Microstructure and Phase Composition Changes in Polymer Fiber-Modified Thermacoat™ Lining Exposed to Contact with Liquid Steel

Multicomponent clay and cenosphere linings protecting ceramic parts exposed to contact with liquid metal during continuous steel casting (CSC) are intended to diminish thermo-mechanical stresses at the beginning of this process. They are effective in their role, but due to their brittle nature, parts of them come off during transport or mounting. The admixture of polypropylene fibers into linings helps to alleviate problems with handling such parts, though the interaction of such a modified material with liquid steel should be re-assessed. The present experiment involved the preparation of a crucible with a Thermacoat™ (Vesuvius, Skawina, Poland) lining with the addition of Belmix™ (Belgian Fibers Group NV, Mouscron, Belgium) fibers and filling it with a drop of liquid steel. Next, the crucible was sectioned and the changes in its microstructure and phase composition were investigated with optical, scanning and transmission electron microscopy (OM/SEM/TEM) methods. This showed that the modified lining retained its non-wetting property against the steel of the non-modified material. The part with the lining, being in direct contact with the liquid steel, developed a highly porous layer filled with AlSiOx amorphous flakes with some larger blocky Al2O3 and SiO2 particles. Right below this, a heat-affected zone (HAZ) consisting of fine γ-Al2O3 platelets immersed in amorphous silica was formed. Some of the voids with a size corresponding to polymer fiber diameter carried significant carbon deposits on their walls. The performed investigation indicated that the polymer fiber-modified linings were capable of withstanding at least short-term contact with liquid steel without instantaneous defragmentation, i.e., they retained the good high-temperature properties of the non-modified material.