High-performance high-temperature steel for energy equipment suitable for extreme environment and preparation method thereof

Abstract

The invention discloses high-performance high-temperature steel for energy equipment suitable for an extreme environment and a preparation method of the high-temperature steel, and belongs to the technical field of high-temperature alloy materials. Waste steel circulation refining and residual element precise regulation and control are fully fused, waste steel efficient circulation utilization is achieved through a converter + LF / RH technology, CO2 emission and cost are reduced, and the energy consumption is reduced. And meanwhile, the residual element Sb in the waste steel is regulated to the beneficial interval of 0.002-0.010%, the high-temperature strength is improved through the grain refinement effect of the waste steel, grain boundary embrittlement is inhibited by combining the vacuum degassing and controlled rolling technology, collaborative innovation of waste steel resource recycling and high-temperature steel performance optimization is achieved, and the beneficial effects of green manufacturing and high performance are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature alloy materials, and in particular relates to a high-performance high-temperature steel for energy equipment suitable for extreme environments and a preparation method thereof. Background Art

[0002] With the rapid development of the global economy and the growing demand for energy, energy equipment faces unprecedented challenges. In extreme operating environments such as nuclear power, aerospace, and petrochemicals, energy equipment must withstand harsh conditions such as high temperatures, high pressures, and severe corrosion, placing extremely high demands on material performance. While traditional high-temperature steels have met some of these requirements, iron-based materials such as martensitic heat-resistant steels can experience significant degradation of their high-temperature strength due to the coarsening of precipitated phases when subjected to long-term service above 600°C. In coupled corrosive environments containing sulfur and chlorine, the surface protective films of traditional Cr-Mo steels are prone to failure, making their corrosion resistance insufficient for long-term service. Furthermore, existing high-temperature steel preparation processes have numerous shortcomings. For one thing, traditional processes struggle to precisely control alloy composition, resulting in unstable high-temperature steel performance. Furthermore, complex heat treatment processes not only increase production costs but can also lead to microstructure and performance variations due to temperature variations, resulting in insufficient material performance yields and reliability assessments. Scrap steel, as the core raw material for electric furnace steelmaking, has the significant advantages of low carbon emissions and high resource recycling rate. As the amount of steel reserves increases, the output of scrap steel continues to grow. Its large-scale utilization can reduce dependence on high-grade iron ore and improve the economic benefits of enterprises.

[0003] Chinese patent CN102330035A discloses a heat-resistant steel, a heat-resistant steel pipe, and a manufacturing method thereof. By optimizing the composition and manufacturing method, and in particular utilizing its original ingot soaking temperature control technology, the high-temperature performance of the heat-resistant steel is significantly improved, meeting the needs of supercritical power generation units. However, its high cost, complex process, and unclear performance of the material in other extreme environments may limit its promotion in emerging fields such as nuclear power and hydrogen energy.

[0004] Chinese patent CN104195460A discloses an austenitic heat-resistant steel with high-temperature steam corrosion resistance and good high-temperature strength. Its main chemical composition, by mass percentage, is as follows: C: 0.035-0.15%, Si: ≤1.5%, Mn: 0.4-2.0%, Cr: 20-26%, Ni: 20-28%, Co: 1.0-2.0%, Nb: 1.1-2.0%, Cu: 2.6-4.0%, V: 0.10-0.50%, N: 0.1-0.4%, Zr: 0.001-0.080%, B: 0.002-0.020%, W: 1.5-5.0%, Mo: 0.5-3.0%, and Ce: 0.001-0.030%. Through multi-element synergistic strengthening and microstructure optimization, it breaks through the high-temperature performance bottleneck of traditional austenitic steel and is suitable for ultra-supercritical power generation and petrochemical fields. However, it uses vacuum induction melting and multi-step forging blanking processes, which place strict demands on production equipment and affect the efficiency of large-scale production.

[0005] Chinese patent CN102071361A discloses a high-temperature resistant steel for oil-well pipes and a manufacturing method thereof. Through collaborative innovation in alloying design and process, this steel overcomes the strength degradation problem of traditional oil-well pipes at high temperatures, making it suitable for harsh environments such as oilfield fires. However, the steel contains a high proportion of precious metal elements, significantly increasing the cost of raw materials, and the material's performance in temperatures exceeding 500°C or in complex corrosive media is unclear.

[0006] Chinese patent CN105452515A discloses a high-chromium heat-resistant steel. Its main chemical composition, by mass percentage, is as follows: C: 0.08% to 0.13%, Si: 0.15% to 0.45%, Mn: 0.1% to 1.0%, Ni: 0.01% to 0.5%, Cr: 10.0% to 11.5%, Mo: 0.3% to 0.6%, V: 0.10% to 0.25%, Nb: 0.01% to 0.06%, N: 0.015% to 0.07%, B ≤ 0.005%, and Al ≤ 0.04%. Through composition optimization and process synergy, the steel achieves breakthroughs in high-temperature strength and oxidation resistance without relying on expensive elements. It is suitable for ultra-supercritical pressure boilers, but the material's performance at temperatures exceeding 650°C or in complex corrosive environments is not specified.

[0007] Chinese patent CN106636903A discloses a high-temperature resistant steel plate. Through the synergistic effect of a multi-element alloy system and a multi-scale strengthening mechanism, the hot rolling, cold rolling, gradient cooling and boron microalloying processes are precisely controlled. Its temperature resistance reaches 2800°C, which is significantly better than traditional heat-resistant steels. However, no data on long-term creep, fatigue life or oxidation degradation at high temperatures is provided, making it impossible to determine its actual service stability.

[0008] Chinese patent CN107747045A discloses a 400MPa grade Cl-resistant - Environmental corrosion steel bars and their manufacturing methods, this patent improves the corrosion resistance of steel bars through the synergistic effect of alloy elements, and makes full use of the different strengthening mechanisms of alloy elements to carry out comprehensive strengthening and toughening design. - Environmentally corrosive steel bars do not contain Sb, and actual production conditions are not considered. In actual production, most steelmaking processes use scrap steel in converters, which cannot avoid residual elements in the scrap steel. Residual Sb, among other elements, can adversely affect the properties of the steel, thereby affecting its corrosion resistance and toughening properties.

[0009] Therefore, developing a high-temperature steel that can operate stably under extreme working environments and an efficient preparation method using recycled scrap steel is of great significance for improving the overall performance and reliability of energy equipment. Summary of the Invention

[0010] The present invention proposes a high-performance high-temperature steel for energy equipment suitable for extreme environments and a preparation method thereof. The present invention aims to break through the bottleneck of existing technologies through innovative alloy design and optimized preparation process, and provide a high-performance and high-reliability high-temperature steel material for the field of energy equipment. The high-performance high-temperature steel for energy equipment suitable for extreme environments of the present invention still has good performance under the premise of containing Sb element.

[0011] To achieve the above objectives, the present invention provides the following technical solutions:

[0012] One of the technical solutions of the present invention:

[0013] The present invention provides a high-performance high-temperature steel for energy equipment suitable for extreme environments. The chemical composition of the steel, calculated by mass percentage, is as follows: C: 0.08-0.14%, Si: 0.30-0.40%, Mn: 0.20-0.80%, Cr: 8.80-9.25%, Mo: 0.8-1.2%, N: 0.03-0.08%, V: 0.10-0.26%, Nb: 0.05-0.10%, Sb: 0.002-0.010%, Ni: 0-0.40%, P≤0.006%, S≤0.002%, and the balance is Fe and unavoidable impurity elements.

[0014] Furthermore, the thickness of the high-performance high-temperature steel for energy equipment suitable for extreme environments is 15 to 25 mm, the structure is tempered martensite without delta ferrite, the average effective grain size is less than 8.5 μm, and the average lath width of the recovered martensite is 211 to 260 nm. Since there is no re-austenitization process, the original austenite grains show flat deformation characteristics, and the average original austenite grain size is less than 30 μm.

[0015] The high-performance, high-temperature steel for energy equipment suitable for extreme environments of the present invention has a lower yield strength of 653 to 749 MPa, a tensile strength of 807 to 892 MPa, an elongation after fracture of 19.6 to 22.6%, a strength-ductility product of 17.483 to 18.238 GPa·%, and a uniform corrosion rate of less than 0.025 mm / year in complex media. The steel's yield strength meets the API standard 80 steel grade (552 to 758 MPa) requirements within the operating temperature range of 500°C to 750°C. The high-performance, high-temperature steel for energy equipment suitable for extreme environments of the present invention maintains excellent performance despite containing the element Sb.

[0016] The second technical solution of the present invention:

[0017] The present invention also provides a method for preparing the high-performance high-temperature steel for energy equipment suitable for extreme environments, comprising the following steps:

[0018] 1) Weigh and batch the raw materials according to mass percentage, and the raw materials contain scrap steel;

[0019] 2) Smelting the raw materials to obtain molten iron, heat-treating the molten iron, and then performing converter smelting, LF refining, and RH vacuum degassing to obtain molten steel that meets the requirements, casting the molten steel to obtain billets, and then forging to obtain steel billets;

[0020] 3) performing a homogenizing treatment and descaling on the steel billet to obtain a homogenized steel billet;

[0021] 4) subjecting the homogenized steel billet to two-stage temperature-controlled hot rolling, wherein the two-stage temperature-controlled hot rolling comprises a rough rolling stage and a finishing rolling stage, wherein the rough rolling stage is performed in the austenite recrystallization region in two passes, and the finishing rolling stage is performed in the austenite non-recrystallization region in two passes;

[0022] 5) After normalizing and tempering treatment, the high-performance high-temperature steel for energy equipment suitable for extreme environments is obtained.

[0023] Furthermore, in step 1), the raw materials include scrap steel and pig iron smelted from iron ore.

[0024] Furthermore, in step 2), the time of the temperature raising and slagging stage in the early stage of LF refining is 10 to 15 minutes; the opening of the dust removal cover during LF refining is controlled at 40% to 60%, and the bottom blowing gas adopts the full-process argon control mode;

[0025] And / or, during the RH vacuum degassing process, the RH net circulation is not less than 10 minutes, and the static time before pouring is not less than 15 minutes, so as to keep the slag surface in the ladle in a surging state without exposing the molten steel surface;

[0026] And / or, the entire process of obtaining the billet by casting is carried out under protective conditions, the superheat of the molten steel is below 30° C., and the casting is carried out at a constant casting speed, preferably a billet casting speed of 1.0 m / min.

[0027] Furthermore, in step 2), during the billet smelting process, LF and RH are used to refine the molten steel outside the furnace. The time for the early stage of LF refining temperature and slag removal is 10 to 15 minutes, during which medium and high-grade slag removal is used. At the same time, the entire refining process pays attention to arc submergence. The opening of the dust removal cover of the LF process is controlled at 40% to 60%, and the bottom blowing gas adopts the full-process argon control mode. Ensure that the LF furnace produces white slag, ensure that S in the steel is ≤ 0.001%, strictly control the gas content of H, O, N and other gases in the steel, require that the RH net circulation shall not be less than 10 minutes, and the standing time before pouring shall not be less than 15 minutes. Keep the slag surface in the ladle in a surging state without exposing the molten steel surface. At the same time, the inclusions in the steel are modified by composite deoxidizer treatment to maximize the purity of the steel. During the billet smelting process, the casting of the billet obtained by casting is a continuous casting process, and protective casting is used throughout the continuous casting process to prevent the molten steel from being secondary oxidized. The superheat of the molten steel is controlled below 30°C to minimize defects such as center porosity and center segregation. To ensure the intrinsic quality of the billet, the billet drawing speed is controlled at 1.0m / min, and casting is carried out at a constant drawing speed. Soft reduction technology is used at the end of continuous casting to fully improve the intrinsic quality of the billet.

[0028] Exemplarily, in step 2), the composite deoxidizer is selected from the Al-Ca-Si composite deoxidizer produced by Anshan Iron and Steel Group, and the dosage is 1.2 kg / ton of steel.

[0029] Furthermore, in step 3), the soaking treatment is performed at a temperature of 1200-1250° C. for 1.5-3 hours. The soaking treatment can eliminate casting stress and reduce segregation, thereby obtaining a homogenized steel billet.

[0030] Furthermore, in step 4), the cumulative reduction rate in the rough rolling stage is 50-60%, and the final rolling temperature is 1000-1100°C; and / or, the cumulative reduction rate in the finish rolling stage is 40-50%, and the final rolling temperature is 850-900°C.

[0031] Furthermore, in step 4), the thickness of the intermediate billet obtained after rough rolling is 30 to 50 mm; the thickness of the steel plate obtained after finish rolling is 15 to 25 mm.

[0032] Furthermore, in step 5), the normalizing temperature is 950-1100° C., and the normalizing time is 10-60 min; the tempering temperature is 720-780° C., and the tempering holding time is 30-90 min.

[0033] Compared to traditional methods, the present invention utilizes recycled scrap steel for refining. Through an optimized, short-cycle production process consisting of billet smelting, casting, forging, homogenization, two-stage controlled rolling, normalizing, and tempering, the present steel exhibits significantly superior high-temperature mechanical properties compared to comparable steels. Using the present steel and manufacturing method, the high-performance, extreme-environment-suitable, high-temperature steel for energy equipment produced not only exhibits excellent high-temperature tensile properties, effectively resisting short-term high-temperature overloads caused by environmental uncertainties, improving its performance, but also exhibits excellent high-temperature durability, effectively resisting casing damage caused by creep under prolonged high-temperature conditions. The present high-performance, extreme-environment-suitable, high-temperature steel not only exhibits excellent high-temperature oxidation resistance, effectively mitigating the reduction in casing load capacity due to oxidation thinning, but also exhibits excellent resistance to CO2 corrosion, effectively meeting the requirements of demanding environments. The present method is highly efficient, has simple influencing factors, and has a wide range of applicability, facilitating large-scale industrial production and promotion.

[0034] The third technical solution of the present invention:

[0035] The present invention also provides for the use of the high-performance, extreme environment energy equipment high-temperature steel in high-performance, extreme environment energy equipment. Exemplarily, the high-performance, extreme environment energy equipment is selected from a supercritical generator set, an ultra-supercritical generator set, an ultra-supercritical pressure boiler, or a gas turbine.

[0036] Compared with the prior art, the present invention has the following advantages and technical effects:

[0037] The present invention fully integrates the recycling of scrap steel and the precise control of residual elements. Through the converter + LF / RH process, it realizes the efficient recycling of scrap steel, reduces CO2 emissions and costs, and at the same time controls the residual element Sb in the scrap steel to the beneficial range of 0.002-0.010%. Its grain refining effect is used to improve the high-temperature strength. Combined with vacuum degassing and controlled rolling technology, it realizes the synergistic innovation of recycling scrap steel resources and optimizing the performance of high-temperature steel, and has the advantages of both green manufacturing and high performance.

[0038] The short-time equalization treatment adopted in the present invention can improve the segregation of alloy components to the greatest extent. At the same time, since the equalization treatment time is short, it will not cause major changes to the microstructure of the material, thereby avoiding the microstructure from transforming to a state that weakens the mechanical properties.

[0039] The present invention adopts two-stage temperature-controlled hot rolling, with rough rolling with a reduction of no more than 60% in the first stage and finishing rolling with a reduction of more than 40% in the second stage, which can lay a solid foundation for subsequent high-redundant tensile strength, high and low temperature impact toughness, and high elongation. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0041] Figure 1 This is a schematic diagram of the process flow of the method for preparing high-performance high-temperature steel for energy equipment suitable for extreme environments according to the present invention. DETAILED DESCRIPTION

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0044] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0045] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0046] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0047] An embodiment of the present invention provides a high-performance high-temperature steel for energy equipment suitable for extreme environments, the chemical composition of which is, by mass percentage, as follows: C: 0.08-0.14%, Si: 0.30-0.40%, Mn: 0.20-0.80%, Cr: 8.80-9.25%, Mo: 0.8-1.2%, N: 0.03-0.08%, V: 0.10-0.26%, Nb: 0.05-0.10%, Sb: 0.002-0.010%, Ni: 0-0.40%, P≤0.006%, S≤0.002%, and the remainder is Fe and unavoidable impurity elements.

[0048] To address the challenges of previous high-performance, high-temperature steels for energy equipment suitable for extreme environments, such as insufficient high-temperature tensile and oxidation resistance, complex processes, and low production efficiency, which have hindered industrial production, the present invention utilizes a more optimized method to produce high-performance, high-temperature steels for energy equipment suitable for extreme environments. This high-performance, high-temperature steel for energy equipment suitable for extreme environments exhibits high high-temperature strength, high toughness, and high elongation, while offering high production efficiency and a wide range of applications.

[0049] In the technical solution of the present invention, the role of alloying elements is:

[0050] Carbon in steel can form carbides with alloying elements, strengthening it and increasing its strength and hardness. However, excessive carbon content can reduce the toughness of the steel. This invention controls the carbon (C) content to 0.08-0.14%, ensuring both strength and toughness.

[0051] Silicon increases the strength and hardness of steel while also enhancing its oxidation resistance. Excessive silicon content increases the brittleness of the steel, worsening its processing properties and potentially leading to hot brittleness. Too low a silicon content prevents it from effectively enhancing its strength and oxidation resistance. The present invention controls the silicon (Si) content to 0.30% to 0.40%, effectively improving the steel's oxidation resistance in high-temperature environments while maintaining good processing properties.

[0052] Manganese enhances the strength and toughness of steel, and also acts as a deoxidizer and desulfurizer, improving its quality and workability. Excessive manganese content can increase the brittleness of steel. Too low a manganese content prevents its full deoxidation, desulfurization, and strengthening effects, affecting the purity and strength of the steel. The present invention controls the manganese (Mn) content to 0.20% to 0.80%, fully realizing its comprehensive benefits while ensuring the workability of the steel.

[0053] Chromium is a key element in improving steel's oxidation and corrosion resistance. Excessive chromium content increases costs, can cause brittleness, and reduces steel ductility. Too low a chromium content prevents the formation of a dense oxide film, resulting in insufficient oxidation resistance and difficulty maintaining stable performance in high-temperature environments. The present invention controls the chromium (Cr) content to 8.80-9.25%, enabling the steel to form a dense oxide film in high-temperature environments, effectively protecting the steel substrate.

[0054] Molybdenum improves steel's high-temperature strength and creep properties. Excessive molybdenum content increases costs and can cause embrittlement, reducing the steel's toughness. Too low a molybdenum content undermines its high-temperature strengthening properties, leading to performance degradation during long-term high-temperature service. This invention controls the molybdenum (Mo) content to 0.8% to 1.2%, ensuring the steel's stability in high-temperature service while maintaining cost-effectiveness.

[0055] Nitrogen can form nitrides with alloying elements, playing a role in precipitation strengthening. Nitrogen can also refine grains, improving strength and toughness. Excessive nitrogen content will lead to increased aging sensitivity and brittleness of steel, especially unstable performance during long-term service at high temperatures. If the nitrogen content is too low, its precipitation strengthening effect cannot be effectively exerted, making it difficult to optimize the steel's structure. The present invention controls the nitrogen (N) content to 0.03-0.08%, optimizing the steel's structure and performance while avoiding the adverse effects of excessive nitrogen content.

[0056] The present invention controls the vanadium (V) and niobium (Nb) content to 0.10-0.26% and 0.05-0.10%, respectively. Vanadium and niobium refine grains, improving the strength and toughness of steel while also enhancing its creep resistance. Excessive vanadium content increases costs and may cause embrittlement, impacting the steel's workability; too low a vanadium content undermines its strengthening properties. Excessive niobium content increases costs and may cause abnormal grain growth, impacting the uniformity of the steel; too low a niobium content undermines its grain-refining properties.

[0057] The present invention controls the antimony (Sb) content to 0.002-0.010%. Antimony can inhibit the growth of austenite grains, allowing the steel to maintain a fine and uniform grain structure at high temperatures, thereby improving the thermal stability and high-temperature strength of the steel. However, when the Sb content exceeds 0.010%, due to the large atomic radius and low diffusion coefficient of Sb, it is easy to segregate at the grain boundaries, forming a continuous or semi-continuous segregation layer, which reduces the grain boundary bonding strength.

[0058] Nickel improves steel's strength, toughness, and corrosion resistance. Excessive nickel content significantly increases costs, while the marginal benefit of improved performance gradually decreases. Too low a nickel content undermines its performance-enhancing properties, particularly in corrosion resistance and low-temperature toughness. Based on practical needs, the present invention controls the nickel (Ni) content to 0% to 0.40%, achieving a balance between cost and performance.

[0059] P will increase the cold brittleness of steel, and S will cause hot brittleness. The present invention requires strict control of phosphorus (P) ≤ 0.006% and sulfur (S) ≤ 0.002% to reduce the adverse effects of impurity elements on steel properties.

[0060] In the high-performance high-temperature steel for energy equipment suitable for extreme environments of the present invention, C forms carbides for strengthening, Si solid solution strengthens, and Mn deoxidizes and desulfurizes, and the three synergistically balance strength and toughness and refine grains; Cr forms an oxide film, Mo enhances film adhesion, and Ni improves interfacial bonding, jointly improving oxidation resistance and corrosion resistance. At the same time, a small amount of Ni (≤0.40%) can synergize with Cr / Mo to improve toughness and corrosion resistance, reduce dependence on precious elements, and balance costs; V / Nb forms carbonitride precipitation strengthening, N refines grains and synergistically inhibits austenite growth, improving strength and creep resistance, while Sb adsorbs grain boundaries to inhibit grain growth, forming a "double barrier" with V / Nb carbonitrides, enhancing grain boundary strength, and avoiding segregation embrittlement; Mn / Ca solid dissolves sulfides, reduces S / P segregation, and cooperates with high-basicity slag to remove impurities, reducing the risk of cold brittleness / hot brittleness.

[0061] In an embodiment of the present invention, the thickness of high-performance high-temperature steel for energy equipment suitable for extreme environments is 15 to 25 mm, the structure is tempered martensite without delta ferrite, the average effective grain size is less than 8.5 μm, and the average lath width of the recovered martensite is 211 to 260 nm. Since there is no re-austenitization process, the original austenite grains show flat deformation characteristics, and the average original austenite grain size is less than 30 μm.

[0062] The high-performance, high-temperature steel for energy equipment suitable for extreme environments of the present invention has a lower yield strength of 653 to 749 MPa, a tensile strength of 807 to 892 MPa, an elongation after fracture of 19.6 to 22.6%, a strength-ductility product of 17.483 to 18.238 GPa·%, and a uniform corrosion rate of less than 0.025 mm / year in complex media. The steel's yield strength meets the API standard 80 steel grade (552 to 758 MPa) requirements within the operating temperature range of 500°C to 750°C. The high-performance, high-temperature steel for energy equipment suitable for extreme environments of the present invention maintains excellent performance despite containing the element Sb.

[0063] The embodiment of the present invention also provides a method for preparing high-performance high-temperature steel for energy equipment suitable for extreme environments. The process flow diagram is as follows: Figure 1 As shown, the following steps are included:

[0064] 1) Weigh and batch the raw materials according to mass percentage, and the raw materials contain scrap steel;

[0065] 2) Smelting the raw materials to obtain molten iron, which is then heat-treated, followed by converter smelting, LF refining, and RH vacuum degassing to obtain molten steel that meets the requirements. The molten steel is cast to obtain billets, which are then forged to obtain steel billets.

[0066] 3) The steel billet is subjected to a homogenizing treatment and descaling to obtain a homogenized steel billet;

[0067] 4) The homogenized steel billet is subjected to two-stage temperature-controlled hot rolling, the two-stage temperature-controlled hot rolling being a rough rolling stage and a finishing rolling stage. The rough rolling stage is carried out in the austenite recrystallization zone in two passes, and the finishing rolling stage is carried out in the austenite non-recrystallization zone in two passes.

[0068] 5) After normalizing and tempering treatment, high-performance high-temperature steel suitable for energy equipment in extreme environments is obtained.

[0069] In an embodiment of the present invention, in step 1), the raw materials include scrap steel and pig iron smelted from iron ore.

[0070] In an embodiment of the present invention, in step 2), during the billet smelting process, LF and RH are used to perform off-furnace refining on the molten steel. The initial temperature rise and slagging stage of LF refining lasts for 10 to 15 minutes, during which medium and high-grade slagging is used. At the same time, the entire refining process is carried out with attention to arc submergence. The opening of the dust cover of the LF process is controlled at 40% to 60%, and the bottom blowing gas adopts a full-process argon control mode. The LF furnace is guaranteed to produce white slag, ensuring that the sulfur content in the steel is ≤ 0.001%, and the gas content of H, O, N, etc. in the steel is strictly controlled. The RH net circulation is required to be not less than 10 minutes, and the standing time before pouring is not less than 15 minutes. The slag surface in the ladle is kept in a surging state without exposing the molten steel surface. At the same time, a composite deoxidizer is used to modify the inclusions in the steel to maximize the purity of the steel. During the billet smelting process, the casting of the billet obtained by casting is a continuous casting process, and the continuous casting adopts protective casting throughout the continuous casting process to prevent the molten steel from being secondary oxidized. The molten steel superheat is controlled below 30°C to minimize defects such as central porosity and central segregation. To ensure the intrinsic quality of the steel billet, the billet drawing speed is controlled at 1.0 m / min, with constant drawing speed casting. A soft reduction technique is employed at the end of continuous casting to fully improve the intrinsic quality of the billet. For example, in step 2), the composite deoxidizer is selected from an Al-Ca-Si composite deoxidizer produced by Anshan Iron and Steel, with a dosage of 1.2 kg / ton of steel.

[0071] In an embodiment of the present invention, in step 3), the soaking treatment temperature is 1200-1250°C and the duration is 1.5-3 hours. Soaking treatment eliminates casting stress and reduces segregation, resulting in a homogenized steel billet. After soaking treatment, descaling is performed using a mixture of hard particles and water to remove iron oxide scale. The hard particles used are selected from steel or aluminum shots. Soaking treatment is a critical step in metalworking, heating the metal to a uniform temperature. This process helps improve the metal's workability and eliminate internal stress, but it can also cause the metal surface to react with oxygen. At high temperatures, iron atoms on the metal surface combine with oxygen to form iron oxide. This iron oxide gradually accumulates on the metal surface, forming a dense oxide layer, known as scale. This scale typically appears scaly, hence the name "scale." The primary purpose of descaling is to remove the scale on the metal surface. This scale not only affects the metal's appearance but can also reduce its corrosion resistance and workability. Descaling can restore the metal's surface finish and improve its quality.

[0072] In an embodiment of the present invention, in step 4), the cumulative reduction rate in the rough rolling stage is 50-60%, the final rolling temperature is 1000-1100°C, and the thickness of the intermediate billet obtained after rough rolling is 30-50 mm; the cumulative reduction rate in the finishing rolling stage is 40-50%, the final rolling temperature is 850-900°C, and the thickness of the steel plate obtained after finishing rolling is 15-25 mm.

[0073] In an embodiment of the present invention, in step 5), the normalizing temperature is 950-1100° C., and the normalizing time is 10-60 min; the tempering temperature is 720-780° C., and the tempering holding time is 30-90 min.

[0074] Compared to traditional methods, the present invention utilizes recycled scrap steel for refining. Through an optimized, short-cycle production process consisting of billet smelting, casting, forging, homogenization, two-stage controlled rolling, normalizing, and tempering, the present steel exhibits significantly superior high-temperature mechanical properties compared to comparable steels. Using the present steel and manufacturing method, the high-performance, extreme-environment-suitable, high-temperature steel for energy equipment produced not only exhibits excellent high-temperature tensile properties, effectively resisting short-term high-temperature overloads caused by environmental uncertainties, improving its performance, but also exhibits excellent high-temperature durability, effectively resisting casing damage caused by creep under prolonged high-temperature conditions. The present high-performance, extreme-environment-suitable, high-temperature steel not only exhibits excellent high-temperature oxidation resistance, effectively mitigating the reduction in casing load capacity due to oxidation thinning, but also exhibits excellent resistance to CO2 corrosion, effectively meeting the requirements of demanding environments. The present method is highly efficient, has simple influencing factors, and has a wide range of applicability, facilitating large-scale industrial production and promotion.

[0075] The present invention also provides for the use of the aforementioned high-performance, extreme-environment energy equipment high-temperature steel in high-performance, extreme-environment energy equipment. Exemplarily, the high-performance, extreme-environment energy equipment is selected from supercritical power generation units, ultra-supercritical power generation units, ultra-supercritical pressure boilers, gas turbines, steel for nuclear power equipment, or steel for hydrogen energy equipment.

[0076] Unless otherwise specified, the room temperature in the present invention is 25±2°C.

[0077] All raw materials used in the examples and comparative examples of the present invention were purchased from commercial sources.

[0078] In the following embodiments and comparative examples of the present invention, the performance test standard is: GB / T 4338-2020 "High-temperature tensile test method for metallic materials".

[0079] For example, the creep-rupture test process is as follows: using a standard cylindrical specimen with a diameter of 5mm, a constant tensile stress of 100MPa is applied in the temperature range of 500-650°C to conduct a long-term creep-rupture test, with an expected rupture time of 5000 hours. For high-temperature conditions ≥750°C, the stress level of 100MPa is maintained constant, and an accelerated creep-rupture test is conducted, with the expected rupture time shortened to 3000 hours. This test method simulates the long-term service behavior of energy equipment in extreme high-temperature environments by controlling the temperature gradient and stress load. The creep deformation and rupture time of the specimen are recorded in accordance with GB / T2039-2012 "Metallic Materials Uniaxial Tension Creep Test Method", providing data support for the evaluation of the material's high-temperature durability performance.

[0080] The steam oxidation test procedure was set at 650°C, the same temperature used for creep rupture testing. During the test, the average thickness of the oxide layer on the surface of the test sample was measured using an optical microscope after 1000 hours of steam oxidation. This method evaluated steam oxidation resistance. The samples were small steel specimens measuring 15 mm x 20 mm x 10 mm, taken from heat-treated plates.

[0081] With reference to NACE TM0177-2016 "Laboratory test method for stress corrosion cracking and hydrogen-induced cracking of metals in H2S environment" and NACE MR0175 / ISO 15156-2 "Materials for use in H2S-containing environments in oil and gas production in the petroleum and natural gas industry", the energy equipment was simulated in the presence of CO2, H2S, Cl - The uniform corrosion rate, localized corrosion and stress corrosion cracking (SCC) sensitivity of high temperature steel are tested in complex media such as corrosion environment.

[0082] After testing, the high-performance high-temperature steel for energy equipment suitable for extreme environments prepared by the present invention has a uniform corrosion rate of less than 0.025 mm / a in complex media, which is significantly better than traditional high-temperature steel.

[0083] Ultra-supercritical power generation refers to power generation technology that utilizes ultra-supercritical parameters. Ultra-supercritical parameters generally refer to pressures exceeding 5000 psi and temperatures exceeding 1130°F, achieving extremely high thermal efficiency. Ultra-supercritical boilers typically refer to boilers with a main steam pressure of ≥27 MPa.

[0084] LF refining technology, also known as Ladle Furnace refining technology, is an indispensable off-furnace refining process in modern steel production. Its core lies in deep deoxidation, desulfurization, alloying and temperature control of primary molten steel through arc heating, white slag refining, argon stirring and other means, thereby significantly improving the cleanliness and composition uniformity of the molten steel.

[0085] RH-vacuum degassing technology is a key off-furnace refining process in the field of steel smelting. It was jointly developed by the German Ruhrstahl Steel Company and Heraeus in 1956. This technology achieves deep degassing, decarburization, deoxidation and composition adjustment through the circulation of molten steel in a vacuum environment, significantly improving the purity and performance of steel.

[0086] Strength and plasticity product, also known as static toughness, is the tensile strength of metal materials (usually refers to tensile strength, expressed as σ b The product of strength and elongation (expressed by δ) and fracture elongation (expressed by δ) is calculated as follows: Strength-ductility product = σ b ×δ. This indicator can comprehensively reflect the strength and plasticity of the material, because high-strength materials may have poor plasticity, and high-plasticity materials may lack strength, and the strength-plasticity product balances these two aspects of performance. The unit of the strength-plasticity product is usually obtained by multiplying the units of tensile strength and elongation. In the International System of Units (SI), the unit of tensile strength is Pascal (Pa), but in actual engineering applications, because the Pascal unit is small, megapascal (MPa) or gigapascal (GPa) is often used as the unit of tensile strength. Elongation is a dimensionless quantity, usually expressed as a percentage (%). Therefore, the unit of the strength-plasticity product is usually MPa multiplied by a percentage (MPa·%) or gigapascal multiplied by a percentage (GPa·%).

[0087] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0088] The technical solution of the present invention is further illustrated by the following examples.

[0089] Example 1

[0090] A high-performance high-temperature steel for energy equipment suitable for extreme environments has the following chemical composition, calculated by mass percentage: C: 0.11%, Si: 0.30%, Mn: 0.63%, Cr: 8.97%, Mo: 1.0%, N: 0.08%, V: 0.18%, Nb: 0.05%, Sb: 0.002%, Ni: 0.40%, P≤0.006%, S≤0.002%, and the balance being Fe and unavoidable impurity elements.

[0091] The preparation method of the high-performance high-temperature steel for energy equipment suitable for extreme environments is as follows:

[0092] 1) Billet selection: The raw materials are weighed and proportioned according to the above mass percentages. The raw materials consist of iron ore, coke, flux (limestone and dolomite), alloy additives (ferrochrome, ferromolybdenum, ferrosilicon, ferromanganese, nickel plate and manganese nitride), and industrial recycled scrap steel (carbon steel and low-alloy steel scrap, excluding high-alloy scrap). The scrap steel must be sorted to remove oil, rust and non-metallic impurities, and the size must be controlled between 50 and 300 mm to meet the requirements of converter smelting.

[0093] 2) Billet smelting: After the raw materials are smelted to obtain molten iron, the molten iron is heat treated, followed by converter smelting, LF refining, and RH vacuum degassing to obtain molten steel that meets the requirements. The molten steel is cast to obtain ingots, which are then forged to obtain billets. The specific operations are as follows:

[0094] ① The time for the early stage of LF refining temperature raising and slagging is 10 minutes, during which medium and high-grade slagging is used. At the same time, the arc is buried during the entire refining process. The opening of the dust removal cover of the LF process is controlled at 40%, and the bottom blowing gas adopts the full-process argon control mode. Before the formation of foamy slag, low current and low voltage (current and voltage are 20kA and 170V respectively) are used for operation. As the foamy slag is formed, the current and voltage are increased in turn (increased to 32kA and 225V respectively), and the power supply is continued for 4 minutes, and then the bag is soft-blown with argon for 21 minutes;

[0095] Ensure that the LF furnace produces white slag and that the S content in the steel is ≤ 0.002%. Strictly control the H, O, N and other gas contents in the steel. Require a 10-minute RH net circulation and a 17-minute standing time before pouring. Keep the slag surface in the ladle in a surging state without exposing the molten steel. At the same time, use a composite deoxidizer treatment to modify the inclusions in the steel to maximize the purity of the steel.

[0096] ② Protective casting is used throughout the continuous casting process to prevent the molten steel from being secondary-oxidized and to control the superheat of the molten steel below 30°C, thereby minimizing the occurrence of defects such as central porosity and central segregation. The continuous casting billet drawing speed is controlled at 1.0m / min and casting is performed at a constant drawing speed to ensure the intrinsic quality of the continuous casting billet.

[0097] Soft reduction technology is used at the end of continuous casting to fully improve the internal quality of the ingot. After the ingot comes off the line, it is slowly cooled to 200℃ and surface grinding is performed to remove iron oxide scale and surface defects. After passing ultrasonic testing, it is transferred to the forging process.

[0098] ③ After the ingot is placed in the furnace, the temperature is raised to 850℃ at a rate of 150℃ / h, kept at this temperature for 1 hour, then raised to 1200℃ and kept at this temperature for 3.5 hours to ensure uniform temperature in the core. The cross-drawing method is used, with a reduction rate of ≥15% per pass, and the slab is finally forged. After forging, it is air-cooled to 500℃ and then slowly cooled to 200℃ in the furnace.

[0099] 3) Soaking treatment: The steel billet is subjected to a soaking treatment at a temperature of 1200°C for 1.5 hours in a walking beam furnace to eliminate casting stress and reduce segregation to obtain a homogenized steel billet; after soaking treatment, a mixture of hard particles and water (the mass ratio of hard particles to water is 1:1; the hard particles are fine sand and steel shot, and the mass ratio of the two is 1:2.5) is used to descale and remove iron oxide scale;

[0100] 4) Temperature-controlled rolling: The homogenized steel billet after descaling is subjected to two-stage temperature-controlled hot rolling. The rough rolling stage is carried out in the austenite recrystallization zone, in two passes, with a cumulative reduction rate of 54% in the rough rolling stage and a final rolling temperature of 980°C. The thickness of the intermediate billet obtained by rough rolling is 39 mm; the finishing rolling stage is carried out in the austenite non-recrystallization zone in two passes, with a cumulative reduction rate of 46% in the finishing rolling stage and a final rolling temperature of 850°C. The thickness of the steel plate obtained by finishing rolling is 25 mm. High-pressure water is used for descaling during the rolling process;

[0101] 5) Normalizing + tempering: The normalizing temperature is 980℃ and the normalizing time is 15min; then high-temperature tempering is carried out, the tempering temperature is 780℃, and the tempering holding time is 60min, to obtain steel with a yield strength in the high temperature range of 500℃ to 750℃ that meets the requirements of API standard 80 steel grade (552~758MPa).

[0102] The high-performance high-temperature steel for energy equipment suitable for extreme environments prepared in this embodiment has a thickness of 25 mm, and the structure is a tempered martensite structure without δ-ferrite. The average effective grain size is 7.5 μm, and the average lath width of the recovered martensite is 260 nm. Since there is no re-austenitization process, the original austenite grains show flat deformation characteristics, and the average original austenite grain size is 27 μm.

[0103] The corrosion medium in the corrosion test was water containing 5wt% NaCl + 0.5wt% CH3COOH + 1.5vol% CO2 + 0.1vol% H2S (pH = 3.2). After testing, the corrosion rate was 0.021mm / a (uniform corrosion), pitting corrosion was observed, the pitting depth was ≤50μm, and it did not penetrate the sample surface.

[0104] After testing, the high-performance high-temperature steel for energy equipment suitable for extreme environments prepared in this embodiment has a creep rupture time of 5010 hours at 500°C and 100 MPa stress, and a creep rupture time of 3050 hours at 775°C and 100 MPa stress, which meets the requirements of GB / T 713.7-2023 "Steel plates and steel strips for pressure equipment Part 7: Stainless steel and heat-resistant steel".

[0105] After testing, the high-performance high-temperature steel for energy equipment suitable for extreme environments prepared in this embodiment has a lower yield strength of 704 MPa, a tensile strength of 847 MPa, an elongation after fracture of 20.8%, and a strength-ductility product of 17.618 GPa·%.

[0106] Example 2

[0107] A high-performance high-temperature steel for energy equipment suitable for extreme environments has the following chemical composition, calculated by mass percentage: C: 0.14%, Si: 0.40%, Mn: 0.45%, Cr: 8.80%, Mo: 1.2%, N: 0.06%, V: 0.20%, Nb: 0.10%, Sb: 0.005%, Ni: 0.20%, P≤0.006%, S≤0.002%, and the balance being Fe and unavoidable impurity elements.

[0108] The preparation method of the high-performance high-temperature steel for energy equipment suitable for extreme environments is as follows:

[0109] 1) Billet selection: The raw materials are weighed and proportioned according to the chemical mass percentage of high-performance, extreme-environment-suitable high-temperature steel for energy equipment. The raw materials consist of iron ore, coke, flux (limestone and dolomite), alloy additives (ferrochrome, ferromolybdenum, ferrosilicon, ferromanganese, nickel plate, and manganese nitride), and industrial recycled scrap (carbon steel and low-alloy steel scrap, excluding high-alloy scrap). The scrap must be sorted to remove oil, rust, and non-metallic impurities, and the size must be controlled between 50 and 300 mm to meet the requirements of converter smelting.

[0110] 2) Billet smelting: After the raw materials are smelted to obtain molten iron, the molten iron is heat treated, followed by converter smelting, LF refining, and RH vacuum degassing to obtain molten steel that meets the requirements. The molten steel is cast to obtain billets, which are then forged to obtain steel billets. The specific operations are as follows:

[0111] Molten steel undergoes off-furnace refining using LF and RH. The initial heating and slagging phase of LF refining lasts 12 minutes, during which medium- and high-grade slagging is used. Arc submersion is maintained throughout the refining process. The dust cover opening in the LF process is controlled at 45%, and the bottom blowing is performed using fully controlled argon. Before foamy slag forms, low current and voltage (23kA and 160V, respectively) are used. As foamy slag forms, the current and voltage are gradually increased (40kA and 240V, respectively). Power is continued for 4 minutes, followed by a 20-minute soft argon blowdown. White slag is ensured in the LF furnace, with sulfur content in the steel ≤ 0.002%. Gas contents such as H, O, and N are strictly controlled. A 12-minute clean RH cycle is required, with a 15-minute standstill period before pouring. The slag surface in the ladle is kept surging without exposing the molten steel. A composite deoxidizer treatment is used to modify inclusions in the steel to maximize steel purity.

[0112] The casting and forging processes are the same as in Example 1;

[0113] 3) Soaking treatment: The steel billet is subjected to a soaking treatment at a temperature of 1238°C for 2.5 hours in a walking beam furnace to eliminate casting stress and reduce segregation to obtain a homogenized steel billet; after soaking treatment, a mixture of hard particles and water (the mass ratio of hard particles to water is 1:1; the hard particles are fine sand and steel shot, and the mass ratio of the two is 1:2.5) is used to descale and remove iron oxide scale;

[0114] 4) Temperature-controlled rolling: The homogenized steel billet after descaling is subjected to two-stage temperature-controlled hot rolling. The rough rolling stage is carried out in the austenite recrystallization zone and is rolled in two passes. The cumulative reduction rate in the rough rolling stage is 60%, the final rolling temperature is 1100°C, and the thickness of the intermediate billet obtained by rough rolling is 50mm; the finishing rolling stage is carried out in the austenite non-recrystallization zone and is rolled in two passes. The cumulative reduction rate in the finishing rolling stage is 44%, the final rolling temperature is 900°C, and the thickness of the intermediate billet obtained by finishing rolling is 19mm. High-pressure water is used for descaling during the rolling process;

[0115] 5) Normalizing + tempering: normalizing temperature is 1100℃, normalizing time is 10min; then high temperature tempering is carried out, tempering temperature is 760℃, tempering holding time is 90min, to obtain steel with yield strength in the service temperature range of 500℃ to 750℃ that meets the requirements of API standard 80 steel grade (552~758MPa);

[0116] The high-performance high-temperature steel for energy equipment suitable for extreme environments prepared in this embodiment has a thickness of 19 mm, and the structure is a tempered martensite structure without δ-ferrite. The average effective grain size is 8.2 μm, and the average lath width of the recovered martensite is 211 nm. Since there is no re-austenitization process, the original austenite grains show flat deformation characteristics, and the average original austenite grain size is 25 μm.

[0117] The corrosion test medium used water (pH = 2.8) containing 7wt% NaCl, 1.0wt% CH3COOH, 2.0vol% CO2, and 0.2vol% H2S. The corrosion rate was 0.018mm / a (uniform corrosion), with pitting observed. The pitting depth was ≤50μm and did not penetrate the sample surface. Cr2O3 and NiS-rich layers were detected in the oxide film, effectively inhibiting medium penetration.

[0118] After testing, the high-performance high-temperature steel for energy equipment suitable for extreme environments prepared in this embodiment has a creep rupture time of 5112 hours at 650°C and 100 MPa stress, and a creep rupture time of 3020 hours at 760°C and 100 MPa stress, which meets the requirements of GB / T 713.7-2023 "Steel plates and steel strips for pressure equipment Part 7: Stainless steel and heat-resistant steel".

[0119] After testing, the high-performance high-temperature steel for energy equipment suitable for extreme environments prepared in this embodiment has a lower yield strength of 749 MPa, a tensile strength of 892 MPa, an elongation after fracture of 19.6%, and a strength-ductility product of 17.483 GPa·%.

[0120] Example 3

[0121] A high-performance high-temperature steel for energy equipment suitable for extreme environments has the following chemical composition, calculated by mass percentage: C: 0.09%, Si: 0.32%, Mn: 0.80%, Cr: 9.25%, Mo: 1.1%, N: 0.03%, V: 0.26%, Nb: 0.07%, Sb: 0.008%, Ni: 0%, P≤0.006%, S≤0.002%, and the balance being Fe and unavoidable impurity elements.

[0122] The preparation method of the high-performance high-temperature steel for energy equipment suitable for extreme environments is as follows:

[0123] 1) Billet selection: The raw materials are weighed and proportioned according to the chemical mass percentage of high-performance, extreme-environment-suitable high-temperature steel for energy equipment. The raw materials consist of iron ore, coke, flux (limestone and dolomite), alloy additives (ferrochrome, ferromolybdenum, ferrosilicon, ferromanganese, nickel plate, and manganese nitride), and industrial recycled scrap (carbon steel and low-alloy steel scrap, excluding high-alloy scrap). The scrap must be sorted to remove oil, rust, and non-metallic impurities, and the size must be controlled between 50 and 300 mm to meet the requirements of converter smelting.

[0124] 2) Billet smelting: After the raw materials are smelted to obtain molten iron, the molten iron is heat treated, followed by converter smelting, LF refining, and RH vacuum degassing to obtain molten steel that meets the requirements. The molten steel is cast to obtain ingots, which are then forged to obtain billets. The specific operations are as follows:

[0125] The molten steel is refined outside the furnace using LF and RH. The initial stage of LF refining, during which the temperature rise and slag removal, takes 13 minutes. During this period, medium and high-grade slag removal is used. At the same time, the arc is buried during the entire refining process. The opening of the dust removal cover in the LF process is controlled at 60%, and the bottom blowing gas adopts the full-process argon control mode. Before the formation of foamy slag, low current and low voltage are used (the current and voltage are 22kA and 150V respectively). As the foamy slag is formed, the current and voltage are increased in sequence (the current and voltage are 35kA and 280V respectively). The power is continued for 5 minutes, and then the ladle is soft-blown with argon for 22 minutes. The LF furnace is guaranteed to produce white slag, and the S content in the steel is ensured to be ≤0.002%. The content of gases such as H, O, and N in the steel is strictly controlled. The RH net circulation is required to be 12 minutes, and the standing time before pouring is 16 minutes. The slag surface in the ladle is kept in a surging state without exposing the molten steel surface. At the same time, the inclusions in the steel are modified by composite deoxidizer treatment to maximize the purity of the steel.

[0126] The casting and forging processes are the same as in Example 1;

[0127] 3) Soaking treatment: The steel billet is subjected to a soaking treatment at a temperature of 1250°C for 1.5 minutes in a walking beam furnace to eliminate casting stress and reduce segregation to obtain a homogenized steel billet; after soaking treatment, a mixture of hard particles and water (the mass ratio of hard particles to water is 1:1; the hard particles are fine sand and steel shot, and the mass ratio of the two is 1:2.5) is used to descale and remove iron oxide scale;

[0128] 4) Temperature-controlled rolling: The homogenized steel billet after descaling is subjected to two-stage temperature-controlled hot rolling. The rough rolling stage is carried out in the austenite recrystallization zone and is rolled in two passes. The cumulative reduction rate in the rough rolling stage is 50%, the final rolling temperature is 1056°C, and the thickness of the intermediate billet obtained by rough rolling is 30mm; the finishing rolling stage is carried out in the austenite non-recrystallization zone and is rolled in two passes. The cumulative reduction rate in the finishing rolling stage is 44%, the final rolling temperature is 875°C, and the thickness of the steel plate after finishing rolling is 18mm. High-pressure water is used for descaling during the rolling process;

[0129] 5) Normalizing + tempering: The normalizing temperature is 1050℃ and the normalizing time is 45min; then high-temperature tempering is carried out, the tempering temperature is 720℃, and the tempering holding time is 60min, to obtain steel with a yield strength in the high temperature range of 500℃ to 750℃ that meets the requirements of API standard 80 steel grade (552~758MPa).

[0130] The high-performance high-temperature steel for energy equipment suitable for extreme environments prepared in this embodiment has a thickness of 22 mm, and the structure is a tempered martensite structure without δ-ferrite. The average effective grain size is 7.8 μm, and the average lath width of the recovered martensite is 235 nm. Since there is no re-austenitization process, the original austenite grains show flat deformation characteristics, and the average original austenite grain size is 28 μm.

[0131] The corrosion test medium used water (pH 3.5) containing 3wt% NaCl, 0.3wt% CH3COOH, and 1.0vol% CO2. The corrosion rate was 0.015mm / year (uniform corrosion), meeting the "high CO2 corrosion resistance" requirement of NACE MR0175. After corrosion, the matrix structure remained tempered martensite, with no evidence of intergranular corrosion.

[0132] After testing, the high-performance high-temperature steel for energy equipment suitable for extreme environments prepared in this embodiment has a creep rupture time of 5063 hours at 580°C and 100 MPa stress, and a creep rupture time of 3123 hours at 768°C and 100 MPa stress, which meets the requirements of GB / T 713.7-2023 "Steel plates and steel strips for pressure equipment Part 7: Stainless steel and heat-resistant steel".

[0133] After testing, the high-performance high-temperature steel for energy equipment suitable for extreme environments prepared in this embodiment has a lower yield strength of 672 MPa, a tensile strength of 822 MPa, an elongation after fracture of 21.7%, and a strength-ductility product of 17.837 GPa·%.

[0134] Example 4

[0135] A high-performance high-temperature steel for energy equipment suitable for extreme environments has the following chemical composition, calculated by mass percentage: C: 0.08%, Si: 0.38%, Mn: 0.20%, Cr: 9.12%, Mo: 0.8%, N: 0.05%, V: 0.10%, Nb: 0.09%, Sb: 0.010%, Ni: 0.35%, P≤0.006%, S≤0.002%, and the balance being Fe and unavoidable impurity elements.

[0136] The preparation method of the high-performance high-temperature steel for energy equipment suitable for extreme environments is as follows:

[0137] 1) Billet selection: The raw materials are weighed and proportioned according to the chemical mass percentage of high-performance, extreme-environment-suitable high-temperature steel for energy equipment. The raw materials consist of iron ore, coke, flux (limestone and dolomite), alloy additives (ferrochrome, ferromolybdenum, ferrosilicon, ferromanganese, nickel plate, and manganese nitride), and industrial recycled scrap (carbon steel and low-alloy steel scrap, excluding high-alloy scrap). The scrap must be sorted to remove oil, rust, and non-metallic impurities, and the size must be controlled between 50 and 300 mm to meet the requirements of converter smelting.

[0138] 2) Billet smelting: After the raw materials are smelted to obtain molten iron, the molten iron is heat treated, followed by converter smelting, LF refining, and RH vacuum degassing to obtain molten steel that meets the requirements. The molten steel is cast to obtain ingots, which are then forged to obtain billets. The specific operations are as follows:

[0139] Molten steel undergoes off-furnace refining using LF and RH processes. The initial heating and slagging phase of LF refining lasts 15 minutes, during which medium- and high-grade slagging is used. Arc submersion is maintained throughout the refining process. The dust cover opening in the LF process is controlled at 55%, and the bottom blowing is performed using fully controlled argon. Before foamy slag forms, low current and voltage are used (25kA and 200V, respectively). As foamy slag forms, the current and voltage are gradually increased (30kA and 300V, respectively). Power is continued for 4 minutes, followed by a 24-minute soft argon blowdown, allowing the ladle to be suspended. White slag is ensured in the LF furnace, with sulfur content in the steel ≤ 0.002%. Gas contents such as H, O, and N are strictly controlled. A 13-minute clean RH cycle is required, and an 18-minute standing period is required before pouring. The slag surface in the ladle is kept surging without exposing the molten steel. A composite deoxidizer treatment is used to modify inclusions in the steel to maximize steel purity.

[0140] The casting and forging processes are the same as in Example 1;

[0141] 3) Soaking treatment: The steel billet is subjected to a soaking treatment at a temperature of 1250°C for 2 hours in a walking beam furnace to eliminate casting stress and reduce segregation to obtain a homogenized steel billet; after soaking treatment, a mixture of hard particles and water (the mass ratio of hard particles to water is 1:1; the hard particles are fine sand and steel shot, and the mass ratio of the two is 1:2.5) is used to descale and remove iron oxide scale;

[0142] 4) Temperature-controlled rolling: The homogenized steel billet after descaling is subjected to two-stage temperature-controlled hot rolling. The rough rolling stage is carried out in the austenite recrystallization zone and is rolled in two passes. The cumulative reduction rate in the rough rolling stage is 54%, the final rolling temperature is 1078°C, and the thickness of the intermediate billet obtained by rough rolling is 48mm; the finishing rolling stage is carried out in the austenite non-recrystallization zone and is rolled in two passes. The cumulative reduction rate in the finishing rolling stage is 47%, the final rolling temperature is 883°C, and the thickness of the steel plate after finishing rolling is 15mm. High-pressure water is used for descaling during the rolling process;

[0143] 5) Normalizing + tempering: The normalizing temperature is 950℃ and the normalizing time is 60min; then high-temperature tempering is carried out, the tempering temperature is 750℃, and the tempering holding time is 45min, to obtain steel with a yield strength in the operating temperature range of 500℃ to 750℃ that meets the requirements of API standard 80 steel grade (552~758MPa).

[0144] The high-performance high-temperature steel for energy equipment suitable for extreme environments prepared in this embodiment has a thickness of 15 mm, and the structure is a tempered martensite structure without δ-ferrite. The average effective grain size is 8.0 μm, and the average lath width of the recovered martensite is 240 nm. Since there is no re-austenitization process, the original austenite grains show flat deformation characteristics, and the average original austenite grain size is 29 μm.

[0145] The corrosion medium in the corrosion test was water containing 10wt% NaCl + 1.5wt% CH3COOH + 2.5vol% CO2 + 0.3vol% H2S (pH = 2.5). After testing, the corrosion rate was 0.017mm / a (uniform corrosion), and no SCC fracture occurred under 80% yield strength stress.

[0146] After testing, the high-performance high-temperature steel for energy equipment suitable for extreme environments prepared in this embodiment has a creep rupture time of 5100 hours at 650°C and 100 MPa stress, and a creep rupture time of 3100 hours at 750°C and 100 MPa stress, which meets the requirements of GB / T 713.7-2023 "Steel plates and steel strips for pressure equipment Part 7: Stainless steel and heat-resistant steel".

[0147] Testing shows that the high-performance high-temperature steel for energy equipment suitable for extreme environments prepared in this embodiment has a lower yield strength of 653 MPa, a tensile strength of 807 MPa, an elongation after fracture of 22.6%, and a strength-ductility product of 18.238 GPa·%, meeting the requirements of relevant protocol standards.

[0148] Comparative Example 1

[0149] A high-temperature steel having a chemical composition, by mass percentage, of C: 0.11%, Si: 0.30%, Mn: 0.63%, Cr: 8.97%, Mo: 1.0%, N: 0.08%, V: 0.18%, Nb: 0.05%, Sb: 0.020%, Ni: 0.40%, P ≤ 0.006%, S ≤ 0.002%, with the remainder being Fe and unavoidable impurity elements. Sb is an unavoidable residual element in scrap steel, so an excess amount of Sb was added in Comparative Example 1 compared to Example 1 to verify the effect of Sb on the properties of the high-temperature steel.

[0150] The preparation method of the above-mentioned high-temperature steel is the same as that in Example 1.

[0151] The high-temperature steel obtained in Comparative Example 1 was subjected to the same performance tests as in Example 1. The test results are shown in Table 2. In Comparative Example 1, in which an excessive amount of Sb was added, not only did the excessive amount of Sb fail to inhibit the growth of austenite grains, but it also caused a large number of Sb atoms to segregate at the grain boundaries, weakening the grain boundary bonding force and reducing the grain boundary strengthening effect. This resulted in the high-temperature steel being inferior to Example 1 in terms of yield strength, tensile strength, plasticity, and corrosion resistance. The yield strength and tensile strength decreased significantly, the elongation decreased significantly, and the uniform corrosion rate increased sharply in a simulated corrosion environment. This proves that the addition of Sb will seriously damage the performance of high-temperature steel, which further highlights the importance and scientific nature of the present invention in precisely controlling the Sb element content.

[0152] Comparative Example 2

[0153] A high-temperature steel having a chemical composition, by mass percentage, of C: 0.11%, Si: 0.30%, Mn: 0.63%, Cr: 8.97%, Mo: 1.0%, N: 0.08%, V: 0.18%, Nb: 0.05%, Sb: 0.002%, Ni: 0.40%, P≤0.006%, S≤0.002%, and the remainder being Fe and unavoidable impurity elements (i.e., the composition of the high-temperature steel in this comparative example is the same as that in Example 1).

[0154] Compared with Example 1, this comparative example only changes the temperature-controlled rolling stage to single-stage rolling. The preparation method of the above-mentioned high-temperature steel is as follows:

[0155] Steps 1) to 3) are the same as in Example 1,

[0156] 4) Temperature-controlled rolling: The descaled homogenized billet is rolled in a single stage, with the entire process being rolled in the austenite recrystallization zone, with a cumulative reduction of 60%, a final rolling temperature of 1100°C, and directly rolled to a finished product with a thickness of 25 mm, eliminating the rolling in the non-recrystallization zone in the finishing rolling stage.

[0157] 5) Normalizing + tempering: same as in Example 1.

[0158] The high-temperature steel obtained in Comparative Example 2 was subjected to the same performance tests as in Example 1. The test results are shown in Table 2. In Comparative Example 2, which adopts traditional single-stage rolling, the martensite laths are coarsened and the dislocation strengthening effect is weakened because deformation is not carried out in the unrecrystallized zone of austenite. As a result, the high-temperature strength, endurance performance and strength-toughness matching are significantly lower than those of the high-temperature steel in Example 1 of the present invention. This proves the key role of the two-stage temperature-controlled rolling process in refining the structure and improving the comprehensive mechanical properties.

[0159] The chemical compositions and weight percentages (wt%) of the steel plates of Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 1, and the properties of the steel plates of Examples 1 to 4 and Comparative Examples 1 to 2 are shown in Table 2.

[0160] Table 1 Chemical composition and mass percentage (wt%) of the steel plates of Examples 1 to 4 and Comparative Examples 1 to 2

[0161]

[0162]

[0163] Table 2 Properties of the steel plates of Examples 1 to 4 and Comparative Examples 1 to 2

[0164]

[0165] In summary, compared to traditional methods, the present invention utilizes recycled scrap steel for refining. Through the optimization of a short production process consisting of billet smelting + casting + forging + homogenization + two-stage controlled rolling + normalizing + tempering, the steel grade of the present invention exhibits significantly superior high-temperature mechanical properties compared to the comparative steel. Using the steel grade and manufacturing method of the present invention, the high-performance, extreme-environment-suitable, high-temperature steel for energy equipment produced not only exhibits excellent high-temperature tensile properties, effectively resisting short-term high-temperature overloads caused by environmental uncertainties, thus improving its performance, but also possesses excellent high-temperature durability, effectively resisting casing damage caused by material creep under prolonged high-temperature conditions. The high-performance, extreme-environment-suitable, high-temperature steel of the present invention not only exhibits excellent high-temperature oxidation resistance, effectively mitigating the problem of reduced casing load-bearing capacity due to oxidation thinning, but also exhibits excellent resistance to CO2 corrosion, effectively meeting the requirements of harsh environments. The method of the present invention is highly efficient, has simple influencing factors, and has a wide range of applicability, facilitating large-scale industrial production and promotion.

[0166] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A high-performance high-temperature steel for energy equipment suitable for extreme environments, characterized by: Its chemical composition, in terms of mass percentage, is: C: 0.08-0.14%, Si: 0.30-0.40%, Mn: 0.20-0.80%, Cr: 8.80-9.25%, Mo: 0.8-1.2%, N: 0.03-0.08%, V: 0.10-0.26%, Nb: 0.05-0.10%, Sb: 0.002-0.010%, Ni: 0-0.40%, P≤0.006%, S≤0.002%, and the remainder is Fe and unavoidable impurity elements.

2. The high-performance high-temperature steel for energy equipment suitable for extreme environments according to claim 1 is characterized in that: The high-performance high-temperature steel for energy equipment suitable for extreme environments has a thickness of 15 to 25 mm, a structure of tempered martensite without delta ferrite, an average effective grain size of less than 8.5 μm, an average lath width of the recovered martensite of 211 to 260 nm, and original austenite grains exhibiting flat deformation characteristics, with an average original austenite grain size of less than 30 μm.

3. A method for preparing high-performance high-temperature steel for energy equipment suitable for extreme environments according to any one of claims 1 to 2, characterized in that: The following steps are involved: 1) Weigh and batch the raw materials according to mass percentage, and the raw materials contain scrap steel; 2) Smelting the raw materials to obtain molten iron, heat-treating the molten iron, and then performing converter smelting, LF refining, and RH vacuum degassing to obtain molten steel that meets the requirements, casting the molten steel to obtain billets, and then forging to obtain steel billets; 3) performing a homogenizing treatment and descaling on the steel billet to obtain a homogenized steel billet; 4) subjecting the homogenized steel billet to two-stage temperature-controlled hot rolling, wherein the two-stage temperature-controlled hot rolling comprises a rough rolling stage and a finishing rolling stage, wherein the rough rolling stage is performed in the austenite recrystallization region in two passes, and the finishing rolling stage is performed in the austenite non-recrystallization region in two passes; 5) After normalizing and tempering treatment, the high-performance high-temperature steel for energy equipment suitable for extreme environments is obtained.

4. The method for preparing high-performance high-temperature steel for energy equipment suitable for extreme environments according to claim 3, characterized in that: In step 1), the raw materials include scrap steel and pig iron smelted from iron ore.

5. The method for preparing high-performance high-temperature steel for energy equipment suitable for extreme environments according to claim 3, characterized in that: In step 2), the temperature raising and slagging stage in the early stage of LF refining lasts for 10 to 15 minutes; the dust cover opening during LF refining is controlled at 40% to 60%, and the bottom blowing gas adopts the full-process argon control mode; And / or, during the RH vacuum degassing process, the RH net circulation is not less than 10 minutes, and the static time before pouring is not less than 15 minutes, so as to keep the slag surface in the ladle in a surging state without exposing the molten steel surface; And / or, the entire process of obtaining the billet by casting is carried out under protective conditions, the superheat of the molten steel is below 30° C., and the casting is performed at a constant casting speed.

6. The method for preparing high-performance high-temperature steel for energy equipment suitable for extreme environments according to claim 3, characterized in that: In step 3), the temperature of the soaking treatment is 1200-1250° C., and the time is 1.5-3 hours.

7. The method for preparing high-performance high-temperature steel for energy equipment suitable for extreme environments according to claim 3, characterized in that: In step 4), the cumulative reduction rate in the rough rolling stage is 50-60%, and the finishing rolling temperature is 1000-1100°C; And / or, the cumulative reduction rate in the finishing rolling stage is 40-50%, and the final rolling temperature is 850-900°C.

8. The method for preparing high-performance high-temperature steel for energy equipment suitable for extreme environments according to claim 7, characterized in that: In step 4), the thickness of the intermediate billet obtained after rough rolling is 30 to 50 mm; the thickness of the steel plate obtained after finish rolling is 15 to 25 mm.

9. The method for preparing high-performance high-temperature steel for energy equipment suitable for extreme environments according to claim 3, characterized in that: In step 5), the normalizing temperature is 950-1100° C., and the normalizing time is 10-60 min; the tempering temperature is 720-780° C., and the tempering holding time is 30-90 min.

10. Use of the high-performance high-temperature steel for energy equipment suitable for extreme environments according to any one of claims 1 to 2 in high-performance energy equipment suitable for extreme environments, characterized in that: The high-performance extreme environment applicable energy equipment is selected from supercritical generator sets, ultra-supercritical generator sets, ultra-supercritical pressure boilers or gas turbines.

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