WO2006106999A1 - Process for producing hot-dipped hot-rolled steel sheet - Google Patents

Process for producing hot-dipped hot-rolled steel sheet Download PDF

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Publication number
WO2006106999A1
WO2006106999A1 PCT/JP2006/306987 JP2006306987W WO2006106999A1 WO 2006106999 A1 WO2006106999 A1 WO 2006106999A1 JP 2006306987 W JP2006306987 W JP 2006306987W WO 2006106999 A1 WO2006106999 A1 WO 2006106999A1
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WO
WIPO (PCT)
Prior art keywords
hot
steel sheet
furnace
rolled steel
reduction
Prior art date
Application number
PCT/JP2006/306987
Other languages
French (fr)
Japanese (ja)
Inventor
Makoto Katube
Masayuki Miyake
Original Assignee
Nippon Steel Corporation
Nippon Steel Engineering Co., Ltd.
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Publication date
Application filed by Nippon Steel Corporation, Nippon Steel Engineering Co., Ltd. filed Critical Nippon Steel Corporation
Priority to BRPI0607715-3B1A priority Critical patent/BRPI0607715B1/en
Priority to US11/887,176 priority patent/US20080283157A1/en
Priority to JP2007511220A priority patent/JP4619404B2/en
Priority to CN2006800111120A priority patent/CN101155935B/en
Publication of WO2006106999A1 publication Critical patent/WO2006106999A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C—CHEMISTRY; METALLURGY
    • 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
    • C21D9/561—Continuous furnaces for strip or wire with a controlled atmosphere or vacuum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/003—Apparatus
    • C23C2/0038—Apparatus characterised by the pre-treatment chambers located immediately upstream of the bath or occurring locally before the dipping process
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0222—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating in a reactive atmosphere, e.g. oxidising or reducing atmosphere
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/022—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by heating
    • C23C2/0224—Two or more thermal pretreatments
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/02—Pretreatment of the material to be coated, e.g. for coating on selected surface areas
    • C23C2/024—Pretreatment of the material to be coated, e.g. for coating on selected surface areas by cleaning or etching
    • 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
    • C21D1/76—Adjusting the composition of the atmosphere
    • 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
    • C21D8/0278—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular surface treatment

Definitions

  • the present invention relates to a method for producing a hot-rolled hot-rolled steel sheet in which a hot-rolled steel sheet manufactured by a thin slab continuous forging method is melted.
  • This thin slab continuous forging method is characterized in that the steel sheet is sent directly from the continuous forging process to the rolling process. For this reason, it is extremely energy efficient compared to conventional continuous forging machines that require a number of processes such as billet cooling, defect inspection, defect removal, and heating between the continuous forging process and the rolling process. It is efficient and equipment costs can be kept low. Furthermore, the fact that this thin slab continuous forging machine can be used with electric furnaces that use scrap as a raw material is also a major factor that has attracted attention.
  • steel sheets manufactured by the thin slab continuous forging method have the problem that it is more difficult to create surface quality than steel sheets manufactured by conventional continuous forging machines. For this reason, until recently, the continuous slab forging method was not widely used. In addition, there is very little information on hot-rolled steel sheets produced by the thin slab continuous forging method, and when hot-dip galvanizing is applied to these hot-rolled steel sheets, The method used for this was applied as it was.
  • the “non-oxidation furnace method” is used as a method for hot-rolling hot-rolled steel sheets. In this method, hot-rolled steel sheets are continuously passed through a non-oxidation furnace-, a reduction furnace (annealing furnace), and a cooling furnace, and are heated to high temperatures for oxidation-reduction treatment.
  • an Fe layer can be formed on the surface of a hot-rolled steel sheet by oxidizing in a non-oxidizing furnace and then reducing in a reduction furnace.
  • An oxide film such as FeO on the surface of the steel sheet makes it difficult for the adhesion of the melt to adhere, so removing this from the surface of the steel sheet has the effect of improving the plating wettability against hot dipping.
  • the conventional melt-meshing equipment as described above is designed mainly for passing cold-rolled steel sheets, so the heating rate in the heating zone is approximately 10 ° C / s to 20 ° CZ. It was in the range of s.
  • the maximum temperature during annealing is 640 ° C. It was normal to adjust the temperature to about C ⁇ 660 ° C.
  • Thin slab continuous forging machines have a very narrow width compared to conventional continuous forging machines, and the main inlet nozzle has a special structure. Nozzle clogging easily occurs. Therefore, in order to prevent this, in thin slab continuous forging machines, Ca is added to the ladle to lower the melting point of alumina.
  • the forged slabs of 50 to 80 mm are sent directly to the rolling process for rolling while maintaining a high temperature.
  • This hot rolling mill is a hot rolling mill equivalent to the conventional finishing mill in the hot rolling process, and it rolls from 1.2 mm to 4 mm to produce hot rolled steel sheets.
  • a tunnel furnace with a long residence time is used to keep the thin slab warm, so the amount of scale generated on the slab surface before rolling is large.
  • hot-rolled steel sheets manufactured using the thin slab continuous forging method have a higher amount of smashed knots than conventional continuous forging machines. This is because, in the thin slab continuous forging method, the forged steel sheet is directly fed to the rolling process while being kept at a high temperature and rolled, so that Fe 3 C and C are likely to remain separated on the steel sheet surface. is there. If a large amount of Fe 3 C or the like remains on the surface of the hot-rolled steel sheet, when it is oxidized in a non-oxidizing furnace, C reacts with oxygen, and the formation of the Fe oxide film is partially delayed. As a result, unevenness and pits are generated in the oxide film.
  • the present invention has been made in view of the above problems, and particularly for preventing unplating that occurs on the plating surface when hot-rolling steel sheets manufactured by a thin slab continuous forging method are fused.
  • in mass% C: 0 • 0 3% or more, S i: 0.0 2% or more, M n: 0.1
  • a steel plate produced by forging and hot rolling steel containing 5% or more and C a: 0.0 0 1% or more by the thin slab continuous forging method has a maximum steel plate temperature of 5500 ° C or more 6 The temperature is lower than 50 ° C, the heating rate is 25 ° C / sec or more and heating is performed for 15 seconds or more, and oxidation treatment is performed.
  • the temperature of the steel plate temperature is 5700 ° C or higher and the heat treatment is carried out so that the time is 25 seconds or more and 45 seconds or less.
  • Method for producing a steel sheet is provided.
  • the hot dip may be hot dip galvanized.
  • a hot-rolled hot-rolled steel sheet manufacturing facility that melts and bonds steel sheets manufactured by forging and hot rolling using a thin slab continuous forging method, which are used for oxidation and for reduction.
  • a ratio of the length along the conveying direction of the steel sheet between the furnace used for oxidation and the furnace used for reduction is 0.5 or more and 0.9 or less, Equipment for manufacturing hot-dip hot-rolled steel sheets is provided.
  • the time for the steel sheets to pass through the furnace for the oxidation may be 15 seconds or more and 25 seconds or less.
  • Fig. 1 is a block diagram of a preferred hot-rolled steel sheet manufacturing facility with hot-dip galvanized steel according to the present invention.
  • FIG. 2 is a diagram illustrating temperature changes in a non-oxidation furnace and an annealing furnace of a suitable hot-rolled galvanized steel sheet manufacturing facility according to the present invention.
  • Figure 3 is a diagram before and after the oxidation of a hot-rolled steel sheet manufactured by the thin slab continuous forging method.
  • A shows the hot-rolled steel sheet before oxidation
  • (b) shows the hot-rolled steel sheet after oxidation according to the present invention
  • (c) shows the hot-rolled steel sheet after oxidation according to the prior art.
  • FIG. 4 is a diagram before and after reducing the hot-rolled steel sheet oxidized in a non-oxidizing furnace.
  • CT indicates the hot-rolled steel sheet before reduction
  • e The reduced hot-rolled steel sheet
  • f indicates the hot-rolled steel sheet with insufficient reduction
  • g indicates the hot-rolled steel sheet with excessive reduction.
  • Fig. 5 is a block diagram of the cleaning device in front of the fusion fitting equipment. BEST MODE FOR CARRYING OUT THE INVENTION
  • the hot-dip galvanized steel sheet manufactured by the hot-dip galvanized hot-rolled steel sheet manufacturing method is used as a hot-dip galvanized steel sheet as defined in JISG 330.
  • C a 0.0 0 1
  • Steel sheets produced by rolling and rolling steel containing 1% or more by the thin slab continuous forging method are used.
  • C a is less than 0.001%, nozzle clogging may not be prevented, so addition of more Ca is usually added in the steelmaking process. This is done by adding A 1, C a S i, F e C a, or metallic Ca.
  • FIG. 1 is a configuration diagram of a suitable hot-dip galvanized hot-rolled steel sheet manufacturing facility 1 according to the present invention.
  • This hot-dip galvanized hot-rolled steel sheet manufacturing facility is arranged between the delivery reel 1 0 which is the starting point of the molten zinc plating process line, the take-up reel 1 1 which is the end point, and the reels 10 and 1 1.
  • Preheated furnace (not shown) installed, non-oxidizing furnace 1 2, annealing furnace 1 5 including reduction zone 1 3 and cooling zone 1 4, molten zinc plating bath 1 6, wiping device 1 7, and cooling furnace Consists of 1-8.
  • Sending relay 10 is mass%, C: 0.0 3% or more, S i. 0 2% or more, M n: 0.15% or more, C a: 0.0 0 1 After steel is forged by the continuous slab forging method, it is rolled as it is without lowering the temperature. It is a reel on which a hot-rolled steel plate manufactured in this way is wound.
  • the non-oxidizing furnace 12 is a furnace with a length in the steel-plate transport direction of, for example, 15 m or more and 25 m or less for oxidizing the hot-rolled steel sheet sent from the delivery reel.
  • the plate speed is 120 m, so the oxidation time of the hot-rolled steel sheet in the non-oxidizing furnace 12 is 7 seconds or more and 12 seconds or less.
  • the fuel-air ratio in the non-oxidizing furnace 1 2 is set to 0.9 or more and 0.98 or less.
  • the length in the transfer direction when the preheating furnace is added to the non-oxidizing furnace 12 is set to 30 m or more and 50 m or less, for example.
  • the total oxidation time (passage time) in the non-oxidizing furnace 1 2 and the preheating furnace is 15 to 25 seconds.
  • An annealing furnace 15 arranged continuously in a non-oxidizing furnace 1 2 includes a reduction zone 1 3 for reducing the oxidized hot-rolled steel sheet, and then a cooling zone 1 for cooling the hot-rolled steel sheet.
  • This is a furnace with a length in the transport direction of, for example, 70 m or more and 100 m or less.
  • the reduction time of the hot-rolled steel sheet in the annealing furnace 15 is, for example, 5 70 ° C or more, which is relatively fast. It takes 25 to 45 seconds in the area.
  • H 2 and N 2 are used as the atmosphere in the annealing furnace 15.
  • the reduction zone 13 in which reduction is mainly performed consists of a reduction furnace and a soaking furnace, or only a reduction furnace, and its length in the transfer direction is set to, for example, 50 m or more and 7 O m or less. ing.
  • the hot-dip galvanizing tank 16 is a tank for smashing hot-rolled steel sheets to attach the hot-dip.
  • the wiping device 17 is a device that wipes excess molten metal adhering to the hot-rolled steel sheet with gas.
  • the cooling furnace 18 is a furnace for cooling the hot-rolled steel sheet afterwards.
  • FIG. 2 shows the temperature change of the steel sheet surface when the hot-rolled steel sheet passes through the non-oxidation-furnace 12, reduction zone 1 3, and cooling zone 1 4 of the hot-rolled steel plate manufacturing facility 1.
  • a hot-rolled steel sheet manufactured by a thin slab continuous forging method is sent out from the delivery reel 10, proceeds on the line, enters the non-oxidation furnace 12 through the preheating furnace.
  • the temperature of the hot-rolled steel sheet that entered the non-oxidizing furnace 1.2 is increased so that the maximum steel sheet temperature is not less than 5500 ° C and less than 600 ° C.
  • the surface of the hot-rolled steel sheet is oxidized by heating for 25 to 25 seconds at temperatures of 25 ° CZ to 15 seconds.
  • the time for oxidation treatment here is the pre-tropical and non-oxidizing furnace transit time.
  • Figure 3 shows the hot-rolled steel sheet surface before and after this oxidation treatment.
  • Fig. 3 (a) shows the hot-rolled steel plate before oxidation
  • Fig. 3 (b) shows the hot-rolled steel plate after oxidation according to the present invention
  • Fig. 3 (c) shows that according to the prior art. The hot-rolled steel sheet after being oxidized is shown.
  • the rate of temperature rise in section I in Fig. 2 By setting the rate of temperature rise in section I in Fig. 2 to 25 ° C / sec or higher, which is faster than the conventional rate of temperature rise described above, the effect of preventing non-plating can be obtained.
  • the heating rate in section I is 25 seconds and less than 2 seconds, the oxide Ca a and Ca succinate produced by the addition of Ca, the luminum aluminate, and the smut Fe 3 C, etc. This causes non-plating.
  • Set the heating rate to 25 / sec or more. The reason why non-plating is prevented will be described below.
  • the Fe oxide film on the surface of the hot-rolled steel sheet is formed by the reaction of Fe atoms in the. Further, F e when the oxide film is generated, since the S i and M n present in the steel sheet is also F e Similarly oxide, F e under the oxide film S i ⁇ 2 and M n O A secondary oxide film is produced.
  • the F e oxide film is produced, the C a O and F e 3 C, etc. illustrated in FIG. 3 (a) that adhered to the steel sheet surface, the generation of F e oxide film is inhibited, The pit 19 shown in Fig. 3 (c) is formed.
  • Fe 3 C In the case of Fe 3 C, it decomposes into C and reacts with oxygen, inhibiting the formation of the Fe oxide film, as shown in Fig. 3 (c).
  • the pit 1 9 As described above, the pit 1 9 is formed, as shown in FIG. 3 (c), 2-order oxide film such as S i 0 2 and M n O will come out to the surface. Secondary oxide film such as these S i O 2 and M n O Since degrade the wettability with molten zinc plated, thereby to generate a non-coating when the molten zinc plated.
  • the rate of temperature increase was set to a high value of 25 ° CZ seconds or more, and the rate of Fe oxide film formation was increased.
  • Oxide film formation occurs mainly due to the movement of Fe to the surface, so if the oxide film formation rate is high, Ca O, Fe 3 C, etc. will be pushed out to the steel plate surface as a result. Even if pits are generated with O, Fe 3 C, etc., an Fe oxide film is also formed at the bottom.
  • Fe 2 03 is generated on the pole surface layer of the steel sheet described below, Fe 3 O 4 is formed below it, and Fe O is formed below it. Below 5 70 ° C, Fe 2 0 3
  • the properties of the steel sheet surface after the temperature rising process are as follows from the inside: Fe (steel sheet), oxides of S i or M n, or S i and M n, as shown in Fig. 3 (b).
  • secondary oxide film comprising a composite oxide, thereon, F ea O 4 and F e O or oxide film consisting of F e O, C a O on the surface, there exists F e 3 C, C A_ ⁇ , There is a pit under F e 3 C, but the F e O layer exists.
  • the maximum steel plate temperature in the non-oxidizing furnace is set to less than 600 ° C, excessive oxide film formation is prevented. If the maximum steel sheet temperature in the non-oxidizing furnace is 60 ° C or higher, an oxide film is excessively generated, and the oxide film remains in the subsequent reduction process.
  • the time for keeping the temperature rising rate at 25 or more seconds is 15 seconds or more ⁇ . In less than 5 seconds, there is not enough oxide thickness, As a result, the secondary oxide film composed of S i or M n oxide or S i and M n complex oxide is exposed to the surface without being covered with the FeO film.
  • the oxidized hot-rolled steel sheet travels on the line and enters the reduction zone 13 in the annealing furnace 15.
  • the annealing furnace 15 first, in the reduction zone 1 3, the steel sheet is heated so that the maximum steel plate temperature is not less than 700 ° C and not more than 7600 ° C, and then proceeds to the cooling zone 14. And cooled.
  • the hot-rolled steel sheet is reduced in the reduction zone 13 and cooling zone 14 in the annealing furnace for a period of 25 to 45 seconds with the steel plate temperature kept at 570 ° C or higher.
  • the time from temperature point R to temperature point U, where the steel plate temperature is 5700 ° C is set to 25 to 45 seconds.
  • the reason why the temperature of the reduction treatment is limited to a temperature range of 5.70 ° C or higher is as follows. In other words, at 5 70 or higher, € ⁇ becomes the main component of 6 oxides and is reduced, while at less than 570 ° C, Fe 30 4 becomes the main component of Fe oxides and reduced. F e O is compared to F e 3 ⁇ 4, the process temperature is also likely to be also available reducing high. Therefore, the reduction treatment of F e O is more controllable than the reduction treatment of F e 30 4 .
  • Fig. 4 shows the surface of the hot-rolled steel sheet before and after the above reduction treatment.
  • the hot-rolled steel sheet before reduction treatment is (d), the hot-rolled steel sheet that has been reduced without excess (e), the hot-rolled steel sheet with insufficient reduction treatment (f), and the heat that is excessively reduced.
  • the rolled steel sheet is (g).
  • C 30 and € 3 C shown in Fig. 3 are not shown. This is because these C a O and F e 3 C pass through the annealing furnace 13 and the like. This is because the reducing atmosphere is blown off from the steel sheet surface by the flow of H 2 and N 2 etc.
  • a secondary oxide film of Si or Mn oxide or a composite oxide of Si and Mn formed on Fe is also shown in Fig. 4 as "-S i O 2 , The description is simplified as n O ".
  • the oxide film in the form of Fig. 3 (b) is moderately reduced, as shown in Fig. 4 (e).
  • Fe steel plate
  • S i or M n oxide or S i secondary oxide film comprising a composite oxide of M n exist film made F e thereon, C a O on the surface, pit of F e 3 C was present in the force the bottom remaining
  • the hot-rolled steel sheet in the form with the Fe layer is made to have a steel sheet temperature of 5700 ° C or higher so that the highest steel sheet temperature is 700 ° C or higher and 760 ° C or lower.
  • the surface of the hot-rolled steel sheet shown in Fig. 4 (d) is reduced in the annealing furnace 15 without excess or deficiency.
  • the Fe oxide film formed by the non-oxidized film is all reduced to Fe layer.
  • the F e layer 2 Tsugisan of film such as S i O 2 and M N_ ⁇ generated by acid treatment and reduction treatment or the like even completely covers. Degradation of plating wettability with hot dip zinc plating The secondary oxide film such as S i 0 2 and M n O is completely covered, so the plating wettability is very good and no plating occurs. .
  • the annealing furnace 1 Reduction within 5 becomes excessive.
  • the Fe oxide film is sufficiently reduced to form the Fe layer.
  • S i and M n have higher oxidizing power than Fe, the secondary oxide layer of S i O 2 and M n 0 is not removed even when the Fe oxide film is reduced in the annealing furnace 15. It grows excessively and appears on the surface of the steel sheet. As described above, S i 0 2 and M n 0 deteriorate the plating wettability of the steel sheet, resulting in non-plating.
  • the reduced hot-rolled steel sheet proceeds on the line from the annealing furnace 15 to a hot-dip zinc plating tank 16 heated to a predetermined temperature, and is crushed to adhere the molten zinc plating. .
  • the hot-rolled steel sheet with hot-dip galvanized steel advances on the line, and the amount of hot-dip galvanized steel on the hot-rolled steel sheet is adjusted to a predetermined value by the wiping device 17.
  • the hot-rolled steel sheet travels on the line and is cooled in the cooling furnace 18.
  • the temperature of the hot-rolled steel sheet in the non-oxidizing furnace 12 is increased so that the highest steel sheet temperature is not less than 55 ° C and less than 60 ° C. Since it was heated and oxidized for 15 to 25 seconds at a temperature of ° C / second or more, when an Fe oxide film was formed, it was picked up by a Fe 3 C and other Ca and oxides of Ca. Even if pit 19 is generated, the bottom of pit 19 is covered with the Fe oxide film.
  • the hot-rolled steel sheet is kept at a temperature of 5700 ° C or higher so that the maximum steel plate temperature is 70 ° C or higher and 7600 ° C or lower. Since the heat treatment was reduced for 25 to 45 seconds, the Fe oxide film on the surface of the hot-rolled steel sheet was reduced without excess or deficiency. Further, secondary oxidation layer of S i 0 2 and M n O also not come to the surface. Therefore, the occurrence of non-plating is prevented.
  • the length in the transport direction of the furnace used for oxidation (preheating furnace and non-oxidizing furnace 12) is set to 30 m or more and 50 m or less, and the furnace used for the return-( The length of the reduction zone 1 3) in the conveyance direction was set to 50 m or more and 70 m or less.
  • the furnace used for the return-( The length of the reduction zone 1 3) in the conveyance direction was set to 50 m or more and 70 m or less.
  • non-plating occurs by setting the length ratio of the furnace used for oxidation and the furnace used for reduction along the conveying direction to be 0.5 or more and 0.9 or less. Can be prevented.
  • the furnace used for oxidation and the furnace used for reduction are set to appropriate lengths with no excess or deficiency, so investment in equipment costs is optimized.
  • the hot-rolled steel sheet is delivered from the delivery reel, but may be directly connected to a line for performing the thin slab continuous forging method.
  • the hot-rolled steel sheet is sent from the delivery reel to the non-oxidation furnace, but before being sent to the non-oxidation furnace, processing such as pickling and surface scrubbing may be performed. .
  • the hot-rolled steel sheet is fed from the feed reel into the non-oxidizing furnace and oxidized. It may be provided.
  • an annealing furnace including a reduction zone and a cooling zone is used.
  • separate furnaces such as a reduction furnace and a cooling furnace are used. May be.
  • hot dip galvanizing is used as the hot dip, but aluminum, lead, tin, etc. may be used in addition to zinc.
  • the present invention is particularly effective for hot-rolled steel sheets.
  • the reason for this is presumably that the surface of the hot-rolled steel plate is rougher than the surface of the cold-rolled steel plate, has a larger grain boundary, has a larger surface area, is easier to oxidize and reduce, and has a higher growth rate of the oxide layer.
  • the hot-rolled steel sheet with a good plating state obtained under the oxidation and reduction conditions of the present invention Applying the conventional formulas for estimating the amount of oxidation and reduction of a cold-rolled steel sheet to calculate the amount of oxidation and reduction of a hot-rolled steel sheet
  • the formula for estimating the amount of oxidation of a cold-rolled steel sheet is based on preheating furnace and non-oxidation
  • the amount of oxidation is estimated from two variables: the time spent in the furnace and the temperature reached by the steel sheet.
  • the formula for estimating the reduction amount of cold-rolled steel sheets estimates the reduction quantity from two variables: the time spent in the furnace where the reduction treatment is performed and the ultimate temperature of the steel sheet.
  • the reduction amount when the temperature of the reduction furnace is 570 ° C or higher and the reduction amount when it is lower than 570 ° C are calculated separately, and the sum of the two is calculated.
  • Estimated reduction amount is not shown, they can be derived from experiments.
  • the hot-rolled steel sheet obtained by hot-rolling the flakes obtained with a thin slab forging machine is oxidized and reduced under the suitable oxidation and reduction conditions specified in the present invention, and the oxidation amount and reduction amount at that time was obtained from the above formulas for estimating the amount of oxidation and reduction.
  • the oxidation amount was about 0.1 2 to 0.2 mgZm 2 and the reduction amount was about 0.2 to 0.3 5 mg / m 2 .
  • These values are the amount of oxidation of the cold-rolled sheet obtained by the same formula 0. l O. 'SmgZm 2 , Reduction amount is smaller than 0.4 5 to lmg Z m 2 .
  • the oxidation rate and reduction rate are faster than in the case of cold-rolled steel sheets. It can be estimated that a value smaller than the value of is obtained.
  • the oxidation time and reduction time can be shortened compared to when applied to cold-rolled steel sheets.
  • the length of the furnace for oxidation and reduction can be shortened, and the hot-dip zinc plating facility can be made smaller.
  • the front surface of the melt-meshing equipment of the present invention is an alkali that does not use electrolytic cleaning comprising an alkali spray tank 20, an alkali scrubber tank 2 1, a hot water rinse tank 2 2, and a hot air dryer 2 3.
  • An alkaline scrubber is installed with a cleaning device and nylon brush 24.
  • electrolytic cleaning which is generally used, is not used, is that when a hot-rolled steel sheet is manufactured by a thin slab continuous forging machine and a hot rolling machine directly connected to this, the surface of the steel sheet is removed after hot rolling.
  • Pickling and applying antifungal agent but since the time from pickling to melting is about 2 days or less, the amount of antifungal agent applied may be less than usual. Because.
  • the surface of the steel plate after pickling contains a smaller amount of antifungal agent, such as Fe 3 C, it adheres to the surface using an alkaline cleaning device that does not use electrolytic cleaning. It performed Al force Risukuraba with a nylon brush after washing the anti ⁇ Ya F e 3 C, etc., to remove the anti ⁇ Ya F e 3 C and the like.
  • This cleaning usually removes the fungicide that has been burned and removed in the heating furnace.
  • oxygen in the atmosphere is used stably for oxidation of the steel sheet surface. Therefore, the amount of oxide film produced is stable, This is a preferable condition for the prevention of stable unsettledness.
  • the rate of temperature increase in the oxidation process was set to 25 ° C / s and that the reduction time was shorter than that of the conventional cold-rolled steel sheet, resulting in an increase in the yield point of the steel sheet. This is presumably due to the fact that it is possible to pass through below the strain that causes elongation, so that there is no occurrence of hip folding.
  • the normal sheet feeding speed in the current technology is 90 mpm to 180 mpm
  • the present invention can be applied to newly install or remodel a fusion fitting equipment having this speed range.
  • the upper limit of the plate-feeding speed of the fusion fitting equipment is about 180 mpm.
  • this technology can be applied even if a fusing device with a higher sheet feeding speed is available.
  • the lower limit of the plate feed speed is not limited as long as the conditions of the present invention can be realized.
  • Table 1 shows the percentages of each of the four types of hot-rolled steel sheets A, B, -C, and D manufactured using the thin slab continuous forging method.
  • Table 2 shows the various conditions and the results when hot-rolled steel sheets with hot-dip galvanized steel were produced from these four types of hot-rolled steel sheets using the method for manufacturing hot-rolled steel sheets with hot-dip galvanized steel according to the present invention. Shown in The hot-rolled steel sheet with hot dip galvanized steel is made by passing four types of hot-rolled steel sheets through a preheating furnace, non-oxidation furnace, reduction furnace, soaking furnace, and cooling furnace to perform oxidation treatment, reduction treatment, and cooling. It was processed and then hot-dip zinc plating was performed.
  • the adhesion amount of molten zinc was in the range of 80 to 120 g Zm 2 (single side).
  • Table 2 data Nos. 1 to 4 are examples that satisfy all of the conditions specified in the present invention, and the surface of the hot-rolled hot-rolled steel sheet produced is in a very good condition. ing.
  • Tables 5 through 9 shown in Table 2 are comparative examples that do not satisfy any of the conditions specified in the present invention.
  • the surface of the hot-dip hot-rolled steel sheet produced was not plated or The plating is in poor condition such as scale residue.
  • Table 3 shows the percentages of the components of two types of hot-rolled steel sheets A and B manufactured using the thin slab continuous forging method.
  • Hot-rolled steel sheet with hot-dip galvanized steel is manufactured by oxidizing two types of hot-rolled steel sheets in a preheating furnace and non-oxidation furnace, reducing them in a reduction zone (reduction furnace and soaking furnace), and then hot-dip galvanizing. And went.
  • the preheating furnace and the non-oxidizing furnace correspond to the furnace used for oxidation
  • the reduction zone corresponds to the furnace used for reduction.
  • Data Nos. 3 and 4 shown in Table 4 indicate that the length of the preheating furnace is fixed at 17 m, the length of the deoxidizer is fixed at 21 m, the cooling conditions are changed, and the length of the reduction zone is simulated. Adjusted to 4 1 m and 78 m. Reduction time is 1 It is a value calculated from the feeding speed of 20 m / min.
  • data numbers 1 and 2 indicate that the ratio of the total length of the preheating furnace and the non-oxidizing furnace to the length of the reduction zone is 0.5 or more and 0.9 or less as defined in the present invention.
  • the surface of the hot dip galvanized hot-rolled steel sheet is in a very good plating condition.
  • data numbers 3 and 4 shown in Table 4 indicate that the ratio of the total length of the preheating furnace and the non-oxidation furnace to the length of the reduction zone is outside the range of 0.5 or more and 0.9 or less specified in the present invention.
  • the surface of the hot-rolled steel sheet with molten zinc plated is in a poor plating condition such as non-plating.
  • the present invention is implemented within the plate speed range shown in the above example.
  • the upper limit of the plate feed speed is about 18 O m pm with the current technology.
  • this technology can be applied even if a fusing device with a higher sheet feeding speed is available.
  • the lower limit of the plate feed speed is not limited as long as the conditions of the present invention can be realized. Since the normal sheet feeding speed in the current technology is 90 mpm to 180 mpm, some hot-dip zinc plating equipment may have an economic ton of Zr h limit. In such a case, the plate passing speed decreases as the plate thickness increases, so the time required to pass through the oxidation furnace increases, and as a result, the heating rate decreases. In this case, a part of the heating process may be operated so as to satisfy the heating rate of the present invention. Industrial applicability

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Abstract

A steel sheet produced by casting a steel containing at least 0.03 mass% carbon, at least 0.02 mass% silicon, at least 0.15 mass% manganese, and at least 0.001 mass% calcium by the thin-slab continuous casting method and hot-rolling the cast is oxidized by heating it at a heating rate of 25 °C/sec or higher to a maximum steel-sheet temperature of 550-650°C, excluding 650°C, for at least 15 seconds. The sheet is then reduced by heating it to a maximum steel-sheet temperature of 700-760°C in such a manner that the time period in which the steel sheet temperature is 570°C or higher is 25-45 seconds. Thereafter, the steel sheet is plated by hot dipping to produce a hot-dipped hot-rolled steel sheet.

Description

明 細 書 -溶融めつき熱延鋼板の製造方法 技術分野 .  Makisho-Manufacturing method of hot-rolled steel sheet with fusion mate.
本発明は， 薄スラブ連続錡造法で製造された熱延鋼板を溶融めつ きする溶融めつき熱延鋼板の製造方法に関する。 背景技術  The present invention relates to a method for producing a hot-rolled hot-rolled steel sheet in which a hot-rolled steel sheet manufactured by a thin slab continuous forging method is melted. Background art
近年， 省エネルギー化及びコス ト削減の必要性から， 特開平 2— 1 9 7 3 5 8号公報に記載されるような薄スラブ連続铸造法 （Th i n In recent years, due to the need for energy saving and cost reduction, the thin slab continuous fabrication method (Th i n
S l ab Cas t i ng P roc e s s) を用いた鋼板製造技術が世界的に脚光 を浴びるようになつてきた。 この薄スラブ連続铸造法は， 鋼板が連 続踌造工程から圧延工程に直送される点に特徴がある。 このため， 連続铸造工程と圧延工程との間に， 鋼片の冷却， 欠陥検査， 欠陥除 去， 及び加熱等の多数の工程を必要とする従来式の連続铸造機に比 ベ， 非常にエネルギー効率がよく， 設備費用も低く抑えることがで きる。 さらに， この薄スラブ連続铸造機を， スクラップを原料にす る電炉と共に利用可能であることも注目を集めることになつた大き な要因である。 Steel plate manufacturing technology using Slab Cas ti Proc s s) has come into the spotlight worldwide. This thin slab continuous forging method is characterized in that the steel sheet is sent directly from the continuous forging process to the rolling process. For this reason, it is extremely energy efficient compared to conventional continuous forging machines that require a number of processes such as billet cooling, defect inspection, defect removal, and heating between the continuous forging process and the rolling process. It is efficient and equipment costs can be kept low. Furthermore, the fact that this thin slab continuous forging machine can be used with electric furnaces that use scrap as a raw material is also a major factor that has attracted attention.
しかし， 薄スラブ連続铸造法で製造した鋼板は， 従来の連続铸造 機で製造した鋼板よりも表面品質の作り込みが難しいという問題点 がある。 そのため， 最近まで薄スラブ連続铸造法は， 広く普及して いなかった。 また， 薄スラブ連続铸造法で製造された熱延鋼板に対 する情報も非常に少なく， この熱延鋼板に対して溶融亜鉛めつきを する際には， 従来の連続錡造機による熱延鋼板に対して用いる方法 をそのまま ^適用していた。 熱延鋼板を溶融亜鉛めつきする方法としては， 一般に 「無酸化炉 方式」 が用いられる。 この方法では， 熱延鋼板を連続的に無酸化炉 -， 還元炉 （焼鈍炉） ， 及び冷却炉を通過させて， 高温加熱して酸化 - 還元処理を行う。 このように， 無酸化炉内で酸化処理してから還 元炉内で還元処理することによって， 熱延鋼板表面に F e層を形成 することができる。 鋼板表面の F e O等の酸化膜は溶融めつきを付 着し難くするので， 鋼板の表面からこれを除去することによって溶 融めっきに対するめっき濡れ性を向上させる効果がある。 However, steel sheets manufactured by the thin slab continuous forging method have the problem that it is more difficult to create surface quality than steel sheets manufactured by conventional continuous forging machines. For this reason, until recently, the continuous slab forging method was not widely used. In addition, there is very little information on hot-rolled steel sheets produced by the thin slab continuous forging method, and when hot-dip galvanizing is applied to these hot-rolled steel sheets, The method used for this was applied as it was. Generally, the “non-oxidation furnace method” is used as a method for hot-rolling hot-rolled steel sheets. In this method, hot-rolled steel sheets are continuously passed through a non-oxidation furnace-, a reduction furnace (annealing furnace), and a cooling furnace, and are heated to high temperatures for oxidation-reduction treatment. In this way, an Fe layer can be formed on the surface of a hot-rolled steel sheet by oxidizing in a non-oxidizing furnace and then reducing in a reduction furnace. An oxide film such as FeO on the surface of the steel sheet makes it difficult for the adhesion of the melt to adhere, so removing this from the surface of the steel sheet has the effect of improving the plating wettability against hot dipping.
上記のような従来の溶融メツキ設備は， 冷延鋼板を通板すること を主な目的で設計されているので， 加熱帯での昇温速度はほぼ 1 0 °C / s 〜 2 0 °C Z s の範囲であった。 更に， この溶融メツキ設備を 使用して熱延鋼板にメツキ処理を行う場合には， 一般的な鋼におい ては再結晶烤鈍を行う必要は無いので， 焼鈍時の最高温度は 6 4 0 °C〜 6 6 0 °C程度に調整するのが普通であった。  The conventional melt-meshing equipment as described above is designed mainly for passing cold-rolled steel sheets, so the heating rate in the heating zone is approximately 10 ° C / s to 20 ° CZ. It was in the range of s. In addition, when the hot-rolled steel sheet is subjected to a squeeze treatment using this melt-meshing equipment, there is no need to recrystallize in general steel, so the maximum temperature during annealing is 640 ° C. It was normal to adjust the temperature to about C ~ 660 ° C.
なお， 他の方法として 「どぶ漬けめつき法 （フラックス法） 」 等 も知られている。 この方法では， 鋼板表面に塩化亜鉛， 塩化アンモ ニゥム等のフラックスを塗布し， 鋼板表面を活性化させて溶融めつ きに対する濡れ性を向上させる。 しかしながら， この方法は， 連続 的な製造が難しいことやめつき密着性の点で溶融めつき鋼板製造に はあまり一般的ではない。  Other methods are also known, such as the “Dubu pickles method (flux method)”. In this method, fluxes such as zinc chloride and ammonium chloride are applied to the steel sheet surface, and the steel sheet surface is activated to improve the wettability against melting. However, this method is not very common for the production of molten galvanized steel sheets because of the difficulty of continuous production and adhesive adhesion.
薄スラブ連続铸造法を用いて製造した熱延鋼板に， 上述した 「無 酸化炉方式のめっき設備」 を用いた溶融めつき鋼板製造方法で溶融 亜鉛めつきを行う と， 溶融亜鉛めつき圧延鋼板の表面に不めっきが 発生する。 これは， 薄スラブ連続铸造法に特有の C a添加に一因す るものと考えられる。  When hot-rolled steel sheets manufactured using the thin slab continuous forging method are hot-dip galvanized by the hot-dip galvanized steel sheet manufacturing method using the “non-oxidizing furnace type plating equipment” described above, Non-plating occurs on the surface. This is thought to be due to the Ca addition characteristic of the continuous slab forging method.
薄スラブ連続铸造機は， 従来の連続铸造機に比べて铸型の幅が非 常に狭く， 主入ノズルも特殊構造をしているので， アルミナによる ノズル詰まりが生じやすい。 そこで， これを防止するために， 薄ス ラブ連続铸造機では， 取鍋内に C aを添加してアルミナの融点を下 -げている。 Thin slab continuous forging machines have a very narrow width compared to conventional continuous forging machines, and the main inlet nozzle has a special structure. Nozzle clogging easily occurs. Therefore, in order to prevent this, in thin slab continuous forging machines, Ca is added to the ladle to lower the melting point of alumina.
薄スラブ連続铸造法では， 踌造された 5 0 m mから 8 0 m m程度 のスラブを高温に保ったまま圧延工程に直送して圧延する。 この熱 間圧延機は， 従来の熱間圧延工程の仕上げ圧延機に相当する熱間圧 延機であり， 1 . 2 m mから 4 m m程度の厚みまで圧延して， 熱延 鋼板を製造する。 この場合に， 薄スラブを保温するために， 滞在時 間が長いトンネル炉を用いるので， 圧延前のスラブ表面に生成する スケールの量が多い。  In the thin slab continuous forging method, the forged slabs of 50 to 80 mm are sent directly to the rolling process for rolling while maintaining a high temperature. This hot rolling mill is a hot rolling mill equivalent to the conventional finishing mill in the hot rolling process, and it rolls from 1.2 mm to 4 mm to produce hot rolled steel sheets. In this case, a tunnel furnace with a long residence time is used to keep the thin slab warm, so the amount of scale generated on the slab surface before rolling is large.
前述したように添加して薄スラブ内に残存した C aは上記のスケ ール内で酸化して， C a Oの形態で留まる。 その結果， この C a添 加によって生.成された酸化物 C a Oが， メツキ工程での無酸化炉内 で酸化する際に， 熱延鋼板表面の酸化膜にむらゃピッ 卜を生じさせ て， 溶融亜鉛めつきとのめっき濡れ性を部分的に劣化させ， めっき 不良が生じていると考えられる。  As described above, Ca remaining in the thin slab after addition is oxidized in the scale and remains in the form of CaO. As a result, when the oxide C a O formed by this Ca addition is oxidized in a non-oxidizing furnace in the plating process, it causes unevenness in the oxide film on the surface of the hot-rolled steel sheet. Thus, the plating wettability with the hot dip galvanizing is partially degraded, and it is thought that defective plating occurs.
また， 薄スラブ連続铸造法を用いて製造した熱延鋼板は， 従来の 連続铸造機に比べてスマツ 卜の量が多くなることが観察されている 。 これは， 薄スラブ連続铸造法では， 踌造された鋼板を高温に保つ たまま圧延工程に直送して圧延するので， F e 3 C及び Cが鋼板表 面に分離したまま残存しやすいためである。 熱延鋼板の表面にこれ らの F e 3 C等が多く残存すると， 無酸化炉内で酸化をする際に， Cが酸素と反応して， F eの酸化膜の生成が部分的に遅れて， 酸化 膜にむらやピッ トが生成される。 これらのむらやピッ トも， 亜鉛と のめつき濡れ性を低下させてめっき不良を生じさせると考えられる 更に， 薄スラブ連続铸造法を用いて製造した熱延鋼板を， 従来の 溶融めつきラインで製造すると腰折れが発生することが判った。 特 に 2 mm以上の厚みの熱延鋼板で顕著に腰折れが発生した。 この理 -由は， 従来の溶融めつきラインで製造すると， 加熱， 焼鈍段階で必 要以上に降伏点が下がる為に， 特に 2 mm以上の板厚の熱延鋼板を 通板すると.， メツキ後の通板ラインで腰折れが生じる為である。 In addition, it has been observed that hot-rolled steel sheets manufactured using the thin slab continuous forging method have a higher amount of smashed knots than conventional continuous forging machines. This is because, in the thin slab continuous forging method, the forged steel sheet is directly fed to the rolling process while being kept at a high temperature and rolled, so that Fe 3 C and C are likely to remain separated on the steel sheet surface. is there. If a large amount of Fe 3 C or the like remains on the surface of the hot-rolled steel sheet, when it is oxidized in a non-oxidizing furnace, C reacts with oxygen, and the formation of the Fe oxide film is partially delayed. As a result, unevenness and pits are generated in the oxide film. These unevenness and pits are also thought to reduce plating wettability with zinc and cause plating defects. In addition, hot-rolled steel sheets manufactured using a thin slab continuous forging method are It has been found that hip breakage occurs when the product is manufactured on a melt-on line. In particular, hip folding occurred significantly in hot-rolled steel sheets with a thickness of 2 mm or more. The reason for this is that, when manufactured with the conventional fusion staking line, the yield point drops more than necessary during the heating and annealing stages, so when a hot-rolled steel sheet with a thickness of 2 mm or more is passed through. This is because hip breakage occurs in the later threading line.
腰折れを防止するため， 従来， メツキ後に鋼板を加熱して降伏点 を調整する技術や， メツキ後の通板ラインのロール径を大きく して 曲げ歪量を小さくする技術が提案されているが， 前者の技術は操業 が煩雑になる。 後者の技術は， ロールプロフィルなどを精度良く加 ェして径の大きいロールを製造することは， 高度な技術と加工設備 を要するので， その結果としてロールの製造費用が従来よりも， か なり高くなる。 発明の開示  In order to prevent hip folding, conventionally, a technique for adjusting the yield point by heating the steel sheet after plating, and a technique for reducing the bending strain by increasing the roll diameter of the threading line after plating are proposed. The former technique is cumbersome to operate. In the latter technique, it is necessary to add a roll profile and the like to manufacture a roll with a large diameter, which requires advanced technology and processing equipment. As a result, the cost of manufacturing the roll is significantly higher than before. Become. Disclosure of the invention
本発明は， 上記課題に鑑みてなされたものであり， 薄スラブ連続 銬造法で製造した熱延鋼板を溶融めつきする際に， 特に， めっき表 面に発生する不めっきを防止するための手段を提供するものである 上記課題を解決するために， 本発明によれば， 質量％で， C ： 0 • 0 3 %以上， S i : 0. 0 2 %以上， M n : 0. 1 5 %以上， C a ： 0. 0 0 1 %以上を含有する鋼を薄スラブ連続铸造法で铸造及 び熱間圧延して製造した鋼板を， 最高到達鋼板温度が 5 5 0 °C以上 6 5 0 °C未満であって， 昇温速度が 2 5 °C/秒以上で 1 5秒以上の 間加熱して酸化処理し， 最高到達鋼板温度が 7 0 0 °C以上 7 6 0で 以下であって， 鋼板温度が 5 7 0 °C以上である時間が、 2 5秒以上 4 5秒以下であるように加熱して還元処理し， その後， 溶融めつき することによりなる溶融めつき熱延鋼板の製造方法が提供される。 なお， 上記の溶融めつき熱延鋼板の製造方法において， 溶融めつ きを溶融亜鉛めつきにしてもよい。 The present invention has been made in view of the above problems, and particularly for preventing unplating that occurs on the plating surface when hot-rolling steel sheets manufactured by a thin slab continuous forging method are fused. In order to solve the above problems, according to the present invention, in mass%, C: 0 • 0 3% or more, S i: 0.0 2% or more, M n: 0.1 A steel plate produced by forging and hot rolling steel containing 5% or more and C a: 0.0 0 1% or more by the thin slab continuous forging method has a maximum steel plate temperature of 5500 ° C or more 6 The temperature is lower than 50 ° C, the heating rate is 25 ° C / sec or more and heating is performed for 15 seconds or more, and oxidation treatment is performed. The temperature of the steel plate temperature is 5700 ° C or higher and the heat treatment is carried out so that the time is 25 seconds or more and 45 seconds or less. Method for producing a steel sheet is provided. In the above hot-rolled hot-rolled steel sheet manufacturing method, the hot dip may be hot dip galvanized.
また， 本発明によれば， 薄スラブ連続铸造法で铸造及び熱間圧延 して製造した鋼板を溶融めつきする溶融めつき熱延鋼板の製造設備 であって， 酸化に供する炉と還元に供する炉とを有し， 前記酸化に 供する炉と前記還元に供する炉との， 前記鋼板の搬送方向に沿った 長さの比は， 0 . 5以上 0 . 9以下であることを特徴とする， 溶融 めっき熱延鋼板の製造設備が提供される。  In addition, according to the present invention, there is provided a hot-rolled hot-rolled steel sheet manufacturing facility that melts and bonds steel sheets manufactured by forging and hot rolling using a thin slab continuous forging method, which are used for oxidation and for reduction. A ratio of the length along the conveying direction of the steel sheet between the furnace used for oxidation and the furnace used for reduction is 0.5 or more and 0.9 or less, Equipment for manufacturing hot-dip hot-rolled steel sheets is provided.
なお， 上記溶融めつき熱延鋼板の製造設備において， 前記鋼板が 前記酸化に供する炉を通過する時間を 1 5秒以上 2 5秒以下にして もよい。  In the production facility for hot-rolled hot-rolled steel sheets, the time for the steel sheets to pass through the furnace for the oxidation may be 15 seconds or more and 25 seconds or less.
本発明によれば， 薄スラブ連続铸造法で製造した熱延鋼板を溶融 めっきする際に， めっき表面に発生する不めっきを防止することが 可能となる。 また， 腰折れを発生することなく溶融めつきすること も可能となる。 図面の簡単な説明  According to the present invention, it is possible to prevent non-plating generated on the plating surface when hot-rolling a hot-rolled steel sheet manufactured by a thin slab continuous forging method. It is also possible to melt and melt without causing hip breaks. Brief Description of Drawings
図 1は， 本発明に係る好適な溶融亜鉛めつき熱延鋼板製造設備の 構成図である。  Fig. 1 is a block diagram of a preferred hot-rolled steel sheet manufacturing facility with hot-dip galvanized steel according to the present invention.
図 2は， 本発明に係る好適な溶融亜鉛めつき熱延鋼板製造設備の 無酸化炉及び焼鈍炉での温度変化を説明した図である。  FIG. 2 is a diagram illustrating temperature changes in a non-oxidation furnace and an annealing furnace of a suitable hot-rolled galvanized steel sheet manufacturing facility according to the present invention.
図 3は， 薄スラブ連続铸造法により製造された熱延鋼板を， 酸化 する前後の図である。 （ a ) は酸化する前の熱延鋼板を示し， （ b ) は本発明によって酸化された後の熱延鋼板を示し， （ c ) は従来 技術によって酸化された後の熱延鋼板を示す。  Figure 3 is a diagram before and after the oxidation of a hot-rolled steel sheet manufactured by the thin slab continuous forging method. (A) shows the hot-rolled steel sheet before oxidation, (b) shows the hot-rolled steel sheet after oxidation according to the present invention, and (c) shows the hot-rolled steel sheet after oxidation according to the prior art.
図 4は， 無酸化炉で酸化された熱延鋼板を， 還元する前後の図で ある。 （ cT) は還元する前の熱延鋼板を示し， （ e ) 'は過不足なく 還元された熱延鋼板を， （ f ) は還元が不十分な熱延鋼板を， （ g ) は還元が過剰な熱延鋼板をそれぞれ示す。 Figure 4 is a diagram before and after reducing the hot-rolled steel sheet oxidized in a non-oxidizing furnace. (CT) indicates the hot-rolled steel sheet before reduction, and (e) ' The reduced hot-rolled steel sheet, (f) indicates the hot-rolled steel sheet with insufficient reduction, and (g) indicates the hot-rolled steel sheet with excessive reduction.
図 5は， 溶融めつき設備前面の洗浄装置の構成図である。 発明を実施するための最良の形態  Fig. 5 is a block diagram of the cleaning device in front of the fusion fitting equipment. BEST MODE FOR CARRYING OUT THE INVENTION
以下， 図面を参照しながら， 本発明の好適な実施形態について説 明をする。 なお， 本明細書及び図面において， 実質的に同一の機能 構成を有する要素については， 同一の符号を付した。  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, elements having substantially the same functional configuration are denoted by the same reference numerals.
本発明では， 溶融亜鉛めつき熱延鋼板製造方法で製造する溶融め つき鋼板として， J I S G 3 3 0 2に定める溶融亜鉛めつき鋼 板 S GH C , S GH 3 4 0 , S GH 4 0 0 , S GH 4 4 0 , S GH 5 4 0等を対象とし， 質量％で， C : 0. 0 3 %以上， S i : 0. 0 2 %以上，. M n : 0. 1 5 %以上， C a : 0. 0 0 1 %以上を含 有する鋼を薄スラブ連続銬造法で铸造 ， 圧延して製造した鋼板を用 レ る。  In the present invention, the hot-dip galvanized steel sheet manufactured by the hot-dip galvanized hot-rolled steel sheet manufacturing method is used as a hot-dip galvanized steel sheet as defined in JISG 330. S GH C, S GH 3 400, S GH 400 , S GH 4 4 0, S GH 5 4 0, etc., by mass%, C: 0.0 3% or more, S i: 0.0 2% or more,. M n: 0.1 5% or more , C a: 0.0 0 1 Steel sheets produced by rolling and rolling steel containing 1% or more by the thin slab continuous forging method are used.
C aは ， 0 . 0 0 1 %未満では， ノズル詰まりが防止できないこ とがあるので , それ以上含有される C aの添加は通常， 製鋼工程 で， 脱酸した後の溶鋼中に C a A 1 や C a S i もしくは F e C a， メタリツク C aを添加することにより行われる。  If C a is less than 0.001%, nozzle clogging may not be prevented, so addition of more Ca is usually added in the steelmaking process. This is done by adding A 1, C a S i, F e C a, or metallic Ca.
図 1は , 本発明に係る好適な溶融亜鉛めっき熱延鋼板製造設備 1 の構成図である。 この溶融亜鉛めつき熱延鋼板製造設備は， 溶融亜 鉛めつき工程ラインの始点である送出 Uール 1 0， 終点である巻取 リール 1 1， それらのリール 1 0， 1 1間に配設された予熱炉 （図 示せず） ， 無酸化炉 1 2， 還元帯 1 3 と冷却帯 1 4とを含む焼鈍炉 1 5， 溶融亜鉛めつき槽 1 6， ワイビング装置 1 7， 及び冷却炉 1 8で構成される。  FIG. 1 is a configuration diagram of a suitable hot-dip galvanized hot-rolled steel sheet manufacturing facility 1 according to the present invention. This hot-dip galvanized hot-rolled steel sheet manufacturing facility is arranged between the delivery reel 1 0 which is the starting point of the molten zinc plating process line, the take-up reel 1 1 which is the end point, and the reels 10 and 1 1. Preheated furnace (not shown) installed, non-oxidizing furnace 1 2, annealing furnace 1 5 including reduction zone 1 3 and cooling zone 1 4, molten zinc plating bath 1 6, wiping device 1 7, and cooling furnace Consists of 1-8.
送出リーリレ 1 0は， 質量％で， C ： 0. 0 3 %以上， S i ·· 0. 0 2 %以上， M n : 0. 1 5 %以上， C a : 0. 0 0 1 %以上を含 有する鋼を， 薄スラブ連続铸造法で铸造後， 温度を下げずにそのま -ま圧延して製造した熱延鋼板が巻かれたリールである。 Sending relay 10 is mass%, C: 0.0 3% or more, S i. 0 2% or more, M n: 0.15% or more, C a: 0.0 0 1 After steel is forged by the continuous slab forging method, it is rolled as it is without lowering the temperature. It is a reel on which a hot-rolled steel plate manufactured in this way is wound.
無酸化炉 1 2は, 送出リールから送出された熱延鋼板を酸化する ための， 鋼.板の搬送方向の長さが例えば 1 5 m以上 2 5 m以下の炉 である。 この実施の形態の場合， 通板速度が 1 2 0 mノ分であるの で， 無酸化炉 1 2内での熱延鋼板の酸化時間は 7秒以上 1 2秒以下 になる。 無酸化炉 1 2内の燃料空気比は， 0. 9以上 0. 9 8以下 程度に設定されている。 また， 無酸化炉 1 2に予熱炉を加えた搬送 方向の長さは， 例えば 3 0 m以上 5 0 m以下に設定されている。 無 酸化炉 1 2 と予熱炉における全体酸化時間 （通過時間） は， 1 5秒 以上 2 5秒以下になる。  The non-oxidizing furnace 12 is a furnace with a length in the steel-plate transport direction of, for example, 15 m or more and 25 m or less for oxidizing the hot-rolled steel sheet sent from the delivery reel. In this embodiment, the plate speed is 120 m, so the oxidation time of the hot-rolled steel sheet in the non-oxidizing furnace 12 is 7 seconds or more and 12 seconds or less. The fuel-air ratio in the non-oxidizing furnace 1 2 is set to 0.9 or more and 0.98 or less. In addition, the length in the transfer direction when the preheating furnace is added to the non-oxidizing furnace 12 is set to 30 m or more and 50 m or less, for example. The total oxidation time (passage time) in the non-oxidizing furnace 1 2 and the preheating furnace is 15 to 25 seconds.
無酸化炉 1 2に連続的に配設された焼鈍炉 1 5は， 酸化された熱 延鋼板を還元するための還元帯 1 3 と， その後に熱延鋼板を冷却す るための冷却帯 1 4とから構成され， その搬送方向の長さが例えば 7 0 m以上 1 0 0 m以下の炉である。 この実施の形態の場合， 通板 速度が 1 2 0 m 分であるので， 焼鈍炉 1 5内で.の熱延鋼板の還元 時間は， 例えば， 比較的還元が早い 5 7 0 °C以上の領域で 2 5秒以 上 4 5秒以下になる。 また， H2 及び N 2 等を焼鈍炉 1 5内の雰囲 気とする。 なお， 還元が主に行われる還元帯 1 3は， 還元炉及び均 熱炉， 若しくは還元炉のみで構成され， その搬送方向の長さは， 例 えば 5 0 m以上 7 O m以下に設定されている。 An annealing furnace 15 arranged continuously in a non-oxidizing furnace 1 2 includes a reduction zone 1 3 for reducing the oxidized hot-rolled steel sheet, and then a cooling zone 1 for cooling the hot-rolled steel sheet. This is a furnace with a length in the transport direction of, for example, 70 m or more and 100 m or less. In this embodiment, since the plate speed is 1 20 m, the reduction time of the hot-rolled steel sheet in the annealing furnace 15 is, for example, 5 70 ° C or more, which is relatively fast. It takes 25 to 45 seconds in the area. In addition, H 2 and N 2 are used as the atmosphere in the annealing furnace 15. Note that the reduction zone 13 in which reduction is mainly performed consists of a reduction furnace and a soaking furnace, or only a reduction furnace, and its length in the transfer direction is set to, for example, 50 m or more and 7 O m or less. ing.
溶融亜鉛めつき槽 1 6は， 熱延鋼板を浸潰させて溶融めつきを付 着させるための槽である。 ワイビング装置 1 7は， 熱延鋼板に付着 した過剰の溶融金属を気体により払拭する装置である。 冷却炉 1 8 は， その後に熱延鋼板を冷却するための炉である。  The hot-dip galvanizing tank 16 is a tank for smashing hot-rolled steel sheets to attach the hot-dip. The wiping device 17 is a device that wipes excess molten metal adhering to the hot-rolled steel sheet with gas. The cooling furnace 18 is a furnace for cooling the hot-rolled steel sheet afterwards.
次に， 述の溶融亜鉛めつき熱延鋼板製造設備 1 を用いた溶融亜 鉛めつき熱延鋼板製造方法を図 2〜図 4を用いて説明する。 Next, the molten sublimation using the hot-rolled steel sheet manufacturing facility 1 described above was used. A method for producing a lead-plated hot-rolled steel sheet will be described with reference to FIGS.
図 2は， 熱延鋼板が溶融亜鉛めつき熱延鋼板製造設備 1 の無酸化 -炉 1 2， 還元帯 1 3 , 及び冷却帯 1 4を通過する際の鋼板表面の温 度変化を示した図である。 図 2において， 熱延鋼板が無酸化炉 1 2 に進入する?显度点が 0， 無酸化炉 1 2から退出する温度点が P， 還 元帯 1 3の還元炉に進入する温度点が Q , 還元帯 1 3の還元炉から 退出して還元帯 1 3の均熱炉に侵入する温度点が S , 還元帯 1 3の 均熱炉から退出して冷却帯 1 4に進入する温度点が T， そして， 冷 却帯 1 4から退出する温度点が Vである。  Figure 2 shows the temperature change of the steel sheet surface when the hot-rolled steel sheet passes through the non-oxidation-furnace 12, reduction zone 1 3, and cooling zone 1 4 of the hot-rolled steel plate manufacturing facility 1. FIG. In Fig. 2, the hot rolled steel sheet enters the oxidation furnace 1 2? The display point is 0, the temperature point exiting the oxidation furnace 1 2 is P, and the temperature point entering the reduction furnace in the reduction zone 1 3 is Q, the temperature point exiting from the reduction furnace in the reduction zone 1 3 and entering the soaking furnace in the reduction zone 1 3 is the temperature point exiting from the soaking furnace in the reduction zone 1 3 and entering the cooling zone 1 4 Is T, and the temperature point exiting from the cooling zone 14 is V.
まず， 薄スラブ連続铸造法で製造された熱延鋼板が， 送出リール 1 0から送出されて， ライン上を進行し， 予熱炉を経て無酸化炉 1 2内に入る。  First, a hot-rolled steel sheet manufactured by a thin slab continuous forging method is sent out from the delivery reel 10, proceeds on the line, enters the non-oxidation furnace 12 through the preheating furnace.
無酸化炉 1. 2内に入った熱延鋼板は， 図 2の区間 Iに示すように ， 最高到達鋼板温度が 5 5 0 °C以上 6 0 0 °C未満になるように， 昇 温速度 2 5 °C Z秒以上で 1 5秒以上 2 5秒以下の間， 加熱されて， 熱延鋼板の表面が酸化処理される。 ここで酸化処理される時間とは ， 予熱帯と無酸化炉の通過時間である。  As shown in section I of Fig. 2, the temperature of the hot-rolled steel sheet that entered the non-oxidizing furnace 1.2 is increased so that the maximum steel sheet temperature is not less than 5500 ° C and less than 600 ° C. The surface of the hot-rolled steel sheet is oxidized by heating for 25 to 25 seconds at temperatures of 25 ° CZ to 15 seconds. The time for oxidation treatment here is the pre-tropical and non-oxidizing furnace transit time.
この酸化処理の前後の熱延鋼板表面を図 3 に示す。 図 3 ( a ) は ， 酸化する前の熱延鋼板を示し， 図 3 ( b ) は本発明によって酸化 された後の熱延鋼板を示し， そして， 図 3 ( c ) は， 従来技術によ つて酸化された後の熱延鋼板を示す。  Figure 3 shows the hot-rolled steel sheet surface before and after this oxidation treatment. Fig. 3 (a) shows the hot-rolled steel plate before oxidation, Fig. 3 (b) shows the hot-rolled steel plate after oxidation according to the present invention, and Fig. 3 (c) shows that according to the prior art. The hot-rolled steel sheet after being oxidized is shown.
図 2の区間 I での昇温速度を， 上述した従来の昇温速度よりも速 い 2 5 °C /秒以上に設定したことにより， 不めっきの発生を防止す る効果が得られる。 これに対して， 区間 I での昇温速度を 2 5で 秒未満にすると， C a添加によって生成された酸化物 C a〇及び力 ルシゥム—アルミネート， 並びにスマッ トの F e 3 C等が原因で不 めっきが発生してしまう。 昇温速度を 2 5で/秒以上'に設定したこ とで不めっきが防止される理由を以下に説明する。 By setting the rate of temperature rise in section I in Fig. 2 to 25 ° C / sec or higher, which is faster than the conventional rate of temperature rise described above, the effect of preventing non-plating can be obtained. On the other hand, if the heating rate in section I is 25 seconds and less than 2 seconds, the oxide Ca a and Ca succinate produced by the addition of Ca, the luminum aluminate, and the smut Fe 3 C, etc. This causes non-plating. Set the heating rate to 25 / sec or more. The reason why non-plating is prevented will be described below.
図 3 ( a ) に示すように， 熱延鋼板表面の F e酸化膜は， . F e層 -の F e原子が表層に移動し， 酸素と反応して生成される。 また， F e酸化膜が生成される際には， 鋼板内に存在する S i及び M nも F e同様に酸化されるので， F e酸化膜の下には S i 〇 2 及び M n O 等の 2次酸化膜が生成される。 ここで， F e酸化膜が生成される際 に， 図 3 ( a ) に示す C a Oや F e 3 C等が鋼板表面に付着してい ると， F e酸化膜の生成が阻害され， 図 3 ( c ) に示すピッ ト 1 9 を形成してしまう。 F e 3 Cの場合は， Cに分解されて酸素と反応 し， 図 3 ( c ) に示すように， F e酸化膜の生成を阻害する。 上述 のように， ピッ ト 1 9が形成されると， 図 3 ( c ) に示すように， S i 02 及び M n O等の 2次酸化膜が表面に出てしまう。 これら S i O 2 及び M n O等の 2次酸化膜は， 溶融亜鉛めつきとの濡れ性を 劣化させるので， 溶融亜鉛めつきをする際に不めっきを発生させて しまう。 As shown in Fig. 3 (a), the Fe oxide film on the surface of the hot-rolled steel sheet is formed by the reaction of Fe atoms in the. Further, F e when the oxide film is generated, since the S i and M n present in the steel sheet is also F e Similarly oxide, F e under the oxide film S i 〇 2 and M n O A secondary oxide film is produced. Here, when the F e oxide film is produced, the C a O and F e 3 C, etc. illustrated in FIG. 3 (a) that adhered to the steel sheet surface, the generation of F e oxide film is inhibited, The pit 19 shown in Fig. 3 (c) is formed. In the case of Fe 3 C, it decomposes into C and reacts with oxygen, inhibiting the formation of the Fe oxide film, as shown in Fig. 3 (c). As described above, the pit 1 9 is formed, as shown in FIG. 3 (c), 2-order oxide film such as S i 0 2 and M n O will come out to the surface. Secondary oxide film such as these S i O 2 and M n O Since degrade the wettability with molten zinc plated, thereby to generate a non-coating when the molten zinc plated.
そこで， 本願では， 昇温速度を 2 5 °CZ秒以上と高い値に設定し ， F e酸化膜の生成速度を大きく した。  Therefore, in this application, the rate of temperature increase was set to a high value of 25 ° CZ seconds or more, and the rate of Fe oxide film formation was increased.
加熱温度が高くなると， 酸化膜の生成は促進されるので， 加熱速 度が大きいほど， 酸化膜の生成速度が大きくなる。 酸化膜の生成は 主に F eの表面への移動で起きるので， 酸化膜の生成速度が大きい と， 結果的に C a Oや F e 3 C等を鋼板表面に押し出すことになり , C a Oや F e 3 C等でたとえピッ トが生成されても底部にも F e 酸化膜が形成されることになる。 As the heating temperature increases, the formation of oxide film is promoted, so the higher the heating rate, the higher the oxide film formation rate. Oxide film formation occurs mainly due to the movement of Fe to the surface, so if the oxide film formation rate is high, Ca O, Fe 3 C, etc. will be pushed out to the steel plate surface as a result. Even if pits are generated with O, Fe 3 C, etc., an Fe oxide film is also formed at the bottom.
この作用は， 加熱時には， 鋼板表面の酸素濃度が高いので， 鋼板 の極表面には F e 2 O 3 (へマタイ ト） が形成されていると推定さ れる。 F e 2 〇 3 の生成は， 酸素が鋼板の内側に拡散することで進 行すると言'われている。 このことから， 結果的に C a' Oや F e 3 C 等を鋼板表面に押し出されていると考えられる。 This effect is presumed to be due to the formation of Fe 2 O 3 (hematite) on the extreme surface of the steel sheet because the oxygen concentration on the steel sheet surface is high during heating. Generation of F e 2 〇 3, oxygen is we saying 'With progression by diffusion inside the steel sheet. As a result, C a 'O and F e 3 C Etc. are thought to be extruded on the steel sheet surface.
表面の F e酸化膜の内部の酸素濃度は， 表層から内部になるほど -少なくなるので， F e 2 O 3 の下側には， 5 7 0 °C以下では F e 3 The oxygen concentration inside the Fe oxide film on the surface decreases as it goes from the surface layer to the inside. Therefore, below F e 2 O 3 , F e 3
O 4 (マグネタイ 卜） が生成して， 5 7 0 °C以上では F e o (ウス タイ ト） が生成する。 これらの F e 3 04 や F e Oは F eイオンの 外方拡散により成長する。 そこで， 5 7 O t 以上では 刖記の鋼板 の極表層には F e 2 03 が生成し， その下には F e 3 O 4 ， その下 には F e Oが生成する。 5 7 0 °C未満では極表層には F e 2 〇 3 がO 4 (Magnetite 卜) is generated, and Feo (Wustite) is generated above 5700 ° C. These F e 3 0 4 and F e O grow by outward diffusion of Fe ions. Therefore, at 5 7 Ot or more, Fe 2 03 is generated on the pole surface layer of the steel sheet described below, Fe 3 O 4 is formed below it, and Fe O is formed below it. Below 5 70 ° C, Fe 2 0 3
， その下には F e 3 O 4 が生成する。 Under this, Fe 3 O 4 is formed.
これらの， F e Oや F e 2 O 3 の下には， 鋼中の S ίや M n濃度 が高い場合には， S i もしくは M nの酸化物もしくは S i と M nの 複合酸化物からなる 2次酸化膜が生成する。 Under these F e O and F e 2 O 3 , when the concentration of S ί and M n in the steel is high, the oxide of S i or M n or the composite oxide of S i and M n A secondary oxide film consisting of
もしも， C a Oや F e 3 C等が鋼板表面に付着していて , 表面に 押し出されない状態が発生すると， C a Oや F e 3 C等により， 表 層からの酸素の供給が遮断されるので， C a O F e 3 C等の下に は， 直接， S i もしくは M nの酸化物もしくは S i と nの複合酸 化物からなる 2次酸化膜が生成する。 この場合には， 引さ If C a O or F e 3 C adheres to the surface of the steel plate and does not push out, the oxygen supply from the surface is blocked by C a O or F e 3 C. Therefore, a secondary oxide film consisting of an oxide of S i or M n or a complex oxide of S i and n is directly formed under C a OF e 3 C. In this case, pull
処理の過程で， 表面の C a Oや F e 3 C等が落ちると S i あしく は M nの酸化物もしくは S i と M nの複合酸化物が表面に露出した 状態のピッ トが生成されて， その結果， メツキ後に不メッキが検出 される。 In the course of processing, S i Ashiku When C a O and F e 3 C of the surface falls in the pit in the state exposed on the surface a composite oxide of oxide or S i and M n M n of the generated As a result, non-plating is detected after plating.
しかし， 前述したように， 昇温速度を 2 5 °C/秒以上と高い値に 設定した場合には， 鋼板表面に付着した C a 0や F e 3 C等が， 表 面に押し出されるので， 押し出された後のピッ 卜の酸素濃度が高く なり， この部分に F e 3 O 4 や F e'〇が生成するので， S i もしく は M nの酸化物もしくは S i と M nの複合酸化物が表面に露出した 状態になる とは無い。 ' これにより， C a Oや F e 3 C等の阻害を受けて F e酸化膜に， 図 3 ( b ) に示すピッ ト 1 9が形成されても， このピッ ト 1 9の底 -部にも F e酸化膜が形成される。 従って， S i O 2 及び M n O等の 2次酸化膜が F e酸化膜で覆われて鋼板表面に出てこない。 However, as described above, when the heating rate is set to a high value of 25 ° C / sec or higher, C a 0, Fe 3 C, etc. adhering to the steel plate surface are pushed out to the surface. , The oxygen concentration in the pipe after the extrusion becomes high, and Fe 3 O 4 and F e'O are formed in this part. Therefore, the oxides of S i or M n or S i and M n The composite oxide is not exposed on the surface. ' Thus, the F e oxide film receives the inhibition of such C a O and F e 3 C, be formed pit 1 9 shown in FIG. 3 (b), the bottom of the pit 1 9 - the part Also Fe oxide film is formed. Thus, S i O 2 and the secondary oxide film such as M n O does not come out to the covered with steel sheet surface F e oxide film.
すなわち.， 昇温過程を終了した時の鋼板表面の性状は， 図 3 ( b ) に示す様に， 内側から， F e (鋼板） ， S i もしくは M nの酸化 物もしくは S i と M nの複合酸化物からなる 2次酸化膜， その上に ， F e a O 4 と F e Oもしくは F e Oからなる酸化膜， 表面に C a O, F e 3 Cが存在して， C a〇， F e 3 Cの下にピッ トは有るが， F e O層が存在している形態になっている。 In other words, the properties of the steel sheet surface after the temperature rising process are as follows from the inside: Fe (steel sheet), oxides of S i or M n, or S i and M n, as shown in Fig. 3 (b). secondary oxide film comprising a composite oxide, thereon, F ea O 4 and F e O or oxide film consisting of F e O, C a O on the surface, there exists F e 3 C, C A_〇 , There is a pit under F e 3 C, but the F e O layer exists.
これに対して， 昇温速度を 2 5 °CZ秒未満に設定すると， C a O や F e 3 C等が表面に押し出されにくいので， 図 3 ( c ) のように ， S i もしくは M nの酸化物もしくは S i と M nの複合酸化物から なる 2次酸化膜が表面に出てしまう。 On the other hand, if the heating rate is set to less than 25 ° CZ seconds, C a O, F e 3 C, etc. are difficult to be pushed out to the surface, so S i or M n as shown in Fig. 3 (c). Or a secondary oxide film composed of a complex oxide of S i and M n appears on the surface.
なお， F e (鋼板） 上の S i もしくは M nの酸化物もしくは S i と M nの複合酸化物からなる 2次酸化膜を， 図 3 ( b ) ， ( c ) で は， " S i O 2 , M n O" と簡略化して記載した。 Note that a secondary oxide film consisting of S i or M n oxide or a composite oxide of S i and M n on F e (steel plate) is shown in Figs. 3 (b) and 3 (c) as "S i O 2 , M n O "
また， 無酸化炉内での最高到達鋼板温度を 5 5 0 °C以上に設定し たことにより， 酸化層が均一に生成されて， 酸化膜表層部分に存在 する C a Oや F e 3 C等の除去が容易になる効果が得られる。 この 効果は， 最高到達鋼板温度を 5 5 0 °C未満にすると得られない。 In addition, by setting the maximum temperature of the steel sheet in the non-oxidizing furnace to 5500 ° C or higher, an oxide layer is uniformly formed and C a O and F e 3 C existing in the surface layer of the oxide film. The effect of facilitating the removal of etc. is obtained. This effect cannot be obtained if the maximum steel sheet temperature is less than 5500 ° C.
さらに， 無酸化炉内での最高到達鋼板温度を 6 0 0 °C未満に設定 したことにより， 酸化膜の過剰の生成が防止される。 無酸化炉内で の最高到達鋼板温度を 6 0 0 °C以上にすると， 酸化膜が過剰に生成 され， 後の還元処理で酸化膜が残存してしまう。  In addition, by setting the maximum steel plate temperature in the non-oxidizing furnace to less than 600 ° C, excessive oxide film formation is prevented. If the maximum steel sheet temperature in the non-oxidizing furnace is 60 ° C or higher, an oxide film is excessively generated, and the oxide film remains in the subsequent reduction process.
この場合に， 昇温速度を 2 5で 秒以上に保持する時間は 1 5秒 以上とす^。 1 5秒未満では， 充分な酸化膜厚みが有られないで， その結果， S i もしくは M nの酸化物もしくは S i と M nの複合酸 化物からなる 2次酸化膜が F e〇膜で覆われる事無く表面に露出し -てしまう。 In this case, the time for keeping the temperature rising rate at 25 or more seconds is 15 seconds or more ^. In less than 5 seconds, there is not enough oxide thickness, As a result, the secondary oxide film composed of S i or M n oxide or S i and M n complex oxide is exposed to the surface without being covered with the FeO film.
次に， 図 2の区間 IIに示すように， 酸化された熱延鋼板は， ライ ン上を進行し， 焼鈍炉 1 5内の還元帯 1 3に入る。 焼鈍炉 1 5内で は， まず， 還元帯 1 3で， 最高到達鋼板温度が 7 0 0 °C以上 7 6 0 °C以下になるように， 加熱されて， その後， 冷却帯 1 4に進められ て冷却される。 熱延鋼板は， 焼鈍炉内の還元帯 1 3及び冷却帯 1 4 において， 鋼板温度を 5 7 0 °C以上に保った状態で 2 5秒以上 4 5 秒以下の間， 還元処理される。 即ち， 図 2において， 鋼板温度が 5 7 0 °Cである温度点 Rから温度点 Uまでの時間が， 2 5秒以上 4 5 秒以下に設定される。  Next, as shown in Section II in Fig. 2, the oxidized hot-rolled steel sheet travels on the line and enters the reduction zone 13 in the annealing furnace 15. In the annealing furnace 15, first, in the reduction zone 1 3, the steel sheet is heated so that the maximum steel plate temperature is not less than 700 ° C and not more than 7600 ° C, and then proceeds to the cooling zone 14. And cooled. The hot-rolled steel sheet is reduced in the reduction zone 13 and cooling zone 14 in the annealing furnace for a period of 25 to 45 seconds with the steel plate temperature kept at 570 ° C or higher. In other words, in Fig. 2, the time from temperature point R to temperature point U, where the steel plate temperature is 5700 ° C, is set to 25 to 45 seconds.
ここで， 5. 7 0 °C以上の温度の領域に還元処理の温度を限った理 由は次の通りである。 すなわち， 5 7 0 以上では €〇が 6酸 化物の主体になり還元されるのに対し， 5 7 0 °C未満では， F e 3 04 が F e酸化物の主体になり還元される。 F e Oは F e 3 〇 4 に 比べて， 処理温度も高いこともあり還元されやすい。 したがって， F e Oを還元処理する方が， F e 3 04 を還元処理するよりも制御 しゃすいためである。 Here, the reason why the temperature of the reduction treatment is limited to a temperature range of 5.70 ° C or higher is as follows. In other words, at 5 70 or higher, € ○ becomes the main component of 6 oxides and is reduced, while at less than 570 ° C, Fe 30 4 becomes the main component of Fe oxides and reduced. F e O is compared to F e 3 〇 4, the process temperature is also likely to be also available reducing high. Therefore, the reduction treatment of F e O is more controllable than the reduction treatment of F e 30 4 .
上記の還元処理の前後の熱延鋼板表面を図 4に示す。 還元処理す る前の熱延鋼板が （ d) ， 過不足なく還元処理された熱延鋼板が （ e ) ， 還元処理が不十分な熱延鋼板が （ f ) , 及び還元処理が過剰 な熱延鋼板が （ g) である。 なお， 図 4において， 図 3 に示した C 3〇及び € 3 Cが図示されていないが， これは， これらの C a O 及び F e 3 Cが， 焼鈍炉 1 3等を通過する際に還元雰囲気 H2 及び N 2 等の流れにより鋼板表面から吹き飛ばされてしまうためである なお， F e (鋼板） 上に形成される S i もしくは M nの酸化物も しくは S i と M nの複合酸化物からなる 2次酸化膜を， 図 4でも" - S i O 2 , n O " と簡略化して記載した。 Fig. 4 shows the surface of the hot-rolled steel sheet before and after the above reduction treatment. The hot-rolled steel sheet before reduction treatment is (d), the hot-rolled steel sheet that has been reduced without excess (e), the hot-rolled steel sheet with insufficient reduction treatment (f), and the heat that is excessively reduced. The rolled steel sheet is (g). In Fig. 4, C 30 and € 3 C shown in Fig. 3 are not shown. This is because these C a O and F e 3 C pass through the annealing furnace 13 and the like. This is because the reducing atmosphere is blown off from the steel sheet surface by the flow of H 2 and N 2 etc. Note that a secondary oxide film of Si or Mn oxide or a composite oxide of Si and Mn formed on Fe (steel plate) is also shown in Fig. 4 as "-S i O 2 , The description is simplified as n O ".
その結果， 図 3 ( b ) の形態の酸化膜が適度に還元されて図 4 ( e ) の様に.， 内側から， F e (鋼板） ， S i もしくは M nの酸化物 もしくは S i と M nの複合酸化物からなる 2次酸化膜， その上に F eからなる膜が存在して， 表面に C a O， F e 3 Cが存在していた ピッ トは残存する力 その底には F e層が存在している形態になる 熱延鋼板を， 最高到達鋼板温度が 7 0 0 °C以上 7 6 0 °C以下にな るように， 鋼板温度を 5 7 0 °C以上に保った状態で 2 5秒以上 4 5 秒以下の間， 還元処理することにより， 図 4 ( d ) に示す熱延鋼板 の表面が焼鈍炉 1 5内で過不足なく還元される。 As a result, the oxide film in the form of Fig. 3 (b) is moderately reduced, as shown in Fig. 4 (e). From the inside, Fe (steel plate), S i or M n oxide or S i secondary oxide film comprising a composite oxide of M n, exist film made F e thereon, C a O on the surface, pit of F e 3 C was present in the force the bottom remaining The hot-rolled steel sheet in the form with the Fe layer is made to have a steel sheet temperature of 5700 ° C or higher so that the highest steel sheet temperature is 700 ° C or higher and 760 ° C or lower. By maintaining the temperature for 25 to 45 seconds, the surface of the hot-rolled steel sheet shown in Fig. 4 (d) is reduced in the annealing furnace 15 without excess or deficiency.
即ち， 図 4 ( e ) に示すように， 無酸化膜で生成された F e酸化 膜が， 還元処理されて全て F e層になる。 また， この F e層は， 酸 化処理及び還元処理等で生成される S i O 2 及び M n〇等の 2次酸 化膜も完全に覆っている。 溶融亜鉛めつきとのめっき濡れ性を劣化 させる S i 0 2 及び M n O等の 2次酸化膜が， 完全に覆われている ので， めっき濡れ性が非常に良好となり， 不めっきは発生しない。 In other words, as shown in Fig. 4 (e), the Fe oxide film formed by the non-oxidized film is all reduced to Fe layer. Also, the F e layer 2 Tsugisan of film such as S i O 2 and M N_〇 generated by acid treatment and reduction treatment or the like even completely covers. Degradation of plating wettability with hot dip zinc plating The secondary oxide film such as S i 0 2 and M n O is completely covered, so the plating wettability is very good and no plating occurs. .
これに対して， 最高到達鋼板温度が 7 0 0 °C未満である場合又は 鋼板温度を 5 7 0 °C以上に保つ時間が 2 5秒未満である場合には， 焼鈍炉 1 5内での還元が不十分になり， 図 4 ( f ) に示すように， F e酸化膜が残存してしまう。 従って， この F e酸化膜が， 溶融め つきに対するめっき濡れ性を劣化させるので不めっきが発生してし まう。  On the other hand, if the maximum steel sheet temperature is less than 700 ° C, or if the time for keeping the steel sheet temperature above 5700 ° C is less than 25 seconds, The reduction becomes insufficient, and the Fe oxide film remains as shown in Fig. 4 (f). Therefore, this Fe oxide film degrades the plating wettability against fusion plating, and unplating will occur.
また， 最高到達鋼板温度が 7 6 0 °Cを超過する場合又は鋼板温度 を 5 7 0 以上に保つ時間が 4 5秒を超過する場合には， 焼鈍炉 1 5内での還元が過剰になる。 この場合， 図 4 ( g ) に示すように， F e酸化膜は， 十分に還元処理されて F e層が形成される。 しかし -ながら， S i及び M nは F eよりも酸化力が強いので， F e酸化膜 が焼鈍炉 1 5で還元される際にも S i O 2 及び M n〇の二次酸化層 は過剰に成長し， 鋼板表面に出てしまう。 前述したように， S i 〇 2 及び M n 0は，' 鋼板のめっき濡れ性を劣化させるので， 不めっき が生じてしまう。 If the maximum steel sheet temperature exceeds 7600 ° C, or if the time for maintaining the steel sheet temperature at 5700 or higher exceeds 45 seconds, the annealing furnace 1 Reduction within 5 becomes excessive. In this case, as shown in Fig. 4 (g), the Fe oxide film is sufficiently reduced to form the Fe layer. However, since S i and M n have higher oxidizing power than Fe, the secondary oxide layer of S i O 2 and M n 0 is not removed even when the Fe oxide film is reduced in the annealing furnace 15. It grows excessively and appears on the surface of the steel sheet. As described above, S i 0 2 and M n 0 deteriorate the plating wettability of the steel sheet, resulting in non-plating.
次に， 還元された熱延鋼板は， ライン上を焼鈍炉 1 5から所定温 度に加熱された溶融亜鉛めつき槽 1 6 に進行し， 浸潰されて溶融亜 鉛めつきが付着される。  Next, the reduced hot-rolled steel sheet proceeds on the line from the annealing furnace 15 to a hot-dip zinc plating tank 16 heated to a predetermined temperature, and is crushed to adhere the molten zinc plating. .
次に， 溶融亜鉛めつきの付着した熱延鋼板は， ライン上を進行し ， 熱延鋼板上の溶融亜鉛めつき付着量がワイビング装置 1 7で所定 量に調整される。  Next, the hot-rolled steel sheet with hot-dip galvanized steel advances on the line, and the amount of hot-dip galvanized steel on the hot-rolled steel sheet is adjusted to a predetermined value by the wiping device 17.
次に， 熱延鋼板は， ライン上を進行し， 冷却炉 1 8内で冷却され る。  Next, the hot-rolled steel sheet travels on the line and is cooled in the cooling furnace 18.
以上の実施の形態では， 無酸化炉 1 2内に入った熱延鋼板を， 最 高到達鋼板温度が 5 5 0 °C以上 6 0 0 °C未満になるように， 昇温速 度 2 5 °C /秒以上で 1 5秒以上 2 5秒以下の間， 加熱酸化処理した ので， F e酸化膜が生成される際に， F e 3 C等のスマッ ト及び C a系酸化物によってピッ ト 1 9が生じても， このピッ ト 1 9の底部 が F e酸化膜によって覆われる。 In the above embodiment, the temperature of the hot-rolled steel sheet in the non-oxidizing furnace 12 is increased so that the highest steel sheet temperature is not less than 55 ° C and less than 60 ° C. Since it was heated and oxidized for 15 to 25 seconds at a temperature of ° C / second or more, when an Fe oxide film was formed, it was picked up by a Fe 3 C and other Ca and oxides of Ca. Even if pit 19 is generated, the bottom of pit 19 is covered with the Fe oxide film.
また， 以上の実施の形態では， 酸化された熱延鋼板を， 最高到達 鋼板温度が 7 0 0 °C以上 7 6 0 °C以下になるように， 鋼板温度を 5 7 0 °C以上に保った状態を 2 5秒以上 4 5秒以下の間， 加熱して還 元処理したので， 熱延鋼板表面の F e酸化膜が過不足なく還元され る。 さらに， S i 0 2 及び M n Oの二次酸化層も表面に出てこない 。 従って， 不めっきの発生が防 される。 また， 以上の実施の形態では， 酸化に供する炉 （予熱炉及び無酸 化炉 1 2 ) の搬送方向の長さを 3 0 m以上 5 0 m以下に設定し， 還 -元に供する炉 （還元帯 1 3 ) の搬送方向の長さを 5 0 m以上 7 0 m 以下に設定した。 実験により， 酸化に供する炉と還元に供する炉と の， 熱延鋼板の搬送方向に沿った長さの比が， 0 . 5以上 0 . 9以 下の場合に， 良好なめっき状態が得られることが判明した。 本実施 の形態において， 酸化に供する炉と還元に供する炉との搬送方向に 沿った長さの比を， 0 . 5以上 0 . 9以下になるように設定するこ とで， 不めっきの発生を防止できる。 また， 酸化に供する炉と還元 に供する炉が， 過不足の無い適正な長さに設定されるので， 設備コ ス トの投資が適正化される。 In the above embodiment, the hot-rolled steel sheet is kept at a temperature of 5700 ° C or higher so that the maximum steel plate temperature is 70 ° C or higher and 7600 ° C or lower. Since the heat treatment was reduced for 25 to 45 seconds, the Fe oxide film on the surface of the hot-rolled steel sheet was reduced without excess or deficiency. Further, secondary oxidation layer of S i 0 2 and M n O also not come to the surface. Therefore, the occurrence of non-plating is prevented. In the above embodiment, the length in the transport direction of the furnace used for oxidation (preheating furnace and non-oxidizing furnace 12) is set to 30 m or more and 50 m or less, and the furnace used for the return-( The length of the reduction zone 1 3) in the conveyance direction was set to 50 m or more and 70 m or less. Experiments show that a good plating condition can be obtained when the ratio of the length along the conveying direction of the hot-rolled steel sheet between the furnace used for oxidation and the furnace used for reduction is 0.5 or more and 0.9 or less. It has been found. In this embodiment, non-plating occurs by setting the length ratio of the furnace used for oxidation and the furnace used for reduction along the conveying direction to be 0.5 or more and 0.9 or less. Can be prevented. In addition, the furnace used for oxidation and the furnace used for reduction are set to appropriate lengths with no excess or deficiency, so investment in equipment costs is optimized.
以上， 添付図面を参照しながら本発明の好適な実施形態について 説明したが， .本発明は係る例に限定されない。 当業者であれば， 特 許請求の範囲に記載された技術的思想の範疇内において，' 各種の変 更例又は修正例に想到し得ることは明らかであり， それらについて も当然に本発明の技術的範囲に属するものと了解される。  The preferred embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person skilled in the art can conceive of various modifications or modifications within the scope of the technical idea described in the scope of the patent claims, and these are naturally also included in the present invention. It is understood that it belongs to the technical scope.
また， 上述した実施形態においては， 熱延鋼板が送出'リールから 送出されているが， 薄スラブ連続铸造法を行うラインに直接接続さ れてもよい。  In the embodiment described above, the hot-rolled steel sheet is delivered from the delivery reel, but may be directly connected to a line for performing the thin slab continuous forging method.
また， 上述した実施形態においては， 熱延鋼板が送出リールから 無酸化炉に送出されるが， 無酸化炉に送出される前に酸洗及び表面 のスクラブ処理等の処理が行われてもよい。  In the above-described embodiment, the hot-rolled steel sheet is sent from the delivery reel to the non-oxidation furnace, but before being sent to the non-oxidation furnace, processing such as pickling and surface scrubbing may be performed. .
また， 上述した実施形態においては， 熱延鋼板が送出リールから 無酸化炉内に送出されて酸化されているが， 酸化の前に酸洗及び表 面のスクラブ処理等の処理のための装置を設けてもよい。  In the embodiment described above, the hot-rolled steel sheet is fed from the feed reel into the non-oxidizing furnace and oxidized. It may be provided.
また， 上述した実施形態においては， 還元帯及び冷却帯を含む焼 鈍炉を用い" rいるが， 還元炉及び冷却炉等のように別個の炉を用い てもよい。 In the embodiment described above, an annealing furnace including a reduction zone and a cooling zone is used. However, separate furnaces such as a reduction furnace and a cooling furnace are used. May be.
また， 上述した実施形態においては， 溶融めつきとして溶融亜鉛 -めっきを用いているが， 亜鉛以外にアルミニウム， 鉛， 錫等を用い てもよい。  In the embodiment described above, hot dip galvanizing is used as the hot dip, but aluminum, lead, tin, etc. may be used in addition to zinc.
また， 上,述した実施形態においては， 本発明は， 熱延鋼板におい て特に効果を発揮する。 この理由は， 熱延鋼板の表面の方が冷延鋼 板の表面よりも， 粒界が粗く， 表面積が大きく， 酸化及び還元が容 易であり， 酸化層の成長速度が大きいためと推定される。  In the embodiment described above, the present invention is particularly effective for hot-rolled steel sheets. The reason for this is presumably that the surface of the hot-rolled steel plate is rougher than the surface of the cold-rolled steel plate, has a larger grain boundary, has a larger surface area, is easier to oxidize and reduce, and has a higher growth rate of the oxide layer. The
ここで， 冷延鋼板の溶融亜鉛めつき条件における酸化量及び還元 量と比較するために， 本発明の酸化， 還元条件下で良好なめっき状 態が得られた熱延鋼板に対して， '従来的な冷延鋼板の酸化量， 還元 量を推定する式を適用して， 熱延鋼板の酸化量と還元量を算出する 冷延鋼板の酸化量を推定する式は， 予熱炉及び無酸化炉内に滞在 する時間と鋼板の到達温度との 2変数から酸化量を推定する。 冷延 鋼板の還元量を推定する式は， 還元処理を行う炉内に滞在する時間 と鋼板の到達温度との 2変数から還元量を推定する。 この還元量を 推定する際には， 還元炉の温度が 5 7 0 °C以上の場合の還元量と， 5 7 0 °C未満の場合の還元量とを別個に算出し， 両者の和を還元量 と推定する。 これらの酸化量及び還元量を推定する式の具体的な形 は示さないが， 実験から導出可能である。  Here, in order to compare the oxidation amount and reduction amount of the cold-rolled steel sheet under the hot dip galvanizing condition, the hot-rolled steel sheet with a good plating state obtained under the oxidation and reduction conditions of the present invention Applying the conventional formulas for estimating the amount of oxidation and reduction of a cold-rolled steel sheet to calculate the amount of oxidation and reduction of a hot-rolled steel sheet The formula for estimating the amount of oxidation of a cold-rolled steel sheet is based on preheating furnace and non-oxidation The amount of oxidation is estimated from two variables: the time spent in the furnace and the temperature reached by the steel sheet. The formula for estimating the reduction amount of cold-rolled steel sheets estimates the reduction quantity from two variables: the time spent in the furnace where the reduction treatment is performed and the ultimate temperature of the steel sheet. When estimating the reduction amount, the reduction amount when the temperature of the reduction furnace is 570 ° C or higher and the reduction amount when it is lower than 570 ° C are calculated separately, and the sum of the two is calculated. Estimated reduction amount. Although specific forms of these equations for estimating oxidation and reduction are not shown, they can be derived from experiments.
薄スラブ铸造機で得られた铸片を熱延して得られた熱延鋼板を， 本発明で規定する好適な酸化， 還元の条件下で酸化， 還元し， その 際の酸化量， 還元量の値を上記酸化量， 還元量を推定する式より求 めた。 その結果， 酸化量は 0. 1 2〜 0. 2mgZm2 程度になり ， 還元量は 0. 2〜 0. 3 5mg/m2 程度になった。 これらの値 は， 同じ式 り得られる冷延板の酸化量 0. l O .' SmgZm2 ， 還元量 0 . 4 5〜l m g Z m 2 に比べて小さくなつている。 The hot-rolled steel sheet obtained by hot-rolling the flakes obtained with a thin slab forging machine is oxidized and reduced under the suitable oxidation and reduction conditions specified in the present invention, and the oxidation amount and reduction amount at that time Was obtained from the above formulas for estimating the amount of oxidation and reduction. As a result, the oxidation amount was about 0.1 2 to 0.2 mgZm 2 and the reduction amount was about 0.2 to 0.3 5 mg / m 2 . These values are the amount of oxidation of the cold-rolled sheet obtained by the same formula 0. l O. 'SmgZm 2 , Reduction amount is smaller than 0.4 5 to lmg Z m 2 .
上記結果から， 冷延鋼板の場合よりも酸化速度及び還元速度が速 -いので熱延鋼板を溶融亜鉛めつきする際の好適な酸化量及び還元量 の計算値が冷延鋼板の場合のそれらの値より も小さい値が得られて いると推定できる。  From the above results, the oxidation rate and reduction rate are faster than in the case of cold-rolled steel sheets. It can be estimated that a value smaller than the value of is obtained.
本発明を熱延鋼板の溶融亜鉛めつきに適用することにより， 冷延 鋼板に適用する場合に比べて， 酸化時間， 還元時間を短縮できる。 また， 酸化や還元を行う炉の長さを短くすることができ， 溶融亜鉛 めつき設備を小型化できる。  By applying the present invention to hot dip galvanizing of hot-rolled steel sheets, the oxidation time and reduction time can be shortened compared to when applied to cold-rolled steel sheets. In addition, the length of the furnace for oxidation and reduction can be shortened, and the hot-dip zinc plating facility can be made smaller.
ところで， 本発明の溶融メツキ設備の前面には， 図 5に示すよう に， アルカリスプレータンク 2 0， アルカリスクラバタンク 2 1 , 温水リンスタンク 2 2 , ホッ トェアドライヤ 2 3よりなる電解洗浄 を用いないアルカリ洗浄装置とナイロンブラシ 2 4によるアルカリ スクラバを設置している。 一般的に用いられている電解洗浄を用い ない理由は， 薄スラブ連続铸造機と， これに直結した熱間圧延機で 熱延鋼板を製造する場合には， 熱間圧延した後に， 鋼板表面を酸洗 して， 防鲭剤を塗布するが， 酸洗してから溶融メツキを行うまでの 時間が 2 日以内程度であり短い為に， 防鲭剤の塗布量が通常より少 なくても良いためである。  By the way, as shown in FIG. 5, the front surface of the melt-meshing equipment of the present invention is an alkali that does not use electrolytic cleaning comprising an alkali spray tank 20, an alkali scrubber tank 2 1, a hot water rinse tank 2 2, and a hot air dryer 2 3. An alkaline scrubber is installed with a cleaning device and nylon brush 24. The reason why electrolytic cleaning, which is generally used, is not used, is that when a hot-rolled steel sheet is manufactured by a thin slab continuous forging machine and a hot rolling machine directly connected to this, the surface of the steel sheet is removed after hot rolling. Pickling and applying antifungal agent, but since the time from pickling to melting is about 2 days or less, the amount of antifungal agent applied may be less than usual. Because.
しかし， 酸洗後の鋼板表面には， 通常よりも少ない量の防鲭剤ゃ F e 3 C等が残存しているので， 電解洗浄を用いないアルカリ洗浄 装置を用いて表面に付着している防鲭剤ゃ F e 3 C等を洗浄した後 にナイロンブラシによるアル力リスクラバを行い， 防鲭剤ゃ F e 3 C等を除去する。 However, since the surface of the steel plate after pickling contains a smaller amount of antifungal agent, such as Fe 3 C, it adheres to the surface using an alkaline cleaning device that does not use electrolytic cleaning. It performed Al force Risukuraba with a nylon brush after washing the anti鲭剤Ya F e 3 C, etc., to remove the anti鲭剤Ya F e 3 C and the like.
この洗浄により， 通常は， 加熱炉で燃焼除去している防鲭剤は除 去させるので， 加熱炉では， 鋼板表面の酸化に安定して雰囲気中の 酸素が使用される。 したがって， 酸化膜の生成量が安定するので， 安定した不メツキの防止には好ましい条件になる。 This cleaning usually removes the fungicide that has been burned and removed in the heating furnace. In the heating furnace, oxygen in the atmosphere is used stably for oxidation of the steel sheet surface. Therefore, the amount of oxide film produced is stable, This is a preferable condition for the prevention of stable unsettledness.
なお， 薄スラブ铸造機で得られた铸片を熱延して得られた熱延鋼 Note that hot-rolled steel obtained by hot-rolling the flakes obtained with a thin slab forging machine
-板を対象とした時の酸化量と還元量の適正の比は， 実験により 0 . -The appropriate ratio between the amount of oxidation and the amount of reduction when using a plate as a target is 0.
4〜 0 . 5 5程度であることが判明した。 これに対し， 従来の冷延 鋼板の場合には， 0 . 2〜 1 . 2程度と値にばらつきがあった。  It was found to be about 4 to 0.55. In contrast, in the case of conventional cold-rolled steel sheets, the values varied from about 0.2 to 1.2.
さらに、 本発明のような酸化工程， 還元工程を用いると， 薄スラ ブ連続铸造機で製造したスラブを直接熱延して製造した熱延鋼板の 厚みが 2 m m以上であっても， メツキ後の工程で， 通常の 1 5 0 0 m mの径の搬送口一ルを用いても腰折れが発生しないことを確認し た。  Furthermore, when the oxidation process and reduction process as in the present invention are used, even if the thickness of a hot-rolled steel sheet produced by directly hot-rolling a slab produced by a thin slab continuous forging machine is 2 mm or more, In this process, it was confirmed that the hips did not break even when a normal 1500 mm diameter transfer port was used.
この理由は， 酸化工程での昇温速度を 2 5 °C / s としたことと， 還元時間を従来の冷延鋼板の還元工程よりも短く したことで， 鋼板 の降伏点が高くなり， 降伏伸びを生じる歪以下で通板出来る様にな つた為に， 腰折れを発生することが無くなつたためと推定される。 なお， 現状の技術での， 通常の通板速度は 9 0 m p m〜 1 8 0 m p mであるので， 本発明を適用して， この速度範囲を有する溶融め つき設備を新設または改造できる。 溶融めつき設備の通板速度の上 限は， 現状の技術では 1 8 0 m p m程度である。 しかし， もしも， 更に通板速度が大きい溶融めつき設備が出来ても， 本技術は適用で きる。 また， 通板速度の下限は， 本発明の条件を実現できれば， い く らでも良い。  The reason for this is that the rate of temperature increase in the oxidation process was set to 25 ° C / s and that the reduction time was shorter than that of the conventional cold-rolled steel sheet, resulting in an increase in the yield point of the steel sheet. This is presumably due to the fact that it is possible to pass through below the strain that causes elongation, so that there is no occurrence of hip folding. In addition, since the normal sheet feeding speed in the current technology is 90 mpm to 180 mpm, the present invention can be applied to newly install or remodel a fusion fitting equipment having this speed range. With the current technology, the upper limit of the plate-feeding speed of the fusion fitting equipment is about 180 mpm. However, this technology can be applied even if a fusing device with a higher sheet feeding speed is available. Also, the lower limit of the plate feed speed is not limited as long as the conditions of the present invention can be realized.
溶融亜鉛めつき設備の中には， 垆の経済的トン Z h r制限を行つ ている場合があり， この様な場合には， 板厚が厚くなると通板速度 を下げるので， 酸化炉を通過する時間が長くなり， その結果， 平均 の昇温速度は小さくなる。 この場合には， 昇温工程の一部が， 本発 明の昇温速度を満足するように操業しても良い。 実施例 1 Some hot-dip galvanizing facilities have an economic ton limit of Z ton Z hr. In such a case, the plate speed decreases as the plate thickness increases, so it passes through the oxidation furnace. As a result, the average heating rate decreases. In this case, part of the heating process may be operated to satisfy the heating rate of the present invention. Example 1
薄スラブ連続铸造法を用いて製造した 4種類の熱延鋼板 A , B， - C , 及び Dの各成分を質量％で表したものを表 1 に示す。  Table 1 shows the percentages of each of the four types of hot-rolled steel sheets A, B, -C, and D manufactured using the thin slab continuous forging method.
表 1  table 1
Figure imgf000021_0001
本発明に係る溶融亜鉛めつき熱延鋼板製造の方法を用いて， これ ら 4種の熱延鋼板から溶融亜鉛めつき熱延鋼板を製造した際の， 種 々の条件及びその結果を表 2に示す。 溶融亜鉛めつき熱延鋼板の製 造は， 4種の熱延鋼板を予熱炉， 無酸化炉， 還元炉， 均熱炉， 及び 冷却炉内を通過させて， 酸化処理， 還元処理， 及び冷却処理し， そ の後， 溶融亜鉛めつきして行った。
Figure imgf000021_0001
Table 2 shows the various conditions and the results when hot-rolled steel sheets with hot-dip galvanized steel were produced from these four types of hot-rolled steel sheets using the method for manufacturing hot-rolled steel sheets with hot-dip galvanized steel according to the present invention. Shown in The hot-rolled steel sheet with hot dip galvanized steel is made by passing four types of hot-rolled steel sheets through a preheating furnace, non-oxidation furnace, reduction furnace, soaking furnace, and cooling furnace to perform oxidation treatment, reduction treatment, and cooling. It was processed and then hot-dip zinc plating was performed.
溶融亜鉛めつきの付着量は 8 0〜 1 2 0 g Z m 2 (片面） の範囲 であった。 The adhesion amount of molten zinc was in the range of 80 to 120 g Zm 2 (single side).
表 2  Table 2
Figure imgf000021_0002
表 2に示すように， データ番号 1〜 4は， 本発明で規定する条件 を全て満たす実施例であり， 製造された溶融亜鉛めつき熱延鋼板の 表面は， 非常に良好なめつき状態になっている。 一方， 表 2に示すデ一夕番号 5 〜 9は， 本発明で規定する条件の いずれかを満たさない比較例であり， 製造された溶融亜鉛めつき熱 -延鋼板の表面は， 不めっき又はスケール残り等のめっき不良状態に なっている。 実施例 2
Figure imgf000021_0002
As shown in Table 2, data Nos. 1 to 4 are examples that satisfy all of the conditions specified in the present invention, and the surface of the hot-rolled hot-rolled steel sheet produced is in a very good condition. ing. On the other hand, Tables 5 through 9 shown in Table 2 are comparative examples that do not satisfy any of the conditions specified in the present invention. The surface of the hot-dip hot-rolled steel sheet produced was not plated or The plating is in poor condition such as scale residue. Example 2
薄スラブ連続錡造法を用いて製造した 2種類の熱延鋼板 A及び B の各成分を質量％で表したものを表 3 に示す。  Table 3 shows the percentages of the components of two types of hot-rolled steel sheets A and B manufactured using the thin slab continuous forging method.
表 3
Figure imgf000022_0001
本発明に係る溶融亜鉛めつき熱延鋼板製造の方法を用いて， これ ら 2種の熱延鋼板から溶融亜鉛めつき熱延鋼板を製造した際の種々 の条件及びその結果を表 4に示す。 溶融亜鉛めつき熱延鋼板の製造 は， 2種の熱延鋼板を予熱炉及び無酸化炉で酸化処理し， 還元帯 （ 還元炉及び均熱炉） で還元処理し， その後， 溶融亜鉛めつきして行 つた。 なお， この実験においては， 予熱炉及び無酸化炉が酸化に供 する炉に相当し， 還元帯が還元に供する炉に相当する。 Table 3
Figure imgf000022_0001
Table 4 shows the various conditions and the results when the hot-rolled galvanized steel sheet was manufactured from these two types of hot-rolled steel sheets using the method for manufacturing hot-dip galvanized steel sheets according to the present invention. . Hot-rolled steel sheet with hot-dip galvanized steel is manufactured by oxidizing two types of hot-rolled steel sheets in a preheating furnace and non-oxidation furnace, reducing them in a reduction zone (reduction furnace and soaking furnace), and then hot-dip galvanizing. And went. In this experiment, the preheating furnace and the non-oxidizing furnace correspond to the furnace used for oxidation, and the reduction zone corresponds to the furnace used for reduction.
表 4  Table 4
Figure imgf000022_0002
表 4に示すデータ番号 3及び.4は， 予熱炉の長さを 1 7 m， 無酸 化炉の長さを 2 1 mに固定し， 冷却条件を変化させ， 還元帯の長さ が擬似的 4 1 mと 7 8 mになるように調整した。 還元時間は， 1 2 0 m/分の通板速度から， 算出した値である。
Figure imgf000022_0002
Data Nos. 3 and 4 shown in Table 4 indicate that the length of the preheating furnace is fixed at 17 m, the length of the deoxidizer is fixed at 21 m, the cooling conditions are changed, and the length of the reduction zone is simulated. Adjusted to 4 1 m and 78 m. Reduction time is 1 It is a value calculated from the feeding speed of 20 m / min.
表 4に示すように， データ番号 1及び 2は， 予熱炉及び無酸化炉 - の合計の長さと還元帯の長さとの比が， 本発明で規定する 0. 5以 上 0. 9以下の範囲内にある条件を満たす実施例であり， 製造され た溶融亜鉛めつき熱延鋼板の表面は， 非常に良好なめっき状態にな つている。  As shown in Table 4, data numbers 1 and 2 indicate that the ratio of the total length of the preheating furnace and the non-oxidizing furnace to the length of the reduction zone is 0.5 or more and 0.9 or less as defined in the present invention. In this example, the surface of the hot dip galvanized hot-rolled steel sheet is in a very good plating condition.
一方， 表 4に示すデータ番号 3及び 4は， 予熱炉及び無酸化炉の 合計の長さと還元帯の長さとの比が， 本発明で規定する 0. 5以上 0. 9以下の範囲から外れている比較例であり， 製造された溶融亜 鉛めつき熱延鋼板の表面は， 不めっき等のめっき不良状態になって いる。  On the other hand, data numbers 3 and 4 shown in Table 4 indicate that the ratio of the total length of the preheating furnace and the non-oxidation furnace to the length of the reduction zone is outside the range of 0.5 or more and 0.9 or less specified in the present invention. In this comparative example, the surface of the hot-rolled steel sheet with molten zinc plated is in a poor plating condition such as non-plating.
なお， 本発明は， 上記の実施例に示した通板速度範囲で実施して いる。 この場合に， 通板速度の上限は， 現状の技術では 1 8 O m p m程度である。 しかし， もしも， 更に通板速度が大きい溶融めつき 設備が出来ても， 本技術は適用できる。  It should be noted that the present invention is implemented within the plate speed range shown in the above example. In this case, the upper limit of the plate feed speed is about 18 O m pm with the current technology. However, this technology can be applied even if a fusing device with a higher sheet feeding speed is available.
また， 通板速度の下限は， 本発明の条件を実現できれば， いく ら でも良い。 現状の技術での， 通常の通板速度は 9 0 m p m〜 1 8 0 mp mであるので， 溶融亜鉛めつき設備の中には， 炉の経済的トン Zh r制限を行っている場合があり， この様な場合には， 板厚が厚 くなると通板速度を下げるので， 酸化炉を通過する時間が長くなり , その結果， 昇温速度は小さくなる。 この場合には， 昇温工程の一 部が， 本発明の昇温速度を満足するように操業しても良い。 産業上の利用可能性  The lower limit of the plate feed speed is not limited as long as the conditions of the present invention can be realized. Since the normal sheet feeding speed in the current technology is 90 mpm to 180 mpm, some hot-dip zinc plating equipment may have an economic ton of Zr h limit. In such a case, the plate passing speed decreases as the plate thickness increases, so the time required to pass through the oxidation furnace increases, and as a result, the heating rate decreases. In this case, a part of the heating process may be operated so as to satisfy the heating rate of the present invention. Industrial applicability
本発明によれば， 薄スラブ連続铸造法で製造した熱延鋼板を溶融 亜鉛めつきする場合において， めっき表面に発生する不めっきを防 止する際に有効である。  According to the present invention, when hot-rolled steel sheets manufactured by a thin slab continuous forging method are hot-dip galvanized, it is effective in preventing non-plating generated on the plating surface.

Claims

請 求 の 範 囲 The scope of the claims
1. 質量％で， C : 0. 0 3 %以上， S i : 0. 0 2 %以上， M n ： 0. 1 5 %以上， C a : 0. 0 0 1 %以上を含有する鋼を薄ス ラブ連続铸.造法で铸造及び熱間圧延して製造した鋼板を， 1. Steel containing, by mass%, C: 0.03% or more, Si: 0.02% or more, Mn: 0.15% or more, Ca: 0.00 1% or more Thin slab continuous forging. Steel sheet manufactured by forging and hot rolling
最高到達鋼板温度が 5 5 0 °C以上 6 5 0 °C未満であって， 昇温速 度が 2 5 °C/秒以上で 1 5秒以上の間加熱して酸化処理し，  The maximum steel sheet temperature is 55 ° C or more and less than 65 ° C, the heating rate is 25 ° C / sec or more and it is heated for 15 seconds or more and oxidized.
最高到達鋼板温度が 7 0 0 °C以上 7 6 0 °C以下であって， 鋼板温 度が 5 7 0 °C以上である時間が、 2 5秒以上 4 5秒以下であるよう に加熱して還元処理し，  Heat the steel sheet so that the maximum steel plate temperature is 700 ° C or higher and 76 ° C or lower, and the time when the steel plate temperature is 57 ° C or higher is 25 seconds or more and 45 seconds or less. Reduced,
その後， 溶融めつきすることを特徴とする， 溶融めつき熱延鋼板 の製造方法。  A method for manufacturing hot-rolled hot-rolled steel sheets, which is then melt-bonded.
2. 前記溶融めつきは， 溶融亜鉛めつきであることを特徴とする ， 請求の範囲 1 に記載の溶融めつき熱延鋼板の製造方法。  2. The method for producing a hot-rolled hot-rolled steel sheet according to claim 1, wherein the hot-dip galvanizing is hot-dip galvanizing.
3. 薄スラブ連続铸造法で铸造及び熱間圧延して製造した鋼板を 溶融めつきする溶融めつき熱延鋼板の製造設備であって，  3. A production facility for hot-rolled hot-rolled steel sheets that melts and smelts steel sheets produced by forging and hot rolling using a thin slab continuous forging method,
酸化に供する炉と還元に供する炉とを有し，  A furnace for oxidation and a furnace for reduction;
前記酸化に供する炉と前記還元に供する炉との， 前記鋼板の搬送 方向に沿った長さの比は， 0. 5以上 0. 9以下であることを特徴 とする， 溶融めつき熱延鋼板の製造設備。  The ratio of the length along the conveying direction of the steel sheet between the furnace used for oxidation and the furnace used for reduction is 0.5 or more and 0.9 or less. Manufacturing equipment.
4. 前記鋼板が前記酸化に供する炉を通過する時間は， 1 5秒以 上 2 5秒以下であることを特徴とする， 請求の範囲 3に記載の溶融 めっき熱延鋼板の製造設備。  4. The hot-rolled hot-rolled steel sheet manufacturing equipment according to claim 3, wherein the time required for the steel sheet to pass through the furnace for oxidation is 15 seconds or more and 25 seconds or less.
PCT/JP2006/306987 2005-03-30 2006-03-27 Process for producing hot-dipped hot-rolled steel sheet WO2006106999A1 (en)

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