Microstructural evolution and mechanical properties of duplex TRIP steel produced by strip casting

In the present study, a duplex TRIP steel (Fe-0.232C-2.0Si-2.39Mn-2.01Al wt%) was successfully produced by a novel processing route involving twin-roll strip casting (TRSC), heat treatment, cold rolling and annealing for the first time. The evolution of microstructure during the entire processing route was extensively studied that included determination of mechanical properties and fractography of tensile specimens of annealed sheets. It was observed that the as-cast strip microstructure consisted of ferrite and martensite. The morphology at the surface and the center was dendritic and equiaxed, respectively. On using an appropriate heat treatment schedule (heat treatment at 780 °C for 10 min followed by direct quenching), a duplex structure of ferrite and retained austenite (RA) in the heat-treated strip was obtained that was suitable for cold rolling. Annealing temperature was very critical for microstructure and mechanical properties of the annealed sheets. Annealing at 780 °C for 5 min followed by direct quenching yielded a duplex structure of ferrite and RA (volume fraction of ~22%), which exhibited an excellent combination of tensile strength and total elongation of 945 MPa and 28.56%, respectively.