Effect of carbon on high temperature creep property of a Ni-20Cr alloy

Changes in the creep resistance and dislocation substructure with addition of carbon have been studied in the temperature range between 900 - 1050 deg C, by using high purity Ni-20Cr alloys containing carbon up to 0.032 wt%. The creep resistance of the alloy increased at the temperatures less than 1000 deg C, with increasing of carbon content dissolved in γ-matrix. Such a strengthening effect was presumed to be caused by solid solution of carbon, and was associated with increase in dislocation density within subgrains. At 1050 deg C, the formation of subgrains or the dynamic recrystallization took place in the alloy with 0.032 wt% carbon and these microstructural changes brought the decrease in the creep resistance of the alloy. The precipitation of carbide (M7C3) at the grain boundaries significantly increased the creep resistance, and this phenomenon was very similar to the grain boundary precipitation strengthening effect by α2-W phase in Ni-Cr-W alloys. (author)