2000 Volume 18 Issue 3 Pages 438-448
The hot cracking susceptibilities of HP-modified heat-resisting cast alloys exposed at the elevated temperature for the long term were evaluated by the miniature spot-Varestraint testing. The as-cast, aging and/or used (service exposed) specimens of seven types of the HP-modified alloys were employed for the spot-Varestraint testing. Ductility-dip cracking as well as liquation cracking was occurred in HAZ of each specimen after the spot-Varestraint testing. The ductility-dip cracking susceptibilities of alloys except for HP43AZ much increased in aged and used conditions compared with as-cast condition, while the liquation cracking susceptibilities did not change so much during long term aging. The ductility-dip cracking susceptibility of HP43AZ containing zirconium was remarkably restrained even in used condition. It was deduced that the improvement in the ductility-dip cracking susceptibility of HP43AZ was attributed to reducing the occupied ratio of microconstituents on cellular dendrite boundary by the zirconium addition which possessed refinement effect of dendritic cell.