Martensite heat-resistant steel and manufacturing method and application thereof

Abstract

The invention relates to the technical field of heat-resistant stainless steel, and particularly discloses martensite heat-resistant steel and a manufacturing method and application thereof. According to the manufacturing method of the martensitic heat-resistant steel, by precisely controlling the technological conditions of the working procedures of smelting, AOD refining, LF refining, VD vacuum refining, forging, annealing and the like, the strength, toughness and plasticity of the prepared martensitic heat-resistant steel are effectively improved, the grain structure of the heat-resistant steel is effectively refined, the grain size ranges from 7.5 grades to 8.5 grades, the sum of inclusions ranges from 3 grades to 4.5 grades, Rp0.2 ranges from 800 MPa to 900 MPa, Rm is smaller than or equal to 1100 MPa, A is larger than or equal to 14%, Z is larger than or equal to 40%, and the yield of the heat-resistant steel is increased. The HBW is 280N / mm < 2 >-305N / mm < 2 >, the KV2 is greater than or equal to 30J, and the Rm (400 DEG C) is greater than or equal to 650 DEG C, so that a solid and reliable material support is provided for the ultra-supercritical steam turbine, and the material is particularly suitable for manufacturing parts such as a wheel disc of the ultra-supercritical steam turbine and the like, and has a relatively high practical value.

Description

Technical Field

[0001] The invention relates to the technical field of heat-resistant stainless steel, and in particular to a martensitic heat-resistant steel and a manufacturing method and application thereof. Background Art

[0002] With the continuous growth of global energy demand and the increasing requirements for environmental protection, improving the efficiency of thermal power generation has become a key direction for the development of the power industry. Ultra-supercritical steam turbine technology has emerged as a new generation of efficient and clean power generation technology. Ultra-supercritical units have higher steam parameters (main steam pressure ≥30MPa, main steam temperature ≥650℃). Compared with traditional subcritical and supercritical units, they can significantly improve power generation efficiency, reduce coal consumption and emissions of pollutants such as carbon dioxide. Long-term stable operation in such a high-temperature and high-pressure steam environment places extremely stringent requirements on the materials used in key components of steam turbines.

[0003] As a new type of iron-based heat-resistant alloy, 13Cr10Mo1W1VNbN heat-resistant steel shows good high-temperature strength, creep resistance, oxidation resistance and corrosion resistance under the synergistic effect of multiple alloy elements such as chromium Cr, molybdenum Mo, tungsten W, vanadium V, niobium Nb and nitrogen N. At the same time, compared with nickel-based alloys, it has the advantages of lower cost and lower density, and has been widely used in the field of ultra-supercritical steam turbines.

[0004] The 13Cr10Mo1W1VNbN heat-resistant steel prepared by the current process tends to form a coarse columnar crystal structure. This structure is uneven in morphology and has many defects and stress concentration points inside, which seriously reduces the plasticity and toughness of the steel, thereby limiting the further improvement of the comprehensive performance of the heat-resistant steel. At the same time, the heat-resistant steel has a high degree of alloying, a narrow range of suitable hot working temperatures, is difficult to process, and has a high risk of cracking, which affects the long-term stability of the steel. Therefore, it is necessary to develop a new preparation method for 13Cr10Mo1W1VNbN heat-resistant steel to meet the requirements of ultra-supercritical steam turbines for high-performance heat-resistant steel. Summary of the invention

[0005] Aiming at the problems existing in the preparation process of the existing 13Cr10Mo1W1VNbN heat-resistant steel, such as coarse grains and easy cracking during the processing, the present invention provides a martensitic heat-resistant steel and a manufacturing method and application thereof.

[0006] To solve the above technical problems, the technical solution provided by the embodiment of the present invention is:

[0007] In a first aspect, the present invention provides a method for manufacturing a martensitic heat-resistant steel, comprising the following steps:

[0008] S1, melting the raw materials in an electric arc furnace to obtain molten steel with a C content ≥ 1.5%;

[0009] S2, adding slag-making auxiliary materials to the molten steel for slag-making and decarburization, after slag-making, slag-making is removed, chromium-carbon alloy is added, and then a mixed gas of oxygen and argon with a reduced oxygen concentration gradient is introduced in stages for blowing, W, Mo, V, and Nb are added in sequence during the blowing process, and when C≤0.08% and Si≤0.02% in the molten steel, aluminum particles are added for primary reduction, and after the primary reduction is completed, slag-making auxiliary materials and silicon-calcium alloy are added for secondary reduction to obtain reduced molten steel;

[0010] S3, subjecting the reduced molten steel to LF refining and VD vacuum refining to obtain molten steel with Al≤0.01%, Si≤0.12%, O≤0.0035%, and H≤0.0001%, and casting to obtain a steel ingot;

[0011] S4, heating the steel ingot to 1160°C-1180°C and keeping the temperature, then roughening and drawing to obtain a first-fire forging billet; heating the first-fire forging billet to 1120°C-1140°C and keeping the temperature, then roughening and drawing to obtain a second-fire forging billet; heating the second-fire forging billet to 1120°C-1140°C and keeping the temperature, then drawing to obtain a third-fire forging billet; after forging, air-cooling to 480°C-520°C, loading into an annealing furnace, and furnace-cooling to 200°C-250°C;

[0012] S5, heating the forging billet to 640°C-660°C at a rate of 60°C / min-90°C / min, keeping the temperature for 20h-25h, then cooling the billet to 200°C-250°C at a rate of 40°C / min-60°C / min, air-cooling the billet to 160°C-180°C, then heating the billet to 640°C-660°C at a rate of 60°C / min-90°C / min, keeping the temperature for 25h-30h, then cooling the billet to ≤20 ...60°C / min, air-cooling the billet to 160°C-180°C, then heating the billet to 640°C-660°C at a rate of 60°C / min-90

[0013] S5, subjecting the forging to a modulated heat treatment to obtain a martensitic heat-resistant steel.

[0014] Compared with the prior art, the manufacturing method of martensitic heat-resistant steel provided by the present invention, in the AOD refining process, by adopting the oxygen-containing mixed gas with gradually reduced oxygen concentration in stages, controlling the addition time of each alloy element, and adopting the method of two reductions, not only effectively reduces the oxygen content in the molten steel, creating good conditions for subsequent refining, but also helps to control the morphology of inclusions, improve the purity of molten steel, and at the same time, can also minimize the burning and segregation of alloy elements, which is conducive to accurately controlling the content of alloy elements. By controlling Al, Si, O, and H in a lower range through LF refining and VD vacuum refining, the stability of the lattice structure of the material at high temperature can be improved, and the aggregation and diffusion of oxygen and hydrogen at positions such as grain boundaries can be avoided, reducing the weakening of grain boundaries, so that the material can better resist creep deformation when subjected to stress at high temperature, and at the same time, the hot working window of the material can be reduced, and the generation of hot working cracks can be reduced. The three-stage annealing at a specific temperature is conducive to grain refinement and uniform organization. Furthermore, the specific annealing system adopted causes the grains in the steel to undergo a recrystallization process, so that the originally elongated or broken grains re-nucleate and grow to form fine equiaxed crystals. At the same time, the above-mentioned specific annealing system can promote the uniform precipitation of some alloy carbides (such as Cr-Mo-WV-Nb composite carbides). These fine and evenly distributed precipitated phases can serve as pinning points to hinder the movement of grain boundaries, further refine the grains, and also play a role in precipitation strengthening, thereby improving the strength of the material.

[0015] The present invention effectively reduces the contents of C, Al, Si, O and H in molten steel by controlling the oxygen blowing decarburization mode during the AOD smelting process, the order of adding alloys and the secondary reduction mode, controls the inclusion level, improves the purity of molten steel, and is conducive to accurately controlling the content of alloy elements; at the same time, the three-fire drawing and a specific annealing system are used to effectively refine the grains, further homogenize the structure, significantly reduce the thermal stress and crack risks, thereby being conducive to significantly improving the plasticity and toughness of the material, and greatly improving the comprehensive performance of martensitic heat-resistant steel.

[0016] Furthermore, in S2, the slag-making auxiliary materials include lime and fluorite.

[0017] Furthermore, in S2, in the slag making and decarbonization process, the total amount of lime and fluorite added is 30kg / t to 60kg / t, wherein the mass ratio of lime to fluorite is (1.5 to 2.5):1.

[0018] Furthermore, in S2, the slag making time is 5 minutes to 10 minutes.

[0019] Furthermore, in S2, in the secondary reduction process, the amount of lime added is 15kg / t to 25kg / t, and the amount of fluorite added is 10kg / t to 18kg / t.

[0020] Furthermore, in S2, the amount of aluminum particles added is 1kg / t to 2kg / t.

[0021] Furthermore, in S2, the amount of silicon-calcium alloy added is 0.5kg / t to 1kg / t.

[0022] By properly controlling the amount of aluminum particles or silicon-calcium alloy added, the shape and size of inclusions can be controlled, thereby improving the purity of the molten steel.

[0023] Furthermore, in S2, the time of the primary reduction is 7 minutes to 15 minutes.

[0024] Furthermore, in S2, the secondary reduction time is 5 min to 10 min.

[0025] It should be noted that the temperature of the molten steel is controlled to be no less than 1500°C during the primary reduction and secondary reduction processes.

[0026] Through two reduction operations, the oxygen content in the molten steel can be reduced to an extremely low level, providing good conditions for subsequent refining. At the same time, the microstructure of the steel can be better controlled, making the distribution of alloy elements in the molten steel more uniform, which is conducive to the strengthening mechanisms such as precipitation strengthening, thereby facilitating the preparation of higher performance steel.

[0027] Furthermore, in S2, introducing a mixed gas of oxygen and argon with a decreasing oxygen concentration gradient in stages specifically comprises the following steps:

[0028] A mixed gas of oxygen and argon is introduced into the molten steel in the order of the volume ratio of oxygen to argon being (3-7):1, (2-4):1, (0.5-1.5):1, 1:(2-4), and 1:(2-6). The blowing time for each stage is 15 min to 25 min.

[0029] It should be noted that, in S2, the mixed gas of oxygen and argon is introduced into the molten steel by side blowing.

[0030] The use of a phased decarburization method can achieve efficient decarburization while reducing the oxidation loss of alloying elements in the molten steel. At the same time, through the subsequent two reduction methods, it is also easier for the oxidized alloying elements to return to the molten steel, further reducing the loss of alloying elements. In addition, the phased decarburization can also make the molten steel agitation relatively stable, and the inclusions (such as oxide inclusions) generated in the molten steel are more likely to float to the surface of the molten steel under the action of buoyancy and molten steel convection and enter the slag for removal, avoiding the situation where the inclusions are re-mixed into the molten steel or difficult to effectively separate due to violent oxygen blowing and stirring, improving the purity of the molten steel and reducing the adverse effects of inclusions on the final performance of the steel.

[0031] Furthermore, in S3, during the LF refining, calcium silicon powder or aluminum powder is added to the reduced molten steel for diffusion deoxidation 2 to 3 times to control Al≤0.01%, Si≤0.12%, and O≤0.0035% in the molten steel.

[0032] Furthermore, in the VD vacuum refining, under the condition of vacuum degree ≤67Pa, argon gas is introduced into the molten steel at a flow rate of 15L / min~20L / min, and the argon blowing time is 20min~30min. After breaking the air, nitrogen gas is introduced to control the N content in the molten steel to 0.045%~0.06%.

[0033] By using the preferred VD vacuum degassing, the H content in the molten steel can be controlled below 0.0001%, thereby significantly reducing the occurrence of hydrogen embrittlement problems, improving the machinability of the steel, and reducing the generation of cracks during the machining process.

[0034] Further, in S4, the temperature is increased to 1160℃~1180℃ by gradient heating, which specifically includes the following steps: first, the steel ingot is kept at 480℃~520℃ for 1.5h~2.5h, then the temperature is increased to 800℃~850℃ at a rate of 60℃ / h~100℃ / h, and the temperature is kept for 2h~3h, and then the temperature is increased to 1160℃~1180℃ at a rate of 60℃ / h~100℃ / h, and the temperature is kept for 2h~4h.

[0035] The optimal heating procedure can provide a good foundation for the deformation of the steel, making the structural changes of the steel more coordinated during the deformation process. The optimal heating method is helpful to improve the toughness and ductility of the steel, avoid the generation of structural defects during the deformation process, and thus reduce the possibility of cracks during subsequent processing and use.

[0036] Furthermore, in S4, the deformation of the first-fire roughing is 30% to 40%, and the deformation of the elongation is 40% to 60%; the deformation of the second-fire roughing is 30% to 50%, and the deformation of the elongation is 80% to 90%; the deformation of the third-fire elongation is 120% to 150%.

[0037] Furthermore, in S4, in the first fire-drawing step, the heat preservation time at 1160°C to 1180°C is 2h to 4h. In the second fire-drawing step, the heat preservation time at 1120°C to 1140°C is 2h to 3h. In the third fire-drawing step, the heat preservation time at 1120°C to 1140°C is 2h to 3h.

[0038] Further, in S5, the heat treatment specifically includes: firstly heating the forging to 1050°C-1100°C, keeping it at that temperature for 1h-2h, and oil cooling it to room temperature; then heating the forging to 650°C-750°C, keeping it at that temperature for 2h-3h, and air cooling it to room temperature.

[0039] Furthermore, the chemical composition of the martensitic heat-resistant steel is: C 0.11%~0.14%, Si≤0.12%, Mn0.4%~0.5%, S≤0.005%, P≤0.01%, Cr 10.0%~10.6%, Ni0.7%~0.8%, Mo 1.0%~1.1%, W 0.9%~1.0%, V 0.15%~0.25%, Al≤0.01%, N0.045%~0.060%, Nb 0.04%~0.06%, O≤0.0035%, H≤0.0001%, and the balance is Fe and unavoidable impurities.

[0040] The present invention also provides a martensitic heat-resistant steel, characterized in that it is prepared by any of the above-mentioned methods for manufacturing martensitic heat-resistant steel.

[0041] In a third aspect, the present invention also provides the use of martensitic heat-resistant steel in ultra-supercritical steam turbine disks.

[0042] The manufacturing method of the martensitic heat-resistant steel provided by the present invention effectively improves the strength and toughness and plasticity of the prepared martensitic heat-resistant steel by accurately controlling the process conditions of smelting, AOD refining, LF refining, VD vacuum refining, forging and annealing, and effectively refines the grain structure of the heat-resistant steel. The grain size is 7.5 to 8.5, the total inclusions are 3 to 4.5, and the Rp 0.2 800MPa~900MPa, R m ≤1100MPa, A≥14%, Z≥40%, HBW280N / mm 2 ~305N / mm 2 , KV2 ≥ 30J, R m (400℃)≥650℃, providing solid and reliable material support for ultra-supercritical steam turbines, and is especially suitable for manufacturing ultra-supercritical steam turbine discs and other components, with high practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1The metallographic structure diagram of the 13Cr10Mo1W1VNbN heat-resistant steel prepared in Example 1;

[0044] Figure 2 This is the metallographic structure diagram of the 13Cr10Mo1W1VNbN heat-resistant steel prepared in Example 2. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0046] In order to better illustrate the present invention, further examples are given below.

[0047] Example 1

[0048] The embodiment of the present invention provides a 13Cr10Mo1W1VNbN heat-resistant steel, the chemical composition of which is:

[0049] C 0.118%, Si 0.06%, Mn 0.44%, P 0.007%, S 0.0004%, Cr 10.32%, Ni 0.72%, Mo 1.06%, W 0.96%, V 0.19%, Al 0.002%, N 0.05%, Nb 0.046%, O 0.0032%, H 0.00005%, and the balance is Fe and inevitable impurities.

[0050] The preparation steps of the above 13Cr10Mo1W1VNbN heat-resistant steel are as follows:

[0051] S1, add scrap steel and metal raw materials in proportion, control the temperature of the electric arc furnace to 1650℃, until all the raw materials in the furnace are turned into molten steel, take samples for analysis of all elements, control the C in the molten steel to be ≥1.5%, and then tap;

[0052] S2, adding molten steel into an AOD furnace, adding lime and fluorite in a mass ratio of 2:1, the total addition amount is 50kg / t, making slag, the slag making time is 6min, after removing the slag, adding ferrochrome, and then introducing a mixed gas of oxygen and argon in stages for blowing, the introduction order is 3:1→2:1→0.5:1→1:2→1:3 according to the volume ratio of oxygen and argon, the introduction time of each stage is 15min, and alloying elements are added in the order of W, Mo, V, and Nb during the blowing process, when C≤0.08% and Si≤0.02% in the molten steel, adding 1kg / t of aluminum particles, the reduction time is 10min, and then adding 2.5kg / t of lime, 10kg / t of fluorite, and 1kg / t of silicon-calcium blocks, the reduction time is 8min, and the temperature of the molten steel is controlled to be not less than 1500℃ during the reduction process;

[0053] S3, adding the molten steel into the LF refining bag, adding calcium silicon powder or aluminum powder for diffusion deoxidation, the specific steps are:

[0054] Add 2kg / t of calcium silicon powder to the molten steel for diffusion deoxidation, white slag, control the temperature at 1650℃, introduce a large flow of argon (flow ≥ 25L / min), stir for 5min, take samples for analysis of all elements, fine-tune the composition, heat to 1650℃, add 1.5kg / t of calcium silicon powder to continue diffusion deoxidation, take samples for analysis, add 0.6kg / t of calcium silicon powder again, keep the white slag for 30min, skim the slag, and put it into VD vacuum refining bag;

[0055] S4, evacuate to below 67Pa, introduce argon, soft blow for 26min, argon flow rate 18L / min, break the air, introduce nitrogen, control the nitrogen content in the molten steel to 0.046%, control the temperature of the molten steel to 1570℃ for pouring, demoulding, and obtain a steel ingot;

[0056] S5, first keep the steel ingot at 500℃ for 2h, then heat it to 830℃ at a rate of 70℃ / h, keep it for 2h, then heat it to 1170℃ at a rate of 70℃ / h, keep it for 3h, start forging, roughen the steel ingot from the original 1.8m to 1.2m, then stretch it to 1.9m, then return to the furnace and reheat it to 1125℃ and keep it for 3h, do the second roughening, roughen it from the original 1.9m to 1.3m, then stretch it to 2.4m, return to the furnace and reheat it to 1130℃ and keep it for 2h, do the third fire stretching, stretch it from the original 2.4m to 5.3m; after forging, air cool it to 500℃, put it into the annealing furnace, furnace cool it to 200℃, and perform the annealing process;

[0057] S6, heating the forging billet to 650°C at a rate of 75°C / min, keeping the temperature for 22h, then cooling it to 200°C at a rate of 40°C / min, air-cooling it to 160°C, then heating it to 650°C at a rate of 75°C / min, keeping the temperature for 26h, then cooling it to ≤200°C at a rate of 40°C / min, air-cooling it to 160°C;

[0058] S7, heat the forging to 1100°C, keep it warm for 1 hour, oil cool it to room temperature, heat the forging to 700°C, keep it warm for 2 hours, and air cool it to room temperature to obtain 13Cr10Mo1W1VNbN heat-resistant steel.

[0059] Example 2

[0060] The embodiment of the present invention provides a 13Cr10Mo1W1VNbN heat-resistant steel, the chemical composition of which is:

[0061] C 0.124%, Si 0.06%, Mn 0.44%, P 0.007%, S 0.0009%, Cr 10.33%, Ni 0.72%, Mo 1.04%, W 0.95%, V 0.19%, Al 0.002%, N 0.05%, Nb 0.044%, O 0.0031%, H 0.00007%, and the balance is Fe and inevitable impurities.

[0062] The preparation steps of the above 13Cr10Mo1W1VNbN heat-resistant steel are as follows:

[0063] S1, add scrap steel and metal raw materials in proportion, control the temperature of the electric arc furnace to 1550℃, until all the raw materials in the furnace are turned into molten steel, take samples to analyze all elements, control the C in the molten steel to be ≥1.5%, and then tap;

[0064] S2, adding molten steel into an AOD furnace, adding lime and fluorite in a mass ratio of 1.5:1, the total amount added is 60kg / t, making slag, the slag making time is 5min, after removing the slag, adding ferrochrome, and then introducing a mixed gas of oxygen and argon in stages for blowing, the introduction order is according to the volume ratio of oxygen and argon: 5:1→3:1→1:1→1:3→1:4, the introduction time of each stage is 25min, and alloy elements are added in the order of W, Mo, V, and Nb during the blowing process, when C≤0.08% and Si≤0.02% in the molten steel, adding 2kg / t of aluminum particles, the reduction time is 7min, and then adding 15kg / t of lime, 15kg / t of fluorite, and 0.5kg / t of silicon-calcium blocks, the reduction time is 5min, and the temperature of the molten steel is controlled to be not less than 1500°C during the reduction process;

[0065] S3, adding the molten steel into the LF refining bag, adding calcium silicon powder or aluminum powder for diffusion deoxidation, the specific steps are:

[0066] Add 1.5kg / t of calcium silicon powder to the molten steel for diffusion deoxidation, white slag, control the temperature at 1640℃, introduce a large flow of argon (flow ≥ 25L / min), stir for 4min, take samples for analysis of all elements, fine-tune the composition, heat to 1640℃, add 1kg / t of calcium silicon powder to continue diffusion deoxidation, take samples for analysis, add 0.5kg / t of calcium silicon powder again, keep the white slag for 20min, skim the slag, and put it into VD vacuum refining bag;

[0067] S4, evacuate to below 67Pa, introduce argon, soft blow for 20min, argon flow rate 15L / min, break the air, introduce nitrogen, control the nitrogen content in the molten steel to 0.05%, control the temperature of the molten steel to 1570℃ for pouring, demoulding, and obtain a steel ingot;

[0068] S5, first keep the steel ingot at 480℃ for 2.5h, then heat it to 820℃ at a rate of 80℃ / h, keep it for 3h, then heat it to 1160℃ at a rate of 80℃ / h, keep it for 4h, start forging, roughen the steel ingot from the original 1.8m to 1.1m, then stretch it to 1.7m, then return to the furnace and reheat it to 1130℃ and keep it for 3h, do the second roughening, roughen it from the original 1.7m to 0.9m, then stretch it to 1.7m, return to the furnace and reheat it to 1135℃ and keep it for 2h, do the third fire stretching, stretch it from the original 1.7m to 4.2m; after forging, air cool it to 520℃, put it into the annealing furnace, furnace cool it to 250℃, and perform the annealing process;

[0069] S6, heating the forging billet to 645°C at a rate of 70°C / min, keeping the temperature for 21h, then cooling it to 200°C at a rate of 60°C / min, air-cooling it to 160°C, then heating it to 645°C at a rate of 70°C / min, keeping the temperature for 27h, then cooling it to ≤200°C at a rate of 60°C / min, air-cooling it to 160°C;

[0070] S7, heat the forging to 1070℃, keep it for 1h, oil cool it to room temperature, heat the forging to 700℃, keep it for 2h, air cool it to room temperature, and obtain 13Cr10Mo1W1VNbN heat-resistant steel.

[0071] Example 3

[0072] The embodiment of the present invention provides a 13Cr10Mo1W1VNbN heat-resistant steel, the chemical composition of which is:

[0073] C 0.129%, Si 0.06%, Mn 0.44%, P 0.007%, S 0.0017%, Cr 10.22%, Ni 0.71%, Mo 1.06%, W 0.96%, V 0.19%, Al 0.002%, N 0.051%, Nb 0.046%, O 0.0031%, H 0.00009%, and the balance is Fe and inevitable impurities.

[0074] The preparation steps of the above 13Cr10Mo1W1VNbN heat-resistant steel are as follows:

[0075] S1, add scrap steel and metal raw materials in proportion, control the temperature of the electric arc furnace to 1700℃, wait until all the raw materials in the furnace are transformed into molten steel, take samples to analyze all elements, control the C in the molten steel to be ≥1.5%, and then tap;

[0076] S2, adding molten steel into an AOD furnace, adding lime and fluorite in a mass ratio of 2.5:1, the total amount added is 40kg / t, making slag, the slag making time is 8min, after removing the slag, adding ferrochrome, and then introducing a mixed gas of oxygen and argon in stages for blowing, the introduction order is 7:1→4:1→1.5:1→1:4→1:5 according to the volume ratio of oxygen and argon, the introduction time of each stage is 20min, and alloy elements are added in the order of W, Mo, V, and Nb during the blowing process, when C≤0.08% and Si≤0.02% in the molten steel, adding 1kg / t of aluminum particles, the reduction time is 15min, and then adding 25kg / t of lime, 12kg / t of fluorite, and 0.8kg / t of silicon-calcium blocks, the reduction time is 10min, and the temperature of the molten steel is controlled to be not less than 1500℃ during the reduction process;

[0077] S3, adding the molten steel into the LF refining bag, adding calcium silicon powder or aluminum powder for diffusion deoxidation, the specific steps are:

[0078] Add 1.5kg / t of calcium silicon powder to the molten steel for diffusion deoxidation, white slag, control the temperature at 1630℃, introduce a large flow of argon (flow ≥ 25L / min), stir for 3min, take samples to analyze all elements, fine-tune the composition, heat to 1630℃, add 0.5kg / t of calcium silicon powder to continue diffusion deoxidation, take samples for analysis, add 1kg / t of calcium silicon powder again, keep the white slag for 25min, skim the slag, and put it into VD vacuum refining bag;

[0079] S4, evacuate to below 67Pa, introduce argon, soft blow for 25min, argon flow rate 16L / min, break the air, introduce nitrogen, control the nitrogen content in the molten steel to 0.05%, control the temperature of the molten steel to 1575℃ for pouring, demoulding, and obtain a steel ingot;

[0080] S5, first keep the steel ingot at 520℃ for 1.5h, then heat it to 850℃ at a rate of 100℃ / h, keep it for 2h, then heat it to 1180℃ at a rate of 100℃ / h, keep it for 2h, start forging, roughen the steel ingot from the original 1.8m to 0.9m, then stretch it to 1.4m, then return to the furnace and reheat it to 1120℃ and keep it for 3h, do the second roughening, roughen it from the original 1.4m to 0.9m, then stretch it to 1.7m, return to the furnace and reheat it to 1130℃ and keep it for 3h, do the third fire stretching, stretch it from the original 1.7m to 4m; after forging, air cool it to 490℃, put it into the annealing furnace, furnace cool it to 230℃, and perform the annealing process;

[0081] S6, heating the forging billet to 660°C at a rate of 90°C / min, keeping the temperature for 20h, then cooling it to 250°C at a rate of 50°C / min, air-cooling it to 180°C, then heating it to 660°C at a rate of 90°C / min, keeping the temperature for 25h, then cooling it to ≤200°C at a rate of 50°C / min, air-cooling it to 180°C;

[0082] S7, heat the forging to 1100℃, keep it warm for 1h, oil cool it to room temperature, heat the forging to 670℃, keep it warm for 2h, air cool it to room temperature, and obtain 13Cr10Mo1W1VNbN heat-resistant steel.

[0083] Example 4

[0084] The embodiment of the present invention provides a 13Cr10Mo1W1VNbN heat-resistant steel, the chemical composition of which is:

[0085] C 0.123%, Si 0.06%, Mn 0.44%, P 0.007%, S 0.0008%, Cr 10.52%, Ni 0.71%, Mo 1.06%, W 0.96%, V 0.19%, Al 0.002%, N 0.049%, Nb 0.046%, O 0.0029%, H 0.00006%, and the balance is Fe and inevitable impurities.

[0086] The preparation steps of the above 13Cr10Mo1W1VNbN heat-resistant steel are as follows:

[0087] S1, add scrap steel and metal raw materials in proportion, control the temperature of the electric arc furnace to 1600℃, until all the raw materials in the furnace are turned into molten steel, take samples to analyze all elements, control the C in the molten steel to be ≥1.5%, and then tap;

[0088] S2, adding molten steel into an AOD furnace, adding lime and fluorite in a mass ratio of 2.2:1, the total addition amount is 30kg / t, making slag, the slag making time is 10min, after removing the slag, adding ferrochrome, and then introducing a mixed gas of oxygen and argon in stages for blowing, the introduction order is 3:1→2:1→1:1→1:3→1:6 according to the volume ratio of oxygen and argon, the introduction time of each stage is 18min, and alloy elements are added in the order of W, Mo, V, and Nb during the blowing process, when C≤0.08% and Si≤0.02% in the molten steel, adding 1.5kg / t of aluminum particles, the reduction time is 10min, and then adding 18kg / t of lime, 18kg / t of fluorite, and 1kg / t of silicon-calcium blocks, the reduction time is 6min, and the temperature of the molten steel is controlled to be not less than 1500°C during the reduction process;

[0089] S3, adding the molten steel into the LF refining bag, adding calcium silicon powder or aluminum powder for diffusion deoxidation, the specific steps are:

[0090] Add 1.6kg / t of calcium silicon powder to the molten steel for diffusion deoxidation, white slag, control the temperature at 1650℃, introduce a large flow of argon (flow ≥ 25L / min), stir for 5min, take samples for analysis of all elements, fine-tune the composition, heat to 1650℃, add 1.2kg / t of calcium silicon powder to continue diffusion deoxidation, take samples for analysis, add 0.6kg / t of calcium silicon powder again, keep the white slag for 28min, skim the slag, and put it into VD vacuum refining bag;

[0091] S4, evacuate to below 67Pa, introduce argon, soft blow for 30min, argon flow rate 15L / min, break the air, introduce nitrogen, control the nitrogen content in the molten steel to 0.05%, control the temperature of the molten steel to 1565℃ for pouring, demoulding, and obtain a steel ingot;

[0092] S5, first keep the steel ingot at 510℃ for 2h, then heat it to 800℃ at a rate of 60℃ / h, keep it for 3h, then heat it to 1160℃ at a rate of 60℃ / h, keep it for 4h, start forging, roughen the steel ingot from the original 1.8m to 1.0m, then stretch it to 1.4m, then return to the furnace and reheat it to 1140℃ and keep it for 2h, do the second roughening, roughen it from the original 1.4m to 0.8m, then stretch it to 1.5m, return to the furnace and reheat it to 1140℃ and keep it for 2h, do the third fire stretching, stretch it from the original 1.5m to 3.7m; after forging, air cool it to 480℃, put it into the annealing furnace, furnace cool it to 240℃, and perform the annealing process;

[0093] S6, heating the forging billet to 640°C at a rate of 60°C / min, keeping the temperature for 25h, then cooling it to 240°C at a rate of 55°C / min, air-cooling it to 175°C, then heating it to 640°C at a rate of 60°C / min, keeping the temperature for 30h, then cooling it to ≤200°C at a rate of 55°C / min, air-cooling it to 175°C;

[0094] S7, heat the forging to 1100℃, keep it warm for 1h, oil cool it to room temperature, heat the forging to 720℃, keep it warm for 3h, air cool it to room temperature, and obtain 13Cr10Mo1W1VNbN heat-resistant steel.

[0095] The head and tail components and gas balance of the rods produced in Examples 1 to 4 were checked to meet the standard requirements.

[0096] The inclusion grade and grain size of the bars produced in Examples 1 to 4 were tested, and the results are shown in Table 1.

[0097] Table 1

[0098]

[0099]

[0100] As can be seen from the above table, in the rods produced in Examples 1 to 4, the B fine level is 1 to 1.5, the B coarse level is 0 to 1.5, the D fine level is 1.5, the D coarse level is 0.5, the total inclusions are 3 to 4.5, the grain size is 7.5 to 8.5, and there is no mixed crystal phenomenon. The metallographic structure diagrams of the rods prepared in Examples 1 and 2 are as follows: Figure 1-2 shown.

[0101] The performance tests of the bars produced in Examples 1 to 4 were carried out according to GB / T 228.1 metal material tensile test, GB / T 229 metal material Charpy pendulum impact test method, GB / T 231.1 metal material Brinell hardness test, and GB / T 2975 steel grade steel product mechanical properties test sampling location and sample preparation standards. The results are shown in Table 2.

[0102] Table 2

[0103]

[0104] Note: The two data in the same cell in the table are the maximum and minimum values ​​of 15 bars prepared in each embodiment randomly sampled for testing.

[0105] According to the GB / T 4162A grade standard, the flaw detection pass rate of the bars prepared in Examples 1 to 4 is 100%.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for producing martensitic heat-resistant steel, characterized in that: The steps include: S1, melting the raw materials in an electric arc furnace to obtain molten steel with a C content ≥ 1.5%; S2, adding slag-making auxiliary materials to the molten steel for slag-making and decarburization, after slag-making, slag-making is removed, chromium-carbon alloy is added, and then a mixed gas of oxygen and argon with a reduced oxygen concentration gradient is introduced in stages for blowing, W, Mo, V, and Nb are added in sequence during the blowing process, and when C≤0.08% and Si≤0.02% in the molten steel, aluminum particles are added for primary reduction, and after the primary reduction is completed, slag-making auxiliary materials and silicon-calcium alloy are added for secondary reduction to obtain reduced molten steel; S3, subjecting the reduced molten steel to LF refining and VD vacuum refining to obtain molten steel with Al≤0.01%, Si≤0.12%, O≤0.0035%, and H≤0.0001%, and casting to obtain a steel ingot; S4, heating the steel ingot to 1160°C-1180°C and keeping the temperature, then roughening and drawing to obtain a first-fire forging billet; heating the first-fire forging billet to 1120°C-1140°C and keeping the temperature, then roughening and drawing to obtain a second-fire forging billet; heating the second-fire forging billet to 1120°C-1140°C and keeping the temperature, then drawing to obtain a third-fire forging billet; after forging, air-cooling to 480°C-520°C, loading into an annealing furnace, and furnace-cooling to 200°C-250°C; S5, heating the forging billet to 640°C-660°C at a rate of 60°C / min-90°C / min, keeping the temperature for 20h-25h, then cooling the billet to 200°C-250°C at a rate of 40°C / min-60°C / min, air-cooling the billet to 160°C-180°C, then heating the billet to 640°C-660°C at a rate of 60°C / min-90°C / min, keeping the temperature for 25h-30h, then cooling the billet to ≤20 ...60°C / min, air-cooling the billet to 160°C-180°C, then heating the billet to 640°C-660°C at a rate of 60°C / min-90 S5, subjecting the forging to a modulated heat treatment to obtain a martensitic heat-resistant steel.

2. The method for producing martensitic heat-resistant steel according to claim 1, characterized in that: In S2, the slag-making auxiliary materials include lime and fluorite.

3. The method for producing martensitic heat-resistant steel according to claim 2, characterized in that: In S2, in the slag making and decarbonization process, the total amount of lime and fluorite added is 30kg / t to 60kg / t, wherein the mass ratio of lime to fluorite is (1.5 to 2.5):1; and / or In S2, in the secondary reduction process, the amount of lime added is 15kg / t to 25kg / t, and the amount of fluorite added is 10kg / t to 18kg / t.

4. The method for producing martensitic heat-resistant steel according to claim 1, characterized in that: In S2, the amount of aluminum particles added is 1kg / t to 2kg / t; and / or In S2, the amount of silicon-calcium alloy added is 0.5kg / t to 1kg / t; and / or In S2, the time of the primary reduction is 7 min to 15 min; and / or In S2, the secondary reduction time is 5 min to 10 min.

5. The method for producing martensitic heat-resistant steel according to claim 1, characterized in that: In S2, the step of introducing a mixed gas of oxygen and argon with a decreasing oxygen concentration gradient in stages specifically comprises the following steps: A mixed gas of oxygen and argon is introduced into the molten steel in the order of the volume ratio of oxygen to argon being (3-7):1, (2-4):1, (0.5-1.5):1, 1:(2-4), and 1:(2-6). The blowing time for each stage is 15 min to 25 min.

6. The method for producing martensitic heat-resistant steel according to claim 1, characterized in that: In S3, during the LF refining, calcium silicon powder or aluminum powder is added to the reduced molten steel for diffusion deoxidation 2 to 3 times to control Al≤0.01%, Si≤0.12%, and O≤0.0035% in the molten steel; In the VD vacuum refining, under the condition of vacuum degree ≤ 67Pa, argon gas is introduced into the molten steel at a flow rate of 15L / min to 20L / min, and the argon blowing time is 20min to 30min. After breaking the air, nitrogen gas is introduced to control the nitrogen content in the molten steel to be 0.045% to 0.06%.

7. The method for producing martensitic heat-resistant steel according to claim 1, characterized in that: In S4, the temperature is raised to 1160°C to 1180°C by a gradient heating method, specifically comprising the following steps: firstly, the steel ingot is kept at 480°C to 520°C for 1.5h to 2.5h, then the temperature is raised to 800°C to 850°C at a rate of 60°C / h to 100°C / h, and the temperature is kept for 2h to 3h, and then the temperature is raised to 1160°C to 1180°C at a rate of 60°C / h to 100°C / h, and the temperature is kept for 2h to 4h; and / or In S4, the deformation of the first fire roughing is 30% to 40%, and the deformation of the elongation is 40% to 60%; the deformation of the second fire roughing is 30% to 50%, and the deformation of the elongation is 80% to 90%; the deformation of the third fire elongation is 120% to 150%; and / or In S5, the heat treatment specifically includes: firstly heating the forging to 1050°C-1100°C, keeping it at that temperature for 1h-2h, and cooling it to room temperature with oil; then heating the forging to 650°C-750°C, keeping it at that temperature for 2h-3h, and cooling it to room temperature with air.

8. The method for producing martensitic heat-resistant steel according to claim 1, characterized in that: The chemical composition of the martensitic heat-resistant steel is: C 0.11%-0.14%, Si≤0.12%, Mn 0.4%-0.5%, S≤0.005%, P≤0.01%, Cr10.0%-10.6%, Ni 0.7%-0.8%, Mo 1.0%-1.1%, W0.9%-1.0%, Al≤0.01%, N0.045%-0.060%, Nb 0.04%-0.06%, O≤0.0035%, H≤0.0001%, and the balance is Fe and unavoidable impurities.

9. A martensitic heat-resistant steel, characterized in that: The martensitic heat-resistant steel is prepared by the method for producing martensitic heat-resistant steel according to any one of claims 1 to 8.

10. Use of the martensitic heat-resistant steel according to claim 9 in an ultra-supercritical steam turbine disk.

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