Electrical Steel: Properties, Types, Production And Applications

GNEE electrical steel coil

What is electrical steel?

Electrical steel is a ferromagnetic material composed of iron with varying amounts of silicon (Si), ranging from 1% to 6.5%. The development of electrical steel was prompted by electrical equipment that required steel that could reduce heat dissipation, a problem that resulted in wasted energy. Iron was found to be the most economically sound option, but its impurities were not optimal. It was found that the addition of silicon increased resistivity, increased magnetic permeability, and reduced hysteresis losses. The most widely used commercial electrical steel contains about 3.25% Si, as higher silicon content tends to make the resulting material too brittle to be cold rolled. Electrical steel with 6.5% silicon content has the most improved magnetic and electrical properties, but requires additional thermomechanical processing to overcome its brittleness and limited ductility.

Properties of electrical steel

The addition of silicon in iron greatly improves the physical properties of electrical steels. Electrical steels have the following desirable properties for supporting the generation, distribution and consumption of electricity:

• High permeability - increased capacity to support magnetic fields
• Low magnetostriction - low tendency to expand or contract in magnetic fields
• High electrical resistivity - lessens the core loss by reducing the eddy current component
• Decreased hysteresis loss - low hysteresis loss means less wasted energy in the form of heat from alternating magnetising force.

Types of electrical steel

Non-oriented fully processed electrical steel

Non-oriented, fully processed electrical steel has varying silicon levels that range from 0.5% to 3.25% Si. It has uniform magnetic properties in all directions. This type of electrical steel does not require recrystallisation processes to develop its properties. The low silicon alloy grades provide better magnetic permeability and thermal conductivity. For high alloy grades, better performance is expected in high frequencies, with very low losses. This type is excellent for magnetic circuits in motors, transformers, and electrical system housing. This fully processed type provides difficulty in punchability due to a completed annealing process. Organic coatings are added to improve lubrication in the punching process .

Non-oriented semi-processed electrical steel

Non-oriented semi-processed electrical steels are largely non-silicon alloyed steel and are annealed at low temperatures after the final cold rolling. The end-user, however, has to provide the final stress-relief anneal according to the steel’s intended application. The punchability of this electrical steel type is better than the non-oriented fully processed type, so organic coatings are not required. Non-oriented semi-processed grades are good core materials for small rotors, stators, and small power transformers .

Grain-oriented electrical steel

Grain-oriented electrical steels are composed of iron with 3% Si content with grains oriented to deliver high permeability and low energy loss. Grain-oriented grades have strong crystallographic properties. This type undergoes a recrystallisation process resulting in an enhanced grain structure that exhibits better magnetic properties in the rolling direction of the sheet. Grain-oriented steels are mostly used for non-rotating applications, such as transformers .

electrical steel coil

What is electrical steel used for?

Electrical steels, with their advantageous magnetic performance, are vital in many electrical systems. Below are some of the applications where electrical steel cores are used [6]:

Rotating machines:

• Electrical vehicle driving motors
• Hermetic motors
• Alternating current (AC) motors
• Intermittent service motors

Static machines:

• Power and distribution transformers
• Reactors and magnetic amplifiers
• Welding transformers
• Audio transformers
• Current transformers
• Magnetic switches and relays
• Electrical ballast

 oriented silicon steel