REDUCTION OF CHROMITE IN LIQUID FE-CR-C-SI ALLOYS

The kinetics and the mechanism of the reduction of chromite in Fe-Cr-C -Si alloys were studied in the temperature range of 1534-degrees-C to 1702-degrees-C under an inert argon atmosphere. The rotating cylinder technique was used. The melt consisted of 10 and 20 wt pct chromium, t he carbon content varied from 2.8 wt pct to saturation, and the silico n content varied from 0 to 2 wt pct. The rotational speed of the chrom ite cylinder ranged from 100 to 1000 rpm. The initial chromium to iron ratios of the melts varied between 0.11 and 0.26. In Fe-C melts, the effect of rotational speed on the reduction of chromite was very limit ed. Carbon saturation (5.4 wt pct) of the alloy caused the reduction t o increase 1.5 times over the reduction observed in the unsaturated (4 .87 wt pct) alloy at a given rotational speed. The addition of chromiu m to the carbon-saturated Fe-C alloy increased the reduction rate. The addition of silicon to the liquid phase increased the reduction rate drastically. The reduction of chromite in Fe-Cr-C melts is hindered be cause of the formation of, approximately, a 1.5-mm-thick M7C3-type car bide layer around the chromite cylinders. This carbide layer did not f orm when silicon was present in the melt. It was found that the reduct ion rate is controlled by the liquid-state mass transfer of oxygen. Th e calculated apparent activation energies for diffusion were 102.9 and 92.9 kJ/mol of oxygen in the Si-O and C-O systems, respectively.