FERRITE FORMATION CHARACTERISTICS IN SI-MN TRIP STEELS

If the austenite-to-proeutectoid ferrite reaction is the first phase t ransformation which occurs during cooling of a hypoeutectoid steel, gr owth of ferrite takes place by rejection of carbon into the untransfor med austenite, such that the carbon content of the austenite increases with increasing ferrite volume fraction. The carbon enrichment of aus tenite affects the state of retained austenite in the final microstruc ture. Such an effect is important when designing microstructures of tr ansformation induced plasticity (TRIP) steels, which are a new class o f high formable steels. These grades of TRIP steels, which are in exce ss of Si and Mn, make use of ferrite and bainite as the major micro-co mponents. This work details the results of a systematic investigation on the ferrite formation characteristics and their effects on the stat e of the retained austenite. The results showed that the retained aust enite volume fraction increases with the amount of ferrite and, after a plateau, decreases. Furthermore, the presence of acicular ferrite re sulted in a significant increase in the quantity of the retained auste nite.