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SynopsisThe influence of Al and Ti on the hot cracking tendency of the weld heat affected zone (HAZ) in Incoloy 800 has been examined and assessed by the hot ductility characteristics measured by the weld thermal cycle simulator. The major results are summarized as follows:(1) Both Al and Ti expand the brittle temperature range (BTR) and increase the HAZ cracking tendency.(2) The predominant cause of the HAZ cracking is the grain boundary liquation.(3) The influence of Ti on the grain boundary liquation is far greater than that of Al.(4) The enhancement of grain boundary liquation by Ti is attributable to the constitutional liquation of Ti (CN) phase that exists in the grain boundary.