What is electrical steel?

Anyone who’s been around transformers knows the importance of electrical steel but for those of us that haven’t here’s a quick tutorial.
 
Let’s start with the commonly used synonyms for electrical steel. This steel is often referred to as E-steel, silicon steel, transformer steel, grain oriented steel and or non-grain oriented steel. All of these are ways to express the specialty steel which the coils of a transformer sit on. It’s this very special steel which produces specific magnetic properties.
 
Electrical steel is anywhere from two to four times the price of regular mild steel (aka carbon steel) and it’s because it’s comprised of very different contents. What’s important to note is the metallurgy of electrical steel. Electrical steel is about 5-6% silicon. Silicon increases electrical resistivity and lowers the core loss. Also, with electrical steel the presence of carbon, sulfur, oxygen and nitrogen must be kept very low since they would decrease the magnetic permeability. Carbon is especially bad since it can cause aging which would increase the power losses over time.
 

If the steel is made without special processing to control the crystal orientation then it is called non-grain oriented steel (abbreviated as CRNGO…cold rolled non grain oriented steel). If the steel is processed in such a way that the optimal properties are developed in the rolling direction, due to a tight control of the crystal orientation relative to the sheet then it’s called grain oriented electrical steel (abbreviated as CRGO…cold rolled grain oriented). This is the much more expensive than CRNGO or NGO for short but the losses are far better.
 
There are very few mills that make electrical steel and even fewer that make the good quality electrical steel which is needed to comply with the US efficiency standards. In fact, the United States only has one producer of electrical steel and that company is called AK Steel. There was a second a few years back (ATI) but they’ve since removed themselves from electrical steel altogether. The other good mills are in Japan (NIPPON AND JFE) Germany (THYSSEN) and China (BAO STEEL). There are a few other mills but they are not as widely accepted since they have larger than normal variances between batches.
 
There are various ways to assemble the core. The names of which are step lapped or V-notch, scrapless, 5 legged, butt cut,
wound core, and unicore. Future “Did You Know” publications will go into each and the benefits associated to them.