Crack initiation mechanisms for corrosion fatigue of austenitic stainless steel

Corrosion fatigue tests on annealed type 316 (UNS S31600) stainless steel (SS) showed the maximum stress level for failure in 0.5 M sodium chloride (NaCl) aqueous solution at pH = 4.2 was one-third lower than in air after a similar number of cycles. Crack initiation mechanisms of corrosion fatigue were studied by scanning electron microscopy (SEM) of prepolished specimen surfaces. Fatigue tests were conducted at sufficiently high stresses to cause formation of intensive slip bands. Interaction of the acidic saline solution with the slip bands caused pitting corrosion along the slip bands. A mechanism for crack initiation resulting from pit formation and crack coalescence was suggested to explain the decrease in the maximum stress level for corrosion fatigue of austenitic SS, which exhibited passive behavior and generally good corrosion resistance in 0.5 M NaCl solution at pH = 4.2.