Plasticity-Induced Martensitic Transformation around Semi-Elliptical Surface Cracks in Fatigue of an Austenitic Stainless Steel

The present study investigates plasticity-induced martensitic transformation around semi-elliptical cracks in an austenitic stainless steel SUS304 fatigued at room temperature. Distributions of the volume fraction of α′ martensitic phase around semi-elliptical fatigue cracks were measured by ferrite scope. The results were compared with vertical magnetic flux density B z , distributions above and below the cracks in specimens magnetized by a strong electromagnet. It was revealed that the distance between the outermost peaks of the B z distributions 2l showed good linear correlations with surface crack length 2a. The maximum and the minimum values of B z , B zmax and B zmin , also showed linear relations with maximum stress intensity factors at the surface tip K amax and at the depth position K bmax . These results imply that not only 2a but K anax and K bmax values can be estimated in an electromagnetic non-destructive way.