Microstructure, Texture, and Tensile Properties of a Severely Warm-Rolled and Annealed Duplex Stainless Steel

The effect of severe warm-rolling and annealing is studied in a duplex stainless steel (DSS). For this purpose, a duplex steel is warm-rolled at 625 degrees C to 90, 95, and 98% reduction in thickness and then isothermally annealed at 1175 degrees C for time ranging from 2 to 120min. Ultrafine microstructure is achieved during warm-rolling. Austenite shows continuous grain refinement up to the highest strain level, but ferrite shows saturation in grain refinement beyond 90% reduction. The structural evolution in the two phases is consistent with the texture evolution. Austenite shows transition from copper-type to brass-type texture with increasing deformation, while ferrite shows strong RD fiber (RD//< 110 >) as compared to ND fiber (ND//< 111 >) components, but no significant change in texture beyond 90% reduction in thickness. A typical bamboo-type morphology evolves during isothermal annealing for short duration, which transforms into globular morphology with increasing annealing time due to the interpenetration of the two phases. Ferrite shows stronger RD fiber due to recovery. In contrast, profuse annealing twins and retained the deformation texture in austenite indicate discontinuous recrystallization without preferential orientation selection. Ultrahigh strength (> 1GPa) is achieved after warm-rolling. Annealing results in increased ductility at the expense of strength.