6.5 wt% 방향성 규소강판의 철손특성 및 미세조직에 관한 연구 = (A) study on iron loss behaviors and microstructures of 6.5 wt% grain-oriented silicon steel

다국어 초록 (Multilingual Abstract)

Silicon steel has been widely used in electrical appliances and devices, such as transformers and motor cores, because of its excellent soft magnetic properties and low cost. In recent years, however, further reductions in the magnetic loss in silicon steel have been sought in order to improve efficiency in electrical appliances. It is well known that the magnetic properties of silicon steel are strongly dependent on the strip thickness, silicon concentration, grain size, and crystallographic texture. Among these factors, the increase in silicon content is one of the most effective ways to reduce eddy current loss, resulting in efficiency improvements in high frequency transformers and motors. Furthermore, the magnetostriction value of silicon steel is reduced to almost zero when the silicon content reaches 6.5 wt%, which can result in a sharp reduction in hysteresis loss. Nevertheless, the application of 6.5 wt% silicon steel to transformers and motor cores has been limited because it is too brittle to use conventional rolling techniques. The brittleness of high silicon steel stems from the formation of two different ordered phases, B2 (FeSi) and D03 (Fe3Si), which are known to alter the magnetic properties of the steel. However, the specific relationship between the ordered phases and the magnetic properties in high silicon steel is still unclear. One of key challenges in the use of high silicon steel is, therefore, to understand how ordered phases contribute to the magnetic loss properties.
As previously mentioned, the brittleness of high silicon steel makes it difficult to use conventional rolling techniques in fabrication. To overcome this problem, several methods such as chemical vapor deposition process were suggested. The suggested method requires complex and long procedures, thus a more simplified fabrication method is strongly demanded.
In this study, SiO2 textiles were used to control the amount of silicon in thin-gauged grain oriented silicon steel. Silicon content was controlled through the diffusion of Si generated from SiO2 decomposition. Fabricated 6.5 wt% GO silicon steel had a superior iron loss property compared with other composition due to increase the resistivity and decrease the antiphase boundary density. High resistivity decreased the eddy current loss and the antiphase boundary exercised bad influence to hysteresis and anomalous losses due to act as pinning centers in the magnetic domain wall.
As a result, the minimum iron loss was found at a state of the lowest antiphase boundary density that was obtained by furnace cooling and low temperature annealing at 600 ℃. These results indicate that the reduction of antiphase density is one of key points for improving the iron loss property.
Furthermore, the effect of the D03 antiphase boundary transformation on iron loss property in the 6.5 wt% GO silicon steel was investigated through homogenizing annealing at 600 ℃. With increasing the annealing time, the antiphase domains increased and the boundary character of D03 antiphase changed from 1/4<111> to 1/2<100> more than 3 hr. These new boundaries were anisotropically grown, which increased a lancet domain density. And this increase of the lancet domain density led to increase the iron loss. There results suggest that the formation of the D03 1/2<100> antiphase boundary should be controlled to reduce the iron loss property in 6.5 wt% silicon steel.

목차 (Table of Contents)

• Chapter I. Introduction
• Chapter II. Literature Review
• 2.1. Grain-oriented silicon steel
• 2.2. Iron loss components of silicon steel
• 2.3. Improvement of iron loss property of silicon steel
• 2.3.1. Texture control for improved iron loss
• 2.3.2. Thinner-gauged silicon steel
• 2.3.3. Magnetic domain refinement
• 2.3.4. Perfection of magnetic domain
• 2.3.5. Increase of the silicon contents
• 2.4. Microstructure of 6.5 wt% silicon steel
• 2.5. Interaction between APBs and magnetic domain walls
• Chapter III. Experimental Procedures
• 3.1. Fabrication of 3.0 wt% GO silicon steel
• 3.2. Fabrication of 6.5 wt% GO silicon steel
• 3.3. Heat treatment processes for low iron loss in 6.5 wt% GO silicon steel
• 3.4. Measurement of magnetic properties
• 3.5. Microstructure characterization
• 3.6. Magnetic domain observation
• Chapter IV. Results and Discussion
• 4.1. 6.5 wt% GO silicon steel
• 4.2. Improvement of iron loss in 6.5 wt% GO silicon steel
• 4.2.1. Effect of silicon content on iron loss of high silicon steel
• 4.2.2. Effect of cooling rate on iron loss of 6.5 wt% GO silicon steel
• 4.2.3. Effect of low temperature annealing on iron loss of 6.5 wt% GO silicon steel
• 4.2.4. Effect of D03 APBs transformation on iron loss of 6.5 wt% GO silicon steel
• 4.3. Application for transformer
• Chapter V. Summary
• References
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