Transformer cores are normally made from

ANS:C - grain oriented Fe-Si alloy

Transformer cores are typically made from grain-oriented Fe-Si (iron-silicon) alloy. Grain-oriented electrical steel is a specially processed form of silicon steel that exhibits superior magnetic properties, making it ideal for transformer cores. The silicon content in the alloy helps to reduce energy losses due to eddy currents by increasing the electrical resistance of the material. Additionally, the grain orientation process aligns the crystal grains in the direction of the magnetic field, further enhancing the magnetic properties and reducing core losses. Soft ferrites are commonly used in high-frequency applications such as inductors and transformers operating at frequencies above a few kHz. High-purity iron and Al-Ni-Co (aluminum-nickel-cobalt) alloys are not typically used for transformer cores due to their inferior magnetic properties compared to grain-oriented Fe-Si alloy.