Microstructural evolution and mechanical response of 304 stainless steel joint diffusion-bonded with micro-deformation

This study explicates the microstructural evolution and mechanical response of the joints of 304 stainless steel developed through micro-deformation diffusion bonding. The diffusion-bonded interface comprised the refined grains embedded with the intergranular M23C6 carbides and complex oxides, which was induced by dynamic recrystallization at 950 °C. The refined grains persisted at the bonding temperature of 950 °C due to the dynamic equilibrium of dislocations and pinning effect of intergranular particles. As the bonding temperature was raised to 1000 °C, the combination-grow up of grains was initiated caused by sufficient thermal activation and complete dissolution of M23C6 carbides. The interface was entirely migrated at 1050 and 1100 °C, and notably, the migration of interfacial grain boundaries played a greater role in diffusion bonding with an increase of bonding temperature. The interface with refined grains permitted a high joint strength (or impact load), while was incompetent to enhancing plasticity and particularly impact toughness. The migrated interface, in contrast, was provided with exceptional plasticity and impact toughness, attributed to its enhanced resistance to crack propagation. The joint prepared at 1050 °C for 60 min exhibited the optimum combination of ultimate tensile strength, fracture elongation, and impact toughness, and the ductile fracture was observed passing through the substrate instead of along the interface. In addition, the comprehensive performance of joints was degraded when the grains were excessively coarsened at 1100 °C for 60 min.