Abstract
Iron–silicon alloys with up to 6.5 wt.% Si offer an improvement of soft magnetic properties in electrical steels compared to conventional electrical steel grades. However, steels with high Si contents are very brittle and cannot be produced by cold rolling. In addition to solid solution hardening, it is assumed that the B2- and DO3-superlattice structures are responsible for the poor cold workability. In this work, two cast strips with 6.0 wt.% Si were successfully produced by the twin roll strip casting process and cooled differently by secondary cooling. The aim of the different cooling strategies was to suppress the formation of the embrittling superlattice structures and thus enable further processing by cold rolling. A comprehensive material characterization allows for the understanding of the influence of casting parameters and cooling strategies on segregation, microstructure and superlattice structure. The results show that both cooling strategies are not sufficient to prevent the formation of B2- and DO3-structures. Although the dark field images show a condition which is far from equilibrium, the achieved condition is not sufficient to ensure cold processing of the material.
Highlights
Non-grain-oriented electrical sheets are widely used in the field of electrical engineering, for example in electric motors, transformers and power generators
The carbon content is limited to a maximum of 56 ppm, which is beneficial to the magnetic properties of electrical steels
It was shown that a Fe–6.0Si alloy can in principle be processed by means of twin roll casting
Summary
Non-grain-oriented electrical sheets are widely used in the field of electrical engineering, for example in electric motors, transformers and power generators. The use of electrical steel with 6.5 wt.% Si exhibits excellent soft magnetic properties. Si increases electrical resistivity and lowers eddy current losses [1]. Increasing Si contents are accompanied by decreasing ductility and workability. This is due to the increase in solid solution strengthening and the formation of embrittling B2 (Pm-3m) and DO3 (Fm-3m) superlattice structures [3]. Since the aforementioned eddy current losses are increasing with the sheet thickness, alloys for application in high frequency electrical drives are usually produced in thicknesses of 0.2–0.35 mm. Due to embrittlement at high Si contents, the preferred electrical steel thicknesses for industrial use in the relevant application areas cannot be achieved with conventional methods at such high Si contents. A Si content of less than 3.5 wt.% is realized as a compromise between good properties and economical production [4]
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