Method for establishing thermal deformation constitutive model suitable for austenite and dynamic transformation interval
By establishing a thermal deformation constitutive model suitable for austenite and dynamic transition intervals, the problem that existing models cannot accurately predict the stress and strain relationships is solved, and accurate prediction and numerical simulation optimization forming process under wide temperature changes are achieved, which is suitable for the thermal deformation process of steel materials.
Patent Information
- Application Number
- CN202510586396.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-08
- Publication Date
- 2025-08-08
AI Technical Summary
The existing thermal deformation constitutive model cannot accurately predict the stress and strain relationship of steel materials in the austenite and dynamic ferrite phase transition intervals, resulting in difficulty in product quality control during thermal processing.
Establish a thermal deformation constitutive model suitable for austenite and dynamic transition intervals, obtain the stress and strain relationship through high-temperature physical simulation experiments, and correct the model coefficients to construct a viscoplastic thermal deformation constitutive model, considering the work hardening, dynamic recovery and phase transition behavior of austenite and ferrite.
It realizes accurate prediction of the thermal deformation process of steel materials under wide temperature changes, has a wide range of application, conforms to actual processing conditions, is accurate in prediction results, and has small errors, and is suitable for numerical simulation and optimization forming processes.
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Figure CN120452635A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of plastic forming process of metal materials, and more particularly, relates to a method for establishing a thermal deformation constitutive model applicable to austenite and dynamic transformation intervals. Background Art
[0002] Steel materials play an important role in all areas of the national economy and national construction. Among them, low-carbon alloy steel has low production costs, good welding performance and mechanical properties, and is widely used in carrying equipment, infrastructure construction, and pressure vessels. With the continuous improvement of the comprehensive mechanical performance requirements of low-carbon alloy steel, the stable production of low-carbon low-alloy steel with high plasticity, toughness, high strength and stability on an industrial scale has become a key research task in the steel industry. Thermomechanical processing includes: rolling, extrusion, forging, etc. During the processing, the material undergoes high-temperature plastic deformation. Through the refined design of the thermal deformation process parameters, it is possible to achieve industrial-scale production of steel materials that meet the requirements of shape, size, and organizational performance.
[0003] The thermal deformation constitutive model is a mathematical language that establishes the quantitative relationship between the history of thermal mechanical processing and the evolution of the material's microstructure and macroscopic deformation resistance. An accurate thermal deformation constitutive model is of great significance for effectively designing thermal mechanical processing parameters, improving product microstructure and performance, controlling product shape and size, and rationally distributing equipment loads. However, in actual hot working processes, the material temperature undergoes a continuous decrease, either actively or passively. For example, the plate and strip experience biting and exiting during the hot rolling process. From the inlet to the outlet side of the rolling interface, the surface metal continuously decreases its surface deformation temperature during the deformation process due to heat exchange with the rolls, causing the carbon steel material to experience a complete austenite range and a dynamic ferrite phase transformation range under drastic temperature changes. Currently, there is no thermal deformation constitutive relationship that can couple the thermal deformation behavior of the austenite range and the dynamic ferrite phase transformation range, resulting in difficulties in product quality control during the hot working of carbon steel materials.
[0004] Therefore, it is urgent to establish a thermal deformation constitutive model applicable to the austenite and dynamic ferrite transformation range to accurately predict the stress-strain relationship of materials under a wide range of temperature changes, which is of great significance and practical value for the shape and controllability of the plastic forming process of steel materials. Summary of the Invention
[0005] In response to the above-mentioned defects or upgrade and optimization needs of the existing technology, the present invention provides a method for establishing a thermal deformation constitutive model applicable to the austenite and dynamic transformation ranges. Its purpose is to provide a method and idea for constructing a thermal deformation constitutive model of steel materials to address the above-mentioned problems, so that the model is more suitable for predicting the stress-strain relationship in the actual processing process of steel materials, and solve the problem that existing general models are difficult to accurately predict the stress-strain relationship of thermal deformation of steel materials under a wide range of temperature changes.
[0006] The method for establishing a hot deformation constitutive model applicable to the austenite and dynamic transformation range includes the following steps: S1: The stress-strain relationship of the hot deformation process in the single-pass complete austenite interval and the stress-strain relationship of the hot deformation process in the dynamic ferrite transformation interval are obtained through high-temperature physical simulation experiments and preprocessed; S2: Based on the stress-strain relationship of the single-pass hot deformation process in the complete austenite interval and the dynamic ferrite transformation interval in S1, the model coefficients are modified according to the viscoplastic hot deformation constitutive model applicable to the austenite and dynamic transformation intervals.
[0007] Preferably, the acquisition and preprocessing of the stress-strain relationship during the single-pass fully austenitic hot deformation process in S1 includes the following sub-steps: S1-1: Select the size 8×12mm or A 10×15mm cylindrical compression specimen was subjected to single-pass high-temperature compression tests at different strain rates and deformation temperatures at the fully austenitic temperature. The engineering stress-strain relationship in the fully austenitic region was obtained and converted into a single-pass true stress-strain relationship based on the strain conversion relationship. S1-2: Correct the obtained true stress-strain relationship by friction and adiabatic heating; S1-3: Based on the corrected true stress-strain relationship, the yield stress under different deformation conditions in the complete austenite range is obtained ; S1-4: Obtain the work hardening rate-stress relationship in the fully austenitic range, and further obtain the critical strain of dynamic recrystallization under different deformation conditions in the fully austenitic range , the dynamic recovery stage and dynamic recrystallization stage of the hot deformation process in the complete austenite range are distinguished.
[0008] Preferably, the acquisition and preprocessing of the stress-strain relationship during the thermal deformation process of the single-pass dynamic ferrite transformation interval in S1 includes the following sub-steps: S1-5: Select the size 8×12mm or A 10×15mm cylindrical compression specimen was subjected to single-pass high-temperature compression tests at different strain rates and deformation temperatures between the full austenite temperature and the dynamic ferrite transformation temperature. The engineering stress-strain relationship in the dynamic ferrite transformation range was obtained and converted into a single-pass true stress-strain relationship based on the strain conversion relationship. S1-6: Apply friction and adiabatic heating correction to the obtained true stress-strain relationship; S1-7: Based on the corrected true stress-strain relationship, the yield stress under different deformation conditions in the dynamic ferrite transformation range is obtained ; S1-8: Obtain the work hardening rate-stress relationship in the dynamic ferrite transformation range, and further obtain the critical strain of dynamic ferrite phase transformation under different deformation conditions in the dynamic ferrite transformation range. , the non-dynamic ferrite phase transformation stage and the dynamic ferrite phase transformation stage of the thermal deformation process in the dynamic ferrite transformation range are distinguished.
[0009] Preferably, the viscoplastic thermal deformation constitutive model for austenite and dynamic transformation intervals in S2 includes the following formula: (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) in, is the flow stress; is the ferrite content; is the austenite flow stress; is the ferrite flow stress; is the non-thermal component of austenite flow stress; is the thermal component of austenite flow stress; is the normalized dislocation density in austenite; is the austenite strain rate; is the normalized dislocation density evolution rate in austenite; and are the rate of change of dynamic recrystallization degree in austenite and the degree of dynamic recrystallization in austenite respectively; The strain borne by austenite; and are the rate of change of austenite dynamic recrystallization inoculation degree and the degree of austenite dynamic recrystallization inoculation degree respectively; is the non-thermal component of ferrite flow stress; is the thermal component of ferrite flow stress; is the normalized dislocation density in ferrite; is the dynamic ferrite transformation rate; is the overall strain rate; is the ferrite strain rate; , , , , , , , , , , , , , is the model coefficient 1 to the model coefficient 19, where , , , , , , , , The temperature dependence is calculated using the following formula, with other coefficients being constants; (14) in, , , , , , , , , , , , , , , , , , For model coefficients 20 to 38, The gas constant is 8.314, is the deformation temperature.
[0010] Preferably, the modification of the coefficients of the viscoplastic thermal deformation constitutive model applicable to the austenite and dynamic transformation regions in S2 includes the following sub-steps: S2-1: Based on the true stress-strain curve relationship of the dynamic recovery stage of the hot deformation process in the fully austenite range after differentiation, and the true stress-strain curve relationship of the stage before the dynamic ferrite phase transformation during the hot deformation process in the dynamic ferrite phase transformation range, all model coefficients of the viscoplastic hot deformation constitutive model applicable to the austenite and dynamic transformation ranges, excluding dynamic recrystallization behavior and dynamic ferrite phase transformation behavior, are solved; S2-2: Using the yield stress, dynamic recrystallization critical strain, and dynamic ferrite transformation critical strain obtained in S1, solve the following yield stress model, dynamic recrystallization critical strain model, and dynamic ferrite transformation critical strain coefficient; (15) (16) (17) in, , , , , , , , , , , , The model coefficient is 39 to the model coefficient is 51; S2-3: Based on the model coefficients solved in S2-1 and the yield stress and dynamic recrystallization critical strain calculation model solved in S2-2, all model coefficients related to the dynamic recrystallization behavior of austenite in the viscoplastic hot deformation constitutive model applicable to austenite and dynamic transformation range are solved using the true stress-strain curve relationship during the hot deformation process in the complete austenite range; S2-4: Based on the model coefficients solved in S2-1 and the yield stress and dynamic ferrite phase transformation critical strain calculation model solved in S2-2, all model coefficients related to the dynamic ferrite phase transformation behavior in the viscoplastic hot deformation constitutive model applicable to the austenite and dynamic transformation range are solved using the true stress-strain curve relationship of the thermal deformation process after the dynamic ferrite phase transformation occurs in the dynamic ferrite phase transformation range.
[0011] Preferably, the calculation process of the viscoplastic thermal deformation constitutive model applicable to the austenite and dynamic transformation range is as follows: first, determine whether the current deformation temperature is in the dynamic ferrite phase transformation range. If not, calculate the flow stress-strain relationship of the complete austenite phase transformation range according to formulas (1)-(7). If so, calculate the flow stress-strain relationship of the dynamic ferrite phase transformation range according to formulas (1)-(13).
[0012] Preferably, the yield stress during thermal deformation is estimated from the intersection of the elastic stage straight line with the stress curve when the straight line is offset by 0.02 true strain.
[0013] In general, the above technical solutions conceived by the present invention can achieve the following beneficial effects compared with the prior art.
[0014] (1) The constitutive model of the present invention is consistent with actual processing conditions. It takes into account the work hardening, dynamic recovery, and dynamic recrystallization of austenite, the strain-induced dynamic precipitation of austenite into ferrite, the work hardening, dynamic recovery, and dynamic recrystallization of ferrite, and the strain distribution behavior between austenite and ferrite, thus achieving an accurate prediction of the stress-strain relationship during the hot deformation process in the austenite and dynamic ferrite transformation range. (2) The constitutive model of the present invention has a wide range of applications and requires less data: through actual testing, it has been proven that this method is applicable to both the hot deformation process in the complete austenite range and the hot deformation process in the ferrite transformation range, and is also applicable to numerical simulation optimization of forming processes, which is more in line with the actual situation of the material processing process; (3) The constitutive model of the present invention accurately predicts the results: Compared with the experimental results under sampling conditions, the correlation coefficient between the constitutive model of the present invention and the steady-state single-pass compression test results is 0.98837, the average relative error is 3.519%, and the average absolute error is 5.9232 MPa. Therefore, the numerical method of the present invention is reliable and trustworthy, and the flow stress prediction value of the constitutive model is relatively accurate. BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Figure 1 The flowchart of the constitutive model construction method of the present invention is shown.
[0016] Figure 2 The figure shows the comparison between the experimental values of flow stress in a randomly selected single-pass compression and the predicted values obtained using the method of the present invention. DETAILED DESCRIPTION
[0017] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely for the purpose of explaining the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
[0018] The method for establishing a hot deformation constitutive model applicable to the austenite and dynamic transformation range includes the following steps: S1: The stress-strain relationship of the single-pass fully austenite hot deformation process and the stress-strain relationship of the dynamic ferrite transformation hot deformation process are obtained through high-temperature physical simulation experiments and preprocessed; S2: Based on the stress-strain relationship of the hot deformation process in the single-pass complete austenite interval and the dynamic ferrite transformation interval in S1, the model coefficients are modified according to the viscoplastic hot deformation constitutive model applicable to the austenite and dynamic transformation intervals; The acquisition and preprocessing of the stress-strain relationship during the single-pass fully austenitic hot deformation process in S1 includes the following sub-steps: S1-1: Select the size 8×12mm or A 10×15mm cylindrical compression specimen was subjected to single-pass high-temperature compression tests at different strain rates and deformation temperatures at the fully austenitic temperature. The engineering stress-strain relationship in the fully austenitic region was obtained and converted into a single-pass true stress-strain relationship based on the strain conversion relationship. S1-2: Correct the obtained true stress-strain relationship by friction and adiabatic heating; S1-3: Based on the corrected true stress-strain relationship, the yield stress under different deformation conditions in the complete austenite range is obtained ; S1-4: Obtain the work hardening rate-stress relationship in the fully austenitic range, and further obtain the critical strain of dynamic recrystallization under different deformation conditions in the fully austenitic range , the dynamic recovery stage and dynamic recrystallization stage of the hot deformation process in the complete austenite range are distinguished.
[0019] S1-5: Select the size 8×12mm or A 10×15mm cylindrical compression specimen was subjected to single-pass high-temperature compression tests at different strain rates and deformation temperatures between the full austenite temperature and the dynamic ferrite transformation temperature. The engineering stress-strain relationship in the dynamic ferrite transformation range was obtained and converted into a single-pass true stress-strain relationship based on the strain conversion relationship. S1-6: Apply friction and adiabatic heating correction to the obtained true stress-strain relationship; S1-7: Based on the corrected true stress-strain relationship, the yield stress under different deformation conditions in the dynamic ferrite transformation range is obtained ; S1-8: Obtain the work hardening rate-stress relationship in the dynamic ferrite transformation range, and further obtain the critical strain of dynamic ferrite phase transformation under different deformation conditions in the dynamic ferrite transformation range. , the non-dynamic ferrite phase transformation stage and the dynamic ferrite phase transformation stage of the thermal deformation process in the dynamic ferrite transformation range are distinguished.
[0020] The viscoplastic thermal deformation constitutive model for austenite and dynamic transformation in S2 includes the following formulas: (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) in, is the flow stress; is the ferrite content; is the austenite flow stress; is the ferrite flow stress; is the non-thermal component of austenite flow stress; is the thermal component of austenite flow stress; is the normalized dislocation density in austenite; is the austenite strain rate; is the normalized dislocation density evolution rate in austenite; and are the rate of change of dynamic recrystallization degree in austenite and the degree of dynamic recrystallization in austenite respectively; is the strain borne by austenite; and are the rate of change of austenite dynamic recrystallization inoculation degree and the degree of austenite dynamic recrystallization inoculation degree respectively; is the non-thermal component of ferrite flow stress; is the thermal component of ferrite flow stress; is the normalized dislocation density in ferrite; is the dynamic ferrite transformation rate; is the overall strain rate; is the ferrite strain rate; , , , , , , , , , , , , , is the model coefficient 1 to the model coefficient 19, where , , , , , , , , The temperature dependence is calculated using the following formula, with other coefficients being constants; (14) in, , , , , , , , , , , , , , , , , , For model coefficients 20 to 38, The gas constant is 8.314, is the deformation temperature.
[0021] The coefficient modification of the viscoplastic thermal deformation constitutive model for austenite and dynamic transformation in S2 includes the following sub-steps: S2-1: Based on the true stress-strain curve relationship of the dynamic recovery stage of the hot deformation process in the fully austenite range after differentiation, and the true stress-strain curve relationship of the stage before the dynamic ferrite phase transformation during the hot deformation process in the dynamic ferrite phase transformation range, all model coefficients of the viscoplastic hot deformation constitutive model applicable to the austenite and dynamic transformation ranges, excluding dynamic recrystallization behavior and dynamic ferrite phase transformation behavior, are solved; S2-2: Using the yield stress, dynamic recrystallization critical strain, and dynamic ferrite transformation critical strain obtained in S1, solve the following yield stress model, dynamic recrystallization critical strain model, and dynamic ferrite transformation critical strain coefficient; (15) (16) (17) in, , , , , , , , , , , , It is model coefficient thirty-nine to model coefficient fifty-one.
[0022] S2-3: Based on the model coefficients solved in S2-1 and the yield stress and dynamic recrystallization critical strain calculation model solved in S2-2, all model coefficients related to the dynamic recrystallization behavior of austenite in the viscoplastic hot deformation constitutive model applicable to austenite and dynamic transformation range are solved using the true stress-strain curve relationship during the hot deformation process in the complete austenite range; S2-4: Based on the model coefficients solved in S2-1 and the yield stress and dynamic ferrite phase transformation critical strain calculation model solved in S2-2, all model coefficients related to the dynamic ferrite phase transformation behavior in the viscoplastic hot deformation constitutive model applicable to the austenite and dynamic transformation range are solved using the true stress-strain curve relationship of the thermal deformation process after the dynamic ferrite phase transformation occurs in the dynamic ferrite phase transformation range.
[0023] The calculation process of the viscoplastic thermal deformation constitutive model applicable to the austenite and dynamic transformation range is as follows: first, determine whether the current deformation temperature is in the dynamic ferrite phase transformation range. If not, calculate the flow stress-strain relationship of the complete austenite phase transformation range according to formulas (1)-(7). If it is, calculate the flow stress-strain relationship of the dynamic ferrite phase transformation range according to formulas (1)-(13).
[0024] The yield stress during thermal deformation is estimated by the intersection of the elastic stage straight line with the stress curve when it deviates by 0.02 true strain.
[0025] The present invention is described using the constitutive model of a single-pass compression test of 12CrNiMoA low-carbon alloy steel as an example. Figure 1 shown.
[0026] Processing 12CrNiMoA low carbon alloy steel into The single-pass compression test of 8×12mm cylindrical compression specimen was carried out on a Gleeble3800 physical simulation test machine. During the single-pass hot compression test, the specimen was first heated to 1150℃ at 10℃ / s and kept warm for 240s to ensure that the internal microstructure of the specimen was completely austenitized. Then, under the control of a thermocouple, the temperature was reduced to 800℃, 850℃, 900℃, 950℃, 1000℃, and 1050℃ at a cooling rate of 5℃ / s, and kept warm for 120s to ensure uniform temperature inside the specimen. Subsequently, the specimens were heated at 0.01, 0.1, 1, and 10s, respectively. -1 Isothermal compression experiments were conducted at a strain rate of 1000 s. When the sample compression reached 60%, it was removed from the equipment and rapidly water quenched. Based on these experiments, 24 engineering stress-engineering strain curves were obtained, and all of them were converted to true stress-strain curves. At deformation temperatures of 800°C and 850°C, the material was in the dynamic ferrite phase transformation range, while at deformation temperatures of 900°C, 950°C, 1000°C, and 1050°C, the material was in the full austenite range.
[0027] The true stress-strain curve is corrected by considering the influence of friction and adiabatic heating phenomenon; based on the corrected true stress-strain relationship in the complete austenite interval, the yield stress under different deformation conditions in the complete austenite interval is obtained. , where the yield stress The stress value at 0.02 true strain is used as the representative; further, the work hardening rate-stress relationship is obtained, and the work hardening rate is the derivative of stress with respect to strain. The critical strain of dynamic recrystallization under different deformation conditions is obtained. , the dynamic recovery stage and dynamic recrystallization stage of the thermal deformation process are distinguished, among which the critical strain of dynamic recrystallization is , according to the second-order derivative of the work hardening rate to stress is zero, the corresponding strain value is obtained. Based on the corrected true stress-strain relationship in the dynamic ferrite phase transformation range, the yield stress under different deformation conditions in the dynamic ferrite phase transformation range is obtained. , where the yield stress The stress value at the true strain of 0.02 is used as the representative; further, the work hardening rate-stress relationship is obtained, and the critical strain of dynamic ferrite phase transformation under different deformation conditions is obtained. , the non-dynamic ferrite phase transformation stage and the dynamic ferrite phase transformation stage during the thermal deformation process are distinguished, among which the critical strain of the dynamic ferrite phase transformation is , according to the second-order derivative of the work hardening rate with respect to the stress is zero, the corresponding strain value is obtained.
[0028] According to formulas (15)-(17), based on the least squares method, with temperature and strain rate as independent variables and yield stress, dynamic recrystallization critical strain, and dynamic ferrite phase transformation critical strain under different conditions as dependent variables, the yield stress model, dynamic recrystallization critical strain model, and dynamic ferrite phase transformation critical strain model coefficients are solved.
[0029] Under different deformation conditions, 20 points were selected at equal intervals on the stress-strain curve of the dynamic recovery stage in the complete austenite interval and the stress-strain curve of the non-dynamic ferrite phase transformation stage in the dynamic ferrite phase transformation interval under different deformation conditions. Based on the constitutive model of the present invention, with the minimum relative error between the predicted stress value and the actual stress value as the objective function, the MATLAB software genetic optimization algorithm toolkit was used to correct the austenite dynamic recovery related model coefficients in the constitutive model of the present invention, including: , , .
[0030] Twenty points were selected at equal intervals on the stress-strain curve of the dynamic recrystallization stage in the complete austenite interval under different deformation conditions. Based on the constitutive model of the present invention, the relative error between the predicted stress value and the actual stress value was minimized as the objective function. The MATLAB software genetic optimization algorithm toolkit was used to modify the austenite dynamic recrystallization related model coefficients in the constitutive model of the present invention, including: , , , , , .
[0031] Under different deformation conditions, 20 points were selected at equal intervals on the stress-strain curve of the dynamic ferrite phase transformation stage in the dynamic ferrite phase transformation interval. Based on the constitutive model of the present invention, the relative error between the predicted stress value and the actual stress value was minimized as the objective function. The MATLAB software genetic optimization algorithm toolkit was used to modify the dynamic ferrite phase transformation related model coefficients in the constitutive model of the present invention, including: , , , , , , .
[0032] When the material undergoes thermal deformation, it is first determined whether it is in the complete austenite range or the dynamic ferrite phase transformation range. If it is in the complete austenite range, it is determined whether dynamic recrystallization occurs under the current conditions and further calculates the flow stress. If it is in the dynamic ferrite phase transformation range, it is determined whether dynamic ferrite phase transformation occurs under the current conditions and further calculates the flow stress.
[0033] Comparison of the flow stress experimental values in a randomly selected single-pass compression and the predicted values obtained using the method of the present invention, such as Figure 2 As shown, the correlation coefficient is 0.98837, the average relative error is 3.519%, and the average absolute error is 5.9232 MPa; in summary, the method of establishing a thermal deformation constitutive model applicable to austenite and dynamic transformation range of the present invention is a reliable and feasible numerical analysis method, which is suitable for fields such as numerical simulation and optimization of forming processes in material processing.
[0034] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.
Claims
1. Establish a thermal deformation constitutive model method applicable to austenite and dynamic transformation range, characterized by: The steps include: S1: The stress-strain relationship of the hot deformation process in the single-pass complete austenite interval and the stress-strain relationship of the hot deformation process in the dynamic ferrite transformation interval are obtained through high-temperature physical simulation experiments and preprocessed; S2: Based on the stress-strain relationship of the single-pass hot deformation process in the complete austenite interval and the dynamic ferrite transformation interval in S1, the model coefficients are modified according to the viscoplastic hot deformation constitutive model applicable to the austenite and dynamic transformation intervals.
2. The method for establishing a thermal deformation constitutive model applicable to austenite and dynamic transformation ranges according to claim 1, characterized in that: The acquisition and preprocessing of the stress-strain relationship during the single-pass fully austenitic hot deformation process in S1 includes the following sub-steps: S1-1: Select the size 8×12mm or A 10×15mm cylindrical compression specimen was subjected to single-pass high-temperature compression tests at different strain rates and deformation temperatures at the fully austenitic temperature. The engineering stress-strain relationship in the fully austenitic region was obtained and converted into a single-pass true stress-strain relationship based on the strain conversion relationship. S1-2: Correct the obtained true stress-strain relationship by friction and adiabatic heating; S1-3: Based on the corrected true stress-strain relationship, the yield stress under different deformation conditions in the complete austenite range is obtained ; S1-4: Obtain the work hardening rate-stress relationship in the fully austenitic region, and further obtain the critical strain of dynamic recrystallization under different deformation conditions in the fully austenitic region , the dynamic recovery stage and dynamic recrystallization stage of the hot deformation process in the complete austenite range are distinguished.
3. The method for establishing a thermal deformation constitutive model applicable to austenite and dynamic transformation ranges according to claim 1, characterized in that: The acquisition and preprocessing of the stress-strain relationship during the thermal deformation process of the single-pass dynamic ferrite transformation interval in S1 includes the following sub-steps: S1-5: Select the size 8×12mm or A 10×15mm cylindrical compression specimen was subjected to single-pass high-temperature compression tests at different strain rates and deformation temperatures between the full austenite temperature and the dynamic ferrite transformation temperature. The engineering stress-strain relationship in the dynamic ferrite transformation range was obtained and converted into a single-pass true stress-strain relationship based on the strain conversion relationship. S1-6: Apply friction and adiabatic temperature rise corrections to the obtained true stress-strain relationship; S1-7: Based on the corrected true stress-strain relationship, the yield stress under different deformation conditions in the dynamic ferrite transformation range is obtained ; S1-8: Obtain the work hardening rate-stress relationship in the dynamic ferrite transformation range, and further obtain the critical strain of dynamic ferrite phase transformation under different deformation conditions in the dynamic ferrite transformation range. , the non-dynamic ferrite phase transformation stage and the dynamic ferrite phase transformation stage of the thermal deformation process in the dynamic ferrite transformation range are distinguished.
4. The method for establishing a thermal deformation constitutive model applicable to austenite and dynamic transformation ranges according to claim 1, characterized in that: The viscoplastic thermal deformation constitutive model for austenite and dynamic transformation in S2 includes the following formulas: （1） （2） （3） （4） （5） （6） （7） （8） （9） （10） （11） （12） （13） in, is the flow stress; is the ferrite content; is the austenite flow stress; is the ferrite flow stress; is the non-thermal component of austenite flow stress; is the thermal component of austenite flow stress; is the normalized dislocation density in austenite; is the austenite strain rate; is the normalized dislocation density evolution rate in austenite; and are the rate of change of dynamic recrystallization degree in austenite and the degree of dynamic recrystallization in austenite respectively; is the strain borne by austenite; and are the rate of change of austenite dynamic recrystallization inoculation degree and the degree of austenite dynamic recrystallization inoculation degree respectively; is the non-thermal component of ferrite flow stress; is the thermal component of ferrite flow stress; is the normalized dislocation density in ferrite; is the dynamic ferrite transformation rate; is the overall strain rate; is the ferrite strain rate; , , , , , , , , , , , , , is the model coefficient 1 to the model coefficient 19, where , , , , , , , , The temperature dependence is calculated using the following formula, with other coefficients being constants; （14） in, , , , , , , , , , , , , , , , , , For model coefficients 20 to 38, The gas constant is 8.314, is the deformation temperature.
5. The method for establishing a thermal deformation constitutive model applicable to austenite and dynamic transformation ranges according to claim 1, characterized in that: The coefficient modification of the viscoplastic thermal deformation constitutive model for austenite and dynamic transformation in S2 includes the following sub-steps: S2-1: Based on the true stress-strain curve relationship of the dynamic recovery stage of the hot deformation process in the fully austenite range after differentiation, and the true stress-strain curve relationship of the stage before the dynamic ferrite phase transformation during the hot deformation process in the dynamic ferrite phase transformation range, all model coefficients of the viscoplastic hot deformation constitutive model applicable to the austenite and dynamic transformation ranges, excluding dynamic recrystallization behavior and dynamic ferrite phase transformation behavior, are solved; S2-2: Using the yield stress, dynamic recrystallization critical strain, and dynamic ferrite transformation critical strain obtained in S1, solve the following yield stress model, dynamic recrystallization critical strain model, and dynamic ferrite transformation critical strain coefficient; （15） （16） （17） in, , , , , , , , , , , , The model coefficient is 39 to the model coefficient is 51; S2-3: Based on the model coefficients solved in S2-1 and the yield stress and dynamic recrystallization critical strain calculation model solved in S2-2, all model coefficients related to the dynamic recrystallization behavior of austenite in the viscoplastic hot deformation constitutive model applicable to austenite and dynamic transformation range are solved using the true stress-strain curve relationship during the hot deformation process in the complete austenite range; S2-4: Based on the model coefficients solved in S2-1 and the yield stress and dynamic ferrite phase transformation critical strain calculation model solved in S2-2, all model coefficients related to the dynamic ferrite phase transformation behavior in the viscoplastic hot deformation constitutive model applicable to the austenite and dynamic transformation range are solved using the true stress-strain curve relationship of the thermal deformation process after the dynamic ferrite phase transformation occurs in the dynamic ferrite phase transformation range.
6. The method for establishing a thermal deformation constitutive model applicable to austenite and dynamic transformation ranges according to claim 1, characterized in that: The calculation process of the viscoplastic thermal deformation constitutive model applicable to the austenite and dynamic transformation range is as follows: first, determine whether the current deformation temperature is in the dynamic ferrite phase transformation range. If not, calculate the flow stress-strain relationship of the complete austenite phase transformation range according to formulas (1)-(7). If it is, calculate the flow stress-strain relationship of the dynamic ferrite phase transformation range according to formulas (1)-(13).
7. The method for establishing a thermal deformation constitutive model applicable to austenite and dynamic transformation ranges according to claim 1, characterized in that: The yield stress during thermal deformation is estimated by the intersection of the elastic stage straight line with the stress curve when it is offset by 0.02 true strain.