Characterization of pearlite grains in plain carbon steel by Barkhausen emission

Abstract

Barkhausen emission (BE) measurements are made on a series of plain carbon steel samples with different carbon contents. Different heat treatments are used to produce a ferrite–pearlite structure for the samples with hypoeutectoid compositions (C<0.76 wt.%), and a cementite–pearlite structure for those with hypereutectoid compositions (C>0.76 wt.%). It is found that as the carbon content increases, the BE signal increases for the hypoeutectoid steel samples but decreases for the hypereutectoid samples. The maximum BE signal is detected in samples with carbon content closest to the eutectoid composition (0.76 wt.%C) at which the volume fraction of pearlite is largest. Therefore, it is evident that the BE signal increases monotonically with pearlite content for both hypoeutectoid and hypereutectoid samples. However, no trivial or obvious relationship is found between the BE signal and the carbon content. It is also observed that the BE peaks of the hypereutectoid samples tend to shift to the lower field region as the content of carbon increases, such shift is due to the pinning effect of the increasing proeutectoid cementite on the domain walls.