Method for predicting strength and plasticity of medium manganese steel based on austenite inverse phase transformation kinetics

Abstract

The invention discloses a method for predicting the strength and plasticity of medium manganese steel based on austenite inverse phase transformation kinetics, and belongs to the technical field of metal and alloy preparation. The method comprises the following steps: respectively establishing a Gibbs free energy change rate and an energy dissipation equation at a block phase and an interface; establishing a generalized stability analytic expression, and obtaining generalized stability according to the driving force and the energy barrier; and according to the driving force and the generalized stability, designing a process parameter combination based on a large driving force-large generalized stability criterion. According to the method, the austenite inverse phase change model is established on the basis of the thermodynamic extreme value principle, compared with a traditional diffusion phase change model, element diffusion, interface migration, interaction between diffusion and an interface and the like are considered at the same time, and the phase change dynamic process can be well predicted.

Description

Technical Field

[0001] The invention belongs to the technical field of metal and alloy preparation, and specifically relates to a method for predicting the strength and plasticity of medium manganese steel based on austenite reverse phase transformation dynamics. Background Art

[0002] As one of the representatives of the third generation of high-strength steel, medium manganese steel has improved mechanical properties due to the more stable austenite, and is widely used in the aviation and automotive fields. This stability is achieved by increasing the manganese content in the austenite grains and optimizing the kinetic process of austenite reverse transformation (ART). However, in the process of preparing medium manganese steel with good performance, due to different process parameters of austenite reverse transformation, such as isothermal temperature and holding time, the microstructure and element distribution will be different, thus affecting the material properties. Most experiments use trial and error methods, which greatly reduces production efficiency and increases costs. In addition, most of the kinetic description models of austenite reverse transformation lack experimental verification, which restricts the application and promotion of the models.

[0003] Generally speaking, with the increase of isothermal temperature and holding time, the austenite content can be increased, but the hard phase martensite is reduced, and the stability of austenite is also affected, which is also related to the composition. In order to control the microstructure and element distribution, phase transformation models such as semi-analytical mixed mode models and cellular automation models have been widely studied. By relaxing the assumptions of single diffusion control or element near-equilibrium in the classical diffusion model, the transformation dynamics of the reverse phase transformation of austenite are explained. However, since the diffusion-controlled phase transformation model lacks a description of the energy change of the phase transformation, that is, the thermodynamic driving force and kinetic energy barrier, and does not consider the process-phase transformation-performance system, it is impossible to achieve the quantitative design of the best match of isothermal temperature and holding time. Summary of the invention

[0004] In view of the deficiencies in the above-mentioned background technology, the present invention provides a method for predicting the strength and plasticity of medium manganese steel based on the austenite reverse phase transformation kinetics. Based on the thermodynamic extreme principle, the present invention predicts the phase transformation kinetics process, couples the austenite reverse phase transformation heat treatment process parameters of the medium manganese steel, and proposes a thermo-dynamic criterion of large driving force-large generalized stability, so as to achieve quantitative design of the optimal process parameter combination to obtain a structure with good strength and plasticity, which is conducive to the promotion of the ART process.

[0005] The first object of the present invention is to provide a method for predicting the strength and plasticity of medium manganese steel based on austenite reverse transformation kinetics, comprising: The Gibbs free energy change rate and energy dissipation equations in the bulk phase and interface are established respectively; Establishing the interface migration kinetics model: Substitute the Gibbs free energy change rate and energy dissipation equation at the interface into the thermodynamic extreme value principle expression at the interface to obtain the interface migration velocity and the concentration of each element at the interface; predict the content of the generated phase austenite based on the interface migration velocity; Substituting the Gibbs free energy change rate and energy dissipation equation in the bulk phase into the thermodynamic extreme value principle expression in the bulk phase, the second diffusion theorem expression is obtained; Substituting the concentration of each element at the interface into the expression of the second diffusion theorem, the distribution of element concentration in the bulk phase, i.e., the transient solute field, is obtained; Establishing the generalized stability applicable to the reverse transformation of austenite: Define the interface migration driving force expression, and obtain the interface migration driving force according to the concentration of each element at the interface; obtain the energy barrier expression according to the interface migration velocity expression; The analytical formula of generalized stability is established, and the generalized stability is obtained according to the driving force and energy barrier; According to the driving force and generalized stability, the process parameter combination is designed based on the large driving force-large generalized stability criterion.

[0006] Preferably, the Gibbs free energy change rates in the bulk phase and at the interface are:

[0007] In the formula, Indicates the left side position of the austenite phase; Indicates the interface position between austenite and ferrite; Indicates the right side position of the ferrite phase; represents the rate of change of Gibbs free energy of the bulk phase; and Respectively Harmony The chemical potential of the iron solute is ” means iron; and Respectively Harmony Mutually The chemical potential of the solute, superscript " " means replacing the solute, " represents interstitial solute; and Respectively Harmony Mutually flux of solutes;

[0008] In the formula, represents the rate of change of Gibbs free energy at the interface; and Respectively Harmony The chemical potential at the iron-solute interface is ” means iron; and Respectively Harmony Mutually The chemical potential at the solute interface, and Respectively Harmony Mutually solute flux at the interface; is the molar volume; Indicates the interface migration speed; Indicates the total number of solute types; Represents variables at the interface.

[0009] Preferably, the Gibbs free energy dissipation in the bulk phase and at the interface is:

[0010]

[0011] In the formula, and represent the Gibbs free energy dissipation in the bulk phase and at the interface, respectively; and are the diffusion rates of atoms in the bulk and at the interface, respectively, where ; , where M is the interface mobility.

[0012] Preferably, the thermodynamic extreme principle expression at the interface is:

[0013] In the formula, is the Lagrange multiplier; represents the symbol of variation; Prediction of the content of austenite in the generated phase based on the interface migration rate

[0014] In the formula, represents the austenite formation fraction; It represents the length of the interface from the left side of austenite; S represents the total length of austenite and ferrite.

[0015] Preferably, the thermodynamic extreme value principle expression in the block is:

[0016] In the formula, represents the symbol of variation; represents the rate of change of Gibbs free energy of bulk phase; represents the Gibbs free energy dissipation of the bulk phase.

[0017] Preferably, the driving force of interface migration is expressed as:

[0018] in

[0019]

[0020] In the formula, , are the initial concentration on the ferrite side or austenite side of the interface and the corresponding equilibrium concentration, respectively; represents the position fraction of solute i at the interface at time t; represents the strain energy caused by phase change; For temperature and composition Related parameters.

[0021] Preferably, the energy barrier expression is:

[0022] in

[0023]

[0024] In the formula, represents the gas constant, 8.314 J / mol / K; represents the phase transition temperature; Indicates the speed of sound propagation in metal, 1000m / s; Indicates the interface migration speed; It represents the difference between the bulk diffusion activation energy and the interface migration activation energy.

[0025] Preferably, the generalized stability is:

[0026] In the formula, represents the activation energy of transient interface migration; represents the initial interface migration activation energy; represents the driving force for transient interface migration; Represents the initial interface migration driving force.

[0027] Preferably, among the designed process parameter combinations, the best process parameter combination is an isothermal temperature of 660° C. and a holding time of 30 min.

[0028] The second object of the present invention is to provide an application of the above method in improving the strength and plasticity of medium manganese steel.

[0029] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for predicting the strength and plasticity of medium manganese steel based on the austenite reverse phase transformation kinetics. The present invention establishes an austenite reverse phase transformation model based on the thermodynamic extreme principle. Compared with the traditional diffusion phase transformation model, the element diffusion, interface migration and the interaction between diffusion and interface are taken into account at the same time, and the phase transformation kinetics process can be well predicted.

[0030] The present invention follows the large driving force-large generalized stability criterion and proposes a new strategy to simultaneously improve material strength and plasticity: the large driving force in the initial state of phase transformation corresponds to low isothermal temperature to improve material strength, and the large generalized stability in the final state of phase transformation corresponds to long-term heat preservation to improve material plasticity.

[0031] The process design strategy proposed in the present invention can optimize the process of controlling two parameters simultaneously: isothermal temperature and holding time, find the best match between the two process parameters, and optimize the actual production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of the method proposed by the present invention for predicting the austenite reverse transformation kinetics and material strength and plasticity.

[0033] Figure 2 In order to predict the austenite reverse transformation kinetics in the embodiments of the present invention, thermal expansion experiments were performed to verify it.

[0034] Figure 3 Driving force, energy barrier and generalized stability calculated for the model in the embodiment of the present invention.

[0035] Figure 4 It is the yield strength and uniform elongation of the plate after heat treatment with different process parameters in the embodiment of the present invention.

[0036] Figure 5 1 and 2 are tensile engineering stress-strain curves at different temperatures, as well as offset yield strength and uniform elongation in the embodiments of the present invention. DETAILED DESCRIPTION

[0037] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0038] The purpose of the present invention is to propose a quantitative process design method for the ART process, coupling the two process parameters of isothermal temperature and holding time and the diffusion-controlled phase change model based on the thermodynamic extreme principle, and according to the thermo-dynamic criterion of large driving force-large generalized stability, find the process parameters that can simultaneously obtain good strength and plasticity, and use this result to guide the preparation of medium manganese steel plates under the on-site ART process.

[0039] In order to achieve the above object, the present invention provides a method for predicting the strength and plasticity of medium manganese steel based on austenite reverse transformation kinetics, comprising: The Gibbs free energy change rate and energy dissipation equations in the bulk phase and interface are established respectively; Establishing the interface migration kinetics model: Substitute the Gibbs free energy change rate and energy dissipation equation at the interface into the thermodynamic extreme value principle expression at the interface to obtain the interface migration velocity and the concentration of each element at the interface; predict the content of the generated phase austenite based on the interface migration velocity; Substituting the Gibbs free energy change rate and energy dissipation equation in the bulk phase into the thermodynamic extreme value principle expression in the bulk phase, the second diffusion theorem expression is obtained. Substituting the concentration of each element at the interface into the expression of the second diffusion theorem, the distribution of element concentration in the bulk phase, i.e., the transient solute field, is obtained; Establishing the generalized stability applicable to the reverse transformation of austenite: Define the interface migration driving force expression, and obtain the interface migration driving force according to the concentration of each element at the interface; obtain the energy barrier expression according to the interface migration velocity expression; The analytical formula of generalized stability is established, and the generalized stability is obtained according to the driving force and energy barrier; According to the driving force and generalized stability, the process parameter combination is designed based on the large driving force-large generalized stability criterion.

[0040] Among them, the Gibbs free energy change rates in the bulk phase and at the interface are:

[0041] In the formula, Indicates the left side position of the austenite phase; Indicates the interface position between austenite and ferrite; Indicates the right side position of the ferrite phase.

[0042] represents the rate of change of Gibbs free energy of the bulk phase; and Respectively Harmony The chemical potential of the iron solute is ” means iron; and Respectively Harmony Mutually The chemical potential of the solute, superscript " " means replacing the solute, " represents interstitial solute; and Respectively Harmony Mutually flux of solutes;

[0043] In the formula, represents the rate of change of Gibbs free energy at the interface; and Respectively Harmony The chemical potential at the iron-solute interface is ” means iron; and Respectively Harmony Mutually The chemical potential at the solute interface, and Respectively Harmony Mutually solute flux at the interface; is the molar volume; Indicates the interface migration speed; Represents the total number of solute types.

[0044] It should be noted that is a whole, representing the molar volume.

[0045] Represents variables at the interface.

[0046] The Gibbs free energy dissipation in the bulk phase and at the interface is:

[0047]

[0048] In the formula, and represent the Gibbs free energy dissipation in the bulk phase and at the interface, respectively; and are the diffusion rates of atoms in the bulk and at the interface, respectively, where ; , where M is the interface mobility.

[0049] The expression of the thermodynamic extreme principle at the interface is:

[0050] In the formula, is the Lagrange multiplier; Represents the symbol of variation.

[0051] Prediction of the content of austenite in the generated phase based on the interface migration rate

[0052] In the formula, represents the austenite formation fraction; It represents the length of the interface from the left side of austenite; S represents the total length of austenite and ferrite.

[0053] The expression of the thermodynamic extreme principle in the block is:

[0054] In the formula, represents the symbol of variation; represents the rate of change of Gibbs free energy of bulk phase; represents the Gibbs free energy dissipation of the bulk phase.

[0055] The driving force of interface migration is expressed as:

[0056] in

[0057]

[0058] In the formula, , are the initial concentration on the ferrite side or austenite side of the interface and the corresponding equilibrium concentration, respectively; represents the interface at time t i site fraction of solute; represents the strain energy caused by phase change.

[0059] For temperature and composition Related parameters.

[0060] The energy barrier expression is:

[0061] in

[0062]

[0063] In the formula, represents the gas constant, 8.314 J / mol / K; represents the phase transition temperature; Indicates the speed of sound propagation in metal, 1000m / s; Indicates the interface migration speed; It represents the difference between the bulk diffusion activation energy and the interface migration activation energy.

[0064] The generalized stability is:

[0065] In the formula, represents the activation energy of transient interface migration; represents the initial interface migration activation energy; represents the driving force for transient interface migration; Represents the initial interface migration driving force.

[0066] Among the designed process parameter combinations, the best process parameter combination is an isothermal temperature of 660° C. and a holding time of 30 min.

[0067] In one embodiment, a method for predicting the strength and plasticity of medium manganese steel based on austenite reverse transformation kinetics comprises the following specific steps: 1) Establish the Gibbs free energy change and energy dissipation equations, which are divided into two parts: bulk phase and interface; 2) Establishing an interfacial migration kinetic model 2.1) Substitute the Gibbs free energy change and energy dissipation equations at the interface obtained in step 1) into the thermodynamic extreme value principle expression to solve the interface migration velocity and the concentration of each element at the interface; predict the content of the generated phase austenite based on the interface migration velocity; 2.2) Substitute the Gibbs free energy change and energy dissipation equations in the bulk phase obtained in step 1) into the expression of the thermodynamic extreme value principle to solve the expression of the second diffusion theorem; Substitute the concentrations of each element at the interface obtained in step 2.1) into the diffusion equation to solve the distribution of element concentrations in the bulk phase, that is, the transient solute field; 3) Establishing generalized stability applicable to reverse transformation of austenite 3.1) Propose an expression for the driving force of interface migration, which can be calculated based on the concentration of each element at the interface obtained in 2.1); solve the energy barrier expression based on the expression of interface migration velocity; 3.2) Establish the analytical expression of generalized stability and solve the generalized stability based on the driving force and energy barrier obtained in 3.1).

[0068] 3.3) Apply the driving force obtained in step 3.1) and the generalized stability obtained in step 3.2) to design a process parameter combination according to the large driving force-large generalized stability criterion.

[0069] Further, in step 1), the Gibbs free energy change rate is:

[0070]

[0071] in and are the Gibbs free energy change rates in the bulk phase and at the interface, respectively. ( ) represents iron (substitution solute, interstitial solute), Represents variables at the interface. and They are Position fractions and chemical potentials of components. is the solute flux. is the molar volume.

[0072] The interface mass conservation expression is:

[0073] The Gibbs free energy dissipation in the bulk phase and at the interface is:

[0074]

[0075] in and are the diffusion rates of atoms in the bulk and at the interface, respectively; , where M is the interface mobility.

[0076] Furthermore, the general formula of the thermodynamic extreme principle at the interface described in step 2.1) is:

[0077] in is the Lagrange multiplier. The austenite formation fraction is calculated based on the calculated velocity:

[0078] Furthermore, the general formula of the thermodynamic extreme value principle in the block described in step 2.2) is:

[0079] Furthermore, the driving force equation in step 3.2) is:

[0080] in

[0081]

[0082] in , are the initial concentrations of the ferrite side (manganese) or austenite side (carbon) at the interface and the corresponding equilibrium concentrations, is a parameter related to temperature and composition.

[0083] The energy barrier equation is:

[0084] in

[0085]

[0086] Furthermore, the generalized stability equation in step 3.2) is:

[0087] The present invention provides an application of the above method in improving the strength and plasticity of medium manganese steel.

[0088] In order to illustrate that the method provided by the present invention can find the best combination of austenite reverse phase transformation process parameters, the following description is made in conjunction with the accompanying drawings.

[0089] See also Figure 1 In order to find the best combination of two austenite reverse phase transformation process parameters and obtain high strength and high uniform elongation performance, taking Fe-0.2C-8Mn (in wt.%) alloy as an example, the present invention proposes a process design method, comprising the following steps: 1) The general formula of the thermodynamic extremum principle at the interface described in step 2.1) is: (1) in is the Lagrange multiplier. For the three dissipation fluxes in the above equation ( ) are varied respectively, we can get the interface migration rate equation: (2) (3) The interface mass conservation expression is: (4) Therefore, combining (2-4), the isothermal temperature T = 620 ~ 660 ° C (between Ac1 and Ac3 obtained by the thermal expansion curve of continuous heating, such as Figure 2 As shown), the holding time t = 3 ~ 30min can be substituted to obtain the unknown variable: interface velocity , the concentration of each element at the interface .

[0090] Calculate the austenite formation fraction based on the calculated velocity: (5) The calculation results are presented in Figure 3 middle.

[0091] 2) Calculate the phase transition driving force and energy barrier based on the element concentrations at the interface calculated in 1).

[0092] The driving force expression is: (6a) in (6b) (6c) in , are the initial concentrations of the ferrite side (manganese) or austenite side (carbon) at the interface and the corresponding equilibrium concentrations, It is a parameter related to temperature and composition, which is calculated by Thermo-Calc. The calculation results are as follows Figure 4 As shown in a, the transient driving force is Figure 4 As shown in b.

[0093] The energy barrier expression is: (7a) in (7b) (7c) 3) According to equations (6) and (7), the driving force and energy barrier of interface migration can be solved and substituted into the generalized stability equation: (8) The generalized stability of interface migration can be solved.

[0094] First, a cylindrical sample (5 mm in diameter, 10 mm in length) was heated continuously at a heating rate of 10 °C / s using a thermal expansion instrument to determine the temperature of the two-phase region. Figure 2 As shown in the figure, Ac1 and Ac3 are 440℃ and 720℃ respectively, mainly concentrated in 600-700℃, so the austenite reverse phase transformation process in this study adopts three temperatures of 620, 640, and 660℃. The kinetic curves ( Figure 3 a) Austenite content measured after phase transformation ( Figure 3 c) Obtain the change process of austenite content during phase transformation ( Figure 3 d (open symbols) and compared it with the transition fraction calculated by the model using equation (5) ( Figure 3 d solid line) for comparison. At the three different temperatures of the experiment, both have a good match. According to the thermal expansion curve, it is observed that there is no turning point in the curve during the cooling process, that is, no martensitic phase transformation occurs. Therefore, the current model can accurately predict the austenite content obtained under process conditions of different temperatures and different holding times.

[0095] The driving forces, energy barriers and generalized stability calculated at different temperatures are compared. Figure 4 As shown in Figure 2, as the isothermal temperature increases, the initial driving force decreases ( Figure 4 a), the generalized stability of the final state increases under the same transformation time ( Figure 4 b). Similarly, with the extension of the holding time, the final generalized stability increases continuously, especially the generalized stability at 660℃ increases rapidly. When following the large driving force-large generalized stability criterion, phase transition at a higher temperature can obtain a relatively large driving force and large generalized stability.

[0096] According to the above process design method, this embodiment also operates a specific example, and selects the following process parameters to perform isothermal austenite reverse phase transformation heat treatment on Fe-0.2C-8Mn (wt.%) alloy: T=620, 640, 660℃ and holding time t=180, 600, 1200, 1800s, which are hereinafter recorded as ART620 (640 or 660)-180 (600 or 1200 or 1800). The yield strength and uniform elongation under the above process are compared to verify the effectiveness of the method of the present invention, as follows: Figure 5 (a) is the tensile engineering stress-strain curve of the sample kept at 620℃ for 180, 600, 1200 and 1800 s, all of which show continuous yield behavior. Correspondingly, the values ​​of 0.2% offset yield strength and uniform elongation obtained under all conditions are shown in Figure 2. Figure 5 As shown in (b), the yield strength and uniform elongation of the ART620-180 sample are 1035 MPa and 8.6%, respectively. As the holding time increases, the yield strengths of ART620-600, ART620-1200 and ART620-1800 decrease to 905, 787 and 690 MPa, respectively, and the uniform elongation increases to 10.8%, 13.6% and 15.2%, respectively. It is worth noting that the yield strength decreases with the increase of uniform elongation. Figure 4 As shown in (b) and 5(b), the driving force is the highest and the generalized stability is the lowest, forming the ART620-180 sample with the highest yield strength and the lowest uniform elongation. The ART660-1800 sample has the lowest yield strength and the highest uniform elongation, which corresponds to the lowest driving force and the highest generalized stability of ART. Therefore, for the current situation of ART, it can be concluded that there is a correlation between phase transition thermodynamics and mechanical properties. In other words, the greater the driving force, the higher the yield strength, the greater the generalized stability, and the better the uniform elongation. The conditions for obtaining higher yield strength and good plasticity are indeed the same as the above predictions, that is, the performance obtained by ART660-1800 is better, the yield strength of 664 MPa is not much lower than the yield strength of 690 MPa of ART620-1800, and its uniform elongation of 26.9% is 77% higher than the uniform elongation of 15.2% of ART620-1800. The present invention only designs two process parameters, isothermal temperature and holding time. By exploring the effects of different component contents on the thermodynamic driving force, kinetics and generalized stability of the material, component design and mechanical property prediction are carried out.

Claims

1. A method for predicting the strength and plasticity of medium manganese steel based on austenite reverse transformation kinetics, characterized in that: include: The Gibbs free energy change rate and energy dissipation equations in the bulk phase and interface are established respectively; Establishing the interface migration kinetics model: Substitute the Gibbs free energy change rate and energy dissipation equation at the interface into the thermodynamic extreme value principle expression at the interface to obtain the interface migration velocity and the concentration of each element at the interface; predict the content of the generated phase austenite based on the interface migration velocity; Substituting the Gibbs free energy change rate and energy dissipation equation in the bulk phase into the thermodynamic extreme value principle expression in the bulk phase, the second diffusion theorem expression is obtained; Substituting the concentration of each element at the interface into the expression of the second diffusion theorem, the distribution of element concentration in the bulk phase, i.e., the transient solute field, is obtained; Establishing the generalized stability applicable to the reverse transformation of austenite: Define the interface migration driving force expression, and obtain the interface migration driving force according to the concentration of each element at the interface; The energy barrier expression is obtained based on the interface migration velocity expression; The analytical formula of generalized stability is established, and the generalized stability is obtained according to the driving force and energy barrier; According to the driving force and generalized stability, the process parameter combination is designed based on the large driving force-large generalized stability criterion.

2. The method for predicting the strength and plasticity of medium manganese steel based on austenite reverse transformation dynamics according to claim 1 is characterized in that: The Gibbs free energy change rates in the bulk phase and at the interface are: In the formula, Indicates the left side position of the austenite phase; Indicates the interface position between austenite and ferrite; Indicates the right side position of the ferrite phase; represents the rate of change of Gibbs free energy of the bulk phase; and Respectively Harmony Chemical potential of the phase iron solute, superscript " ” means iron; and Respectively Harmony Mutually The chemical potential of the solute, superscript " " indicates replacement of solute, " represents interstitial solute; and Respectively Harmony Mutually flux of solutes; In the formula, represents the rate of change of Gibbs free energy at the interface; and Respectively Harmony Chemical potential at the interface of phase iron and solute, superscript " ” means iron; and Respectively Harmony Mutually The chemical potential at the solute interface, and Respectively Harmony Mutually solute flux at the interface; is the molar volume; Indicates the interface migration speed; Indicates the total number of solute types; Represents variables at the interface.

3. The method for predicting the strength and plasticity of medium manganese steel based on austenite reverse transformation dynamics according to claim 2 is characterized in that: The Gibbs free energy dissipation in the bulk phase and at the interface is: In the formula, and represent the Gibbs free energy dissipation in the bulk phase and at the interface, respectively; and are the diffusion rates of atoms in the bulk and at the interface, respectively, where ; , where M is the interface mobility.

4. The method for predicting the strength and plasticity of medium manganese steel based on austenite reverse transformation dynamics according to claim 1, characterized in that: The expression of the thermodynamic extreme principle at the interface is: In the formula, is the Lagrange multiplier; represents the symbol of variation; Predict the content of austenite produced according to the interface migration rate: In the formula, represents the austenite formation fraction; It represents the length of the interface from the left side of austenite; S represents the total length of austenite and ferrite.

5. The method for predicting strength and plasticity of medium manganese steel based on austenite reverse transformation dynamics according to claim 1, characterized in that: The expression of the thermodynamic extreme principle in the block is: In the formula, represents the symbol of variation; represents the rate of change of Gibbs free energy of bulk phase; represents the Gibbs free energy dissipation of the bulk phase.

6. The method for predicting the strength and plasticity of medium manganese steel based on austenite reverse transformation dynamics according to claim 1, characterized in that: The driving force of interface migration is expressed as: in In the formula, , are the initial concentration on the ferrite side or austenite side of the interface and the corresponding equilibrium concentration, respectively; represents the position fraction of solute i at the interface at time t; represents the strain energy caused by phase change; For temperature and composition Related parameters.

7. The method for predicting strength and plasticity of medium manganese steel based on austenite reverse transformation kinetics according to claim 1, characterized in that: The energy barrier expression is: in In the formula, represents the gas constant, 8.314 J / mol / K; represents the phase transition temperature; Indicates the speed of sound propagation in metal, 1000m / s; Indicates the interface migration speed; It represents the difference between the bulk diffusion activation energy and the interface migration activation energy.

8. The method for predicting strength and plasticity of medium manganese steel based on austenite reverse transformation kinetics according to claim 1, characterized in that: The generalized stability is: In the formula, represents the activation energy of transient interface migration; represents the initial interface migration activation energy; represents the driving force for transient interface migration; Represents the initial interface migration driving force.

9. The method for predicting strength and plasticity of medium manganese steel based on austenite reverse transformation kinetics according to claim 1, characterized in that: Among the designed process parameter combinations, the best process parameter combination is an isothermal temperature of 660° C. and a holding time of 30 min.

10. Use of the method according to any one of claims 1 to 9 in improving the strength and plasticity of medium manganese steel.

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