The influence of thermal cycling on the oxidation and oxide spallation of a 1%Cr–0.5%Mo low-carbon steel

The oxidation and oxide spallation of 1%Cr–0.5%Mo low carbon steel disks in dry oxygen was studied isothermally at 800°C (1073 K) and in thermal cycling between 800 and 600°C (1073 and 873K) followed by cooling at rates from 3 to 100°C/min. Mostly parabolic oxidation kinetics were observed. Thin scales (10 ) were more prone to spalling than thicker scales (20 ). The thickness and growth imperfections of an inner scale layer enriched in chromium, molybdenum, and silicon strongly influenced the probability of cohesive failure exceeding that of adhesive failure of the scale. Cohesive failures in the bulk scale during thermal cycling were probably nucleated at voids and microcracks produced in the initial isothermal period of scale growth. The number of segmented scale layers that became detached during cycling was governed by the number of parallel rows of voids in the scale and not necessarily by the number of cycles.