Influence of sulphur and vanadium additions on toughness of bainitic steels

The Charpy impact toughness of bainitic steels, in the longitudinal directi on, was increased by appropriate additions of sulphur and vanadium. The Cha rpy impact value in the longitudinal direction was highest when the sulphur content was 0.1 wt-%. A suppression of austenite grain growth by manganese sulphides was recognised when the austenitising temperature was higher tha n 1373 K. Furthermore, it was found that bainite packets were refined by an increase in sulphur content, because manganese sulphides existing in the a ustenite grains promoted bainite transformation. The main effect of the van adium addition was probably to enhance the above effect by precipitation of vanadium carbonitrides on the manganese sulphides. Accordingly, an increas e in toughness with additions of sulphur and vanadium may be attributed to bainite packet refinement resulting from the suppression of austenite grain growth and the promotion of intragranular bainite transformation by mangan ese sulphides. MST/4813.