METHOD FOR CONTINUOUSLY ANNEALING STEEL STRIP AND HOT-DIP GALVANIZATION METHOD

• Main Authors: NAKAZATO, KAZUKI, SATO, NOBUYUKI, IRI, MASATO, TAKAHASHI, HIDEYUKI
• Format: Patent
• Language: English; French; German
• Published: 22.10.2014
• Subjects: BLASTING; CHEMICAL SURFACE TREATMENT; CHEMISTRY; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATIONOR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY IONIMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; COATING MATERIAL WITH METALLIC MATERIAL; COATING METALLIC MATERIAL; DETAILS OR ACCESSORIES OF FURNACES, KILNS, OVENS, OR RETORTS,IN SO FAR AS THEY ARE OF KINDS OCCURRING IN MORE THAN ONE KINDOF FURNACE; DIFFUSION TREATMENT OF METALLIC MATERIAL; FURNACES; FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; HEATING; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION INGENERAL; KILNS; LIGHTING; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; MECHANICAL ENGINEERING; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; OPEN SINTERING OR LIKE APPARATUS; OVENS; RETORTS; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THESURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; WEAPONS

Formation of oxides of elements susceptible to oxidation such as Si and Mn contained in the steel of steel strips due to concentration of the elements susceptible to oxidation in the surfaces of the steel strips during annealing is suppressed. A vertical annealing furnace including a heating zone, a soaking zone, and a cooling zone is used in which a portion of gas in the furnace is introduced into a refiner that is disposed outside of the furnace to decrease the dew point of the gas and the gas whose dew point has been decreased is returned into the furnace. A connection part between the soaking zone and the cooling zone is disposed in an upper portion of the furnace. Suction ports through which the gas in the furnace is sucked so as to be introduced into the refiner are disposed in a portion of the cooling zone near the connection part between the soaking zone and the cooling zone and in an upper portion of the soaking zone. Feed ports through which the gas from the refiner is returned to the furnace are disposed in the connection part between the soaking zone and the cooling zone and in a lower portion of the soaking zone. A gas suction rate Qo1 in the portion of the cooling zone near the connection part between the soaking zone and the cooling zone, a gas suction rate Qo2 in the upper portion of the soaking zone, a gas feed rate Qi1 in the connection part between the soaking zone and the cooling zone, a gas feed rate Qi2 in the lower portion of the soaking zone, a supply rate Qf1 of the atmosphere gas into the cooling zone and a zone subsequent to the cooling zone, a supply rate Qf2 of the atmosphere gas into the soaking zone, an internal volume Vs of the soaking zone, and an average furnace temperature Ts of the soaking zone satisfy relationships including 0.3 x Qf1 < Qo1.