High-temperature oxidation behavior of 2 1/4Cr-1Mo steel in air - Part 2: Scale growth, metal loss kinetics, and stress enhancement factors during creep testing

The oxide-scale growth and metal loss kinetics during oxidation in air of 2 1/4 Cr-1 Mo steel were studied at 600, 700, and 800 degreesC for times up to 1000 h, with cylindrical specimens similar to creep test pieces. The sca le thickness (x) was observed to exhibit a gradually decreasing growth rate with the exposure time (t) according to approximated parabolic behavior of type x(2) = K-os.t at the temperature levels of 700 and 800 degreesC. The coefficient K-os exhibited Arrhenius-type temperature dependence with an ac tivation energy value of 212 kJ/mol. At 600 degreesC, parabolic behavior wa s not verified, and the scale thickness growth follows better a relation of type log(x) = A + B log(t). The metal thickness (y) was observed to exhibi t a gradually decreasing loss rate with the exposure time according to para bolic behavior of type y(2) = Kml.t at the three temperature levels. The co efficient K-ml also exhibited Arrhenius-type dependence with an activation energy value of 215 kJ/mol. These two values of Q are close do the value fo r diffusion of iron an the chromium-rich internal oxide layer formed in the material. Based on the equations of metal loss kinetics, the variation of the cross-sectional area of the specimens with time could be determined and plots of stress enhancement factors developed to assess the effect of oxid ation on creep testing results.