Effect of Annealing on the Microstructure, Texture and Mechanical Properties of a Dual-Phase Ultrahigh-strength TWIP Steel

The present study investigates the effect of annealing time and temperature on the microstructural restoration (by recovery and recrystallization), texture evolution and tensile properties of a dual-phase TWIP steel. The samples, which were initially hot rolled-air cooled followed by being in solution treated condition, subsequent 50 pct cold rolled condition and different annealing conditions (temperatures ranging from 500 degrees C to 1000 degrees C for 5 minutes to 2 hours), were subjected to microstructural characterization using optical and transmission electron microscopy, electron backscatter diffraction analysis, tensile testing and fractographic study. The deformation-induced ferrite (DIF) transformation due to cold deformation, the evolution of the grain structure and texture in both austenite and ferrite, and the change in the DIF fraction (accompanying the recrystallization annealing treatment) are critically analyzed. The optimum combination of strength and ductility is achieved in the partially recrystallized samples annealed at 700 degrees C for 30 minutes (UTS: 859 MPa, total elongation: 37 pct) and 900 degrees C for 30 minutes (UTS: 708 MPa, total elongation: 63 pct).The effects of DIF on the evolution of microstructure and texture during annealing and the final properties are discussed.