When the graphite particles retained in the steel after quenching, the fatigue property of the steel deteriorates significantly.

In this study, effects of the conditions of induction hardening on the fatigue properties of the graphitized steel after induction hardening and tempering were investigated.

In graphitized steel, the depth of the hardened layer was increased with the decrease in the movement speed at induction hardening. However, the graphitized steel which was induction hardened in higher moving speed, showed longer life in roller pitting test in spite of the relatively shallower hardened zone.

In the graphitized steel which was hardened in higher moving speed, macroscopic cracks had run into the matrix, so as to avoid the defects caused by graphite. The hardness of martensite near graphite was higher in comparison with the matrix after induction hardening in higher moving speed because of the presence of a region with high C concentration around the graphite.

Effect of austenite（γ）phase stability in local deformation region on deformation energy of ferrite（α）-γ duplex stainless steel obtained by tensile test was investigated. The results revealed that uniform deformation energy showed the same value for both γ-stable and unstable duplex stainless steels. On the other hand, local deformation energy of γ-stable duplex stainless steel was larger comparing γ-unstable duplex stainless steel. In γ-unstable duplex stainless steel, nano-indentation hardness difference between α and transformed martensite （α′） phases increased remarkably beneath fractured surface. Low voltage FE-SEM observations revealed that voids grew rapidly at the grain boundary between α and α′ phases beneath the fractured surface.

From these results, it was concluded that the amount of local deformation energy in γ-unstable duplex stainless steel decreased due to the rapid void-growth at the grain boundary between α and α′ phases beneath the fracture surface.