Abstract
Aluminide coating, intended for application in ultra-supercritical boilers with a steam temperature of 650 °C, was deposited on the inner surface of Super304H steel tube in combination with its heat treatment. Relevant thermophysical, chemical, and mechanical properties of aluminized Super304H were characterized. The results indicated that the aluminide coating significantly improved steam oxidation resistance of Super304H by forming an extremely thin Al2O3 scale. This was superior to shot-peening treatment and use of steels with a higher Cr content. The aluminide coating showed very limited impact on the thermophysical properties of the matrix alloy due to its thin nature. The tensile strength and creep-rupture properties of Super304H were all within the allowable range for Super304H steel according to the ASME code. The high intrinsic strength of FeAl intermetallics slightly improved the yield strength of aluminized Super304H and microcracks relieved the stress in the coating, thus causing creep fracture on the uncoated side of samples. This research suggested that slurry aluminide coatings could be a viable option for application of Super304H steel in supercritical boilers with higher steam temperatures.
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