Postbreakaway oxidation kinetics of two ferritic steels

The time needed to reach breakaway oxidation, weight gain at the breakaway point, and the postbreakaway oxidation rate are three important variables which, along with others, play an important role in causing boiler tube failure. In this paper an attempt has been made to study the behavior of two ferritic steels-21/4Cr-1Mo and 9Cr-1Mo. Postbreakaway oxidation kinetics of these two alloys have been studied at temperatures in the range 900–1100°C in pure oxygen for a short duration (maximum of 3 hr). No breakaway was observed at 900°C under these conditions. Postoxidation kinetics are linear at first, followed by a slower oxidation rate. The results have been substantiated by the postoxidation studies using SEM, EDAX, and X-ray diffraction.