Abstract
1. Raising the cobalt concentration from 0 to 40% improves the oxidation resistance of Ni−20Cr alloys, since the amount of Cr2O3 in the scale increases. The oxidation resistance is highest for the alloy with 40% Co. Larger amounts of Co up to 70% lead to the formation of CoO in the scale and smaller amounts of chromium oxide, which has a negative effect on the oxidation resistance of Ni−Cr alloys. 2. The addition of up to 25% Fe to Ni−20Cr−Co alloys reduces the amount of Cr2O3 in the scale and lowers the oxidation resistance. With larger amounts of Fe the amount of Cr2O3 in the scale again increases, the oxidation resistance increasing correspondingly. Alloys with 45% Fe have the same oxidation resistance as alloys without Fe.
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