Papers by Author: Kyung Jun Ko

Abstract: During abnormal grain growth, a few Goss grains grow exclusively fast and consume the matrix grains. The Goss abnormally-growing grain (AGG) has peculiar features which are irregular grain boundaries and very high frequency of peninsular grains nearby the growth front of AGG and island grains trapped inside AGG. These features might provide a clue for clarifying the mechanism of Goss AGG. The experimentally-observed microstructural feature and grain boundary characterization of Goss were approached by the solid-state wetting mechanism. In this study, observing the three-dimensional wetting morphology in serial section images of Goss AGG by EBSD, we report some direct microstrucrual evidence supporting solid-state wetting mechanism for Goss AGG. The solid-state wetting mechanism for the evolution of the Goss AGG in Fe-3%Si steel explains the microstructural features evolved during secondary recrystallization, which cannot be approached by the conventional theories based on the grain boundary mobility.

Abstract: Grain oriented electrical steels should have low core loss and high magnetic flux density. These properties are closely related with sharpness of {110} texture after secondary recrystallization. This Goss texture develops by abnormal grain growth during secondary recrystallization annealing. Based on experimental results, a general suggestion which estimates the magnetic properties after secondary recrystallization from a primary recrystallized texture can be made. For a material to have better magnetic properties after secondary recrystallization, its primary recrystallized texture should have not only larger number of ideal Goss grains, but also lower frequency of low angle grain boundary around those Goss grains.

Abstract: In order to verify the origin of Goss nuclei for secondary recrystallization in Fe-3%Si steel, the effect of cold-rolling direction on the secondary recrystallization was examined in this study. The cold-rolling direction was rotated through 0 ~ 90 degrees about the hot-rolling direction on normal direction axis of hot-rolled sheet. In spite of the different initial texture before cold rolling, the 88% cold rolled texture was formed by similar α and γ fiber regardless of the rotation of cold rolling direction. Likewise, regardless of the cold rolling direction, the primary recrystallized sheets had a similar texture. In particular, the area fraction of Goss component (tolerance angle within 15º) in the primary recrystallized sheets was increased in the cold rolling condition of rotating through 60, 90 degrees from the hot rolling direction. After high temperature annealing at 1200°C, the secondary recrystallized grain was fully evolved in the all conditions. The sharpness of Goss texture in secondary recrystallized sheet was decreased as increasing the rotation angle of cold rolling direction.

Abstract: Desirable magnetic properties for grain oriented electrical steels are low core loss and high magnetic flux density. These properties are closely related with sharpness of {110} texture. This Goss texture develops by abnormal grain growth during secondary recrystallization annealing. Based on experimental results, a general suggestion which estimates the magnetic properties after completion of secondary recrystallization from a primary recrystallized texture can be proposed. For a material to have better magnetic properties after completion of secondary recrystallization, it should have a primary recrystallized texture in which there are not only large number of ideal Goss grains, but also lower frequency of low angle grain boundary around those Goss grains.