Formation Mechanism of Transition Layer Weld/Substrate Interface of S32304/Q390C Composite Material

S32304/Q390C welded joints with two kinds of transition layer weld shapes were prepared by the same welding method and different welding parameters. The microstructure, element, mechanical properties and dislocation density at the interface between the transition layer weld and substrate of the two joints were characterized. The formation mechanism of the interface of the transition layer weld/substrate was discussed. The results show that during the welding process of the transition layer weld, the carbon of the substrate area diffuses to the transition layer weld area, and the chromium of the transition layer weld area diffuses to the substrate area, both carbon and chromium accumulate at the side of the transition layer weld. When the welding energy of the transition layer weld increases, the deformed grains and dislocations density in the substrate area increase, and the driving force of atom diffusion in the interface area increases, which increases the displacement of diffusion. The thickness of the decarburization layer on the side of the substrate increases, CrC is formed, hardness increases, and the plastic deformation performance decreases. At the same, average grain size and low-angle grain boundaries increase, and grain texture is in the < 111 > direction (i.e., atomic diffusion direction).