Vanadium in Bainitic Steels: A Review of Recent Developments

Abstract

Recent works at KIMAB and Arcelor Research indicate that the mechanical properties of bainitic steels can be improved with V-microalloying. This is potentially important since there is expected to be a shift from existing precipitation hardened HSLA steels towards bainitic types as demand arises for higher strength. Although the bainitic transformation temperature is too low to promote precipitation strengthening, it seems that fine V(C, N) particles can effectively prevent the recovery of the dislocation structure of the bainite during coiling of hot-rolled strip product, giving an increase in strength. There are also indications that vanadium combined with nitrogen in bainitic steel promotes the formation of lower-bainite, referring to a bainitic microstructure with smaller crystallographic units delineated by high-angled boundaries, with associated increase in strength and good toughness. Recent investigations on bainitic rail steels in Japan and Europe demonstrate that vanadium is also useful to give fine laths microstructures and improve wear resistance.