N.H. Heo

Tertiary recrystallization and magnetic induction under various annealing atmospheres in thin-gauged 3% Si–Fe strip

Surface-energy-induced secondary or tertiary recrystallization by grains with a specific surface plane can be freely governed in thin-gauged 3% Si–Fe strips by controlling the bulk content of sulfur and annealing atmosphere. During a vacuum or hydrogen annealing process, a convex profile in segregated-sulfur concentration is formed due to evaporation or desorption of segregated sulfur as a hydrogen sulfide, corresponding to a trough in magnetic induction. High magnetic induction is obtained after the annealing treatments. Final annealing under an argon atmosphere caused a saturation in segregated-sulfur concentration with annealing time. Under this extremely high segregated sulfur, grains of high index crystal plane including {111} continued to grow, resulting in low magnetic induction.

Nucleation and development of Goss texture and magnetic induction in thin-gauged 3% Si–Fe alloy

Nucleation and development of Goss texture have been investigated in high-purity 3% silicon–iron alloy strips. During final annealing, under a high vacuum, Goss texture can form independently from cold-rolled matrix at the early stage of primary recrystallization, regardless of any pre-existing Goss texture near the strip surface. The formation mechanism of the new Goss texture probably follows the oriented nucleation theory, which is due to segregated sulfur present on the strips in a final annealing time. Goss texture in the primary recrystallization develops into the final Goss texture or not, depending on cold rolling conditions.

Sulfur evaporation and magnetic induction in thin-gauged 3%Si-Fe sheets

Singly oriented 3%Si-Fe is one of the most popular soft magnetic materials. Used as the core material of pole and power transformers, it is highly oriented to (110)[001] Goss texture and has one direction of easy magnetization in the rolling plane. The formation mechanism of Goss texture in thin-gauged 3%Si-Fe sheets can be explained by considering the influence of impurities (especially, sulfur) on the surface energy of (110) and other planes. It is the purpose of this study to investigate the effect of sulfur evaporation on the magnetic induction in thin-gauged 3%Si-Fe sheets by prolonged holding of silicon-iron melts or by annealing of hot-rolled plates.

Nucleation, selective growth and magnetic induction in 3% Si-Fe strips

In this article, the 40 or 100/spl mu/m thick 3% Si-Fe strips with final cold rolling reduction of 30% that contain 90ppm sulphur were heated up to 1200/spl deg/C with various heating rates, prior to isothermal annealing at 1200/spl deg/C under a flowing hydrogen atmosphere. A prominent difference in final texture and magnetic induction was observed after final annealing, depending on heating rates and strip thickness.

Interfacial segregation kinetics of sulfur and magnetic induction influenced by hydrogen flow rate in thin-gauged 3% Si-Fe strip

Effects of flow rate of hydrogen and final reduction on final texture and magnetic induction have been investigated in 3% Si-Fe alloy strips containing 90-ppm sulfur. After final annealing under a flowing hydrogen atmosphere of 10 l/min, the strip showed a magnetic induction value (B/sub 10/) higher than 1.9 T, whereas only about 1.6 T was obtained at a flow rate of 3 l/min. Within the range of final reduction in thickness of 30%-60%, the final texture and the magnetic induction revealed little dependence on final reduction. Auger electron spectroscopy indicated that the strong dependence of magnetic induction on the flow rate of hydrogen was due to the difference in segregation kinetics of sulfur at the strip surface. The selective growth kinetics also supported a correlation between segregation kinetics of sulfur, texture development, and magnetic induction.

Initial recrystallization texture and magnetic induction in single-oriented electrical steel

Initial recrystallization texture is influenced by the bulk content of sulfur and by the final reduction. At a given bulk content of sulfur, a lower final reduction is favorable for obtaining the initial {011} Goss texture. Under a fixed final reduction, a lower bulk content of sulfur is good for this purpose. As the intensity of initial Goss texture increases, it is easier to obtain magnetic induction (B/sub 10/). This is because the probability, that the initial Goss grains survive within the time range of highly segregated sulfur and have a chance for surface-energy-induced selective growth, becomes higher under the later segregated-sulfur-free condition.

Effects of segregated sulfur on recrystallization texture and magnetic induction in thin-gauged 3% silicon steel

During final annealing at 1200/spl deg/C under a high vacuum, changes in recrystallization texture with final annealing time were observed in thin-gauged 3% Si-Fe alloys. In the alloy containing 30 ppm bulk sulfur, the recrystallization texture varied from the {111} to the {001} and finally to the {110} Goss texture, resulting in higher magnetic induction than 1.90 T. The trough in magnetic induction, which corresponds to the relatively high surface-segregated sulfur range, is due to the magnetically detrimental effect of those textures, i.e. the {111} and the {001} . In the alloy containing 6 ppm bulk sulfur, the correlation between magnetic induction and surface-segregated sulfur was the same as that in the other alloy. These results clearly indicate that the surface energy induced recrystallization in the thin-gauged 3% Si-Fe alloys is strongly affected by the segregation and the evaporation of sulfur.

Effects of Rolling Conditions on Grain Orientation and Magnetic Properties of Thin-Gauged 3% Si-Fe Sheets

3% Si-Fe sheets are widely used as core material of large transformers, large rotating machines and pole transformers due to characteristic soft magnetic properties, where energy losses during magnetization are critically concerned. The magnetic characteristics in silicon iron arises from a preferred grain orientation, i.e. (110) [001] Goss texture which forms after cold rolling followed by secondary recrystallization. In this paper, effects of rolling direction on the grain orientation and magnetic properties of the thin-gauged 3% Si-Fe sheets are investigated.

Effects of flow rate of hydrogen on selective growth kinetics and magnetic induction in thin-gauged 3% Si-Fe strip

During final annealing, microalloyed sulfur in thin-gauged silicon steel segregates to the strip surface and on grain boundaries and thus affects the texture development. With increasing flow rate of hydrogen, the profile of magnetic induction was shifted to a shorter annealing time, and the time range of lower magnetic induction was drastically shortened. This is ascribed to the faster depletion of surface-segregated sulfur that accelerates surface-energy-induced selective growth of (110)[001] Goss grains. After final annealing for 14.4 ks, the strips showed a high magnetic induction of about 1.9 T. By controlling the surface segregation behavior of sulfur, it is possible to achieve the surface-energy-induced selective growth of grains favorable for magnetic induction in thin-gauged silicon steel.

Study on surface magnetic domain structure of thin-gauged 3%Si-Fe strips using scanning electron microscope with polarization analyzer

Scanning Electron Microscopy with Polarization Analysis (SEMPA) was used to image the surface magnetic domain structure of the 100 ㎛ thick 3% Si-Fe sheet. The thin-gauged 3% Si-Fe strips with magnetic induction (B_(10)) from 1.98 to 1.57 Tesla were prepared via conventional metallurgical processes including melting, hot- and cold-rolling, intermediate annealing and final annealing. Using SEMPA, it was observed that the B_(10) (1.98 T) Tesla sample was almost composed of 180° stripe domains which are parallel to rolling direction. On the other hand the 3% Si-Fe sheet with B_(10) (1.57 T) Tesla was composed of large 180° stripe domains that are slanted about 30° to the rolling direction and complex magnetic domain structures like tree and zigzag pattern. The 180° stripe domains, which covered a major part of the sample, had (110) Goss texture parallel to the rolling direction. The domain walls between 180° stripe domains were the conventional Bloch type walls. On the other hand, the 90° domains, which covered minor part on edge of the sample, were observed in (200) grains. The domain walls between 90° domains were the Neel type walls. In high magnification, the elliptical singularity at the Neel walls was clearly observed.