Brazeability Of UNS 32101 and UNS S32304 Lean Duplex Stainless Steels

Abstract: Lean duplex stainless steels are a group of stainless steels with a broad field of applications, in particular in conditions where AISI 316L stainless steels are utilized. Brazeability is one issue which should be addressed when joining is taking into account. Lean duplex are less prone to intermetallic phase precipitation at brazing temperature than duplex and superduplex stainless steels. In this work the brazeability of lean duplex UNS S32101 and UNS S32304 were studied. The objective of this work is characterize the microstructure in the brazed joint gap of UNS S32101 and S32304 as a function brazing conditions (time and joint gap) for a constant temperature (1100^oC). The experiments were carried out in an industrial hydrogen continuous furnace, at a brazing temperature of 1100^oC for 10 and 30 min, using a BNi-7 filler metal. The experiments were held using an edge test sample with 0.05, 0.3 and 0.5 mm joint gap end. Joints were characterized by optical microscopy, X-ray diffraction and scanning electron microscopy using back scattered electrons images and dispersive energy microanalysis. Depending upon the gap size, a continuous Ni-rich austenitic phase or continuous eutectic phases were produced in the joint gap, with a gap less than 0.03 mm. In the case of UNS S32102 and UNS S32304 it was observed a NiCrP and Ni-rich fcc eutectic microstructure, with (Ni,Cr,Fe)₃P phase. The best brazing condition was achieved for 0,03 mm and a brazing time of 10 min, for both LDSS.

Keywords: weldability, brazeability, duplex stainless steel, brazing, intermetallic phases.