Abstract
Effect of B addition on the Si and Mn selective surface oxidation behavior of low carbon steels was investigated, by glow discharged spectroscopy, secondary electron microscopy, transmission electron microscopy, and auger electron spectroscopy, after recrystallization annealing. The oxides composed mainly of Si and Mn for B-free steel, and of B, Si and Mn for B-added steel. For B-free steel, fine selective surface oxides, which covered most of the steel surface, were observed. For B-added steel, gross globular selective surface oxides were observed on the steel surface, with partially bare Fe surface. For B-added steel, B-Si-Mn compound oxide is considered to be in molten phase in annealing, because the melting point of the compound oxide is lowered than the annealing temperature. As a result, the compound oxide is considered to coagulate and grow during annealing, due to the surface tension effect. The amount of Si and Mn selective surface oxidation was suppressed about 1/3 for B-free steel, compared with that of B-added steel, because of insufficient oxygen supply through the protective oxidation layer. For B-added steel, the selective surface oxidation was promoted, because oxidation layer was considered to be non protective. Only B addition of 5 ppm was enough, for the promotion of the Si and Mn selective surface oxidation.
