iam talking abt carbon steel of composition:-C=0.15wt% Mn=0.60wt% P=0.035wt% S=0.04wt% Cu=0.20 (min)wt%....
The composition of the steel is almost tertiary to many other considerations, except that there are certain elements and percentages of elements which tend to affect the crystaline structure in the steel. The most basic question is whether the crystaline arrangement of atoms in the steel is martensitic or austenitic, and many factors influence that. In general, martensitic structure is magnetic and austenitic structure doesn't respond much to magnetic fields, but there are varying degrees of martensitic and austenitic -- there is never a pure state. Read the articles at bottom.
The composition you mention is not a low carbon steel.The carbon and manganese content are high enough to mean that the crystal grain size will be small. A very large grain size is needed in steels for transformers,motors etc.The large grain size and lack of carbides in low silicon steels for magnetic purposes allows the easy movement of magnetic domain walls.Transformer steels typically have a carbon content of about 0.003% and 3.5%Si with the phosphorus and sulphur at a tenth of the levels you mention.The high Si content increases the electrical resistivity of the magnetic core and reduces the power loss from eddy currents(the core metal has voltages generated in it by the changing magnetic fields) and the power lost in eddy currents heats up a transformers core so it needs extra cooling;the loss is inversely proportional to the resistivity and 3.5%Si increases resistivity of iron by a very large amount.The presence of high silicon with ultra low carbon and manganese level allows the soft magnetic steels to be annealed at very high temperatures(850 to 1100deg C)without a phase change so that the crystals have 10,000 to 10,000,000 times the volume of the crystals in heat-treatable (Just)steel you mention.Fine for playing with and demonstrating electromagnetism but not as electrical engineering feedstuff.
