Electrical steel (also called silicon steel or lamination steel) is the magnetic core material in every electric traction motor. The grade you specify is locked in early in the design cycle, and it determines both motor efficiency and a meaningful share of bill-of-materials cost. This guide covers the specification logic and what to verify when sourcing electrical steel from China.
Why electrical steel specification matters more in traction motors
In a fixed-speed industrial motor, a 1% efficiency difference is a rounding error on the electricity bill. In a traction motor, core loss converts directly into reduced vehicle range and additional battery cost. A motor running at 95% instead of 93% efficiency needs roughly 3% less battery capacity for the same range. At pack level that is a significant cost difference.
Core loss has two components: hysteresis loss, dominant at low frequency, and eddy current loss, dominant at high frequency. Grade selection is essentially a trade-off between these two losses, manufacturing cost, and stator slot fill.
The four specification axes
1. Silicon content
Higher silicon content raises electrical resistivity, which suppresses eddy current loss. Standard non-oriented grades run 1.5 to 3.5 percent Si. Above roughly 3.5 percent the material becomes brittle and punching becomes difficult, so most traction motor grades sit in the 2.5 to 3.5 percent range.
2. Thickness
Eddy current loss scales with the square of thickness. Traction motors typically use 0.20 to 0.35 mm material. Thinner gauge reduces loss but worsens stacking factor, handling difficulty and cost. High-speed motors above 10,000 rpm commonly use 0.20 to 0.27 mm, while lower-speed designs are often more economical at 0.35 mm.
3. Grade designation
Chinese electrical steel grades follow GB/T 2521.1, which maps closely to IEC 60404-8-4. The designation encodes thickness and specific loss: 50W270 means 0.50 mm thickness with a maximum specific total loss of 2.70 W/kg at 1.5 T and 50 Hz. Traction motor grades typically sit between 35W230 and 35W300.
4. Insulation coating
Coating type matters as much as the steel itself. Common coatings are C5 (inorganic, good weldability, moderate insulation), C6 (organic-inorganic, better insulation for larger motors), and C3 or C4 for specific processing routes. If your stack is welded or interlocked, the coating must survive the stress relief or annealing cycle.
Non-oriented versus grain-oriented
Grain-oriented steel has much lower loss in the rolling direction but is unsuitable for the rotating field of a motor stator. It belongs in transformer cores and axial flux machines with a defined flux path. Almost all radial flux traction motors use non-oriented steel.
What to verify with a Chinese supplier
- Loss test data from an actual Epstein strip test (IEC 60404-2), not a datasheet copy. Ask for the report showing measured P1.5/50 and P1.0/400 values at the specified thickness.
- Stacking factor and coating thickness consistency, since these determine how the laminated core performs after punching.
- Burr height after punching if the supplier also stamps. Burrs above 0.05 mm cause inter-lamination shorts and cancel out the low loss you paid for.
- Annealing capability. If your process requires stress relief annealing, confirm the coating is designed for it. Applying the wrong coating then annealing degrades insulation and raises loss.
- Supply continuity for thin gauge. Capacity for 0.20 to 0.27 mm high grade non-oriented steel is concentrated among a few producers. Confirm the supplier holds stock or has a committed allocation rather than buying into the spot market.
Common sourcing mistakes
- Specifying by datasheet typical values instead of guaranteed maximums. A grade guarantee is a maximum. A supplier quoting typical loss has committed to nothing.
- Treating all 35W230 as equivalent. Reproducibility between heats varies, so require per-heat test data on the first three production lots.
- Discovering coating incompatibility with your downstream process only after tooling is cut.
- Comparing price per kilogram without normalising for density and stacking factor, which change the effective material cost per finished core.
Sourcing from Hunan
Hunan province hosts a cluster of electrical steel and laminated core suppliers serving both domestic EV programs and export orders, supported by the province steel and advanced materials industrial base. LiiFoo maintains verified supplier profiles across the advanced steel materials cluster with documented certifications and process capability.
To request specification matched quotes or sample lots with full test reports, see our advanced steel materials cluster or contact our sourcing team.
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