Modifying inclusion types and shapes by rare earth metals addition to low carbon steel

Abstract

The formation of pure RE oxides (as REP3) is possible, when the sulphur content in steel is very low such as 0.014% and RE sulphide is formed when the RE content is higher than 0.015% and the ratio of(Ce+La)/S:S0.46. The formation of globular RE oxysulphide is probable if sulphur content is higher than 0.015%, and when RE content increases, the bean seed inclusion changes to globular form. After RE addition, the primary RE oxides are formed first, then react with manganese sulphide and form type I, II and III and transform into globular RE oxysulphide of type I-b, which is harmless to the properties. The secondary RE sulphides can form during solidification surrounding the oxysuIphide cores, when the oxygen content in steel is low.