Hot corrosion behavior and mechanical properties of austenitic stainless AISI 321 joints brazed with BNi-2

This study investigates the hot corrosion behavior and mechanical properties of 321 stainless-steel joints vacuum-brazed with BNi-2 filler metal at 1050 °C with different holding times. At shorter holding times (10–30 min), blocky Cr-borides precipitate in athermal solidification zone (ASZ), and finer Cr-borides form in diffusion-affected zone (DAZ). Extending the holding time to 60 min markedly suppresses boride formation. The diffusion-affected zone experiences the most severe corrosion owing to chromium depletion in the matrix, whereas the nickel-rich isothermal solidification zone (ISZ) demonstrates superior corrosion resistance. Hot corrosion initiates with electrochemical dissolution of the oxide film, followed by chloride-activated corrosion, leading to the formation of multi-layered corrosion products. The joint brazed for 60 min exhibited a tensile strength of 505 MPa and an elongation of 11.2%, outperforming those produced with shorter holding times. Although a slight increase in strength was observed after two hot corrosion cycles due to solute diffusion, further cycling resulted in progressive degradation of mechanical properties, with the 60-minute joint showing the least reduction. These findings highlight the beneficial effects of prolonged brazing time on both the corrosion resistance and mechanical integrity of the stainless-steel joint.