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Characterization of ultra-fine grained steel samples produced by high pressure torsion via magnetic barkhausen noise analysis

Bayramoğlu, Sadık
High Pressure Torsion (HPT) is one of the most widely used severe plastic deformation methods which enable to obtain a crack free ultra-fine grained bulk material with improved mechanical properties like increased strength and toughness. In the process, a disc shaped sample is pressed between two anvils and deformed via surface friction forces by rotating one of the anvils. The aim of this study is to nondestructively characterize the variations in the deformation uniformity of the severely deformed steel disks. Two sets of low carbon steel samples were obtained by applying the unconstrained and constrained HPT process up to 6 turns. Magnetic Barkhausen Noise (MBN) method was used in order to evaluate the samples in a nondestructive manner via a commercial device. The results of the MBN measurements were verified with those of conventional methods such as; x-ray diffraction (XRD), metallographic examination and hardness measurements. The initial stages of HPT revealed the effects of conventional plastic deformation on MBN; however with further straining, grain size refinement prevailed and caused increase in MBN signals.