An engineer asked us recently why we kept pushing back on his spec for standard 0.35mm CRNGO in a new high-speed traction motor design. Fair question — 0.35mm is the mainstream choice for plenty of EV motors, and it’s cheaper. But his design ran the rotor considerably faster than typical, which meant a much higher electrical frequency at the core than his spec sheet implied. At that frequency, 0.35mm wasn’t going to hold up the way he expected. We’ve had this conversation enough times that it’s worth writing down properly: thickness in EV traction motor steel isn’t really a grade decision. It’s a frequency decision, and getting it wrong either wastes money or wastes efficiency. For how this fits into the broader picture of where each electrical steel grade belongs, see our electrical steel applications guide.
Core Key Points
- Eddy current loss in electrical steel scales roughly with the square of thickness for a given frequency — halving the thickness roughly quarters this loss component, which is why thinner gauges matter so much more as frequency climbs.
- JFE Steel’s own research shows thin-gauge electrical steel (compared against 0.35mm) can cut iron loss by roughly 25-30% at comparable operating conditions.
- 0.35mm non-oriented silicon steel remains the mainstream choice for mass-produced EV traction motors, according to industry sourcing data — it’s not obsolete, it’s correct for a large share of current motor designs.
- Thin-gauge electrical steel for EV applications is typically produced in the 0.10-0.35mm range, with the thinnest grades (below 0.20mm) reserved for the highest-frequency, highest-speed motor designs.
- The cost premium for going thinner isn’t linear — each step down in thickness costs progressively more per ton, due to compounding rolling yield loss and slower line speeds.
Why Thickness and Frequency Are Linked
Eddy currents are loops of induced current that form within the steel itself as the magnetic field alternates. Thicker material gives those loops more cross-sectional area to circulate in, meaning more loss. The relationship isn’t linear — eddy current loss scales roughly with thickness squared, so a modest reduction in thickness produces an outsized reduction in this loss component.
At standard 50/60 Hz grid frequency, this effect is small enough that thickness barely matters for grade selection. But EV traction motors don’t operate anywhere near grid frequency at the core — depending on motor speed and pole count, the electrical frequency the core actually experiences can run into the hundreds of Hz, sometimes higher for high-speed motor designs. That’s exactly where eddy current loss, and therefore thickness, starts to dominate the efficiency picture.
What Different Thickness Bands Are Actually For
| Thickness | Typical Use Case |
|---|---|
| 0.35mm | Mainstream EV traction motors, standard industrial motors — mass production, moderate frequency |
| 0.20-0.30mm | Higher-speed EV motor designs where standard thickness starts showing meaningful loss penalties |
| 0.10-0.20mm | High-speed, high-frequency traction motor designs where every efficiency point matters and cost is secondary to performance |
Tata Steel’s own technical materials note that industrial motor laminations typically run 0.35-0.50mm thick, while the trend in EV traction motors specifically has been toward meaningfully thinner gauges — not because thinner is inherently better, but because traction motor operating frequencies increasingly demand it.
The Cost Curve as You Go Thinner
Going from 0.35mm to 0.20mm isn’t a proportional cost increase, and it’s worth understanding why before committing to a spec. Thinner rolling passes reduce yield (more material is lost to processing at each additional rolling step), and line speeds slow down to maintain dimensional control at reduced thickness. Both effects compound as you go thinner, so the cost curve steepens rather than staying flat.
This is exactly why “just spec the thinnest available grade” is bad advice by default — you’ll pay a real, non-trivial premium for headroom your motor’s actual operating frequency may not need. It’s the same yield-loss economics we break down from the CRGO side in our CRGO steel price per ton guide.
When Standard 0.35mm Is Still the Right Answer
0.35mm non-oriented silicon steel remains the mainstream choice for mass-produced EV traction motors for a reason: for a large share of current motor designs, particularly those running at more moderate rotor speeds, the frequency the core experiences doesn’t push eddy current loss high enough to justify the cost of going thinner.
The honest answer to “should I use ultra-thin steel” almost always starts with “what’s your actual operating frequency at the core, not the nameplate RPM” — and that’s a calculation worth doing before the spec gets written, not after a prototype underperforms on the dyno.
FAQ
Is ultra-thin silicon steel always better for EV motors?
No. It’s better specifically when operating frequency at the core is high enough that eddy current loss in standard-thickness steel becomes a meaningful efficiency penalty. For motors running at more moderate frequencies, the added cost of ultra-thin steel isn’t recovered by the efficiency gain.
How much does thickness actually affect core loss?
Eddy current loss scales roughly with the square of thickness for a given frequency, so a proportionally modest reduction in thickness produces a larger reduction in this loss component — which is why the effect matters so much more at high frequency than at standard grid frequency.
What thickness range is typical for EV traction motor steel?
Generally 0.10-0.35mm, with 0.35mm remaining the mainstream choice for mass-produced motors and the thinnest grades (below 0.20mm) reserved for high-speed, high-frequency designs where the efficiency gain justifies the cost.
Why isn’t the cost of thinner steel a simple linear increase?
Thinner rolling passes reduce production yield and require slower line speeds to hold dimensional tolerance, and both effects get worse as thickness decreases — so the cost curve steepens rather than climbing in a straight line.
Tell us your motor’s actual operating frequency at the core — not just the RPM rating — and we’ll tell you honestly whether the thickness you’re specifying is doing useful work or just adding cost. Half the time it’s one or the other, rarely both.
