Oxide Transformation during Sintering of Cr and Mn Prealloyed Water Atomized Steel Powder

Water atomized steel powders, prealloyed with elements with high oxygen affinity like manganese and chromium, contain small amount of oxides on the initial powder surface and in its interior. Modern powder manufacturing routes allow industrial production of water-atomized steel powders of high purity. However, further oxide products formation and their transformation during consolidation process remain unclear. The present study deals with the modelling of oxides transformation in dependence on sintering atmosphere, temperature profile and powder composition based on the analysis of specimens from interrupted sintering trials using advanced analysis techniques (HRSEM+EDX). Results indicate that composition and especially amount of the oxide products are strongly determined by the conditions during heating stage. Controlled conditions allow to minimize formation of stable oxide products and so to lower sintering temperature/time for obtaining oxide-free sintered parts. Oxide transformation processes occur in accordance with the thermodynamic stability of oxides in the line Fe2O3→FeO→Fe2MnO4→Cr2FeO4→Cr2O3→MnCr2O4→MnO/MnSiOx→SiO2