Effect of pre-annealing prior to cold rolling on the precipitation, microstructure and magnetic properties of strip-cast non-oriented electrical steels

doi:10.1016/j.jmst.2017.08.002

摘要/Abstract

Abstract:

A novel processing route involving strip casting, pre-annealing treatment, cold rolling and recrystallization annealing was applied to a Fe-2.6%Si steel to improve the magnetic properties. The impact of as-cast strip pre-annealing on the microstructure, texture, precipitation and magnetic properties were investigated by electron probe micro-analysis, transmission electron microscopy, and X-ray diffraction analysis, etc. It was found that the precipitation of second-phase particles during strip casting was restrained by rapid solidification. The absence of pre-annealing led to the occurrence of a large amount of 20-50 nm MnS precipitates in the final annealed sheets, which is responsible for fine grains and high core loss (4.01 W/kg) due to grain boundary pinning effect. Although the microstructure and texture of 900-1000 °C pre-annealed samples were similar to those of as-cast strip, significant grain coarsening together with the strengthening of λ-fiber texture was observed in the 1100 °C pre-annealed strips. In comparison with the case of as-cast strip, a higher amount of large-sized precipitates consisting of manganese sulfide and/or aluminum nitride occurred in matrix after pre-annealing. Correspondingly, in the final annealed sheets, the number density of precipitates with sizes smaller than 100 nm was substantially reduced, and 100-200 nm and 200-500 nm sized particles became more dominant in samples subjected to 30-min and 120-min pre-annealing treatments respectively. In addition, the average grain size of final annealed sheets increased with the pre-annealing temperature and time because of the weakened pining effect of coarsen precipitates. Ultimately, the magnetic induction of samples subjected to pre-annealing was slightly increased and ranged from 1.73 T to 1.75 T owing to the enhancement of {100} recrystallization texture, and simultaneously the core loss significantly decreased until a minimum of 3.26 W/kg was reached. Nevertheless, large number of 200-500 nm particles presented during pre-annealing for 120 min could weaken the improvement in core loss which is likely associated with the pinning effect on magnetic domain wall.

Key words: Strip casting, Non-oriented electrical steel, As-cast strip annealing, Precipitates, Magnetic properties

. [J]. 材料科学与技术, 2017, 33(12): 1465-1474.

Xu Yunbo, Jiao Haitao, Zhang Yuanxiang, FengFang, Lu Xiang, Wang Yang, Cao Guangming, Li Chenggang, Misra R.D.K.. Effect of pre-annealing prior to cold rolling on the precipitation, microstructure and magnetic properties of strip-cast non-oriented electrical steels[J]. J. Mater. Sci. Technol., 2017, 33(12): 1465-1474.

图/表 14

Fig. 1. Schematic of twin-roll strip casting and processing route.

Fig. 2. Microstructure (a) and texture (b) of as-cast strip.

Fig. 3. Morphology and size distribution of the precipitates in the as-cast strip.

Fig. 4. Optical micrograph of different pre-annealed strips: (a) 900 °C, 30 min; (b) 1000 °C, 30 min; (c) 1100 °C, 30 min; (d) 900 °C, 120 min; (e) 1000 °C, 120 min; (f) 1100 °C, 120 min.

Fig. 5. φ2 = 45° section ODF of the different pre-annealed strips: (a) 900 °C, 120 min; (b) 1000 °C, 120 min; (c) 1100 °C, 120 min.

Fig. 6. Morphology of precipitates in pre-annealed strips: (a) 900 °C, 30 min; (b) 1000 °C, 30 min; (c) 1100 °C, 30 min; (d) 900 °C, 120 min; (e) 1000 °C, 120 min; (f) 1100 °C, 120 min, and EDS spectra (g-i) of typical precipitates.

Fig. 7. Size distribution of the precipitates in the pre-annealed strips.

Fig. 8. φ2 = 45° section ODF of the cold-rolled sheets subjected to different pre-annealing processes: (a) no pre-annealing; (b) 900 °C, 120 min; (c) 1000 °C, 120 min; (d) 1100 °C, 120 min.

Fig. 9. Average grain size of the final annealed sheets.

Fig. 10. φ2 = 45° section ODF of final annealed sheets subjected to different pre-annealing processes: (a) no pre-annealing; (b) 900 °C, 120 min; (c) 1000 °C, 120 min; (d) 1100 °C, 120 min.

Fig. 11. TEM morphology and EDS spectra of precipitates in the final annealed sheets which were not subject to pre-annealing.

Fig. 12. Morphologies of precipitates in the final sheets of strips subjected to different pre-annealing processes: (a) 900 °C, 30 min; (b) 1000 °C, 30 min; (c) 1100 °C, 30 min; (d) 900 °C, 120 min; (e) 1000 °C, 120 min; (f) 1100 °C, 120 min, and EDS spectra (g-i) of typical precipitates.

Fig. 13. Size distribution of the precipitates in the final annealed sheets.

Fig. 14. Magnetic properties of the final annealed sheets.

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