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Analysis of abnormal grain growth and improvement in grain-oriented electrical steel based on solid-state wetting mechanism : 고상 젖음 이론을 바탕으로 접근한 비정상 입자 성장 분석과 전기강판의 개선
DC Field | Value | Language |
---|---|---|
dc.contributor.advisor | 황농문 | - |
dc.contributor.author | 나태욱 | - |
dc.date.accessioned | 2017-07-13T05:53:00Z | - |
dc.date.available | 2017-07-13T05:53:00Z | - |
dc.date.issued | 2016-08 | - |
dc.identifier.other | 000000136721 | - |
dc.identifier.uri | https://hdl.handle.net/10371/118094 | - |
dc.description | 학위논문 (박사)-- 서울대학교 대학원 : 재료공학부, 2016. 8. 황농문. | - |
dc.description.abstract | Abnormal grain growth(AGG) occurs frequently in many metallic systems. One of the famous examples is the Goss grain which abnormally grows during secondary recrystallization in Fe-3%Si steel. This phenomenon is already used for the grain-oriented electrical steel but its mechanism has not been clearly understood.
The sub-boundary enhanced solid-state wetting has been suggested to explain the mechanism of AGG. This theory suggests that the sub-boundary increases the wetting probability and the increased wetting probability enhances AGG. In this paper, based on this theory, microstructure and morphology of abnormally growing grains and matrix grains are analyzed and the grain-oriented electrical steel is improved. At the first, misorientation measurements at the growth front of abnormally growing grains in 5052 aluminum alloy were made using electron back-scattered diffraction (EBSD). When a three-dimensional morphology of solid-state wetting along a triple junction line is observed on a two-dimensional section, two kinds of morphologies could be observed. One is a morphology of penetrating the grain boundary when the section is parallel to the triple junction line. Grain boundary energies, which were estimated from misorientation measurements of the three grains in the penetrating morphology, satisfied the energetic condition for wetting along the triple junction line. Misorientation measurements showed that some matrix grains away from the growth front of abnormally growing grains had the same crystallographic orientation as that of the abnormally growing grain. This result implies that the abnormal grain growth in 5052 aluminum alloy occurs by the mechanism of sub-boundary enhanced solid-state wetting. The morphology of abnormally growing grains are predicted by three-dimensional Monte Carlo simulation and the real three-dimensional morphology is reconstructed by serial sectioning. The simulation was performed with sub-boundaries, precipitates and real crystallographic orientations of matrix grains. In the simulation, AGG occurs only when the both of sub-boundaries and precipitates exist. Form this simulation result, AGG occurs based on sub-boundary enhanced solid-state wetting mechanism. The real three-dimensional morphologies of abnormally growing grains are extremely similar to that of simulated abnormally growing grains. Both grains have island, peninsular grains and extremely irregular shape. This result shows that the factors are applied realistically in the simulation. Because the simulation shows realistic AGG, the behavior of abnormal grain growth was analyzed by the simulation. The simulation shows that the sub-boundary energy and the crystallographic orientation of matrix grains determine the velocity of AGG. According the analysis, the rate of AGG is determined by texture of matrix grains. And the texture can be controlled by asymmetric rolling. By the asymmetric rolling, the AGG rate are fastened and the magnetic properties of the grain-oriented electrical steel is improved. | - |
dc.description.tableofcontents | CHAPTER 1. Introduction 1
1.1 Abnormal grain growth in metallic system 1 1.2 Solid-state wetting 4 1.3 Sub-boundary enhanced solid-state wetting 7 CHAPTER 2. Misorientation angle analysis near the growth front of abnormally growing grains in 5052 aluminum alloy 10 2.1 Mechanism of sub-boundary enhanced solid-state wetting 10 2.2 Experimental Procedure 15 2.3 Misorientation angle analysis near the growth front of abnormally growing grains in 5052 aluminum alloy 18 CHAPTER 3. Reproduction of three-dimensional morphology of abnormally growing grains by MC simulation 27 3.1 Introduction 27 3.2 Reconstruction of the three-dimensional morphology of abnormally growing grain 28 3.3 The time evolution of the abnormally growing grain morphology reconstructed from the simulation data 31 3.4 The relation between two-dimensional microstructure and three-dimensional morphology 33 CHAPTER 4. Observation of three-dimensional morphology of abnormally growing grains by serial section 37 4.1 Experimental procedure 37 4.2 Three-dimensional morphology reconstructed by serial sectioned images of Goss grain 38 4.3 Similarity of three-dimensional morphology between real Goss grain and simulated Goss grain 46 4.4 Three-dimensional morphological evidence of solid-state wetting 48 CHAPTER 5. Three-dimensional simulation for abnormal growth behavior 52 5.1 Effect of sub-boundary energy on abnormal grain growth rate 52 5.2 Effect of texture on abnormal grain growth rate 57 CHAPTER CHAPTER 6. Improvement in grain-oriented electrical steel by symmetric rolling 62 6.1 Texture difference between at the surface and at the center 62 6.2 Experimental procedure 67 6.3 Texture of hot-rolled sample produced by asymmetric rolling and symmetric rolling 70 6.4 Texture of 1st and 2nd recrystallized samples produced by asymmetric rolling and symmetric rolling 77 CHAPTER 7. Conclusion 81 CHAPTER 8. Parallel Monte-Carlo simulations for the effect of precipitates and sub-boundaries on abnormal grain growth in Fe-3%Si stee 84 8.1 Introduction 84 8.2 Implementation of simulation conditions 86 8.3 Simulation results 92 8.4 Comparisons between simulation and experimental results 101 8.5 Three-dimensional morphologies of abnormally-growing Goss grains 112 Reference 114 요약(국문초록) 121 | - |
dc.format | application/pdf | - |
dc.format.extent | 4394718 bytes | - |
dc.format.medium | application/pdf | - |
dc.language.iso | en | - |
dc.publisher | 서울대학교 대학원 | - |
dc.subject | Abnormal grain growth | - |
dc.subject | Solid-state wetting | - |
dc.subject | sub-boundary | - |
dc.subject | grain boundary energy | - |
dc.subject | three-dimensional morphology | - |
dc.subject | Monte-Carlo simulation | - |
dc.subject | serial sectioning | - |
dc.subject | asymmetric rolling | - |
dc.subject.ddc | 620 | - |
dc.title | Analysis of abnormal grain growth and improvement in grain-oriented electrical steel based on solid-state wetting mechanism | - |
dc.title.alternative | 고상 젖음 이론을 바탕으로 접근한 비정상 입자 성장 분석과 전기강판의 개선 | - |
dc.type | Thesis | - |
dc.contributor.AlternativeAuthor | Na, Tae-Wook | - |
dc.description.degree | Doctor | - |
dc.citation.pages | 124 | - |
dc.contributor.affiliation | 공과대학 재료공학부 | - |
dc.date.awarded | 2016-08 | - |
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