An Experimental Approach for Correlation of the Magnetic Barkhausen Noise to Microstructural Changes and Residual Stress in Welding Joints

Accurate measurement of the residual stress in welded joints is still a major challenge for both welding quality control and non-destructive testing. One of the most recent and innovative magnetic techniques for this purpose, known as Magnetic Barkhausen Noise (MBN), is based on the reorganization of magnetic domains (regions with uniform magnetic orientations) in the presence of a varying magnetic field in the studied ferromagnetic material. A significant difficulty in using this method for the analysis of welded joints lies in evaluating of the contribution that each altered material property induces in the resulting noise signal. Therefore, the objective of this study was to correlate the MBN signal with the typical changes that occur in the weld bead and its specific regions during the welding process applied to ASTM A36 steel. Thus, the root mean square (RMS) value of the signal was correlated with micro- and macrostructural changes in the joint, as well as with hardness and residual stress state, including its tensile and compressive magnitudes, demonstrating to be an effective non-destructive tool for characterizing of welded structures.