METAL DUSTING OF NICKEL-BASED ALLOYS

The carburization behavior of nine commercial nickel-based alloys and four iron-nickel-chromium alloys was investigated at 650 degrees C in a carburizing carbon monoxide (CO)-H-2 hydrogen oxide (H2O) gas with a carbon activity (a(c)) of a(c) >> 1. The iron-nickel-chromium alloys suffered severe metal dusting after a very short test period. Nickel-b ased alloys were generally less susceptible to metal dusting than iron -based alloys. Nickel-based alloys with chromium concentrations of 25% and above, on the other hand, showed no significant evidence of metal dusting even after 10,000 h of exposure. It was found that these allo ys were protected against metal dusting by the formation of a dense, s elf-healing chromia scale, which prevented the penetration of carbon i nto the base metal.