CHAPTER 3 Characterisation of Thermal Oxide Scales on Stainless Steels (original) (raw)
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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.
The Use of EBSD to Characterise the High Temperature Oxides Formed on Low Alloy and Stainless Steels
Materials Science and Technology, 2006
Exposure of steel to high temperatures in air leads to the formation of an oxide scale, the composition and structure of which depends sensitively on the oxidation conditions and the alloying elements contained within the steel. In this paper the oxide scale structures formed on low alloy and stainless steels are characterised using Electron Backscatter Diffraction (EBSD) in the SEM. In low alloy steels this crystallographic information enables both the phases within the scale (i.e. haematite, magnetite and wüstite) and orientation relationships between them to be established. This showed that both strong preferred growth within the phase layers, and orientational relationships between phase layers, can occur depending on the composition and oxidation conditions. For the scales on stainless steels the technique enabled the two crystallographic structures that form; corundum and spinel to be isolated. These structures can be easily differentiated using the EBSD data alone, but the individual phases within them can only be distinguished by using the chemical data, collected simultaneously with the EBSD data, because of their crystallographic similarity. This technique revealed two discrete phases for each structure within the oxide scales. For the spinel structure this consisted of a predominantly chromium and iron containing layer adjacent to the substrate below a coarse grained phase composed of nickel and iron. Meanwhile an iron rich (haematite) layer at the upper scale surface and a thin chromium rich phase that exists within the fine-grained lower scale both possessed the corundum structure.
The Use of EBSD to Study the Microstructural Development of Oxide Scales on 316 Stainless Steel
316 stainless steel has been oxidised at 1200 degrees C in air for varying times and with different cooling rates. The resulting scales were examined using optical and electron microscopy techniques including electron backscatter diffraction (EBSD) and energy dispersive X-ray spectroscopy (EDS). It was found that the scales on a sample oxidised for 4 hours consists of three layers; the lowest layer is a fine equiaxed region which has a uniform distribution of chromium which is similar to the base metal, followed by a larger equiaxed layer with very little chromium content but a high iron content, with a final layer of columnar grains of which some are rich in nickel. With a slower cooling rate a large amount of internal oxidation within the metallic substrate was observed which showed a chromium content higher than the oxidised metal.
The oxidation of duplex stainless steel at Moderately elevated temperatures
Materiali in Tehnologije
The surface oxidation of DSS 2205 duplex stainless steel was studied by X-ray photoelectron spectroscopy (XPS). Two different techniques were used to produce thin oxide layers on polished and sputter-cleaned duplex stainless-steel samples. These samples were exposed to a 10-5 mbar pressure of pure oxygen inside the vacuum chamber and oxidized with an oxygen plasma from room temperature up to 300 °C. The experiments were made with the alloy after a controlled oxidation with oxygen atoms created in an inductively coupled plasma. The experiments were performed in the temperature interval from room temperature up to 300 °C. The compositions of the modified oxidized surfaces were determined from the XPS survey scans, and the chemistry of selected elements from the higher-energy-resolution scansof the appropriate peaks. Various Fe/Cr oxidized layers and various oxide thicknesses were observed and correlated withthe temperature. It was found that all the techniques produced oxide layers wi...
Journal of Materials Science, 1990
Stainless steels of type SUS304 and SUS316 were chemically treated and heated at various temperatures, and the oxide films formed on the surface were analysed by Auger electron spectrometry and conversion electron M6ssbauer spectrometry. The outermost oxide layers of stainless steels were enriched with iron and chromium after heat treatment below 600 ~ C and above 700 ~ respectively. It was found that at least two magnetic components of iron species were present in the oxide layers of stainless steel heated below 600 ~ C and that the fine particles of iron oxide are produced in the inner oxide layers of the samples prepared by heating at temperatures higher than 700 ~ C. Only paramagnetic iron species were detected in the oxide layers of the stainless steel prepared by chemical treatment. The structures of the oxide layers produced by those heat and chemical treatments are proposed.
Materials and Corrosion, 2002
In situ Raman spectroscopy experiments have been performed to determine both growth and thermal stresses of chromia scales formed at 750 8C in oxygen on a stabilized ferritic stainless steel Fe-18Cr-TiNb. The measured growth stresses were shown to be highly compressive, near À 2 GPa. Cooling down and reheating cycles under inert gas showed that the thermal stresses were slightly compressive when cooling down (À 0.2 GPa), and reversible when heating up, showing their perfect thermo-elastic origin. Measurements, with temperature changes, of the deflection of oxidized samples after removal of one side oxide confirmed the Raman measurements and allowed to derive the actual value of the thermal expansion coefficient of the oxide scale: a ox 10.75 Â 10 À6 K À1 .
On the Structure of Initial Oxide Films on Stainless Steel in High Temperature Water and Vapor
Transactions of the Japan Institute of Metals, 1970
The present authors have studied the structures and chemical compositions of oxide films produced on surfaces of 18-8 and vapor on the structures and chemical compositions of the oxides were investigated through electron microscopy, transmission electron diffraction and X-ray microanalysis. Main results obtained are as follows: (1) A corundum type oxide produced on a mechanically polished surface of 18-8 stainless steel at the early stage of oxidatype oxide has been changed to a spinel type oxide containing Ni after a prolonged heating time (24hr). (2) After heating in high temperature vapor (dryness: 0.18) of 18-8 stainless steel, the corundum and spinel type oxides are found on both mechanically and chemically (or electrolytically) polished surfaces. In the case of the higher dryness (1.0), however, the corundum type oxides are detected on the three differently polished surfaces. (3) On heating 18Cr stainless steel in high temperature water and vapor under the same conditions, the oxide films are of the corundum type containing Fe and Cr. This evidence throws a light on the contribution of Ni to the formation of the spinel type oxides detected in the initial oxide films of 18-8 stainless steel.
Photoelectrochemical characterization of thermal oxide developed on metal and model alloys
2013
High Temperature Corrosion (HTC), in various and severe atmospheres, of continually more elaborated (composition, micro–structure) metallic alloys, is a rather complex industrial and scientific topic. PhotoElectroChemistry (PEC) acquired a special place in the characterization of physico–chemical and electronic properties of the highly heterogeneous oxidation layers formed in HTC. Through studies of model but industrially representative samples (duplex stainless steel, Ni–base alloy 690), this work presents the development and validation of an experimental set–up allowing for the first time to use the whole set of PEC techniques at the mesoscopic level (typically 30 µm), as well as the validation of an original model of photocurrent energy spectra, developed at SIMaP, allowing to well describe, and accurately fit the latter spectra, and thus yielding, notably, precise bandgap values for the semiconducting components of the thermal scale.
Analysis of oxide film on stainless steel via position-sensitive atom probe
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1994
Thermal oxide films formed on the surface of a type 316 stainless steel were atomically characterized by a recently built position-sensitive atom probe (POSAP). Oxidation on the clean field evaporated surface was pertormed at temperatures of 350 "C for 5 min, 475°C for 1, 5, and 15 min, and 600°C for 5 min in oxygen at a pressure of lO-4 TOlT. The POSAP analysis has clarified that the oxide-steel interfaces at 350 "C for 5 min, and 475 "C for 1 and 5 min are very sharp, while the interfaces at 475°C for 15 min and 600 °C for 5 min have subnanometer level roughness. In spite of the difference in oxidation temperature and time, the oxygen concentration in the oxide films is in the range from 35 to 50%, and Ni and Mo tend to segregate to the oxide-steel interface. Furthermore at 475°C for 15 min and at 600 °C for 5 min, Ni and Mo segregate to the top surface region as well as to the interface. The oxide film has a triplex structure consisting of the top surface region being chromium rich oxide, the inner region being iron rich oxide, and the interface being chromium rich oxide. The Mo segregation is localized in a few nanometers in size and appears to inhibit the oxide formation in those segregated regions.
Stainless steels of type SUS304 and SUS316 were chemically treated and heated at various temperatures, and the oxide films formed on the surface were analysed by Auger electron spectrometry and conversion electron M6ssbauer spectrometry. The outermost oxide layers of stainless steels were enriched with iron and chromium after heat treatment below 600 ~ C and above 700 ~ respectively. It was found that at least two magnetic components of iron species were present in the oxide layers of stainless steel heated below 600 ~ C and that the fine particles of iron oxide are produced in the inner oxide layers of the samples prepared by heating at temperatures higher than 700 ~ C. Only paramagnetic iron species were detected in the oxide layers of the stainless steel prepared by chemical treatment. The structures of the oxide layers produced by those heat and chemical treatments are proposed.