Very high cycle fatigue behaviour of austenitic stainless steel and the effect of strain-induced martensite

Metastable austenitic stainless steels are known to undergo a partial transformation of austenite into martensite as a consequence of plastic deformation. This transformation process depends on the chemical composition, the accumulative strain as well as the strain rate, the temperature and the microstructure. As most manufacturing processes of metallic components lead to plastic deformation in the material, the utilization of this transformation effect to adjust the monotonic and cyclic strength behaviour for the highly stressed areas of a component is evident. It is shown that monotonic and cyclic strength properties can be systematically changed by controlling the deformation-induced martensite content. The austenitic stainless steel studied was found to show a constant fatigue limit from 106 to 109 cycles that is primarily attributed to the strengthening effect of martensitic transformation. Load-increase tests were used to estimate an optimum martensite content in predeformed specimens to reach a maximum fatigue limit.