FRACTOGRAPHIC INVESTIGATION OF CHROMIUM-ALLOYED PM STEELS SINTERED IN ATMOSPHERES WITH VARYING HYDROGEN CONTENT

摘要

Chromium usage in PM steels is extensive today due its attractive properties. On the other hand its high affinity to oxygen requires a strict control over the sintering atmosphere used. In order to investigate the effect of the atmosphere composition in terms of hydrogen content (0%-3%-10%) on the characteristics of the reaction products, the fracture surface of pressed and sintered specimens of chromium-alloyed water atomized steel powders was studied using high resolution scanning electron microscopy combined with energy dispersive EDX analysis (SEM+EDX). For all applied conditions the formation of particulate reaction products, rich in strong oxide-forming elements, was identified. The oxide reduction was enhanced in the samples processed in hydrogen containing atmospheres. The study shows that careful adjustment of the sintering atmosphere in terms of purity and composition leads to the significant reduction of the oxides content and so better developed inter-particle necks.