THERMODYNAMIC AND KINETIC ASPECTS OF OXIDE TRANSFORMATION DURING SINTERING OF CR-PREALLOYED PM STEELS

Paper in proceeding, 2014

Despite high purity of the commercially available Cr prealloyed powder grades, factors affecting stable oxide formation during sintering process are not fully understood. Hence, thermodynamic and kinetic simulation of the oxide formation/transformation on the prior powder surface and further developed inter-particle necks during whole sintering process is performed. Thermodynamic and kinetic modeling (Thermo-Calc and HSC Chemistry) was performed based on the results from the analysis of amount, morphology and composition of the oxide phases inside the inter-particle necks (HRSEM+EDX and XPS). Possible scenarios of oxide reduction/formation/transformation for Fe-Cr-(Mn)-C powder systems were evaluated in dependence on processing parameters (sintering atmosphere composition, temperature profile, etc.). Results indicate that oxide transformation occurs in accordance with the thermodynamic stability of oxides where spinel MnCr2O4 was identified as the most stable oxide phase at applied sintering conditions. Controlled conditions during heating stage minimize formation of stable oxide products and produces oxide-free sintered parts.