Influences of carbon and silicon on blister formation in scale surface during high temperature oxidation of carbon steels

Abstract

The in-situ blistering phenomena of the scale ‘surface’ was investigated on three carbon steels with respect to carbon and silicon concentrations, such as 0.05 wt%C, 0.2 wt%C, and 0.2 wt%C-0.2 wt%Si. The oxidation and blistering kinetics and blister area fraction during high temperature oxidation were analyzed. The average thickness of the surface scale by oxidation during isothermal holding from 800 to 1200 °C in dry air was observed to decrease when the amount of carbon increased and/or when Si was inserted additionally. Thus, the blistering behavior depended primarily on a change in oxidation temperature (T _ox ) as well as amounts of carbon and silicon in the matrix. It is also revealed that such blister formation would be triggered by growth of internal stress and active generations of CO and/or CO₂ gases at the interface between the scale and matrix since carbon would result in an increase in the blister formation by generating CO and/or CO₂ gas. In addition, silicon might play an important role in preventing the blister formation at T _ox below 900 °C by reducing the thickness of the surface scale whilst silicon might enhance the blister formation by means of the appreciable micro-void formation in the scale layer at T _ox higher 900 °C.