High-Temperature Oxidation Behavior of 214Cr-1Mo Steel in Air–Part 2: Scale Growth, Metal Loss Kinetics, and Stress Enhancement Factors During Creep Testing

Abstract

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°C for times up to 1000 h, with cylindrical specimens similar to creep test pieces. The scale thickness (x) was observed to exhibit a gradually decreasing growth rate with the exposure time (t) according to approximated parabolic behavior of type x2=Kos⋅t at the temperature levels of 700 and 800°C. The coefficient Kos exhibited Arrhenius-type temperature dependence with an activation energy value of 212 kJ/mol. At 600°C, parabolic behavior was 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 exhibit a gradually decreasing loss rate with the exposure time according to parabolic behavior of type y2=Kml⋅t at the three temperature levels. The coefficient Kml also exhibited Arrhenius-type dependence with an activation energy value of 215 kJ/mol. These two values of Q are close do the value for diffusion of iron on 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 oxidation on creep testing results.