More power and efficiency for electrical vehicles with new iCARe^® 420 Save electrical steel

While the driving range of electric vehicles (EVs) can be enhanced by installing more batteries, this is costly for consumers. Another approach is to optimise the entire electric powertrain as one by considering the performance, weight, and cost of all its components and materials. Additional improvements in driving range can be achieved by utilising advanced electrical steels such as ArcelorMittal’s iCARe^® range. Now there’s a new member of the iCARe^® family: iCARe^® 420 Save which combines low losses with improved and guaranteed yield strength, resulting in an increase in the power density and energy efficiency of electric traction motors.

Electrical steels are found in every part of a modern vehicle – from the small motors which drive mirrors and seats to the larger machines that are used in the propulsion systems of hybrid or full EVs. Traction motors and generators in those alternative drive trains are particularly dependent on highly efficient electrical steels.

The high energy efficiency of ArcelorMittal’s electrical steel offer can help to maximise driving range. They also allow machine designers to downsize the cooling systems electric motors need, reducing overall vehicle weight.

In parallel, our electrical steels allow motor designers to achieve the highest possible mechanical torque and power levels. However, the power density of the electric traction motor must be optimised to ensure the motor’s peak mechanical output can be achieved at the lowest mass and volume.

The relative importance of efficiency and power density depends on the type of EV and its performance requirements. Similarly, the motors and generators used in electrified propulsion systems must be optimised by selecting the most appropriate electrical steel.

ArcelorMittal offers a full range of electrical steels and advanced characterization and modelling tools to give electrical machine makers the greatest range of options. For example, ArcelorMittal has developed the iCARe^® range of innovative, non-oriented, fully processed electrical steel grades to meet the requirements of automotive traction applications. ArcelorMittal’s iCARe^® steels offer has been adapted and optimised to ensure the lowest losses are achieved at a medium frequency range of around 400 Hertz (Hz).

The iCARe^® range already includes three families of electrical steels for different applications: iCARe^® Save, iCARe^® Torque, and iCARe^® Speed. The steels in the iCARe^® Speed family offer the highest mechanical strength, making them ideal for compact, high-speed rotors with higher power density. But to obtain these high mechanical strength values, the magnetic power losses of ArcelorMittal’s iCARe^® Speed grades are slightly impacted. For this reason, iCARe^® Speed grades are only approved for rotor applications in synchronous machines.

To overcome this limitation, a new iCARe^® family was recently launched by ArcelorMittal. Known as iCARe^® 420 Save, the new grades are low loss electrical steels which have an improved guaranteed yield strength of 420 megapascals (MPa).

The iCARe^® 420 Save family offers higher mechanical strength than standard iCARe^® Save grades, but without any detrimental effect on its magnetic properties (such as magnetic power losses). This makes iCARe^® 420 Save the best choice to enhance the magnetic properties of stators, while providing the necessary mechanical properties needed for rotors. Another advantage is that both stators and rotors can be punched from the same grade of iCARe^® 420 Save, which reduces cost.

Popular iCARe^® 420 Save grades include:

• 420 Save 27-15: guaranteed loss level of less than 15 W/kg at 400Hz and 1T at 0.27 mm thick
• 420 Save 30-16: guaranteed loss level of less than 16 W/kg at 400Hz and 1T at 0.30 mm thick.

The improved and guaranteed yield strength (420 MPa) of iCARe^® 420 Save grades allows for rotor design improvements. When combined with the low core losses of the grade (which are particularly useful in the stator), these mechanical rotor design improvements can increase overall performance.

The enhanced mechanical properties of the iCARe^® 420 Save grades are useful in electrical machine topologies where its higher yield strength can be exploited. That may involve optimising the machine’s mechanical design and/or increasing its rotation speed to enhance power density. iCARe^® 420 Save grades are particularly useful for reducing iron losses in high-speed hybrid and electric traction machines.

ArcelorMittal has already begun commercial production of iCARe^® 420 Save at our mill in St-Chély d’Apcher (France). The steels can be shipped almost anywhere in the world.

ArcelorMittal’s iCARe^® range includes specific grades for different performance requirements. They include:

• iCARe^® Save: These grades have the lowest magnetic power losses at frequencies around 400 Hz. That improves the efficiency of the electric motor which reduces battery energy usage. It also limits heat dissipation in the magnetic cores of electric motors which allows cooling systems to be downsized. iCARe^® Save grades are particularly useful for high frequency machines.
• iCARe^® Torque: Grades which have the highest magnetic polarisation values for a given magnetic field. This allows OEMs to realise a higher motor torque for a given size of electric motor (in other words more torque density), which improves the motor’s breakaway torque and results in higher vehicle acceleration. OEMs can also economise on conducting materials such as copper or aluminium, while maintaining the same level of motor torque.
• iCARe^® Speed grades have the highest mechanical strength and are ideal for compact, high-speed rotors with higher power density. To obtain these high mechanical strength values, the magnetic power losses of ArcelorMittal’s iCARe^® Speed grades are slightly impacted. For this reason, iCARe^® Speed grades are only approved for rotor applications in synchronous machines.