The quality of steel may be seriously affected by the surface defects that appear on slab surfaces after hot rolling. These defects are related to iron oxidation and, in order to reduce the occurrence of these defects, it is necessary to better understand the formation of iron oxides during high temperature oxidation and the oxide descaling mechanisms. However, systematic research tools and experimental strategies for addressing these issues have not yet been developed. In addition, the mechanisms of oxide cracking and failure have not been understood. In this thesis, research tools and strategies are proposed for studying the high temperature oxidation of low carbon steels. These tools allow the presentation of new data on the phase composition of iron oxides at elevated temperature, characteristics of iron oxide formation, oxide microstructure and texture, oxide defects, and stress distributions in different oxide layers, as well as residual stresses. The microscopic model that was proposed for description of oxide failure allows better understanding of the mechanism for surface defect formation during hot rolling. To describe the dynamics of phase composition changes in textured oxides at elevated temperature, a new phase analysis method is proposed. This x-ray diffraction phase analysis is based on the Rietveld and Dickson's methods, and is used for investigating the effect of alloying elements on the oxidation process. This method was also adopted to track in-situ phase composition changes during high temperature oxidation of commercial low carbon steels. The structure of oxides on low carbon steels, pure iron, and Si-steels was systematically examined by orientation imaging microscopy (OIM). It is demonstrated that OIM can be an invaluable tool for visualizing the oxide microstructure texture and studies of oxide defects. In order to simulate industrial hot rolling of oxidized steel sheet, high temperature oxidations tests were made in the tube furnace up to 950°C, in air. The oxidation process and microstructure development were described using OIM maps including image quality (IQ) and inverse pole figure (IPF) maps. The three different iron oxides phases could be distinguished and the characteristics of oxides with different oxidation histories were compared. Iron oxides developed during high temperature oxidation consisted of wustite (FeO), magnetite (Fe304), and hematite (Fe20s) structures with varying texture, grain shape and size. In order to understand the mechanical properties of iron oxides, residual stresses in the three iron oxides phases were assessed using a specially designed x-ray stress measurement system. The stress distributions in the oxide layers were also simulated using finite element simulation of the hot rolling process.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.19519 |
| Date | January 2003 |
| Creators | Kim, Bae-Kyun |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Mining, Metals and Materials Engineering) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 002021278, Theses scanned by McGill Library. |
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