2001 年 50 巻 9 号 p. 949-953
Fatigue tests were performed using (α+γ) duplex stainless steel specimens which had been deformed superplastically in the various strain range. The effect of the changes in the variables such as microstructure and surface roughness of the specimens during superplastic deformation on the fatigue strength of the deformed specimens were investigated. The fatigue strength of the superplastically deformed duplex satainless was found to decrease with increasing in the superplastic straining. The reduction in the fatigue strength was caused by the coarsening of the grains and the increasing in surface roughness of the specimens during superplastic flow. The fatigue strength of the specimens was also proved to be not affected by the formation of cavities during superplastic flow. Moreover, it was shown that the increase in surface roughness of the specimens with the superplastic straining was large at the initial stage of straining and this behavior resulted in the remarkable reduction in the fatigue strength of the specimens. The post-deformed fatigue strength of the specimens with the surface polished treatment, however, could be improved by superplastic straining up to 200%.