Nonoriented electrical steels are mainly used as the core materials in motors and generators. The magnetic properties required for these materials are low core loss, high magnetic induction and high magnetic permeability. These magnetic properties of nonoriented electrical steels are mainly influenced by grain size and crystallographic texture. All research to improve the magnetic properties so far has focused on grain growth through the control of chemical compositions and various processing parameters. However, in the manufacturing techniques of nonoriented electrical steels, the control of grain size is approaching its limit. Since there is still enough room to improve the magnetic properties through the control of texture, future research in nonoriented electrical steels should be concentrated on the optimization of crystallographic texture. / Recrystallization texture itself has long been a subject of research because the origin of recrystallization texture provides a high level of scientific interest. Despite much research on recrystallization texture, the mechanism of the formation of recrystallization texture is still disputed. This dispute is associated with the complexity of microstructural inhomogeneity formed in the deformed state, different nucleation rates for different orientations of deformed grains and different growth rates of nuclei into the neighboring deformed matrix. However, the advent of Orientation Imaging Microscopy (OIM) has contributed to a remarkable progress in the area of recrystallization texture, and stimulated research on the annealing texture in low carbon and interstitial free steels. Conversely, no systematic research on the evolution of the annealing texture in nonoriented electrical steels has yet been done. / The mechanism of texture evolution during recrystallization in the nonoriented electrical steels containing 1% and 2% Si respectively, a main objective of this thesis, is investigated from electron backscatter diffraction (EBSD) measurements on the materials with different recrystallization fractions. Based on obtained results, the mechanism for the formation of the recrystallization texture is proposed. The behavior of deformed grains of specific orientations is also discussed in terms of image quality value introduced by EBSD techniques. In addition, the origin of nuclei of specific orientations is suggested from observed EBSD results. / The texture development during grain growth, another main objective of this thesis, is investigated. Furthermore, a mechanism of texture development during grain growth is proposed based on the misorientation angle distribution with adjacent grains and the average size of grains of specific orientations. / Some useful means to optimize the magnetic properties through texture control in nonoriented electrical steels are studied. The effect of initial grain size prior to cold rolling on texture evolution during both the recrystallization stage and the grain growth stage is clarified. In addition, the effects of temper rolling reduction and annealing time on texture development during final annealing are examined. A mechanism of texture transformation by strain induced boundary migration (SIBM) is suggested by means of the introduction of image quality value in EBSD techniques. Finally, the effect of heating rate on texture development during final annealing is investigated, and the reason for texture change due to different heating rates is discussed.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.83087 |
| Date | January 2002 |
| Creators | Park, Jong-Tae, 1962- |
| Contributors | Szpunar, Jerzy A. (advisor) |
| 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: 001984836, proquestno: AAINQ88547, Theses scanned by UMI/ProQuest. |
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