Abstract
PWSCC testing of Alloy 182 and 152 welds was conducted using 1/2 compact tension (CT) specimens at 325 ℃ in simulated primary water environments of a PWR, and a surface oxidation test using plate specimens was conducted in the same autoclave for 3600 hours. The average measured crack growth rate of Alloy 182 was found to be 1.0 x 10-7 mm/s, while that of Alloy 152 was 2.4 x 10-9 mm/s at K = 30 MPa√m. The cracking of Alloy 182 showed a purely intergranular aspect, and it was revealed from a microscopic investigation that oxygen diffused into the grain boundaries from the external primary water. As a result of oxygen penetration, Cr oxides formed at the oxidized grain boundaries, resulting in Ni depletion. On the other hand, Alloy 152 showed a mixed (intergranular and transgranular) cracking morphology. Oxygen scarcely diffused into the grain boundaries and intergranular oxidation was not found in the case of Alloy 152. Therefore, it is considered that the different resistance to PWSCC is closely correlated with the surface oxidation phenomena, which originates mainly from the different Cr contents in these alloys.
