A method for preparing a heat-resistant and radiation-resistant ultrafine-grained martensitic steel

Abstract

The application discloses a preparation method of a heat-resistant and radiation-resistant ultra-fine grain martensitic steel and belongs to the field of metal structural materials. 12 The ceramic oxide powder replaces Y2O3 and Ti powder added in preparation of a traditional oxide dispersion strengthened steel (ODS); the ODS steel with an ultra-fine grain structure is prepared through high-energy ball milling and spark plasma sintering, and a martensitic structure is obtained through a special heat treatment process. Compared with the preparation processes of the traditional ODS steel and the martensitic steel, the method can obtain the martensitic structure with small grains without a complex thermal mechanical treatment process. The material has a tensile strength of 1000-1200 MPa at room temperature, has an elongation of 16-20%, and has a high-temperature strength of 280-320 MPa at 650 DEG C.

Description

Technical Field

[0001] The invention relates to high-temperature resistant and radiation-resistant metal structural materials for fission reactors and fusion reactors, and in particular provides a method for preparing heat-resistant and radiation-resistant ultrafine-grained martensitic oxide dispersion-strengthened steel. Background Art

[0002] Oxide dispersion-strengthened (ODS) steel is considered a key candidate structural material for nuclear reactors due to its excellent high-temperature creep and radiation resistance. The superior performance of ODS steel stems from the high density of nano-oxides dispersed throughout the steel. These nano-oxides hinder grain growth and dislocation migration, effectively improving the material's mechanical properties. Furthermore, the nano-oxide / matrix interface effectively captures helium bubbles generated by neutron irradiation, mitigating the material's radiation swelling.

[0003] The properties of ODS steels are primarily determined by the nature of the oxides and the matrix structure. Initially, the mainstream oxide addition was Y2O3, which offers a high melting point and radiation resistance. However, a single Y2O3 phase tends to coarsen at high temperatures, resulting in limited strengthening. Subsequently, researchers discovered that the addition of oxygen-philic elements such as Ti, Si, and Zr to ODS steels can generate smaller ternary oxide phases, thereby improving the material's performance. This has laid a solid foundation for the manipulation of the microstructure and properties of ODS steels. Currently, the primary ODS steel designed for fusion reactors both domestically and internationally is 9Cr-ODS steel, such as ODS-Eurofer in Europe and ODS-CLF in China. Unlike high-Cr ferritic ODS alloys, 9Cr-ODS steel retains the matrix composition of traditional heat-resistant martensitic steels. This is because the low Cr content prevents radiation hardening, and martensitic structures offer better impact and radiation resistance than polygonal ferrites. Traditional heat-resistant martensitic steels can be obtained through standard heat treatment (i.e., normalizing and tempering) followed by air cooling. However, the following problems still exist in the preparation of 9Cr-ODS steel:

[0004] 1) Adding nano-oxides to 9Cr-ODS steel will prevent the formation of martensite because nanoparticles have an extremely high pinning effect on grain boundaries. In the austenitizing temperature range (~950-1200℃), the phase transformation driving force for the transformation of some ferrite to austenite is insufficient to overcome the Zener pinning force of the nanoparticles. Therefore, compared with traditional heat-resistant martensitic steels, the high-temperature microstructure of 9Cr-ODS steel is usually austenite and retained ferrite, and it is difficult to obtain a complete martensitic structure through general heat treatment.

[0005] 2) The radiation resistance of the nanophase is also very important for the engineering application of 9Cr-ODS steel. Studies have found that ordinary nano-precipitated phases are easily amorphized under high-temperature irradiation, thereby losing their crystal structure characteristics. Therefore, it is necessary to ensure that the added nano-oxide has a more stable structure. Summary of the Invention

[0006] In view of this, the present invention provides a method for preparing heat-resistant and radiation-resistant ultrafine-grained martensitic steel, which can effectively improve the heat resistance and radiation resistance of ODS steel.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing heat-resistant and radiation-resistant ultrafine-grained martensitic steel, using atomized spherical powder and Sc4Zr3O 12 The oxide powders are mixed and the materials are prepared by ball milling, spark plasma sintering and heat treatment.

[0009] Specifically, the present invention provides a method for preparing heat-resistant and radiation-resistant ultrafine-grained martensitic steel, comprising the following steps: high-energy ball milling of selected martensitic steel atomized powder and oxide powder, wherein the atomized powder comprises: 8.5-9.5 wt.%, 1-2 wt.%, Mn 0.3-0.6 wt.%, V 0.1-0.3 wt.%, Ta 0.1-0.3 wt.%, C 0.05-0.15 wt.%, and the remainder is Fe; based on the mass of the martensitic steel atomized powder, the mass of the added Sc4Zr3O1 powder is 0.2-1.0 wt.%; and the oxide powder is Sc4Zr3O1 powder.

[0010] Furthermore, the material preparation method comprises the following steps:

[0011] S1、Sc4Zr3O 12 Synthesis of oxide: Scandium nitrate hydrate and stearic acid are mixed to obtain mixture A, and zirconium nitrate hydrate and stearic acid are mixed to obtain mixture B; mixture A is heated until the stearic acid melts and stirred to obtain mixed solution C; mixture B is heated until the stearic acid melts and stirred to obtain mixed solution D, and mixed solution C and mixed solution D are mixed; acid and base are added dropwise to make the mixed solution milky white colloid, the colloid is dried, calcined, and ground to refine the powder to less than 200 nm to obtain Sc4Zr3O 12 powder.

[0012] Preferably, scandium nitrate hydrate and stearic acid are weighed in a molar ratio of 1:8 to 1:15, and mixed to obtain a mixture A; zirconium nitrate hydrate and stearic acid are weighed in a molar ratio of 1:8 to 1:15, and mixed to obtain a mixture B; mixture A is heated in a water bath until the stearic acid melts, and stirred to obtain a mixed solution C; mixture B is heated in a water bath until the stearic acid melts, and stirred to obtain a mixed solution D; mixed solution C and mixed solution D are mixed, stirred, and acid and base are added dropwise to make the mixed solution milky white colloid; the colloid is dried for 10 to 18 hours and then calcined in a muffle furnace for 1 to 5 hours at a calcination temperature of 800 to 1200°C; the calcined white powder is ground to refine the powder to less than 200 nm;

[0013] S2. Powder Alloying: Electrodes are made from Chinese low-activated martensitic (CLAM) steel. Discharge is performed to melt the end surface of the CLAM steel in contact with the arc. High-speed centrifugal force is then used to eject the metal droplets, completing the powder preparation process. The dried CLAM steel powder is weighed: based on the mass of the CLAM steel powder, the CLAM steel powder comprises 8.5-9.5 wt.% Cr, 1-2 wt.% W, 0.3-0.6 wt.% Mn, 0.1-0.3 wt.% V, 0.1-0.3 wt.% Ta, and 0.05-0.15 wt.%. 0.2-1.0 wt.% Sc4Zr3O is added to the dried CLAM steel powder. 12 The powder is ball-milled with grinding balls to obtain alloyed powder;

[0014] Preferably, the dried atomized powder and Sc4Zr3O 12 The powder is placed in a stainless steel jar together with the grinding balls, evacuated and then filled with high-purity argon gas. The process is repeated 3-5 times and then ball milled at a speed of 280-380 r / min for 36-72 h to obtain alloyed powder.

[0015] S3, spark plasma sintering: the alloyed powder is cold pressed into shape, sintered, and then cooled to room temperature in the furnace and the sintered sample is taken out. The sintering process is kept in a vacuum state;

[0016] Preferably, 10-20 g of alloyed powder is placed in a graphite mold with a diameter of 20-30 mm, wrapped with graphite paper and cold-pressed into a mold, and then placed in a sintering device. The sintering pressure is 55-70 MPa, the heating rate is 60-100 ° C / min, and the temperature is raised to 1000-1070 ° C and kept at this temperature for 5-8 minutes. The sintered sample is then taken out after cooling to room temperature in the furnace.

[0017] S4. Heat treatment: The sintered sample is heated, kept warm, and air-cooled to room temperature for normalizing. The sample is then heated, kept warm, and then air-cooled to room temperature for tempering.

[0018] Preferably, the general heat treatment process is specifically as follows: the sample is placed in a muffle furnace, the temperature is raised at a rate of 8-15℃ / min, and after the temperature is raised to 1050℃, the sample is kept at this temperature for 30-90min, then the sample is taken out and air-cooled to room temperature, and then the sample is placed in a muffle furnace again, the temperature is raised to 750℃ at a rate of 8-15℃ / min, and after the temperature is kept at 750℃ for 90-120min, the sample is air-cooled to room temperature. Preferably, the ODS martensitic steel heat treatment process is specifically as follows: the sample is placed in a muffle furnace, the temperature is raised at a rate of 8-15℃ / min, and after the temperature is raised to 1300℃, the sample is kept at this temperature for 30-90min, then the sample is cooled to room temperature in the furnace at a rate of 5℃ / min, and then the temperature is raised to 1050℃ at a rate of 8-15℃ / min, and after the temperature is kept at 1050℃ for 30-90min, the sample is air-cooled to room temperature, and then the temperature is raised to 750℃ at a rate of 8-15℃ / min, and after the temperature is kept at 750℃ for 90-120min, the sample is air-cooled to room temperature.

[0019] Further, after the heat treatment, an EBSD sample is prepared by an electrolytic polishing method. The EBSD sample preparation method has been described in the published invention patent (CN114894826A) of the research group, and will not be repeated here.

[0020] The application further provides a preparation method of the heat-resistant and radiation-resistant ultra-fine-grained martensitic steel, which is prepared by the preparation method as described above.

[0021] Compared with the prior art, the application has the following beneficial effects:

[0022] The application realizes the preparation of the heat-resistant and radiation-resistant ultra-fine-grained martensitic steel, and the Sc4Zr3O 12 oxide replaces the nano Y2O3 phase added in the preparation of the traditional ODS steel, on the one hand, the nano phase is improved in the anti-radiation amorphization, because the δ-A4B3O 12 structure has good anti-radiation performance; on the other hand, the ultra-fine-grained martensitic steel is obtained, and has good tensile properties.

[0023] The application is suitable for various iron-based high-temperature structural materials with ultra-fine grains, can improve the heat resistance and radiation resistance of the materials, and compared with the traditional ODS steel, the performance is improved without increasing the preparation cost. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is the XRD pattern of the Sc4Zr3O 12 oxide in Example 1;

[0025] Figure 2 is the secondary electron image and the EBSD pattern of the (a) 9Cr-ODS steel in Example 1;

[0026] Figure 4is the SEM image of 9Cr-ODS steel in Example 2;

[0027] Figure 5 (a) Secondary electron image and (b) EBSD map of 9Cr-ODS steel in Comparative Example 1;

[0028] Figure 6 is the SEM image of 9Cr-ODS steel in Comparative Example 2;

[0029] Figure 3 Graphs showing the room temperature and high temperature tensile results of (a) 9Cr-ODS steel in Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0030] The embodiments of the present invention are described in detail below. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be understood as limiting the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0032] The present invention provides a method for preparing heat-resistant and radiation-resistant ultrafine-grained martensitic ODS steel, wherein the heat resistance mentioned in this article refers to the high-temperature structural stability and good high-temperature strength of the material, the radiation resistance is due to the addition of radiation-resistant oxides, and the ultrafine grains refer to grains less than 1μm; the oxide dispersion strengthened (ODS) steel is the conventional definition in this field, and conventional ODS steels in this field are all suitable for the sample preparation method of this article, which will not be elaborated in detail here.

[0033] The preparation method comprises the following steps: preparing Sc4Zr3O by chemical synthesis 12 Powder is used to replace the nano Y2O3 phase added in the preparation of traditional ODS steel to improve the radiation resistance of the nano phase. The specific process is as follows:

[0034] Scandium nitrate hydrate and stearic acid, zirconium nitrate hydrate and stearic acid are weighed in a molar ratio of 1:10; the mixture is heated in a 90°C water bath for about 30 minutes until the stearic acid melts, and magnetically stirred for about 120 minutes to make the mixed solution uniform. The scandium nitrate solution dissolved in stearic acid and the zirconium nitrate solution are then mixed and magnetically stirred for 30 minutes. Acid and alkali are added dropwise to make the mixed solution milky white colloid. The colloid is dried for 10-18 hours and then calcined at 800-1200°C for 1-5 hours. The powder is then ground with a ceramic ball mill for 10-20 hours to refine the powder particle size to less than 200 nm.

[0035] In a further solution, the mixed powder is ball milled, and the dried matrix powder and Sc4Zr3O 12 Oxide powder. The mixed powder and grinding balls are placed in a stainless steel jar. The large and small balls have diameters of 10 mm and 5 mm, respectively, with a mass ratio of 1:5. The jar is evacuated and then filled with high-purity argon gas. This process is repeated 3-5 times. The jar is then ball-milled at a speed of 300 rpm for 48 hours to obtain an alloyed powder. This process aims to improve the alloying degree of the powder, refine the oxides, and increase the amount of oxides dissolved.

[0036] A further solution involves spark plasma sintering after ball milling. The specific process involves heating to 1050°C at a rate of 100°C / min, holding for 5 minutes, and then cooling to room temperature before removing the sintered sample. The sintering process is performed under vacuum.

[0037] Preferably, in some specific embodiments of the present invention, a heat treatment process is performed after ball milling and spark plasma sintering, and a complete martensitic structure can be obtained by a suitable heat treatment process. According to an embodiment of the present invention, there are two heat treatment processes: 1) using a wire cutting machine to cut the test sample, the test sample is placed in a muffle furnace, the heating rate is 10 ° C / min, the temperature is increased to 1050 ° C and then kept at this temperature for 60 minutes, the sample is taken out and air-cooled to room temperature, and then the sample is placed in a muffle furnace, the temperature is increased at 10 ° C / min to 750 ° C, kept at this temperature for 120 minutes, and then air-cooled to room temperature; 2) the sample is placed in a tube furnace, the heating rate is 10 ° C / min, the temperature is increased to 1300 ° C and kept at this temperature for 60 minutes, and the temperature is cooled to room temperature at 5 ° C / min with the furnace, and then the temperature is increased to 1050 ° C at 10 ° C / min, kept at this temperature for 60 minutes, and then air-cooled to room temperature, and then the temperature is increased to 750 ° C at 10 ° C / min, kept at this temperature for 120 minutes, and then air-cooled to room temperature. The first heat treatment scheme, which only involves normalizing and tempering, is suitable for the ODS steel in Example 1 but not for conventional ODS steel, as described in Comparative Example 1. The second heat treatment scheme adds a high-temperature heat treatment step. At high temperatures, this overcomes the pinning effect of the nanoparticles, allowing the unaustenitized residual ferrite grains to directly transform into delta-ferrite. A uniform austenitic structure is then obtained through austenitization, and martensitic structure is obtained through cooling. This second scheme can achieve martensitic structure in conventional ODS steel, as described in Comparative Example 2.

[0038] The present invention will be described below by way of specific examples. It should be noted that the following specific examples are for illustrative purposes only and are not intended to limit the scope of the present invention in any way. In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents used are all commercially available.

[0039] The anhydrous ethanol, ammonia water, scandium nitrate hydrate, zirconium nitrate hydrate, stearic acid, dichromate trioxide and titanium powder used in the examples of the present invention are all commercially available analytical grade reagents.

[0040] The equipment used for calcination in the embodiment of the present invention is a GSL-1200X muffle furnace.

[0041] The spark plasma sintering equipment in the embodiment of the present invention is model SE-607-FCZ.

[0042] The XRD diffractometer used in the embodiment of the present invention is of the model X'Pert Powder, PANAlytical.

[0043] The SEM device used to observe the sample morphology in the embodiment of the present invention is a ΣIGMA from the German ZEISS company, equipped with an electron backscattered diffraction (EBSD) probe; the device model is NORDLYS.

[0044] Example 1

[0045] The composition (mass fraction %) of the heat-resistant and radiation-resistant ultrafine-grained martensitic steel in this embodiment is Fe-9Cr-1.5W-0.4Mn-0.15Ta-0.2V-0.1C-0.5Sc4Zr3O 12 , the sample preparation steps are as follows:

[0046] S1. Oxide synthesis: Scandium nitrate hydrate and stearic acid, zirconium nitrate hydrate and stearic acid were weighed in a molar ratio of 1:10, with a molar ratio of scandium to zirconium of 4:3. The mixture was heated in a 90°C water bath for about 30 minutes until the stearic acid melted, and magnetically stirred for 120 minutes until the mixed solution was uniform. The scandium nitrate solution dissolved in stearic acid was then mixed with the zirconium nitrate solution, and magnetically stirred for 30 minutes. Dilute ammonia water was added at a rate of 1-5 mL / min until the pH of the solution reached 6.5, so that the mixed solution became milky white colloid. The colloid was dried for 12 hours and then calcined in a muffle furnace at 1000°C for 4 hours. The calcined white powder was ground for 10 hours to refine the powder to less than 200 nm.

[0047] S2. Powder Alloying: Electrodes are made from Chinese low-activation martensitic (CLAM) steel. Discharge is used to melt the CLAM steel end face in contact with the arc. High-speed centrifugal force is then used to eject the metal droplets, completing the powder preparation process. The CLAM steel powder composition is: Cr 8.68 wt.%, W 1.43 wt.%, Mn 0.31 wt.%, V 0.23 wt.%, Ta 0.21 wt.%, C 0.13 wt.%, and the balance is Fe. The average particle size is 69 μm. 89.55 g of dried low-activation steel atomized powder and 0.45 g of Sc4Zr3O 12 The powder was placed in a stainless steel jar together with 900 g of grinding balls. After vacuuming, the jar was filled with high-purity argon gas. The mixture was ball-milled 3-5 times at a speed of 300 r / min for 48 h to obtain alloyed powder.

[0048] S3, spark plasma sintering: 20g of alloyed powder was wrapped with graphite paper and cold pressed into shape. The powder was then placed in a sintering device. The temperature was raised to 1050°C at a rate of 100°C / min and kept at that temperature for 5min. The powder was then cooled to room temperature and the sintered sample was taken out. The vacuum state was maintained during the sintering process.

[0049] S4. Heat treatment: Grind the graphite paper on the surface of the sintered sample clean, cut the test sample using a wire cutting machine, place the test sample in a muffle furnace, heat it up at a rate of 10°C / min, heat it up to 1050°C and keep it there for 60 minutes, take out the sample and air cool it to room temperature, then place the sample in a muffle furnace again, heat it up to 750°C at a rate of 10°C / min, keep it there for 120 minutes, and then air cool it to room temperature.

[0050] Figure 1 Sc4Zr3O in Example 1 12 XRD pattern of oxide, Figure 2 (a) Secondary electron image and (b) EBSD map of 9Cr-ODS steel in Example 1. XRD test showed that the single phase Sc4Zr3O with good crystallinity was obtained. 12 The sample was characterized by EBSD. The results showed that the ultrafine-grained martensitic ODS steel was obtained, with an average grain size of 0.92μm and uniform grain size without obvious bimodal distribution. The room temperature tensile strength of the material reached 1075MPa, the elongation was as high as 18%, and the strength at 650℃ reached nearly 300MPa (such as Figure 3 shown).

[0051] Example 2

[0052] The composition of the heat-resistant and radiation-resistant martensitic steel in this comparative example is Fe-9Cr-1.5W-0.4Mn-0.15Ta-0.2V-0.1C-0.5Sc4Zr3O12 , the sample preparation steps are as follows:

[0053] S1, oxide synthesis: same as in Example 1;

[0054] S2. Powder alloying: same as in Example 1;

[0055] S3, spark plasma sintering: same as in Example 1;

[0056] S4. Heat treatment: Place the sample in a tubular furnace, heat up at a rate of 10°C / min, heat to 1300°C, keep warm for 60 min, cool to room temperature at a rate of 5°C / min, heat to 1050°C at a rate of 10°C / min, keep warm for 60 min, then air-cool to room temperature, then heat to 750°C at a rate of 10°C / min, keep warm for 120 min, then air-cool to room temperature.

[0057] Figure 4 This is the SEM image of the 9Cr-ODS steel in Example 2. After scanning electron microscopy observation, the test sample can also obtain a martensitic structure under the high-temperature heat treatment process, and the austenite grain size of the sample does not exceed 10μm, which is similar to the grain size of traditional martensitic steel, but coarser than the grains of the sample in Example 1.

[0058] Comparative Example 1

[0059] The composition of the heat-resistant and radiation-resistant martensitic steel in this comparative example is Fe-9Cr-1.5W-0.4Mn-0.15Ta-0.2V-0.1C-0.13Ti-0.3Y2O3, and the sample preparation steps are as follows:

[0060] S1. Powder alloying: Same as Example 1, except that 0.12 g of Ti powder, 0.27 g of Y2O3 powder and 89.63 g of atomized powder were weighed after drying;

[0061] S2, spark plasma sintering: same as in Example 1;

[0062] S3. Heat treatment: same as in Example 1.

[0063] Figure 5 (a) Secondary electron image and (b) EBSD map of the 9Cr-ODS steel in Comparative Example 1. EBSD was used to characterize the sample's microstructure. The results show that the average grain size of the ODS steel in Comparative Example 1 is 0.9 μm, similar to that in Example 1, but the grain distribution is uneven, with both ultrafine grains less than 500 nm and coarse grains greater than 7 μm present. A large number of polygonal ferrite grains are also present. The material has a room temperature tensile strength of 1012 MPa and a high-temperature tensile strength of 244 MPa at 650°C. Compared to Example 1, its room temperature strength is similar, but its high-temperature strength is 20% lower.

[0064] Comparative Example 2

[0065] The composition of the heat-resistant radiation-resistant martensitic steel in the present comparative example is Fe-9Cr-1.5W-0.4Mn-0.15Ta-0.2V-0.1C-0.13Ti-0.3Y2O3, and the sample preparation steps are as follows:

[0066] S1, powder alloying: same as Comparative Example 1;

[0067] S2, spark plasma sintering: same as Example 1;

[0068] S3, heat treatment: same as Example 2.

[0069] Figure 6 For the SEM image of the 9Cr-ODS steel in Comparative Example 2, after scanning electron microscope observation, the ODS steel sample in Comparative Example 2 uses the same heat treatment process as in Example 2, and also obtains a martensitic structure, but compared with Example 2, the austenite grain size of the sample is larger, exceeding 10 μm.

[0070] The technical features of the above-described examples can be combined arbitrarily, and in order to make the description simple, all possible combinations of the technical features in the above-described examples are not described, however, as long as the combination of the technical features does not exist contradictory, it should be considered as the scope covered by the present specification. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for preparing heat-resistant and radiation-resistant ultrafine-grained martensitic steel, characterized by: Atomized spherical powder and Sc4Zr3O 12 The oxide powders are mixed and the material is prepared by ball milling, spark plasma sintering and heat treatment; The atomized spherical powder is prepared by the following method: using Chinese low-activated martensitic (CLAM) steel to make an electrode, discharging the CLAM steel end surface and the arc contact area to be molten, then using rotating centrifugal force to throw out metal droplets to complete the powder preparation process, and sieving to obtain a powder with a particle size of 200-300 mesh, the powder having the following composition by weight percentage: Cr 8.5-9.5 wt.%, W1-2 wt.%, Mn 0.3-0.6 wt.%, V 0.1-0.3 wt.%, Ta 0.1-0.3 wt.%, C 0.05-0.15 wt.%, and the remainder Fe; The Sc4Zr3O 12 The mass ratio of oxide powder to atomized spherical powder is 1:500~1:100; the heat treatment is a common heat treatment process or an ODS martensitic steel heat treatment process; the common heat treatment process is specifically: placing the sample obtained after sintering in a muffle furnace, heating it to 1050°C at a heating rate of 10-15°C / min, and keeping it warm for 30-90min, then taking out the sample and air cooling it to room temperature, then placing the sample in a muffle furnace, heating it to 750°C at a heating rate of 8-15°C / min, and keeping it warm for 90-120min, and then air cooling it to room temperature; the ODS The martensitic steel heat treatment process is specifically as follows: placing the sample obtained after sintering in a muffle furnace, heating it to 1300°C at a heating rate of 10-15°C / min, holding it for 30-90 minutes, then cooling it to room temperature at a cooling rate of 5°C / min, then heating it to 1050°C at a heating rate of 8-15°C / min, holding it for 30-90 minutes, then air cooling it to room temperature, then heating the sample to 750°C at a heating rate of 8-15°C / min, holding it for 90-120 minutes, and then air cooling it to room temperature. The composition of the ultrafine-grained martensitic steel is: Cr 8.5-9.5 wt.%, W 1-2 wt.%, Mn 0.3-0.6 wt.%, V 0.1-0.3 wt.%, Ta 0.1-0.3 wt.%, C 0.05-0.15 wt.%, Sc4Zr3O12: 0.2-1.0wt.%, and the rest is Fe.

2. The method for preparing heat-resistant and radiation-resistant ultrafine-grained martensitic steel according to claim 1, characterized in that: Synthesis of Sc4Zr3O using the sol-gel method 12 Oxide powder.

3. The method for preparing heat-resistant and radiation-resistant ultrafine-grained martensitic steel according to claim 1, characterized in that: The ball milling process includes: grinding Sc4Zr3O 12 The mass ratio of oxide powder, ceramic balls and powder is 20:1, the volume of alcohol occupies 2 / 3 of the ceramic jar, the rotation speed of the ball mill is 200-300 r / min, and the grinding time is 10-20h.

4. The method for preparing heat-resistant and radiation-resistant ultrafine-grained martensitic steel according to claim 1, characterized in that: The ball milling comprises: 12 The powder and atomized spherical powder are mechanically alloyed, the ball-to-material mass ratio is between 10:1 and 15:1, the ball mill rotation speed is 280-380 r / min, and the grinding time is 36-72h.

5. The method for preparing heat-resistant and radiation-resistant ultrafine-grained martensitic steel according to claim 1, characterized in that: The spark plasma sintering process includes: placing the alloy powder obtained by ball milling into a graphite mold, heating it to 1000-1070°C at a heating rate of 60-100°C / min, and keeping it warm for 5-8 minutes, then cooling it to room temperature with the furnace and taking it out for use.

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