The relationship between sheared cut surface and strain induced martensitic transformation is discussed. The mechanism of shearing and breaking and separation in blanking is, first of all, a shear cut surface is generated by shear slip of the material, and when shear slip progresses, cracks in the material to be worked are seen from near the tool edge of the punch and die occurs. And the crack grows and it is known that the material leads to separation [15]. In the case of this experiment, 304 stainless steel is. It is inferred that fracture occurred in the same step as the mechanism. Although 304 stainless steel is a material with high ductility, as shear deformation progresses, the shear deformation region causes deformation-induced martensitic transformation. The strain induced martensitic phase is known to be a brittle material. Therefore, the material in the shear deformation area is brittle and is changing to an environment in which cracks easily occur. As a result, it is inferred that fracture occurred in the cut surface. On the other hand, in the case of 316L, it is hard to cause martensitic transformation, so it is assumed that the ductility is maintained, that is, no cracking occurs in the shear deformation area and eventually separation occurs without the occurrence of fracture surface. From the results that austenite stability affects the machined surface quality, it can be inferred to be affected by the processing temperature and the processing speed. These issues will be addressed in the future.