Preamble

In steelmaking, the impurities like carbon, silicon, manganese, phosphorus and sulphur are removed from hot metal through a combination of gas/metal, gas/slag and gas/metal/slag reactions so as to produce steel of desired chemistry and cleanliness (cleanliness refers to the inclusions). Science of steelmaking involves equilibrium concentration of an impurity between the phases for a given set of temperature and pressure,and the rate of transfer of an impurity from the hot metal.

Equilibrium between the phases:

The phases in steelmaking are hot metal, molten slag and gas. Hot metal is a multi-component solution in which impurities like carbon, silicon, manganese, phosphorus and sulphur are dissolved in very low amount (total concentration of all the impurities is approximately 5% to 6%) in iron. Slag is a solution of predominantly oxides with small amounts of sulphides, phosphides, silicates etc. Composition of the solutions in steelmaking is conveniently expressed either as weight% (Wt%) or mole fraction(N). The mole fraction of the ith component in a solution of n components is

(1)