Dependence of oxidation behaviour on silicon content of 20%Cr austenitic steels

Abstract

In this paper, the role of silicon in the oxidation of a series of 20Cr–25Ni niobium stabilised steels containing silicon in the range 0–2·25 wt-% is explored. Oxidation tests were carried out in thermobalances at 900°C in a CO2 based gas at 1 atm (~100 kPa) total pressure for exposure periods extending to 1·12 × 106 s (310 h). The oxidation kinetics were parabolic in all cases with a rate constant that achieved a minimum value in alloys containing ~0·6 wt-%Si. By contrast, the extent of oxide spallation on cooling was least in the silicon free and dilute alloys and increased progressively with increasing silicon level. The results are discussed in relation to the morphology of the oxide layers. Comparison is also made with a previously published complementary study on steels of similar composition, but containing a dispersion of titanium nitride particles.MST/1018