M0H Grain-Oriented Silicon Steel Sheet: Properties, Processing and Applications

What Is Grain-Oriented Silicon Steel Sheet?

Grain-oriented (GO) silicon steel is a flat-rolled electrical steel in which the crystal grains are aligned along the rolling direction through controlled hot rolling, cold rolling and final annealing. This Goss texture makes the easy magnetization direction coincide with the rolling direction, giving very high permeability and low core loss along that axis - exactly what transformer cores need, because the magnetic flux in a wound or stacked core follows a defined path.

GO steel is classified by magnetic polarization at 800 A/m (B8). Conventional grain-oriented (CGO) grades have B8 below about 1.88 T, while high magnetic induction (HiB) grades reach 1.88-1.95 T. Products in the M0H family are ordered by grade designation, nominal thickness and guaranteed loss class, which must be stated explicitly on the specification sheet.

Manufacturing Process

Raw material: low-carbon steel with about 3% silicon, selected for its high resistivity and low magnetostriction.

Hot rolling: elongates the grains along the rolling direction and prepares the strip for further reduction.

Annealing and cold rolling: a two-stage route with intermediate annealing brings the strip to final thickness, typically 0.23, 0.27, 0.30 or 0.35 mm.

Decarburization and insulation coating: removes residual carbon to control magnetic aging and applies a phosphate-based coating that provides interlaminar insulation and acts as a base for stress-relief annealing.

Final annealing: develops the Goss texture and the final magnetic properties in a controlled atmosphere.

Magnetic and Mechanical Properties

Specified properties follow IEC 60404-8-7 and ASTM A876: specific total loss at 1.7 T and 50 Hz (P17/50), magnetic polarization at 800 A/m (B8), lamination factor, coating class and dimensional tolerances. Typical P17/50 values range from about 0.9 W/kg for the thinnest HiB grades to about 1.4 W/kg for 0.35 mm CGO grades, with B8 at or above 1.88 T for HiB material. The table below summarizes the common thickness classes.

Nominal thickness (mm)	Typical P17/50 range (W/kg)	Typical use
0.23	0.90-1.00	Large power transformers, lowest-loss cores
0.27	0.95-1.10	Power and large distribution transformers
0.30	1.05-1.20	Distribution transformers, reactors
0.35	1.20-1.40	Distribution transformers, wound cores

Values are typical published ranges for standard GO grades; guaranteed figures are confirmed against the material certificate before delivery.

Applications

Power and distribution transformer cores, the dominant application, where the fixed flux direction allows the anisotropic material to be fully exploited.

Wound cores for current transformers and instrument transformers.

Reactor cores and saturable magnetic components.

Cores for special machines and magnetic amplifiers operating at power frequency.

Note that rotating machines such as motors and generators use non-oriented steel because their flux direction rotates; grain-oriented material is reserved for transformer-type applications where the flux path is fixed.

Handling and Processing Notes

Shearing and punching create burrs that can short-circuit adjacent laminations; deburr the edges and verify interlaminar insulation resistance.

Wound and bent cores require stress-relief annealing at about 800 C in a protective atmosphere to restore permeability after mechanical working.

Handle with gloves and keep coils dry; coating damage increases eddy-current loss between laminations.

Verify coating integrity after processing using the surface insulation resistance test described in GB/T 2522 and IEC 60404-1.1.

Standards

Product specifications: IEC 60404-8-7 (GO steel), GB/T 2521, ASTM A876. Test methods: Epstein frame per IEC 60404-2 and GB/T 3655, single-sheet tester per IEC 60404-3, and coating resistance per GB/T 2522.

Frequently Asked Questions

What is the difference between CGO and HiB steel?

The boundary is magnetic polarization at 800 A/m (B8): CGO grades are below about 1.88 T, HiB grades reach 1.88-1.95 T. HiB material offers lower core loss for the same thickness and is preferred for large power transformers where loss capitalization is significant.

Which thickness should I choose?

Thinner material gives lower eddy-current loss but costs more and has a lower lamination factor. In practice, 0.30 mm suits distribution transformers, while 0.23-0.27 mm is used for large power transformers; 0.35 mm remains common for wound and small cores.

Why is GO steel used in transformers but not motors?

Because it is anisotropic: performance is excellent along the rolling direction and poor across it. Transformer flux follows a fixed path, but motor flux rotates, so motors use non-oriented steel.

How is core loss measured?

By the Epstein frame method per IEC 60404-2 and GB/T 3655, or with a single-sheet tester per IEC 60404-3, at the rated induction and frequency, usually 1.7 T and 50 Hz for GO material.

What standards govern GO silicon steel?

IEC 60404-8-7, GB/T 2521 and ASTM A876 define grades and guaranteed properties; GB/T 2522 and IEC 60404-1.1 cover coating and lamination tests.

How is the material supplied?

As coils, slit strips or cut sheets, with or without insulation coating. Confirm width, mass, inner and outer diameter for coils, and the required grade, thickness and loss class in the purchase specification.