Initiation and Propagation Behavior of a Fatigue Crack of Maraging Steel in High Humidity

The effect of humidity on the fatigue properties of 18% Ni maraging steels with different hardness and aging structure was investigated under rotating bending fatigue by varying relatively humidity from 25% to 95%. It was found that the initiation and the early propagation of a fatigue crack were accelerated in high humidity, which caused to a large decrease in fatigue strength of the alloys. In fact, the fatigue strength at 10 7 cycles obtained in RH 85% was less than a half of that in RH25%. Meanwhile, successive observation on surface fatigue progress and the fractographic analysis of fractured specimens elucidated that anodic dissolution was the main reason for promoting crack initiation whilst hydrogen embrittlement due to cathode reaction was responsible for the acceleration of crack propagation. However, the acceleration of crack propagation was suppressed by the formation of reverted austenite.