Evolution of Microstructure and Texture during Isothermal Annealing of a Heavily Warm-rolled Duplex Steel

Abstract

The evolution of microstructure and texture during isothermal annealing of a heavily warm-rolled duplex steel (DSS) was studied. For this purpose a DSS steel was hot rolled, homogenized at 1448 K and subsequently warm-rolled to 90% reduction in thickness at 698 K and 898 K. This was followed by isothermal annealing at 1448 K for different time intervals up to 7200 seconds. Lamellar microstructure with alternate arrangement of deformed ferrite and austenite bands was observed in the as warm-rolled condition. The ferrite in DSS warm-rolled at 698 K showed much stronger α-fiber (Rolling direction (RD)//<110>) than γ-fiber (Normal direction (ND)//<111>) as compared to the ferrite in DSS warm-rolled at 898 K. The austenite in warm-rolled DSS showed a predominantly pure metal (or copper type) texture. Upon annealing the lamellar morphology of the as warm-rolled structure transformed into a bamboo type morphology for short annealing time but finally broke down with increasing isothermal annealing time due to mutual interpenetration of the two phases. Retention of deformation texture components and presence of annealing twins in austenite indicated discontinuous recrystallization. Despite differences of texture in the as warm-rolled condition the ferrite in annealed DSS showed much stronger α-fiber as compared to γ-fiber due to strong recovery behavior of ferrite during annealing. The texture evolution in the two phases was not affected by the presence of the other phase while grain growth was significantly restricted due to the presence of the other phase.