The effect of iron-based filler metal element on the properties of brazed stainless steel joints for EGR cooler applications

As an alternative to the traditional nickel-based filler metals, new-type iron-based filler metal has become a development trend for stainless steel brazing in exhaust gas recirculation (EGR) cooler fabrication, aiming at decreasing brazing temperature and obtaining higher joint strength with minimal erosion as well as better corrosion resistance. In particular, achieving the satisfying properties with inexpensive raw materials is desirable for broad industrial applications at an economic cost. A new type of iron-based filler metal was designed and developed for SUS304 stainless steel brazing. The effect of B and Mo content on interface microstructure, lap-joint shear strength, microhardness, and corrosion resistance of brazed seam was investigated. The optimum brazing parameters were achieved at 1050 °C-20 min. Both brazing temperature and holding time are critical factors for controlling the interface microstructure and hence the mechanical properties of the brazed joints. The interface microstructure and erosion of T-joints were observed and analyzed. Additionally, results from the evaluation on wettability, shear strength, and corrosion resistance have been benchmarked against commercial iron-based and nickel-based filler metals. Finally, tensile strength tests of brazed joint with developed iron-based filler metal in a form of paste and amorphous foil were conducted at both room temperature and high temperature.