Non-destructive characterisation of welding induced anisotropy in steel by magnetic Barkhausen noise

摘要

The magnetic Barkhausen noise (MBN) technique was used to investigate the welding induced magnetic anisotropy in steel. A stress concentration region was created by placing a weld bead on a specimen surface without machining. MBN measurements were made on the other surface of the specimen along the weld direction and perpendicular to it in a line that crosses the weld direction. The stress distribution at the back of the weld bead, as deduced from the MBN measurements was found to be dependant on the magnetic field direction in the heat affected zone. The MBN variation across the weld line with magnetic field parallel to the weld bead was found to be due to residual tensile stresses. The heat induced anisotropy was completely eliminated by shot peening the HAZ material as revealed by MBN intensity. It was concluded that the directional MBN measurements could be used to characterise the induced anisotropy and hence asses the thermal residual stresses distribution near a localized stresses concentration regions.