Calculation method for quenching deformation of 42CrMo forged piece

Abstract

The application discloses a kind of 42CrMo forge piece quenching deformation calculation methods, this calculation method is based on the cooling test result under three different cooling rates, obtain the thermal expansion rate with the change curve of temperature, after the sample after cooling under three rates is ground, polished, corroded and observed metallographic structure, the volume fraction of ferrite, pearlite, bainite and martensite is counted, and organization transformation model is established;Again using finite element software counteracts the phase change dynamics model parameters of 42CrMo steel and the thermal expansion rate curve of different organizations, to solve the technical problems that phase change expansion cannot be predicted in the process of 42CrMo forge piece quenching deformation calculation, improve the precision of forge piece quenching deformation calculation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of forging quenching technology, in particular to a 42CrMo forging quenching deformation calculation method. BACKGROUND

[0002] During quenching, due to the different cooling rates and different phase transformation at different positions of the forging, temperature stress and phase transformation stress will be caused, which will further cause the deformation of the forging and reduce the dimensional accuracy of the forging. Accurate prediction of the quenching deformation of the forging is the basis for quenching deformation control and reverse deformation compensation of the forging die. However, due to the imperfect establishment of the quenching analysis model, the quenching deformation calculation accuracy is not high.

[0003] When steel cools, it will transform from austenite to ferrite, pearlite, bainite or martensite structure. The thermal expansion rates of different structures are different, and the structures obtained at different cooling rates are also different. The main difficulty in quenching deformation calculation lies in predicting the content of each room temperature structure of the steel at different cooling rates and determining the thermal expansion of different structures, and establishing an accurate model.

[0004] In the process of realizing the present application, the inventors have found that, in terms of quenching deformation calculation,

[0005] The patent document with application number 202410361339 proposes a method for calculating the deformation amount of a ring-shaped workpiece during induction quenching. The deformation amount is obtained according to the shape before and after quenching, but this patent does not involve the calculation of different structures.

[0006] The patent document with application number 202410738277 proposes a method and system for calculating the deformation of a gear during carburizing and quenching. The plastic strain increment and quenching deformation of the gear are calculated based on the TTT curve, the first volume fraction and the second volume fraction, but this patent does not provide the thermal expansion rate of different structures.

[0007] Gan Yong et al. (Gan Yong. China Materials Engineering Encyclopedia, Volume 3: Steel Materials Engineering (Lower), Chemical Industry Press, 2006.) provided the linear expansion coefficient of 42CrMo in Table 13.2-165 of their book, but also did not provide the thermal expansion rate of different structures.

[0008] Yuan Jingzhi (Yuan Jingzhi, Numerical Simulation and Process Optimization of Quenching Process of 42CrMo Large Forgings. Shandong University, 2020.) provided the thermal expansion coefficients of different structures in his thesis Figure 3-1 ; Pan Weiping (Pan Weiping, Numerical Simulation and Experimental Verification of Heat Treatment Process of Shaft Forgings. Shandong University, 2018.) also provided the linear expansion coefficients of different structures in Table 4-1 of his thesis, but the 42CrMo thermal expansion rate curve obtained by using the above two groups of data to calculate the thermal expansion rate of 42CrMo at a certain cooling rate over time is shown in Figure 1 .Figure 1 It can be seen that the actual thermal expansion rate curve will rise to a certain extent at 120-140 s; while using the data in the above two papers to calculate, the calculated 42CrMo expansion rate curve does not observe the rise of the expansion rate;

[0009] Xue Yanjun's paper (Xue Yanjun. Research on Low Pressure Carburizing Structure, Fatigue Performance and Quenching Deformation of Heavy-Duty Gear Steel, General Research Institute of Steel, 2024.) mentions that the rise of thermal expansion rate of steel during cooling is caused by phase transformation, from Figure 1 It can also be seen that the total shrinkage rate during cooling is about 1.0%, but the phase transformation expansion is about 0.24%, accounting for 24% of the total shrinkage, and if the phase transformation expansion of the steel during cooling is ignored, it will obviously cause a larger deviation. SUMMARY

[0010] In order to solve the problems existing in the prior art, the present application proposes a 42CrMo forged piece quenching deformation calculation method.

[0011] Invention concept: based on the cooling test results of three groups of different cooling rates, the phase transformation kinetics model parameters and the thermal expansion rate curves of different organizations of 42CrMo steel are calculated by using finite element software, so as to solve the technical problem that the phase transformation expansion cannot be predicted in the calculation process of 42CrMo forged piece quenching deformation, and improve the calculation precision of forged piece quenching deformation.

[0012] Therefore, the technical scheme of the present application is: a 42CrMo forged piece quenching deformation calculation method, the specific method is:

[0013] S1. Process a round bar with a diameter of 6 mm and a length of 98 mm, drill a hole in the middle of the sample and weld a thermocouple, heat to 850℃, then cool the sample at cooling rates of -1 ℃ / s, -10 ℃ / s and -53 ℃ / s, respectively, the room temperature structure of the cooled 42CrMo is ferrite and pearlite, bainite and martensite, respectively, use a thermal dilatometer to measure the change of the diameter of the sample at the welded thermocouple, and obtain the thermal expansion rate curve with temperature;

[0014] S2. Grind, polish and etch the samples cooled at three rates, and then observe the metallographic structure, count the volume fraction of ferrite, pearlite, bainite and martensite, and establish an organization transformation model;

[0015] The Leblond phase transformation model is used to represent the percentage of phase transformation, and the phase transformation model parameters of the transformation of austenite to ferrite, pearlite and bainite are valued; the percentage of austenite to martensite transformation is described by the Koistinen-Marburger model, the martensite transformation starting temperature is 310 DEG C, and the Koistinen-Marburger coefficient is 0.12 / K, K is the Kelvin temperature;

[0016] S3. According to the thermal expansion rate curves obtained at three rates, the thermal expansion rate curves of different organizations of 42CrMo steel are calculated by using finite element software; in S1, the thermal expansion rates of ferrite, pearlite, bainite and martensite are adjusted at three cooling rates, so that the calculated thermal expansion rate curves are consistent with the actual curves; that is, the thermal expansion rate curves of ferrite / pearlite, bainite and martensite at three cooling rates are obtained;

[0017] S4. The thermal expansion rates at different cooling rates are further unified to calculate the phase transformation expansion at different cooling rates:

[0018] When the cooling rate is-1 ℃ / s, the proportions of bainite, martensite and ferrite / pearlite are B1, M1 and P1 respectively, and the calibrated expansion rates of bainite, martensite and ferrite / pearlite under this condition are EB1, EM1 and EP1 respectively, and the comprehensive expansion rate E1 is:

[0019] E1=B1·EB1+M1·EM1+P1·EP1 (Formula 1)

[0020] When the cooling rate is-10 ℃ / s, the proportions of bainite, martensite and ferrite / pearlite are B2, M2 and P2 respectively, and the calibrated expansion rates of bainite, martensite and ferrite / pearlite under this condition are EB2, EM2 and EP2 respectively, and the comprehensive expansion rate E2 is:

[0021] E2=B2·EB2+M2·EM2+P2·EP2 (Formula 2)

[0022] When the cooling rate is-53 ℃ / s quenching cooling, the proportions of bainite, martensite and ferrite / pearlite are B3, M3 and P3 respectively, and the calibrated expansion rates of bainite, martensite and ferrite / pearlite under this condition are EB3, EM3 and EP3 respectively, and the comprehensive expansion rate E3 is:

[0023] E3=B3·EB3+M3·EM3+P3·EP3 (Formula 3)

[0024] After E1, E2, E3 are obtained in formula 1-formula 3, let EB, EM, EP be the thermal expansion rates of the unified bainite, martensite and ferrite / pearlite respectively, then there are:

[0025] E1=B1·EB+M1·EM+P1·EP (Formula 4)

[0026] E2=B2·EB+M2·EM+P2·EP (Formula 5)

[0027] E3=B3·EB+M3·EM+P3·EP (Formula 6)

[0028] In formula 4-formula 6, EB, EM, EP are unknown numbers, which can be solved by formula 4-formula 6 to obtain EB, EM, EP; 50 temperature points are taken in the range of 20-850 DEG C, and the thermal expansion rates of bainite, martensite and ferrite / pearlite at different temperatures are calculated, so that the curves of EB, EM, EP changing with temperature at several temperatures can be obtained.

[0029] Through comparison of the thermal expansion rate curves of the sample calculated at three cooling rates and the thermal expansion rate curves actually measured, it is found that the phase change expansion in the quenching deformation process of the 42CrMo round bar is accurately predicted, and the average deviation is 3.8%.

[0030] Beneficial effects: Compared with the prior art, the quenching deformation calculation method of the 42CrMo forging of the present application can accurately predict the phase change expansion of 42CrMo during cooling, can adapt to various cooling rates, and has high precision in calculating the quenching deformation of the forging. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 It is the curve of the thermal expansion rate of 42CrMo changing with time in the actual certain rate cooling process calculated in the technical background of the present application.

[0032] Figure 2 It is the thermal expansion rate curve of bainite of the present application.

[0033] Figure 3 It is the thermal expansion rate curve of martensite of the present application.

[0034] Figure 4 It is the thermal expansion rate curve of pearlite of the present application.

[0035] Figure 5 It is the comparison of the thermal expansion rate curves of the sample calculated at three cooling rates and the thermal expansion rate curves actually measured. DETAILED DESCRIPTION

[0036] The technical solutions of the present application will be described clearly and completely in combination with the drawings, but the embodiments should not be understood as a limitation of the present application.

[0037] The specific application of the present application is described below in combination with the example of quenching deformation calculation of 42CrMo round bar, and the specific implementation method is as follows:

[0038] S1. Process the round bar with a diameter of 6 mm and a length of 98 mm, punch and weld a thermocouple in the middle of the sample, heat to 850℃, and then cool the sample at cooling rates of -1 ℃ / s, -10 ℃ / s and -53 ℃ / s respectively, the room temperature microstructure of the 42CrMo after cooling is ferrite and pearlite, bainite and martensite respectively, use a thermal dilatometer to measure the change of the diameter of the sample at the welded thermocouple, and obtain the curve of thermal expansion rate versus temperature;

[0039] S2. After grinding, polishing and etching, observe the metallographic structure of the samples cooled at the three rates, count the volume fraction of ferrite, pearlite, bainite and martensite, and establish a microstructure transformation model; the specific scheme is referred to in the following reference: Deng Q W, Chen R C, Lv G J, et al. Quenching microstructure transformation of high-strength steel automobile steering knuckle. Transactions of Materials and Heat Treatment, 2024, 45(4): 197-206.

[0040] The percentage of phase transformation is represented by the Leblond phase transformation model, and the phase transformation model parameters of the transformation of austenite to ferrite, pearlite and bainite are shown in Tables 1-3, respectively, and K and L in the table are model coefficients, which are functions of temperature, with a unit of 1 / s; the percentage of austenite to martensite transformation is described by the Koistinen-Marburger model, the martensite transformation starting temperature is 310℃, and the Koistinen-Marburger coefficient is 0.12 / K, and / K is the Kelvin temperature;

[0041] Table 1 Phase transformation model parameters of austenite to ferrite

[0042]

[0043] Table 2 Phase transformation model parameters of austenite to pearlite

[0044]

[0045] Table 3 Phase transformation model parameters of austenite to bainite

[0046]

[0047] S3. According to the curves of thermal expansion rate versus temperature obtained at the three rates, use finite element software to inversely calculate the thermal expansion rate curves of different microstructures of 42CrMo steel;

[0048] Take -53 ℃ / s as an example, the thermal expansion rates of martensite and bainite are adjusted to make Figure 1 The calculated thermal expansion rate curve is consistent with the actual curve, so in S1, the thermal expansion rates of ferrite, pearlite, bainite and martensite are adjusted respectively under three cooling rates to make the calculated thermal expansion rate curve consistent with the actual curve; the thermal expansion rates of ferrite and pearlite are set to be the same, i.e. the thermal expansion rate curves of ferrite, pearlite, bainite and martensite under three cooling rates are obtained;

[0049] S4. Further unify the thermal expansion rates under different cooling rates to calculate the phase transition expansion under different cooling rates:

[0050] When cooling at a cooling rate of -1 ℃ / s, the proportions of bainite, martensite and ferrite+pearlite are B1, M1 and P1 respectively, the calibrated expansion rates of bainite, martensite and ferrite+pearlite under this condition are EB1, EM1 and EP1 respectively, and the comprehensive expansion rate E1 is:

[0051] E1=B1·EB1+M1·EM1+P1·EP1 (Formula 1)

[0052] When cooling at a cooling rate of -10 ℃ / s, the proportions of bainite, martensite and ferrite+pearlite are B2, M2 and P2 respectively, the calibrated expansion rates of bainite, martensite and ferrite+pearlite under this condition are EB2, EM2 and EP2 respectively, and the comprehensive expansion rate E2 is:

[0053] E2=B2·EB2+M2·EM2+P2·EP2 (Formula 2)

[0054] When quenching cooling at a cooling rate of -53 ℃ / s, the proportions of bainite, martensite and ferrite+pearlite are B3, M3 and P3 respectively, the calibrated expansion rates of bainite, martensite and ferrite+pearlite under this condition are EB3, EM3 and EP3 respectively, and the comprehensive expansion rate E3 is:

[0055] E3=B3·EB3+M3·EM3+P3·EP3 (Formula 3)

[0056] After obtaining E1, E2 and E3 according to Formula 1-Formula 3, let EB, EM and EP be the unified thermal expansion rates of bainite, martensite and ferrite+pearlite respectively, then:

[0057] E1=B1·EB+M1·EM+P1·EP (Formula 4)

[0058] E2=B2·EB+M2·EM+P2·EP (Formula 5)

[0059] E3 = B3 EB + M3 EM + P3 EP (Formula 6)

[0060] In the formulas 4-6, EB, EM, EP are unknown numbers, which can be solved by simultaneously solving the formulas 4-6; in the range of 20-850℃, 50 temperature points are taken, the thermal expansion rates of the bainite, martensite, ferrite / pearlite at different temperatures are calculated respectively, so that the curves of EB, EM, EP changing with temperature at several temperatures can be obtained, as shown in the formulas 7-9. Figure 2 、 Figure 3 、 Figure 4

[0061] By comparing the thermal expansion rate curves of the samples calculated at three cooling rates with the thermal expansion rate curves actually measured, as shown in the formulas 10-12, it can be seen from the formulas 13-15 that the phase transformation expansion in the quenching deformation process of the 42CrMo round bar is accurately predicted, and the average deviation is 3.8%. Figure 5 Figure 5

[0062] The details not described in the specification are the known technology in the art.

[0063] Through the description of the above processing method, those skilled in the art should understand that the present application is not limited to the above specific embodiments, and the improvements and substitutions of the known technology in the art based on the present application all fall within the protection scope of the present application, which should be limited by the claims.​​​

Claims

The calculation method for quenching deformation of 1.42CrMo forgings is as follows: S1. A round bar with a diameter of 6 mm and a length of 98 mm was machined. A hole was drilled in the middle of the sample and a thermocouple was welded on. The sample was heated to 850℃ and then cooled at quenching rates of -1℃ / s, -10℃ / s, and -53℃ / s, respectively. The room temperature microstructure of 42CrMo after cooling was ferrite and pearlite, bainite, and martensite, respectively. The change in diameter at the point where the thermocouple was welded on the sample was measured using a thermal expansion meter to obtain the curve of thermal expansion coefficient as a function of temperature. S2. After grinding, polishing, and etching the samples cooled at three different rates, observe the metallographic structure, count the volume fractions of ferrite, pearlite, bainite, and martensite, and establish a microstructure transformation model. The Leblond phase transformation model was used to represent the percentage of phase transformation, and the phase transformation model parameters for the transformation of austenite to ferrite, pearlite, and bainite were set. The percentage of austenite to martensite transformation was described using the Koistinen-Marburger model, with the martensite transformation initiation temperature at 310℃ and the Koistinen-Marburger coefficient at 0.12 / K, where / K is the Kelvin temperature. S3. Based on the thermal expansion coefficient versus temperature curves obtained at the three cooling rates, the thermal expansion coefficient curves of different microstructures of 42CrMo steel were calculated using finite element software. At the three cooling rates in S1, the thermal expansion coefficients of ferrite, pearlite, bainite, and martensite were adjusted respectively to make the calculated thermal expansion coefficient curves fit the actual curves. The thermal expansion coefficients of ferrite and pearlite were set to be the same, thus obtaining the thermal expansion coefficient curves of ferrite / pearlite, bainite, and martensite at the three cooling rates. S4. Further standardize the thermal expansion coefficients under different cooling rates to calculate phase change expansion under different cooling rates: When cooling is performed at a cooling rate of -1 ℃ / s, the proportions of bainite, martensite, and ferrite / pearlite are B1, M1, and P1, respectively. Under these conditions, the calibrated expansion rates of bainite, martensite, and ferrite / pearlite are EB1, EM1, and EP1, respectively. The overall expansion rate E1 is: E1=B1·EB1+M1·EM1+P1·EP1 (Formula 1) When cooling is performed at a cooling rate of -10 ℃ / s, the ratios of bainite, martensite, and ferrite / pearlite are B2, M2, and P2, respectively. Under these conditions, the calibrated expansion rates of bainite, martensite, and ferrite / pearlite are EB2, EM2, and EP2, respectively. The overall expansion rate E2 is: E2 = B2·EB2 + M2·EM2 + P2·EP2 (Formula 2) When quenching is performed at a cooling rate of -53 ℃ / s, the proportions of bainite, martensite, and ferrite / pearlite are B3, M3, and P3, respectively. Under these conditions, the calibrated expansion rates of bainite, martensite, and ferrite / pearlite are EB3, EM3, and EP3, respectively. The overall expansion rate E3 is: E3=B3·EB3+M3·EM3+P3·EP3 (Formula 3) After obtaining E1, E2, and E3 from Formulas 1-3, let EB, EM, and EP be the thermal expansion rates of the unified bainite, martensite, and ferrite / pearlite, respectively. Then we have: 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 Formulas 4-6, EB, EM, and EP are unknowns. EB, EM, and EP can be solved by simultaneously solving Formulas 4-6. By taking 50 temperature points within the range of 20-850℃ and calculating the thermal expansion rates of bainite, martensite, and ferrite / pearlite at different temperatures, the curves of EB, EM, and EP as a function of temperature at several temperatures can be obtained. By comparing the calculated thermal expansion coefficients of the samples under three cooling rates with the actual experimentally measured thermal expansion coefficient curves, it was found that the phase transformation expansion during the quenching and deformation process of 42CrMo round bars was accurately predicted, with an average deviation of 3.8%.

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