Non-destructive detection of damage in an austenitic stainless steel SUS 304 by the use of martensitic transformation

Abstract

The present study investigates a method for the non-destructive detection of damage in an austenitic stainless steel SUS 304 by the use of martensitic transformation. Volume fraction of α' martensite transformed in uniformly stretched SUS304 plates was measured and expressed as a function of the applied strain levelε. The distributions of α' phase in the plastic wake regions produced around fatigue cracks were then electromagnetically measured in fatigued SUS 304 plate specimens. The results were compared with the distributions of magnetic flux density B_{z} above the fatigue cracks in the specimens magnetized by a strong magnetic field higher than 0.4 T. It was revealed that the B_{z} distributions reflected the α" phase distributions in the wake regions: i.e., the distance between the points where B_{z} reached the minimum and the maximum had a high correlation with the fatigue crack length, and the minimum and the maximum values of B_{z} showed a linear relationship with the applied stress intensity factor range ΔK. These results imply that not only the crack length but also the fatigue damage can be detected effectively in an electromagnetic non-destructive way.