Relations Between Oxidation Kinetics and Chromium Diffusion in Stainless Steels

摘要

The cyclic and isothermal oxidation behaviours of stabilized and non-stabilized ferritic and austenitic stainless steels were compared. Ferritic grades exhibited parabolic kinetics in both oxidation conditions. The protectiveness of chromia scales was maintained owing primarily to a far faster Cr-supply rate than the Cr-consumption rate. Consequently, a constant and high enough interfacial Cr-content was noted and mechanical induced chemical failure (MICF) was avoided; although spallation of the oxide scale was observed during cyclic oxidation. Austenitic grades also exhibited parabolic kinetics during isothermal oxidation but a significant mass loss during cyclic oxidation due to spallation of nodular iron oxides. Actually, all the austenitic grades were sensitive to MICF because of their high values of k_p/D_(Cr) implying interfacial Cr-content decreasing with oxidation time. Stabilizers (Ti, Nb) had no significant effect on the resistance of ferritic stainless steels to MICF; whereas, for the austenitics, Nb-addition enabled delay of the formation of iron oxides.