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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

HIGH-RESISTIVITY ELECTRICAL STEEL THIN STRIP BY HYBRID DEFORMATION PROCESSING

Brhayan Stiven Puentes Rodriquez (13148703) 25 July 2022 (has links)
<p>    </p> <p>Electrical steels are one type of soft magnetic material. They are based on Fe-Si alloys and are widely used for magnetic cores in transformers and electric motors. It is well known that Fe- 6.5Si wt% is the most efficient composition; however, at such a high silicon concentration (6.5wt.% = 12.1 at.% Si in Fe), the poor workability of the alloy makes it unacceptable for industrial production via conventional sheet steel rolling processes. This problem was approached in two different ways. First, a machining-based approach that suppresses the mechanisms that lead to cracking during conventional rolling was implemented for processing of thin metal strips. Two related machining-based sheet production technologies called free machining (FM), and hybrid cutting extrusion (HCE) were used to produce strips of high resistivity electrical steel. The maximum strip width achieved was 50 mm, and it was produced with a combination of FM and light rolling with a surface roughness comparable to cold-rolled sheet surfaces. Second, a new experimental alloy Fe-4Si-4Cr wt% was developed with improved magnetic properties compared to ~ Fe-3.2Si wt% and outstanding workability. Results report that the new experimental alloy has an electrical resistivity of 85 ± 3 𝜇Ω ∙ 𝑐𝑚 which is higher than Fe-6.5%Si. Also, the results on the Fe-4Si-4Cr workability show that this new alloy can withstand 75% cold-rolled reduction. The magnetic properties characterization was done via standard stacked toroid testing, and results show that Fe-4Si-4Cr experimental alloy exhibits excellent magnetic performance with a reduction in core losses of 33% at 400 Hz compared to commercial alloys with ~ Fe-3.2Si wt%. Recrystallization kinetics and texture evolution in the experimental alloy were evaluated for traditionally rolled and machining-based samples. Results were used to construct annealing maps. These maps represent the stages of the annealing process for a range of temperature versus time conditions, i.e., the annealing maps are a graphical summary showing the different stages of the annealing process for the Fe-4Si-4Cr experimental alloy in the two conditions. Despite the significant differences in the deformation texture of the two conditions, the recrystallization kinetics were similar. Finally, the two conditions retained the as-deformed texture in the intermediate annealing but to a lesser degree after completing a full anneal. In the case of the rolled sample, it is possible to trace the original texture fibers (γ-fiber, the partial α-fiber, and the θ -fiber) in the fully annealed data, but the texture intensity is just 2.5 mrd. On the other hand, the texture of the fully annealed HCE sample changes as compared to the as-deformed condition, located close to (110)[112] with a surprisingly strong peak of ~ 25 mrd. </p>

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