Simulation Analysis on Martempering in Salt Bath Technology for Carburized Distortion Sample
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UCTION
IN the martempering in salt bath technology (MISBT), the austenitized iron and steel are immersed in the salt bath at a temperature above the martensite transformation temperature (Ms) for a suitable period of time and then cooled in air. The martensite transformation then proceeds at a slow rate in air. The MISBT is a salt bath-stepped quenching process, as shown in Figure 1. As can be seen from the figure, the specimen has a rapid cooling rate at the high-temperature region in the salt bath. This phenomenon reduces the possibility of nonmartensite transformation. Most martensite transformation occurs in air with a slow cooling rate. The transformation stress will be lower in the martensitic transformation region. Therefore, the MISBT can not only ensure the surface hardness and core toughness, but also it can reduce the distortion of the specimen. It is widely used in industry for locomotive and wind gears.
XIN WANG is with the Zhengzhou Research Institute of Mechanical Engineering CO., LTD., No. 10, Fengyang Street, Hightech Zone, Zhengzhou, 450000, P.R. China and also with the Mechanical Engineering College, Henan University of Engineering, No. 1, Xianghe Road, Xinzheng, 451191, P.R. China. Contact e-mail: [email protected] BAOKUI LI and MIN GU are with the Zhengzhou Research Institute of Mechanical Engineering CO., LTD. Manuscript submitted May 6, 2019. Article published online May 29, 2019 3758—VOLUME 50A, AUGUST 2019
The carburizing-quenching process has been a leading method of gear heat treatment. But because of the temperature, microstructure, and stress difference between the surface and the core, the distortion of the gear in the carburizing-quenching process has become a major defect and technical difficulty in the gear manufacturing process.[1] The control of gear distortion is a systematic project, and there are many influencing factors. The distortion performance of the gear material is an important factor, which plays a decisive role. At present, the C-shaped distortion sample was widely used for the distortion test of gear material in the world.[2] There are mainly the oil and salt bath in the quenching media of carburizing gears. By comparison with the oil-quenching process (OQP), the main difference of the MISBT is the salt-quenching process. There has been some research on the salt-quenching process. Dubal[3] analyzed the characteristics of salt-quenching and stated that the salt-quenching process had no vapor phase barrier in the initial stage of quenching. Quench defects can be easily changed by changing the temperature in the salt-quenching process, so the salt-quenching process could minimize distortion and was successfully applied to the processes such as austempering, martempering, and their numerous modifications in the manufacturing industry. Raygan et al.[4] used AISI 1045 steel as the material and compared the microstructure and surface properties between salt-quenching and oil-quenching. He found that 1045 steel had a fine microstructure and improved the surface properties after sal
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