Slag-steel reactions in the refining of Advanced High-Strength Steel

Abstract

The high aluminum concentration in advanced high-strength steels lowers the oxygen activity at the steel-slag interface, compared with conventional low-carbon aluminum-killed steels. The lower oxygen activity affects the rate and equilibrium extent of steel-slag reactions. One result of the lower oxygen activity is a higher concentration of dissolved magnesium, leading to faster conversion of alumina inclusions to spinel inclusions, and spinel to periclase – as demonstrated in previous work. The current study concerns the dissolution of nitrogen in ladle slag as nitride ions. Laboratory results of the rate and extent of nitrogen removal are compared with model predictions, confirming that substantial nitrogen removal is possible. While aluminum nitride was found in some steel samples after solidification, aluminum nitride does not appear to play a role in nitrogen removal from liquid steel to liquid slag.