METHOD OF CONTINUOUS ANNEALING OF STEEL STRIP, DEVICE FOR CONTINUOUS ANNEALING OF STEEL STRIP, METHOD OF MANUFACTURING HOT-DIP GALVANIZED STEEL STRIP, AND DEVICE FOR MANUFACTURING HOT-DIP GALVANIZED STEEL STRIP

摘要

Provided is a method of continuous annealing of steel strips capable of realizing at low cost a low-dew-point annealing environment not prone to the problems of pickup defect occurrence and furnace wall damage, and an annealing atmosphere which prevents easily oxidizable element such as Si and Mn in the steel from becoming concentrated in the surface of the steel strip and forming oxides of the easily oxidizable element such as Si and Mn, and which is suitable to annealing of steel strips containing easily oxidizable element such as Si and Mn. A vertical annealing furnace is configured such that: a heating zone and a soaking zone are provided in which the steel strip is conveyed vertically, and a separating wall is provided in the heating zone-soaking zone for separating the atmosphere in the furnace; an atmosphere gas is supplied from outside of the furnace into the furnace, and the gas in the furnace is discharged from a steel strip introduction section at the bottom of the heating zone; a part of the gas in the furnace is sucked in and discharged to a refiner having a deoxygenation device and a dehumidifier device disposed outside the furnace, removing oxygen and water in the gas and lowering the dew point, and the gas with the lowered dew point is returned back into the furnace. When annealing a steel strip in this vertical annealing furnace, the temperature of the steel strip at a position beyond the separating wall is controlled to 550-700°C.