Characterization of pure iron and (130 p.p.m.) carbon–iron binary alloy by Barkhausen noise measurements: study of the influence of stress and microstructure

The aim of this work is to measure and characterize the ferromagnetic noise from high purity iron and 130 p.p.m. carbon–iron alloy in various physical and metallurgical conditions. This is the basis of an industrial development of Barkhausen noise as a non-destructive evaluation technique of microstructural changes. The amplitudes and shapes of Barkhausen signals are correlated with the grain size in pure iron and with the presence of interstitial carbon atoms in the iron matrix (magnetic after effect phenomena) in 130 p.p.m. carbon–iron alloy. This technique is also very sensitive to the location (inter- or intragranular precipitations), the nature (cementite or epsilon carbide), the density and size (coalescence effect) of carbide precipitates and internal stresses. The influence of microstructure is analyzed in terms of Bloch wall interactions with crystal defects as pinning points, closure domains or dislocation configurations.