C.R.G.O Steel is electrical grade steel that makes up the core of transformers. C.R.G.O Steel grains are much larger than the size of regular steel; 2mm-5mm where regular steel is about 0.5mm. This size difference helps to reduce hystereses loss*. Also the Chemical composition of G.O. steel has a higher percentage of silicon which in turn increases the resistance compared to regular steel which reduces eddy currents*

Hystereses Loss: The power expended in a magnetic material as a result of the lack of correspondence between the changes in induction resulting from the increase or decrease of magnetising force (which is a result of it being cyclic, i.e. alternating)

Eddy Current Loss: This component of core loss is the energy lost by the circulating current induced in the metal by the variation of magnetic fields in the metal. Therefore, more uniform the magnetic field in the metal, lower the eddy current losses.