Microstructure evolution in ultrafine-grained interstitial free steel processed by high pressure torsion

Abstract

Commercial interstitial free steel was processed by high pressure torsion (HPT) at room temperature up to 5 revolutions. HPT resulted in strong grain refinement. The microstructure after HPT was inhomogeneous with refined grains mainly in regions near the specimen periphery, while coarse only slightly fragmented grains were observed in specimen centre. The microstructure inhomogeneity was continuously smeared out with increasing number of rotations by extending the fine grain region from specimen periphery towards its centre. However, even after 5 revolutions the microstructure remained inhomogeneous characterized by slightly coarser grains in central regions as compared to peripheral regions of the specimen. Positron annihilation spectroscopy (PAS) and X-ray line profile analysis (XLPA) were employed to characterize the structure inhomogeneity in individual specimens. Microstructure and dislocation density evolution were correlated with mechanical properties characterized by a detail microhardness measurement throughout the individual specimens. © Published under licence by IOP Publishing Ltd.