Abstract
The authors have shown that martensitic transformation can occur in the plastic wake regions around cracks in SUS304 austenitic stainless steel fatigued at room temperature in air. They have also discovered that there are strong correlations of crack length and volume fraction of transformed martensitie with the parameters of the leakage magnetic flux density distributions induced by the magnetization of the ferromagnetic martensitic phase around fatigue cracks. The electromagnetic characterization of the martensitic transformation is easy to make and can afford a macroscopic view of the martensitic phase in the length scale of the order of some millimeters. The electromagnetic method, however, cannot derive mesoscopic or smaller scale information about the martensitic transformation. The present study investigates the morphologies of the plasticity-induced martensite in different length scales. The authors used a ferrite scope and a flux gate sensor for macroscopic measurements. They also used an X-ray diffractometer having a focal size of 30μm for mesoscopic measurements of some ten micrometers and an electron back-scatter diffraction pattern (EBSP) analyzer for sub-micrometer measurements. The presentation will specify the difference in the morphologies of the martensite in the different length scales and show the correlations between the multiscale morphorogies.
