Jfe Steel Corporation

Kazuki Nakazato

Nobuyuki Sato

Hideyuki Takahashi

Takeshi Yokota

Satoru Ando

Reiko Sugihara

Hiroyuki Masuoka

Hidetaka Kawabe

Shoichiro Taira

Takamasa Fujii

Masato Iri

Shigeyuki Aizawa

Motoki Takada

A facility for continuously manufacturing a galvanized steel sheet includes a continuous annealing furnace, a snout, and a galvanization bath. The furnace is divided into a heating zone, a soaking zone, and a cooling zone. The bath is directly connected to the furnace through the snout. The facility has a dewpoint meter and a spray port and a suction port for a furnace gas that are provided in at least one of the zones, gas cyclic paths which connect the spray port and the suction port to a refiner, and a dewpoint meter and a humidification device that are provided in the snout. The gas cyclic paths are separately formed for the respective connected zones. The refiner functions so that a measured value of the dewpoint meter is equal to a target dewpoint, and the humidification device functions so that a measured value of the dewpoint meter in the snout is equal to a target dewpoint for the snout.

Facility having a continuous annealing furnace and a galvanization bath and method for continuously manufacturing hot-dip galvanized steel sheet

A steel sheet has a microstructure including ferrite phase: 40% to 60%, bainite phase: 10% to 30%, tempered martensite phase: 20% to 40%, and retained austenite phase: 5% to 20% by volume fraction, and satisfying a condition that a ratio of tempered martensite phase having major axis length &#x2266;5 &#x3bc;m to a total volume fraction of the tempered martensite phase is 80% to 100%.

High-strength cold-rolled steel sheet and method for manufacturing the same

Provided is a vertical annealing furnace, in which a heating zone and a soaking zone are communicated with each other in the upper part of the furnace, in which a part of the furnace other than the communicated parts is separated by a dividing wall, in which part of the furnace gas is suctioned into a refiner having a deoxidation device and a dehumidification device which is placed outside the furnace to decrease the dew point of the gas by removing oxygen and moisture from the gas and such that the resultant gas having a decreased dew point is returned into the furnace, in which a gas suction port into the refiner is located in the lower part of the connection part between the soaking zone and the cooling zone and in which one or more gas suction ports are located in the parts of the heating zone and/or the soaking zone outside of an area within 6 m in the vertical direction and 3 m in the longitudinal direction of the furnace from the steel strip entrance in the lower part of the heating zone.

Continuous annealing furnace for steel strip, continuous annealing method, continuous galvanizing apparatus and method for manufacturing galvanized steel strip (as amended)

An annealing and manufacturing method of hot-dip galvanized steel strips includes suppression of oxide formation of elements in the steel strips. An annealing furnace includes a heating zone, a soaking zone, and a cooling zone in which a portion of gas is introduced to decrease the gas dew point. A gas suction rate Qoin a portion of the cooling zone, a gas suction rate Qoin an upper portion and a gas feed rate Qiin a lower portion of the soaking zone, a gas feed rate Qiin a connection part between the soaking and cooling zones, an atmosphere gas supply rate Qfinto the cooling zone and its subsequent zone, an atmosphere gas supply rate Qfinto 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&#xd7;Qf&#x3c;Qo

Continuous annealing method and a manufacturing method of hot-dip galvanized steel strips

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Tokyo, Japan

Kazuki Nakazato