Hot- and Cold-Rolled Low-Carbon Manganese TRIP Steels

An alternative alloy and processing concept has been studied to evaluate the feasibility of producing low-carbon TRIP steels. Conventional hot-rolling, cold-rolling, and batch annealing processes were simulated with three laboratory heats of varying manganese content. The hot-rolled steels were found to be fully hardenable with conventional hot-strip mill processing, and subsequent batch annealing simulations produced significant retained austenite levels. The combination of the prior martensitic microstructure in the as-hot-rolled condition, and subsequent ferrite-martensite-austenite microstructures created by annealing, resulted in remarkable combinations of strength and ductility. Tensile strengths exceeding 1400 MPa were observed in the as-hot-rolled condition, and when annealed at the highest temperatures and longest durations, with total elongations of approximately 10 percent. Ductility increased markedly when samples were annealed at approximately 650°C. While this treatment reduced the tensile strength to 600-1000 MPa, total elongation exceeded 30% in many cases. UTS*TE products greater than 30,000 MPa-% were observed.