Numerical Simulation of Carbide NbC Liquating Behavior in Heat-Affected-Zone during Welding of Superalloy

摘要

To predict the propensity of superalloy to heat-affected-zone (HAZ) liquation cracking, FORTRAN procedures were developed based on heat transfer and mass diffusion model and the constitutional liquation of precipitate (NbC) at grain boundaries was simulated numerically. The results show that with the increase of the rate of welding thermal cycle, the dissolution of precipitate prior to liquation decreases and the thickness of liquid film caused by constitutional liquation increases. Higher heating rate inhibits the further melting of adjacent matrix and the subsequent solidification of liquid by liquid-to-γ mode, then creates a liquid film of greater thickness when temperature is down to the eutectic point, which will promote HAZ micro-fissuring. Finally the conclusions drawn from simulation were verified indirectly by hot ductility tests on a low-expansion superalloy.