The Effects of Water Vapor on the Oxidation Behavior of Alumina Forming Austenitic Stainless Steels

Abstract

The isothermal oxidation behavior of three alumina forming austenitic (AFA) stainless steels with varying composition was studied at 650 and 800°C in dry air and gases which contained water vapor. The AFA alloys exhibited better oxidation resistance than a ''good chromia former'' at 650°C, particularly in H 2 Ocontaining atmospheres by virtue of alumina-scale formation. Although the AFA alloys were more resistant than chromia formers, their oxidation resistance was degraded at 650°C in the presence of water vapor. In dry air the AFA alloys formed, thin continuous alumina scales, whereas in Ar-4%H 2 -3%H 2 O the areas of continuous alumina were reduced and Fe oxide-rich nodules and regions of Cr, Mnrich oxides formed. In some regions internal oxidation of the aluminum occurred in the H 2 O-containing gas. The alloy OC8 had slightly better resistance than OC4 or OC5 in this atmosphere. The alumina-forming capability of the AFA alloys decreases with increasing temperature and, at 800°C, they are borderline alumina formers, even in dry air. The oxidation resistance of all three alloys was degraded at 800°C in atmospheres, which contained water vapor (Air-10%H 2 O, Ar-3%H 2 O and Ar-4%H 2 -3%H 2 O). The areas, which formed continuous alumina, were reduced in these atmospheres and areas of internal oxidation occurred. However, as a result of the borderline alumina-forming capability of the AFA alloys it was not possible to determine which of the H 2 O-containing atmospheres was more severe or to rank the alloys in terms of their performance. The experimental results indicate that the initial microstructure of the AFA alloys also plays a role in their oxidation performance. Less protective oxides formed at 800°C when alloy OC8 was equilibrated before exposure rather than being exposed in the as-processed condition.

Oxidation behaviour of Super 304H stainless steel in supercritical water

“…Due to relatively high creep strength and good corrosion resistance, austenitic stainless steels are currently used widely in ultra-supercritical units. Up to now, many researchers studied oxidation characteristics in high-temperature steam environment of austenitic stainless steels [3][4][5][6][7][8][9][10][11][12][13][14]. Typical austenitic steels form nominally two-layered scales under steam conditions.…”

Research Progress of Alumina-Forming Austenitic Stainless Steels: A Review

“…And it was found that the higher the water vapor content, the worse the oxidation resistance. N. M. Yanar et al [ 23 ] found that OC4 steel had better oxidation resistance in 3% water vapour than in 10% at 800 °C. This explains that OC4 steel can form a continuous alumina protective scale in a 3% water vapour environment but has internal oxidation in 10% water vapour.…”

Gradient Cr–AlN composite coating prepared on alumina-forming austenitic steel

“…Many previous studies [11][12][13] have shown that one of the most effective ways to enhance wear resistance and surface hardness is by coating it. Coating technology can be broadly categorised into two groups: one is thermal diffusion type, including gas diffusion infiltration, hot dip coating, packcementation, 13 and high-energy beam surface treatment 14,15 ; the other is deposition type, including physical vapour deposition, [16][17][18][19] chemical vapour deposition, [20][21][22] electroplating, 23,24 spraying, 25,26 micro-arc oxidation, 27,28 etc. Pack-cementation is an efficient, simple, mature, and low-cost approach for preparing metallic and ceramic coatings on metals and alloys.…”