12Cr ferritic steel with high-strength heterostructure and preparation method of 12Cr ferritic steel

Abstract

The invention relates to the technical field of nuclear reactor high-strength steel preparation, in particular to 12Cr ferritic steel with a high-strength heterostructure and a preparation method thereof.The preparation method comprises the following steps that Cr, W, Ti and Fe serve as raw materials, pre-alloyed powder is obtained through atomization pulverization, the pre-alloyed powder and Y2O3 powder are mixed and subjected to mechanical ball milling in a ball mill, and the 12Cr ferritic steel with the high-strength heterostructure is obtained; mixed powder obtained after ball milling is loaded into a stainless steel sheath for degassing and seal welding, then the mixed powder is put into hot isostatic pressing equipment for curing forming, after furnace cooling is conducted to the room temperature, the mixed powder is put into a heat treatment furnace for heat preservation, hot rolling deformation is conducted after heat preservation, finally annealing treatment is conducted, and the 12Cr ferritic steel with the high-strength heterostructure is obtained. The problem that the plasticity of traditional 12Cr ferrite steel is reduced due to the fact that a homogeneous microstructure and oxide nanoparticles are excessively dispersed and distributed, and therefore the requirements for room temperature and high-temperature strength under the current service condition are difficult to meet is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of high-strength steel for nuclear reactors, and specifically to a 12Cr ferritic steel with a high-strength heterogeneous structure and a preparation method thereof. Background Art

[0002] High-temperature and high-pressure environments such as nuclear fusion reactors and supercritical power generation units pose extremely high requirements for the performance of structural materials. 12Cr ferritic steel is widely regarded as one of the key structural materials for the fourth-generation nuclear reactor due to its excellent high-temperature strength, irradiation swelling resistance, and creep resistance.

[0003] However, traditional 12Cr ferritic steel has limitations in mechanical properties. Its homogeneous microstructure leads to a significant decrease in plasticity. In addition, the excessive dispersion of oxide nanoparticles will further refine the grains and hinder the movement of dislocations, thereby exacerbating the reduction in plasticity. The combined effect of these factors makes the existing 12Cr ferritic steel difficult to meet the requirements for room-temperature and high-temperature strength under current service conditions, and in high-temperature and high-pressure environments, due to insufficient plasticity, it is difficult to effectively resist irradiation-induced embrittlement and swelling problems, limiting its application in long-term high-temperature service.

[0004] Therefore, it is necessary to invent a 12Cr ferritic steel with a high-strength heterogeneous structure and a preparation method to solve the above problems. Summary of the Invention

[0005] In order to solve the problem that traditional 12Cr ferritic steel has a decrease in plasticity due to its homogeneous microstructure and excessive dispersion of oxide nanoparticles, making it difficult to meet the requirements for room-temperature and high-temperature strength under current service conditions and limiting its application in long-term high-temperature service, the present invention provides a 12Cr ferritic steel with a high-strength heterogeneous structure and a preparation method thereof.

[0006] The present invention is implemented by adopting the following technical solutions: A preparation method of a 12Cr ferritic steel with a high-strength heterogeneous structure, comprising the following steps: S1: Using Cr, W, Ti, and Fe as raw materials, pre-alloyed powder is obtained by atomization powder making. The mass percentages of the raw materials of the pre-alloyed powder are Cr: 12%, W: 2%, Ti: 0.2%, and the balance is Fe. The pre-alloyed powder and Y2O3 powder are mixed in a mass ratio of 99.65:0.35, mechanically ball-milled in a ball mill, and protected by argon to obtain the ball-milled mixed powder; S2: The ball-milled mixed powder is filled into a stainless steel jacket, and the powder in the stainless steel jacket is degassed at a temperature of 450°C until the vacuum degree of the stainless steel jacket reaches 0.002 Pa; S3: Hermetically seal the stainless steel jacket with a vacuum degree of 0.002 Pa, and place it in a hot isostatic pressing equipment for solidification and forming. The forming temperature is 1150 °C, the heat preservation time is 3 h, the forming pressure is 150 Mpa. After cooling to room temperature in the furnace, a 12Cr ferritic steel sample is obtained; S4: Place the obtained 12Cr ferritic steel sample in a heat treatment furnace for heat preservation. After cooling the heat-preserved 12Cr ferritic steel sample, perform hot rolling deformation, and then cool it to room temperature to obtain a rolled 12Cr ferritic steel; S5: Anneal the rolled 12Cr ferritic steel to obtain a 12Cr ferritic steel with a high-strength heterogeneous structure.

[0007] Further, in step S1: The ball-to-material ratio in the ball mill is 10:1.

[0008] Further, in step S1: The ball milling speed of the ball mill is 250 rpm, and the ball milling time is 30 h.

[0009] Further, in step S4: The heat preservation temperature of the heat treatment furnace is 1100 °C, and the heat preservation time is 30 min.

[0010] Further, in step S4: The heat-preserved 12Cr ferritic steel sample is cooled to 880 °C for hot rolling deformation, and the deformation amount is 60% - 85%.

[0011] Further, in step S5: The annealing temperature of the annealing treatment is 700 °C, and it is heat-preserved at this temperature for 10 min - 60 min.

[0012] A 12Cr ferritic steel with a high-strength heterogeneous structure, which is obtained based on the preparation method of a 12Cr ferritic steel with a high-strength heterogeneous structure described in the present invention.

[0013] The key to the present invention lies in the composition design of the pre-alloyed powder, the process parameters of hot rolling, and the process parameters of subsequent annealing treatment. The raw materials and mass percentages of the pre-alloyed powder are Cr: 12%, W: 2%, Ti: 0.2%, and the balance is Fe, which determines that the 12Cr ferritic steel to be prepared has ferrite as the stable phase at room temperature and high temperature; the process parameters of hot rolling enable the energy within the grains of the 12Cr ferritic steel sample to be released in a high-temperature environment, thereby undergoing dynamic recrystallization to form equiaxed grains. During this process, the interaction between the grain boundaries and the nano-oxide particles promotes the dissolution and re-precipitation of the nano-oxide particles. These precipitated nano-oxide particles are linearly arranged along the rolling direction. This process not only optimizes the grain structure but also enhances the layered heterogeneous characteristics of the material, thereby improving the mechanical properties of the 12Cr ferritic steel at room temperature and high temperature; for the as-rolled 12Cr ferritic steel obtained after hot rolling deformation and cooling to room temperature, its matrix is a ferrite structure. After annealing treatment, the dislocations in its matrix are reduced, and the internal stress of the material is lowered, thereby enhancing the plasticity of the 12Cr ferritic steel.

[0014] Through the composition design of the 12Cr ferritic steel and the adjustment of the hot rolling process in the present invention, the 12Cr ferritic steel no longer has a homogeneous microstructure but forms a heterogeneous structure feature with a layered distribution of grain sizes. At the same time, the nano-oxide particles are distributed along the rolling direction, enabling the as-rolled 12Cr ferritic steel to exhibit good mechanical properties at room temperature and 650 °C. Through the improvement of the annealing process, the plasticity of the 12Cr ferritic steel at room temperature and 650 °C is further enhanced. Description of the Drawings

[0015] Figure 1 It is an electron backscatter diffraction (EBSD) photograph of the as-rolled 12Cr ferritic steel with a deformation of 60% obtained in Example 1 of the present invention.

[0016] Figure 2 It is a scanning electron microscopy (SEM) photograph of the as-rolled 12Cr ferritic steel with a deformation of 60% obtained in Example 1 of the present invention.

[0017] Figure 3 It is a tensile property curve graph of the as-rolled 12Cr ferritic steel with a deformation of 60% obtained in Example 1 of the present invention at room temperature and 650 °C.

[0018] Figure 4 It is an electron backscatter diffraction (EBSD) photograph of the as-rolled 12Cr ferritic steel with a deformation of 85% obtained in Example 2 of the present invention.

[0019] Figure 5Tensile property curves of the 12Cr ferritic steel with a high-strength heterogeneous structure obtained in Example 1 of the present invention at room temperature and 650 °C.

[0020] Figure 6 Tensile property curves of the 12Cr ferritic steel with a high-strength heterogeneous structure obtained in Example 2 of the present invention at room temperature and 650 °C.

[0021] Figure 7 Tensile property curves of the as-rolled 12Cr ferritic steel with a deformation of 85% obtained in Example 2 of the present invention at room temperature and 650 °C. Detailed implementation manners

[0022] A preparation method of a 12Cr ferritic steel with a high-strength heterogeneous structure, comprising the following steps: S1: Using Cr, W, Ti, and Fe as raw materials, pre-alloyed powder is obtained by atomization powder making, and the mass percentages of the raw materials of the pre-alloyed powder are Cr: 12%, W: 2%, Ti: 0.2%, and the balance is Fe. The pre-alloyed powder and Y2O3 powder are mixed at a mass ratio of 99.65:0.35, mechanically ball-milled in a ball mill, the ball-to-material ratio is 10:1, the ball-milling rotation speed is 250 rpm, the ball-milling time is 30 h, and argon protection is used to obtain the ball-milled mixed powder; S2: The ball-milled mixed powder is loaded into a stainless steel jacket, and the powder in the stainless steel jacket is degassed at a temperature of 450 °C until the vacuum degree of the stainless steel jacket reaches 0.002 Pa; S3: The stainless steel jacket with a vacuum degree of 0.002 Pa is sealed and welded, and then put into a hot isostatic pressing device for solidification molding. The molding temperature is 1150 °C, the heat preservation time is 3 h, the molding pressure is 150 Mpa, and after cooling to room temperature with the furnace, a 12Cr ferritic steel sample is obtained; S4: The obtained 12Cr ferritic steel sample is put into a heat treatment furnace for heat preservation. The heat preservation temperature is 1100 °C, the heat preservation time is 30 min, and the heat-preserved 12Cr ferritic steel sample is cooled to 880 °C for hot rolling deformation, and the deformation amount is 60% - 85%. Then, after cooling to room temperature, an as-rolled 12Cr ferritic steel is obtained.

[0023] S5: The as-rolled 12Cr ferritic steel is annealed, the annealing temperature is 700 °C, and it is heat-preserved at this temperature for 10 min - 60 min to obtain a 12Cr ferritic steel with a high-strength heterogeneous structure.

[0024] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. Example 1

[0025] A preparation method of a 12Cr ferritic steel with a high-strength heterogeneous structure includes the following steps: S1: Using Cr, W, Ti, and Fe as raw materials, pre-alloyed powder is obtained by atomization powder making. The mass percentages of the raw materials of the pre-alloyed powder are Cr: 12%, W: 2%, Ti: 0.2%, and the balance is Fe. The pre-alloyed powder and Y2O3 powder are mixed at a mass ratio of 99.65:0.35, and mechanical ball milling is carried out in a QM-3SP4 planetary ball mill. The ball-to-material ratio is 10:1, the ball milling speed is 250 rpm, the ball milling time is 30 h, and argon protection is used to obtain the ball-milled mixed powder.

[0026] S2: The ball-milled mixed powder is filled into a stainless steel jacket, and the powder in the stainless steel jacket is degassed at a temperature of 450°C until the vacuum degree of the stainless steel jacket reaches 0.002 Pa.

[0027] S3: The stainless steel jacket with a vacuum degree of 0.002 Pa is sealed and welded, and then put into a hot isostatic pressing device for solidification forming. The forming temperature is 1150°C, the holding time is 3 h, the forming pressure is 150 Mpa. After cooling to room temperature with the furnace, a 12Cr ferritic steel sample is obtained.

[0028] S4: The obtained 12Cr ferritic steel sample is put into a heat treatment furnace for holding. The holding temperature is 1100°C, the holding time is 30 min. The heat-treated 12Cr ferritic steel sample is cooled to 880°C for hot rolling deformation, and the deformation amount is 60%. Then, after cooling to room temperature, a rolled 12Cr ferritic steel with a deformation amount of 60% is obtained.

[0029] Figure 1 This is the electron backscatter diffraction (EBSD) photo of the rolled 12Cr ferritic steel with a deformation amount of 60% obtained in this example. It can be seen from the figure that after rolling treatment, the microstructure of the rolled 12Cr ferritic steel is elongated along the rolling direction to a certain extent. The grains mainly show an equiaxed shape, and there are large differences in the sizes of ferrite blocks, presenting the characteristics of a high-strength heterogeneous structure. This heterogeneous structure effectively improves the room temperature and high-temperature mechanical properties of the rolled 12Cr ferritic steel with a deformation amount of 60%.

[0030] Figure 2This is a scanning electron microscopy (SEM) photograph of the as-rolled 12Cr ferritic steel with a 60% deformation obtained in this example. It can be clearly seen from the figure that the nano-oxide particles are linearly arranged along the rolling direction.

[0031] Figure 3 This is the tensile property curve of the as-rolled 12Cr ferritic steel with a 60% deformation obtained in this example at room temperature and 650 °C. At room temperature, the tensile strength of the as-rolled 12Cr ferritic steel with a 60% deformation is 793 MPa, the yield strength is 564 Mpa, and the elongation is 13.75%; at 650 °C, the tensile strength of the as-rolled 12Cr ferritic steel with a 60% deformation is 290 MPa, the yield strength is 275 Mpa, and the elongation is 13.87%.

[0032] S5: Anneal the as-rolled 12Cr ferritic steel with a 60% deformation in a muffle furnace at an annealing temperature of 700 °C and hold for 40 min at this temperature to obtain the 12Cr ferritic steel with a high-strength heterogeneous structure.

[0033] Figure 5 This is the tensile property curve of the 12Cr ferritic steel with a high-strength heterogeneous structure obtained in this example at room temperature and 650 °C. At room temperature, the tensile strength of the 12Cr ferritic steel with a high-strength heterogeneous structure obtained in this example is 739 MPa, the yield strength is 504 Mpa, and the elongation is 23.2%; at 650 °C, its tensile strength is 317 MPa, the yield strength is 292 Mpa, and the elongation is 24.1%. Example 2

[0034] A preparation method of 12Cr ferritic steel with a high-strength heterogeneous structure includes the following steps: S1: Using Cr, W, Ti, and Fe as raw materials, obtain pre-alloyed powder by atomization powder making. The mass percentages of the raw materials of the pre-alloyed powder are Cr: 12%, W: 2%, Ti: 0.2%, and the balance is Fe. Mix the pre-alloyed powder and Y2O3 powder according to a mass ratio of 99.65:0.35, conduct mechanical ball milling in a QM-3SP4 planetary ball mill with a ball-to-material ratio of 10:1, a ball milling speed of 250 rpm, and a ball milling time of 30 h, and use argon protection to obtain the ball-milled mixed powder.

[0035] S2: Load the ball-milled mixed powder into a stainless steel jacket, degas the powder in the stainless steel jacket at a temperature of 450 °C until the vacuum degree of the stainless steel jacket reaches 0.002 Pa.

[0036] S3: Hermetically seal the stainless steel jacket with a vacuum degree reaching 0.002 Pa, and place it in a hot isostatic pressing equipment for solidification and forming. The forming temperature is 1150 °C, the heat preservation time is 3 h, the forming pressure is 150 Mpa. After cooling to room temperature with the furnace, a 12Cr ferritic steel sample is obtained.

[0037] S4: Place the obtained 12Cr ferritic steel sample in a heat treatment furnace for heat preservation. The heat preservation temperature is 1100 °C, and the heat preservation time is 30 min. Cool the heat-preserved 12Cr ferritic steel sample to 880 °C for hot rolling deformation, and the deformation amount is 85%. Then, after cooling to room temperature, a rolled 12Cr ferritic steel with a deformation amount of 85% is obtained.

[0038] Figure 4 This is the electron backscatter diffraction (EBSD) photograph of the rolled 12Cr ferritic steel with a deformation amount of 85% obtained in this embodiment. It can be seen from the figure that compared with the grains of the rolled 12Cr ferritic steel with a deformation amount of 60% in Example 1, the grains of the rolled 12Cr ferritic steel with a deformation amount of 85% are no longer equiaxed grains, but show certain layered characteristics.

[0039] Figure 7 This is the tensile property curve graph of the rolled 12Cr ferritic steel with a deformation amount of 85% obtained in this embodiment at room temperature and 650 °C. At room temperature, the tensile strength of the rolled 12Cr ferritic steel with a deformation amount of 85% is 808 MPa, the yield strength is 652 Mpa, and the elongation is 19.9%; at 650 °C, the tensile strength of the rolled 12Cr ferritic steel with a deformation amount of 85% is 379 MPa, the yield strength is 353 Mpa, and the elongation is 23.9%. By comparison Figure 3 it can be known that compared with the rolled 12Cr ferritic steel with a deformation amount of 60%, the rolled 12Cr ferritic steel with a deformation amount of 85% obtained in this embodiment has significantly improved tensile strength, yield strength and plasticity at room temperature and 650 °C respectively, especially the tensile strength, yield strength and plasticity at 650 °C are more significantly improved.

[0040] S5: Anneal the rolled 12Cr ferritic steel with a deformation amount of 85% in a muffle furnace. The annealing temperature is 700 °C, and keep it at this temperature for 15 min to obtain a 12Cr ferritic steel with a high-strength heterogeneous structure.

[0041] Figure 6Tensile property curves of the 12Cr ferritic steel with a high-strength heterostructure obtained in this example at room temperature and 650 °C. At room temperature, the tensile strength of the 12Cr ferritic steel with a high-strength heterostructure obtained in this example is 797 MPa, the yield strength is 617 Mpa, and the elongation is 20.3%; at 650 °C, the tensile strength of the 12Cr ferritic steel with a high-strength heterostructure obtained in this example is 336 MPa, the yield strength is 315 Mpa, and the elongation is 22.73%. By comparison Figure 7 It can be seen that after annealing treatment, when the 12Cr ferritic steel with a high-strength heterostructure obtained in this example is compared with the rolled 12Cr ferritic steel with a deformation of 85%, although the tensile strength and yield strength at room temperature and 650 °C both decrease slightly, the plasticity at room temperature has been significantly improved.

[0042] By comparison Figure 5 with Figure 6 It can be seen that when the 12Cr ferritic steel with a high-strength heterostructure obtained in Example 1 is compared with the 12Cr ferritic steel with a high-strength heterostructure obtained in this example, although the tensile strength and yield strength at room temperature and 650 °C both decrease slightly, the plasticity at room temperature and 650 °C has been significantly improved, indicating that 12Cr ferritic steels with different strength and plasticity combinations can be obtained by adjusting the hot rolling process parameters and annealing time.

[0043] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

Claims

1. A method for preparing 12Cr ferrite steel with high strength heterogeneous structure, characterized in that: The following steps are involved: S1: Using Cr, W, Ti and Fe as raw materials, a pre-alloyed powder is obtained by atomization powder making, and the mass percentages of the raw materials of the pre-alloyed powder are Cr: 12%, W: 2%, Ti: 0.2%, and the balance is Fe. The pre-alloyed powder is mixed with Y2O3 powder in a mass ratio of 99.65:0.35, and mechanically ball milled in a ball mill under argon protection to obtain a mixed powder after ball milling; S2: The ball-milled mixed powder is placed in a stainless steel sheath, and the powder in the stainless steel sheath is degassed at a temperature of 450°C until the vacuum degree of the stainless steel sheath reaches 0.002Pa; S3: The stainless steel sheath with a vacuum degree of 0.002Pa is sealed and welded, and then placed in a hot isostatic pressing device for curing and molding. The molding temperature is 1150°C, the holding time is 3h, and the molding pressure is 150Mpa. After cooling to room temperature with the furnace, a 12Cr ferrite steel sample is obtained; S4: placing the obtained 12Cr ferrite steel sample in a heat treatment furnace for heat preservation, cooling the heat-insulated 12Cr ferrite steel sample and then performing hot rolling deformation, and then cooling to room temperature to obtain rolled 12Cr ferrite steel; S5: annealing the rolled 12Cr ferrite steel to obtain a 12Cr ferrite steel with a high-strength heterogeneous structure.

2. The method for preparing a 12Cr ferrite steel with a high-strength heterogeneous structure according to claim 1, characterized in that: In step S1: the ball-to-material ratio in the ball mill is 10:

1.

3. The method for preparing a 12Cr ferrite steel with a high-strength heterogeneous structure according to claim 1, characterized in that: In step S1: the ball milling speed is 250 rpm, and the ball milling time is 30 h.

4. The method for preparing a 12Cr ferrite steel with a high-strength heterogeneous structure according to claim 1, characterized in that: In step S4: the heat treatment furnace is kept at a temperature of 1100° C. for 30 minutes.

5. The method for preparing a 12Cr ferrite steel with a high-strength heterogeneous structure according to claim 1, characterized in that: In step S4: the 12Cr ferrite steel sample after heat preservation is cooled to 880°C and hot rolled, and the deformation amount is 60% to 85%.

6. The method for preparing a 12Cr ferrite steel with a high-strength heterogeneous structure according to claim 1, characterized in that: In step S5: the annealing temperature of the annealing treatment is 700° C., and the temperature is kept at 700° C. for 10 min to 60 min.

7. A 12Cr ferrite steel with a high-strength heterogeneous structure, wherein the 12Cr ferrite steel is obtained based on the preparation method of the 12Cr ferrite steel with a high-strength heterogeneous structure according to any one of claims 1 to 6.

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