Question

Why only is a soft metal like iron and not a hard metal like steel used in an electromagnet circuit

Answer 1

A material with higher permeability and less conductivity is chosen for the transformer core.

High permeability so that it can easily allow the magnetic field through it and low conductivity so that the strength of Eddy current is less and hence losses are less.

Such materials are iron , steel (steel has better permeability than iron) , it is ferromagnaric material and have high permeability, but it also have good conductivity hence to decrease the conductivity 4- 5 % of silicon is added to it , hence the material is called silicon steel.