CN114032369B - Method for regulating and controlling tissue structure of 304 metastable austenitic stainless steel - Google Patents
Method for regulating and controlling tissue structure of 304 metastable austenitic stainless steel Download PDFInfo
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- C21D1/04—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering with simultaneous application of supersonic waves, magnetic or electric fields
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
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Abstract
The invention discloses a method for regulating and controlling a tissue structure of 304 metastable austenitic stainless steel. Firstly, carrying out middle-low temperature stretching pre-deformation treatment on stainless steel, and introducing deformation defects such as dislocation, stacking fault, deformation zone and the like into an annealed metastable austenitic stainless steel structure according to different deformation amounts; further utilizing a medium-temperature isothermal process to eliminate residual stress in the stainless steel structure; finally, the stainless steel is subjected to cryogenic treatment under the action of a magnetic field by utilizing the coupling action of the magnetic field and the cryogenic environment, and the effective content of martensite is introduced into the metastable austenitic stainless steel structure, so that the regulation and control of the structure of the metastable austenitic stainless steel structure of 304 type is realized.
Description
Technical Field
The invention belongs to the technical field of production of metastable austenitic stainless steel, and particularly relates to a regulating and controlling method of a microstructure of 304 metastable austenitic stainless steel.
Background
The 304 metastable austenitic stainless steel has the advantages of easy processing, corrosion resistance, oxidation resistance and the like, and is widely applied to the manufacturing fields of tableware, ships, rail transit and the like. In the design process of the 304 metastable austenitic stainless steel, in order to ensure good corrosion resistance and oxidation resistance, a high alloy design concept is adopted, and a large amount of alloy elements such as Cr, ni and the like are added into a structure, so that the room-temperature structure of the metastable austenitic stainless steel is stable single-phase austenite. This results in a metastable austenitic stainless steel of type 304 having a lower yield strength, making it unusable for high strength components in the field of industrial production. Therefore, how to increase the yield strength of type 304 metastable austenitic stainless steel has become a challenge for its development.
At present, the method for improving the yield strength of the steel material mainly comprises fine grain strengthening, phase change strengthening and dislocation strengthening. Aiming at the 304 metastable austenitic stainless steel, the realization of fine grain strengthening can only utilize the large-pressure deformation combined with the low-temperature annealing treatment process, and utilize deformation to induce the reverse phase transformation of martensite or the recrystallization of a deformation substructure to realize the refinement of the original structure.
The dislocation reinforcement is realized by introducing dislocation through large deformation, and the yield strength of the material is improved by utilizing the processing hardening of the dislocation, however, the ductility and the processing hardening performance of the material are deteriorated due to a large number of dislocation defects in the material structure under the process, and meanwhile, the corrosion resistance of the type 304 metastable austenitic stainless steel is reduced.
The transformation strengthening is an important method for improving the yield strength of the steel material by introducing strengthening phase martensite into the steel material structure, and has the advantages of low cost, good strength improving effect and the like. However, a large amount of stable austenite alloy elements exist in the metastable austenitic stainless steel structure of type 304, so that the room temperature structure is stable austenite, and martensite is difficult to be introduced even under the condition of deep cooling. Therefore, how to introduce the strengthening phase martensite into the 304 metastable austenitic stainless steel is a difficult problem to increase its yield strength by martensite transformation strengthening.
For the above problems, the inventors have proposed in the prior work that a process means of room temperature pre-deformation can be used to introduce a slip band defect into an austenitic structure, and the slip band is used as a nucleation point of martensitic transformation to excite variable temperature martensitic transformation, so that martensite is successfully introduced into austenitic stainless steel. However, the actual results show that the austenitic stainless steel is treated by the above process, and at most martensite with a volume fraction of about 10% can be introduced into the structure. The amount of martensite introduced does not exhibit a linear relationship with the amount of the slip zone introduced. This fact reveals that the above process is insufficient to introduce a greater amount of martensite into austenitic stainless steel, which restricts further improvement of the yield strength of austenitic stainless steel. Therefore, how to introduce more martensite (10% or even 15% or more) into a type 304 metastable austenitic stainless steel becomes a challenge to increase the yield strength of that steel grade with transformation strengthening.
Disclosure of Invention
The invention aims at the defects existing in the prior 304 metastable austenitic stainless steel in the martensite introducing process (room temperature pre-deformation and deep cooling treatment): the method is characterized in that the type of the nucleation point is single, residual stress and phase transformation driving force are single in the structure, and the method for increasing the plastic deformation capacity of austenitic stainless steel by increasing medium-low temperature heat preservation treatment before pre-deformation and eliminating internal stress in the structure by increasing medium-temperature isothermal treatment after pre-deformation is proposed to improve the growth condition of martensite laths. In addition, in order to increase the types of nucleation points, pre-deformation processes with different temperatures are designed to introduce more types of martensite phase transformation nucleation points (dislocation, fault, slip zone and the like) and improve the nucleation conditions of the martensite lath. Further, in order to increase the driving force of the martensitic transformation, the present invention proposes to provide the martensitic transformation with a transformation driving force by using a coupling action mechanism of a magnetic field and a temperature field (magnetic field+cryogenic treatment), and promote the martensitic transformation. In addition, in order to introduce more martensite into the structure, long-time isothermal treatment is designed in the stage of cryogenic treatment, and the final martensite content in the austenitic stainless steel is improved by utilizing the combined action of variable-temperature martensitic transformation and isothermal martensitic transformation of deformation-induced nucleation points, so that the austenitic stainless steel obtains a duplex structure of austenite and martensite, and further the yield strength of the 304 type metastable austenitic stainless steel is enhanced by utilizing martensitic transformation.
The technical purpose of the invention is achieved by the following scheme.
In order to achieve the above object, the present invention is achieved by the following means:
the invention provides a method for regulating and controlling a tissue structure of 304 metastable austenitic stainless steel, which comprises the following steps:
(1) Stretching and pre-deforming the annealed 304 metastable austenitic stainless steel at 100-300 ℃;
(2) Carrying out isothermal treatment at 250-350 ℃ on the stainless steel subjected to the pre-deformation treatment, and then cooling to room temperature;
(3) And (3) directly putting the stainless steel obtained through the treatment in the step (2) into a cryogenic environment for cryogenic treatment, and then heating the stainless steel to room temperature.
As a preferred aspect of the present invention, in the stretching pre-deformation treatment in the step (1), the deformation amount is 7 to 11% and the strain rate is 10 -3 /s。
Preferably, the deformation amount in the step (1) is 9%.
Preferably, the isothermal treatment temperature in the step (2) is 300 ℃, and the isothermal treatment time is 4-6 minutes.
Preferably, the isothermal time in step (2) is 5 minutes.
Preferably, the cryogenic treatment in step (3) is performed in an environment where a magnetic field is applied.
Preferably, the strength of the applied magnetic field in the step (3) is 7-9T.
As the preferable mode of the invention, the temperature of the cryogenic treatment in the step (3) is-150 to-180 ℃, and the cryogenic treatment time is 30-60 minutes.
Preferably, in the present invention, the temperature of the cryogenic treatment in the step (3) is-180 ℃, the time of the cryogenic treatment is 60 minutes, and the strength of the applied magnetic field is 9T.
Preferably, the temperature rise rate in step (3) is 20 ℃/min.
Further, step (a) is optionally further performed before step (1), wherein the step (a) is specifically: heating the annealed 304 type metastable austenitic stainless steel plate to 100-300 ℃, and carrying out heat preservation treatment for 10-20 minutes.
Preferably, in the present invention, the incubation temperature in the step (a) is 200 ℃ and the incubation time is 20 minutes.
In a second aspect, the present invention provides a metastable austenitic stainless steel type 304, prepared according to the method described above.
In the present invention, all the treatment times are the holding times after the type 304 metastable austenitic stainless steel reaches the set treatment temperature, without particular explanation.
The type 304 metastable austenitic stainless steel has high heat stability of austenite in a structure due to a high aggregate design concept, and martensite is difficult to form even under a cryogenic condition. Nucleation defects and phase transformation driving forces are preconditions for austenite to martensite transformation. According to the existing martensite phase transformation nucleation theory, the smaller the nucleation trend of nucleation defects is, the larger the driving force required by phase transformation is. Since the nucleation defects in the type 304 metastable austenitic stainless steel have a small nucleation tendency, the transformation driving force is insufficient to drive the nucleation defects in the grains to undergo martensitic transformation even under the condition of liquid nitrogen cryogenic cooling.
Aiming at the difficult problem that a large amount of martensite cannot be introduced into the 304 metastable austenitic stainless steel by the room temperature pre-deformation and cryogenic treatment process, the inventor carries out in-depth analysis. The research shows that the technology is only based on a nucleation mechanism, and the nucleation point (slip zone) is actively introduced, so that the martensitic transformation is promoted. In fact, martensitic transformation involves both nucleation and growth processes, and both processes have an important impact on martensitic transformation.
However, the above process only considers the introduction of martensite phase transformation nucleation points, and only introduces a single type of nucleation points (slip bands), and does not consider the growth of martensite laths. The martensitic transformation is an expansion type transformation, and internal stress in the material structure suppresses the martensitic transformation. In the above process, the pre-deformation means introduces internal stress into the tissue as well as the slip bands into the tissue.
Therefore, the room temperature pre-deformation and cryogenic treatment process only introduces single type of slip zone defects of nucleation points, and the influence of internal stress on the growth of martensite laths is not considered, so that the process is a main reason that a large amount of martensite cannot be introduced. In addition, the prior art only utilizes temperature-varying martensitic transformation to induce martensite, and does not use isothermal martensitic transformation to induce martensite. The driving force of the transformation is an important factor affecting the martensitic transformation, and the prior art only uses a cryogenic treatment means (chemical driving force) to trigger the martensitic transformation, but does not consider the introduction of other energy means as the driving force of the martensitic transformation.
The invention is based on the defects of the prior art method for introducing martensite into the material structure by the room temperature pre-deformation and cryogenic treatment process, which is proposed by the prior work of the inventor, and the invention applies the medium temperature heat preservation treatment after the stretching pre-deformation, so as to eliminate the internal stress introduced by the stretching pre-deformation and improve the growth condition of the martensite lath in the martensite phase transformation process.
In addition, the invention adopts middle-low temperature stretching pre-deformation treatment, and can actively introduce different types of deformation substructures such as stacking faults, dislocation, deformation bands and the like into an austenitic structure in an annealed state by setting different deformation temperatures, thereby providing nucleation points with larger nucleation trend for martensitic transformation, and further regulating the quantity of nucleation defects and the like by regulating the deformation temperature and the deformation degree. The driving force for the transformation is also a precondition for the martensitic transformation to occur.
In contrast, the invention designs a magnetic field and low temperature field coupling action process, and utilizes the superposition of magnetic energy and chemical driving force to provide the driving force of martensitic transformation for deformed core points with larger nucleation trend, such as deformation bands, faults, dislocation and the like, so as to promote martensitic transformation. In addition, by designing long-time cryogenic treatment, the invention utilizes the combined action of variable-temperature martensitic transformation and isothermal martensitic transformation to introduce more martensite into the 304-type metastable austenitic stainless steel.
In conclusion, the method realizes the introduction of martensite in the 304 type metastable austenitic stainless steel through the coupling effect of the processes such as middle-low temperature stretching pre-deformation, middle-temperature isothermal, deep cooling treatment under the action of a magnetic field and the like, and further improves the yield strength of the 304 type metastable austenitic stainless steel.
According to the method, the 304 type metastable austenitic stainless steel is subjected to stretching pre-deformation treatment at a set temperature, different types of deformation defects (the deformation temperature is from high to low, the types of deformation substructures are in sequence of stacking faults, dislocation, deformation bands and the like) are obtained by using the stretching pre-deformation treatment at different temperatures, and meanwhile, the introduced quantity of the deformation defects is adjusted according to the stretching pre-deformation degree; the deformed 304 metastable austenitic stainless steel is subjected to medium-temperature isothermal treatment, so that residual stress in a tissue can be eliminated; in addition, the 304 metastable austenitic stainless steel subjected to isothermal treatment is put into a low-temperature environment with a magnetic field, and the nuclear defect introduced by deformation is subjected to martensitic transformation by utilizing the superposition of magnetic energy and chemical free energy, so that the tissue structure of the metastable austenitic stainless steel is changed.
Compared with the prior art, the invention has the following beneficial effects:
(1) Aiming at the defects of room temperature pre-deformation and deep cooling treatment process: the invention provides isothermal treatment after deformation, and improves the growth condition of a martensite lath; the deformation temperature is changed to regulate the type of the martensite nucleation point, so that the nucleation trend of the nucleation point is improved; magnetic field energy is introduced, and the coupling effect of a magnetic field and a low-temperature field is utilized to improve the driving force of martensitic transformation; the martensite transformation is promoted by adopting the combined action of temperature change and isothermal martensite transformation. Through the improvement of the process, the method increases the introduced amount of martensite in the 304 type metastable austenitic stainless steel from no more than 10 percent to more than 30 percent (volume fraction) in the prior art, solves the problem of low introduced martensite content in the prior art, increases the adjustment range of the introduced amount of martensite in the 304 type metastable austenitic stainless steel, and can realize active adjustment and control of the martensite content.
(2) The invention introduces magnetic field energy to promote martensitic transformation, has simple production process and low cost, and provides a new direction for industrial production.
Detailed Description
In order to make the objects, technical solutions and effects of the present invention more clear and clear, the present invention will be described in further detail with reference to examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Example 1
A method for regulating and controlling a tissue structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) Taking 1mm thick hot rolled annealed 304 metastable austenitic stainless steel, carrying out stretching pre-deformation treatment on the metastable austenitic stainless steel at 200 ℃, wherein the deformation amount is 9%, and the strain rate is 10 -3 /s；
(2) Heating the stretched pre-deformed 304 metastable austenitic stainless steel to 300 ℃, carrying out isothermal treatment for 5 minutes, and then cooling to room temperature;
(3) The 304 metastable austenitic stainless steel is put into a cryogenic environment of minus 180 ℃ with 9T magnetic field, and is treated by the coupling effect of the magnetic field and minus 180 ℃ low-temperature field for 60 minutes;
(4) The treated stainless steel was warmed to room temperature at a rate of 20 c/min.
Experimental results: through the treatment of the process, martensite with the volume fraction of 35% is introduced into the structure of the type 304 metastable austenitic stainless steel.
Example 2
A method for regulating and controlling a tissue structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) Taking 2mm thick hot rolled annealed 304 metastable austenitic stainless steel, stretching and pre-deforming at 100 ℃ to obtain a deformation of 7% and a strain rate of 10 -3 /s；
(2) Heating the stretched pre-deformed 304 metastable austenitic stainless steel to 250 ℃, carrying out isothermal treatment for 4 minutes, and then cooling to room temperature;
(3) The 304 metastable austenitic stainless steel is put into a cryogenic environment of-150 ℃ with 7T magnetic field, and is treated by the coupling effect of the magnetic field and the low-temperature field of-150 ℃ for 30 minutes;
(4) The treated stainless steel was warmed to room temperature at a rate of 20 c/min.
Experimental results: through the treatment of the process, martensite with the volume fraction of 32% is introduced into the structure of the type 304 metastable austenitic stainless steel.
Example 3
A method for regulating and controlling a tissue structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) Taking 3mm thick hot rolled annealed 304 metastable austenitic stainless steel, and carrying out stretching pre-deformation treatment on the metastable austenitic stainless steel at 300 ℃, wherein the deformation is 11%, and the strain rate is 10 < -3 >/s;
(2) Heating the stretched pre-deformed 304 metastable austenitic stainless steel to 350 ℃, carrying out isothermal treatment for 6 minutes, and then cooling to room temperature;
(3) The 304 metastable austenitic stainless steel is put into a cryogenic environment of-165 ℃ with an applied 8T magnetic field, and is treated by the coupling effect of the magnetic field and a low-temperature field of-165 ℃ for 45 minutes;
(4) The treated stainless steel was warmed to room temperature at a rate of 20 c/min.
Experimental results: through the treatment of the process, martensite with the volume fraction of 33% is introduced into the structure of the type 304 metastable austenitic stainless steel.
Example 4
A method for regulating and controlling a tissue structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) Heating a 1mm thick hot rolled annealed 304 metastable austenitic stainless steel plate to 200 ℃, and carrying out heat preservation treatment for 20 minutes;
(2) The 304 metastable austenitic stainless steel is subjected to stretching pre-deformation treatment at 200 ℃, the deformation amount is 9 percent, and the strain rate is 10 -3 /s；
(3) Heating the stretched pre-deformed 304 metastable austenitic stainless steel to 300 ℃, preserving heat for 5 minutes, and then cooling to room temperature;
(4) The 304 metastable austenitic stainless steel is put into a cryogenic environment of minus 180 ℃ with 9T magnetic field, and is treated by the coupling effect of the magnetic field and minus 180 ℃ low-temperature field for 60 minutes;
(5) The treated stainless steel was warmed to room temperature at a rate of 20 c/min.
Experimental results: through the treatment of the process, martensite with the volume fraction of 37% is introduced into the structure of the type 304 metastable austenitic stainless steel.
Comparative example 1
A method for regulating and controlling a tissue structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) Taking 1mm thick hot rolled annealed 304 metastable austenitic stainless steel, and carrying out room temperature stretching pre-deformation treatment on the metastable austenitic stainless steel, wherein the deformation is 9%, and the strain rate is 10 -3 /s；
(2) Directly putting the stretched pre-deformed 304 metastable austenitic stainless steel into a cryogenic environment at the temperature of minus 180 ℃ for cryogenic treatment for 60 minutes;
(3) The treated stainless steel was warmed to room temperature at a rate of 20 c/min.
Experimental results: through the treatment of the process, martensite with the volume fraction of 6% is introduced into the structure of the type 304 metastable austenitic stainless steel.
Comparative example 2
A method for regulating and controlling a tissue structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) Heating hot rolled annealed type 304 metastable austenitic stainless steel with the thickness of 1mm to 300 ℃, preserving heat for 5 minutes, and then cooling to room temperature;
(2) Directly putting the 304 metastable austenitic stainless steel into a cryogenic environment at the temperature of minus 180 ℃ for cryogenic treatment, wherein the treatment time is 60 minutes;
(3) The treated stainless steel was warmed to room temperature at a rate of 20 c/min.
Experimental results: through the treatment of the process, martensite with the volume fraction of 2% is introduced into the structure of the type 304 metastable austenitic stainless steel.
Comparative example 3
A method for regulating and controlling a tissue structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) Heating hot rolled annealed type 304 metastable austenitic stainless steel with the thickness of 1mm to 300 ℃, preserving heat for 5 minutes, and then cooling to room temperature;
(2) The 304 metastable austenitic stainless steel is put into a cryogenic environment of minus 180 ℃ with 9T magnetic field, and is treated by the coupling effect of the magnetic field and minus 180 ℃ low-temperature field for 60 minutes;
(3) The treated stainless steel was warmed to room temperature at a rate of 20 c/min.
Experimental results: through the treatment of the process, martensite with the volume fraction of 8% is introduced into the structure of the type 304 metastable austenitic stainless steel.
Comparative example 4
A method for regulating and controlling a tissue structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) Taking 1mm thick heatThe rolling annealed 304 type metastable austenitic stainless steel is subjected to stretching pre-deformation treatment at 200 ℃, the deformation amount is 9 percent, and the strain rate is 10 -3 /s；
(2) Directly putting the stretched pre-deformed 304 metastable austenitic stainless steel into a cryogenic environment of-180 ℃ with a 9T magnetic field applied, and treating the metastable austenitic stainless steel by utilizing the coupling effect of the magnetic field and a low-temperature field of-180 ℃ for 60 minutes;
(3) The treated stainless steel was warmed to room temperature at a rate of 20 c/min.
Experimental results: through the treatment of the process, martensite with the volume fraction of 12% is introduced into the structure of the type 304 metastable austenitic stainless steel.
Comparative example 5
A method for regulating and controlling a tissue structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) Taking 1mm thick hot rolled annealed 304 metastable austenitic stainless steel, carrying out stretching pre-deformation treatment on the metastable austenitic stainless steel at 200 ℃, wherein the deformation amount is 9%, and the strain rate is 10 -3 /s；
(2) Heating the stretched pre-deformed 304 metastable austenitic stainless steel to 300 ℃, preserving heat for 5 minutes, and then cooling to room temperature;
(3) Directly putting the 304 metastable austenitic stainless steel into a cryogenic environment at the temperature of minus 180 ℃ for cryogenic treatment, wherein the treatment time is 60 minutes;
(4) The treated stainless steel was warmed to room temperature at a rate of 20 c/min.
Experimental results: through the treatment of the process, martensite with the volume fraction of 13% is introduced into the structure of the type 304 metastable austenitic stainless steel.
Comparing the results of analysis examples with comparative examples 1-5, the following conclusions can be drawn:
(1) As can be seen from the results of comparative analysis examples and comparative examples 1 to 5, the volume fraction of martensite in the 304-type metastable austenitic stainless steel can be remarkably improved by means of medium-low temperature pre-deformation, isothermal treatment after deformation, introduction of magnetic field energy and the like on the basis of room temperature pre-deformation and cryogenic treatment in the prior art. Comparative examples 2 and 3 failed to increase the amount of martensite introduced due to the lack of the pre-deformation step even after the subsequent isothermal treatment + magnetic field cryogenic treatment.
(2) Since the medium-low temperature deformation and the medium-temperature isothermal treatment are not performed in comparative example 1, the magnetic field environment is not adopted in the cryogenic treatment; in comparative example 2, the pre-deformation step was omitted, and the magnetic field environment was not used in the cryogenic treatment; the pre-deformation step was omitted in comparative example 3; the procedure of the medium temperature isothermal treatment was omitted in comparative example 4; the cryogenic treatment in comparative example 5 did not employ a magnetic field environment; resulting in that the volume fraction of martensite introduced in the obtained stainless steel is not as expected. From this, it is clear that the conditions of medium-low temperature pre-deformation, medium-temperature isothermal treatment after deformation and deep cooling treatment in a magnetic field environment are indispensable, and only the synergistic effect of the above conditions can effectively improve the introduced amount of martensite in the type 304 metastable austenitic stainless steel structure, which is far more than 10% in the prior art.
The above detailed description describes the analysis method according to the present invention. It should be noted that the above description is only intended to help those skilled in the art to better understand the method and idea of the present invention, and is not intended to limit the related content. Those skilled in the art may make appropriate adjustments or modifications to the present invention without departing from the principle of the present invention, and such adjustments and modifications should also fall within the scope of the present invention.
Claims (6)
1. A method for regulating and controlling a tissue structure of 304 metastable austenitic stainless steel is characterized by comprising the following steps:
(1) Stretching and pre-deforming the annealed 304 metastable austenitic stainless steel at 100-300 ℃; in the stretching pre-deformation treatment, the deformation amount is 7-11%, and the strain rate is 10 -3 /s；
(2) Carrying out isothermal treatment at 250-350 ℃ on the stainless steel subjected to the pre-deformation treatment, and then cooling to room temperature; the isothermal treatment time is 4-6 minutes;
(3) The non-aqueous phase obtained by the treatment of the step (2)Directly putting the stainless steel into a cryogenic environment for cryogenic treatment, and then heating the stainless steel to room temperature; the cryogenic treatment is carried out in an environment of applying a magnetic field, wherein the strength of the applied magnetic field is 7-9T; the cryogenic treatment temperature is-150 DEG C ~ The cryogenic treatment time is 30-60 minutes at the temperature of minus 180 ℃.
2. The method of claim 1, wherein the isothermal treatment in step (2) is at a temperature of 300 ℃.
3. The method of claim 1, wherein the rate of temperature rise in step (3) is 20 ℃/min.
4. A method according to any one of claims 1-3, wherein step (a) is optionally further carried out before step (1), said step (a) being in particular: heating the annealed 304 type metastable austenitic stainless steel plate to 100-300 ℃, and carrying out heat preservation treatment for 10-20 minutes.
5. The method of claim 4, wherein the soak temperature in step (a) is 200 ℃ and the soak time is 20 minutes.
6. Type 304 metastable austenitic stainless steel produced by the method according to any of claims 1-5.
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