METHOD FOR CONTINUOUSLY ANNEALING STEEL STRIP, APPARATUS FOR CONTINUOUSLY ANNEALING STEEL STRIP, METHOD FOR MANUFACTURING HOT-DIP GALVANIZED STEEL STRIP, AND APPARATUS FOR MANUFACTURING HOT-DIP GALVANIZED STEEL STRIP

摘要

There is provided a method for continuously annealing a steel strip containing an easily oxidizable element, such as Si or Mn, that can form a low-dew-point annealing atmosphere at low cost with rare occurrence of pickup defects and little damage to furnace walls and an annealing atmosphere at low cost that is suitable for annealing of the steel strip with little formation of an oxide of the easily oxidizable element, such as Si or Mn, resulting from the enrichment of the easily oxidizable element, such as Si or Mn, in steel on a surface of the steel strip. The method for continuously annealing a steel strip includes: annealing the steel strip in a vertical annealing furnace, including a heating zone and a soaking zone through which the steel strip is vertically conveyed, an atomosphere in the furnace being separated by a partition disposed within a space spanning from the heating zone to the soaking zone. An atmosphere gas is supplied from an outside of the furnace into the furnace to form a furnace gas that is discharged from a steel strip entrance at a lower portion of the heating zone, a part of the furnace gas is sucked and discharged into a refiner, which is disposed outside of the furnace, including a deoxygenator and a dehumidifier such that oxygen and moisture in the part of the furnace gas are removed to form a gas having a lowered dew point, and the gas having a lowered dew point is returned into the furnace. The method further includes controlling a temperature of the steel strip passing through the partition to a range of 550°C to 700°C.