INVESTIGATION OF THE MAGNETIC-FIELD AND STRESS DEPENDENCE OF 180-DEGREES DOMAIN-WALL MOTION IN PIPELINE STEEL USING MAGNETIC BARKHAUSEN NOISE

Magnetic Barkhausen noise (MBN) measurements were performed on 2% Mn pipeline steel samples as a function of magnetic field (H) and as a function of orientation of an applied sweep field for various tensile and compressive stress values. For the magnetic field dependent measurements, the H field and stress were applied along the same axis, which was aligned within 10-degrees of the sample's magnetic easy axis. Tensile stresses between 210 MPa and 0 and compressive stresses between 0 and -200 MPa were applied. The MBN signal was observed to initially increase with H followed by a decrease and eventual suppression of the MBN signal at higher H values. The application of tensile stress increased the total MBN signal and increased the field at which suppression occurred, while the application of compressive stress decreased the total signal with a corresponding decrease in the suppression field value. The stress and low-field behaviour of the MBN signal was correlated with the irreversible differential permeability (mu(IDP)) measured in a similar 2% Mn pipeline steel sample. The behaviour of the MBN signal as a function of H and stress was attributed to the effect of these parameters on the relative population and/or size of 180-degrees domain walls, that is, the total 180-degrees domain wall area, within the sample.