Finite element simulation method for preheat treatment of cold roll
Through the finite element simulation method, the material properties and tissue changes of the cold rolls are calculated, which solves the problem of difficult to measure the internal stress of the cold rolls, and realizes the efficient heat treatment process optimization of the cold rolls, improving its mechanical properties and life.
Patent Information
- Application Number
- CN202510396588.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-31
- Publication Date
- 2025-07-18
AI Technical Summary
The prior art is difficult to accurately measure the residual stress inside the cold roll, which affects its mechanical properties and service life. The traditional method requires damage to the workpiece for testing and cannot be used in actual production.
The finite element simulation method is used to calculate the material properties through the simulation software JMatPro and combine the experiment to supplement the parameters, establish a simulation model, simulate the structure and stress distribution of cold rolls during the heat treatment process, and use DEFORM software to set boundary conditions and heat treatment process to predict the structure and residual stress distribution of rollers of different material.
Accurate simulation of the structure and stress distribution of cold rolls during heat treatment is achieved, key adjustable parameters are clarified, and the service life and performance of cold rolls are improved. The method can be written into a standard process for promotion and use.
Smart Images
Figure CN120337639A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of heat treatment, and particularly relates to a finite element simulation method for the preliminary heat treatment of cold rolling rolls. Background Art
[0002] China's steel production has been increasing year by year, with an annual output reaching 1 billion tons. Among them, the usage ratio of cold-rolled sheets has also increased significantly. Cold rolling rolls are the main consumables in rolling production. During the cold rolling process, the cost of cold rolling roll consumption accounts for approximately one-fourth of the production cost. In the roll manufacturing industry, forged steel cold rolling rolls are high-tech and high-value-added products, which are the key tools affecting the quality of cold-rolled products and have a great impact on the production cost and production efficiency of enterprises. Therefore, how to improve the material properties of cold rolling rolls and thus extend their service life has become an urgent problem to be solved. With the continuous improvement of the output and quality of cold-rolled products, during the use of rolls, in order to achieve goals such as free rolling, reducing roll consumption, and rolling high-performance sheets, the requirements for the hardness, wear resistance, and toughness of rolls are becoming increasingly stringent. Therefore, higher requirements are also placed on the material and manufacturing process of rolls.
[0003] Among various research directions, the microstructure and residual stress run through the entire life cycle of roll design, production, processing, and service, and are of great significance to various properties of rolls and their long-life reliable service. During the heat treatment process, thermal stress mainly results from the uneven temperature distribution inside the material during the heating and cooling stages, leading to thermal expansion and contraction effects. For example, during the quenching process, the rapid cooling of the external material causes a sharp contraction, but the internal part is not fully cooled, forming significant tensile and compressive stress gradients, which deeply affect the mechanical properties and service life of the material.
[0004] In metal heat treatment, phase transformation stress also plays a key role. This stress mainly occurs during the process of the material transforming from one crystal phase to another. For example, during the quenching process of steel parts, when austenite transforms into martensite structure, volume expansion causes phase transformation stress, resulting in the generation of internal stress in the material. Phase transformation stress not only changes the mechanical properties of the material but may also trigger the generation and propagation of microcracks, thereby reducing the fatigue life and corrosion resistance of the material.
[0005] Generally, X-ray diffraction method (XRD) and ultrasonic measurement method are used to measure stress, but these two methods can only measure the stress on the surface of the workpiece. To detect internal stress, the workpiece must be damaged, which is difficult to carry out during the actual production and use of cold rolling rolls. Summary of the Invention
[0006] The purpose of the present invention is to solve the above problems and provide a finite element simulation method for the preliminary heat treatment of cold rolling rolls.
[0007] The technical solution for achieving the object of the present invention is: a finite element simulation method for the preliminary heat treatment of cold rolling rolls, comprising the following steps: S1. Determination of the material properties of the steel for cold rolling rolls; According to the chemical composition of the steel for cold rolling rolls, the performance parameters and TTT curves of each phase are calculated by the simulation software JMatPro, and the missing performance parameters are supplemented through experiments to determine the overall properties of the material containing each phase.
[0008] In the above step S1, the calculated performance parameters include thermal properties, mechanical properties, and phase transformation parameters; the calculated phase transformation parameters include the material parameters of austenite, pearlite, bainite, and martensite, excluding the material parameters of cementite.
[0009] In the above step S1, the performance parameters supplemented through experiments are the material parameters of cementite.
[0010] In the above step S1, the TTT curve is obtained by tempering the steel for cold rolling rolls at different temperatures and times, measuring its carbide content, and thus obtaining the TTT curves of carbide and other phase structures.
[0011] S2. Setting various parameters required for heat treatment simulation; The material parameters obtained in step S1 are added to the material list of the simulation software DEFORM, and a finite element geometric simulation model is established based on the actual size of the cold rolling roll. The material properties are added, the number of meshes is determined according to the model, the boundary conditions are set according to the actual production situation, the phase structure distribution of the initial state is set, and finally the heat treatment schedule and the corresponding medium properties are set.
[0012] S3. Establishing the regulation relationship between the heat treatment process and the structure and residual stress of the steel for cold rolling rolls; Data on the changes of temperature, stress, strain, hardness, and structure with time and position are obtained through finite element simulation calculations. Combining with the realistic theory of phase transformation during the heat treatment process, the change laws of the structure and residual stress of the cold rolling roll during the heat treatment process are obtained, and the regulation relationship between the heat treatment process and the structure and residual stress of the steel for cold rolling rolls is established, and the accuracy of the finite element calculation is verified by combining with the measured data.
[0013] In the above step S3, it also includes analyzing the influence of the heat treatment process parameters of the cold rolling roll on the structure and residual stress by controlling variables; the variables include quenching temperature, tempering temperature, and tempering time.
[0014] The positive effects of the present invention are: (1) The finite element simulation method for the preliminary heat treatment of cold rolling rolls according to the present invention uses simulation software to calculate material properties based on material compositions, and supplements the missing material parameters through various experimental and testing methods. The obtained data from the above calculations and experiments are used to carry out numerical simulation / experimental research on the temperature field evolution during heat treatment. A simulation model is established in combination with finite element software. The TTT curves of cementite and other phase structures are obtained by measuring the carbide content at different temperatures and different tempering times, so that the distribution of the structure and stress of the cold rolling roll during the heat treatment process can be calculated more accurately through the simulation software. Prediction models for the structure and residual stress distribution of typical specifications of working rolls with different heat treatment processes and different materials are established, the key adjustable parameters of the heat treatment process corresponding to the structure and residual stress distribution are clarified, and a control conversion relationship is established.
[0015] (2) The method of the present invention also has reference significance for simulating the heat treatment structure and stress changes of other metal components and is worthy of being promoted and used; in addition, the finite element simulation method of the present invention can be compiled into a standard implementation process for further promotion and use. Brief Description of the Drawings
[0016] Figure 1 It is a flow chart of the finite element simulation method for the preliminary heat treatment of cold rolling rolls according to the present invention.
[0017] Figure 2 It is an interface of the material property parameters of the steel for cold rolling rolls determined in step S1 of Example 1.
[0018] Figure 3 It is an interface of the phase transformation parameters determined in step S1 of Example 1.
[0019] Figures 4a to 4d They are respectively the TTT curves of austenite → pearlite, austenite → bainite, martensite → cementite, and martensite → low-carbon martensite determined in step S1 of Example 1.
[0020] Figure 5 It is a directory of the simulation parameters input into the simulation software DEFORM in step S2 of Example 1.
[0021] Figure 6 It is a sectional view of the experimental roll in step S3 of Example 1.
[0022] Figures 7a to 7d They are respectively the contour maps of temperature, strain, stress, and hardness obtained from the simulation calculations in step S3 of Example 1 during austenitization, after oil cooling, during tempering, and after air cooling.
[0023] Figures 8a to 8d They are respectively the contour maps of each structure obtained from the simulation calculations in step S3 of Example 1 during austenitization, after oil cooling, during tempering, and after air cooling.
[0024] Figures 9a to 9c They are the stress conditions after heat treatment processes with different quenching temperatures, different tempering temperatures, and different tempering times in the control simulation experiment in step S3 of Example 1 respectively.
[0025] Figures 10a to 10c They are the microstructural conditions after heat treatment processes with different quenching temperatures, different tempering temperatures, and different tempering times in the control simulation experiment in step S3 of Example 1 respectively. Specific Embodiments
[0026] (Example 1) The finite element simulation method for the preliminary heat treatment of cold rolling rolls in this embodiment has the following steps: S1. Determine the material properties of the steel for cold rolling rolls.
[0027] Input the material composition of the steel for cold rolling rolls into the "DEFORM-HT" module of the simulation software JMatPro to generate the material parameters required by the simulation software DEFORM. The simulation software JMatPro can only calculate the material parameters of austenite, pearlite, bainite, and martensite. The material parameters of cementite need to be obtained through experiments.
[0028] See Figure 2 , the material parameters required by the simulation software DEFORM mainly include plastic parameters, elastic parameters, thermal parameters, hardness parameters, electromagnetic parameters, phase transformation parameters, etc. Among them, plastic parameters, elastic parameters, thermal parameters, and phase transformation parameters are included in the initial material file, and the hardness parameters refer to the hardness of various phase microstructures at room temperature. Taking the elastic parameters as an example, the Young's modulus, Poisson's ratio, and coefficient of thermal expansion need to be input.
[0029] See Figure 3 , the phase transformation parameters specifically include 10 items: (1) austenite → pearlite, (2) austenite → bainite, (3) austenite → martensite, (4) pearlite → austenite, (5) bainite → austenite, (6) martensite → austenite, (7) martensite → cementite, (8) martensite → low-carbon martensite, (9) cementite → austenite, (10) low-carbon martensite → austenite. Among them, the first, second, and third phase transformation parameters are included in the initial material file, and the phase transformation relationship of martensite → cementite in the seventh item is measured through experiments.
[0030] In the phase transformation model, for diffusion (TTT curve), the TTT curve of this phase transformation needs to be input (see the TTT curves of each phase transformation in Figures 4a to 4d ); for the martensite phase transformation model, the start transformation temperature and 50% transformation temperature need to be input; in the formula of diffusion (simplified), first input the values of coefficients A and D, usually -4 and 2, and then input the start temperature and end temperature of austenitization.
[0031] The martensite→cementite phase transformation relationship was measured experimentally. First, the material was tempered at different temperatures and times, and then the volume fraction of carbide was measured to obtain the start and end times of cementite transformation at different temperatures.
[0032] S2. Set various parameters required for heat treatment simulation.
[0033] Input various simulation parameters in the simulation software DEFORM. Figure 5 is the directory for inputting simulation parameters, including: 1. Initialization, 2. Material list, 3. Geometry, 4. Mesh, 5. Define material, 6. Boundary conditions, 7. Medium details, 8. Scheduling.
[0034] In 1. Initialization, select axisymmetry, and the modes are phase change, diffusion, and deformation.
[0035] Add the material file obtained in step S1 in 2. Material list.
[0036] Add the model file with the format of dxf at 3. Geometry. This file is generated by the modeling software solidworks according to the engineering drawing.
[0037] Set the number of meshes to 5000 in 4. Mesh, and then click to generate the mesh.
[0038] Select the material file obtained in step S1 added in 2. Material list in 5. Define material.
[0039] Select the axis of symmetry corresponding to the axisymmetric model in 6. Boundary conditions, and set the constraint conditions that the velocities in the x and y directions are 0 according to the actual fixing situation of the experimental roll.
[0040] Add the medium required for simulation in 7. Medium details, select the heat transfer area and input the heat transfer coefficient. The heat transfer area is the area where the corresponding medium contacts the object.
[0041] Set the ambient temperature and heat transfer medium for each heating stage in 8. Scheduling. The specific data is determined according to the preliminary heat treatment process in actual production. In this embodiment, it is specifically "Quenching: 350°C, 4h → 600°C, 8h → 980°C, 16h → oil cooling for 130min; Tempering: 350°C, 8h → 620°C, 24h → air cooling after furnace discharging".
[0042] S3. Establish the regulation relationship between the heat treatment process and the microstructure and residual stress of the cold-rolled roll steel.
[0043] S31. To better display the simulation data, select 3 cross-sections on the experimental roll. For details, see Figure 6 .
[0044] Both Line 1 and Line 2 are on the roll body. Line 1 is 200 mm away from the left side of the roll body, and Line 2 is at the center of the roll body. Line 3 is at the roll neck and is 625 mm away from the lifting end.
[0045] Four time points, namely 69962 seconds (7000 steps), 97620 seconds (12807 steps), 178848 seconds (21000 steps), and 290220 seconds (32143 steps), are selected in terms of time, corresponding to the austenitizing stage, after oil cooling, during tempering, and after air cooling respectively.
[0046] S32. Use the simulation software DEFORM for simulation operations to obtain the operation results. For details, see Figures 7a to 7d and Figures 8a to 8d .
[0047] Figures 7a to 7d They are the contour maps of temperature, strain, stress, and hardness at the austenitizing stage, after oil cooling, during tempering, and after air cooling respectively. It can be seen from each figure that: the change of temperature basically conforms to the heat treatment process curve. The temperature at the roll body surface and both ends of the experimental roll changes relatively fast, while the temperature change inside the roll body is relatively slow; the stress increases rapidly during oil quenching and decreases during tempering. The stress and strain are mainly concentrated on the roll body surface and the connection between the roll body and both ends; the hardness decreases during quenching and increases during oil quenching. The hardness gradually decreases from the roll body surface to the roll body center at the roll body part.
[0048] Figures 8a to 8d They are the contour maps of each microstructure (austenite, pearlite, bainite, martensite, cementite, and low-carbon martensite) at the austenitizing stage, after oil cooling, during tempering, and after air cooling respectively. It can be seen from each figure that: during austenitizing, the entire experimental roll is basically completely austenitized, and the total volume fraction of other phase microstructures is less than 2%; after oil cooling, the roll body surface and both ends are mainly martensite and low-carbon martensite, and the inside of the roll body is mainly austenite; during tempering and after air cooling, the distribution of each microstructure is similar. The roll body surface and both ends are mainly martensite and low-carbon martensite, and the inside of the roll body is mainly pearlite and bainite. The retained austenite is extremely small and mainly distributed on the surface of both ends of the roll body and the connection between the roll body and both ends. The cementite is less and mainly distributed on the roll body surface and both ends of the experimental roll.
[0049] In the heat treatment process, the factors that have a greater impact on the microstructure and residual stress are the quenching temperature, tempering temperature, and tempering time. In this simulation, the quenching temperature is 980 °C, and the tempering temperature and tempering time are 620 °C and 24 h. To explore their effects on the microstructure and residual stress, the control variable method is used. Based on the original heat treatment process, the quenching temperature is changed to 950 °C and 930 °C, the tempering temperature is changed to 600 °C and 570 °C, and the tempering time is changed to 20 h and 15 h. Six groups of control simulation experiments are set up to observe the regulation relationship between the heat treatment process and the microstructure and residual stress. The results of the control simulation experiments are respectively shown in Figures 9a to 9c and Figures 10a to 10c .
[0050] Figures 9a to 9c They are the stress conditions after heat treatment processes with different quenching temperatures, different tempering temperatures, and different tempering times respectively. As can be seen from Figure 9a : When other conditions remain unchanged and the quenching temperature changes, within a certain range, an increase in the quenching temperature will increase the compressive stress and decrease the tensile stress; as can be seen from Figure 9b : When other conditions remain unchanged and the tempering temperature changes, within a certain range, an increase in the tempering temperature will increase both the compressive stress and the tensile stress; as can be seen from Figure 9c : When other conditions remain unchanged and the tempering time changes, within the tempering time of 15 - 20 h, there is a certain time when the compressive stress is the smallest and the tensile stress is the largest, and the specific time needs to be further determined.
[0051] Figures 10a to 10c They are the microstructure conditions after heat treatment processes with different quenching temperatures, different tempering temperatures, and different tempering times respectively. As can be seen from Figure 10a : When other conditions remain unchanged and the quenching temperature changes, within a certain range, an increase in the quenching temperature will slightly decrease the martensite volume fraction and slightly increase the volume of low-carbon martensite; as can be seen from Figure 10b : When other conditions remain unchanged and the tempering temperature changes, when the tempering temperature drops to 570 °C, the volume fraction of cementite increases significantly, and the volume fractions of martensite and low-carbon martensite both decrease; as can be seen from Figure 10c : When other conditions remain unchanged and the tempering time changes, it has little effect on the volume fractions of each phase.
Claims
1. A finite element simulation method for the preliminary heat treatment of cold rolling rolls, characterized in that, The following steps are included: S1. Determine the material properties of the cold rolling roll steel; Based on the material composition of the cold rolling roll steel, calculate the performance parameters and TTT curves of each phase through the simulation software JMatPro, and supplement the missing performance parameters through experiments to determine the overall properties of the material containing each phase; S2. Set various parameters required for heat treatment simulation; Add the material parameters obtained in step S1 to the material list of the simulation software DEFORM, establish a finite element geometric simulation model based on the actual size of the cold rolling roll, add material properties, determine the number of meshes according to the model, set boundary conditions according to the actual production situation, set the phase structure distribution in the initial state, and finally set the heat treatment schedule and the corresponding medium properties; S3. Establish the regulation relationship between the heat treatment process and the structure and residual stress of the cold rolling roll steel; Obtain the data of temperature, stress, strain, hardness, and structure changing with time and position through finite element simulation calculation, combine with the realistic theory of phase transformation during the heat treatment process to obtain the changing rules of the structure and residual stress of the cold rolling roll during the heat treatment process, establish the regulation relationship between the heat treatment process and the structure and residual stress of the cold rolling roll steel, and verify the accuracy of the finite element calculation by combining with the measured data.
2. The finite element simulation method for the preliminary heat treatment of cold rolling rolls according to claim 1, characterized in that: In the above step S1, the calculated performance parameters include thermal properties, mechanical properties, and phase transformation parameters; the calculated phase transformation parameters include the material parameters of austenite, pearlite, bainite, and martensite, excluding the material parameters of cementite.
3. The finite element simulation method for preliminary heat treatment of cold rolling rolls according to claim 1, characterized in that: In the above step S1, the performance parameters supplemented by the experiment are the material parameters of cementite.
4. The finite element simulation method for preliminary heat treatment of cold rolling rolls according to claim 1, wherein: In the above step S1, the TTT curve is obtained by tempering the cold rolling roll steel at different temperatures and different times and measuring its carbide content, so as to obtain the TTT curves of carbide and other phase structures.
5. The finite element simulation method for preliminary heat treatment of cold rolling rolls according to claim 1, characterized in that: In the above step S3, it also includes analyzing the influence of the heat treatment process parameters of the cold rolling roll on the structure and residual stress by controlling variables; the variables include quenching temperature, tempering temperature, and tempering time.