Microtexture development during equibiaxial tensile deformation in monolithic and dual phase steels

Subgrain texture and microstructure evolution in individual ferrite grains in single (so called interstitial-free) and dual phase (DP) steel sheets with various martensitic fractions during stepwise equibiaxial deformation was observed by high resolution electron backscatter diffraction (EBSD) measurement on a special deformation stage positioned inside a scanning electron microscope chamber. The micromechanical effect of hard martensite islands on adjacent ferrite grains in DP steels was analyzed by comparing the microstructural changes in the two steels. The strain partitioning between ferrite and martensite in DP steel, the development of orientation gradients in ferrite grains near martensite islands, and the surface height variation were observed via a combination of high resolution transmission electron microscopy, EBSD, and atomic force microscopy. From these microstructural and geometrical observations the main effect of the hard martensite islands was to shed strain into the adjacent ferrite, thus inducing strain gradients, orientation spread, geometrically necessary dislocations and increased surface height variation.