Texture development in cold rolled and annealed C-Mn-Si and C-Mn-Al-Si TRIP steels

Abstract

The texture of two transformation induced plasticity steels has been studied by means of crystallographic orientation mapping. Texture measurements were carried out on ferrite, bainite, and austenite. The polygonal ferrite and the bainite texture, both bcc, could be distinguished based on the image quality parameter of the electron backscattering diffraction measurement. Both bcc textures were very similar, the main difference being the more pronounced 111alpha ND ND=normal direction and 110alpha RD RD=rolling direction fibre textures in the polygonal ferrite. The fcc texture was a strong gamma deformation texture, characterised by the beta fibre. The presence of the alpha fibre confirmed the strong 110gamma ND direction, which was previously detected by means of X ray diffraction XRD. The measured fcc and bcc textures were used to calculate orientation distribution function transformations according the Bain, Kurdjumov-Sachs, and Nishiyama-Wasserman orientation relationships. The predicted cube component {001}gamma 100gamma, which was missing in the measured texture, of gammaret indicates a variant selection for the gammaalphaB transformation. In addition it was shown that crystallographic orientation mapping could be used to make reliable phase fraction determinations, which were previously based on the light optical microscopy of colour etched specimens. This also proves that XRD determination of gammaret is flawed owing to the strong texturing of all phases present in the microstructure.