High temperature oxidation of austenitic stainless steels: effect of sulfur content on scale adhesion (original) (raw)
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OXIDATION OF METALS, 2011
The influence of surface preparation on the stress and adhesion of oxide scales formed on the ferritic stainless steel AISI 441 was studied. Steel coupons were surface-finished to different degrees of surface roughness from 400-grit SiC through to 1-micron diamond, and were also electropolished to remove the work hardened surface. Initial metal roughness was measured by optical profilometry. Oxidation was carried out at 800°C under synthetic air for 100 h. Oxide residual stress was derived from the Raman shift of the main chromia line, and adhesion of oxide scales was quantitatively obtained using forced spallation by tensile straining. The results show that surface hardening is the most influential factor on adhesion, with the high dislocation-containing mirror-polished samples exhibiting the lowest adhesion energy (*4 J m-2), and the electropolished samples with non-mechanically affected surface exhibiting the highest adhesion energy (17 J m-2). Recrystallisation of the subsurface zone during heating to the oxidation temperature is thought to be the most influential factor reducing scale adhesion.
CHAPTER 3 Characterisation of Thermal Oxide Scales on Stainless Steels
Solid State Phenomena
This chapter aims at reviewing the characterisation techniques that are commonly used for high temperature oxidation study, especially on stainless steels. In addition, the experimental studies about the high temperature oxidation i.e. thermogravimetric method and chromium volatilisation measurement are explained. The various kinds of characterisation techniques for physico-chemical and electronic properties of thermal oxide scales are reviewed, starting from optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), focused ion beam coupled with scanning electron microscope (FIB/SEM), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (RS), and photoelectrochemical characterisation (PEC). The review focuses on the basic concepts and shows how the characterising tools can be applied to thermal oxide characterisation.
ISIJ International, 1994
The influence of alloy surface preparation as induced by mechanical polishing and electropolishing on the oxidation behaviour of AISI 316 stainless steel in dry air under non-isothermal heating (6 K•min~1) followed by isothermal holding at 1 423 K is reported. Mechanically polished surfaces exhibit a shorter incubation period for initial oxidation but better oxidation resistance during isothermal holding as compared to electropolished surfaces. Such observation is attributed to enhancedoutward diffusion of Cr for easy and early establishment of Cr-rich oxide layer on the mechanically polished surfaces. Themorphologies of the scales and nature of their adherenceto the alloy substrates have beencharacterized by SEM. Distribution of the alloying elements like Ni. Cr, Mn, Mo. Si as well as Fe and oxygen across the oxide layers and the type of compounds formed have been examined by EPMA. EDSand XRD techniques. SEM examinations of the alloy/scale cross section for the mechanically polished and oxidized steel, supplementedby the X-ray imagesof the respective elements, indicate preferential formation of a continuous Cr-rich layer near the oxidelair interface along with two continuous bandsof dopedCr203at the scale/alloy region. Onthe other hand, the scale formed on electropolished surfaces of the steel showsfragmented Ni-rich and Cr-rich oxide areas at the bottom region of the scale with mostly compact Fe303-rich layer at the oxide/air interface.
Materials Science and Engineering: A, 2003
The inverted blister test was used to study the adhesion of chromium-rich oxide scales thermally grown on several ferritic stainless steels. With this technique, a quantitative determination of the adhesion energy of the oxide on its substrate was possible. The adhesion energy is found to vary between 3 and 170 J m (2 depending on the specimens. It appears that the parameters influencing adhesion are oxide thickness and the nature of the minor alloying elements present in the alloy. The microstructural observation of both sides of the oxide/alloy interface after debonding provides important information on adhesion and spallation. #
Influence of surface preparation on oxidation of stainless steels at high temperature
Surface and Interface Analysis, 1993
Fourier transform infrared specular reflectance spectra at variable incidence have been recorded in order to characterize the oxide layers formed on both mechanically polished and etched surfaces of stainless steels (AISI 304 and 316). Depending on the surface preparation, the major oxides are either Cr2O3 and MnCr2O4 for polished samples or α-Fe2O3 and Fe3O4 for etched samples in the early stages of the oxidation in air at 900°C. Secondary ion mass spectrometry depth profiles confirm the schematic structure of oxide films (developed on polished surfaces during longer exposures) deduced from infrared reflectance study.
Grain-Size Effects on the High-Temperature Oxidation of Modified 304 Austenitic Stainless Steel
Oxidation of Metals, 2013
The high-temperature oxidation behavior of modified 304 austenitic stainless steels in a water vapor atmosphere was investigated. Samples were prepared by various thermo mechanical treatments to result in different grain sizes in the range 8-30 lm. Similar R3 grain boundary fraction was achieved to eliminate any grain-boundary characteristics effect. Samples were oxidized in an air furnace at 700°C with 20 % water vapor atmosphere. On the fine-grained sample, a uniform Cr 2 O 3 layer was formed, which increased the overall oxidation resistance. Whereas on the coarse-grained sample, an additional Fe 2 O 3 layer formed on the Cr-rich oxide layer, which resulted in a relatively high oxidation rate. In the fine-grained sample, grain boundaries act as rapid diffusion paths for Cr and provided enough Cr to form Cr 2 O 3 oxide on the entire sample surface.
Le Journal de Physique IV, 1993
Stainless steels of type AISI 304 and 316 were heated in air (1-5-15 minutes at 900-1000-1 100 OC) and the oxide layers formed on the surface were analyzed by XRD, CEMS, SIMS and FTIR. At these temperatures the main oxides are CrgOs and a spinel close to MnCr204 for polishing samples (with Fez03 for the chemically cleaned samples). The oxidation induces a Cr and Mn depletion from the metallic substratum and a phase transformation y (f.c.c.) + cu (b.c.c.) in a thin layer of the stee!s near the oxidesmetal interface.
The oxidation behavior of grade 304L stainless steel (SS) subjected to different surface finishing (machining and grinding) operations was followed in situ by contact electric resistance (CER) and electrochemical impedance spectroscopy (EIS) measurements using controlled distance electrochemistry (CDE) technique in high purity water (conductivity < 0.1 S cm −1 ) at 300 • C and 10 MPa in an autoclave connected to a recirculation loop system. The results highlight the distinct differences in the oxidation behavior of surface worked material as compared to solution annealed material in terms of specific resistivity and low frequency Warburg impedance. The resultant oxide layer was characterized for (a) elemental analyses by glow discharge optical emission spectroscopy (GDOES) and (b) morphology by scanning electron microscopy (SEM). Oxide layers with higher specific resistivity and chromium content were formed in case of machined and ground conditions. Presence of an additional ionic transport process has also been identified for the ground condition at the metal/oxide interface. These differences in electrochemical properties and distinct morphological features of the oxide layer as a result of surface working were attributed to the prevalence of heavily fragmented grain structure and presence of martensite.