Effect of elemental redistribution on the failure of centrifugally cast HK40 alloy
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An HK40 steam-reforming tube that ruptured after 35,000 h of operation was analyzed to identify the causes of failure. Analysis of the fracture surface and cross sections indicated extensive and localized corrosion associated with the primary crack site. The fracture surface showed three distinct types of propagation morphology at the inner, middle, and outer portions of the pipe. Severe localized corrosion at interdendritic grain boundaries was detected at the inner pipe, while at the middle, cracks propagated transgranularly along primary carbides. Elemental mapping and line profiles showed a correlation between rupture behavior and the elemental segregation of chromium, manganese, carbon, and silicon at the inner and middle regions. Sulfur, encountered as a contaminant in natural gas, was also detected at these regions. Based on the characteristics exhibited by the fracture surface, failure was attributed to oxidation and fracture enhanced by the elemental redistribution of chromium, carbon, manganese, nickel, and silicon.
Keywordselemental segregation failure HK40 oxidation spalling
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