Liu Kui

Secondary Precipitation Behavior of Nitride in the Electro-slag Remelted Structure of Alloy 690

The precipitation and evolution of secondary nitrides (S-nitrides) in the Alloy 690 electro-slag remelted (ESR) structure were investigated. Experimental results indicate that S-nitrides precipitated in the interdendritic region of the ESR structure at temperatures higher than 1100xa0°C. S-nitrides could spread throughout the entire interdendritic area after sufficient exposure, and they were more numerous and much finer than primary nitrides. Furthermore, after studying the evolution of S-nitride particles at 1100, 1200 and 1300xa0°C, it was determined that the precipitation of S-nitrides was controlled by the diffusion of nitrogen. In addition, by investigating the elemental segregation of ESR structure and calculating critical Ti concentrations, S-nitride precipitation was found to be thermodynamically inevitable in the Alloy 690 ESR structure.