Cooling rate effect on vacuum brazed joint properties for 2205 duplex stainless steels

The influence of cooling rates and fillers on the mechanical properties and corrosion resistance of vacuum brazed joints for two types of 2205 duplex stainless steels was investigated. The amount of a sigma phase precipitated in the duplex stainless steel (DSS) was increased at a slow cooling rate. When the cooling rate was increased to 0.25 °C s−1, the suppression of sigma-phase precipitation was observed. As for the mechanical property of the brazed joints, shear strengths of the vacuum brazed joints were obtained in the range 46–79, 110–135, and 173–250 MPa for filler material of BNi-7 powder, BNi-3 powder, and copper foil, respectively. Most of the brazed joints were ruptured at the brazed gap. However, the joints of GMTC 2205 DSS, using BNi-3 filler and Cu foil under the cooling rate of 0.1 and 0.067 °C s−1, were broken at parent metal. The ruptures at parent metal were caused by a large amount of brittle σ-phase precipitation on the substrate. Besides, owing to the dissimilarity between the filler composition and DSS, galvanic corrosion behavior was observed when placing the brazed joints in a chloride solution.