Desulfurization of Molten Steel by Passing Steel Droplets through the Slag Layer

Abstract

One of the most important works in the steelmaking process is decreasing the sulfur content of steel. Sulfur could make cracks on the steel while casting. Therefore, in special steels such as API steel, the sulfur content should be controlled very low (<~10 ppm). Sulfur can affect the sensitivity of corrosion cracking while the steel is exposed in hydrogen sulfide containing environment. In order to prevent reduction of any other mechanical properties of steel, controlling sulfur should have more attention. The present study focused on desulfurization of molten steel after the secondary steelmaking process with low initial sulfur content ([%S]0: 0.003 ~ 0.01 mass pct.). The method used in the present study was dropping the molten steel droplets onto the slag layer composed of CaO-Al2O3-MgO at 1600°C in two zone heater furnace. The steel droplets were desulfurized while passing through the slag layer (dynamic contact) and were accumulated at the bottom of the slag layer in a crucible (static contact). A kinetic analysis was carried out together with model calculation and it showed that experiment with high sulfide capacity slag exhibited higher desulfurization rate. The mass of steel used in the experiment also influenced extent of the desulfurization. The obtained rate constant under the dynamic condition was higher than that reported in literature for static reaction between slag and steel. The influence of increasing the surface area of droplet is also discussed.