Non-Grain-Oriented Electrical Steel: Uses, Grades and Selection
Sep 26, 2023
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What Non-Grain-Oriented Electrical Steel Is
Non-grain-oriented electrical steel, also called non-oriented silicon steel, is a soft magnetic iron-silicon alloy in which silicon is the main alloying element, typically about 0.5-3.2% by mass, while carbon is held at a very low level, usually no more than about 0.005%. The silicon addition raises electrical resistivity and the low carbon content reduces hysteresis loss, so together they cut the energy that would otherwise be lost as heat when the material is magnetised in an alternating field.
The term non-grain-oriented refers to the fact that the crystal grains have no preferred orientation relative to the rolling direction. Permeability and core loss are therefore essentially isotropic, that is, nearly the same in any in-plane direction.
Why Isotropy Decides the Application
In a rotating machine the flux path sweeps through every direction of the lamination plane as the rotor turns. A material that performs evenly in all directions keeps the loss predictable in every rotor position, and that is why non-grain-oriented steel became the default core material for motors and generators. Grain-oriented steel is processed so that most grains align with the rolling direction; it delivers lower core loss and higher flux density, but only along that one axis, which suits static transformer cores rather than rotating machines.
The selection rule is therefore simple: rotating flux takes non-grain-oriented steel, static flux takes grain-oriented steel.
Main Applications
Non-grain-oriented electrical steel is bought almost exclusively as slit strip or as stamped laminations for the following families of equipment.
| Application area | Typical parts | Notes |
|---|---|---|
| Motors, medium and small | Stator and rotor lamination stacks of AC induction motors, permanent-magnet synchronous motors and DC motors | The dominant use of this material; laminated stacks limit eddy-current loss in the rotating flux field |
| Generators | Stator and rotor cores of small and medium generators, including portable and standby units | The same rotating-flux logic as motors; isotropic properties keep loss uniform |
| Small transformers and reactors | Core laminations of small distribution transformers, instrument transformers and reactors | Chosen where cost and punching behaviour matter more than the lowest possible no-load loss; large power transformers use grain-oriented steel |
| Relays and contactors | Magnetic circuits, armatures and yokes | Low-carbon non-oriented grades punch cleanly and magnetise quickly |
| Household appliance motors | Compressor motors, fan motors, washing-machine and vacuum motors | High-volume stamping to tight dimensional tolerances; both fully processed and semi-processed grades are used |
| Traction and EV drive motors | High-frequency stator cores of traction motors | Thin gauge, low-loss grades are typical because the drive runs at elevated frequency |
Typical Grades and Reference Performance
Non-grain-oriented steel is supplied as fully processed or semi-processed strip, normally 0.35-0.65 mm thick for standard motor work, and the grade name encodes thickness and core loss. In the Chinese designation 50W470 of GB/T 2521.1, the 50 is the nominal thickness of 0.50 mm, the letter W marks non-oriented steel, and 470 is the guaranteed maximum core loss of 4.70 W/kg measured at 1.5 T and 50 Hz. The equivalent designation in EN 10106 for fully processed strip is M470-50A, and ASTM A677 covers fully processed non-oriented electrical steel using a comparable classification logic based on thickness and guaranteed core loss at 15 kG and 60 Hz.
| Designation | Thickness | Core loss P1.5/50 max | Flux density | Standard |
|---|---|---|---|---|
| 50W470 | 0.50 mm | 4.70 W/kg | B50 not less than 1.65 T | GB/T 2521.1 |
| M470-50A | 0.50 mm | 4.70 W/kg | B2500 not less than 1.67 T | EN 10106, fully processed |
| ASTM A677 grades | 0.47-0.50 mm | Guaranteed loss class at 15 kG / 60 Hz | Induction per the grade table | ASTM A677, fully processed |
These are the guaranteed figures used for material selection, and a mill certificate may quote tighter values. Semi-processed grades of EN 10106, for example M470-50S, remain available for customers who anneal the laminations after stamping in order to develop the final magnetic properties themselves.
Non-Grain-Oriented versus Grain-Oriented Steel
Buyers often confuse the two materials because both are sold under the name silicon steel. The comparison below is the practical way to separate them in a specification.
| Property | Non-grain-oriented | Grain-oriented |
|---|---|---|
| Grain structure | Random orientation, isotropic magnetic properties | Grains aligned with the rolling direction |
| Core loss | Higher; standard grades around 4.70 W/kg at 1.5 T and 50 Hz | Lower; thin high-grade strip reaches roughly 0.75-0.85 W/kg at 1.7 T and 50 Hz |
| Flux density | B50 typically not less than 1.6 T | B8 typically not less than 1.8 T for high-permeability grades |
| Magnetic behaviour | Same in all in-plane directions | Best along the rolling direction, weaker across it |
| Typical applications | Motor and generator cores, small transformer and reactor cores, relays, appliance motors | Power and distribution transformer cores, where flux follows one direction |
| Governing standards | GB/T 2521.1, EN 10106, ASTM A677 | GB/T 2521.2, EN 10107, ASTM A876 |
How Non-Grain-Oriented Steel Is Made
Fully processed non-grain-oriented electrical steel follows six stages from melt to finished lamination.
Steelmaking and continuous casting: low-carbon iron is alloyed with silicon and melted, then cast into slabs with the residuals held under control.
Hot rolling: the slabs are rolled into strip, and the hot-rolled coil becomes the starting point of the finished product.
Pickling: oxide scale is removed from the hot-rolled surface so that the cold mill starts from clean metal.
Cold rolling: the strip is reduced to final gauge, typically 0.35-0.65 mm for motor grades.
Final annealing: recrystallisation annealing develops the random grain structure that gives the material its isotropic magnetic behaviour.
Insulating coating and slitting: an inorganic or semi-organic coating is applied to keep inter-laminar eddy-current loss low, and the strip is slit to the width needed for stamping.
Customers receive the material as coils, slit coils or pre-stamped laminations, which are then welded, bonded or clamped into motor stators and rotors or into small transformer cores.
FAQ
Q: What is non-grain-oriented electrical steel used for?
It is used mainly for the stator and rotor cores of medium and small motors, for generators, for small transformer and reactor cores, for relays and contactors, and for the drive motors of household appliances and traction drives.
Q: What is the difference between non-grain-oriented and grain-oriented steel?
Non-grain-oriented steel has randomly oriented grains, so its magnetic properties are nearly the same in every direction, which suits rotating machines. Grain-oriented steel has grains aligned with the rolling direction, so it has lower loss and higher flux density along one axis, which suits transformer cores.
Q: What does the grade name 50W470 mean?
The 50 is the nominal thickness of 0.50 mm, the W indicates non-oriented electrical steel, and 470 is the guaranteed maximum core loss of 4.70 W/kg at 1.5 T and 50 Hz under GB/T 2521.1.
Q: Which thickness should be selected?
Standard motor grades are usually 0.35 mm, 0.50 mm or 0.65 mm. Thinner strip lowers eddy-current loss at a given frequency but raises the number of laminations and the stamping cost, so the choice follows the operating frequency and the acceptable loss budget.
Q: What is the difference between fully processed and semi-processed strip?
Fully processed strip is delivered with its final magnetic properties already developed. Semi-processed strip is delivered without the final anneal, and the customer develops the properties after stamping; it punches more easily but requires an annealing furnace.
Q: Does the insulating coating affect performance?
Yes. The coating insulates each lamination from its neighbours, which limits inter-laminar currents and reduces eddy-current loss in the finished stack; the coating thickness also affects the stacking factor of the core.