Corrosion fatigue behavior of 17-4 PH stainless steel in different tempers

Corrosion fatigue (CF) behavior in an aerated 3.5 wt% NaCl solution has been investigated for 17-4 PH stainless steels heat treated in three conditions, namely, solution annealed (SA), peak-aged (H900), and overaged (H1150) tempers. CF tests, including both high-cycle fatigue (HCF) and fatigue crack growth (FCG), were performed as a function of load ratio and frequency. S-N curves showed that smooth specimens in H900 temper under all applied cyclic loading conditions exhibited longer CF lives than H1150 while those in the SA temper lie between them. However, the Stage II FCG rates in H900 temper were significantly greater than the H1150 and SA tempers at 20 Hz but comparable to the H1150 and SA tempers at 1 Hz. This implies crack initiation and Stage I cracking played the major role in determining the entire CF life for smooth specimen. Results also indicate that an increase in load ratio results in an increase in FCG rate and reduction of fatigue life. The CF lives at low stress levels for SA temper were increased as a result of a decrease in cyclic loading frequency from 20 to 1 Hz, which might be explained by the depassivation-dissolution-repassivation processes.