Abstract
Gas metal arc welding (GMAW) is applied to fabricate the QP1180 steel welded joint. The formation of the Widmanstatten ferrite (WF) in weld metal (WM) and its effect on the cold crack generation for QP1180 welded joint was systematically discussed. It is found that the inhomogeneous distribution of the WF can result in the lowest microhardness (∼275 HV) in the WM. High cooling rate, large grain size, low content of element C and high content of element Mn in the region near the WM together trigger the formation of WF, and their epitaxial growth can lead to their extension into the heat affected zone (HAZ) along the prior austenite grain boundaries. As a result, the micro-cracks are formed at the interface between the WF and martensite. Subsequently, the harder martensite with large size further promotes the propagation of the micro-cracks along the grain boundaries in the HAZ, forming the intergranular fracture eventually.
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