On the Non-Metallic Inclusion and Austenite Grain Size of Plain Carbon Steel (Effect of Calcium on Iron and Steel Making)

Abstract

Steels containing 0.3 to 0.5%C were melted in alumina-lined graphite crucibles 3 kg in capacity by a high frequency induction furnace. These steels were prepared from electrolytic iron and pig iron. The melt was deoxidized with electrolytic manganese, metallic silicon and different amounts of aluminum ranging from 0 to 0.16%, and cast into metal molds, but a part of the melt was added with the iron-calcium base alloy before casting. After forging, non-metallic inclusions in the steels and the grain coarsening temperature were investigated. The results are summarized as follows: While addition of the iron-calcium base alloy to the molten steel deoxidized only with manganese and silicon is effective in reducing the amount of inclusions belonging to type A and at the same time in increasing the grain coarsening temperature, its addition to the molten steel deoxidized with manganese, silicon and aluminum considerably decreases the amount of oxides, especially, of alumina, and increases the amount of aluminum nitride as compared with the case without addition of the iron-calcium alloy. Addition of this alloy contributes also to the reduce of the grain size which improves the steel property. It is assumed that this reduce of the grain size may be attributed partly to the increase of the amount of aluminum nitride caused by addition of aluminum and the alloy in question. The grain size of aluminum- or calcium-killed steels is rapidly coarsened above a certain temperature, while that of rimmed steels is progressively coarsened with increasing temperature above the transformation range.