Abstract
The present study investigates plasticity-induced martensitic phase transformation around part-through cracks in a nonmagnetic austenitic stainless steel SUS 304 fatigued at room temperature in air. Spatial distributions of the volume fraction V_<α'> of α' martensitic phase around semi-elliptical fatigue cracks emanating from artificial notches having different aspect ratios were measured with ferrite scope. The results were compared with the distributions of vertical magnetic flux density B_z above the cracks in the specimens magnetized by a strong electromagnet. It was revealed that the B_z distributions above and below the surface cracks reflected the α' phase distributions in the plastic wake regions produced around the cracks: i.e., the distance between the points where B_z reached the maximum and the minimum values B_<zmax> and B_<zmin> had linear correlations with surface crack length 2a. The B_<zmax> and the B_<zmin> values also showed linear relations with maximum stress intensity factors at the surface tip K_<amax> and at the depth position K_<bmax>. Each relation, i.e., 2a vs. 2l, B_<zmax> vs. K_<amax>, etc. can be represented by a single straight line regardless of the stress ratio and of the aspect ratio of initial notches.
