Effect of Additional Elements of Silver Filler Alloys one Microstructure and Corrosion Resistance of Brazed Stainless Steel Joints

Abstract

The effect of additional elements of silver filler alloys on the corrosion resistance of brazed stainless steel joints have been investigated in relations to the microstructure of filler alloys and brazed interface. Corrosion tests were made in 0.4 mol/l NaCl +0.005 mol/l CuCl₂·2H₂O at 25°C. Addition of Mn enhanced the corrosion of filler alloy itself by yielding β phase. Additions of Si, Sn, Sb and Ni improved the corrosion resistance, above all Ni addition appreciably improved the interfacial corrosion resistance. The mechanism of improvement of corrosion resistance at brazed interface by Ni addition were thoght to be as follows. Ni depleted zone was formed at brazed interface of stainless steel side in the case that the stainless steel was brazed with Ni free filler alloys. The Ni depleted zone was changed into ferrite phase during brazing and was less corrosion resistant compared with stainless steel matrix, whereas the zone was not formed in the case that brazed with Ni bearing filler alloy. Therefore, Ni addition into filler alloy maintained the relatively good interfacial corrosion resistance by preventing the formation of less corrosion resistant Ni depleted zone.