On the influence of tempered microstructures on magnetic Barkhausen emission in ferritic steels

TLDR: In this paper, a two-stage process of irreversible magnetic domain wall movement during magnetization is proposed considering the lath or grain boundaries and second-phase precipitates as the two major obstacles to domain-wall movement.

Abstract: Magnetic Barkhausen emission (MBE) has been used to characterize various microstructures in tempered 0.2 wt% C steel, 2.25Cr—1Mo steel and 9Cr—1Mo steel samples (where the composition is in approximate weight per cent). A two-stage process of irreversible magnetic domain wall movement during magnetization is proposed considering the lath or grain boundaries and second-phase precipitates as the two major obstacles to domain-wall movement. The domain walls overcome these two major obstacles over a range of critical field strengths with some mean values, characteristic of the obstacles. If these two mean values are close to each other, then a single peak, sometimes associated with slope changes, appears in the MBE behaviour. On the other hand, if the mean values are widely separated, then two-peak MBE behaviour appears to indicate the influence of these two major obstacles separately. Based on this, the influence of the dissolution of martensite and/or bainite and the precipitation and growth of the...