Abstract
The present work was undertaken to examine the mechanism in the improvement of HAZ cracking susceptibility of cast alloy 718 welds by addition of rare earth metals (La, Ce). The HAZ cracking susceptibility of La, Ce-added specimens have been discussed in terms of the intergranular liquation, microconstituents and impurity segregation at grain boundaries. The isothermal liquation test result suggested that, in the case of specimens with up to 0.3 mass% La and Ce, the reduced HAZ cracking susceptibility could be attributed to the decrease in intergranular liquation. The microscopic observation revealed that the cause of reduced intergranular liquation in La and Ce containing specimens was responsible for the reduction in the amount of laves cluster and sulfur segregation at grain boundaries due to grain-refining and sulfur-scavenging effects of La and Ce. Furthermore, the increased HAZ cracking susceptibility and grain boundary liquation at over 0.3 mass% La and Ce addition was due to the increase in low-melting point Ni7La2 and Ni2Ce present at grain boundaries.
