Effect of non-metallic inclusions and shrinkage cavities on the dynamic fracture toughness of a high-strength G42CrMo4 cast steel

Abstract

The formation and clustering of non-metallic inclusions was investigated by applying a steel casting simulator. In a fully controlled atmosphere, the oxygen content of the steel melt was intentionally increased. At a specified level, the steel was deoxidized by pure aluminum. After the treatment, the melt was cooled down in the crucible. The effects of the inclusions and the cavities were determined by means of metallography, tensile tests, dynamic fracture toughness tests, and fractography. Metallographic results show that alumina particles have a strong tendency to aggregate at the walls of the crucible. Neglecting this aggregation, a relatively homogeneous distribution of alumina inclusions was observed. Furthermore, the solidified steel exhibited manganese sulphide inclusions and shrinkage cavities. The results of the tensile tests revealed a relatively low ductility. Fractographic examinations showed that both non-metallic inclusions and shrinkage cavities promoted ductile fracture. Results of dynamic fracture toughness tests revealed a relatively large scatter in the dynamic crack resistance. This was analogously attributed to the damaging effect of the non-metallic inclusions and the shrinkage cavities. Fractographic investigations showed that not only alumina inclusions but preferentially manganese sulphide inclusions affected the failure behavior of the investigated steel.