A Simple Model for Hardness and Residual Stress Profiles Prediction for Low-Alloy Nitrided Steel, Based on Nitriding-Induced Tempering Effects

Nitriding of low-alloy steels is widely used for gears and bear- ings in aerospace industry. Some highly stressed surfaces re- quire high nitrided depth, which involves long time/high tem- perature nitriding treatment. This study focused on identifying process parameter effects on hardness and residual stress pro- files in a large range of nitriding time and temperature. We demonstrate that core and case can be considered as two ma- terials, softening of which can be predicted by two tempering laws. In addition, a basic relationship was derived from the nitriding depth and a pseudo-diffusion coefficient, allowing prediction of the hardness profile. Residual stress results show that the diffusion controlled effect can also be used to predict residual stress profile affected depth. Likewise, the tempering controlled effect can be used to predict surface and maximum values of the residual stress profile.