HiPPES – High Performing and Processible Electrical Steels
The performance of e-machines is affected by many aspects, with the materials being used for the rotor and stator being important in influencing the torque generated and losses during operation. Electrical steels are widely used for e-machines and are based on a binary Fe-Si composition with minor other alloying additions and processed to achieve a non-grain orientated (NGO) microstructure. Whilst this material offers good properties / price, development of electrical steels has remained relatively limited with small improvements in performance based on better texture control. However, in recent years further binary based Fe-Si alloys have been produced in the laboratory with a Fe-6.5Si having been shown to offer superior properties particularly for high speed motors. However, this steel is not processable in conventional steel plants due to its low ductility, requiring an expensive vapour deposition / heat treatment process to diffuse Si into the strip. The resultant material is inherently brittle making it more challenging to manufacture into laminations than Fe-3 Si steel. Whilst other metal alloys, such as Fe-Co systems, are also available for high speed / high performance e-machines there is a need for improved performance low cost electrical steels.
This project acts to remove the shackles of the binary Fe-Si based approach in electrical steel development, and to show the potential of new alloys that can give a dramatic improvement in core properties, matching, or exceeding, the characteristics of Fe-6.5Si. The aim of the work is to carry out a proof of concept approach to developing a new family of electrical steels with improved magnetic / electrical properties whilst being processable using current commercial production routes. The initial approach is to match the magnetic / electrical properties of Fe-6.5 Si steel with significantly enhanced processability e.g. high ductility. This will be achieved through the following objectives:
- Use of fundamental scientific principles, thermodynamic and kinetic prediction tools to investigate the compositional space for electrical steels.
- Use of the WMG Rapid Alloy Production (RAP) facility to cast (figure 1), roll, heat treat and produce final strip product of both a current (for benchmarking) and a novel ultra-high performing electrical steel.
- Use of magnetic and electrical testing to assess the performance of the new steel compared to current grades according to industry standards.
- Use of e-machine FE model to determine the potential performance benefit of the new steel.
The work will involve experts from the Advanced Steel Research Centre (ASRC) and the Electric Machines Research Group (EMRG) from WMG, University of Warwick.
Figure 1. Vacuum induction melting for production of bespoke steel compositions of 4.5 – 7 kg ingot size (left) and casting of small (approximately 1 kg) ingots in air (right).