Very High Cycle Fatigue Behavior of Austenitic Stainless Steel in Annealed and Predeformed Condition

Engineering components in service nowadays are designed for a large number of loading cycles (similar to 109), which makes fatigue behavior in this cycle range (designated as very high cycle fatigue [VHCF]) a topic of significant interest. The present study aims to investigate the high cycle fatigue (HCF) and VHCF behavior in type 304 stainless steel in two different conditions (annealed and with a martensite volume fraction of similar to 45 %) through low cycle fatigue predeformation at a subzero temperature. A fatigue diagram in the form of an S-N curve extending up to the VHCF range is generated, which shows different HCF and VHCF behaviors for the annealed and predeformed conditions. Further tests are carried out at different R ratios to generate constant-life Haigh diagrams for both conditions. Although no failure is observed in the VHCF range under the annealed condition, an internal crack initiation mode is observed under the predeformed condition (Type II behavior), which is attributed to the enhanced notch sensitivity under VHCF cycling induced by a significant extent of strain-induced martensite formed during predeformation. To address the influence of varying load history under service, specimens were prefatigued in HCF, followed by VHCF cycling. The HCF-VHCF boundary is found to be significantly impacted by the prior HCF damage, with lowering of the fatigue limit under VHCF.