Abstract
In order to lighten the weight of connecting rods, which are put into service with the surface as forged, mechanical properties, especially fatigue strength of the forged surface should be improved. In powder forged material, surface defects such as decarburized layer, surface roughness, and non-sintered area(NSA) which is peculiar to this material are observed.
In order to develop the optimum strengthening process, the authors quantitatively analyzed the effects of these surface defects on mechnical properties. As a result, NSA acts as a notch as well as decreasing the effective cross sectional area, and is the dominant factor which reduces fatigue strength among these surface defects. In the case of P/F material which has no NSA at all, effects of decarburization and surface roughness are mostly the same as carbon steel. In order to improve the fatigue strength noticeably, the NSA should be completely removed.
