Thermodynamic equilibria in the steel industry

The steel industry is dedicated to the production of cast iron, iron and steel, and the various materials encountered by the steelworker are :

• ore, usually solid ;

• metal, liquid at the time of production, then solid ;

• slag, a mixture of liquid oxides in equilibrium with the metal;

• refractories that can react with metal or slag;

• gases, even if they are not considered a material.

Thermodynamics applied to steelmaking reactions therefore deals with the following points:

• problems associated with ore reduction ;

• reactions between metal and slag ;

• behavior of refractories in their environment ;

• dissolution of gases in metals.

These last three points, in particular, will be addressed in two subsequent articles [M7221] and [M7222].

It enables us to define the optimum processing conditions, depending on the starting material (ore or recovered scrap) and the objectives pursued: target composition, permissible impurity content.

Subsequent heat treatments, which help to refine the mechanical properties of the final material, are not examined in this article, which deals only with thermodynamics applied to steelmaking equilibria.

This article offers the steel engineer a few thermodynamic reminders, an expression, as a function of temperature, of the free enthalpies of transition and vaporization of the elements, as well as an expression of the free enthalpies of excess mixing for the main metal solutions.