Abstract
The oxidation behavior of Fe-18Cr-10Ni and Fe-20Cr-10Ni steels containing 1 to 3%Si and Fe-20Cr-10Ni-2.5Si steels containing rare earth elements up to 0.22% has been investigated under continuous and cyclic oxidation conditions in air in a temperature range from 800 to 1100°C by a thermogravimetric method, metallography, X-ray diffraction, and EPMA.
In both the continuous and cyclic oxidation conditions, the weight gain curves have steps of the protective stage breakthrough stage (spalling stage in the cyclic condition), and heating stage. The increase of silicon and chromium contents improves the oxidation resistance.
The marked improvement of scale adherence is attained by the addition of rare earth elements, which delay the beginning of the spalling in the cyclic oxidation.
With the addition of rare earth elements, the growth of chromium depleted zone is restrained, consequently the formation of the stratified oxide which causes the spalling in cyclic oxidation is depressed.
In addition, the network of SiO2 grows deeply into the substrate and prevents the propagation of the stratified oxide along chromium depleted zone, therefore the scale adherence is improved remarkably.
