| ZHANG Zeyu,DENG Xiaohu,FAN Yuanyuan,WANG Huizhen,ZHOU Leyu,XU Yueming,JU Dongying.Multi-field Coupling Simulation Analysis of 20MnCrS5 Vacuum Low Pressure Carburizing and Gas Quenching[J],53(15):194-205 |
| Multi-field Coupling Simulation Analysis of 20MnCrS5 Vacuum Low Pressure Carburizing and Gas Quenching |
| Received:July 31, 2023 Revised:November 27, 2023 |
| View Full Text View/Add Comment Download reader |
| DOI：10.16490/j.cnki.issn.1001-3660.2024.15.018 |
| KeyWord:vacuum carburizing numerical simulation COSMAP carbon content hardness 20MnCrS5 gear steel |
| Author | Institution |
| ZHANG Zeyu |
School of Mechanical Engineering, Tianjin Vocational and Technical Normal University, Tianjin , China |
| DENG Xiaohu |
School of Mechanical Engineering, Tianjin Vocational and Technical Normal University, Tianjin , China |
| FAN Yuanyuan |
Ningbo Tian'an Group Co., Ltd., Zhejiang Ningbo , China |
| WANG Huizhen |
Beijing Institute of Mechanical and Electrical Engineering Co., Ltd., Beijing , China |
| ZHOU Leyu |
Beijing Institute of Mechanical and Electrical Engineering Co., Ltd., Beijing , China |
| XU Yueming |
Beijing Institute of Mechanical and Electrical Engineering Co., Ltd., Beijing , China |
| JU Dongying |
Saitama Institute of Technology, Fukaya 3, Japan |
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| Abstract: |
| Vacuum low-pressure carburizing stands as an advanced surface heat treatment technique, conferring strengthened casing with heightened fatigue resistance to transmission gears. In this study, a comprehensive approach, encompassing experimental research, computational simulations, and theoretical analysis were adopted to scrutinize the microstructural evolution within the vacuum low-pressure carburizing process of 20MnCrS5 gear steel. A multi-field coupling model, considering the synergistic effects of temperature, concentration, phase transformation, and stress, was introduced to simulate the vacuum carburizing process specific to 20MnCrS5 steel. The carbon diffusion model was used to incorporate the growth kinetics of carbide phases and compute concentration-dependent diffusion coefficients. The phase transformation behavior was characterized using the Johnson-Mehl-Avrami equation. Simulating the quenching process involved determining the heat convection coefficient based on an inverse analysis of cooling curves. Complex diffusion boundary conditions were implemented to depict alternating carburization and diffusion during industrial vacuum carburizing. Furthermore, diffusion boundary conditions were established to simulate the inherent alternating diffusion and strong carburization in vacuum carburizing. Corrections were applied to hardness calculation equations, and a simulation model was developed for the vacuum low-pressure carburizing process, followed by high-pressure gas quenching. It was recognized that three-dimensional models often demanded more nodes and elements, necessitating higher computing resources, a pragmatic approach was explored. In certain scenarios, a two-dimensional model was preferred to enhance computational efficiency. Two finite element models were constructed:one in two-dimensional axisymmetric geometry and the other in three-dimensional solid geometry. These models simulated the vacuum carburizing process for cylindrical rod samples (ϕ15 mm×100 mm) under varying process parameters. Results demonstrated that the two-dimensional axisymmetric model and the three-dimensional solid model exhibited comparable computational accuracy, offering practical alternatives while significantly improving computational efficiency. The simulation results, especially the simulated carbon distribution, closely aligned with experimental data under varying process parameters, affirming the utility of the refined model and equations. This study delved into carbon concentration, microstructural evolution, and performance patterns under different process conditions, offering crucial insights. Key findings included the minimal impact of pulse interval on carburization, increased carburized layer depth and a more uniform carbon concentration distribution under longer diffusion times and moderately strong carburization conditions, and heightened non-martensitic phase formation after quenching at elevated carburization temperatures, resulting in a greater hardened layer depth. Optimal vacuum carburizing for 20MnCrS5 alloy, satisfying bending fatigue strength requirements for heavy-duty gears, was determined as 930 ℃ for 42 min and diffusion for 140 min for vacuum carburizing based on experimental optimization. The model was subsequently applied to simulate the vacuum carburizing process of a standard gear specimen following the German FZG (Forschungsstelle für Zahnräder und Getriebebau) standard. Results accurately depicted carbon concentration distribution at various gear positions, providing additional validation of the model's accuracy. This study elucidates the microstructural evolution in the vacuum low-pressure carburizing process of 20MnCrS5 gear steel, offering valuable insights for advancing vacuum carburizing processes for intricate components. Furthermore, it contributes fresh insights into the composition-microstructure-property relationship in the vacuum carburizing process through an integrated theoretical and experimental approach. The model serves as a guide for the customized heat treatment of alloy steel gears, considering vacuum carburizing techniques for optimal mechanical performance. |
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