Abstract
The effect of shot-peening, surface rolling and induction hardening on the rotary bending fatigue strength of sintered ferrous alloy was investigated. The main results obtained are as follows:
(1) The fatigue limit of plain specimens is raised by shot-peening, but the increment of the fatigue limit is small due to the notch effect of the pores flattened by the shot-peening. The notch effect of flattened pores increases as the original density decreases. The fatigue limit of specimens resintered after shot-peened is higher than that of specimens processed only by shot-peening, because the flattened pores disappeared during the resintering after shot-peening.
(2) The fatigue limit of notched specimens is considerably raised by surface rolling.
(3) The fatigue limit is raised by induction hardening. The rate of increase of fatigue limit is larger in the case of notched specimens than plain specimens. The analysis of induction hardened plain specimens shows that the change of microstructure of the specimen caused by the induction hardening contributes little to the increase of the fatigue limit due to the reasoning that, as is easily predicted, the notch effect of the pores is more serious in the case of martensitic structure.
