Study of magnetization processes and the generation of magnetoacoustic and Barkhausen emissions in ferritic/pearlitic steel

Magnetoacoustic emission (MAE), Barkhausen emission (BE), and hysteresis loop measurements have been made on steel specimens heat treated to produce ferritic/pearlitic structures with various volume fractions of ferrite V-alpha. It was found that in the low-field region the BE activity decreases whereas the MAE signal increases with V-alpha. Increasing V-alpha also results in a decrease in the initial peak height of MAE profiles and the formation of outer peaks in BE profiles. It was observed by Lorentz microscopy that in ferrite non-180 degrees domain wall motion occurs readily in the low-field region, while in pearlite significant 180 degrees domain wall motion takes place only when a reversed field was applied. These results can account for the variations in the MAE and BE profiles with V-alpha. The sensitivity of the MAE and BE profiles to V-alpha enables both techniques to be exploited for monitoring the ferrite content of steel components. (C) 1999 American Institute of Physics. [S0021-8979(99)53408-7].