Metallurgical factors contributing to HAZ cracking susceptibility in cast alloy 718 welds and its improvement by cerium addition |
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Authors: | Insu Woo Kazutoshi Nishimoto |
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Affiliation: | (1) Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, 567-0047 Ibaraki, Osaka, Japan;(2) Department of Manufacturing Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, 565-0871 Suita, Osaka, Japan |
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Abstract: | A study was carried out to determine the effect of cerium addition on HAZ cracking susceptibility in cast alloy 718 welds.
The cause of HAZ cracking was also investigated using commercial cast alloy 718 varying in grain size at three levels. The
hot cracking test results for commercial cast alloy 718 indicated that the fine-grained alloy was less sensitive to HAZ cracking.
Furthermore, cerium addition of up to 0.3 wt.% was found to have a beneficial effect in reducing HAZ cracking susceptibility.
When cerium addition exceeds 0.3 wt%, HAZ cracking susceptibility increased further. The mechanism of HAZ cracking was found
to be related to intergranular liquation caused by the eutectic melting of sulfur containing a laves cluster at the grain
boundaries. The degree of grain boundary liquation in the fine-grained specimen was less than that of the coarse-grained specimen
due to a decrease in the amount of laves cluster and sulfur segregation in it at the grain boundaries, which seems to be responsible
for a reduction in hot cracking susceptibility in the fine-grained specimen. Microscopic observation suggested that the improved
HAZ cracking susceptibility in cerium containing alloy could be attributed to a reduction in the amount of laves cluster and
sulfur segregation in it at grain boundaries due to the grain size reduction and sulfur-scavenging effects of cerium. |
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Keywords: | HAZ cracking cast alloy 718 intergranular liquation laves cluster cerium |
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