Effect of Hot Band Annealing Temperature on the Magnetic Properties of Low-carbon Electrical Steels

The effect of hot band annealing temperature, range from 700-1000°C, on the magnetic properties of low-carbon electrical steels measured at 10, 15 and 17 kG inductions have been investigated. The grain microstructures of hot bands were changed by annealing at various temperature. Small grains are observed in the as hot-rolled band and hot band annealed at 700°C. Large columnar grains are observed in the hot band annealed at 800°C. Duplex structure with fine grains at the central portion of the plate and large columnar grains near the surface are observed in the hot band annealed at 900°C. Uniform medium size grains are observed in the hot band annealed at 1000°C. In addition, the size of manganese sulfide inclusions in the hot bands increased with increasing annealing temperature. After final annealing at 820°C for 1 min, grain size of low-carbon electrical steels increased with increasing hot band annealing temperature. After final annealing, low-carbon electrical steel with hot band annealing at 800°C developed favorable texture for magnetic properties. At three different inductions, ac core loss and hysteresis loss decreased with increasing hot band annealing temperature in 700-900°C. At 10 kG induction, ac and dc permeability increased with increasing hot band annealing temperature. Low-carbon electrical steel with hot band annealing at 800°C exhibited maximum ac and dc permeability under 15 kG induction. However, the steel with hot band annealing at 900°C obtained maximum ac and dc permeability and maximum magnetic flux density under 17 kG induction. Magnetic properties of the steel were improved when hot bands were annealed at temperature higher than 800°C, when it was compared with the as hot-rolled steel.