Brazing of Ferritic Stainless Steel with Ni-25Cr-6P-1.5Si-0.5B-1.5Mo Amorphous Brazing Foil Having a Liquidus of 1243 K with Continuous Conveyor Belt Furnace in Low-Oxygen Atmosphere

Abstract

Exhaust gas recirculation (EGR) coolers are a standard technology for reducing the emission and fuel consumption levels of internal combustion engines. These coolers are composed of stainless steel brazed with Ni-based brazing filler metals that can internally withstand high exhaust gas temperatures and corrosive environments. The use of continuous conveyor belt furnaces has increased in brazing because the investment and operating costs are lower than those of conventional vacuum furnaces. Therefore, the demand for brazing at low temperatures must be considered to improve the durability of the conveyor belt. A novel Ni-based amorphous brazing foil with a liquidus temperature of 1243 K and a high corrosion resistance has been commercialized to meet the abovementioned demand. In this report, by using a continuous conveyor belt furnace in a low-oxygen atmosphere, the brazeability of the brazing foil on ferritic stainless steel, the microstructure resulting from the interfacial reaction between the brazing foil and ferritic stainless steel, and the shear strength of a ferritic stainless steel single-lap joint brazed with the brazing foil were investigated. Therefore, the novel brazing foil showed good spreadability on ferritic stainless steel. Moreover, the ferritic stainless steel single-lap joint that was brazed with the brazing foil demonstrated approximately the same shear strength as that brazed with a conventional brazing filler metal.

Fig. 9 Magnified optical micrographs of the cross-sections of SUS430 single-lap joints brazed with MBF67 foils at (a) 1353 K and (b) 1443 K for 10 min.