Microstructure and electrochemical properties of the bonding zone of AISI 316L steel joined with a Fe-based amorphous foil

The effect of temperature and holding time on the microstructure and corrosion resistance of the junction zone of AISI 316L stainless steel (SS) bonded to itself with Fe75Cr8P10B7 filler alloy was investigated. The brazing alloy was prepared in the laboratory in the form of amorphous ribbons and its melting temperature was determined by differential thermal analysis (DTA) to be 1571 K. The joining process was carried out in a chamber with controlled Ar atmosphere at two temperatures: 1173 and 1273 K for different holding times not exceeding 40 min. Joining took place by the mechanism of diffusion bonding. The joints produced at 1273 K for 40 min exhibited no porosity in the reaction zones and presented the best quality. Scanning electron microscopy (SEM) characterization of the bonding zone revealed an improvement in the quality of the joints brazed at 1173 K for 20 min and longer. These samples had continuous base metal–filler alloy interfaces with minimum porosity. At 1273 K the bonding interfaces diffused and for the samples held for 40 min completely vanished and porosity disappeared. Even the presence of particle precipitates the bonding zone showed acceptable resistance to localised corrosion in non-aggressive electrolytes. SEM study revealed that irregularly precipitated particles and other phases of about 10 μm in size formed in the interlayer during the joining process. The presence of σ-phase in samples bonded at 1273 K promoted preferential dissolution in the bonding zone in NaCl solution.