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. © 1990, The Iron and Steel Institute of Japan. All rights reserved.