PRELIMINARY RESULTS ON POSSIBLE EFFECTS OF OXIDATION ON CREEP CURVES OF 21/4 Cr -1 Mo STEEL TESTED IN AIR

摘要

The metal loss kinetics during oxidation in air of 21/4 Cr-lMo steel was studied at 600, 700 and 800℃ for times up to 1000 hours using cylindrical specimens of 2.5mm diameter similar to standard testpieces used in creep testing. The metal thickness reduction (y) was observed to vary with the exposure time (t) according to parabolic expression of type y~2 = K_(ml)t at the three temperature levels. The coefficient K_(ml) exhibited an Arrhenius type temperature dependence with an apparent activation energy value of 215 kJ/mol. These equations were used to evaluate the reduction in the load bearing cross-sectional area and corresponding stress enhancement factors as function of time, temperature and specimen diameter. Based on θ -methodology concepts, a procedure is suggested for quantitatively assessing the distortion caused by oxidation on creep curves obtained with cylindrical specimens having different diameters.