Approach to saturation in textured soft magnetic materials
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otivation for this article is to demonstrate the influence of texture (crystallographic-preferred orientation) on the magnetic properties of sheets of soft magnetic materials, such as iron. The technological application of interest is that of rotating electrical machinery in which the magnetic field experienced by the material rotates in a plane. The key parameter is the “core loss” or specific power loss, commonly expressed as a power per unit mass, which can be related to the magnetic permeability of the material. There are various measures of permeability; for example, initial permeability is sensitive to aspects of microstructure other than texture. Examples are domain structure and secondphase particles that act as pinning points. The focus in this article is on (the secant) permeability at large applied fields. This choice is made in order to investigate the influence of texture in the range where rotation of the local magnetization vector dominates the magnetic response of the material. In this sense, the article follows the Stoner–Wohlfarth model.[1] After describing the model, an example is given of its application to cold-rolled magnetic lamination (CRML) steels. These steels are quite different from the much better known grain-oriented silicon steels, which have 3 pct silicon and undergo a complex and expensive thermomechanical processing to develop the Goss texture ({110}具001典).[2] The CRML steels are similar to mild steels used in automotive and appliance bodies but have small amounts of silicon and other elements added to raise their resistivity and, thereby, reduce the core loss. Their thermomechanical processing is designed to produce low core loss and high permeability that, in metallurgical terms, requires a decarburized microstructure with large grain size and near random texture.[3] A.D. ROLLETT, Professor, and M.L. STORCH, Graduate Student, are with the Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213-3890. E.J. HILINSKI, Senior Research Project Engineer, and S.R. GOODMAN, Senior Research Consultant, are with the Research and Technology Center, U.S. Steel Group, Monroeville, PA 15146. Manuscript submitted September 2, 1999. METALLURGICAL AND MATERIALS TRANSACTIONS A
Previous work has shown that texture varies from one batch to another in such steels and that texture may play a role in the magnetic properties.[4,5,6] Recent work on nonoriented steels has demonstrated how sensitive the magnetic properties are to subtle variations in processing conditions.[2] Specifically, the sheet is temper rolled to a reduction in the 0 to 10 pct range and, then, annealed in a controlled atmosphere that often contains hydrogen. The final annealing step is known as the quality development anneal (QDA) because it is critical for developing the desired magnetic properties. The core loss and permeability are dependent on the temper reduction and the surface roughness of the rolls, among other parameters. High permeability, post-QDA was associated with anisotropy in th
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