Characterization of a δ/γ duplex stainless steel

A duplex stainless steel was investigated in both as-received sheet and after annealing at temperatures ranging from 850 to 1100°C. The sheet presents a deformation texture in both phases, austenite and ferrite, induced by cold rolling. Microstructure in the as-received material consists of island-like austenitic grains in a ferrite matrix. These austenitic grains are elongated with an average size of 6, 20 and 40 m along the normal (ND), transversal (TD) and rolling direction (RD). Quantitative texture measurements demonstrated that texture components are distributed mainly along the -fiber (ND ‹100›) and -fiber (RD ‹110›) for the ferrite and the -fiber (ND ‹110›) for the austenite. After recrystallization, a decrease in the intensity of the mean fibers and an increase in the minor components was observed in both, ferrite and austenite. Therefore, a similar texture was reached in both phases after annealing at 1050°C. Microstructural characterization after annealing at temperatures above 850°C showed that the elongated austenitic grains transform in colonies of equiaxic grains of about 10–15 m in size. These colonies are surrounded by a ferritic matrix at annealing temperatures above 1000°C or by a laminar microstructure at temperatures below 950°C. This laminar microstructure includes sigma phase and austenite formed from delta ferrite, and untransformed delta ferrite.