Design of novel high strength bainitic steels: Part 1

Mixed microstructures consisting of fine plates of upper bainitic ferrite s eparated by thin films of stable retained austenite have seen many applicat ions in recent years. There may also be some martensite present, although c arbides are avoided by the judicious use of silicon as an alloying element. The essential principles governing the optimisation of such microstructure s are well established, particularly that large regions of unstable high ca rbon retained austenite must be avoided. With careful design, impressive co mbinations of strength and toughness have been reported for high silicon ba initic steels. The aim of the present work,vas to ascertain how far these c oncepts could be extended to achieve unprecedented combinations of strength and toughness in bulk samples subjected to continuous cooling transformati on, consistent with certain hardenability and processing requirements. Thus , this paper (part 1 of a two part study) deals with the design, using phas e transformation theory, of a series of bainitic alloys, given a set of ind ustrial constraints. Part 2 of the study concerns the experimental verifica tion of the design process. (C) 2001 IoM Communications Ltd.