Effects of thermomechanical processing in αplusγ region on retained austenite parameters of TRIP-aided dual-phase steels

The effects of thermomechanical processing (TMP) on retained austenite parameters of Si-Mn TRIP-aided dual-phase (TDP) steels were investigated to improve the press formability. One pass 30 similar to 50% reduction in alpha + gamma region just after intercritical annealing increased Volume fraction of the retained austenite with a slight decrease in the carbon concentration. Also, it achieved uniformly fine structure consisting of ferrite, bainite and retained austenite. Most of the retained austenite, however, coexisted with bainite or bainitic ferrite as a mixed second phase, differing from the conventional TDP steel subjected to only heat-teatment. Additions of carbon, manganese, silicon and phosphorous to the TMP steels increased further volume fraction and total carbon concentration of the retained austenite, except silicon addition of 2.5 mass%.