Cold Rolled Grain Oriented (CRGO) Silicon Steel | Properties Applications and Importance
Cold-Rolled Grain-Oriented steel (CRGO) is a high-grade electrical steel specifically made to have a preferred crystal grain orientation which helps in improving its magnetic properties. Because of this, CRGO is widely used in Transformer core. These Materials are produced through a series of complex manufacturing process
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Historical significance
The rise of electrical machines (motors, transformers) created a need for steels with lower magnetic loss. In 1900s, Hadfield discovered that adding Silicon in Iron increases electrical resistivity, reduces eddy current loss, and improve magnetic properties of the Iron-Silicon Alloy. The hot rolled silicon steels still had poor magnetic properties.
Goss published a landmark paper in 1934 describing a unique grain orientation: {110} <001>, now known as the Goss texture or Cube-on-Edge (COE) orientation. He discovered that this texture dramatically improves magnetic properties of the silicon steel. This discovery is considered the birth of grain-oriented electrical steel.
What Is CRGO Steel?
CRGO (Cold-Rolled Grain-Oriented) electrical steel is a ferromagnetic steel produced by controlled cold rolling and annealing so that its microstructure develops a strong Goss texture {110} <001>. In this structure, the direction of easiest magnetization lies along the rolling direction.
This engineered crystallographic orientation gives CRGO steel very high magnetic permeability, low core loss, low magnetostriction in the rolling direction.
Why Grain Alignment Matters for Magnetic Flux
Magnetic flux prefers to travel along the easy direction of magnetization in a crystal.
In iron-silicon steel, the easiest path for magnetization is the <001> direction.
When grains are aligned so that their <001> directions point along the rolling direction, magnetic flux:
- moves easily
- needs very little magnetizing force (H) i.e. thin BH Curve.
- generates less heat
- loses less energy in each AC cycle.
Key Properties & Characteristics of CRGO Steel
- High magnetic permeability. High Magnetic Induction.
- Low core losses (both Hysteresis and Eddy current losses) and high efficiency.
- Directional magnetic behavior (rolling direction).
- Low Magnetostriction (i.e low contraction and expansion of material in cyclic magnetic loading).
Applications of CRGO Steel
The most common use of CRGO steel is in Transformers core. Be it a distribution transformer, power transformer or instrument transformers (CT/PT), core of these transformers are made of CRGO Materials.
CRGO steel is also used in Reactor Core such as shunt reactors and Line Reactors. They are also used in high efficiency inductor and Power chokes.
They are also used in voltage stabilizers as core for Buck/Boost or Autotransformers. They are also used in isolation transformers and even in uninterruptible power supply system.
CRGO vs CRNO Steel: What’s the Difference?
CRGO (Cold Rolled Grain Oriented) Steel
In CRGO steels Grains are aligned so the easy direction of magnetization lies along the rolling direction. Magnetic properties of CRGO steel are highly directional. Hence they are used where magnetic flux mostly flows in one direction such as transformers.
CRNO (Cold-Rolled Non-Oriented)
In CRNO (Cold-Rolled Non-Oriented) steels, grains are randomly oriented. Magnetic properties are the same in all directions. CRNO steels are Suitable for applications where flux rotates or reverses in multiple directions. These are used in Motors and Generators where magnetic flux is rotating in nature.
Grades of CRGO materials:
1. Traditional M-Grades (Common in India, USA, Older Standards):
| Grade | Typical Thickness | Typical Core Loss @ 1.5 T (W/kg) | Quality |
| M0H / M0 | 0.18–0.23 mm | Very Low | Premium / Super Hi-B |
| M3 | 0.23 mm | Low | High-grade |
| M4 | 0.27 mm | Medium-Low | Standard transformer grade |
| M5 | 0.30 mm | Medium | Distribution transformer grade |
| M6 | 0.35 mm | High | Older/low-cost applications |
Meaning of “M” Grades:
- Lower number = better performance
- Thinner lamination = lower eddy current loss
Hi-B Grades (High-Permeability CRGO)
Hi-B grades are improved CRGO with extremely low losses due to better grain orientation, Precise inhibitor control, Domain refinement (laser scribing) etc. Common Hi-B grades include H0, H2, H4, H6
Conclusion
CRGO (Cold-Rolled Grain-Oriented) steel is a special type of electrical steel engineered through controlled cold rolling to develop the Goss texture. It has exceptionally low core loss, high permeability, high induction, and low magnetostriction in the rolling direction. These unique magnetic characteristics make CRGO the global standard material for transformer cores. This enables high energy efficiency, reduced heat generation, and quiet operation in power and distribution transformers, UPS systems, stabilizers, and other power-conditioning equipment.
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