Effect of Heat Treatment Process on Microstructure and Crystallography of 20CrMnTiH Spur Bevel Gear
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JMEPEG https://doi.org/10.1007/s11665-020-05169-y
Effect of Heat Treatment Process on Microstructure and Crystallography of 20CrMnTiH Spur Bevel Gear Xuan Hu, Lin Hua, Xinghui Han, and Wuhao Zhuang (Submitted August 7, 2020; in revised form September 9, 2020; Accepted: 21 September 2020) Obtaining excellent mechanical properties of spur bevel gear has been widely emphasized, owing to its indispensable effect on momentum. However, the conventional long-time and high-temperature heat treatment can cause microstructure coarsening, which dramatically decreases the mechanical properties. Since the normalizing process can significantly modulate the mechanical properties of spur bevel gears by adjusting their microstructure and crystallography behaviors, in the present study, the normalizing before or after carburizing heat treatment processes (NBCP and NACP, respectively) were proposed. The effect of heat treatment processes on the microstructure and crystallography of gear specimens was investigated. The results show that both NBAP and NACP had a strong effect on microstructure refinement and hardness improvement compared to the conventional process. NBCP raised the tendency for AlN precipitation, which could retard the microstructure coarsening during carburizing. Furthermore, NACP directly promoted the precipitation of globular Cr-rich M3C carbides which achieved the strongest pinning effect and brought about extremely fine microstructure. For crystallographic analysis, the 24 martensite variants in all gear specimens held Kurdjumov–Sachs orientation relationship to parent austenite. The orientations of martensite variants in gear specimens applying conventional process and NBCP were distributed regularly. However, the orientations of martensite variants in NACP gear specimen did not follow the strict rule for variant selection inside prior austenite grains owing to the distortive effect of diffuse M3C carbides on the matrix, and the adjacent martensite variants possessed less sharing of {110} habit plane compared to NBCP and conventional process. Keywords
20CrMnTiH steel, crystallography, heat treatment, microhardness, microstructure refinement, spur bevel gear
1. Introduction The spur bevel gear has been extensively utilized in automotive industries for its efficient momentum transfer function (Ref 1-3). To effectively enhance the mechanical properties of spur bevel gear, carburizing heat treatment has been widely applied in industrial production for decades (Ref 4, 5). The high-hardness superficial layer forms during the subsequent quenching, thus lead to the increasing of gear performance (Ref 5-7). However, due to the long-time and high-temperature heating process of conventional carburizing heat treatment, excessive and uncontrolled microstructure coarsening has been greatly facilitated in the spur bevel gears Xuan Hu, School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China; Hubei Key Laboratory of Advanced Technology for Automotive Components, Wuhan University of Technology,
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