Water Vapor Oxidation of Ferritic 441 and Austenitic 316L Stainless Steels at 1100°C for Short Duration

Abstract

A ferritic 441 and an austenitic 316L steels have been exposed to wet argon at 1100 °C. This study focus on the characterization of the oxide scales formed after different exposure times in the range of 2.5-20 min. Raman spectroscopy, XRD, SEM and XPS have been used. For all exposure times, 316L forms a breakaway type thick oxide scale (rupture of the pre-existing passivating film) with iron oxides on its outer part and a mix of spinels with Fe, Cr and Ni for its inner part. For lower water vapor partial pressure, iron oxides are constituted of wüstite. For higher water vapor partial pressure, iron oxides are constituted of a layer of hematite over a layer of magnetite slightly enriched in chromium. Due to strong oxidation condition, oxide scale is not always homogeneous and iron oxides spallation may occur. For 2.5 min of oxidation on 441, a very thin layer of protective chromium oxide is formed. For longer exposure time, an almost homogeneous and much thicker layer mainly consisting of Cr 2 O 3 is produced. The thickness varies slightly and gradually from 4 to 20 min of oxidation. There are Mn-Cr spinels mixed with the chromium oxide. The most external part is strongly enriched in Mn and Fe in a spinel structure. The diffusivity of chromium is regarded as the main cause of the difference of oxidation behavior. In both cases, the first step is a very thin chromium oxide layer. When the oxidation conditions becomes too strong in terms of exposure time or water vapor partial pressure, this oxide layer breaks. The ferritic steel is able to heal and thicken its protective chromium oxide, preventing the breakaway. The healing would be due to the high diffusivity of chromium. The thickening would be caused by the presence of the Mn-Cr spinels which are a less effective diffusion barrier. The lower diffusivity of chromium in austenite promotes the breakaway.

Corrosion and Oxidation Behavior of Polymer Derived Ceramic Coatings With Passive Glass Fillers on Aisi441 Stainless Steel

“…Beneficial effect of the PDC coating with the fillers in terms of oxidation protection of the steel substrate was observed at 900°C, with the mass gain about one half of that in uncoated steel oxidized under the same conditions, while at 1000°C and 1100°C no protective effect of the coating was observed. Oxidation of stainless steel substrate yielded passivation Cr 2 O 3 , layer with some TiO 2 and a (Mn,Cr) 3 …”

“…Static tests were carried out at the temperature of 200°C with the duration of the test between 1 and 8 days. The ratio between the sample surface and the volume of corrosive liquid (S/V) was held constant at 0.7 ± 0.03 cm 3 . For determination of each experimental data point two specimens were placed in one reactor with 20 ml of the corrosion medium.…”

“…However, the corrosion and oxidation performance of the steel is not sufficient for a long-term operation at higher temperatures [1]. A non-protective (Mn,Cr) 3 O 4 spinel layer is formed at the surface when the steel is exposed to oxidation environment at T > 800°C, together with a protective Cr 2 O 3 underneath the (Mn,Cr) 3 O 4 spinel layer [2]. Some authors report that the oxide film is composed of chromia (Cr 2 O 3 ) or chromiumrich iron oxide ((Cr,Fe) 2 O 3 ) in the inner part and by a manganese-chromium spinel oxide (Mn,Cr) 3 O 4 in the outer part [3,4].…”

“…A non-protective (Mn,Cr) 3 O 4 spinel layer is formed at the surface when the steel is exposed to oxidation environment at T > 800°C, together with a protective Cr 2 O 3 underneath the (Mn,Cr) 3 O 4 spinel layer [2]. Some authors report that the oxide film is composed of chromia (Cr 2 O 3 ) or chromiumrich iron oxide ((Cr,Fe) 2 O 3 ) in the inner part and by a manganese-chromium spinel oxide (Mn,Cr) 3 O 4 in the outer part [3,4]. At the metal/oxide interface, a silica (SiO 2 ) layer is also typically observed [5].…”

Design of stainless steel porous surfaces by oxide reduction with hydrogen

“…In the first step an oxide scale is built using specific steel grade and oxidation conditions. This step has been studied in previous investigations [10,11]. In the second step, after obtaining the oxide scale on a significant thickness, samples have been reduced using an adapted reduction time to obtain satisfactory morphologies.…”