High-temperature-oxidation-resistant martensite heat-resistant steel and preparation method thereof

Abstract

The martensite heat-resistant steel comprises the following components in percentage by weight: 0.08 to 0.10 percent of C, not more than 0.45 percent of Si, 0.02 to 0.06 percent of Mg, not more than 0.003 percent of P, not more than 0.003 percent of S, 0.01 to 0.03 percent of Als, 8.5 to 9.5 percent of Cr, 2.2 to 2.8 percent of W, 2.0 to 2.8 percent of Co, 0.02 to 0.05 percent of Nb, 0.16 to 0.24 percent of V, 0.30 to 0.68 percent of Cu, not more than 0.002 percent of O, 0.004 to 0.018 percent of N, 0.005 to 0.009 percent of B, 0.01 to 0.03 percent of rare earth lanthanum, 0.02 to 0.04 percent of rare earth cerium and not more than 0.04 percent of rare earth neodymium. The preparation method comprises the following steps: smelting and pouring; carrying out electroslag remelting; naturally cooling; heating the steel ingot; forging into a pipe blank or a plate blank; naturally cooling to room temperature; tempering is conducted; and naturally cooling to room temperature. According to the invention, the endurance strength is greater than 120MPa at 625 DEG C for 105 hours; after high-temperature steam oxidation at 625 DEG C for 400 hours, the oxidation weight gain is reduced by 60% compared with that of a P92 material and is reduced by 20% or above compared with that of a P93 material.

Description

Technical Field

[0001] The present invention relates to high-end equipment steels used in the fields of electric power, aerospace, petrochemical, metallurgy, etc., and a preparation method thereof, and particularly relates to a high-temperature oxidation-resistant martensitic heat-resistant steel and a preparation method thereof. Background Art

[0002] In the development of modern industry, extremely high requirements are put forward for the high-temperature resistance performance of materials in many fields; in a high-temperature environment above 600 °C, ordinary steel cannot meet the requirements, and heat-resistant steel emerges as the times require. Heat-resistant steel not only needs to have strength and hardness at high temperatures, but also needs to have good oxidation resistance, corrosion resistance and other properties to ensure stability and reliability under harsh working conditions. It plays an indispensable role in key industries such as energy, aerospace, and chemical industry, and its performance directly affects the operating efficiency, service life and safety of related equipment. Therefore, the research and application of heat-resistant steel above 600 °C have always been the focus of the material field.

[0003] In the research and development of heat-resistant steel alloys above 600 °C abroad, there are mainly austenitic heat-resistant steels, nickel-based superalloys and 9% - 12% Cr martensitic heat-resistant steels. Taking the steel used in ultra-supercritical power plant boilers as an example, austenitic heat-resistant alloys such as TP347H, Super304H (S30432) and HR3C (TP310HCbN) have been developed, and they have become the three austenitic heat-resistant alloys with the largest consumption in 600 °C ultra-supercritical power plant boilers. However, there are certain defects. For example, the high-temperature strength of TP347H is relatively low; although Super304H has excellent high-temperature strength, its oxidation and corrosion resistance is slightly low; although HR3C has good oxidation and corrosion resistance, its impact toughness and high-temperature strength are slightly low.

[0004] In order to meet the service conditions of the superheater / reheater of higher-grade ultra-supercritical power plant boilers, Nippon Steel & Sumitomo Metal Corporation in Japan developed the NF709 alloy based on 20Cr-25Ni steel, but it has low creep strength and will embrittle after long-term aging.

[0005] Sandvik in Sweden proposed adding elements such as tungsten, cobalt, and copper on the basis of NF709. Although a new steel grade with excellent high-temperature performance and corrosion resistance was obtained, the degree of alloying is high and the cost is relatively expensive.

[0006] Compared with the above-mentioned heat-resistant steels, 9% - 12% Cr martensitic heat-resistant steel has the characteristics of low cost, small thermal expansion coefficient, good thermal stability, etc., and also has economy and practicability, but there are also deficiencies such as low creep strength or high alloy content. For example, the literature with the US patent number US20090007991A1 proposed "A 9% Cr ferritic heat-resistant steel 9Cr0.5Mo1.8WNbVN based on the improvement of P92", but its high-temperature creep strength is relatively low.

[0007] In addition, the National Institute for Materials Science of Japan has proposed a 9Cr3W3CoBN series of martensitic heat-resistant steel. Its chemical composition in weight percentage is carbon (C) 0.07 - 0.12%, silicon (Si) ≤ 0.5%, manganese (Mn) 0.3 - 0.7%, phosphorus (P) ≤ 0.02%, sulfur (S) ≤ 0.01%, chromium (Cr) 8.5 - 9.5%, tungsten (W) 2.0 - 2.5%, molybdenum (Mo) 0.2 - 0.5%, cobalt (Co) 2.8 - 3.2%, niobium (Nb) 0.03 - 0.10%, vanadium (V) 0.16 - 0.25%, copper (Cu) 0.5 - 1.0%, nitrogen (N) 0.010 - 0.020%, boron (B) 0.006 - 0.015%, nickel (Ni) ≤ 0.12%, and the balance is iron (Fe) and inevitable impurity elements. Its main chemical composition contains iron (Fe) as the matrix. The carbon (C) content is usually within a certain range to ensure the basic strength and hardness of the steel. The chromium (Cr) element content is relatively high, which helps to improve the oxidation and corrosion resistance of the steel. Alloying elements such as molybdenum (Mo) and tungsten (W) enhance its high-temperature strength. Boron (B) and nitrogen (N) elements are used to stabilize the lath martensite structure and optimize the tissue stability of the steel at high temperatures. After 100,000 hours of long-term aging at 625°C, its creep strength reaches above the 100 MPa level, significantly higher than the about 85 MPa level of traditional P92 heat-resistant steel.

[0008] The University of Science and Technology Beijing has proposed a new type of austenitic heat-resistant alloy SP2215. Its chemical composition is based on 22Cr-15Ni, and by adding appropriate amounts of alloying elements such as Cu, Nb, and N, multi-phase composite strengthening is formed in the austenitic matrix. It has excellent high-temperature creep strength and oxidation and corrosion resistance. After 100,000 hours of long-term aging at 650°C, its creep strength reaches the 140 MPa level. After 2000 hours of high-temperature steam oxidation test at 650°C, the thickness of the oxide film on the polished surface is 17.31 μm, and the thickness of the inner layer of the oxide film is 5.23 μm. However, its alloying element content is high and the cost performance is low.

[0009] The document with Chinese Patent Publication No. CN103045962B proposed "Steel G115 for Ultra-supercritical Thermal Power Units with Steam Temperature and Its Preparation Method". Its chemical composition in weight percentage is carbon 0.06 - 0.10%, silicon 0.1 - 0.5%, manganese 0.2 - 0.8%, phosphorus ≤0.004%, sulfur ≤0.002%, chromium 8.0 - 9.5%, tungsten 2.5 - 3.5%, cobalt 2.5 - 3.5%, niobium 0.03 - 0.07%, vanadium 0.10 - 0.30%, copper 0.80 - 1.20%, nitrogen 0.006 - 0.010%, boron 0.010 - 0.016%, rare earth cerium 0.01 - 0.04%, nickel ≤0.01%, aluminum ≤0.005%, titanium ≤0.01%, zirconium ≤0.01%, and the balance is iron and inevitable impurity elements; by adjusting the Cu content in the heat-resistant steel, the strength of the invented steel is improved, and at the same time, the contents of elements such as Ni and Al are controlled, as well as the heating process and the optimal heat treatment process system.

[0010] The document with Chinese Patent Publication No. CN 119392112A disclosed "A Rare Earth Heat-resistant Steel and Its Manufacturing Method". Its chemical composition in weight percentage is carbon 0.08 - 0.12%, silicon 0.2 - 0.4%, manganese 0.3 - 0.5%, chromium 8.2 - 9.2%, molybdenum 0.90 - 1.05%, vanadium 0.18 - 0.22%, niobium 0.06 - 0.10%, aluminum ≤0.012%, oxygen ≤0.0020%, nitrogen 0.045 - 0.055%, rare earth 0.02 - 0.08%, the rare earth is Ce and Y, and the content of Ce is not less than 0.01%; rare earth Y and Ce are added to the heat-resistant steel simultaneously, and their ratio is controlled to be not less than 1:2; to improve the dispersion strengthening effect, the inclusion grade is significantly reduced. At 550°C, its tensile strength is above 430 MPa and its yield strength is above 370 MPa; however, regarding the high-temperature creep strength and oxidation and corrosion resistance of this heat-resistant steel, there is no public report in this document and the results are unknown. Summary of the Invention

[0011] The present invention aims to overcome the deficiencies existing in the prior art and provides a 9% Cr martensitic heat-resistant steel material that can improve the oxidation resistance and high-temperature creep strength, that is, at 625°C and 10 5 h conditions, the creep strength > 120 MPa, the heat consumption rate is not less than 0.85%, the oxidation weight gain is significantly reduced, and the oxidation resistance ability is significantly improved, and its preparation method.

[0012] Measures to achieve the above objectives:

[0013] A high-temperature oxidation-resistant martensitic heat-resistant steel, the components and their weight percentage contents are as follows: C: 0.08 - 0.10%, Si not exceeding 0.45%, Mg: 0.02 - 0.06%, P ≤ 0.003%, S ≤ 0.003%, Als: 0.01 - 0.03%, Cr: 8.5 - 9.5%, W: 2.2 - 2.8%, Co: 2.0 - 2.8%, Nb: 0.02 - 0.05%, V: 0.16 - 0.24%, Cu: 0.30 - 0.68%, O ≤ 0.002%, N: 0.004 - 0.018%, B: 0.005 - 0.009%, rare earth lanthanum: 0.01 - 0.03%, rare earth cerium: 0.02 - 0.04%, rare earth neodymium not exceeding 0.04%, and the balance is Fe and inevitable impurity elements.

[0014] Preferably: the weight percentage content of Cu is 0.30 - 0.52%.

[0015] Preferably: the weight percentage content of rare earth lanthanum is 0.015 - 0.027%.

[0016] Preferably: the weight percentage content of rare earth neodymium is 0.01 - 0.038%.

[0017] A method for preparing a high-temperature oxidation-resistant martensitic heat-resistant steel, the steps are as follows:

[0018] 1) Smelting and casting into an electrode ingot

[0019] During smelting, first smelt the raw materials into molten steel. When the contents of elements other than rare earths are adjusted to reach the set values, then add rare earth lanthanum ferroalloy, rare earth neodymium ferroalloy and rare earth cerium ferroalloy according to the requirements of the set values; control the casting into an electrode ingot with a length of 100 - 600 mm;

[0020] 2) Performing electroslag remelting on the electrode ingot;

[0021] 3) Obtaining an ingot after natural cooling;

[0022] 4) Heating the ingot, controlling the heating austenitizing temperature at 1150 - 1180 °C, and holding at this temperature for 60 -

[0023] 120 min;

[0024] 5) Forging into the required tube blank or plate blank, and controlling the temperature at the end of forging not to be lower than 915 °C;

[0025] 6) Natural cooling to room temperature;

[0026] 7) Performing tempering treatment, controlling the tempering temperature at 740 - 780 °C, and holding at this temperature for 180 - 300 min;

[0027] 8) Cool naturally to room temperature.

[0028] Preferably, the austenitizing temperature of the steel ingot is controlled at 1160-1170° C. and is kept at this temperature for 60-90 minutes.

[0029] Preferably, the temperature at the end of forging is not less than 950°C.

[0030] Preferably, the tempering temperature is 740-770°C and kept at this temperature for 180-270 minutes.

[0031] Functions and mechanisms of the components and main processes in the present invention

[0032] Carbon: C is the most economical and effective strengthening element in steel. C can form precipitate carbides with elements such as Cr, W, Nb and V, and improve the high-temperature creep performance of the material through dispersion strengthening and other methods; C is also an austenite-forming element, which simulates the formation of high-temperature δ-ferrite and improves the high-temperature creep strength of the material. However, too high C content is not good for the welding performance of the material; at the same time, it will also consume too much solid solution elements (such as Cr, W), inhibit the precipitation of MX-type carbonitride phase in nanometer size, and negatively affect the creep performance of the material. Therefore, the C content of the steel of the present invention is controlled in the range of 0.08-0.10%.

[0033] Silicon: Si is beneficial to the high-temperature steam corrosion resistance of heat-resistant steel, and can significantly improve the tempering stability and strength of steel; however, excessive Si content will reduce the high-temperature endurance strength of the material. Therefore, the Si content of the steel of the present invention is controlled to not exceed 0.45%.

[0034] Magnesium: Mg can stabilize harmful elements P and S in steel and improve the hot working performance of the material; however, if the content is too high, it will increase the cost and reduce the creep strength of the material. Therefore, the content of Mg in the steel of the present invention is controlled at 0.02-0.06%.

[0035] Phosphorus: P is a harmful element in steel, which can easily cause center segregation of the ingot. It is easy to segregate to the grain boundary during the subsequent hot rolling heating process, which significantly increases the brittleness of the steel. At the same time, based on cost considerations and without affecting the performance of the steel, its content is controlled below 0.003%.

[0036] Sulfur: Sulfur is a very harmful element. Sulfur in steel often exists in the form of sulfides. Such sulfide inclusions will deteriorate the toughness of steel and cause anisotropy of performance. Therefore, the sulfur content in steel should be controlled as low as possible. Considering the manufacturing cost, the sulfur content in steel is controlled below 0.003%.

[0037] Als: Aluminum is added for deoxidation to reduce the oxygen content in the steel and prevent rare earth elements from being oxidized, thereby reducing the high-temperature performance of the material. When the Als content is less than 0.01%, its effect cannot be exerted. On the other hand, adding a large amount of aluminum easily forms alumina agglomerate inclusions. Therefore, the aluminum content is controlled in the range of 0.01 - 0.03%.

[0038] Chromium: Cr is an important element for improving corrosion resistance and oxidation resistance. As the Cr content increases, the steam corrosion resistance of the steel significantly increases. When the Cr content is too high, δ-ferrite will be generated in the steel, reducing the high-temperature thermal strength of the material and increasing the material cost at the same time. Therefore, the Cr content of the steel in this invention is selected in the range of 8.5 - 9.5%.

[0039] Tungsten: W is a typical solid-solution strengthening element and also promotes the precipitation of MX-type carbonitrides in the form of nanoparticles. However, too much of it will lead to the formation of δ-ferrite, reducing strength and toughness. Therefore, in the steel of this invention, the W content is in the range of 2.2 - 2.8%.

[0040] Niobium: Nb is a strong C and N compound-forming element, which can form a nanoscale second phase, hinder the growth of austenite grains, refine austenite grains, effectively improve the high-temperature creep strength of the material, and also improve the plastic toughness of the steel. However, excessive Nb will combine with C to form coarse carbonitrides, reducing the material strength. Therefore, its total content is controlled in the range of 0.02 - 0.05%.

[0041] Vanadium: V is also a strong C and N compound-forming element, which can form a nanoscale second phase. When its content is less than 0.16%, it is not enough to form a high-density MX-type nano-strengthening phase in the steel matrix. However, when the mass percentage exceeds 0.24%, it is easy to form coarse carbonitrides, reducing the creep fracture strength. Therefore, in the steel of this invention, the vanadium content is controlled in the range of 0.16 - 0.24%.

[0042] Copper: Cu is a typical solid-solution strengthening element. It can be dissolved in the matrix to precipitate fine Cu-rich phases, improving the high creep strength of heat-resistant steel and having a fine-grained structure and oxidation resistance. When the Cu content is low, the number of nano-sized Cu-rich phases precipitated in the matrix is small, and the strengthening effect is weak. When the Cu content is high, it will seriously reduce the high-temperature plasticity of the steel. Therefore, the Cu content of the steel in this invention is controlled in the range of 0.30 - 0.68%.

[0043] Nitrogen: N can combine with carbon and elements such as V, Nb, and Cr to form MX-type carbonitride strengthening phases, thereby improving the high-temperature rupture and creep strength of steel. However, when the mass percentage exceeds 0.018%, a coarse complex nitride Z phase rich in V, Nb, and Cr is easily precipitated during long-term service at high temperatures, reducing the MX nano-precipitation phase and the high-temperature rupture strength of the material. Therefore, the N content of the steel of the present invention is controlled within 0.02%.

[0044] Oxygen: O is a harmful element in steel, which easily forms oxides with Cu, Ce, and La, thereby reducing the endurance strength and creep properties of heat-resistant steel. Generally, the lower the O content, the better, but considering the production cost, the O content of the steel of the present invention is controlled within 0.002%.

[0045] Boron: Boron can be concentrated at grain boundaries and lath boundaries to strengthen grain boundaries and lath boundaries; it also has the function of stabilizing M 23 The effect of C6 type carbide is to significantly improve creep rupture strength. However, too high boron content will form borides, reduce creep rupture strength, and be disadvantageous to hot working process. In the steel of the present invention, the mass percentage of boron is controlled between 0.005 and 0.009%.

[0046] Rare earth cerium, lanthanum, neodymium: Ce, La and Nd can be segregated at the grain boundaries of steel, play the role of strengthening grain boundaries and lath boundaries, increase the grain boundary area, hinder dislocation movement and grain boundary sliding, thereby improving the stability of the material at high temperatures; they also promote the enrichment of alloy elements in the oxide film in the steel, improve the density and stability of the oxide film, effectively prevent oxygen atoms from diffusing into the steel matrix, and improve the oxidation resistance and high-temperature corrosion resistance of heat-resistant steel. At the same time, it has strong chemical activity and can react with harmful elements such as oxygen and sulfur in steel to generate high-melting-point compounds, thereby playing a role in purifying molten steel. Considering that La, Ce, and Nd are rare earth elements and are expensive; excessive use may form too many rare earth compound inclusions in the steel, and these inclusions may become crack sources, reducing the toughness and high-temperature performance of the steel. Therefore, the present invention controls the rare earth La0.01-0.03%, Ce0.02-0.04%, and Nd in the steel not exceeding 0.04%.

[0047] The reason why the ingot is heated and austenitized at 1150-1180°C and kept at this temperature for 60-120 minutes is that when the temperature reaches 1180°C, the austenite in the steel begins to transform into high-temperature delta ferrite, which reduces the high-temperature endurance strength of the material; when the temperature is lower than 1150°C, the blank is significantly cooled during the forging process, which will lead to excessive final forging temperature of the material, and easily cause defects such as shear bands, local flow and voids.

[0048] The reason why the temperature at the end of forging in the present invention is controlled not to be lower than 915 °C is that when the temperature is lower than this value, the material begins to transform from austenite structure into other structures, resulting in mixed crystals in the forgings and affecting the material properties.

[0049] The reason why the tempering temperature in the present invention is controlled within the range of 740 - 780 °C and held at this temperature for 180 - 300 min is that within this temperature range, it is beneficial for the microalloying elements Nb and V to fully play their roles, promoting the precipitation of carbides and the distribution of alloying elements in different phases, thereby improving the heat resistance, strength, toughness and other properties of the steel. If the tempering temperature is too low, the stress cannot be effectively eliminated; if it is too high, grain growth may occur, reducing the strength and toughness of the steel.

[0050] Compared with the prior art, the present invention can improve the oxidation resistance and high-temperature creep strength of 9% Cr martensitic heat-resistant steel materials, that is, under the conditions of 625 °C and 10 5 h, the creep strength > 120 MPa; meanwhile, after 400 hours of high-temperature steam oxidation test at 625 °C, the oxidation weight gain is reduced by 60% compared with the traditional P92 material (9Cr2W3Co), and by more than 20% compared with the P93 material (9Cr3W3CoBN). The oxidation weight gain is significantly reduced and the oxidation resistance is significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 is the metallographic structure diagram of the steel in the present invention after forging and air cooling;

[0052] Figure 2 is Figure 1 the metallographic structure of the steel after tempering treatment;

[0053] Figure 3 is the hot processing diagram of the steel in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0054] The present invention will be described in detail below:

[0055] Table 1 is the chemical composition list of each embodiment and comparative example of the present invention;

[0056] Table 2 is the main heat treatment process parameters of each embodiment of the present invention;

[0057] Table 3 is the mechanical properties of the heat-resistant steel of each embodiment of the present invention;

[0058] Table 4 is the comparison of oxidation weight gain of the heat-resistant steel of each embodiment of the present invention.

[0059] Each embodiment of the present invention is produced according to the following steps:

[0060] 1) Smelting and casting into electrode ingots

[0061] During smelting, the raw materials are first smelted into molten steel. After adjusting the contents of elements other than rare earth to reach the set values, rare earth lanthanum-iron alloy, rare earth neodymium-iron alloy, and rare earth cerium-iron alloy are added according to the requirements of the set values; control the pouring to form an electrode ingot of 100-600 mm;

[0062] 2) Carry out electroslag remelting on the electrode ingot;

[0063] 3) Obtain an ingot after natural cooling;

[0064] 4) Heat the ingot, control the austenitizing temperature at 1150-1180 °C, and hold at this temperature for 60-

[0065] 120 min;

[0066] 5) Forge into the required tube blank or plate blank, and control the temperature at the end of forging not to be lower than 915 °C;

[0067] 6) Naturally cool to room temperature;

[0068] 7) Carry out tempering treatment, control the tempering temperature at 740-780 °C, and hold at this temperature for 180-300 mm;

[0069] 8) Naturally cool to room temperature.

[0070] Table 1 Chemical composition list (wt%) of each example and comparative example of the present invention

[0071]

[0072]

[0073] Continued Table 1

[0074]

[0075] Table 2 Main heat treatment process parameters of each example of the present invention

[0076]

[0077]

[0078] Table 3 Mechanical properties of heat-resistant steel of each example of the present invention

[0079]

[0080] Table 4 Comparison of oxidation weight gain of heat-resistant steel of each example of the present invention (g / mm 2 )

[0081]

[0082]

[0083] As can be seen from Tables 3 and 4, the components manufactured by the present invention can reach a high-temperature creep strength performance of more than 120 MPa under the service environment of 625 °C for 10 5 h, and the oxidation weight gain is significantly reduced and the oxidation resistance is significantly improved, showing a better improvement compared with the traditional 9% Cr heat-resistant steel material.

[0084] This specific embodiment is only the best enumeration and is not a restrictive implementation of the technical solution of the present invention.

Claims

1. A high-temperature oxidation-resistant martensitic heat-resistant steel, the components and their weight percentage contents are as follows: C: 0.08 - 0.10%, Si not exceeding 0.45%, Mg: 0.02 - 0.06%, P ≤ 0.003%, S ≤ 0.003%, Als: 0.01 - 0.03%, Cr: 8.5 - 9.5%, W: 2.2 - 2.8%, Co: 2.0 - 2.8%, Nb: 0.02 - 0.05%, V: 0.16 - 0.24%, Cu: 0.30 - 0.68%, O ≤ 0.002%, N: 0.004 - 0.018%, B: 0.005 - 0.009%, rare earth lanthanum: 0.01 - 0.03%, rare earth cerium: 0.02 - 0.04%, rare earth neodymium not exceeding 0.04%, and the balance is Fe and inevitable impurity elements.

2. The austenitic heat-resistant steel with high-temperature oxidation resistance according to claim 1, characterized in that: The weight percentage content of Cu is in the range of: 0.30 - 0.52%.

3. The austenitic heat-resistant steel resistant to high-temperature oxidation according to claim 1, characterized in that: The weight percentage content of rare earth lanthanum is in the range of: 0.015 - 0.027%.

4. The austenitic heat-resistant steel with high-temperature oxidation resistance according to claim 1, characterized in that: The weight percentage content of rare earth neodymium is in the range of: 0.01 - 0.038%.

5. A method for preparing a high-temperature oxidation-resistant martensitic heat-resistant steel as described in claim 1, the steps are as follows: 1) Smelting and casting into an electrode ingot During smelting, first smelt the raw materials into molten steel. When the contents of elements other than rare earths are adjusted to reach the set values, then add rare earth lanthanum ferroalloy, rare earth neodymium ferroalloy and rare earth cerium ferroalloy according to the requirements of the set values; control the casting into an electrode ingot with a length of 100 - 600 mm. 2) Subject the electrode ingot to electroslag remelting; 3) Obtain an ingot after natural cooling; 4) Heat the ingot, control the heating austenitizing temperature at 1150 - 1180 °C, and hold at this temperature for 60 - 120 min; 5) Forge into the required tube blank or plate blank, and control the temperature at the end of forging not to be lower than 915 °C; 6) Naturally cool to room temperature; 7) Carry out tempering treatment, control the tempering temperature at 740 - 780 °C, and hold at this temperature for 180 - 300 min; 8) Naturally cool to room temperature.

6. The preparation method of a high-temperature oxidation-resistant martensitic heat-resistant steel according to claim 5, characterized in that: The heating temperature of the ingot is controlled at the austenitizing temperature of 1160 - 1170 °C, and hold at this temperature for 60 - 90 min.

7. The preparation method of a high-temperature oxidation-resistant martensitic heat-resistant steel according to claim 5, characterized in that: The temperature at the end of forging is not lower than 950 °C.

8. The preparation method of a high-temperature oxidation-resistant martensitic heat-resistant steel according to claim 5, characterized in that: The tempering temperature is at 740 - 770 °C, and hold at this temperature for 180 - 270 min.

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