US20240360528A1 - Quenching apparatus, quenching method, and method of manufacturing metal sheet - Google Patents

Quenching apparatus, quenching method, and method of manufacturing metal sheet Download PDF

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US20240360528A1
US20240360528A1 US18/683,982 US202218683982A US2024360528A1 US 20240360528 A1 US20240360528 A1 US 20240360528A1 US 202218683982 A US202218683982 A US 202218683982A US 2024360528 A1 US2024360528 A1 US 2024360528A1
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cooling
metal sheet
sheet
metal
fluid
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Soshi Yoshimoto
Hirokazu Kobayashi
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JFE Steel Corp
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JFE Steel Corp
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    • 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
    • C21D9/573—Continuous furnaces for strip or wire with cooling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
    • B21B45/02—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for lubricating, cooling, or cleaning
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
    • C21D1/22—Martempering
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/60—Aqueous agents
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/63—Quenching devices for bath quenching
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/62—Quenching devices
    • C21D1/667—Quenching devices for spray quenching
    • 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
    • C21D11/00—Process control or regulation for heat treatments
    • C21D11/005—Process control or regulation for heat treatments for cooling
    • 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
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0242—Flattening; Dressing; Flexing
    • 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
    • C21D9/573—Continuous furnaces for strip or wire with cooling
    • C21D9/5735—Details
    • C21D9/5737—Rolls; Drums; Roll arrangements
    • 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
    • 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
    • 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
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D3/00—Electroplating: Baths therefor
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/22—Electroplating: Baths therefor from solutions of zinc
    • 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
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/008—Martensite
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

  • This application relates to a quenching apparatus that performs annealing while continuously conveying a metal sheet, a quenching method, and a method of manufacturing a metal sheet.
  • shape defects such as warps, wavy deformations, and the like are generated in the metal sheet. This is caused by thermal contraction or the like of the metal sheet due to being rapidly cooled by a cooling fluid.
  • the temperature of the metal sheet changes from a temperature Ms at which a martensitic transformation starts to a temperature Mf at which the martensitic transformation ends, sudden thermal contraction and transformation expansion occur at the same time.
  • Patent Literature 1 proposes a method of restraining a metal sheet by a pair of restraining rolls, which are provided in a cooling fluid, when the temperature of the metal sheet is in the range of (TMs+150) (° C.) to (TMf ⁇ 150) (° C.), where TMs (° C.) is a Ms temperature at which a martensitic transformation of the metal sheet starts and TMf (° C.) is a Mf temperature at which the martensitic transformation ends.
  • Patent Literature 2 discloses that, while a metal sheet is restrained by restraining rolls, a distance between a position at which cooling of the metal sheet by a cooling fluid is started and the restraining rolls is controlled by a movable masking member when a quenching method in which cooling is performed by jetting water through a plurality of water jetting nozzles to surfaces of the metal sheet is performed.
  • Patent Literature 1 there is proposed a method in which a metal sheet with a temperature from (TMs+150) (° C.) to (TMf ⁇ 150) (° C.), where TMs (° C.) is the Ms temperature at which a martensitic transformation of the metal sheet starts and TMf (° C.) is the Mf temperature at which the martensitic transformation ends, is caused to pass the restraining rolls.
  • the disclosed embodiments have been made to solve such problems, and an object of the disclosed embodiments is to provide a quenching apparatus capable of suppressing generation of variations in the shape of a metal sheet at the time of quenching, a quenching method, and a method of manufacturing a metal-sheet product.
  • a metal-sheet quenching apparatus that cools a metal sheet while conveying the metal sheet, the metal-sheet quenching apparatus including: a cooling tank in which a cooling fluid is to be stored and the metal sheet is cooled by being immersed in the cooling fluid; a restraining roll that is installed inside the cooling tank and that conveys the metal sheet cooled in the cooling tank while restraining the metal sheet in a thickness direction; a water-level adjustor that adjusts a height of a fluid surface of the cooling fluid inside the cooling tank, the fluid surface being a cooling start position of the metal sheet; and a position control device that controls the height of the fluid surface of the cooling fluid inside the cooling tank by controlling an operation of the water-level adjustor.
  • the water-level adjustor includes an adjustment tank that stores the cooling fluid and that is connected to the cooling tank, a supply source that supplies the cooling fluid to the adjustment tank, and a weir that controls discharge of the cooling fluid from the adjustment tank, and the height of the fluid surface of the cooling fluid inside the cooling tank is adjusted by adjusting a stored amount of the cooling fluid inside the adjustment tank.
  • v (mm/s) is the line speed of the metal sheet
  • T1(° C.) is the cooling start temperature
  • T2(° C.) is the target temperature
  • CV(° C./s) is the cooling rate of cooling of the metal sheet in the cooling tank.
  • a metal-sheet quenching method in which a metal sheet is cooled while being conveyed including: immersing the metal sheet in a cooling fluid that is stored in a cooling tank and cooling the metal sheet with a cooling start position set at a height of a fluid surface of the cooling fluid inside the cooling tank, in which the height of the fluid surface of the cooling fluid inside the cooling tank is adjusted such that the metal sheet is restrained at a position at which the metal sheet has a target temperature by a restraining roll.
  • v (mm/s) is the line speed of the metal sheet
  • T1(° C.) is the cooling start temperature
  • T2(° C.) is the target temperature
  • CV(° C./s) is the cooling rate of cooling of the metal sheet.
  • a method of manufacturing a metal sheet comprising performing any of a hot-dip galvanizing treatment, an electro-galvanizing treatment, or a hot-dip galvannealing treatment on a high strength steel sheet obtained by the method described in [15].
  • a water-level adjustor at the time of quenching of a metal sheet to adjust the height of a fluid surface of a cooling fluid inside a cooling tank, the fluid surface being a cooling start position, it is possible to control the distance from the cooling start position to a restraining roll. Consequently, it is possible to suppress variations in the shape of the metal sheet generated during quenching.
  • FIG. 1 is a schematic diagram in which a quenching apparatus according to an embodiment of the disclosed embodiments is illustrated.
  • FIG. 2 is a schematic diagram in which one example of a water-level adjustor in FIG. 1 is illustrated.
  • FIG. 3 is a schematic diagram in which one example of the definition of a warp amount of a metal sheet is illustrated.
  • FIG. 4 is a graph showing a relationship between a line speed and a target temperature in an example of the disclosed embodiments.
  • FIG. 5 is a graph showing a relationship between a line speed and a warp amount of a metal sheet in an example of the disclosed embodiments.
  • FIG. 6 is a graph showing a relationship between a line speed and a target temperature in Comparative example 1.
  • FIG. 7 is a graph showing a relationship between a line speed and a warp amount of a metal sheet in Comparative example 1.
  • FIG. 8 is a graph showing a relationship between a line speed and a target temperature in Comparative example 2.
  • FIG. 9 is a graph showing a relationship between a line speed and a warp amount of a metal sheet in Comparative example 2.
  • FIG. 1 is a schematic diagram in which a quenching apparatus according to an embodiment of the present disclosure is illustrated.
  • a quenching apparatus 1 in FIG. 1 performs quenching of a steel material as, for example, a metal sheet S and is employed in cooling facilities provided at the exit side of a soaking zone of a continuous annealing furnace.
  • the quenching apparatus 1 for a metal sheet in FIG. 1 includes a cooling device 10 that cools the metal sheet S and restraining rolls 20 that restrain the cooled metal sheet S in a thickness direction.
  • the cooling device 10 cools the metal sheet S by using a cooling fluid CF and includes a cooling tank 11 in which the cooling fluid CF is stored and a plurality of nozzles 12 installed inside the cooling tank 11 and through which the cooling fluid CF is jetted to the surfaces of the metal sheet S.
  • Water is stored as the cooling fluid CF in the cooling tank 11 , and, for example, the metal sheet S is immersed in the water from the upper surface of the cooling tank 11 toward a conveyance direction BD.
  • a sink roll 2 that changes the conveyance direction of the metal sheet S is installed inside the cooling tank 11 .
  • the plurality of nozzles 12 are formed by, for example, slit nozzles or the like and are installed on two surface sides of the metal sheet S to be arranged in the conveyance direction of the metal sheet S. Consequently, the metal sheet S is cooled by the cooling fluid CF inside the cooling tank 11 and the cooling fluid CF that is jetted through the plurality of nozzles 12 . Cooling the metal sheet S by thus using both the cooling tank 11 and the plurality of nozzles 12 stabilizes the boiling state of the surfaces of the metal sheet S and enables uniform shape control.
  • cooling that uses an oil or an ionic fluid as the cooling fluid CF may be employed.
  • the plurality of nozzles 12 are installed inside the cooling tank 11 in the example in FIG. 1 , the method of cooling is not limited thereto as long as the method can cool the metal sheet S in a preset temperature range.
  • the metal sheet S may be cooled by only the cooling tank 11 without the use of the nozzles 12 .
  • the restraining rolls 20 restrain the metal sheet S cooled by the cooling device 10 in the thickness direction and these rolls 20 are respectively installed on both surfaces of metal sheet S inside the cooling tank 11 .
  • a pair of the restraining rolls 20 are installed to face each other in FIG. 1 but may be installed at positions displaced from each other in the conveyance direction as long as the restraining rolls 20 are configured to perform restraining.
  • the restraining rolls 20 are not limited to being provided as a pair.
  • a plurality of pairs or a plurality of the restraining rolls 20 may be provided. In such a case, positions of the restraining roll pairs as a whole may be collectively controlled.
  • quenching of the metal sheet S is performed by immersing the metal sheet S in the cooling fluid CF stored in the cooling tank 11 . Therefore, a cooling start position SP of the metal sheet S varies depending on the water level in the cooling tank 11 .
  • the metal quenching apparatus 1 thus has a function of varying the cooling start position SP by varying the height of the fluid surface in the cooling tank 11 .
  • the metal quenching apparatus 1 includes a water-level adjustor 30 that adjusts the height of the fluid surface of the cooling fluid CF contained in the cooling tank 11 , and a position control device 40 that controls the operation of the water-level adjustor 30 .
  • FIG. 2 is a schematic diagram in which one example of the water-level adjustor 30 in FIG. 1 is illustrated.
  • the water-level adjustor 30 in FIG. 2 includes an adjustment tank 31 in which the cooling fluid CF is stored, a supply source 32 that supplies the cooling fluid CF to the adjustment tank 31 , and a weir 33 that controls discharge of the cooling fluid CF inside the adjustment tank 31 .
  • the adjustment tank 31 and the cooling tank 11 are connected to each other by a discharge pipe 34 through which the cooling fluid CF is discharged from the cooling tank 11 and a supply pipe 35 through which the cooling fluid CF is supplied to the cooling tank 11 .
  • the discharge pipe 34 and the supply pipe 35 are provided below the fluid surface so as not to impede a boiling phenomenon and jetting through the nozzles 12 .
  • the discharge pipe 34 and the supply pipe 35 may be integrated together.
  • the heights of the fluid surfaces in the adjustment tank 31 and the cooling tank 11 are adjusted to be the same due to the atmospheric pressure. Consequently, it is possible to adjust the height of the fluid surface in the cooling tank 11 by, for example, adjusting the stored amount in the adjustment tank 31 while monitoring the height of the fluid surface in the adjustment tank 31 . Consequently, it is also possible to adjust the cooling start position SP. Specifically, when the cooling start position SP is to be raised, the cooling fluid CF is supplied from the supply source 32 into the adjustment tank 31 to increase the stored amount. Consequently, the height of the fluid surface in the cooling tank 11 , in other words, the cooling start position SP is raised.
  • the weir 33 When the cooling start position SP is to be lowered, the weir 33 is moved, in other words, the weir 33 is lowered and the cooling fluid CF inside the adjustment tank 31 overflows the weir 33 , and the cooling fluid CF is thereby discharged from the adjustment tank 31 . Consequently, the height of the fluid surface in the cooling tank 11 , in other words, the cooling start position SP is lowered.
  • the water-level adjustor 30 is not limited to having the configuration in FIG. 2 and may include a pump or the like that supplies and discharges the cooling fluid CF to/from the cooling tank 11 and may adjust the height of the fluid surface by immersing or removing an object of a volume that is determined at the time of design in/from the adjustment tank 31 .
  • a pump or the like that supplies and discharges the cooling fluid CF to/from the cooling tank 11 and may adjust the height of the fluid surface by immersing or removing an object of a volume that is determined at the time of design in/from the adjustment tank 31 .
  • the position control device 40 is formed by a hardware resource such as a computer and controls the height of the fluid surface of the cooling fluid CF inside the cooling tank 11 by controlling the water-level adjustor 30 .
  • the position control device 40 controls the operation of the water-level adjustor 30 to adjust the height of the fluid surface of the cooling fluid CF inside the cooling tank 11 such that the metal sheet S is restrained at a position RP at which the metal sheet S has a target temperature.
  • the target temperature is preferably set in the temperature range of (TMs+150) (° C.) to (TMf ⁇ 150) (° C.), where TMs(° C.) is a Ms temperature at which a martensitic transformation of the metal sheet S starts and TMf(° C.) is a Mf temperature at which the martensitic transformation ends. Consequently, the restraining rolls 20 can restrain a deformation of the metal sheet S at a position at which sudden thermal contraction and transformation expansion occur at the same time in the metal sheet S and can suppress the deformation of the metal sheet S at the time of quenching.
  • the position control device 40 calculates a distance d from the target cooling start position SP of cooling of the metal sheet S by the cooling fluid CF to the position RP at which the metal sheet S has the target temperature and adjusts the height of the fluid surface of the cooling fluid CF inside the cooling tank 11 on the basis of the calculated distance d. At this time, the position control device 40 calculates the distance d by using a line speed v (mm/s), a cooling start temperature T1 (° C.), and a target temperature T2(° C.) of the metal sheet S, and a cooling rate CV(° C./s) of cooling of the metal sheet S by the cooling device 10.
  • the cooling start temperature T1(° C.) denotes the temperature of the metal sheet S at the time when cooling of the metal sheet S is started, specifically, the temperature of the metal sheet S just before the cooling start position SP.
  • the temperature of the metal sheet S just before reaching the cooling start position SP can be calculated on the basis of a cooled state of the metal sheet S until reaching the cooling start position SP or the quenching apparatus 1 .
  • the temperature of the metal sheet S is measured at the exit side of a soaking zone of a continuous annealing furnace by a contactless thermometer.
  • the target temperature T2 denotes a target value of the temperature of the metal sheet S at the position RP at which the metal sheet S is restrained by the restraining rolls 20 .
  • the cooling rate CV(° C./s) can be expressed using a sheet thickness t of the metal sheet S and a coefficient ⁇ (°C. ⁇ mm/s), which indicates cooling conditions such as the shape of the nozzles or the type, the temperature, the jetting amount of the cooling fluid CF that is to be jetted, by Formula (2) below.
  • the cooling rate CV (° C./s) or ⁇ (° C. ⁇ mm/s) that is previously obtained through an experiment, a numerical analysis, and the like is stored. Then, the position control device 40 obtains the distance d by using Formula (1) or Formula (3) and adjusts the height of the fluid surface of the cooling fluid CF inside the cooling tank 11 such that the metal sheet S is restrained at a position corresponding to the obtained distance d.
  • the cooling rate CV may be set to 1500(° C./s), which is an intermediate value in the aforementioned range.
  • a may be treated as 1250(° C. ⁇ mm/s), which is an intermediate value.
  • cooling conditions ⁇ obtained by the above-described cooling rate CV, the sheet thickness t, and Formula (2) may be set.
  • the cooling rate CV is thus decreases.
  • the height of the fluid surface is preferably higher than a position at which the fluid jet stream from each of the nozzles 12 hits the metal sheet S.
  • the range of the height of the fluid surface from the nozzles 12 in other words, the distance between the fluid surface and the nozzles 12 is preferably, for example, more than or equal to 30 mm and less than or equal to 2000 mm.
  • the fluid surface fluctuates due to an influence of the fluid jet streams from the nozzles 12 . Specifically, a periodical vertical movement of the fluid surface is generated, which makes the cooling capacity with respect to the metal sheet S unstable. As a result, the temperature (restrain temperature) at a portion at which the metal sheet S is restrained by the restraining rolls 20 fluctuates, and there is a possibility of generation of a periodical shape variation in the metal sheet S.
  • the upper limit value of the aforementioned distance is preferably determined, as appropriate, on the basis of metallurgical characteristics of the metal sheet S, the line speed v, the cooling rate CV, and the like.
  • rapid cooling in a transformation temperature range is required in order to obtain desired metal characteristics by liquid quenching. Therefore, in consideration that the range of the line speed in a step of general quenching of a metal sheet is 10 m/min to 600 m/min, it is not preferable that the upper limit value be more than 2000 mm. This is because, when the upper limit value is more than 2000 mm, there is a high possibility that a sufficient cooling capacity with respect to the metal sheet S in the transformation temperature range is not obtained.
  • the distance between the fluid surface and the nozzles 12 be more than or equal to 30 mm and less than or equal to 2000 mm. Further, it is more preferable that the distance be more than or equal to 50 mm and less than or equal to 1000 mm in order to further stabilize the fluid surface and obtain an effective cooling rate.
  • the metal sheet S is cooled by the cooling device 10 while the metal sheet S is conveyed, and quenching of the metal sheet S is performed.
  • the height of the fluid surface of the cooling fluid CF inside the cooling tank 11 is adjusted such that the metal sheet S is restrained from two sides in the thickness direction of the metal sheet S at the position RP at which the metal sheet S has the target temperature T2.
  • the position control device 40 calculates the distance d by using Formula (1) or Formula (3) mentioned above and adjusts the height of the fluid surface of the cooling fluid CF inside the cooling tank 11 such that the metal sheet S is restrained at a position corresponding to the calculated distance d. Note that adjustment of the height of the fluid surface can be successively performed also during quenching of the metal sheet S. For example, the position control device 40 may calculate the distance d and adjust the height of the fluid surface at a timing when the line speed v is changed.
  • the line speed of the metal sheet S fluctuates even with respect to a single metal sheet S (in one coil). Therefore, it is more preferable, since a yield at portions such as a leading end and a tail end of the metal sheet S where the speed decreases can be improved, that the height of the fluid surface be movable with the metal sheet S being restrained by the restraining rolls 20 .
  • the position control device 40 may calculate the distance d and adjust the height of the fluid surface for every set period.
  • the operation of the water-level adjustor 30 is controlled to adjust the height of the fluid surface, which is the cooling start position SP, of the cooling fluid CF inside the cooling tank 11 . Consequently, it is possible to restrain the metal sheet S having the target temperature T2 by the restraining rolls 20 regardless of conditions of manufacture of the metal sheet S. As a result, it is possible to suppress shape defects of the metal sheet S generated due to conditions of manufacture of the metal sheet S during quenching in continuous annealing facilities.
  • the temperature of the metal sheet S conveyed to the quenching apparatus 1 varies depending on conditions of manufacture of the metal sheet S, for example, the line speed v, the cooling start temperature T1 of the metal sheet S, the sheet thickness t of the metal sheet S, and the like. Therefore, when the distance d is set to be constant regardless of conditions of manufacture, the temperature of the metal sheet S when the metal sheet S reaches the restraining rolls 20 also varies.
  • adjusting the height of the fluid surface of the cooling fluid CF inside the cooling tank 11 is effective to solve this problem, in other words, to accurately control the shape of the metal sheet S at an optimal temperature position that varies depending on conditions of manufacture. It is possible by adjusting the height of the fluid surface of the cooling fluid CF inside the cooling tank 11 to restrain the metal sheet S in an intended temperature range even when conditions of manufacture vary.
  • the deformation suppressing effect is increased in particular when the metal sheet S is a high strength steel sheet (high tensile strength steel sheet).
  • high tensile strength steel sheet a high strength steel sheet
  • application to manufacture of a steel sheet whose tensile strength is more than or equal to 580 MPa is preferable. While the upper limit of the tensile strength is not particularly limited, the tensile strength may be less than or equal to 2000 MPa in one example.
  • high strength steel sheet high tensile strength steel sheet
  • a high strength cold rolled steel sheet high strength cold rolled steel sheet
  • a hot-dip galvanized steel sheet an electro-galvanized steel sheet
  • a hot-dip galvannealed steel sheet and the like that are obtained by performing a surface treatment on high strength cold rolled steel sheets.
  • composition of the high strength steel sheet there is presented an example in which, in mass %, C is contained by more than or equal to 0.04% and less than or equal to 0.35%, Si is contained by more than or equal to 0.01% and less than or equal to 2.50%, Mn is contained by more than or equal to 0.80% and less than or equal to 3.70%, P is contained by more than or equal to 0.001% and less than or equal to 0.090%, S is contained by more than or equal to 0.0001% and less than or equal to 0.0050%, sol.Al is contained by more than or equal to 0.005% and less than or equal to 0.065%, at least one or more of Cr, Mo, Nb, V, Ni, Cu, and Ti are each contained, as necessary, by less than or equal to 0.5%, B and Sb are each further contained, as necessary, by less than or equal to 0.01%, and the remainder is constituted by Fe and incidental impurities.
  • the metal sheet is not limited to a steel sheet and may be a
  • the steel sheet As an example, quenching of a high tensile strength cold rolled steel sheet (hereinafter, referred to as the steel sheet) that is in a tensile strength class of 1470 MPa and that has the sheet thickness t of 1.0 mm and a sheet width of 1000 mm was performed by using the quenching apparatus 1 according to the aforementioned embodiment.
  • the composition of the steel sheet in the tensile strength class of 1470 MPa C is contained by 0.20%, Si is contained by 1.0%, Mn is contained by 2.3%, P is contained by 0.005%, and S is contained by 0.002% in mass %.
  • a temperature TMs which is the Ms temperature of the steel sheet, is 300° C.
  • a temperature TMf which is the Mf temperature thereof, is 250° C. Therefore, the target temperature T2 of the steel sheet at a time of passing the restraining rolls 20 may be simply set in the range of 450° C. to 100° C.
  • the target temperature T2 was set to 400° C.
  • the cooling start temperature T1 was set to 800° C.
  • the temperature of the cooling fluid CF was substantially 30° C.
  • the cooling rate CV was set to 1500(° C./s).
  • Ten steel sheets after being cooled were collected at every 100 m in the longitudinal direction (that is, the same direction as the conveyance direction of the steel sheets), and the warp amount of each of the steel sheets was checked.
  • FIG. 3 is a schematic diagram in which one example of the definition of the warp amount is illustrated. As illustrated in FIG. 3 , the warp amount was defined as a height from a ground contact surface to a highest position of a steel sheet when the steel sheet was placed on a horizontal surface.
  • FIG. 4 is a graph showing the relationship between the line speed v and the target temperature in the present example
  • FIG. 5 is a graph showing the relationship between the line speed v and the warp amount of a metal sheet in the present example.
  • the temperature (° C.) of each of the steel sheets at the time of passing the restraining rolls 20 was 400 ⁇ 25° C., even when the line speed v was varied, as a result of adjusting the height of the fluid surface of the cooling fluid CF in accordance with the line speed v and varying the distance d.
  • FIG. 6 is a graph showing the relationship between the line speed v and the target temperature in Comparative example 1
  • FIG. 7 is a graph showing the relationship between the line speed v and the warp amount of a metal sheet in Comparative example 1.
  • FIG. 8 is a graph showing the relationship between the line speed v and the target temperature in Comparative example 2
  • FIG. 9 is a graph showing the relationship between the line speed v and the warp amount of the metal sheet S in Comparative example 2.
  • the distance d was controlled by moving the movable masking member with the restraining rolls 20 being fixed and controlling the cooling start position.
  • Other conditions were set to be the same as those in the example of the disclosed embodiments, and the aforementioned steel sheet was manufactured.
  • the temperature (° C.) of the steel sheet at the time of passing the restraining rolls 20 greatly varied in Comparative example 2 regardless of the line speed v (mm/s) and was uncontrollable. Therefore, under all of conditions, there was a case in which the temperature (° C.) of the steel sheet at the time of passing the restraining rolls 20 was out of the range of 450° C. to 100° C., which is the target temperature T2. Then, as illustrated in FIG. 9 , under all of conditions, there was the steel sheet in which the warp amount of the steel sheet was more than 10 mm, and the effect of suppressing a deformation of the steel sheet was insufficient. As a result, a variation, which is a difference between the maximum value and a minimum value of the warp amount, was increased to 9.2 mm.
  • the disclosed embodiments are not limited to the aforementioned embodiment, and various changes can be added thereto.
  • the target temperature T2 is (TMs+150) (° C.) to (TMf ⁇ 150) (° C.) in the example presented in the aforementioned embodiment, the target temperature T2 is not limited thereto.
  • the target temperature T2 may be not limited to (TMs+150) (° C.) to (TMf ⁇ 150) (° C.) when absence of variations in the shape of the metal sheet S in terms of, for example, the warp amount and the like is simply required from the point of view of ensuring flexibility in processing and operation in subsequent steps.
  • the target temperature T2 is previously determined in consideration of a predicted shape (for example, the warp amount) while ensuring of flexibility in processing and operation in subsequent steps and the like are taken into consideration.
  • the distance d from the cooling start position to the restraining rolls 20 is controlled.
  • the temperature of the metal sheet S at the time of passing the restraining rolls 20 is caused to be the previously determined target temperature T2 so that variations in the shape of the metal sheet S, in other words, the warp amount of the metal sheet S defined in FIG. 3 is 4 mm or less.
  • the restraining rolls 20 may be configured to move in the longitudinal direction of the metal sheet S, in other words, the conveyance direction of the metal sheet S.
  • the quenching apparatus 1 for the metal sheet S may include a roll moving device that is constituted by, for example, a motor or the like and that moves the restraining rolls 20 .
  • the distance d is controlled by both the height of the fluid surface of the cooling fluid CF and the position of the restraining rolls 20 .
  • the distance d can be quickly adjusted by moving the restraining rolls 20 in the conveyance direction of the metal sheet S while the height of the fluid surface is raised.
  • the distance d can be minutely controlled by, for example, roughly adjusting the distance d by the water-level adjustor 30 and finely adjusting the distance d by the positional adjustment of the restraining rolls 20 .
  • Example 1 to 5 in each of which the distance between the fluid surface and the hitting position was more than or equal to 30 mm, a periodical warp fluctuation in the longitudinal direction of the steel sheet was not seen. In addition, a tendency in which the maximum warp amount in the width direction of the steel sheet collected at every 100 m decreased with increases in the aforementioned distance and the line speed v was seen. In other words, it was possible in Examples 1 to 5 to cause the cooling of the steel sheet in the initial stage to be slow cooling by setting the fluid surface height to be higher than the hitting position of the fluid jet stream from each of the nozzles by more than or equal to 30 mm. Consequently, it was possible to reduce a stress generated by sudden thermal contraction, possible to suppress the deformation of the shape of the steel sheet, and possible to reduce the warp amount of the steel sheet.

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AU530384B2 (en) * 1979-06-28 1983-07-14 Nippon Kokan Kabushiki Kaisha Controlled cooling of steel strip to effect continuous annealing
JPS5855533A (ja) * 1981-09-28 1983-04-01 Nippon Kokan Kk <Nkk> 有機酸によるストリツプの無酸化焼入方法
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