CN114032369A - Method for regulating 304 type metastable austenitic stainless steel tissue structure - Google Patents
Method for regulating 304 type metastable austenitic stainless steel tissue structure Download PDFInfo
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- 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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Abstract
The invention discloses a method for regulating and controlling a 304 type metastable austenitic stainless steel tissue structure. Firstly, carrying out low-medium temperature stretching pre-deformation treatment on stainless steel, and introducing deformation defects such as dislocation, stacking fault, deformation band and the like into an annealed metastable austenitic stainless steel structure at different deformation quantities; further eliminating residual stress in the stainless steel structure by using a medium-temperature isothermal process; and finally, carrying out cryogenic treatment on the stainless steel under the action of the magnetic field by utilizing the coupling action of the magnetic field and the cryogenic environment, and introducing effective content of martensite into the metastable austenitic stainless steel structure, thereby realizing the regulation and control of the 304 type metastable austenitic stainless steel structure.
Description
Technical Field
The invention belongs to the technical field of metastable austenitic stainless steel production, and particularly relates to a method for regulating and controlling a microstructure of 304 type metastable austenitic stainless steel.
Background
The 304 type 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 type metastable austenite stainless steel, in order to ensure that the metastable austenite stainless steel has 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 in the structure, so that the room temperature structure of the metastable austenite stainless steel is stable single-phase austenite. This results in metastable austenitic stainless steel type 304 having a low yield strength, which makes it impossible to apply it to high-strength members in the field of industrial production. Therefore, how to increase the yield strength of the type 304 metastable austenitic stainless steel becomes a difficult problem for the development thereof.
At present, methods for improving the yield strength of steel materials mainly comprise fine grain strengthening, phase change strengthening and dislocation strengthening. Aiming at the type 304 metastable austenitic stainless steel, the realization of fine grain strengthening can only utilize deformation under high pressure and low temperature annealing treatment process, and utilizes deformation to induce reverse phase transformation of martensite or recrystallization of deformation substructure to realize the refinement of original structure.
The dislocation strengthening is realized by introducing dislocation through large deformation and improving the yield strength of the material by utilizing the work hardening, however, the ductility and toughness and the work hardening performance of the material are deteriorated due to a large amount of dislocation defects in the material structure under the process, and the corrosion resistance of the type 304 metastable austenitic stainless steel is reduced.
The phase transformation strengthening is an important method for improving the yield strength of the steel material by introducing a strengthening phase martensite into the steel material structure, and the method has the advantages of low cost, good strength improvement effect and the like. However, the type 304 metastable austenitic stainless steel has a large amount of stable austenitic alloy elements in the structure, so that the room temperature structure is stable austenite, and martensite is difficult to be introduced even under a cryogenic condition. Therefore, how to introduce the strengthening phase martensite into the metastable austenitic stainless steel of type 304 is a difficult problem of improving the yield strength by utilizing the martensite transformation strengthening.
In order to solve the problems, the inventor has proposed in the previous work that a process means of room temperature pre-deformation can be adopted to introduce the defect of the slip band into the austenite structure, and the slip band is used as a nucleation particle of the martensite phase transformation to excite the temperature-variable martensite phase transformation, so as to successfully introduce the martensite into the austenitic stainless steel. However, the practical results show that the austenitic stainless steel is treated by the process, and only martensite with the volume fraction of about 10% can be introduced into the structure at most. The amount of martensite introduced does not have a linear relationship with the amount of slip band introduced. This fact reveals that the above process is insufficient to introduce a greater content of martensite into the austenitic stainless steel, which limits further improvement of the yield strength of the austenitic stainless steel. Therefore, how to introduce more martensite (10% or even more than 15%) into the metastable austenitic stainless steel type 304 becomes a difficult problem for improving the yield strength of the steel type by utilizing the transformation strengthening.
Disclosure of Invention
Aiming at the defects of the martensite introduction process (room temperature predeformation and cryogenic treatment) in the conventional 304 type metastable austenite stainless steel: the nucleation mass point type is single, the residual stress and the phase change driving force in the structure are single, and the method for improving the growth condition of the martensite lath by increasing the plastic deformation capacity of the austenitic stainless steel through increasing the medium-low temperature heat preservation treatment before the pre-deformation and increasing the medium-temperature isothermal treatment to eliminate the internal stress in the structure after the pre-deformation is provided. In addition, in order to increase the types of nucleation particles, a pre-deformation process with different temperatures is designed to introduce more types of martensite phase transformation nucleation particles (dislocation, stacking fault, slip band and the like) and improve the nucleation condition of martensite laths. Further, in order to increase the driving force of the martensite transformation, the invention provides a magnetic field and temperature field coupling mechanism (magnetic field + cryogenic treatment) for providing the transformation driving force for the martensite transformation to promote the martensite transformation. In addition, in order to introduce more martensite into the structure, long-time isothermal treatment is designed in the cryogenic treatment stage, the final martensite content in the austenitic stainless steel is increased by utilizing the combined action of temperature-changing martensite phase transformation and isothermal martensite phase transformation of deformation-introduced nucleation particles, so that the austenitic stainless steel obtains an austenite-martensite dual-phase structure, and the yield strength of the 304 type metastable austenitic stainless steel is further increased by utilizing martensite phase transformation strengthening.
The technical purpose of the invention is realized by the following scheme.
In order to achieve the above object, the present invention is realized by:
the invention provides a method for regulating and controlling a 304 type metastable austenitic stainless steel tissue structure, which comprises the following steps:
(1) carrying out stretching pre-deformation treatment on the annealed 304 type metastable austenitic stainless steel at the temperature of 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 by the treatment in the step (2) into a cryogenic environment for cryogenic treatment, and then heating the stainless steel to room temperature.
Preferably, in the pre-stretching treatment in step (1), the amount of deformation 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 to 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 step (3) is 7 to 9T.
Preferably, the temperature of the deep cooling treatment in the step (3) is-150 to-180 ℃, and the time of the deep cooling treatment is 30 to 60 minutes.
Preferably, in the step (3), the temperature of the cryogenic treatment is-180 ℃, the time of the cryogenic treatment is 60 minutes, and the applied magnetic field strength is 9T.
As a preferable aspect of the present invention, the temperature increase rate in the step (3) is 20 ℃/min.
Further, step (a) is optionally further implemented before step (1), and specifically, step (a) is as follows: 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 step (a), the heat-insulating treatment temperature is 200 ℃ and the heat-insulating treatment time is 20 minutes.
In a second aspect, the invention provides a metastable austenitic stainless steel of type 304, prepared according to the above method.
In the present invention, all the treatment times are the holding time after the type 304 metastable austenitic stainless steel reaches the set treatment temperature, unless otherwise specified.
The type 304 metastable austenitic stainless steel has high heat stability of austenite in the structure due to high total design concept, and is difficult to form martensite even under the condition of deep cooling. Nucleation defects and the driving force for the transformation are prerequisites for the transformation of austenite to martensite. According to the existing martensite phase transformation nucleation theory, the smaller the nucleation tendency of the nucleation defect is, the larger the driving force required by the phase transformation is. Since the nucleation defects in the type 304 metastable austenitic stainless steel have little tendency to nucleate, the driving force of the transformation is insufficient to drive the nucleation defects in the crystal grains to undergo martensitic transformation even under the cryogenic condition of liquid nitrogen.
The inventor carries out deep analysis on the difficult problem that a large amount of martensite cannot be introduced into the 304 type metastable austenitic stainless steel by the room temperature predeformation and cryogenic treatment process. Researches show that the process promotes the martensite phase transformation by actively introducing nucleation particles (slip bands) only according to a nucleation mechanism. In fact, the martensitic transformation involves both nucleation and growth processes, and both processes have a significant effect on the martensitic transformation.
However, the above process only takes into account the introduction of martensite phase transformation nucleation sites and only a single type of nucleation sites (slip bands) are introduced, without taking into account the growth of martensite laths. The martensitic transformation is an expansion type transformation, and the internal stress in the material structure can inhibit the martensitic transformation. In the above process, the pre-deformation means introduces internal stress into the tissue at the same time as the slip bands are introduced into the tissue.
Therefore, the room-temperature predeformation and cryogenic treatment process only introduces a single type of nucleation point slip band defect, does not consider the influence of internal stress on the growth of the martensite lath, and is the main reason why the process cannot introduce a large amount of martensite. In addition, the prior art only utilizes the temperature-variable martensite transformation to introduce the martensite, and does not use the isothermal martensite transformation to introduce the martensite. The driving force of the transformation is an important factor influencing the martensitic transformation, and the prior art only utilizes a cryogenic treatment means (chemical driving force) to trigger the martensitic transformation, and does not consider introducing other energy means as the driving force of the martensitic transformation.
Based on the defects of the process method for introducing martensite into the material structure by the room temperature pre-deformation and cryogenic treatment process proposed by the earlier work of the inventor, the invention applies the medium temperature heat preservation treatment after the stretching pre-deformation, eliminates the internal stress introduced by the stretching pre-deformation and improves the growth condition of the martensite lath in the martensite phase transformation process.
In addition, the invention adopts medium-low temperature stretching pre-deformation treatment, different types of deformation substructures such as faults, dislocation, deformation bands and the like can be actively introduced into the annealed austenite structure by setting different deformation temperatures, nucleation mass points with larger nucleation tendency are provided for martensite phase transformation, and the number of nucleation defects and other characteristics are regulated and controlled by regulating and controlling the deformation temperature and the deformation degree. The driving force for the transformation is also a prerequisite for the martensitic transformation to take place.
In contrast, the invention designs a magnetic field and low-temperature field coupling effect process, and utilizes the superposition effect of magnetic energy and chemical driving force to provide driving force for martensite phase transformation for deformation nuclear particles such as deformation zones, stacking faults, dislocations and the like with larger nucleation tendency, thereby promoting the martensite transformation. In addition, the invention introduces more martensite into the 304 type metastable austenite stainless steel by designing the cryogenic treatment for a long time and utilizing the combined action of the temperature-changing martensite phase transformation and the isothermal martensite phase transformation.
In conclusion, the martensite in the 304 type metastable austenitic stainless steel is introduced through the coupling effect of the processes of medium and low temperature stretching pre-deformation, medium temperature isothermal, cryogenic treatment under the action of a magnetic field and the like, so that the yield strength of the 304 type metastable austenitic stainless steel is improved.
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 stacking faults, dislocation, deformation bands and the like in sequence) are obtained by utilizing the stretching pre-deformation treatment at different temperatures, and the introduction quantity of the deformation defects is adjusted according to the stretching pre-deformation degree; the medium-temperature isothermal treatment is carried out on the deformed 304 type metastable austenitic stainless steel, which can help to eliminate the residual stress in the structure; in addition, the 304 type metastable austenitic stainless steel after isothermal treatment is put into a low-temperature environment with a magnetic field, and the nucleation defect introduced by deformation is subjected to martensite phase 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 the room temperature predeformation and cryogenic treatment process: the type of nucleation mass point is single, the internal stress in the structure limits the growth of martensite, the type of phase change driving force is single, and the like, the invention provides that the isothermal treatment is applied after the deformation, and the growth condition of the martensite lath is improved; the deformation temperature is changed to regulate the type of martensite nucleation particles, and the nucleation tendency of the nucleation particles is improved; magnetic field energy is introduced, and the driving force of martensite phase transformation is improved by utilizing the coupling effect of a magnetic field and a low-temperature field; the martensite transformation is promoted by the combined action of temperature change and isothermal martensite transformation. Through the process improvement, the introduction amount of martensite in the 304 type metastable austenitic stainless steel is increased to be more than 30 percent (volume fraction) from no more than 10 percent in the prior art, the problem of low martensite content introduced in the prior art is solved, the regulation range of the martensite introduction amount in the 304 type metastable austenitic stainless steel is enlarged, and the active regulation and control of the martensite content can be realized.
(2) The invention introduces magnetic field to promote martensite phase 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 clearer and clearer, the present invention is further described in detail below with reference to examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Example 1
A method for regulating and controlling a structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) taking 1mm thick hot-rolled annealed 304 type metastable austenite stainless steel, and carrying out stretching pre-deformation treatment on the stainless steel at 200 ℃, wherein the deformation is 9 percent, and the strain rate is 10-3/s；
(2) Heating the stretched and pre-deformed 304 type metastable austenitic stainless steel to 300 ℃, carrying out isothermal treatment for 5 minutes, and then cooling to room temperature;
(3) putting the 304 type metastable austenite stainless steel into a cryogenic environment of minus 180 ℃ applying a 9T magnetic field, and treating the stainless steel by utilizing the coupling action of the magnetic field and a minus 180 ℃ low-temperature field, wherein the treatment time is 60 minutes;
(4) the treated stainless steel was allowed to warm to room temperature at a rate of 20 ℃/min.
The experimental results are as follows: through the process treatment, the martensite with the volume fraction of 35 percent is introduced into the structure of the type 304 metastable austenitic stainless steel.
Example 2
A method for regulating and controlling a structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) taking hot-rolled annealed 304 type metastable austenite stainless steel with the thickness of 2mm, and carrying out stretching pre-deformation treatment on the stainless steel at the temperature of 100 ℃, wherein the deformation is 7 percent, and the strain rate is 10 percent-3/s；
(2) Heating the stretched and pre-deformed 304 type metastable austenitic stainless steel to 250 ℃, carrying out isothermal treatment for 4 minutes, and then cooling to room temperature;
(3) putting the 304 type metastable austenite stainless steel into a cryogenic environment with the temperature of-150 ℃ and applying a 7T magnetic field, and treating the stainless steel by utilizing the coupling action of the magnetic field and a low-temperature field with the temperature of-150 ℃ for 30 minutes;
(4) the treated stainless steel was allowed to warm to room temperature at a rate of 20 ℃/min.
The experimental results are as follows: through the process treatment, 32 volume percent of martensite is introduced into the structure of the type 304 metastable austenitic stainless steel.
Example 3
A method for regulating and controlling a structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) taking hot-rolled annealed 304 type metastable austenitic stainless steel with the thickness of 3mm, and carrying out stretching pre-deformation treatment on the stainless steel at the temperature of 300 ℃, wherein the deformation amount is 11 percent, and the strain rate is 10-3/s;
(2) heating the stretched and pre-deformed 304 type metastable austenitic stainless steel to 350 ℃, carrying out isothermal treatment for 6 minutes, and then cooling to room temperature;
(3) putting the 304 type metastable austenitic stainless steel into a cryogenic environment with-165 ℃ and 8T magnetic field, and treating the stainless steel by utilizing the coupling action of the magnetic field and the-165 ℃ low-temperature field, wherein the treatment time is 45 minutes;
(4) the treated stainless steel was allowed to warm to room temperature at a rate of 20 ℃/min.
The experimental results are as follows: through the process treatment, 33% of martensite is introduced into the structure of the type 304 metastable austenitic stainless steel.
Example 4
A method for regulating and controlling a structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) heating a hot-rolled annealed 304 type metastable austenitic stainless steel plate with the thickness of 1mm to 200 ℃, and carrying out heat preservation treatment for 20 minutes;
(2) the 304 type metastable austenite stainless steel is subjected to stretching pre-deformation treatment at the temperature of 200 ℃, the deformation amount is 9 percent, and the strain rate is 10-3/s；
(3) Heating the stretched and pre-deformed 304 type metastable austenitic stainless steel to 300 ℃, preserving heat for 5 minutes, and then cooling to room temperature;
(4) putting the 304 type metastable austenite stainless steel into a cryogenic environment of minus 180 ℃ applying a 9T magnetic field, and treating the stainless steel by utilizing the coupling action of the magnetic field and a minus 180 ℃ low-temperature field, wherein the treatment time is 60 minutes;
(5) the treated stainless steel was allowed to warm to room temperature at a rate of 20 ℃/min.
The experimental results are as follows: through the process treatment, 37 volume percent of martensite is introduced into the structure of the type 304 metastable austenitic stainless steel.
Comparative example 1
A method for regulating and controlling a structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) taking 1mm thick hot-rolled annealed 304 type metastable austenite stainless steel, and carrying out room-temperature stretching pre-deformation treatment on the stainless steel, wherein the deformation is 9 percent, and the strain rate is 10-3/s；
(2) Directly putting the stretched and pre-deformed 304 type metastable austenite stainless steel into a cryogenic environment at the temperature of minus 180 ℃ for cryogenic treatment for 60 minutes;
(3) the treated stainless steel was allowed to warm to room temperature at a rate of 20 ℃/min.
The experimental results are as follows: through the process treatment, the martensite with the volume fraction of 6 percent is introduced into the structure of the type 304 metastable austenitic stainless steel.
Comparative example 2
A method for regulating and controlling a structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) heating hot-rolled annealed 304 type 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 type metastable austenite stainless steel into a cryogenic environment at minus 180 ℃ for cryogenic treatment for 60 minutes;
(3) the treated stainless steel was allowed to warm to room temperature at a rate of 20 ℃/min.
The experimental results are as follows: through the process treatment, 2% of martensite is introduced into the structure of the type 304 metastable austenitic stainless steel.
Comparative example 3
A method for regulating and controlling a structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) heating hot-rolled annealed 304 type metastable austenitic stainless steel with the thickness of 1mm to 300 ℃, preserving heat for 5 minutes, and then cooling to room temperature;
(2) putting the 304 type metastable austenite stainless steel into a cryogenic environment of minus 180 ℃ applying a 9T magnetic field, and treating the stainless steel by utilizing the coupling action of the magnetic field and a minus 180 ℃ low-temperature field, wherein the treatment time is 60 minutes;
(3) the treated stainless steel was allowed to warm to room temperature at a rate of 20 ℃/min.
The experimental results are as follows: through the process treatment, 8% of martensite is introduced into the structure of the type 304 metastable austenitic stainless steel.
Comparative example 4
A method for regulating and controlling a structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) taking 1mm thick hot-rolled annealed 304 type metastable austenite stainless steel, and carrying out stretching pre-deformation treatment on the stainless steel at the temperature of 200 ℃, wherein the deformation amount is 9 percent, and the strain rate is 10-3/s；
(2) Directly putting the stretched and pre-deformed 304 type metastable austenite stainless steel into a cryogenic environment at minus 180 ℃ applying a 9T magnetic field, and treating the stainless steel by utilizing the coupling action of the magnetic field and a low-temperature field at minus 180 ℃ for 60 minutes;
(3) the treated stainless steel was allowed to warm to room temperature at a rate of 20 ℃/min.
The experimental results are as follows: through the process treatment, 12 volume percent of martensite is introduced into the structure of the type 304 metastable austenitic stainless steel.
Comparative example 5
A method for regulating and controlling a structure of a type 304 metastable austenitic stainless steel comprises the following steps:
(1) taking 1mm thick hot-rolled annealed 304 type metastable austenite stainless steel, and carrying out stretching pre-deformation treatment on the stainless steel at the temperature of 200 ℃, wherein the deformation amount is 9 percent, and the strain rate is 10-3/s；
(2) Heating the stretched and pre-deformed 304 type metastable austenitic stainless steel to 300 ℃, preserving heat for 5 minutes, and then cooling to room temperature;
(3) directly putting the 304 type metastable austenite stainless steel into a cryogenic environment at minus 180 ℃ for cryogenic treatment for 60 minutes;
(4) the treated stainless steel was allowed to warm to room temperature at a rate of 20 ℃/min.
The experimental results are as follows: through the process treatment, 13 volume percent of martensite is introduced into the structure of the type 304 metastable austenitic stainless steel.
Comparing the results of the examples and comparative examples 1-5, the following conclusions can be drawn:
(1) comparing the results of the comparative examples 1 to 5, it can be seen that the volume fraction of martensite in the type 304 metastable austenitic stainless steel can be significantly improved by means of medium and 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, due to the lack of the pre-deformation step, the amount of martensite incorporation could not be increased even after the subsequent isothermal treatment + magnetic field cryogenic treatment.
(2) Since the middle-low temperature deformation and middle-temperature isothermal treatment are not carried out in the comparative example 1, the magnetic field environment is not adopted in the deep cooling treatment; the step of pre-deformation is omitted in the comparative example 2, and the magnetic field environment is not adopted in the deep cooling treatment; the step of pre-deformation is omitted in comparative example 3; the step of medium temperature isothermal treatment is omitted in comparative example 4; comparative example 5 in which the deep cooling treatment did not employ a magnetic field environment; thereby leading to the unexpected incorporation of martensite volume fraction in the obtained stainless steel. Therefore, the conditions for carrying out medium-low temperature pre-deformation, medium-temperature isothermal treatment after deformation and cryogenic treatment under the magnetic field environment are indispensable, and the introduction amount of martensite in the 304 type metastable austenitic stainless steel structure can be effectively increased by far more than 10% in the prior art only by the synergistic effect of the conditions.
The above detailed description section specifically describes the analysis method according to the present invention. It should be noted that the above description is only for the purpose of helping those skilled in the art better understand the method and idea of the present invention, and not for the limitation of the related contents. The present invention may be appropriately adjusted or modified by those skilled in the art without departing from the principle of the present invention, and the adjustment and modification also fall within the scope of the present invention.
Claims (10)
1. A method for regulating and controlling a structure of a 304 type metastable austenitic stainless steel is characterized by comprising the following steps:
(1) carrying out stretching pre-deformation treatment on the annealed 304 type metastable austenitic stainless steel at the temperature of 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 by the treatment in the step (2) into a cryogenic environment for cryogenic treatment, and then heating the stainless steel to room temperature.
2. The method according to claim 1, wherein in the stretching pre-deformation treatment in the step (1), the deformation amount is 7-11%, and the strain rate is 10-3/s。
3. The method according to claim 1, wherein the isothermal treatment temperature in the step (2) is 300 ℃ and the isothermal treatment time is 4 to 6 minutes.
4. The method according to claim 1, wherein the cryogenic treatment in step (3) is performed in an environment in which a magnetic field is applied.
5. The method of claim 4, wherein the magnetic field strength applied in step (3) is 7-9T.
6. The method according to claim 1, wherein the temperature of the cryogenic treatment in the step (3) is from-150 ℃ to-180 ℃ and the time of the cryogenic treatment is from 30 minutes to 60 minutes.
7. The method according to claim 1, wherein the temperature increase rate in step (3) is 20 ℃/min.
8. The process according to any one of claims 1 to 7, characterized in that step (1) is optionally preceded by a further step (a), 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.
9. The method of claim 8, wherein the incubation temperature in step (a) is 200 ℃ and the incubation time is 20 minutes.
10. Metastable austenitic stainless steel of type 304, produced according to the method of any of claims 1-9.
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