1300MPa-grade hydroelectric steel and preparation method thereof

Abstract

The invention relates to 1300MPa-grade hydroelectric steel and a preparation method thereof, and belongs to the technical field of steel and iron material preparation. The 1300 MPa grade hydroelectric steel is prepared from the following chemical elements in percentage by weight: 0.13 percent to 0.16 percent of C, 0.25 percent to 0.32 percent of Si, 1.15 percent to 1.25 percent of Mn, 0.04 percent to 0.07 percent of Al, 0.34 percent to 0.46 percent of Cr, 1.60 percent to 1.70 percent of Ni, 0.25 percent to 0.35 percent of Mo, 0.0048 percent to 0.0052 percent of Ti, 0.035 percent to 0.045 percent of Nb, 0.15 percent to 0.24 percent of Cu, 0.0009 percent to 0.0012 percent of B, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S and the balance of Fe and inevitable impurities. The hydroelectric steel disclosed by the invention has the advantages of good low-temperature toughness and strength balance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steel material preparation, and particularly relates to a 1300MPa-grade hydroelectric steel and a preparation method thereof. BACKGROUND

[0002] With the rapid development of deep water and high-power hydroelectric projects, hydroelectric equipment faces more severe service environments and complex working conditions. Key components such as water turbines, runners, pressure pipelines and main shaft systems have higher requirements for the strength, toughness, fatigue resistance and weldability of materials. Especially under the long-term action of high water pressure, high speed and alternating load, traditional medium-strength hydroelectric steel has been difficult to meet the requirements of structural safety and service life of the equipment. Extreme environments such as high cold and high altitude further aggravate the challenge to material performance, requiring hydroelectric steel to have high strength, high toughness and excellent low-temperature performance to ensure the stable and reliable operation of hydroelectric equipment.

[0003] At present, the research and development of hydroelectric steel mainly focuses on 1000MPa-grade quenched and tempered steel systems, which usually adds multiple alloying elements such as Ni, Mo and Cr, and combines complex heat treatment processes such as continuous casting, controlled rolling and controlled cooling, offline quenching and multiple tempering to improve performance. For example, the public patent CN117821846 A uses the addition of strengthening elements such as V, Mo and Ni, and relies on the traditional quenching and tempering route of "controlled rolling + water cooling + offline quenching + multiple tempering" to achieve excellent low-temperature toughness (-80℃ impact ≥100J), but its tensile strength has not yet broken through 1000MPa, and the process flow is complex, the cycle is long, and the requirements for equipment and process control are strict, which limits the industrialization promotion. At the same time, the patent uses continuous casting process, which is difficult to meet the forming needs of some thick specifications or multi-purpose die castings.

[0004] With the continuous expansion of the construction scale of hydroelectric power stations, especially the application of deep water and high-power hydroelectric power stations, the strength and comprehensive performance of existing hydroelectric steel gradually cannot meet the actual engineering requirements. Under extreme working conditions, the equipment often affects the long-term stability due to material fatigue failure and plastic deformation, and the traditional 1000MPa-grade hydroelectric steel has been unable to meet the requirements of high bearing and large working pressure. The contradiction between material strength and toughness is particularly prominent, and the increase in strength often accompanies the decrease in toughness, which in turn weakens the fatigue resistance. Therefore, how to realize the synergistic optimization of the strength and toughness of hydroelectric steel and ensure that the material still has excellent fatigue resistance and ductility under high pressure, high load and extreme environment has become a key technical problem to improve the core reliability of large hydroelectric equipment. SUMMARY

[0005] The present application aims to overcome the deficiencies of the prior art and provide a 1300MPa-grade hydroelectric steel and a preparation method thereof. The steel plate has the synergistic properties of strength and toughness, and the preparation process is simple, stable and suitable for large-scale industrial application.

[0006] To achieve the above object, the technical scheme adopted by the present application is:

[0007] In a first aspect, the present application provides a 1300MPa grade hydroelectric steel consisting of the following chemical elements by weight percentage: C: 0.13% to 0.16%, Si: 0.25% to 0.32%, Mn: 1.15% to 1.25%, Al: 0.04% to 0.07%, Cr: 0.34% to 0.46%, Ni: 1.60% to 1.70%, Mo: 0.25% to 0.35%, Ti: 0.0048% to 0.0052%, Nb: 0.035% to 0.045%, Cu: 0.15% to 0.24%, B: 0.0009% to 0.0012%, P: ≤0.02%, S: ≤0.01%, and the balance being Fe and unavoidable impurities.

[0008] The mechanism of action of each alloying element in the hydroelectric steel plate of the present application is as follows:

[0009] C element is a key alloying element in the steelmaking process, mainly through its solid solution strengthening and the formation of carbide precipitation strengthening, thereby greatly improving the yield strength and hardness of the steel. C element can also promote the transformation of austenite to martensite or bainite, improve the degree of refinement of the structure and the matching of strength and toughness. The content control is particularly critical, excessive C leads to excessive coarse carbide precipitation, inducing crack sensitivity and brittle failure, reducing plasticity and toughness; insufficient C content will not significantly improve the strength, and will easily lead to insufficient austenite stability, affecting the subsequent heat treatment effect. The C content is limited to 0.13% to 0.16% by mass percentage by the present application, which has good strength and toughness.

[0010] Si as a deoxidizer, promotes the morphological transformation of oxide inclusions in steel, which is beneficial to improve the distribution of inclusions and their interfacial bonding strength, thereby indirectly improving the toughness. The solid solution strengthening effect of Si improves the strength and hardness of the matrix, especially the heat resistance and corrosion resistance. However, excessive Si content will lead to carbide segregation and increase of non-metallic inclusions, reducing plasticity and toughness, and easily causing brittle fracture and hot cracking, which should be strictly controlled within a reasonable range. The Si content is limited to 0.25% to 0.32% by mass percentage by the present application, which has good strength and toughness.

[0011] The mechanism of Mn element in steel is diversified. Mn is a strong deoxidizer and desulfurizer, which can purify the molten steel, reduce inclusions, and effectively improve the purity of the steel. Mn can also improve the matrix strength through solid solution strengthening. Mn can also refine the austenite grain, promote grain boundary movement, optimize phase transformation kinetics, promote the formation of fine and uniform bainite structure, and significantly improve toughness and plasticity. Its effect on improving low temperature impact toughness is particularly obvious, and it improves the hot working performance of the steel and enhances the plastic deformation ability, which is beneficial to the implementation of subsequent cold working and welding process. The mass percentage of Mn is limited to 1.15% to 1.25% by the present application, so that the steel has good strength and toughness.

[0012] Al element as a high-efficiency deoxidizer can purify the molten steel, significantly reduce the number and size of inclusions, and improve the purity and low temperature toughness of the steel. Al can also refine the austenite grain and promote dynamic recrystallization during high temperature deformation, improving the uniformity of the structure. The aluminum oxide inclusions formed by Al have the characteristics of being small and stable in shape, which can strengthen the grain boundary and help improve the thermal fatigue resistance and corrosion resistance of the steel. The mass percentage of Al is limited to 0.04% to 0.07% by the present application, so that the steel has good strength and toughness.

[0013] Cr can strengthen the matrix structure by promoting the precipitation of bainite and martensite, and improve the strength and hardness. Cr has good oxidation resistance and corrosion resistance, which enhances the durability of the steel in complex water environment. Cr can also improve the high temperature strength through solid solution strengthening, improve the hardening ability of the steel, reduce the brittleness of martensite, promote the refinement of the structure, and increase the stability of the grain boundary, thereby improving the toughness and fatigue resistance. Therefore, the mass percentage of Cr is limited to 0.34% to 0.46% by the present application, so that the steel has good strength and toughness.

[0014] Ni element as an austenite stabilizer can improve the toughness and plasticity of the steel in low temperature environment, significantly reduce the impact brittleness transition temperature, and adapt to deep water and high cold environment. Ni can improve the overall strength through solid solution strengthening, and improve the corrosion resistance and thermal stability of the steel. The stabilizing effect of Ni on austenite also optimizes the phase transformation path, promotes the formation of fine and uniform martensite or bainite, reduces the brittle phase in the structure, and improves the fatigue resistance and fracture toughness. Therefore, the mass percentage of Ni is limited to 1.60% to 1.70% by the present application, so that the steel has good strength and toughness.

[0015] Mo element has good solid solution strengthening effect, can stabilize austenite phase, delay grain coarsening at high temperature, improve the high temperature strength and creep resistance of steel. Mo also promotes the refinement and uniform distribution of carbides, strengthens the precipitation strengthening mechanism. By improving the hardenability, Mo improves the hardening depth and microstructure uniformity of the steel, reduces the overheating sensitivity. Its improvement of steel toughness is mainly due to the reduction of brittle phase precipitation, optimization of interface bonding, reduction of grain boundary carbide aggregation, and improvement of overall toughness. Although the cost is higher, but its performance advantage is indispensable in high-end hydroelectric steel. Therefore, the Mo mass percentage is limited to 0.25% to 0.35% by the present application, so that it has good strength and toughness.

[0016] Ti element has strong nitrogen and carbon affinity, and can form fine and stable TiN and TiC particles during smelting and hot working, effectively inhibiting austenite grain growth, playing a significant role in grain refinement and pinning grain boundaries, and improving the basic strength and toughness of the steel. In addition, TiC can also achieve dispersion strengthening during subsequent heat treatment, synergistically enhancing the yield strength and fatigue performance with NbC and Mo2C carbides, and also has a positive effect on the high temperature stability and welding performance of the steel. Therefore, the Mo mass percentage is limited to 0.0048% to 0.0052% by the present application, so that it has good strength and toughness.

[0017] Nb element forms fine and stable carbide or nitride particles in steel, achieving effective precipitation strengthening, significantly improving yield strength and creep resistance. The grain refinement effect of Nb improves the microstructure uniformity, and improves the plasticity and toughness. Its improvement of welding performance lies in reducing the tendency of hot cracking and improving the microstructure stability of the welded joint, which is suitable for the manufacture of large structural parts. Therefore, the Nb mass percentage is limited to 0.035% to 0.045% by the present application, so that it has good strength and toughness.

[0018] Cu in steel mainly exists in the form of solid solution strengthening and precipitation strengthening, which can improve the yield strength and corrosion resistance of steel. During quenching and tempering, Cu element can form nanoscale precipitates, which can further improve the strength of the material, delay dislocation movement and crack propagation, and improve the service stability of the steel under high load and corrosion medium. At the same time, Cu can also improve the corrosion resistance of the steel in complex working conditions such as wet heat and sand, and enhance the durability of the equipment. Therefore, the Cu mass percentage is limited to 0.15% to 0.24% by the present application, so that it has good strength and toughness.

[0019] B content is extremely small, but has a significant effect on the hardenability of steel. B is enriched at the grain boundary, can strengthen the grain boundary binding, inhibit the precipitation of carbides at the grain boundary, reduce the grain boundary embrittlement, greatly improve the crack resistance and overall toughness of the steel. In addition, B improves the microstructure of the weld heat affected zone, improves the strength and toughness of the welded joint, and reduces the sensitivity of welding defects. Therefore, by optimizing the content of B in the present application to 0.0009-0.0012%, the steel has good strength and toughness.

[0020] S and P elements are both harmful impurities, which are controlled within a certain range.

[0021] The present application precisely controls the content of elements such as Ni, Mo, Mn, Cr, Nb, Ti and Cu to ensure the uniformity of the composition and the control of inclusions. Mo and Cr improve the hardenability, Nb and Ti generate dispersed carbonitride to inhibit grain growth and achieve precipitation strengthening, Cu participates in solid solution strengthening and improves corrosion resistance and enhances corrosion resistance and crack propagation resistance, Ni and Mo synergistically improve the low temperature toughness and fracture resistance of the material. Finally, a microstructure composed of fine lath martensite, bainite and dispersed carbides is obtained, in which the lath martensite provides high matrix strength, the bainite helps to improve plasticity and toughness, and the dispersed distribution of strong carbide forming elements effectively inhibits grain growth and provides precipitation strengthening effect. The multi-phase composite structure of the water and power steel obtained by the present application has high strength, high plasticity and excellent low temperature impact performance, and the water and power steel has high strength and good toughness, ensuring that the material still has excellent fatigue resistance and ductility under high pressure, high load and extreme environment.

[0022] As a preferred embodiment of the first aspect, the thickness of the water and power steel is 30-50 mm; the yield strength of the water and power steel is ≥1000 MPa, the tensile strength is ≥1300 MPa, the impact toughness at-40℃ is ≥55 J, and the elongation after fracture is >15%.

[0023] By controlling the element composition and content ratio of the water and power steel, the water and power steel with a thickness of 30-50 mm has high strength and good toughness, the yield strength is ≥1000 MPa, the tensile strength is ≥1300 MPa, the impact toughness at-40℃ is ≥55 J, and the elongation after fracture is >15%.

[0024] As a preferred embodiment of the first aspect, the thickness of the water and power steel is 30-50 mm; the yield strength of the water and power steel is ≥1000 MPa, the tensile strength is ≥1300 MPa, the impact toughness at-40℃ is ≥55 J, and the elongation after fracture is >15%.

[0025] In a second aspect, the present application provides a preparation method of the water and electricity steel of the first aspect, and the method comprises the steps of sequentially performing converter smelting, LF (ladle furnace) refining, RH (Ruhrstahl-Heraeus) vacuum treatment, thick slab continuous casting, heating, rolling and cooling.

[0026] The preparation process of the present application is simple, adopts smelting, casting, controlled rolling and controlled cooling process, omits the quenching and tempering heat treatment process, simplifies the existing production process, and significantly shortens the production cycle.

[0027] LF refining (ladle furnace) is one of the most core secondary refining technologies in modern steel smelting, especially indispensable in high-quality water and electricity steel production. It realizes deep desulfurization, precise temperature control, composition fine-tuning and inclusion control by secondary refining of the primary molten steel (from converter or electric furnace) in the ladle.

[0028] RH vacuum treatment (Ruhrstahl-Heraeus, abbreviated as RH) is the top secondary refining technology in steel smelting, which is specialized in ultra-low gas content (hydrogen, nitrogen, oxygen) and ultra-high purity molten steel production. In the manufacture of high-end thick steel plates such as water and electricity steel, RH treatment is crucial to prevent hydrogen-induced cracking (HIC) and improve low-temperature toughness. The working process includes vacuum start, argon-driven circulation, deep degassing, alloy fine-tuning and purification.

[0029] As a preferred embodiment of the second aspect, the converter smelting is specifically: the molten iron is subjected to converter smelting after conventional desulfurization treatment; the sulfur content after desulfurization treatment of the molten iron is controlled to be ≤0.0012%; and the double-slag method is used for converter smelting, and P is controlled to be ≤0.008%.

[0030] The method for desulfurizing the molten iron is: under high basicity conditions, the sulfur element in the molten iron is reacted with the desulfurizing agent to generate stable sulfide and enter the slag by spraying lime powder, magnesium powder or lime-magnesium composite powder into the molten iron, so as to realize effective removal of sulfur.

[0031] As a preferred embodiment of the second aspect, the LF refining is specifically: white slag operation method is used for desulfurization and deoxidization.

[0032] The white slag method operation is: 1) lime, fluorite and refining agent are added to the molten steel in the LF furnace to control the total content of FeO and MnO in the slag to be ≤1.5%, forming a white refining slag with high basicity and low oxide; 2) under the action of argon stirring, the molten steel and the white slag are fully reacted, the sulfur in the molten steel reacts with CaO in the slag to generate stable CaS and enter the slag, realizing desulfurization; 3) the low oxide content in the slag reduces the dissolved oxygen in the molten steel, and cooperates with the carbon-oxygen reaction and the action of aluminum, silicon and other deoxidizers to further remove the residual oxygen in the molten steel, realizing the deoxidization target.

[0033] As a preferred embodiment of the second aspect, the RH vacuum treatment is specifically: the vacuum degree of the RH vacuum treatment is ≤3.0 mbar, and the vacuum holding time is ≥15 min; after the vacuum ends, calcium treatment is performed, and then the static stirring time is ≥12 min.

[0034] As a preferred embodiment of the second aspect, the heating is specifically: the 150-250 mm thick slab is heated in a soaking furnace, the heating temperature is 1000-1150℃, the holding time is 1.5-2.5 h, and the mold casting blank is obtained.

[0035] The present application finds that the heating temperature and the holding time will affect the performance of the hydroelectric steel, therefore, by optimization, when the heating temperature is 1000-1150℃ and the holding time is 1.5-2.5 h, the performance of the hydroelectric steel is better.

[0036] As a preferred embodiment of the second aspect, the rolling is specifically: the mold casting blank is rolled by a two-stage rolling process of rough rolling and finish rolling.

[0037] The rough rolling opening temperature is 1050-1100℃, 6 passes of rolling are performed, the intermediate two passes of reduction rate are ≥25%, the cumulative compression ratio of rough rolling is ≥3.0, and the blank thickness is 48-80 mm.

[0038] The present application sets the rough rolling opening temperature to 1050-1100℃, which can ensure that the blank is in the complete austenite zone, which is beneficial to dynamic recrystallization, thereby refining the grains and eliminating segregation and porosity defects in the as-cast structure. The intermediate two passes of reduction rate in the rough rolling process are set to ≥25% respectively, which can ensure that the blank is fully compacted and internal defects are eliminated, thereby improving the density and subsequent processing performance of the steel.

[0039] The finish rolling opening temperature is 900-950℃, 3 passes of rolling are performed, the pass reduction rate is 9%-20%, the cumulative reduction rate is ≤50%, and the finish rolling temperature is ≥800℃.

[0040] The present application sets the finish rolling opening temperature to 900-950℃, which can avoid high-temperature grain growth while ensuring a suitable recrystallization process, thereby obtaining stable and fine austenite structure. The finish rolling process adopts 3 passes of rolling, the total pass reduction rate is set to 9%-20%, and the cumulative reduction rate is ≤50%, which can ensure that the rolling is completed in a suitable temperature range, avoid the risk of cracking caused by low-temperature rolling, and ensure that the austenite is transformed into fine and uniform ferrite / pearlite or bainite structure in the subsequent cooling process, thereby significantly improving the strength and toughness of the steel and the stability of the structure.

[0041] As a second aspect preferred embodiment, the cooling, in particular: using laminar flow water cooling method, cooling rate > 10℃ / s, the initial cooling temperature is 750-800℃, and the final cooling temperature is room temperature.

[0042] The laminar flow water cooling method is a process method for realizing controlled uniform cooling by uniformly acting on the surface of the steel material through multiple layers of water curtain.

[0043] The laminar flow water cooling method guarantees the performance through the following mechanisms: grain refinement: rapid cooling inhibits grain growth, improves strength and low temperature impact toughness; phase transformation control: precise cooling path (such as accelerating through the pearlite transformation zone) promotes the formation of bainite, optimizes the strength and toughness match; reduce the harm of sulfur segregation: uniform cooling reduces the enrichment of sulfides at grain boundaries, inhibits the risk of thermal brittleness and lamellar tearing. Due to the large coverage area of the laminar flow water cooling method, the stress concentration in the steel plate can be reduced, the warping deformation can be avoided, and the toughness can be improved. Therefore, the laminar flow water cooling method is selected for cooling in the present application. The present application finds that the cooling rate will affect the performance of the final hydroelectric steel, and through optimization, it is found that the cooling rate of the laminar flow water cooling method is > 10℃ / s, and the performance of the hydroelectric steel is better.

[0044] Compared with the prior art, the present application has the following beneficial effects:

[0045] The preparation process of the present application is simple, adopts smelting, casting, heating, controlled rolling and controlled cooling process, omits the quenching and tempering heat treatment process, simplifies the existing production process, significantly shortens the production cycle, reduces the energy consumption and cost requirements, and has good industrialization and popularization prospect. The controlled rolling and controlled cooling stage in the preparation method of the present application adopts high temperature rolling combined with laminar flow water cooling, so that the austenite grains are fully refined and bainite and part of martensite structure are formed.

[0046] The present application realizes the synergistic improvement of the strength and toughness of the hydroelectric steel by the design of a multi-alloy system and the synergistic regulation of the microstructure evolution process. By reasonably designing the contents of alloying elements such as Ni, Mo, Mn, Cr and Nb, the uniformity of the chemical composition and the control of inclusions are ensured, which lays a foundation for subsequent microstructure regulation. In the controlled-rolling and controlled-cooling stage, high-temperature rolling and laminar water cooling technology are adopted to fully refine the austenite grains, and under a high cooling rate, bainite and part of martensite structure are induced. Mo and Cr significantly improve the hardenability, and Nb effectively inhibits the recrystallization of austenite and promotes the precipitation of dispersed carbides. In the final quenching process, the microstructure is further transformed into a mixed structure of fine lath martensite and bainite, and under the joint action of Ni and Mo, good low-temperature toughness and strength balance are obtained. The dispersed Nb and Mo carbide particles realize precipitation strengthening and improve the crack propagation resistance. The finally formed composite multi-phase structure is composed of fine martensite, bainite and dispersed carbides, which not only ensures high strength but also has good plasticity and excellent low-temperature impact performance, meeting the high reliability requirements of hydroelectric equipment under extreme service conditions.

[0047] The hydroelectric steel plate prepared by the present application has excellent strength, plasticity and toughness performance indicators: yield strength ≥ 1000 MPa, tensile strength ≥ 1300 MPa, elongation after fracture ≥ 15%, and impact energy KV2 value at -40℃ ≥ 55J, which can meet the stringent requirements of strength, ductility and low-temperature toughness under extreme service conditions such as deep water, high water pressure and high coldness, effectively improving the structural safety and service life of hydroelectric equipment. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The microstructure schematic diagram of the hydroelectric steel plate of Example 1 at 1 / 2 thereof is shown in the figure;

[0049] Figure 2 The microstructure schematic diagram of the hydroelectric steel plate of Example 2 at 1 / 2 thereof is shown in the figure;

[0050] Figure 3 The microstructure schematic diagram of the hydroelectric steel plate of Example 3 at 1 / 2 thereof is shown in the figure. DETAILED DESCRIPTION

[0051] In order to better illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described below in combination with specific examples.

[0052] Example 1

[0053] The present embodiment provides a method for preparing 1300MPa-grade hydroelectric steel, which comprises the steps of sequentially performing converter smelting, LF refining, RH vacuum treatment, thick slab continuous casting, heating, rolling and cooling:

[0054] The converter smelting, specifically: the molten iron is subjected to conventional desulfurization treatment and then subjected to converter smelting; the sulfur content after the desulfurization treatment of the molten iron is controlled to be ≤0.0012%; a double-slag method is used in the converter, and P is controlled to be ≤0.008%;

[0055] The LF refining, specifically: white slag operation is used for desulfurization and deoxidization;

[0056] The RH vacuum treatment, specifically: the vacuum degree of the RH vacuum treatment is 3.0 mbar, and the vacuum holding time is 15 min; after the vacuum ends, calcium treatment is performed, and then the static stirring time is 12 min;

[0057] The heating, specifically: the 150 mm thick slab is heated in a soaking furnace, the heating temperature is 1050℃, and the heat preservation time is 1.5 h, to obtain a mold casting blank;

[0058] The rolling, specifically: the mold casting blank is subjected to a two-stage rolling process of rough rolling and finish rolling; the rough rolling starting temperature is 1050℃, and the slab is rolled by 6 passes, and the intermediate two passes are each ≥25% in reduction rate, the reduction rates of the 6 passes are 10.0%, 12.0%, 25.8%, 26.4%, 10.0% and 17.8% respectively, the cumulative compression ratio of the rough rolling is not less than 3.125, and the thickness of the slab is 48 mm; the finish rolling starting temperature is 900℃, and the slab is rolled by 3 passes, and the reduction rates of each pass are 15.6%, 18.5% and 9.1% respectively, and the final rolling temperature is 800℃, and the thickness of the mold casting blank is 30 mm;

[0059] The cooling, specifically: the slab is cooled by a laminar flow water cooling method, the starting cooling temperature is 750℃, the cooling rate is 12.6℃ / s, and the slab is cooled to room temperature, to obtain a finished product of water power steel with a thickness of 30 mm.

[0060] Example 2

[0061] The embodiment provides a preparation method of 1300 MPa grade water power steel, and the method comprises the following steps in sequence: converter smelting, LF refining, RH vacuum treatment, thick slab continuous casting, heating, rolling and cooling.

[0062] The converter smelting, specifically: the molten iron is subjected to conventional desulfurization treatment and then subjected to converter smelting; the sulfur content after the desulfurization treatment of the molten iron is controlled to be ≤0.0012%; a double-slag method is used in the converter, and P is controlled to be ≤0.008%;

[0063] The LF refining, specifically: white slag operation is used for desulfurization and deoxidization;

[0064] The RH vacuum treatment, specifically: the vacuum degree of the RH vacuum treatment is 2.9 mbar, and the vacuum holding time is 15 min; after the vacuum ends, calcium treatment is performed, and then the static stirring time is 12 min;

[0065] The heating, specifically: the 200mm thick slab is heated in a soaking furnace, the heating temperature is 1080℃, and the holding time is 2h, to obtain the mold casting blank;

[0066] The rolling, specifically: the mold casting blank is rolled by a rough rolling and a finish rolling two-stage rolling process; the rough rolling starting temperature is 1075℃, and the blank is rolled by 6 passes, the intermediate two passes are each ≥25% in reduction ratio, the reduction ratios of the 6 passes are respectively: 10.0%, 12.0%, 26.3%, 27.5%, 10.0% and 14.7%, the cumulative compression ratio of the rough rolling is 3.08, and the thickness of the blank is 65mm; the finish rolling starting temperature is 920℃, and the blank is rolled by 3 passes, the reduction ratios of each pass are respectively 16.3%, 18.6% and 9.2%, the final rolling temperature is 835℃, and the thickness of the mold casting blank is 40mm;

[0067] The cooling, specifically: the mold casting blank is cooled by a laminar flow water cooling method, the starting cooling temperature is 780℃, the cooling rate is 11.3℃ / s, and the final cooling temperature is room temperature, to obtain the finished product of the hydroelectric steel with a thickness of 40mm.

[0068] Example 3

[0069] The embodiment provides a preparation method of 1300MPa-grade hydroelectric steel, and the method comprises the steps of sequentially performing converter smelting, LF refining, RH vacuum treatment, thick slab continuous casting, heating, rolling and cooling:

[0070] The converter smelting, specifically: the molten iron is subjected to the converter smelting after being subjected to conventional desulfurization treatment; the sulfur content of the molten iron after the desulfurization treatment is controlled to be ≤0.0012%; the converter adopts a double-slag method, and the P is controlled to be ≤0.008%;

[0071] The LF refining, specifically: white slag operation is adopted for desulfurization and deoxidization;

[0072] The RH vacuum treatment, specifically: the vacuum degree of the RH vacuum treatment is 3.0mbar, the vacuum holding time is 15min; after the vacuum ends, calcium treatment is performed, and then the static stirring time is 12min;

[0073] The heating, specifically: the 250mm thick slab is heated in a soaking furnace, the heating temperature is 1150℃, and the holding time is 2.5h, to obtain the mold casting blank;

[0074] The rolling, in particular: the mold casting blank is rolled by a two-stage rolling process of rough rolling and finish rolling; the rough rolling opening rolling temperature is 1100℃, and the blank is rolled by 6 passes, the intermediate two passes are each ≥25%, the 6 passes are respectively 10.0%, 12.0%, 25.5%, 28.0%, 10.0% and 16.3%, the cumulative compression ratio of the rough rolling is not less than 3.125, and the thickness of the blank is 80mm; the finish rolling opening rolling temperature is 950℃, and the blank is rolled by 3 passes, the down pressure rate of each pass is respectively 17.1%, 19.5% and 10.5%, and the final rolling temperature is 850℃, and the thickness of the mold casting blank is 50mm.

[0075] The cooling, in particular: the laminar flow water cooling mode is used for cooling, the starting cooling temperature is 800℃, the cooling rate is 10.5℃ / s, and the final cooling is to room temperature, so that the water power steel with a thickness of 50mm is prepared.

[0076] The chemical composition of the water power steel in Examples 1-3 is shown in the following table:

[0077] Table 1

[0078] Chemical composition (%) Example 1 Example 2 Example 3 C 0.13 0.15 0.16 Si 032 0.30 0.25 Mn 1.15 1.20 1.25 Al 0.07 0.06 0.04 Cr 0.34 0.40 0.46 Ni 1.70 1.67 1.60 Mo 0.25 0.31 0.35 Ti 0.0052 0.0050 0.0048 Nb 0.035 0.041 0.045 Cu 0.15 0.22 0.24 B 0.0012 0.0010 0.0009 P ≤0.02 ≤0.02 ≤0.02 S ≤0.01 ≤0.01 ≤0.01

[0079] The difference between Comparative Example 1 and Example 1 is that the mass percentage of chemical elements is different, and the rest is the same as Example 1. The mass percentage of chemical elements of the water power steel in Comparative Example 1 is specifically: C: 0.10%, Si: 0.36%, Mn: 1.0%, Al: 0.09%, Cr: 0.30%, Ni: 1.9%, Mo: 0.21%, Ti: 0.0060%, Nb: 0.031%, Cu: 0.11%, B: 0.0005%, P: ≤0.02%, S: ≤0.01%, and the balance is Fe and unavoidable impurities.

[0080] The difference between Comparative Example 2 and Example 1 is that the mass percentage of chemical elements is different, and the rest is the same as Example 1. The mass percentage of chemical elements of the water power steel in Comparative Example 2 is specifically: C: 0.18%, Si: 0.20%, Mn: 1.35%, Al: 0.02%, Cr: 0.50%, Ni: 1.4%, Mo: 0.38%, Ti: 0.0043%, Nb: 0.048%, Cu: 0.28%, B: 0.0015%, P: ≤0.02%, S: ≤0.01%, and the balance is Fe and unavoidable impurities.

[0081] Comparative Example 3

[0082] The difference between Comparative Example 3 and Example 1 is that C: 0.05%; the rest is the same as Example 1.

[0083] Comparative Example 4

[0084] Comparative Example 4 differs from Example 1 in that C: 0.25%; the rest is the same as Example 1.

[0085] Comparative Example 5 differs from Example 1 in that Mn is absent, part of which is replaced by Fe; the rest is the same as Example 1.

[0086] Comparative Example 6 differs from Example 1 in that Cr is absent, part of which is replaced by Fe; the rest is the same as Example 1.

[0087] Comparative Example 7 differs from Example 1 in that Ni is absent, part of which is replaced by Fe; the rest is the same as Example 1.

[0088] Comparative Example 8 differs from Example 1 in that Mo is absent, part of which is replaced by Fe; the rest is the same as Example 1.

[0089] Comparative Example 9 differs from Example 1 in that Nb is absent, part of which is replaced by Fe; the rest is the same as Example 1.

[0090] Comparative Example 10 differs from Example 1 in that Cu is absent, part of which is replaced by Fe; the rest is the same as Example 1.

[0091] Comparative Example 11 differs from Example 1 in that the heating, specifically: the 150mm thick slab is heated in a soaking furnace, the heating temperature is 1200℃, and the holding time is 1.5h, to obtain a mold casting blank.

[0092] Comparative Example 12 differs from Example 1 in that the cooling, specifically: ordinary water cooling is used, and the cooling rate is 8.5℃ / s.

[0093] Test Example to Test the Properties of Hydroelectric Steel Prepared in Examples and Comparative Examples

[0094] Test method: according to GB / T 228.1-2021, the yield strength, tensile strength and elongation after fracture of the above prepared steel are tested; at the same time, according to GB / T 229-2007, V-shaped notch specimen is used to test the impact energy of the above prepared steel at-40℃.

[0095] The test results are shown in the following table:

[0096] Table 2

[0097]

[0098] As can be seen from the above table, the water and electricity steel of embodiments 1-3 has low temperature toughness and strength balance, realizing the synergistic improvement of strength and toughness of the water and electricity steel. It can be seen that, by means of the multi-element alloy system design and the synergistic regulation of the controlled-zoning and controlled-cooling, the water and electricity steel plate with toughness and high strength is successfully prepared, the tensile strength of which is greater than 1300 MPa (specifically in the range of 1300-1320 MPa), and the elongation after fracture is greater than 15% (specifically in the range of 15-17.5%). As can be seen from the comparison between embodiment 1 and embodiments 2 and 3, the preparation process and the ratio of chemical elements of embodiment 1 are the best scheme of the present application, and the water and electricity steel prepared has the maximum tensile strength.

[0099] As can be seen from the comparison between comparative examples 1-2 and embodiment 1, the content ratio of the chemical elements selected in the present application is the key, if it is not within the range defined in the present application, the performance of the water and electricity steel will be affected.

[0100] As can be seen from the comparison between comparative example 3 and embodiment 1, due to the reduction of the content of low-C martensite and carbide, the solid solution strengthening and the effect of carbide precipitation are weakened, so that the yield strength and tensile strength are reduced, but the reduction of carbide makes the structure more uniform, and the crack initiation source is reduced, so that the elongation after fracture and the low temperature impact toughness are improved.

[0101] As can be seen from the comparison between comparative example 4 and embodiment 1, due to the increase of the content of high-C lath martensite and the promotion of the generation of coarse carbide, the matrix strength is significantly improved, so that the yield strength and tensile strength are increased, but the coarse carbide becomes the crack initiation source, resulting in the decrease of ductility and the significant deterioration of low temperature impact toughness.

[0102] As can be seen from the comparison between comparative example 5 and embodiment 1, due to the lack of high-Mn content, the stability of austenite is reduced, the critical phase transition temperature is increased, the austenite transformation is advanced, the coarse and non-uniform structure is formed, the dissolution and diffusion regulation of Mn to carbon is lacking, the carbide precipitation is limited, the dispersion strengthening effect is insufficient, and the strength and toughness and low temperature performance are decreased.

[0103] As can be seen from the comparison between comparative example 6 and embodiment 1, due to the weakening of the carbide strengthening effect and solid solution strengthening effect of Cr, the yield strength and tensile strength are decreased; at the same time, the lack of Cr makes the multi-phase interface lack of passivation and stabilization, so that the low temperature impact toughness is decreased.

[0104] As can be seen from the comparison between comparative example 7 and embodiment 1, due to the disappearance of the stabilization effect and low temperature toughening effect of Ni on austenite, the lath martensite structure becomes brittle, the elongation after fracture is decreased, so that the low temperature impact toughness is sharply reduced, and the low temperature brittleness tendency is significantly shown.

[0105] Compared with Example 1, the precipitation strengthening effect is weakened due to the disappearance of the Mo dispersion carbide formation, and the yield strength and tensile strength decrease; at the same time, the Mo pinning effect on dislocations is weakened, and the crack propagation resistance decreases, thereby the low-temperature impact toughness decreases.

[0106] Compared with Example 1, the austenite grains grow significantly due to the disappearance of the Nb fine-grain strengthening and carbonitride precipitation strengthening, resulting in a significant decrease in yield strength and tensile strength, and the coarse grains reduce the uniformity of the structure and the ability of dislocation coordinated deformation, thereby the low-temperature impact toughness significantly decreases.

[0107] Compared with Example 1, the yield strength and tensile strength slightly decrease due to the weakening of the solid solution strengthening effect of Cu, and the absence of Cu has limited effect on the morphology of martensite and bainite, so the ductility and low-temperature toughness change little, and the low-temperature impact toughness only slightly decreases.

[0108] Compared with Example 1, it can be seen from Examples 11-12 that the heating temperature is important to the water and electricity steel plate, the cast blank in Example 11 is heated to 1200℃ and kept for a long time in the heating stage, resulting in serious growth of austenite grains, and the structure is coarsened after controlled cooling, thereby reducing the strength, plasticity and toughness. In Example 12, the ordinary water cooling (cooling rate of 8.5℃ / s) is adopted, and the insufficient cooling rate cannot effectively control the structure transformation and refinement, resulting in a decrease in the content of bainite and martensite, and insufficient precipitation strengthening, thereby the strength, toughness and plasticity are all adversely affected.

[0109] The above results show that the precise control of the ratio of key alloying elements and the controlled rolling and controlled cooling process in the present application is crucial for obtaining a composite multi-phase structure with excellent comprehensive performance.

[0110] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A 1300 MPa grade hydroelectric steel, characterized in that, consists of the following mass percentage of chemical elements: C: 0.13%~0.16%, Si: 0.25%~0.32%, Mn: 1.15%~1.25%, Al: 0.04%~0.07%, Cr: 0.34%~0.46%, Ni: 1.60%~1.70%, Mo: 0.25%~0.35%, Ti: 0.0048%~0.0052%, Nb: 0.035%~0.045%, Cu: 0.15%~0.24%, B: 0.0009%~0.0012%, P: ≤0.02%, S: ≤0.01%, the balance being Fe and inevitable impurities. The thickness of the hydroelectric steel is 30~50mm; the yield strength of the hydroelectric steel is ≥1000MPa, the tensile strength is ≥1300MPa, the impact toughness at-40℃ is ≥55J, and the elongation after fracture is >15%.

2. The hydroelectric steel of claim 1, wherein, The yield strength of the hydroelectric steel is 1000~1100MPa, the tensile strength is 1300~1320MPa, the impact toughness at-40℃ is 55~60J, and the elongation after fracture is 15~17%.

3. The hydroelectric steel of claim 2, wherein, The method comprises the steps of sequentially carrying out converter smelting, LF refining, RH vacuum treatment, thick slab continuous casting, heating, rolling and cooling.

4. A method of producing the hydroelectric steel according to any one of claims 1 to 3, characterized in that, The converter smelting, specifically: the molten iron is subjected to desulfurization treatment and then subjected to converter smelting; the sulfur content after the desulfurization treatment of the molten iron is controlled to be ≤0.0012%; the double-slag method is adopted for the converter smelting, wherein P is controlled to be ≤0.008%.

5. The method of claim 4, wherein the water is heated to a temperature of 80°C to 100°C. The LF refining, specifically: the white slag operation method is adopted for desulfurization and deoxidization.

6. The method of claim 4, wherein the water is heated to a temperature of 80°C to 100°C. The RH vacuum treatment, specifically: the vacuum degree of the RH vacuum treatment is ≤3.0mbar, and the vacuum holding time is ≥15min; after the vacuum ends, calcium treatment is carried out, and the static stirring time is ≥12min.

7. The method of claim 4, wherein the water is heated to a temperature of 80°C to 100°C. The heating, specifically: the 150~250mm thick slab is heated in a soaking furnace, the heating temperature is 1000-1150℃, the holding time is 1.5~2.5h, and a mold casting blank is obtained.

8. The method of claim 4, wherein the water is heated to a temperature of about 80°C to about 100°C. The rolling, specifically: the mold casting blank is subjected to a two-stage rolling process of rough rolling and finish rolling; 9. The method of claim 4, wherein the water is heated to a temperature of about 80°C to about 100°C. The rough rolling stage: the rough rolling starting temperature is 1050~1100℃, the rolling is carried out for 6 passes, the intermediate two passes are subjected to a reduction of ≥25%, the cumulative compression ratio of the rough rolling is ≥3.0, and the blank thickness is 48~80mm; The finish rolling stage: the finish rolling starting temperature is 900~950℃, the rolling is carried out for 3 passes, the pass reduction is 9%~20%, the cumulative reduction is ≤50%, and the finish rolling temperature is ≥800℃. The cooling, specifically: the laminar flow water cooling method is adopted for cooling, the starting cooling temperature is 750~800℃, the cooling rate is >10℃ / s, and the final cooling is to room temperature.

10. The method of claim 4, wherein the water is heated to a temperature of about 80°C to about 100°C. ​

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