PURPOSE: To prevent the occurrence of temp. difference in a circumferential direction in the outside periphery of a coil and also to prevent the occurrence of the deviation of sheet thickness at the time of cold rolling, by annealing a coil of high carbon steel strip under a high concentration hydrogen gas atmosphere in a bell-type tight annealing furnace.

CONSTITUTION: A coil of a high carbon steel strip having 0.50-1.1wt.% C content is annealed at 650-850°C under a high concentration hydrogen gas atmosphere consisting of ≥75% hydrogen and the balance nitrogen by using a bell-type tight annealing furnace. Since hydrogen concentration is increased by about 4-12 times, as compared with conventional 6-20% hydrogen concentration, in the annealing gas atmosphere in an inner cover, the occurrence of temp. difference in a circumferential direction in the outside periphery of the coil resulting from the temp. difference in the circumferential direction of the inner cover can be prevented owing to the high thermal conductivity of hydrogen. Further, owing to the high thermal conductivity of hydrogen, annealing efficiency can be improved.