Effect of B and Si on Microstructure and Corrosion Resistance of 316L Stainless Steel Brazed Joints

The corrosion behavior of 316L stainless steel joints brazed with three commercial nickel-based filler metals (Ni-7Cr-2.8B-4.5Si, Ni-14.3Cr-3.5B, and Ni-18.5Cr-9.8Si) was comparatively investigated. The B-containing joints form dispersed CrB-type borides, while the Si-only joint develops continuous band-like Ni3Si intermetallics along the seam center. Electrochemical measurements show that the Ni-Cr-B joint exhibits the highest polarization resistance, whereas the Ni-Cr-Si joint shows the most compact passive film. However, cross-sectional corrosion morphology reveals that the Ni-Cr-Si joint suffers the deepest localized attack due to the continuous Ni3Si phase acting as preferential corrosion channels. In contrast, the Ni-Cr-B joint exhibits shallow and uniform corrosion with minimal strength degradation (0.45% loss), while the Ni-Cr-B-Si joint shows the most severe reduction (47% loss) due to preferential attack along boride boundaries, which is facilitated by pre-existing solidification pores in the non-isothermal solidification zone. These findings demonstrate that corrosion resistance is governed by the distribution and continuity of second phases, providing guidance for filler metal selection in corrosive environments.