Research on the Characteristics and Atomic Diffusion Behavior of the Interface of Transition Layer Weld/Base Layer Weld in Stainless Steel Composite Material

Aimed at improving the mechanical performance of welded joints in stainless steel composite materials, this research investigates the evolutionary characteristics of microstructure at the interface between the transition layer weld and base layer weld through electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) analytical techniques. In addition, molecular dynamics simulation methods are employed to conduct an in-depth study on the atomic diffusion behavior during the welding process. The results show that carbon and chromium atoms undergo asymmetric diffusion at the interface, forming a decarburized and a carburized zone. The diffusion coefficient of carbon atoms was the largest, with the diffusion mechanism being interstitial diffusion. Followed by chromium atoms, the diffusion coefficient of Fe was the smallest. On the base layer weld side, two structural zones with different grain sizes were formed; the zone close to the interface was a coarse ferrite microstructure with the lower geometrically necessary dislocation density, the zone far from the interface was a finer-grained ferrite and pearlite microstructure. As the welding heat input of the transition layer weld increases, the average density of geometrically necessary dislocations, the decarburized layer thickness, the average grain size, and the diffusion coefficients of Cr and C atoms at the interface all exhibit a concomitant upward trend. Concurrently, a carbon–chromium compound precipitates at the interface.