JP4119804B2 - High-strength galvannealed steel sheet with excellent adhesion and method for producing the same - Google Patents
High-strength galvannealed steel sheet with excellent adhesion and method for producing the same Download PDFInfo
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- JP4119804B2 JP4119804B2 JP2003207880A JP2003207880A JP4119804B2 JP 4119804 B2 JP4119804 B2 JP 4119804B2 JP 2003207880 A JP2003207880 A JP 2003207880A JP 2003207880 A JP2003207880 A JP 2003207880A JP 4119804 B2 JP4119804 B2 JP 4119804B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 121
- 239000010959 steel Substances 0.000 title claims description 121
- 238000004519 manufacturing process Methods 0.000 title claims description 34
- 238000007747 plating Methods 0.000 claims description 91
- 238000005275 alloying Methods 0.000 claims description 41
- 238000001816 cooling Methods 0.000 claims description 37
- 229910001566 austenite Inorganic materials 0.000 claims description 32
- 238000005246 galvanizing Methods 0.000 claims description 30
- 238000000137 annealing Methods 0.000 claims description 25
- 229910001335 Galvanized steel Inorganic materials 0.000 claims description 18
- 239000008397 galvanized steel Substances 0.000 claims description 18
- 230000003647 oxidation Effects 0.000 claims description 18
- 238000007254 oxidation reaction Methods 0.000 claims description 18
- 229910052748 manganese Inorganic materials 0.000 claims description 14
- 229910052710 silicon Inorganic materials 0.000 claims description 14
- 238000002441 X-ray diffraction Methods 0.000 claims description 13
- 230000009467 reduction Effects 0.000 claims description 13
- 229910052799 carbon Inorganic materials 0.000 claims description 11
- 238000005097 cold rolling Methods 0.000 claims description 9
- 239000012535 impurity Substances 0.000 claims description 9
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 9
- 229910000859 α-Fe Inorganic materials 0.000 claims description 9
- 229910052802 copper Inorganic materials 0.000 claims description 8
- 238000002485 combustion reaction Methods 0.000 claims description 7
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 6
- 229910052739 hydrogen Inorganic materials 0.000 claims description 6
- 239000001257 hydrogen Substances 0.000 claims description 6
- 230000036961 partial effect Effects 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 5
- 229910052725 zinc Inorganic materials 0.000 claims description 5
- 229910045601 alloy Inorganic materials 0.000 claims description 4
- 239000000956 alloy Substances 0.000 claims description 4
- 239000010960 cold rolled steel Substances 0.000 claims description 4
- 238000007598 dipping method Methods 0.000 claims description 3
- 239000000126 substance Substances 0.000 claims description 3
- 229910000905 alloy phase Inorganic materials 0.000 claims description 2
- 229910004298 SiO 2 Inorganic materials 0.000 claims 1
- 239000010410 layer Substances 0.000 description 32
- 238000000034 method Methods 0.000 description 22
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 description 18
- 230000000694 effects Effects 0.000 description 14
- 238000010438 heat treatment Methods 0.000 description 12
- 229910000734 martensite Inorganic materials 0.000 description 12
- 229910052681 coesite Inorganic materials 0.000 description 11
- 229910052906 cristobalite Inorganic materials 0.000 description 11
- 229910001562 pearlite Inorganic materials 0.000 description 11
- 239000000377 silicon dioxide Substances 0.000 description 11
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 11
- 229910052682 stishovite Inorganic materials 0.000 description 11
- 229910052905 tridymite Inorganic materials 0.000 description 11
- 230000000717 retained effect Effects 0.000 description 9
- 230000008569 process Effects 0.000 description 7
- 238000007586 pull-out test Methods 0.000 description 7
- 230000009466 transformation Effects 0.000 description 7
- 238000000227 grinding Methods 0.000 description 6
- 230000000670 limiting effect Effects 0.000 description 6
- 239000011701 zinc Substances 0.000 description 6
- 229910001563 bainite Inorganic materials 0.000 description 5
- 239000011324 bead Substances 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 5
- 230000007797 corrosion Effects 0.000 description 5
- 238000005260 corrosion Methods 0.000 description 5
- 239000007789 gas Substances 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 229910052698 phosphorus Inorganic materials 0.000 description 5
- 238000005096 rolling process Methods 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- 239000002390 adhesive tape Substances 0.000 description 4
- 230000007423 decrease Effects 0.000 description 4
- 238000005098 hot rolling Methods 0.000 description 4
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 229910052759 nickel Inorganic materials 0.000 description 4
- 230000001590 oxidative effect Effects 0.000 description 4
- 238000003825 pressing Methods 0.000 description 4
- 238000012545 processing Methods 0.000 description 4
- 238000003303 reheating Methods 0.000 description 4
- 238000012360 testing method Methods 0.000 description 4
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 3
- 229910001567 cementite Inorganic materials 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 229910052760 oxygen Inorganic materials 0.000 description 3
- 239000001301 oxygen Substances 0.000 description 3
- 238000005554 pickling Methods 0.000 description 3
- 230000002829 reductive effect Effects 0.000 description 3
- 229920006395 saturated elastomer Polymers 0.000 description 3
- 239000002344 surface layer Substances 0.000 description 3
- 229910018137 Al-Zn Inorganic materials 0.000 description 2
- 229910018573 Al—Zn Inorganic materials 0.000 description 2
- 229920000298 Cellophane Polymers 0.000 description 2
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 2
- 229910052787 antimony Inorganic materials 0.000 description 2
- 230000004888 barrier function Effects 0.000 description 2
- 229910052797 bismuth Inorganic materials 0.000 description 2
- 239000004566 building material Substances 0.000 description 2
- 229910052791 calcium Inorganic materials 0.000 description 2
- 239000012141 concentrate Substances 0.000 description 2
- 238000005520 cutting process Methods 0.000 description 2
- 230000003111 delayed effect Effects 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 230000001771 impaired effect Effects 0.000 description 2
- 239000003112 inhibitor Substances 0.000 description 2
- 229910052745 lead Inorganic materials 0.000 description 2
- 229910052749 magnesium Inorganic materials 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 2
- 229910052814 silicon oxide Inorganic materials 0.000 description 2
- 230000001629 suppression Effects 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- 229910052718 tin Inorganic materials 0.000 description 2
- 229910052719 titanium Inorganic materials 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 229910001297 Zn alloy Inorganic materials 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 229910052785 arsenic Inorganic materials 0.000 description 1
- 229910052790 beryllium Inorganic materials 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 238000005238 degreasing Methods 0.000 description 1
- 230000001934 delay Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 229910052735 hafnium Inorganic materials 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 230000006698 induction Effects 0.000 description 1
- 229910052744 lithium Inorganic materials 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000003595 mist Substances 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000005855 radiation Effects 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000005204 segregation Methods 0.000 description 1
- 230000000087 stabilizing effect Effects 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- 229910052721 tungsten Inorganic materials 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Landscapes
- Coating With Molten Metal (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、高強度合金化溶融亜鉛めっき鋼板及びその製造方法に係わり、更に詳しくは優れた密着性を有し、種々の用途、例えば建材用や自動車用鋼板として適用できるめっき鋼板に関するものである。
【０００２】
【従来の技術】
耐食性の良好なめっき鋼板として合金化溶融亜鉛めっき鋼板がある。この合金化溶融亜鉛めっき鋼板は、通常、鋼板を脱脂後、無酸化炉にて予熱し、表面の清浄化および材質確保のために還元炉にて還元焼鈍を行い、溶融亜鉛浴に浸漬し、付着量制御した後合金化を行うことによって製造される。その特徴として、耐食性およびめっき密着性等に優れることから、自動車、建材用途等を中心として広く使用されている。
【０００３】
特に近年、自動車分野においては衝突時に乗員を保護するような機能の確保と共に燃費向上を目的とした軽量化を両立させるために、めっき鋼板の高強度化が必要とされてきている。
【０００４】
加工性を悪化させずに鋼板を高強度化するためには、ＳｉやＭｎ、Ｐといった元素を添加することが有効であるが、これらの元素の添加は合金化を遅延させるため、軟鋼に比べて高温長時間の合金化を必要とする。この高温長時間の合金化は、鋼板中に残存していたオーステナイトをパーライトに変態させ、加工性を低下させるため、結果として添加元素の効果を相殺することになる。
【０００５】
こうした合金化溶融亜鉛めっき鋼板の加工性を向上させることを目的として本発明者らは、加工性の優れた高強度合金化溶融亜鉛めっき鋼板及びその製造方法を先に提案した（特許文献１参照）。
【０００６】
また、こうした鋼板の製造方法として、高強度と高延性を兼ね備え、めっき密着性と合金化処理性にも優れた溶融亜鉛めっき鋼板及び合金化溶融亜鉛めっき鋼板の製造方法（例えば、特許文献２参照）や、プレス成形性およびめっき密着性に優れる高強度合金化溶融亜鉛めっき鋼板の製造方法（例えば、特許文献３参照）等が提案されている。
が示されている。
【０００７】
【特許文献１】
特開２００３−１０５５１６号公報
【特許文献２】
特開平１１−１３１１４５号公報
【特許文献３】
特開２００１−１４００２２号公報
【０００８】
【発明が解決しようとする課題】
しかし、前記特許文献１に開示される技術では、密着性が十分確保されていない。また、特許文献２や特許文献３に示される製造方法では、製造条件の範囲が極めて広く記述されているが、めっきの合金化と鋼板の加工性向上を両立させる製造条件が記載されておらず、実際の生産における有用性に乏しい。
【０００９】
そこで、本発明は上記問題点を解決し、密着性の優れた高強度合金化溶融亜鉛めっき鋼板と、その製造方法を提案するものである。
【００１０】
【課題を解決するための手段】
本発明者らは、高強度鋼板のめっき処理について鋭意研究を重ねた結果、Ｃ、Ｓｉ、Ｍｎが一定量以上添加された鋼を、熱処理条件及びめっき条件を最適化した連続溶融亜鉛めっき設備でめっき処理することにより、密着性の優れた高強度合金化溶融亜鉛めっき鋼板を製造できることを見いだして本発明をなした。
すなわち、本発明の要旨とするところは、以下の通りである。
【００１１】
（１） 質量％で、
Ｃ：０．０５〜０．１５％、
Ｓｉ：０．３〜２．５％、
Ｍｎ：１．５〜２．８％、
Ｐ：０．０３％以下、
Ｓ：０．０２％以下、
Ａｌ：０．００５〜０．５％、
Ｎ：０．００６０％以下を含有し、
残部Ｆｅおよび不可避的不純物からなり、さらに％Ｃ、％Ｓｉ、％ＭｎをそれぞれＣ、Ｓｉ、Ｍｎ含有量とした時に（％Ｍｎ）／（％Ｃ）≧１２かつ（％Ｓｉ）／（％Ｃ）≧４が満たされる高強度鋼板の上に、Ｆｅを含有し、残部がＺｎおよび不可避的不純物からなる合金化溶融亜鉛めっき層を有する鋼板において、このめっきの合金相のη相、ζ相、δ 1 相、Γ相のｄ＝１．２３７、ｄ＝１．２６、ｄ＝１．２７９、ｄ＝１．２２２のＸ線回折強度Ｉδ1、Ｉζ、Ｉη、ＩΓとＳｉ標準板のｄ＝３．１３のＸ線回折強度ＩＳｉとの比Ｉδ1／ＩＳｉ、Ｉζ／ＩＳｉ、Ｉη／ＩＳｉ、ＩΓ／ＩＳｉが、Ｉη／ＩＳｉ≦０．０００６、ＩΓ／ＩＳｉ≦０．０００６であり、Ｉδ１／ＩＳｉとＩζ／ＩＳｉの１種または２種が０．０００６以上であることを特徴とする密着性の優れた高強度合金化溶融亜鉛めっき鋼板。
【００１２】
（２） 高強度鋼板とめっき層との界面から鋼板側にＳｉＯ2の内部酸化物の平均含有率が０．８〜５．０質量％である鋼層を０．１μｍ以上、１０μｍ以下形成することを特徴とする前記（１）に記載の密着性の優れた高強度合金化溶融亜鉛めっき鋼板。
【００１３】
（３） 質量％で、Ｎｉ：０．０１〜５．０％、Ｃｕ：０．０１〜５．０％の１種または２種を含有する高強度鋼板であることを特徴とする前記（１）または（２）に記載の密着性の優れた高強度合金化溶融亜鉛めっき鋼板。
【００１４】
（４） 引張強さＦ（ＭＰａ）と伸びＬ（％）の関係が
Ｌ≧５１−０．０３５×Ｆ
を満足することを特徴とする前記（１）乃至（３）のいずれかに記載の密着性の優れた高強度合金化溶融亜鉛めっき鋼板。
【００１５】
（５） 前記（１）乃至（４）のいずれかに記載の化学成分からなる組成のスラブをＡｒ3点以上の温度で仕上圧延を行い、５０〜８５％の冷間圧延を施した後、連続溶融亜鉛めっき設備で７５０℃以上８８０℃以下のフェライト、オーステナイトの二相共存温度域で焼鈍し、その最高到達温度から６５０℃までを平均冷却速度０．５〜１０℃／秒で、引き続いて６５０℃から５００℃までを平均冷却速度３℃／秒以上で冷却し、さらに５００℃から平均冷却速度０．５℃／秒以上で４２０℃〜４６０℃まで冷却し、且つ、５００℃からめっき浴までを２５秒以上２４０秒以下保持した後、溶融亜鉛めっき処理を行うことによって、前記冷延鋼板の表面上に溶融亜鉛めっき層を形成し、次いで、前記溶融亜鉛めっき層が形成された前記鋼板に対し合金化処理を施すことによって、前記鋼板の表面上に合金化溶融亜鉛めっき層を形成する合金化溶融亜鉛めっき鋼板の製造方法において、
まず、前記焼鈍処理を、
酸化帯において燃焼空気比０．９〜１．２の雰囲気中にて酸化せしめ、その後の還元帯において、水分圧と水素分圧の対数ｌｏｇ（ＰＨ ２ Ｏ／ＰＨ ２ ）が下式、
０．５〔Ｓｉ％〕−３≦ｌｏｇ（ＰＨ ２ Ｏ／ＰＨ ２ ）≦−０．８
但し、〔Ｓｉ％〕：鋼板中のＳｉ含有量（ｍａｓｓ％）
を満たす雰囲気で還元を行い、
次に前記溶融亜鉛めっき処理を、浴中有効Ａｌ濃度：０．０７〜０．０９２ｍａｓｓ％、残部がＺｎおよび不可避的不純物からなる成分組成の溶融亜鉛めっき浴中で行い、そして、前記合金化処理を、
４５０≦Ｔ≦４１０×ｅｘｐ（２×〔Ａｌ％〕）
但し、〔Ａｌ％〕：亜鉛めっき浴中の浴中有効Ａｌ濃度（ｍａｓｓ％）
を満足する温度Ｔ（℃）において行うことを特徴とする、密着性の優れた高強度合金化溶融亜鉛めっき鋼板の製造方法。
【００１６】
（６） 前記（５）に記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、浴中有効Ａｌ濃度を、
〔Ａｌ％〕≦０．０９２−０．００１×〔Ｓｉ％〕2
但し、〔Ｓｉ％〕：鋼板中のＳｉ含有量（ｍａｓｓ％）
を満足する浴中有効Ａｌ濃度（ｍａｓｓ％）において行うことを特徴とする、密着性の優れた高強度合金化溶融亜鉛めっき鋼板の製造方法。
【００１７】
（７） 前記（５）または（６）記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、溶融めっき後４００℃以下の温度に冷却されるまでの時間を３０秒以上１２０秒以下とすることを特徴とする、密着性の優れた高強度合金化溶融亜鉛めっき鋼板の製造方法。
【００１８】
（８） 前記（５）及至（７）のいずれかに記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、溶融亜鉛めっき浴の温度を４７０℃未満とすることを特徴とする、密着性の優れた高強度合金化溶融亜鉛めっき鋼板の製造方法。
【００１９】
（９） 前記（５）及至（８）のいずれかに記載の高強度合金化溶融亜鉛めっき鋼板の製造方法において、焼鈍後４００℃以上４５０℃以下まで冷却した後、４３０℃以上４７０℃以下まで再加熱を行い、溶融亜鉛めっき処理を行うことを特徴とする密着性の優れた高強度合金化溶融亜鉛めっき鋼板の製造方法。
【００２１】
【発明の実施の形態】
以下に本発明を詳細に説明する。
【００２２】
まず、Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ａｌ、Ｎの数値限定理由について述べる。Ｃはマルテンサイトや残留オーステナイトによる組織強化で鋼板を高強度化しようとする場合に必須の元素である。Ｃの含有量を０．０５％以上とする理由は、Ｃが０．０５％未満ではミストや噴流水を冷却媒体として焼鈍温度から急速冷却することが困難な溶融亜鉛めっきラインにおいてセメンタイトやパーライトが生成しやすく、必要とする引張強さの確保が困難であるためである。一方、Ｃの含有量を０．１５％以下とする理由は、Ｃが０．１５％を超えると、スポット溶接で健全な溶接部を形成することが困難となると同時にＣの偏析が顕著となり加工性が劣化するためである。
【００２３】
Ｓｉは鋼板の加工性、特に伸びを大きく損なうことなく強度を増す元素として０．３〜２．５％添加しかつＣ含有量の４倍以上の質量％とする。Ｓｉの含有量を０．３％以上とする理由は、Ｓｉが０．３％未満では必要とする引張強さの確保が困難であるためであり、Ｓｉの含有量を２．５％以下とする理由は、Ｓｉが２．５％を超えると強度を増す効果が飽和すると共に延性の低下が起こるためである。またＣ含有量の４倍以上の質量％とすることで、めっき直後に行う合金化処理のための再加熱でパーライトおよびベイナイト変態の進行を著しく遅滞させ、室温まで冷却後にも体積率で３〜２０％のマルテンサイトおよび残留オーステナイトがフェライト中に混在する金属組織とすることができる。
【００２４】
ＭｎはＣとともにオーステナイトの自由エネルギーを下げるため、めっき浴に鋼帯を浸漬するまでの間にオーステナイトを安定化する目的で１．５％以上添加する。またＣ含有量の１２倍以上の質量％を添加することにより、めっき直後に行う合金化処理のための再加熱でパーライトおよびベイナイト変態の進行を著しく遅滞させ、室温まで冷却後にも体積率で３〜２０％のマルテンサイトおよび残留オーステナイトがフェライト中に混在する金属組織とできる。しかし添加量が過大になるとスラブに割れが生じやすく、またスポット溶接性も劣化するため、２．８％を上限とする。
【００２５】
Ｐは一般に不可避的不純物として鋼に含まれるが、その量が０．０３％を超えるとスポット溶接性の劣化が著しいうえ、本発明におけるような引張強さが４９０ＭＰａを超すような高強度鋼板では靭性とともに冷間圧延性も著しく劣化するため、その含有量は０．０３％以下とする。Ｓも一般に不可避的不純物として鋼に含まれるが、その量が０．０２％を超えると、圧延方向に伸張したＭｎＳの存在が顕著となり、鋼板の曲げ性に悪影響をおよぼすため、その含有量は０．０２％以下とする。
【００２６】
Ａｌは鋼の脱酸元素として、またＡｌＮによる熱延素材の細粒化、および一連の熱処理工程における結晶粒の粗大化を抑制し材質を改善するために０．００５％以上添加する必要がある。ただし、０．５％を超えるとコスト高となるばかりか、表面性状を劣化させるため、その含有量は０．５％以下とする。Ｎもまた一般に不可避的不純物として鋼に含まれるが、その量が０．０６％を超えると、伸びとともに脆性も劣化するため、その含有量は０．００６％以下とする。
【００２７】
また、鋼板を高強度化するために、ＳｉやＭｎ、Ｐといった元素を添加するとめっき濡れ性が低下することがあるため、めっき濡れ性を向上させるためにＮｉ、Ｃｕを添加すると有効である。
【００２８】
Ｎｉを添加することによってめっき濡れ性が向上する理由は明確ではないが、連続溶融亜鉛めっき設備で焼鈍を行う際、表面に濃化し、ＳｉやＭｎ、Ｐといっためっき濡れ性を低下させる元素の表面濃化を抑制する効果があると考えられる。この効果は０．０１％以上添加すると明確になる。ただし、添加量が５．０％を超えると加工性の劣化を招くと共にコストアップの原因にもなるので、５．０％を上限とした。
【００２９】
Ｃｕはめっき濡れ性を向上させると共にめっき密着性を向上させる上で有効な元素である。Ｃｕを添加することによってめっき濡れ性、密着性が向上する理由もまた明確ではないが、連続溶融亜鉛めっき設備で焼鈍を行う際、表面に濃化し、ＳｉやＭｎ、Ｐといっためっき濡れ性を低下させる元素の表面濃化を抑制するNiの効果を補助する効果があると考えられる。この効果は０．０１％以上添加すると明確になる。ただし、添加量が５．０％を超えると加工性の劣化を招くと共にコストアップの原因にもなるので、５．０％を上限とした。
【００３０】
ＮｉとＣｕは同時に添加することで相乗効果を発揮し、より少量の添加でめっき濡れ性を向上させることができる。従って、同時に添加する場合、Ｎｉ添加量は０．０１％以上１．０％未満、Ｃｕ添加量は０．０１％以上０．５％未満が好ましい。
【００３１】
また、これらを主成分とする鋼にＮｂ、Ｔｉ、Ｂ、Ｍｏ、Ｃｕ、Ｓｎ、Ｚｎ、Ｚｒ、Ｗ、Ｃｏ、Ｃａ、希土類元素（Ｙを含む）、Ｖ、Ｔａ、Ｈｆ、Ｐｂ、Ｍｇ、Ａｓ、Ｓｂ、Ｂｉを合計で１％以下含有しても本発明の効果を損なわず、その量によっては耐食性や加工性が改善される等好ましい場合もある。
【００３２】
次に、合金化溶融亜鉛めっき層について述べる。本発明において、合金化溶融亜鉛めっき層とは、合金化反応によってＺｎめっき中に鋼中のＦｅが拡散しできたＦｅ−Ｚｎ合金を主体としためっき層のことである。このめっき層はＦｅの含有率の違いにより、η相、ζ相、δ1相、Γ相と呼ばれる合金層が形成される。この内、η相はめっきが軟らかくプレス時に金型と凝着してフレーキングと呼ばれるめっき剥離を起こしやすい。また、Γ相は硬くて脆いため、加工時にパウダリングと呼ばれるめっき剥離を起こしやすい。従って、η相、Γ相を限りなく少なくし、めっき層をζ相とδ1相のいずれか１種または２種以上とすることによりめっき密着性を向上させることができる。ここで、めっき層中にはΓ1相と呼ばれる硬くて脆い相も存在することが知られているが、Ｘ線回折強度からはΓ相とΓ1相を区別することができないため、Γ相とΓ1相を合わせてΓ相として取り扱う。
【００３３】
具体的には、η相、ζ相、δ1相、Γ相を示すｄ＝１．２７９、ｄ＝１．２６、ｄ＝１．２３７、ｄ＝１．２２２のＸ線回折強度Ｉδ1、Ｉζ、Ｉη、ＩΓとＳｉ標準板のｄ＝３．１３のＸ線回折強度ＩＳｉとの比Ｉδ1／ＩＳｉ、Ｉζ／ＩＳｉ、Ｉη／ＩＳｉ、ＩΓ／ＩＳｉを、Ｉη／ＩＳｉ≦０．０００６、ＩΓ／ＩＳｉ≦０．０００６とし、Ｉδ1／ＩＳｉとＩζ／ＩＳｉのいずれかの１種または２種が０．０００６以上とする。
【００３４】
Ｉη／ＩＳｉを０．０００６以下に限定した理由は、Ｉη／ＩＳｉが０．０００６以下ではη相は極微量であり、めっき密着性の低下が見られないためである。
【００３５】
また、ＩΓ／ＩＳｉを０．０００６以下に限定した理由は、ＩΓ／ＩＳｉが０．０００６以下ではΓ相は極微量であり、めっき密着性の低下が見られないためである。
【００３６】
Ｉδ1／ＩＳｉとＩζ／ＩＳｉのいずれかの１種または２種が０．０００６以上に限定した理由は、Ｉδ1／ＩＳｉとＩζ／ＩＳｉのいずれかの１種または２種が０．０００６以上では、めっき層がδ1相とζ相のいずれかの１種または２種が主体となり、めっき密着性の低下が見られないためである。
【００３７】
本発明鋼板は、溶融亜鉛めっき浴中あるいは亜鉛めっき中にＰｂ、Ｓｂ、Ｓｉ、Ｓｎ、Ｍｇ、Ｍｎ、Ｎｉ、Ｃｒ、Ｃｏ、Ｃａ、Ｃｕ、Ｌｉ、Ｔｉ、Ｂｅ、Ｂｉ、希土類元素の１種または２種以上を含有、あるいは混入してあっても本発明の効果を損なわず、その量によっては耐食性や加工性が改善される等好ましい場合もある。合金化溶融亜鉛めっきの付着量については特に制約は設けないが、耐食性の観点から２０ｇ／ｍ2以上、経済性の観点から１５０ｇ／ｍ2以下で有ることが望ましい。
【００３８】
本発明において加工性の優れた高強度合金化溶融亜鉛めっき鋼板とは、引張強さＴＳが４９０ＭＰａ以上で、引張強さＦ（ＭＰａ）と伸びＬ（％）の関係が、Ｌ≧５１−０．０３５×Ｆ
を満足する性能を持つ鋼板である。
【００３９】
伸びＬを［５１−０．０３５×Ｆ］％以上と限定した理由は、Ｌが［５１−０．０３５×Ｆ］より低い場合、深絞り等の厳しい加工のときに破断する等加工性が不十分であるためである。
【００４０】
本発明において、高強度鋼板とめっき層との界面から鋼板側にＳｉＯ2の内部酸化物の平均含有率が０．８〜５．０質量％である鋼層を０．１μｍ以上、１０μｍ以下形成するとさらに密着性が向上する。高強度鋼板とめっき層との界面から鋼板側にＳｉＯ2の内部酸化物が存在すると密着性が向上する理由は、焼鈍過程で鋼板内にＳｉの内部酸化物が生成することによって、鋼板表面にＳｉの外部酸化膜が生成することを抑制するためであると考えられる。
【００４１】
Ｓｉの内部酸化物は、粒状や線状になって鋼板中に存在し、顕微鏡観察において明瞭に区別できる。本発明において、ＳｉＯ2の内部酸化物を含有する鋼層とは、顕微鏡観察においてＳｉＯ2の内部酸化物が観察される層である。また、ＳｉＯ2の内部酸化物の平均含有率とは、この鋼層中に含まれるＳｉＯ2の含有率を示し、ＳｉＯ2の内部酸化物を含有する鋼層の厚みとは、鋼板表面からＳｉＯ2の内部酸化物が観察される部分までの幅を示す。
【００４２】
ＳｉＯ2の内部酸化物の含有率の測定は、ＳｉＯ2の質量％が測定できればどの様な方法でも構わないが、ＳｉＯ2の内部酸化物を含有する層を酸で溶解し、ＳｉＯ2を分離させた後、質量を測定する方法が確実である。また、ＳｉＯ2の内部酸化物を含有する鋼層の厚みの測定方法も特に規定しないが、断面から顕微鏡観察で測定する方法が確実である。
【００４３】
本発明において、ＳｉＯ2の内部酸化物の平均含有率を０．８〜５．０質量％に限定した理由は、０．８質量％未満では外部酸化膜の抑制が不十分でめっき密着性を向上させる効果がみられないためであり、５．０質量％を超えるとめっき密着性を向上させる効果が飽和するためである。
【００４４】
また、ＳｉＯ2の内部酸化物を含有する鋼層の厚みを０．１〜１０μｍに限定した理由は、０．１μｍ未満では外部酸化膜の抑制が不十分でめっき密着性を向上させる効果がみられないためであり、１０μｍを超えるとめっき密着性を向上させる効果が飽和するためである。
【００４５】
次に、製造条件の限定理由について述べる。その目的はマルテンサイトおよび残留オーステナイトを３〜２０％含む金属組織とし、高強度とプレス加工性が良いことが両立させることにある。マルテンサイトおよび残留オーステナイトの体積率が３％未満の場合には高強度とならない。一方、マルテンサイトおよび残留オーステナイトの体積率が２０％を超えると、高強度ではあるものの鋼板の加工性が劣化し、本発明の目的が達成されない。
【００４６】
熱間圧延に供するスラブは特に限定するものではなく、連続鋳造スラブや薄スラブキャスター等で製造したものであればよい。また鋳造後直ちに熱間圧延を行う連続鋳造−直送圧延（ＣＣ−ＤＲ）のようなプロセスにも適合する。
【００４７】
熱間圧延の仕上温度は鋼板のプレス成形性を確保するという観点からＡｒ3 点以上とする必要がある。熱延後の冷却条件や巻取温度は特に限定しないが、巻取温度はコイル両端部での材質ばらつきが大ききなることを避け、またスケール厚の増加による酸洗性の劣化を避けるためには７５０℃以下とし、また部分的にベイナイトやマルテンサイトが生成すると冷間圧延時に耳割れを生じやすく、極端な場合には板破断することもあるため５５０℃以上とすることが望ましい。冷間圧延は通常の条件でよく、フェライトが加工硬化しやすいようにマルテンサイトおよび残留オーステナイトを微細に分散させ、加工性の向上を最大限に得る目的からその圧延率は５０％以上とする。一方、８５％を超す圧延率で冷間圧延を行うことは多大の冷延負荷が必要となるため現実的ではない。
【００４８】
ライン内焼鈍方式の連続溶融亜鉛めっき設備で焼鈍する際、その焼鈍温度は７５０℃以上８８０℃以下のフェライト、オーステナイト二相共存域とする。焼鈍温度が７５０℃未満では再結晶が不十分であり、鋼板に必要なプレス加工性を具備できない。８８０℃を超すような温度で焼鈍することは鋼帯表面にＳｉやＭｎの酸化物層の成長が著しく、めっき不良が起こりやすくなるため好ましくない。また引き続きめっき浴へ浸漬し、冷却する過程で、６５０℃までを緩冷却しても十分な体積率のフェライトが成長せず、６５０℃からめっき浴までの冷却途上でオーステナイトがマルテンサイトに変態し、その後合金化処理のための再加熱でマルテンサイトが焼き戻されてセメンタイトが析出するため高強度とプレス加工性の良いことの両立が困難となる。
【００４９】
鋼帯は焼鈍後、引き続きめっき浴へ浸漬する過程で冷却されるが、この場合の冷却速度は、その最高到達温度から６５０℃までを平均０．５〜１０℃／秒で、引き続いて６５０℃から５００℃までを平均冷却速度３℃／秒以上で冷却し、さらに５００℃から平均冷却速度０．５℃／秒以上で４２０℃〜４６０℃まで冷却し、且つ、５００℃からめっき浴までを２５秒以上２４０秒以下保持する。
【００５０】
６５０℃までを平均０．５〜１０℃／秒とするのは加工性を改善するためにフェライトの体積率を増すと同時に、オーステナイトのＣ濃度を増すことにより、その生成自由エネルギーを下げ、マルテンサイト変態の開始する温度をめっき浴温度以下とすることを目的とする。６５０℃までの平均冷却速度を０．５℃／秒未満とするためには連続溶融亜鉛めっき設備のライン長を長くする必要がありコスト高となるため、６５０℃までの平均冷却速度は０．５℃／秒以上とする。
【００５１】
６５０℃までの平均冷却速度を０．５℃／秒未満とするためには、最高到達温度を下げ、オーステナイトの体積率が小さい温度で焼鈍することも考えられるが、その場合には実際の操業で許容すべき温度範囲に比べて適切な温度範囲が狭く、僅かでも焼鈍温度が低いとオーステナイトが形成されず目的を達しない。
【００５２】
一方、６５０℃までの平均冷却速度を１０℃／秒を超えるようにすると、フェライトの体積率の増加が十分でないばかりか、オーステナイト中Ｃ濃度の増加も少ないため、鋼帯がめっき浴に浸漬される前にその一部がマルテンサイト変態し、その後合金化処理のための加熱でマルテンサイトが焼き戻されてセメンタイトとして析出するため高強度と加工性の良いことの両立が困難となる。
【００５３】
６５０℃から５００℃までの平均冷却速度を３℃／秒以上とするのは、その冷却途上でオーステナイトがパーライトに変態するのを避けるためであり、その冷却速度が３℃／秒未満では本発明で規定する温度で焼鈍し、また６５０℃まで冷却したとしてもパーライトの生成を避けられない。平均冷却速度の上限は特に規定しないが、平均冷却速度２０℃／秒を超えるように鋼帯を冷却することはドライな雰囲気では困難である。
【００５４】
５００℃からの平均冷却速度を０．５℃／秒以上とするのは、その冷却途上でオーステナイトがパーライトに変態するのを避けるためであり、その冷却速度が０．５℃／秒未満では本発明で規定する温度で焼鈍し、また５００℃まで冷却したとしてもパーライトの生成を避けられない。平均冷却速度の上限は特に規定しないが、平均冷却速度２０℃／秒を超えるように鋼帯を冷却することはドライな雰囲気では困難である。また、冷却終了温度を４２０〜４６０℃とするのは、オーステナイト中へのＣの濃化が促進され加工性の優れた高強度合金化溶融亜鉛めっきが得られるためである。
【００５５】
５００℃からめっき浴までを２５秒以上２４０秒以下保持する理由は、２５秒未満ではオーステナイト中へのＣの濃化が不十分となり、オーステナイト中のＣ濃度が、室温でのオーステナイトの残留を可能とする水準まで到達しないためであり、２４０秒を超えると、ベイナイト変態が進行し過ぎて、オーステナイト量が少なくなり、十分な量の残留オーステナイトを生成できないためである。
【００５６】
さらにこの５００℃からめっき浴まで保持する間、一度４００〜４５０℃の温度まで冷却し、保持するとオーステナイト中へのＣの濃化が促進され加工性の優れた高強度合金化溶融亜鉛めっきが得られる。ただし、４３０℃以下でめっき浴中へ板を浸漬させ続けるとめっき浴が冷却され凝固するため、４３０〜４７０℃の温度まで再加熱を行った後、溶融亜鉛めっき処理を行う必要がある。
【００５７】
本発明の合金化溶融亜鉛めっき鋼板の製造において、用いる溶融亜鉛めっき浴はＡｌ濃度が浴中有効Ａｌ濃度Ｃで０．０７〜０．０９２ｍａｓｓ％に調整する。ここでめっき浴中の有効Ａｌ濃度とは、浴中Ａｌ濃度から浴中Ｆｅ濃度を差し引いた値である。
【００５８】
有効Ａｌ濃度を０．０７〜０．０９２ｍａｓｓ％に限定する理由は、有効Ａｌ濃度が０．０７％よりも低い場合には、めっき初期の合金化バリアとなるＦｅ−Ａｌ−Ｚｎ相の形成が不十分であってめっき処理時にめっき鋼板界面に脆いΓ相が厚くできるため、加工時のめっき皮膜密着力が劣る合金化溶融亜鉛めっき鋼板しか得られないためである。一方、有効Ａｌ濃度が０．０９２％よりも高い場合には、高温長時間の合金化が必要となり、鋼中に残存していたオーステナイトがパーライトに変態するため、高強度と加工性の良いことの両立が困難となる。
【００５９】
更に、本発明において合金化処理時の合金化温度を
４５０≦Ｔ≦４１０×ｅｘｐ（２×〔Ａｌ％〕）
但し、〔Ａｌ％〕：亜鉛めっき浴中の浴中有効Ａｌ濃度（ｍａｓｓ％ ）
を満足する温度Ｔ（℃）において行う。
【００６０】
合金化温度Ｔを４５０℃以上、４１０×ｅｘｐ（２×〔Ａｌ％〕）℃以下に限定した理由は、合金化温度Ｔが４５０℃よりも低いと合金化が進行しないか、或いは合金化の進行が不十分で合金化未処理となりめっき表層が密着性の劣るη相に覆われるためである。また、Ｔが４１０×ｅｘｐ（２×〔Ａｌ％〕）℃よりも高いと、合金化が進み過ぎてめっき鋼板界面に脆いΓ相が厚くできるため、加工時のめっき密着力が低下するためである。
【００６１】
本発明において合金化温度が高すぎると鋼中に残存していたオーステナイトがパーライトに変態し、目的の高強度と加工性を両立した鋼板を得ることができない。従って、Ｓｉの添加量が大きくなり難合金化するほど、加工性を向上させるためには、浴中有効Ａｌ濃度を低下させ合金化温度を下げることが有効となる。
【００６２】
具体的には、
〔Ａｌ％〕≦０．０９２−０．００１×〔Ｓｉ％〕2
但し、〔Ｓｉ％〕：鋼板中のＳｉ含有量（ｍａｓｓ％）
を満足する浴中有効Ａｌ濃度（ｍａｓｓ％）においてめっきを行う。
有効Ａｌ濃度を０．０９２−０．００１×〔Ｓｉ％〕2％以下に限定する理由は、有効Ａｌ濃度が０．０９２−０．００１×〔Ｓｉ％〕2％より高い場合には、高温長時間の合金化が必要となり、鋼中に残存していたオーステナイトがパーライトに変態し、加工性が劣化するためである。
【００６３】
溶融めっき後４００℃以下の温度に冷却されるまでの時間を３０秒以上１２０秒以下に限定する理由は、３０秒未満では合金化が不十分で合金化未処理となりめっき表層が密着性の劣るη相に覆われるためであり、１２０秒を越えると、ベイナイト変態が進行し過ぎて、オーステナイト量が少なくなり、十分な量の残留オーステナイトを生成できないためである。
【００６４】
本発明において合金化炉加熱方式については特に限定するものではなく、本発明の温度が確保できれば、通常のガス炉による輻射加熱でも、高周波誘導加熱でもかまわない。また、合金化加熱後の最高到達板温度から冷却する方法も、問うものではなく、合金化後、エアーシール等により、熱を遮断すれば、開放放置でも十分であり、より急速に冷却するガスクーリング等でも問題ない。
【００６５】
溶融亜鉛めっき浴の温度を４７０℃未満に限定する理由は、４７０℃以上ではめっき初期の合金化バリアとなるＦｅ−Ａｌ−Ｚｎ相の形成が進み過ぎ合金化温度を上昇させるため、特にＳｉ添加量の高い鋼種で加工性を低下させる原因となり易いためである。浴温の下限は特に限定しないが、亜鉛の融点が４１９．４７℃であることから、物理的にそれ以上の浴温でしか溶融めっきできない。
本発明において、ＳｉＯ2の内部酸化物を含有する鋼層を積極的に生成させるため、連続式溶融めっきラインの焼鈍過程でＳｉを酸化させる方法が有効である。
【００６６】
具体的には、連続式溶融めっきラインにおける酸化帯で鉄酸化膜を数千Å生成させる。鉄酸化膜中はＳｉが拡散し難いため、これによりＳｉの外部酸化が抑制され、鉄酸化膜の下にＳｉＯ2の内部酸化物を含有する鋼層が生成される。但し、鉄酸化膜を形成せしめる時の酸化帯の燃焼空気比はＳｉの外部酸化を抑制するに十分な鉄酸化膜を生成するため０．９以上必要であり、０．９未満の場合は十分な鉄酸化膜を形成せしめることができない。又、燃焼空気比が１．２を超えると酸化帯内で形成される鉄酸化膜厚が厚すぎて、次の還元帯、めっき浴内で還元しきれなくなり、酸化膜層がめっき層の下に残るため、めっき密着性を低下させてしまう。よって、酸化帯の燃焼空気比は０．９〜１．２の範囲に調節する必要がある。
【００６７】
次に、還元帯において、水分圧と水素分圧の対数ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）が下式
０．５ＣSi−３≦ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）≦−０．８
を満たす雰囲気で還元を行う。還元帯では、Ｈ2を１〜７０質量％の範囲で含むＮ2ガスを用いる。また、水分圧と水素分圧（ＰＨ2Ｏ／ＰＨ2）は炉内に水蒸気を導入することにより操作する。ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）を−０．８以下とした理由は、ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）が−０．８を超えると酸化帯で生成した鉄の酸化膜を還元できないためである。また、ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）を０．５ＣSi−３以上とした理由は、ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）が０．５ＣSi−３未満ではＳｉの外部酸化が起こり鋼板表面にＳｉＯ2の外部酸化膜を生成し、めっき密着性を低下させるためである。
【００６８】
即ち、還元帯は鉄の酸化膜を還元し、ＳｉＯ2を内部酸化状態にする雰囲気にする必要がある。ここで、Ｓｉの内部酸化とは鋼板内に拡散した酸素が合金の表層付近でＳｉと反応して酸化物を析出する現象である。内部酸化現象は、酸素の内方への拡散速度がＳｉの外方への拡散速度よりはるかに早い場合、即ち雰囲気中の酸素ポテンシャルが比較的高いかもしくはＳｉの濃度が低い場合に起こる。このときＳｉはほとんど動かずその場で酸化されるため、めっき密着性低下の原因である鋼板表面へのＳｉ濃化を防ぐことができる。
【００６９】
【実施例】
以下、実施例により本発明を具体的に説明する。
【００７０】
（実施例１）
表１に示す組成からなるスラブを１１５０℃に加熱し、仕上温度９１０〜９３０℃で４．５ｍｍの熱間圧延鋼帯とし、５８０〜６８０℃で巻き取った。酸洗後、冷間圧延を施して１．６ｍｍの冷間圧延鋼帯とした後、ライン内焼鈍方式の連続溶融亜鉛めっき設備を用いて表２に示すような条件の熱処理とめっきを行い、合金化溶融亜鉛めっき鋼板を製造した。連続溶融亜鉛めっき設備は、無酸化炉による加熱後、還元帯で還元・焼鈍を行う方式を使用した。酸化帯の燃焼空気比は０．９５に調節し、還元帯は、Ｈ2を１０質量％含むＮ2ガスに水蒸気を導入し水分圧と水素分圧の対数ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）が−１〜−３となるように調節した。
【００７１】
引張強さ（ＴＳ）、伸び（Ｅｌ）は、各鋼板からＪＩＳ５号試験片を切り出し、常温での引張試験を行うことにより求めた。引張強さは４９０ＭＰａ以上を合格とし、伸びは〔５１−０．０３５×引張強さ〕％以上を合格とした。
【００７２】
めっきの付着量は、被膜をインヒビター入りの塩酸で溶解し、質量法により測定した。
【００７３】
Ｘ線回折は、η相、ζ相、δ1相、Γ相を示すｄ＝１．２７９、ｄ＝１．２６、ｄ＝１．２３７、ｄ＝１．２２２のＸ線回折強度Ｉδ1、Ｉζ、Ｉη、ＩΓとＳｉ標準板のｄ＝３．１３のＸ線回折強度ＩＳｉとの比Ｉδ1／ＩＳｉ、Ｉζ／ＩＳｉ、Ｉη／ＩＳｉ、ＩΓ／ＩＳｉを測定した。
【００７４】
密着性は、ビード引き抜き試験を行い、パウダリング性を評価した。試験条件を以下に示す。
・サンプル引き抜き巾：３０ｍｍ
・金型：片側が肩Ｒ１ｍｍＲの角ビード（凸部は４×４ｍｍ）凸型、反対側が肩Ｒ１ｍｍＲの凹型
・押しつけ荷重：１２００ｋｇ
・引き抜き速度：２００ｍｍ／ｍｉｎ
・塗油：防錆油塗布
【００７５】
パウダリング性の評価は、引き抜き試験を行ったサンプルに密着テープ（セロハンテープ）を貼って、はがし、密着テープに付着しためっきの剥離の程度を目視で観察した。めっき層がまったく剥離しないものを合格、めっきが相当程度剥離したものを不合格とした。
【００７６】
評価結果は表２に示す通りである。番号１は鋼中のＣ含有量が本発明の範囲外であるため引張り強さが不足した。番号２は鋼中のＳｉ含有量が本発明の範囲外であるため引張り強さ、伸び共に不合格であった。番号３は鋼中のＰ含有量が本発明の範囲外であるため伸びが不合格であった。番号９は鋼中のＭｎ含有量が本発明の範囲外であるため引張り強さ、伸び共に不合格であった。
【００７７】
番号１２、２６、３３は合金化温度が本発明の範囲外であるため伸びとパウダリング性が不合格であった。番号２４は鋼中のＳｉ含有量／Ｃ含有量が本発明の範囲外であるため伸びが不合格であった。番号２９は鋼中のＭｎ含有量が本発明の範囲外であるため伸びが不合格であった。番号３０は鋼中のＣ含有量が本発明の範囲外であるため伸びが不合格であった。これら以外の本発明品は、めっき密着性が優れており、高強度で加工性が良好な合金化溶融亜鉛めっき鋼板であった。
【００７８】
（実施例２）
表１のＲに示す組成からなるスラブを１１５０℃に加熱し、仕上温度９１０〜９３０℃で４．５ｍｍの熱間圧延鋼帯とし、５８０〜６８０℃で巻き取った。酸洗後、冷間圧延を施して１．６ｍｍの冷間圧延鋼帯とした後、ライン内焼鈍方式の連続溶融亜鉛めっき設備を用いて表３に示すような条件の熱処理とめっきを行い、合金化溶融亜鉛めっき鋼板を製造した。連続溶融亜鉛めっき設備は、無酸化炉による加熱後、還元帯で還元・焼鈍を行う方式を使用した。酸化帯の燃焼空気比は表３に示す値に調節し、還元帯は、Ｈ2を１０質量％含むＮ2ガスに水蒸気を導入し水分圧と水素分圧の対数ｌｏｇ（ＰＨ2Ｏ／ＰＨ2）が表３に示す値となるように調節した。
【００７９】
焼鈍は、８２０℃で行い、その最高到達温度から６５０℃までを平均冷却速度１℃／秒で、引き続いて６５０℃から５００℃までを平均冷却速度４℃／秒で冷却し、さらに５００℃から平均冷却速度１．７℃／秒以上で４５０℃まで冷却し、且つめっき浴まで４５０℃で保持し、５００℃からめっき浴までを３０秒確保した後、溶融亜鉛めっき処理を行った。
【００８０】
引張強さ（ＴＳ）、伸び（Ｅｌ）は、各鋼板からＪＩＳ５号試験片を切り出し、常温での引張試験を行うことにより求めた。引張強さは４９０ＭＰａ以上を合格とし、伸びは〔５１−０．０３５×引張強さ〕％以上を合格とした。
【００８１】
めっきの付着量は、被膜をインヒビター入りの塩酸で溶解し、質量法により測定した。
【００８２】
Ｘ線回折は、η相、ζ相、δ1相、Γ相を示すｄ＝１．２７９、ｄ＝１．２６、ｄ＝１．２３７、ｄ＝１．２２２のＸ線回折強度Ｉδ1、Ｉζ、Ｉη、ＩΓとＳｉ標準板のｄ＝３．１３のＸ線回折強度ＩＳｉとの比Ｉδ1／ＩＳｉ、Ｉζ／ＩＳｉ、Ｉη／ＩＳｉ、ＩΓ／ＩＳｉを測定した。
【００８３】
密着性は、平板引き抜き試験を行い、フレーキング性を、ビード引き抜き試験を行い、パウダリング性を評価した。試験条件を以下に示す。
平板引き抜き試験
・サンプル引き抜き巾：３０ｍｍ
・金型：平板
・押しつけ荷重：１２００ｋｇ
・引き抜き速度：２００ｍｍ／ｍｉｎ
・塗油：防錆油塗布
ビード引き抜き試験
・サンプル引き抜き巾：３０ｍｍ
・金型：片側が肩Ｒ１ｍｍＲの角ビード（凸部は４×４ｍｍ）凸型、反対側が肩Ｒ１ｍｍＲの凹型
・押しつけ荷重：１２００ｋｇ
・引き抜き速度：２００ｍｍ／ｍｉｎ
・塗油：防錆油塗布
【００８４】
フレーキング性の評価は、摩擦係数０．１５以下で引き抜けたものを合格、引き抜き荷重がセレーションをおこし、摩擦係数の測定ができなかったものを不合格とした。
【００８５】
パウダリング性の評価は、引き抜き試験を行ったサンプルに密着テープ（セロハンテープ）を貼って、はがし、密着テープに付着しためっきの剥離の程度を目視で観察した。めっき層がまったく剥離しないものを合格、めっきが相当程度剥離したものを不合格とした。
【００８６】
めっき濡れ性は、通板したコイルの不めっき面積率を以下に示す評点づけで判定した。評点は３以上を合格とした。
４：不めっき面積率１％未満
３：不めっき面積率１％以上５％未満
２：不めっき面積率５％以上１０％未満
１：不めっき面積率１０％以上
【００８７】
評価結果は表３に示す通りである。番号４は有効Ａｌ量が本発明の範囲外であるため、適切な合金化温度で合金化ができず、密着性が不合格であった。番号５は有効Ａｌ量が本発明の範囲外であるため、めっき鋼板界面に脆いΓ相ができ、密着性が不合格であった。番号６は有効Ａｌ量が本発明の範囲外であるため、適切な合金化温度で合金化ができず、密着性が不合格であった。番号７は有効Ａｌ量が本発明の範囲外であるため、合金化温度が本発明の範囲外となり、伸びと密着性が不合格であった。番号８は酸化帯の空気比が本発明の範囲外であるため、ＳｉＯ2を含有する内部酸化層が形成されず、密着性、めっき濡れ性が不合格であった。番号１９はｌｏｇ（ＰＨ2Ｏ／ＰＨ2）が本発明の範囲外であるため、ＳｉＯ2の外部酸化層が形成され、密着性、めっき濡れ性が不合格であった。
【００８８】
これら以外の本発明品は、めっき密着性が優れており、高強度で加工性が良好な合金化溶融亜鉛めっき鋼板であった。
また、番号２０〜２３は鋼板中にＮｉ、Ｃｕが添加されていないため、番号９〜１２に比べると不めっきが出やすい傾向が見られた。
【００８９】
【表１】
【表２】
【表３】
【発明の効果】
以上述べたように、本発明は密着性、加工性に優れる高強度合金化溶融亜鉛めっき鋼板とその製造方法を提供することを可能としたものであり、産業の発展に貢献するところが極めて大である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-strength galvannealed steel sheet and a method for producing the same, and more particularly to a plated steel sheet that has excellent adhesion and can be applied as a steel sheet for various uses such as building materials and automobiles. .
[0002]
[Prior art]
An alloyed hot-dip galvanized steel sheet is available as a plated steel sheet having good corrosion resistance. This alloyed hot-dip galvanized steel sheet is usually preheated in a non-oxidizing furnace after degreasing the steel sheet, subjected to reduction annealing in a reducing furnace to clean the surface and secure the material, and immersed in a hot-dip zinc bath, It is manufactured by alloying after controlling the amount of adhesion. As its feature, it is excellent in corrosion resistance, plating adhesion, etc., it is widely used mainly for automobiles, building materials and the like.
[0003]
In recent years, in particular, in the automobile field, it has been necessary to increase the strength of plated steel sheets in order to ensure the function of protecting passengers in the event of a collision and to reduce the weight for the purpose of improving fuel efficiency.
[0004]
It is effective to add elements such as Si, Mn, and P to increase the strength of the steel sheet without degrading workability. However, the addition of these elements delays alloying, so compared to mild steel. High temperature and long time alloying is required. This alloying for a long time at a high temperature transforms the austenite remaining in the steel sheet into pearlite and lowers the workability. As a result, the effect of the additive element is offset.
[0005]
In order to improve the workability of such an alloyed hot-dip galvanized steel sheet, the present inventors previously proposed a high-strength alloyed hot-dip galvanized steel sheet having excellent workability and a method for producing the same (see Patent Document 1). ).
[0006]
Moreover, as a manufacturing method of such a steel plate, a hot-dip galvanized steel plate having both high strength and high ductility and excellent in plating adhesion and alloying processability and a manufacturing method of an alloyed hot-dip galvanized steel plate (see, for example, Patent Document 2) ), A method for producing a high-strength galvannealed steel sheet excellent in press formability and plating adhesion (see, for example, Patent Document 3) and the like.
It is shown.
[0007]
[Patent Document 1]
JP 2003-105516 A
[Patent Document 2]
Japanese Patent Laid-Open No. 11-131145
[Patent Document 3]
Japanese Patent Laid-Open No. 2001-140022
[0008]
[Problems to be solved by the invention]
However, the technique disclosed in Patent Document 1 does not ensure sufficient adhesion. Moreover, in the manufacturing method shown by patent document 2 and patent document 3, although the range of manufacturing conditions is described very widely, the manufacturing conditions which make alloying of plating and the workability improvement of a steel plate are not described. It is not useful in actual production.
[0009]
Therefore, the present invention solves the above problems and proposes a high-strength galvannealed steel sheet having excellent adhesion and a method for producing the same.
[0010]
[Means for Solving the Problems]
As a result of intensive research on the plating treatment of high-strength steel sheets, the present inventors have conducted continuous hot-dip galvanizing equipment with optimized heat treatment conditions and plating conditions for steel to which a certain amount of C, Si, and Mn has been added. The present invention was made by finding that a high-strength galvannealed steel sheet with excellent adhesion can be produced by plating.
That is, the gist of the present invention is as follows.
[0011]
(1) In mass%,
C: 0.05 to 0.15%,
Si: 0.3 to 2.5%,
Mn: 1.5 to 2.8%,
P: 0.03% or less,
S: 0.02% or less,
Al: 0.005 to 0.5%,
N: 0.0060% or less,
(% Mn) / (% C) ≧ 12 and (% Si) / (% C) when the remaining Fe and unavoidable impurities are used, and when% C,% Si, and% Mn are C, Si, and Mn contents, respectively. ) In a steel plate having an alloyed hot-dip galvanized layer containing Fe and the balance consisting of Zn and inevitable impurities on a high-strength steel plate satisfying ≧ 4,Alloy phase η phase, ζ phase, δ 1 Phase, Γ phased =1.237, D = 1.26, d =1.279, D = 1.222 X-ray diffraction intensity Iδ1, Iζ, Iη, IΓ and the ratio Iδ of the X-ray diffraction intensity ISi of d = 3.13 of the Si standard plate1/ ISi, Iζ / ISi, Iη / ISi, and IΓ / ISi are Iη / ISi ≦ 0.0006 and IΓ / ISi ≦ 0.0006, and one or two of Iδ1 / ISi and Iζ / ISi are 0.00. A high-strength galvannealed steel sheet with excellent adhesion, characterized by being 0006 or more.
[0012]
(2) From the interface between the high-strength steel plate and the plating layer to the steel plate side, SiO2The steel layer having an average content of internal oxide of 0.8 to 5.0% by mass is formed in a range of 0.1 μm or more and 10 μm or less. High strength alloyed hot dip galvanized steel sheet.
[0013]
(3) The high-strength steel sheet containing 1 type or 2 types of Ni: 0.01 to 5.0% and Cu: 0.01 to 5.0% by mass% (1) ) Or a high-strength galvannealed steel sheet having excellent adhesion as described in (2).
[0014]
(4) The relationship between tensile strength F (MPa) and elongation L (%)
L ≧ 51−0.035 × F
The high-strength galvannealed steel sheet with excellent adhesion according to any one of the above (1) to (3), wherein:
[0015]
(5) A slab having a composition comprising the chemical component according to any one of (1) to (4) above is replaced with Ar.ThreeAfter finishing rolling at a temperature above the point and performing cold rolling at 50 to 85%, annealing is performed at a continuous hot-dip galvanizing facility in the two-phase coexistence temperature range of 750 ° C. or more and 880 ° C. or less of ferrite and austenite, From the highest temperature to 650 ° C., the average cooling rate is 0.5 to 10 ° C./second, and subsequently from 650 ° C. to 500 ° C. is cooled at an average cooling rate of 3 ° C./second or more. The surface of the cold-rolled steel sheet is cooled to 420 ° C. to 460 ° C. at 5 ° C./second or more and held from 500 ° C. to the plating bath for 25 seconds or more and 240 seconds or less, and then hot dip galvanized. An galvanized layer is formed on the surface of the steel sheet by applying an alloying treatment to the steel sheet on which the galvanized layer is formed. The method of manufacturing a galvannealed steel sheet,
First, the annealing treatment
In the oxidation zone, oxidation was performed in an atmosphere having a combustion air ratio of 0.9 to 1.2, and in the subsequent reduction zone, the logarithm log (PH) of water pressure and hydrogen partial pressure 2 O / PH 2 )
0.5 [Si%]-3 ≦ log (PH 2 O / PH 2 ) ≤ -0.8
However, [Si%]: Si content in the steel sheet (mass%)
Reduction in an atmosphere that satisfies
nextThe hot dip galvanizing treatment is performed in a hot dip galvanizing bath having a component composition consisting of an effective Al concentration in the bath of 0.07 to 0.092 mass%, the balance being Zn and inevitable impurities, and the alloying treatment is performed.
450 ≦ T ≦ 410 × exp (2 × [Al%])
However, [Al%]: Effective Al concentration in the galvanizing bath (mass%)
A method for producing a high-strength galvannealed steel sheet with excellent adhesion, characterized in that it is carried out at a temperature T (° C.) that satisfies the following conditions.
[0016]
(6) In the method for producing a high-strength galvannealed steel sheet according to (5), the effective Al concentration in the bath is
[Al%] ≦ 0.092−0.001 × [Si%]2
However, [Si%]: Si content in the steel sheet (mass%)
A method for producing a high-strength galvannealed steel sheet having excellent adhesion, characterized in that it is carried out at an effective Al concentration (mass%) in a bath that satisfies the following conditions.
[0017]
(7) In the method for producing a high-strength galvannealed steel sheet according to (5) or (6), the time until cooling to a temperature of 400 ° C. or less after hot dipping is 30 seconds to 120 seconds. A method for producing a high-strength galvannealed steel sheet having excellent adhesion, characterized in that
[0018]
(8) In the method for producing a high-strength galvannealed steel sheet according to any one of (5) to (7), the temperature of the hot dip galvanizing bath is less than 470 ° C. The manufacturing method of the high-strength alloying hot-dip galvanized steel sheet which was excellent in.
[0019]
(9) In the method for producing a high-strength galvannealed steel sheet according to any one of (5) to (8) above, after cooling to 400 ° C. to 450 ° C. after annealing, to 430 ° C. to 470 ° C. A method for producing a high-strength galvannealed steel sheet having excellent adhesion, characterized by performing reheating and galvanizing treatment.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
[0022]
First, the reasons for limiting the numerical values of C, Si, Mn, P, S, Al, and N will be described. C is an essential element for increasing the strength of a steel sheet by strengthening the structure with martensite or retained austenite. The reason why the C content is 0.05% or more is that when C is less than 0.05%, cementite and pearlite are not easily formed in a hot dip galvanizing line where mist or jet water is difficult to rapidly cool from the annealing temperature. This is because it is easy to produce and it is difficult to ensure the required tensile strength. On the other hand, the reason why the C content is 0.15% or less is that when C exceeds 0.15%, it becomes difficult to form a sound weld by spot welding, and at the same time, segregation of C becomes prominent. This is because the property deteriorates.
[0023]
Si is added in an amount of 0.3 to 2.5% as an element that increases the strength without significantly impairing the workability of the steel sheet, in particular, the elongation, and is set to 4% or more by mass of the C content. The reason why the Si content is 0.3% or more is that it is difficult to ensure the required tensile strength when Si is less than 0.3%, and the Si content is 2.5% or less. The reason for this is that when Si exceeds 2.5%, the effect of increasing the strength is saturated and the ductility is lowered. Further, by setting the mass to 4% by mass or more of the C content, the progress of pearlite and bainite transformation is significantly delayed by reheating for the alloying treatment performed immediately after plating, and 3% by volume even after cooling to room temperature. A metal structure in which 20% martensite and retained austenite are mixed in ferrite can be obtained.
[0024]
Since Mn lowers the free energy of austenite together with C, 1.5% or more is added for the purpose of stabilizing austenite until the steel strip is immersed in the plating bath. Moreover, by adding 12% or more by mass% of the C content, the progress of pearlite and bainite transformation is significantly delayed by reheating for alloying performed immediately after plating, and 3% by volume even after cooling to room temperature. A metal structure in which ˜20% martensite and retained austenite are mixed in ferrite can be obtained. However, if the amount added is excessive, cracks are likely to occur in the slab and spot weldability deteriorates, so the upper limit is 2.8%.
[0025]
P is generally contained in steel as an unavoidable impurity. However, when its amount exceeds 0.03%, the spot weldability is significantly deteriorated, and in a high-strength steel sheet having a tensile strength exceeding 490 MPa as in the present invention. Since the cold rolling property is remarkably deteriorated together with the toughness, the content is set to 0.03% or less. S is also generally contained in steel as an unavoidable impurity. However, if the amount exceeds 0.02%, the presence of MnS stretched in the rolling direction becomes significant, which adversely affects the bendability of the steel sheet. 0.02% or less.
[0026]
Al is a deoxidizing element for steel, and it is necessary to add 0.005% or more in order to improve the material by suppressing the grain refinement of the hot rolled material by AlN and the coarsening of crystal grains in a series of heat treatment steps. . However, if it exceeds 0.5%, not only the cost increases, but also the surface properties deteriorate, so the content is made 0.5% or less. N is also generally contained in steel as an unavoidable impurity, but if its amount exceeds 0.06%, the brittleness deteriorates with elongation, so its content is made 0.006% or less.
[0027]
Further, when elements such as Si, Mn, and P are added to increase the strength of the steel sheet, the plating wettability may be lowered. Therefore, it is effective to add Ni and Cu in order to improve the plating wettability.
[0028]
The reason why plating wettability is improved by adding Ni is not clear, but when annealing in continuous hot dip galvanizing equipment, the surface of elements that concentrate on the surface and reduce plating wettability such as Si, Mn, and P It is thought that there is an effect of suppressing concentration. This effect becomes clear when 0.01% or more is added. However, if the addition amount exceeds 5.0%, the workability is deteriorated and the cost is increased, so 5.0% was made the upper limit.
[0029]
Cu is an element effective in improving plating wettability and improving plating adhesion. The reason why plating wettability and adhesion are improved by adding Cu is also not clear, but when annealing is performed in a continuous hot dip galvanizing facility, it concentrates on the surface and reduces plating wettability such as Si, Mn, and P. It is considered that there is an effect of assisting the effect of Ni that suppresses the surface concentration of the element to be made. This effect becomes clear when 0.01% or more is added. However, if the addition amount exceeds 5.0%, the workability is deteriorated and the cost is increased, so 5.0% was made the upper limit.
[0030]
When Ni and Cu are added simultaneously, a synergistic effect is exhibited, and the plating wettability can be improved by adding a smaller amount. Therefore, when adding simultaneously, Ni addition amount is 0.01% or more and less than 1.0%, and Cu addition amount is 0.01% or more and less than 0.5%.
[0031]
In addition, Nb, Ti, B, Mo, Cu, Sn, Zn, Zr, W, Co, Ca, rare earth elements (including Y), V, Ta, Hf, Pb, Mg, Even if the total content of As, Sb, and Bi is 1% or less, the effects of the present invention are not impaired, and depending on the amount, it may be preferable that the corrosion resistance and workability are improved.
[0032]
Next, the alloyed hot-dip galvanized layer will be described. In the present invention, the alloyed hot dip galvanized layer is a plated layer mainly composed of an Fe—Zn alloy in which Fe in steel can diffuse during Zn plating by an alloying reaction. This plating layer has η phase, ζ phase, δ1An alloy layer called a Γ phase is formed. Of these, the η phase is soft in plating and tends to adhere to the mold during pressing and cause plating peeling called flaking. Further, since the Γ phase is hard and brittle, plating peeling called powdering is liable to occur during processing. Therefore, the η phase and Γ phase are reduced as much as possible, and the plating layer is divided into ζ phase and δ phase.1The plating adhesion can be improved by using any one or more of the phases. Here, in the plating layer, Γ1It is known that a hard and brittle phase called a phase exists, but from the X-ray diffraction intensity, Γ phase and Γ phase1Because the phases cannot be distinguished, the Γ phase and Γ phase1The phases are combined and treated as a Γ phase.
[0033]
Specifically, η phase, ζ phase, δ1X-ray diffraction intensity Iδ of d = 1.279, d = 1.26, d = 1.237, d = 1.222 indicating a Γ phase1, Iζ, Iη, IΓ and the ratio Iδ of the X-ray diffraction intensity ISi of d = 3.13 of the Si standard plate1/ ISi, Iζ / ISi, Iη / ISi, and IΓ / ISi are set to Iη / ISi ≦ 0.0006 and IΓ / ISi ≦ 0.0006, and Iδ1One or two of / ISi and Iζ / ISi is set to 0.0006 or more.
[0034]
The reason why Iη / ISi is limited to 0.0006 or less is that when Iη / ISi is 0.0006 or less, the η phase is very small, and the plating adhesion is not deteriorated.
[0035]
Further, the reason why IΓ / ISi is limited to 0.0006 or less is that when IΓ / ISi is 0.0006 or less, the Γ phase is extremely small, and the plating adhesion is not deteriorated.
[0036]
Iδ1The reason why one or two of / ISi and Iζ / ISi is limited to 0.0006 or more is Iδ1When either one or two of / ISi and Iζ / ISi is 0.0006 or more, the plating layer is δ1This is because one or two of the phase and the ζ phase are mainly used, and the plating adhesion is not deteriorated.
[0037]
The steel sheet of the present invention is one of Pb, Sb, Si, Sn, Mg, Mn, Ni, Cr, Co, Ca, Cu, Li, Ti, Be, Bi, and rare earth elements during hot dip galvanizing bath or galvanizing. Alternatively, even if two or more kinds are contained or mixed, the effects of the present invention are not impaired, and depending on the amount, there are cases where the corrosion resistance and workability are improved, and so on. There are no particular restrictions on the amount of galvanized alloying, but 20 g / m from the viewpoint of corrosion resistance.2Above, 150 g / m from the viewpoint of economy2It is desirable that
[0038]
In the present invention, the high strength alloyed hot dip galvanized steel sheet having excellent workability has a tensile strength TS of 490 MPa or more, and the relationship between tensile strength F (MPa) and elongation L (%) is L ≧ 51-0. .035xF
It is a steel plate with performance that satisfies
[0039]
The reason why the elongation L is limited to [51-0.035 × F]% or more is that, when L is lower than [51-0.035 × F], the workability such as breaking when severe processing such as deep drawing is performed. This is because it is insufficient.
[0040]
In the present invention, from the interface between the high-strength steel plate and the plating layer to the steel plate side, SiO2Adhesion is further improved when a steel layer having an average internal oxide content of 0.8 to 5.0% by mass is formed in a range of 0.1 μm to 10 μm. From the interface between the high-strength steel plate and the plating layer,2The reason why the adhesion is improved when the inner oxide is present is to suppress the formation of an outer oxide film of Si on the surface of the steel sheet due to the generation of the inner oxide of Si in the steel sheet during the annealing process. it is conceivable that.
[0041]
The internal oxide of Si is granular or linear and exists in the steel sheet, and can be clearly distinguished by microscopic observation. In the present invention, SiO2The steel layer containing the internal oxide is SiO in the microscopic observation.2This is a layer in which the inner oxide is observed. In addition, SiO2The average content of internal oxide of SiO is the SiO contained in this steel layer.2Content of SiO 22The thickness of the steel layer containing the internal oxide of2The width to the portion where the internal oxide is observed is shown.
[0042]
SiO2The measurement of the content of internal oxide of SiO 22Any method can be used as long as it can measure the mass% of SiO 2.2The layer containing the internal oxide of2After separating, the method of measuring the mass is reliable. In addition, SiO2A method for measuring the thickness of the steel layer containing the internal oxide is not particularly specified, but a method of measuring by a microscopic observation from a cross section is reliable.
[0043]
In the present invention, SiO2The reason why the average content of the internal oxide is limited to 0.8 to 5.0% by mass is that when the content is less than 0.8% by mass, the suppression of the external oxide film is insufficient and the effect of improving the plating adhesion is seen. This is because the effect of improving plating adhesion is saturated when the content exceeds 5.0% by mass.
[0044]
In addition, SiO2The reason why the thickness of the steel layer containing the inner oxide is limited to 0.1 to 10 μm is that if the thickness is less than 0.1 μm, the suppression of the outer oxide film is insufficient and the effect of improving the plating adhesion is not seen. Yes, when the thickness exceeds 10 μm, the effect of improving plating adhesion is saturated.
[0045]
Next, the reasons for limiting the manufacturing conditions will be described. The purpose is to provide a metal structure containing 3 to 20% martensite and retained austenite, and to achieve both high strength and good press workability. When the volume ratio of martensite and retained austenite is less than 3%, the strength is not high. On the other hand, if the volume ratio of martensite and retained austenite exceeds 20%, the workability of the steel sheet is deteriorated although it is high in strength, and the object of the present invention is not achieved.
[0046]
The slab to be used for hot rolling is not particularly limited as long as it is manufactured with a continuously cast slab or a thin slab caster. It is also suitable for processes such as continuous casting-direct rolling (CC-DR) in which hot rolling is performed immediately after casting.
[0047]
The hot rolling finishing temperature is Ar from the viewpoint of ensuring the press formability of the steel sheet.Three Need to be more than point. The cooling conditions and coiling temperature after hot rolling are not particularly limited, but the coiling temperature is to avoid large material variations at both ends of the coil and to avoid pickling deterioration due to increased scale thickness. Is not more than 750 ° C., and if bainite or martensite is partially formed, it is easy to cause an ear crack during cold rolling, and in extreme cases, the plate may be broken. Cold rolling may be performed under ordinary conditions, and the rolling rate is set to 50% or more for the purpose of finely dispersing martensite and retained austenite so that the ferrite is easily work-hardened to maximize workability. On the other hand, it is not realistic to perform cold rolling at a rolling rate exceeding 85% because a large cold rolling load is required.
[0048]
When annealing is performed in a continuous hot-dip galvanizing facility using an in-line annealing method, the annealing temperature is in the range of 750 ° C. or more and 880 ° C. or less of ferrite and austenite. If the annealing temperature is less than 750 ° C., recrystallization is insufficient and the press workability necessary for the steel sheet cannot be achieved. Annealing at a temperature exceeding 880 ° C. is not preferable because the growth of an oxide layer of Si or Mn is remarkable on the surface of the steel strip and plating defects are likely to occur. Further, in the process of immersing and cooling in the plating bath, even if it is slowly cooled to 650 ° C., ferrite with a sufficient volume ratio does not grow, and austenite transforms to martensite during cooling from 650 ° C. to the plating bath. Then, since re-heating for alloying treatment martensite is tempered and cementite is precipitated, it is difficult to achieve both high strength and good press workability.
[0049]
The steel strip is cooled in the process of subsequent immersion in the plating bath after annealing, and the cooling rate in this case is an average of 0.5 to 10 ° C./second from the maximum temperature to 650 ° C., and subsequently 650 ° C. To 500 ° C. at an average cooling rate of 3 ° C./second or more, further cooling from 500 ° C. to 420 ° C. to 460 ° C. at an average cooling rate of 0.5 ° C./second or more, and from 500 ° C. to the plating bath. Hold for 25 to 240 seconds.
[0050]
The average of 0.5 to 10 ° C./second up to 650 ° C. is to increase the volume fraction of ferrite in order to improve workability, and at the same time, to increase the C concentration of austenite, thereby lowering its free energy of formation, The purpose is to set the temperature at which site transformation starts to be equal to or lower than the plating bath temperature. In order to make the average cooling rate up to 650 ° C. less than 0.5 ° C./second, it is necessary to lengthen the line length of the continuous hot dip galvanizing equipment, resulting in high costs. 5 ° C / second or more.
[0051]
In order to make the average cooling rate up to 650 ° C. less than 0.5 ° C./second, it is possible to lower the maximum temperature and to anneal at a temperature at which the volume fraction of austenite is small. If the appropriate temperature range is narrower than the allowable temperature range, and even if the annealing temperature is low, austenite is not formed and the purpose is not achieved.
[0052]
On the other hand, if the average cooling rate up to 650 ° C. exceeds 10 ° C./second, the increase in the volume fraction of ferrite is not sufficient, and the increase in the C concentration in austenite is small, so the steel strip is immersed in the plating bath. A part of the material transforms into martensite before being heated, and then martensite is tempered by heating for alloying treatment and precipitates as cementite, so that it is difficult to achieve both high strength and good workability.
[0053]
The reason why the average cooling rate from 650 ° C. to 500 ° C. is 3 ° C./second or more is to avoid the transformation of austenite to pearlite during the cooling, and the cooling rate is less than 3 ° C./second. Even if it is annealed at a temperature specified in (1) and cooled to 650 ° C., the formation of pearlite is inevitable. Although the upper limit of the average cooling rate is not particularly defined, it is difficult to cool the steel strip so that the average cooling rate exceeds 20 ° C./second in a dry atmosphere.
[0054]
The reason for setting the average cooling rate from 500 ° C. to 0.5 ° C./s or more is to avoid the transformation of austenite to pearlite during the cooling process. Even if annealing is performed at the temperature specified in the invention and cooling to 500 ° C., generation of pearlite is inevitable. Although the upper limit of the average cooling rate is not particularly defined, it is difficult to cool the steel strip so that the average cooling rate exceeds 20 ° C./second in a dry atmosphere. The reason why the cooling end temperature is set to 420 to 460 ° C. is that concentration of C in austenite is promoted and high strength alloyed hot dip galvanizing excellent in workability is obtained.
[0055]
The reason for maintaining the temperature from 500 ° C. to the plating bath for 25 seconds or more and 240 seconds or less is that if less than 25 seconds, the concentration of C in the austenite becomes insufficient, and the C concentration in the austenite allows austenite to remain at room temperature. This is because when the time exceeds 240 seconds, the bainite transformation proceeds too much, the amount of austenite decreases, and a sufficient amount of retained austenite cannot be generated.
[0056]
Furthermore, while holding from 500 ° C. to the plating bath, once cooled to 400 to 450 ° C. and held, concentration of C in the austenite is promoted and high strength alloyed hot dip galvanizing with excellent workability is obtained. It is done. However, if the plate is continuously immersed in the plating bath at 430 ° C. or lower, the plating bath is cooled and solidified. Therefore, after reheating to a temperature of 430 to 470 ° C., it is necessary to perform a hot dip galvanizing treatment.
[0057]
In the production of the alloyed hot dip galvanized steel sheet of the present invention, the hot dip galvanizing bath used has an Al concentration adjusted to 0.07 to 0.092 mass% with an effective Al concentration C in the bath. Here, the effective Al concentration in the plating bath is a value obtained by subtracting the Fe concentration in the bath from the Al concentration in the bath.
[0058]
The reason for limiting the effective Al concentration to 0.07 to 0.092 mass% is that when the effective Al concentration is lower than 0.07%, the formation of an Fe—Al—Zn phase that becomes an alloying barrier at the initial stage of plating is performed. This is because only the galvannealed steel sheet with poor plating film adhesion at the time of processing can be obtained because it is insufficient and the brittle Γ phase can be thickened at the interface of the plated steel sheet during the plating process. On the other hand, when the effective Al concentration is higher than 0.092%, alloying for a long time at high temperature is required, and austenite remaining in the steel is transformed into pearlite, so that high strength and workability are good. It becomes difficult to achieve both.
[0059]
Furthermore, in the present invention, the alloying temperature during the alloying treatment is
450 ≦ T ≦ 410 × exp (2 × [Al%])
However, [Al%]: Effective Al concentration in the galvanizing bath (mass%)
At a temperature T (° C.) satisfying
[0060]
The reason why the alloying temperature T is limited to 450 ° C. or more and 410 × exp (2 × [Al%]) ° C. or less is that the alloying does not proceed when the alloying temperature T is lower than 450 ° C. This is because the progress is insufficient and the alloying is untreated, and the plating surface layer is covered with the η phase having poor adhesion. Also, if T is higher than 410 × exp (2 × [Al%]) ° C., alloying proceeds too much, and a brittle Γ phase can be made thick at the plated steel plate interface, so that the plating adhesion during processing decreases. is there.
[0061]
In the present invention, if the alloying temperature is too high, the austenite remaining in the steel is transformed into pearlite, and a steel sheet having both the desired high strength and workability cannot be obtained. Therefore, as the amount of Si added increases and the alloy becomes harder, it is effective to lower the alloying temperature by reducing the effective Al concentration in the bath in order to improve the workability.
[0062]
In particular,
[Al%] ≦ 0.092−0.001 × [Si%]2
However, [Si%]: Si content in the steel sheet (mass%)
Plating is performed at an effective Al concentration (mass%) in the bath satisfying the above.
Effective Al concentration is 0.092-0.001 × [Si%]2The reason for limiting to less than or equal to% is that the effective Al concentration is 0.092-0.001 × [Si%]2If it is higher than%, alloying for a long time at a high temperature is required, and austenite remaining in the steel is transformed into pearlite, which deteriorates workability.
[0063]
The reason for limiting the time until cooling to a temperature of 400 ° C. or less after hot dipping to 30 seconds or more and 120 seconds or less is that if less than 30 seconds, alloying is insufficient and alloying is untreated, and the plating surface layer has poor adhesion. This is because it is covered with the η phase, and if it exceeds 120 seconds, the bainite transformation proceeds too much, the amount of austenite decreases, and a sufficient amount of retained austenite cannot be generated.
[0064]
In the present invention, the alloying furnace heating method is not particularly limited. If the temperature of the present invention can be secured, radiation heating by a normal gas furnace or high frequency induction heating may be used. In addition, the method of cooling from the highest plate temperature after alloying heating is not questioned. If the heat is shut off by air seal etc. after alloying, it is sufficient to leave open, and the gas that cools more rapidly There is no problem with cooling.
[0065]
The reason for limiting the temperature of the hot dip galvanizing bath to less than 470 ° C. is that the formation of the Fe—Al—Zn phase, which becomes an alloying barrier at the initial stage of plating, proceeds excessively at 470 ° C. or higher, so that the alloying temperature is raised. This is because a high amount of steel tends to cause a decrease in workability. The lower limit of the bath temperature is not particularly limited, but since the melting point of zinc is 419.47 ° C., the hot-dip plating can only be physically performed at a higher bath temperature.
In the present invention, SiO2In order to positively generate a steel layer containing the internal oxide, a method of oxidizing Si during the annealing process of the continuous hot dip plating line is effective.
[0066]
Specifically, thousands of iron oxide films are formed in an oxidation zone in a continuous hot dip plating line. Since it is difficult for Si to diffuse in the iron oxide film, this suppresses external oxidation of Si, so that SiO under the iron oxide film2A steel layer containing the internal oxide of is produced. However, the combustion air ratio in the oxidation zone when forming the iron oxide film is required to be 0.9 or more in order to produce an iron oxide film sufficient to suppress external oxidation of Si. An iron oxide film cannot be formed. Also, if the combustion air ratio exceeds 1.2, the iron oxide film formed in the oxidation zone is too thick to be reduced in the next reduction zone and plating bath, and the oxide film layer is below the plating layer. Therefore, the plating adhesion is deteriorated. Therefore, it is necessary to adjust the combustion air ratio in the oxidation zone to a range of 0.9 to 1.2.
[0067]
Next, in the reduction zone, the logarithm log of the water pressure and the hydrogen partial pressure (PH2O / PH2)
0.5CSi-3 ≦ log (PH2O / PH2) ≤ -0.8
Reduce in an atmosphere that satisfies In the reduction zone, H2N in the range of 1 to 70% by mass2Use gas. Also, moisture pressure and hydrogen partial pressure (PH2O / PH2) Is operated by introducing water vapor into the furnace. log (PH2O / PH2) Is -0.8 or less because log (PH2O / PH2) Exceeds −0.8, the iron oxide film formed in the oxidation zone cannot be reduced. Log (PH2O / PH2) 0.5CSi-3 or higher is log (PH2O / PH2) Is 0.5CSiIf it is less than -3, external oxidation of Si occurs and SiO on the steel sheet surface.2This is because an external oxide film is formed and plating adhesion is lowered.
[0068]
That is, the reduction zone reduces the iron oxide film, and SiO2It is necessary to make the atmosphere into an internal oxidation state. Here, the internal oxidation of Si is a phenomenon in which oxygen diffused in the steel sheet reacts with Si in the vicinity of the surface layer of the alloy to precipitate an oxide. The internal oxidation phenomenon occurs when the inward diffusion rate of oxygen is much faster than the outward diffusion rate of Si, that is, when the oxygen potential in the atmosphere is relatively high or the concentration of Si is low. At this time, since Si hardly moves and is oxidized in situ, it is possible to prevent Si concentration on the surface of the steel sheet, which is a cause of deterioration of plating adhesion.
[0069]
【Example】
Hereinafter, the present invention will be described specifically by way of examples.
[0070]
Example 1
A slab having the composition shown in Table 1 was heated to 1150 ° C. to form a hot-rolled steel strip of 4.5 mm at a finishing temperature of 910 to 930 ° C., and wound at 580 to 680 ° C. After pickling and cold rolling to make a 1.6 mm cold rolled steel strip, heat treatment and plating under the conditions shown in Table 2 are performed using a continuous hot dip galvanizing facility with an in-line annealing method, An alloyed hot dip galvanized steel sheet was produced. The continuous hot-dip galvanizing equipment used a method of reducing and annealing in a reduction zone after heating in a non-oxidizing furnace. The combustion air ratio in the oxidation zone is adjusted to 0.95, and the reduction zone is H2N containing 10% by mass2Water vapor is introduced into the gas and the logarithm log of the water pressure and the hydrogen partial pressure (PH2O / PH2) Was adjusted to -1 to -3.
[0071]
Tensile strength (TS) and elongation (El) were determined by cutting out a JIS No. 5 test piece from each steel plate and conducting a tensile test at room temperature. The tensile strength was 490 MPa or more, and the elongation was [51-0.035 × tensile strength]% or more.
[0072]
The adhesion amount of plating was measured by a mass method after dissolving the film with hydrochloric acid containing an inhibitor.
[0073]
X-ray diffraction is η phase, ζ phase, δ1X-ray diffraction intensity Iδ of d = 1.279, d = 1.26, d = 1.237, d = 1.222 indicating a Γ phase1, Iζ, Iη, IΓ and the ratio Iδ of the X-ray diffraction intensity ISi of d = 3.13 of the Si standard plate1/ ISi, Iζ / ISi, Iη / ISi, and IΓ / ISi were measured.
[0074]
For adhesion, a bead pull-out test was performed to evaluate powdering properties. Test conditions are shown below.
・ Sample drawing width: 30mm
-Mold: Square bead with one side shoulder R1mmR (convex part is 4x4mm) convex, concave side with shoulder R1mmR on the opposite side
・ Pressing load: 1200kg
・ Pullout speed: 200mm / min
・ Oiling: Antirust oil applied
[0075]
The powdering property was evaluated by applying an adhesive tape (cellophane tape) to a sample subjected to a pull-out test, peeling off, and visually observing the degree of peeling of the plating adhered to the adhesive tape. The case where the plating layer did not peel at all was accepted, and the case where the plating was peeled off to some extent was rejected.
[0076]
The evaluation results are as shown in Table 2. No. 1 had insufficient tensile strength because the C content in the steel was outside the range of the present invention. In No. 2, since the Si content in the steel was outside the range of the present invention, both tensile strength and elongation were not acceptable. No. 3 was a failure of elongation because the P content in the steel was outside the scope of the present invention.It was. NumberNo. 9 failed in both tensile strength and elongation because the Mn content in the steel was outside the range of the present invention.
[0077]
Nos. 12, 26, and 33 indicate that the alloying temperature is out of the range of the present invention, so that the elongation and powdering properties are not acceptable.It was. NumberIn No. 24, the Si content / C content in the steel was out of the scope of the present invention, so the elongation was not acceptable.It was. NumberIn No. 29, the elongation was unacceptable because the Mn content in the steel was outside the range of the present invention. In No. 30, the C content in the steel was outside the range of the present invention, so the elongation was not acceptable. The products of the present invention other than these were alloyed hot-dip galvanized steel sheets having excellent plating adhesion, high strength and good workability.
[0078]
(Example 2)
A slab having the composition shown in R of Table 1 was heated to 1150 ° C. to form a hot-rolled steel strip of 4.5 mm at a finishing temperature of 910 to 930 ° C., and wound at 580 to 680 ° C. After pickling and cold rolling to make a 1.6 mm cold rolled steel strip, heat treatment and plating under the conditions shown in Table 3 using a continuous hot dip galvanizing facility of in-line annealing method, An alloyed hot dip galvanized steel sheet was produced. The continuous hot-dip galvanizing equipment used a method of reducing and annealing in a reduction zone after heating in a non-oxidizing furnace. The combustion air ratio in the oxidation zone is adjusted to the values shown in Table 3, and the reduction zone is H2N containing 10% by mass2Water vapor is introduced into the gas and the logarithm log of the water pressure and the hydrogen partial pressure (PH2O / PH2) Was adjusted to the value shown in Table 3.
[0079]
Annealing is performed at 820 ° C., from the highest temperature reached to 650 ° C. at an average cooling rate of 1 ° C./second, subsequently from 650 ° C. to 500 ° C. at an average cooling rate of 4 ° C./second, and further from 500 ° C. The steel sheet was cooled to 450 ° C. at an average cooling rate of 1.7 ° C./second or more, and kept at 450 ° C. until the plating bath was maintained for 30 seconds from 500 ° C. to the plating bath, and then hot dip galvanized.
[0080]
Tensile strength (TS) and elongation (El) were determined by cutting out a JIS No. 5 test piece from each steel plate and conducting a tensile test at room temperature. The tensile strength was 490 MPa or more, and the elongation was [51-0.035 × tensile strength]% or more.
[0081]
The adhesion amount of plating was measured by a mass method after dissolving the film with hydrochloric acid containing an inhibitor.
[0082]
X-ray diffraction is η phase, ζ phase, δ1X-ray diffraction intensity Iδ of d = 1.279, d = 1.26, d = 1.237, d = 1.222 indicating a Γ phase1, Iζ, Iη, IΓ and the ratio Iδ of the X-ray diffraction intensity ISi of d = 3.13 of the Si standard plate1/ ISi, Iζ / ISi, Iη / ISi, and IΓ / ISi were measured.
[0083]
For adhesion, a flat plate pull-out test was performed, flaking properties were evaluated, a bead pull-out test was performed, and powdering properties were evaluated. Test conditions are shown below.
Flat plate pull-out test
・ Sample drawing width: 30mm
・ Mold: Flat plate
・ Pressing load: 1200kg
・ Pullout speed: 200mm / min
・ Oiling: Antirust oil applied
Bead pull-out test
・ Sample drawing width: 30mm
-Mold: Square bead with one side shoulder R1mmR (convex part is 4x4mm) convex, concave side with shoulder R1mmR on the opposite side
・ Pressing load: 1200kg
・ Pullout speed: 200mm / min
・ Oiling: Antirust oil applied
[0084]
The evaluation of the flaking property was determined to be acceptable if the friction coefficient was 0.15 or less, and rejected if the extraction load was serrated and the friction coefficient could not be measured.
[0085]
The powdering property was evaluated by applying an adhesive tape (cellophane tape) to a sample subjected to a pull-out test, peeling off, and visually observing the degree of peeling of the plating adhered to the adhesive tape. The case where the plating layer did not peel at all was accepted, and the case where the plating was peeled off to some extent was rejected.
[0086]
The plating wettability was determined by rating the unplated area ratio of the passed coil as shown below. A score of 3 or more was accepted.
4: Non-plated area ratio less than 1%
3: Non-plating area ratio 1% or more and less than 5%
2: Non-plating area ratio 5% or more and less than 10%
1: 10% or more of non-plating area ratio
[0087]
The evaluation results are as shown in Table 3. In No. 4, since the effective Al amount was outside the range of the present invention, alloying could not be performed at an appropriate alloying temperature, and the adhesion was not acceptable. In No. 5, since the effective Al amount was outside the range of the present invention, a brittle Γ phase was formed at the plated steel plate interface, and the adhesion was not acceptable. In No. 6, since the effective Al amount was outside the range of the present invention, alloying could not be performed at an appropriate alloying temperature, and the adhesion was not acceptable. In No. 7, since the effective amount of Al was outside the range of the present invention, the alloying temperature was outside the range of the present invention, and the elongation and adhesion were unacceptable. No. 8 is SiO because the air ratio of the oxidation zone is outside the scope of the present invention.2The internal oxide layer containing no carbon was formed, and adhesion and plating wettability were unacceptable.It was. NumberIssue 19 is log (PH2O / PH2) Is outside the scope of the present invention, so SiO2The external oxide layer was formed, and the adhesion and plating wettability were unacceptable.
[0088]
The products of the present invention other than these were alloyed hot-dip galvanized steel sheets having excellent plating adhesion, high strength and good workability.
Moreover, since Ni and Cu were not added to the steel plates of Nos. 20 to 23, there was a tendency for non-plating to occur more easily than Nos. 9 to 12.
[0089]
[Table 1]
[Table 2]
[Table 3]
【The invention's effect】
As described above, the present invention makes it possible to provide a high-strength alloyed hot-dip galvanized steel sheet having excellent adhesion and workability and a method for producing the same, and contributes greatly to industrial development. is there.
Claims (9)
Ｃ：０．０５〜０．１５％、
Ｓｉ：０．３〜２．５％、
Ｍｎ：１．５〜２．８％、
Ｐ：０．０３％以下、
Ｓ：０．０２％以下、
Ａｌ：０．００５〜０．５％、
Ｎ：０．００６０％以下を含有し、
残部Ｆｅおよび不可避的不純物からなり、さらに％Ｃ、％Ｓｉ、％ＭｎをそれぞれＣ、Ｓｉ、Ｍｎ含有量とした時に（％Ｍｎ）／（％Ｃ）≧１２かつ（％Ｓｉ）／（％Ｃ）≧４が満たされる高強度鋼板の上に、Ｆｅを含有し、残部がＺｎおよび不可避的不純物からなる合金化溶融亜鉛めっき層を有する鋼板において、このめっきの合金相のη相、ζ相、δ 1 相、Γ相のｄ＝１．２３７、ｄ＝１．２６、ｄ＝１．２７９、ｄ＝１．２２２のＸ線回折強度Ｉδ1、Ｉζ、Ｉη、ＩΓとＳｉ標準板のｄ＝３．１３のＸ線回折強度ＩＳｉとの比Ｉδ1／ＩＳｉ、Ｉζ／ＩＳｉ、Ｉη／ＩＳｉ、ＩΓ／ＩＳｉが、Ｉη／ＩＳｉ≦０．０００６、ＩΓ／ＩＳｉ≦０．０００６であり、Ｉδ1／ＩＳｉとＩζ／ＩＳｉの１種または２種が０．０００６以上であることを特徴とする密着性の優れた高強度合金化溶融亜鉛めっき鋼板。% By mass
C: 0.05 to 0.15%,
Si: 0.3 to 2.5%,
Mn: 1.5 to 2.8%,
P: 0.03% or less,
S: 0.02% or less,
Al: 0.005 to 0.5%,
N: 0.0060% or less,
(% Mn) / (% C) ≧ 12 and (% Si) / (% C) when the remaining Fe and unavoidable impurities are used, and when% C,% Si, and% Mn are C, Si, and Mn contents, respectively. ) In a steel plate having an alloyed hot-dip galvanized layer containing Fe and the balance consisting of Zn and inevitable impurities on a high-strength steel plate satisfying ≧ 4, the alloy phases of this plating are η phase, ζ phase, [delta] 1-phase, gamma-phase d = 1.237, d = 1.26, d = 1.279, X -ray diffraction intensity i? 1 of d = 1.222, Iζ, Iη, the IΓ and Si standard plate d = The ratios Iδ 1 / ISi, Iζ / ISi, Iη / ISi, and IΓ / ISi of the X-ray diffraction intensity ISi of 3.13 are Iη / ISi ≦ 0.0006, IΓ / ISi ≦ 0.0006, and Iδ 1 One or two of / ISi and Iζ / ISi must be 0.0006 or more Adhesion excellent high strength galvannealed steel sheet characterized.
Ｌ≧５１−０．０３５×Ｆ
を満足することを特徴とする請求項１乃至請求項３のいずれかに記載の密着性の優れた高強度合金化溶融亜鉛めっき鋼板。The relationship between tensile strength F (MPa) and elongation L (%) is
L ≧ 51−0.035 × F
The high-strength alloyed hot-dip galvanized steel sheet with excellent adhesion according to any one of claims 1 to 3, wherein:
まず、前記焼鈍処理を、
酸化帯において燃焼空気比０．９〜１．２の雰囲気中にて酸化せしめ、その後の還元帯において、水分圧と水素分圧の対数ｌｏｇ（ＰＨ ２ Ｏ／ＰＨ ２ ）が下式、
０．５〔Ｓｉ％〕−３≦ｌｏｇ（ＰＨ ２ Ｏ／ＰＨ ２ ）≦−０．８
但し、〔Ｓｉ％〕：鋼板中のＳｉ含有量（ｍａｓｓ％）
を満たす雰囲気で還元を行い、
次に前記溶融亜鉛めっき処理を、浴中有効Ａｌ濃度：０．０７〜０．０９２ｍａｓｓ％、残部がＺｎおよび不可避的不純物からなる成分組成の溶融亜鉛めっき浴中で行い、そして、前記合金化処理を、
４５０≦Ｔ≦４１０×ｅｘｐ（２×〔Ａｌ％〕）
但し、〔Ａｌ％〕：亜鉛めっき浴中の浴中有効Ａｌ濃度（ｍａｓｓ％）
を満足する温度Ｔ（℃）において行うことを特徴とする、密着性の優れた高強度合金化溶融亜鉛めっき鋼板の製造方法。A slab having a composition comprising the chemical component according to any one of claims 1 to 4 is finish-rolled at a temperature of Ar 3 or higher and subjected to cold rolling of 50 to 85%, followed by continuous hot dip galvanization. Annealing in the two-phase coexisting temperature range of ferrite and austenite at 750 ° C. or more and 880 ° C. or less in the equipment, and from the highest temperature to 650 ° C. at an average cooling rate of 0.5 to 10 ° C./s, followed by 650 ° C. to 500 ° C. Is cooled at an average cooling rate of 3 ° C./second or more, further cooled from 500 ° C. to 420 ° C. to 460 ° C. at an average cooling rate of 0.5 ° C./second or more, and from 500 ° C. to the plating bath for 25 seconds. After holding for 240 seconds or less, a hot dip galvanizing treatment is performed to form a hot dip galvanized layer on the surface of the cold rolled steel plate, and then an alloy is formed on the steel plate on which the hot dip galvanized layer is formed. In the method for producing an alloyed hot-dip galvanized steel sheet, which forms an alloyed hot-dip galvanized layer on the surface of the steel sheet by applying a chemical treatment,
First, the annealing treatment
Oxidation is performed in an atmosphere having a combustion air ratio of 0.9 to 1.2 in the oxidation zone, and in the subsequent reduction zone, the logarithm log (PH 2 O / PH 2 ) of water pressure and hydrogen partial pressure is expressed by
0.5 [Si%]-3 ≦ log (PH 2 O / PH 2 ) ≦ −0.8
However, [Si%]: Si content in the steel sheet (mass%)
Reduction in an atmosphere that satisfies
Next, the hot dip galvanizing treatment is carried out in a hot dip galvanizing bath having an effective Al concentration in the bath of 0.07 to 0.092 mass%, the balance being Zn and inevitable impurities, and the alloying treatment. The
450 ≦ T ≦ 410 × exp (2 × [Al%])
However, [Al%]: Effective Al concentration in the galvanizing bath (mass%)
A method for producing a high-strength galvannealed steel sheet with excellent adhesion, characterized in that it is carried out at a temperature T (° C.) that satisfies the following conditions.
〔Ａｌ％〕≦０．０９２−０．００１×〔Ｓｉ％〕2
但し、〔Ｓｉ％〕：鋼板中のＳｉ含有量（ｍａｓｓ％）
を満足する浴中有効Ａｌ濃度（ｍａｓｓ％）において行うことを特徴とする、密着性の優れた高強度合金化溶融亜鉛めっき鋼板の製造方法。The method for producing a high-strength galvannealed steel sheet according to claim 5, wherein the effective Al concentration in the bath is
[Al%] ≦ 0.092-0.001 × [Si%] 2
However, [Si%]: Si content in the steel sheet (mass%)
A method for producing a high-strength galvannealed steel sheet having excellent adhesion, characterized in that it is carried out at an effective Al concentration (mass%) in a bath that satisfies the requirements.
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| KR102344787B1 (en) | 2017-07-31 | 2021-12-30 | 닛폰세이테츠 가부시키가이샤 | hot dip galvanized steel |
| KR102345533B1 (en) | 2017-07-31 | 2021-12-31 | 닛폰세이테츠 가부시키가이샤 | hot dip galvanized steel |
| EP3663426A4 (en) | 2017-07-31 | 2020-11-25 | Nippon Steel Corporation | Zinc hot-dipped steel sheet |
| CN111492075B (en) | 2017-12-15 | 2021-10-12 | 日本制铁株式会社 | Steel sheet, hot-dip galvanized steel sheet, and alloyed hot-dip galvanized steel sheet |
| JP7086666B2 (en) | 2018-03-23 | 2022-06-20 | 株式会社神戸製鋼所 | Manufacturing method of alloyed hot-dip galvanized steel sheet |
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