Surface Characteristics and Distortion Analysis of the Case-Hardened Helical Gears: A Comparison of Different Case-Hardening Treatments

Abstract

In this study, the effect of different case-hardening treatments on microstructure, hardness distribution, surface roughness parameters, and dimensional changes was investigated for helical-toothed gears made of 16MnCr5 and 21NiCrMo2 steels. Gas carburizing, gas carburizing–double quenching, low-pressure carburizing, and plasma-nitriding treatments were performed as case-hardening processes. The surface characteristics and distortion analyses of the case-hardened helical gears were examined using an optical microscope, hardness tester, profilometer, and micrometer. In order to ensure adequate pitting and bending strength, the required minimum effective case depth and minimum total case depth values were provided by the performed case-hardening treatments. In the gears, the largest dimensional increase after the heat treatments occurred at the end of the gas carburizing due to the long treatment times at high processing temperatures. The surface roughness values obtained through all performed case-hardening treatments necessitated the finishing processes. © 2019, The Indian Institute of Metals - IIM.