Prediction Method of Fatigue Strength of Gas Soft-Nitrided and Ion Nitrided Steels

Nitriding heat-treatment is often used to improve the fatigue strength of steel automobile parts. However, there is no established method for predicting fatigue strength. We thus conducted rotational bending fatigue experiments using different nitriding heat-treatment conditions, materials and notch shapes as variables, with the objective of establishing a means for predicting fatigue strength in nitriding heat-treated material. As a result, we have found that it is possible to predict the fatigue strength of nitriding heat-treated material using the √(area) Parameter Model fatigue-strength prediction formula for high-strength steel proposed, when consideration is given to post-nitriding heat-treatment hardness, residual stress, surface layers of nitriding compounds, inclusions and other factors.