Fatigue Behaviour of 16Mn Steel in Air and 3.5% NaCl Solution

The fatigue behaviour of 16Mn steel in air and 3.5% NaCl solution were studied by dumble-shaped plate type specimens. The S-N curves show that the fatigue strength of 16Mn steel in 3.5% NaCl solution was much lower than that in air. The fatigue limit of it in air was 200 MPa, but there was no fatigue limit in 3.5% NaCl solution. Surface and fractography observation results show that the fatigue cracks in air were initiated from the matrix of surface, while most of fatigue cracks in 3.5% NaCl solution were initiated from surface pits, except for some from the matrix of surface. The typical feature of the fatigue crack propagation region in air was fatigue striations, while that in 3.5% NaCl solution was intergranular crack characteristic. It was found that the fatigue limit of 16Mn steel in air could be predicted by empirical equation, and the predicted fatigue limit was agreeable to the experimental fatigue limit.