Abstract
Ferritic stainless steels such as Fe-2.25Cr-1Mo-1Zr, Fe-25Cr-1Zr and Fe-13Cr-8Ni-2Mo-1Zr with ultra-fine grain size of 0.2μm were prepared by hot extrusion after mechanical alloying. Axial fatigue life tests for plane round bar specimens of these steels were conducted at 473K. The higher fatigue strengths of these steels at 473K were observed as compared with those of conventional steels such as SAE8740 and SNB16. Fatigue strength expressed as maximum stress at 3 × 106 cycles for Fe-2.25Cr-1Mo-1Zr, Fe-13Cr-8Ni-2Mo-1Zr and Fe-25Cr-1Zr were 1150, 1150 and 1350MPa, respectively. Transranular fracture surfaces were predominantly observed at crack initiation and propagation area. Striation was observed at defined region of crack propagation area. It can be concluded that the higher fatigue strength of ferritic stainless steels with ultra-fine grain size of 0.2μm is strongly governed by delay of crack initiation.
