PURPOSE: To manufacture the nonoriented silicon steel plate with uniform magnetic characteristics by executing the cold rolling to the steel sheet of the final thickness and annealing below a specific temperature after heating, annealing and cooling of the hot-rolled steel sheet of the specific composition under the specific conditions.
CONSTITUTION: The hot-rolled steel sheet made of ultra low carbon steel where the content of Si+2Al is ≤2.0% is rapidly heated to the temperature range above the Ac3 transformation point at the temperature rising speed of ≥100°C/sec. and kept for ≤1 second at the temperature to be annealed. After the annealed hot-rolled plate is rapidly cooled to the temperature below the Ar3 transformation point at the cooling speed of ≥100°C/sec., the plate is cold rolled to obtain the product of the final thickness. The rapid heating or the rapid cooling in these processes is executed by charging the plate while the steel plate S being passed between two pairs of rolls R1, R2 and rapidly heated to the temperature above the AC3 transformation point or rapidly cooled at P point by the roll R2 on the heated side respectively. After this cold-rolled steel sheet is left unchanged or blanked, it is heated to the temperature ≥700°C, and annealed to manufacture the nonoriented silicon steel plate excellent in the magnetic characteristics.
KOSUGE KENJI
SADAMASA TAKASHI
