Crack growth behavior of Co-based alloy (30Cr-4W-Bal.Co) was investigated in a simulated PWR primary water at temperature ranging from 250 to 320°C using half-inch size compact tension specimen (1/2TCT). Crack growth rate measurements were performed in hydrogenated (DH: 30cc/kg H2O at STP) water environment, which contained 500 ppm B and 2 ppm Li. All tests were performed under the constant-load condition, and the target stress intensity factor was 30 MPa • m1/2.
As a result, significant crack growth was observed in the simulated PWR primary water, when the high stress intensity factor was applied. Simple 1/T dependence was observed on crack growth rate of forged Co-based alloy in the high temperature water. According to cross sectional observation of the CT specimens, several crack pass were identified ex, carbide and Co-matrix boundary, trans- and inter- granular of the Co-matrix, and crack in the Cr carbides. Preferential corrosion at Co-matrix near the carbide/matrix boundary were observed both forged and as welded Co-based alloys in the high temperature water. Such as preferential corrosion might affect crack growth behavior. This suggested that crack growth behaviors of forged and as-welded Co-based materials could also be similar in the high temperature water.