Abstract
The decarburization and surface oxidation reactions were observed during the decarburization annealing cycle of a 3 wt–%Si regular grain oriented electrical steel. Annealing was carried out at four H2O/H2 ratios in the range 0·14–0·7 and three temperatures (787, 843, and 899°C) for time periods of up to 30 min. Gravimetric, chemical, and microstructural analyses indicate that the oxidation and decarburization reactions are kinetically related; e.g. at lower H2O/H2 ratios, less total oxidation and decarburization are observed at the higher soak temperatures. This behaviour is reversed as the ambient H2O/H2 ratio is increased. The microstructural analysis indicates the presence of an amorphous phase and finely dispersed particles of silica (SiO2) and fayalite (Fe2 SiO4) in the scale. These data were analysed on the basis of the transition between internal and external oxidation and the data compared favourably with values predicted by existing theories.
MST/139
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