Multiple pass axi-symmetrical forward spiral extrusion of interstitial-free (IF) steel

Mechanical property changes and microstructure evolution after multi-pass axi-symmetrical forward spiral extrusion (MPAFSE) on Ti-IF steel were studied. Torsion tests on the samples processed by the MPAFSE indicated that the process has improved the yield and ultimate tensile strength at the expense of the material ductility. Existing analytical and experimental studies of the AFSE proved a radial gradient of deformation for a single pass AFSE. However, it will be shown here that in the MPAFSE, the hardness distribution becomes homogenized after 4-pass of deformation which is due to “the friction induced deformation” during the process. Also, Electron Back Scattered Diffraction (EBSD) assessments of the processed samples revealed the effect of shear deformation during the MPAFSE on the formation of low angle grain boundaries (LAGBs) the intensity of which is proportional to the number of the MPAFSE passes. Based on the EBSD observations, the homogenization of material after the MPAFSE can also be correlated to the saturation of microstructure/LAGBs after successive passes of deformation. The texture analysis, in plane normal to the extrusion direction, suggested that despite the texture development during MPAFSE, the subsequent mechanical properties were not considerably affected.