WO2014017034A1 - Method for producing high-strength hot-dip galvanized steel sheets - Google Patents

Method for producing high-strength hot-dip galvanized steel sheets Download PDF

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WO2014017034A1
WO2014017034A1 PCT/JP2013/004173 JP2013004173W WO2014017034A1 WO 2014017034 A1 WO2014017034 A1 WO 2014017034A1 JP 2013004173 W JP2013004173 W JP 2013004173W WO 2014017034 A1 WO2014017034 A1 WO 2014017034A1
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vol
less
hot
steel sheet
dip galvanized
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Japanese (ja)
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麻衣 宮田
洋一 牧水
善継 鈴木
長滝　康伸
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Ｊｆｅスチール株式会社
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/01—Layered products comprising a layer of metal all layers being exclusively metallic
    • B32B15/013—Layered products comprising a layer of metal all layers being exclusively metallic one layer being formed of an iron alloy or steel, another layer being formed of a metal other than iron or aluminium
    • 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
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
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    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • 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
    • 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
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/04—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the coating material
    • C23C2/06—Zinc or cadmium or alloys based thereon
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C2/00—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor
    • C23C2/34—Hot-dipping or immersion processes for applying the coating material in the molten state without affecting the shape; Apparatus therefor characterised by the shape of the material to be treated
    • C23C2/36—Elongated material
    • C23C2/40—Plates; Strips
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • 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
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0236—Cold rolling
    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0273—Final recrystallisation annealing

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
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  • Chemical Kinetics & Catalysis (AREA)
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  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
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Abstract

A method for producing high-strength hot-dip galvanized steel sheets having excellent surface stability is provided. Hot-dip galvanization is carried out on cold-rolled steel sheets containing, in mass%, 0.040 to 0.200% carbon, 0.70 to 2.30% silicon, 0.80 to 2.80% manganese, not more than 0.100% phosphorus, not more than 0.010% sulfur, not more than 0.100% aluminum, and not more than 0.0080% nitrogen, with the remainder comprising iron and incidental impurities. Hot-dip galvanization is carried out after heating the cold-rolled steel sheets at a temperature of 400 to 750°C in an atmosphere containing 0.10 ≤ O2 ≤ 20 vol% and 1 ≤ H2O ≤ 50 vol%, then heating the steel sheets at a temperature of 600 to 850°C in an atmosphere containing 0.01 ≤ O2 ≤ 0.10 vol% and 1 ≤ H2O ≤ 20 vol%, and then maintaining the steel sheets in a temperature range of 750 to 900°C for 15 to 600 seconds in an atmosphere containing 0.05 ≤ H2 ≤ 3.0 vol% and a dew point of 0°C or less.

Description

高強度溶融亜鉛めっき鋼板の製造方法Method for producing high-strength hot-dip galvanized steel sheet
　本発明は、自動車部材として好適な表面安定性に優れた高強度溶融亜鉛めっき鋼板の製造方法に関する。 The present invention relates to a method for producing a high-strength hot-dip galvanized steel sheet having excellent surface stability suitable as an automobile member.
　近年、地球環境の保護意識の高まりから、自動車のＣＯ２排出量削減に向けた燃費改善が強く求められている。これに伴い、車体材料の高強度化での薄肉化を図り、車体を軽量化しようとする動きが活発となってきている。しかしながら、鋼板の高強度化により、延性の低下が懸念される。このため、高強度高延性鋼板の開発が望まれている。 In recent years, with the increasing awareness of global environmental protection, there has been a strong demand for improved fuel efficiency to reduce CO 2 emissions from automobiles. Along with this, movements to reduce the thickness of the vehicle body by increasing the strength of the vehicle body material and to reduce the weight of the vehicle body have become active. However, due to the increase in strength of the steel sheet, there is a concern about a decrease in ductility. For this reason, development of a high-strength and highly ductile steel sheet is desired.
　鋼板の高強度化にはＳｉ、Ｍｎ、Ｐ、Ａｌ等の固溶強化元素の添加が行われる。中でもＳｉやＡｌは鋼の延性を損なわずに高強度化できる利点があり、特にＳｉ含有鋼板は高強度高延性鋼板として有望である。しかし、Ｓｉを多量に含有する高強度鋼板を母材とする溶融亜鉛めっき鋼板及び合金化溶融亜鉛めっき鋼板を製造する場合、以下の問題がある。 Addition of solid solution strengthening elements such as Si, Mn, P and Al is performed to increase the strength of the steel sheet. Among these, Si and Al have an advantage that the strength can be increased without impairing the ductility of the steel. In particular, the Si-containing steel plate is promising as a high strength and high ductility steel plate. However, when producing a hot-dip galvanized steel sheet and an alloyed hot-dip galvanized steel sheet that use a high-strength steel sheet containing a large amount of Si as a base material, there are the following problems.
　溶融亜鉛めっき鋼板の製造においては、非酸化性雰囲気中あるいは還元雰囲気中にて６００～９００℃程度での加熱焼鈍を行い、表層の酸化膜が極めて少ない状態で溶融亜鉛浴へ浸漬し亜鉛めっきを付着させる。なお、この表層の酸化膜は溶融亜鉛との濡れ性を低下させるため、酸化膜が残った状態で溶融亜鉛浴へ浸漬しても亜鉛が十分に付着せず不めっきが生じる。 In the manufacture of hot dip galvanized steel sheets, heat annealing is performed at about 600 to 900 ° C. in a non-oxidizing atmosphere or a reducing atmosphere, and immersed in a hot dip galvanizing bath with extremely little oxide film on the surface layer to perform galvanization. Adhere. Since the surface oxide film reduces wettability with molten zinc, even when immersed in a molten zinc bath with the oxide film remaining, zinc does not adhere sufficiently and unplating occurs.
　しかし、鋼中のＳｉは易酸化性元素であり、一般的に用いられる非酸化性雰囲気中あるいは還元雰囲気中だとＦｅ酸化膜は除去できてもＳｉの酸化は阻止できず、酸化物が表面に濃化し結果として不めっきが生じる。また、不めっきに至らなかった場合でも、付着量制御性に劣るか、または合金化が著しく遅延するという問題がある。特に、合金化の遅延により鋼板の長手および幅方向で合金化速度の差が出やすいため、均一な表面の合金化溶融亜鉛めっき鋼板を得ることが困難となる。 However, Si in steel is an easily oxidizable element, and in a commonly used non-oxidizing atmosphere or reducing atmosphere, even if the Fe oxide film can be removed, the oxidation of Si cannot be prevented, and the oxide is on the surface. As a result, non-plating occurs. Further, even when no plating is not achieved, there is a problem that the adhesion amount controllability is inferior or alloying is significantly delayed. In particular, since the difference in alloying speed tends to occur in the longitudinal and width directions of the steel sheet due to the delay in alloying, it becomes difficult to obtain a galvannealed steel sheet having a uniform surface.
　これらの問題に対し、特許文献１では、鋼板を焼鈍後に酸洗することで表面に濃化した酸化物を強制的に除去し、その後、再び焼鈍し溶融亜鉛めっきを行う方法が開示されている。また、特許文献２では溶融めっきに先立って硫黄または硫黄化合物をＳ量として０．１～１０００ｍｇ／ｍ２付着させた後、水素を含む非酸化性雰囲気中で焼鈍することにより表層に硫化物を生成し、その上に亜鉛めっき層を生成する方法が開示されている。また、特許文献３では、あらかじめ酸化性雰囲気中で鋼板を加熱し、所定以上の酸化速度にて表面にＦｅ酸化膜を急速に生成させることでＳｉの表面濃化を阻止し、その後Ｆｅ酸化膜を還元焼鈍することにより、溶融亜鉛との濡れ性を改善することが開示されている。 For these problems, Patent Document 1 discloses a method of forcibly removing oxides concentrated on the surface by pickling after annealing the steel sheet, and then annealing again to perform hot dip galvanizing. . Further, in Patent Document 2, sulfur or a sulfur compound is deposited in an amount of 0.1 to 1000 mg / m 2 prior to hot dipping, and then annealed in a non-oxidizing atmosphere containing hydrogen to form sulfide on the surface layer. A method for producing and forming a galvanized layer thereon is disclosed. In Patent Document 3, a steel plate is heated in an oxidizing atmosphere in advance, and an Fe oxide film is rapidly formed on the surface at an oxidation rate of a predetermined value or more to prevent Si surface concentration, and thereafter an Fe oxide film. It is disclosed that the wettability with molten zinc is improved by reducing annealing.
日本国特許第３９５６５５０号公報Japanese Patent No. 3957550 日本国特開平１１－５０２２３号公報Japanese Unexamined Patent Publication No. 11-50223 日本国特許第２５８７７２４号公報Japanese Patent No. 2587724
　しかしながら、特許文献１ではＳｉの表面濃化物を除去するための酸洗設備が新たに必要なことからコストがかかるという問題がある。 However, in Patent Document 1, there is a problem in that the cost increases because a pickling facility for removing the Si surface concentrate is newly required.
　特許文献２でも溶融めっきに先立って硫黄または硫黄化合物を付着させる設備を新たに追加する必要が生じる。 Also in Patent Document 2, it is necessary to newly add equipment for attaching sulfur or a sulfur compound prior to hot dipping.
　特許文献３ではＦｅ酸化膜を急速に厚くすることから、Ｆｅ酸化膜厚を前面に亘って均一にするのが困難である。その結果、Ｆｅ酸化膜が厚い場所ではその後の還元が不十分になる。また、Ｆｅ酸化膜が薄い場所では早い段階で還元されるため亜鉛めっき浴までの間にＳｉの表面濃化が生じる。このようにＦｅ酸化膜が厚い場所、薄い場所のいずれにおいても、不均一な酸化膜の存在により、鋼帯の長手および幅方向で付着量や合金化度のムラが生じる。 In Patent Document 3, since the Fe oxide film is rapidly thickened, it is difficult to make the Fe oxide film uniform over the front surface. As a result, the subsequent reduction becomes insufficient at a place where the Fe oxide film is thick. In addition, since the Fe oxide film is reduced at an early stage in the place where the Fe oxide film is thin, the surface concentration of Si occurs before the galvanizing bath. As described above, in any place where the Fe oxide film is thick or thin, the presence of the non-uniform oxide film causes unevenness in the amount of adhesion and the degree of alloying in the longitudinal and width directions of the steel strip.
　上記のように、溶融亜鉛めっき鋼板の高強度化と表面特性の両立を図ることを目的とした従来の技術では、設備追加によるコストの増加が生じるか、または鋼帯長手および幅方向における付着量や合金化度のムラが発生、すなわち表面の安定性に欠けるのが実態であった。 As described above, the conventional technology aimed at achieving both high strength and surface characteristics of hot-dip galvanized steel sheet results in increased costs due to the addition of equipment, or the amount of adhesion in the longitudinal and width directions of the steel strip. In fact, the degree of alloying was uneven, that is, the surface was not stable.
　本発明は、かかる事情に鑑み、高強度を有し、かつ、表面安定性に優れた溶融亜鉛めっき鋼板を製造する方法を提供することを目的とする。 In view of such circumstances, an object of the present invention is to provide a method for producing a hot-dip galvanized steel sheet having high strength and excellent surface stability.
　まず、Ｓｉ濃度が高い鋼板については、Ｆｅ酸化膜生成によるＳｉ表面濃化抑制技術が効果的で、コスト的にも有利であると考えられる。しかし、Ｓｉ表面濃化抑制のためＦｅ酸化膜を過剰に厚くすると、前述のようにＦｅもしくはＳｉの酸化膜が不均一に残存し鋼帯の長手および幅方向で付着量や合金化度のムラが生じてしまう。そこで本発明者らはこの課題を解決するため鋭意検討を重ねた結果、以下の知見を得た。Ｆｅ酸化膜の生成量を最小限にとどめることで鋼帯の長手および幅方向などの場所による酸化膜厚の差を少なくする。と同時に、亜鉛めっき浴への浸漬直前でＦｅ酸化膜の還元が完了する程度の還元速度にとどめることでＳｉが再び表面濃化することを阻止する。その結果、Ｓｉを含有しても高強度かつ鋼帯の長手および幅方向などの場所による付着量や合金化度のムラが少ない鋼板を製造できる。 First, for steel sheets with a high Si concentration, it is considered that the technology for suppressing the enrichment of Si surface by the formation of an Fe oxide film is effective and advantageous in terms of cost. However, if the Fe oxide film is excessively thick in order to suppress Si surface concentration, the Fe or Si oxide film remains non-uniformly as described above, resulting in uneven adhesion and alloying degree in the longitudinal and width directions of the steel strip. Will occur. Therefore, as a result of intensive studies to solve this problem, the present inventors have obtained the following knowledge. By minimizing the amount of Fe oxide film produced, the difference in oxide film thickness depending on the location of the steel strip in the longitudinal and width directions is reduced. At the same time, the surface concentration of Si is prevented from being concentrated again by limiting the reduction rate so that the reduction of the Fe oxide film is completed immediately before immersion in the galvanizing bath. As a result, even if Si is contained, a steel sheet having high strength and less unevenness in the amount of adhesion and the degree of alloying depending on places such as the longitudinal and width directions of the steel strip can be produced.
　さらに具体的な製造方法として、加熱工程を２段階に分けて実施し、積極的なＦｅ酸化膜生成は第１加熱工程だけにとどめ、次の第２加熱工程でＦｅ酸化膜が過剰にならないよう調整し、次に通常よりも低いＨ２濃度で還元速度を抑えながら均熱処理する。 As a more specific manufacturing method, the heating process is divided into two stages, the active Fe oxide film generation is limited to the first heating process, and the Fe oxide film is not excessive in the next second heating process. Next, soaking is performed while suppressing the reduction rate at a lower H 2 concentration than usual.
　具体的には、本発明は以下の特徴を有する。
［１］質量％で、Ｃ：０．０４０～０．２００％、Ｓｉ：０．７０～２．３０％、Ｍｎ：０．８０～２．８０％、Ｐ：０．１００％以下、Ｓ：０．０１０％以下、Ａｌ：０．１００％以下、Ｎ：０．００８０％以下を含有し、残部がＦｅおよび不可避的不純物の成分組成である冷間圧延鋼板に溶融亜鉛めっきを施すに際し、第１加熱工程では、０．１０ｖｏｌ％≦Ｏ２≦２０ｖｏｌ％、１ｖｏｌ％≦Ｈ２Ｏ≦５０ｖｏｌ％を含有する雰囲気中で４００～７５０℃の温度で加熱し、次いで、第２加熱工程では、０．０１ｖｏｌ％≦Ｏ２＜０．１０ｖｏｌ％、１ｖｏｌ％≦Ｈ２Ｏ≦２０ｖｏｌ％を含有する雰囲気中で６００～８５０℃の温度で加熱し、次いで、均熱工程では、０．０５ｖｏｌ％≦Ｈ２≦３．０ｖｏｌ％を含み露点が０℃以下の雰囲気中で７５０～９００℃の温度域で１５～６００秒保持した後、溶融亜鉛めっきを施すことを特徴とする表面安定性に優れた高強度溶融亜鉛めっき鋼板の製造方法。
［２］質量％で、さらに、Ｃｒ：０．０５～１．００％、Ｖ：０．００５～０．５００％、Ｍｏ：０．００５～０．５００％、Ｎｉ：０．０５～１．００％、Ｃｕ：０．０５～１．００％、Ｔｉ：０．０１０～０．１００％、Ｎｂ：０．０１０～０．１００％、Ｂ：０．０００３～０．００５０％のうちから選ばれる少なくとも１種の元素を含有することを特徴とする前記［１］に記載の表面安定性に優れた高強度溶融亜鉛めっき鋼板の製造方法。
［３］前記第１加熱工程は、直火炉または無酸化炉により１．００≦空気比≦１．２５の条件で行い、前記第２加熱工程は、直火炉または無酸化炉により空気比＜１．００の条件で行うことを特徴とする前記［１］または前記［２］に記載の表面安定性に優れた高強度溶融亜鉛めっき鋼板の製造方法。
［４］溶融亜鉛めっきを施した後、さらに合金化処理を行うことを特徴とする前記［１］～［３］のいずれかに記載の表面安定性に優れた高強度溶融亜鉛めっき鋼板の製造方法。 Specifically, the present invention has the following features.
[1] By mass%, C: 0.040 to 0.200%, Si: 0.70 to 2.30%, Mn: 0.80 to 2.80%, P: 0.100% or less, S: When hot-dip galvanizing is performed on a cold-rolled steel sheet containing 0.010% or less, Al: 0.100% or less, N: 0.0080% or less, and the balance being the component composition of Fe and inevitable impurities, In one heating step, heating is performed at a temperature of 400 to 750 ° C. in an atmosphere containing 0.10 vol% ≦ O 2 ≦ 20 vol%, 1 vol% ≦ H 2 O ≦ 50 vol%, and then in the second heating step, 0 .01 vol% ≦ O 2 <0.10 vol%, 1 vol% ≦ H 2 O ≦ 20 vol%, heated at a temperature of 600 to 850 ° C., and then in the soaking step, 0.05 vol% ≦ H 2 ≦ 3.0vol% included and dew point is 0 ° C or higher A method for producing a high-strength hot-dip galvanized steel sheet with excellent surface stability, characterized by holding a hot-dip galvanizing after holding in a lower atmosphere at a temperature range of 750-900 ° C for 15-600 seconds.
[2] By mass%, Cr: 0.05-1.00%, V: 0.005-0.500%, Mo: 0.005-0.500%, Ni: 0.05-1. 00%, Cu: 0.05 to 1.00%, Ti: 0.010 to 0.100%, Nb: 0.010 to 0.100%, B: 0.0003 to 0.0050% The method for producing a high-strength hot-dip galvanized steel sheet having excellent surface stability according to the above [1], comprising at least one element selected from the above.
[3] The first heating step is performed in a direct-fired furnace or a non-oxidizing furnace under a condition of 1.00 ≦ air ratio ≦ 1.25, and the second heating step is performed in a direct-fired furnace or a non-oxidizing furnace with an air ratio <1. The method for producing a high-strength hot-dip galvanized steel sheet having excellent surface stability according to [1] or [2], which is performed under the condition of 0.000.
[4] Production of a high-strength hot-dip galvanized steel sheet with excellent surface stability according to any one of [1] to [3], wherein the alloying treatment is further performed after hot-dip galvanizing Method.
　なお、本明細書において、鋼の成分を示す％はすべて質量％である。また、本発明において、「高強度溶融亜鉛めっき鋼板」とは、引張強度ＴＳが５４０ＭＰａ以上である溶融亜鉛めっき鋼板および合金化処理を行った溶融亜鉛めっき鋼板である。また、「表面安定性」とは、不めっきなどの外観不良がなく、しかも鋼帯長手および幅方向における付着量や合金化度のムラが少ないことを意味する。 In addition, in this specification, all% which shows the component of steel is the mass%. In the present invention, the “high-strength hot-dip galvanized steel sheet” is a hot-dip galvanized steel sheet having a tensile strength TS of 540 MPa or more and a hot-dip galvanized steel sheet subjected to alloying treatment. “Surface stability” means that there is no appearance defect such as non-plating, and there is little unevenness in the amount of adhesion and the degree of alloying in the longitudinal and width directions of the steel strip.
　本発明によれば、高強度を有し、かつ表面安定性に優れた溶融亜鉛めっき鋼板が得られる。また、新たな設備を必要とせずコストの増加が生じることがない。本発明の溶融亜鉛めっき鋼板を、例えば、自動車構造部材に適用することにより車体軽量化による燃費改善を図ることができる。 According to the present invention, a hot-dip galvanized steel sheet having high strength and excellent surface stability can be obtained. In addition, no new equipment is required and the cost does not increase. By applying the hot dip galvanized steel sheet of the present invention to, for example, an automobile structural member, fuel efficiency can be improved by reducing the weight of the vehicle body.
　以下に、本発明の詳細を説明する。まず、本発明の成分組成について説明する。 Details of the present invention will be described below. First, the component composition of the present invention will be described.
　Ｃ：０．０４０～０．２００％
　Ｃはオーステナイト生成元素であり、鋼板組織を複合化し強度と延性の向上に有効な元素である。Ｃ量が０．０４０％未満では、鋼板の強度の確保が難しい。一方、Ｃ量が０．２００％を超えると、溶接部および熱影響部の硬化が著しく溶接部の機械的特性が劣化するため、スポット溶接性、アーク溶接性等が低下する。よって、Ｃ量は０．０４０％以上０．２００％以下とする。好ましくは０．０５０％以上０．１４０％以下である。より好ましくは０．０７０％以上０．１２０％以下である。 C: 0.040 to 0.200%
C is an austenite-forming element and is an element effective for improving the strength and ductility by compounding the steel sheet structure. If the C content is less than 0.040%, it is difficult to ensure the strength of the steel sheet. On the other hand, if the amount of C exceeds 0.200%, the welded part and the heat-affected zone are significantly hardened, and the mechanical properties of the welded part are deteriorated. Therefore, the C content is 0.040% or more and 0.200% or less. Preferably it is 0.050% or more and 0.140% or less. More preferably, it is 0.070% or more and 0.120% or less.
　Ｓｉ：０．７０～２．３０％
　Ｓｉはフェライト生成元素であり、焼鈍板のフェライトの固溶強化および加工硬化能の向上に有効な元素でもある。強度確保の上でＳｉ量は０．７０％以上必要である。一方、２．３０％超えでは、後述する製造方法においても不均一な酸化膜の残存に伴う付着量ムラや合金化度ムラが避けられない。よってＳｉ量は０．７０％以上２．３０％以下とする。 Si: 0.70-2.30%
Si is a ferrite-forming element, and is also an element effective for enhancing the solid solution strengthening and work hardening ability of the ferrite of the annealed plate. In order to ensure the strength, the Si amount needs to be 0.70% or more. On the other hand, if it exceeds 2.30%, even in the manufacturing method described later, unevenness in the amount of adhesion and unevenness in the degree of alloying due to non-uniform oxide film remaining are unavoidable. Therefore, the Si amount is set to 0.70% or more and 2.30% or less.
　Ｍｎ：０．８０～２．８０％
　Ｍｎは、オーステナイト生成元素であり、焼鈍板の強度確保に有効な元素である。Ｍｎ量は０．８０％未満では強度の確保が難しい。従って、Ｍｎ量は０．８０％以上必要であり、より好ましくは１．２０％以上である。一方、Ｍｎの過剰な添加は溶接性を損なうため、Ｍｎ量は２．８０％以下とする。 Mn: 0.80 to 2.80%
Mn is an austenite generating element and is an element effective for securing the strength of the annealed plate. If the amount of Mn is less than 0.80%, it is difficult to ensure the strength. Therefore, the amount of Mn needs to be 0.80% or more, more preferably 1.20% or more. On the other hand, excessive addition of Mn impairs weldability, so the Mn content is 2.80% or less.
　Ｐ：０．１００％以下
　Ｐは、鋼の強化に有効な元素であるが、０．１００％を超えて添加すると、粒界偏析により脆化を引き起こし、耐衝撃性を劣化させる。また、Ｐ量が０．１００％を超えると合金化速度を大幅に遅延させる。従って、Ｐ量は０．１００％以下とする。好ましくは０．０２０％以下である。 P: 0.100% or less P is an element effective for strengthening steel, but if added over 0.100%, it causes embrittlement due to segregation at the grain boundaries and deteriorates impact resistance. On the other hand, if the amount of P exceeds 0.100%, the alloying rate is significantly delayed. Therefore, the P amount is 0.100% or less. Preferably it is 0.020% or less.
　Ｓ：０．０１０％以下
　Ｓは、ＭｎＳなどの介在物となって、耐衝撃性の劣化や溶接部のメタルフローに沿った割れの原因となるので極力低い方がよいが、製造コストの面からＳ量は０．０１０％以下とする。好ましくは０．００５％以下である。 S: 0.010% or less Since S becomes inclusions such as MnS and causes deterioration of impact resistance and cracks along the metal flow of the weld, it is better to be as low as possible. Therefore, the S content is 0.010% or less. Preferably it is 0.005% or less.
　Ａｌ：０．１００％以下
　Ａｌの過剰な添加は、酸化物系介在物の増加による表面性状や成形性の劣化を招き、コスト高にもなるため、Ａｌ量は０．１００％以下とする。好ましくは０．０５０％以下である。 Al: 0.100% or less Excessive addition of Al leads to deterioration of surface properties and moldability due to an increase in oxide inclusions, resulting in high costs. Therefore, the Al content is 0.100% or less. Preferably it is 0.050% or less.
　Ｎ：０．００８０％以下
　Ｎは、鋼の耐時効性を最も大きく劣化させる元素であり、少ないほど好ましい。Ｎ量が０．００８０％を超えると耐時効性の劣化が顕著となる。従って、Ｎ量は０．００８０％以下とする。 N: 0.0080% or less N is an element that most deteriorates the aging resistance of steel. When the N content exceeds 0.0080%, deterioration of aging resistance becomes remarkable. Therefore, the N content is 0.0080% or less.
　残部はＦｅおよび不可避的不純物である。ただし、これらの成分元素に加えて、以下の合金元素を必要に応じて添加することができる。 The balance is Fe and inevitable impurities. However, in addition to these component elements, the following alloy elements can be added as necessary.
　Ｃｒ：０．０５～１．００％、Ｖ：０．００５～０．５００％、Ｍｏ：０．００５～０．５００％、Ｎｉ：０．０５～１．００％、Ｃｕ：０．０５～１．００％、Ｔｉ：０．０１０～０．１００％、Ｎｂ：０．０１０～０．１００％、Ｂ：０．０００３～０．００５０％以下から選ばれる少なくとも１種
　Ｃｒ、Ｖ、Ｍｏ、Ｎｉ、Ｃｕは鋼の強化に有効な元素であり、本発明で規定した範囲内であれば鋼の強化に使用して差し支えない。その効果は、Ｃｒを含有する場合であればその含有量が０．０５％以上、Ｖを含有する場合であればその含有量が０．００５％以上、Ｍｏを含有する場合であればその含有量が０．００５％以上、Ｎｉを含有する場合であればその含有量が０．０５％以上、Ｃｕを含有する場合であればその含有量が０．０５％以上で得られる。しかしながら、Ｃｒを含有する場合にその含有量が１．００％、Ｖを含有する場合にその含有量が０．５００％、Ｍｏを含有する場合にその含有量が０．５００％、Ｎｉを含有する場合にその含有量が１．００％、Ｃｕを含有する場合にその含有量が１．００％を超えると、著しい強度上昇による延性の低下の懸念が生じる。また、コストアップの要因にもなる。したがって、これらの元素を添加する場合には、その量をそれぞれＣｒは０．０５％以上１．００％以下、Ｖは０．００５％以上０．５００％以下、Ｍｏは０．００５％以上０．５００％以下、Ｎｉは０．０５％以上１．００％以下、Ｃｕは０．０５％以上１．００％以下とする。 Cr: 0.05-1.00%, V: 0.005-0.500%, Mo: 0.005-0.500%, Ni: 0.05-1.00%, Cu: 0.05- At least one selected from 1.00%, Ti: 0.010 to 0.100%, Nb: 0.010 to 0.100%, B: 0.0003 to 0.0050% or less Cr, V, Mo, Ni and Cu are effective elements for strengthening steel, and may be used for strengthening steel as long as they are within the range defined in the present invention. The effect is 0.05% or more if Cr is contained, 0.005% or more if V is contained, and Mo is contained if Mo is contained. If the amount is 0.005% or more and Ni is contained, the content is 0.05% or more, and if Cu is contained, the content is 0.05% or more. However, when Cr is contained, the content is 1.00%, when V is contained, the content is 0.500%, and when Mo is contained, the content is 0.500% and Ni is contained. When the content is 1.00% and Cu is contained when the content exceeds 1.00%, there is a concern that the ductility is lowered due to a significant increase in strength. In addition, the cost increases. Therefore, when these elements are added, the amounts of Cr are 0.05% or more and 1.00% or less, V is 0.005% or more and 0.500% or less, and Mo is 0.005% or more and 0 or less, respectively. .500% or less, Ni is 0.05% or more and 1.00% or less, and Cu is 0.05% or more and 1.00% or less.
　Ｔｉ、Ｎｂは鋼の析出強化に有効な元素である。その効果は、Ｔｉを含有する場合であればその含有量が０．０１０％以上、Ｎｂを含有する場合であればその含有量が０．０１０％以上で得られる。しかしながら、Ｔｉを含有する場合にその含有量が０．１００％、Ｎｂを含有する場合にその含有量が０．１００％を超えると、著しい強度上昇による延性の低下の懸念が生じる。また、コストアップの要因にもなる。従って、Ｔｉ、Ｎｂを添加する場合には、その添加量をＴｉは０．０１０％以上０．１００％以下、Ｎｂは０．０１０％以上０．１００％以下とする。 Ti and Nb are effective elements for precipitation strengthening of steel. The effect is obtained at a content of 0.010% or more if Ti is contained, and at a content of 0.010% or more if Nb is contained. However, when the content is 0.100% when Ti is contained and the content exceeds 0.100% when Nb is contained, there is a concern that ductility is lowered due to a significant increase in strength. In addition, the cost increases. Therefore, when adding Ti and Nb, the addition amount is set to 0.010% or more and 0.100% or less for Ti and 0.010% or more and 0.100% or less for Nb.
　Ｂは鋼の強化に有効な元素であり、その効果は、Ｂ量を０．０００３％以上にすることで得られる。しかしながら、Ｂ量が０．００５０％を超えると、著しい強度上昇による延性の低下の懸念が生じる。また、コストアップの要因にもなる。したがって、Ｂを添加する場合には、その量を０．０００３％以上０．００５０％以下とする。 B is an element effective for strengthening steel, and the effect can be obtained by making the amount of B 0.0003% or more. However, if the amount of B exceeds 0.0050%, there is a concern that the ductility is lowered due to a significant increase in strength. In addition, the cost increases. Therefore, when adding B, the amount is made 0.0003% or more and 0.0050% or less.
　次に、本発明の表面安定性に優れた高強度溶融亜鉛めっき鋼板の製造方法について説明する。 Next, a method for producing a high-strength hot-dip galvanized steel sheet having excellent surface stability according to the present invention will be described.
　前記に記載の成分組成を有する鋼スラブを、通常は熱間圧延工程において加熱後、粗圧延、仕上げ圧延を施し、その後、酸洗工程で熱延板表層のスケールを除去した後、冷間圧延する。ここで、例えば薄手鋳造などにより熱延工程の一部もしくは全部を省略して製造してもよい。冷間圧延した鋼板に以下の第１加熱工程、次いで第２加熱工程、次いで均熱工程からなる熱処理を行った後に溶融亜鉛めっきを施す。 The steel slab having the component composition described above is usually heated in a hot rolling process, then subjected to rough rolling and finish rolling, and then the scale of the hot-rolled sheet surface layer is removed in a pickling process, followed by cold rolling. To do. Here, for example, a part or all of the hot rolling process may be omitted by thin casting or the like. The cold-rolled steel sheet is subjected to a heat treatment consisting of the following first heating step, then the second heating step, and then the soaking step, followed by hot dip galvanization.
　以下、本発明の熱処理条件を詳細に説明する。 Hereinafter, the heat treatment conditions of the present invention will be described in detail.
　第１加熱工程：０．１０ｖｏｌ％≦Ｏ２≦２０ｖｏｌ％、１ｖｏｌ％≦Ｈ２Ｏ≦５０ｖｏｌ％を含有する雰囲気中で４００～７５０℃の温度で加熱
　第１加熱工程にて鋼板の表面にＦｅ酸化膜を生成させるため、Ｏ２は酸化に十分な量が必要であり０．１０ｖｏｌ％以上とする。なお、経済的な理由からＯ２濃度の上限は大気レベルの２０ｖｏｌ％以下とする。酸化を促進するためにＨ２Ｏ濃度は１ｖｏｌ％以上とする。一方、加湿コストを考慮してＨ２Ｏ濃度は５０ｖｏｌ％以下とする。加熱後の温度が４００℃未満では鋼板は酸化しにくく、７５０℃を超えると酸化膜が過剰となり最終的に不均一に残存する。このため、第１加熱工程の温度は４００℃以上７５０℃以下とする。なお、室温から４００℃までの加熱方法は限定しない。例えば、加熱炉内の未燃ガスを回収し空気を加えて再燃焼させる予熱方式などが通常用いられる。 First heating step: heating at a temperature of 400 to 750 ° C. in an atmosphere containing 0.10 vol% ≦ O 2 ≦ 20 vol%, 1 vol% ≦ H 2 O ≦ 50 vol%. In order to generate an oxide film, O 2 must have a sufficient amount for oxidation and is 0.10 vol% or more. For economic reasons, the upper limit of the O 2 concentration is 20 vol% or less of the atmospheric level. In order to promote oxidation, the H 2 O concentration is set to 1 vol% or more. On the other hand, considering the humidification cost, the H 2 O concentration is set to 50 vol% or less. If the temperature after heating is less than 400 ° C., the steel sheet is difficult to oxidize, and if it exceeds 750 ° C., the oxide film becomes excessive and finally remains unevenly. For this reason, the temperature of a 1st heating process shall be 400 degreeC or more and 750 degrees C or less. In addition, the heating method from room temperature to 400 degreeC is not limited. For example, a preheating method in which unburned gas in the heating furnace is collected and re-burned by adding air is usually used.
　第２加熱工程：０．０１ｖｏｌ％≦Ｏ２＜０．１０ｖｏｌ％、１ｖｏｌ％≦Ｈ２Ｏ≦２０ｖｏｌ％を含有する雰囲気中で６００～８５０℃の温度で加熱
　第２加熱工程ではＦｅ酸化膜が過剰になるのを防止し、次の均熱工程で還元しうる程度にＦｅ酸化膜の生成を調整する。そのため第２加熱工程は弱い還元雰囲気とする。この際に還元し過ぎないように、Ｏ２濃度は０．０１ｖｏｌ％以上とする。一方、Ｏ２濃度が０．１０ｖｏｌ％以上では酸化膜が還元しないのでＯ２濃度は０．１０ｖｏｌ％未満とする。 Second heating step: heating at a temperature of 600 to 850 ° C. in an atmosphere containing 0.01 vol% ≦ O 2 <0.10 vol%, 1 vol% ≦ H 2 O ≦ 20 vol% In the second heating step, an Fe oxide film is formed The formation of the Fe oxide film is adjusted to such an extent that it can be reduced and reduced in the next soaking step. Therefore, the second heating step is a weak reducing atmosphere. At this time, the O 2 concentration is set to 0.01 vol% or more so as not to reduce too much. On the other hand, when the O 2 concentration is 0.10 vol% or more, the oxide film is not reduced, so the O 2 concentration is less than 0.10 vol%.
　また、還元し過ぎないようにＨ２Ｏ濃度は１ｖｏｌ％以上とする。一方、Ｈ２Ｏが多量に含まれると酸化が進行するため、Ｈ２Ｏ濃度は２０ｖｏｌ％以下とする。 Further, the H 2 O concentration is 1 vol% or more so as not to reduce too much. On the other hand, since oxidation proceeds when a large amount of H 2 O is contained, the H 2 O concentration is set to 20 vol% or less.
　加熱後の温度が６００℃未満では還元反応が進行せず、８５０℃超えは加熱コストがかかるため、第２加熱工程の温度は６００℃以上８５０℃以下とする。 When the temperature after heating is less than 600 ° C., the reduction reaction does not proceed, and when it exceeds 850 ° C., heating costs are required. Therefore, the temperature of the second heating step is 600 ° C. or more and 850 ° C. or less.
　均熱工程：０．０５ｖｏｌ％≦Ｈ２≦３．０ｖｏｌ％を含み露点が０℃以下の雰囲気中で７５０～９００℃の温度域で１５～６００秒保持
　均熱工程は、第２加熱工程に引き続いて行われる。本工程では、Ｆｅ酸化膜の還元処理および鋼板組織の調整を行う。酸化膜を還元するためにはＨ２濃度は０．０５ｖｏｌ％以上必要である。一方、Ｈ２濃度が３．０ｖｏｌ％を超えると還元速度が速くなりすぎるため、均熱工程の早い段階でＦｅの還元が終了し、亜鉛めっき浴への浸漬までの間にＳｉが表面濃化する。したがって、Ｈ２濃度は０．０５ｖｏｌ％以上３．０ｖｏｌ％以下とする。露点は０℃を超えると酸化鉄が還元しにくくなるため、露点は０℃以下とする。一方、露点が－６０℃未満では工業的に実施が困難であるため、露点は－６０℃以上が好ましい。鋼板温度が７５０℃未満または保持時間が１５秒未満では還元速度が遅くなるため未還元のＦｅ酸化膜が残存してしまう。一方、鋼板温度が９００℃超えまたは保持時間が６００秒超えでは、均熱工程の早い段階でＦｅの還元が終了し、亜鉛めっき浴への浸漬までの間にＳｉが表面濃化する。従って均熱工程の温度と時間は７５０～９００℃の温度域で１５～６００秒保持とする。なお、Ｆｅ酸化膜の還元処理および鋼板組織の調整を行うという効果が得られる範囲で板温が上昇する条件で行う場合もある。 Soaking step: 0.05 vol% ≦ H 2 ≦ 3.0 vol% in an atmosphere having a dew point of 0 ° C. or less and holding at a temperature range of 750 to 900 ° C. for 15 to 600 seconds. Continued. In this step, the Fe oxide film is reduced and the steel sheet structure is adjusted. In order to reduce the oxide film, the H 2 concentration needs to be 0.05 vol% or more. On the other hand, when the H 2 concentration exceeds 3.0 vol%, the reduction rate becomes too fast, so the reduction of Fe is completed at an early stage of the soaking process, and the surface of Si is concentrated before being immersed in the galvanizing bath. To do. Therefore, the H 2 concentration is set to 0.05 vol% or more and 3.0 vol% or less. If the dew point exceeds 0 ° C, iron oxide is difficult to reduce, so the dew point is 0 ° C or less. On the other hand, if the dew point is less than −60 ° C., it is difficult to implement industrially, so the dew point is preferably −60 ° C. or higher. If the steel plate temperature is less than 750 ° C. or the holding time is less than 15 seconds, the reduction rate becomes slow, so an unreduced Fe oxide film remains. On the other hand, when the steel plate temperature exceeds 900 ° C. or the holding time exceeds 600 seconds, the reduction of Fe is completed at an early stage of the soaking process, and Si is concentrated on the surface until dipping in the galvanizing bath. Therefore, the temperature and time of the soaking process are maintained for 15 to 600 seconds in the temperature range of 750 to 900 ° C. In some cases, the plate temperature is increased within a range in which the effect of reducing the Fe oxide film and adjusting the steel sheet structure can be obtained.
　なお、加熱温度の範囲について、第１加熱工程と第２加熱工程と均熱工程で重複する温度域が存在する。次の工程で前の工程より温度が低下した場合でも、各工程で定める温度域内であれば本発明の効果は損なわれない。ただし、いったん温度を下げてから再びそれ以上に加熱するのはコスト的に不利であり、第１加熱工程＜第２加熱工程＜均熱工程の順に温度を上げるのが好ましい。 In addition, about the range of heating temperature, the temperature range which overlaps with a 1st heating process, a 2nd heating process, and a soaking process exists. Even when the temperature is lower than the previous step in the next step, the effect of the present invention is not impaired as long as it is within the temperature range determined in each step. However, it is disadvantageous in cost to once lower the temperature and then heat it again. It is preferable to raise the temperature in the order of the first heating step <second heating step <soaking step.
　さらに、第１加熱工程を直火炉（ＤＦＦ）または無酸化炉（ＮＯＦ）により行う場合、燃焼ガスに対する空気の比率、すなわち空気比は１．００以上１．２５以下の条件で行うことが好ましい。これは空気比が１．００未満では鋼板は酸化せず、１．２５を超えると過剰な酸化により第２加熱工程以降での還元が困難になるためである。また、第２加熱工程を直火炉（ＤＦＦ）または無酸化炉（ＮＯＦ）により行う場合、燃焼ガスに対する空気の比率、すなわち空気比は１．００未満の条件で行うことが好ましい。これは空気比が１．００以上であると鋼板表面の酸化鉄を還元することができないからである。なお、空気比が０．６０未満であると燃焼効率が悪くなるため、実用的な空気比は０．６０以上である。 Furthermore, when the first heating step is performed by a direct-fired furnace (DFF) or a non-oxidizing furnace (NOF), it is preferable that the ratio of air to combustion gas, that is, the air ratio is 1.00 or more and 1.25 or less. This is because if the air ratio is less than 1.00, the steel sheet does not oxidize, and if it exceeds 1.25, the reduction after the second heating step becomes difficult due to excessive oxidation. Moreover, when performing a 2nd heating process by a direct-fired furnace (DFF) or a non-oxidation furnace (NOF), it is preferable to carry out on the conditions that the ratio of the air with respect to combustion gas, ie, air ratio, is less than 1.00. This is because the iron oxide on the steel sheet surface cannot be reduced when the air ratio is 1.00 or more. Note that if the air ratio is less than 0.60, the combustion efficiency deteriorates, so the practical air ratio is 0.60 or more.
　上記加熱工程および均熱工程の熱処理を施した後、冷却し、溶融亜鉛めっき浴に浸漬して溶融亜鉛めっきを施す。次いで、必要に応じて合金化処理を行う。溶融亜鉛めっきおよび合金化処理の方法は通常の方法でよく、より好ましい条件について以下に示す。 After performing the heat treatment in the heating step and the soaking step, it is cooled and immersed in a hot dip galvanizing bath to carry out hot dip galvanizing. Next, an alloying treatment is performed as necessary. The hot dip galvanizing and alloying methods may be ordinary methods, and more preferable conditions are shown below.
　溶融亜鉛めっき鋼板の製造には浴温４４０～５５０℃、浴中Ａｌ濃度が０．１４～０．２４％の亜鉛めっき浴を用い、合金化溶融亜鉛めっき鋼板の製造には浴温４４０～５５０℃、浴中Ａｌ濃度が０．１０～０．２０％の亜鉛めっき浴を用いる。 A galvanized bath having a bath temperature of 440 to 550 ° C. and an Al concentration in the bath of 0.14 to 0.24% is used for manufacturing the hot dip galvanized steel sheet, and a bath temperature of 440 to 550 is used for manufacturing the galvannealed steel sheet. Use a galvanizing bath with an Al concentration of 0.10 to 0.20% in the bath.
　浴温が４４０℃未満では浴内における温度変動により低温部でＺｎの凝固が生じる可能性があるため不適であり、５５０℃を超えると浴の蒸発が激しく、気化したＺｎが炉内へ付着するため操業上問題がある。さらに、めっき時に合金化が進行するため過合金になりやすい。 If the bath temperature is lower than 440 ° C., it is not suitable because Zn may solidify in the low temperature due to temperature fluctuations in the bath. If it exceeds 550 ° C., the bath evaporates vigorously, and vaporized Zn adheres to the furnace. Therefore, there are operational problems. Furthermore, since alloying proceeds during plating, it tends to be overalloyed.
　溶融亜鉛めっき鋼板を製造する時に浴中Ａｌ濃度が０．１４％未満になるとＦｅ－Ｚｎ合金化が進みめっき密着性が悪化し、０．２４％超になるとＡｌ酸化物による欠陥が発生する。合金化溶融亜鉛めっき鋼板を製造する時に浴中Ａｌ濃度が０．１０％未満になるとζ相が多量に生成しパウダリング性が悪化し、０．２０％超になるとＦｅ－Ｚｎ合金化が進まない。 When producing a hot-dip galvanized steel sheet, if the Al concentration in the bath is less than 0.14%, Fe—Zn alloying progresses and plating adhesion deteriorates, and if it exceeds 0.24%, defects due to Al oxide occur. When an alloyed hot-dip galvanized steel sheet is produced, if the Al concentration in the bath is less than 0.10%, a large amount of ζ phase is generated and powdering properties deteriorate, and if it exceeds 0.20%, Fe-Zn alloying progresses. Absent.
　合金化処理は４６０℃より高く、５８０℃未満で行うのが最適である。４６０℃以下では合金化進行が遅く、５８０℃以上では過合金により地鉄界面に生成する硬くて脆いＺｎ－Ｆｅ合金層が生成しすぎてめっき密着性が劣化するだけでなく、残留オーステナイト相が分解するため、強度が低下する。 The alloying treatment is optimally performed at a temperature higher than 460 ° C. and lower than 580 ° C. At 460 ° C or lower, alloying progresses slowly, and at 580 ° C or higher, a hard and brittle Zn-Fe alloy layer formed at the iron-iron interface due to overalloy is formed too much, resulting in deterioration of plating adhesion as well as residual austenite phase. Since it decomposes, the strength decreases.
　表１に示す成分組成を有し、残部がＦｅおよび不可避的不純物よりなる鋼を転炉にて溶製し、連続鋳造法にてスラブとした。得られたスラブを１２００℃に加熱後、２．３～４．５ｍｍの各板厚まで熱間圧延を行い、巻き取りを行った。次いで、得られた熱延板を酸洗し、冷間圧延を施して板厚０．６～１．０ｍｍ、板幅１２００～１５００ｍｍの冷間圧延鋼板とした。その後、雰囲気調整が可能な炉において表２－１または表３－１に示す熱処理条件（表２－１、表３－１において気体の濃度を表す％はｖｏｌ％を意味する）にて第１加熱工程、第２加熱工程および均熱工程を行った。この際、第１加熱工程と第２加熱工程はＤＦＦ型加熱炉またはＮＯＦ型加熱炉で行った。燃料ガスにはコークス炉で発生するＣガスを用いた。均熱工程はＲＴＦ型加熱炉で行い雰囲気ガスとしてＨ２、Ｎ２および不可避的不純物を含むガスを供給した。引き続き、０．１３～０．１９％の濃度でＡｌを含有したＺｎ浴にて溶融亜鉛めっき処理を施し、溶融亜鉛めっき鋼板（ＧＩと称すこともある）を得た。その後、必要に応じて合金化処理を施し、合金化溶融亜鉛めっき鋼板（ＧＡと称すこともある）を得た。 Steel having the component composition shown in Table 1 and the balance being Fe and inevitable impurities was melted in a converter and made into a slab by a continuous casting method. The obtained slab was heated to 1200 ° C., and then hot-rolled to a thickness of 2.3 to 4.5 mm and wound up. Next, the obtained hot-rolled sheet was pickled and cold-rolled to obtain a cold-rolled steel sheet having a sheet thickness of 0.6 to 1.0 mm and a sheet width of 1200 to 1500 mm. Thereafter, in the furnace capable of adjusting the atmosphere, the first heat treatment was performed under the heat treatment conditions shown in Table 2-1 or Table 3-1 (in Tables 2-1 and 3-1,% representing the gas concentration means vol%). A heating step, a second heating step, and a soaking step were performed. At this time, the first heating step and the second heating step were performed in a DFF type heating furnace or a NOF type heating furnace. C gas generated in a coke oven was used as the fuel gas. The soaking process was performed in an RTF type heating furnace, and a gas containing H 2 , N 2 and inevitable impurities was supplied as an atmospheric gas. Subsequently, hot dip galvanizing treatment was performed in a Zn bath containing Al at a concentration of 0.13 to 0.19% to obtain a hot dip galvanized steel sheet (sometimes referred to as GI). Thereafter, an alloying treatment was performed as necessary to obtain an alloyed hot-dip galvanized steel sheet (sometimes referred to as GA).
　本発明では、溶融亜鉛めっき鋼板表面の不めっきや押し疵などの外観不良の有無、幅方向の付着量差および合金化度差で表面安定性の評価を行った。なお、付着量は蛍光Ｘ線量を測定し検量線から求めた。また、合金化度とはＸ線回折法により測定しためっき皮膜中のＦｅ含有率である。鋼板の板幅の１／４位置、１／２位置、３／４位置および鋼板両端部からそれぞれ１００ｍｍ位置の合計５箇所で付着量および合金化度を測定し、最大値と最小値の差で評価した。評価の標記を以下に示す。
×：外観不良あり
△：外観不良なし、かつ、付着量差＞３ｇ／ｍ２または合金化度差＞１．５％
○：外観不良なし、かつ、付着量差≦３ｇ／ｍ２、かつ、合金化度差≦１．５％
ただし、合金化処理を施さない場合は、合金化度は評価の対象外とする。 In the present invention, the surface stability was evaluated based on the presence or absence of appearance defects such as unplating and pressing iron on the surface of the hot-dip galvanized steel sheet, the difference in the amount of adhesion in the width direction, and the difference in the degree of alloying. The amount of adhesion was obtained from a calibration curve by measuring the fluorescent X-ray dose. The degree of alloying is the Fe content in the plating film measured by the X-ray diffraction method. Measure the amount of adhesion and the degree of alloying at a total of 5 positions, 1/4 position, 1/2 position, 3/4 position and 100 mm position from both ends of the steel sheet, and the difference between the maximum value and the minimum value. evaluated. The title of the evaluation is shown below.
×: Appearance defect Δ: Appearance defect is not found, and the adhesion amount difference> 3 g / m 2 or alloying degree difference> 1.5%
○: No appearance failure, adhesion amount difference ≦ 3 g / m 2 , and alloying degree difference ≦ 1.5%
However, the degree of alloying is not subject to evaluation when no alloying treatment is performed.
　また、引張試験は、引張方向が鋼板の圧延方向と直角方向となるようにサンプルを採取したＪＩＳ５号試験片を用いて、ＪＩＳ　Ｚ　２２４１に準拠して行い、引張強度（ＴＳ）を測定した。
得られた結果を表２－２および表３－２に示す。 In addition, the tensile test was performed in accordance with JIS Z 2241 using a JIS No. 5 test piece obtained by taking a sample so that the tensile direction was perpendicular to the rolling direction of the steel sheet, and the tensile strength (TS) was measured.
The obtained results are shown in Table 2-2 and Table 3-2.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000005
　表２（表２－１、表２－２）、表３（表３－１、表３－２）より、本発明例の溶融亜鉛めっき鋼板および合金化溶融亜鉛めっき鋼板帯は、いずれもＴＳが５４０ＭＰａ以上であり、表面安定性にも優れている。一方、比較例では、付着量差または合金化度差が大きく表面安定性に劣っている。 From Table 2 (Table 2-1 and Table 2-2) and Table 3 (Table 3-1 and Table 3-2), the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet band of the examples of the present invention are both TS. Is 540 MPa or more and is excellent in surface stability. On the other hand, in the comparative example, the adhesion amount difference or the alloying degree difference is large and the surface stability is inferior.
　本発明によれば、高強度（５４０ＭＰａ以上の引張強度ＴＳ）を有し、かつ、表面安定性に優れた高強度溶融亜鉛めっき鋼板が得られる。本発明の高強度溶融亜鉛めっき鋼板を、例えば、自動車構造部材に適用することにより車体軽量化による燃費改善を図ることができる。 According to the present invention, a high-strength hot-dip galvanized steel sheet having high strength (tensile strength TS of 540 MPa or more) and excellent surface stability can be obtained. By applying the high-strength hot-dip galvanized steel sheet of the present invention to, for example, an automobile structural member, fuel efficiency can be improved by reducing the weight of the vehicle body.

Claims (4)

  1. 　質量％で、Ｃ：０．０４０～０．２００％、Ｓｉ：０．７０～２．３０％、Ｍｎ：０．８０～２．８０％、Ｐ：０．１００％以下、Ｓ：０．０１０％以下、Ａｌ：０．１００％以下、Ｎ：０．００８０％以下を含有し、残部がＦｅおよび不可避的不純物からなる冷間圧延鋼板に溶融亜鉛めっきを施すに際し、
    　第１加熱工程では、０．１０≦Ｏ２≦２０ｖｏｌ％、１≦Ｈ２Ｏ≦５０ｖｏｌ％を含有する雰囲気中で４００～７５０℃の温度で加熱し、
    　次いで、第２加熱工程では、０．０１≦Ｏ２＜０．１０ｖｏｌ％、１≦Ｈ２Ｏ≦２０ｖｏｌ％を含有する雰囲気中で６００～８５０℃の温度で加熱し、
    　次いで、均熱工程では、０．０５≦Ｈ２≦３．０ｖｏｌ％を含み露点が０℃以下の雰囲気中で７５０～９００℃の温度域で１５～６００秒保持した後、溶融亜鉛めっきを施すことを特徴とする高強度溶融亜鉛めっき鋼板の製造方法。     By mass%, C: 0.040 to 0.200%, Si: 0.70 to 2.30%, Mn: 0.80 to 2.80%, P: 0.100% or less, S: 0.010 % Or less, Al: 0.100% or less, N: 0.0080% or less, and when the hot dip galvanizing is performed on the cold-rolled steel sheet with the balance being Fe and inevitable impurities,
    In the first heating step, heating is performed at a temperature of 400 to 750 ° C. in an atmosphere containing 0.10 ≦ O 2 ≦ 20 vol%, 1 ≦ H 2 O ≦ 50 vol%,
    Next, in the second heating step, heating is performed at a temperature of 600 to 850 ° C. in an atmosphere containing 0.01 ≦ O 2 <0.10 vol%, 1 ≦ H 2 O ≦ 20 vol%,
    Next, in the soaking process, hot galvanizing is performed after holding for 15 to 600 seconds in a temperature range of 750 to 900 ° C. in an atmosphere containing 0.05 ≦ H 2 ≦ 3.0 vol% and having a dew point of 0 ° C. or less. A method for producing a high-strength hot-dip galvanized steel sheet.
  2. 　質量％で、さらに、Ｃｒ：０．０５～１．００％、Ｖ：０．００５～０．５００％、Ｍｏ：０．００５～０．５００％、Ｎｉ：０．０５～１．００％、Ｃｕ：０．０５～１．００％、Ｔｉ：０．０１０～０．１００％、Ｎｂ：０．０１０～０．１００％、Ｂ：０．０００３～０．００５０％のうちから選ばれる少なくとも１種の元素を含有することを特徴とする請求項１に記載の高強度溶融亜鉛めっき鋼板の製造方法。 Further, Cr: 0.05 to 1.00%, V: 0.005 to 0.500%, Mo: 0.005 to 0.500%, Ni: 0.05 to 1.00%, At least one selected from Cu: 0.05 to 1.00%, Ti: 0.010 to 0.100%, Nb: 0.010 to 0.100%, B: 0.0003 to 0.0050% The method for producing a high-strength hot-dip galvanized steel sheet according to claim 1, comprising a seed element.
  3. 　前記第１加熱工程は、直火炉または無酸化炉により１．００≦空気比≦１．２５の条件で行い、
    　前記第２加熱工程は、直火炉または無酸化炉により空気比＜１．００の条件で行うことを特徴とする請求項１または請求項２に記載の高強度溶融亜鉛めっき鋼板の製造方法。     The first heating step is performed in a direct-fired furnace or a non-oxidizing furnace under the condition of 1.00 ≦ air ratio ≦ 1.25,
    The method for producing a high-strength hot-dip galvanized steel sheet according to claim 1 or 2, wherein the second heating step is performed in a direct-fired furnace or a non-oxidizing furnace under an air ratio <1.00 condition.
  4. 　溶融亜鉛めっきを施した後、さらに合金化処理を行うことを特徴とする請求項１～３のいずれか一項に記載の高強度溶融亜鉛めっき鋼板の製造方法。 The method for producing a high-strength hot-dip galvanized steel sheet according to any one of claims 1 to 3, wherein the alloying treatment is further performed after the hot-dip galvanizing.
PCT/JP2013/004173 2012-07-23 2013-07-04 Method for producing high-strength hot-dip galvanized steel sheets WO2014017034A1 (en)

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JP6740973B2 (en) * 2017-07-12 2020-08-19 Ｊｆｅスチール株式会社 Method for manufacturing hot-dip galvanized steel sheet

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