Formation of Nitrogen-Pearlite in the Diffusion Bonding of Sialon to 316L Stainless Steel

The objective of this study is to investigate the interface reaction and diffusion bonding between 316L stainless steel and sialon. Bonding was carried out in a hot press at 1250°C under the pressure of 15 MN/m2 for 1 hour and was cooled slowly in the furnace to prevent the mismatch between the sialon and the steel. Scanning Electron microscopy (SEM) revealed the interdiffusion and intereaction between the steel and the sialon. The elements diffusing into sialon were illustrated by the Energy Dispersive Spectrometer (EDS) analysis where the presence of Fe, Cr, Ni and Mn are significant. The formation of nitrogen pearlite can be described as a result of the reaction between the stainless steel and the silicon nitride component of sialon which release nitrogen. Mechanical behaviour of the nitrogen diffused layer was also investigated using microhardness tester and at the reaction layer an increase in hardness was observed. Conclusion can be deduced that the formation of nitrogen pearlite in the stainless steel is quite significant especially on joining sialon to as-received nitrogen-free austenite stainless steel. The formation of nitrogen pearlite could be understood by the diffusion of nitrogen into the stainless steel. Thus, the continuous precipitates form lamellar nitrogen pearlite.