| Fe-based nanocrystalline alloy obtained extensive research and the applicationdue to its excellent soft magnetic properties, mainly high permeability and low ironloss. The mechanism of the alloys with high permeability is the formation of thespecial kind of amorphous/nanocrystalline two-phase coupling structure. Thenanocrystalline grains with size of about20nm are evenly distributed in the amorphousmatrix. While the problem is, it’s forming conditions is exacting and the heat treatmenttemperature range is narrow. When the size of this kind of transformer cores is largeand thick, the cores will release a large amount of crystallization heat, and it is difficultto transfer out, which leads to the significant self temperature-rise in a very short time.Once the temperature-rise is much higher than the setting annealing temperature, itwill destroy the soft magnetic properties of cores directly, and finally affects theproduction efficiency and the qualification rate of the alloy cores. Thus, thepreparation、crystallization behavior and soft magnetic properties of Fe-Si-B-Cu-Nb-Vamorphous/nanocrystalline alloy used for high precision current transformer coreswere investigated in this paper. A process of low-temperature pre-annealing wasproposed to achieve the purpose of releasing crystallization heat slowly, themechanism of release crystallization heat slowly was also discussed. In addition, alow-boron Fe-based Fe75.5Si13.5B7Cu1Nb1.5V1.5alloy with high toughness and highpermeability under high frequency were prepared.DTA results showed that, the initial crystallization temperature ofFe73.5Si13.5B9Cu1Nb2V1amorphous alloy is488℃. It is generally recognized thatcrystallization of amorphous alloy will not occur when the temperature is lower thanthe initial crystallization temperature. With real-time monitoring of the internaltemperature of the iron core, it was found that the latent heat can be slowly releasedand the core temperature can be well controlled by pre-annealing at around470℃. Both DSC and XRD results suggested that more primary crystallization took place athigher pre-annealing temperature. Quantitatively,63.13%of primary crystallizationoccurred with heat released by pre-annealing at475℃for100min, which onlyresulted in a small temperature-rise of17℃at the core. After being pre-annealed at475℃for100min and finally annealed at542℃for60min, the initial permeabilityμiof the Fe73.5Si13.5B9Cu1Nb2V1nanocrystalline alloy core can reach181200Gs/Oe.The study on the pre-annealing process of the Fe72.6Si15B9Cu0.8Nb2.6amorphousalloy was also carried out. It was found that, when the pre-annealing temperature islower than475℃, the phenomenon of temperature-rise did not occur in the stage ofpre-annealing, but did happen severely in the subsequent stage of crystallizationannealing. After being pre-annealed at480℃for120min, the temperature-risephenomenon of cores appeared slowly in the stage of pre-annealing, and decreasedsignificantly in the stage of crystallization annealing. When the pre-annealingtemperature reaches490℃, the temperature-rise phenomenon occurred obviously inthe stage of pre-annealing, but almost disappeared in the stage of crystallizationannealing.A low-boron Fe-based Fe75.5Si13.5B7Cu1Nb1.5V1.5alloy with high toughness andhigh permeability were prepared by a single-roller melt spinner. The results showedthat: the toughness of as-prepared amorphous Fe75.5Si13.5B7Cu1Nb1.5V1.5alloy ribbon isbetter than that of the conventional Fe73.5Si13.5B9Cu1Nb3alloy ribbon. The amorphousFe75.5Si13.5B7Cu1Nb1.5V1.5alloy ribbon is not broken after being folded. It is found thatthe relative magnetic permeability of the Fe75.5Si13.5B7Cu1Nb1.5V1.5alloy decreasesslowly with frequency after being optimally annealed at530℃for60min. Under highfrequency the relative permeability of nanocrystalline Fe75.5Si13.5B7Cu1Nb1.5V1.5alloyis higher than that of nanocrystalline Fe73.5Si13.5B9Cu1Nb3alloy. |
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