Effect of Carbon Source on Oxide Reduction in Cr-Prealloyed PM Steels

Paper in proceeding, 2013

Modern chromium-alloyed water-atomized steel powder grades are characterised by high purity with low amount of surface oxide. Surface oxide is formed by two types of oxides: thin iron oxide layer, covering more than 90% of the powder surface and thermodynamically stable particulate oxide. Therefore, the reduction of the surface oxide, required for the development of inter-particle necks, proceeds in two stages. Present work is focused on the analysis of the effect of three different carbon sources – synthetic graphite, natural graphite and carbon black – on the reduction of the mentioned surface oxides in Cr-alloyed PM steels. Efficiency of this reduction by means of the different carbon sources was studied by thermal analysis. Oxide composition and amount as well as oxide transformation mechanism were studied on specimens from interrupted sintering trials using advanced analysis techniques (HRSEM+EDX). Results indicate that efficient reduction of both kinds of surface oxides, modified carbon source is preferred.