A martensitic heat-resistant steel and its manufacturing method and application

Abstract

The present invention relates to the technical field of heat-resistant stainless steel, and specifically discloses a martensitic heat-resistant steel, a manufacturing method thereof, and an application thereof. 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 precisely 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, with a grain size of 7.5 to 8.5, a total inclusion content of 3 to 4.5, and an Rp of 0.05. 0.2 800MPa~900MPa, R m ≤1100MPa, A≥14%, Z≥40%, HBW is 280N / mm 2 ~305N / mm 2 , KV2≥30J, R m (400℃)≥650℃, providing solid and reliable material support for ultra-supercritical steam turbines, especially suitable for manufacturing ultra-supercritical steam turbine discs and other components, with high practical value.

Description

Technical Field

[0001] The present 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 continued growth of global energy demand and 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 the turbine.

[0003] As a new type of iron-based heat-resistant alloy, 13Cr10Mo1W1VNbN heat-resistant steel exhibits good high-temperature strength, creep resistance, oxidation resistance and corrosion resistance under the synergistic effect of multiple alloying 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] Current processes for producing 13Cr10Mo1W1VNbN heat-resistant steel often lead to a coarse columnar structure. This uneven structure, characterized by numerous internal defects and stress concentration points, significantly reduces the steel's plasticity and toughness, limiting further improvements in its overall performance. Furthermore, the steel's high alloying degree and narrow suitable hot working temperature range make processing difficult, leading to a high risk of cracking and impacting its long-term stability. Therefore, it is necessary to develop a novel method for producing 13Cr10Mo1W1VNbN heat-resistant steel that meets the high-performance heat-resistant steel requirements of ultra-supercritical steam turbines. 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 its manufacturing method and application.

[0006] To solve the above technical problems, the technical solutions provided by the embodiments of the present invention are:

[0007] In a first aspect, the present invention provides a method for manufacturing 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 carbon content ≥1.5%;

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

[0010] S3, performing LF refining and VD vacuum refining on the reduced molten steel 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 1160-1180° C. and keeping the temperature, then roughening and drawing to obtain a first-fire forging billet; heating the first-fire forging billet to 1120-1140° C. and keeping the temperature, then roughening and drawing to obtain a second-fire forging billet; heating the second-fire forging billet to 1120-1140° C. and keeping the temperature, then drawing to obtain a third-fire forging billet; after forging, air-cooling to 480-520° C., charging into an annealing furnace, and furnace cooling to 200-250° 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 20-25 hours, then cooling the billet to 200-250°C at a rate of 40°C / min-60°C / min, removing the billet from the furnace and air-cooling the billet to 160-180°C, then heating the billet to 640-660°C at a rate of 60°C / min-90°C / min, keeping the temperature for 25-30 hours, then cooling the billet to ≤200°C at a rate of 40°C / min-60°C / min, removing the billet from the furnace and air-cooling the billet;

[0013] S5, performing a modulation heat treatment on the forging to obtain martensitic heat-resistant steel.

[0014] Compared with the prior art, the manufacturing method of martensitic heat-resistant steel provided by the present invention, during the AOD refining process, by adopting the method of blowing in oxygen-containing mixed gas with gradually decreasing oxygen concentration in stages, controlling the addition time of each alloying 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 and improve the purity of the molten steel. At the same time, it can also minimize the burning and segregation of alloying elements, which is conducive to accurately controlling the content of alloying elements. By controlling Al, Si, O, and H in a lower range through LF refining and VD vacuum refining, the stability of the material's lattice structure at high temperatures 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 temperatures. At the same time, it can also reduce the thermal processing window of the material and reduce the generation of thermal processing cracks. Performing triple-annealing at a specific temperature is beneficial for grain refinement and microstructure homogenization. Furthermore, the specific annealing regime employed causes the grains in the steel to recrystallize, allowing previously elongated or broken grains to re-nucleate and grow, forming fine equiaxed crystals. Simultaneously, the specific annealing regime promotes the uniform precipitation of alloy carbides (such as Cr-Mo-WV-Nb composite carbides). These fine and evenly distributed precipitates act as pinning points, hindering the movement of grain boundaries and further refining the grains. They also contribute to precipitation strengthening, thereby increasing the material's strength.

[0015] The present invention effectively reduces the contents of C, Al, Si, O and H in molten steel by controlling the oxygen blowing and decarburization method during the AOD smelting process, the order of adding alloys and the use of a secondary reduction method, thereby controlling the level of inclusions, improving the purity of the molten steel and facilitating the precise control of the content of alloying elements. At the same time, the use of three-fire drawing and a specific annealing system effectively refines the grains, further homogenizes the structure, significantly reduces thermal stress and crack risks, and thus significantly improves the plasticity and toughness of the material, greatly improving the comprehensive performance of the 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 1 kg / t to 2 kg / t.

[0021] Furthermore, in S2, the amount of the silicon-calcium alloy added is 0.5 kg / t to 1 kg / 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 for 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 implementation of strengthening mechanisms such as precipitation strengthening, thereby facilitating the preparation of higher performance steel.

[0027] Furthermore, in S2, the step of introducing a mixed gas of oxygen and argon with a decreasing oxygen concentration gradient in stages specifically includes 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 15-25 minutes.

[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 and gradual decarburization method not only achieves efficient decarburization, but also helps reduce the oxidation loss of alloying elements in the molten steel. At the same time, through the subsequent two reduction methods, it is also beneficial to make it easier for the oxidized alloying elements to return to the molten steel, further reducing the loss of alloying elements. In addition, the phased and gradual decarburization method can also make the molten steel agitation relatively stable. The inclusions generated in the molten steel (such as oxide inclusions) are more likely to float to the surface of the molten steel under the action of buoyancy and molten steel convection, enter the slag, and be removed. This avoids the situation where the inclusions are re-mixed into the molten steel or difficult to effectively separate due to violent oxygen blowing and stirring, thereby 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 silicate powder or aluminum powder is added to the reduced molten steel in 2 to 3 times for diffusion deoxidation, and Al, Si, and O in the molten steel are controlled to be ≤0.01%, ≤0.12%, and ≤0.0035%.

[0032] Furthermore, in the VD vacuum refining, under the condition of vacuum degree ≤67Pa, argon 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 is introduced to control the nitrogen content in the molten steel to 0.045% to 0.06%.

[0033] By using the preferred VD vacuum degassing method, 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] Furthermore, in S4, the temperature is raised to 1160℃~1180℃ by a gradient heating method, which specifically includes the following steps: first, the steel ingot is kept at 480℃~520℃ for 1.5h~2.5h, then the temperature is raised to 800℃~850℃ at a rate of 60℃ / h~100℃ / h, and the temperature is kept for 2h~3h, and then the temperature is raised to 1160℃~1180℃ at a rate of 60℃ / h~100℃ / h, and the temperature is kept for 2h~4h.

[0035] The optimized heating schedule provides a good foundation for deformation during the drawing process, ensuring more coordinated structural changes in the steel. Furthermore, the optimized heating method helps improve the steel's toughness and ductility, preventing structural defects during the drawing process and thus reducing the likelihood of cracks during subsequent processing and use.

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

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

[0038] Furthermore, in S5, the heat treatment specifically includes: first heating the forging to 1050°C to 1100°C, keeping it warm for 1h to 2h, oil cooling it to room temperature, then heating the forging to 650°C to 750°C, keeping it warm for 2h to 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 discs.

[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 precisely 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%, HBW is 280N / mm 2 ~305N / mm 2 , KV2≥30J, R m (400℃)≥650℃, providing solid and reliable material support for ultra-supercritical steam turbines, especially suitable for manufacturing ultra-supercritical steam turbine discs and other components, with high practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1This is the 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 solutions 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 intended 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 having the following chemical composition:

[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-mentioned 13Cr10Mo1W1VNbN heat-resistant steel are as follows:

[0051] S1, adding scrap steel and metal raw materials in proportion, controlling the temperature of the electric arc furnace to 1650℃, until all the raw materials in the furnace are converted into molten steel, taking samples for full element analysis, controlling the carbon content of the molten steel to be ≥1.5%, and then tapping;

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

[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 as follows:

[0054] Add 2kg / t of calcium silicate powder to the molten steel for diffusion deoxidation, white slag, control the temperature at 1650℃, introduce a large flow of argon (flow rate ≥ 25L / min), stir for 5 minutes, take samples for analysis of all elements, fine-tune the composition, heat to 1650℃, add 1.5kg / t of calcium silicate powder to continue diffusion deoxidation, take samples for analysis, add 0.6kg / t of calcium silicate powder again, keep the slag white for 30 minutes, skim off the slag, and put it into the 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 molten steel temperature to 1570℃ for casting, demoulding, and obtain a steel ingot;

[0056] S5, first, the steel ingot is kept at 500℃ for 2h, then heated to 830℃ at a rate of 70℃ / h, kept for 2h, and then heated to 1170℃ at a rate of 70℃ / h, kept for 3h, and then forging begins. The steel ingot is upset from the original 1.8m to 1.2m, and then stretched to 1.9m. After that, it is returned to the furnace and reheated to 1125℃ and kept for 3h, and then upset for the second time, from the original 1.9m to 1.3m, and then stretched to 2.4m. After that, it is returned to the furnace and reheated to 1130℃ and kept for 2h, and then stretched for the third time, from the original 2.4m to 5.3m. After forging, it is air-cooled to 500℃, loaded into an annealing furnace, furnace-cooled to 200℃, and annealing process is performed.

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

[0058] S7, heat the forging to 1100℃, keep it warm for 1 hour, oil cool it to room temperature, heat the forging to 700℃, 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 having the following chemical composition:

[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 unavoidable impurities.

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

[0063] S1, adding scrap steel and metal raw materials in proportion, controlling the temperature of the electric arc furnace to 1550℃, until all the raw materials in the furnace are converted into molten steel, taking samples for full element analysis, controlling the carbon content of the molten steel to be ≥1.5%, and then tapping;

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

[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 as follows:

[0066] Add 1.5kg / t of calcium silicate powder to the molten steel for diffusion deoxidation, keep the slag white, control the temperature at 1640℃, introduce a large flow of argon (flow rate ≥ 25L / min), stir for 4 minutes, take samples for analysis of all elements, fine-tune the composition, heat to 1640℃, add 1kg / t of calcium silicate powder to continue diffusion deoxidation, take samples for analysis, add 0.5kg / t of calcium silicate powder again, keep the slag white for 20 minutes, skim off the slag, and put it into the 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 molten steel temperature to 1570℃ for casting, demoulding, and obtain a steel ingot;

[0068] S5, first, the steel ingot is kept at 480℃ for 2.5h, then heated to 820℃ at a rate of 80℃ / h, kept for 3h, and then heated to 1160℃ at a rate of 80℃ / h, kept for 4h, and then forging begins. The steel ingot is upset from the original 1.8m to 1.1m, and then stretched to 1.7m. After returning to the furnace and reheating to 1130℃ and keeping for 3h, a second upset is performed, from the original 1.7m to 0.9m, and then stretched to 1.7m. After returning to the furnace and reheating to 1135℃ and keeping for 2h, a third stretch is performed, from the original 1.7m to 4.2m. After forging, it is air-cooled to 520℃, loaded into an annealing furnace, furnace-cooled to 250℃, and annealing process is performed.

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

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

[0071] Example 3

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

[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-mentioned 13Cr10Mo1W1VNbN heat-resistant steel are as follows:

[0075] S1, adding scrap steel and metal raw materials in proportion, controlling the temperature of the electric arc furnace to 1700℃, until all the raw materials in the furnace are converted into molten steel, taking samples for full element analysis, controlling the carbon content of the molten steel to be ≥1.5%, and then tapping;

[0076] S2, adding molten steel to an AOD furnace, adding lime and fluorite in a mass ratio of 2.5:1, with a total addition amount of 40kg / t, making slag, and the slag making time is 8min. After the slag is pulled out, ferrochrome is added, and then a mixed gas of oxygen and argon is introduced in stages for blowing. The introduction order is as follows according to the volume ratio of oxygen and argon: 7:1→4:1→1.5:1→1:4→1:5, and the introduction time of each stage is 20min. During the blowing process, alloying elements are added in the order of W, Mo, V, and Nb. When C≤0.08% and Si≤0.02% in the molten steel, 1kg / t of aluminum particles is added, and the reduction time is 15min. Then 25kg / t of lime, 12kg / t of fluorite, and 0.8kg / t of silicon-calcium blocks are added, and the reduction time is 10min. During the reduction process, the temperature of the molten steel is controlled to be not less than 1500°C;

[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 as follows:

[0078] Add 1.5kg / t of calcium silicate powder to the molten steel for diffusion deoxidation, keep the slag white, control the temperature at 1630℃, introduce a large flow of argon (flow rate ≥ 25L / min), stir for 3 minutes, take samples for analysis of all elements, fine-tune the composition, heat to 1630℃, add 0.5kg / t of calcium silicate powder to continue diffusion deoxidation, take samples for analysis, add 1kg / t of calcium silicate powder again, keep the slag white for 25 minutes, skim off the slag, and put it into the 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 molten steel temperature to 1575℃ for casting, demoulding, and obtain a steel ingot;

[0080] S5, first, the steel ingot is kept at 520℃ for 1.5h, then heated to 850℃ at a rate of 100℃ / h, kept warm for 2h, and then heated to 1180℃ at a rate of 100℃ / h, kept warm for 2h, and then forging begins. The steel ingot is upset from the original 1.8m to 0.9m, and then stretched to 1.4m. After that, it is returned to the furnace and reheated to 1120℃ and kept warm for 3h, and then upset for the second time, from the original 1.4m to 0.9m, and then stretched to 1.7m. After that, it is returned to the furnace and reheated to 1130℃ and kept warm for 3h, and then stretched for the third time, from the original 1.7m to 4m. After forging, it is air-cooled to 490℃, loaded into an annealing furnace, furnace-cooled to 230℃, and annealing process is performed.

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

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

[0083] Example 4

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

[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 unavoidable impurities.

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

[0087] S1, adding scrap steel and metal raw materials in proportion, controlling the temperature of the electric arc furnace to 1600℃, until all the raw materials in the furnace are converted into molten steel, taking samples for full element analysis, controlling the carbon content of the molten steel to be ≥1.5%, and then tapping;

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

[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 as follows:

[0090] Add 1.6 kg / t of calcium silicate powder to the molten steel for diffusion deoxidation, keep the slag white, control the temperature at 1650°C, introduce a large flow of argon (flow rate ≥ 25 L / min), stir for 5 minutes, take samples for analysis of all elements, fine-tune the composition, heat to 1650°C, add 1.2 kg / t of calcium silicate powder to continue diffusion deoxidation, take samples for analysis, add 0.6 kg / t of calcium silicate powder again, keep the slag white for 28 minutes, skim off the slag, and put it into the 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 molten steel temperature to 1565℃ for casting, demoulding, and obtain a steel ingot;

[0092] S5, first, the steel ingot is kept at 510℃ for 2h, then heated to 800℃ at a rate of 60℃ / h, kept for 3h, and then heated to 1160℃ at a rate of 60℃ / h, kept for 4h, and then forging begins. The steel ingot is upset from the original 1.8m to 1.0m, and then stretched to 1.4m. After that, it is returned to the furnace and reheated to 1140℃ and kept for 2h, and then upset for the second time, from the original 1.4m to 0.8m, and then stretched to 1.5m. After that, it is returned to the furnace and reheated to 1140℃ and kept for 2h, and then stretched for the third time, from the original 1.5m to 3.7m. After forging, it is air-cooled to 480℃, loaded into an annealing furnace, furnace-cooled to 240℃, and annealing process is performed.

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

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

[0095] The head and tail composition and gas balance of the rods produced in Examples 1 to 4 were tested 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 table above, the B fineness level in the rods produced in Examples 1 to 4 is 1 to 1.5, the B coarseness level is 0 to 1.5, the D fineness level is 1.5, the D coarseness 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 organization diagrams of the rods prepared in Examples 1 and 2 are shown as follows: Figures 1 and 2 shown.

[0101] The bars produced in Examples 1 to 4 were subjected to performance tests in accordance with 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 randomly sampled and tested in each example.

[0105] According to the GB / T 4162A standard, the flaw detection test of the bars prepared in Examples 1 to 4 was conducted with a qualified rate of 100%.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection 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 carbon content ≥1.5%; S2, adding molten steel to an AOD furnace, adding slag-making auxiliary materials to the molten steel for slag decarburization, skimming the slag after slag formation, adding chromium-carbon alloy, and then introducing a mixed gas of oxygen and argon with a reduced oxygen concentration gradient in stages for blowing, adding W, Mo, V, and Nb in sequence during the blowing process, and when C≤0.08% and Si≤0.02% in the molten steel, adding aluminum particles for primary reduction, and after the primary reduction is completed, adding slag-making auxiliary materials and silicon-calcium alloy for secondary reduction to obtain reduced molten steel; S3, performing LF refining and VD vacuum refining on the reduced molten steel 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, gradually heating the steel ingot to 1160° C.-1180° C. and keeping the temperature, then performing 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 performing 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 performing 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, taking it out of the furnace and air-cooling it 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 ≤200°C at a rate of 40°C / min~60°C / min, taking it out of the furnace and air-cooling it; S6, subjecting the forging to quenching and tempering heat treatment to obtain martensitic heat-resistant steel; In S2, the mixed gas of oxygen and argon is introduced into the molten steel by side blowing, which specifically includes 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 (3-7):1, (2-4):1, (0.5-1.5):1, 1:(2-4), and 1:(2-6). The blowing time of each stage is 15-25 minutes. In S4, the temperature is raised to 1160℃~1180℃ in a gradient heating manner, which specifically includes the following steps: first, the steel ingot is kept at 480℃~520℃ for 1.5h~2.5h, then the temperature is raised to 800℃~850℃ at a rate of 60℃ / h~100℃ / h, and the temperature is kept for 2h~3h, and then the temperature is raised to 1160℃~1180℃ at a rate of 60℃ / h~100℃ / h, and the temperature is kept for 2h~4h.

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

3. The method for producing martensitic heat-resistant steel according to claim 2, wherein: 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~25kg / t, and the amount of fluorite added is 10kg / t~18kg / t.

4. The method for producing martensitic heat-resistant steel according to claim 1, wherein: In S2, the amount of aluminum particles added is 1kg / t to 2kg / t; and / or In S2, the amount of the silicon-calcium alloy added is 0.5kg / t to 1kg / t; and / or In S2, the time for 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, wherein: In S3, during the LF refining, calcium silicate powder or aluminum powder is added to the reduced molten steel in 2 to 3 times for diffusion deoxidation, and Al, Si, and O in the molten steel are controlled to be ≤0.01%, ≤0.12%, and ≤0.0035%; During the VD vacuum refining, argon is introduced into the molten steel at a flow rate of 15 L / min to 20 L / min under the condition of a vacuum degree of ≤67 Pa, and the argon blowing time is 20 min to 30 min. After breaking the air, nitrogen is introduced to control the nitrogen content in the molten steel to be 0.045% to 0.06%.

6. The method for producing martensitic heat-resistant steel according to claim 1, wherein: In S4, the deformation of the first fire is 30% to 40%, and the deformation of the elongation is 40% to 60%; the deformation of the second fire is 30% to 50%, and the deformation of the elongation is 80% to 90%; the deformation of the third fire is 120% to 150%; and / or In S6, the heat treatment specifically includes: first heating the forging to 1050°C~1100°C, keeping it warm for 1h~2h, oil cooling to room temperature, then heating the forging to 650°C~750°C, keeping it warm for 2h~3h, and air cooling to room temperature.

7. The method for producing martensitic heat-resistant steel according to claim 1, wherein: 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%, Cr 10.0%-10.6%, Ni 0.7%-0.8%, Mo 1.0%-1.1%, W 0.9%-1.0%, V 0.15%-0.25%, Al≤0.01%, N 0.045%-0.060%, Nb 0.04%-0.06%, O≤0.0035%, H≤0.0001%, and the balance is Fe and unavoidable impurities.

8. A martensitic heat-resistant steel, characterized in that: The martensitic heat-resistant steel is prepared by the method for producing the martensitic heat-resistant steel according to any one of claims 1 to 7.

9. Use of the martensitic heat-resistant steel according to claim 8 in an ultra-supercritical steam turbine disk.

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