CHARACTERIZATION OF MICROSTRUCTURE OF ALLOY 52M WELD METAL NEAR THE FUSION BOUNDARY AND OXIDE FILMS FORMED IN SIMULATED PWR PRIMARY WATER

摘要

Alloy 52M weld metal samples are taken fromlocations at distances of 1.1 mm, 2.3 mm, 10 mm awayfrom the fusion boundary (FB) to low alloy steel,representing the first dilution zone, the second dilutionzone and the undiluted zone of Alloy 52M butteringlayer. Cr and Ni contents in the second dilution zone arelower than that in the first dilution zone, which arehigher than that in the undiluted zone. Oxide filmsformed on these Alloy 52M samples in simulatedpressurized water reactor (PWR) primary water at 325°C are duplex-layered with the Fe-rich outer oxide layerof large and scattered particles, and the Cr-rich innerlayer of small and dense particles. With increasing thedistance from the fusion boundary, the thickness of theinner oxide layer decreases. Cr oxide along the grainboundary is observed. The change of main alloyelements and the resultant change of oxidation behaviorin PWR primary water are consistent with the observedSCC behavior.