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Electrical Steel and Soft Magnetic Alloys

Electrical steel is iron with 1–4 % silicon, rolled to 0.23–0.65 mm sheet and coated with an insulating varnish so that stacked laminations carry flux with minimal eddy-current and hysteresis loss. Non-oriented grades (M19, M36, 35W270, B50A470) are isotropic and go into rotating machines; the EN and GB numbers encode thickness and loss — 35W270 is 0.35 mm sheet losing 2.70 W/kg at 1.5 T and 50 Hz. Grain-oriented CRGO (M103-27N, 30Q130, 23QG090) is magnetically far softer along the rolling direction and is what transformer cores are wound or stacked from. The page also lists the nickel-iron and cobalt-iron alloys used where permeability, saturation or a matched expansion coefficient matters more than cost.

Popular electrical steel grades

Compare in the explorer
GradeYield, MPaTensile, MPaDensity, g/cm³MachinabilityWeldabilityBest for
M193404607.65FairFairHigh-efficiency motor and generator laminations
M365508808.19PoorPoorGeneral-purpose motor laminations
35W2703404707.65FairFairGB / IEC 0.35 mm non-oriented sheet, 2.7 W/kg
50W4703104407.7FairGoodLow-cost 0.50 mm motor and choke laminations
B50A4703054507.7GoodFairGB 0.50 mm non-oriented sheet for motors
CRGO3053457.65FairPoorGrain-oriented transformer core steel
M456209508.1PoorPoorNon-oriented electrical coil

All 47 electrical steel grades

Choose electrical steel for

Motor and generator stator and rotor stacks, transformer and inductor cores, relay and solenoid yokes, magnetic shields, and glass-sealed electronic packages — any part whose job is to carry magnetic flux or to hold dimension against temperature rather than to bear load.

Look elsewhere when

The part is structural or must be hard (1045, 4140 — silicon steel is soft and brittle when bent), it is a solid rather than laminated magnetic part at DC or low frequency (low-carbon 1008 / 1010 or pure iron works and machines far better), the field is above about 2 T (only cobalt-iron reaches it), or the frequency is above about 10–20 kHz (ferrites, nanocrystalline or amorphous ribbon have lower loss than any silicon steel).

Yield strength against elongation at break, Electrical steel among every steel grade

No materials in view have both of these properties.

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Electrical steel by application

Traction and servo motors
M19 or 35W270 at 0.35 mm, or 35W250 / 35A250 where the efficiency class demands it; thinner 0.20–0.27 mm sheet for high-speed machines above a few hundred hertz fundamental. Stacks are laser-cut for prototypes and stamped for volume.
Transformers and inductors
CRGO M103-27N / 27Q120 for wound and stacked distribution cores, 23QG090 for the lowest no-load loss; M36 or 50W470 non-oriented for small chokes and 400 Hz aircraft transformers where cost rules.
Compact high-flux devices
Hiperco 50 and Permendur (Fe-Co 50) for aerospace generator and actuator cores that must be small and light; anneal after cutting to recover permeability.
Shielding, sensors and sealed packages
Mu-metal, Supermalloy and 1J85 for magnetic shields and current-transformer cores; Kovar (4J29) for glass-to-metal seals; Invar 36 and Alloy 42 where near-zero thermal expansion matters.

Working with electrical steel

Cutting
Laminations are laser-cut for prototypes and short runs and progressive-die stamped above a few thousand pieces; both leave a work-hardened, magnetically damaged edge zone roughly one sheet thickness wide that raises core loss. Wire EDM cuts stacks cleanly for small prototype motors. Burrs must stay under about 0.05 mm or they short adjacent laminations.
Stacking and joining
Stacks are interlocked, riveted, bonded (backlack adhesive coating) or laser-welded along the back; every weld bead is a shorted turn, so keep welds few, short and on the outside diameter. Insulating coating classes C5 and C6 survive a stress-relief anneal; C3 does not.
Heat treatment
A stress-relief anneal at 750–800 °C in a dry, non-oxidizing atmosphere for about 2 hours restores the properties lost at cut edges and in forming — worth 10–20 % on core loss for small motors. Grain-oriented CRGO must not be bent or annealed above its coating limit after slitting; Fe-Co alloys need their own 800–850 °C anneal to develop permeability.
Machining
Avoid it. Silicon steel sheet is too thin and too brittle to machine as a stack except by grinding or EDM; the nickel-iron and cobalt-iron alloys machine like a gummy stainless and are work-hardened by cutting, so parts are finished, then annealed. Kovar and Invar 36 machine acceptably at low speeds with sharp tools and turn best in the annealed state.

Other steel series

Electrical Steel and Soft Magnetic Alloys — frequently asked

What is electrical steel?

Electrical steel is iron with 1–4 % silicon, rolled to 0.23–0.65 mm sheet and coated with an insulating varnish so that stacked laminations carry flux with minimal eddy-current and hysteresis loss. Non-oriented grades (M19, M36, 35W270, B50A470) are isotropic and go into rotating machines; the EN and GB numbers encode thickness and loss — 35W270 is 0.35 mm sheet losing 2.70 W/kg at 1.5 T and 50 Hz. Grain-oriented CRGO (M103-27N, 30Q130, 23QG090) is magnetically far softer along the rolling direction and is what transformer cores are wound or stacked from. The page also lists the nickel-iron and cobalt-iron alloys used where permeability, saturation or a matched expansion coefficient matters more than cost.

Which grade of electrical steel should I use?

M19 (0.35 mm, close to 35W270) is the default for high-efficiency motors and generators; M36, M45 or 50W470 / B50A470 (0.50 mm) for cost-driven motors and chokes where the extra loss is acceptable, and 35W250 or 35A250 when the efficiency class pushes losses lower. Transformer cores use grain-oriented CRGO — M103-27N or 27Q120 for distribution transformers, 23QG090 laser-scribed high-permeability sheet for the lowest no-load loss. Hiperco 50 and Permendur (49 % Co) give about 2.3 T saturation for aerospace motors and actuators that must be small; Mu-metal, Supermalloy and 1J85 (80 % Ni) give the highest permeability for shielding and sensor cores; Invar 36, Kovar and Alloy 42 are the low-expansion iron-nickel grades for glass-to-metal seals and precision structures rather than magnetics.

Which grade of electrical steel is the strongest?

Fe-Co 50 (unalloyed) has the highest yield strength in the series at 800 MPa; M45 follows at 620 MPa. Values are for each grade's default condition.

Which grade of electrical steel is easiest to machine?

B50A470 (machinability good, 55/100), then M400-50A (50/100).

Is electrical steel heat-treatable?

No. These grades are strengthened by cold work and softened by annealing, not by heat treatment; the conditions are listed on each grade page.

M19 or M36 for a motor?

M19 in 0.35 mm sheet has typically 20–30 % lower core loss than M36 in 0.47–0.50 mm, which shows up directly as motor efficiency and cooler running, at a higher cost per stack because more, thinner laminations must be cut and handled. Use M19 for IE3 / IE4 efficiency classes and high-frequency or high-speed machines; M36 (or 50W470) for cost-driven low-speed motors, chokes and designs that are not thermally limited.

What is the difference between grain-oriented and non-oriented electrical steel?

Grain-oriented (CRGO) is about 3 % Si sheet processed so that the crystal grains line up with the rolling direction: along that axis it has far lower loss and higher permeability, so it is used where flux runs one way — transformer cores and wound cut cores. Across the rolling direction it is worse than non-oriented sheet. Non-oriented (CRNGO: M19, 35W270) has random grain orientation and nearly equal properties in every direction, which rotating machines need because the flux direction sweeps around the stator.