Characterization of oxide on the water-atomized FeMn powder surface

The characterization of surface oxides composition and the depth distribution of oxides in water-atomized steel powder is vital to adjust the reduction condition for sufficient removal of the oxides. To systematically analyze the composition, depth distribution and morphology of surface oxides in water-atomized low alloy steel powder containing manganese (0.3 wt.%), X-ray photoelectron spectroscopy (XPS) combined with Ar-cluster-ion sputtering, X-ray diffraction (XRD), scanning electron microscope (SEM) and energy disperse spectroscopy (EDS) were utilized. The results show that surface oxygen exists in the form of “Oxides Island”, and the surface oxygen content is much higher than the bulk. In the unreduced powder, the oxygen-rich surface layer contains 67% of total oxygen within a depth of 1800 nm (0.072R, R denotes the radius of the powder); while for the reduced powder, the oxygen-rich surface layer contains 28% of the total oxygen in the powder within a depth of 80 nm (0.0032R). The oxygen depth distribution curves fit well with exponential decay function as Y = f(x) = A1exp(− x/t1) + A2exp(− x/t2) + y0. The oxides mainly exist in the forms of γ-Fe2O3, FeO, Mn2O3 and MnO in the unreduced powder and γ-Fe2O3, FeO, Mn2O3 in the reduced powder.