Temperature dependence of carbon deposits within oxide scale on CrMoV steel in atmospheric and supercritical CO2.

CrMoV steel was exposed to 500, 550, and 600 °C for up to 120 h in 0.1 and 10 MPa CO 2. A significant change in carbon deposition content was not observed in the 0.1 MPa CO 2, in contrast to the high carbon content at 550 °C and 10 MPa CO 2. The formation of internal Fe-rich M 3 C carbides and super saturation of steel grains with dissolves carbon at 550 °C but not at 500 and 600 °C may be responsible for this difference. The effect of carbon deposition on the outward Fe diffusion via vacancy or interstitial sites was also discussed. • Effect of temperature (500–600 °C) on carbon depositions within the scale develop on CrMoV steel was investigated. • Carbon contents increased with temperature up to 550 °C and then decreased with temperature in supercritical CO 2. • Formation Fe-rich M 3 C carbides were favored at 550 °C while their formation was delayed at 500 and 600 °C. • It is suggested that the carbon depositions can affect the point defects' contribution to the outward Fe diffusion. • Carbon depositions within the scale consisted of amorphous carbon, graphite, or both. [ABSTRACT FROM AUTHOR]