Abstract
Powder Metallurgy Process (hereafter PM process) is known as one of the suitable processes to get net shape components with reasonable costs. However dynamic mechanical properties like fatigue strength were not sufficient.
In order to improve fatigue strength of PM components, the selection of a suitable alloying system followed by optimum PM processes is one of the important things and the conditions of secondary operations like a heat treatment and a shot peening are the other important things. Resultant stress from residual stress and stress profile from loading was used to estimate the optimized secondary operations. At last 670MPa of fatigue strength has been achieved for 1.5Cr0.5Mo pre alloyed steel powder, compacted at 800MPa at 140˚C, followed by heat treatment and shot peening. The value is tremendously high when considered the level of PM steels some years ago. Consideration of the resultant stress helped us to understand the mechanism of the improvement of fatigue strength.
Then the possibility to apply PM components for an actual gear in a car transmission was investigated by using simulation and fatigue limit diagram. The actual static stress of the root of teeth of a gear for a manual transmission was also measured by loading a certain torque on the input shaft.Finally a frequency for each gear has been estimated under a certain condition. The result indicates that the requirement for each gear is different. Therefore there is possibility to derive the performance of materials more by optimizing secondary operations. A stress profile of a sprocket is also presented as another type of component that requires completely different performance.
Keywords: PM steels, Fatigue Strength, Stress Profile, Secondary Operations, Safety Factor