Microstructural investigation of the oxide scale on low carbon steel (original) (raw)
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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.
Surface and Coatings Technology, 2015
Both orientational and geometrical characteristics of grains in tertiary oxide scales have been quantitatively investigated using the electron backscatter diffraction (EBSD) technique. Phase and orientation mappings demonstrate that the {001} planes of magnetite and the {0001} planes of hematite are parallel to the direction of oxide growth. Pole figures (PFs) as scattering plots clearly display the direct correlation between the orientations and microstructure sites of magnetite grains. Magnetite grains develop a strong rotated cube texture component that shifts to the {100}b 210N component, whereas those with the grain size of 1-5 μm develop the {001}b 100N cube texture component. The refined magnetite grains surrounding the abnormal ones can be a combined process, including magnetite pro-eutectoid during hot rolling and cooling and re-oxidation during air-cooling. Our findings offer insights toward further understanding of the link between the geometrical and orientation parameters of grains with respect to the deformation behaviour of oxide scales formed at elevated temperatures.
Study of the morphology of oxide scale formedon hot-rolled steel
2014
Mechanism of oxide scales formation on steel during hot rolling process is delicately determined and their structures are extremely complex. This work is part of larger studies made to understand the oxide scale behavior. Therefore, the morphology of oxides is determined by optical microscopy. Identification of the mechanical properties of oxide scales is achieved by micro-hardness measurement. The work has revealed a variation of microstructure in several layers of oxide. It was obtained that the oxide scales consisting mainly of wustite FeO, magnetite Fe3O4 and hematite Fe2O3 owing to the formation of voids and cracks in the scales, especially on the outer layer where it is high porous. The intermediate layers is thicker than others oxide layers. The outer layer has a lowest hardness and highest porosity.
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.
2014
Initial stage oxidation characteristics of the modified 9Cr-1Mo steel in ambient air at 650°C have been investigated, for exposure times ranging from 5 to 500 h. Oxygen flux from the gas phase causes high initial oxidation rate, but the growth kinetics do not follow parabolic law. In ''as-received'' condition, binary oxides of Fe and Cr were found as native oxides. Upon oxidation, segregation of Mn resulted in the formation of MnCr 2 O 4 along with FeCr 2 O 4 and binary oxides of Fe, Cr and Mn. Thus, the initial oxide scale constitutes multiple oxides with delineated interface, unlikely to have a layered structure.
Examination of Oxide Scales of Hot Rolled Steel Products
ISIJ International, 2005
Porosities in the scale layer and wavy scale-steel interfaces are two common artefacts generated during metallographic preparation of oxide scale samples. This paper presents the techniques used by the authors to effectively remove porosities in the scale and reduce the waviness of the scale-steel interface so that the true scale structures can be examined. The techniques have been successfully applied to the examination of oxide scales on hot-rolled steel with various thicknesses and structures.
Understanding phase transformations in steels using modern electron microscopy techniques
2015
The advantages and limitations of electron back-scattering diffraction coupled with energy dispersive X-ray spectroscopy and of transmission Kikuchi diffraction in relation to the in-depth characterisation of steel microstructures containing phases with similar lattice parameters and/or precipitates are discussed. An inhouse developed EBSD map post-processing methodology provided insights into the mechanisms of bainite formation. Disciplines Engineering | Science and Technology Studies Publication Details Pereloma, E. V., Saleh, A. A., Spanke, H. Th., Al-Harbi, F. & Gazder, A. A. (2015). Understanding phase transformations in steels using modern electron microscopy techniques. Asia Steel International Conference (Asia Steel 2015): proceedings (pp. 68-71). Japan: Iron and Steel Institute of Japan. This conference paper is available at Research Online: http://ro.uow.edu.au/eispapers/5115 Understanding phase transformations in steels using modern electron microscopy techniques Elena V....
Real-time observations of the oxidation of mild steel at high temperature by neutron diffraction
Metallurgical and Materials Transactions B, 1996
The in situ characterization of the phase composition of iron oxides, ''scale,'' that form on low carbon steel during oxidation at elevated temperatures was carried out using the neutron diffraction technique. Growths in the intensities of diffraction peaks from the crystal planes of the various oxides (Fe x O, Fe 3 O 4 , and Fe 2 O 3 ) were monitored on-line. The volume fractions of the oxides in the scale were calculated on the basis of ideal structure factors and measured relative intensities of diffraction peaks. These were selected from a small region of the diffraction pattern. Calculated volume fractions of these oxides in the scale layer were in agreement with the area fractions obtained from scanning electron microscopy (SEM) analysis of the scale.