Because the loss of silicon steel sheet in alternating magnetic field is very small, silicon steel sheet is mainly used as magnetic material in transformer. Silicon steel sheets can be divided into hot rolling and cold rolling. Cold rolled silicon steel strip has the advantages of small volume, light weight and high efficiency because of its high permeability and low loss. The properties of hot-rolled silicon steel strip are slightly inferior to those of cold-rolled silicon steel strip.

Ordinary EI transformers are made of silicon steel sheets into E-type and I-type sheets with a thickness of 0.35–0.5 mm, and then inserted into the windings after heat treatment. Most of these iron cores are hot-rolled silicon steel sheets (the high-quality silicon steel sheets with high silicon content are D4 1, D42, D43, D30 1). The iron cores of ring-type and C-type transformers are wound with cold-rolled silicon steel sheets, and C-type transformers are cut after heat treatment and dipping in paint.

The commonly used models of several high-quality silicon steel sheets are as follows: d 41–d42, and the maximum magnetic flux density (unit–GS gauss) is10000–12000 GS; D43, the maximum magnetic flux density is11000–12000gs; D30 1, maximum magnetic flux density12000–14000gs.