High frequency stage I corrosion fatigue of austenitic stainless steel (316L)

High frequency (123 Hz) fatigue crack propagation studies were conducted under rising ΔK conditions (R-ratio=0.22) on single edge notch specimens of austenitic stainless steel (type 316L) that contained an annealed precrack. Tests were conducted in near neutral (pH 5.5) solutions of 1 M NaCl and 1 M NaCl+0.01 M Na2S2O3 under potentiostatically controlled conditions and in desicated air. Attention was directed primarily to the near threshold behavior and the stage I (crystallographic) region of cracking. Good mixing between the crack solution and bulk solution was obtained and crack retardation and arrest effects due to surface roughness induced closure were minimized at high anodic potentials by electrochemical erosion. Thermodynamic considerations showed that hyderogen played no role in fatigue crack propagation. Analysis of the results in terms of the estimated effective cyclic stress intensity, ΔKeff, showed a systematic effect of potential on the average crack growth increment per cycle, da/DN. Anodic dissolution processes make an insignificant contribution to da/dN. A model is proposed for stage 1 fatigue cracking based on the effect of oxide nucleation rate on restricted slip reversal. The essential features of the model relevant to cracking in aqueous environments and in desiccated air.