Increasing the Upper Temperature Oxidation Limit of Alumina Forming Austenitic Stainless Steels in Air with Water Vapor

Abstract

A family of alumina-forming austenitic (AFA) stainless steels is under development for use in aggressive oxidizing conditions from *600-900°C. These alloys exhibit promising mechanical properties but oxidation resistance in air with water vapor environments is currently limited to *800°C due to a transition from external protective alumina scale formation to internal oxidation of aluminum with increasing temperature. The oxidation behavior of a series of AFA alloys was systematically studied as a function of Cr, Si, Al, C, and B additions in an effort to provide a basis to increase the upper-temperature oxidation limit. Oxidation exposures were conducted in air with 10% water vapor environments from 800-1000°C, with post oxidation characterization of the 900°C exposed samples by electron probe microanalysis (EPMA), scanning and transmission electron microscopy, and photo-stimulated luminescence spectroscopy (PSLS). Increased levels of Al, C, and B additions were found to increase the upper-temperature oxidation limit in air with water vapor to between 950 and 1000°C. These findings are discussed in terms of alloy microstructure and possible gettering of hydrogen from water vapor at second phase carbide and boride precipitates.

Performance of chromia- and alumina-forming Fe- and Ni-base alloys exposed to metal dusting environments: The effect of water vapor and temperature

“…For the alumina-forming Febase alloys, FeCrAlY behaved very well except after the exposure at 550°C (which will be addressed in a future paper [33]). While ferritic FeCrAlY has little creep strength at 650°C, the AFA alloys were designed to have high creep strength due to their nanocarbide precipitates [29,30] as well as good oxidation resistance in air and wet air by the formation of an alumina scale [28,48]. A consequence of this balancing of oxidation resistance and mechanical properties is that austenitic AFA is not as ''strong'' an aluminaformer as ferritic FeCrAlY type alloys, perhaps due to slower Al diffusion in austenite.…”

Investigation into the failure mechanism of chromia scale thermally grown on an austenitic stainless steel in pure steam

“…Austenitic stainless steels with relatively high Cr and Ni, on the other hand, can be used in higher temperatures due to their combination of relatively good creep strength and high temperature oxidation resistance [9]. Extensive studies [10][11][12][13][14][15][16][17][18][19] in recent years on the oxidation of austenitic stainless steels (e.g.…”

Investigation of microstructure and liquid lead corrosion behavior of a Fe-18Ni-16Cr-4Al base alumina-forming austenitic stainless steel

“…Apart from potential strengthen effect, Laves phase is also benefit for the precipitation of B2-NiAl phase, which is considered not only an important strengthen phase for Fe-Ni-Cr-Al alloy [9,12], but also important to the oxidation resistance of the steels. As NiAl can continuous supply Al for the formation of dense continuous alumina scale, namely provide a reservoir effect [15,[28][29][30][31]. For better understanding the performance of alumina forming austenitic stainless steels, it is necessary to pay more attention on the annealing behavior of the precipitates and investigate their strengthen effects.…”