Twin-roll casting of high silicon electrical steel

• Applicant: Professor Dr.-Ing. Gerhard Hirt
• Subject Area: Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 432395971

Non-grain oriented electrical steel sheets are silicon alloyed iron alloys and are used in rotors and stators of electric motors due to their soft magnetic properties. For industrial use in the relevant application areas, electrical sheet thicknesses of 0.1-1 mm are preferred. By increasing the Si content of the alloy of the electrical sheet, the soft magnetic losses can be significantly reduced. It can be seen from the literature that excellent soft magnetic properties can be achieved at a Si content of 6.5 wt%. However, the electrical sheets become brittle with increasing Si content and the processing of the electrical sheets by rolling, for example, is considerably impaired. If the alloy content is too high, the electrical steel breaks during rolling, so that the required thicknesses cannot be achieved. For this reason, alloys produced via the classic flat steel production route consisting of continuous casting, hot rolling and cold rolling, are limited to 3.5% by weight silicon. Strip casting allows near-net-shape cast strip with a thickness of 1-3 mm to be produced directly from the melt. In this way, it is possible on the one hand to reduce the process chain considerably and thus save resources. On the other hand, near-net-shape casting considerably reduces the rolling effort, so that higher Si contents should be realized compared with the conventional route. During the first funding period, it was possible to demonstrate the feasibility in principle of producing alloys with 6.5 wt.% and 4.5 wt.% Si by strip casting, hot rolling and semi-hot rolling in the thickness range 0.35-0.55 mm. The soft magnetic measurements that can be obtained with this method already show promising results. In order to exploit the full potential of the strip casting process and the high-silicon alloys, the aim in a further funding period is to achieve thinner sheet thicknesses and to further optimize the metallurgical purity of the cast strips, the surface quality and the final annealing parameters. Furthermore, the understanding of how the texture in the final annealed state can be optimized by superheating during strip casting and how the Si segregation present in the strip-cast material influences the soft magnetic properties is to be intensified.

• DFG Programme: Research Grants