Automotive traction motor designers in 2026 specify electrical steel in the 0.20-0.35 mm gauge band, with silicon content clustered at 2.5-3.2 wt% for non-oriented grades [S3]. The decision pivots on core loss at the operating frequency, magnetic flux density, and manufacturability into stacked or wound laminations.
Selection today is a four-axis exercise: grade family (CRNGO vs CRGO), thickness, coating system, and yield strength for high-speed rotor burst survival. A typical 2026 spec sheet for a 400 V-class e-machine will reference 0.25 mm non-oriented silicon steel with a guaranteed core loss under 10 W/kg at 1.5 T and 400 Hz, and a guaranteed minimum polarisation around 1.55-1.65 T at 5000 A/m [S3].
CRNGO vs CRGO: When the Lamination Justifies the Cost
CRNGO (cold-rolled non-oriented) electrical steel is the default stator and rotor material in modern traction motors, where the rotating flux demands isotropic magnetic properties in the rolling plane [S3]. CRGO (grain-oriented) is reserved for wound components with a fixed flux direction, such as distribution transformers and some high-reactance stationary motor stators; it is rarely used in rotating automotive stacks [S3][S7].
For a 150 kW-class EV drive unit, a CRNGO grade at 0.25 mm typically delivers 8-12 W/kg core loss at 1.5 T/400 Hz, while a 0.35 mm CRNGO of similar chemistry runs 13-18 W/kg at the same induction point. A 0.20 mm thin-gauge CRNGO can drop that figure into the 6-9 W/kg range, but at 25-40% higher unit cost and lower stacking factor. Grain-oriented electrical steel produced for transformer cores in the 0.23-0.30 mm band, with grades such as B20P090, is widely available from Chinese mills and carries 50-70% lower loss in the rolling direction, yet the 3-5x directional anisotropy makes it unsuitable for a rotating rotor [S7].
Silicon Content, Grain Size, and What the 3 wt% Number Buys
Increasing silicon content raises electrical resistivity, which cuts eddy-current loss, but the trade-off is harder cold-rolling and thinner gauges. Modern 3% Si non-oriented grades represent the upper practical limit for cold-rolled product; beyond roughly 3.5 wt% Si the steel becomes brittle enough that conventional cold rolling is no longer viable without special processing [S3].
For automotive applications, 2.5-3.2 wt% Si is the working window. At 2.5 wt% Si, resistivity is roughly 45 microhm-cm and 0.35 mm gauge is easy to punch; at 3.2 wt% Si, resistivity rises to about 55 microhm-cm, but die wear accelerates and burr limits tighten. Grain size control is the other lever: larger grains reduce hysteresis loss but worsen mechanical strength, so high-speed rotor designs often accept slightly higher loss in exchange for the burst margin. Refer to the silicon steel reference entry for the underlying metallurgy and the alloy steel entry for context on how electrical grades sit inside the broader alloy family.
Coatings, Annealing, and the Real Source of Production Variability
Most 2026 OEM-grade electrical steel is supplied with a C3 or C5 insulation coating (organic, inorganic, or organic-inorganic hybrid) plus a thin MgO-based stress-relief layer inherited from the high-temperature annealing step. Decarburisation and final annealing under H2-N2 atmosphere are where the magnetic properties are set, and where process variability is born [S3].
Research on the first soaking stage in annular furnaces shows that H2O concentration in the interlayer atmosphere of a tightly wound coil can reach roughly 80 vol% near the bottom of the coil, driving surface oxidation that degrades magnetic performance at the outer ring and the bottom of the coil. The same work shows that improving the diffusion conditions at the bottom surface of the coil can significantly reduce the oxidising partial pressure in the interlayer space [S3]. For automotive lamination buyers, the practical message is that mills running tight, taller coils show more coil-edge loss scatter than mills running multiple smaller coils per furnace; specifying the maximum acceptable end-of-coil loss deviation in the PO is now standard practice.
Mechanical Constraints: High-Speed Rotors and Burst Strength
Rotor burst speed in a 20,000 rpm-class traction motor is the second filter on the grade list. Silicon steel's tensile strength sits in the 400-550 MPa range depending on temper rolling, versus 600-700 MPa for a martensitic electrical steel or a 0.1 mm Cobalt-Iron lamination. Most 2026 traction motors stay in the 15,000-18,000 rpm band, where 0.25-0.30 mm CRNGO with a tensile strength of 470-520 MPa passes burst margins with a hoop stress safety factor above 1.4. [S7]
For 25,000 rpm+ designs, half the mass is taken out of the rotor lamination and the grade is pushed to 0.20 mm with controlled yield. The trade is a 15-20% increase in lamination cost and tighter flatness tolerance, typically +/- 0.015 mm. The adjacent guide on Tool and die steel grades mapped to energy equipment gives a useful side reference for how yield and fatigue figures into electrical grade specification.
Stamping, Welding, and Stack-Factor Realities
Most automotive traction motor stators are still made by progressive die stamping of interlocked laminations, with a stack factor target of 0.95-0.97 for press-fit stacks and 0.97-0.98 for bonded stacks. Burr height after stamping is a real cost driver: every 10 micrometres of extra burr on a 0.25 mm part cuts stacking factor by roughly 1 percentage point and can short adjacent laminations if the C3 coating is damaged. [S3]
Laser welding of the segmented stator stack has largely replaced TIG and electron-beam welding for 400 V-class drives, with a typical weld pitch of 6-10 mm and a weld width of 0.4-0.6 mm. The heat-affected zone in CRNGO silicon steel loses roughly 15-25% of its permeability locally; segmented stators are designed so the welds sit outside the main flux path where possible. For the broader question of how the lamination arrives in the warehouse, the Carbon steel reference entry covers plain-carbon grades that are sometimes used as the back-iron in non-rotating, lower-frequency components, but never as the active magnetic material in a traction motor.
Supplier Geography and Lead Times in 2026
Chinese mills continue to dominate the CRNGO supply chain, with multiple producers offering 0.20-0.35 mm silicon steel in the B20A300, B30A300, and equivalent families. Shanghai JISCO Electrical Technology Co., Ltd., established in 2020, is one of the listed manufacturers of cold-rolled electrical steel and transformer cores, marketing HIB-oriented silicon steel, CRNGO, and dry-type transformer cores as part of its product line [S7]. Exporters in Liaoning offer related automotive-grade spring and structural steels, with grades such as 65Mn/60Si2MnA used for suspension components but not as electrical steel [S4].
For OEM procurement teams, the realistic 2026 lead time from PO to dock in Europe is 10-14 weeks for standard 0.25-0.35 mm CRNGO, and 18-24 weeks for thin-gauge 0.20 mm or higher-silicon (3.2 wt%) grades. Spot pricing for the most common B30A300-grade 0.30 mm CRNGO sat in the 1,500-1,800 USD/tonne band through the first half of 2026, with thin-gauge 0.20 mm product running 30-45% above that.
Selection Checklist: 8 Numbers to Lock Before the PO
Before a silicon steel PO is released for an automotive program, eight concrete numbers should be locked in writing: (1) core loss in W/kg at 1.5 T/400 Hz and at 1.0 T/1000 Hz, (2) minimum polarisation B50 in T, (3) lamination thickness in mm with a +/- 5 micrometres tolerance, (4) Si content in wt% with a defined band, (5) coating type and thickness per side, (6) maximum burr height after stamping, (7) stacking factor target, and (8) end-of-coil loss deviation. A spec that omits at least one of these, particularly the loss deviation, is the most common source of rotor-to-rotor performance scatter on production lines. [S3]
Trackable signals for the next quarter: any move to 0.18 mm thin-gauge for 25,000 rpm+ programs, and any Tier-1 announcements of integrated stator-rotor lamination contracts. The silicon nitride and silicon carbide encyclopedia entries cover adjacent ceramic materials that show up as rotor sleeves in high-speed motors, and are worth a read once the electrical steel grade is fixed.