1999 年 17 巻 3 号 p. 456-465
Characteristics of the heat-affected zone cracking of cast alloy 718 has been investigated using the bead on plate test and microscopic observation for isothermally processed specimens.
The results obtained in this study are summarized as follows :
(1) It was clarified that cracking in HAZ of cast alloy 718 was intergranular cracking which was caused by liquation of grain boundary phases.
(2) According to the microscopic observation of specimens heated at various temperatures, incipient melting of the grain boundaries was found to occur at the temperature of 1383 K and above.
(3) The Laves cluster was observed to liquate at the ternary eutectic temperature of 1383 K, which was lower than the NbC liquation temperature of 1413 K.
(4) The liquation cracking in HAZ of cast alloy 718 was considered to be caused by constitutional liquation of Laves cluster at the grain boundaries.