THE INFLUENCE OF PEARLITE ON BARKHAUSEN NOISE GENERATION IN PLAIN CARBON-STEELS

Barkhausen noise refers to the abrupt, discontinuous changes in magnetization which result from domain walls overcoming barriers to their movement. Barkhausen noise is sensitive to a number of parameters, notably stress level (for which it is being examined as a basis for non-destructive evaluation) and microstructure. The present study investigates the influence of pearlite content on the pulse height distribution of the magnetic Barkhausen noise signal in plain carbon steels. The responses of purely pearlitic and purely ferritic microstructures are determined to be quite different. Samples containing no pearlite display a narrow, symmetrical distribution of relatively small pulse heights. The behaviour of the pearlitic steel is quite different, however, exhibiting an asymmetrical pulse height distribution with a significant tail extending to comparatively large pulse heights (approximately four times that of the maximum for the ferrite signal). Steels containing both ferrite and pearlite produce signal distributions between the two extremes, but contain no significant tail and also appear to tend toward larger pulse heights than what would be expected for a purely "composite" distribution. Results are explained in terms of differences in domain wall pinning behaviour between the various microstructures.