2020 年 38 巻 1 号 p. 1-10
Solidification cracking and liquation cracking susceptibility of four kinds of alloy 617 commercial filler metals were evaluated by Varestraint test, in order to clarify a fundamental effect of each solute element in the alloy. Fracture surface of cracking in alloy 617 multipass welds by GTA welding exhibited a possibility of occurrence of both solidification cracking and liquation cracking. Brittle temperature ranges (BTR) of the liquation cracking at each alloy were almost same, however the BTRs of solidification cracking indicated significant difference. Complex carbide composed carbon, titanium and niobium was formed in the weld metal in the case of the smallest BTR for the solidification cracking, in other words alloy 617 including a lot of titanium and niobium indicated a good susceptibility for the solidification cracking.
Numerical simulation of solidification segregation of alloy 617 was carried out to reveal the solidification behavior at terminal stage of the alloy. The solidification segregation analysis suggested that solidification cracking susceptibility was attributed the carbide formation depending on the solidification segregation of carbon, titanium and niobium. In the alloy containing titanium and niobium, the carbide formation occurred at the terminal stage of the solidification. Therefore, solidification completed temperature increased because the amount of carbon in residual liquid decreased after the carbide formation.