Oxidation Inhibition Mechanism and Performance of a New Protective Coating for Slab Reheating of 3% Si-steel

Abstract

This study was carried out to clarify the properties and antioxidation mechanisms of newly developed oxidation inhibitor consisting of refractory powder-SiO₂-Si-SiC-synthetic mica-colloidal silica-surface active agent and caking bond. By applying this type of oxidation inhibitor to grain-oriented silicon steel, it was possible to achieve significant reductions in scaling and production of fayalite-based slag, thereby substantially increasing yield.
During heating, Al₂O₃ is formed as a result of the decomposition by Si (metallic silicon) of mullite (3Al₂O₃·2SiO₂) contained in refractory powder. Furthermore, the fine SiC powder is oxidized and changes gradually to protective cristobalite-SiO₂(C-SiO₂) layer which acts as an excellent barrier to oxygen diffusion from atmosphere. The protective C-SiO₂ is not formed from the C-SiO₂ which is added initially in the oxidation inhibitor but is newly formed through the oxidation process of the SiC.
On the other hand, Al₂O₃ which is formed by the decomposition of mullite becomes Al₂O₃·SiO₂ in combination with SiO₂. On the steel surface, however, it becomes highly protective FeO·Al₂O₃ or 3FeO·Al₂O₃·3SiO₂ layer and, at the same time, it prevents the formation of low melting point material such as fayalite (2FeO·SiO₂).
It has been clarified that this oxidation inhibitor exhibits the excellent antioxidability due to superposed effect of above-mentioned reactions.