昇温時界面反応が箔状ろう材による黄銅ろう付に及ぼす影響

抄録

Brass is used for piping components because of its excellent workability. Brass and stainless steel are used for piping components, and brazing is used for airtightness. Pb was added to brass to improve machinability. However, with the revision of the Drinking Water Quality Standards Law, lead–free free–cutting brass with Bi or Si added instead of Pb has been developed and put into practical use. Bi and Si are known to affect braze ability and further research is needed. Previous studies have shown that brazing between brass and stainless steel is affected not only by additive elements but also by temperature. When brazed at high temperatures (around 800°C), brass is prone to be brisk due to high temperature dezincification phenomenon. Therefore, it is known that brazing at low temperatures (around 700°C) prevents the phenomenon of dezincification and prevents Zn contained in the base metal from diffusing into the brazing filler metal. To obtain a brazed joint when brazing brass to stainless steel, we have been investigating appropriate brazing temperatures. In this study, we investigated the effect of interfacial reactions on brazing during the heating process when brazing is performed at relatively low temperatures. Furthermore, the heating time was aimed at clarifying the interfacial reaction during brazing brass and stainless steel.

Lead–free brass with Bi added and austenitic stainless steel SUS304 were used as base materials. BAg–7, a foil–type Ag–based brazing material, was used as the brazing material. Furnace brazing was performed using an electric furnace of the type. Brazing temperatures were 700°C and 740°C, and brazing holding time was 5 minutes.

Comparisons were also made by changing the heating rate. The brazing was evaluated by observing the microstructure under an optical microscope and mapping elemental analysis by EPMA.