PLASTIC STABILITY OF RETAINED AUSTENITE IN THE COLD-ROLLED 0.14-PERCENT-C-1.9-PERCENT-SI-1.7-PERCENT-MN SHEET STEEL

Mechanical properties of a 0.14%C-1.9%Si-1.7%Mn TRIP steel have been studied especially from the aspect of the plastic stability of retained austenite which was varied by changing bainite transformation time at 400 degrees C. The plastic stability of retained austenite and the strength-ductility balance at room temperature are improved with the increase in C content in retained austenite after optimizing the bainite transformation time in the continuous annealing process. Martensitic transformation can occur from the plastically unstable retained austenite with low C content. The kinetics model for deformation-induced martensitic transformation explains the experimentally obtained change in volume fraction of retained austenite with plastic strain in terms of the C content in retained austenite.