Low-Carbon Manganese TRIP Steels

Abstract

The development of TRansformation Induced Plasicity (TRIP) steels has seen much activity in recent years, due to the promise of very high formability combined with high strength. The accepted method for production of as-hot-rolled TRIP steel employs multistage runout table cooling and coiling in the bainitic transformation temperature regime. As an alternative to confronting the production difficulties the accepted strategy presents, a program was begun to evaluate the potential of 0.1C-6.0Mn steels processed in a more conventional manner. Three laboratory heats were melted to consider the effect of manganese content on processing and properties. The 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 austenite created during annealing, resulted in remarkable combinations of strength and ductility. In the as-hot-rolled condition, tensile strengths exceeding 1400 MPa were observed, with total elongations of approximately 10 percent. Optimum properties were found when samples were annealed at approximately 650°C. While this treatment reduced the tensile strength to 800-1000 MPa, the total elongation increased to between 30 percent and 40 percent. UTS*TE products exceeding 30,000 MPa-% were observed, making these materials attractive for high strength, high ductility applications.