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Abstract
Sintered steel specimens with density levels of up to 7·6 g cm−3 have been prepared from Cr–Mo and Mo prealloyed powders. The fatigue response has been studied using an ultrasonic resonance testing device that enabled testing up to 109 cycles. It showed that the fatigue endurance strength can be drastically increased by raising the density and that the sintering conditions are effective, though less than the density. The existence of a true fatigue limit was disproved up to 109 cycles for all materials tested, with sintered steels thus being similar to wrought ones. Cr–Mo steels was shown to be superior to Mo alloyed grades due to the markedly finer as sintered microstructure and higher sintering activity. Fatigue crack initiation was found to originate from pores at first at multiple sites, with microstructural orientation being dominant compared to the direction of stress; with progressive loading, some cracks join to form a propagating macrocrack from which the final failure then starts.
This work has been carried out within the international project ‘Höganäs Chair’ organised and financially supported by Höganäs AB, Sweden.