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US20180105916A1 - Continuous hot-dip metal coating method and continuous hot-dip metal coating line - Google Patents

Continuous hot-dip metal coating method and continuous hot-dip metal coating line Download PDF

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Publication number
US20180105916A1
US20180105916A1 US15/565,986 US201615565986A US2018105916A1 US 20180105916 A1 US20180105916 A1 US 20180105916A1 US 201615565986 A US201615565986 A US 201615565986A US 2018105916 A1 US2018105916 A1 US 2018105916A1
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Prior art keywords
snout
steel strip
continuous hot
bath
temperature
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US15/565,986
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English (en)
Inventor
Hideyuki Takahashi
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JFE Steel Corp
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JFE Steel Corp
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Priority claimed from PCT/JP2016/001013 external-priority patent/WO2016170720A1/ja
Assigned to JFE STEEL CORPORATION reassignment JFE STEEL CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: TAKAHASHI, HIDEYUKI
Publication of US20180105916A1 publication Critical patent/US20180105916A1/en
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C23C2/0032—Apparatus specially adapted for batch coating of substrate
    • C23C2/00322—Details of mechanisms for immersing or removing substrate from molten liquid bath, e.g. basket or lifting mechanism
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C23C2/0034—Details related to elements immersed in bath
    • C23C2/00342—Moving elements, e.g. pumps or mixers
    • C23C2/00344—Means for moving substrates, e.g. immersed rollers or immersed bearings
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C23C2/0035—Means for continuously moving substrate through, into or out of the bath
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C23C2/0038—Apparatus characterised by the pre-treatment chambers located immediately upstream of the bath or occurring locally before the dipping process
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C23C2/0038—Apparatus characterised by the pre-treatment chambers located immediately upstream of the bath or occurring locally before the dipping process
    • C23C2/004—Snouts
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/26—After-treatment
    • C23C2/261—After-treatment in a gas atmosphere, e.g. inert or reducing atmosphere
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips

Definitions

  • the disclosure relates to a continuous hot-dip metal coating method and continuous hot-dip metal coating line used to continuously manufacture, for example, a hot-dip galvanized steel sheet.
  • a steel strip whose surface has been cleaned is continuously annealed in an annealing furnace, and cooled to a predetermined temperature.
  • the steel strip is then entered into a molten zinc bath, to be hot-dip galvanized.
  • the annealing and cooling in the annealing furnace are typically performed in a reducing atmosphere.
  • a passage called a snout that is rectangular in section is provided between the annealing furnace and a coating tank containing the molten zinc bath.
  • a sink roll is installed in the molten zinc bath.
  • the steel strip Having entered the molten zinc bath, the steel strip changes its traveling direction by the sink roll, and moves upward.
  • the steel strip pulled up from the molten zinc bath is adjusted to have a predetermined coating thickness by gas wiping nozzles. After this, the steel strip is cooled, and guided to subsequent steps.
  • the snout is connected to a cooling zone (steel strip delivery side) in the annealing furnace, and so the inside of the snout normally has a reducing atmosphere.
  • the oxide film formed on the molten zinc bath surface in the snout is therefore not firm. Accordingly, when the steel strip enters the molten zinc bath, molten zinc is exposed on the bath surface due to vibration or the like, and zinc evaporates from the bath surface into the snout. In such a case, molten zinc evaporates to the saturation vapor pressure at the atmospheric temperature in the snout.
  • Zinc vapor reacts with oxygen present in a very small amount in the reducing atmosphere gas, to form an oxide. Even in the case where zinc vapor is not oxidized, when the vapor pressure of zinc vapor reaches the saturation vapor pressure or more, part of zinc vapor phase-changes to zinc in the liquid phase or the solid phase. In particular, since the snout is merely made of a thin heat-resistant material, the temperature of the inner wall surface of the snout tends to be less than or equal to the saturation temperature at the vapor pressure of zinc vapor due to the influence of external air. In a site where the temperature is less than or equal to the saturation temperature, zinc vapor becomes zinc powder and adheres to the inner surface of the snout.
  • ash-caused defects Quality defects such as non-coating portions caused by ash generated due to zinc vapor in the snout are hereafter referred to as “ash-caused defects”.
  • JP H8-176773 A (PTL 1) describes a technique of heating the snout with a heater and insulating the outside of the heater with a heat insulator so that the temperature difference between the molten bath temperature and each of the atmospheric temperature and inner wall temperature in the snout is 150° C. or less, thus preventing ash adhesion to the snout inner wall.
  • JP H8-302453 A (PTL 2) describes a technique of installing a suction blower in the molten bath and connecting, to the suction side of the suction blower, a suction tube that has a suction port at a position higher than the bath surface in the snout, to discharge zinc vapor in the snout to outside the system.
  • JP H6-330271 A (PTL 3) describes a technique of setting the atmosphere in the snout to non-oxidizing gas for a steel sheet and to oxidizing gas for molten zinc to suppress the generation of fumes (zinc vapor).
  • the technique in PTL 1 can reduce the crystallization of zinc vapor on the snout inner wall, that is, the generation of ash, to some extent by heating the snout.
  • the generation of zinc vapor from the molten zinc bath surface itself cannot be prevented, and so ash is inevitably generated in a site that is not heated. The technique thus cannot eliminate a potential risk of ash adhering to the steel strip.
  • the effect of reducing ash-caused defects by each of the techniques in PTL 1 to PTL 3 is insufficient.
  • the techniques in PTL 1 to PTL 3 also have the following problem.
  • the suitable oxidizability of the atmosphere in the snout (especially near the bath surface) varies depending on an operation condition such as the chemical composition of the steel strip, the annealing condition in the annealing, or the component of the molten metal bath. Accordingly, when the operation condition is switched over, the oxidizability of the atmosphere in the snout needs to be changed promptly.
  • the techniques in PTL 1 to PTL 3 however, the oxidizability of the atmosphere in the snout cannot be changed stably and promptly.
  • the presence of large natural convection in the snout makes it impossible to stably and promptly change the oxidizability of the atmosphere in the snout.
  • an oxide film with at least a predetermined thickness needs to be formed on the bath surface.
  • the oxide film thickness needs to be limited to a predetermined thickness or less. This means an oxide film with an optimum thickness needs to be formed in order to reduce both ash-caused defects and oxide film-caused defects.
  • a continuous hot-dip metal coating method comprising: continuously annealing a steel strip in an annealing furnace; and continuously supplying the steel strip after the annealing into a coating tank containing a bath of molten metal, to metal-coat the steel strip, wherein while the steel strip traveling from the annealing furnace to the molten metal bath passes through a space defined by a snout that is located on a steel strip delivery side of the annealing furnace and has an end immersed in the molten metal bath, oxidizing gas is supplied into the snout, a temperature of an inner wall surface of the snout is maintained at 150° C. or less below a temperature of the molten metal bath, and an atmospheric temperature of an upper portion in the snout is maintained at 100° C. or less below the temperature of the molten metal bath.
  • a continuous hot-dip metal coating line comprising: an annealing furnace that continuously anneals a steel strip; a coating tank containing a bath of molten metal; a snout located on a steel strip delivery side of the annealing furnace, having an end immersed in the molten metal bath, and defining a space through which the steel strip continuously supplied from the annealing furnace into the molten metal bath passes; a heating unit provided on an outer wall of the snout and in an upper portion in the snout; a gas supply mechanism connected to the snout; and a controller that controls the heating unit and the gas supply mechanism to supply oxidizing gas into the snout, maintain a temperature of an inner wall surface of the snout as 150° C. or less below a temperature of the molten metal bath, and maintain an atmospheric temperature of an upper portion in the snout at 100° C. or less below the temperature of the molten metal bath.
  • FIG. 1 is a schematic view of a continuous hot-dip galvanizing line 100 according to one of the disclosed embodiments
  • FIG. 2 is a view illustrating half of the inside of a snout 14 in FIG. 1 from the transverse center of a steel strip P;
  • FIG. 3 is an enlarged schematic view of the snout 14 in FIG. 1 ;
  • FIG. 4 is a graph illustrating the relationship between the oxidizability of the bath surface atmosphere and the defect rate
  • FIG. 5A is a graph illustrating the relationship between the oxidizability of the bath surface atmosphere and the defect rate for high Si-containing steel and low Si-containing steel;
  • FIG. 5B is a graph illustrating the relationship between the oxidizability of the bath surface atmosphere and the oxide film thickness for a high Al-containing bath and a low Al-containing bath;
  • FIG. 6A is a graph illustrating the relationship between the dew point in the snout and the defect rate for steel type A;
  • FIG. 6B is a graph illustrating the relationship between the dew point in the snout and the defect rate for steel type B.
  • FIG. 7 is a graph illustrating the change of the dew point in the snout in each of Examples 1 to 3 and Comparative Examples 1 and 2.
  • a continuous hot-dip galvanizing line 100 and a continuous hot-dip galvanizing method using the continuous hot-dip galvanizing line 100 according to one of the disclosed embodiments are described below.
  • the continuous hot-dip galvanizing line 100 includes an annealing furnace 10 , a coating tank 12 , and a snout 14 .
  • the annealing furnace 10 is a device that continuously anneals a steel strip P passing through the annealing furnace 10 , and includes a heating zone, a soaking zone, and a cooling zone arranged side by side in this order. Only the cooling zone is illustrated in FIG. 1 .
  • the annealing furnace may have a well-known structure or any structure. Reducing gas or non-oxidizing gas is typically supplied into the annealing furnace. As the reducing gas, H 2 —N 2 mixed gas is typically used. An example of such gas is gas (dew point: about ⁇ 60° C.) having a composition containing H 2 : 1 vol % to 20 vol % with the balance being N 2 and incidental impurities.
  • non-oxidizing gas gas (dew point: about ⁇ 60° C.) having a composition containing N 2 and incidental impurities.
  • the annealed steel strip P is cooled to about 470° C. to 500° C. in the cooling zone.
  • the coating tank 12 contains a molten zinc bath 12 A.
  • the snout 14 is located on the steel strip delivery side of the annealing furnace 10 .
  • the snout 14 is connected to the cooling zone in this embodiment.
  • a snout end 14 A is immersed in the molten zinc bath 12 A.
  • the snout 14 is a member that defines the space through which the steel strip P continuously supplied from the annealing furnace 10 into the molten zinc bath 12 A passes.
  • a turndown roll 26 for changing the traveling direction of the steel strip P from horizontal to obliquely downward is located in an upper portion in the snout 14 .
  • the part of the snout 14 that defines the space through which the steel strip P having passed through the turndown roll 26 passes is rectangular in section perpendicular to the traveling direction of the steel strip P.
  • the steel strip P passes through the inside of the snout 14 , and continuously enters the molten zinc bath 12 A.
  • a sink roll 28 and support rolls 30 are installed in the molten zinc bath 12 A. Having entered the molten zinc bath 12 A, the steel strip P is changed upward in the sheet passing direction by the sink roll 28 , and then guided by the support rolls 30 to leave the molten zinc bath 12 A. The steel strip P is thus hot-dip galvanized.
  • the continuous hot-dip galvanizing line 100 includes a gas supply mechanism 20 connected to the snout 14 .
  • the gas supply mechanism 20 includes: a first pipe 22 A through which hydrogen gas passes; a second pipe 22 B through which nitrogen gas passes; a third pipe 22 C through which water vapor as oxidizing gas passes; flow rate adjusting valves 24 attached to these pipes; a fourth pipe 22 D through which mixed gas obtained by mixing the gases supplied from these pipes passes; and a fifth pipe 22 E connected to the fourth pipe 22 D and has its tip located inside the snout 14 .
  • the first pipe 22 A and the third pipe 22 C are connected to the second pipe 22 B.
  • the oxidizing gas is not limited, and may be gas containing water vapor, oxygen, carbon dioxide, or the like.
  • Gas containing water vapor is preferable because its oxidizability is not excessively high and so it is easy to be managed, is inexpensive, and is easy to be measured in oxidizability by a dew point meter.
  • a heater 16 as a heating unit is placed on the outer wall of the snout 14 , and covered with a heat insulator 18 .
  • the heater 16 covers the whole outer wall except the tip portion of the snout 14 (near the bath surface).
  • a heater 17 as a heating unit is also placed in the upper portion in the snout. Since the upper portion in the snout has significant influence on the occurrence of heat convection as described later, providing the heater 17 ensures that the atmospheric temperature of the upper portion in the snout is increased.
  • a controller controls the heaters 16 and 17 and the gas supply mechanism 20 to supply the oxidizing gas into the snout 14 and maintain the temperature of the inner wall surface of the snout 14 at (a temperature of the molten metal bath ⁇ 150° C.) or more and the atmospheric temperature of the upper portion in the snout 14 at (the temperature of the molten metal bath ⁇ 100° C.) or more.
  • a controller controls the heaters 16 and 17 and the gas supply mechanism 20 to supply the oxidizing gas into the snout 14 and maintain the temperature of the inner wall surface of the snout 14 at (a temperature of the molten metal bath ⁇ 150° C.) or more and the atmospheric temperature of the upper portion in the snout 14 at (the temperature of the molten metal bath ⁇ 100° C.) or more.
  • FIG. 4 illustrates the concept of such an optimum level.
  • the oxidizability is low, no oxide film forms on the bath surface or, even when an oxide film forms, the oxide film is very thin. In this case, oxide film-caused defects are unlikely to occur, but zinc evaporates actively and so ash-caused defects increase.
  • the oxidizability is high, a thick oxide film serves as a protective film and zinc hardly evaporates. In this case, ash-caused defects are unlikely to occur, but oxide film-caused defects occur a lot.
  • both ash-caused defects and oxide film-caused defects can be reduced to low level by precisely controlling the dew point of the atmosphere near the bath surface within the range of about a predetermined point (target dew point) ⁇ 4° C.
  • the target dew point can be determined by the below-mentioned method once the operation conditions other than the target dew point are determined.
  • Main convection in the snout includes an accompanying flow that occurs due to the movement of the steel strip, a heat convection flow associated with the temperature difference in the snout, and a pressure flow caused by the pressure difference in the snout.
  • the influence of heat convection flow is dominant.
  • the temperature difference of the inside of the snout from the outside of the snout is 400° C. or more.
  • the atmospheric temperature of the upper portion in the snout tends to be 200° C. to 300° C.
  • the wind velocity by heat convection is about 4 m/s to 5 m/s, which is considerably higher than a typical value of a steel strip accompanying flow of 1 m/s.
  • the steel strip is highest in temperature in the snout, the steel strip temperature is normally higher than the bath temperature only by about 10° C. Hence, the temperature of the molten metal bath is used as the reference temperature in the disclosure. Since the heat convection flow and the steel strip accompanying flow are in opposite directions, the convection in the snout is greatly reduced if the magnitude of the heat convection flow can be limited to not more than twice the magnitude of the steel strip accompanying flow.
  • the atmospheric temperature of the upper portion in the snout is preferably (the temperature of the molten metal bath+100° C.) or less. Although the convection in the snout is more stabilized when the atmospheric temperature of the upper portion is higher (the presence of a low density substance in the upper portion contributes to a stable state), the stabilizing effect is saturated if the atmospheric temperature of the upper portion is more than (the temperature of the molten metal bath+100° C.).
  • the temperature of the inner wall surface of the snout is preferably (the temperature of the molten metal bath+0° C.) or less.
  • upper portion in the snout in the disclosure means the region in the snout within 1 m from the surface of the turndown roll. In FIG. 3 , the upper portion in the snout is the region within 1 m from the surface of the turndown roll 26 in the snout 14 .
  • the oxidation state of the bath surface in the snout can be maintained ideally, so that both ash-caused defects and oxide film-caused defects can be almost eliminated. Further, the oxidizability of the atmosphere in the snout can be changed stably and promptly. Hence, when an operation condition is switched over, the oxidizability of the atmosphere in the snout can be promptly changed according to the changed operation condition.
  • the oxidizing gas supplied into the snout is preferably nitrogen gas containing water vapor or nitrogen-hydrogen mixed gas containing water vapor.
  • the dew point of the oxidizing gas may be set as appropriate depending on the composition of the molten bath, the steel type to be manufactured, and other operation conditions, but tends to be favorable in the range of about ⁇ 20° C. to ⁇ 35° C.
  • the oxidizing gas supply amount depends on various operation conditions, in the case where the conditions other than the temperature of the inner wall surface of the snout and the atmospheric temperature of the upper portion in the snout are the same, the same dew point can be achieved with a supply amount of about 1 ⁇ 4 as compared with when the temperature of the inner wall surface and the atmospheric temperature of the upper portion are outside the ranges according to the disclosure.
  • the oxidizing gas supply amount can thus be reduced to the minimum necessary amount for forming an appropriate oxide film.
  • the oxidizing gas is preferably supplied into the snout 14 from both edges of the snout in the steel strip transverse (width) direction.
  • the reason why the fifth pipe 22 E having a gas supply port is located on the side surface of the snout 12 is that, since the temperature near the side surface in the snout tends to be low and so a downward flow usually occurs near the side surface, the oxidizing gas can be efficiently delivered to near the bath surface.
  • the height of the gas supply port from the bath surface may be about 100 mm to 3000 mm. If the height is less than 100 mm, the gas is highly likely to directly reach the bath surface, causing an increase in concentration distribution of the oxidizing gas near the bath surface. If the height is more than 3000 mm, the gas concentration decreases due to a long distance from the bath surface, so that a large amount of gas is needed.
  • the suitable oxidizability of the atmosphere near the bath surface in the snout varies depending on an operation condition such as the chemical composition of the steel strip, the annealing condition in the annealing, or the component of the molten zinc bath.
  • an operation condition such as the chemical composition of the steel strip, the annealing condition in the annealing, or the component of the molten zinc bath.
  • the two curves illustrated in FIG. 4 can shift right or left depending on the operation condition. This is described below, with reference to FIGS. 5A and 5B as an example.
  • ash-caused defects and oxide film-caused defects correlate to the thickness of the oxide film formed on the bath surface, as mentioned above.
  • ash-caused defects relate to the amount of ash and its adhesion rate
  • oxide film-caused defects relate to the amount of oxide film and its adhesion rate.
  • FIG. 5A illustrates an example of the influence of the chemical composition of the steel strip on the suitable oxidizability of the atmosphere near the bath surface in the snout.
  • the steel strip contains a lot of oxidizable element such as Si, Mn, or Al
  • a large amount of oxide is concentrated on the surface of the steel strip immediately before entering the molten bath. If the steel strip is coated in such a surface concentration state, the oxide film easily adheres to the steel strip, that is, the adhesion rate of the oxide film is high, facilitating oxide film-caused defects.
  • the amount of ash hardly depends on the surface concentration state of the steel strip, and so the chemical composition of the steel strip hardly influences ash-caused defects.
  • the surface concentration state of the steel strip also differs depending on the annealing condition such as the annealing temperature and the furnace dew point.
  • the annealing condition also influences oxide film-caused defects, but hardly influences ash-caused defects.
  • FIG. 5B illustrates an example of the influence of the component of the molten zinc bath on the suitable oxidizability of the atmosphere near the bath surface in the snout.
  • FIG. 5B illustrates an example of the influence of the component of the molten zinc bath on the suitable oxidizability of the atmosphere near the bath surface in the snout.
  • the Al concentration in the bath is higher, an oxide film forms on the bath surface more easily.
  • a high Al-containing bath causes fewer ash-caused defects, and more oxide film-caused defects.
  • the two curves in FIG. 4 shift to the left.
  • the amount of water vapor in the oxidizing gas is changed depending on the operation condition, as the suitable dew point of the atmosphere near the bath surface, i.e. the target dew point, differs depending on the operation condition.
  • the amount of water vapor in the oxidizing gas is typically 100 ppm or more.
  • the relationship between the dew point in the snout and the defect rates of ash-caused defects and oxide film-caused defects may be preliminarily investigated to determine the target dew point in the snout under the operation condition.
  • the amount of water vapor in the oxidizing gas may then be determined based on the target dew point determined for the operation condition.
  • the amount of water vapor in the oxidizing gas may be changed based on the target dew point corresponding to the changed operation condition.
  • the relationship between the dew point in the snout and the defect rates of ash-caused defects and oxide film-caused defects as illustrated in FIG. 4 can be determined by preliminarily recognizing the tendency of the correspondence between the dew point in the snout and the defect rate of each type of defect in past operation. Whether or not each type of defect occurs may be visually determined.
  • the size of a visually observable defect is about 100 ⁇ m or more.
  • the rate of defect occurrence per 0.5 m in length is defined as “defect rate”.
  • a defect rate of 1% means one defect per 50 m.
  • the aforementioned dew point in the snout needs to be the dew point immediately above the bath surface (near the bath surface). In the case where the actual dew point measurement location is not immediately above the bath surface, the following adjustment is performed. In a state where heat convection in the snout is eliminated according to the disclosure, there is hardly any dew point distribution in the snout, and so the actual measured dew point can be directly used as the dew point in the snout. If there is heat convection in the snout, however, the actual measured dew point is corrected to the dew point near the bath surface. This correction can be performed using the dew point distribution predicted from flow analysis.
  • the difference in dew point is +5° C.
  • the difference in water ratio is 150 ppm. Accordingly, the dew point obtained by adding the value corresponding to 150 ppm to the actual measured dew point value at a height of 500 mm can be used as the bath surface dew point.
  • Examples of the operation condition influencing the suitable oxidizability of the atmosphere near the bath surface in the snout include the steel type (the chemical composition of the steel strip), the annealing condition in the annealing, and the component of the molten zinc bath. At least one of these operation conditions is preferably used to obtain the information in FIG. 4 beforehand.
  • the information in FIG. 4 is preliminarily investigated for each steel type scheduled to pass through the line, to determine the target dew point.
  • the amount of water vapor in the oxidizing gas is changed so that the target dew point corresponds to the changed steel type.
  • the disclosure is not limited to the foregoing embodiment, and equally applies to the case of continuously hot-dip metal coating a steel strip.
  • each steel strip (hereafter referred to as “steel type A”) having a chemical composition containing, in mass %, C: 0.001%, Si: 0.01%, Mn: 0.1%, P: 0.003%, S: 0.005%, and Al: 0.03% with the balance being Fe and incidental impurities and having a sheet thickness of 0.6 mm to 1.2 mm, a sheet width of 900 mm to 1250 mm, and a tensile strength of 270 MPa was entered into the molten zinc bath at a sheet passing speed of 60 mpm to 100 mpm, to manufacture a hot-dip galvanized steel sheet.
  • the fifth pipe having a gas supply port was located on the side surface of the snout, and the height of the gas supply port from the bath surface was 500 mm, as illustrated in FIG. 2 .
  • the relationship between the dew point in the snout and the defect rates of ash-caused defects and oxide film-caused defects was preliminarily investigated from past operation data.
  • FIG. 6A illustrates the results. Based on FIG. 6A , the target dew point in the snout was determined to be ⁇ 30° C. This indicates that both ash-caused defects and oxide film-caused defects are reduced to low level if the dew point in the snout can be controlled within the range of about ⁇ 30° C. ⁇ 4° C.
  • the dew point of the atmosphere in the snout was measured over time, by a dew point meter provided in a dew point measurement hole 32 B at a height of 500 mm in the center portion of the back of the snout in FIG. 2 .
  • the flow rate of the supplied gas was changed so that the measured dew point was closer to the target dew point. This control was performed by typical PID control logic.
  • a histogram of the measured dew point in each of test examples No. 1 to 7 is listed in Table 2. For each of test examples No.
  • the dew point meter needs to be at a lower position near the bath surface. According to the disclosure, however, there is hardly any dew point distribution in the snout, so that the dew point near the bath surface can be accurately determined even when the dew point measurement is performed at a height of 500 mm.
  • the dew point meter cannot be installed in the lower portion of the snout due to the risk of zinc vapor adhering to the sensor part of the dew point meter if the dew point meter is at a low position such as a height of about 100 mm from the bath surface. While the gas measuring instrument was the dew point meter in this example as water vapor was used in the oxidizing gas, in the case of using oxidizing gas other than water vapor, a measuring instrument for detecting such gas needs to be installed.
  • defect rate of each of ash-caused defects and oxide film-caused defects was evaluated by the following method. Whether or not each type of defect occurred was visually determined. The size of a visually observable defect is about 100 ⁇ m or more. The rate of defect occurrence per 0.5 m in length is defined as “defect rate”, and listed in Table 1. A defect rate of 1% means one defect per 50 m.
  • No. 1 (Example) is an example with no temperature difference among the bath temperature, the wall surface temperature, and the upper portion temperature. There was little variation in dew point, and as a result ash-caused defects and oxide film-caused defects hardly occurred.
  • No. 2 (Example) is an example with a low wall surface temperature
  • No. 3 (Example) is an example with a low atmospheric temperature of the snout upper portion. In these examples, the dew point of the atmosphere in the snout was able to be controlled within the management range ( ⁇ 30° C. ⁇ 4° C.), as a result of which each defect rate was kept at low level. Moreover, in No. 1 to 3, the gas supply flow rate was sufficiently reduced as compared with No. 5.
  • No. 4 is an example with the wall surface temperature being outside the range according to the disclosure
  • No. 5 is an example with the atmospheric temperature of the snout upper portion being outside the range according to the disclosure.
  • the dew point of the atmosphere in the snout was unable to be controlled within the management range ( ⁇ 30° C. ⁇ 4° C.), as a result of which many ash-caused defects or oxide film-caused defects occurred.
  • No. 6 (Comparative Example) is an example without water vapor supply and without heating by the heaters. In this case, the dew point was low around ⁇ 40° C. and so oxide film-caused defects did not occur, but a large number of ash-caused defects occurred.
  • No. 7 (Comparative Example), the dew point was stable because there was no temperature difference, but was low around ⁇ 40° C., so that a large number of ash-caused defects occurred.
  • each steel strip (hereafter referred to as “steel type B”) having a chemical composition containing, in mass %, C: 0.12%, Si: 1.0%, Mn: 1.7%, P: 0.006%, S: 0.006%, and Al: 0.03% with the balance being Fe and incidental impurities and having a sheet thickness of 0.6 mm to 1.2 mm, a sheet width of 900 mm to 1250 mm, and a tensile strength of 780 MPa was used.
  • FIG. 6B illustrates the results.
  • the speed of changing the dew point of nitrogen-hydrogen mixed gas containing water vapor was examined, in a state of the bath temperature, the wall surface temperature, and the upper portion temperature in No. 1 to 5 (Examples 1 to 3 and Comparative Examples 1 and 2) in Table 1. As illustrated in FIG. 7 , the supply dew point was changed from ⁇ 35° C. to ⁇ 20° C. at 50 minutes.
  • Example 1 the bath temperature, the wall surface temperature, and the upper portion temperature were all set to 450° C., and so there was hardly any heat convection. Accordingly, the measured dew point changed substantially in the same way as the change of the dew point of the supplied gas. The dew point in the snout can thus be directly controlled using the dew point of the supplied gas, which is very advantageous in terms of quality management. In Examples 2 and 3, the changed dew point had some delay as compared with Example 1, but was able to follow the supply dew point after about 30 minutes, which is sufficient in terms of quality management.
  • the disclosed continuous hot-dip metal coating method and continuous hot-dip metal coating line can reduce both non-coating caused by metal vapor generated in a snout and non-coating caused by an oxide film on a molten metal bath surface in the snout.

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EP3967780A4 (en) * 2019-07-10 2022-05-11 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) PROCESS FOR PRODUCTION OF HOT GALVANIZED STEEL SHEET AND ALLOY HOT GALVANIZED STEEL SHEET
US20220298617A1 (en) * 2019-08-30 2022-09-22 Micromaterials Llc Apparatus and methods for depositing molten metal onto a foil substrate
US11692257B2 (en) * 2018-03-12 2023-07-04 Arcelormittal Method for dip-coating a metal strip
US20240318290A1 (en) * 2021-07-14 2024-09-26 Jfe Steel Corporation Method for manufacturing hot-dip galvanized steel sheet
EP4495281A1 (de) 2023-07-21 2025-01-22 voestalpine Stahl GmbH Verfahren zum aufbringen einer schicht auf ein stahlflachprodukt

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CN111394675B (zh) * 2020-04-15 2021-10-29 马鞍山钢铁股份有限公司 降低热镀锌锌蒸汽的方法
CN115836140B (zh) * 2020-07-29 2025-10-24 杰富意钢铁株式会社 渣滓缺陷预测方法、渣滓缺陷减少方法、热浸镀锌钢板的制造方法、合金化热浸镀锌钢板的制造方法、渣滓缺陷预测模型的生成方法、渣滓缺陷预测装置以及渣滓缺陷预测终端系统
KR20230174250A (ko) * 2021-06-25 2023-12-27 제이에프이 스틸 가부시키가이샤 강판의 부도금 결함 예측 방법, 강판의 결함 저감 방법, 용융 아연 도금 강판의 제조 방법, 및 강판의 부도금 결함 예측 모델의 생성 방법

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US11692257B2 (en) * 2018-03-12 2023-07-04 Arcelormittal Method for dip-coating a metal strip
US12435387B2 (en) 2018-03-12 2025-10-07 Arcelormittal Method for dip-coating a metal strip
EP3967780A4 (en) * 2019-07-10 2022-05-11 Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.) PROCESS FOR PRODUCTION OF HOT GALVANIZED STEEL SHEET AND ALLOY HOT GALVANIZED STEEL SHEET
US20220298617A1 (en) * 2019-08-30 2022-09-22 Micromaterials Llc Apparatus and methods for depositing molten metal onto a foil substrate
US20220298616A1 (en) * 2019-08-30 2022-09-22 Micromaterials Llc Apparatus and methods for depositing molten metal onto a foil substrate
US11597989B2 (en) * 2019-08-30 2023-03-07 Applied Materials, Inc. Apparatus and methods for depositing molten metal onto a foil substrate
US11597988B2 (en) * 2019-08-30 2023-03-07 Applied Materials, Inc. Apparatus and methods for depositing molten metal onto a foil substrate
US20240318290A1 (en) * 2021-07-14 2024-09-26 Jfe Steel Corporation Method for manufacturing hot-dip galvanized steel sheet
EP4495281A1 (de) 2023-07-21 2025-01-22 voestalpine Stahl GmbH Verfahren zum aufbringen einer schicht auf ein stahlflachprodukt
WO2025021387A1 (de) 2023-07-21 2025-01-30 Voestalpine Stahl Gmbh Verfahren zum aufbringen einer schicht auf ein stahlflachprodukt

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