Characterization of the Chemistry of Oxides Formed on the Surface of Water-atomized Steel Particles during Annealing

Water-atomized (WA) steel powders are inevitably oxidized due to the chemical reaction between molten metal and water vapor. Minimization of surface oxides is essential for forming strong metallic bonds during sintering. However, the efficiency of H2-annealing is dependant on oxide chemistry, which is rarely made of pure/stoichiometric species. The objective here was to perform an in-depth characterization of the oxides found on WA steel particles to understand their behaviour during H2-annealing. It investigates the relationship between the chemical composition of pre-alloyed steels(Cr, Mn, Mo, Si), the chemical composition of the surface oxides and their modification due to H2-annealing. Particular attention is given to the impact of the difference between Si(wt.%) and Mn(wt.%) contents on powder oxidation. Characterization was performed using scanning and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy. Characterization before and after annealing provided insights into the dynamics of oxides reduction according to powder chemistry.