Ferrite Formation Characteristics in Si-Mn TRIP Steels
If the austenite-to-proeutectoid ferrite reaction is the first phase transformation which occurs during cooling of a hypoeutectoid steel, growth of ferrite takes place by rejection of carbon into the untransformed austenite, such that the carbon content of the austenite increases with increasing ferrite volume fraction. The carbon enrichment of austenite affects the state of retained austenite in the final microstructure. Such an effect is important when designing microstructures of transformation induced plasticity (TRIP) steels, which are a new class of high formable steels. These grades of TRIP steels, which are in excess of Si and Mn, make use of ferrite and bainite as the major micro-components. This work details the results of a systematic investigation on the ferrite formation characteristics and their effects on the state of the retained austenite. The results showed that the retained austenite volume fraction increases with the amount of ferrite and, after a plateau, decreases. Furthermore, the presence of acicular ferrite resulted in a significant increase in the quantity of the retained austenite.
- ISIJ international
ISIJ international 37(6), 583-589, 1997-06-15
The Iron and Steel Institute of Japan