Stellite 12 alloy was cladded on the surface of Thrust runner of a main pump using HIP technology. After product testing, lots of corrosions were found on the hard layer. SEM and EDS analysis technologies were used in order to find out the causes and mechanism inducing these corrosions. SEM results indicated that two kinds of corrosions locating on the hard layer. One type is central corrosion pit, another type is Selective Phase Corrosion (SPC).EDS showed that the central and adjacent corrosive areas were rich in carbon, low in cobalt, chromium and tungsten elements for the first type of corrosion. As for the second type of corrosion, EDS indicated that the corrosive zones were typically high in tungsten, chromium and carbon, and low in cobalt. Meanwhile, the presence of sulfur and chlorine elements may aggravate the initiation and continuation of corrosion.

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