Microstructure and texture changes in a low-alloyed TRIP-aided steel induced by small plastic deformation

Abstract

The microstructures and the textures of TRIP-assisted and Dual Phase steel in undeformed state and after 10% strain applied parallel to the rolling direction of the steel sheet were studied by optical microscopy, EBSD, TEM and XRD. It was found that the strain-induced transformation of retained austenite to martensite leads to localized deformation of ferrite close to the ferrite/martensite phase boundaries and the formation of a composite skeleton of several phases (bainite, retained austenite and martensite), clasping the ferrite grains, which thereby decrease in size. Ferrite and retained austenite deform simultaneously to minimize the local stresses at the phase boundaries, until the strain-induced martensitic transformation takes place. The compositelike strengthening behaviour in a TRIP-aided steel might be expressed by the decreasing free path of dislocations in ferrite due to the enlarging and thickening of the multiphase skeleton as plastic deformation progresses, without changing significantly the main texture components in the material. © 2006 ISIJ.