42CrMo forge piece quenching deformation calculation method

Abstract

The invention discloses a 42CrMo forge piece quenching deformation calculation method, which comprises the following steps: based on three groups of cooling test results at different cooling rates, obtaining a change curve of a thermal expansion coefficient along with temperature, grinding, polishing and corroding a sample cooled at the three rates, observing a metallographic structure, and calculating the quenching deformation of a 42CrMo forge piece. Counting the volume fractions of ferrite, pearlite, bainite and martensite, and establishing a structure transformation model; and then, finite element software is used for inversely calculating phase change kinetic model parameters of the 42CrMo steel and thermal expansion coefficient curves of different tissues, so that the technical problem that phase change expansion cannot be predicted in the quenching deformation calculation process of the 42CrMo forge piece is solved, and the quenching deformation calculation precision of the forge piece is improved.

Description

Technical Field

[0001] The invention relates to the technical field of forging quenching, and in particular to a method for calculating quenching deformation of a 42CrMo forging. Background Art

[0002] During the quenching process, the temperature and phase transformation at different locations of the forging are not synchronized, which will cause temperature stress and phase transformation stress, thereby causing deformation of the forging and reducing the dimensional accuracy of the forging. Accurately predicting the quenching deformation of forgings is the basis for quenching deformation regulation of forgings and reverse deformation compensation of forging dies. However, due to the incomplete establishment of the quenching analysis model, the calculation accuracy of quenching deformation is not high.

[0003] When steel is cooled, it transforms from austenite to ferrite, pearlite, bainite or martensite. Different structures have different thermal expansion rates, and different structures are obtained at different cooling rates. The main difficulty in quenching deformation calculation is to predict the content of each room temperature structure of steel at different cooling rates and determine the thermal expansion of different structures, and establish an accurate model.

[0004] In the process of realizing the present invention, the inventors: in the calculation of quenching deformation, Patent document No. 202410361339 proposes a method for calculating the deformation of rings during induction quenching, and obtains the quenching deformation based on the shapes before and after quenching, but the patent does not involve the calculation of different organizations; Patent document No. 202410738277 proposes a method and system for calculating gear carburizing and quenching deformation, which calculates the plastic strain increment and quenching deformation of the gear based on the TTT curve, the first volume fraction, and the second volume fraction. However, the patent does not provide the thermal expansion coefficients of different tissues. Gan Yong et al. (Gan Yong. China Materials Engineering Encyclopedia, Volume 3: Iron and Steel Materials Engineering (Part 2), Chemical Industry Press, 2006.) gave the linear expansion coefficient of 42CrMo in Table 13.2-165 of their book, but also did not provide the thermal expansion coefficient of different structures; Yuan Jingzhi (Yuan Jingzhi, Numerical simulation and process optimization of quenching process of 42CrMo large forgings. Shandong University, 2020.) Figure 3-1 The thermal expansion coefficients of different organizations are given in the paper; Pan Weiping (Pan Weiping, Numerical Simulation and Experimental Verification of Heat Treatment Process of Shaft Forgings. Shandong University, 2018.) also provides the linear expansion coefficients of different organizations in Table 4-1 of his paper, but the curve of the change of thermal expansion rate of 42CrMo with time during a certain rate of cooling calculated by the above two sets of data is as follows Figure 1 As shown, from Figure 1It can be seen that the actual thermal expansion rate curve will show a certain degree of increase at 120-140 s; however, when the data in the above two papers are used for calculation, the calculated 42CrMo expansion rate curve does not observe an increase in expansion rate; Xue Yanjun's paper (Xue Yanjun. Research on low-pressure carburizing structure, fatigue properties and quenching deformation of heavy-duty gear steel, Central Iron and Steel Research Institute, 2024.) mentioned that the increase in the thermal expansion rate of steel during cooling is caused by phase transformation. Figure 1 It can also be seen that the total shrinkage during cooling is about 1.0%, but the phase change expansion is about 0.24%, accounting for 24% of the total shrinkage. If the phase change expansion of steel during cooling is ignored, it will obviously lead to relatively large deviations. Summary of the invention

[0005] In order to solve the problems existing in the prior art, the present invention proposes a calculation method for quenching deformation of 42CrMo forgings.

[0006] Invention concept: Based on the cooling test results at three different cooling rates, finite element software is used to inversely calculate the phase transformation kinetic model parameters of 42CrMo steel and the thermal expansion coefficient curves of different structures, thereby solving the technical problem of being unable to predict the phase transformation expansion during the quenching deformation calculation process of 42CrMo forgings and improving the calculation accuracy of quenching deformation of forgings.

[0007] To this end, the technical solution of the present invention is: a method for calculating the quenching deformation of 42CrMo forgings, the specific method is: S1. Process a round bar with a diameter of 6 mm and a length of 98 mm, punch a hole in the middle of the sample and weld a thermocouple, heat it to 850℃, and then cool the sample at a cooling rate of -1℃ / s, -10℃ / s, and -53℃ / s. The room temperature microstructures of 42CrMo after cooling are ferrite and pearlite, bainite, and martensite, respectively. Use a thermal expansion instrument to measure the change in diameter of the sample where the thermocouple is welded, and obtain the curve of thermal expansion rate changing with temperature. S2. Grind, polish and corrode the samples after cooling at three cooling rates, observe the metallographic structure, calculate the volume fractions of ferrite, pearlite, bainite and martensite, and establish a microstructure transformation model; The Leblond phase transformation model is used to represent the percentage of phase transformation, and the phase transformation model parameters of austenite to ferrite, pearlite, and bainite are set. The percentage of austenite to martensite transformation is described by the Koistinen-Marburger model, the martensite transformation start temperature is 310℃, the Koistinen-Marburger coefficient is 0.12 / K, and K is the Kelvin temperature. S3. Based on the thermal expansion rate versus temperature curves obtained at three rates, the thermal expansion rate curves of different structures of 42CrMo steel were inversely calculated using finite element software; at the three cooling rates in S1, the thermal expansion rates of ferrite, pearlite, bainite, and martensite were adjusted respectively so that the calculated thermal expansion rate curves fit the actual curves; that is, the thermal expansion rate curves of ferrite / pearlite, bainite, and martensite at the three cooling rates were obtained; S4. The thermal expansion coefficients at different cooling rates are further unified to calculate the phase change expansion at different cooling rates: When the cooling rate is -1 ℃ / s, the ratios of bainite, martensite, and ferrite / pearlite are B1, M1, and P1, respectively. Under this condition, the calibrated expansion rates of bainite, martensite, and ferrite / pearlite are EB1, EM1, and EP1, respectively. The comprehensive expansion rate E1 is: E1=B1·EB1+M1·EM1+P1·EP1 (Formula 1) When the cooling rate is -10 ℃ / s, the ratios of bainite, martensite, and ferrite / pearlite are B2, M2, and P2, respectively. Under this condition, the calibrated expansion rates of bainite, martensite, and ferrite / pearlite are EB2, EM2, and EP2, respectively. The comprehensive expansion rate E2 is: E2=B2·EB2+M2·EM2+P2·EP2 (Formula 2) When the cooling rate is -53 ℃ / s, the ratios of bainite, martensite, and ferrite / pearlite are B3, M3, and P3, respectively. Under this condition, the calibrated expansion rates of bainite, martensite, and ferrite / pearlite are EB3, EM3, and EP3, respectively. The comprehensive expansion rate E3 is: E3=B3·EB3+M3·EM3+P3·EP3 (Formula 3) After obtaining E1, E2, and E3 from Formula 1-Formula 3, let EB, EM, and EP be the unified thermal expansion coefficients of bainite, martensite, and ferrite / pearlite, respectively, then: E1=B1·EB+M1·EM+P1·EP (Formula 4) E2=B2·EB+M2·EM+P2·EP (Formula 5) E3=B3·EB+M3·EM+P3·EP (Formula 6) In formula 4-6, EB, EM, and EP are unknown variables, and EB, EM, and EP can be solved by combining formula 4-6; 50 temperature points are taken in the range of 20-850℃, and the thermal expansion coefficients of bainite, martensite, and ferrite / pearlite at different temperatures are calculated respectively, and the curves of EB, EM, and EP changing with temperature at several temperatures can be obtained; By comparing the thermal expansion coefficient curves of the samples calculated at three cooling rates with those obtained from actual experimental measurements, it was found that the phase change expansion of 42CrMo round bars during quenching deformation was accurately predicted with an average deviation of 3.8%.

[0008] Beneficial effects: Compared with the prior art, the 42CrMo forging quenching deformation calculation method of the present invention can accurately predict the phase change expansion of 42CrMo during cooling, can adapt to a variety of cooling rates, and can calculate the quenching deformation of the forging with high accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 It is a curve of the change of the thermal expansion rate of 42CrMo with time during the actual cooling process at a certain rate obtained by calculation in the technical background of the present invention.

[0010] Figure 2 This is the thermal expansion coefficient curve of bainite of the present invention.

[0011] Figure 3 It is the thermal expansion coefficient curve of the martensite of the present invention.

[0012] Figure 4 This is the thermal expansion coefficient curve of pearlite of the present invention.

[0013] Figure 5 The thermal expansion rate curves of the samples calculated at three cooling rates of the present invention are compared with the thermal expansion rate curves measured experimentally. DETAILED DESCRIPTION

[0014] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings, but this embodiment should not be understood as limiting the present invention.

[0015] The following describes the specific application of the present invention in conjunction with an example of quenching deformation calculation of a 42CrMo round bar, and the specific implementation method is as follows: S1. Process a round bar with a diameter of 6 mm and a length of 98 mm, punch a hole in the middle of the sample and weld a thermocouple, heat it to 850℃, and then cool the sample at a cooling rate of -1℃ / s, -10℃ / s, and -53℃ / s. The room temperature microstructures of 42CrMo after cooling are ferrite and pearlite, bainite, and martensite, respectively. Use a thermal expansion instrument to measure the change in diameter of the sample where the thermocouple is welded, and obtain the curve of thermal expansion rate changing with temperature. S2. Grind, polish and corrode the samples after cooling at three cooling rates, observe the metallographic structure, calculate the volume fractions of ferrite, pearlite, bainite and martensite, and establish a microstructure transformation model; for the specific scheme, refer to: Deng Qingwen, Chen Rongchuang, Lv Jiajun, et al. Microstructure transformation of high-strength steel automobile steering knuckle during quenching. Journal of Materials Heat Treatment, 2024, 45(4): 197-206. The Leblond phase transformation model is used to represent the percentage of phase transformation. The phase transformation model parameter values ​​of austenite to ferrite, pearlite, and bainite are shown in Tables 1 to 3, respectively. K and L in the table are model coefficients, which are functions of temperature and are in units of 1 / s. The percentage of austenite to martensite transformation is described using the Koistinen-Marburger model. The martensite transformation start temperature is 310°C, and the Koistinen-Marburger coefficient is 0.12 / K, where / K is the Kelvin temperature. Table 1 Parameters of the phase transformation model from austenite to ferrite Table 2 Parameters of the phase transformation model from austenite to pearlite Table 3 Parameters of the phase transformation model from austenite to bainite S3. Based on the thermal expansion rate versus temperature curves obtained at three rates, the thermal expansion rate curves of different structures of 42CrMo steel were back-calculated using finite element software; Taking -53 ℃ / s as an example, by adjusting the thermal expansion rate of martensite and bainite Figure 1 The thermal expansion coefficient curve calculated in S1 is consistent with the actual curve. In this way, the thermal expansion coefficients of ferrite, pearlite, bainite and martensite are adjusted respectively at the three cooling rates in S1, so that the thermal expansion coefficient curves calculated are consistent with the actual curves. The thermal expansion coefficients of ferrite and pearlite are set to be the same, that is, the thermal expansion coefficient curves of ferrite, pearlite, bainite and martensite at the three cooling rates are obtained. S4. The thermal expansion coefficients at different cooling rates are further unified to calculate the phase change expansion at different cooling rates: When the cooling rate is -1 ℃ / s, the proportions of bainite, martensite, ferrite + pearlite are B1, M1, and P1 respectively. Under this condition, the calibrated expansion rates of bainite, martensite, ferrite + pearlite are EB1, EM1, and EP1 respectively, and the comprehensive expansion rate E1 is: E1=B1·EB1+M1·EM1+P1·EP1 (Formula 1) When the cooling rate is -10 ℃ / s, the ratios of bainite, martensite, ferrite + pearlite are B2, M2, and P2 respectively. Under this condition, the calibrated expansion rates of bainite, martensite, ferrite + pearlite are EB2, EM2, and EP2 respectively, and the comprehensive expansion rate E2 is: E2=B2·EB2+M2·EM2+P2·EP2 (Formula 2) When the cooling rate is -53 ℃ / s, the proportions of bainite, martensite, ferrite + pearlite are B3, M3, and P3 respectively. Under this condition, the calibrated expansion rates of bainite, martensite, ferrite + pearlite are EB3, EM3, and EP3 respectively, and the comprehensive expansion rate E3 is: E3=B3·EB3+M3·EM3+P3·EP3 (Formula 3) After obtaining E1, E2, and E3 from Formula 1-Formula 3, let EB, EM, and EP be the unified thermal expansion coefficients of bainite, martensite, and ferrite + pearlite, respectively, then: E1=B1·EB+M1·EM+P1·EP (Formula 4) E2=B2·EB+M2·EM+P2·EP (Formula 5) E3=B3·EB+M3·EM+P3·EP (Formula 6) In formula 4-6, EB, EM, and EP are unknown variables. EB, EM, and EP can be solved by combining formula 4-formula 6. Take 50 temperature points in the range of 20-850℃, calculate the thermal expansion coefficients of bainite, martensite, and ferrite / pearlite at different temperatures, and then you can get the curves of EB, EM, and EP changing with temperature at several temperatures, such as Figure 2 , Figure 3 , Figure 4 As shown; The thermal expansion rate curves of the samples calculated at three cooling rates are compared with those obtained from actual experimental measurements. Figure 5 shown; from Figure 5 It can be seen that the phase transformation expansion of 42CrMo round bar during quenching deformation is accurately predicted with an average deviation of 3.8%.

[0016] Parts not described in detail in this specification are well-known technologies in the art.

[0017] Through the description of the above processing method, technicians in the relevant technical field should understand that the present invention is not limited to the above-mentioned specific implementation methods. Improvements and substitutions using the well-known technology in the field on the basis of the present invention all fall within the protection scope of the present invention and should be defined by the claims.

Claims

1.42CrMo forging quenching deformation calculation method, the specific method is: S1. Process a round bar with a diameter of 6 mm and a length of 98 mm, punch a hole in the middle of the sample and weld a thermocouple, heat it to 850℃, and then cool the sample at a cooling rate of -1℃ / s, -10℃ / s, and -53℃ / s. The room temperature microstructures of 42CrMo after cooling are ferrite and pearlite, bainite, and martensite, respectively. Use a thermal expansion instrument to measure the change in diameter of the sample where the thermocouple is welded, and obtain the curve of thermal expansion coefficient changing with temperature. S2. Grind, polish and corrode the samples after cooling at three cooling rates, observe the metallographic structure, calculate the volume fractions of ferrite, pearlite, bainite and martensite, and establish a microstructure transformation model; The Leblond phase transformation model is used to represent the percentage of phase transformation, and the phase transformation model parameters of austenite to ferrite, pearlite, and bainite are respectively determined; the percentage of austenite to martensite transformation is described by the Koistinen-Marburger model, the martensite transformation start temperature is 310℃, the Koistinen-Marburger coefficient is 0.12 / K, and / K is the Kelvin temperature; S3. Based on the thermal expansion rate versus temperature curves obtained at three rates, the thermal expansion rate curves of different structures of 42CrMo steel were inversely calculated using finite element software; at the three cooling rates in S1, the thermal expansion rates of ferrite, pearlite, bainite, and martensite were adjusted respectively so that the calculated thermal expansion rate curves were consistent with the actual curves; the thermal expansion rates of ferrite and pearlite were set to be the same, that is, the thermal expansion rate curves of ferrite / pearlite, bainite, and martensite at three cooling rates were obtained; S4. The thermal expansion coefficients at different cooling rates are further unified to calculate the phase change expansion at different cooling rates: When the cooling rate is -1 ℃ / s, the ratios of bainite, martensite, and ferrite / pearlite are B1, M1, and P1, respectively. Under this condition, the calibrated expansion rates of bainite, martensite, and ferrite / pearlite are EB1, EM1, and EP1, respectively. The comprehensive expansion rate E1 is: E1=B1·EB1+M1·EM1+P1·EP1 (Formula 1) When the cooling rate is -10 ℃ / s, the ratios of bainite, martensite, and ferrite / pearlite are B2, M2, and P2, respectively. Under this condition, the calibrated expansion rates of bainite, martensite, and ferrite / pearlite are EB2, EM2, and EP2, respectively. The comprehensive expansion rate E2 is: E2=B2·EB2+M2·EM2+P2·EP2 (Formula 2) When the cooling rate is -53 ℃ / s, the ratios of bainite, martensite, and ferrite / pearlite are B3, M3, and P3, respectively. Under this condition, the calibrated expansion rates of bainite, martensite, and ferrite / pearlite are EB3, EM3, and EP3, respectively. The comprehensive expansion rate E3 is: E3=B3·EB3+M3·EM3+P3·EP3 (Formula 3) After obtaining E1, E2, and E3 from Formula 1-Formula 3, let EB, EM, and EP be the unified thermal expansion coefficients of bainite, martensite, and ferrite / pearlite, respectively, then: E1=B1·EB+M1·EM+P1·EP (Formula 4) E2=B2·EB+M2·EM+P2·EP (Formula 5) E3=B3·EB+M3·EM+P3·EP (Formula 6) In formula 4-formula 6, EB, EM, and EP are unknown variables, and EB, EM, and EP can be solved by combining formula 4-formula 6; Take 50 temperature points in the range of 20-850℃, calculate the thermal expansion coefficients of bainite, martensite, ferrite / pearlite at different temperatures, and then get the curves of EB, EM, EP changing with temperature at several temperatures; By comparing the thermal expansion coefficient curves of the samples calculated at three cooling rates with those obtained from actual experimental measurements, it was found that the phase change expansion of 42CrMo round bars during quenching deformation was accurately predicted with an average deviation of 3.8%.

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