GRAIN BOUNDARY CHEMISTRY CONTRIBUTIONS TO INTERGRANULAR HOT CRACKING

Abstract
This report presents recent findings concerning the role of intergranular chemistry in the mechanism of intergranular hot cracking IHC during welding. The IHC of the weld heat affected zone during welding has long been suspected of some relationship to residual elements. Until now, that relationship in nickel alloys had been lost due to the roles that bulk concentration, volume fraction of second phase, and heat treatment played in establishing the intergranular chemistry of the alloy. Experiments in this study correlated the IHC susceptibility with bulk sulfur and heat treatment. It is shown that increasing sulfur from 0.0008 to 0.009 weight percent caused a modest increase in IHC. However, heat treatment had a three fold greater effect on IHC than the sulfur range tested. It is postulated that, although an increase in bulk sulfur increases the intergranular sulfur level, heat treatment has a more potent effect on IHC through combined segregation and precipitation reactions. Auger spectroscopy, metallography, and IHC data are presented in defense of these arguments.