Method for predicting strength and ductility of medium manganese steel based on austenite reverse phase transformation kinetics

Abstract

The application discloses a method for predicting strength and plasticity of medium manganese steel based on austenite reverse phase transformation dynamics, and belongs to the technical field of metal and alloy preparation. The method comprises the following steps: establishing the Gibbs free energy change rate and energy dissipation equation of bulk phase and interface, respectively; establishing a generalized stability analytical expression, and obtaining the generalized stability according to the driving force and energy barrier; and designing the process parameter combination based on the large driving force-large generalized stability criterion according to the driving force and the generalized stability. The austenite reverse phase transformation model is established based on the thermodynamic extremum principle, compared with the traditional diffusion phase transformation model, the element diffusion, interface migration and interaction between diffusion and interface are simultaneously considered, and the phase transformation dynamics process can be well predicted.

Description

Technical Field

[0001] This invention belongs to the field of metal and alloy preparation technology, specifically relating to a method for predicting the strength and plasticity of manganese steel based on the dynamics of austenite reverse phase transformation. Background Technology

[0002] Medium-manganese steel, as one of the representatives of third-generation high-strength steels, has improved mechanical properties due to the greater stability of austenite, and is widely used in the aerospace and automotive fields. This stability is achieved by increasing the manganese content within the austenite grains and optimizing the kinetics of the inverse austenite transformation (ART). However, in the process of preparing high-performance medium-manganese steel, different process parameters for the ART, such as isothermal temperature and holding time, will lead to different microstructures and elemental distributions, thus affecting material properties. Most experiments employ trial and error methods, which significantly reduces production efficiency and increases costs. Furthermore, most kinetic description models of the ART lack experimental verification, thus restricting the application and promotion of these models.

[0003] Generally, increasing isothermal temperature and holding time increases austenite content but decreases hard martensite, and also affects austenite stability, which is also related to composition. To control microstructure and elemental distribution, semi-analytical mixing model models and cellular automated simulator models have been widely studied for phase transformation. These models elucidate the transformation kinetics of the inverse austenite phase transformation by relaxing the assumptions of single diffusion control or near-equilibrium elements present in classical diffusion models. However, because diffusion-controlled phase transformation models lack descriptions of phase transformation energy changes—i.e., thermodynamic driving force and kinetic energy barrier—and do not consider the process-phase transformation-performance system, they cannot achieve quantitative design for the optimal combination of isothermal temperature and holding time. Summary of the Invention

[0004] To address the shortcomings of the aforementioned background technology, this invention provides a method for predicting the strength and plasticity of medium manganese steel based on austenitic reverse phase transformation kinetics. Based on the principle of thermodynamic extrema, this invention predicts the phase transformation kinetics process, couples the process parameters of austenitic reverse phase transformation heat treatment of medium manganese steel, and proposes a thermo-kinetic criterion with large driving force and large generalized stability to achieve quantitative design of optimal process parameter matching to obtain a microstructure with good strength and plasticity, which is conducive to the promotion of ART process.

[0005] The first objective of this invention is to provide a method for predicting the strength and plasticity of manganese steel based on the kinetics of austenite inverse phase transformation, comprising: Establish the Gibbs free energy change rate and energy dissipation equations for the bulk phase and the interface, respectively; Establish an interface migration dynamics model: Substituting the Gibbs free energy change rate and energy dissipation equation at the interface into the thermodynamic extremum principle expression at the interface, the interface migration rate and the concentration of each element at the interface are obtained; the content of austenite phase is predicted based on the interface migration rate. Substituting the rate of change of Gibbs free energy and the energy dissipation equation within the bulk phase into the thermodynamic extremum principle expression within the bulk phase, we obtain the expression for the second diffusion theorem. By substituting the element concentrations at the interface into the expression of the second diffusion theorem, the element concentration distribution of the bulk phase, i.e., the transient solute field, can be obtained. Establish a generalized stability applicable to the reverse phase transformation of austenite: Define the expression for the interface migration driving force, and obtain the interface migration driving force based on the concentration of each element at the interface; obtain the energy barrier expression based on the interface migration velocity expression. Establish an analytical expression for generalized stability and obtain generalized stability based on the driving force and energy barrier; Based on the driving force and generalized stability, and using the large driving force-large generalized stability criterion, the combination of process parameters is designed.

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

[0007] In the formula, Indicates the left-hand position of the austenitic phase; Indicates the location of the interface between austenite and ferrite; Indicates the right-hand side position of the ferrite phase; Represents the rate of change of Gibbs free energy in the bulk phase; and They represent Harmony The chemical potential of the iron solute, indicated by the superscript " "Indicates iron; and They represent Harmony Mutually The chemical potential of the solute, indicated by the superscript " "Indicates substitution of solute", Indicates interstitial solute; and They represent Harmony Mutually Solute flux;

[0008] In the formula, This represents the rate of change of Gibbs free energy at the interface; and They represent Harmony Chemical potential at the iron-solute interface, superscript " "Indicates iron; and They represent Harmony Mutually Chemical potential at the solute interface and They represent Harmony Mutually Flux at the solute interface; Volume is the molar volume; Indicates the interface transition speed; Indicates the total number of solute types; This represents a variable in the user interface.

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

[0010]

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

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

[0013] In the formula, For Lagrange multipliers; Indicates variational symbols; Predicting the content of austenite phase based on interface migration rate.

[0014] In the formula, Indicates the austenite fraction; This indicates the distance from the interface to the left side of the austenite; S represents the total length of the austenite and ferrite interval.

[0015] Preferably, the expression for the thermodynamic extremum principle within the bulk is:

[0016] In the formula, Indicates variational symbols; This represents the rate of change of Gibbs free energy in the bulk phase; This represents the Gibbs free energy dissipation of the bulk phase.

[0017] Preferably, the expression for the interface migration driving force is:

[0018] in

[0019]

[0020] In the formula, , These represent the initial ferrite or austenite concentration at the interface and the corresponding equilibrium concentration, respectively. This represents the fraction of solute position i at the interface at time t; This represents the strain energy caused by the phase transition; For temperature and composition The relevant parameters.

[0021] Preferably, the energy barrier expression is:

[0022] in

[0023]

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

[0025] The preferred generalized stability is:

[0026] In the formula, Indicates the activation energy of transient interface migration; Indicates the initial interface migration activation energy; This indicates the driving force of transient interface migration; This indicates the initial interface migration driving force.

[0027] Preferably, the optimal combination of process parameters is an isothermal temperature of 660°C and a holding time of 30 minutes.

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

[0029] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a method for predicting the strong plasticity of manganese steel based on the dynamics of austenite inverse phase transformation. This invention establishes an austenite inverse phase transformation model based on the principle of thermodynamic extrema. Compared with the traditional diffusion phase transformation model, it takes into account element diffusion, interface migration, and the interaction between diffusion and interface, and can make good predictions on the phase transformation dynamics process.

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

[0031] The process design strategy proposed in this invention can optimize a process that controls two parameters simultaneously: isothermal temperature and holding time, find the optimal combination between the two process parameters, and optimize actual production efficiency. Attached Figure Description

[0032] Figure 1 This is a flowchart of the method for predicting the kinetics of austenite inverse phase transformation and the strength and plasticity of materials proposed in this invention.

[0033] Figure 2 In an embodiment of the present invention, the predicted austenite reverse phase transformation dynamics were verified by thermal expansion experiments.

[0034] Figure 3 The driving force, energy barrier, and generalized stability are calculated by the model in the embodiments of the present invention.

[0035] Figure 4 The yield strength and uniform elongation of the plates after heat treatment with different process parameters are shown in the embodiments of the present invention.

[0036] Figure 5 The tensile stress-strain curves, offset yield strength, and uniform elongation are shown in the embodiments of the present invention at different temperatures. Detailed Implementation

[0037] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0038] The purpose of this invention is to propose a quantitative process design method for the ART process, which couples two process parameters, isothermal temperature and holding time, with a diffusion-controlled phase transition model based on the thermodynamic extremum principle. Based on the thermo-dynamic criterion of large driving force and large generalized stability, process parameters that simultaneously achieve good strength and plasticity are found. This result can be used to guide the preparation of medium manganese steel plates under the ART process in the field.

[0039] To achieve the above objectives, this invention provides a method for predicting the strength and plasticity of manganese steel based on austenite inverse phase transformation kinetics, comprising: Establish the Gibbs free energy change rate and energy dissipation equations for the bulk phase and the interface, respectively; Establish an interface migration dynamics model: Substituting the Gibbs free energy change rate and energy dissipation equation at the interface into the thermodynamic extremum principle expression at the interface, the interface migration rate and the concentration of each element at the interface are obtained; the content of austenite phase is predicted based on the interface migration rate. Substituting the rate of change of Gibbs free energy and the energy dissipation equation within the bulk phase into the thermodynamic extremum principle expression within the bulk phase, we obtain the expression for the second diffusion theorem. By substituting the element concentrations at the interface into the expression of the second diffusion theorem, the element concentration distribution of the bulk phase, i.e., the transient solute field, can be obtained. Establish a generalized stability applicable to the reverse phase transformation of austenite: Define the expression for the interface migration driving force, and obtain the interface migration driving force based on the concentration of each element at the interface; obtain the energy barrier expression based on the interface migration velocity expression. Establish an analytical expression for generalized stability and obtain generalized stability based on the driving force and energy barrier; Based on the driving force and generalized stability, and using the large driving force-large generalized stability criterion, the combination of process parameters is designed.

[0040] The rates of change of Gibbs free energy at the bulk phase and the interface are respectively:

[0041] In the formula, Indicates the left-hand position of the austenitic phase; Indicates the location of the interface between austenite and ferrite; This indicates the right-hand side position of the ferrite phase.

[0042] Represents the rate of change of Gibbs free energy in the bulk phase; and They represent Harmony The chemical potential of the iron solute, indicated by the superscript " "Indicates iron; and They represent Harmony Mutually The chemical potential of the solute, indicated by the superscript " "Indicates substitution of solute", Indicates interstitial solute; and They represent Harmony Mutually Solute flux;

[0043] In the formula, This represents the rate of change of Gibbs free energy at the interface; and They represent Harmony Chemical potential at the iron-solute interface, superscript " "Indicates iron; and They represent Harmony Mutually Chemical potential at the solute interface and They represent Harmony Mutually Flux at the solute interface; Volume is the molar volume; Indicates the interface transition speed; This indicates the total number of solute types.

[0044] It should be noted that, It is a single entity representing the volume of a mole.

[0045] This represents a variable in the user interface.

[0046] The Gibbs free energy dissipation at the bulk phase and the interface are as follows:

[0047]

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

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

[0050] In the formula, For Lagrange multipliers; Represents the variational symbol.

[0051] Predicting the content of austenite phase based on interface migration rate.

[0052] In the formula, Indicates the austenite fraction; This indicates the distance from the interface to the left side of the austenite; S represents the total length of the austenite and ferrite interval.

[0053] The expression for the thermodynamic extremum principle within a block is:

[0054] In the formula, Indicates variational symbols; This represents the rate of change of Gibbs free energy in the bulk phase; This represents the Gibbs free energy dissipation of the bulk phase.

[0055] The expression for the interface migration driving force is:

[0056] in

[0057]

[0058] In the formula, , These represent the initial ferrite or austenite concentration at the interface and the corresponding equilibrium concentration, respectively. Indicates the interface at time t. i position fraction of solute; This represents the strain energy caused by the phase transition.

[0059] For temperature and composition The relevant parameters.

[0060] The energy barrier expression is:

[0061] in

[0062]

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

[0064] Generalized stability is:

[0065] In the formula, Indicates the activation energy of transient interface migration; Indicates the initial interface migration activation energy; This indicates the driving force of transient interface migration; This indicates the initial interface migration driving force.

[0066] The optimal combination of process parameters is an isothermal temperature of 660℃ and a holding time of 30min.

[0067] In one embodiment, a method for predicting the strength and plasticity of manganese steel based on austenite inverse phase transformation kinetics includes the following steps: 1) Establish the Gibbs free energy change and energy dissipation equations, divided into two parts: the bulk phase and the interface phase; 2) Establish an interface migration dynamics model 2.1) Substitute the Gibbs free energy change and energy dissipation equation at the interface obtained in step 1) into the thermodynamic extremum principle expression to solve for the interface migration rate and the concentration of each element at the interface; predict the content of the austenite phase to be generated based on the interface migration rate. 2.2) Substitute the Gibbs free energy change and energy dissipation equations within the bulk phase obtained in step 1) into the thermodynamic extremum principle expression to solve for the expression of the second diffusion theorem; substitute the element concentrations at the interface obtained in step 2.1) into the diffusion equation to solve for the element concentration distribution in the bulk phase, i.e., the transient solute field. 3) Establish a generalized stability applicable to the reverse phase transformation of austenite. 3.1) Propose an expression for the interface migration driving force, which can be obtained from the element concentrations at the interface obtained in 2.1); solve for the energy barrier expression based on the interface migration velocity expression. 3.2) Establish the analytical expression for generalized stability, and solve for 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 the combination of process parameters according to the large driving force-large generalized stability criterion.

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

[0070]

[0071] in and These represent the rate of change of Gibbs free energy at the bulk phase and the interface, respectively. (Subscript) ( ) represents iron (substitute solute, interstitial solute). This represents a variable in the user interface. and They are respectively Position fractions and chemical potentials of components. This represents the solute flux. The volume is the molar volume.

[0072] The expression for the conservation of interface quality is:

[0073] The Gibbs free energy dissipation at the bulk phase and the interface are as follows:

[0074]

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

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

[0077] in For Lagrange multipliers. Calculate the austenite fraction based on the calculated velocity:

[0078] Furthermore, the general formula for the thermodynamic extremum principle within the block described in step 2.2) is:

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

[0080] in

[0081]

[0082] in , These represent the initial ferrite (manganese) or austenite (carbon) concentration at the interface and the corresponding equilibrium concentration. These are parameters related to temperature and composition.

[0083] The energy barrier equation is:

[0084] in

[0085]

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

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

[0088] To illustrate that the method provided by this invention can find the optimal combination of austenitic reverse phase transformation process parameters, the following description is provided in conjunction with the accompanying drawings.

[0089] See Figure 1 To find the optimal combination of two austenitic reverse phase transformation process parameters and simultaneously obtain high strength and high uniform elongation, taking Fe-0.2C-8Mn (in wt.%) alloy as an example, this invention proposes a process design method, including the following steps: 1) The general formula for the thermodynamic extremum principle at the interface mentioned in step 2.1) is: (1) in For the three dissipative fluxes in the above equation ( By performing variational analysis on each part, we can obtain the interface migration rate equation: (2) (3) The expression for the conservation of interface quality is: (4) Therefore, combining (2-4), the isothermal temperature T = 620~660℃ (between Ac1 and Ac3 obtained from the thermal expansion curve of continuous heating, as shown in the figure) Figure 2 As shown), the insulation time t = 3~30min can be substituted to calculate the unknown variable: interface speed. Concentration of each element at the interface .

[0090] Calculate the austenite 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 concentrations of each element at the interface obtained in 1).

[0092] The expression for driving force is: (6a) in (6b) (6c) in , These represent the initial ferrite (manganese) or austenite (carbon) concentration at the interface and the corresponding equilibrium concentration. This is a parameter related to temperature and composition, obtained from Thermo-Calc equilibrium calculations. Initial driving force. The calculation results are as follows Figure 4 As shown in a, the transient driving force is as follows: Figure 4 As shown in b.

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

[0094] First, the temperature of the two-phase region was determined by continuously heating a cylindrical sample (5 mm in diameter and 10 mm in length) at a heating rate of 10 °C / s using a thermal dilatometer. The results are as follows: Figure 2 As shown, Ac1 and Ac3 are 440℃ and 720℃ respectively, mainly concentrated in the 600-700℃ range. Therefore, this study uses three temperatures of 620, 640, and 660℃ for the austenitic reverse phase transformation process. Kinetic curves were obtained using a thermal dilatometer after holding at each of the three temperatures for 30 min (heating and cooling rates were both 10℃ / s). Figure 3 a) The austenite content measured after the phase transformation ( Figure 3 c) Obtain the process of austenite content change during the phase transformation ( Figure 3 (d hollow symbol), and use equation (5) to calculate the transformation fraction ( Figure 3 The two models were compared (d solid line). At three different experimental temperatures, both showed good matching. The thermal expansion curves showed no inflection point during cooling, indicating no martensitic transformation occurred. Therefore, the current model can accurately predict the austenite content under different holding times at different temperatures.

[0095] The driving force, energy barrier, and generalized stability calculated at different temperatures were compared. The results are as follows: Figure 4 As shown, the initial driving force decreases with increasing isothermal temperature. Figure 4 a) The final state generalized stability increases under the same transition time. Figure 4 (b) Similarly, with increasing holding time, the final-state generalized stability continuously increases, especially at 660℃ where the generalized stability increases rapidly. When following the large driving force-large generalized stability criterion, phase transitions at higher temperatures can yield relatively large driving forces and large generalized stability.

[0096] Based on the above process design method, this embodiment also operates a specific example, selecting the following process parameters to perform isothermal austenitic 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 then denoted 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) shows the tensile stress-strain curves of the specimens after holding at 620 °C for 180, 600, 1200, and 1800 s, all exhibiting continuous yielding behavior. Correspondingly, the values ​​of the 0.2% offset yield strength and uniform elongation obtained under all conditions are as follows: Figure 5 As shown in (b), the yield strength and uniform elongation of the ART620-180 specimen were 1035 MPa and 8.6%, respectively. With increasing holding time, the yield strengths of ART620-600, ART620-1200, and ART620-1800 decreased to 905, 787, and 690 MPa, respectively, while the uniform elongation increased to 10.8%, 13.6%, and 15.2%, respectively. Notably, the yield strength decreased with increasing uniform elongation. Figure 4 As shown in (b) and 5(b), the highest driving force and the lowest generalized stability resulted in the ART620-180 specimen with the highest yield strength and the lowest uniform elongation. Conversely, the ART660-1800 specimen exhibited the lowest yield strength and the highest uniform elongation, corresponding to the lowest driving force and the highest generalized stability in ART. Therefore, for the current situation of ART, it can be concluded that there is a correlation between phase change thermodynamics and mechanical properties. That is, 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 predicted above; that is, the ART660-1800 exhibits better performance, with a yield strength of 664 MPa, which is not significantly lower than the 690 MPa of ART620-1800, while its uniform elongation of 26.9% is 77% higher than the 15.2% of ART620-1800. This invention only designed 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, it conducts component design and predicts mechanical properties.

Claims

1. A method for predicting the strength and plasticity of manganese steel based on the dynamics of austenite inverse phase transformation, characterized in that, include: Establish the Gibbs free energy change rate and energy dissipation equations for the bulk phase and the interface, respectively; Establish an interface migration dynamics model: Substituting the Gibbs free energy change rate and energy dissipation equation at the interface into the thermodynamic extremum principle expression at the interface, the interface migration rate and the concentration of each element at the interface are obtained; the content of austenite phase is predicted based on the interface migration rate. Substituting the rate of change of Gibbs free energy and the energy dissipation equation within the bulk phase into the thermodynamic extremum principle expression within the bulk phase, we obtain the expression for the second diffusion theorem. By substituting the element concentrations at the interface into the expression of the second diffusion theorem, the element concentration distribution of the bulk phase, i.e., the transient solute field, can be obtained. Establish a generalized stability applicable to the reverse phase transformation of austenite: Define the expression for the interface migration driving force, and obtain the interface migration driving force based on the concentration of each element at the interface; The energy barrier expression is obtained from the interface migration speed expression; Establish an analytical expression for generalized stability and obtain generalized stability based on the driving force and energy barrier; Based on the driving force and generalized stability, and using the large driving force-large generalized stability criterion, the combination of process parameters is designed. The rates of change of Gibbs free energy at the bulk phase and the interface are respectively: In the formula, Indicates the left-hand position of the austenitic phase; Indicates the location of the interface between austenite and ferrite; Indicates the right-hand side position of the ferrite phase; Represents the rate of change of Gibbs free energy in the bulk phase; and They represent Harmony The chemical potential of the iron solute, indicated by the superscript " "Indicates iron; and They represent Harmony Mutually Chemical potential of solute, superscript " "Indicates substitution of solute," Indicates interstitial solute; and They represent Harmony Mutually Solute flux; In the formula, This represents the rate of change of Gibbs free energy at the interface; and They represent Harmony Chemical potential at the iron-solute interface, superscript " "Indicates iron; and They represent Harmony Mutually Chemical potential at the solute interface and They represent Harmony Mutually Flux at the solute interface; Volume is the molar volume; Indicates the interface transition speed; Indicates the total number of solute types; Represents variables in the interface; The Gibbs free energy dissipation at the bulk phase and the interface are as follows: In the formula, and These represent the Gibbs free energy dissipation at the bulk phase and the interface, respectively. and These are the diffusion rates of atoms within the bulk and within the interface, respectively. ; , where M is the interface mobility; The thermodynamic extremum principle expression at the interface is: In the formula, For Lagrange multipliers; Indicates variational symbols; Predict the content of austenite phase based on interface migration rate: In the formula, Indicates the austenite fraction; This indicates the length of the interface from the left side of the austenite; S represents the total length of the austenite and ferrite interval. The expression for the thermodynamic extremum principle within a block is: In the formula, Indicates variational symbols; This represents the rate of change of Gibbs free energy in the bulk phase; This represents the Gibbs free energy dissipation of the bulk phase; The expression for the interface migration driving force is: in In the formula, , These represent the initial ferrite or austenite concentration at the interface and the corresponding equilibrium concentration, respectively. This represents the fraction of solute position i at the interface at time t; This represents the strain energy caused by the phase transition; For temperature and composition Relevant parameters; The energy barrier expression is: in In the formula, This represents the gas constant, 8.314 J / mol / K; Indicates the phase transition temperature; This represents the speed of sound in metal, 1000 m / s; Indicates the interface transition speed; This represents the difference between the bulk diffusion activation energy and the interface migration activation energy. Generalized stability is: In the formula, Indicates the activation energy of transient interface migration; Indicates the initial interface migration activation energy; This indicates the driving force of transient interface migration; This indicates the initial interface migration driving force.

2. The method for predicting the strength and plasticity of manganese steel based on austenite inverse phase transformation kinetics according to claim 1, characterized in that, The optimal combination of process parameters is an isothermal temperature of 660℃ and a holding time of 30min.

3. The application of the method of claim 1 or 2 in improving the strength and plasticity of medium manganese steel.

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