Study of microstructural inhomogeneity and its effects on mechanical properties of multi-layer laser welded joint

摘要

Hybrid laser-arc welding is an emerging joining technology which has a promising prospect in thick plate manufacturing. In this paper, the thick plate butt joint of 16MnDR with 20 mm was successfully connected by using multi-layer laser welding technology. On this basis, the microstructural inhomogeneity and its influences on mechanical properties of the multi-layer welded joint were further investigated. The results indicated that microstructure of the multi-layer welded joint is inhomogeneous for two reasons: firstly, different heat inputs and cooling rates caused the microstructural inhomogeneity of different layers; secondly, different thermal cycles at different locations within inter-laminar zones led to disparate microstructure transformation and further intensified the microstructural inhomogeneity of the multi-layer welded joint. As a result, mechanical properties of the welded joint are obviously influenced by the microstructural inhomogeneity. From layer 1 to layer 4, the hardness distribution showed an overall downward trend and fluctuated obviously in inter-laminar zones. Besides, ductile fracture happened in all impact specimens, and the impact toughness decreased from layer 1 to layer 4 owing to the microstructural inhomogeneity and increasing microvoids. In addition, the uncleaned contamination between layers weakened the tensile strength of the welded joint. Thus, it is necessary for the multi-layer welding procedure to clear up former welds effectively before latter welding.