Deformation and transformation behavior in micropiercing of SUS304

Processing technologies for fine-grained austenitic stainless steel SUS304, including the stability of boundary edge between burnished surface and fractured surface have been developed. However, the deformation mechanism related to the grain size is not clear. Here, we report the relationship between the grain deformation and transformation mechanism in micropiercing of SUS304. We investigated the effects on the grain phase and the misorientation angle in process-affected zones at circumferential direction by EBSD (electron backscatter diffraction) analysis. The result shows that the frequency of the austenitic phase and the strain-induced martensitic phase were affected by grain size strongly. This phenomenon was influenced by distribution of austenitic phase. The selection of an appropriate grain size may be required to enable micropiercing with high accuracy.