Evolutions of microstructure and magnetic properties of heatproof domain-refined silicon steel during annealing and its application

Abstract

Heatproof domain-refined grain-oriented (DRGO) silicon steel is an ideal material for the manufacture of S15-type ultra-high efficiency transformer with three-dimensional wound-core (TDWC). In this paper, the microstructure, grain orientation, and magnetic performance of 23ZDMH80 heatproof silicon steel during stress-relief annealing were investigated by scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) techniques. Based on heatproof DRGO steel, the Epstein-SST (single sheet tester) conversion factor and equivalent magnetic path length were calculated, and then an ultra-high energy efficiency transformer was developed. Results show that, the average size of micrograins in notched region increased from 42.3 μm to 68.2 μm after annealing at 850 ℃ for 0–8 h. The orientations of micrograins grown on large-size Goss grain included not only the non-〈0 0 1〉 orientations, such as {210} 〈−241〉, {215} < 1–20>, and {1 1 0} < 1–12}, which were harmful to the magnetic properties, but also the favorable {1 0 0} 〈0 0 1〉 and Goss. Correspondingly, the core loss of 5 pairs of Epstein specimens first decreased then increased slowly (the growth rates below 1.2%) during annealing. The Epstein-SST conversion factor δP for 23ZDMH80 heatproof steel was 8.6% (higher than 5.0% the value recommended by IEC standard), and the equivalent magnetic path length was 0.489 m. Finally, the developed 10 kV/400 kVA transformer with TDWC presented ultra low no-load loss of 289 W, load loss of 3072 W, and noise of 35.4 dB, it means significant advantage of energy conservation and environmental protection.