Barkhausen noise from plain carbon steels: analysis of the influence of microstructure

The characteristics of the Barkhausen noise phenomenon are investigated for various crystalline microstructures of plain steels. The measurements of the magnetic Barkhausen noise (MBN) and of the acoustic Barkhausen noise (ABN) are performed using the same magnetisation rate for different materials, specially developed to provide fully reproducible experimental conditions. The MBN fingerprints of single constituent steels (ferrite, pearlite and martensite) are first studied. Then, examples of MBN characteristics for more complex microstructures are presented. The results concerning single constituent steels are discussed in terms of shape, amplitude and position of the MBN and ABN fingerprints, taking into account two main aspects: the elementary Barkhausen events (sources), linked to the interaction of the magnetic domain microstructure with the crystalline microstructure, and the propagation of the electromagnetic waves in the material as well as its detection at the pick-up coil, both strongly influencing the frequency spectrum of the detected signal. This approach enables us to get a better understanding of the dependency of Barkhausen noise on the crystalline microstructure, which is then used to explain the characteristics of MBN observed for more complex microstructures.