水素を含む54℃のホウ酸水中における690合金溶接金属の粒界割れ感受性について

抄録

Since alloy 690 and its welds are superior materials for PWSCC susceptibility, application for many components of PWR has been increased instead of alloy 600. It has recently been reported that the materials show intergranular cracking and reduction of fracture toughness in low temperature water with high hydrogen. In this study, fracture toughness tests at slow loading rate were conducted to clarify the possibility of low temperature cracking (LTC) in simulated PWR primary environment. While LTC occured in water with DH=30 cc/kgH₂O and 150 cc/kgH₂O at 54°C, no LTC was observed without hydrogen even in low temperature water. Also, fracture resistance of the specimens, in which LTC was observed, decreased significantly compared with that in air. The results indicate that LTC is an issue only in hydrogenated water. In addition, the effect of pre-immersion in high temperature hydrogenated water on susceptibility of LTC was investigated and showed not to accelerate LTC. As hydrogen content in tested specimen was almost same independent of dissolved hydrogen of test water, the possibility that hydrogen was charged into specimen during laboratory test would be low. One of mechanism of LTC was considered that constant hydrogen supply to crack tip resulted in the ductility loss of material.