METHOD FOR CONTINUOUSLY ANNEALING STEEL STRIP AND HOT DIP ZINCING METHOD

摘要

PROBLEM TO BE SOLVED: To prevent readily oxidizable elements contained in steel, such as Si and Mn, from concentrating in the surface of a steel strip during annealing and thereby forming oxides of the readily oxidizable elements.

SOLUTION: In a method for continuously annealing a steel strip, a vertical annealing furnace which includes a heating zone, a soaking zone, and a cooling zone and in which part of furnace gas is introduced into a refiner disposed outside the furnace to be reduced in dew point and the gas having a lowered dew point is returned to the furnace is used. A section joining the soaking zone and the cooling zone is arranged in an upper part of the furnace, a suction port for the furnace gas to be introduced into the refiner is provided in the cooling zone in the vicinity of the section joining the soaking zone and the cooling zone and in an upper part of the soaking zone, and a discharge port for the gas returning from the refiner is provided in the section joining the soaking zone and the cooling zone and in the lower part of the soaking zone. An amount of suction gas Qo1 from the cooling zone in the vicinity of the section joining the soaking zone and the cooling zone, an amount of suction gas Qo2 from the upper part of the soaking zone, an amount of discharge gas Qi1 into the section joining the soaking zone and the cooling zone, an amount of discharge gas Qi2 into the lower part of the soaking zone, a feeding amount Qf1 of atmospheric gas to the cooling zone and the subsequent zone, a feeding amount Qf2 of atmospheric gas to the soaking zone, an internal volume Vs of the soaking zone, and an average furnace temperature Ts in the soaking zone satisfy relationships, such as 0.3×Qf1COPYRIGHT: (C)2012,JPO&INPIT