Plastic deformation necessarily accompanies fracture even in high hardness steels such as ball bearing steel, though it is within a very shallow layer just under the fracture surface. The depth of the plastic deformation zone can he determined by X-ray measurement of half value breadth. However, in the case of high hardness steel, the half value breadth is not changed significantly by this kind of plastic deformation. On the contrary, residual stress on the fractured surface was found to change remarkably depending on the mode of fracture such as static, fatigue or delayed types.