Brazed stainless steel joints are critical in heat exchanger applications but often suffer from residual stresses and brittle intermetallics. Using in-situ synchrotron X-ray diffraction and fluorescence at the DanMAX beamline, we investigated Fe-based filler joints in SS316 under tensile loading. Elemental mapping and phase analysis revealed distinct interfacial solidification zones (ISZ), athermal solidification zones (ASZ), and diffusion-affected zones (DAZ). Relative to the base composition, the ISZ showed an average Ni enrichment of ∼35%, while the ASZ exhibited localized Mo and Cr enrichment of up to ∼40% and ∼10%, respectively. The diffusion affected zone was strongly asymmetric, spanning approximately 400μm on one side of the ∼250μm wide joint and approximately 200μm on the other. Strain tensor mapping showed strong elastic anisotropy and stress localization at boride-rich zones, correlating with the observed fracture path. The results demonstrate the capability of synchrotron-based analysis to provide comprehensive insight into the interplay between chemical composition, microstructure, and stress in governing joint integrity, thereby informing strategies for improving toughness through process optimization.