Annealing atmosphere, magnetic induction, and the number of {110} grains in inhibitor-free 3 pct Si-Fe alloys
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The 3 pct Si-Fe alloy strips are used for cores of pole transformers. The strips are composed of {110}001 Goss grains in which the {110} plane is laid on the rolling plane and the 001 direction is parallel to the rolling direction. The reason that the {110}001 Goss texture in the alloy strips is important is because the texture contains the easy magnetization direction. The formation mechanism of the {110}001 Goss texture in the 3 pct Si-Fe alloy strips has been suggested in light of the nucleation[1,2] and the surface-energy-induced selective grain growth.[3,4] That is, the crystallographic orientation of the nuclei in a rolled metal takes after that of the rolled metal. In the case with a surface energy advantage, the orientation of the surface nuclei, however, is quite different from that of the rolled surface: the formation of the {110}001 nuclei from the rolled {111}112 surface. The selective grain growth, which is directly influenced by the surface segregation concentration of sulfur, governs the final texture in the material. By controlling various variants, only the {110}001 grains can be obtained after final annealing. This is because among the {110}uvw grains containing the Goss grains, only the {110}001 grains that are the greatest in number survive through selective growth. Thin-gaged strips of 0.1-mm thickness were prepared from 2.5-mm-thick inhibitor-free 3 pct Si-Fe alloy plates containing 72 ppm sulfur through multistage cold rolling processes including intermediate annealing. Final thickness reduction was fixed at 60 pct. The strips were isothermally annealed under hydrogen atmospheres (1.5, 3, and 15 l H2/ min) or under a high vacuum of 7 106 Torr. All of the heat treatments were performed in a quartz tube of outer diameter 50 mm, which was enclosed by a tube furnace. At each annealing step, the quartz tube was drawn from the tube furnace and then air quenched. Magnetic induction, B10(T),
N.H. HEO is with the Advanced Technology Center, Korea Electric Power Research Institute, Yusung, Taejon 305-380, Korea. Contact e-mail: [email protected] Manuscript submitted June 16, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
of strips with dimensions of 5 (width) 100 (length) 0.1 (thickness) mm3 was measured under an external magnetic field of 1000 A/m with a direct current fluxmeter using an open circuit method. The orientation distribution functions and an etch-pit method were used for texture analyses. Depending on the roll diameter and the number of the rolling pass, the thin-gaged 3 pct Si-Fe alloy strips show a quite different cold rolling surface texture, as shown in Figure 1. In the case of the lesser number of the rolling pass, the cold-rolled strip consists of the near {111}112 and {100}011 textures. With increasing the number of the rolling pass, the rolling texture is changed to the {110}001 texture. Figures 2 through 4 are related to the cold rolling texture of Figure 1(a). In the thin-gaged 3 pct Si-Fe alloy strips, the initial {110}001 annealing texture o
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