High-entropy stainless steel that can withstand 900℃, its preparation process and applications

Abstract

This invention discloses a high-entropy stainless steel capable of withstanding 900℃, its preparation process, and its applications, relating to the field of stainless steel technology. The high-entropy stainless steel capable of withstanding 900℃, by weight percentage, comprises: C≤0.20%, N 0.08~0.50%, Ni 18.0~48.0%, Cu 0.05~4.0%, Mo 0~10.0%, Cr 18.0~20.0%, Co 0.02~0.80%, Si≤1.0%, Mn≤3.0%, S≤0.015%, P≤0.035%, and high-entropy alloying elements 0.21~7.0%. The technical solution of this invention uses Fe as the matrix, C and N as interstitial strengthening and precipitation strengthening elements, combined with high contents of Ni, Cr, Mo, and Cu, and a small amount of high-entropy alloying elements, which can effectively improve the solid solution strengthening and precipitation strengthening effects, and increase the high-temperature strength of the material.

Description

Technical Field

[0001] This invention relates to the field of stainless steel technology, and in particular to a high-entropy stainless steel that can withstand 900°C, its preparation process, and its applications. Background Art

[0002] With the technological advancements in aerospace, nuclear power, and petrochemical fields, higher demands are being placed on the high-temperature materials used in corresponding equipment. Currently, commonly used materials in industries such as petrochemicals and nuclear power include 800 series stainless steel and 310 series stainless steel.

[0003] A typical example of the 800 series is 800H stainless steel. 800H stainless steel is an iron-nickel-based high-temperature alloy, renowned for its strength, excellent oxidation resistance, and resistance to carburization at 800℃. Its chemical composition includes 0.15~0.60wt% Ti and 0.15~0.60wt% Al. Ti and Al can stabilize C and N, forming TiC, TiN, and AlN, which exhibit good stability in steel. However, Al4C3 shows relatively poor stability. Although the nitrides formed by Ti and Al can inhibit carbides (Cr...) 23 C6 and other substances diffuse and improve the surface resistance to high-temperature oxidation of materials, but they do not contribute much to high-temperature strength, resulting in a significant decrease in material strength above 800°C.

[0004] The most typical examples of the 310 series are 310S stainless steel and 310HNb stainless steel. 310S stainless steel can serve for extended periods at 600-800℃, but it may exhibit chromium (Cr) content. 23 C6 precipitation leads to Cr depletion at grain boundaries. At 750–900℃, brittle FeCr intermetallic compounds precipitate, resulting in a significant decrease in the material's impact toughness. In GB / T 150.2 "Pressure Vessels" materials section, Table C.2 lists the allowable stress for high-alloy steel plates, specifying an allowable service temperature of 800℃ for 310S stainless steel. However, the allowable stresses at 700℃ and 800℃ are only 19 MPa and 8 MPa, respectively. Due to the very low allowable stress at 700–800℃, 310S stainless steel is typically not used in pressure vessels, pipelines, boiler equipment, and heat exchangers operating above 700℃.

[0005] 310HNb is made by maintaining a certain carbon content (0.04~0.10wt%) on the basis of 310S and adding the stabilizing element Nb. It is commonly used in burner nozzles, heat treatment furnace linings, radiant tubes, supercritical boiler tubes, petrochemical cracking furnace tubes, and heat exchanger components. Although 310HNb stainless steel has better high-temperature stability than 310S stainless steel, the increase in high-temperature strength is not significant, making it difficult to use in high-temperature environments above 800℃. Summary of the Invention

[0006] The main objective of this invention is to propose a high-entropy stainless steel that can withstand 900°C, its preparation process, and its application, aiming to solve the problem of low strength of existing 800 series and 310 series austenitic stainless steel materials in high-temperature environments above 800°C.

[0007] To achieve the above objectives, this invention proposes a high-entropy stainless steel capable of withstanding 900℃, the composition of which, by weight percentage, is: C (carbon) ≤0.20wt%, N (nitrogen) 0.08~0.50wt%, Ni (nickel) 18.0~48.0wt%, Cu (copper) 0.05~4.0wt%, Mo (molybdenum) 0~10.0wt%, Cr (chromium) 18.0~20.0wt%, Co (cobalt) 0.02~0.80wt%, Si (silicon) ≤1.0wt%, Mn (manganese) ≤3.0wt%, S (sulfur) ≤0.015wt%, P (phosphorus) ≤0.035wt%, high-entropy alloying elements 0.21~7.0wt%, and the balance being Fe (iron) and unavoidable impurities;

[0008] The high-entropy alloying elements include at least Zr (zirconium), Nb (niobium), and W (tungsten).

[0009] Optionally, the high-entropy alloying elements further include Ti (titanium), Hf (hafnium), Al (aluminum), V (vanadium), and Ta (tantalum), and the sum of the weight contents of Zr, Ti, Hf, and Al is 0.02~0.95wt%, the sum of the weight contents of Nb and V is 0.04~1.2wt%, and the sum of the weight contents of W and Ta is 0.15~4.8wt%.

[0010] Preferably, the sum of the weight contents of Zr, Ti, Hf and Al is 0.26~0.81wt%, the sum of the weight contents of Nb and V is 0.43~1.03wt%, and the sum of the weight contents of W and Ta is 0.24~2.81wt%.

[0011] Optionally, the equivalent of Ni is Ni eq The equivalent of Cr is Cr eq , and Ni eq With Cr eq The ratio is ≥0.85;

[0012] Among them, Ni eq =W(Ni)+30W(C)+25W(N)+0.5[W(Mn)+W(Co)]+0.25W(Cu);

[0013] Cr eq =W(Cr)+1.5[W(Mo)+W(Si)]+0.75∑W(Xi);

[0014] In the formula, W(Ni) is the weight content of Ni, W(C) is the weight content of C, W(N) is the weight content of N, W(Mn) is the weight content of Mn, W(Co) is the weight content of Co, W(Cu) is the weight content of Cu, W(Cr) is the weight content of Cr, W(Mo) is the weight content of Mo, and W(Si) is the weight content of Si; ∑W(Xi) is the sum of the weight contents of Zr, Ti, Hf, Al, Nb, V, W, and Ta.

[0015] Specifically, ∑W(Xi)=W(Zr)+W(Ti)+W(Hf)+W(Al)+W(Nb)+W(V)+W(W)+W(Ta); where W(Zr) is the weight content of Zr, W(Ti) is the weight content of Ti, W(Hf) is the weight content of Hf, W(Al) is the weight content of Al, W(Nb) is the weight content of Nb, W(V) is the weight content of V, W(W) is the weight content of W, and W(Ta) is the weight content of Ta.

[0016] Preferably, Ni eq With Cr eq The ratio is ≥1.1; more preferably, Ni eq With Cr eq The ratio is 1.13 to 1.16.

[0017] Optionally, M O The weight content is ≤1 / 3 (M O (The sum of the weight content of Cr and the weight content of Cr).

[0018] Optionally, the weight content of N is more than twice the weight content of C, and the sum of the weight content of N and the weight content of C is ≥0.15wt%.

[0019] Optionally, the high-entropy stainless steel that can withstand 900°C further includes 0.001~0.005wt% B (boron).

[0020] Preferably, the high-entropy stainless steel that can withstand 900°C further includes 0.003 wt% B.

[0021] Optionally, the high-entropy stainless steel capable of withstanding 900°C further includes 0.005~0.080wt% of RE (rare earth elements), wherein the RE is selected from at least one element selected from La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Y (yttrium), and Sc (scandium).

[0022] Preferably, the high-entropy stainless steel that can withstand 900°C further includes 0.02 wt% Ce.

[0023] This invention also proposes a preparation process for high-entropy stainless steel that can withstand 900℃, comprising the following steps: smelting and casting the raw material of the high-entropy stainless steel that can withstand 900℃ to obtain a billet; forging the billet into a forging, or rolling it into a plate, or rolling / drawing it into a pipe; subjecting the forging, plate, or pipe to solution treatment at 1000~1150℃, cooling, and pickling to obtain the high-entropy stainless steel that can withstand 900℃.

[0024] The present invention also proposes the application of the high-entropy stainless steel described above, which can withstand 900°C, in pressure vessels, pipelines, boiler equipment, and heat exchange equipment with a heat resistance temperature below 900°C.

[0025] In the technical solution of this invention, Fe, or Fe and Ni, is used as the matrix, and C and N are used as interstitial strengthening and precipitation strengthening elements. This achieves interstitial solid solution strengthening and precipitation strengthening effects. Combined with high contents of Ni, Cr, Mo, and Cu, a good solid solution substitution effect can be achieved. Furthermore, the addition of a small amount of high-entropy alloying elements can further improve the solid solution strengthening effect. While ensuring that the material's microstructure is austenitic, the high-temperature strength of the material is effectively improved. Cr and Mo can provide excellent corrosion resistance and high-temperature oxidation resistance to the passivation film on the stainless steel surface. Cu can further strengthen the passivation film on the stainless steel surface, and Cu and Ni are infinitely miscible. At high temperatures, Cu-rich precipitation strengthening phases will also occur, which can play a precipitation strengthening role.

[0026] C and N are the main interstitial strengthening and precipitation strengthening elements. High-entropy alloying elements have a greater affinity for carbon and nitrogen than Cr, and the high-entropy compounds formed with C and N (carbides and nitrides containing high-entropy alloying elements) have higher melting points than chromium carbide and chromium nitride. This pins carbon and nitrogen within the grains and grain boundaries, resulting in a dispersed distribution and significantly improving the high-temperature strength of the material. The formation of carbides and nitrides involves both a sequential order and a competitive mechanism. C in steel is far more reactive than N, and its diffusion rate is faster. Adding N to form clustered high-entropy compounds is beneficial for C stability, and the N content must be higher than the C content to effectively stabilize C.

[0027] During the cooling process of stainless steel smelting, casting, and crystallization, nitrogen (N) preferentially forms nitrides with elements that have a strong affinity for it. If high-entropy alloying elements include Zr, Ti, Hf, Al, Nb, V, W, and Ta, nanoscale composite nitrides containing Ti, Zr, Hf, Al, V, Nb, and Cr will preferentially precipitate at approximately 900–1070 °C. Subsequently, below 900 °C, nanoscale composite carbides containing Ti, Zr, Hf, Ta, V, Nb, W, Mo, and Cr will form. Furthermore, due to the binding properties of Co, nitrides and carbides agglomerate together to form nanoscale mixed precipitates, pinning C and N within the grains and grain boundaries. These precipitates are disordered and dispersed throughout the material matrix, preventing the carbides from forming a network at grain boundaries at high temperatures. This improves the material's resistance to intergranular corrosion and high-temperature creep. The addition of Co also stabilizes the second-phase precipitates and contributes to the formation of a surface oxide film. Since carbides and nitrides have limited ability to consume high-entropy alloying elements, the surplus high-entropy alloying elements are arranged in an ordered state within the crystal in a solid solution state, replacing and arranging with iron atoms, and improving the solid solution strengthening performance.

[0028] The addition of rare earth elements can not only further remove sulfur and oxygen from molten steel, but also modify the fine sulfides and oxides remaining in the steel, transforming them into high-melting-point spherical and spindle-shaped particles, thus spheroidizing inclusions and improving the material's thermoplasticity. The use of Co and rare earth elements to strengthen grain boundaries maintains a high level of plasticity and toughness in the material.

[0029] Compared with traditional 800H stainless steel and 310HNb stainless steel, the stainless steel material provided by this invention has significantly improved strength while still possessing sufficient plasticity and toughness, giving the material good deformation processing performance and weldability, and making it well-suited for high-temperature environments of 800~900℃. Attached Figure Description

[0030] Figure 1 The metallographic structure of the stainless steel sheet prepared in Example 1 is observed under a 100x optical microscope.

[0031] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0033] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0034] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited to "first" and "second" may explicitly or implicitly include at least one of such features. In addition, if "and / or" or "and / or" appears in the full text, its meaning includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, solution B, or solutions that satisfy both A and B. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the ability of ordinary technicians in this field to implement. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0035] This invention proposes a high-entropy stainless steel that can withstand 900℃. Its composition, by weight percentage, is: C ≤0.20wt%, N 0.08~0.50wt%, Ni 18.0~48.0wt%, Cu 0.05~4.0wt%, Mo 0~10.0wt%, Cr 18.0~20.0wt%, Co 0.02~0.80wt%, Si≤1.0wt%, Mn≤3.0wt%, S≤0.015wt%, P≤0.035wt%, high-entropy alloying elements 0.21~7.0wt%, and the balance being Fe and unavoidable impurities; wherein the high-entropy alloying elements include at least Zr, Nb, and W.

[0036] In the technical solution of this invention, C and N, as well as high-entropy alloying elements, are added to the iron matrix. Under the premise that the austenitic structure of the material remains unchanged, the interstitial elements C and N can combine with high-entropy alloying elements to form intermetallic compounds (nitrides containing high-entropy alloys and carbides containing high-entropy alloys). Under the action of Co as a binder, multiple intermetallic compounds form copolymers with mixed entropy and adhere to the atomic groups alloyed with Fe-Ni-Cr basic elements. The resulting second-phase precipitates are diffusely embedded in the austenite and coexist harmoniously with the austenite, forming a high-entropy effect, which can significantly improve the high-temperature strength of the material.

[0037] Furthermore, in high-entropy stainless steel materials with second-phase precipitates, due to the interaction and repulsion between multiple elements, the diffusion between these atoms is slower than the diffusion of a single element, i.e., a "delayed diffusion effect" occurs. The diffusion coefficient is very low, and they are more difficult to diffuse, liquefy or rearrange than other alloys under the same heat, which makes the material have excellent stability.

[0038] Because the elements composing high-entropy alloys have different atomic sizes, their substitutional atoms and the resulting high-entropy compounds will cause lattice distortion, increasing the material's hardness. Precipitates composed of high-entropy compounds are formed by the accumulation of numerous atomic clusters, resulting in a greater lattice distortion effect. This creates a localized stress field around the precipitate, hindering dislocation slip and further improving the material's hardness and strength.

[0039] The stainless steel provided by this invention can be made not only into plates, but also into pipes and flange forgings. These plates, pipes and forgings can be used to manufacture heating furnaces, boilers, pressure vessels, conveying pipelines, heat exchangers, air coolers and high-temperature structural components, as well as other high-temperature and high-pressure environments that require corrosion resistance and wear resistance.

[0040] Furthermore, the high-entropy alloying elements also include Ti, Hf, Al, V and Ta, and the sum of the weight contents of Zr, Ti, Hf and Al is 0.02~0.95wt%, the sum of the weight contents of Nb and V is 0.04~1.2wt%, and the sum of the weight contents of W and Ta is 0.15~4.8wt%.

[0041] By adopting the above technical solution and using Zr, Ti, Hf, Al, Nb, V, W and Ta as high-entropy alloying elements, the high-entropy effect can be effectively improved and the high-temperature strength of the material can be increased.

[0042] Furthermore, the equivalent of Ni is Ni eq The equivalent of Cr is Cr eq , and Ni eq With Cr eq The ratio is ≥0.85;

[0043] Among them, Ni eq =W(Ni)+30W(C)+25W(N)+0.5[W(Mn)+W(Co)]+0.25W(Cu);

[0044] Cr eq =W(Cr)+1.5[W(Mo)+W(Si)]+0.75∑W(Xi);

[0045] In the formula, W(Ni) is the weight content of Ni, W(C) is the weight content of C, W(N) is the weight content of N, W(Mn) is the weight content of Mn, W(Co) is the weight content of Co, W(Cu) is the weight content of Cu, W(Cr) is the weight content of Cr, W(Mo) is the weight content of Mo, and W(Si) is the weight content of Si; ∑W(Xi) is the sum of the weight contents of Zr, Ti, Hf, Al, Nb, V, W, and Ta.

[0046] By adopting the above technical solution, and by controlling the ratio of nickel equivalent to chromium equivalent to not less than 0.85, ferrite residue in the microstructure of the material can be avoided, thereby improving the high-temperature stability of stainless steel.

[0047] Furthermore, M O The weight content is ≤1 / 3 (M O (The sum of the weight content of Cr and the weight content of Cr).

[0048] By adopting the above technical solution, the addition of Mo can improve the high-temperature oxidation resistance and high-temperature strength of stainless steel. However, excessive Mo content can easily cause segregation. Therefore, the weight content of Mo should be controlled to not exceed one-third of the sum of the weight contents of Mo and Cr.

[0049] Furthermore, the weight content of N is more than twice the weight content of C, and the sum of the weight content of N and the weight content of C is ≥0.15wt%.

[0050] While the increase in carbon and nitrogen directly enhances the mechanical properties of the material by adopting the above technical solutions, excessive carbon and nitrogen will precipitate carbides and nitrides at the grain boundaries, which will have an adverse effect on the forming and welding of the material. Therefore, it is necessary to further control the content of nitrogen and carbon.

[0051] Furthermore, the high-entropy stainless steel capable of withstanding 900°C also includes 0.001~0.005wt% B.

[0052] By adopting the above technical solution and adding a specific amount of B, the formability of the smelted billet during the later hot working can be effectively improved, and the high-temperature strength of the material can be improved to a certain extent.

[0053] Furthermore, the high-entropy stainless steel capable of withstanding 900°C also includes 0.005~0.080wt% RE, wherein the RE is selected from at least one element selected from La, Ce, Pr, Nd, Y and Sc.

[0054] By adopting the above technical solution, adding RE (rare earth elements) during steelmaking can not only reduce harmful inclusions such as sulfides and oxides, but also promote the dispersion and precipitation of high-entropy nitrides, adsorb carbides, and inhibit Cr.23 C6 grain boundary segregation. Rare earth elements spheroidize inclusions, improve the thermoplasticity of the material, reduce the risk of cracking in continuously cast or ingot-cast billets, and improve the toughness of the weld heat-affected zone.

[0055] This invention also proposes a preparation process for high-entropy stainless steel that can withstand 900℃, comprising the following steps: smelting and casting the raw material of the high-entropy stainless steel that can withstand 900℃ to obtain a billet; forging the billet into a forging, or rolling it into a plate, or rolling / drawing it into a pipe; subjecting the forging, plate, or pipe to solution treatment at 1000~1150℃, cooling, and pickling to obtain the high-entropy stainless steel that can withstand 900℃.

[0056] Furthermore, the smelting process includes the following steps: smelting raw materials of Fe, Cr, Ni, Mo, Mn and Cu in an electric furnace, adding CaO and CaF2 for dephosphorization, and controlling the P content in the molten steel to be below 0.035 wt%.

[0057] The molten steel obtained from electric arc furnace smelting is refined using AOD (argon-oxygen decarburization). This involves removing phosphorus (P) and carbon (C) through a mixture of oxygen and argon, controlling the C content to the target level. Deep deoxidation is achieved by adding aluminum, silicon, and calcium-based deoxidizers, partially reducing chromium oxide formed during high-temperature oxidation to Cr, controlling the oxygen content below 30 ppm. Deep desulfurization is then performed through calcium addition, controlling the S content to the target level. The contents of Cr, Ni, Mo, Mn, Cu, and Si are adjusted to the target levels. Then, raw materials containing high-entropy alloying elements (excluding Ti, Zr, and Al) and Co are added. Argon is used for stirring to ensure the added elements are fully dissolved and mixed. Nitrogen and argon are then switched, and turbulent agitation of the molten steel increases nitrogen content, allowing the nitrogen to fully react with the high-entropy alloying elements and Co in the molten steel to form carbonitrides, while controlling the N content to meet the target level. After the AOD stage smelting is completed, more than 50% of the high-phosphorus slag is removed, reducing the P content in the molten steel to the target level.

[0058] The molten steel obtained from AOD refining is then refined in an LF (ladle refining furnace). The temperature of the molten steel is controlled at 1500~1650℃, and the content of high-entropy alloying elements and Co is adjusted to meet the target content. Raw materials such as Ti, Zr and Al are added, and the mixture is stirred thoroughly with argon gas. The principle of argon gas flotation is used to further remove fine oxide slag from the molten steel, resulting in a casting liquid with higher purity.

[0059] In the above technical solution, by controlling the oxygen content to be below 30 ppm, the formation of oxide inclusions by reacting with oxygen after the addition of high-entropy alloying elements is avoided. Ti, Zr, and Al are more reactive with N and O at high temperatures than other high-entropy alloying elements. To avoid segregation during smelting, Ti, Zr, and Al are added after other high-entropy alloying elements have been added and formed stable compounds, so that the resulting compounds are more uniform and stable.

[0060] Furthermore, under an argon protective atmosphere, the casting liquid is cast using continuous casting or ingot casting; the raw material for RE can be added to the ladle before casting, or added to the flowing casting liquid formed during the casting process.

[0061] Furthermore, the method for forging the cast billet into a plate includes: casting the casting liquid by die casting under an argon protective atmosphere, controlling the casting temperature at 1540~1560℃, and cutting off the head and tail of the cast billet to obtain the forged billet.

[0062] The forging billet is cut into blanks, heated in a furnace, and held at 1080~1200℃ for at least 60 minutes. After being removed from the furnace, the billet is forged into a square forging, which is then cut into plates to obtain shaped plates. If the temperature of the billet drops to around 900℃ during the forging process, the billet should be reheated to above 1080℃ to continue forging.

[0063] After forming, the sheet metal is roughly machined to approximately the dimensions specified in the drawings, then subjected to solution heat treatment, immediately water-cooled after being removed from the furnace, and finally precision machined to the dimensions specified in the drawings to obtain high-entropy stainless steel forged sheet metal that can withstand 900℃.

[0064] Furthermore, the solution treatment temperature is 1000~1150℃, and the solution treatment time is calculated as 1~5 minutes per millimeter of thickness of forgings, plates or pipes.

[0065] In the above technical solution, the present invention controls the solution heat treatment temperature between 1000 and 1150°C to prevent grain growth during the solution treatment process and control the grain size of the stainless steel plates, pipes and forgings produced.

[0066] The present invention also proposes the application of the high-entropy stainless steel described above, which can withstand 900°C, in pressure vessels, pipelines, boiler equipment, and heat exchange equipment with a heat resistance temperature below 900°C.

[0067] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0068] Examples 1-4

[0069] Examples 1-4 provide a high-entropy stainless steel capable of withstanding 900℃, the chemical composition and content of which are shown in Table 1 below. A preparation process for a high-entropy stainless steel capable of withstanding 900℃ includes the following steps:

[0070] (1) The raw materials Fe, Cr, Ni, Mo, Mn and Cu are smelted in an electric furnace as the furnace charge of 10000 kg of molten steel. The content of SiO2 during the metallurgical reaction is calculated. Sufficient CaO and CaF2 are added to maintain the basicity of the high basicity slag system between 2.6 and 3.2. The temperature is controlled between 1500℃ and 1600℃ for oxygen blowing dephosphorization. After dephosphorization, the oxygen blowing amount is increased and decarburization is carried out between 1650℃ and 1750℃. After decarburization, ferrosilicon is added to perform preliminary reduction treatment on the Cr2O3 oxidized at high temperature. More than 60% of the high phosphorus slag is removed and the content of P is controlled below 0.035wt%.

[0071] (2) The molten steel obtained from electric furnace smelting is refined by AOD (Alternating Oxygen Deoxidation). P and C are removed by top-blowing oxygen and bottom-blowing argon, controlling the C content to the target level. Deep deoxidation is achieved by adding aluminum, silicon, and calcium-based deoxidizers, and chromium oxide formed by high-temperature oxidation is partially reduced to Cr. The oxygen content is controlled below 30 ppm. Deep desulfurization is achieved by adding calcium, controlling the S content to the target level. The contents of Cr, Ni, Mo, Mn, Cu, and Si are adjusted to the target levels. Then, microalloying elements other than Ti, Zr, and Al, as well as Co, are added. Argon is used to stir the mixture until the added elements are fully dissolved and mixed. Nitrogen and argon are then switched, and turbulent agitation of the molten steel is used to increase nitrogen content. This allows the nitrogen to fully react with the high-entropy alloying elements and Co in the molten steel to generate carbonitrides, while controlling the N content to meet the target level. After the AOD smelting stage, more than 50% of the high-phosphorus slag is removed to control the P content to the target level.

[0072] (3) The steel liquid obtained by AOD refining is subjected to LF refining. The temperature of the steel liquid is controlled at 1560℃~1650℃. The content of microalloying elements and Co is adjusted to meet the target content. Raw materials of Ti, Zr and Al are added. Argon gas is used to stir the mixture thoroughly to make the metallurgical reaction more complete and uniform. The air flotation principle of argon gas is used to make the small inclusions remaining in the steel float into the slag system, thereby obtaining a casting liquid with higher purity.

[0073] (4) Under the protection of argon, the casting liquid is cast by mold casting, and the casting temperature is controlled at 1540~1560℃. The casting billet is cut off to obtain the forging billet.

[0074] (5) Cut the forging billet into blanks, heat the billet in the furnace, and hold it at 1080~1200℃ for more than 60 minutes. Remove the billet from the furnace and forge it into a square forging with a thickness of 100mm × width of 150mm × length of 200mm. Then cut it into plates with a thickness of 20mm × width of 150mm × length of 200mm to obtain the shaped plates. If the temperature of the billet drops to about 900℃ during the forging process, the billet should be reheated to above 1080℃ to continue forging.

[0075] (6) After forming the plate, rough process it to the approximate size specified in the drawing, perform solution heat treatment at a temperature of 1050℃ for 60 minutes, immediately water cool it after taking it out of the furnace, and then finish process it to the size specified in the drawing to obtain a high-entropy stainless steel forged plate that can withstand 900℃.

[0076] Table 1. Chemical composition and content of stainless steel (unit: wt%)

[0077] Example 1 Example 2 Example 3 Example 4 C 0.07 0.01 0.12 0.20 N 0.17 0.14 0.31 0.50 Ni 25.40 18.10 30.60 48.0 Cu 1.53 0.05 2.94 4.0 Mo 4.67 1.06 7.22 9.48 Cr 20.40 19.50 22.40 19.61 Co 0.19 0.02 0.43 0.80 Si 0.41 0.12 0.75 0.94 Mn 1.01 0.63 1.98 2.75 S 0.01 0.01 0.01 0.01 P 0.02 0.02 0.02 0.02 Zr 0.05 0.00 0.17 0.26 Ti 0.01 0.06 0.19 0.15 Al 0.20 0.00 0.45 0.54 Nb 0.28 0.08 0.57 0.65 V 0.15 0.08 0.46 0.55 W 0.21 0.06 1.85 2.21 Ta 0.03 0.09 0.96 2.03 Fe and unavoidable impurities margin margin margin margin Example 5

[0078] This embodiment is based on Example 1, the difference being that the chemical composition of the high-entropy stainless steel that can withstand 900℃ also includes 0.003wt% B. In step (3), when adding Ti, Zr and Al raw materials, the raw material with B is added. The rest is the same as in Example 1. Example 6

[0079] This embodiment is based on embodiment 1, the difference being that the chemical composition of the high-entropy stainless steel that can withstand 900℃ also includes 0.02wt% Ce. In step (4), the raw material of Ce is added to the ladle before casting, and then the casting liquid is cast. The rest is the same as in embodiment 1. Comparative Example 1

[0080] The sheet material used in this comparative example is commercially available 800H stainless steel sheet. Comparative Example 2

[0081] The sheet material used in this comparative example is commercially available 310HNb stainless steel sheet.

[0082] Performance test

[0083] The plates from Examples 1-6 and Comparative Examples 1-2 were subjected to room temperature tensile tests and high temperature tensile tests. The room temperature tensile tests were conducted according to GB / T 228.1-2021 "Metallic Materials - Tensile Testing - Part 1: Room Temperature Test Method"; the high temperature tensile tests were conducted according to GB / T 228.2-2015 "Metallic Materials - Test Methods - Part 2: High Temperature Test Method". The test results are shown in Table 2 below.

[0084] Table 2 Results of room temperature tensile test and high temperature tensile test

[0085]

[0086] As can be seen from the test results in Table 2, the stainless steel plates prepared in Examples 1 to 6 of the present invention have excellent high-temperature strength and better high-temperature performance than other iron-nickel based stainless steels such as 800H and 310HNb in high-temperature environments at 900℃ and below.

[0087] The metallographic structure of the stainless steel sheet prepared in Example 1 was observed under a 100x optical microscope. Figure 1 As shown. By Figure 1 As can be seen, the metallographic structure of the material is pure austenite with no ferrite residue. Furthermore, the austenite in the field of view contains subgrains and twins, with no obvious second-phase precipitates, only extremely small dispersed particles. Metallographic images show that it has more twins than conventional austenitic stainless steel. These twins not only improve strength but also provide better resistance to high-temperature creep.

[0088] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A high-entropy stainless steel resistant to 900℃, characterized in that, By weight percentage, its composition is as follows: C ≤0.20wt%, N 0.08~0.50wt%, Ni 18.0~48.0wt%, Cu 0.05~4.0wt%, Mo 0~10.0wt%, Cr 18.0~20.0wt%, Co 0.02~0.80wt%, Si≤1.0wt%, Mn≤3.0wt%, S≤0.015wt%, P≤0.035wt%, high-entropy alloying elements 0.21~7.0wt%, and the balance being Fe and unavoidable impurities; The high-entropy alloying elements include at least Zr, Nb, and W; The high-entropy alloying elements also include Ti, Hf, Al, V and Ta, and the sum of the weight contents of Zr, Ti, Hf and Al is 0.02~0.95wt%, the sum of the weight contents of Nb and V is 0.04~1.2wt%, and the sum of the weight contents of W and Ta is 0.15~4.8wt%.

2. The high-entropy stainless steel resistant to 900℃ as described in claim 1, characterized in that, The equivalent of Ni is Ni eq The equivalent of Cr is Cr eq , and Ni eq With Cr eq The ratio is ≥0.85; Among them, Ni eq =W(Ni)+30W(C)+25W(N)+0.5[W(Mn)+W(Co)]+0.25W(Cu); Cr eq =W(Cr)+1.5[W(Mo)+W(Si)]+0.75∑W(Xi); In the formula, W(Ni) is the weight content of Ni, W(C) is the weight content of C, W(N) is the weight content of N, W(Mn) is the weight content of Mn, W(Co) is the weight content of Co, W(Cu) is the weight content of Cu, W(Cr) is the weight content of Cr, W(Mo) is the weight content of Mo, and W(Si) is the weight content of Si; ∑W(Xi) is the sum of the weight contents of Zr, Ti, Hf, Al, Nb, V, W, and Ta.

3. The high-entropy stainless steel resistant to 900℃ as described in claim 1, characterized in that, The weight content of Mo is ≤1 / 3 (the sum of the weight content of Mo and the weight content of Cr).

4. The high-entropy stainless steel resistant to 900℃ as described in claim 1, characterized in that, The weight content of N is more than twice the weight content of C, and the sum of the weight content of N and the weight content of C is ≥0.15wt%.

5. The high-entropy stainless steel resistant to 900℃ as described in claim 1, characterized in that, The high-entropy stainless steel, which is resistant to 900°C, also contains 0.001 to 0.005 wt% B.

6. The high-entropy stainless steel resistant to 900℃ as described in claim 1, characterized in that, The high-entropy stainless steel resistant to 900℃ also includes 0.005~0.080wt% RE, wherein the RE is selected from at least one element selected from La, Ce, Pr, Nd, Y and Sc.

7. A process for preparing high-entropy stainless steel resistant to 900℃ as described in any one of claims 1 to 6, characterized in that, The process includes the following steps: smelting and casting the components of high-entropy stainless steel resistant to 900℃ to obtain a billet; forging the billet into forgings, rolling it into plates, or rolling / drawing it into pipes; and performing solution treatment on the forgings, plates, or pipes at 1000~1150℃, followed by pickling after cooling to obtain the high-entropy stainless steel resistant to 900℃.

8. The application of a high-entropy stainless steel with a temperature resistance of 900°C as described in any one of claims 1 to 6 in pressure vessels, pipelines, boiler equipment, and heat exchange equipment with a heat resistance temperature below 900°C.

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