Silicon Steel Classification: Grain-Oriented vs Non-Oriented Grades Explained

What Is Silicon Steel

Silicon steel, also called electrical steel, is a soft magnetic alloy of iron with 0.5-6.5% silicon. The silicon content raises electrical resistivity, which reduces eddy currents and therefore core loss in alternating-flux applications. Silicon steel is the standard core material for transformers, motors, generators and electromagnetic components, and its classification determines both the magnetic performance and the cost of the finished device.

Primary Classification: Hot-Rolled vs Cold-Rolled

Silicon steel was originally produced by hot rolling. Hot-rolled silicon steel has loose thickness control, rough surfaces and high core loss, and it has been progressively eliminated from transformer and motor production because its energy performance cannot meet modern efficiency requirements. Cold-rolled silicon steel replaced it in almost every application because cold rolling gives precise strip thickness, better surface quality and controlled magnetic properties. Within cold-rolled silicon steel there are two families: grain-oriented and non-oriented.

Cold-Rolled Grain-Oriented Silicon Steel (CRGO)

Grain-oriented silicon steel is processed so that the crystal grains are aligned in the rolling direction, giving very high permeability and low loss when flux flows along the rolling direction. Because of this directionality it is used in transformer cores, where the flux path can be designed to follow the grain. It is therefore also called transformer silicon steel. Two performance tiers are recognised in practice:

Conventional grain-oriented (CGO) grades, with magnetic induction of about 1.82 T under standard test conditions.

High magnetic induction (HiB) grades, which reach about 1.92 T. Higher induction means a smaller core for the same flux, lower iron loss and copper loss, and a lower total material cost of the transformer.

HiB steel is preferred for high-voltage and large-capacity transformers because its lower specific loss allows larger units to be built with acceptable efficiency. The two decisive indicators of grain-oriented silicon steel are magnetic induction and specific total loss: higher induction improves permeability and shrinks the core, while lower specific loss reduces the energy wasted in magnetising the core over the transformer's 20-30 year life.

Cold-Rolled Non-Oriented Silicon Steel

Non-oriented silicon steel has no preferred grain direction, so its magnetic properties are similar in all directions within the sheet plane. This makes it the natural material for rotating machines: motors and generators, where the flux direction rotates and cannot follow a single rolling direction. Non-oriented grades are also used in small transformers, reactors, relays and magnetic shielding. They are available across a wide range of loss classes and thicknesses (commonly 0.35 mm, 0.50 mm and 0.65 mm) to suit different machine designs and manufacturing methods.

How the Grades Are Designated and Tested

Grain-oriented grades are commonly designated by their guaranteed maximum specific total loss at 1.7 T / 50 Hz and their thickness. Non-oriented grades are designated by their loss at 1.5 T / 50 Hz. Testing and magnetic property measurement follow the international series IEC 60404, and in China the corresponding national standards are the GB/T 2522 series for magnetic property measurement methods and the relevant product standards for oriented and non-oriented grades. Buyers should always verify that the declared loss values are backed by certified test certificates from the steel producer.

Selection Logic in Practice

Frequently Asked Questions

Q1. What is the difference between oriented and non-oriented silicon steel? Grain-oriented steel has aligned crystal grains giving excellent properties along the rolling direction, and is used where flux follows one direction, such as transformer cores. Non-oriented steel is isotropic and is used where flux rotates, such as motor and generator cores.

Q2. Why is HiB steel called high magnetic induction? HiB grades achieve magnetic induction of about 1.92 T under standard test conditions, compared with about 1.82 T for conventional oriented grades. The higher induction allows the same transformer to be built with a smaller core, reducing iron and copper loss and material cost.

Q3. Is hot-rolled silicon steel still used? Hot-rolled silicon steel is largely eliminated from modern production because of high core loss and poor consistency. Cold-rolled grades now dominate the market for transformers, motors and generators.

Q4. What do the loss figures on a silicon steel grade mean? They are the guaranteed maximum specific total loss of the material, measured per IEC 60404 test methods, at a defined flux density and frequency. Grain-oriented grades are typically rated at 1.7 T / 50 Hz, non-oriented grades at 1.5 T / 50 Hz.

Q5. Can non-oriented steel be used in a transformer core? Yes, small transformers and some reactor designs use non-oriented steel, but grain-oriented steel gives lower loss and higher induction for the same weight in directional-flux designs, so it is the standard choice for distribution and power transformers.

Q6. What standards govern silicon steel quality? Magnetic property measurement follows IEC 60404 (with GB/T 2522 in China), and product specifications follow the corresponding product standards of the steel grade. Certified test certificates should be supplied with each consignment.