High-temperature high-strength plastic ferrite martensite steel and method for manufacturing the same

Abstract

The application relates to a high-temperature high-strength plastic ferrite martensite steel and a preparation method thereof, the preparation method comprises the following steps: (1) obtaining original ferrite martensite steel through heat treatment of a steel ingot; (2) performing cold plastic deformation processing on the original ferrite martensite steel obtained in the step (1) at a temperature of not higher than 50 DEG C to obtain nanocrystalline or ultrafine-grain ferrite martensite steel; and (3) performing annealing treatment on the nanocrystalline or ultrafine-grain ferrite martensite steel obtained in the step (2) to obtain high-temperature high-strength plastic ferrite martensite steel. The ferrite martensite steel prepared by the application can have high strength and plasticity at a high temperature of 550 DEG C, so that the application prospect of the ferrite martensite steel in engineering application is further improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal materials, and particularly relates to a high-temperature high-strength and high-plasticity ferritic martensitic steel and a preparation method thereof. BACKGROUND

[0002] Ferritic martensitic steel has high thermal conductivity, high high-temperature mechanical properties and low thermal expansion coefficient, and has good application prospects in power plants, advanced nuclear energy and high-temperature application fields. At the same time, it also has good anti-irradiation swelling and embrittlement performance, and is one of the candidate structural materials for nuclear fusion reactors and nuclear fission reactors. However, its high-temperature strength and anti-irradiation performance still need to be further improved in view of the more severe service environment of the fourth generation nuclear reactor.

[0003] For ferritic martensitic steel, the strength can be improved by adding alloying elements for solid solution strengthening, adding second phase particles such as oxides or carbides for dispersion strengthening, or grain refinement for fine-grain strengthening. Among them, solid solution strengthening and dispersion strengthening need to be realized by adding additional elements or second phases, while grain refinement does not need to be realized. Severe plastic deformation to refine the grain size to nanocrystalline or ultrafine crystalline scale is one of the common strengthening strategies for metal materials. However, due to the balance between strength and plasticity, the high strength brought by severe plastic deformation will inevitably reduce the plasticity of the metal material, making it difficult to be practically applied in engineering.

[0004] For example, the patent CN113528979A discloses a new RAFM steel and a heat treatment process thereof. The patent obtains a ferritic martensitic steel with excellent room temperature and high-temperature strength by adjusting the heat treatment process. However, the strength of the steel at high temperature is relatively high, but the plasticity is relatively low, so the high-temperature strength and plasticity matching needs to be further improved. SUMMARY

[0005] The purpose of the present application is to provide a high-temperature high-strength and high-plasticity ferritic martensitic steel and a preparation method thereof to solve the above problems.

[0006] The present application achieves the above-mentioned purpose by the following technical solutions:

[0007] As an aspect of the present application, the present application provides a preparation method of a high-temperature high-strength and high-plasticity ferritic martensitic steel, comprising the following steps:

[0008] (1) obtaining an original ferritic martensitic steel by heat treating a steel ingot;

[0009] (2) performing cold plastic deformation processing on the original ferritic martensitic steel obtained in step (1) at a temperature not higher than 50 DEG C to obtain a nanocrystalline or ultrafine crystalline ferritic martensitic steel;

[0010] (3) annealing the nanocrystalline or ultrafine-grained ferrite-martensite steel obtained in step (2) to obtain a high-temperature high-strength and high-ductility ferrite-martensite steel.

[0011] As a further optimization of the present application, step (1) is specifically that the ingot is first homogenized at 1100℃ for 3 hours and then forged to obtain a billet, with a forging deformation ratio of 5:1; the forged billet is then placed in a heating furnace at 1100℃ for 1 hour and then opened for rolling, with a deformation of 50%; the opened billet is then placed in a heating furnace at 800℃ for 1 hour and then rolled, with a deformation of 30% and 2 rolling passes; the rolled billet is then held at 980-1050℃ for 0.5-1.5 hours and then quenched in water; and finally, the quenched billet is held at 650-760℃ for 0.5-3 hours and then air-cooled to obtain the original ferrite-martensite steel.

[0012] As a further optimization of the present application, step (2) is specifically that the cold plastic deformation processing is one or more of swaging, rolling, forging or extrusion, with a total strain of ≥1.

[0013] As a further optimization of the present application, step (3) is specifically that the nanocrystalline or ultrafine-grained ferrite-martensite steel obtained in step (1) is annealed in a protective atmosphere at 200-500℃ for 0.5-10 hours.

[0014] As a further optimization of the present application, the protective atmosphere is one or more of nitrogen or argon.

[0015] As another aspect of the present application, the present application provides a high-temperature high-strength and high-ductility ferrite-martensite steel prepared according to any of the above preparation methods.

[0016] As a further optimization of the present application, the high-temperature high-strength and high-ductility ferrite-martensite steel is composed of the following components by mass percentage: 0.08-0.14% C, 8-12% Cr, 1.0-2.0% W, 0-1.5% Si, 0.3-0.8% Mn, 0.1-0.3% V, 0.1-0.3% Ta, 0-0.03% Zr, and the balance of Fe.

[0017] As a further optimization of the present application, the high-temperature high-strength and high-ductility refers to that the tensile strength of the ferrite-martensite steel is 699-860 MPa and the total elongation is 23-31% at 550℃.

[0018] The present application has the following advantages:

[0019] The present application performs cold plastic deformation processing on the obtained original ferrite martensite steel at low temperature to obtain nanocrystalline or ultra-fine grain ferrite martensite steel with a large number of pre-dislocation. Subsequently, by controlling the heat treatment process to control the dislocation behavior, the pre-dislocation is evolved into a dislocation cell structure or a subgrain substructure, and the size of the substructure is less than 200 nm, and has good high-temperature stability, so that the ferrite martensite steel of the present application has high strength and plasticity at high temperature (550℃). BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the electron backscattering image provided by the present application (in the figure, a is the original ferrite martensite steel (T-FM); b is the ferrite martensite steel extruded 4 times (E-FM); c is the high-temperature high-strength plastic ferrite martensite steel (E&A-FM)).

[0021] Figure 2 is the transmission electron microscope image provided by the present application (in the figure, a is the original ferrite martensite steel (T-FM); b is the ferrite martensite steel extruded 4 times (E-FM); c is the high-temperature high-strength plastic ferrite martensite steel (E&A-FM)).

[0022] Figure 3 is the engineering stress-strain curve of the original ferrite martensite steel (T-F / M), the original ferrite martensite steel annealed at 300℃ (T&A-F / M), the ferrite martensite steel after extrusion 4 times (E-F / M) and the high-temperature high-strength plastic ferrite martensite steel (E&A-F / M) provided by the present application (in the figure, a is about 20℃ at room temperature; b is 550℃). DETAILED DESCRIPTION

[0023] The following detailed description of the application will be further described in conjunction with the accompanying drawings, and it is necessary to point out here that the following detailed description is only used to further illustrate the application, and cannot be understood as limiting the scope of protection of the application. Those skilled in the art can make some non-essential improvements and adjustments to the application according to the above application content.

[0024] Example 1

[0025] The present embodiment provides a high-temperature high-strength plastic ferrite martensite steel, which is composed of the following components in mass percentage: 0.12% C, 9% Cr, 1.5% W, 0.7% Si, 0.5% Mn, 0.2% V, 0.1% Ta, 0.01% Zr, and the balance is Fe.

[0026] The preparation method comprises the following steps:

[0027] (1) The commercial steel ingot containing the above components is homogenized at 1100°C for 3 hours before forging, with a deformation ratio of 5:1, and then the forged steel billet is placed in a heating furnace at 1100°C for 1 hour before rolling, with a deformation of 50%; then the rolled sample is placed in a heating furnace at 800°C for 1 hour before rolling, with a deformation of 30%, and rolling is performed in 2 passes; then the rolled sample is quenched in water at 1020°C for 1 hour, and finally air cooled at 700°C for 1.5 hours, to obtain the original ferrite-martensite steel (T-F / M);

[0028] (2) The original ferrite-martensite steel (T-F / M) is subjected to 4 passes of equal channel angular extrusion at room temperature (about 20°C) to achieve a total strain of 4.12, and then the extruded sample is annealed at 300°C for 2 hours to obtain the high-temperature high-strength plastic ferrite-martensite steel (E&A-F / M).

[0029] Firstly, the microstructure of the high-temperature high-strength plastic ferrite-martensite steel (E&A-F / M) and the original ferrite-martensite steel (T-F / M) is analyzed, Figure 1 a is the electron backscattering result of the original ferrite-martensite steel (T-F / M), Figure 1 b is the electron backscattering result of the ferrite-martensite steel (E-F / M) after 4 passes of extrusion, Figure 1 c is the electron backscattering result of the high-temperature high-strength plastic ferrite-martensite steel (E&A-F / M).

[0030] Figure 2 a is the transmission electron microscopy result of the original ferrite-martensite steel (T-F / M), Figure 2 b is the transmission electron microscopy result of the ferrite-martensite steel (E-F / M) after 4 passes of extrusion, Figure 2 c is the transmission electron microscopy result of the high-temperature high-strength plastic ferrite-martensite steel (E&A-F / M).

[0031] Combining Figure 1 It can be seen that the initial microstructure of the original ferrite-martensite steel (T-F / M) is destroyed after extrusion, forming a super-fine layered structure with a layer thickness of about 102 nm, and this super-fine layered structure does not change significantly after annealing at 300°C. Combining Figure 2 It can be seen that the initial microstructure of the original ferrite-martensite steel (T-F / M) is mainly tempered martensite and residual dislocations, and a large number of pre-dislocations are observed in the super-fine layered structure after 4 passes of extrusion, and these pre-dislocations form a large number of high-temperature stable substructures after annealing at 300°C.

[0032] Subsequently, the high-temperature high-strength plastic ferrite-martensite steel (E&A-F / M) and the original ferrite-martensite steel (T-F / M) are subjected to room temperature and 550°C high-temperature mechanical property tests.

[0033] Figure 3 a is the engineering stress-strain curve of the original ferritic martensitic steel (T-F / M), the original ferritic martensitic steel annealed at 300℃ (T&A-F / M), the ferritic martensitic steel after 4 passes of extrusion (E-F / M) and the high-temperature high-strength plastic ferritic martensitic steel (E&A-F / M) at room temperature (about 20℃). The tensile strength of the high-temperature high-strength plastic ferritic martensitic steel (E&A-F / M) prepared in the embodiment at room temperature is 1355 MPa, and the total elongation is 12.8%. Compared with the ferritic martensitic steel after 4 passes of extrusion (E-F / M), the strength is slightly reduced, and the plasticity is obviously improved. The tensile strength and plasticity of the original ferritic martensitic steel before and after annealing are not much different, the tensile strength is about 940 MPa, and the total elongation is about 18%. This is mainly because the original ferritic martensitic steel is obtained by quenching and tempering, and thus has good thermal stability. Therefore, compared with the original ferritic martensitic steel, the tensile strength of the high-temperature high-strength plastic ferritic martensitic steel at room temperature is obviously improved, and the plasticity is slightly reduced.

[0034] Figure 3 b is the engineering stress-strain curve of the original ferritic martensitic steel (T-F / M), the original ferritic martensitic steel annealed at 300℃ (T&A-F / M), the ferritic martensitic steel after 4 passes of extrusion (E-F / M) and the high-temperature high-strength plastic ferritic martensitic steel (E&A-F / M) at 550℃. The tensile strength of the high-temperature high-strength plastic ferritic martensitic steel (E&A-F / M) prepared in the embodiment at 550℃ is 860 MPa, and the total elongation is 31%. As a comparison, the tensile strength of the ferritic martensitic steel after 4 passes of extrusion (E-F / M) at 550℃ is 490 MPa, and the total elongation is 45%. The tensile strength of the original ferritic martensitic steel before and after annealing at 300℃ changes little, and is maintained at about 590-600 MPa, and the elongation is 22%.

[0035] In summary, the tensile strength of the high-temperature high-strength plastic ferritic martensitic steel at room temperature is increased by about 44% compared with that of the original ferritic martensitic steel, and the total elongation is reduced by about 29%. The tensile strength of the high-temperature high-strength plastic ferritic martensitic steel at 550℃ is increased by about 43% compared with that of the original ferritic martensitic steel, and the total elongation is increased by 41%, realizing the synergistic improvement of the strength and plasticity at 550℃.

[0036] The high-temperature tensile strength of the ferritic martensitic steel reported in the invention patent CN113528979A at 550℃ is 958 MPa, and the total elongation is 22%, and the product of strength and plasticity obtained therefrom is 21076 MPa·%, which is lower than 26660 MPa·% of the present application, that is, the product of strength and plasticity of the high-temperature high-strength plastic ferritic martensitic steel of the present application is increased by about 26.5% than that reported in the invention patent CN113528979A, and has better high-temperature strength and plasticity matching.

[0037] Example 2

[0038] The difference from Example 1 is that step (2) is that the original ferritic martensitic steel obtained in step (1) is subjected to 4 passes of equal channel angular extrusion at room temperature (about 20℃) to achieve a total strain of 4.12, and then the extruded sample is annealed at 500℃ for 2 hours to obtain a high-temperature high-strength plastic ferritic martensitic steel.

[0039] The high-temperature high-strength plastic ferritic martensitic steel prepared above is subjected to material tensile test at room temperature (about 20℃) and 550℃, and the results show that the room temperature tensile strength of the high-temperature high-strength plastic ferritic martensitic steel prepared above is 1248 MPa, and the total elongation is 15%; the room temperature tensile strength of the original ferritic martensitic steel is about 940 MPa, and the total elongation is about 18%, so the room temperature tensile strength of the high-temperature high-strength plastic ferritic martensitic steel prepared above is increased by about 33% than that of the original ferritic martensitic steel, and the total elongation is decreased by about 16.7%.

[0040] The 550℃ high-temperature tensile strength of the high-temperature high-strength plastic ferritic martensitic steel prepared above is 823 MPa, and the total elongation is 28%; the 550℃ high-temperature tensile strength of the original ferritic martensitic steel is about 602 MPa, and the total elongation is about 22%, so the 550℃ high-temperature tensile strength of the high-temperature high-strength plastic ferritic martensitic steel prepared above is increased by about 37% than that of the original ferritic martensitic steel, and the total elongation is increased by about 27.3%, and the high-temperature strength and plasticity are also improved.

[0041] Example 3

[0042] The difference from Example 1 is that step (2) is that the original ferritic martensitic steel obtained in step (1) is subjected to 1 pass of equal channel angular extrusion at room temperature (about 20℃) to achieve a total strain of 1.03, and then the extruded sample is annealed at 500℃ for 2 hours to obtain a high-temperature high-strength plastic ferritic martensitic steel.

[0043] The high-temperature high-strength plastic ferritic martensitic steel prepared above is subjected to material tensile test at room temperature (about 20°C) and 550°C, and the results show that the tensile strength of the high-temperature high-strength plastic ferritic martensitic steel at room temperature is 1038 MPa, and the total elongation is 18%; the tensile strength of the original ferritic martensitic steel at room temperature is about 940 MPa, and the total elongation is about 18%, so the tensile strength of the high-temperature high-strength plastic ferritic martensitic steel prepared above at room temperature is increased by about 10% compared with that of the original ferritic martensitic steel, and the total elongation is basically unchanged. The high-temperature tensile strength of the high-temperature high-strength plastic ferritic martensitic steel prepared above at 550°C is 699 MPa, and the total elongation is 24%; the high-temperature tensile strength of the original ferritic martensitic steel at 550°C is about 602 MPa, and the total elongation is about 22%, so the high-temperature tensile strength of the high-temperature high-strength plastic ferritic martensitic steel prepared above at 550°C is increased by about 16% compared with that of the original ferritic martensitic steel, and the total elongation is increased by about 9.1%, and the high-temperature strength and plasticity are also improved coordinately.

[0044] The high-temperature high-strength plastic ferritic martensitic steel formed by annealing at 500°C after 1-pass extrusion is lower than that after 4-pass extrusion because the strain amount of 1-pass is low, the pre-existing dislocations are lower than those after 4-pass extrusion, so the number of substructures generated during annealing at the same temperature is lower than that after 4-pass extrusion, and in addition, the grain refinement effect of 1-pass extrusion is also lower than that of 4-pass extrusion.

[0045] Example 4

[0046] The difference from Example 1 is that step (2), the original ferritic martensitic steel obtained in step (1) is subjected to cold rolling at room temperature (about 20°C) with a total deformation amount of about 75%, achieving a total equivalent strain amount of about 1.6, and then the cold-rolled sample is annealed at 300°C for 2 hours to obtain a high-temperature high-strength plastic ferritic martensitic steel.

[0047] The high-temperature high-strength plastic ferritic martensitic steel prepared above is subjected to material tensile test at room temperature (about 20°C) and 550°C, and the results show that the tensile strength of the high-temperature high-strength plastic ferritic martensitic steel prepared above at room temperature is about 1100 MPa, and the total elongation is about 16%; the tensile strength of the original ferritic martensitic steel at room temperature is about 940 MPa, and the total elongation is about 18%, so the tensile strength of the high-temperature high-strength plastic ferritic martensitic steel prepared above at room temperature is increased by about 17% compared with that of the original ferritic martensitic steel, and the total elongation is decreased by about 11%.

[0048] The 550℃ high temperature tensile strength of the high temperature high strength plastic ferrite martensite steel prepared above is about 720MPa, and the total elongation is about 23%; the 550℃ high temperature tensile strength of the original ferrite martensite steel is about 602MPa, and the total elongation is about 22%, thus the 550℃ high temperature tensile strength of the high temperature high strength plastic ferrite martensite steel prepared above is increased by about 20% than that of the original ferrite martensite steel, and the total elongation is increased by about 4%, thus the high temperature strength and plasticity are improved simultaneously.

[0049] Example 5

[0050] The difference from Example 1 is that the step (2) is that the original ferrite martensite steel obtained from step (1) is subjected to one pass equal channel angular extrusion with a total strain of 1.03 after liquid nitrogen immersion (so that the surface temperature of the original ferrite martensite steel before extrusion is about -10℃), and then the extruded sample is annealed at 300℃ for 2 hours to obtain the high temperature high strength plastic ferrite martensite steel.

[0051] The high temperature high strength plastic ferrite martensite steel prepared above is subjected to material tensile test at room temperature (about 20℃) and 550℃ high temperature, and the results show that the room temperature tensile strength of the high temperature high strength plastic ferrite martensite steel prepared above is about 1050MPa, and the total elongation is about 17%; the room temperature tensile strength of the original ferrite martensite steel is about 940MPa, and the total elongation is about 18%, thus the room temperature tensile strength of the high temperature high strength plastic ferrite martensite steel prepared above is increased by about 12% than that of the original ferrite martensite steel, and the total elongation is decreased by about 5.6%.

[0052] The 550℃ high temperature tensile strength of the high temperature high strength plastic ferrite martensite steel prepared above is about 710MPa, and the total elongation is about 23%; the 550℃ high temperature tensile strength of the original ferrite martensite steel is about 602MPa, and the total elongation is about 22%, thus the 550℃ high temperature tensile strength of the high temperature high strength plastic ferrite martensite steel prepared above is increased by about 18% than that of the original ferrite martensite steel, and the total elongation is increased by about 4%, thus the high temperature strength and plasticity are improved simultaneously.

[0053] The above embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as the limitation of the patent scope of the present application. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the protection scope of the present application.

Claims

1. A method of manufacturing a high temperature high strength ductile ferritic- martensitic steel, characterized in that: The method comprises the following steps: (1) obtaining original ferrite martensite steel by heat treating a steel ingot; (2) performing 4-pass equal-channel angular extrusion on the original ferrite martensite steel obtained in step (1) at room temperature to achieve a total strain of 4.12, thereby obtaining nanocrystalline or ultrafine-grained ferrite martensite steel; (3) annealing the nanocrystalline or ultrafine-grained ferrite martensite steel obtained in step (2) in a protective atmosphere at 300 DEG C for 0.5-10 hours, thereby obtaining high-temperature high-strength plastic ferrite martensite steel; The high-temperature high-strength plastic ferrite martensite steel is composed of the following components by mass percentage: 0.08-0.14% C, 8-12% Cr, 1.0-2.0% W, 0-1.5% Si, 0.3-0.8% Mn, 0.1-0.3% V, 0.1-0.3% Ta, 0-0.03% Zr, and the balance of Fe.

2. A method of producing a high temperature high strength plastic ferritic martensitic steel according to claim 1, characterized in that: In step (1), the steel ingot is first homogenized at 1100 DEG C for 3 hours and then forged to obtain a steel blank, with a forging deformation ratio of 5:1; the forged steel blank is then placed in a heating furnace at 1100 DEG C for 1 hour and then opened for rolling, with a deformation of 50%; the opened steel blank is then placed in a heating furnace at 800 DEG C for 1 hour and then rolled, with a deformation of 30% and 2 rolling passes; the rolled steel blank is then held at 980-1050 DEG C for 0.5-1.5 hours, quenched in water, and finally held at 650-760 DEG C for 0.5-3 hours and then air-cooled, thereby obtaining the original ferrite martensite steel.

3. The method of claim 1, wherein the high temperature high strength plastic ferritic martensitic steel is prepared by the steps of: The protective atmosphere is one or more of nitrogen and argon. ​ 4. High-temperature high-strength plastic ferrite martensite steel prepared by the preparation method according to any one of claims 1-3.

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