Influence of As-sintered material strength on the improvement of fatigue behaviour by surface rolling

In this investigation fatigue-life curves of two low- and high-strength PM-steels Fe-1.5%Cu (Phi = 7.15 g/ccm) and Fe-8.0%Ni-1.0%Mo-0.5%C (Phi = 7.35 g/ccm) are compared for three different notch factors in as-sintered and surface rolled conditions under constant amplitude as well as under variable amplitude loading. The results are interpreted on the basis of microstructural features, microhardness and residual-stress distributions. The paper presents statistically based design data about the improvement of fatigue strength by surface rolling of PM-parts under consideration of stress concentration and loading mode.