Tham khảo tài liệu 'asm metals handbook - desk edition (asm_ 1998) ww part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Fig. 2 Effect of alloying elements on electrical resistivity of iron Addition of silicon in sufficient amounts eliminates the allotropic transformation in iron. Consequently silicon-iron can be annealed at high temperature to promote grain growth thus facilitating development of preferred grain orientation. However room-temperature saturation induction is reduced by alloy additions other than cobalt see Fig. 3 . Fig. 3 Effect of alloying elements on room-temperature saturation induction of iron Effects of Heat Treatment. Magnetic materials such as iron-nickel alloys in the cold-rolled condition must be annealed to develop the desired grain structure and magnetic properties. Annealing conditions required for silicon steels depend on processing carried out by the supplier and on cost-versus-performance factors. Semi-processed grades must be annealed near 840 C 1550 F after stamping of laminations for removal of carbon and development of magnetic properties. Fully processed grades of non-oriented or grain-oriented steels require annealing in the range 750 to 875 C 1375 to 1600 F only for removal of fabrication stresses. For wide laminations used in a flat condition as in large power transformers low-stress strip requiring no annealing is available. Effects of Grain Size. For most applications grain size should be as large as possible for nonoriented materials Fig. 4 . In oriented grades of silicon steel optimum magnetic properties are usually obtained with grain sizes of 2 to 10 mm depending on the degree of crystal orientation increases in grain size above 10 mm are accompanied by significant increases in both domain-wall spacing and eddy-current losses. fif ộrặiní piif fflrti7 Fig. 4 Relationship between grain size and hysteresis loss for high-purity iron at B 1 T 10 kG Effects of Grain Orientation. All ferromagnetic crystals are magnetically anisotropic--that is they have different magnetic properties in different crystallographic directions. In nickel the .
