2022 Volume 61 Issue 1 Pages 248-253
Brass has been used for piping components because of its excellent machinability and workability. In recent years, due to the revision of the Drinking Water Quality Standards Law, the weighted average value of Pb in brass used for piping components is regulated to be less than 0.25 mass%. Therefore, Pb-free free-cutting brass with Bi or Si added as a substitute element for Pb has been developed and put into practical use.
When brass is used for valves, stainless steel with high strength and corrosion resistance may be used for piping. In the case of a combination of Pb-free free-cutting brass and stainless steel, it is necessary to clarify “the effect of the difference in thermal conductivity between the two on the brazing process” and “the effect of added elements such as Bi and Si on braze ability,” but it is not known. In this study, brazing was performed at controlled temperatures by changing the volume ratio and temperature conditions.
Interfacial reaction between molten brazing filler metal/stainless steel occurred slightly at 680°C for 20 minutes. So that sound brass/stainless steel brazed joint was not obtained. According to cross-sectional microstructure observation results and EPMA elemental analysis results at the brazed joint at 830°C, Bi alloy layer at the brazed joint and Ni disappearance layer at the interface between brazed layer and stainless steel base metal were recognized under uniform heating condition during brazing. On the other hand, under non-uniform heating condition, sound brazed joint was obtained.
