The role of microstructural development in the hydrothermal corrosion of cast and HIPed Stellite 6 analogues in simulated PWR conditions

The corrosion behaviour of cast and HIPed Stellite 6 analogue materials in PWR-simulating conditions was investigated. The cast alloy exhibited localised corrosion at the boundary between the matrix and the M7C3 carbides, with this being attributed to chromium depletion in the matrix associated with the carbide growth. In contrast, the HIPed alloy exhibited no localised corrosion. The carbon content of the cast Stellite 6 analogue was right at the top end of the range indicated in the Stellite 6 specification: this results in a high fraction of carbides and a general depletion of the chromium content of the matrix.