Abstract
Vastly different microstructures are formed in 304LN austenitic and Fecralloy® ferritic stainless steel joints brazed with Ni-15Cr-1.4B-7.25Si (MBF-51) and Ni-19Cr-1.5B-7.3Si (MBF-50), filler metals, respectively. These joints were cut from an industrial heat exchanger and a metallic catalyst support that were subjected to a short optimal brazing cycle in a vacuum furnace. A detailed description is given of the composition and morphology of phases evolved in these brazements, as a result of complex metallurgical reactions between the base and filler metals. A new metallurgical reaction was discovered between Fe-20Cr-5Al Fecralloy base metal (BM) having b.c.c. crystal lattice, and the Ni and B from MBF-50 (Ni-19Cr-1.5B-7.25Si) brazing filler metal (FM). This reaction resulted in the precipitation of fine, regularly distributed Nix (Al)y particles in the base metal matrix phase, thus strengthening Fecralloy brazements. The microstructure discovered in this work is remarkably similar to that of conventional precipitation-hardened, heat resistant alloys. Therefore, these joints can withstand years of service in the brutal environment observed in automotive exhaust pipes.
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Leone, E.A., Rabinkin, A. & Sarna, B. Microstructure of Thin-Gauge Austenitic and Ferritic Stainless Steel Joints Brazed using Metglas® Amorphous Foil. Weld World 50, 3–15 (2006). https://doi.org/10.1007/BF03266509
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DOI: https://doi.org/10.1007/BF03266509