CHANGES IN OXIDE CHEMISTRY DURING CONSOLIDATION OF Cr/Mn WATER ATOMIZED STEEL POWDER

Modern water atomization methods allow industrial production of high-purity water atomized powder grades prealloyed with chromium and manganese. Surface coverage by oxide islands, formed by a variety of mixed oxides of chromium and manganese with higher thermodynamic stability, is below 10% that assumes good sinterability of such PM grades. However, there is still a risk of formation of oxides products on the powder surface during critical stages of powder consolidation, especially during heating stage. Therefore present work is focused on effect of alloying elements content on the possible scenarios of oxides reduction/formation/transformation in Fe-Cr-Mn-C powder systems. Accurate analysis of specimens, sampled during different stages of sintering process, by advanced analysis techniques (HR SEM+EDX) was combined with thermodynamic modelling of oxides stability. Obtained results indicate that oxide transformation process is governed by thermodynamic stability of present oxide phases in the line: Fe2O3→FeO→Fe2MnO4→Cr2FeO4→Cr2O3→MnCr2O4→MnO/MnSiOx→SiO2