Bending fatigue behavior of metastable and stable austenitic stainless steels with different surface morphologies

The surface morphology has a significant influence on the fatigue behavior of components. For austenitic stainless steels (ASSs), this issue is even more pronounced due to their metastability. Based on the complex deformation mechanisms of metastable ASSs, which include dislocation slip, deformation twinning, and deformation-induced martensitic phase transformation, the metastable stainless steel AISI 347 was investigated in this study together with the stable AISI 904L as a reference material. 4-point bending fatigue tests with load ratio R = 0.1 and testing frequency f = 10 Hz at ambient temperature were carried out on specimens with 5 technically relevant surfaces morphologies: mechanical polished, milled, micro-shot peened, laser shock-peened, and ultrasonic modified. Systematic material characterizations were carried out to clarify the key influences of these morphologies on the fatigue behavior. Deformation-induced martensite layers were proven to improve the fatigue life in metastable austenitic steels, which open perspectives to extend the lifetime of components.