High temperature resistant high entropy stainless steel and its preparation process and application

Abstract

The present invention discloses high-temperature resistant high-entropy stainless steel, its preparation process and application, and relates to the technical field of stainless steel. The composition of the high-temperature resistant high-entropy stainless steel includes: C 0.03-0.15wt%, N 0.08-0.30wt%, Si≤1.0wt%, Mn≤3.0wt%, S≤0.015wt%, P≤0.035wt%, Cr 16.0-22.0wt%, Ni 9.0-14.0wt%, microalloying elements 0.18-3.6wt%, Mo 0.04-4.0wt%, Co 0.05-0.80wt%, RE 0-0.10wt%. In the technical solution of the present application, C and N can form nano-scale second phase precipitates with microalloying elements such as Ti, Zr, Hf, Ta, V, W and Nb in the crystal, which not only has the effects of solid solution strengthening and precipitation strengthening, but also has a significant improvement in the high-temperature strength of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of stainless steel, and in particular to high-temperature resistant high-entropy stainless steel and a preparation process thereof. Background Art

[0002] 347H (S34709 in the ASME standard) is available in plates, tubes, and forgings, and is commonly used in high-temperature environments in nuclear power, thermal power, solar molten salt reactors, and the petrochemical industry. Following the introduction of the ASME standard in my country, the corresponding grade is S34779 in the GB / T24511 and GB / T713.7 stainless steel plate and strip standards.

[0003] The chemical composition characteristics of 347H are as follows: Carbon (C) 0.04~0.10wt%, Silicon (Si) ≤1.0wt%, Manganese (Mn) ≤2.0wt%, Sulfur (S) ≤0.03wt%, Phosphorus (P) ≤0.045wt%, Chromium (Cr) 17.0~19.0wt%, Nickel (Ni) 9.0~13.0wt%, Niobium (Nb) 8 times the carbon content ~1.1wt%. 347H uses Nb as a stabilizing element for C, producing niobium carbide precipitation in the material matrix to avoid the formation of chromium carbide (Cr) at the grain boundaries during welding thermal cycles and high temperature environments. 23 C6). Niobium carbide remains relatively stable at high temperatures around 600°C and does not diffuse to grain boundaries, thus meeting the requirements for long-term safe and reliable operation at high temperatures.

[0004] While TP347H material can operate reliably in high-temperature environments around 600°C, its strength decreases significantly above 600°C. While the ASME code and GB / T150 standard cover design temperatures up to 700°C, its use in environments above 650°C is generally not recommended due to the material's strength and safety risks. In supercritical (SC) and ultra-supercritical (USC) thermal power plants, TP347H is commonly used in boiler superheater and reheater tubes, where steam temperatures typically range from 600°C to 625°C, lower than 650°C. Therefore, the use of TP347H in high-temperature environments above 650°C still has certain limitations. Summary of the Invention

[0005] The main purpose of the present invention is to propose a high-temperature resistant high-entropy stainless steel and its preparation process, aiming to solve the problem that the existing 347H has a large strength drop in a high-temperature environment above 650°C.

[0006] To achieve the above objectives, the present invention provides a high-temperature resistant, high-entropy stainless steel, comprising, by weight percentage, the following components: C (carbon) 0.03-0.15wt%, N (nitrogen) 0.08-0.30wt%, Si (silicon) ≤1.0wt%, Mn (manganese) ≤3.0wt%, S (sulfur) ≤0.015wt%, P (phosphorus) ≤0.035wt%, Cr (chromium) 16.0-22.0wt%, Ni (nickel) 9.0-14.0wt%, microalloying elements 0.18-3.6wt%, Mo (molybdenum) 0.04-4.0wt%, Co (cobalt) 0.05-0.80wt%, RE (rare earth elements) 0-0.10wt%, and the balance being Fe (iron) and unavoidable impurities.

[0007] The microalloying elements are selected from at least three elements of Ti (titanium), Zr (zirconium), Hf (hafnium), Ta (tantalum), V (vanadium), W (tungsten) and Nb (niobium).

[0008] Preferably, RE is at least one element selected from La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Y (yttrium) and Sc (scandium); further preferably, the content of RE is 0.005-0.08 wt%.

[0009] Optionally, the microalloying elements include Ti, Zr, Hf, Ta, V, W and Nb, and the sum of Ti and Zr contents is 0.02-0.5wt%, the sum of Hf and Ta contents is 0-0.5wt%, V 0.04-0.8wt%, W 0.04-0.8wt%, and Nb 0.08-1.0wt%.

[0010] Optionally, the N content is more than twice the C content.

[0011] The present invention also proposes a preparation process of high-temperature resistant high-entropy stainless steel, comprising the following steps: smelting and casting the raw materials of the high-temperature resistant high-entropy stainless steel to obtain a rolled billet, forging the rolled billet into a forging, or rolling it into a plate, or rolling / drawing it into a pipe; solution treating the forging, plate or pipe, cooling it and then pickling it to obtain the high-temperature resistant high-entropy stainless steel.

[0012] Optionally, the smelting comprises the following steps: smelting raw materials of Fe, Cr, Ni, Mo, Mn and Si in an electric furnace, adding CaO and CaF2 for desulfurization and dephosphorization, and controlling the S content in the molten steel to be below 0.015wt% and the P content to be below 0.035wt%;

[0013] The molten steel obtained from electric furnace smelting is subjected to AOD (argon oxygen decarburization) refining. Carbon is removed by blowing a mixture of oxygen and argon to control the carbon content to the target content. The Cr, Ni, Mo, Mn, and Si contents are also adjusted to the target contents. Deep deoxidation is performed by adding ferrosilicon, Al, and Ca to control the oxygen content below 30 ppm. Then, microalloying element raw materials other than Ti and Zr, as well as Co raw materials, are added. After stirring with argon, nitrogen is switched to the flow. The turbulent agitation of the molten steel is used to increase nitrogen, so that the nitrogen fully reacts with the microalloying elements and Co in the molten steel to form nitrides. The nitrogen content is controlled to meet the target content.

[0014] The molten steel obtained by AOD refining is subjected to LF (ladle refining furnace) refining, the contents of microalloying elements and Co are adjusted to meet the target contents, the molten steel temperature is controlled at 1580~1650℃, Ti and Zr raw materials are added, and the molten steel is fully stirred with argon to obtain a casting liquid.

[0015] Optionally, the casting comprises the following steps: casting the casting liquid by continuous casting or die casting under an argon protective atmosphere;

[0016] The raw materials of RE can be added into the ladle before casting, or added into the flowing casting liquid during casting. The flowing casting liquid refers to the flowing casting liquid formed in the process of conveying the casting liquid.

[0017] Optionally, the temperature during the solution treatment is 1000-1080° C., and the solution treatment time is calculated based on 1-5 minutes per millimeter of the thickness of the forging, plate or pipe.

[0018] The present invention also proposes the use of any of the above-mentioned high-temperature resistant high-entropy stainless steels in pressure vessels, pipelines, boiler equipment and heat exchange equipment with a heat-resistant temperature below 750°C.

[0019] While maintaining the material's austenitic structure, the technical solution of this invention controls the carbon content while simultaneously adding a specific amount of nitrogen. This promotes the formation of interstitial solid solutions of carbon and nitrogen within the austenite lattice, thereby achieving interstitial strengthening. Both carbon and nitrogen react with microalloying elements to form nanoscale dispersed second-phase precipitates within the grains and at grain boundaries. For example, carbides containing tungsten carbide and nitrides containing niobium nitride form mixed entropy copolymers, which possess a high entropy value and significantly enhance the material's high-temperature strength compared to existing single compounds (niobium carbide).

[0020] In the copolymers with mixed entropy formed, the coexistence of multiple elements makes the diffusion behavior complex. 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, the "delayed diffusion effect" will appear, that is, the diffusion coefficient will decrease. Under the same heat, they will be more difficult to diffuse, liquefy or rearrange than other alloys, making the material have excellent stability at high temperatures.

[0021] The atoms of the elements that make up the high-entropy alloy have different sizes. The precipitates composed of high-entropy compounds are formed by the accumulation of numerous atomic clusters, which causes a greater lattice distortion effect. A local stress field is formed around them, which hinders the slip of dislocations and further improves the hardness and strength of the material.

[0022] Co acts as a binder for carbides and nitrides, allowing a variety of precipitates to mix together, making nano-scale precipitates more stable, improving the toughness and high-temperature performance of the material, and also helping to form a surface oxide film, making the material more corrosion-resistant. After the casting liquid is cast and solidified, different nitrides gradually precipitate above 900°C, and then meet with carbides precipitated below 900°C. Through the bonding effect of Co, a variety of compounds are mixed together to form a composite precipitated strengthening phase, making the nano-scale precipitates more stable. These high-melting point strengthening phases are pinned within the crystal, stabilizing C and N very well and preventing them from diffusing to the grain boundaries. In addition, cobalt and RE can significantly increase the grain boundary energy of stainless steel, thereby improving the ductility behavior of the grain boundaries and giving the material sufficient plasticity and toughness.

[0023] These strengthening phases composed of multiple stabilizing elements essentially have the high hardness and high melting point characteristics of the ceramic phase and will not decompose or diffuse at high temperatures. They not only have the effects of solid solution strengthening and precipitation strengthening, but also have a significant improvement on the high-temperature strength of the material.

[0024] 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, transmission pipelines, heat exchangers, air coolers and high-temperature structural parts. They can also be used to make turbine disks and turbine blades for high-temperature turbines below 750°C, as well as other high-temperature and high-pressure environments that require corrosion resistance and wear resistance.

[0025] Compared to conventional 347H stainless steel, the high-entropy stainless steel provided by this invention boasts significantly improved strength while maintaining sufficient plasticity and toughness, resulting in excellent deformation and weldability. This increased strength allows for reduced design thicknesses for pipelines and pressure vessels. This reduction in wall thickness significantly reduces the amount of weld metal required, which in turn significantly reduces weld stress in welded joints and reduces the risk of stress corrosion cracking during device operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The metallographic structure diagram of the stainless steel plate prepared in Example 3 observed under a 100x optical microscope provided by the present invention;

[0027] Figure 2 The metallographic structure diagram of the stainless steel plate obtained in Example 3 observed under a 1000x optical microscope provided by the present invention;

[0028] Figure 3 The metallographic structure diagram of the stainless steel plate obtained in Example 3 observed under a 10,000x optical microscope provided by the present invention;

[0029] Figure 4 The atomic spectrum of the distribution of W atoms in the grains of the stainless steel plate obtained in Example 3 is observed at a 50,000x field of view provided by the present invention;

[0030] Figure 5 The atomic spectrum of the distribution of Fe atoms in the grains of the stainless steel plate prepared in Example 3 is observed at a 50,000x field of view provided by the present invention.

[0031] 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

[0032] 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.

[0033] 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.

[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] The present invention provides a high-temperature resistant high-entropy stainless steel. The stainless steel comprises, by weight percentage, the following components: C 0.03-0.15wt%, N 0.08-0.30wt%, Si≤1.0wt%, Mn≤3.0wt%, S≤0.015wt%, P≤0.035wt%, Cr 16.0-22.0wt%, Ni 9.0-14.0wt%, microalloying elements 0.18-3.6wt%, Mo 0.04-4.0wt%, Co 0.05-0.80wt%, RE 0-0.10wt%, and the balance being Fe and unavoidable impurities. The microalloying elements are selected from at least three elements of Ti, Zr, Hf, Ta, V, W, and Nb.

[0036] In the technical solution of the present invention, a specific content of microalloying elements is added to form a substitutional solid solution to improve the high-temperature performance of the material. By limiting the carbon content and adding nitrogen at the same time, the nitrogen content is controlled within a certain range of ≥0.08wt%, which promotes the formation of interstitial solid solutions of carbon and nitrogen in the austenite lattice, thereby improving the strength of the material. C and nitrogen form nanoscale second-phase high-entropy precipitates with the microalloying elements within the crystal, resulting in lattice distortion. During the deformation process of the material, dislocation movement is hindered through a bypass mechanism, thereby improving the strength and high-temperature creep performance of the material.

[0037] It should be noted that while C and N have a direct strengthening effect on the mechanical properties of the material, excessive C and N can easily precipitate carbides and nitrides at grain boundaries, affecting the material's high-temperature performance and hindering its forming and welding. Therefore, the C content is controlled to be 0.03-0.15 wt%, and the N content is controlled to be 0.08-0.30 wt%. Preferably, the N content is at least twice the C content. RE is selected from one of La, Ce, Pr, Nd, Y, and Sc, and the RE content is 0.005-0.08 wt%.

[0038] Furthermore, the microalloying elements include Ti, Zr, Hf, Ta, V, W, and Nb, with the sum of Ti and Zr being 0.02-0.5 wt%, the sum of Hf and Ta being 0-0.5 wt%, V 0.04-0.8 wt%, W 0.04-0.8 wt%, and Nb 0.08-1.0 wt%. Given the high prices of Ta and Hf, they may be added as needed in practical applications.

[0039] The present invention also provides a process for preparing high-temperature-resistant, high-entropy stainless steel, comprising the following steps: smelting and casting the raw material of the high-temperature-resistant, high-entropy stainless steel to obtain a rolled billet; forging the rolled billet into a forging, rolling it into a plate, or rolling / drawing it into a tube; and solution treating the forging, plate, or tube, cooling it, and then pickling it to obtain the high-temperature-resistant, high-entropy stainless steel. It should be noted that rolling / drawing refers to a combination of rolling and drawing.

[0040] Furthermore, the smelting comprises the following steps: subjecting raw materials of Fe, Cr, Ni, Mo, Mn and Si to electric furnace smelting, adding CaO and CaF2 for desulfurization and dephosphorization, and controlling the S content in the molten steel to be below 0.015wt% and the P content to be below 0.035wt%;

[0041] The molten steel obtained by electric furnace smelting is subjected to AOD refining. Carbon is removed by blowing a mixture of oxygen and argon to control the carbon content to a target content, and the contents of Cr, Ni, Mo, Mn, and Si are adjusted to target contents. Deep deoxidation is performed by adding ferrosilicon, Al, and Ca to control the oxygen content to below 30 ppm. Then, raw materials of microalloying elements (excluding Ti and Zr) and Co are added. After stirring with argon, nitrogen is switched to the flow. Nitrogen is added by turbulent agitation of the molten steel to allow the nitrogen to fully react with the microalloying elements and Co in the molten steel to form nitrides, and the nitrogen content is controlled to meet the target content.

[0042] The molten steel obtained by AOD refining is subjected to LF refining, the contents of microalloying elements and Co are adjusted to meet the target contents, the molten steel temperature is controlled at 1580~1650℃, Ti and Zr raw materials are added, and the molten steel is fully stirred with argon to obtain a casting liquid.

[0043] In the above technical solution, the addition of aluminum, silicon, and calcium reduces the oxygen content to below 30 ppm, preventing the reaction of the added microalloying elements with oxygen to form oxide inclusions. Zr and Ti react more actively with nitrogen and oxygen at high temperatures than other microalloying elements. To avoid segregation during smelting, Zr and Ti are added after the other microalloying elements have been added and formed into stable compounds, resulting in a more uniform and stable compound.

[0044] Specifically, the casting liquid is cast in an argon protective atmosphere by continuous casting or mold casting. The raw materials of RE can be added into the ladle before casting, or added into the flowing casting liquid during casting.

[0045] Furthermore, the temperature during the solution treatment is 1000-1080° C., and the solution treatment time is calculated based on 1-5 minutes per millimeter of the thickness of the forging, plate or pipe.

[0046] In the above technical solution, austenitic stainless steel experiences rapid grain growth above 1080°C. Excessively coarse grains in austenitic stainless steel can lead to cracking in the heat-affected zone (HAZ) during welding and high-temperature stress relaxation due to grain boundary sliding resistance. To improve the reliability of welded joints and enhance high-temperature performance, the present invention controls the solution heat treatment temperature between 1000°C and 1080°C to prevent grain growth during the solution treatment process. This results in a grain size of 4 to 10 for the resulting stainless steel plates, pipes, and forgings.

[0047] The present invention also proposes an application of the high-temperature resistant high-entropy stainless steel in pressure vessels, pipelines, boiler equipment and heat exchange equipment with a heat-resistant temperature below 750°C.

[0048] 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.

[0049] Examples 1-3

[0050] Examples 1 to 3 provide a high-temperature resistant high-entropy stainless steel, the chemical composition and content of which are shown in Table 1 below. A preparation process for high-temperature resistant high-entropy stainless steel comprises the following steps:

[0051] (1) The raw materials of Fe, Cr, Ni, Mo, Mn and Si are smelted in an electric furnace, and CaO and CaF2 are added for desulfurization and dephosphorization. The S content in the molten steel is controlled below 0.015wt% and the P content is controlled below 0.035wt%.

[0052] (2) The molten steel obtained by electric furnace smelting is subjected to AOD refining, and carbon is removed by blowing a mixture of oxygen and argon to control the C content to the target content, and the contents of Cr, Ni, Mo, Mn and Si are adjusted to the target contents. Deep deoxidation is carried out by adding ferrosilicon, Al and Ca to control the oxygen content below 30 ppm. Then, raw materials of microalloying elements other than Ti and Zr and raw materials of Co are added, and nitrogen is switched after stirring with argon. The turbulent flow of the molten steel is used to increase nitrogen, so that the nitrogen reacts fully with the microalloying elements and Co in the molten steel to form nitrides, and the N content is controlled to meet the target content.

[0053] (3) The molten steel obtained by AOD refining is subjected to LF refining, and the contents of microalloying elements and Co are adjusted to meet the target contents. The temperature of the molten steel is controlled at 1600°C, and the raw materials of Ti and Zr are added. The molten steel is fully stirred with argon to obtain a casting liquid.

[0054] (4) Under the condition of argon protective atmosphere, the casting liquid is cast by die casting, the casting temperature is controlled at 1520~1580℃, and the casting billet is cut off to obtain the forging billet.

[0055] (5) Cut the forging blank, heat it in the furnace, and keep it at 1100-1150℃ for more than 60 minutes. After it is taken 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. In order to avoid the precipitation of carbides below 900℃, the final forging temperature is specified to be 900℃. If the blank drops to about 900℃ during the forging process, it should be reheated to above 1080℃ and continue forging.

[0056] (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 50 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 obtain a high-temperature resistant high-entropy stainless steel forging plate.

[0057] Table 1 Chemical composition and content of Examples 1 to 3 (unit: wt%)

[0058] Example C N Si Mn Cr Ni Ti Zr V W Nb Mo Co Fe and impurities 1 0.03 0.08 0.31 1.05 16.18 9.07 0.01 0.01 0 0.08 0.08 0.04 0.05 margin 2 0.144 0.3 0.88 2.96 21.94 13.88 0.25 0.25 0.8 0.8 1.0 4.0 0.8 margin 3 0.042 0.15 0.35 1.11 18.87 9.78 0.12 0.12 0.11 0.24 0.26 2.6 0.11 margin Example 4

[0059] This embodiment is based on embodiment 3, with the difference that the chemical composition of the high-temperature resistant high-entropy stainless steel also includes La (lanthanum) with a content of 0.01 wt%; in step (4), the raw material of La is added to the ladle before casting, and then the casting liquid is cast.

[0060] Comparative Example 1

[0061] This comparative example is the commercially available S34709 (347H) board.

[0062] Performance test

[0063] The plates of Examples 1 to 4 and Comparative Example 1 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 Tests on 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 for Metallic Materials" Part 2: High Temperature Test Method. The test results are shown in Table 2 below.

[0064] Table 2 Results of room temperature tensile test and high temperature tensile test

[0065] Test conditions Test items Example 1 Example 2 Example 3 Example 4 Comparative Example 1 normal temperature <![CDATA[Tensile strength R m (MPa)]]> 602 715 677 680 574 <![CDATA[Yield strength R p0.2 (MPa)]]> 346 395 377 378 240 600℃ <![CDATA[Tensile strength R m (MPa)]]> 383 487 429 433 321 <![CDATA[Yield strength R p0.2 (MPa)]]> 174 234 204 206 98 650℃ <![CDATA[Tensile strength R m (MPa)]]> 351 453 394 399 285 <![CDATA[Yield strength R p0.2 (MPa)]]> 166 228 202 203 93 700℃ <![CDATA[Tensile strength R m (MPa)]]> 295 396 338 340 239 <![CDATA[Yield strength R p0.2 (MPa)]]> 141 214 181 184 71 750℃ <![CDATA[Tensile strength R m (MPa)]]> 239 325 280 283 185 <![CDATA[Yield strength R p0.2 (MPa)]]> 124 198 166 167 60

[0066] From the test results in Table 2, it can be seen that the strength of the plate produced in the present application is much higher than that of the S34709 / 347H stainless steel plate of the ASME standard.

[0067] If the materials in this case are used for the design, manufacture and use of pressure vessels, the allowable stress is calculated by dividing the yield strength by a coefficient of 1.5. The allowable stress of the stainless steel plate produced in Example 3 of this application is as high as 121 MPa at 700°C, and at 750°C, the allowable stress is also as high as 111 MPa. It can be seen that the stainless steel plate produced in this application has excellent high-temperature performance.

[0068] The metallographic structure of the stainless steel plate obtained in Example 3 was observed under a 100x optical microscope. Figure 1 As shown. Figure 1 It can be seen that under a 100x optical microscope, the metallographic structure of the material is pure austenite with no residual ferrite. There are subgrains and twins in the austenite in the field of view, and no obvious second phase precipitates can be seen, only extremely small dispersed particles. From the metallographic photos, it can be observed that there are more twins than conventional austenitic stainless steel. Twins are a coherent interface whose sudden change in crystallographic orientation hinders dislocation slip, similar to the role of grain boundaries. Dislocations need to consume additional energy to pass through or bypass twin boundaries, thereby increasing strength. The more twins there are, the greater the contribution to strength, but at the same time some plasticity and toughness will be sacrificed. While twins increase strength, they also have better resistance to high-temperature creep.

[0069] The metallographic structure of the stainless steel plate obtained in Example 3 was observed under a 1000x optical microscope. Figure 2 As shown. Figure 2 It can be seen that tiny white precipitate particles can only be observed when the electron microscope is magnified to more than 1000 times. Judging from the electron microscope scale, these dispersed precipitates are all nano-scale particles.

[0070] The metallographic structure of the stainless steel plate obtained in Example 3 was observed under a 10,000x optical microscope. Figure 3 As shown. Figure 3 Under a 10,000x electron microscope, the large, scaled second-phase particles are all larger than 100 nm. These scaled precipitates contribute to the strengthening mechanism of dislocation bypass during lattice deformation. However, the larger number of second-phase precipitates smaller than 100 nm contribute to the strengthening mechanism of dislocation cutting during lattice deformation. These second-phase precipitates hinder dislocation motion, significantly contributing to the material's high-temperature creep performance.

[0071] By performing electron microscopy and energy spectrum analysis on the stainless steel plate obtained in Example 3, point scanning was performed by backscattering in a 10,000x field of view to collect the second phase high entropy precipitates. Through backscattering energy spectrum analysis of the second phase precipitates, it was found that these precipitates not only contained high entropy compounds formed by Zr, Nb, W, V and Co with C and N, but also accompanied by major alloying elements such as Cr, Ni, Fe, Mn and Si. These nanoclusters of high entropy compounds aggregate together to form a pinning effect, which can prevent Cr from forming Cr with C. 23 The single compound of C6 aggregates toward the grain boundaries.

[0072] Under a 50,000x field of view, the stainless steel plate prepared in Example 3 was subjected to an energy spectrum scan (excluding the precipitated phase) to obtain a high-magnification atomic spectrum. Figure 4 This is a high-magnification atomic spectrum of the distribution of W atoms in the grains. Figure 5 This is a high-magnification atomic spectrum of the distribution of Fe atoms in the grains. Figures 4 and 5 It can be seen that the distribution density of Fe atoms in the field of view is the largest, and elements such as W, Nb, and Co are distributed very evenly in the lattice of iron atoms and have been completely replaced in the lattice arrangement of the iron atoms, playing a strengthening role of solid solution substitution.

[0073] 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 temperature resistant high entropy stainless steel, characterized in that: The composition is as follows by weight percentage: C 0.03-0.15wt%, N 0.08-0.30wt%, Si≤1.0wt%, Mn≤3.0wt%, S≤0.015wt%, P≤0.035wt%, Cr 16.0-22.0wt%, Ni 9.0-14.0wt%, microalloying elements 0.18-3.6wt%, Mo 0.04-4.0wt%, Co 0.05-0.80wt%, RE 0-0.10wt%, and the balance is Fe and unavoidable impurities; The microalloying elements are Ti, Zr, Hf, Ta, V, W and Nb, wherein the sum of Ti and Zr content is 0.02-0.5wt%, the sum of Hf and Ta content is 0-0.5wt%, V 0.04-0.8wt%, W 0.04-0.8wt%, and Nb 0.08-1.0wt%; The preparation process of the high-temperature resistant high-entropy stainless steel comprises the following steps: smelting and casting the raw material of the high-temperature resistant high-entropy stainless steel to obtain a rolled billet; forging the rolled billet into a forging, or rolling it into a plate, or rolling / drawing it into a pipe; solution treating the forging, plate or pipe, cooling it, and then pickling it to obtain the high-temperature resistant high-entropy stainless steel; The smelting process includes the following steps: smelting raw materials of Fe, Cr, Ni, Mo, Mn and Si in an electric furnace, adding CaO and CaF2 for desulfurization and dephosphorization, and controlling the S content in the molten steel to be below 0.015wt% and the P content to be below 0.035wt%; The molten steel obtained by electric furnace smelting is subjected to AOD refining, and carbon is removed by blowing a mixture of oxygen and argon to control the carbon content to a target content, and the contents of Cr, Ni, Mo, Mn and Si are adjusted to target contents. Deep deoxidation is performed by adding ferrosilicon, Al and Ca to control the oxygen content to below 30 ppm. Then, microalloying element raw materials other than Ti and Zr and Co raw material are added. After stirring with argon, nitrogen is switched to flow. Nitrogen is added by utilizing turbulent stirring of the molten steel, so that the nitrogen fully reacts with the microalloying elements and Co in the molten steel to form nitrides, and the nitrogen content is controlled to meet the target content. The molten steel obtained by AOD refining is subjected to LF refining, the contents of microalloying elements and Co are adjusted to meet the target contents, the molten steel temperature is controlled at 1580~1650℃, Ti and Zr raw materials are added, and the molten steel is fully stirred with argon to obtain a casting liquid.

2. The high temperature resistant high entropy stainless steel according to claim 1, characterized in that The N content is more than twice the C content.

3. The high temperature resistant high entropy stainless steel according to claim 1, characterized in that RE is at least one element selected from La, Ce, Pr, Nd, Y and Sc, and the content of RE is 0.005-0.08 wt %.

4. The high temperature resistant high entropy stainless steel according to claim 1, characterized in that Casting includes the following steps: Under the condition of argon protective atmosphere, the casting liquid is cast by continuous casting or mold casting; The raw materials for RE are added to the ladle before casting, or, during casting, to the flowing casting liquid.

5. The high temperature resistant high entropy stainless steel according to claim 1, characterized in that The temperature during solution treatment is 1000~1080℃, and the time of solution treatment is calculated as 1~5 minutes per millimeter of thickness of forgings, plates or pipes.

6. Use of the high-temperature resistant high-entropy stainless steel according to any one of claims 1 to 5 in pressure vessels, pipelines, boiler equipment and heat exchange equipment with a heat-resistant temperature of 750°C or below.

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