Fatigue behaviour and fracture mechanism of a 316 stainless steel hardened by carburizing

Fatigue behaviour and fracture mechanism of a carburized 316 stainless steel were studied under rotary bending in laboratory air and in 3% NaCl aqueous solution using materials with two different case depths. In laboratory air, the carburized materials showed considerably higher fatigue strength compared with the untreated material, and the fatigue lives of the material with thick case were longer than those of the material with thin case, but the fatigue limits were the same, which increased by 30% with respect to the fatigue limit of the untreated material. In 3% NaCl aqueous solution, the carburized materials exhibited no reduction in fatigue strength, indicating the excellent corrosion resistance of the carburized case. Regardless of environment and stress level, fatigue cracks always initiated underneath the carburized case at a very early stage of fatigue life and subsequently grew predominantly into the core material. Small crack growth behaviour was also similar in both environments, thus the fracture mechanism of the carburized materials was unaffected by corrosive environment.