FRACTURE SURFACES STUDIED ON PM STEELS PREPARED FROM PREALLOYED STEEL POWDERS AND SINTERED IN DIFFERENT ATMOSPHERES

摘要

Fracture surface analyses were performed on carbon-free PM steels prepared from atomized prealloyed steel powder grades with different contents of alloying elements (Mn, Cr) which were sintered in different atmospheres (H_2, Ar, N_2/H_2, vacuum) at 1300°C. The results of impact energy measurements show lower impact energy for materials sintered in Ar and vacuum. The materials sintered in hydrogen containing atmospheres show high impact energies which are confirmed by SEM examination. The fracture surfaces of materials sintered in vacuum and Ar atmospheres show intergranular decohesion failure mode, and materials sintered in H_2 and N_2/H_2 show local plastic deformation. Generally, low impact energy and excessive grain growth were more pronounced the lower the alloy content.