before quenching, which is beneficial to the grain refinement of the finished steel plate and solves the problem of insufficient strength, having great technical advantages.

[0033] ③ Compared with the preparation method of the conventional 1000 MPa grade hydroelectric steel, the preparation method of the 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent in the present invention can fundamentally solve the problem of insufficient strength of the low carbon equivalent high strength and toughness hydroelectric steel plate, and can bring significant economic value to the enterprise. Description of the Drawings

[0034] Figure 1 Metallographic microstructure diagram at the 1 / 4 position of the 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent prepared in Example 1;

[0035] Figure 2 Metallographic microstructure diagram at the 1 / 4 position of the 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent prepared in Example 2;

[0036] Figure 3 Metallographic microstructure diagram at the 1 / 4 position of the 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent prepared in Example 3;

[0037] Figure 4 Metallographic microstructure diagram at the 1 / 4 position of the 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent prepared in Example 4;

[0038] Figure 5 Metallographic microstructure diagram at the 1 / 4 position of the 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent prepared in Example 5;

[0039] Figure 6 Metallographic microstructure diagram at the 1 / 4 position of the 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent prepared in Example 6. Detailed Embodiments

[0040] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited in any way. To avoid repetition, in the following embodiments, the raw materials are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0041] A 1000MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent. The components and mass percentages of the hydroelectric steel plate are as follows: C: 0.08% - 0.12%; Si: 0.05% - 0.30%; Mn: 0.60% - 1.05%; P ≤ 0.006%; S ≤ 0.002%; Cr: 0.40% - 0.60%; Mo: 0.45% - 0.70%; Ni: 1.65% - 3.00%; B: 0.0007% - 0.0013%; Ti: 0.005% - 0.017%; Nb: 0.01% - 0.03%; Al: 0.020% - 0.055%; Cu ≤ 0.30%; the balance is iron and inevitable impurities.

[0042] The thickness of the 1000MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent is 40 - 108mm, the lowest carbon equivalent Ceq is 0.42, and the hardenability index DI ≥ 0.65 × plate thickness;

[0043] Among them, the carbon equivalent Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14; in the formula, each element symbol represents the mass percentage of the corresponding element.

[0044] A preparation method of the above-mentioned 1000MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent. The preparation method includes processes such as smelting, casting, online rolling, sectional quenching, and tempering heat treatment. The specific steps are as follows:

[0045] ① Smelting: Use high-purity hot metal, operate by the double slag method, and perform deep desulfurization treatment; use LF and RH for secondary refining of the molten steel. The LF furnace makes white slag to ensure that [S] in the steel ≤ 0.001%, the net circulation time of RH is not less than 10min, and the standing time before casting is not less than 15min;

[0046] ② Casting: Adopt protective casting throughout the continuous casting process, and control the superheat of the molten steel below 30°C;

[0047] ③ Rolling and sectional quenching: Send the continuous casting billet to the heating furnace, the heating temperature is 1100°C - 1200°C, the net holding time is 8.5 - 10h, adopt the two-stage rolling method of rough rolling and finish rolling, and set different rolling passes according to the finished plate thickness; after finish rolling, use laminar flow cooling to perform sectional quenching on the steel plate, and the cooling temperature is 60°C - 150°C;

[0048] ④ Heat treatment: The temperature of the quenching process is 890°C - 930°C, and the net holding time is 0.5 - 3.5min / mm; the temperature of the tempering process is 540°C - 600°C, and the net holding time is 1.0 - 4.0min / mm.

[0049] For the parts not described in the following examples, they are the same as the description content of the above specific implementation manners.

[0050] Example 1

[0051] A 1000MPa - grade ultra - high strength and toughness hydroelectric steel plate with low carbon equivalent. The chemical composition of the hydroelectric steel plate in Example 1 is shown in Table 1; the balance is iron and inevitable impurities.

[0052] Table 1 Chemical composition of hydroelectric steel plates in Examples 1 - 6 (wt%)

[0053] C Si Mn P S Ni Cr Mo Al Nb Ti B Ceq Example 1 0.08 0.05 0.60 0.005 0.0006 1.65 0.40 0.45 0.045 0.01 0.005 0.0007 0.42 Example 2 0.08 0.07 1.00 0.005 0.0006 1.75 0.52 0.53 0.050 0.025 0.007 0.0008 0.53 Example 3 0.10 0.07 1.00 0.005 0.0006 1.75 0.52 0.52 0.055 0.025 0.007 0.0009 0.56 Example 4 0.10 0.07 1.00 0.005 0.0006 1.95 0.52 0.55 0.055 0.025 0.010 0.0009 0.56 Example 5 0.11 0.17 1.05 0.005 0.0006 1.95 0.60 0.70 0.055 0.03 0.015 0.0010 0.64 Example 6 0.12 0.30 1.05 0.005 0.0006 3.00 0.54 0.55 0.055 0.03 0.017 0.0013 0.63

[0054] A preparation method of the above - mentioned 1000MPa - grade ultra - high strength and toughness hydroelectric steel plate with low carbon equivalent. The preparation method includes processes such as smelting, casting, online rolling, sectional quenching, and quenching and tempering heat treatment. The specific steps are as follows:

[0055] ① Smelting: Adopt the process of deep desulfurization of hot metal + converter smelting + secondary refining + vacuum treatment + continuous casting. Prepare continuous casting billets strictly according to the composition in Table 1. In the smelting process, high - purity hot metal is required, and deep desulfurization treatment is carried out by the double - slag method. Use LF and RH for secondary refining of molten steel. The LF furnace makes white slag to ensure that [S] in the steel ≤ 0.001%, the net circulation time of RH is 15min, and the standing time before casting is 20min. Keep the slag surface in the ladle in a surging state and do not expose the molten steel surface. Modify the inclusions in the steel through the treatment of composite deoxidizer to maximize the purity of the steel quality, so that in the smelting and melting composition of the hydroelectric steel plate, H ≤ 3ppm, TO ≤ 50ppm, N ≤ 70ppm.

[0056] ② Casting: Adopt protective casting throughout the continuous casting process to avoid secondary oxidation of molten steel. Control the superheat of molten steel at 20℃ and control the casting speed of the continuous casting billet at 1.1m / min.

[0057] ③ Rolling and sectional quenching: Send the continuous casting billet to the heating furnace, the heating temperature is 1170℃ - 1190℃, the net holding time is 8.5h. Adopt the two - stage rolling method of rough rolling and finish rolling, and set different rolling passes according to the finished plate thickness. The starting rolling temperature in the rough rolling stage is 1100℃, and the finishing rolling temperature is 1030℃; the starting rolling temperature of finish rolling is 960℃, and the finishing rolling temperature is 940℃; the total reduction ratio is 82%, among which, the reduction ratio of at least three passes ≥ 20%, and the thickness of the finished steel plate is 40mm;

[0058] After finish rolling, use laminar cooling to carry out sectional quenching on the steel plate, and the cooling temperature is 80℃.

[0059] ④ Heat treatment: Quench the obtained steel plate, the quenching temperature is 930℃, and the net holding time is 2.5min / mm; the tempering temperature is 540℃, and the net holding time is 1.0min / mm.

[0060] The low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate prepared in Example 1 has a metallographic microstructure at 1 / 4 of the thickness direction as follows Figure 1 shown. The microstructure at 1 / 4 of the steel plate is tempered martensite + granular bainite + lath bainite structure, and the content of lath bainite is much higher than that of granular bainite. The tensile properties and impact properties at 1 / 4 of the steel plate in Example 1 are shown in Table 2 and Table 3 respectively.

[0061] Table 2 Tensile properties at various positions of the 40 mm thick hydroelectric steel plate prepared in Example 1

[0062]

[0063] Table 3 Impact properties at various positions of the 40 mm thick hydroelectric steel plate prepared in Example 1

[0064]

[0065] Example 2

[0066] A low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate. The chemical composition of the hydroelectric steel plate in Example 2 is shown in Table 1; the balance is iron and inevitable impurities.

[0067] A preparation method of the above low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate. The preparation method includes processes such as smelting, casting, online rolling, sectional quenching, and tempering heat treatment. The specific steps are as follows:

[0068] ① Smelting: Adopt the process of deep desulfurization of hot metal + converter smelting + secondary refining + vacuum treatment + continuous casting. Strictly prepare the continuous casting billet according to the composition requirements in Table 1. High-purity hot metal is required during the smelting process, and deep desulfurization treatment is carried out by the double slag method operation; LF and RH are used for secondary refining of the molten steel. The LF furnace makes white slag to ensure that [S] in the steel ≤ 0.001%, the net circulation time of the RH is 10 - 30 min, and the static time before casting is 15 - 30 min; keep the slag surface in the ladle in a surging state and do not expose the molten steel surface. Modify the inclusions in the steel through the treatment of the composite deoxidizer to maximize the steel quality purity, so that H ≤ 3 ppm, TO ≤ 50 ppm, and N ≤ 70 ppm in the smelting and melting composition of the hydroelectric steel plate.

[0069] ② Casting: The whole process of continuous casting adopts protective casting to avoid secondary oxidation of the molten steel. Control the superheat of the molten steel at 30 °C and control the casting speed of the continuous casting billet at 1.0 m / min.

[0070] ③ Rolling and step quenching: The continuous casting billet is sent into a heating furnace, heated at a temperature of 1170°C - 1190°C, with a net holding time of 9 h. A two-stage rolling method of rough rolling and finish rolling is adopted, and different rolling passes are set according to the finished plate thickness. The starting rolling temperature in the rough rolling stage is 1100°C, and the finishing rolling temperature is 1010°C. The starting rolling temperature in the finish rolling is 980°C, and the finishing rolling temperature is 920°C. The total reduction ratio is 81%. Among them, the reduction ratio of at least three passes is ≥20%, and the finished thickness of the steel plate is 56 mm.

[0071] After finish rolling, step quenching of the steel plate is carried out by laminar cooling, and the cooling temperature is 60°C.

[0072] ④ Heat treatment: The obtained steel plate is quenched, and the temperature of the quenching process is 930°C, with a net holding time of 0.20 min / mm; the temperature of the tempering process is 590°C, with a net holding time of 3.5 min / mm.

[0073] The low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate prepared in Example 2, the metallographic microstructure at 1 / 4 of the thickness direction is as Figure 2 shown. The microstructure at 1 / 4 of the steel plate is tempered sorbite + lath bainite. The tensile properties and impact properties at 1 / 4 of the thickness direction of the hydroelectric steel plate prepared in Example 2 are shown in Table 4 and Table 5 respectively.

[0074] Table 4 Tensile properties of each position of the 56 mm thick hydroelectric steel plate prepared in Example 2

[0075]

[0076] Table 5 Impact properties of each position of the 56 mm thick hydroelectric steel plate prepared in Example 2

[0077]

[0078] Example 3

[0079] A low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate, the chemical composition of the hydroelectric steel plate in Example 3 is shown in Table 1; the balance is iron and unavoidable impurities.

[0080] A preparation method of the above low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate, the preparation method includes processes such as smelting, casting, online rolling and step quenching, quenching and tempering heat treatment, etc., and the specific steps are as follows:

[0081] ① Smelting: The process of iron bath deep desulfurization + converter smelting + secondary refining + vacuum treatment + continuous casting is adopted. The continuous casting billets are prepared strictly according to the composition in Table 1. High-purity hot metal is required during the smelting process, and deep desulfurization treatment is carried out by the double slag method; LF and RH are used for secondary refining of the molten steel. The LF furnace makes white slag to ensure that [S] in the steel ≤ 0.001%. The net circulation time of the RH is 15 min, and the standing time before casting is 20 min; Keep the slag surface in the ladle in a surging state and the molten steel surface is not exposed. The inclusions in the steel are modified by treatment with a composite deoxidizer to maximize the purity of the steel quality, so that in the smelting and melting composition of the hydroelectric steel plate, H ≤ 3 ppm, TO ≤ 50 ppm, N ≤ 70 ppm.

[0082] ② Casting: Protective casting is adopted throughout the continuous casting process to avoid secondary oxidation of the molten steel. The superheat of the molten steel is controlled at 20 °C, and the casting speed of the continuous casting billet is controlled at 1.2 m / min.

[0083] ③ Rolling and sectional quenching: The continuous casting billets are sent into the heating furnace, the heating temperature is 1170 °C - 1190 °C, and the net heat preservation time is 9 h. The two-stage rolling method of rough rolling and finish rolling is adopted, and different rolling passes are set according to the finished plate thickness; The starting rolling temperature in the rough rolling stage is 1100 °C, and the finishing rolling temperature is 1040 °C; The starting rolling temperature of the finish rolling is 960 °C, and the finishing rolling temperature is 940 °C; The total reduction ratio is 77%. Among them, the reduction ratio of at least three passes ≥ 20%, and the finished thickness of the steel plate is 70 mm;

[0084] After finish rolling, sectional quenching of the steel plate is carried out by laminar cooling, and the cooling temperature is 80 °C.

[0085] ④ Heat treatment: The obtained steel plate is quenched, the quenching temperature is 930 °C, and the net heat preservation time is 2.5 min / mm; The tempering temperature is 570 °C, and the net heat preservation time is 3.5 min / mm.

[0086] The metallographic microstructure at the 1 / 4 position in the thickness direction of the low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate prepared in Example 3 is as Figure 3 shown. The microstructure at the 1 / 4 position of the steel plate is tempered martensite + granular bainite + lath bainite structure, and the content of lath bainite is much higher than that of granular bainite. The tensile properties and impact properties at the 1 / 4 position of the steel plate in Example 3 are shown in Table 6 and Table 7 respectively.

[0087] Table 6 Tensile properties of each position of the 70 mm thick hydroelectric steel plate prepared in Example 3

[0088]

[0089] Table 7 Impact properties of each position of the 70 mm thick hydroelectric steel plate prepared in Example 3

[0090]

[0091] Example 4

[0092] A 1000MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent. The chemical composition of the hydroelectric steel plate in Example 4 is shown in Table 1; the balance is iron and inevitable impurities.

[0093] A preparation method of the above-mentioned 1000MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent. The preparation method includes processes such as smelting, casting, online rolling, sectional quenching, and tempering heat treatment. The specific steps are as follows:

[0094] ① Smelting: Adopt the process of deep desulfurization of hot metal + converter smelting + secondary refining + vacuum treatment + continuous casting. Prepare the continuous casting billet strictly according to the composition in Table 1. High-purity hot metal is required during the smelting process, and deep desulfurization treatment is carried out by the double slag method; LF and RH are used for secondary refining of the molten steel. The LF furnace makes white slag to ensure that [S] in the steel ≤ 0.001%, the net circulation time of RH is not less than 10 min, and the static time before casting is not less than 15 min; keep the slag surface in the ladle in a surging state and not expose the molten steel surface. Modify the inclusions in the steel through the treatment of the composite deoxidizer to maximize the purity of the steel quality, so that H ≤ 3 ppm, TO ≤ 50 ppm, and N ≤ 70 ppm in the smelting and melting composition of the hydroelectric steel plate.

[0095] ② Casting: Protective casting is adopted throughout the continuous casting process to avoid secondary oxidation of the molten steel. Control the superheat of the molten steel to be 25°C and the casting speed of the continuous casting billet to be 0.8 m / min.

[0096] ③ Rolling and sectional quenching: Send the continuous casting billet into the heating furnace, with a heating temperature of 1170°C - 1190°C and a net holding time of 9.5 h. Adopt a two-stage rolling method of rough rolling and finish rolling, and set different rolling passes according to the finished plate thickness; the starting rolling temperature in the rough rolling stage is 1100°C, and the finishing rolling temperature is 1030°C; the starting rolling temperature of the finish rolling is 970°C, and the finishing rolling temperature is 960°C; the total reduction ratio is 73%, among which, the reduction ratio of at least three passes ≥ 20%, and the finished thickness of the steel plate is 80 mm;

[0097] After finish rolling, sectional quenching of the steel plate is carried out by laminar cooling, and the cooling temperature is 100°C.

[0098] ④ Heat treatment: Quench the obtained steel plate, with a quenching temperature of 920°C and a net holding time of 3.5 min / mm; the temperature of the tempering process is 540°C and the net holding time is 3.0 min / mm.

[0099] For the 1000MPa grade ultra-high strength and toughness hydroelectric steel plate prepared in Example 4, the metallographic microstructure at 1 / 4 of the thickness direction is as Figure 4As shown, the microstructure at the 1 / 4 position of the steel plate is tempered martensite + granular bainite + lath bainite structure. The tensile properties and impact properties at the 1 / 4 position of the steel plate in Example 4 are shown in Table 8 and Table 9 respectively.

[0100] Table 8 Tensile properties of each position of the 80-mm-thick hydroelectric steel plate prepared in Example 4

[0101]

[0102] Table 9 Impact properties of each position of the 80-mm-thick hydroelectric steel plate prepared in Example 4

[0103]

[0104] Example 5

[0105] A low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate. The chemical composition of the hydroelectric steel plate in Example 5 is shown in Table 1; the balance is iron and unavoidable impurities.

[0106] A preparation method of the above low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate. The preparation method includes processes such as smelting, casting, online rolling, sectional quenching, and tempering heat treatment. The specific steps are as follows:

[0107] ① Smelting: Adopt the process of deep desulfurization of hot metal + converter smelting + secondary refining + vacuum treatment + continuous casting. Prepare the continuous casting billet strictly according to the composition in Table 1. High-purity hot metal is required during the smelting process, and deep desulfurization treatment is carried out by the double slag method; LF and RH are used for secondary refining of the molten steel. The LF furnace makes white slag to ensure that [S] in the steel ≤ 0.001%, the net circulation time of the RH is not less than 10 min, and the standing time before pouring is not less than 15 min; keep the slag surface in the ladle in a surging state and not expose the molten steel surface, and modify the inclusions in the steel through the treatment of the composite deoxidizer to maximize the purity of the steel quality, so that H ≤ 3 ppm, TO ≤ 50 ppm, and N ≤ 70 ppm in the smelting and melting composition of the hydroelectric steel plate.

[0108] ② Casting: Protective casting is adopted throughout the continuous casting process to avoid secondary oxidation of the molten steel. Control the superheat of the molten steel to be 25°C and the casting speed of the continuous casting billet to be 0.9 m / min.

[0109] ③ Rolling and sectional quenching: Send the continuous casting billet into the heating furnace, with a heating temperature of 1170°C to 1190°C and a net holding time of 9.5 h. Adopt the two-stage rolling method of rough rolling and finish rolling, and set different rolling passes according to the finished plate thickness; the starting rolling temperature in the rough rolling stage is 1100°C, and the finishing rolling temperature is 1030°C; the starting rolling temperature of the finish rolling is 980°C, and the finishing rolling temperature is 950°C; the total reduction ratio is 68%, among which, the reduction ratio of at least three passes ≥ 20%, and the finished thickness of the steel plate is 95 mm;

[0110] After finish rolling, laminar cooling is used to perform segmented quenching on the steel plate, and the cooling temperature is 120°C.

[0111] ④ Heat treatment: Quench the obtained steel plate at a quenching temperature of 930°C with a net holding time of 3.5 min / mm; the tempering process temperature is 560°C with a net holding time of 3.0 min / mm.

[0112] For the low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate prepared in Example 5, the metallographic microstructure at 1 / 4 of the thickness direction is as Figure 5 shown. The microstructure at 1 / 4 of the steel plate is tempered martensite + granular bainite + lath bainite structure. The tensile properties and impact properties at 1 / 4 of the steel plate in Example 5 are shown in Table 10 and Table 11 respectively.

[0113] Table 10 Tensile properties of each position of the 95 mm thick hydroelectric steel plate prepared in Example 5

[0114]

[0115] Table 11 Impact properties of each position of the 95 mm thick hydroelectric steel plate prepared in Example 5

[0116]

[0117] Example 6

[0118] A low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate. The chemical composition of the hydroelectric steel plate in Example 6 is shown in Table 1; the balance is iron and unavoidable impurities.

[0119] A preparation method of the above low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate. The preparation method includes processes such as smelting, casting, online rolling, segmented quenching, and tempering heat treatment. The specific steps are as follows:

[0120] ① Smelting: Adopt the process of deep desulfurization of hot metal + converter smelting + secondary refining + vacuum treatment + continuous casting. Prepare continuous casting billets strictly according to the composition in Table 1. High-purity hot metal is required during the smelting process, and deep desulfurization treatment is carried out by the double slag method; LF and RH are used for secondary refining of the molten steel. The LF furnace makes white slag to ensure that [S] in the steel ≤ 0.001%, the net circulation of the RH is not less than 10 min, and the standing time before pouring is not less than 15 min; keep the slag surface in the ladle in a surging state and do not expose the molten steel surface. Modify the inclusions in the steel through the treatment of composite deoxidizer to maximize the purity of the steel quality, so that H ≤ 3 ppm, TO ≤ 50 ppm, and N ≤ 70 ppm in the smelting and melting composition of the hydroelectric steel plate.

[0121] ② Casting: Protect the casting throughout the continuous casting process to avoid secondary oxidation of the molten steel. Control the superheat of the molten steel to be 25°C and control the casting speed of the continuous casting billet to be 1.2 m / min.

[0122] ③ Rolling and sectional quenching: The continuous casting billet is sent into a heating furnace, with a heating temperature of 1170°C - 1190°C and a net holding time of 9.5 h. A two-stage rolling method of rough rolling and finish rolling is adopted, and different rolling passes are set according to the finished plate thickness; the starting rolling temperature in the rough rolling stage is 1100°C, and the finishing rolling temperature is 1030°C; the starting rolling temperature in the finish rolling is 960°C, and the finishing rolling temperature is 930°C; the total reduction ratio is 64%, among which, the reduction ratio of at least three passes is ≥20%, and the finished thickness of the steel plate is 108 mm.

[0123] After finish rolling, sectional quenching of the steel plate is carried out by laminar cooling, and the cooling temperature is 150°C.

[0124] ④ Heat treatment: The obtained steel plate is quenched, with a quenching temperature of 930°C and a net holding time of 3.5 min / mm; the temperature of the tempering process is 600°C, and the net holding time is 4.0 min / mm.

[0125] For the low-carbon equivalent 1000 MPa grade ultra-high strength and toughness hydroelectric steel plate prepared in Example 6, the metallographic microstructure at 1 / 4 of the thickness direction is as Figure 6 shown. The microstructure at 1 / 4 of the steel plate is tempered martensite + granular bainite + lath bainite structure. The tensile properties and impact properties at 1 / 4 of the steel plate in Example 6 are shown in Table 12 and Table 13 respectively.

[0126] Table 12 Tensile properties of each position of the 108 mm thick hydroelectric steel plate prepared in Example 6

[0127]

[0128] Table 13 Impact properties of each position of the 108 mm thick hydroelectric steel plate prepared in Example 6

[0129]

[0130] For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible changes and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A 1000MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent, characterized in that, The components and mass percentages of the hydroelectric steel plate are as follows: C: 0.08% - 0.12%; Si: 0.05% - 0.30%; Mn: 0.60% - 1.05%; P ≤ 0.006%; S ≤ 0.002%; Cr: 0.40% - 0.60%; Mo: 0.45% - 0.70%; Ni: 1.65% - 3.00%; B: 0.0007% - 0.0013%; Ti: 0.005% - 0.017%; Nb: 0.01% - 0.03%; Al: 0.020% - 0.055%; Cu ≤ 0.30%; the balance is iron and unavoidable impurities.

2. The electrolytic sheet steel according to claim 1, wherein The thickness of the steel plate is 40 - 108 mm, the lowest carbon equivalent Ceq is 0.42, and the hardenability index DI ≥ 0.65 × plate thickness; Among them, the carbon equivalent Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14; in the formula, each element symbol represents the mass percentage of the corresponding element.

3. A preparation method of a 1000MPa grade ultra-high strength and toughness hydroelectric steel plate with low carbon equivalent as described in claim 1, characterized in that, The preparation method includes smelting, casting, rolling, sectional quenching, and tempering heat treatment processes. The specific steps are as follows: ① Smelting: Use high-purity molten iron, operate by the double slag method, and perform deep desulfurization treatment; use LF and RH for secondary refining of the molten steel. The LF furnace makes a white slag to ensure that [S] in the steel ≤ 0.001%, the net circulation time of the RH is not less than 10 min, and the standing time before pouring is not less than 15 min; ② Casting: Use protective casting throughout the continuous casting process, and control the superheat of the molten steel below 30°C; ③ Rolling and sectional quenching: Send the continuous casting billet to the heating furnace, the heating temperature is 1100°C - 1200°C, the net holding time is 8.5 - 10 h, adopt the two-stage rolling method of rough rolling and finish rolling, and set different rolling passes according to the finished plate thickness; after finish rolling, use laminar cooling to perform sectional quenching on the steel plate, and the cooling temperature is 60°C - 150°C; ④ Heat treatment: The temperature of the quenching process is 890°C - 930°C, and the net holding time is 0.5 - 3.5 min / mm; the temperature of the tempering process is 540°C - 600°C, and the net holding time is 1.0 - 4.0 min / mm.

4. The preparation method according to claim 3, characterized in that, During the casting process in step ②, control the drawing speed of the continuous casting billet to be 0.8 - 1.2 m / min.

5. The preparation method according to claim 3, characterized in that During the rolling process in step ③, the starting rolling temperature in the rough rolling stage is 1050°C - 1150°C, and the final rolling temperature is 1000°C - 1050°C.

6. The preparation method according to claim 3, wherein During the rolling process in step ③, the starting rolling temperature of the finish rolling is 960°C - 980°C, and the final rolling temperature is above 900°C; the total reduction ratio is 64% - 82%, among which, the reduction ratio of at least three passes ≥ 20%.

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