Surface composition of the steel powders pre-alloyed with manganese

The determination of the surface oxide layer composition is vital to facilitate the adjustment of the sintering conditions for sufficient removal of the surface oxides for providing strong metal bonding between the metal particles during sintering. To systematically investigate the composition, morphology and thickness of the surface oxide the influence of manganese content from 0.3 to 1.8 wt.% on the surface products composition in the case of water atomized steel powder was evaluated. Analysis of the powder surfaces by X-ray photoelectron spectroscopy and high-resolution scanning electron microscopy in combination with X-ray microanalysis showed that powder particles in all cases are covered by heterogeneous oxide layer, composed of particulate features of thermodynamically stable oxides (Cr-Mn-Si) and homogeneous iron surface oxide layer in between. For increasing alloying content the fraction of stable oxide cations in the surface layer increases linearly, whereas the thickness of the iron oxide layer decreases. Moreover, from the investigation of the sintering and degassing behavior by thermal analysis coupled with mass-spectrometry (TG/DTA + MS), three different stages of carbothermal reduction process were observed and their correlation with surface oxides composition was established during sintering in argon.