Abstract
Effects of sulphur addition on the Charpy impact properties of various continuously cooled bainitic steels with different prior austenite grain size, hardness, and content of retained austenite were investigated and compared with martensitic steels. The impact properties of 1473 K austenitised bainitic steels were improved with increasing sulphur content up to 0·1 wt-%, while the impact properties of martensitic steels were deteriorated with increasing sulphur content. The crack initiation energy of bainitic steels increased with the increase of sulphur content because the structure units surrounded by the high angle boundaries were refined with the increase of manganese sulphide inclusions which caused the expansion of ductile fracture area. On the other hand, the impact energy, particularly the crack propagation energy, of martensitic steels decreased with increasing sulphur content because the nucleation sites of voids increased with the increase of manganese sulphide inclusions in the ductile fracture region.
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