Influence of borides dissolution during the homogenization treatment on the mechanical properties and fracture behavior of austenitic stainless steel brazed joints

The effects of borides dissolution during the homogenization treatment on the mechanical properties and fracture behavior of austenitic stainless steel brazed joints are investigated. The microstructure evolution of brazed joints is investigated by field emission scanning electron microscope (FE-SEM) and electron probe microanalyser (EPMA). The mechanical properties of brazed joints are investigated by microhardness test and tensile test of T-shape brazing specimen. In particular, electron back scatter diffraction (EBSD) measurement is conducted to study the fracture behavior of brazed joints. The results show that the diffusion affected zone of the brazed joints contains substantial Cr enriched boride precipitates with different morphologies. The homogenization treatment effectively eliminates the boride precipitates and significantly reduces the difference in chemical composition between different zones. The boride precipitates experience the fragmentation and dissolution during the homogenization treatment. In addition, the microhardness of the diffusion affected zone gradually decreases as the homogenization time increases. The maximum force of the tensile test increases first and then decreases as the homogenization treatment time increases. The fracture mechanism of the brazed joints is discussed. After the homogenization treatment, the fracture position of brazed joints changes from the diffusion affected zone to the base metal. It is attributed to that the dissolution of boride precipitates enhances the binding force of grain boundaries and improve the cracking resistance of the diffusion affected zone.