This research aims to investigate the relationship between the metal magnetic memory (MMM) signals of Q345 welded steel and its mechanical characteristics including the range of stress concentration zone and the tensile stress. A series of tensile experiments were carried out to measure the tangential residual magnetic field (RMF) on the surface of Q345 steel welded specimens under the action of stress. The variation of tangential RMF and the characteristic parameters (the peak-peak width and the peak-peak amplitude) of tangential RMF gradient curve were investigated. It was found that the tangential magnetic field curve of welded specimen has abnormal magnetic changes in the weld joint area. An analysis of the tangential RMF gradient curve shows that the range of stress concentration zone of welded specimen can be evaluated by the peak-peak width which is nearly constant under different tensile stress. Furthermore, the peak-peak amplitude of the tangential RMF gradient curve has quartic polynomial relationship with tensile stress and it is a potentially useful indictor of the tensile stress in welded steel.

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