CN105934288B - Heat treatment method of AHSS hot-rolled coil, cold rolling method using same and heat treatment device - Google Patents

Heat treatment method of AHSS hot-rolled coil, cold rolling method using same and heat treatment device Download PDF

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Publication number
CN105934288B
CN105934288B CN201580004858.8A CN201580004858A CN105934288B CN 105934288 B CN105934288 B CN 105934288B CN 201580004858 A CN201580004858 A CN 201580004858A CN 105934288 B CN105934288 B CN 105934288B
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China
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hot
heat treatment
rolled
rolled coil
temperature
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CN201580004858.8A
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CN105934288A (en
Inventor
郑昌规
金亨田
刘智元
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Posco Holdings Co ltd
Posco Holdings Inc
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Posco Co Ltd
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Priority claimed from KR1020140175568A external-priority patent/KR101591792B1/en
Priority claimed from KR1020140177699A external-priority patent/KR101612760B1/en
Priority claimed from KR1020150080524A external-priority patent/KR101662559B1/en
Application filed by Posco Co Ltd filed Critical Posco Co Ltd
Publication of CN105934288A publication Critical patent/CN105934288A/en
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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
    • 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
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
    • 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
    • B21B45/0203—Cooling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES OR PROFILES, OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
    • B21C47/00—Winding-up, coiling or winding-off metal wire, metal band or other flexible metal material characterised by features relevant to metal processing only
    • B21C47/26—Special arrangements with regard to simultaneous or subsequent treatment of the material
    • 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
    • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
    • C21D1/767—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material with forced gas circulation; Reheating thereof
    • 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
    • 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 by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • 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
    • C21D9/0006—Details, accessories not peculiar to any of the following furnaces
    • 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
    • C21D9/0056—Furnaces through which the charge is moved in a horizontal straight path
    • 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
    • C21D9/562—Details
    • 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
    • C21D2221/00—Treating localised areas of an article
    • C21D2221/02—Edge parts
    • 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
    • C21D2221/00—Treating localised areas of an article
    • C21D2221/10—Differential treatment of inner with respect to outer regions, e.g. core and periphery, respectively

Abstract

Discloses a heat treatment method of an AHSS hot-rolled coil. The heat treatment method of the AHSS hot-rolled coil comprises the following steps: a hot-rolled coil generation step of hot-rolling and cooling a rolled material, and then rolling the material to prepare a hot-rolled coil; a first cooling step of cooling to a temperature at which phase transition is completed to generate a hard phase at an edge portion of the hot rolled coil; a hot-rolled coil edge strength weakening step of heating only an edge portion of the hot-rolled coil to a tempering temperature, and then holding at the tempering temperature for a predetermined time to perform a heat treatment so that the edge portion of the hot-rolled coil subjected to the first cooling step has a strength similar to that of a central portion of the hot-rolled coil; and a second cooling step of cooling the hot-rolled coil subjected to the step of weakening the edge strength of the hot-rolled coil.

Description

Heat treatment method of AHSS hot-rolled coil, cold rolling method using same and heat treatment device
Technical Field
The present invention relates to a hot-rolled coil heat treatment method and a heat treatment apparatus for performing heat treatment by heating a wound coil.
Background
A hot rolling process performed in a steel production process is a process in which a slab produced in a blast furnace or the like is reheated in a heating furnace to a temperature suitable for rolling, then rolled by a series of rolling devices such as a Roughing Mill (Roughing Mill) and a Finishing Mill (Finishing Mill) into a hot rolled steel sheet in the form of a strip (strip), cooled by a cooling facility, and then wound into a coil form by a winding machine. The rolled hot rolled sheet is stacked in a yard (yard) and cooled in air, and then transported to a cold rolling mill or shipped as a product.
In the air cooling process, material deviation occurs at the edge of the hot rolled coil and the inside of the hot rolled coil, which are in contact with the atmosphere, due to a difference in cooling rate, which causes a strip breakage or a strip deflection phenomenon in the cold rolling as a subsequent process, thereby causing a production failure.
On the other hand, the hot-rolled or cold-rolled steel strip is wound into a coil form for transportation and storage. In order to reduce material variation or obtain desired physical properties in the future, the rolled strip coils are often heated and heat-treated.
As a method of heating the strip, a batch method of accommodating a rolled strip in a heating facility and heating the rolled strip, and a continuous method of heating the rolled strip by a heating device while the rolled strip is being re-spread and transferred are known. Among them, the batch processing method can perform work in a rolled plate state, does not require equipment for unwinding and winding the rolled plate, and occupies a small space, and thus has an advantage that the equipment scale can be reduced as compared with the continuous method.
A typical batch-type rolled sheet heating apparatus includes a heating furnace for accommodating rolled sheets therein, a heating device for heating the inside of the heating furnace, a circulation fan for circulating hot air inside the heating furnace, and a rolled sheet saddle provided on the inner bottom surface of the heating furnace for stacking the rolled sheets.
In this rolled sheet heating apparatus, by the operation of the circulation fan, hot air inside the heating furnace circulates inside the heating furnace and heats rolled sheets stacked in the heating furnace. A typical rolling heating apparatus is in the form of a circulation fan that blows hot air downward from the upper portion of a heating furnace.
The circulated hot air flows downward from the air supply fan and heats one side surface of the coil to reach the bottom surface of the heating furnace, and the hot air changes direction and flows to the opposite side surface to heat and rise the opposite side surface of the coil. The whole body is in a circulating mode around the rolling plate. A part of the hot gas heats the hollow portion of the rolled sheet while flowing to the opposite side through the hollow portion of the rolled sheet (inside the rolled sheet).
However, in the case of this wrap heating apparatus, most of the hot gas flows outside the side surfaces and the outer peripheral surface of the wrap, and thus the hot gas flowing into the hollow portion of the wrap is relatively rare. In addition, the lower surface of the rolling plate is shielded by the rolling plate saddle, so that hot air cannot touch the rolling plate saddle. Therefore, it is difficult to uniformly heat the rolled sheet as a whole, and there is a limitation in obtaining a uniform heat treatment effect as a whole.
Disclosure of Invention
Technical problem to be solved
Embodiments of the present invention are directed to providing a heat treatment method capable of reducing material variation in a width direction of an Advanced High Strength Steel (AHSS) hot-rolled coil and a cold rolling method using the same.
Further, embodiments of the present invention are directed to providing a heat treatment apparatus capable of uniformly heating a rolled sheet as a whole to obtain a uniform heat treatment effect.
(II) technical scheme
According to an aspect of the present invention, there may be provided a heat treatment method of an AHSS hot-rolled coil, including: a heat treatment method of an AHSS hot-rolled coil comprises the following steps: a hot-rolled coil generation step of hot-rolling and cooling a rolled material, and then rolling the material to prepare a hot-rolled coil; a first cooling step of cooling to a temperature at which phase transition is completed to generate a hard phase at an edge portion of the hot-rolled coil; a hot-rolled coil edge strength weakening step of heating only an edge portion of the hot-rolled coil to a tempering temperature, holding the heated edge portion at the tempering temperature for a predetermined time, and performing a heat treatment so that the edge portion of the hot-rolled coil subjected to the first cooling step has a strength similar to a strength of a central portion of the hot-rolled coil; and a second cooling step of cooling the hot-rolled coil subjected to the hot-rolled coil edge strength weakening step.
In addition, in the hot rolled sheet edge strength weakening step, the tempering temperature includes 400 to 700 ℃.
In addition, in the hot rolled coil generating step, the temperature of the hot rolled coil that is completed to be wound includes 500 to 700 ℃.
In addition, in the first cooling step, the temperature at which the phase transition is completed includes a range of normal temperature to 400 ℃.
In addition, in the first cooling step, the width of the edge portion of the hot-rolled strip includes an 1/4 area with respect to the entire width of the hot-rolled strip.
The hot-rolled sheet has a tensile strength of 780MPa or more.
The heating in the hot-rolled strip edge strength weakening step includes rapid heating such that a region of 1/4 or more in the width direction of the hot-rolled strip with respect to the entire width of the hot-rolled strip from the edge of the hot-rolled strip reaches the tempering temperature.
In the hot-rolled strip edge strength weakening step, the predetermined time is set to a time range obtained by the following numerical expression:
the mathematical formula is as follows: x ═ temperature X (7.0+ log (time)), (temperature in degrees kelvin, time in minutes)
Wherein the temperature is the tempering temperature, and X is more than or equal to 7600 and less than or equal to 8600.
In addition, the second cooling step includes the steps of: cooling the edge portion of the hot-rolled sheet at a cooling rate of 3 ℃/min or more.
According to another aspect of the present invention, there is provided a cold rolling method for manufacturing a cold rolled steel sheet from an AHSS hot rolled coil having a tensile strength of 780MPa or more, first cooling an edge portion of the AHSS hot rolled coil, which is wound at a temperature of 500 to 700 ℃, to a temperature in a range of normal temperature to 400 ℃ to complete a phase transformation of the edge portion into a hard phase, reheating only the edge portion transformed into the hard phase by the phase transformation, holding the reheated edge portion at a temperature in a range of 400 to 700 ℃ for 30 to 480 minutes to weaken the edge portion, and performing cold rolling after secondarily cooling the AHSS hot rolled coil weakened in strength at a rate of 3 ℃/min or more.
According to still another aspect of the present invention, there is provided a heat treatment apparatus for heat-treating a hot-rolled coil, including a heat treatment furnace including: the heating chamber is used for a conveying vehicle for stacking and conveying the hot rolled coil to enter; a plurality of heating devices that are provided on a heat insulating wall surface forming the heating chamber and heat the hot-rolled coil; wherein the plurality of heating devices comprise: a first burner provided in the heating chamber for temperature control of the heating chamber; second burners provided on both side walls of the heating chamber for heating both side surfaces of the hot-rolled strip; and a hot air supply unit that supplies hot air into the rolled sheet of the hot-rolled sheet.
The hot air supply unit collects high-temperature exhaust gas discharged from the heating chamber and can inject the high-temperature exhaust gas into the rolled sheet of the hot-rolled sheet.
In addition, the first burner includes a flame burner, which may be disposed at a top wall of the heating chamber such that the sprayed flame does not directly contact the hot rolled coil.
Further, the second burner includes a radiant burner for heating both side surfaces of the hot rolled strip by radiant heat, and the radiant burner may be disposed on the side wall so as to face a side surface between a center and a lower end of the hot rolled strip.
In addition, the hot wind supply part includes: a nozzle that sprays hot air into the inside of the hot-rolled coil; a recovery duct connected to an exhaust duct for discharging high-temperature gas inside the heating chamber, and supplying exhaust gas flowing in the exhaust duct to the nozzle; a damper that regulates supply of exhaust gas from the exhaust duct to the recovery duct; and a blower that provides a blowing force for moving the exhaust gas flowing in the recovery duct to the nozzle side.
The heat treatment furnace may include a tunnel-shaped main body having a ceiling wall and two side walls, and having a front surface, a rear surface, and a lower portion that are open, the open lower portion may be closed by the transport vehicle when the transport vehicle enters the heating chamber, and the open front surface and the open rear surface may be closed by an opening/closing door provided in the heat treatment furnace.
Further, the heating chamber may have an insulating structure formed by insulating panels disposed on the top wall and the both side walls formed by the insulating wall surfaces and on the upper surface of the transport vehicle.
In addition, still include sealing device, when the transfer cart gets into heating chamber, to the both sides wall with the gap between the transfer cart seals.
In addition, the sealing device includes: a rotating arm rotatably coupled to a lower end side of the sidewall of the main body and including a heat insulating material for sealing the gap; a driving unit that drives the rotating arm such that the heat insulating material is movable between a first position where the heat insulating material seals the gap and a second position spaced apart from the gap.
Further, the control unit may control the plurality of heating devices such that the temperature in the heating chamber is maintained at a temperature higher than a target heating temperature of the hot rolled strip at an initial stage of heating of the hot rolled strip, and the temperature in the heating chamber is maintained at the target heating temperature after a predetermined time has elapsed.
The heat treatment furnace is provided with two transport carts which are provided on both sides of the heat treatment furnace so as to be movable back and forth along a rail, and the two transport carts can alternately enter the heating chamber and exit the heating chamber.
According to still another aspect of the present invention, there may be provided a heat treatment apparatus including: a heating furnace that accommodates and heats the rolled sheet; a circulating device for circulating hot gas inside the heating furnace; and a guide portion that guides a part of the hot gas flowing around the rolled sheet inside the heating furnace to a hollow portion of the roll.
The guide portion includes a guide plate extending from a side wall of the heating furnace facing a side surface of the roll toward the hollow portion of the roll.
In addition, the baffle includes a sloped baffle surface that is sloped with respect to the centerline of the roll to direct the flowing hot gas to the hollow of the roll.
The baffle may be formed such that a thickness of a coupling end coupled to the side wall of the heating furnace is larger than a thickness of a free end facing the hollow portion of the roll.
In addition, the width of the deflector toward the free end of the hollow portion of the rolled plate may be set to a size equal to or smaller than the diameter of the hollow portion of the rolled plate.
The minimum width of the coupling end of the baffle plate coupled to the side wall of the heating furnace may be set to a length equal to or greater than the diameter of the hollow portion of the wrap plate, and the maximum width may be set to a length equal to or less than the outer diameter of the wrap plate.
In addition, the guide parts may be respectively disposed at both side walls of the heating furnace opposite to both side surfaces of the coil.
In addition, the inclined guide surface may be provided in a curved surface form.
In addition, the flow guide portion further includes: a coupling member mounted to a sidewall of the heating furnace, for rotatably supporting a coupling end of the baffle for angle adjustment of the baffle; a support part supporting the baffle in an angularly adjustable state.
In addition, the flow guide portion further includes: a guide rail mounted on a side wall of the heating furnace; a coupling member movably mounted to the guide rail and supporting a coupling end of the baffle; a moving device that moves the coupling member.
Further, the circulating means is configured to blow hot gas from an upper portion of the heating furnace to a bottom surface of the heating furnace through a space between one side surface of the roll and the side wall of the heating furnace.
The baffle may be disposed at a height between the center of the wrap and the upper end of the hollow portion of the wrap when guiding the descending hot gas, and may be disposed at a height between the center of the wrap and the lower end of the hollow portion of the wrap when guiding the ascending hot gas via the lower portion of the wrap.
The heat exchanger further comprises a corner guide part which is arranged on the corner where the bottom surface of the heating furnace intersects with the side wall and is provided with a flow guide surface inclined relative to the bottom surface of the heating furnace for converting the flow direction of hot gas.
The heating furnace further includes a wrap supporting device disposed on a bottom surface side of the heating furnace, supporting a lower outer peripheral surface of the wrap, and having a plurality of ventilation flow paths formed in a plurality of directions for circulating hot air.
In addition, the rolled sheet supporting device includes: a plurality of support blocks which are arranged at intervals and have ventilation flow paths of which the side surfaces are communicated with the upper surface; and a plurality of partition members provided in a spaced state from each other on the upper surface of each support block, for partitioning the rolled sheet from the upper surface of the support block while supporting the rolled sheet.
According to still another aspect of the present invention, there may be provided a heat treatment apparatus including: a heating furnace that accommodates and heats the wound roll; a circulating device for circulating hot gas inside the heating furnace; and a wrap supporting device which is disposed on the bottom surface side of the heating furnace, supports the lower outer peripheral surface of the wrap, and has a plurality of ventilation flow paths formed in a plurality of directions for the circulation of hot air.
(III) advantageous effects
The embodiment of the invention reduces the material deviation of the AHSS hot-rolled coil in the width direction, thereby preventing the wrinkles and poor shapes caused by the material deviation in the cold rolling.
In addition, in the embodiment of the present invention, since only the edge portion of the AHSS hot-rolled sheet is heated, the internal oxidation due to reheating can be minimized, and the scale peelability can be ensured in the pickling process before the cold rolling.
In addition, with the heat treatment apparatus of the embodiment of the present invention, the guide portion guides a part of the hot gas flowing around the rolled sheet to the hollow portion of the rolled sheet, and thus it is possible to minimize a temperature deviation between the outside of the rolled sheet and the hollow portion in the process of heating the roll. Therefore, the rolled sheet is uniformly heated as a whole, and a uniform heat treatment effect can be obtained.
In the heat treatment apparatus according to the embodiment of the present invention, since the hot gas smoothly approaches the lower outer circumferential surface side of the wrap by the multi-directional ventilation flow paths formed in the wrap supporting device, it is possible to minimize the temperature deviation between the upper portion and the lower portion of the wrap and to achieve uniform heating as a whole.
In the heat treatment apparatus according to the embodiment of the present invention, the hot gas circulating inside the heating furnace is guided by the corner guide portion provided at the lower portion of the heating furnace, so that the flow velocity can be maintained and the direction can be switched, thereby achieving smooth circulation of the hot gas.
Drawings
Fig. 1 is a diagram showing a hot rolling process of an embodiment of the present invention.
Fig. 2 is a flowchart illustrating a heat treatment method of an embodiment of the present invention.
Fig. 3 is a graph showing temperature changes during heat treatment of an embodiment of the present invention.
FIG. 4 is a graph showing the strength of the hot rolled coil in the width direction before heat treatment according to the embodiment of the present invention.
Fig. 5 is a graph showing the strength after heat treatment at different heat treatment reheating starting temperatures of the example of the invention.
FIG. 6 is a graph showing the microstructure before different heat treatments, the heat treatment temperature, and the change in strength with time of the heat treatment in the example of the present invention.
FIG. 7 is a graph showing the combined variables of temperature and time of FIG. 6 for the x-axis.
Fig. 8 is a graph showing the presence or absence of the strength weakening effect by heat-treating the highest temperature according to an embodiment of the present invention.
FIG. 9 is a graph showing temperature changes at two points, an edge portion of a hot rolled coil and an inside of the hot rolled coil, during heat treatment according to an embodiment of the present invention.
Fig. 10 is a graph showing a widthwise temperature distribution of a hot rolled coil during heat treatment of an embodiment of the present invention.
Fig. 11 is a graph showing a comparison between the widthwise material deviation of a hot rolled coil subjected to a heat treatment according to an embodiment of the present invention and the conventional case.
Fig. 12 is a view schematically showing a heat treatment apparatus of a first embodiment of the present invention.
Fig. 13 is a view showing a state in which the transport vehicle of the first embodiment of the present invention enters the heat treatment furnace.
Fig. 14 is a diagram schematically showing a sealing device of the first embodiment of the present invention.
Fig. 15 is a sectional view showing the internal structure of the heat treatment furnace of the first embodiment of the present invention.
Fig. 16 is a diagram for explaining the arrangement structure of the radiation burner of the first embodiment of the present invention.
Fig. 17 is a diagram schematically showing a hot air supply portion of the first embodiment of the present invention.
Fig. 18 is a control block diagram showing temperature control for the heat treatment furnace of the first embodiment of the present invention.
Fig. 19 is a graph showing a two-step temperature control method in the heat treatment furnace of the first embodiment of the present invention.
Fig. 20 is a graph showing the temperature change of the hot-rolled sheet when two temperature modes are applied in the heat treatment furnace of the first embodiment of the present invention.
Fig. 21 is a view showing two transport carts arranged on both sides of a heat treatment furnace according to a first embodiment of the present invention.
Fig. 22 is a perspective view showing a heat treatment apparatus of a second embodiment of the present invention.
Fig. 23 is a sectional view taken along line ii-ii of fig. 22.
Fig. 24 is a perspective view showing a baffle of a baffle portion of a heat treatment apparatus of a second embodiment of the present invention.
Fig. 25 is a perspective view showing a corner guide of a heat treatment apparatus according to a second embodiment of the present invention.
Fig. 26 is a perspective view showing a modification of the corner deflector of the heat treatment apparatus according to the second embodiment of the present invention.
Fig. 27 is a perspective view showing a roll supporting device of a heat treatment apparatus of a second embodiment of the present invention.
Fig. 28 is a view showing a modification of the partition member attached to the support block of the heat treatment apparatus according to the second embodiment of the present invention.
Fig. 29 and 30 are diagrams showing modifications of the baffle portion of the heat treatment apparatus according to the second embodiment of the present invention.
Fig. 31 and 32 are views showing modifications of the flow guide portion of the heat treatment apparatus according to the second embodiment of the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The embodiments to be described below are provided as examples in order to enable those skilled in the art to fully convey the concept of the present invention. The present invention is not limited to the embodiments described below, and may be implemented in other forms. In order to clearly explain the present invention, portions irrelevant to the explanation are omitted in the drawings, and in the drawings, the width, length, thickness, and the like of the constituent members may be enlarged for convenience. Throughout the specification, the same reference numerals denote the same constituent elements.
Fig. 1 is a diagram illustrating a hot rolling process of an embodiment of the present invention, fig. 2 is a flowchart illustrating a heat treatment method of an embodiment of the present invention, and fig. 3 is a diagram illustrating a temperature change during the heat treatment of an embodiment of the present invention.
Referring to fig. 1 to 3, the cold rolling method of the embodiment of the present invention includes a hot rolled coil generating step S10, a first cooling step S20, a hot rolled coil edge strength weakening step S30, a second cooling step S40, and a cold rolling step S50.
The hot-rolled-sheet generation step S10 is a step of rolling the slab S1 to produce an Advanced High Strength Steel (AHSS) hot-rolled sheet 20 having a tensile Strength of 780MPa or more, which is finally wound in a rolled sheet form. Specifically, the slab S1 is heated to a temperature suitable for rolling in the heating furnace 10, the slab S1 heated in the heating furnace 10 is subjected to width rolling and thickness rolling in the roughing mill 11 composed of 3 to 4 stands to produce a strip S2, and then the strip S3 having a desired thickness can be rolled into a strip S3 having a desired thickness by final thickness rolling in the finishing mill 12 composed of 6 to 7 stands. Then, the strip S3 is cooled to a predetermined temperature while passing through the cooling process 13 and then supplied to the coiler 14, and the cooled strip S3 may be coiled in the coiler 14 to produce a hot rolled coil 20. The slab S1, the strip S2, and the strip S3 are hereinafter referred to as a rolled material S, and the rolled material S includes a Dual-Phase steel (DP steel) having a tensile strength of 780MPa or more and a transformation induced Plasticity (TRIP steel) as a high-strength hot-rolled steel sheet (AHSS). In addition, the temperature T1 of the hot rolled coil 20 at the time point of winding by the winder 14 after hot rolling may have a range of 500 to 700 ℃.
The first cooling step S20 is a step of maintaining a sufficient cooling rate and cooling to a temperature at which the phase transformation is completed so as to generate hard phases (martensite and bainite) at the edge portion of the hot rolled coil 20 wound by means of the winder 14.
In the first cooling step S20, the temperature at which the phase transition is completed corresponds to the heat treatment reheating starting temperature T2 in fig. 3, and may include a range of normal temperature to 400 ℃. The temperature at which the phase transition is completed will be described with reference to fig. 4 and 5. FIG. 4 is a graph showing the strength of the hot rolled coil in the width direction before heat treatment according to the embodiment of the present invention. Fig. 5 is a graph showing the post-heat treatment strength at different heat treatment reheating starting temperatures of the examples of the present invention. As shown in fig. 5, when the reheating starting temperature is 400 ℃ or lower, the strength after the heat treatment is weakened as compared with the strength of the hot-rolled coil before the heat treatment in fig. 4, but when it is 400 ℃ or higher, the strength is not greatly weakened. This is because, if the reheating start temperature is 400 ℃ or higher, the phase transformation is not completely achieved, and therefore, the hard phase is newly generated in the second cooling step S40 after reheating as in the hot rolled coil generation step S10. Therefore, it is preferable to cool to a temperature of 400 ℃ or less at which the phase transformation is completed at the edge portion of the hot-rolled coil 20 in the first cooling step S20. In the first cooling step S20, the steel sheet may be cooled to a temperature at which the phase change is completed by using a temperature difference between the normal temperature and the hot rolled sheet in a state of being stacked on the ground of a factory yard or a sheet storage.
The hot-rolled-strip edge strength weakening step S30 is a step of heating the hard phase at the edge portion of the hot-rolled strip 20 generated in the first cooling step S20 to a tempering temperature T3, and then maintaining the temperature at the tempering temperature T3 for a predetermined time to perform a heat treatment so that the edge portion of the hot-rolled strip 20 has a strength similar to the strength of the central portion of the hot-rolled strip 20.
Specifically, the hot rolled sheet edge strength weakening step S30 may include: a heating step S31 of heating only the edge portion of the hot rolled coil 20 to a tempering temperature T3 (e.g., 400 to 700 ℃); the temperature maintaining step S32 maintains the tempering temperature T3 for a predetermined time required for the tempering effect to be exhibited.
In the heating step S31, heating may be performed so that a region of 1/4 or more (a boundary exhibiting high strength due to the hard phase shown in fig. 4) from the edge of the hot rolled coil 20 toward the width direction of the hot rolled coil 20 with respect to the entire width of the hot rolled coil 20 reaches the tempering temperature T3.
In the temperature maintaining step S32, after the edge portion (e.g., 1/4 region with respect to the entire width) of the hot rolled coil 20 reaches the tempering temperature T3, the hot rolled coil 20 is softened by being maintained at the tempering temperature T3 for a predetermined time such that the edge portion of the hot rolled coil 20 has a strength similar to that of the central portion of the hot rolled coil 20.
The relationship between the tempering temperature T3 and the holding time of the tempering temperature T3 will be described with reference to fig. 6 to 8. Fig. 6 is a graph showing changes in strength of the microstructure before the heat treatment, the heat treatment temperature, and the heat treatment time in the example of the present invention, fig. 7 is a graph showing a combination variable of the temperature and the time in fig. 6 by using the x-axis, and fig. 8 is a graph showing the presence or absence of the strength weakening effect according to the maximum heat treatment temperature in the example of the present invention.
First, referring to fig. 6, the microstructure before heat treatment is classified into three types, F + M (ferrite + martensite), F + P (ferrite + pearlite), and As-R (ferrite + pearlite, 1/4 width position of the rolled sheet that is air-cooled after rolling), where F + M belongs to the structure of the edge of the rolled sheet, As-R belongs to the structure of the central portion of the rolled sheet, and F + P belongs to the structure between the edge and the central portion of the rolled sheet. In both cases, F + M and F + P, the strength weakening effect is not large regardless of the time when the heat treatment temperature is 400 ℃. Conversely, it is found that the strength is greatly reduced in a short time as the heat treatment temperature is kept higher.
Referring to fig. 7, fig. 7 is a graph showing the combined variables of temperature and time of fig. 6 for the x-axis, and temperature-time-intensity data for a specific microstructure form a line. The combined temperature and time variable is defined as X (Hollomon-Jaffe parameter) as follows.
Mathematical formula 1: x ═ temperature X (7.0+ log (time)), (temperature Kelvin) temperature, time in minutes)
However, the intensity values of the respective microstructures are different from each other, but converge to the same intensity value as the X value increases. Since the material variation in the width direction of the rolled sheet is eliminated if the intensity value is equal to the intensity of the initial As-R structure, the ranges of the heat treatment temperature and the heat treatment time can be found based on the X value at that time. However, as shown in fig. 8, if the heat treatment temperature reaches 700 ℃ or more, cementite is decomposed into austenite, and then in the cooling process, a hard phase is regenerated, and thus, the heat treatment effect disappears. Therefore, the heat treatment temperature should be selected to be 700 ℃ or lower. Therefore, the tempering temperature T3 may have a value in the range of 400 ℃ to 700 ℃. In addition, in FIG. 7, the holding time at the tempering temperature T3 (e.g., 600 ℃) as a temperature corresponding to a portion (shaded portion) where the strengths of the edge portion and the center portion of the hot rolled coil 20 become the same belongs to the interval 7600. ltoreq.X.ltoreq.8600, and if it is substituted into the numerical expression 1, it is 7600. ltoreq.873 (7.0+ log (time)). ltoreq.8600, and the heat treatment holding time may have a value of 55.8 minutes. ltoreq.time. ltoreq. 709.7 minutes. Wherein, when the holding time is less than about 56 minutes, the heat treatment effect is not large, and when more than 710 minutes, the strength of the edge portion of the hot rolled coil 20 is excessively weakened, thereby being weaker than that of the central portion of the hot rolled coil 20.
On the other hand, in the heating step S31, only the edge portion of the hot rolled strip 20, which needs to be weakened in strength, may be rapidly heated to reach the tempering temperature T3, so that the internal oxidation of the hot rolled strip 20 caused by reheating can be minimized. Specifically, fig. 9 is a graph showing temperature changes at two points, i.e., an edge portion (r) and an inner portion (r) of the hot rolled coil 20 during the heat treatment, in which the temperature of the edge portion of the hot rolled coil 20 rapidly rises to an upper limit temperature (700 ℃) because the hot rolled coil 20 is heated from the outside during the heat treatment, and the inner portion of the hot rolled coil 20 is slowly heated. At this time, the heat treatment was started at each widthwise position from the time point when the temperature passed the lower limit temperature (400 ℃). If it is displayed as the widthwise temperature distribution of the hot rolled coil 20, it is as shown in FIG. 10. Wherein the heat treatment region is between (i) and (ii), and the temperature in the region should be kept between the upper limit and the lower limit. The second position is a boundary point showing high strength due to the hard phase, and if the graph of FIG. 4 is taken as a reference, the distance between the first and second positions should have a value equal to or greater than 1/4 of the width of the hot rolled strip 20. The heat treatment time, which is the time during which the region between (i) and (ii) of the hot rolled coil is maintained between the upper limit and the lower limit of the heat treatment temperature shown in fig. 9, is from the start of the heat treatment to the completion of the heat treatment, and the entire in-furnace time includes the time of starting the temperature rise, and thus is longer than the actual heat treatment time, and means from the start of heating to the completion of the heat treatment. Therefore, the rapid heating is performed to shorten the time from the heating start time to the tempering temperature T3, which is more advantageous in suppressing the internal oxidation of the hot rolled coil 20.
The second cooling step S40 is a step of cooling the hot-rolled strip 20, whose structure is softened, to normal temperature through the hot-rolled strip edge strength weakening step S30. At this time, the hot rolled coil 20 is in a state in which the structure is softened, and therefore, re-hardening by the cooling rate does not occur, but the edge portion of the hot rolled coil 20 may be cooled at the cooling rate of 3 ℃/min or more in order to minimize the influence of internal oxidation by the heat treatment.
[ examples ]
Fig. 11 is a graph comparing and displaying a widthwise material deviation of a hot rolled coil heat-treated according to an embodiment of the present invention with a conventional case. The hot rolled coil 20 was high tensile 980DP with dimensions of 2150mm outer diameter, 762mm inner diameter and 1200mm width. The heat treatment conditions used were such that after rolling, the steel sheet was cooled at room temperature for 48 hours or more, then reheated, and then held at 550 ℃ for 4 hours, followed by rapid cooling treatment. In the air-cooled material which has not been subjected to any treatment after rolling, the material deviation between the edge portion and the central portion is about 250MPa or more, and when a conventional annealing box (box) is used, the material deviation in the width direction is reduced to 150MPa or less. Further, it was confirmed that, in the case of applying the present invention, since the material softening of the large edge portion occurs, the material variation in the width direction can be reduced to 50MPa or less.
The heat treatment apparatus according to the first embodiment of the present invention will be explained below.
Fig. 12 is a view schematically showing a heat treatment apparatus according to a first embodiment of the present invention, and fig. 13 is a view showing a state in which a transport vehicle according to the first embodiment of the present invention enters a heat treatment furnace.
Referring to fig. 12, the heat treatment apparatus 30 of the first embodiment of the present invention roughly includes a transport cart 40 and a heat treatment furnace 50.
The transport cart 40 may be used to cool the hot rolled strip 20 in the first cooling step S20 while stacking and transporting the hot rolled strip 20 generated in the hot rolled strip generating step S10.
The transport vehicle 40 may include a flat-plate-shaped transport vehicle body 43 to which wheels 42 that move along rails 41 installed in a factory are attached. The carriage body 43 is movable forward and backward along the rails 41 by means of wheels 42, and the wheels 42 are rotatable forward and backward by means of a drive unit not shown in the figure.
The carriage main body 43 is made of steel or steel alloy having high strength for stable support of the hot rolled coil 20, and a heat insulating panel 44 made of refractory material may be disposed on the upper surface of the carriage main body 43 for heat insulation.
Further, a plurality of saddles 45 may be disposed on the upper surface of the heat insulating panel 44 at predetermined intervals in the longitudinal direction to support the hot rolled sheet 20.
The plurality of hot rolled strips 20 may be cooled before entering the heat treatment furnace 50 in a state of being supported by the plurality of saddles 45, respectively.
The transfer cart 40 on which the plurality of hot rolled coils 20 are mounted can enter the interior of the heat treatment furnace 50 by moving along the rails 41. At this time, the heat insulation panel 44 of the transfer cart 40 may form a heat insulation structure at the lower portion of the heat treatment furnace 50. For this reason, the transport cart 40 may be provided to have a width slightly smaller than the width of the heat treatment furnace 50, and the length of the transport cart 40 may be provided to be slightly longer than the length of the heat treatment furnace 50.
The carriage 40 is configured to perform the first cooling while supporting the plurality of hot rolled strips 20 on the saddle 45, and after the first cooling is completed, to move along the rail 41 and insert the heat treated furnace 50 into the heat treatment furnace, thereby forming a part of the heat insulating structure of the heat treated furnace 50. Therefore, the work of loading and unloading the plurality of hot rolled coils 20 onto and from the transport vehicle 40 for the heat treatment work can be omitted, and the waiting time of the hot rolled coils 20 required for the heat treatment work can be significantly shortened.
The heat treatment furnace 50 may be provided in the form of a tunnel having a size capable of accommodating the transport vehicle 40. The heat treatment furnace 50 includes a box-shaped main body 51 having an open front, rear, and lower portion, and a heating chamber 60 for heating the hot rolled strip 20 is formed inside the main body 51 when the transfer cart 40 enters.
When the transport cart 40 is inserted into the heat treatment furnace 50, the opened lower portion of the main body 51 is closed by the transport cart 40, and the opened front and rear surfaces of the main body 51 are respectively closed by the opening and closing door 55 slidably attached to the main body 51 in the up-down direction.
Therefore, as shown in fig. 12 and 13, the heating chamber 60 forms a sealed heat insulating space by the top wall 52 of the main body 51, the two side walls 53 and 54 extending downward from the two ends of the top wall 52, the heat insulating panel 44 of the carriage 40 closing the open lower portion of the main body 51, and the opening/closing door 55 closing the open front and rear surfaces of the main body 51.
Specifically, when the opening/closing doors 55 close the front and rear sides of the opening of the main body 51, the lower ends of the opening/closing doors 55 contact the heat insulation panels 44 of the transport vehicle 40 to seal the front and rear sides of the opening of the main body 51, and when the transport vehicle 40 enters the heating chamber 60, the heat insulation panels 44 of the transport vehicle 40 seal the lower part of the main body 51, thereby forming the sealed heating chamber 60 in the heat treatment furnace 50.
The wall surface of the heating chamber 60 formed by the opening/closing door 55, the main body 51, and the transport cart 40 may be formed of a heat insulating wall surface for storing heat inside. That is, the top wall 52 and the side walls 53 and 54 are provided with a refractory material inside the sheet metal forming the external appearance, and the refractory material is attached to the inside of the opening/closing door 55, so that the heating chamber 60 can constitute an insulating structure together with the insulating panel 44 of the transport vehicle 40.
At this time, a predetermined gap may occur between the transport cart 40 and the side walls 53 and 54, and a sealing device 70 may be attached to one side of the main body 51 in order to seal the gap.
Fig. 14 is a diagram schematically showing a sealing device of the first embodiment of the present invention.
Referring to fig. 14, the sealing devices 70 are respectively attached to the lower ends of the two side walls of the main body 51, and are disposed in a plurality of spaced positions along the longitudinal direction of the main body 51 so as to seal the gap t formed between the transport vehicle 40 and the two side walls 53 and 54. The sealing device 70 mounted to one side wall 53 of the body 51 will be explained.
Such a sealing device 70 comprises: a rotating arm 71 rotatably coupled to a lower end side of the sidewall 53 of the main body 51; a driving unit 72 that rotationally drives the rotating arm 71; and a heat insulating material 74 disposed at an end of the rotating arm 71 and movable along a rotating direction of the rotating arm 71 between a first position where the gap t is sealed and a second position where the gap t is spaced apart.
The driving unit 72 may include an electric, electronic, hydraulic, or pneumatic cylinder having a cylinder rod 73 that moves forward and backward, and the cylinder rod 73 may be connected to the rotating arm 71 with a link member 75 as a medium.
The pivot arm 71 may be rotatably provided around a pivot shaft at a lower end of the side wall 53 of the main body 51, and may have one side coupled to the link member 75 by a hinge and the other side provided with a heat insulating material 74 extending a predetermined length in a longitudinal direction of the main body 51. The heat insulating material 74 is detachably coupled to the other side of the rotating arm 71 so that replacement required for maintenance can be performed.
With this configuration, when the cart 40 enters the heating chamber 60, the gap t formed between the cart 40 and the side wall 53 can be sealed by the heat insulating material 74 attached to the end portion of the rotating arm 71 rotated by the driving unit 72, and therefore, it is possible to prevent the exhaust gas or heat in the heating chamber 60 from leaking to the outside through the gap t.
Inside the heat treatment furnace 50, a plurality of heating devices 80 are provided, and the plurality of heating devices 80 are used for heat treating the edge portions of the plurality of hot rolled strips 20 stacked on the transport vehicle 40 after the open portion of the main body 51 is sealed by the open/close door 55, the transport vehicle 40, and the sealing device 70.
Fig. 15 is a sectional view showing the internal structure of a heat treatment furnace according to a first embodiment of the present invention, and fig. 16 is a view for explaining the arrangement structure of a radiation burner according to the first embodiment of the present invention.
Referring to fig. 15 and 16, a plurality of heating devices 80 according to a first embodiment of the present invention includes: a first burner 81 for heating the air inside the heating chamber 60 for temperature control inside the heating chamber 60; a second burner 82 for heating both side surfaces of the hot rolled strip 20 arranged inside the heating chamber 60; and a hot air supply unit 90 for heating the coil interior 21 of the hot rolled coil 20 arranged in the heating chamber 60.
The first Burner 81 may be constituted by a High Speed Flame Burner (High Speed Flame Burner) that burns fuel and rapidly heats air inside the heating chamber 60 by means of Flame.
The first burner 81 may be attached to the top wall 52, installed to emit a flame in a vertical direction, and may be disposed at a position spaced apart from both side surfaces of the hot rolled strip 20 by a predetermined distance (for example, 500mm or more) so that the emitted flame does not directly contact the hot rolled strip 20. This is to prevent the hot rolled strip 20 from becoming uneven due to a local temperature increase when the flame discharged from the first burner 81 directly contacts the hot rolled strip 20.
The second Burner 82 is used to rapidly heat the edge portions of the both side surfaces of the hot rolled coil 20, and may be constituted by a Flat Flame Burner (Flat Flame Burner) that burns fuel on a Flat porous heat generating surface and heats the both side surfaces of the hot rolled coil 20 by the radiant heat.
The second burners 82 may be disposed on both side walls 53 and 54 respectively opposed to both side surfaces of the hot rolled coil 20 disposed in the heating chamber 60, and since the discharge pressure of the combustion gas is not large due to the structure of the radiation burners, two or more sides spaced apart from each other on the left and right sides may be provided on the side wall 53 so as to face the side surface between the center and the lower end of the hot rolled coil 20 with respect to the side surface of one hot rolled coil 20, as shown in fig. 14, in order to heat the hot rolled coil 20 at a uniform temperature in the circumferential direction of the hot rolled coil 20, in consideration of the difference in the vertical temperature of the second burners 82.
The hot air supply portion 90 heats the coil interior 21 of the hot rolled coil 20 having a slow heating rate while the hot rolled coil 20 is heated by the high-temperature gas in the heating chamber 60. That is, the inside 21 of the hot rolled strip 20 is a portion having a long distance from the flames of the first and second burners 81 and 82 and a weak flow of the combustion gas, and thus the heating rate is relatively slower than that of the other portions of the hot rolled strip 20. Therefore, as the hot air supply portion 90 injects hot air to the coil interior 21 of the hot rolled coil 20, temperature deviation occurring in the coil interior 21 of the hot rolled coil 20 can be reduced.
Fig. 17 is a diagram schematically showing a hot air supply portion of the first embodiment of the present invention.
Referring to fig. 17, the hot wind supply part 90 according to the first embodiment of the present invention may be provided in such a manner as to be resupplied to the coil interior 21 side of the hot rolled coil 20 by recovering high-temperature exhaust gas discharged from the heating chamber 60.
For this, the hot wind supply part 90 may include: a nozzle 91 attached to the side walls 53 and 54 so as to face the coil interior 21 of the hot-rolled coil 20 disposed in the heating chamber 60; a recovery duct 92 connected to the exhaust duct 59 through which the high-temperature gas inside the heating chamber 60 is discharged, and supplying the exhaust gas flowing through the exhaust duct 59 to the nozzle 91; a damper 93 that regulates the supply of exhaust gas from the exhaust duct 59 to the recovery duct 92; and a blower 94 for supplying a blowing force for moving the exhaust gas flowing through the recovery duct 92 to the nozzle 91.
With this configuration, the combustion gas generated by the first and second burners 81 and 82 first heats both side surfaces of the hot rolled strip 20 and the outside of the strip, and then is discharged to the outside through the exhaust duct 59. At this time, the temperature of the exhaust gas discharged through the exhaust duct 59 is high, about 700 to 800 degrees. At this time, the hot air supply unit 90 adjusts the opening degree of the damper 93, causes the exhaust gas flowing through the exhaust duct 59 to flow into the recovery duct 92, and then re-sprays the exhaust gas into the coil interior 21 of the hot rolled coil 20 through the nozzle 91, thereby rapidly heating the coil interior 21 of the hot rolled coil 20 having a relatively slow heating rate.
Next, a heat treatment method using the heat treatment apparatus according to the first embodiment of the present invention will be described.
First, as shown in fig. 12, the hot rolled strip 20 produced in the hot rolled strip producing step S10 is transported and stacked on the saddle 45 of the transport vehicle 40.
The hot rolled coils 20 stacked on the carriage 40 are air-cooled while maintaining a sufficient cooling rate until hard phases are formed at the edges of both side surfaces.
Then, the transport cart 40 moves along the rail 41 and enters the inside of the heat treatment furnace 50.
After the transport cart 40 enters the heat treatment furnace 50, the opening/closing door 55 attached to the main body 51 is closed, and the sealing device 70 closes the gap t between the transport cart 40 and the side walls 53 and 54, so that the heat treatment operation is performed in a state where the heating chamber 60 is sealed.
In this case, the hot rolled sheet 20 conveyed by the conveyor 40 does not need to be moved again for the heat treatment work, and therefore the heat treatment work time is shortened. In addition, as shown in fig. 21, in the case where two or more transport carts 40 are provided, while one transport cart 40 enters the heat treatment furnace 50 to perform the heat treatment of the hot rolled strip 20, after the other transport cart 40 performs the first cooling process in a state where the hot rolled strip 20 is loaded and waits, when the heat treatment is completed in the heat treatment furnace 50 and one transport cart 40 is drawn out, the other transport cart 40 may immediately enter the heat treatment furnace 50, so that the operation rate of the heat treatment furnace 50 can be improved. That is, the two transport vehicles 40 and 40a are respectively provided to be movable back and forth along the rails 41 on both sides of the heat treatment furnace 50, and while one transport vehicle 40 passes through the open front of the heat treatment furnace 50 and is loaded into the interior of the heat treatment furnace 50 for heat treatment, the other transport vehicle 40a waits outside the heat treatment furnace 50, and when one transport vehicle 40 completes the heat treatment and is drawn out through the open front of the heat treatment furnace 50, the other transport vehicle 40a is drawn into the interior of the heat treatment furnace 50 through the open rear of the heat treatment furnace 50.
After the heating chamber 60 is sealed, the heat treatment work of the hot rolled strip 20 is performed while the temperature control of the heating chamber 60 is performed by the plurality of heating devices 80.
At this time, as shown in fig. 18, the temperature control of the heating chamber 60 required for the heat treatment of the hot rolled strip 20 can be realized by the control section 100 that controls the plurality of heating devices 80 based on the temperature detected by the temperature sensor 98 that detects the internal temperature of the heating chamber 60.
The control unit 100 may appropriately set the temperature of the heating chamber 60 in consideration of different initial temperatures according to the type of the hot rolled strip 20.
As shown in fig. 19, when reheating the hot rolled coil 20, the control unit 100 drives the plurality of heating devices 80 for the first time in the initial stage of heating to rapidly raise the temperature of the heating chamber 60 so that the temperature in the heating chamber 60 is maintained at a temperature higher than the upper limit temperature (target heating temperature) for the heat treatment of the hot rolled coil 20, and drives the plurality of heating devices 80 for the second time so that the surface temperature of the hot rolled coil 20 does not exceed the target heating temperature after a predetermined time has elapsed and the temperature in the heating chamber 60 is lowered to the upper limit temperature and then maintained at the predetermined temperature, thereby shortening the heat treatment time.
Fig. 20 is a graph showing temperature changes at 300mm of the surface and edge portions of the hot-rolled strip when temperature control in the heating chamber is implemented in the present invention.
In fig. 20, for the case where the condition of holding the heating chamber temperature at 700 ℃ for a given time and the case where the initial temperature is held at 900 ℃ for 1 hour 30 minutes, then lowered to 700 ℃ and held during the heat treatment time, the heat treatment times in the two cases are 9.5 hours and 11.5 hours, respectively, when compared with the time of reaching 550 ℃ at 300mm of the edge portion, there is an effect that the heat treatment time can be shortened by about 2 hours when the temperature control of the heating chamber 60 of the first embodiment of the present invention is performed.
On the other hand, during the heat treatment work of the hot rolled coil 20 performed in the heating chamber 60, both side edge portions of the cooled hot rolled coil 20 and the coil interior 21 can be rapidly heated by the plurality of heating devices 80, which has an energy saving effect due to the use of high-temperature exhaust gas discharged from the heating chamber 60.
When the heat treatment operation is completed in the heating chamber 60, the transport vehicle 40 moves along the rails 41 and is drawn out of the heat treatment furnace 50, and then the second cooling step of the plurality of hot rolled strips 20 stacked on the transport vehicle 40 is performed.
The heat treatment apparatus according to the second embodiment of the present invention will be explained.
As shown in fig. 22 and 23, a heat treatment apparatus according to a second embodiment of the present invention includes: a heating furnace 110 that accommodates a rolled sheet 120; a heating device 130 that heats the inside of the heating furnace 110; a circulation device 140 for circulating hot gas inside the heating furnace 110; a roll supporting device 150 installed on the bottom surface side of the heating furnace 110; and a guide portion 170 guiding a part of the circulated hot gas to the hollow portion 122 of the rolled sheet 120.
The wall of the heating furnace 110 may be made of a sheet iron 110a and a refractory 110b, and a hexahedral structure having a heating space 111 for accommodating the rolled sheet 120 formed therein. Although not shown in the drawings, the heating furnace 110 may have openings formed in the side walls (113, 114) or the top wall 111, and the openings may be opened and closed by doors or covers, in order to allow the rolled sheet 120 to enter the heating space 111 or to discharge the rolled sheet 120 from the heating space 111.
The rolled sheet 120 housed in the heating furnace 110 can be placed with its outer peripheral surface 121 on a rolled sheet supporting device 150 disposed at the central portion of the heating furnace bottom surface 112, and with both side surfaces 123, 124 disposed so as to face the side walls 113, 114 of the heating furnace 110. The open ends of the hollow portion 122 of the rolled sheet 120 face the side walls 113 and 114 of the heating furnace 110, respectively.
As an example shown in fig. 22, the heating device 130 may include a burner that injects a flame into the inside of the heating space 111 to heat the heating space 111 to a temperature required for heat treatment of the rolled sheet 120. The heating device 130 may be installed in a plurality of positions on the top wall 111 or the side walls 113 and 114 of the heating furnace 110 for uniform heating of the heating space 111, but the installation position, the number of installation positions, and the like are not limited to the embodiments.
As shown in fig. 23, the circulation device 140 may include: a blowing fan 141 installed at an upper portion of the heating space 111 adjacent to one side wall to blow the hot air downward; and a driving motor 142 installed at an upper portion of the heating furnace 110 to drive the blowing fan 141.
The circulation device 140 blows hot gas from the upper portion of the heating furnace 110 toward the bottom surface 112 of the heating furnace 110 through a space between the one side surface 123 of the rolled sheet 120 and the side wall 113 of the heating furnace 110. Therefore, the blown hot gas descends from the circulation device 140, heats the one side surface 123 of the wrap 120, reaches the bottom surface of the heating furnace 110, changes its direction, and then flows to the opposite surface through the lower portion of the wrap 120. Then, the hot gas rises again to heat the opposite side 124 of the wrap 120. Here, as an example, the circulation device 140 is installed on the ceiling wall 111 of the heating furnace 110, but the installation position and the number of the circulation devices 140 may be changed, and thus the flow and circulation direction of the hot gas may be changed.
The guide parts 170 are respectively installed at both side walls 113 and 14 of the heating furnace 110, and guide a part of the hot gas flowing around the rolled sheet 120 to the hollow part 122 of the rolled sheet 120, so that the hollow part 122 can be smoothly heated.
As shown in fig. 23 and 24, the flow guide portions 170 on both sides of the heating furnace 110 include flow guide plates 471 extending from the heating furnace side walls 113 and 114 facing the side surfaces 123 and 124 of the rolled sheet 120 toward the hollow portion 122 of the rolled sheet 120.
The baffle 471 includes inclined baffle surfaces 271a and 271b disposed opposite to the flow direction of the hot gas flowing by the operation of the circulation device 140. The inclined guide surfaces 271a and 271b are inclined at a predetermined angle with respect to the center line 125 of the wrap 120, and guide the flowing hot gas to the hollow portion 122 of the wrap 120.
The deflector 471 is formed such that the thickness of the coupling end 271c coupled to the side walls 113 and 114 of the heating furnace 110 is larger than the thickness of the free end 371d of the hollow portion 122 facing the rolled sheet 120 (wedge shape). Therefore, the inclined guide surfaces 271a, 271b are naturally formed on the upper and lower surfaces thereof. In this mode, the bending stress increases toward the coupling end 271c, and thus the free end 371d can be prevented from sagging.
As shown in fig. 23, the hot gas descending from the circulation device 140 is guided by the upper inclined guide surface 171a of the guide plate 171 (right guide plate in the figure) joined to the one side wall 113, and is partially naturally bent toward the roll bending hollow portion 122 side, so that the hot gas can enter the hollow portion 122 of the roll bending 120. The hot gas rising on the opposite side after passing through the lower portion of the wrap 120 is guided by the lower inclined guide surface 171b of the guide plate 171 (left guide plate in the figure) coupled to the side wall 114 on the opposite side, and a part of the hot gas naturally bends and enters the hollow portion 122 of the wrap 120. Thus, the hot air flowing from both sides of the rolling hollow portion 122 to the inside of the hollow portion 122 forms a flow field rotating in the hollow portion 122, thereby improving the heating effect of the rolling hollow portion 122.
In the present embodiment, the inclined guide surfaces 271a and 271b of the guide plates 471 on both sides are arranged to face the upper and lower portions of the heating furnace 110 in order to guide the hot gas descending or ascending in the heating furnace 110 to the rolling hollow portion 122, but the inclined guide surfaces 271a and 271b of the guide plates 471 may be arranged to face the flowing hot gas when the flow direction of the hot gas changes due to a change in the position of the circulation device 140 or the like.
In this embodiment, the inclined guide surfaces 271a and 271b having the same shape are formed on the upper surface and the lower surface of the both side baffles 471, but the inclined guide surfaces may be formed only on the side surface opposite to the flowing hot air. Further, although the present embodiment shows the deflector 471 being attached to both side walls 113 and 114 of the heating furnace 110, the deflector 471, even if attached to only one side, can guide the hot air to the rolled sheet hollow portion 122 to reflect the heating of the hollow portion 122.
Referring to fig. 24, the deflector 471 is configured to be narrower toward the free end 371d (left-right width in the drawing) from the coupling end 271c coupled to the side wall 113 of the heating furnace 110. Therefore, the descending hot gas can partially flow toward the roll bending hollow portion 122, and the rest part bypasses both sides of the baffle 471 and flows to the lower side of the roll bending 120. In the same manner, the hot gas rising on the opposite side may partially flow toward the rolled sheet hollow portion 122, and the rest may flow to the upper side of the rolled sheet 120. The reason why the guide plate 471 is formed in this manner is that when the width of the free end 371d is too large, the guide plate 471 cuts off the descending or ascending hot air, which prevents uniform heating of the rolled sheet 120.
Preferably, the width of the free end 371d of the deflector 471 is set at a length that is the same as or smaller than the diameter of the hollow portion 122 of the rolled sheet 120. This is because, even if the width of the free end 371d is larger than the diameter of the rolled plate hollow portion 122, the flow guided to the rolled plate hollow portion 122 does not increase, but the flow bypassing both sides of the flow guide plate 471 is prevented.
Preferably, the coupling end 271c of the deflector 471 is disposed at a length having a minimum width greater than or equal to the diameter of the central portion 122 of the rolled plate and a maximum width less than or equal to the outer diameter of the rolled plate 120. As an example shown in fig. 29, in the case where the width of the coupling end 271c is the smallest, the flow-guide plate 471 may be rectangular. When the width of the coupling end 271c is larger than the outer diameter of the rolled sheet 120, the flow of the detour flow guide plate 471 is obstructed, which is not preferable.
Referring to fig. 23, the deflector 471 is preferably disposed at a height between the center of the wrap 120 and the upper end of the wrap hollow portion 122 when guiding the descending hot gas. When the hot gas rising through the lower portion of the rolled sheet 120 is guided, it is preferably arranged at a height between the center of the rolled sheet 120 and the lower end of the rolled sheet hollow portion 122.
The hot gas falling from the circulation device 140 is guided by the deflector 471 and flows while being bent toward the lower half side of the rolled sheet hollow portion 122. Therefore, if the height of the baffle 471 is lower than the center of the rolled sheet 120, the flow does not go toward the hollow portion 122, but touches the side surface 123 of the lower portion of the rolled sheet 120 and goes downward, and the heating effect of the hollow portion 122 is not large. In contrast, if the height of the deflector 471 is higher than the upper end of the rolled plate hollow portion 122, the side surface 123 of the upper portion of the rolled plate 120 blocks the flow toward the hollow portion 122, and the heating effect of the hollow portion 122 is not great.
As shown in fig. 23, the heat treatment apparatus of the present embodiment includes corner guides 180, and the corner guides 180 include flow guides 181 for changing the flow direction of hot gas at both corners where the bottom surface 112 of the heating furnace 110 and the side walls 113 and 114 intersect. The one-side corner guide 180 guides the hot gas descending toward the bottom surface 112 of the heating furnace 110 to the lower side of the wrap 120, and the other-side corner guide 180 guides the hot gas passing through the lower side of the wrap 120 upward.
The corner guide 180 may be provided at a length corresponding to the width of the side surfaces 113 and 114 of the heating furnace 110 as shown in fig. 25, and the flow guide surface 181 may be a plane inclined with respect to the bottom surface of the heating furnace in order to smoothly change the direction of the hot gas. Fig. 26 shows a case where the flow guide surface 182 is an inclined inner curved surface as a modification of the corner guide portion 180. By means of such corner guides 180, the hot gas circulating inside the heating furnace 110 can be turned while maintaining the flow rate, thereby enabling smooth circulation of the hot gas.
As shown in fig. 23 and 27, the wrap supporting device 150 disposed on the bottom surface 112 side of the heating furnace 110 includes ventilation flow paths 152, 153, and 154 formed in a plurality of directions for the circulation of hot air.
As shown in fig. 27, the roll sheet supporting device 150 includes: a plurality of support blocks 151 disposed to be spaced apart from each other to secure the air flow passages 152 and 153; and a plurality of spacing members 155 mounted on the upper surface of each support block 151 in a spaced state from each other, for spacing the rolled sheet 120 from the upper surface of the support block 151 while supporting the rolled sheet 120. The lower portions of the supporting blocks 151 may be connected to each other by means of a connecting plate 156.
Each support block 151 may be constructed of a hexahedral structure so as to be able to bear a weight of the rolled sheet 120 of up to about 35 tons. Further, in each support block 151, a ventilation passage 154 communicating with each other is formed in the plurality of side surfaces 151b and the upper surface 151 a.
In the roll supporting device 150, since the plurality of support blocks 151 are disposed to be spaced apart from each other, and the ventilation flow paths 152 and 153 are secured, and the ventilation flow path 154 whose side surface communicates with the upper surface is formed in each support block 151, the hot gas flowing can easily approach the lower side of the outer peripheral surface 121 of the roll 120.
The plurality of partition members 155 partition the wrap outer circumferential surface 121 from the upper surface 151a of the support block 151 while minimizing the support area, thereby ensuring a flow path for flowing hot gas, and thus the lower portion of the wrap 120 can be smoothly heated by the circulating hot gas even in a state where the lower outer circumferential surface 121 of the wrap 120 is supported by the wrap support device 150.
Fig. 28 shows a modification of the partition member. The outer surface of the partition member 158 in fig. 28 contacting the outer peripheral surface 121 of the wrap 120 may be provided in a semi-cylindrical shape. Such a partition member 158 reduces the support area by bringing the outer peripheral surface 121 of the rolled sheet 120 into line contact with the partition member 158, thereby enabling the hot gas to more smoothly approach the outer peripheral surface 121 on the lower side of the rolled sheet.
Thus, in the heat treatment apparatus of the present embodiment, since the flow guide portion 170 having the flow guide plate 471 guides a part of the hot gas flowing around the rolled sheet 120 to the hollow portion 122 of the rolled sheet 120, it is possible to minimize a temperature deviation between the outer surface of the rolled sheet 120 and the hollow portion 122 in heating the rolled sheet 120. Further, since the hot gas can smoothly approach the lower outer peripheral surface 121 side of the wrap 120 by the multi-directional ventilation flow paths 152, 153, 154 formed in the wrap support device 150, the temperature deviation between the upper portion and the lower portion of the wrap 120 can be minimized. Therefore, the rolled sheet 120 can be uniformly heated as a whole, and a uniform heat treatment effect can be obtained.
Fig. 30 shows a modification of the deflector portion 170. The upper and lower inclined guide surfaces 271a and 271b of the deflector 471 in fig. 30 are provided in the form of an inner curved surface. The baffle 471 also has a thickness of the coupling end 271c formed larger than that of the free end 371d, and a width of the free end 371d formed smaller than that of the coupling end 271 c. Further, since the inclined guide surfaces 271a and 271b have the inner curved surface form, the thickness of the middle portion can be smaller than the thickness of the both side ends.
The baffle 471 is guided by the inclined baffle surfaces 271a and 271b having the inner curved surfaces to concentrate the circulating hot air toward the roll bending hollow portion 122, so that the hot air can be guided more smoothly to the roll bending hollow portion 122.
Fig. 31 shows a modification of the flow guide portion. The flow guide part 470 of fig. 31 includes: a coupling member 472 mounted to the side wall 113 of the heating furnace 110 and rotatably supporting a coupling end of the deflector 471; a support 473 that supports the baffle 471 in an angularly adjustable state.
Since the coupling end of the deflector 471 is rotatably coupled to the coupling member 472 by means of the shaft 374, the angle of the deflector 471 can be adjusted in such a manner as to raise or lower the height of the free end 371d, if necessary. Therefore, when the coils of different specifications are heated, the angle of the deflector 471 can be adjusted, and the flow direction of the hot gas flowing toward the coil hollow portion 122 side can be adjusted.
The support 473 has one end rotatably coupled to the lower surface of the spoiler 471 and the other end rotatably coupled to the coupling member 472, thereby being able to support the spoiler 471 in a fixed state. The support 473 may be in the form of a turnbuckle whose length can be adjusted for adjusting the angle of the baffle 471. In addition, when the angle of the deflector 471 needs to be adjusted, the length of the deflector can be changed to different support portions.
Fig. 32 shows another modification of the flow guide portion. The flow guide part 470 of fig. 32 may include: a guide 474 attached to the side wall 113 of the heating furnace 110; a coupling member 472 movably mounted to the guide rail 474 to rotatably support a coupling end of the spoiler 471 for angle adjustment of the spoiler 471; a moving device 475 that moves the coupling member 472; the support 473 supports the baffle 471 in an angularly adjustable state. That is, the angle adjustment and the height adjustment of the deflector 471 can be performed as needed.
The mobile device 475 may include: a screw shaft 475a rotatably supported in a state of being coupled to the coupling member 472 and extending in a moving direction of the guide plate 471 (a longitudinal direction of the guide rail); and a rotating device for rotating the screw shaft 475 a. The rotating means may be constituted by a rotating handle 475b provided at one end of the screw shaft 475a, a driving motor (not shown) for rotating the screw shaft 475a, or the like. However, the moving device may be variously changed to a chain-sprocket system, a rack-and-pinion system, or the like.
In the example of fig. 32, the height adjustment and the angle adjustment of the deflector 471 can be performed, but this may be slightly modified so that the deflector 471 is fixed to the coupling member 472. At this time, the deflector 471 cannot be angularly adjusted, but the height thereof can be adjusted by the operation of the moving device 475, whereby the direction of the hot gas flowing into the rolling plate hollow portion 122 can be adjusted.

Claims (36)

1. A heat treatment method of an AHSS hot-rolled coil comprises the following steps:
a hot-rolled coil generation step of hot-rolling and cooling a rolled material, and then rolling the material to prepare a hot-rolled coil;
a first cooling step of cooling to a temperature at which phase transition is completed to generate a hard phase at an edge portion of the hot-rolled coil;
a hot-rolled coil edge strength weakening step of heating only an edge portion of the hot-rolled coil to a tempering temperature, holding the heated edge portion at the tempering temperature for a predetermined time, and performing a heat treatment so that the edge portion of the hot-rolled coil subjected to the first cooling step has a strength similar to a strength of a central portion of the hot-rolled coil;
a second cooling step of cooling the hot-rolled coil subjected to the hot-rolled coil edge strength weakening step,
wherein, in the step of weakening the edge strength of the hot-rolled coil, the tempering temperature comprises 400 ℃ to 700 ℃.
2. The heat treatment method of the AHSS hot-rolled coil as set forth in claim 1, wherein the temperature of the hot-rolled coil completed in the hot-rolled coil generating step includes 500 ℃ to 700 ℃.
3. The method for heat treating an AHSS hot rolled coil as claimed in claim 1, wherein the temperature at which the phase transformation is completed in the first cooling step includes a range of normal temperature to 400 ℃.
4. The method of heat treating an AHSS hot rolled coil as set forth in claim 3, wherein a width of an edge portion of said hot rolled coil includes an 1/4 area relative to an overall width of said hot rolled coil in said first cooling step.
5. The method for heat-treating an AHSS hot rolled coil as set forth in claim 1, wherein said hot rolled coil has a tensile strength of 780MPa or greater.
6. The heat treatment method for an AHSS hot rolled coil as set forth in claim 5, wherein said heating in said hot rolled coil edge strength weakening step comprises rapid heating such that a region above 1/4 relative to the overall width of said hot rolled coil in a width direction of said hot rolled coil from the edge of said hot rolled coil to said tempering temperature.
7. The method of heat treating an AHSS hot rolled coil as set forth in claim 6, wherein in said hot rolled coil edge strength weakening step,
the predetermined time is set to a time range obtained according to the following mathematical expression:
the mathematical formula is as follows: x ═ temperature X (7.0+ log (time)), temperature in kelvin degrees c, time in minutes,
wherein the temperature is the tempering temperature, and X is more than or equal to 7600 and less than or equal to 8600.
8. The method of heat treating an AHSS hot rolled coil as claimed in claim 1 wherein the second cooling step comprises the steps of: cooling the edge portion of the hot-rolled sheet at a cooling rate of 3 ℃/min or more.
9. A cold rolling method for producing a cold rolled steel sheet from an AHSS hot rolled coil having a tensile strength of 780MPa or more, wherein the edge portion of the AHSS hot rolled coil having a winding temperature in the range of 500 to 700 ℃ is first cooled to a temperature in the range of normal temperature to 400 ℃ to complete a phase transformation of the edge portion into a hard phase, the edge portion is reheated only to complete the phase transformation into the hard phase, the resultant is held at a temperature in the range of 400 to 700 ℃ for 30 to 480 minutes to weaken the strength, and the AHSS hot rolled coil having the weakened strength is subjected to a second cooling at a rate of 3 ℃/min or more, and then cold rolling is performed.
10. A heat treatment apparatus for heat-treating a hot-rolled coil by performing the heat treatment method according to claim 1, comprising a heat treatment furnace provided with: the heating chamber is used for a conveying vehicle for stacking and conveying the hot rolled coil to enter; a plurality of heating devices that are provided on a heat insulating wall surface forming the heating chamber and heat the hot-rolled coil;
wherein the plurality of heating devices comprise: a first burner provided in the heating chamber for temperature control of the heating chamber; second burners provided on both side walls of the heating chamber for heating both side surfaces of the hot-rolled strip; and a hot air supply unit that supplies hot air into the rolled sheet of the hot-rolled sheet.
11. The heat treatment apparatus according to claim 10, wherein the hot air supply portion recovers high-temperature exhaust gas discharged from the heating chamber and sprays the exhaust gas toward the coil interior of the hot-rolled coil.
12. The thermal processing apparatus of claim 10, wherein the first burner comprises a flame burner disposed at a top wall of the heating chamber such that the injected flame does not directly contact the hot rolled sheet.
13. The heat treatment apparatus according to claim 10, wherein the second burners include radiation burners that heat both side surfaces of the hot-rolled strip by means of radiation heat, respectively,
wherein the radiant burner is disposed at the sidewall, and at least one or more are disposed so as to face a side surface between a center and a lower end of the hot rolled coil.
14. The heat treatment apparatus according to claim 11, wherein the hot air supply portion includes: a nozzle that sprays hot air into the inside of the hot-rolled coil; a recovery duct connected to an exhaust duct for discharging high-temperature gas inside the heating chamber, and supplying exhaust gas flowing in the exhaust duct to the nozzle; a damper that regulates supply of exhaust gas from the exhaust duct to the recovery duct; and a blower that provides a blowing force for moving the exhaust gas flowing in the recovery duct to the nozzle side.
15. The heat treatment apparatus according to claim 10, wherein the heat treatment furnace includes a tunnel-shaped main body having a top wall and two side walls and having a front surface, a rear surface, and a lower portion that is open, the open lower portion is closed by the transport vehicle when the transport vehicle enters the heating chamber, and the open front and rear surfaces are closed by an open/close door provided in the heat treatment furnace.
16. The heat treatment apparatus according to claim 15, wherein the heating chamber is formed in an insulating structure by insulating panels disposed on the top wall and the both side walls formed by the insulating wall surfaces and an upper surface of the transport vehicle.
17. The thermal processing device of claim 15, further comprising a sealing device for sealing a gap between said two side walls and said cart when said cart enters said heating chamber.
18. The thermal processing device of claim 17, wherein said sealing device comprises: a rotating arm rotatably coupled to a lower end side of the sidewall of the main body and including a heat insulating material for sealing the gap; a driving unit that drives the rotating arm such that the heat insulating material is movable between a first position where the heat insulating material seals the gap and a second position spaced apart from the gap.
19. The heat treatment apparatus according to claim 10, further comprising a control section that controls the temperature in the heating chamber, wherein the control section controls the plurality of heating apparatuses such that the temperature in the heating chamber is maintained at a temperature higher than a target heating temperature of the hot-rolled strip at an initial stage of heating of the hot-rolled strip and maintained at the target heating temperature after a predetermined time has elapsed.
20. The heat treatment apparatus according to claim 15, wherein two transport vehicles are provided, the transport vehicles being respectively provided on both sides of the heat treatment furnace so as to be movable back and forth along a rail, the two transport vehicles alternately entering and exiting the heating chamber.
21. A heat treatment apparatus that performs the heat treatment method of claim 1, comprising: a heating furnace that accommodates and heats the rolled sheet;
a circulating device for circulating hot gas inside the heating furnace; and
a guide portion that guides a part of the hot gas flowing around the rolled sheet inside the heating furnace to a hollow portion of the roll.
22. The heat treatment apparatus according to claim 21, wherein the flow guide portion includes a flow guide plate which is elongated from a side wall of the heating furnace opposite to a side of the roll toward the hollow portion of the roll.
23. The thermal processing device of claim 22, wherein said deflector comprises a sloped deflector surface that is sloped with respect to a centerline of said roll so as to direct flowing hot gas to a hollow of said roll.
24. The heat treatment apparatus as claimed in claim 23, wherein the baffle is formed in such a manner that a thickness of a coupling end coupled to the side wall of the heating furnace is greater than a thickness of a free end of the hollow portion toward the roll.
25. The thermal processing device of claim 23, wherein a width of the free end of the baffle facing the hollow portion of the rolled sheet is sized to be the same or smaller than a diameter of the hollow portion of the rolled sheet.
26. The heat treatment apparatus according to claim 25, wherein a minimum width of a coupling end of the baffle plate to the side wall of the heating furnace is set to a length of not less than a diameter of a hollow portion of the rolled plate and not more than a maximum width thereof.
27. The heat treatment apparatus according to claim 23, wherein the guide portions are respectively provided to both side walls of the heating furnace which are respectively opposite to both side surfaces of the roll.
28. The thermal processing device of claim 23, wherein said inclined flow guide surfaces are arranged in a curved configuration.
29. The thermal processing device of claim 22, wherein said flow guide further comprises: a coupling member mounted to a sidewall of the heating furnace, for rotatably supporting a coupling end of the baffle for angle adjustment of the baffle; a support part supporting the baffle in an angularly adjustable state.
30. The thermal processing device of claim 22, wherein said flow guide further comprises: a guide rail mounted on a side wall of the heating furnace; a coupling member movably mounted to the guide rail and supporting a coupling end of the baffle; a moving device that moves the coupling member.
31. The heat treatment apparatus according to claim 21, wherein the circulating means is configured to blow hot gas toward the bottom surface of the heating furnace through a space between one side surface of the roll and the side wall of the heating furnace from an upper portion of the heating furnace.
32. The heat treatment apparatus according to claim 31, wherein the baffle plate is disposed at a height between a center of the rolled plate and an upper end of the hollow portion of the rolled plate when guiding the descending hot gas, and at a height between the center of the rolled plate and a lower end of the hollow portion of the rolled plate when guiding the hot gas ascending through a lower portion of the rolled plate.
33. The heat treatment apparatus as claimed in claim 31, further comprising corner guides provided at corners where the bottom surface of the heating furnace meets the side walls, and having flow guide surfaces inclined with respect to the bottom surface of the heating furnace for converting the flow direction of the hot gas.
34. The heat treatment apparatus according to claim 21, further comprising a wrap supporting device which is disposed on a bottom surface side of the heating furnace, supports a lower outer peripheral surface of the wrap, and has ventilation flow paths formed in a plurality of directions for circulation of hot gas.
35. The thermal processing device of claim 34, wherein said rolled sheet support means comprises: a plurality of support blocks which are arranged at intervals and have ventilation flow paths of which the side surfaces are communicated with the upper surface; and a plurality of partition members provided in a spaced state from each other on the upper surface of each support block, for partitioning the rolled sheet from the upper surface of the support block while supporting the rolled sheet.
36. A heat treatment apparatus that performs the heat treatment method of claim 1, comprising:
a heating furnace that accommodates and heats the wound roll;
a circulating device for circulating hot gas inside the heating furnace; and
and a wrap support device which is disposed on the bottom surface side of the heating furnace, supports the lower outer circumferential surface of the wrap, and has a plurality of ventilation flow paths formed in a plurality of directions for the circulation of hot air.
CN201580004858.8A 2014-12-09 2015-10-30 Heat treatment method of AHSS hot-rolled coil, cold rolling method using same and heat treatment device Active CN105934288B (en)

Applications Claiming Priority (7)

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KR10-2014-0175568 2014-12-09
KR1020140175568A KR101591792B1 (en) 2014-12-09 2014-12-09 Heat treating method for advanced high strength steel hot coil and cold rolling method using the same
KR10-2014-0177699 2014-12-10
KR1020140177699A KR101612760B1 (en) 2014-12-10 2014-12-10 Heat treating apparatus for hot coil
KR10-2015-0080524 2015-06-08
KR1020150080524A KR101662559B1 (en) 2015-06-08 2015-06-08 Coil heating equipment
PCT/KR2015/011554 WO2016093493A1 (en) 2014-12-09 2015-10-30 Heat treatment method for ahss hot rolled coils, and cold rolling method using same and heat treatment apparatus

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WO2016093493A1 (en) 2016-06-16
CN105934288A (en) 2016-09-07

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