High-temperature-resistant thermal-fatigue-resistant martensitic steel and preparation method thereof

Abstract

The embodiment of the invention discloses high-temperature-resistant and thermal-fatigue-resistant martensitic steel and a preparation method thereof. The martensitic steel comprises the following components in percentage by mass: 0.15 to 0.60 percent of C (carbon), 0.35 to 0.80 percent of Si (silicon), 0.30 to 1.50 percent of Mn (manganese), 0.50 to 2.50 percent of Cr (chromium), 0.50 to 1.50 percent of Ni (nickel), 0.20 to 1.00 percent of Mo (molybdenum), 0.10 to 1.00 percent of Al (aluminum), 0.05 to 0.50 percent of V (vanadium) and the balance of Fe (iron) and inevitable impurities. The preparation method of the high-temperature-resistant anti-fatigue martensitic steel comprises the following steps: forging a steel billet according to the set composition and proportion; the steel billet is placed in a heating furnace, homogenized at 1200 DEG C for 5 h and then subjected to air cooling; then heat preservation is conducted for 10 min at the temperature of 1200 DEG C, multi-pass rolling is conducted, and the thickness is reduced to 4 mm from 15 mm; and finally, heat preservation is conducted for 10 min at the temperature of 1000 DEG C for austenitizing, tempering is conducted for 6 h at the temperature of 580 DEG C after water cooling is conducted to the room temperature, and the high-temperature-resistant and thermal-fatigue

Description

Technical Field

[0001] This invention belongs to the field of metal smelting technology, specifically relating to a high-temperature resistant and thermal fatigue-resistant martensitic steel and its preparation method. Background Technology

[0002] While traditional martensitic steels possess high room temperature strength and good fatigue properties, their microstructure is prone to recovery and recrystallization at temperatures exceeding 600°C, and carbides readily coarsen, significantly weakening precipitation strengthening and dislocation strengthening. Insufficient high-temperature strength has become a major bottleneck limiting their application in key components such as modern ultra-supercritical units, high-speed stamping dies, high-speed rail brake discs, and rocket engine casings. Particularly concerning is the risk of austenitic inverse transformation under cyclic thermal loading conditions: on the one hand, microstructure instability and a sharp decrease in dislocation density at high temperatures further weaken high-temperature strength; on the other hand, the quenched martensite formed during cooling easily induces hot cracks, severely impairing the material's resistance to thermal fatigue. Therefore, the low-cycle thermal fatigue conditions faced by these components further necessitate materials that simultaneously possess excellent high-temperature strength and resistance to thermal fatigue.

[0003] Currently, the main methods for improving high-temperature strength are mostly through the introduction of fine, dispersed nano-precipitates to refine the microstructure. These precipitates can effectively pin grain boundaries and dislocations, significantly delay the recovery and recrystallization process of the microstructure at high temperatures, and significantly enhance the effect of precipitation strengthening on the strength and hardness of the material. Chinese patent CN116855852A discloses a precipitation-strengthened high-temperature martensitic mold steel and its preparation method, with the following composition: C 0~0.4%, Cr 8.75~11.82%, Ni 6.25~7.50%, Co 7.50~8.50%, Mo 2.25~3.00%, V 0~0.50%, Al 0.55~2.00%, W 1.50~2.75%, Cu 0.50~1.80%, Re 0~0.05%, P<0.015%, S<0.010%, and the remainder being Fe. This patent constructs a composite nano-precipitation system composed of β-NiAl phase, Cu-rich phase, VC carbide, and Laves phase. The β-NiAl and Cu-rich phases are uniformly dispersed in the martensitic matrix, achieving a strengthening effect through a dislocation shearing mechanism, effectively improving room temperature and high temperature strength. VC, as an auxiliary precipitate phase, synergistically enhances the overall performance with the (Fe,Cr)2(W,Mo) type Laves phase, β-NiAl phase, and Cu-rich phase. The yield strength of this steel at 600℃ is 496.3. 10.2 MPa, tensile strength is 556.3. 3.2 MPa, elongation 20.0 1.3%.

[0004] Chinese patent CN101701323A discloses a high-chromium ferritic / martensitic heat-resistant steel for supercritical thermal power units. This steel retains a high chromium content (10-12% by mass) while systematically optimizing the proportions of carbon, cobalt, manganese, nickel, tungsten, molybdenum, niobium, vanadium, and boron, and controlling the mass percentages of nitrogen and titanium within the range of 0.005-0.015%. Through smelting, casting, forging, rolling, and heat treatment, a high-density MX-type nano-reinforcing phase is formed in the steel matrix. The optimized nitrogen and titanium ratio stabilizes the MX phase. During high-temperature service, the MX phase not only acts as a reinforcing phase but also inhibits the precipitation of harmful Z-phase, giving this ferritic / martensitic steel excellent high-temperature creep rupture strength. Simultaneously, the high chromium content also endows it with good high-temperature corrosion resistance.

[0005] Chinese patent CN100357469C discloses a method for manufacturing a high-temperature strength martensitic oxide dispersion-strengthened steel. This steel, by mass percentage, comprises: C 0.05~0.25%, Cr 8.0~12.0%, W 0.1~4.0%, Ti 0.1~1.0%, Y₂O₃ 0.1~0.5%, with the balance being Fe and unavoidable impurities. The key to this method is using argon gas with a purity of not less than 99.9999% as a protective atmosphere to precisely control the excess oxygen content ExO (i.e., the total oxygen content in the steel minus the oxygen content of Y₂O₃), ensuring that it satisfies the following relationship: 0.22 × Ti (mass%) < ExO (mass%) < 0.46 × Ti (mass%). By controlling the Ti content within the range of 0.1~1.0% and coordinating it with the above-mentioned excess oxygen regulation, the micronization and high-density dispersion of Y2O3 particles can be achieved, thereby significantly improving the high-temperature short-time strength and high-temperature long-time creep performance of steel.

[0006] Chinese patent CN102159744B discloses a low-cost heat-resistant steel for engine valves with excellent high-temperature fatigue strength. This steel uses a low-cost Fe-based heat-resistant alloy as its matrix. By precisely controlling the P and N content and optimizing the proportions of elements such as Mo, W, and Nb, it leverages the precipitation strengthening effect of second phases such as carbides and nitrides, as well as the solid solution strengthening effect of alloying elements, to achieve excellent high-temperature strength. In terms of manufacturing process, it first undergoes solution treatment in the temperature range of 1100~1180℃, followed by forging in the temperature range of 700~1000℃. Finally, aging treatment is performed to increase the surface hardness of the engine valve to over 400 HV, ensuring its comprehensive performance under high-temperature service conditions.

[0007] In summary, current technical approaches to improving the high-temperature strength of steel mainly rely on second-phase strengthening and its synergistic mechanism. By introducing nanoscale carbides, nitrides, and other precipitates, and utilizing their pinning dislocations and grain boundaries, softening and deformation of the microstructure at high temperatures are suppressed, significantly improving the material's creep resistance and endurance strength under high-temperature conditions. However, these precipitation-strengthening-only methods, while improving high-temperature strength, typically fail to adequately consider the material's resistance to thermal fatigue under cyclic thermal loading conditions. Summary of the Invention

[0008] In view of this, some embodiments disclose a high-temperature resistant and thermal fatigue-resistant martensitic steel, the composition of which, by mass percentage, includes: C: 0.15-0.60 wt.%, Si: 0.35-0.80 wt.%, Mn: 0.30-1.50 wt.%, Cr: 0.50-2.50 wt.%, Ni: 0.50-1.50 wt.%, Mo: 0.20-1.00 wt.%, Al: 0.10-1.00 wt.%, V: 0.05-0.50 wt.%, with the remainder being Fe and unavoidable impurities.

[0009] On the other hand, some embodiments disclose a method for preparing high-temperature resistant and fatigue-resistant martensitic steel, used to prepare the high-temperature resistant and thermal fatigue-resistant martensitic steel disclosed in the embodiments of the present invention, including:

[0010] Forging steel billets according to the set composition and proportions;

[0011] The steel billet was placed in a heating furnace and homogenized at 1200℃ for 5 hours, then air-cooled.

[0012] Next, the steel is held at 1200℃ for 10 minutes and rolled in multiple passes to reduce the thickness from 15 mm to 4 mm. Finally, it is held at 1000℃ for 10 minutes to austenitize it, then water-cooled to room temperature and tempered at 580℃ for 6 hours to obtain high-temperature resistant and thermal fatigue resistant martensitic steel.

[0013] The method for preparing high-temperature fatigue-resistant martensitic steel disclosed in this invention uses a high-Cr, low-Mn base with the addition of Al and V, effectively increasing the Al phase transformation temperature of the high-temperature martensitic steel. This significantly inhibits recrystallization and recovery behavior, helps maintain a high dislocation density, and thus preserves excellent high-temperature strength. Simultaneously, the higher Al point also suppresses the occurrence of austenite inverse phase transformation during high-temperature service, helping to avoid thermal stress and microcracks caused by quenching martensite formation during subsequent cooling, thereby significantly improving the material's resistance to thermal fatigue. Furthermore, the addition of vanadium further enhances the material's high-temperature strength through a precipitation strengthening mechanism. Building upon this, MC-type nanoprecipitates are further introduced. Through their synergistic effect with the matrix, the high-temperature strength is improved while maintaining the material's structural stability and durability under thermal cycling conditions. Attached Figure Description

[0014] Figure 1 The images show the microstructure of the martensitic steel from Example 1 after being stretched at 700°C; the left image is a SEM image, and the right image is an EBSD inverse pole figure (IPF).

[0015] Figure 2 The image shows the HR-TEM image of the nanoscale MC-type precipitates in the microstructure of the martensitic steel of Example 1 after being stretched at 700℃, with the inset showing its inverse Fourier transform.

[0016] Figure 3 The image shows the microstructure of the martensitic steel in Comparative Example 1 after being stretched at 700℃; the left image is a SEM image, and the right image is an EBSD inverse pole figure (IPF). Detailed Implementation

[0017] The term "embodiment" used herein, as an example, is not necessarily to be construed as superior to or better than other embodiments. Performance testing in these embodiments of the invention, unless otherwise specified, employs conventional testing methods in the art. It should be understood that the terminology used in these embodiments is merely for describing particular implementations and is not intended to limit the scope of the disclosure of these embodiments.

[0018] Unless otherwise stated, the technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the embodiments of this invention pertain; other experimental methods and technical means not specifically noted in the embodiments of this invention refer to experimental methods and technical means commonly used by one of ordinary skill in the art.

[0019] The terms “basic” and “approximately” as used herein are used to describe small fluctuations. For example, they can mean less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as less than or equal to ±0.05%. Numerical data presented or expressed in range format herein are used for convenience and brevity only, and should therefore be interpreted flexibly to include not only the explicitly listed values ​​that define the range, but also all independent values ​​or subranges contained within that range. For example, a numerical range of “1–5%” should be interpreted to include not only the explicitly listed values ​​from 1% to 5%, but also the independent values ​​and subranges within the indicated range. Thus, this numerical range includes independent values ​​such as 2%, 3.5%, and 4%, and subranges such as 1%–3%, 2%–4%, and 3%–5%, etc. This principle also applies to ranges that list only one value. Furthermore, this interpretation applies regardless of the width of the range or the characteristics described.

[0020] In this document, including in the claims, conjunctions such as "comprising," "including," "with," "having," "containing," "involving," and "accommodating" are understood to be open-ended, meaning "including but not limited to." Only the conjunctions "consisting of" and "composed of" are closed conjunctions.

[0021] To better illustrate the content of this invention, numerous specific details are provided in the following detailed embodiments. Those skilled in the art should understand that the invention can be practiced even without certain specific details. In the embodiments, some methods, means, instruments, and devices well-known to those skilled in the art are not described in detail, in order to highlight the main points of the invention.

[0022] Without conflict, the technical features disclosed in the embodiments of the present invention can be combined arbitrarily, and the resulting technical solution belongs to the content disclosed in the embodiments of the present invention.

[0023] In some embodiments, the high-temperature resistant and thermal fatigue-resistant martensitic steel, by weight percentage, comprises the following components: C: 0.15–0.60 wt.%, Si: 0.35–0.80 wt.%, Mn: 0.30–1.50 wt.%, Cr: 0.50–2.50 wt.%, Ni: 0.50–1.50 wt.%, Mo: 0.20–1.00 wt.%, Al: 0.10–1.00 wt.%, V: 0.05–0.50 wt.%, with the balance being Fe and unavoidable impurities.

[0024] Some embodiments disclose methods for preparing high-temperature resistant and fatigue-resistant martensitic steel, including:

[0025] Forging steel billets according to the set composition and proportions;

[0026] The steel billet was placed in a heating furnace and homogenized at 1200℃ for 5 hours, then air-cooled.

[0027] Next, the steel is held at 1200℃ for 10 minutes and rolled in multiple passes to reduce the thickness from 15 mm to 4 mm. Finally, it is held at 1000℃ for 10 minutes to austenitize it, then water-cooled to room temperature and tempered at 580℃ for 6 hours to obtain high-temperature resistant and thermal fatigue resistant martensitic steel.

[0028] The high-temperature resistant and thermal fatigue-resistant martensitic steel disclosed in this invention is based on a high-Cr, low-Mn alloy, with the addition of Al and V. This effectively increases the Al phase transformation temperature of the martensitic steel, thereby significantly suppressing the recrystallization and recovery behavior of the microstructure, which is beneficial for maintaining a high dislocation density and thus maintaining excellent high-temperature strength. Simultaneously, the higher Al point also significantly inhibits the occurrence of austenite reverse phase transformation during high-temperature service, thereby blocking the formation path of brittle quenched martensite during cooling. This innovative alloy design fundamentally maintains the high-temperature strength of the material while avoiding volumetric strain and local stress concentration caused by repeated phase transformations, significantly reducing the tendency for microcrack initiation, and enabling the material to exhibit excellent thermal fatigue resistance and microstructural stability under thermal cycling conditions. Furthermore, high-density, nanoscale MC-type carbides are introduced into the matrix through tempering treatment. These precipitates form a coherent interface with the matrix, and the resulting stress field and strong pinning effect on dislocation movement synergistically enhance the high-temperature strength of the steel, achieving synergistic optimization of thermal fatigue resistance and high-temperature strength.

[0029] The martensitic steel obtained by the above preparation method has a significantly increased Al phase transformation temperature and is strengthened by the dispersion precipitation of nano-MC phase. This martensitic steel exhibits excellent performance in terms of high-temperature strength, thermal fatigue resistance and microstructure stability. It provides a high-performance material preparation method with practical value for key components that are subjected to repeated rapid cooling and heating conditions, such as boiler tubes of ultra-supercritical units, high-speed stamping dies, high-speed rail brake discs and rocket engine casings.

[0030] The technical details are further illustrated below with reference to the embodiments.

[0031] Example 1

[0032] In Example 1, the preparation method of high-temperature resistant and fatigue-resistant martensitic steel includes:

[0033] According to the set composition and proportion, the steel is smelted in an electric arc furnace under an argon atmosphere, and after casting, the steel ingot is forged to obtain a steel billet. The composition of the martensitic steel is: C: 0.25wt.%, Si: 0.43wt.%, Mn: 0.62wt.%, Cr: 1.71wt.%, Ni: 1.08wt.%, Mo: 0.52wt.%, Al: 0.40wt.%, V: 0.20wt.%, with the remainder being Fe and unavoidable impurities.

[0034] The steel billet was placed in a heating furnace and homogenized at 1200℃ for 5 hours, then air-cooled.

[0035] Next, the steel is held at 1200℃ for 10 minutes and rolled in multiple passes to reduce the thickness from 15 mm to 4 mm. Finally, it is held at 1000℃ for 10 minutes to austenitize it, then water-cooled to room temperature and tempered at 580℃ for 6 hours to obtain high-temperature resistant and thermal fatigue resistant martensitic steel.

[0036] Subsequently, the martensitic steel samples were processed into standard tensile specimens and subjected to high-temperature tensile tests at 700℃. After the tensile tests, standard metallographic methods were used to prepare samples for EBSD and SEM observation to analyze the microstructure and degree of recrystallization; simultaneously, a double-spray thinning method was used to prepare transmission electron microscopy (TEM) samples to observe the morphology and distribution of precipitated phases. The results are as follows: Figure 1 , Figure 2 As shown.

[0037] The high-temperature tensile properties are shown in Table 2. Meanwhile, the equilibrium phase diagram of the martensitic steel was calculated using Thermo-Calc software, and the Al phase transformation temperatures are shown in Table 2.

[0038] Example 2

[0039] In Example 2, the preparation method of the high-temperature resistant and fatigue-resistant martensitic steel is the same as in Example 1. The composition of the martensitic steel is: C: 0.16 wt.%, Si: 0.54 wt.%, Mn: 0.54 wt.%, Cr: 1.62 wt.%, Ni: 0.99 wt.%, Mo: 0.56 wt.%, Al: 0.38 wt.%, V: 0.16 wt.%, with the remainder being Fe and unavoidable impurities.

[0040] The high-temperature tensile properties of the martensitic steel specimens from Example 2 are listed in Table 2. Simultaneously, the equilibrium phase diagram of the martensitic steel was calculated using Thermo-Calc software, and the Al phase transformation temperatures are listed in Table 2.

[0041] Example 3

[0042] In Example 3, the preparation method of the high-temperature resistant and fatigue-resistant martensitic steel is the same as in Example 1. The composition of the martensitic steel is: C: 0.22 wt.%, Si: 0.46 wt.%, Mn: 0.71 wt.%, Cr: 1.59 wt.%, Ni: 1.29 wt.%, Mo: 0.56 wt.%, Al: 0.52 wt.%, V: 0.29 wt.%, with the remainder being Fe and unavoidable impurities.

[0043] The high-temperature tensile properties of the martensitic steel specimens in Example 3 are listed in Table 2. Simultaneously, the equilibrium phase diagram of the martensitic steel was calculated using Thermo-Calc software, and the Al phase transformation temperatures are listed in Table 2.

[0044] Example 4

[0045] In Example 4, the preparation method of the high-temperature resistant and fatigue-resistant martensitic steel is the same as in Example 1. The composition of the martensitic steel is: C: 0.24 wt.%, Si: 0.41 wt.%, Mn: 0.59 wt.%, Cr: 1.68 wt.%, Ni: 1.05 wt.%, Mo: 0.55 wt.%, Al: 0.69 wt.%, V: 0.27 wt.%, with the remainder being Fe and unavoidable impurities.

[0046] The high-temperature tensile properties of the martensitic steel specimens in Example 4 are listed in Table 2. Simultaneously, the equilibrium phase diagram of the martensitic steel was calculated using Thermo-Calc software, and the Al phase transformation temperatures are listed in Table 2.

[0047] Comparative Example 1

[0048] In Comparative Example 1, the preparation method of the high-temperature resistant and fatigue-resistant martensitic steel is the same as in Example 1. The composition of the martensitic steel is: C: 0.25 wt.%, Si: 0.43 wt.%, Mn: 1.22 wt.%, Cr: 1.20 wt.%, Ni: 1.11 wt.%, Mo: 0.52 wt.%, with the remainder being Fe and unavoidable impurities.

[0049] The high-temperature tensile properties of the martensitic steel specimen from Comparative Example 1 are listed in Table 2. Simultaneously, the equilibrium phase diagram of the martensitic steel was calculated using Thermo-Calc software, and the Al phase transformation temperatures are listed in Table 2. The microstructure of the martensitic steel from Comparative Example 1 is shown in [Figure 1]. Figure 3 .

[0050] Comparative Example 2

[0051] In Comparative Example 2, the preparation method of the high-temperature resistant and fatigue-resistant martensitic steel is the same as in Example 1. The composition of the martensitic steel is: C: 0.17 wt.%, Si: 0.45 wt.%, Mn: 1.13 wt.%, Cr: 0.93 wt.%, Ni: 1.10 wt.%, Mo: 0.50 wt.%, with the remainder being Fe and unavoidable impurities.

[0052] The high-temperature tensile properties of the martensitic steel specimens in Comparative Example 2 are listed in Table 2. Meanwhile, the equilibrium phase diagram of the martensitic steel was calculated using Thermo-Calc software, and the Al phase transformation temperatures are listed in Table 2.

[0053] Comparative Example 3

[0054] In Comparative Example 3, the preparation method of high-temperature resistant and fatigue-resistant martensitic steel is the same as in Example 1. The composition of the martensitic steel is: C: 0.21 wt.%, Si: 0.53 wt.%, Mn: 1.30 wt.%, Cr: 1.44 wt.%, Ni: 1.03 wt.%, Mo: 0.58 wt.%, with the remainder being Fe and unavoidable impurities.

[0055] The high-temperature tensile properties of the martensitic steel specimens in Comparative Example 3 are listed in Table 2. Meanwhile, the equilibrium phase diagram of the martensitic steel was calculated using Thermo-Calc software, and the Al phase transformation temperatures are listed in Table 2.

[0056] Comparative Example 4

[0057] In Comparative Example 4, the preparation method of the high-temperature resistant and fatigue-resistant martensitic steel is the same as in Example 1. The composition of the martensitic steel is: C: 0.24 wt.%, Si: 0.48 wt.%, Mn: 1.11 wt.%, Cr: 1.36 wt.%, Ni: 1.26 wt.%, Mo: 0.50 wt.%, with the remainder being Fe and unavoidable impurities.

[0058] The high-temperature tensile properties of the martensitic steel specimens in Comparative Example 4 are listed in Table 2. Meanwhile, the equilibrium phase diagram of the martensitic steel was calculated using Thermo-Calc software, and the Al phase transformation temperatures are listed in Table 2.

[0059] The chemical composition of the martensitic steels in Examples 1-4 and Comparative Examples 1-4 is shown in Table 1, and the results of the high-temperature tensile properties of the martensitic samples are listed in Table 2.

[0060] Table 1. Chemical composition (wt.%) of martensitic steels in Examples 1-4 and Comparative Examples 1-4

[0061]

[0062] Table 2 and Table 1: Property List of Martensitic Steels in Examples 1-4 and Comparative Examples 1-4

[0063]

[0064] The results show that the high-temperature resistant and thermal fatigue-resistant martensitic steels prepared in Examples 1-4 are significantly superior to the martensitic steels prepared in Comparative Examples 1-4 in terms of high-temperature yield strength, high-temperature tensile strength and Al phase transformation temperature.

[0065] Analysis of the microstructure of the martensitic steels obtained in Examples 1-4 of this invention after high-temperature tensile testing at 700°C revealed that their microstructure is mainly tempered martensite, with only a small amount of ferrite recrystallization. Thanks to the low degree of recrystallization, the microstructure maintains a high dislocation density, which is a key reason for their high high-temperature strength. Due to the addition of V, a high density of MC-type V-rich precipitates is dispersed in the matrix of the martensitic steels obtained in Examples 1-4. These precipitates effectively hinder dislocation movement, which is an important reason why the martensitic steel still maintains high strength at 700°C. In contrast, the microstructure of the martensitic steels obtained in Comparative Examples 1-4 consists of a dual-phase structure of highly recovered tempered martensite and quenched martensite. The tempered martensite region exhibits a large amount of equiaxed grains due to extensive ferrite recrystallization. This is because the martensitic steels obtained in Comparative Examples 1-4 have lower Cr content and lack Al and V. The reduction in ferrite-stabilizing elements and the increase in austenite-stabilizing element Mn result in an Al transformation temperature significantly lower than that of the martensitic steels obtained in Examples 1-4. This significantly induces the recrystallization process, drastically reduces dislocation density, and noticeably softens the matrix, thus significantly decreasing high-temperature strength. Furthermore, the lower Al transformation temperature causes the martensitic steels obtained in Comparative Examples 1-4 to undergo an inverse austenite transformation during high-temperature processing, forming quenched martensite upon cooling. The presence of this hard and brittle phase severely impairs the material's resistance to thermal fatigue.

[0066] Table 2 shows that the martensitic steels obtained in Examples 1-4 of this invention all achieved a significant increase in the Al phase transformation temperature. This is mainly attributed to the material composition design: based on high Cr and low Mn, with the addition of Al and V. SEM microstructure analysis shows that the martensitic steels obtained in Examples 1-4 all exhibit tempered martensite, while the martensitic steels obtained in Comparative Examples 1-4 show a two-phase structure of tempered martensite and quenched martensite. EBSD analysis further confirms that the higher Al temperature results in a significantly lower degree of recrystallization in the example materials compared to the comparative examples, inhibiting microstructure softening and retaining a higher dislocation density, which provides direct evidence for the excellent high-temperature strength of the examples. More importantly, the addition of V in the examples introduced a dispersed precipitated nanoscale MC phase, producing a significant precipitation strengthening effect. This design approach, which synergistically strengthens the material by increasing the Al phase transformation temperature and introducing the MC phase, successfully achieves a synergistic improvement in the material's high-temperature strength and thermal fatigue resistance.

[0067] In summary, this invention, based on a high-Cr, low-Mn foundation and with the addition of Al and V, achieves a significant increase in the Al phase transformation temperature of martensitic steel and a high-density dispersed distribution of nano-MC precipitates, enabling the material to effectively balance excellent high-temperature strength and good thermal fatigue resistance. On one hand, by rationally controlling the Al phase transformation temperature, this invention significantly suppresses recrystallization and recovery behavior, which helps maintain a high dislocation density and thus preserves excellent high-temperature strength. Simultaneously, the higher Al temperature effectively suppresses the inverse austenite transformation during high-temperature service and avoids the formation of quenched martensite during cooling, thereby significantly improving the material's thermal fatigue resistance and microstructural stability. On the other hand, the strong precipitation strengthening effect generated by the nano-sized MC phase precipitated during tempering further enhances the material's strength at high temperatures. This invention ultimately produces tempered martensitic steel with a high Al phase transformation temperature and uniformly dispersed MC precipitates, which combines excellent high-temperature strength with outstanding resistance to thermal fatigue. It is expected to meet the stringent material performance requirements of key components such as boiler tubes of supercritical units, high-speed stamping dies, high-speed rail brake discs, and rocket engine casings under repeated rapid cooling and heating conditions.

[0068] The technical solutions and technical details disclosed in the embodiments of this invention are merely illustrative of the inventive concept of this invention and do not constitute a limitation on the technical solutions of the embodiments of this invention. Any conventional changes, substitutions, or combinations made to the technical details disclosed in the embodiments of this invention have the same inventive concept as this invention and are within the protection scope of the claims of this invention.

Claims

1. A high-temperature resistant and thermal fatigue-resistant martensitic steel, characterized in that, Its composition, by weight percentage, includes: C: 0.15–0.60 wt.%, Si: 0.35–0.80 wt.%, Mn: 0.30–1.50 wt.%, Cr: 0.50–2.50 wt.%, Ni: 0.50–1.50 wt.%, Mo: 0.20–1.00 wt.%, Al: 0.10–1.00 wt.%, V: 0.05–0.50 wt.%, with the remainder being Fe and unavoidable impurities.

2. A method for preparing high-temperature resistant and fatigue-resistant martensitic steel, used to prepare the martensitic steel according to claim 1, characterized in that, include: Forging steel billets according to the set composition and proportions; The steel billet was placed in a heating furnace and homogenized at 1200℃ for 5 hours, then air-cooled. Next, the steel is held at 1200℃ for 10 minutes and rolled in multiple passes to reduce the thickness from 15 mm to 4 mm. Finally, it is held at 1000℃ for 10 minutes to austenitize it, then water-cooled to room temperature and tempered at 580℃ for 6 hours to obtain high-temperature resistant and thermal fatigue resistant martensitic steel.

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