Formation of retained austenite and effect of retained austenite on elongation in low carbon hot-rolled high strength steels

Austenite stabilization behavior and effect of retained austenite on elongation of Fe-0.2%C-1.5%Si-1.5 similar to 1.7%Mn hot rolled high strength steels were investigated in the mill-scale test. The results are as follows; (1) A large amount of retained austenite (maximum=15vol%) remained in steels as-hot-rolled. (2) The two metallurgical processes (ferrite transformation and bainite transformation) are important for the austenite stabilization. Especially ferrite transformation plays an important role to obtain retained austenite in 0.2%C steels. The volume fraction of retained austenite is in proportion to V-PF/d(PF) (V-PF; volume fraction of polygonal ferrite, d(PF); grain diameter of polygonal ferrite). (3) TS x T.El value increases with the volume fraction of retained austenite. It is to be noted that the TS x T.El values of 25000 similar to 30000MPa .% were obtained, which are higher than those of conventional steels. (4) TS x T.El value was improved by increasing of the plastic stability of retained austenite.