Influence of mechanical surface treatments on the fatigue properties of sintered steels under constant and variable amplitude loading

The present paper describes the influence of shot peening on fatigue properties of the alloys Fe-1.5%Cu and Fe-2.0%Cu-2.5%Ni in the density of 7.4 g/ccm and compares this mechanical surface treatment with the thermal surface treatment carbonitriding. The improvement of the fatigue properties by these treatments under variable amplitude loading exceeding the paricular endurance limits is in the same order of the improvement obtained under constant amplitude loading. Carbonitriding is superiour to shot peening; but shot peening after carbonitriding does not increase fatigue strength. The comparison of fatigue properties under constant and variable amplitude loading gives allowable damage sums which are necessary for fatigue life assessments of randomly loaded sintered parts. (LBF)