Microstructure and texture evolution in dual-phase steels: Competition between recovery, recrystallization, and phase transformation

The microstructure and texture evolution of dual-phase steel sheets with a cold reduction of about 50%, annealed at ferritic and intercritical temperatures, were analyzed by scanning electron microscopy and electron backscatter diffraction. The competition between recrystallization and phase transformation was of particular interest. The sheets were annealed in salt bath or were annealed in a MULTIPAS annealing simulator under variation of annealing temperature, annealing time, and heating rate. For low intercritical temperatures, recrystallization occurred before phase transformation. The sheets showed a similar through-thickness texture inhomogeneity with a plane-strain texture with strong α-fiber and weak γ-fiber as cold rolled sheets and a ferritic-martensitic band structure in the sheet center layers. An inverse correlation between the volume fractions of recrystallized ferrite and martensite was observed. This interdependence is attributed to a different phase transformation kinetics for recyrstallized and deformed ferrite and is discussed in terms of deformation strain energy, diffusion, and number of nucleation sites.