JP6032221B2 - Manufacturing method of high-strength steel sheet - Google Patents
Manufacturing method of high-strength steel sheet Download PDFInfo
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- JP6032221B2 JP6032221B2 JP2014028030A JP2014028030A JP6032221B2 JP 6032221 B2 JP6032221 B2 JP 6032221B2 JP 2014028030 A JP2014028030 A JP 2014028030A JP 2014028030 A JP2014028030 A JP 2014028030A JP 6032221 B2 JP6032221 B2 JP 6032221B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 130
- 239000010959 steel Substances 0.000 title claims description 130
- 238000004519 manufacturing process Methods 0.000 title claims description 15
- 238000006243 chemical reaction Methods 0.000 claims description 59
- 239000000126 substance Substances 0.000 claims description 59
- 238000000137 annealing Methods 0.000 claims description 54
- 238000011282 treatment Methods 0.000 claims description 34
- 238000005260 corrosion Methods 0.000 claims description 27
- 230000007797 corrosion Effects 0.000 claims description 27
- 229910052748 manganese Inorganic materials 0.000 claims description 26
- 229910052710 silicon Inorganic materials 0.000 claims description 26
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 21
- 239000001257 hydrogen Substances 0.000 claims description 20
- 229910052739 hydrogen Inorganic materials 0.000 claims description 20
- 238000004070 electrodeposition Methods 0.000 claims description 17
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims description 16
- 239000011248 coating agent Substances 0.000 claims description 16
- 238000000576 coating method Methods 0.000 claims description 16
- 238000005554 pickling Methods 0.000 claims description 16
- 238000010438 heat treatment Methods 0.000 claims description 13
- 229910052742 iron Inorganic materials 0.000 claims description 12
- 229910052787 antimony Inorganic materials 0.000 claims description 10
- 229910052720 vanadium Inorganic materials 0.000 claims description 10
- 229910052718 tin Inorganic materials 0.000 claims description 9
- 229910052721 tungsten Inorganic materials 0.000 claims description 9
- 229910052715 tantalum Inorganic materials 0.000 claims description 8
- 229910052804 chromium Inorganic materials 0.000 claims description 7
- 229910052802 copper Inorganic materials 0.000 claims description 7
- 229910052750 molybdenum Inorganic materials 0.000 claims description 7
- 229910052759 nickel Inorganic materials 0.000 claims description 7
- 229910052758 niobium Inorganic materials 0.000 claims description 7
- 229910052719 titanium Inorganic materials 0.000 claims description 7
- 229910052782 aluminium Inorganic materials 0.000 claims description 6
- 239000007864 aqueous solution Substances 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 5
- 229910052698 phosphorus Inorganic materials 0.000 claims description 5
- 229910052799 carbon Inorganic materials 0.000 claims description 3
- 229910052717 sulfur Inorganic materials 0.000 claims description 2
- 230000000694 effects Effects 0.000 description 37
- 230000003647 oxidation Effects 0.000 description 30
- 238000007254 oxidation reaction Methods 0.000 description 30
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 29
- 238000000034 method Methods 0.000 description 24
- 239000002344 surface layer Substances 0.000 description 14
- 229910052760 oxygen Inorganic materials 0.000 description 12
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 11
- 239000000463 material Substances 0.000 description 11
- 239000001301 oxygen Substances 0.000 description 11
- 230000001276 controlling effect Effects 0.000 description 9
- 238000005755 formation reaction Methods 0.000 description 7
- 239000007789 gas Substances 0.000 description 7
- 229920006395 saturated elastomer Polymers 0.000 description 7
- 230000015572 biosynthetic process Effects 0.000 description 6
- 238000005868 electrolysis reaction Methods 0.000 description 6
- 239000010960 cold rolled steel Substances 0.000 description 5
- 238000005097 cold rolling Methods 0.000 description 5
- 230000001737 promoting effect Effects 0.000 description 5
- 238000005096 rolling process Methods 0.000 description 5
- 239000000243 solution Substances 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- 229910052796 boron Inorganic materials 0.000 description 4
- 230000006866 deterioration Effects 0.000 description 4
- 239000010410 layer Substances 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 3
- 241000316887 Saissetia oleae Species 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 239000007788 liquid Substances 0.000 description 3
- 229910000734 martensite Inorganic materials 0.000 description 3
- 230000001590 oxidative effect Effects 0.000 description 3
- 238000010422 painting Methods 0.000 description 3
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 description 2
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- 229910019142 PO4 Inorganic materials 0.000 description 2
- 229910004298 SiO 2 Inorganic materials 0.000 description 2
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 2
- 238000001816 cooling Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000005238 degreasing Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000009713 electroplating Methods 0.000 description 2
- 238000005098 hot rolling Methods 0.000 description 2
- 230000001771 impaired effect Effects 0.000 description 2
- 238000005121 nitriding Methods 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 2
- 239000010452 phosphate Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000010791 quenching Methods 0.000 description 2
- 230000000171 quenching effect Effects 0.000 description 2
- 238000001953 recrystallisation Methods 0.000 description 2
- 238000002791 soaking Methods 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 238000005496 tempering Methods 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- KZBUYRJDOAKODT-UHFFFAOYSA-N Chlorine Chemical compound ClCl KZBUYRJDOAKODT-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 239000004566 building material Substances 0.000 description 1
- 229910002091 carbon monoxide Inorganic materials 0.000 description 1
- 125000002091 cationic group Chemical group 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 230000003750 conditioning effect Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 238000007739 conversion coating Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000005261 decarburization Methods 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000002265 prevention Effects 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000000630 rising effect Effects 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 239000011780 sodium chloride Substances 0.000 description 1
- 238000010301 surface-oxidation reaction Methods 0.000 description 1
- 239000013077 target material Substances 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Classifications
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- 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
- C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
- C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
- C21D8/0473—Final recrystallisation annealing
-
- 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
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/26—Methods of annealing
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
-
- 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
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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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
-
- 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
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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
- C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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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
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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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
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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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
- C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
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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
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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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
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
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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
- C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
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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
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
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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
- C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
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- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
- C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling
- C25F1/02—Pickling; Descaling
- C25F1/04—Pickling; Descaling in solution
- C25F1/06—Iron or steel
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
- C21D9/54—Furnaces for treating strips or wire
- C21D9/56—Continuous furnaces for strip or wire
- C21D9/561—Continuous furnaces for strip or wire with a controlled atmosphere or vacuum
Description
本発明は、ＳｉやＭｎの含有量が多い場合でも、優れた化成処理性および電着塗装後の耐食性を有する高強度鋼板およびその製造方法に関するものである。 The present invention relates to a high-strength steel sheet having excellent chemical conversion property and corrosion resistance after electrodeposition coating, and a method for producing the same, even when the content of Si or Mn is large.
近年、自動車の燃費向上および自動車の衝突安全性向上の観点から、車体材料の高強度化によって薄肉化を図り、車体そのものを軽量化しかつ高強度化する要望が高まっている。そのために高強度鋼板の自動車への適用が促進されている。
一般に自動車用鋼板は塗装して使用されており、その塗装の前処理として、リン酸塩処理と呼ばれる化成処理が施される。鋼板の化成処理は塗装後の耐食性を確保するための重要な処理の一つである。
In recent years, from the viewpoint of improving the fuel efficiency of automobiles and improving the collision safety of automobiles, there is an increasing demand for reducing the thickness of the vehicle body by increasing the strength of the vehicle body material and reducing the weight of the vehicle body. Therefore, application of high-strength steel sheets to automobiles is being promoted.
In general, steel plates for automobiles are used after being coated, and as a pretreatment for the coating, a chemical conversion treatment called a phosphate treatment is performed. The chemical conversion treatment of the steel sheet is one of the important treatments for ensuring the corrosion resistance after painting.
鋼板の強度、延性を高めるためには、Ｓｉ、Ｍｎの添加が有効である。しかしながら、連続焼鈍の際に、Ｓｉ、ＭｎはＦｅの酸化が起こらない（Ｆｅ酸化物を還元する）還元性のＮ2＋Ｈ2ガス雰囲気で焼鈍を行った場合でも酸化し、鋼板最表層に選択的にＳｉ、Ｍｎを含む表面酸化物（ＳｉＯ2、ＭｎＯ等、以下、選択表面酸化物と称す）を形成する。この選択表面酸化物が化成処理中の化成皮膜の生成反応を阻害するため、化成皮膜が生成されない微小領域（以後、スケと称することもある）が形成され、化成処理性が低下する。 In order to increase the strength and ductility of the steel sheet, addition of Si and Mn is effective. However, during continuous annealing, Si and Mn are oxidized even when annealing is performed in a reducing N 2 + H 2 gas atmosphere where Fe oxidation does not occur (reducing Fe oxide), and are selected as the outermost layer of the steel sheet. In particular, a surface oxide (SiO 2 , MnO, etc., hereinafter referred to as a selective surface oxide) containing Si and Mn is formed. Since this selective surface oxide inhibits the formation reaction of the chemical conversion film during the chemical conversion treatment, a fine region (hereinafter also referred to as “ske”) where the chemical conversion film is not formed is formed, and the chemical conversion treatment performance is lowered.
ＳｉやＭｎを含有する鋼板の化成処理性を改善する従来技術として、特許文献１では、２０〜１５００ｍｇ/ｍ２の鉄被覆層を電気めっき法を用いて鋼板上に形成する方法が開示されている。しかしながら、この方法では、電気めっき設備が別途必要となり工程が増加する分コストも増大するという問題がある。 As a conventional technique for improving chemical conversion properties of a steel sheet containing Si or Mn, Patent Document 1 discloses a method of forming an iron coating layer of 20 to 1500 mg / m 2 on a steel sheet using an electroplating method. Yes. However, in this method, there is a problem that the cost is increased due to the additional steps required for the electroplating equipment.
また、特許文献２では、Ｍｎ/Ｓｉ比率を規定し、特許文献３ではＮｉを添加することによって、各々リン酸塩処理性を向上させている。しかしながら、その効果は鋼板中のＳｉやＭｎの含有量に依存するものであり、ＳｉやＭｎの含有量が高い鋼板については更なる改善が必要であると考えられる。 Moreover, in patent document 2, Mn / Si ratio is prescribed | regulated, and patent document 3 is improving the phosphate processability by adding Ni, respectively. However, the effect depends on the contents of Si and Mn in the steel sheet, and it is considered that further improvement is necessary for the steel sheet having a high content of Si and Mn.
更に、特許文献４では、焼鈍時の露点を−２５〜０℃にすることで、鋼板素地表面から深さ１μｍ以内にＳｉを含有する酸化物からなる内部酸化層を形成し、鋼板表面長さ１０μｍに占めるＳｉ含有酸化物の割合を８０％以下にする方法が開示されている。しかしながら、特許文献４に記載の方法の場合、露点を制御するエリアが炉内全体を前提としたものであるため、露点の制御性が困難であり安定操業が困難である。また、不安定な露点制御のもとでの焼鈍を行った場合、鋼板に形成される内部酸化物の分布状態にバラツキが認められ、鋼板の長手方向や幅方向で化成処理性のムラ（全体または一部でスケ）が発生する懸念がある。さらに、化成処理性が向上した場合でも、化成処理皮膜の直下にＳｉ含有酸化物が存在することから電着塗装後の耐食性が悪いという問題がある
また、特許文献５では、酸化性雰囲気中で鋼板温度を３５０〜６５０℃に到達させて鋼板表面に酸化膜を形成させ、その後、還元性雰囲気中で再結晶温度まで加熱し冷却する方法が記載されている。しかしながらこの方法では、酸化する方法により鋼板表面に形成される酸化皮膜の厚みに差があり、十分に酸化が起こらなかったり、酸化皮膜が厚くなりすぎて、後の還元性雰囲気中での焼鈍において酸化膜の残留または剥離を生じ、表面性状が悪化する場合がある。実施例では、大気中で酸化する技術が記載されているが、大気中での酸化は酸化物が厚く生成してその後の還元が困難である、あるいは高水素濃度の還元雰囲気が必要である、等の問題がある。
Furthermore, in Patent Document 4, an internal oxide layer made of an oxide containing Si is formed within a depth of 1 μm from the surface of the steel sheet base by setting the dew point during annealing to −25 to 0 ° C., and the steel sheet surface length A method is disclosed in which the proportion of the Si-containing oxide in 10 μm is 80% or less. However, in the case of the method described in Patent Document 4, since the area for controlling the dew point is premised on the entire inside of the furnace, the controllability of the dew point is difficult and stable operation is difficult. In addition, when annealing was performed under unstable dew point control, variations were observed in the distribution of internal oxides formed on the steel sheet, and chemical conversion treatment unevenness in the longitudinal and width directions of the steel sheet (overall) Or there is a concern that a part of the scale may occur. Furthermore, even when the chemical conversion treatment performance is improved, there is a problem that the corrosion resistance after electrodeposition coating is poor because the Si-containing oxide exists immediately below the chemical conversion treatment film. A method is described in which the steel sheet temperature reaches 350 to 650 ° C. to form an oxide film on the steel sheet surface, and then heated and cooled to the recrystallization temperature in a reducing atmosphere. However, in this method, there is a difference in the thickness of the oxide film formed on the surface of the steel sheet due to the oxidation method, and sufficient oxidation does not occur, or the oxide film becomes too thick, and in subsequent annealing in a reducing atmosphere. Oxide film may remain or peel off, and surface properties may deteriorate. In the examples, a technique for oxidizing in the air is described, but oxidation in the air generates a thick oxide and subsequent reduction is difficult, or a reducing atmosphere with a high hydrogen concentration is required. There are problems such as.
さらに、特許文献６では、質量％でＳｉを０．１％以上、および/または、Ｍｎを１．０％以上含有する冷延鋼板について、鋼板温度４００℃以上で鉄の酸化雰囲気下で鋼板表面に酸化膜を形成させ、その後、鉄の還元雰囲気下で前記鋼板表面の酸化膜を還元する方法が記載されている。具体的には、４００℃以上で空気比０．９３以上１．１０以下の直火バーナーを用いて鋼板表面のＦｅを酸化した後、Ｆｅ酸化物を還元するＮ２+Ｈ２ガス雰囲気で焼鈍することにより、化成処理性を劣化させる選択表面酸化を抑制し、最表面にＦｅの酸化層を形成させる方法である。特許文献６には、直火バーナーの加熱温度が具体的に記載されていないが、Ｓｉを多く（概ね０．６％以上）含有する場合には、Ｆｅよりも酸化しやすいＳｉの酸化量が多くなってＦｅの酸化が抑制されたり、Ｆｅの酸化そのものが少なくなりすぎたりする。その結果、還元後の表面Ｆｅ還元層の形成が不十分であったり、還元後の鋼板表面にＳｉＯ２が存在し、化成皮膜のスケが発生する場合がある。 Furthermore, in Patent Document 6, a cold-rolled steel sheet containing 0.1% or more by mass and / or 1.0% or more of Mn by mass%, the surface of the steel sheet in an iron oxidizing atmosphere at a steel sheet temperature of 400 ° C. or more. Describes a method in which an oxide film is formed, and then the oxide film on the surface of the steel sheet is reduced in an iron reducing atmosphere. Specifically, after oxidizing Fe on the surface of the steel sheet using a direct fire burner at 400 ° C. or higher and an air ratio of 0.93 or higher and 1.10 or lower, annealing is performed in an N 2 + H 2 gas atmosphere that reduces Fe oxide. In this method, selective surface oxidation that degrades the chemical conversion property is suppressed, and an Fe oxide layer is formed on the outermost surface. Patent Document 6 does not specifically describe the heating temperature of an open flame burner, but when it contains a large amount of Si (approximately 0.6% or more), the amount of oxidation of Si that is easier to oxidize than Fe. As a result, the oxidation of Fe is suppressed, and the oxidation of Fe itself becomes too small. As a result, the formation of the surface Fe reduction layer after reduction may be insufficient, or SiO 2 may be present on the steel sheet surface after reduction, resulting in the occurrence of a conversion coating.
本発明は、かかる事情に鑑みてなされたものであって、ＳｉやＭｎの含有量が多い場合でも、優れた化成処理性および電着塗装後の耐食性を有する高強度鋼板およびその製造方法を提供することを目的とする。 The present invention has been made in view of such circumstances, and provides a high-strength steel sheet having excellent chemical conversion property and corrosion resistance after electrodeposition coating even when the content of Si and Mn is large, and a method for producing the same The purpose is to do.
従来、Ｓｉ、Ｍｎ等の易酸化性元素を含有する鋼板については化成処理性を改善する目的で積極的に鋼板の内部を酸化させていた。しかし、同時に、内部酸化そのものにより表面に化成処理ムラやスケを発生させたり、電着塗装後の耐食性が劣化する。そこで、本発明者らは、従来の考えにとらわれない新たな方法で課題を解決する方法を検討した。その結果、連続焼鈍する際の加熱工程での昇温速度、雰囲気及び温度を適切に制御することで、鋼板表層部において内部酸化物の形成を抑制し、優れた化成処理性とより高い電着塗装後の耐食性が得られることを知見した。連続焼鈍する際に、加熱工程では、焼鈍炉内温度：４５０℃以上Ａ℃以下（Ａ：５００≦Ａ≦６００）の温度域を昇温速度：７℃/s以上で昇温し、焼鈍炉内での鋼板最高到達温度は６００℃以上７００℃以下であり、鋼板温度が６００℃以上７００℃以下の温度域における鋼板通過時間は３０秒以上１０分以内、雰囲気中の水素濃度は２０ｖｏｌ%以上となるように制御して焼鈍する。次いで、化成処理を行う。加熱工程における焼鈍炉内温度：４５０℃以上Ａ℃以下（Ａ：５００≦Ａ≦６００）の温度域を昇温速度：７℃/s以上、焼鈍炉内での鋼板最高到達温度を６００℃以上７００℃以下とし、鋼板温度が６００℃以上７００℃以下の温度域の雰囲気中の水素濃度を２０ｖｏｌ%以上とすることで、鋼板と雰囲気の界面の酸素ポテンシャルを低下させ、内部酸化が極力起こらずに、Ｓｉ、Ｍｎなどの選択的表面拡散、酸化（以後、表面濃化と呼ぶ）を抑制する。 Conventionally, steel sheets containing oxidizable elements such as Si and Mn have been actively oxidized inside the steel sheet for the purpose of improving chemical conversion treatment. At the same time, however, the internal oxidation itself causes chemical conversion unevenness and scum on the surface, and the corrosion resistance after electrodeposition coating deteriorates. Therefore, the present inventors have studied a method for solving the problem by a new method not confined to the conventional idea. As a result, by appropriately controlling the heating rate, atmosphere and temperature in the heating process during continuous annealing, the formation of internal oxides in the steel sheet surface layer portion is suppressed, and excellent chemical conversion treatment and higher electrodeposition are achieved. It was found that corrosion resistance after painting was obtained. During the continuous annealing, in the heating step, the temperature in the annealing furnace: 450 ° C. or more and A ° C. or less (A: 500 ≦ A ≦ 600) is raised at a rate of temperature increase: 7 ° C./s or more, and the annealing furnace Steel plate maximum temperature is 600 ° C. or more and 700 ° C. or less, steel plate passage time in the temperature range of 600 ° C. or more and 700 ° C. or less is 30 seconds or more and 10 minutes or less, and hydrogen concentration in the atmosphere is 20 vol% or more. It anneals by controlling so that it may become. Next, chemical conversion treatment is performed. Temperature in annealing furnace in heating process: 450 ° C. or more and A ° C. or less (A: 500 ≦ A ≦ 600) Temperature increase rate: 7 ° C./s or more, Maximum steel sheet temperature in annealing furnace is 600 ° C. or more By setting the hydrogen concentration in the atmosphere where the steel sheet temperature is 600 ° C. or more and 700 ° C. or less to 20 vol% or less, the oxygen potential at the interface between the steel plate and the atmosphere is lowered, and internal oxidation does not occur as much as possible. Furthermore, selective surface diffusion and oxidation (hereinafter referred to as surface concentration) such as Si and Mn are suppressed.
このように限定された領域のみの昇温速度と雰囲気中の水素濃度を制御することにより、内部酸化物を形成させず、表面濃化を極力抑制し、スケやムラのない、化成処理性および電着塗装後の耐食性に優れる高強度鋼板が得られることになる。なお、化成処理性に優れるとは、化成処理後のスケ、ムラのない外観を有することを言う。 By controlling the rate of temperature rise and the hydrogen concentration in the atmosphere only in such a limited region, the inner oxide is not formed, the surface concentration is suppressed as much as possible, and there is no scale or unevenness. A high-strength steel sheet having excellent corrosion resistance after electrodeposition coating will be obtained. In addition, having excellent chemical conversion property means having a non-scaling and uneven appearance after chemical conversion treatment.
そして、以上の方法により得られる高強度鋼板は、鋼板表面から１００μm以内の鋼板表層部において、Ｆｅ、Ｓｉ、Ｍｎ、Ａｌ、Ｐ、さらには、Ｂ、Ｎｂ、Ｔｉ、Ｃｒ、Ｍｏ、Ｃｕ、Ｎｉ、Ｓｎ、Ｓｂ、Ｔａ、Ｗ、Ｖのうちから選ばれる１種以上の酸化物の形成が抑制され、その形成量は合計で片面あたり０．０３０ｇ/ｍ２未満に抑制される。これにより、化成処理性に優れ、電着塗装後の耐食性が著しく向上することになる。 And the high-strength steel plate obtained by the above method is Fe, Si, Mn, Al, P, and also B, Nb, Ti, Cr, Mo, Cu, Ni in the steel plate surface layer portion within 100 μm from the steel plate surface. , Sn, Sb, Ta, W and V are suppressed from forming one or more oxides selected from the group consisting of Sn, Sb, Ta, W, and V, and the total amount is suppressed to less than 0.030 g / m 2 per side. Thereby, it is excellent in chemical conversion property and the corrosion resistance after electrodeposition coating improves remarkably.
本発明は上記知見に基づくものであり、特徴は以下の通りである。
［１］質量％で、Ｃ：０．０３〜０．３５％、Ｓｉ：０．０１〜０．５０％、Ｍｎ：３．６〜８．０％、Ａｌ：０．０１〜１．０％、Ｐ≦０．１０％、Ｓ≦０．０１０％を含有し、残部がＦｅおよび不可避的不純物からなる鋼板を連続焼鈍する際に、加熱工程では、焼鈍炉内温度：４５０℃以上Ａ℃以下（Ａ：５００≦Ａ≦６００）の温度域を昇温速度：７℃/s以上で昇温し、焼鈍炉内での鋼板最高到達温度は６００℃以上７００℃以下であり、鋼板温度が６００℃以上７００℃以下の温度域における鋼板通過時間は３０秒以上１０分以内、雰囲気中の水素濃度は２０ｖｏｌ％以上とすることを特徴とする高強度鋼板の製造方法。
［２］前記鋼板は、成分組成として、質量％で、さらに、Ｂ：０．００１〜０．００５％、Ｎｂ：０．００５〜０．０５％、Ｔｉ：０．００５〜０．０５％、Ｃｒ：０．００１〜１．０％、Ｍｏ：０．０５〜１．０％、Ｃｕ：０．０５〜１．０％、Ｎｉ：０．０５〜１．０％、Ｓｎ：０．００１〜０．２０％、Ｓｂ：０．００１〜０．２０％、Ｔａ：０．００１〜０．１０％、Ｗ：０．００１〜０．１０％、Ｖ：０．００１〜０．１０％の中から選ばれる１種以上の元素を含有することを特徴とする上記［１］に記載の高強度鋼板の製造方法。
［３］前記連続焼鈍を行った後、さらに、硫酸を含む水溶液中で電解酸洗を行うことを特徴とする上記［１］または［２］に記載の高強度鋼板の製造方法。
［４］上記［１］〜［３］に記載のいずれかの製造方法により製造され、鋼板表面から１００μm以内の鋼板表層部に生成したＦｅ、Ｓｉ、Ｍｎ、Ａｌ、Ｐ、Ｂ、Ｎｂ、Ｔｉ、Ｃｒ、Ｍｏ、Ｃｕ、Ｎｉ、Ｓｎ、Ｓｂ、Ｔａ、Ｗ、Ｖの中から選ばれる１種以上の酸化物の合計が、片面あたり０．０３０ｇ／ｍ2未満であることを特徴とする高強度鋼板。
The present invention is based on the above findings, and features are as follows.
[1] By mass%, C: 0.03 to 0.35%, Si: 0.01 to 0.50%, Mn: 3.6 to 8.0%, Al: 0.01 to 1.0% , P ≦ 0.10%, S ≦ 0.010%, and when continuously annealing a steel plate consisting of Fe and unavoidable impurities, the temperature in the annealing furnace: 450 ° C. or more and A ° C. or less in the heating step The temperature range (A: 500 ≦ A ≦ 600) is increased at a rate of temperature increase of 7 ° C./s or higher, and the maximum steel sheet temperature in the annealing furnace is 600 ° C. or higher and 700 ° C. or lower. A method for producing a high-strength steel plate, characterized in that the steel plate passage time in a temperature range of from ℃ to 700 ℃ is from 30 seconds to 10 minutes and the hydrogen concentration in the atmosphere is 20 vol% or more.
[2] The steel sheet is in mass% as a component composition, and further B: 0.001 to 0.005%, Nb: 0.005 to 0.05%, Ti: 0.005 to 0.05%, Cr: 0.001-1.0%, Mo: 0.05-1.0%, Cu: 0.05-1.0%, Ni: 0.05-1.0%, Sn: 0.001- Among 0.20%, Sb: 0.001 to 0.20%, Ta: 0.001 to 0.10%, W: 0.001 to 0.10%, V: 0.001 to 0.10% The method for producing a high-strength steel sheet according to the above [1], comprising at least one element selected from the group consisting of:
[3] The method for producing a high-strength steel sheet according to the above [1] or [2], further comprising performing electrolytic pickling in an aqueous solution containing sulfuric acid after the continuous annealing.
[4] Fe, Si, Mn, Al, P, B, Nb, Ti produced by the production method according to any one of [1] to [3] and formed on the steel sheet surface layer within 100 μm from the steel sheet surface. , Cr, Mo, Cu, Ni, Sn, Sb, Ta, W, V, the total of one or more oxides selected from the group consisting of less than 0.030 g / m 2 per side Strength steel plate.
なお、本発明において、高強度鋼板とは、引張強度ＴＳが５９０ＭＰa以上である。また、本発明の高強度鋼板は、冷延鋼板、熱延鋼板のいずれも含むものである。 In the present invention, the high strength steel plate has a tensile strength TS of 590 MPa or more. The high-strength steel sheet of the present invention includes both cold-rolled steel sheets and hot-rolled steel sheets.
本発明によれば、ＳｉやＭｎの含有量が多い場合でも、優れた化成処理性および電着塗装後の耐食性を有する高強度鋼板が得られる。 According to the present invention, a high-strength steel sheet having excellent chemical conversion property and corrosion resistance after electrodeposition coating can be obtained even when the content of Si or Mn is large.
以下、本発明について具体的に説明する。なお、以下の説明において、鋼成分組成の各元素の含有量の単位は「質量％」であり、以下、特に断らない限り単に「％」で示す。
先ず、本発明で最も重要な要件である、鋼板表面の構造を決定する焼鈍条件について説明する。鋼中に多量のＳｉおよびＭｎが添加された高強度鋼板において、耐食性を満足させるためには、腐食の起点となる可能性がある鋼板表層の内部酸化を極力少なくすることが求められる。一方、ＳｉやＭｎの内部酸化を促進させることにより化成処理性を向上させることは可能ではある。しかし、これは上記のように、逆に耐食性の劣化をもたらすことになってしまう。このため、ＳｉやＭｎの内部酸化を促進させる方法以外で、良好な化成処理性を維持しつつ、内部酸化を抑制して耐食性を向上させる必要がある。鋭意検討した結果、本発明では、化成処理性を確保するために焼鈍工程において酸素ポテンシャルを低下させ易酸化性元素であるＳｉやＭｎ等の地鉄表層部における活量を低下させる。そして、これらの元素の外部酸化を抑制し、結果的に化成処理性を改善する。そして、鋼板表層部に形成する内部酸化も抑制され、電着塗装後の耐食性が改善することになる。
Hereinafter, the present invention will be specifically described. In the following description, the unit of the content of each element of the steel component composition is “mass%”, and hereinafter, simply indicated by “%” unless otherwise specified.
First, annealing conditions for determining the structure of the steel sheet surface, which is the most important requirement in the present invention, will be described. In a high-strength steel sheet in which a large amount of Si and Mn is added to the steel, in order to satisfy the corrosion resistance, it is required to minimize the internal oxidation of the steel sheet surface layer that may be a starting point of corrosion. On the other hand, it is possible to improve the chemical conversion property by promoting the internal oxidation of Si and Mn. However, as described above, this leads to deterioration of corrosion resistance. For this reason, it is necessary to suppress the internal oxidation and improve the corrosion resistance while maintaining good chemical conversion properties other than the method of promoting the internal oxidation of Si and Mn. As a result of intensive studies, in the present invention, in order to ensure chemical conversion treatment, the oxygen potential is lowered in the annealing process, and the activity in the surface layer portion of the easily oxidizable elements such as Si and Mn is reduced. And the external oxidation of these elements is suppressed and chemical conversion processability is improved as a result. And the internal oxidation formed in a steel plate surface layer part is also suppressed, and the corrosion resistance after electrodeposition coating will improve.
このような効果は、連続式焼鈍設備において焼鈍を施すに際し、加熱工程において、焼鈍炉内温度：４５０℃以上Ａ℃以下（Ａ：５００≦Ａ≦６００）の温度域を昇温速度：７℃/s以上、かつ、焼鈍炉内での鋼板最高到達温度は６００℃以上７００℃以下であり、鋼板温度が６００℃以上７００℃以下の温度域における鋼板通過時間は３０秒以上１０分以内、雰囲気中の水素濃度：２０ｖｏｌ%以上となるように制御することにより得られる。焼鈍炉内温度：４５０℃以上Ａ℃以下（Ａ：５００≦Ａ≦６００）の温度域を昇温速度：７℃／ｓ以上となるように制御して昇温することにより、表面濃化物の生成を極力抑制する。さらに、鋼板温度が６００℃以上７００℃以下の温度域において雰囲気中の水素濃度を２０ｖｏｌ%以上となるように制御することにより、鋼板と雰囲気の界面の酸素ポテンシャルを低下させ、内部酸化を形成させずに、Ｓｉ、Ｍｎなどの選択的表面拡散、表面濃化を抑制する。結果、スケ、ムラのない優れた化成処理性とより高い電着塗装後の耐食性が得られることになる。 Such an effect is obtained when annealing is performed in a continuous annealing facility, and in the heating step, the temperature range in the annealing furnace is 450 ° C. or more and A ° C. or less (A: 500 ≦ A ≦ 600). / s or more, and the maximum temperature reached in the annealing furnace is 600 ° C. or more and 700 ° C. or less, and the steel plate passage time in the temperature range of 600 ° C. or more and 700 ° C. or less is 30 seconds or more and 10 minutes or less, atmosphere It is obtained by controlling the hydrogen concentration in the solution to 20 vol% or more. The temperature inside the annealing furnace: 450 ° C. or more and A ° C. or less (A: 500 ≦ A ≦ 600) is controlled so that the temperature rise rate is 7 ° C./s or more. Suppress production as much as possible. Furthermore, by controlling the hydrogen concentration in the atmosphere to be 20 vol% or more in the temperature range of 600 ° C. or more and 700 ° C. or less, the oxygen potential at the interface between the steel plate and the atmosphere is lowered, and internal oxidation is formed. In addition, selective surface diffusion and surface concentration of Si, Mn, etc. are suppressed. As a result, excellent chemical conversion processability without scaling and unevenness and higher corrosion resistance after electrodeposition coating can be obtained.
昇温速度を制御する温度域を４５０℃以上とした理由は以下の通りである。４５０℃を下回る温度域では、スケ、ムラの発生、耐食性の劣化等が問題になる程度の表面濃化や内部酸化は起こらない。よって、本発明の効果が発現する温度域である４５０℃以上とする。
また、温度域をＡ℃以下（Ａ：５００≦Ａ≦６００）とした理由は以下の通りである。まず、５００℃を下回る温度域では、昇温速度を７℃／ｓ以上に制御する時間が短く、本発明の効果が小さい。表面濃化の抑制効果が十分でない。このため、Ａは５００以上とする。また、６００℃超えの場合、本発明の効果に何ら問題はないが、焼鈍炉内設備（ロールなど）の劣化、及びコスト増大の観点から、不利となる。したがって、６００℃以下とする。
The reason why the temperature range for controlling the rate of temperature rise is 450 ° C. or higher is as follows. In the temperature range below 450 ° C., surface enrichment and internal oxidation that cause problems such as scale, unevenness, and deterioration of corrosion resistance do not occur. Therefore, the temperature is set to 450 ° C. or higher where the effect of the present invention is manifested.
The reason why the temperature range is set to A ° C. or lower (A: 500 ≦ A ≦ 600) is as follows. First, in the temperature range below 500 ° C., the time for controlling the rate of temperature rise to 7 ° C./s or more is short, and the effect of the present invention is small. The effect of suppressing surface concentration is not sufficient. For this reason, A is set to 500 or more. Moreover, when it exceeds 600 degreeC, there is no problem in the effect of this invention, but it becomes disadvantageous from a viewpoint of deterioration of the equipment (roll etc.) in an annealing furnace, and cost increase. Therefore, it shall be 600 degrees C or less.
昇温速度を７℃／ｓ以上とした理由は以下の通りである。表面濃化の抑制効果が認められるのが昇温速度が７℃／ｓ以上である。昇温速度の上限は特には設けないが、５００℃／ｓ以上では効果は飽和し、コスト的に不利となるため、５００℃／ｓ以下が望ましい。昇温速度を７℃／ｓ以上とすることは、例えばインダクションヒーターを鋼板温度が４５０℃以上Ａ℃以下となる焼鈍炉内に配置することで可能である。 The reason for setting the temperature rising rate to 7 ° C./s or more is as follows. The temperature increasing rate is 7 ° C./s or more to show the effect of suppressing the surface concentration. The upper limit of the rate of temperature rise is not particularly set, but if it is 500 ° C./s or more, the effect is saturated and disadvantageous in terms of cost. It is possible to set the heating rate to 7 ° C./s or more, for example, by placing the induction heater in an annealing furnace in which the steel plate temperature is 450 ° C. or more and A ° C. or less.
焼鈍炉内での鋼板最高到達温度を６００℃以上７００℃以下とした理由は以下の通りである。６００℃未満では良好な材質が得られない。よって、本発明の効果が発現する温度域は、６００℃以上とする。一方、７００℃を上回る温度域では、表面濃化が顕著となり、化成処理性の劣化が酷くなる。さらに、材質の観点からは、７００℃を上回る温度域では、強度と延性のバランスの効果が飽和する。以上のことから、鋼板最高到達温度は６００℃以上７００℃以下とする。 The reason why the maximum temperature of the steel sheet in the annealing furnace is 600 ° C. or more and 700 ° C. or less is as follows. If it is less than 600 ° C., a good material cannot be obtained. Therefore, the temperature range in which the effects of the present invention are manifested is 600 ° C. or higher. On the other hand, in the temperature range exceeding 700 ° C., the surface concentration becomes remarkable, and the chemical conversion processability deteriorates severely. Furthermore, from the viewpoint of the material, the effect of balance between strength and ductility is saturated in a temperature range exceeding 700 ° C. From the above, the maximum temperature reached by the steel sheet is 600 ° C. or more and 700 ° C. or less.
次に、鋼板温度が６００℃以上７００℃以下の温度域における鋼板通過時間を３０秒以上１０分以内とした理由は以下の通りである。３０秒を下回れば目標とする材質（ＴＳ、Ｅｌ）が得られない。一方、１０分を上回れば、強度と延性のバランスの効果が飽和する。 Next, the reason why the steel plate passage time in the temperature range of 600 ° C. or more and 700 ° C. or less is 30 seconds or more and 10 minutes or less is as follows. If it is less than 30 seconds, the target material (TS, El) cannot be obtained. On the other hand, if it exceeds 10 minutes, the effect of balance between strength and ductility is saturated.
鋼板温度が６００℃以上７００℃以下の温度域における雰囲気中の水素濃度を２０ｖｏｌ％以上とした理由は以下の通りである。表面濃化の抑制効果を認め始めるのが水素濃度：２０ｖｏｌ％である。水素濃度の上限は特に設けないが、８０ｖｏｌ％超えでは効果が飽和し、コスト的に不利となるため、８０ｖｏｌ％以下が望ましい。 The reason why the hydrogen concentration in the atmosphere in the temperature range where the steel sheet temperature is 600 ° C. or more and 700 ° C. or less is 20 vol% or more is as follows. It is the hydrogen concentration: 20 vol% that begins to recognize the effect of suppressing surface concentration. The upper limit of the hydrogen concentration is not particularly set, but if it exceeds 80 vol%, the effect is saturated and disadvantageous in terms of cost, so 80 vol% or less is desirable.
次いで、本発明の対象とする高強度鋼板の鋼成分組成について説明する。
Ｃ：０．０３〜０．３５％
Ｃは、鋼組織としてマルテンサイトなどを形成させることで加工性を向上させる。そのためには０．０３％以上必要である。一方、０．３５％を超えると強度が上昇しすぎて、延びが低下し、結果として加工性が劣化する。したがって、Ｃ量は０．０３％以上０．３５％以下とする。
Next, the steel component composition of the high-strength steel sheet that is the subject of the present invention will be described.
C: 0.03-0.35%
C improves workability by forming martensite or the like as a steel structure. For that purpose, 0.03% or more is necessary. On the other hand, if it exceeds 0.35%, the strength increases excessively, the elongation decreases, and as a result, workability deteriorates. Therefore, the C content is 0.03% or more and 0.35% or less.
Ｓｉ：０．０１〜０．５０％
Ｓｉは鋼を強化して良好な材質を得るのに有効な元素ではあるが、易酸化性元素であるため、化成処理性には不利であり、極力添加することは避けるべき元素である。しかし、０．０１％程度は不可避的に鋼中に含まれ、これ以下に低減するためにはコストが上昇してしまう。以上より、０．０１％を下限とする。一方、０．５０％を超えると鋼の強化能や伸び向上効果が飽和してくる。また、化成処理性が劣化する。したがって、Ｓｉ量は０．０１％以上０．５０％以下とする。
Si: 0.01 to 0.50%
Si is an element effective for strengthening steel to obtain a good material, but it is an easily oxidizable element, which is disadvantageous for chemical conversion treatment and should be avoided as much as possible. However, about 0.01% is inevitably contained in steel, and in order to reduce it below this, the cost increases. From the above, 0.01% is made the lower limit. On the other hand, if it exceeds 0.50%, the steel strengthening ability and the effect of improving elongation become saturated. Moreover, chemical conversion processability deteriorates. Therefore, the Si amount is set to 0.01% or more and 0.50% or less.
Ｍｎ：３．６〜８．０％
Ｍｎは鋼の高強度化に有効な元素である。機械特性や強度を確保するためは３．６％以上含有させることが必要である。一方、８．０％を超えると化成処理性の確保、強度と延性のバランスの確保が困難になる。さらに、コスト的に不利となる。したがって、Ｍｎ量は３．６％以上８．０％以下とする。
Mn: 3.6-8.0%
Mn is an element effective for increasing the strength of steel. In order to ensure mechanical properties and strength, it is necessary to contain 3.6% or more. On the other hand, if it exceeds 8.0%, it will be difficult to ensure chemical conversion treatment and to ensure a balance between strength and ductility. Further, it is disadvantageous in terms of cost. Therefore, the Mn content is 3.6% or more and 8.0% or less.
Ａｌ：０．０１〜１．０％
Ａｌは溶鋼の脱酸を目的に添加されるが、その含有量が０．０１％未満の場合、その目的が達成されない。溶鋼の脱酸の効果は０．０１％以上で得られる。一方、１．０％を超えるとコストアップになる。さらに、Ａｌの表面濃化が多くなり、化成処理性の改善が困難になってくる。したがって、Ａｌ量は０．０１％以上１．０％以下とする。
Al: 0.01 to 1.0%
Al is added for the purpose of deoxidizing molten steel, but if the content is less than 0.01%, the purpose is not achieved. The effect of deoxidation of molten steel is obtained at 0.01% or more. On the other hand, if it exceeds 1.0%, the cost increases. Furthermore, the surface concentration of Al increases and it becomes difficult to improve chemical conversion properties. Therefore, the Al content is set to 0.01% to 1.0%.
Ｐ≦０．１０％
Ｐは不可避的に含有される元素のひとつであり、０．００５％未満にするためには、コストの増大が懸念されるため、０．００５％以上が望ましい。一方、Ｐが０．１０％を超えて含有されると溶接性が劣化する。さらに、化成処理性の劣化が激しくなり、本発明をもってしても化成処理性を向上させることが困難になってくる。したがって、Ｐ量は０．１０％以下とし、下限としては０．００５％が望ましい。
P ≦ 0.10%
P is one of the elements inevitably contained, and in order to make it less than 0.005%, there is a concern about an increase in cost, so 0.005% or more is desirable. On the other hand, if P exceeds 0.10%, weldability deteriorates. Furthermore, the chemical conversion processability deteriorates, and even with the present invention, it is difficult to improve the chemical conversion processability. Accordingly, the P content is preferably 0.10% or less, and the lower limit is preferably 0.005%.
Ｓ≦０．０１０％
Ｓは不可避的に含有される元素のひとつである。下限は規定しないが、多量に含有されると溶接性および耐食性が劣化するため０．０１０％以下とする。
S ≦ 0.010%
S is one of the elements inevitably contained. The lower limit is not specified, but if it is contained in a large amount, the weldability and corrosion resistance deteriorate, so the content is made 0.010% or less.
なお、表面品質改善や強度と延性のバランスのさらなる改善をはかるため、Ｂ：０．００１〜０．００５％、Ｎｂ：０．００５〜０．０５％、Ｔｉ：０．００５〜０．０５％、Ｃｒ：０．００１〜１．０％、Ｍｏ：０．０５〜１．０％、Ｃｕ：０．０５〜１．０％、Ｎｉ：０．０５〜１．０％、Ｓｎ：０．００１〜０．２０％、Ｓｂ：０．００１〜０．２０％、Ｔａ：０．００１〜０．１０％、Ｗ：０．００１〜０．１０％、Ｖ：０．００１〜０．１０％の中から選ばれる１種以上の元素を必要に応じて添加してもよい。
これらの元素を添加する場合における適正添加量の限定理由は以下の通りである。
In order to further improve the surface quality and balance between strength and ductility, B: 0.001 to 0.005%, Nb: 0.005 to 0.05%, Ti: 0.005 to 0.05% Cr: 0.001-1.0%, Mo: 0.05-1.0%, Cu: 0.05-1.0%, Ni: 0.05-1.0%, Sn: 0.001 -0.20%, Sb: 0.001-0.20%, Ta: 0.001-0.10%, W: 0.001-0.10%, V: 0.001-0.10% One or more elements selected from the above may be added as necessary.
The reason for limiting the appropriate addition amount in the case of adding these elements is as follows.
Ｂ：０．００１〜０．００５％
Ｂは０．００１％未満では焼き入れ促進効果が得られにくい。一方、０．００５％超えでは化成処理性が劣化する。よって、含有する場合、Ｂ量は０．００１％以上０．００５％以下とする。但し、機械的特性改善上添加する必要がないと判断される場合は添加する必要はない。
B: 0.001 to 0.005%
When B is less than 0.001%, it is difficult to obtain an effect of promoting quenching. On the other hand, if it exceeds 0.005%, chemical conversion processability deteriorates. Therefore, when it contains, B amount shall be 0.001% or more and 0.005% or less. However, when it is judged that it is not necessary to improve the mechanical properties, it is not necessary to add it.
Ｎｂ：０．００５〜０．０５％
Ｎｂは０．００５％未満では強度調整の効果が得られにくい。一方、０．０５％超えではコストアップを招く。よって、含有する場合、Ｎｂ量は０．００５％以上０．０５％以下とする。
Nb: 0.005 to 0.05%
If Nb is less than 0.005%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 0.05%, the cost increases. Therefore, when it contains, Nb amount shall be 0.005% or more and 0.05% or less.
Ｔｉ：０．００５〜０．０５％
Ｔｉは０．００５％未満では強度調整の効果が得られにくい。一方、０．０５％超えでは化成処理性の劣化を招く。よって、含有する場合、Ｔｉ量は０．００５％以上０．０５％以下とする。
Ti: 0.005 to 0.05%
If Ti is less than 0.005%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 0.05%, chemical conversion processability is deteriorated. Therefore, when it contains, Ti amount shall be 0.005% or more and 0.05% or less.
Ｃｒ：０．００１〜１．０％
Ｃｒは０．００１％未満では焼き入れ性効果が得られにくい。一方、１．０％超えではＣｒが表面濃化するため、溶接性が劣化する。よって、含有する場合、Ｃｒ量は０．００１％以上１．０％以下とする。
Cr: 0.001 to 1.0%
When Cr is less than 0.001%, it is difficult to obtain a hardenability effect. On the other hand, if it exceeds 1.0%, the surface of Cr is concentrated, so that the weldability deteriorates. Therefore, when it contains, Cr amount shall be 0.001% or more and 1.0% or less.
Ｍｏ：０．０５〜１．０％
Ｍｏは０．０５％未満では強度調整の効果が得られにくい。一方、１．０％超えではコストアップを招く。よって、含有する場合、Ｍｏ量は０．０５％以上１．０％以下とする。
Mo: 0.05-1.0%
If Mo is less than 0.05%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when contained, the Mo content is 0.05% or more and 1.0% or less.
Ｃｕ：０．０５〜１．０％
Ｃｕは０．０５％未満では残留γ相形成促進効果が得られにくい。一方、１．０％超えではコストアップを招く。よって、含有する場合、Ｃｕ量は０．０５％以上１．０％以下とする。
Cu: 0.05 to 1.0%
If Cu is less than 0.05%, it is difficult to obtain the effect of promoting the formation of the residual γ phase. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when contained, the Cu content is 0.05% or more and 1.0% or less.
Ｎｉ：０．０５〜１．０％
Ｎｉは０．０５％未満では残留γ相形成促進効果が得られにくい。一方、１．０％超えではコストアップを招く。よって、含有する場合、Ｎｉ量は０．０５％以上１．０％以下とする。
Ni: 0.05-1.0%
If Ni is less than 0.05%, the effect of promoting the formation of residual γ phase is difficult to obtain. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when it contains, Ni amount shall be 0.05% or more and 1.0% or less.
Ｓｎ：０．００１〜０．２０％、Ｓｂ：０．００１〜０．２０％
ＳｎやＳｂは鋼板表面の窒化、酸化、あるいは酸化により生じる鋼板表面の数十ミクロン領域の脱炭を抑制する観点から含有することができる。窒化や酸化を抑制することで鋼板表面においてマルテンサイトの生成量が減少するのを防止し、疲労特性や表面品質が改善する。以上の観点から、Ｓｎおよび／またはＳｂを含有する場合は、いずれも０．００１％以上とする。また、いずれかの含有量が０．２０％を超えると靭性の劣化を招くので、０．２０％以下とすることが好ましい。
Sn: 0.001 to 0.20%, Sb: 0.001 to 0.20%
Sn or Sb can be contained from the viewpoint of suppressing decarburization in the region of several tens of microns on the surface of the steel sheet caused by nitriding, oxidation, or oxidation of the steel sheet surface. By suppressing nitriding and oxidation, it is possible to prevent a reduction in the amount of martensite produced on the surface of the steel sheet and improve fatigue characteristics and surface quality. From the above viewpoint, when Sn and / or Sb are contained, both are 0.001% or more. Moreover, since the deterioration of toughness will be caused when either content exceeds 0.20%, it is preferable to set it as 0.20% or less.
Ｔａ：０．００１〜０．１０％
ＴａはＣやＮと炭化物や炭窒化物を形成することで高強度化に寄与し、さらに高降伏比(YR)化に寄与する。さらに、Ｔａは熱延板組織を微細化する作用を有し、この作用により、冷延、焼鈍後のフェライト粒径が微細化される。そして、粒界面積の増大に伴う粒界へのＣ偏析量が増大し、高焼付き硬化量(BH量)を得ることができる。このような観点から、Ｔａは０．００１％以上含有することができる。一方、０．１０％を超える過剰のＴａの含有は、原料コストの増加を招くだけでなく、焼鈍後の冷却過程におけるマルテンサイトの形成を妨げる可能性がある。さらには、熱延板中に析出したＴａＣは、冷間圧延時の変形抵抗を高くし、安定した実機製造を困難にする場合がある。よって、Ｔａを含有する場合は、０．１０％以下とする。
Ta: 0.001 to 0.10%
Ta contributes to high strength by forming carbides and carbonitrides with C and N, and further contributes to high yield ratio (YR). Furthermore, Ta has the effect of refining the hot-rolled sheet structure, and this effect refines the ferrite grain size after cold rolling and annealing. And the amount of C segregation to the grain boundary accompanying the increase in grain boundary area increases, and a high seizure hardening amount (BH amount) can be obtained. From such a viewpoint, Ta can be contained in an amount of 0.001% or more. On the other hand, the inclusion of excess Ta exceeding 0.10% not only increases the raw material cost, but may hinder the formation of martensite in the cooling process after annealing. Furthermore, TaC precipitated in the hot-rolled sheet increases the deformation resistance during cold rolling, and may make it difficult to manufacture a stable actual machine. Therefore, when it contains Ta, it is 0.10% or less.
Ｗ：０．００１〜０．１０％、Ｖ：０．００１〜０．１０％
ＷおよびＶは炭窒化物を形成し、鋼を析出効果により高強度化する作用を有する元素であり、必要に応じて添加できる。このような作用は、Ｗおよび／またはＶを添加する場合、いずれも０．００１％以上含有して認められる。一方、０．１０％を超えて含有する場合、過度に高強度化し、延性が劣化してしまう。以上より、Ｗおよび／またはＶを含有する場合、いずれも０．００１％以上０．１０％以下とする。
W: 0.001-0.10%, V: 0.001-0.10%
W and V are elements that form carbonitrides and have the effect of increasing the strength of steel by precipitation effects, and can be added as necessary. Such an effect is observed when both W and / or V are added, containing 0.001% or more. On the other hand, when it contains exceeding 0.10%, it will become high strength too much and ductility will deteriorate. As mentioned above, when it contains W and / or V, all are 0.001% or more and 0.10% or less.
上記以外の残部はＦｅおよび不可避的不純物である。上記記載の元素以外の元素を含有しても、本発明には何ら悪影響を及ぼすものではなく、その上限は０．１０％とする。 The balance other than the above is Fe and inevitable impurities. Even if elements other than the elements described above are contained, the present invention is not adversely affected, and the upper limit is made 0.10%.
次に、本発明の高強度鋼板の製造方法とその限定理由について説明する。 Next, the manufacturing method of the high strength steel plate of the present invention and the reason for limitation will be described.
上記化学成分を有する鋼を熱間圧延した後、冷間圧延し鋼板とし、次いで、連続焼鈍設備において焼鈍を行う。さらに、硫酸を含む水溶液中で電解酸洗を行うことが好ましい。次いで、化成処理を行う。なお、この時、本発明においては、焼鈍を行う際に、加熱工程では、焼鈍炉内温度：４５０℃以上Ａ℃以下（Ａ：５００≦Ａ≦６００）の温度域を昇温速度：７℃/s以上、かつ、焼鈍炉内での鋼板最高到達温度は６００℃以上７００℃以下であり、鋼板温度が６００℃以上７００℃以下の温度域における鋼板通過時間は３０秒以上１０分以内、雰囲気中の水素濃度は２０ｖｏｌ％以上とする。これは本発明において、最も重要な要件である。なお、上記において、熱間圧延終了後、冷間圧延を施さずに、そのまま焼鈍を行う場合もある。 After the steel having the above chemical components is hot-rolled, it is cold-rolled to obtain a steel plate, and then annealed in a continuous annealing facility. Furthermore, it is preferable to perform electrolytic pickling in an aqueous solution containing sulfuric acid. Next, chemical conversion treatment is performed. At this time, in the present invention, when annealing is performed, in the heating step, the temperature range of the annealing furnace temperature: 450 ° C. or higher and A ° C. or lower (A: 500 ≦ A ≦ 600) is set at a rate of temperature increase: 7 ° C. / s or more, and the maximum temperature reached in the annealing furnace is 600 ° C. or more and 700 ° C. or less, and the steel plate passage time in the temperature range of 600 ° C. or more and 700 ° C. or less is 30 seconds or more and 10 minutes or less, atmosphere The hydrogen concentration inside is 20 vol% or more. This is the most important requirement in the present invention. In the above, after the hot rolling, annealing may be performed as it is without performing cold rolling.
熱間圧延
通常、行われる条件にて行うことができる。
Hot rolling Usually, it can be performed on the conditions performed.
酸洗
熱間圧延後は酸洗処理を行うのが好ましい。酸洗工程で表面に生成した黒皮スケールを除去し、しかる後冷間圧延する。なお、酸洗条件は特に限定しない。
It is preferable to perform a pickling treatment after hot pickling. The black scale formed on the surface in the pickling process is removed, and then cold-rolled. The pickling conditions are not particularly limited.
冷間圧延
４０％以上８０％以下の圧下率で行うことが好ましい。圧下率が４０％未満では再結晶温度が低温化するため、機械特性が劣化しやすい。一方、圧下率が８０％超えでは高強度鋼板であるため、圧延コストがアップするだけでなく、焼鈍時の表面濃化が増加するため、化成処理性が劣化する場合がある。
Cold rolling is preferably performed at a rolling reduction of 40% to 80%. If the rolling reduction is less than 40%, the recrystallization temperature is lowered, and the mechanical characteristics are likely to deteriorate. On the other hand, if the rolling reduction exceeds 80%, the steel sheet is a high-strength steel plate, so that not only the rolling cost is increased, but also the surface concentration during annealing is increased, so that the chemical conversion property may be deteriorated.
冷間圧延した鋼板もしくは熱間圧延した鋼板に対して、焼鈍し、次いで、化成処理を施す。 Cold-rolled steel sheets or hot-rolled steel sheets are annealed and then subjected to chemical conversion treatment.
焼鈍炉では、前段の加熱帯で鋼板を所定温度まで加熱する加熱工程を行い、後段の均熱帯で所定温度に所定時間保持する均熱工程を行う。 In the annealing furnace, a heating process is performed in which the steel sheet is heated to a predetermined temperature in a preceding heating zone, and a soaking process is performed in which the temperature is maintained at a predetermined temperature for a predetermined time in a subsequent soaking zone.
そして、上述したように、加熱工程では、焼鈍炉内温度：４５０℃以上Ａ℃以下（Ａ：５００≦Ａ≦６００）の温度域を昇温速度：７℃/s以上、かつ、焼鈍炉内での鋼板最高到達温度は６００℃以上７００℃以下であり、鋼板温度が６００℃以上７００℃以下の温度域における鋼板通過時間は３０秒以上１０分以内、雰囲気中の水素濃度は２０ｖｏｌ％以上である。 As described above, in the heating step, the temperature range of the annealing furnace temperature: 450 ° C. or more and A ° C. or less (A: 500 ≦ A ≦ 600) is set to a temperature increase rate of 7 ° C./s or more and the annealing furnace is heated. The maximum temperature reached in the steel plate is 600 ° C. or higher and 700 ° C. or lower, the steel plate passage time in the temperature range of 600 ° C. or higher and 700 ° C. or lower is 30 seconds or longer and within 10 minutes, and the hydrogen concentration in the atmosphere is 20 vol% or higher. is there.
焼鈍炉内の気体成分は、窒素、水素および不可避的不純物からなる。本発明効果を損するものでなければ他の気体成分を含有してもよい。 The gaseous components in the annealing furnace consist of nitrogen, hydrogen and unavoidable impurities. Other gas components may be included as long as the effects of the present invention are not impaired.
また、鋼板温度が６００℃以上７００℃以下の温度域以外の温度域、すなわち、６００℃未満、または７００℃を超える温度域の水素濃度は特に制約されないが、水素濃度が１ｖｏｌ％未満では還元による活性化効果が得られず化成処理性が劣化する場合がある。上限は特に規定しないが、５０ｖｏｌ％超えではコストアップし、かつ効果が飽和する。よって、水素濃度は１ｖｏｌ％以上５０ｖｏｌ％以下が好ましい。更には、５ｖｏｌ％以上３０ｖｏｌ％以下が望ましい。また、残部はＮ２および不可避的不純物気体からなる。本発明の効果を損するものでなければ、Ｈ２Ｏ、ＣＯ２、ＣＯ等の他の気体成分を含有してもよい。 In addition, the hydrogen concentration in the temperature range other than the temperature range of 600 ° C. or more and 700 ° C. or less, that is, the temperature range of less than 600 ° C. or more than 700 ° C. is not particularly limited, but if the hydrogen concentration is less than 1 vol%, it is reduced. In some cases, the activation effect cannot be obtained and the chemical conversion property is deteriorated. The upper limit is not particularly specified, but if it exceeds 50 vol%, the cost increases and the effect is saturated. Therefore, the hydrogen concentration is preferably 1 vol% or more and 50 vol% or less. Furthermore, 5 vol% or more and 30 vol% or less are desirable. The balance consists of N 2 and unavoidable impurity gases. Other gas components such as H 2 O, CO 2 and CO may be contained as long as the effects of the present invention are not impaired.
さらに、６００℃以上７００℃以下の温度域から冷却後、必要に応じて焼入れ、焼き戻しを行っても良い。条件は特に限定しないが、焼き戻しは１５０〜４００℃の温度で行うのが好ましい。１５０℃未満では伸びが劣化傾向にあり、４００℃超えでは硬度が低下する傾向にあるためである。 Furthermore, after cooling from a temperature range of 600 ° C. to 700 ° C., quenching and tempering may be performed as necessary. The conditions are not particularly limited, but tempering is preferably performed at a temperature of 150 to 400 ° C. This is because the elongation tends to deteriorate when the temperature is less than 150 ° C., and the hardness tends to decrease when the temperature exceeds 400 ° C.
本発明においては、電解酸洗を実施しなくとも良好な化成処理性は確保可能であるが、焼鈍時に不可避的に発生する微量な表面濃化物を除去し、より良好な化成処理性を確保する目的で、連続焼鈍を行った後、硫酸を含む水溶液中で電解酸洗を行うことが好ましい。 In the present invention, good chemical conversion treatment can be ensured without carrying out electrolytic pickling, but a small amount of surface condensate inevitably generated during annealing is removed to ensure better chemical conversion treatment. For the purpose, it is preferable to perform electrolytic pickling in an aqueous solution containing sulfuric acid after continuous annealing.
電解酸洗に用いる酸洗液は特に限定しないが、硝酸やフッ化水素酸は設備に対する腐食性が強く取り扱いに注意を要するため、好ましくない。また塩酸は陰極から塩素ガスを発生する可能性があり好ましくない。このため、腐食性や環境を考慮すると硫酸の使用が好ましい。硫酸濃度は５質量％以上２０質量％以下が好ましい。硫酸濃度が５質量％未満では導電率が低くなることから電解時の浴電圧が上昇し、電源負荷が大きくなってしまう場合がある。一方、２０質量％超えの場合は、ドラッグアウトによる損失が大きくコスト的に問題となる。 The pickling solution used for electrolytic pickling is not particularly limited, but nitric acid and hydrofluoric acid are not preferable because they are highly corrosive to equipment and require careful handling. Hydrochloric acid is not preferred because it may generate chlorine gas from the cathode. For this reason, use of sulfuric acid is preferable in consideration of corrosivity and environment. The sulfuric acid concentration is preferably 5% by mass or more and 20% by mass or less. If the sulfuric acid concentration is less than 5% by mass, the electrical conductivity will be low, so that the bath voltage during electrolysis will rise and the power load may become large. On the other hand, if it exceeds 20% by mass, a loss due to drag-out is large, which causes a problem in cost.
電解酸洗の条件は特に限定しないが、焼鈍後に形成された不可避的に表面濃化したＳｉやＭｎの酸化物を効率的に除去するため、電流密度が１Ａ/ｄｍ２以上の交番電解とすることが望ましい。交番電解とする理由は、鋼板を陰極に保持したままでは酸洗効果が小さく、逆に鋼板を陽極に保持したままでは電解時に溶出するＦｅが酸洗液中に蓄積し、酸洗液中のＦｅ濃度が増大してしまい、鋼板表面に付着すると乾き汚れ等の問題が発生してしまうためである。 The conditions for the electrolytic pickling are not particularly limited, but in order to efficiently remove the inevitably surface-enriched Si and Mn oxides formed after annealing, an alternating electrolysis with a current density of 1 A / dm 2 or more is used. It is desirable. The reason for alternating electrolysis is that the pickling effect is small when the steel plate is held at the cathode, and conversely, Fe that is eluted during electrolysis accumulates in the pickling solution while the steel plate is held at the anode. This is because if the Fe concentration increases and adheres to the surface of the steel sheet, problems such as dry dirt occur.
電解液の温度は４０℃以上７０℃以下が好ましい。連続電解することによる発熱で浴温が上昇することから、４０℃未満に温度を維持することが困難な場合がある。また、電解槽のライニングの耐久性の観点から温度が７０℃を超えることは好ましくない。尚、４０℃未満の場合、酸洗効果が小さくなるため、４０℃以上が好ましい。 The temperature of the electrolytic solution is preferably 40 ° C. or higher and 70 ° C. or lower. Since the bath temperature rises due to heat generated by continuous electrolysis, it may be difficult to maintain the temperature below 40 ° C. Moreover, it is not preferable that temperature exceeds 70 degreeC from a durable viewpoint of the lining of an electrolytic cell. In addition, since it is less than 40 degreeC, the pickling effect becomes small, 40 degreeC or more is preferable.
以上により、本発明の高強度鋼板が得られる。そして、以下のように、鋼板表面の構造に特徴を有することになる。 As described above, the high-strength steel sheet of the present invention is obtained. And it has the characteristic in the structure of the steel plate surface as follows.
鋼板表面から１００μｍ以内の鋼板表層部では、Ｆｅ、Ｓｉ、Ｍｎ、Ａｌ、Ｐ、さらには、Ｂ、Ｎｂ、Ｔｉ、Ｃｒ、Ｍｏ、Ｃu、Ｎｉ、Ｓｎ、Ｓｂ、Ｔａ、Ｗ、Ｖのうちから選ばれる１種以上の酸化物の合計が片面あたり０．０３０ｇ／ｍ２未満に抑制される。
鋼中に多量のＳｉおよびＭｎが添加された鋼板においては、下地鋼板表層の内部酸化を極力少なくし、化成処理ムラやスケを抑制し、さらに、腐食や高加工時の割れを抑制することが求められる。そこで、本発明では、まず、良好な化成処理性を確保するために焼鈍工程において酸素ポテンシャルを低下させることで易酸化性元素であるＳｉやＭｎ等の地鉄表層部における活量を低下させる。そして、これらの元素の外部酸化を抑制し、地鉄表層部に形成する内部酸化も抑制する。その結果、良好な化成処理性を確保するだけでなく、電着塗装後の耐食性や加工性が向上することになる。このような効果は、下地鋼板表面から１００μｍ以内の鋼板表層部に、Ｆｅ、Ｓｉ、Ｍｎ、Ａｌ、Ｐ、さらには、Ｂ、Ｎｂ、Ｔｉ、Ｃｒ、Ｍｏ、Ｃｕ、Ｎｉ、Ｓｎ、Ｓｂ、Ｔａ、Ｗ、Ｖのうちから選ばれる少なくとも１種の酸化物を合計で０．０３０ｇ／ｍ２未満に抑制することで認められる。酸化物形成量の合計（以下、内部酸化量と称す）が０．０３０ｇ／ｍ２以上では、耐食性および加工性が劣化するばかりでなく、化成処理のスケやムラが生じる。また、内部酸化量を０．０００１ｇ／ｍ２未満に抑制しても、耐食性の改善および加工性向上の効果は飽和するため、内部酸化量の下限は０．０００１ｇ／ｍ２が好ましい。
In the steel plate surface layer portion within 100 μm from the steel plate surface, Fe, Si, Mn, Al, P, and B, Nb, Ti, Cr, Mo, Cu, Ni, Sn, Sb, Ta, W, V The total of one or more selected oxides is suppressed to less than 0.030 g / m 2 per side.
In steel sheets with a large amount of Si and Mn added to the steel, the internal oxidation of the surface of the underlying steel sheet is minimized, chemical conversion treatment unevenness and scale are suppressed, and corrosion and cracking during high processing can be suppressed. Desired. Therefore, in the present invention, first, the activity in the surface layer portion of the iron base such as Si and Mn, which are easily oxidizable elements, is reduced by lowering the oxygen potential in the annealing process in order to ensure good chemical conversion properties. And the external oxidation of these elements is suppressed and the internal oxidation formed in a surface iron surface layer part is also suppressed. As a result, not only good chemical conversion treatment is ensured, but also the corrosion resistance and workability after electrodeposition coating are improved. Such an effect is obtained by applying Fe, Si, Mn, Al, P, and B, Nb, Ti, Cr, Mo, Cu, Ni, Sn, Sb, Ta on the steel sheet surface layer within 100 μm from the surface of the base steel sheet. , W and V, it is recognized by suppressing at least one oxide selected from less than 0.030 g / m 2 in total. When the total oxide formation amount (hereinafter referred to as internal oxidation amount) is 0.030 g / m 2 or more, not only the corrosion resistance and workability are deteriorated, but also the conversion treatment is scaled and uneven. Moreover, even if the internal oxidation amount is suppressed to less than 0.0001 g / m 2 , the effects of improving corrosion resistance and workability are saturated, so the lower limit of the internal oxidation amount is preferably 0.0001 g / m 2 .
以下、本発明を、実施例に基いて具体的に説明する。
表１に示す鋼組成からなる熱延鋼板を酸洗し、黒皮スケール除去した後、表２に示す条件にて冷間圧延し、厚さ１．０ｍｍの冷延鋼板を得た。なお、一部は冷間圧延を実施せず、黒皮スケール除去後の熱延鋼板（厚さ２．０ｍｍ）ままのものも準備した。
Hereinafter, the present invention will be specifically described based on examples.
The hot-rolled steel sheet having the steel composition shown in Table 1 was pickled and the black scale removed, and then cold-rolled under the conditions shown in Table 2 to obtain a cold-rolled steel sheet having a thickness of 1.0 mm. In addition, some did not implement cold rolling, but the thing with the hot-rolled steel plate (thickness 2.0mm) after black scale removal was also prepared.
次いで、上記で得た熱延鋼板、冷延鋼板を、連続焼鈍設備に装入した。焼鈍設備では、表２に示す通り、焼鈍炉内の鋼板温度が４５０℃以上Ａ℃以下（Ａ：５００≦Ａ≦６００）の温度域における昇温速度、焼鈍炉内の鋼板温度が６００℃〜７００℃の温度域における水素濃度および鋼板通過時間、鋼板最高到達温度を制御して通板し、焼鈍した後、水焼入れを行い、３００℃×１４０ｓ間の焼き戻しを行った。引き続き、４０℃、５質量％の硫酸水溶液中に浸漬して酸洗を行った。一部は表２に示す電流密度条件にて、供試材を陽極、陰極の順に３秒ずつとする交番電解で電解酸洗を行い、供試材を得た。なお、上記水素濃度を制御した領域以外の焼鈍炉内の水素濃度は１０ｖｏｌ％を基本とした。また、雰囲気の気体成分は窒素ガスと水素ガスおよび不可避的不純物気体からなり、露点は雰囲気中の水分を吸収除去して制御した。雰囲気中の露点は−３５℃とした。 Next, the hot-rolled steel sheet and cold-rolled steel sheet obtained above were charged into a continuous annealing facility. In the annealing equipment, as shown in Table 2, the steel plate temperature in the annealing furnace is 450 ° C. or more and A ° C. or less (A: 500 ≦ A ≦ 600), and the steel plate temperature in the annealing furnace is 600 ° C. The steel sheet was passed through by controlling the hydrogen concentration in the temperature range of 700 ° C., the steel plate passage time, and the maximum steel plate temperature, annealed, then water quenched, and tempered between 300 ° C. × 140 s. Then, it pickled by being immersed in sulfuric acid aqueous solution of 40 mass% and 5 mass%. A part of the sample was subjected to electrolytic pickling by alternating electrolysis in which the test material was in the order of 3 seconds each in the order of anode and cathode under the current density conditions shown in Table 2 to obtain the test material. The hydrogen concentration in the annealing furnace other than the region where the hydrogen concentration was controlled was basically 10 vol%. The atmospheric gas components were nitrogen gas, hydrogen gas, and inevitable impurity gas, and the dew point was controlled by absorbing and removing moisture in the atmosphere. The dew point in the atmosphere was −35 ° C.
以上により得られた供試材に対して、ＴＳ、Ｅｌを測定した。また、化成処理性および電着塗装後の耐食性を調査した。また、鋼板表層直下の１００μｍまで鋼板表層部に存在する酸化物の量（内部酸化量）を測定した。測定方法および評価基準を下記に示す。 TS and El were measured with respect to the specimens obtained as described above. In addition, chemical conversion properties and corrosion resistance after electrodeposition coating were investigated. In addition, the amount of oxide (internal oxidation amount) present in the steel sheet surface layer up to 100 μm immediately below the steel sheet surface layer was measured. The measurement method and evaluation criteria are shown below.
化成処理性
化成処理液は日本パーカライジング（株）製の化成処理液（パルボンドＬ３０８０（登録商標））を用い、下記方法で化成処理を施した。日本パーカライジング（株）製の脱脂液ファインクリーナー（登録商標）で脱脂したのち、水洗し、次に日本パーカライジング（株）製の表面調整液プレパレンＺ（登録商標）で３０ｓ表面調整を行い、４３℃の化成処理液（パルボンドＬ３０８０）に１２０ｓ浸漬した後、水洗し、温風乾燥した。化成処理後の供試材を走査型電子顕微鏡（ＳＥＭ）で倍率５００倍で無作為に５視野を観察し、化成処理皮膜のスケ面積率を画像処理により測定し、スケ面積率によって以下の評価を行った。○が合格レベルである。
○：１０％以下
×：１０％超
電着塗装後の耐食性
上記の方法で得られた化成処理を施した供試材より寸法７０ｍｍ×１５０ｍｍの試験片を切り出し、日本ペイント（株）製のＰＮ−１５０Ｇ（登録商標）でカチオン電着塗装（焼付け条件：１７０℃×２０分、膜厚２５μｍ）を行った。その後、端部と評価しない側の面をＡｌテープでシールし、カッターナイフにて地鉄に達するクロスカット（クロス角度６０°）を入れ、供試材とした。次に、供試材を５％ＮａＣｌ水溶液（５５℃）中に、２４０時間浸漬後に取り出し、水洗、乾燥後にクロスカット部をテープ剥離し、剥離幅を測定し、以下の評価を行った。○が合格レベルである
○：剥離幅が片側２．５ｍｍ未満
×：剥離幅が片側２．５ｍｍ以上
加工性
加工性は、試料から圧延方向に対して90°方向にJIS５号引張試験片を採取し、JIS Z 2241の規定に準拠してクロスヘッド速度10ｍｍ／ｍｉｎ一定で引張試験を行い、引張り強度（ＴＳ／ＭＰａ）と伸び（Ｅｌ／％）を測定し、ＴＳ×Ｅｌ≧１８０００のものを良好、ＴＳ×Ｅｌ＜１８０００のものを不良とした。
Chemical conversion treatment The chemical conversion treatment liquid (Palbond L3080 (registered trademark)) manufactured by Nippon Parkerizing Co., Ltd. was used as the chemical conversion treatment liquid, and the chemical conversion treatment was performed by the following method. After degreasing with a degreasing liquid Fine Cleaner (registered trademark) manufactured by Nihon Parkerizing Co., Ltd., washing with water, and then adjusting the surface for 30 s with surface conditioning solution preparen Z (registered trademark) manufactured by Nihon Parkerizing Co., Ltd. After being immersed in a chemical conversion treatment solution (Palbond L3080) for 120 s, it was washed with water and dried with warm air. The sample after the chemical conversion treatment was randomly observed with a scanning electron microscope (SEM) at a magnification of 500 times, the scale area ratio of the chemical conversion film was measured by image processing, and the following evaluation was made based on the scale area ratio. Went. ○ is an acceptable level.
○: 10% or less ×: More than 10% Corrosion resistance after electrodeposition coating A test piece having a size of 70 mm × 150 mm was cut out from the test material subjected to chemical conversion treatment obtained by the above method, and PN made by Nippon Paint Co., Ltd. Cationic electrodeposition coating (baking conditions: 170 ° C. × 20 minutes, film thickness 25 μm) was performed with −150 G (registered trademark). Thereafter, the end surface and the side not evaluated were sealed with Al tape, and a cross cut (cross angle 60 °) reaching the ground iron with a cutter knife was used as a test material. Next, the specimen was taken out after being immersed in a 5% NaCl aqueous solution (55 ° C.) for 240 hours, washed with water and dried, and then the tape was peeled off, the peel width was measured, and the following evaluation was performed. ○ is acceptable level ○: Peeling width is less than 2.5 mm on one side ×: Peeling width is 2.5 mm or more on one side Workability is obtained by taking a JIS No. 5 tensile test piece from the sample in a 90 ° direction with respect to the rolling direction. In accordance with the provisions of JIS Z 2241, a tensile test is performed at a constant crosshead speed of 10 mm / min, tensile strength (TS / MPa) and elongation (El /%) are measured, and TS × El ≧ 18000 Good and TS × El <18000 were judged as bad.
鋼板表層１００μmまでの領域における内部酸化量
内部酸化量は、「インパルス炉溶融−赤外線吸収法」により測定する。ただし、素材（すなわち焼鈍を施す前の高強度鋼板）に含まれる酸素量を差し引く必要があるので、本発明では、連続焼鈍後の高強度鋼板の両面の表層部を１００μｍ以上研磨して鋼中酸素濃度を測定し、その測定値を素材に含まれる酸素量ＯＨとし、また、連続焼鈍後の高強度鋼板の板厚方向全体での鋼中酸素濃度を測定して、その測定値を内部酸化後の酸素量ＯＩとした。このようにして得られた高強度鋼板の内部酸化後の酸素量ＯＩと、素材に含まれる酸素量ＯＨとを用いて、ＯＩとＯＨの差（＝ＯＩ−ＯＨ）を算出し、さらに片面単位面積（すなわち１m２）当たりの量に換算した値（ｇ／ｍ２）を内部酸化量とした。
The amount of internal oxidation in the region of the steel sheet surface layer of up to 100 μm is measured by the “impulse furnace melting-infrared absorption method”. However, since it is necessary to subtract the amount of oxygen contained in the material (that is, the high-strength steel plate before annealing), in the present invention, the surface layer portions on both surfaces of the high-strength steel plate after continuous annealing are polished by 100 μm or more in the steel. Measure the oxygen concentration, set the measured value as the amount of oxygen OH contained in the material, measure the oxygen concentration in the steel in the entire thickness direction of the high-strength steel sheet after continuous annealing, and measure the measured value internally. The subsequent oxygen amount OI was used. The difference between OI and OH (= OI-OH) is calculated using the oxygen amount OI after internal oxidation of the high-strength steel plate thus obtained and the oxygen amount OH contained in the material, and further, single-sided unit area (i.e. 1 m 2) value converted into the amount per (g / m 2) as an internal oxide amount.
以上により得られた結果を製造条件と併せて表２に示す。 The results obtained as described above are shown in Table 2 together with the production conditions.
表２から明らかなように、本発明法で製造された高強度鋼板は、Ｓｉ、Ｍｎ等の易酸化性元素を多量に含有する高強度鋼板であるにもかかわらず、化成処理性、電着塗装後の耐食性、加工性に優れることがわかる。一方、比較例では、化成処理性、電着塗装後の耐食性、加工性のいずれか一つ以上が劣る。 As is apparent from Table 2, the high-strength steel sheet produced by the method of the present invention is a high-strength steel sheet containing a large amount of easily oxidizable elements such as Si and Mn, but the chemical conversion treatment property, electrodeposition It can be seen that it has excellent corrosion resistance and workability after painting. On the other hand, in the comparative example, any one or more of chemical conversion property, corrosion resistance after electrodeposition coating, and workability is inferior.
本発明の高強度鋼板は、化成処理性、耐食性、加工性に優れ、自動車の車体そのものを軽量化かつ高強度化するための表面処理鋼板として利用することができる。また、自動車以外にも、素材鋼板に防錆性を付与した表面処理鋼板として、家電、建材の分野等、広範な分野で適用できる。 The high-strength steel sheet of the present invention is excellent in chemical conversion property, corrosion resistance, and workability, and can be used as a surface-treated steel sheet for reducing the weight and strength of the automobile body itself. In addition to automobiles, the steel sheet can be applied in a wide range of fields such as home appliances and building materials as a surface-treated steel sheet provided with rust prevention properties.
Claims (3)
加熱工程では、焼鈍炉内温度：４５０℃以上Ａ℃以下（Ａ：５００≦Ａ≦６００）の温度域を昇温速度：７℃/s以上で昇温し、
焼鈍炉内での鋼板最高到達温度は６００℃以上７００℃以下であり、
鋼板温度が６００℃以上７００℃以下の温度域における鋼板通過時間は３０秒以上１０分以内、雰囲気中の水素濃度は２０ｖｏｌ％以上
とすることを特徴とする、優れた化成処理性および電着塗装後の耐食性を有する高強度鋼板の製造方法。 It is a manufacturing method of the high strength steel plate which performs a chemical conversion treatment after annealing , Comprising: In mass%, C: 0.03-0.35%, Si: 0.01-0.50%, Mn: 3.6-8. 0%, Al: 0.01% to 1.0%, P ≦ 0.10%, S ≦ 0.010%, and when the steel sheet consisting of Fe and inevitable impurities is continuously annealed,
In the heating step, the temperature inside the annealing furnace: 450 ° C. or more and A ° C. or less (A: 500 ≦ A ≦ 600) is raised at a rate of temperature rise: 7 ° C./s or more,
The maximum steel plate temperature in the annealing furnace is 600 ° C or higher and 700 ° C or lower,
Excellent chemical conversion treatment and electrodeposition coating, characterized in that the steel plate passage time in the temperature range of 600 ° C. to 700 ° C. is 30 seconds to 10 minutes and the hydrogen concentration in the atmosphere is 20 vol% or more. A method for producing a high-strength steel sheet having later corrosion resistance .
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| CN201580008846.2A CN106029919A (en) | 2014-02-18 | 2015-02-03 | High-strength steel plate and method for producing high-strength steel plate |
| PCT/JP2015/000460 WO2015125422A1 (en) | 2014-02-18 | 2015-02-03 | High-strength steel plate and method for producing high-strength steel plate |
| US15/119,778 US20170067131A1 (en) | 2014-02-18 | 2015-02-03 | High-strength steel sheet and method of manufacturing high-strength steel sheet |
| EP15751393.8A EP3109330B1 (en) | 2014-02-18 | 2015-02-03 | Method for producing high-strength steel plate |
| MX2016010669A MX2016010669A (en) | 2014-02-18 | 2015-02-03 | High-strength steel plate and method for producing high-strength steel plate. |
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| KR102031452B1 (en) * | 2017-12-24 | 2019-10-11 | 주식회사 포스코 | Cold rolled steel sheet and hot dip zinc-based plated steel sheet having excellent bake hardenability and plating adhesion, and method for manufaturing the same |
| CN108555021B (en) * | 2018-05-17 | 2019-08-27 | 山东钢铁股份有限公司 | A kind of pair of narrow steel strip carries out the method and apparatus of special cross section size reprocessing |
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| JPH05320952A (en) | 1992-05-25 | 1993-12-07 | Nkk Corp | High strength cold rolled steel sheet excellent in corrosion resistance after coating |
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