Degradation of refractories by slags in steelmaking - Corrosion mechanisms and evolution with slag composition

A wide variety of refractory materials are used in a steel mill, with approximately 500 commercial grades for consumable refractories alone. This is due to an ongoing effort to optimize their performance and costs. From the upstream to the downstream sections of the plant, several major families of refractories are used, all of which are absolutely essential and whose development has at times been a key factor in the emergence of steelmaking processes—for example, magnesia-carbon bricks for the oxygen-blown converter process in the 1970s.

During steel production, slags and temperatures vary significantly across different furnaces and equipment; this is the primary reason why different types of refractories must be used. Some refractories are more resistant to slags rich in SiO ₂ , while others are more resistant to slags rich in CaO or FeO _x .

This compatibility between refractories and slags is far from easy to describe and explain. Within the industry, there are very simple best practices, such as “magnesia refractories with lime-rich slag” and “alumina refractories with silica-rich slag.” But these physicochemical concepts are complex, and it is not easy to define the composition thresholds for slags at which one should switch from one category of refractories to another. Furthermore, what are the corrosion mechanisms that would underlie such a rule? There is nothing obvious here.

The purpose of this article is to shed light on the corrosion of refractories, based on calculations of the solubility of various oxides in slag and the viscosity of the slag during this dissolution process.

In addition to the composition and temperature of the slag, these factors are discussed in the article [N 4 853] to explain, as fully as possible, the selection of these major families of refractories for use in steelmaking furnaces. The article presents examples of refractory corrosion caused by steelmaking slag that illustrate the dominant corrosion mechanisms.