High-entropy stainless steel capable of resisting 900 DEG C as well as preparation process and application thereof

Abstract

The invention discloses high-entropy stainless steel capable of resisting 900 DEG C as well as a preparation process and application thereof, and relates to the technical field of stainless steel. The high-entropy stainless steel capable of resisting 900 DEG C comprises the following components in percentage by weight: less than or equal to 0.20% of C, 0.08-0.50% of N, 18.0-48.0% of Ni, 0.05-4.0% of Cu, 0-10.0% of Mo, 18.0-20.0% of Cr, 0.02-0.80% of Co, less than or equal to 1.0% of Si, less than or equal to 3.0% of Mn, less than or equal to 0.015% of S, less than or equal to 0.035% of P and 0.21-7.0% of high-entropy alloy elements. According to the technical scheme, Fe serves as a matrix, C and N serve as interstitial strengthening and precipitation strengthening elements, high-content Ni, Cr, Mo and Cu and a small amount of high-entropy alloy elements are matched, the solid solution strengthening and precipitation strengthening effects can be effectively improved, and the high-temperature strength of the material is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of stainless steel, and in particular to high-entropy stainless steel capable of withstanding temperatures of 900° C., and a preparation process and application thereof. Background Art

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

[0003] The most typical stainless steel in the 800 series is 800H stainless steel, which is an iron-nickel-based high-temperature alloy. It is famous for its strength, excellent oxidation resistance and carburization resistance under high temperature environment of 800℃. Its chemical composition includes 0.15~0.60wt% Ti and 0.15~0.60wt% Al. Ti and Al can stabilize C and N. The formed TiC, TiN and AlN have good stability in steel, but Al4C3 has poor stability in steel. Although the nitride formed by Ti and Al can prevent carbides (Cr 23 C6, etc.) diffuse and improve the high-temperature oxidation resistance of the material surface, but their contribution to high-temperature strength is small, resulting in a large decrease in the strength of the material above 800°C.

[0004] The more typical ones in the 310 series are 310S stainless steel and 310HNb stainless steel. 310S stainless steel can be used for a long time at 600~800℃, but it will have Cr 23 C6 precipitation causes Cr depletion at the grain boundaries, and at temperatures between 750°C and 900°C, FeCr intermetallic compounds, a brittle σ phase, precipitate, significantly reducing the material's impact toughness. The allowable stresses for high-alloy steel plates in Table C.2 of the materials section of GB / T 150.2, "Pressure Vessels," indicate that the permissible operating temperature for 310S stainless steel is 800°C. However, the allowable stresses for this material at 700°C and 800°C are only 19 MPa and 8 MPa, respectively. Because 310S stainless steel exhibits very low high-temperature allowable stresses between 700°C and 800°C, it is typically not used in pressure vessels, piping, boiler equipment, or heat exchange equipment above 700°C.

[0005] 310HNb is a 310S stainless steel with a constant carbon content (0.04-0.10 wt%) and the addition of 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°C. Summary of the Invention

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

[0007] To achieve the above object, the present invention proposes a high-entropy stainless steel capable of withstanding temperatures of 900°C, wherein the composition, by weight percentage, is as follows: 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; The high entropy alloy elements include at least Zr (zirconium), Nb (niobium) and W (tungsten).

[0008] Optionally, the high-entropy alloy 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%.

[0009] Preferably, the sum of the weight contents of Zr, Ti, Hf and Al is 0.26-0.81 wt %, the sum of the weight contents of Nb and V is 0.43-1.03 wt %, and the sum of the weight contents of W and Ta is 0.24-2.81 wt %.

[0010] Alternatively, 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); Wherein, 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.

[0011] Specifically, ∑W(Xi)=W(Zr)+W(Ti)+W(Hf)+W(Al)+W(Nb)+W(V)+W(W)+W(Ta); wherein 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.

[0012] Preferably, Ni eq With Cr eq The ratio is ≥1.1; further preferably, Ni eq With Cr eq The ratio is 1.13~1.16.

[0013] Optionally, M O Weight content ≤ 1 / 3 (M O The sum of the weight content of Cr and the weight content of Cr).

[0014] Optionally, the weight content of N is more than 2 times the weight content of C, and the sum of the weight content of N and the weight content of C is ≥0.15 wt %.

[0015] Optionally, the high-entropy stainless steel capable of withstanding temperatures of 900° C. further comprises 0.001 to 0.005 wt % of B (boron).

[0016] Preferably, the high entropy stainless steel capable of withstanding temperatures of 900° C. further comprises 0.003 wt % of B.

[0017] Optionally, the high-entropy stainless steel resistant to 900°C further includes 0.005-0.080 wt% of RE (rare earth element), wherein the RE is selected from at least one element of La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Y (yttrium) and Sc (scandium).

[0018] Preferably, the high-entropy stainless steel capable of withstanding temperatures of 900° C. further comprises 0.02 wt % of Ce.

[0019] The present invention also proposes a preparation process of high-entropy stainless steel that can withstand 900°C, comprising the following steps: smelting and casting the raw materials of the high-entropy stainless steel that can withstand 900°C to obtain a billet, forging the billet into a forging, or rolling it into a plate, or rolling / drawing it into a pipe; solution treating the forging, plate or pipe at 1000~1150°C, cooling and pickling it to obtain the high-entropy stainless steel that can withstand 900°C.

[0020] The present invention also proposes the use of any of the above-mentioned high-entropy stainless steels capable of withstanding temperatures of 900°C in pressure vessels, pipelines, boiler equipment and heat exchange equipment with a heat-resistant temperature below 900°C.

[0021] In the technical scheme of the present invention, with Fe, or, Fe and Ni as matrix, C and N as interstitial strengthening and precipitation strengthening elements, can play the effect of interstitial solid solution strengthening and precipitation strengthening, cooperate high content of Ni, Cr, Mo and Cu, can play the effect of good solid solution replacement, and add a small amount of high entropy alloying elements can further improve the solid solution strengthening effect, under the premise of ensuring that the material microstructure is austenite, effectively improve the high temperature strength of the material. Cr and Mo can play good corrosion resistance and high temperature oxidation resistance to stainless steel surface passivation film. Cu can further strengthen the stainless steel surface passivation film, and Cu and Ni can be infinitely mutually soluble, and also there will be a precipitation strengthening phase rich in Cu under high temperature conditions, which can play the effect of precipitation strengthening.

[0022] C and N, as the primary interstitial and precipitation strengthening elements, have a greater affinity for carbon and nitrogen than Cr. The high-entropy alloying elements formed with C and N (carbides and nitrides containing these elements) have higher melting points than chromium carbide and chromium nitride. This pins the carbon and nitrogen within the grains and at grain boundaries, creating a diffuse distribution and significantly improving the material's high-temperature strength. The formation of carbides and nitrides occurs sequentially and through a competitive mechanism. C in steel is much more active than N and has a faster diffusion rate. Adding N to form clustered high-entropy compounds helps stabilize C, and the N content must be higher than the C content to stabilize C.

[0023] During the cooling process of stainless steel smelting, casting, and crystallization, nitrogen preferentially forms nitrides with elements with a strong affinity. For high-entropy alloying elements such as Zr, Ti, Hf, Al, Nb, V, W, and Ta, nanoscale composite nitrides containing Ti, Zr, Hf, Al, V, Nb, and Cr preferentially precipitate between 900 and 1070°C. Subsequently, nanoscale composite carbides containing Ti, Zr, Hf, Ta, V, Nb, W, Mo, and Cr form below 900°C. The bonding properties of Co contribute to the aggregation of these nitrides and carbides, forming a nanoscale mixed precipitate phase. This pins carbon and nitrogen within the grains and at grain boundaries, resulting in a disordered precipitation state that is diffusely distributed throughout the material matrix. This prevents the formation of carbides in a network-like pattern at grain boundaries at high temperatures, thereby improving the material's resistance to intergranular corrosion and high-temperature creep. The addition of Co also stabilizes the secondary precipitates and facilitates the formation of a surface oxide film. Since carbides and nitrides have limited capacity 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 to replace iron atoms and improve the solid solution strengthening performance.

[0024] The addition of rare earth elements not only further removes sulfur and oxygen from the molten steel but also modifies the fine sulfides and oxides remaining in the steel, transforming them into high-melting-point spherical and spindle-shaped particles. This spheroidizes inclusions and improves the material's thermoplasticity. Strengthening grain boundaries with Co and rare earth elements maintains high levels of plasticity and toughness.

[0025] Compared with traditional 800H stainless steel and 310HNb stainless steel, the stainless steel material provided by the present invention has greatly improved strength while still having sufficient plasticity and toughness, so that the material has good deformation processing performance and welding performance, and can be well applied to high temperature environments of 800-900°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The metallographic structure of the stainless steel plate prepared in Example 1 was observed under a 100x optical microscope.

[0027] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0029] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture. If the specific posture changes, the directional indications will also change accordingly.

[0030] 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.

[0031] The present invention provides a high-entropy stainless steel capable of withstanding temperatures of 900°C. The stainless steel comprises, by weight percentage, 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 Fe and unavoidable impurities. The high-entropy alloying elements include at least Zr, Nb, and W.

[0032] In the technical solution of the present invention, C and N, as well as high-entropy alloying elements, are added to the iron matrix so that, under the condition that the material maintains the austenitic structure unchanged, the interstitial elements C and N can combine with the high-entropy alloying elements to form intermetallic compounds (nitrides containing high-entropy alloys, and carbides containing high-entropy alloys). Under the action of the Co binder, multiple intermetallic compounds form mixed entropy copolymers and adhere to the atomic clusters alloyed with the Fe-Ni-Cr basic elements. The second phase precipitates formed 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.

[0033] In high-entropy stainless steel materials with second-phase precipitates, due to the interaction and repulsion between multiple elements, the diffusion between these atoms will be slower than the diffusion of a single element, that is, a "delayed diffusion effect" will occur, and the diffusion coefficient is very low. They will be more difficult to diffuse, liquefy or rearrange than other alloys under the same heat, making the material have excellent stability.

[0034] Because the atoms of the elements that make up a high-entropy alloy vary in size, their replacement atoms and the resulting high-entropy compounds cause lattice distortion, enhancing the material's hardness. Precipitates composed of high-entropy compounds are formed by the accumulation of numerous atomic clusters, which cause even greater lattice distortion. This creates a localized stress field around them, hindering dislocation slip and further enhancing the material's hardness and strength.

[0035] The stainless steel provided by the present 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 parts, as well as other high-temperature and high-pressure environments that require corrosion resistance and wear resistance.

[0036] Furthermore, the high entropy alloy 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%.

[0037] By adopting the above technical solution and using Zr, Ti, Hf, Al, Nb, V, W and Ta as high-entropy alloy elements, the high-entropy effect can be effectively improved and the high-temperature strength of the material can be increased.

[0038] 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; 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); Wherein, 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.

[0039] By adopting the above technical solution, by controlling the ratio of nickel equivalent to chromium equivalent to not less than 0.85, the occurrence of ferrite residue in the microstructure of the material is avoided, thereby improving the high-temperature stability of the stainless steel material.

[0040] Furthermore, M O Weight content ≤ 1 / 3 (M O The sum of the weight content of Cr and the weight content of Cr).

[0041] By adopting the above technical solution, the addition of Mo can improve the high-temperature oxidation resistance and high-temperature strength of the stainless steel material. However, too high a content of Mo is likely to cause segregation. Therefore, the weight content of Mo is controlled to be no more than one-third of the sum of the weight contents of Mo and Cr.

[0042] 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 ≥0.15 wt %.

[0043] By adopting the above technical solution, although the increase of carbon and nitrogen has a direct strengthening effect on the mechanical properties of the material, 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, the nitrogen and carbon content needs to be further controlled.

[0044] Furthermore, the high-entropy stainless steel capable of withstanding temperatures of 900° C. further comprises 0.001 to 0.005 wt % of B.

[0045] By adopting the above technical solution and adding a specific content of B, the formability of the smelting billet in the later hot working can be effectively improved, and the high-temperature strength of the material can be improved to a certain extent.

[0046] Furthermore, the high-entropy stainless steel capable of withstanding temperatures of 900° C. further comprises 0.005 to 0.080 wt % of RE, wherein the RE is selected from at least one element of La, Ce, Pr, Nd, Y and Sc.

[0047] 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 Cr23 C6 grain boundary segregation. Rare earth elements spheroidize inclusions, improve the material's thermoplasticity, reduce the risk of cracks in continuous casting or die casting billets, and increase the toughness of the heat-affected zone of welding.

[0048] The present invention also proposes a preparation process of high-entropy stainless steel that can withstand 900°C, comprising the following steps: smelting and casting the raw materials of the high-entropy stainless steel that can withstand 900°C to obtain a billet, forging the billet into a forging, or rolling it into a plate, or rolling / drawing it into a pipe; solution treating the forging, plate or pipe at 1000~1150°C, cooling and pickling it to obtain the high-entropy stainless steel that can withstand 900°C.

[0049] Furthermore, the smelting includes the following steps: smelting the 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 0.035wt%.

[0050] The molten steel obtained from electric furnace smelting undergoes AOD (argon oxygen decarburization) refining. A mixture of oxygen and argon is blown to remove phosphorus and carbon, controlling the carbon content to the target. Deep deoxidation is achieved by adding aluminum, silicon, and calcium deoxidizers, partially reducing the chromium oxide formed by high-temperature oxidation to chromium, controlling the oxygen content to below 30 ppm. Deep desulfurization is also achieved by adding calcium, controlling the sulfur content to the target. The Cr, Ni, Mo, Mn, Cu, and Si contents are adjusted to the target levels. Then, raw materials for high-entropy alloying elements (excluding Ti, Zr, and Al) and Co are added. After stirring with argon to fully dissolve and mix the added elements, nitrogen and argon are switched between the two gases. Turbulent agitation of the molten steel allows nitrogen to react fully with the high-entropy alloying elements and Co in the molten steel to form carbonitrides. The nitrogen content is then controlled to meet the target. After the AOD stage, more than 50% of the high-phosphorus slag is removed to reduce the phosphorus content in the molten steel to the target.

[0051] The molten steel obtained from AOD refining is refined in LF (ladle refining furnace). The temperature of the molten steel is controlled at 1500~1650℃, the content of high-entropy alloy elements and Co is adjusted to meet the target content, Ti, Zr and Al raw materials are added, and the mixture is fully stirred with argon. The flotation principle of argon is used to further remove fine oxide slag in the molten steel to obtain a casting liquid with higher purity.

[0052] In the above technical solution, by controlling the oxygen content below 30 ppm, the reaction of the added high-entropy alloying elements with oxygen to form oxide inclusions is avoided. Ti, Zr, and Al react more actively with N and O at high temperatures than other high-entropy alloying elements. To avoid segregation during smelting, Ti, Zr, and Al are added to the smelting process after the other high-entropy alloying elements have been added and formed into stable compounds, making the resulting compounds more uniform and stable.

[0053] Furthermore, the casting liquid is cast by continuous casting or die casting under argon protective atmosphere; the raw materials of RE can be added into the ladle before casting, or added into the flowing casting liquid formed in the process of conveying the casting liquid during casting.

[0054] Furthermore, the method of forging the cast blank into a plate includes: casting the casting liquid by die casting under an argon protective atmosphere, controlling the casting temperature at 1540-1560°C, cutting the head and tail of the cast blank to obtain a forged blank.

[0055] The forging blank is cut into pieces and heated in a furnace at 1080-1200℃ for more than 60 minutes. After being taken out of the furnace, the blank is forged into a square forging, which is then cut into plates to produce formed plates. If the temperature of the blank drops to around 900℃ during the forging process, it should be reheated to above 1080℃ and forged again.

[0056] The formed plates are rough-machined to the approximate dimensions specified in the drawings, subjected to solution heat treatment, immediately water-cooled after being taken out of the furnace, and then fine-machined to the dimensions specified in the drawings to produce high-entropy stainless steel forging plates that can withstand 900°C.

[0057] Furthermore, the temperature during the solution treatment is 1000-1150° C., and the solution treatment time is calculated as 1-5 minutes per millimeter of the thickness of the forging, plate or pipe.

[0058] 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 obtained stainless steel plates, pipes and forgings.

[0059] The present invention also proposes an application of the high-entropy stainless steel capable of withstanding 900°C as described above in pressure vessels, pipelines, boiler equipment and heat exchange equipment with a heat-resistant temperature below 900°C.

[0060] The technical solutions of the present invention are further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention. Examples 1 to 4

[0061] Examples 1 to 4 provide a high entropy stainless steel capable of withstanding temperatures of 900°C, the chemical composition and content of which are shown in Table 1 below. A process for preparing high entropy stainless steel capable of withstanding temperatures of 900°C comprises the following steps: (1) The raw materials of Fe, Cr, Ni, Mo, Mn and Cu are smelted in an electric furnace according to the charge of 10,000 kg of molten steel. The content of SiO2 during the metallurgical reaction is calculated, and sufficient CaO and CaF2 are added to maintain the alkalinity of the high-alkalinity slag system between 2.6 and 3.2. The temperature is controlled between 1500℃ and 1600℃ for oxygen dephosphorization. After dephosphorization is completed, the oxygen blowing amount is increased and decarburization is carried out between 1650℃ and 1750℃. After decarburization is completed, ferrosilicon is added to perform preliminary reduction treatment on Cr2O3 oxidized at high temperature. More than 60% of the high-phosphorus slag is removed and the P content is controlled below 0.035wt%.

[0062] (2) The molten steel obtained from electric furnace smelting is subjected to AOD refining. P and C are removed by top blowing oxygen and bottom blowing argon. The C content is controlled to the target content. Deep deoxidation is carried out by adding aluminum, silicon, and calcium deoxidizers, and the chromium oxide formed by high-temperature oxidation is partially reduced to Cr. The oxygen content is controlled below 30 ppm. Deep desulfurization is carried out by adding calcium treatment to control the S content to the target content. The contents of Cr, Ni, Mo, Mn, Cu, and Si are adjusted to the target contents. Then, microalloying element raw materials other than Ti, Zr, and Al, as well as Co raw materials, are added. After stirring with argon to fully dissolve and mix the added elements, nitrogen and argon are switched to increase nitrogen by turbulent stirring of the molten steel, so that nitrogen reacts fully with the high-entropy alloying elements and Co in the molten steel to form carbonitrides, and the N content is controlled to meet the target content. After the AOD stage smelting is completed, more than 50% of the high-phosphorus slag is removed to control the P content to the target content.

[0063] (3) The molten steel obtained by AOD refining is subjected to LF refining. The temperature of the molten steel is controlled at 1560℃~1650℃. The contents of microalloying elements and Co are adjusted to meet the target contents. Raw materials of Ti, Zr and Al are added and fully stirred with argon to make the metallurgical reaction more sufficient and uniform. The flotation principle of argon is used to make the tiny inclusions remaining in the steel float up into the slag system, thereby obtaining a casting liquid with higher purity.

[0064] (4) Under the condition of argon protective atmosphere, the casting liquid is cast by die casting, the casting temperature is controlled at 1540~1560℃, and the casting billet is cut off to obtain the forging billet.

[0065] (5) Cut the forging blank, heat it in the furnace, and keep it at 1080-1200℃ for more than 60 minutes. After taking it out of the furnace, 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 formed plates. If the temperature of the blank drops to about 900℃ during the forging process, it should be reheated to above 1080℃ and continue forging.

[0066] (6) The formed plate is rough-machined to the approximate size specified in the drawing, and then subjected to solution heat treatment at a temperature of 1050°C for 60 minutes. After being immediately water-cooled after being taken out of the furnace, it is fine-machined to the size specified in the drawing to produce a high-entropy stainless steel forging plate that can withstand 900°C.

[0067] Table 1 Chemical composition and content of stainless steel (unit: wt%) 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 inevitable impurities margin margin margin margin Example 5

[0068] This embodiment is based on embodiment 1, with the difference that the chemical composition of the high entropy stainless steel capable of withstanding 900°C further includes 0.003 wt% of B. In step (3), when adding the raw materials of Ti, Zr and Al, the raw material of B is added, and the rest remains the same as in embodiment 1. Example 6

[0069] This embodiment is based on embodiment 1, with the difference that the chemical composition of the high-entropy stainless steel capable of withstanding 900°C further includes 0.02 wt% of Ce. In step (4), the Ce raw material is added to the ladle before casting, and then the casting liquid is cast. The rest remains the same as embodiment 1. Comparative Example 1

[0070] The plate of this comparative example is a commercially available 800H stainless steel plate. Comparative Example 2

[0071] The plate of this comparative example is a commercially available 310HNb stainless steel plate. Performance test

[0072] The plates of Examples 1 to 6 and Comparative Examples 1 to 2 were subjected to room temperature tensile tests and high temperature tensile tests. The room temperature tensile test was carried out in accordance with GB / T 228.1-2021 "Tensile Test of Metallic Materials" Part 1, Room Temperature Test Method; the high temperature tensile test was carried out in accordance with GB / T 228.2-2015 "Test Methods of Metallic Materials" Part 2, High Temperature Test Method. The test results are shown in Table 2 below.

[0073] Table 2 Results of room temperature tensile test and high temperature tensile test

[0074] The test results in Table 2 show that the stainless steel sheets prepared in Examples 1 to 6 of the present invention have excellent high-temperature strength and have better high-temperature performance at high temperatures of 900°C or below than other iron-nickel-based stainless steels such as 800H and 310HNb.

[0075] The metallographic structure of the stainless steel plate prepared in Example 1 was observed under a 100x optical microscope. Figure 1 As shown. Figure 1 The metallographic structure of the material is pure austenite, with no residual ferrite. Subgrains and twins are present within the austenite in the field of view, with no obvious second-phase precipitates, only extremely small dispersed particles. The metallographic photographs show a higher number of twins than conventional austenitic stainless steel. Twins enhance strength while also providing improved high-temperature creep resistance.

[0076] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of the present invention.

Claims

1. A high entropy stainless steel capable of withstanding temperatures of 900°C, characterized in that: The composition is as follows by weight percentage: C ≤ 0.20 wt%, N 0.08-0.50 wt%, Ni 18.0-48.0 wt%, Cu 0.05-4.0 wt%, Mo 0-10.0 wt%, Cr 18.0-20.0 wt%, Co 0.02-0.80 wt%, Si ≤ 1.0 wt%, Mn ≤ 3.0 wt%, S ≤ 0.015 wt%, P ≤ 0.035 wt%, high entropy alloying elements 0.21-7.0 wt%, and the balance is Fe and unavoidable impurities; Wherein, the high entropy alloy elements include at least Zr, Nb and W.

2. The high entropy stainless steel capable of withstanding 900°C as claimed in claim 1, characterized in that: The high entropy alloy 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%.

3. The high entropy stainless steel capable of withstanding 900°C as claimed in claim 2, 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); Wherein, 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.

4. The high entropy stainless steel capable of withstanding 900°C as claimed in claim 1, characterized in that: M O Weight content ≤ 1 / 3 (M O The sum of the weight content of Cr and the weight content of Cr).

5. The high entropy stainless steel capable of withstanding 900°C as claimed in claim 1, characterized in that: The weight content of N is more than 2 times the weight content of C, and the sum of the weight content of N and the weight content of C is ≥0.15wt%.

6. The high entropy stainless steel capable of withstanding 900°C as claimed in claim 1, characterized in that: The high-entropy stainless steel capable of withstanding temperatures of 900° C. further comprises 0.001 to 0.005 wt % of B.

7. The high entropy stainless steel capable of withstanding 900°C as claimed in claim 1, characterized in that: The high-entropy stainless steel capable of withstanding temperatures of 900° C. further comprises 0.005 to 0.080 wt % of RE, wherein the RE is selected from at least one element of La, Ce, Pr, Nd, Y, and Sc.

8. A process for preparing high-entropy stainless steel capable of withstanding temperatures of 900°C, characterized in that: The following steps are involved: The raw material of the high-entropy stainless steel capable of withstanding 900°C is smelted and cast to obtain a billet, which is then forged into a forging, rolled into a plate, or rolled / drawn into a pipe. The forging, plate, or pipe is solution treated at 1000-1150°C, cooled, and then pickled to obtain the high-entropy stainless steel capable of withstanding 900°C.

9. Use of the high-entropy stainless steel capable of withstanding 900°C as claimed in any one of claims 1 to 7 in pressure vessels, pipelines, boiler equipment and heat exchange equipment with a heat-resistant temperature below 900°C.

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