A martensitic heat-resistant steel and a method for producing the same

Abstract

A martensitic heat-resistant steel is characterized in that the chemical composition and mass percentage of the martensitic heat-resistant steel are as follows: C 0.08-0.12%, Si 0.8-1.2%, Mn 0.3-0.5%, P≤0.008%, S≤0.005%, Cr 8.7-9.3%, W 2.7-3.3%, Mo 1.8-2.2%, Nb 0.05-0.10%, Ta 0.03-0.05%, V 0.08-0.12%, La 0.05-0.10%, Ce 0.01-0.05%, La+Ce≥0.08%, B 0.005-0.010%, N 0.010-0.015%, and the balance being Fe and inevitable impurities. The martensitic heat-resistant steel has excellent comprehensive properties such as strength and toughness, high-temperature oxidation resistance and the like.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically to the field of martensitic heat-resistant steel technology. Background Technology

[0002] Currently, thermal power generation is the mainstay of the power supply structure, and how to improve the efficiency of coal-fired power conversion has become one of the urgent problems to be solved.

[0003] Supercritical and ultra-supercritical generator sets have a coal conversion efficiency far higher than that of traditional generator sets. A key issue restricting the development of supercritical and ultra-supercritical generator sets is the material preparation technology, especially the production and research and development of key components such as turbine rotors and large-diameter boiler pipes. The materials are required to maintain high strength and resistance to oxidation and corrosion when in steam at 620℃ and above 20MPa.

[0004] The production process of G115 martensitic heat-resistant steel used in large-diameter boiler pipes of the USC unit is quite difficult.

[0005] Patent CN108866453A discloses a martensitic heat-resistant steel and its preparation method. This invention improves the morphology and distribution of precipitated carbonitrides through reasonable composition design and tempering process optimization, thereby improving the high-temperature strength and toughness of the material. However, the absence of grain boundary strengthening elements in the composition design affects the high-temperature creep and durability of the material.

[0006] Patent CN113186470A discloses a martensitic heat-resistant steel material and its preparation method. The invention is characterized by optimizing the content of W, Mo, B, etc., and mainly improving the impact toughness and cold and hot workability of the material. However, the high-temperature oxidation resistance and corrosion resistance of the material are not particularly outstanding.

[0007] Therefore, developing a martensitic heat-resistant steel with a more complete composition system, simpler production process, and more comprehensive product performance is of paramount importance for the development of USC units. Summary of the Invention

[0008] The purpose of this invention is twofold: firstly, to provide a martensitic heat-resistant steel containing elements such as Ta, La, and Ce through reasonable composition design, thereby improving its comprehensive properties such as strength, toughness, and high-temperature oxidation resistance; and secondly, to provide a clean and homogenized production process that ensures the continuity of the material's microstructure and properties.

[0009] To solve the above technical problems, the technical solution of the present invention is: a martensitic heat-resistant steel, wherein the chemical composition and its mass percentage of the martensitic heat-resistant steel are: C 0.08-0.12%, Si 0.8-1.2%, Mn 0.3-0.5%, P≤0.008%, S≤0.005%, Cr 8.7-9.3%, W 2.7-3.3%, Mo 1.8-2.2%, Nb 0.05-0.10%, Ta 0.03-0.05%, V 0.08-0.12%, La 0.05-0.10%, Ce 0.01-0.05%, La+Ce≥0.08%, B 0.005-0.010%, N 0.010-0.015%, with the balance being Fe and unavoidable impurities.

[0010] The above-mentioned method for producing martensitic heat-resistant steel: The martensitic heat-resistant steel is obtained by electroslag remelting, and the composition and mass percentage of the slag used in the electroslag remelting process are as follows: CaF2: 60-65%, CaO: 14-16%, Al2O3: 10-13%, SiO2: 4-7%, B2O3: 2-3%, La2O3: 2-3%, Ce2O3: 1-2%.

[0011] Furthermore, the protective gas for the electroslag remelting process is an argon-nitrogen mixture with an argon-nitrogen volume ratio of 18–20.

[0012] Furthermore, the consumable electrode used in the electroslag remelting process is obtained through vacuum induction furnace smelting and casting processes. In the vacuum induction furnace smelting process, the nitrogen alloying of the molten steel is carried out by gas-phase nitrogen enrichment, with a nitrogen partial pressure of 20,000 to 40,000 Pa, and maintained for 40 to 60 minutes.

[0013] Furthermore, in the vacuum smelting process, the crucible used is a zirconia precast crucible, which is manufactured by pre-pressing and forming the crucible using a press and then sintering it at high temperature.

[0014] The component content in the steel, the component content in the alloy used in the smelting process, and the component content in the slag described in this invention are all mass percentages.

[0015] The beneficial effects of adopting the above technical solution are as follows:

[0016] (1) The composition design was comprehensively optimized, with 8.7-9.3% Cr and 0.8-1.2% Si added to ensure that the matrix has excellent high-temperature oxidation resistance; appropriate amounts of W, Mo and other elements were added to improve the thermal strength of the material; Co was not added to avoid reducing the toughness of the steel; the contents of C, Nb, V, B and N were optimized to refine the grains, improve the precipitation strengthening effect, and improve the strength and toughness of the steel; in addition, the addition of strong carbide elements such as Nb and V can also promote the dissolution of elements such as Cr and Mo into the solid solution and improve the matrix strength.

[0017] (2) The addition of appropriate amount of Ta, together with Nb, effectively compensates for the decrease in antioxidant performance caused by high Mo content; the addition of appropriate amount of rare earth La and Ce increases the grain boundary bonding force and improves the high temperature grain boundary strength of the material; La and Ce can also transform the original oxide film subphase structure FeO+Cr2O3 into the La2O3+CeO2 structure with higher chemical temperature, which significantly improves the high temperature antioxidant capacity.

[0018] (3) The smelting process of this invention is vacuum induction melting + electroslag remelting. The vacuum induction furnace crucible uses a pre-made zirconia crucible with very high chemical stability, which greatly reduces the oxygen supply to the crucible; nitrogen alloying adopts a gas-phase nitrogen enrichment method to avoid the foreign impurities introduced by traditional nitrogen-enriched alloys such as manganese ferronitride and chromium ferronitride, resulting in high cleanliness of molten steel after melting, with low content of impurities such as P and S and low number of inclusions; in the electroslag remelting process, a CaF2-CaO-Al2O3-SiO2-B2O3-La2O3-Ce2O3 slag system matched with the composition is designed to ensure precise control of each component; the lower melting speed can also improve the uniformity of composition and structure. Therefore, the steel ingots produced by this method are of excellent quality and have good product stability. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] Example 1

[0021] Martensitic heat-resistant steel was smelted using a 1t vacuum induction furnace and a Φ400×1500mm crystallizer electroslag furnace.

[0022] The process for each step is as follows:

[0023] (1) Vacuum induction furnace smelting

[0024] Furnace loading: A 274.5 kg pure iron rod is placed at the bottom of the crucible, and 92 kg of metallic chromium and 44 kg of ferrotungsten (W) are placed in the middle. W =75%), 30kg ferromolybdenum (W) Mo=60%), with 274.5kg of pure iron bars placed on top, and 274.5kg of pure iron added to the replenishment bucket; 1.51kg of ferroniobium (W) is added to the secondary silo. Nb =66%), 2.4kg ferrovanadium (W) V =50%), 0.7kg toner, 1.19kg silicon metal, 2.9kg manganese metal, 0.4kg tantalum metal, 0.61kg ferroboron (W B =16.4%), 1 kg of lanthanum metal, and 0.8 kg of cerium metal;

[0025] Melting and refining: Vacuum to ≤10Pa, power on for melting, after some metal material has melted, slowly add pure iron from the feeding tank, after all is melted, heat to 1610℃, adjust vacuum to ≤0.1Pa, refine for 40 minutes, until the molten steel is sampled and tested for [O]≤10ppm, [N]≤10ppm, [H]≤1ppm;

[0026] Alloying and vapor-phase nitrogen enrichment: Stop the vacuum, fill with 20000Pa nitrogen, adjust the temperature to 1530℃, and add ferroniobium, ferrovanadium, carbon powder, metallic silicon, metallic manganese, metallic tantalum, and ferroboron in sequence. After melting and cleaning, check the composition and fine-tune it to meet the requirements; turn off the power to form a film, add rare earth lanthanum and cerium, and stir vigorously for 7 minutes; vapor-phase nitrogen enrichment time is 50 minutes.

[0027] Steel tapping: Adjust the temperature to 1510℃, and cast the steel into Φ300×1850mm round ingots under electric current.

[0028] (2) Electroslag remelting

[0029] Preparation: Stress-relief annealing, grinding, and welding of the vacuum ingot to the dummy electrode; installation of the crystallizer and electrode.

[0030] Slag melting: 50 kg of slag system with a composition of 65% CaF2, 15% CaO, 10% Al2O3, 4% SiO2, 3% B2O3, 2% La2O3, and 1% Ce2O3 is melted in a slag melting furnace, heated to 1600℃, and then injected into a crystallizer;

[0031] Melting: Lower the electrode, apply electricity to melt, control the voltage to 45-51V, the current to 5500-7500A, the melting rate to 320-400Kg / h, and introduce a mixed gas with an argon-nitrogen volume ratio of 18 as a protective gas throughout the process.

[0032] Demolding and annealing: Demolding is performed 2 hours after smelting. During the annealing process, the electroslag ingot is heated to 800°C with the furnace and held for 8 hours. Then the furnace is cooled to room temperature.

[0033] The chemical composition test results of the electroslag ingots obtained by electroslag remelting are listed in Table 1. The performance test results of the electroslag ingots after forging are listed in Table 2.

[0034] Example 2

[0035] Martensitic heat-resistant steel was smelted using a 2t vacuum induction furnace and a Φ500×1500mm crystallizer electroslag furnace.

[0036] The process for each step is as follows:

[0037] (1) Vacuum induction furnace smelting

[0038] Furnace loading: A 544kg pure iron rod is placed at the bottom of the crucible, and 180kg of metallic chromium and 80kg of ferrotungsten (W) are placed in the middle. W =75%), 66.7kg ferromolybdenum (W) Mo =60%), with 544kg pure iron bars placed on top, and 544kg of pure iron added to the replenishment bucket; 2.12kg of ferroniobium (W) is added to the secondary silo. Nb =66%), 4kg ferrovanadium (W) V =50%), 1.8kg toner, 19.8kg silicon metal, 7.8kg manganese metal, 0.6kg tantalum metal, 0.97kg ferroboron (W B =16.4%), 2.8 kg of lanthanum metal, and 0.97 kg of cerium metal;

[0039] Melting and refining: Vacuum to ≤10Pa, power on for melting, after some metal material has melted, slowly add pure iron from the feeding tank, after all is melted, heat to 1630℃, adjust vacuum to ≤0.1Pa, refine for 55min, until the molten steel is sampled and tested for [O]≤10ppm, [N]≤10ppm, [H]≤1ppm;

[0040] Alloying and vapor-phase nitrogen enrichment: Stop the vacuum, fill with 30000Pa nitrogen, adjust the temperature to 1540℃, and add ferroniobium, ferrovanadium, carbon powder, metallic silicon, metallic manganese, metallic tantalum, and ferroboron in sequence. After melting and cleaning, check the composition and fine-tune it to meet the requirements; turn off the power to form a film, add rare earth lanthanum and cerium, and stir vigorously for 8 minutes; vapor-phase nitrogen enrichment time is 50 minutes.

[0041] Steel tapping: Adjust the temperature to 1550℃, and cast the steel into Φ400×2000mm round ingots under electric current.

[0042] (2) Electroslag remelting

[0043] Preparation: Stress-relief annealing, grinding, and welding of the vacuum ingot to the dummy electrode; installation of the crystallizer and electrode.

[0044] Slag melting: 90 kg of slag system with a composition of 64% CaF2, 10% CaO, 13% Al2O3, 7% SiO2, 3% B2O3, 3% La2O3, and 2% Ce2O3 is melted in a slag melting furnace, heated to 1650℃, and then injected into a crystallizer;

[0045] Melting: Lower the electrode and melt by energizing. The entire melting process is controlled with a voltage of 62-80V, a current of 8750-10000A, and a melting rate of 400-500Kg / h. A mixed gas with an argon-nitrogen volume ratio of 19 is introduced as a protective gas throughout the process.

[0046] Demolding and annealing: Demolding is performed 2.5 hours after smelting. The electroslag ingot is heated to 830°C with the furnace, held for 9 hours, and then cooled to room temperature.

[0047] The chemical composition test results of the electroslag ingots obtained by electroslag remelting are listed in Table 1. The performance test results of the electroslag ingots after forging are listed in Table 2.

[0048] Example 3:

[0049] Martensitic heat-resistant steel was smelted using a 1.5t vacuum induction furnace and a Φ450×1500mm crystallizer electroslag furnace.

[0050] The process for each step is as follows:

[0051] (1) Vacuum induction furnace smelting

[0052] Furnace loading: 407.5 kg of pure iron rods are placed at the bottom of the crucible, and 139.5 kg of metallic chromium and 54 kg of ferrotungsten (W) are placed in the middle. W =75%), 55kg ferromolybdenum (W) Mo =60%), with 407.5kg of pure iron bars placed on top, and 407.5kg of pure iron added to the replenishment bucket; 1.13kg of ferroniobium (W) is added to the secondary silo. Nb =66%), 2.4kg ferrovanadium (W) V =50%), 1.65kg toner, 11.85kg silicon metal, 7.35kg manganese metal, 0.75kg tantalum metal, 0.46kg ferroboron (W B =16.4%), 3 kg of lanthanum metal, and 0.24 kg of cerium metal;

[0053] Melting and refining: Vacuum to ≤10Pa, power on for melting, after some metal material has melted, slowly add pure iron from the feeding tank, after all is melted, heat to 1620℃, adjust vacuum to ≤0.1Pa, refine for 45 minutes, until the molten steel is sampled and tested for [O]≤10ppm, [N]≤10ppm, [H]≤1ppm;

[0054] Alloying and vapor-phase nitrogen enrichment: Stop the vacuum, fill with 25000Pa nitrogen, adjust the temperature to 1540℃, and add ferroniobium, ferrovanadium, carbon powder, metallic silicon, metallic manganese, metallic tantalum, and ferroboron in sequence. After melting and cleaning, check the composition and fine-tune it to meet the requirements; turn off the power to form a film, add rare earth lanthanum and cerium, and stir vigorously for 5 minutes; vapor-phase nitrogen enrichment time is 45 minutes.

[0055] Steel tapping: Adjust the temperature to 1520℃, and cast the steel into Φ350×2000mm round ingots under electric current.

[0056] (2) Electroslag remelting

[0057] Preparation: Stress-relief annealing, grinding, and welding of the vacuum ingot to the dummy electrode; installation of the crystallizer and electrode.

[0058] Slag melting: 70 kg of slag system with components of 62% CaF2, 15% CaO, 12% Al2O3, 6% SiO2, 2% B2O3, 2% La2O3, and 2% Ce2O3 is melted in a slag melting furnace, heated to 1650℃, and then injected into a crystallizer;

[0059] Melting: Lower the electrode and melt by energizing. The entire melting process is controlled with a voltage of 44-56V, a current of 6500-8500A, and a melting rate of 360-450Kg / h. A mixed gas with an argon-nitrogen volume ratio of 20 is introduced as a protective gas throughout the process.

[0060] Demolding and annealing: Demolding is carried out 3 hours after the smelting is completed. The electroslag ingot is heated to 800℃ with the furnace, held for 8 hours, and then cooled to room temperature.

[0061] The chemical composition test results of the electroslag ingots obtained by electroslag remelting are listed in Table 1. The performance test results of the electroslag ingots after forging are listed in Table 2.

[0062] Example 4

[0063] Martensitic heat-resistant steel was smelted using a 5t vacuum induction furnace and a Φ600×2500mm crystallizer electroslag furnace.

[0064] The process for each step is as follows:

[0065] (1) Vacuum induction furnace smelting

[0066] Furnace loading: A 1370kg pure iron bar is placed at the bottom of the zirconia crucible, and 445kg metallic chromium and 190kg ferrotungsten (W) are placed in the middle. W =75%), 158.8 kg ferromolybdenum (W) Mo =60%), with 1370kg pure iron bars placed on top, and 1370kg of pure iron added to the replenishment bucket; the secondary silo is filled with 4.55kg of ferroniobium (W Nb =66%), 8.65kg ferrovanadium (W) V =50%), 4.5kg toner, 45kg silicon metal, 17.5kg manganese metal, 2kg tantalum metal, 2.13kg ferroboron (W B =16.4%), 6 kg of lanthanum metal, and 2 kg of cerium metal;

[0067] Melting and refining: Vacuum to ≤10Pa, power on for melting, after some metal material has melted, slowly add pure iron from the feeding tank, after all is melted, heat to 1650℃, adjust vacuum to ≤0.1Pa, refine for 80 minutes, until the molten steel is sampled and tested for [O]≤10ppm, [N]≤10ppm, [H]≤1ppm;

[0068] Alloying and vapor-phase nitrogen enrichment: Stop the vacuum, fill with 40000Pa nitrogen, adjust the temperature to 1550℃, and add ferroniobium, ferrovanadium, carbon powder, metallic silicon, metallic manganese, metallic tantalum, and ferroboron in sequence. After melting and cleaning, test the composition and fine-tune it to meet the requirements; stop the power to form a film, add rare earth lanthanum and cerium, and stir vigorously for 10 minutes; vapor-phase nitrogen enrichment time is 50 minutes.

[0069] Steel tapping: Adjust the temperature to 1530℃, and cast the steel into Φ500×3300mm round ingots under electric current.

[0070] (2) Electroslag remelting

[0071] Preparation: Stress-relief annealing, grinding, and welding of the vacuum ingot to the dummy electrode; installation of the crystallizer and electrode.

[0072] Slag melting: 250 kg of slag system with the composition of 63% CaF2, 16% CaO, 11% Al2O3, 5% SiO2, 2B2O3, 3% La2O3, and 1% Ce2O3 is melted in a slag melting furnace, heated to 1650℃, and then poured into a crystallizer;

[0073] Melting: Lower the electrode and melt by energizing. The entire melting process is controlled with a voltage of 75-95V, a current of 10500-12000A, and a melting rate of 480-600Kg / h. A mixed gas with an argon-nitrogen volume ratio of 19 is introduced as a protective gas throughout the process.

[0074] Demolding and annealing: Demolding is performed 3 hours after smelting. The electroslag ingot is heated to 850°C with the furnace and held for 10 hours. The furnace is then cooled to room temperature.

[0075] The chemical composition test results of the electroslag ingots obtained by electroslag remelting are listed in Table 1. The performance test results of the electroslag ingots after forging are listed in Table 2.

[0076] Table 1

[0077] Element C / ％ Si / % Mn / % P / ％ S / ％ Cr / ％ W / ％ Mo / % La+Ce / % Example 1 0.080 1.18 0.31 0.0062 0.0028 9.21 3.28 1.80 0.101 Example 2 0.11 0.97 0.41 0.0053 0.0022 9.04 3.03 1.97 0.099 Example 3 0.12 0.81 0.49 0.0048 0.0017 9.27 2.72 2.19 0.1092 Example 4 0.088 0.87 0.34 0.0055 0.0016 8.81 2.83 1.81 0.082 Element Nb / % Ta / % V / ％ La / % Ce / % B / ％ N / ％ O / ％ Example 1 0.099 0.042 0.12 0.052 0.049 0.009 0.0143 0.0012 Example 2 0.068 0.031 0.097 0.067 0.032 0.0078 0.0134 0.0010 Example 3 0.05 0.050 0.081 0.099 0.0102 0.005 0.0104 0.0013 Example 4 0.059 0.041 0.089 0.058 0.024 0.0066 0.0121 0.0012

[0078] Table 2

[0079]

[0080]

[0081] For comparison, the performance test results of 9Cr3W3Co, P92, SAVE12AD and G115 on the market are also listed in Table 2. As can be seen from Table 2, the martensitic heat-resistant steel of this invention has a certain degree of superiority in room temperature tensile, impact and 650℃ tensile properties compared with the widely used 9Cr3W3Co, American P92, Japanese SAVE12AD and Chinese G115, which can fully meet the material requirements of USC units.

[0082] Examples 5-8

[0083] Referring to the production process of Examples 1-4, martensitic heat-resistant steel was produced using a vacuum induction furnace, electroslag remelting, and forging process. Its composition and mass percentage are shown in Table 3, the performance test results are shown in Table 4, and the composition and mass percentage of the slag used in the electroslag remelting process are shown in Table 5.

[0084] Table 3

[0085] Element C / ％ Si / % Mn / % P / ％ S / ％ Cr / ％ W / ％ Mo / % La+Ce / % Example 5 0.12 1.11 0.50 0.0057 0.0020 8.91 1.80 1.80 0.11 Example 6 0.10 1.2 0.41 0.0049 0.0024 8.70 1.92 1.97 0.08 Example 7 0.11 0.80 0.49 0.0052 0.0021 9.06 2.20 2.19 0.102 Example 8 0.08 0.97 0.30 0.0058 0.0019 9.30 2.15 1.81 0.09 Element Nb / % Ta / % V / ％ La / % Ce / % B / ％ N / ％ O / ％ Example 5 0.10 0.039 0.08 0.08 0.03 0.005 0.0121 0.0011 Example 6 0.05 0.041 0.097 0.05 0.01 0.008 0.0100 0.0014 Example 7 0.08 0.050 0.089 0.06 0.04 0.007 0.0132 0.0009 Example 8 0.06 0.030 0.12 0.1 0.05 0.01 0.0150 0.0010

[0086] Table 4

[0087]

[0088]

[0089] Table 5

[0090] Element CaF2 / % CaO / % Al2O3 / % SiO2 / % B2O3 / % La2O3 / % Ce2O3 / % Example 5 65 14 10 5 3 2 1 Example 6 60 16 13 4 2 3 2 Example 7 61 15 10 7 3 2.5 1.5 Example 8 62 15 11 6 2.5 2 1.5

[0091] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A martensitic heat-resistant steel, characterized in that, The chemical composition and mass percentage of the martensitic heat-resistant steel are as follows: C 0.08-0.12%, Si 0.8-1.2%, Mn 0.3-0.5%, P ≤0.008%, S ≤0.005%, Cr 8.7-9.3%, W 2.7-3.3%, Mo 1.8-2.2%, Nb 0.05-0.10%, Ta 0.03-0.05%, V 0.08-0.12%, La 0.05-0.10%, Ce 0.01-0.05%, La+Ce ≥0.08%, B 0.005-0.010%, N 0.010-0.015%, and the balance of Fe and inevitable impurities; the martensitic heat-resistant steel is produced by the following method: the martensitic heat-resistant steel is obtained by electroslag remelting, the slag composition and mass percentage used in the electroslag remelting process are as follows: CaF2: 60-65%, CaO: 14-16%, Al2O3: 10-13%, SiO2: 4-7%, B2O3: 2-3%, La2O3: 2-3%, and Ce2O3: 1-2%; the consumable electrode used in the electroslag remelting process is obtained by vacuum induction furnace smelting and pouring processes, and in the vacuum induction furnace smelting process, the nitrogen alloying of the molten steel is carried out by a gas phase nitrogen enrichment method, the nitrogen partial pressure is 20000-40000 Pa, and the nitrogen alloying is maintained for 40-60 min.

2. A method of producing the martensitic heat-resistant steel according to claim 1, characterized by, The martensitic heat-resistant steel is obtained by electroslag remelting, and the slag composition and mass percentage used in the electroslag remelting process are as follows: CaF2: 60-65%, CaO: 14-16%, Al2O3: 10-13%, SiO2: 4-7%, B2O3: 2-3%, La2O3: 2-3%, and Ce2O3: 1-2%.

3. The production method of a martensitic heat-resistant steel according to claim 2, characterized in that, The protective gas used in the electroslag remelting process is argon-nitrogen mixed gas, and the volume ratio of argon to nitrogen is 18-20.

4. The production method of a martensitic heat-resistant steel according to claim 2, characterized in that, The consumable electrode used in the electroslag remelting process is obtained by vacuum induction furnace smelting and pouring processes, and in the vacuum induction furnace smelting process, the nitrogen alloying of the molten steel is carried out by a gas phase nitrogen enrichment method, the nitrogen partial pressure is 20000-40000 Pa, and the nitrogen alloying is maintained for 40-60 min.

5. The production method of a martensitic heat-resistant steel according to claim 4, characterized in that, In the vacuum smelting process, the used crucible is a zirconia preformed crucible.

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