Steel Breakthrough Boosts EV Range, No Battery Increase

Abstract

Reducing iron loss in non-oriented electrical steels is critical for enhancing the efficiency of high-performance electric machines. While bulk microstructural factors such as crystallographic texture and grain size are well-established contributors, the role of surface microstructures formed during final annealing has received less attention. This study examines the influence of final annealing atmosphere-100 % N2, 50 % N2 + 50 % H2, and 100 % H2-on surface microstructural evolution and its correlation with iron loss. Although bulk crystallographic texture and grain size remained comparable across all conditions, significant variations were observed in surface layer composition, interfacial roughness, and near-surface inclusion morphology. Hydrogen-rich atmospheres promoted the formation of smooth, amorphous Al2O3 layers with fine near-surface inclusions, whereas nitrogen-rich conditions yielded thick, crystalline AlN layers with coarse inclusions concentrated near the surface. Iron loss measurements before and after removal of surface microstructure confirmed that these surface features markedly increase loss, primarily through enhanced domain wall pinning. These findings demonstrate a direct relationship between annealing atmosphere and surface microstructure, and establish atmosphere control as a viable route to minimize iron loss in non-oriented electrical steels.

A research team, affiliated with UNIST unveiled a new steel manufacturing process that can improve the driving distance of electric vehicles (EVs) without the need for larger batteries. This breakthrough offers a promising way to enhance the efficiency of EV motors, supporting longer trips on a single charge.

Led by Professors Ju-Young Kim, Sukbin Lee, and Ki-Suk Lee from the Department of Materials Science and Engineering, the research introduces an advanced heat treatment method for electrical steel sheets used in EV motors. The goal is to reduce core energy losses that diminish vehicle range.

During operation, EV motors convert electrical energy into mechanical motion. However, a portion of this energy is lost-primarily due to "iron loss." This loss occurs because the tiny magnetic domains within the steel sheets struggle to keep pace with rapid magnetic field changes-often hundreds of times per second-resulting in energy dissipation. This phenomenon is similar to how a compass needle wavers when subjected to swiftly changing magnetic influences.

Given that iron loss accounts for roughly 25% of total motor energy loss, reducing it can significantly extend the vehicle's range, effectively boosting efficiency.

The research team achieved this by altering the final heat treatment environment. Instead of using nitrogen, they introduced hydrogen into the annealing atmosphere. This change prevented the formation of thick, rough nitride (AlN) layers on the steel surface. Instead, a thin, uniform oxide layer formed, resulting in a smoother surface that reduces magnetic resistance during operation.

Experimental results showed that steel sheets processed with this method exhibited approximately 16% lower hysteresis loss-an indicator of magnetic resistance-and a reduction in overall iron loss by about 8-10%. Such improvements translate into enhanced motor efficiency and increased driving range.

Dr. So-Hyeon Lee, the lead author of the study, explained, "By systematically analyzing how different final heat treatment conditions affect surface microstructure, inclusions, and impurities, we identified an optimal process. Our findings demonstrate that surface microstructures significantly influence iron loss in EV motors."

Professor Kim emphasized, "This approach allows us to reduce iron loss simply by adjusting heat treatment conditions, without the need for major modifications to existing manufacturing equipment." He further added, "It is also a cost-effective solution that can strengthen Korea's position in the global EV industry through advanced material technologies."

The findings of this study have been published in the Journal of Materials Science & Technology (JMST), a leading journal in materials science on December 31, 2025. The research was supported by the National Research Foundation of Korea (NRF) through the Mid-Career Researcher Support Program and the National Strategic Technology Material Development Project, and by the InnoCORE program.

Journal Reference

So-Hyeon Lee, Jiheon Jeon, Younghoon Kim, et al., "Influence of final annealing atmosphere on surface microstructure and iron loss in non-oriented electrical steel," JMST, (2025).