The Design of Hardened Case and Carburizing Process of Subway Gear Based on Spalling Fatigue

It is very important to design the suitable hardened case and carburizing-quenching process for gears. The hardened case was often determined by empirical data or the module (m) and lacked quantitative analysis. The design method of hardened case and carburizing process on subway gear was proposed based on spalling fatigue strength in this study. The minimum hardened case without shallow and deep spalling was designed, and then the specific carburizing process was determined based on Fick’s second law and empirical equations, so that the contact fatigue strength of gears corresponds to the carburizing process. In comparison with experience, the hardened case was determined by m and number of teeth (z₁), the product of m and z₁ played a decisive role. Based on the hardness and contact fatigue test results, the design of the hardened case and specific carburizing process could meet the strength requirements, and when the contact stress increased, shallow or deep spalling appeared on the surface of the designed teeth. So it provided a quantitative analysis method of the carburizing process based on spalling fatigue.