Finite element model-based method for optimizing tempering heat preservation time in tempering process of supporting roller forge piece

Abstract

The invention relates to a method for optimizing tempering heat preservation time in the tempering process of a supporting roller forge piece based on a finite element model, belongs to the technical field of heat treatment of the supporting roller forge piece, and solves at least one of the problems of energy waste, equipment occupation, high product cost and the like caused by overlong tempering time of an existing method. According to the method, the tempering heat preservation time of the supporting roller is optimized by integrating changes of the temperature, the structures and the residual stress, and the reduction or stabilization time of the residual stress is judged according to stress relaxation curves of different structures and is not obtained through finite element simulation in the creep deformation process; according to the method for judging the stress relaxation degree under the conditions of different structures and loads, namely, the stress relaxation curve is normalized, and the method can be directly and repeatedly used for optimizing the tempering heat preservation time of the supporting rollers which are made of the same material and have different specifications and different process parameters.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment of support roll forgings, and in particular to a method for optimizing the tempering holding time of a support roll forging during a quenching and tempering process based on a finite element model. Background Art

[0002] In order to meet the service performance requirements of the support roller forgings, the forged support roller forgings need to be heat treated, of which quenching and tempering heat treatment is one of them, which includes quenching and high-temperature tempering processes. The purpose of tempering of the support roller forgings is to adjust the structure, reduce or eliminate quenching stress, improve toughness and plasticity, obtain the appropriate combination of hardness, strength, plasticity and toughness, and meet different performance requirements. The tempering heat treatment time of the support roller forgings is generally very long, which causes problems such as low equipment turnover rate, high energy consumption, high product cost, and low market competitiveness.

[0003] At present, the formulation of the tempering heat treatment process of support roller forgings mainly relies on experience, supplemented by some physical experiments and simulation calculations, and there are also algorithms combined with machine learning. However, the existing methods have the following problems: 1) The physical experiment is not carried out in combination with the heat treatment process of the support roller forgings, and cannot reflect the distribution of temperature, structure and performance at different positions of the support roller forgings. In addition, if the tempering process is optimized by means of physical experiments alone, the workload is large, time-consuming, and the results may not be comprehensive enough; 2) The finite element simulation method has not established a reasonable creep model for the tempering process. Since the support roller structure is different from the surface to the core during tempering, the structure from the surface to the core is martensite, bainite, and pearlite, respectively, and the degree of creep under different loads is also different. Because the changes in the structure, carbide precipitation, stress, etc. during the tempering process are relatively complex, there is currently no better mathematical model to describe it. Tempering process, and the prediction of residual stress in the tempering process, the current mature commercial software cannot simulate the residual stress of the creep model under different organizations and different loads during the tempering process; 3) The use of machine learning methods to predict processes or performance requires a large amount of actual production sample data to support it. The currently reported prediction process parameters are quenching temperature and tempering temperature, which do not involve tempering time or residual stress. The results of finite element simulation are also used as sample data, but their accuracy is seriously dependent on the accuracy of the finite element model. If the creep model in the tempering process in the finite element model is not established reasonably, then the reliability of the machine learning results using its results as sample data is also questionable.

[0004] In summary, there is currently no comprehensive and accurate method for determining the tempering heat treatment process parameters of support roll forgings in order to optimize the tempering heat treatment process parameters. Summary of the invention

[0005] In view of the above analysis, the present invention aims to provide a method for optimizing the tempering holding time of the support roller forging quenching and tempering process based on a finite element model, so as to solve at least one of the problems of the existing method of determining the tempering time being too long and having poor accuracy.

[0006] In order to achieve the above object, the present invention adopts the following technical solution: A method for optimizing the tempering holding time of a backup roll forging during a quenching and tempering process based on a finite element model comprises the following steps: Step S1: testing the thermophysical parameters and structural transformation parameters of various structures involved in the heat treatment process of the support roller, establishing a finite element model of the heat treatment process of the support roller, and performing temperature-structure coupling simulation; Step S2: According to the temperature-structure coupling simulation results, the temperature curve of the roller body changing with time during the tempering process is extracted and compared with the tempering process to obtain the holding time when the temperature of the roller body is 5°C lower than the holding temperature of the tempering process, which is recorded as t1; Step S3: respectively plotting hardness curves of the support roller surface, sub-surface and core position as a function of tempering and holding time, and performing normalization processing to obtain the shortest tempering and holding time for stable hardness, recorded as t2; Step S4: respectively draw stress relaxation curves of martensite, bainite and pearlite structures under different load conditions during the quenching and tempering heat treatment of the support roller, and perform normalization processing to obtain the shortest tempering and holding time for the residual stress stability of the martensite, bainite and pearlite structures, which are respectively recorded as t31, t32 and t33, and the maximum value among t31, t32 and t33 is recorded as t3; Step S5: The optimized tempering and holding time of the support roller is recorded as t, t=t1+max(t2, t3).

[0007] Furthermore, in step S1, the structure includes martensite, bainite, pearlite, tempered martensite, and bainite tempered structure, the thermophysical parameters include density, specific heat, and thermal conductivity, and the structure transformation parameters refer to the parameters involved in each structure transformation model.

[0008] Furthermore, in step S1, the finite element model is a support roller quenching-tempering model.

[0009] Furthermore, in step S3, the shortest tempering and holding time for stable hardness is the shortest time for which the rate of change of normalized hardness with tempering and holding time is less than 1%.

[0010] Furthermore, step S3 specifically includes: Step S31: according to the finite element model established in step S1, respectively extracting the temperature curves of the roller surface, sub-surface and core position during the tempering process of the backup roller; Step S32: using the experimental sample to perform a quenching and tempering heat treatment experiment according to the temperature curve obtained in step S31, and taking samples at different stages of tempering and heat preservation to perform hardness testing; Step S33: respectively plotting the hardness curves of the roller body surface, sub-surface and core as the tempering and holding time changes, and performing normalization processing to obtain the shortest time when the normalized hardness changes with the tempering and holding time less than 1%, recorded as t2.

[0011] Furthermore, step S4 specifically includes: Step S41: extracting the temperature curves of the roller surface, sub-surface and core during the tempering process of the backup roller according to the finite element model established in step S1; Step S42: using the experimental sample to perform a quenching and tempering heat treatment experiment according to the temperature curve obtained in step S41, and taking samples before the start of tempering and heat preservation, and then performing a stress relaxation experiment; Step S43: respectively draw stress relaxation curves of the roller body surface, sub-surface and core as the tempering holding time changes at different stress levels, perform normalization processing, and obtain the maximum value of the normalized stress value ≤30% and the change rate <1% as the shortest time, recorded as t3.

[0012] Furthermore, step S3 specifically includes: Step S31': According to the CCT curve, the cooling rate of the experimental sample is controlled to obtain different structures contained in the support roller in actual production; Step S32': performing heat treatment experiments with different tempering and heat preservation times on the different structures obtained in step S31', and taking samples at different stages of tempering and heat preservation to perform physical tests on hardness; Step S33': respectively plotting hardness curves of different structures changing with tempering and holding time, and performing normalization processing to obtain the shortest time when the change rate of normalized hardness with tempering and holding time is less than 1%, recorded as t2.

[0013] Furthermore, different structures include martensite, bainite and pearlite. Furthermore, step S4 specifically includes: Step S41': According to the CCT curve, the cooling rate of the experimental sample is controlled to obtain different structures contained in the support in actual production; Step S42': performing stress relaxation experiments at tempering and holding temperature on the different structures obtained in step S41'; Step S43': respectively draw stress relaxation curves of different structures changing with tempering and holding time, and perform normalization processing. The maximum value of the normalized stress value ≤30% and the change rate <1% is the shortest time, recorded as t3.

[0014] Further, the different structures include martensite, bainite and pearlite.

[0015] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: (1) The method of the present invention optimizes the tempering and holding time of the support roller by comprehensively considering the changes in temperature, structure and residual stress. The reduction or stabilization time of the residual stress is determined based on the stress relaxation curves of different structures, rather than being obtained through finite element simulation of the creep process. The method of the present invention is aimed at determining the degree of stress relaxation under different structures and load conditions, that is, normalizing the stress relaxation curve. This method can be directly and repeatedly used to optimize the tempering and holding time of support rollers of the same material with different specifications and different process parameters. Compared with the traditional method relying on experience, the method of the present invention can determine a shorter tempering time and is more accurate than the finite element analysis of the creep model.

[0016] (2) The method of the present invention can greatly shorten the tempering time of the support roller forgings, thereby significantly reducing the manufacturing cost of the products; the method of the present invention can comprehensively and fully optimize the tempering and heat preservation time of the support roller during the tempering heat treatment process from three aspects: temperature, structure and stress.

[0017] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings are only used for the purpose of illustrating specific embodiments and are not to be considered as limiting the present invention. In the entire drawings, the same reference symbols represent the same components; Figure 1 A schematic flow chart of a method for optimizing the tempering holding time of a backup roll forging during a quenching and tempering process based on a finite element model according to the present invention; Figure 2 The temperature curves of the roller body surface, sub-surface (below the hardened layer, bainite structure position) and core position during the tempering process of the support roller in Example 1 of the present invention; Figure 3 The hardness curves of the roller surface, subsurface (below the hardened layer, bainite structure position) and core position as a function of the tempering holding time in Example 1 of the present invention; Figure 4 The normalized hardness curves of the roller surface, subsurface (below the hardened layer, bainite structure position) and core position as a function of tempering holding time in Example 1 of the present invention are shown in FIG. Figure 5: is the stress relaxation curve of the pearlite structure (center position) at different stress levels at the tempering and holding temperature in Example 1 of the present invention; Figure 6 is the normalized stress relaxation curve of the pearlite structure (center position) at different stress levels at the tempering and holding temperature in Example 1 of the present invention; Figure 7 : is the stress relaxation curve of the bainite structure (subsurface position) at different stress levels at the tempering and holding temperature in Example 1 of the present invention; Figure 8 is the normalized stress relaxation curve of the bainite structure (subsurface position) at different stress levels at the tempering and holding temperature in Example 1 of the present invention; Fig. 9 : is the stress relaxation curve of the martensitic structure (surface position) at different stress levels at the tempering and holding temperature in Example 1 of the present invention; Fig.10 It is the normalized stress relaxation curve of the martensitic structure (surface position) at different stress levels at the tempering and holding temperature in Example 1 of the present invention. DETAILED DESCRIPTION

[0019] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0020] A specific embodiment of the present invention, as Figure 1 As shown, a method for optimizing the tempering holding time of a support roller forging during a quenching and tempering process based on a finite element model is disclosed, comprising the following steps: Step S1: testing the thermophysical parameters and structural transformation parameters of various structures involved in the heat treatment process of the support roller, establishing a finite element model of the support roller tempering process, and performing temperature-structure coupling simulation. The finite element model does not calculate the stress field, that is, does not include a creep model; Step S2: According to the temperature-structure coupling simulation results, the temperature curve of the roller body changing with time during the tempering process is extracted and compared with the tempering process to obtain the holding time when the temperature of the roller body is 5°C lower than the holding temperature of the tempering process, which is recorded as t1; Step S3: respectively plotting hardness curves of the support roller surface, sub-surface and core position as a function of tempering and holding time, and performing normalization processing to obtain the shortest tempering and holding time for stable hardness, recorded as t2; Step S4: respectively draw stress relaxation curves of martensite, bainite and pearlite structures under different load conditions during the quenching and tempering heat treatment of the support roller, and perform normalization processing to obtain the shortest tempering and holding time for the residual stress stability of the martensite, bainite and pearlite structures, which are respectively recorded as t31, t32 and t33, and the maximum value among t31, t32 and t33 is recorded as t3; Step S5: The optimized tempering and holding time of the support roller is recorded as t, t=t1+max(t2, t3).

[0021] Compared with the prior art, the method of the present invention optimizes the tempering and holding time of the support roller by comprehensively considering the changes in temperature, organization and residual stress. The reduction or stabilization time of the residual stress is determined based on the stress relaxation curves of different organizations, rather than being obtained through finite element simulation of the creep process. The method of the present invention is aimed at determining the degree of stress relaxation under different organizations and load conditions, that is, normalizing the stress relaxation curve. The method can be directly and repeatedly used to optimize the tempering and holding time of support rollers of the same material with different specifications and different process parameters. Compared with the traditional method relying on experience, the method of the present invention determines a shorter tempering time and is more accurate than the finite element analysis of the creep model.

[0022] The method of the present invention can greatly shorten the tempering time of the support roller forgings, thereby significantly reducing the manufacturing cost of the products; the method of the present invention can comprehensively and fully optimize the tempering and heat preservation time of the support roller in the tempering heat treatment process from three aspects of temperature, structure and stress.

[0023] The finite element model described in the present invention is established by ABAQUS software.

[0024] In a specific embodiment, in step S1, the structure includes martensite, bainite, pearlite, tempered martensite, and bainite tempered structure. The thermophysical parameters include density, specific heat, and thermal conductivity. The structure transformation parameters refer to the parameters involved in each structure transformation model, for example, b, n, and ts parameters in the Avrami equation, α and Ms parameters in the KM equation, etc.

[0025] Specifically, the structural transformation refers to the structural transformation during quenching and tempering, which can be obtained by measuring CCT, TTT or the thermal expansion curve during tempering through data processing.

[0026] In a specific implementation, in step S1, the finite element model is a support roller quenching-tempering model.

[0027] In a specific implementation, in step S3, the shortest tempering and holding time for stable hardness is the shortest time for which the rate of change of normalized hardness with tempering and holding time is less than 1%.

[0028] In a specific implementation, step S3 specifically includes: Step S31: according to the finite element model established in step S1, respectively extracting the temperature curves of the roller surface, sub-surface and core position during the tempering process of the backup roller; Step S32: using the experimental sample to perform a quenching and tempering heat treatment experiment according to the temperature curve obtained in step S31, and taking samples at different stages of tempering and heat preservation to perform hardness testing; Step S33: respectively plotting the hardness curves of the roller body surface, sub-surface and core as the tempering and holding time changes, and performing normalization processing to obtain the shortest time when the normalized hardness changes with the tempering and holding time less than 1%, recorded as t2.

[0029] In a specific implementation, step S3 specifically includes: Step S31': According to the CCT curve, the cooling rate of the experimental sample is controlled to obtain different structures contained in the support roller in actual production; Step S32': performing heat treatment experiments with different tempering and heat preservation times on the different structures obtained in step S31', and taking samples at different stages of tempering and heat preservation to perform physical tests on hardness; Step S33': respectively plotting hardness curves of different structures changing with tempering and holding time, and performing normalization processing to obtain the shortest time when the change rate of normalized hardness with tempering and holding time is less than 1%, recorded as t2.

[0030] Preferably, in step S31 ′, the different structures include martensite, bainite and pearlite.

[0031] In a specific embodiment, step S4 further includes: controlling the cooling rate of the experimental sample according to the CCT curve to obtain the martensite, bainite and pearlite structures obtained in the actual production of the support roller.

[0032] In a specific embodiment, in step S4, the shortest tempering holding time refers to the shortest time for the maximum value of the normalized stress value ≤30% and the change rate <1%.

[0033] In a specific implementation, step S4 specifically includes: Step S41: extracting the temperature curves of the roller surface, sub-surface and core during the tempering process of the backup roller according to the finite element model established in step S1; Step S42: using the experimental sample to perform a quenching and tempering heat treatment experiment according to the temperature curve obtained in step S41, and taking samples before the start of tempering and heat preservation, and then performing a stress relaxation experiment; Step S43: respectively draw stress relaxation curves of the roller surface, sub-surface and core as the tempering and holding time change under different stress levels, perform normalization processing, and obtain the maximum value and shortest time of the normalized stress value ≤30% and the change rate <1%, which is recorded as t3.

[0034] In a specific implementation, step S4 specifically includes: Step S41': According to the CCT curve, the cooling rate of the experimental sample is controlled to obtain different structures contained in the support in actual production; Step S42': performing stress relaxation experiments at tempering and holding temperature on the different structures obtained in step S41'; Step S43': respectively draw stress relaxation curves of different structures changing with tempering and holding time, and perform normalization processing. The shortest time when the maximum value of the normalized stress value is ≤30% and the change rate is <1% is recorded as t3.

[0035] Preferably, in step S41 ′, the different structures include martensite, bainite and pearlite.

[0036] It should be noted that the roller body surface mentioned in the present invention refers to the position of the martensite structure, the subsurface refers to the position of the bainite structure below the hardened layer, and the core refers to the position of the pearlite structure.

[0037] The technical solution of the present invention is further explained below in conjunction with specific embodiments.

[0038] Example 1 A method for optimizing the tempering holding time of a backup roll forging during a quenching and tempering process based on a finite element model comprises the following steps: Step S1: testing the structure, thermophysical parameters and structure transformation parameters of the support roller during the quenching and tempering heat treatment process, establishing a finite element model of the support roller during the quenching and tempering process, and performing temperature-structure coupling simulation, wherein the finite element model is a quenching-tempering insulation model of the support roller; Step S2: extract the temperature curve of the roller body and soul changing with time during the tempering process according to the temperature-structure coupling simulation, and compare it with the tempering process to obtain the holding time when the temperature of the roller body and soul is 5°C lower than the holding temperature of the tempering process. When the holding temperature of the tempering process is 600°C and the temperature of the roller body and soul is 595°C, it is recorded as t1=27h; Step S31: According to the finite element model established in step S1, the temperature curves of the roller surface, sub-surface and core position during the tempering process of the support roller are respectively extracted, such as Figure 2 As shown; Step S32: using the experimental sample to perform a quenching and tempering heat treatment experiment according to the temperature curve obtained in step S31, and taking samples at different stages of tempering and heat preservation to perform a HV10 hardness test; Step S33: Draw the hardness curves of the roller surface, sub-surface and core respectively as the tempering and holding time changes, such as Figure 3 As shown, normalization is performed, such as Figure 4 As shown, the shortest time for which the normalized hardness changes with tempering and holding time is less than 1% is obtained, which is recorded as t2. Experimental tests show that after t2≥10h, the hardness basically tends to be stable, and the change rate is less than 1%, then t2=10h.

[0039] Step S4: According to the temperature curve obtained in step S31, the cooling rate of the experimental sample is controlled to obtain the roller surface (martensite), subsurface (bainite) and core (pearlite) structures of the support roller in actual production, and the stress relaxation curves of the martensite, bainite and pearlite structures under different load conditions are drawn respectively, wherein stress relaxation experiments are carried out on different structures under different loads, the time of the stress relaxation experiment is the tempering and holding time of the support roller before the optimization process (or the end of the experiment when the stress is lower than 20MPa), the stress relaxation load is lower than the yield strength of the structure at the experimental temperature, and the stress relaxation curves of pearlite and pearlite after normalization are as follows: Figure 5 and 6 As shown in Figure 2, the stress relaxation curves of bainite and bainite after normalization are as follows: Figure 7 and 8 As shown in the figure, the stress relaxation curves of martensite and normalized martensite are as follows: Fig. 9 and 10 As shown, the maximum value of the normalized stress relaxation curve is not higher than 30% and the change rate is less than 1%, which is the shortest tempering holding time. The shortest tempering holding times of the pearlite, bainite and martensite structures are respectively recorded as t31, t32 and t33. When t31=12.9h, t32=4.2h and t33=3.6h, the maximum value of t31, t32 and t33 is recorded as t3=12.9h. Step S5: The optimized tempering and holding time of the support roller is recorded as t, t=t1+max(t2, t3)=27h+max(10h, 12.9h)=39.9h.

[0040] After the implementation of this embodiment, according to "GB / T 13313-2008 Roller Shore and Leeb Hardness Test Method" and "GB / T7704-2017 Nondestructive Testing X-ray Stress Measurement Method", the roller body hardness of the product surface is measured to be 68~72Hs, and the surface residual stress measured by X-ray method is -450~-500MPa, which meets the technical requirements.

[0041] Example 2 A method for optimizing the tempering holding time of a backup roll forging during a quenching and tempering process based on a finite element model is the same as that of Example 1, except that: Steps S31, S32, and S33 are steps S31', S32', and S33', respectively, and are specifically as follows: Step S31': According to the CCT curve, the cooling rate of the experimental sample is controlled to obtain different structures contained in the support roller in actual production, and the different structures include martensite, bainite and pearlite; Step S32': performing heat treatment experiments with different tempering and heat preservation times for different structures obtained in step S31', and taking samples at different stages of tempering and heat preservation to perform hardness tests; Step S33': respectively plotting hardness curves of different structures changing with tempering and holding time, and performing normalization processing to obtain the shortest time when the change rate of normalized hardness with tempering and holding time is less than 10%, recorded as t2 = 11h.

[0042] Steps S41, S42, and S43 are steps S41', S42', and S43', respectively, and are specifically as follows: Step S41': According to the CCT curve, the cooling rate of the experimental sample is controlled to obtain different structures obtained in the actual production of the support roller, and the different structures include martensite, bainite and pearlite; Step S42': performing stress relaxation experiments at tempering and holding temperature on the different structures obtained in step S41'; Step S43': respectively draw stress relaxation curves of different structures changing with tempering and holding time, and perform normalization processing. The maximum value of the normalized stress value not higher than 30% and the change rate less than 1% is the shortest time, recorded as t3 = 13.5h.

[0043] The tempering and holding time of the optimized support roller in this embodiment is recorded as t, t=t1+max(t2, t3)=27h+max(11h, 13.5h)=40.5h.

[0044] After the implementation of this embodiment, according to "GB / T 13313-2008 Roller Shore and Leeb Hardness Test Method" and "GB / T7704-2017 Nondestructive Testing X-ray Stress Measurement Method", the roller body hardness of the product surface is measured to be 66~70Hs, and the surface residual stress measured by X-ray method is -400~-480MPa, which meets the technical requirements.

[0045] The tempering time of the support rollers in Examples 1 and 2 is 60 hours based on experience, supplemented by partial physical experiments and simulation calculations, while the tempering time of Example 1 is 39.9 hours and the tempering time of Example 2 is 40.5 hours, both of which are significantly shorter than the traditional method.

[0046] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for optimizing the tempering holding time of a backup roll forging during a quenching and tempering process based on a finite element model, characterized in that: The steps include: Step S1: testing the thermophysical parameters and structural transformation parameters of various structures involved in the heat treatment process of the support roller, establishing a finite element model of the heat treatment process of the support roller, and performing temperature-structure coupling simulation; Step S2: According to the temperature-structure coupling simulation results, the temperature curve of the roller body changing with time during the tempering process is extracted and compared with the tempering process to obtain the holding time when the temperature of the roller body is 5°C lower than the holding temperature of the tempering process, which is recorded as t1; Step S3: respectively plotting hardness curves of the support roller surface, sub-surface and core position as a function of tempering and holding time, and performing normalization processing to obtain the shortest tempering and holding time for stable hardness, recorded as t2; Step S4: respectively draw stress relaxation curves of martensite, bainite and pearlite structures under different load conditions during the quenching and tempering heat treatment of the support roller, and perform normalization processing to obtain the shortest tempering and holding time for the residual stress stability of the martensite, bainite and pearlite structures, which are respectively recorded as t31, t32 and t33, and the maximum value among t31, t32 and t33 is recorded as t3; Step S5: The optimized tempering and holding time of the support roller is recorded as t, t=t1+max(t2, t3).

2. The method for optimizing the tempering holding time of the backup roll forging during the quenching and tempering process based on the finite element model according to claim 1, characterized in that: In step S1, the structure includes martensite, bainite, pearlite, tempered martensite, and bainite tempered structure. The thermophysical parameters include density, specific heat, and thermal conductivity. The structure transformation parameters refer to the parameters involved in each structure transformation model.

3. A method for optimizing the tempering holding time of a backup roll forging during quenching and tempering based on a finite element model according to claim 1 or 2, characterized in that: In step S1, the finite element model is a support roller quenching-tempering model.

4. The method for optimizing the tempering holding time of the backup roll forging during the quenching and tempering process based on the finite element model according to claim 1, characterized in that: In step S3, the shortest tempering and holding time for stable hardness is the shortest time for which the rate of change of normalized hardness with tempering and holding time is less than 1%.

5. The method for optimizing the tempering holding time of the backup roll forging during the quenching and tempering process based on the finite element model according to claim 1, characterized in that: Step S3 specifically includes: Step S31: according to the finite element model established in step S1, respectively extracting the temperature curves of the roller surface, sub-surface and core position during the tempering process of the backup roller; Step S32: using the experimental sample to perform a quenching and tempering heat treatment experiment according to the temperature curve obtained in step S31, and taking samples at different stages of tempering and heat preservation to perform hardness testing; Step S33: respectively plotting the hardness curves of the roller body surface, sub-surface and core as the tempering and holding time changes, and performing normalization processing to obtain the shortest time when the normalized hardness changes with the tempering and holding time less than 1%, recorded as t2.

6. The method for optimizing the tempering holding time of the backup roll forging during the quenching and tempering process based on the finite element model according to claim 5, characterized in that: Step S4 specifically includes: Step S41: extracting the temperature curves of the roller surface, sub-surface and core during the tempering process of the backup roller according to the finite element model established in step S1; Step S42: using the experimental sample to perform a quenching and tempering heat treatment experiment according to the temperature curve obtained in step S41, and taking samples before the start of tempering and heat preservation, and then performing a stress relaxation experiment; Step S43: respectively draw stress relaxation curves of the roller body surface, sub-surface and core as the tempering holding time changes at different stress levels, perform normalization processing, and obtain the maximum value of the normalized stress value ≤30% and the change rate <1% as the shortest time, recorded as t3.

7. The method for optimizing the tempering holding time of the backup roll forging during the quenching and tempering process based on the finite element model according to claim 1, characterized in that: Step S3 specifically includes: Step S31': According to the CCT curve, the cooling rate of the experimental sample is controlled to obtain different structures contained in the support roller in actual production; Step S32': performing heat treatment experiments with different tempering and heat preservation times on the different structures obtained in step S31', and taking samples at different stages of tempering and heat preservation to perform physical tests on hardness; Step S33': respectively plotting hardness curves of different structures changing with tempering and holding time, and performing normalization processing to obtain the shortest time when the change rate of normalized hardness with tempering and holding time is less than 1%, recorded as t2.

8. The method for optimizing the tempering holding time of the backup roll forging during the quenching and tempering process based on the finite element model according to claim 7, characterized in that: Different structures include martensite, bainite and pearlite.

9. A method for optimizing the tempering holding time of a backup roll forging during quenching and tempering based on a finite element model according to claim 7 or 8, characterized in that: Step S4 specifically includes: Step S41': According to the CCT curve, the cooling rate of the experimental sample is controlled to obtain different structures contained in the support in actual production; Step S42': performing stress relaxation experiments at tempering and holding temperature on the different structures obtained in step S41'; Step S43': respectively draw stress relaxation curves of different structures changing with tempering and holding time, and perform normalization processing. The maximum value of the normalized stress value ≤30% and the change rate <1% is the shortest time, recorded as t3.

10. The method for optimizing the tempering holding time of the backup roll forging during the quenching and tempering process based on the finite element model according to claim 9, characterized in that: Different structures include martensite, bainite and pearlite.

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