JP3580541B2 - Surface-treated steel sheet excellent in workability and corrosion resistance of processed part and method for producing the same - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、めっき皮膜中のＡｌ含有量が２０〜９５ｍａｓｓ％の溶融Ａｌ−Ｚｎ系めっき鋼板を下地鋼板とする表面処理鋼板とその製造方法に関する。
【０００２】
【従来の技術】
めっき皮膜中にＡｌを２０〜９５ｍａｓｓ％含有する溶融Ａｌ−Ｚｎ系めっき鋼板は、特公昭４６−７１６１号に示されるように溶融亜鉛めっき鋼板に比べて優れた耐食性を示すことから、近年、建材分野を中心に需要が伸びている。
このめっき鋼板は、酸洗脱スケールした熱延鋼板又はこれをさらに冷間圧延して得られた冷延鋼板を下地鋼板とし、連続式溶融めっき設備において以下のようにして製造される。
【０００３】
連続式溶融めっき設備では、下地鋼板は還元性雰囲気に保持された焼鈍炉内で所定温度に加熱され、焼鈍と同時に鋼板表面に付着する圧延油等の除去、酸化膜の還元除去が行われた後、下端がめっき浴に浸漬されたスナウト内を通って所定濃度のＡｌを含有した溶融亜鉛めっき浴中に浸漬される。めっき浴に浸漬された鋼板はシンクロールを経由してめっき浴の上方に引き上げられた後、めっき浴上に配置されたガスワイピングノズルから鋼板の表面に向けて加圧した気体を噴射することによりめっき付着量が調整され、次いで冷却装置により冷却され、所定のめっき皮膜が形成された溶融Ａｌ−Ｚｎ系めっき鋼板が得られる。
【０００４】
連続式溶融めっき設備における焼鈍炉の熱処理条件及び雰囲気条件、めっき浴組成やめっき後の冷却速度等の操業条件は、所望のめっき品質や材質を確保するために所定の管理範囲で精度よく管理される。
上記のようにして製造されためっき鋼板のめっき皮膜は、主としてＺｎを過飽和に含有したＡｌがデンドライト凝固した部分と、残りのデンドライト間隙の部分からなっており、デンドライトはめっき皮膜の膜厚方向に積層している。このような特徴的な皮膜構造により、溶融Ａｌ−Ｚｎ系めっき鋼板は優れた耐食性を示す。
【０００５】
また、めっき浴には通常１．５ｍａｓｓ％程度のＳｉが添加されているが、このＳｉの働きにより、溶融Ａｌ−Ｚｎ系めっき鋼板はめっき皮膜／下地鋼板界面の合金相成長が抑えられ、合金相厚さは約１〜２μｍ程度である。この合金相が薄ければ薄いほど優れた耐食性を示す特徴的な皮膜構造の部分が多くなるので、合金相の成長抑制は耐食性の向上に寄与する。また、合金相はめっき皮膜よりも固く加工時にクラックの起点として作用するので、合金相の成長抑制はクラックの発生を減少させ、加工性の向上効果をもたらす。また、クラック部は下地鋼板が露出していて耐食性に劣るので、クラックの発生を減じることは加工部耐食性をも向上させる。
【０００６】
通常、めっき浴には不可避的不純物、鋼板やめっき浴中の機器等から溶出するＦｅ、合金相抑制のためのＳｉが含まれるが、それら以外にも何らかの元素が添加されている場合もあり、合金相やめっき皮膜中にはそれら元素が合金或いは単体の形で存在している。
また、溶融Ａｌ−Ｚｎ系めっき鋼板は実用に供されるに当たって溶融めっきままで使用されることは極く稀であり、通常はめっき鋼板表面に化成処理や塗装を施した表面処理鋼板として使用される。
【０００７】
【発明が解決しようとする課題】
溶融Ａｌ−Ｚｎ系めっき鋼板は、折り曲げ等の加工を施すと加工の程度によって被加工部のめっき皮膜にクラックが生じる。このめっき鋼板では、めっき皮膜／下地鋼板界面に存在する約１〜２μｍ厚の合金相がクラックの起点となり、まためっき皮膜のデンドライト間隙部がクラックの伝播経路になることから、同程度の加工を行った場合でも、同一めっき皮膜厚の溶融亜鉛めっき鋼板に比べてクラックが比較的大きく開口する傾向がある。そのため加工の程度によってはクラックが肉眼で視認され、外観を損ねるという問題がある。さらに、上述のように溶融Ａｌ−Ｚｎ系めっき鋼板は、同一めっき皮膜厚の溶融亜鉛めっき鋼板に比べて優れた耐食性を発揮するが、下地鋼板の露出したクラック部はクラックのない部分と比較して耐食性が顕著に低下するという問題もある。
【０００８】
このような問題に対して、例えば特公昭６１−２８７４８号公報には、溶融Ａｌ−Ｚｎ系めっき鋼板に所定の熱処理を施すことによって、めっき鋼板の延性を改善する方法が示されている。
しかしながら、上述したように溶融Ａｌ−Ｚｎ系めっき鋼板は表面に化成処理を施した化成処理鋼板や塗装を施した塗装鋼板として使用されるのが通常である。そして、単に折り曲げ等の加工による加工部でのクラック発生抑止の観点から、上記従来技術のようにめっき皮膜の延性を改善したとしても、必ずしも実用に供される製品としての性能、すなわち化成処理や塗装を行った表面処理鋼板としての加工性や加工部の耐食性が直ちに改善されるものではない。
【０００９】
したがって本発明の目的は、めっき皮膜中のＡｌ含有量が２０〜９５ｍａｓｓ％の溶融Ａｌ−Ｚｎ系めっき鋼板を下地鋼板とし、従来にない優れた加工性及び加工部耐食性が得られる表面処理鋼板及びその製造方法を提供することにある。
【００１０】
【課題を解決するための手段】
上記課題の解決のために本発明者らは、実用製品すなわち溶融Ａｌ−Ｚｎ系めっき鋼板に化成処理を施した表面処理鋼板としての性能に視点を定め、加工性や加工部耐食性を向上させるために最適なめっき皮膜と化成処理皮膜の構成について鋭意検討を行った。その結果、溶融Ａｌ−Ｚｎ系めっき鋼板のめっき皮膜をめっき金属が完全に凝固した状態から特定条件の熱処理を施されたものとし、且つこのめっき皮膜面に特定の化成処理皮膜を形成することにより、従来では達成できなかった極めて優れた加工性と加工部耐食性が得られることを見い出した。
【００１１】
本発明はこのような知見に基づいてなされたもので、その特徴は以下のとおりである。
[1] めっき皮膜中のＡｌ含有量が２０〜９５mass％の溶融Ａｌ−Ｚｎ系めっき鋼板の表面に化成処理皮膜を有する表面処理鋼板であって、
前記溶融Ａｌ−Ｚｎ系めっき鋼板のめっき皮膜は、めっき金属が完全に凝固した状態から１３０〜１８０℃の温度に下記(1)式で規定されるｔ１（ｈｒ）の時間内に昇温加熱した後、１３０〜１８０℃の温度範囲に７時間以上３０時間以内で且つ下記(2 ′ ) 式で規定されるｔ２（ｈｒ）よりも短かい時間保持する熱処理を経て得られためっき皮膜であり、
前記化成処理皮膜はクロメート処理によるＣｒを金属クロム換算で０．１ｍｇ／ｍ２以上１００ｍｇ／ｍ２未満含むことを特徴とする加工性と加工部耐食性に優れた表面処理鋼板。
ｔ１＝（Ｔ−３０）／１０ …… (1)
ｔ ２ ＝（２００−Ｔ）／２ …… (2 ′ )
但し Ｔ：昇温加熱する最高加熱温度（℃）
【００１３】
[2] 上記 [1] の表面処理鋼板において、化成処理皮膜が、めっき皮膜面に水性有機樹脂とクロム酸及び／又はクロム酸の一部を還元したクロム酸化合物を含むクロメート処理液を塗布した後、板温８０〜３００℃の温度で乾燥して得られた皮膜であり、且つ該皮膜中に含まれる有機樹脂量（Ａ）と金属クロム換算でのＣｒ量（Ｂ）の質量比（Ａ）／（Ｂ）が１以上２００未満であることを特徴とする加工性と加工部耐食性に優れた表面処理鋼板。
【００１４】
[3] 上記 [1] の表面処理鋼板において、化成処理皮膜が、めっき皮膜面に形成されるクロメート処理皮膜と、その上層に形成される皮膜であって、水性有機樹脂を含む処理液を塗布して板温８０〜３００℃の温度で乾燥して得られた皮膜とからなることを特徴とする加工性と加工部耐食性に優れた表面処理鋼板。
[4] 上記 [3] の表面処理鋼板において、化成処理皮膜中に含まれる全有機樹脂量（Ａ）と金属クロム換算での全Ｃｒ量（Ｂ）の質量比（Ａ）／（Ｂ）が１以上２００未満であることを特徴とする加工性と加工部耐食性に優れた表面処理鋼板。
【００１５】
[5] 上記 [1] 〜 [4]のいずれかに記載の表面処理鋼板の表面に単層又は複層の塗膜を形成したことを特徴とする塗装鋼板。
[6] めっき皮膜中のＡｌ含有量が２０〜９５mass％の溶融Ａｌ−Ｚｎ系めっき鋼板の表面に化成処理皮膜を有する表面処理鋼板の製造方法であって、
溶融めっきされためっき金属が完全に凝固しためっき皮膜に対して、１３０〜１８０℃の温度に下記(1)式で規定されるｔ１（ｈｒ）の時間内に昇温加熱した後、１３０〜１８０℃の温度範囲に７時間以上３０時間以内で且つ下記(2 ′ ) 式で規定されるｔ２（ｈｒ）よりも短かい時間保持する熱処理を実施する工程と、
ｔ１＝（Ｔ−３０）／１０ …… (1)
ｔ ２ ＝（２００−Ｔ）／２ …… (2 ′ )
但し Ｔ：昇温加熱する最高加熱温度（℃）
めっき皮膜面にクロメート処理によるＣｒを金属クロム換算で０．１ｍｇ／ｍ２以上１００ｍｇ／ｍ２未満含む化成処理皮膜を形成させる工程とを有することを特徴とする加工性と加工部耐食性に優れた表面処理鋼板の製造方法。
【００１７】
[7] 上記 [6] の製造方法において、めっき皮膜に対する熱処理を、下記(1) ， (2) のうちの少なくとも１つの段階で行うことを特徴とする加工性と加工部耐食性に優れた表面処理鋼板の製造方法。
(1) 化成処理皮膜の形成前
(2) 化成処理皮膜の形成後
【００１８】
[8] 上記 [6] 又は [7] の製造方法において、めっき皮膜面に、水性有機樹脂とクロム酸及び／又はクロム酸の一部を還元したクロム酸化合物を含むクロメート処理液を塗布した後、板温８０〜３００℃の温度で乾燥することにより、皮膜中の有機樹脂量（Ａ）と金属クロム換算でのＣｒ量（Ｂ）の質量比（Ａ）／（Ｂ）が１以上２００未満である化成処理皮膜を形成することを特徴とする加工性と加工部耐食性に優れた表面処理鋼板の製造方法。
【００１９】
[9] 上記 [6] 又は [7] の製造方法において、めっき皮膜面に、クロメート処理を施し、次いで水性有機樹脂を含む処理液を塗布して板温８０〜３００℃の温度で乾燥することにより化成処理皮膜を形成することを特徴とする加工性と加工部耐食性に優れた表面処理鋼板の製造方法。
[10] 上記 [9] の製造方法において、めっき皮膜面に、皮膜中に含まれる全有機樹脂量（Ａ）と金属クロム換算での全Ｃｒ量（Ｂ）の質量比（Ａ）／（Ｂ）が１以上２００未満である化成処理皮膜を形成することを特徴とする加工性と加工部耐食性に優れた表面処理鋼板の製造方法。
[11] 上記 [6] 〜 [10] のいずれかに記載の製造方法の工程に加えて、さらに、化成処理皮膜面に１コート又は２コート以上の塗装を施すことを特徴とする塗装鋼板の製造方法。
【００２０】
【発明の実施の形態】
本発明の表面処理鋼板は、めっき皮膜中にＡｌを２０〜９５ｍａｓｓ％含有する溶融Ａｌ−Ｚｎ系めっき鋼板を下地鋼板とする。また耐食性等の観点から、めっき皮膜中のＡｌ量より好ましい範囲は４５〜６５ｍａｓｓ％である。また、めっき皮膜のより好ましい成分組成は、Ａｌ：４５〜６５ｍａｓｓ％、Ｓｉ：０．７〜２．０ｍａｓｓ％、Ｆｅ：１０ｍａｓｓ％未満、残部が不可避的不純物を含む実質的なＺｎであり、このような組成の場合に特に優れた耐食性を発揮する。但し、この溶融Ａｌ−Ｚｎ系めっき鋼板は、そのめっき組成だけで高い加工部耐食性を得ることは難しく、後述する熱履歴（熱処理）を経ること及び上層の化成処理皮膜と組み合せることによってはじめて優れた加工部耐食性が得られる。
また、この溶融Ａｌ−Ｚｎ系めっき鋼板のめっき付着量に特に制限はないが、一般には片面当たり３０〜１２０ｇ／ｍ２程度とすることが適当である。
【００２１】
さらに、本発明の表面処理鋼板において下地鋼板となる溶融Ａｌ−Ｚｎ系めっき鋼板のめっき皮膜は、そのめっき金属が完全に凝固した状態で特定の熱処理を施したものである。すなわちこの熱処理では、溶融めっきされためっき金属が完全に凝固した状態から１３０〜１８０℃の温度に下記(1)式で規定されるｔ１（時間）の時間内に昇温加熱した後、１３０〜１８０℃の温度範囲に７時間以上３０時間以内で且つ下記 (2 ′ ) 式で規定されるｔ２（時間）よりも短かい時間保持する。
ｔ１＝（Ｔ−３０）／１０ …… (1)
ｔ ２ ＝（２００−Ｔ）／２ …… (2 ′ )
但し Ｔ：昇温加熱する最高加熱温度（℃）
【００２２】
めっき皮膜に上記のような熱処理を施した溶融Ａｌ−Ｚｎ系めっき鋼板を下地鋼板とし、そのめっき皮膜面に特定の化成処理皮膜を形成した表面処理鋼板は、極めて優れた加工性と加工部耐食性を示す。
【００２３】
上記熱処理において、めっき皮膜をそのめっき金属が完全に凝固している状態から加熱する際の加熱昇温温度（最高加熱温度）が１３０℃未満では、温度が低過ぎるためにめっき皮膜の加工性向上効果が十分に期待できない。一方、加熱昇温温度が２５０℃を超えるとめっき皮膜／下地鋼板界面の合金相が早く成長するため、却って加工性が阻害されてしまう。また、加工性をさらに厳しく考慮した場合、加熱昇温温度及びその後の保持温度は２００℃以下とすることがより好ましい。本発明では保持温度の上限を１８０℃とする。
【００２４】
また、めっき皮膜をそのめっき金属が完全に凝固している状態から１３０〜１８０℃の温度に昇温加熱するのを上記(1)式で規定されるｔ１（ｈｒ）の時間内に行うのは生産性の観点からであり、昇温加熱時間がこの条件を超えると生産性を損なう。このような昇温加熱を行う際の代表的な方法としては、連続式溶融めっき設備内に加熱機構（例えば、インダクションヒーター、熱風炉など）を設けてインラインで行う方法と、コイルに巻取ったものをオフラインでコイルごと熱処理する方法がある。前者の方法では、上記(1)式で規定されるｔ１（ｈｒ）よりも十分に短い時間で所定の温度に昇温加熱することが可能であるが、後者の方法はオフラインでコイルごと加熱するので、コイルのハンドリング、セッティング、昇温加熱等に時間を要する。したがって、生産性を考慮すると前者の方法が好ましい。勿論、熱処理方法は上述した二つの方法に限ったものではなく、どのような方法を採用しても構わない。
【００２５】
上記のような昇温加熱後、１３０〜１８０℃に保持する時間が３０時間を超えると生産性を著しく低下させるため好ましくない。一方、保持時間が、
ｔ ２ ＝（２８０−Ｔ）／３ …… (2)
上記(2)式で規定されるｔ２（ｈｒ）を超えると、めっき皮膜／下地鋼板界面の合金相が成長して加工性が阻害され、加工性をさらに厳しく考慮した場合、保持時間は上記(2′)式で規定されるｔ２（ｈｒ）よりも短かくすることが好ましい。なお、保持時間の下限は７時間とする。また、昇温加熱後の保持では、めっき鋼板の板温は必ずしも一定でなくてもよい。
【００２６】
めっき皮膜面に形成される化成処理皮膜は、クロメート処理によるＣｒを金属クロム換算で０．１ｍｇ／ｍ２以上１００ｍｇ／ｍ２未満含むものとする。上記のような特定のめっき皮膜面に対して、このような化成処理皮膜を形成することにより加工部耐食性が著しく向上する。なお、この化成処理皮膜は複層皮膜により構成されていてもよく、この場合には皮膜全体として上記Ｃｒを含んでいればよい。したがって、上記Ｃｒは複層皮膜のうちの１層のみに含まれるものであってもよいし、２層以上の皮膜に含まれるものであってもよい。
化成処理皮膜中の金属クロム換算のＣｒ量が０．１ｍｇ／ｍ２未満では加工部耐食性が十分に向上せず、一方、Ｃｒ量が１００ｍｇ／ｍ２以上では加工部耐食性の向上効果が飽和する一方で、Ｃｒ量増加によるＣｒ固定率低下により環境調和性を損う。
【００２７】
また、より好ましい化成処理皮膜としては、水性有機樹脂とクロム酸及び／又はクロム酸の一部を還元したクロム酸化合物を含むクロメート処理液を塗布した後、板温８０〜３００℃の温度で乾燥して得られた皮膜であって、且つ皮膜中に含まれる有機樹脂量（Ａ）と金属クロム換算でのＣｒ量（Ｂ）の重量比（Ａ）／（Ｂ）が１以上２００未満である化成処理皮膜である。
このように化成処理皮膜がＣｒとともに有機樹脂を含むことにより、加工部耐食性がさらに良好になる。
【００２８】
また、このような化成処理皮膜において、有機樹脂量（Ａ）と金属クロム換算でのＣｒ量（Ｂ）の質量比（Ａ）／（Ｂ）が１未満では、有機樹脂が加工部耐食性を向上させる効果が十分に発揮されない。一方、質量比（Ａ）／（Ｂ）が２００以上では、Ｃｒによる加工部耐食性の向上効果が十分に得られない。
また、化成処理皮膜を形成する際にクロメート処理液を塗布した後の乾燥温度が板温で８０℃未満では、温度が低いため適正な化成処理皮膜が形成されず、一方３００℃を超えるとめっき皮膜にさらなる熱が加わるために合金化反応が促進され、却って加工性が低下するおそれがある。
【００２９】
さらに、化成処理皮膜は、クロメート処理皮膜とその上層に形成される特定の皮膜からなることが好ましい。この上層皮膜は、水性有機樹脂を含む処理液を塗布して板温８０〜３００℃の温度で乾燥して得られた皮膜であり、化成処理皮膜をクロメート処理皮膜とその上層の上記皮膜から構成することにより、より優れた加工部耐食性が得られる。
上層皮膜を形成する際に処理液を塗布した後の乾燥温度が板温で８０℃未満では、温度が低いため適正な化成処理皮膜が形成されず、一方、３００℃を超えるとめっき皮膜にさらなる熱が加わるために合金化反応が促進され、却って加工性が低下するおそれがある。
【００３０】
この化成処理皮膜（クロメート処理皮膜＋上層皮膜）中に含まれる金属クロム換算での全Ｃｒ量は０．１ｍｇ／ｍ２以上１００ｍｇ／ｍ２未満であり、その限定理由は上述した通りである。上層皮膜中にＣｒを含有させるか否かは任意であるが、Ｃｒを含む場合には耐食性がより向上する。上層皮膜の膜厚は０．１〜５μｍ程度が好ましく、膜厚が０．１μｍ未満では加工部耐食性の改善効果が十分でなく、一方、５μｍを超えるとロールフォーミング時にロール表面にピックアップを生じるおそれがある。さらに、この化成処理皮膜は、皮膜中に含まれる全有機樹脂量（Ａ）と金属クロム換算での全Ｃｒ量（Ｂ）の質量比（Ａ）／（Ｂ）が１以上２００未満であることが好ましい。全有機樹脂量（Ａ）と金属クロム換算での全Ｃｒ量（Ｂ）の質量比（Ａ）／（Ｂ）が１未満では、有機樹脂が加工部耐食性を向上させる効果が小さく、一方、質量比（Ａ）／（Ｂ）が２００以上ではＣｒによる加工部耐食性の向上効果が小さい。
【００３１】
次に、本発明による上記表面処理鋼板の製造方法について説明する。
本発明の製造方法は、連続式溶融めっき設備などで製造されるめっき皮膜中のＡｌ含有量が２０〜９５ｍａｓｓ％の溶融Ａｌ−Ｚｎ系めっき鋼板を下地鋼板とし、その表面に化成処理皮膜を形成した表面処理鋼板の製造方法であり、溶融めっきされためっき金属が凝固した後のめっき皮膜に対して特定の熱処理を実施する工程と、めっき鋼板の表面に特定の化成処理皮膜を形成させる工程とを有する。なお、熱処理を行う溶融Ａｌ−Ｚｎ系めっき鋼板の好ましいめっき組成やめっき付着量は先に述べた通りである。
【００３２】
本発明の製造方法ではめっき鋼板のめっき皮膜面に特定の化成処理皮膜を形成させるが、めっき皮膜に対する上記特定の熱処理は、(1)化成処理皮膜の形成前、 (2) 化成処理皮膜の形成後（処理液の塗布及びその乾燥工程による皮膜の形成後）、のいずれの段階で行ってもよい。また、これらの２つの段階で行ってもよい。
これらの方式うち、(1)の方式は熱処理工程と化成処理工程の各条件をそれぞれ独立に最適化できるという利点があり、また、 (2) の方式は連続式溶融めっき設備内で全ての処理を行うのに適している。
【００３３】
上記熱処理は、連続式溶融めっき設備内に或いは同設備外に設けられた加熱又は保熱装置などにより行う。例えば、連続式溶融めっき設備内に加熱機構（例えば、インダクションヒーター、熱風炉など）を設けてインラインで連続加熱して行ってもよいし、また、コイルに巻取った後にオフラインでバッチ加熱して行ってもよい。また、めっきライン外の連続処理設備において加熱機構（例えば、インダクションヒーター、熱風炉など）により連続加熱して行ってもよい。さらには、めっきライン内や上記連続処理設備で連続加熱されためっき鋼板をコイルに巻き取った後に適当な保熱又は加熱保持を行ってもよい。但し、加熱又は保熱装置の方式、形状、規模等については特別な制限はなく、要はめっき皮膜に上記の条件で熱処理を行い得るものであればよい。
【００３４】
上述したようにこの熱処理では、めっき皮膜のめっき金属が完全に凝固した状態から１３０〜１８０℃の温度に上記(1)式で規定されるｔ１（時間）の時間内に昇温加熱した後、１３０〜１８０℃の温度範囲に７時間以上３０時間以内で且つ上記 (2 ′ ) 式で規定されるｔ２（時間）よりも短かい時間保持する。
このような熱処理の限定理由や得られる作用効果は先に述べた通りである。
【００３５】
本発明の製造方法では、めっき鋼板のめっき皮膜面に、少なくともクロメート処理を含む１又は２以上の処理を行い、Ｃｒを金属クロム換算で０．１ｍｇ／ｍ２以上１００ｍｇ／ｍ２未満含む化成処理皮膜を形成させる。この化成処理皮膜を形成する工程と上記熱処理工程との前後関係は上述した通りである。
上記クロメート処理では、クロメート処理液をめっき鋼板面に塗布し、通常、水洗することなく８０〜３００℃で乾燥処理する。
先に述べたように、この化成処理皮膜は複層皮膜により構成されていてもよく、この場合には複数の処理が順次行われる。また複層皮膜の場合には皮膜全体として上記Ｃｒを含んでいればよく、したがって、このＣｒは複層皮膜のうちの１層のみに含まれるものであってもよいし、２層以上の皮膜に含まれるものであってもよい。
【００３６】
また、化成処理皮膜の好ましい組成及び処理条件は先に述べた通りである。すなわち、特に好ましい化成処理皮膜は、水性有機樹脂とクロム酸及び／又はクロム酸の一部を還元したクロム酸化合物を含むクロメート処理液を塗布した後、板温８０〜３００℃の温度で乾燥して得られた皮膜であって、且つ皮膜中に含まれる有機樹脂量（Ａ）と金属クロム換算でのＣｒ量（Ｂ）の重量比（Ａ）／（Ｂ）が１以上２００未満である化成処理皮膜である。この場合の限定理由及び作用効果は、先に述べた通りである。
【００３７】
また、上述したようなクロメート処理後、その上層に特定の上層皮膜を形成してもよく、この場合には化成処理皮膜はクロメート処理と上層皮膜との複合皮膜となる。この化成処理皮膜（クロメート処理皮膜＋上層皮膜）中に含まれる金属クロム換算での全Ｃｒ量は０．１ｍｇ／ｍ２以上１００ｍｇ／ｍ２未満である。上層皮膜中にＣｒを含有させるか否かは任意であるが、Ｃｒを含む場合には耐食性がより向上する。上層皮膜の膜厚は０．１〜５μｍ程度が好ましい。また、この化成処理皮膜は、皮膜中に含まれる全有機樹脂量（Ａ）と金属クロム換算での全Ｃｒ量（Ｂ）の質量比（Ａ）／（Ｂ）が１以上２００未満であることが好ましい。上層皮膜は、例えば水性有機樹脂を含む処理液を塗布して板温８０〜３００℃の温度で乾燥して形成させる。なお、以上の各構成の限定理由及び作用効果は、先に述べた通りである。
以上述べた本発明の表面処理鋼板は、その表面に塗装を施すことにより塗装鋼板とすることができる。この塗装は１コート又は２コート以上（例えば、下塗り塗装−上塗り塗装）のいずれでもよい。これにより表面処理鋼板の表面に単層又は複層の塗膜が形成される。
【００３８】
【実施例】
［実施例１］
常法で製造した冷延鋼板（板厚０．５ｍｍ）を連続式溶融めっき設備に通板し、５５％Ａｌ−１．５％Ｓｉ−Ｚｎめっき浴（表１のＮｏ．１〜Ｎｏ．１１）、４０％Ａｌ−１．０％Ｓｉ−Ｚｎめっき浴（表１のＮｏ．１２）及び７０％Ａｌ−１．８％Ｓｉ−Ｚｎめっき浴（表１のＮｏ．１３）を用いて溶融めっきを行った。ラインスピードは１６０ｍ／秒とし、片面めっき付着量は鋼板間のバラツキが７５〜９０ｇ／ｍ２の範囲に収まるようにした。
このようにして得られためっき鋼板に連続式溶融めっき設備のインラインで化成処理を行った。化成処理条件は、アクリルエマルジョン樹脂とクロム酸を樹脂固形分量：Ｃｒ量＝１００：１（質量比）の割合となるように混合した処理液を、金属クロム換算でのＣｒ付着量が２０ｍｇ／ｍ２となるようにめっき鋼板面に塗布し、１２０℃で乾燥した。
【００３９】
このようにして製造した表面処理鋼板をバッチ焼鈍設備に装入し、表１に示す温度条件で熱処理を行った。このときバッチ焼鈍設備内は大気雰囲気としたが、窒素等の不活性ガス雰囲気としてもよい。
【００４０】
熱処理後の表面処理鋼板について、以下の方法により加工性と加工部耐食性を評価した。その結果を表１に示す。
（１） 加工性
表面処理鋼板を１Ｔ曲げしてこの１Ｔ曲げ先端部のクラックを観察し、以下の基準で評価した。
５：２０倍のルーペで観察してもクラックは認められない。
４：目視で観察するとクラックは認められないが、２０倍のルーペで観察するとクラックが認められる。
３：目視で観察してクラックが認められる。
２：目視で観察して大きく開口したクラックが認められる。
１：剥離を伴うクラックが生じている。
【００４１】
（２） 加工部耐食性
表面処理鋼板を３Ｔ曲げした後、５０℃、９８％ＲＨ以上の湿潤試験機に装入して１０００時間経過後の曲げ部からの錆発生状態を観察し、以下の基準で評価した。
５：異常無し
４：一部に軽度の白錆、黒錆の発生有り
３：全面に軽度の白錆、黒錆の発生有り
２：全面に著しい白錆、黒錆の発生有り
１：赤錆発生あり
【００４２】
【表１】
［実施例２］
実施例１と同じ条件で製造されためっき鋼板に連続式溶融めっき設備のインラインで化成処理を行った。化成処理条件は、アクリルエマルジョン樹脂とクロム酸を樹脂固形分量：Ｃｒ量＝１００：１（質量比）の割合となるように混合した処理液を、金属クロム換算でのＣｒ付着量が４０ｍｇ／ｍ２となるようにめっき鋼板面に塗布し、１２０℃で乾燥した。
【００４４】
このようにして製造した表面処理鋼板をバッチ焼鈍設備に装入し、表２に示す温度条件で熱処理を行った。
熱処理後の表面処理鋼板について、以下の方法により加工性と加工部耐食性を評価した。その結果を表２に示す。
（１） 加工性
表面処理鋼板を０Ｔ曲げしてこの０Ｔ曲げ先端部のクラックを観察し、以下の基準で評価した。
５：２０倍のルーペで観察してもクラックは認められない。
４：目視で観察するとクラックは認められないが、２０倍のルーペで観察するとクラックが認められる。
３：目視で観察してクラックが認められる。
２：目視で観察して大きく開口したクラックが認められる。
１：剥離を伴うクラックが生じている。
【００４５】
（２） 加工部耐食性
表面処理鋼板を３Ｔ曲げした後、５０℃、９８％ＲＨ以上の湿潤試験機に装入して２０００時間経過後の曲げ部からの錆発生状態を観察し、以下の基準で評価した。
５：異常無し
４：一部に軽度の白錆、黒錆の発生有り
３：全面に軽度の白錆、黒錆の発生有り
２：全面に著しい白錆、黒錆の発生有り
１：赤錆発生あり
【００４６】
【表２】
図１は、実施例１及び実施例２の各供試材について、めっき皮膜の熱処理における保持時間と加工性との関係を整理して示したもので、この結果から保持時間を本発明範囲とすることにより加工性が顕著に向上することが判る。
また図２は、実施例１の各供試材について加工性と加工部耐食性の評価結果を示したもので、本発明によれば優れた加工性と加工部耐食性を兼ね備えた表面処理鋼板が得られることが判る。
【００４８】
［実施例３］
実施例１と同じ条件で製造されためっき鋼板に連続式溶融めっき設備のインラインで化成処理を行った。化成処理条件は、金属クロム換算でのＣｒ付着量が２０ｍｇ／ｍ２となるようにめっき鋼板面にクロメート処理を施して８０℃で乾燥し、その上層にウレタンエマルジョン樹脂を含む処理液を塗布し、１２０℃で乾燥した。
【００４９】
このようにして製造した表面処理鋼板をバッチ焼鈍設備に装入し、表３に示す温度条件で熱処理を行った。
熱処理後の表面処理鋼板について、以下の方法により加工性と加工部耐食性を評価した。その結果を表３に示す。
（１） 加工性
表面処理鋼板を２Ｔ曲げしてこの２Ｔ曲げ先端部のクラックを観察し、以下の基準で評価した。
５：２０倍のルーペで観察してもクラックは認められない。
４：目視で観察するとクラックは認められないが、２０倍のルーペで観察するとクラックが認められる。
３：目視で観察してクラックが認められる。
２：目視で観察して大きく開口したクラックが認められる。
１：剥離を伴うクラックが生じている。
【００５０】
（２） 加工部耐食性
表面処理鋼板を３Ｔ曲げした後、５０℃、９８％ＲＨ以上の湿潤試験器に装入して２０００時間経過後の曲げ部からの錆発生状態を観察し、以下の基準で評価した。
５：異常無し
４：一部に軽度の白錆、黒錆の発生有り
３：全面に軽度の白錆、黒錆の発生有り
２：全面に著しい白錆、黒錆の発生有り
１：赤錆発生あり
【００５１】
【表３】
【発明の効果】
以上述べたように本発明の表面処理鋼板は、めっき皮膜中のＡｌ含有量が２０〜９５ｍａｓｓ％の溶融Ａｌ−Ｚｎ系めっき鋼板を下地鋼板とする表面処理鋼板でありながら極めて優れた加工性と加工部耐食性を有する。また、本発明の製造方法によれば、このような表面処理鋼板を安定して且つ高い生産性で製造することができる。
【図面の簡単な説明】
【図１】実施例１及び実施例２の各供試材について、めっき皮膜の熱処理における保持時間と加工性との関係を整理して示したグラフ
【図２】実施例１の各供試材について、加工性と加工部耐食性の評価結果を示したグラフ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface-treated steel sheet using a hot-dip Al-Zn plated steel sheet having an Al content of 20 to 95 mass% in a plating film as a base steel sheet and a method for producing the same.
[0002]
[Prior art]
A hot-dip Al-Zn coated steel sheet containing 20 to 95 mass% of Al in a plating film shows excellent corrosion resistance as compared with hot-dip galvanized steel sheet as shown in JP-B-46-7161. Demand is growing mainly in the field.
This plated steel sheet is manufactured as follows in a continuous hot-dip plating facility using a hot-rolled steel sheet subjected to pickling descaling or a cold-rolled steel sheet obtained by further cold rolling the hot-rolled steel sheet as a base steel sheet.
[0003]
In the continuous hot-dip plating equipment, the base steel sheet was heated to a predetermined temperature in an annealing furnace maintained in a reducing atmosphere, and simultaneously with annealing, removal of rolling oil and the like adhering to the steel sheet surface and reduction of the oxide film were performed. Thereafter, the lower end is immersed in a hot-dip galvanizing bath containing a predetermined concentration of Al through a snout immersed in the plating bath. After the steel sheet immersed in the plating bath is lifted above the plating bath via the sink roll, by injecting pressurized gas toward the surface of the steel plate from the gas wiping nozzle arranged on the plating bath The coating weight is adjusted, and then cooled by a cooling device to obtain a molten Al-Zn-based plated steel sheet on which a predetermined plating film is formed.
[0004]
The operating conditions such as the heat treatment conditions and atmosphere conditions of the annealing furnace in the continuous hot-dip plating equipment, the plating bath composition and the cooling rate after plating are precisely controlled within a predetermined control range in order to ensure the desired plating quality and material. You.
The plating film of the plated steel sheet manufactured as described above mainly includes a portion in which Al containing Zn in supersaturation is dendrite solidified and a portion of the remaining dendrite gap, and the dendrites are formed in the thickness direction of the plating film. Laminated. Due to such a characteristic coating structure, the hot-dip Al-Zn plated steel sheet exhibits excellent corrosion resistance.
[0005]
Also, about 1.5 mass% of Si is usually added to the plating bath, and the action of this Si suppresses the growth of the alloy phase at the interface between the plating film and the base steel sheet in the molten Al-Zn plated steel sheet. The phase thickness is about 1-2 μm. The thinner the alloy phase, the greater the number of characteristic film structures exhibiting excellent corrosion resistance. Therefore, suppressing the growth of the alloy phase contributes to the improvement of the corrosion resistance. Further, since the alloy phase is harder than the plating film and acts as a starting point of cracks during processing, suppressing the growth of the alloy phase reduces the occurrence of cracks and brings about an effect of improving workability. In addition, since the cracked portion is inferior in corrosion resistance because the base steel sheet is exposed, reducing the occurrence of cracks also improves the corrosion resistance of the processed portion.
[0006]
Usually, the plating bath contains unavoidable impurities, Fe eluted from a steel plate or equipment in the plating bath, and Si for suppressing an alloy phase, but other elements may be added with some elements, These elements are present in the alloy phase or the plating film in the form of an alloy or a simple substance.
In addition, hot-dip Al-Zn-based coated steel sheets are rarely used as hot-dip as they are put to practical use, and are usually used as surface-treated steel sheets that have been subjected to chemical conversion treatment or painting on the surface of the coated steel sheets. You.
[0007]
[Problems to be solved by the invention]
When a process such as bending is performed on a hot-dip Al-Zn-based plated steel sheet, cracks occur in the plating film of the processed portion depending on the degree of the process. In this plated steel sheet, the alloy phase having a thickness of about 1 to 2 μm existing at the interface between the plating film and the base steel sheet serves as a crack starting point, and the dendrite gap of the plating film serves as a crack propagation path. Even in the case where cracking is performed, cracks tend to open relatively large as compared with a galvanized steel sheet having the same plating film thickness. For this reason, there is a problem that the crack is visually recognized depending on the degree of processing and the appearance is impaired. Further, as described above, the hot-dip Al-Zn coated steel sheet exhibits superior corrosion resistance as compared with a hot-dip galvanized steel sheet having the same plating film thickness, but the exposed cracked portion of the base steel sheet is compared with a crack-free portion. Therefore, there is also a problem that the corrosion resistance is significantly reduced.
[0008]
To cope with such a problem, for example, Japanese Patent Publication No. 61-28748 discloses a method of improving the ductility of a plated steel sheet by subjecting a hot-dip Al-Zn-based plated steel sheet to a predetermined heat treatment.
However, as described above, the hot-dip Al-Zn-based plated steel sheet is generally used as a chemical conversion-treated steel sheet whose surface has been subjected to a chemical conversion treatment or a coated steel sheet which has been coated. And, from the viewpoint of suppressing crack generation in a processed portion simply by processing such as bending, even if the ductility of the plating film is improved as in the above-described conventional technology, the performance as a product to be practically used, that is, The workability of the coated surface-treated steel sheet and the corrosion resistance of the processed part are not immediately improved.
[0009]
Accordingly, an object of the present invention is to provide a surface-treated steel sheet having an unprecedented excellent workability and corrosion resistance in a processed part, using a hot-dip Al-Zn-based coated steel sheet having an Al content of 20 to 95 mass% in a plating film as a base steel sheet. It is to provide a manufacturing method thereof.
[0010]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors set a viewpoint on the performance as a practical product, that is, a surface-treated steel sheet obtained by subjecting a hot-dip Al-Zn-based plated steel sheet to a chemical conversion treatment, in order to improve workability and corrosion resistance of a processed part. The composition of the most suitable plating film and chemical conversion treatment film was studied diligently. As a result, the plating film of the hot-dip Al-Zn-based plated steel sheet is subjected to a heat treatment under specific conditions from a state where the plating metal is completely solidified, and by forming a specific chemical conversion coating film on the plating film surface. It has been found that extremely excellent workability and corrosion resistance of the processed portion, which could not be achieved conventionally, can be obtained.
[0011]
The present invention has been made based on such findings, and the features thereof are as follows.
[1] A surface-treated steel sheet having a chemical conversion coating on the surface of a hot-dip Al-Zn-based plated steel sheet having an Al content of 20 to 95 mass% in a plating film,
The plating film of the hot-dip Al-Zn-based plated steel sheet is from 130 to 130 from a state in which the plating metal is completely solidified.180 ° CT is defined by the following equation (1).1After heating and heating within the time of (hr), 130-180 ° COver temperature range7 hours or moreWithin 30 hours and below(2 ′ ) formulaT defined by2(Hr) is a plating film obtained through a heat treatment for holding for a shorter time than
The chemical conversion coating is obtained by converting Cr by chromate treatment to 0.1 mg / m in terms of metallic chromium.2100mg / m or more2A surface-treated steel sheet excellent in workability and corrosion resistance in a processed part, characterized by containing less than.
t1= (T-30) / 10 ... (1)
t 2 = (200-T) / 2 ... (2 ′ )
However, T: maximum heating temperature for heating (℃)
[0013]
[2] the above [1] ofIn a surface-treated steel sheet, a chemical conversion coating is applied to a plating film surface with an aqueous organic resin and a chromate treatment solution containing chromic acid and / or a chromic acid compound in which a part of chromic acid is reduced. And the mass ratio (A) / (B) of the amount of organic resin (A) contained in the film and the amount of Cr (B) in terms of metallic chromium is 1 or more. A surface-treated steel sheet having excellent workability and corrosion resistance in a processed portion, which is less than 200.
[0014]
[3] the above [1] ofIn a surface-treated steel sheet, a chemical conversion treatment film is a chromate treatment film formed on a plating film surface and a film formed on the chromate treatment film, and a treatment solution containing an aqueous organic resin is applied, and the plate temperature is 80 to 300 ° C. A surface-treated steel sheet having excellent workability and corrosion resistance in a processed part, comprising a film obtained by drying at a temperature of
[Four] the above [3] ofIn the surface-treated steel sheet, the mass ratio (A) / (B) of the total amount of organic resin (A) contained in the chemical conversion coating to the total amount of Cr (B) in terms of metallic chromium is 1 or more and less than 200. Surface treated steel sheet with excellent workability and corrosion resistance in the processed part.
[0015]
[Five] the above [1] ~ [Four]A coated steel sheet wherein a single-layer or multiple-layer coating film is formed on the surface of the surface-treated steel sheet according to any one of the above.
[6] A method for producing a surface-treated steel sheet having a chemical conversion treatment film on the surface of a hot-dip Al-Zn-based plated steel sheet having an Al content of 20 to 95 mass% in a plating film,
For the plating film where the hot-dip plated metal is completely solidified, 130 to180 ° CT is defined by the following equation (1).1After heating and heating within the time of (hr), 130-180 ° COver temperature range7 hours or
t1= (T-30) / 10 ... (1)
t 2 = (200-T) / 2 ... (2 ′ )
However, T: maximum heating temperature for heating (℃)
0.1mg / m of Cr by chromate treatment on the plating film surface in terms of metallic chromium2100mg / m or more2Forming a chemical conversion coating containing less than 10% by weight. A method for producing a surface-treated steel sheet having excellent workability and corrosion resistance in a processed portion.
[0017]
[7] the above [6] ofIn the manufacturing method, the heat treatment for the plating film(1) , (2) ofA method for producing a surface-treated steel sheet having excellent workability and corrosion resistance in a worked portion, wherein the method is performed in at least one of the steps.
(1) Before formation of chemical conversion coating
(2) After formation of chemical conversion coating
[0018]
[8] the above [6] Or [7] ofIn the production method, after applying a chromate treatment solution containing an aqueous organic resin and chromic acid and / or a chromic acid compound in which a part of chromic acid has been reduced to the plating film surface, the plate is dried at a temperature of 80 to 300 ° C. By this, a chemical conversion treatment film is formed in which the mass ratio (A) / (B) of the amount of organic resin (A) in the film to the amount of Cr (B) in terms of chromium metal is 1 or more and less than 200. Of surface-treated steel sheet with excellent workability and corrosion resistance in the processed part.
[0019]
[9] the above [6] Or [7] ofThe manufacturing method is characterized in that a chemical conversion treatment film is formed by subjecting a plating film surface to a chromate treatment, then applying a treatment liquid containing an aqueous organic resin and drying at a plate temperature of 80 to 300 ° C. A method for producing surface-treated steel sheets with excellent workability and corrosion resistance in the processed part.
[Ten] the above [9] ofIn the production method, the mass ratio (A) / (B) of the total amount of organic resin (A) contained in the coating and the total amount of Cr (B) in terms of metallic chromium is 1 or more and less than 200 on the plating film surface. A method for producing a surface-treated steel sheet having excellent workability and corrosion resistance in a processed portion, characterized by forming a chemical conversion coating.
[11] the above [6] ~ [Ten] ofA method for producing a coated steel sheet, wherein one or more coatings are further applied to the surface of the chemical conversion treatment film in addition to the steps of the production method described in any one of the above.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
The surface-treated steel sheet of the present invention uses a hot-dip Al-Zn-based coated steel sheet containing 20 to 95 mass% of Al in a plating film as a base steel sheet. From the viewpoint of corrosion resistance and the like, a more preferable range than the Al content in the plating film is 45 to 65 mass%. Further, a more preferable component composition of the plating film is Al: 45 to 65 mass%, Si: 0.7 to 2.0 mass%, Fe: less than 10 mass%, and the balance is substantially Zn containing unavoidable impurities. Particularly excellent corrosion resistance is exhibited in such a composition. However, it is difficult for this hot-dip Al-Zn-based plated steel sheet to obtain high corrosion resistance in the processed portion only by its plating composition. Corrosion resistance of the processed part is obtained.
Although there is no particular limitation on the coating weight of the hot-dip Al-Zn-based steel sheet, it is generally 30 to 120 g / m2 per side.2Is appropriate.
[0021]
Furthermore, in the surface-treated steel sheet of the present invention, the plating film of the hot-dip Al-Zn-based coated steel sheet serving as the base steel sheet has been subjected to a specific heat treatment in a state where the plated metal is completely solidified. In other words, in this heat treatment, the plated metal that has been hot-dip130~180 ° CT is defined by the following equation (1).1After heating and heating within the time of (hour),180 ° COver temperature range7 hours or
t1= (T-30) / 10 ... (1)
t 2 = (200-T) / 2 ... (2 ′ )
However, T: maximum heating temperature for heating (℃)
[0022]
PlatingThe surface-treated steel sheet in which the coating is subjected to the above heat treatment as described above is used as a base steel sheet, and a specific chemical conversion coating is formed on the surface of the plated film, and has extremely excellent workability and corrosion resistance in the processed part. Show.
[0023]
In the above heat treatment, if the heating temperature (maximum heating temperature) when the plating film is heated from a state in which the plating metal is completely solidified is less than 130 ° C., the temperature is too low and the workability of the plating film is improved. The effect cannot be expected sufficiently. On the other hand, if the heating temperature is higher than 250 ° C., the alloy phase at the interface between the plating film and the base steel sheet grows quickly, which impairs the workability. Further, when workability is more strictly considered, the heating temperature and the subsequent holding temperature are more preferably 200 ° C. or less.In the present invention, the upper limit of the holding temperature is set to 180 ° C.
[0024]
Further, the plating film is changed from a state in which the plating metal is completely solidified to 130 to180 ° CThe heating to the temperature is performed by the time t defined by the above equation (1).1Performing within the time (hr) is from the viewpoint of productivity. If the heating time exceeds this condition, productivity is impaired. As a typical method of performing such heating and heating, there are a method in which a heating mechanism (for example, an induction heater and a hot blast stove is provided) in a continuous hot-dip plating facility and an in-line method, and a method in which a coil is wound around a coil. There is a method of heat-treating the whole product offline with the coil. In the former method, t defined by the above equation (1)1Although it is possible to raise the temperature to a predetermined temperature in a time sufficiently shorter than (hr), the latter method heats the entire coil off-line, so that time is required for handling, setting, heating and heating the coil. It costs. Therefore, the former method is preferable in consideration of productivity. Of course, the heat treatment method is not limited to the two methods described above, and any method may be employed.
[0025]
After heating as described above,180 ° CIf the holding time exceeds 30 hours, the productivity is significantly reduced, which is not preferable. Meanwhile, the holding timeBut,
t 2 = (280-T) / 3 ... (2)
the aboveT defined by equation (2)2If (hr) is exceeded, the alloy phase at the interface between the plating film and the base steel sheet grows and the workability is impaired.ProcessingWhen the characteristics are more strictly considered, the holding time is defined by the above equation (2 ′).2It is preferable to make it shorter than (hr). The lower limit of the holding timeIs 7 hours.Further, in the holding after the heating by heating, the plate temperature of the plated steel sheet does not necessarily have to be constant.
[0026]
The chemical conversion film formed on the plating film surface is obtained by converting Cr by chromate treatment to 0.1 mg / m in terms of metal chromium.2100mg / m or more2Less than. By forming such a chemical conversion coating on the specific plating film surface as described above, the corrosion resistance of the processed portion is significantly improved. The chemical conversion coating may be composed of a multi-layer coating, and in this case, it is sufficient that the entire coating contains the Cr. Therefore, the above Cr may be contained in only one layer of the multi-layer coating, or may be contained in two or more coatings.
The amount of Cr in terms of metallic chromium in the chemical conversion coating is 0.1 mg / m2If it is less than 10, the corrosion resistance of the processed portion is not sufficiently improved, while the Cr content is 100 mg / m2Above, the effect of improving the corrosion resistance of the processed portion is saturated, but the environmental harmony is impaired due to the decrease in the Cr fixing rate due to the increase in the Cr amount.
[0027]
Further, as a more preferable chemical conversion treatment film, after applying an aqueous organic resin and a chromate treatment solution containing chromic acid and / or a chromic acid compound in which a part of chromic acid is reduced, drying is performed at a plate temperature of 80 to 300 ° C. Wherein the weight ratio (A) / (B) of the amount of organic resin (A) contained in the film to the amount of Cr (B) in terms of metallic chromium is 1 or more and less than 200. It is a chemical conversion coating.
When the chemical conversion coating contains an organic resin together with Cr, the corrosion resistance of the processed portion is further improved.
[0028]
In such a chemical conversion coating, if the mass ratio (A) / (B) of the amount of the organic resin (A) to the amount of Cr (B) in terms of chromium metal is less than 1, the organic resin improves the corrosion resistance of the processed portion. Effect is not sufficiently exhibited. On the other hand, mass ratio (A) / (B)ButIf it is 200 or more, the effect of improving the corrosion resistance of the processed portion by Cr cannot be sufficiently obtained.
If the drying temperature after applying the chromate treatment liquid at the time of forming the chemical conversion coating film is less than 80 ° C at the plate temperature, an appropriate chemical conversion coating film cannot be formed due to the low temperature. Since additional heat is applied to the film, the alloying reaction is accelerated, and the workability may be reduced.
[0029]
Further, it is preferable that the chemical conversion treatment film comprises a chromate treatment film and a specific film formed thereon. This upper layer coating is a coating obtained by applying a treatment liquid containing an aqueous organic resin and drying at a plate temperature of 80 to 300 ° C. The chemical conversion coating is composed of a chromate treatment coating and the above-mentioned upper coating. By doing so, more excellent corrosion resistance of the processed portion can be obtained.
If the drying temperature after applying the treatment liquid when forming the upper layer film is less than 80 ° C at the plate temperature, an appropriate chemical conversion film is not formed because the temperature is low. Since the heat is applied, the alloying reaction is accelerated, and the workability may be reduced.
[0030]
The total amount of Cr contained in the chemical conversion coating (chromate coating + upper coating) in terms of metallic chromium is 0.1 mg / m2.2100mg / m or more2And the reason for the limitation is as described above. Whether or not Cr is contained in the upper layer coating is optional, but when Cr is contained, the corrosion resistance is further improved. The thickness of the upper layer film is preferably about 0.1 to 5 μm. If the thickness is less than 0.1 μm, the effect of improving the corrosion resistance of the processed portion is not sufficient. On the other hand, if the thickness exceeds 5 μm, pickup may occur on the roll surface during roll forming. There is. Further, in this chemical conversion coating, the mass ratio (A) / (B) of the total amount of organic resin (A) contained in the coating to the total amount of Cr (B) in terms of metallic chromium is 1 or more and less than 200. Is preferred. When the mass ratio (A) / (B) of the total amount of organic resin (A) to the total amount of Cr (B) in terms of metallic chromium is less than 1, the effect of the organic resin to improve the corrosion resistance of the processed part is small, while the mass Ratio (A) / (B)ButIf it is 200 or more, the effect of improving the corrosion resistance of the processed portion by Cr is small.
[0031]
Next, a method for producing the above-mentioned surface-treated steel sheet according to the present invention will be described.
The production method of the present invention uses a hot-dip Al-Zn plated steel sheet having an Al content of 20 to 95 mass% in a plating film manufactured by a continuous hot-dip plating facility or the like as a base steel sheet and forms a chemical conversion coating on the surface thereof. A step of performing a specific heat treatment on the plating film after the hot-dip plated metal has solidified, and a step of forming a specific chemical conversion coating on the surface of the plated steel sheet. Having. The preferred plating composition and the coating weight of the hot-dip Al-Zn-based coated steel sheet to be subjected to the heat treatment are as described above.
[0032]
In the production method of the present invention, a specific chemical conversion treatment film is formed on the plating film surface of the plated steel sheet, but the specific heat treatment for the plating film is(1)Before formation of chemical conversion coating, (2) Chemical formationIt may be performed at any stage after the formation of the treatment film (after the application of the treatment liquid and the formation of the film by the drying process). Also theseThe twoIt may be performed in stages.
Of these methods,(1)The method has the advantage that each condition of the heat treatment step and the chemical conversion treatment step can be independently optimized., (2) ofThe method is suitable for performing all processes in a continuous hot-dip plating facilityI have.
[0033]
The heat treatment is performed by a heating or heat retaining device provided inside or outside the continuous hot-dip plating facility. For example, a heating mechanism (e.g., induction heater, hot blast stove, etc.) may be provided in the continuous hot-dip plating equipment to perform continuous heating in-line, or may be batch-heated off-line after winding on a coil. May go. Further, the heating may be performed by continuous heating using a heating mechanism (for example, an induction heater or a hot blast stove) in a continuous processing facility outside the plating line. Furthermore, after the plated steel sheet continuously heated in the plating line or the continuous processing facility is wound up into a coil, appropriate heat retention or heat retention may be performed. However, there is no special restriction on the method, shape, scale, etc. of the heating or heat retaining device, and it is essential that the heat treatment be performed on the plating film under the above conditions.
[0034]
As described above, in this heat treatment, the plating metal of the plating film is completely solidified.130~180 ° CThe temperature is defined by t defined by the above equation (1).1After heating and heating within the time of (hour),180 ° COver temperature range7 hours or
The reasons for limiting such heat treatment and the effects obtained are as described above.
[0035]
In the production method of the present invention, the plating film surface of the plated steel sheet is subjected to one or more treatments including at least a chromate treatment, and Cr is converted to 0.1 mg / m in terms of metallic chromium.2100mg / m or more2A chemical conversion coating containing less than is formed. The relationship between the step of forming the chemical conversion coating and the heat treatment step is as described above.
In the above-mentioned chromate treatment, a chromate treatment liquid is applied to the surface of a plated steel sheet, and usually dried at 80 to 300 ° C without washing with water.
As described above, this chemical conversion treatment film may be composed of a multilayer film, and in this case, a plurality of treatments are sequentially performed. In the case of a multilayer coating, the above-mentioned Cr may be contained as a whole in the coating. Therefore, this Cr may be contained in only one of the multilayer coatings, or may be a coating of two or more layers. May be included.
[0036]
The preferred composition and treatment conditions of the chemical conversion treatment film are as described above. That is, a particularly preferred chemical conversion treatment film is formed by applying a chromate treatment solution containing an aqueous organic resin and chromic acid and / or a chromic acid compound in which a part of chromic acid is reduced, and then drying at a plate temperature of 80 to 300 ° C. Wherein the weight ratio (A) / (B) of the amount of organic resin (A) contained in the film to the amount of Cr in terms of chromium metal (B) is 1 or more and less than 200. It is a treated film. The reason for limitation and the operation and effect in this case are as described above.
[0037]
Further, after the above-described chromate treatment, a specific upper film may be formed on the upper layer, and in this case, the chemical conversion film is a composite film of the chromate treatment and the upper film. The total amount of Cr contained in the chemical conversion coating (chromate coating + upper coating) in terms of metallic chromium is 0.1 mg / m2.2100mg / m or more2Is less than. Whether or not Cr is contained in the upper layer coating is optional, but when Cr is contained, the corrosion resistance is further improved. The thickness of the upper layer film is preferably about 0.1 to 5 μm. Further, in this chemical conversion coating, the mass ratio (A) / (B) of the total amount of organic resin (A) contained in the coating to the total amount of Cr (B) in terms of metallic chromium is 1 or more and less than 200. Is preferred. The upper layer film is formed by applying a treatment liquid containing, for example, an aqueous organic resin and drying at a plate temperature of 80 to 300 ° C. The reasons for limitation and the effects of each of the above components are as described above.
The above-described surface-treated steel sheet of the present invention can be made into a coated steel sheet by coating the surface thereof. This coating may be one coat or two or more coats (for example, undercoating-overcoating). Thereby, a single-layer or multiple-layer coating film is formed on the surface of the surface-treated steel sheet.
[0038]
【Example】
[Example 1]
A cold-rolled steel sheet (sheet thickness: 0.5 mm) manufactured by an ordinary method was passed through a continuous hot-dip plating facility, and a 55% Al-1.5% Si-Zn plating bath (No. 1 to No. 11 in Table 1) was used. ), Hot-dip plating using a 40% Al-1.0% Si-Zn plating bath (No. 12 in Table 1) and a 70% Al-1.8% Si-Zn plating bath (No. 13 in Table 1). Was done. The line speed is 160 m / sec, and the coating weight on one side is 75 to 90 g / m, which is uneven between steel sheets.2In the range.
The coated steel sheet thus obtained was subjected to a chemical conversion treatment in a continuous hot-dip plating facility in-line. Chemical conversion treatment conditions are as follows: a treatment liquid in which an acrylic emulsion resin and chromic acid are mixed at a ratio of resin solid content: Cr amount = 100: 1 (mass ratio), and a Cr adhesion amount in terms of metal chromium of 20 mg / m 2.2And dried at 120 ° C.
[0039]
The surface-treated steel sheet produced in this manner was charged into a batch annealing facility, and heat-treated under the temperature conditions shown in Table 1. At this time, the inside of the batch annealing equipment was set to the air atmosphere, but may be set to an inert gas atmosphere such as nitrogen.
[0040]
For the surface-treated steel sheet after the heat treatment, the workability and the corrosion resistance of the processed portion were evaluated by the following methods. Table 1 shows the results.
(1) Workability
The surface-treated steel sheet was bent by 1T, cracks at the tip of the 1T bending were observed, and evaluated according to the following criteria.
No cracks were observed even when observed with a 5:20 loupe.
4: Cracks were not observed when visually observed, but cracks were observed when observed with a 20-power loupe.
3: Cracks are observed by visual observation.
2: A large opening crack is observed by visual observation.
1: A crack accompanied by peeling has occurred.
[0041]
(2) Corrosion resistance of processed part
After the surface-treated steel sheet was bent by 3T, it was charged into a wet test machine at 50 ° C. and 98% RH or higher, and the state of rust generation from the bent portion after 1000 hours had passed was evaluated.
5: No abnormality
4: Some white rust and black rust occurred
3: Mild white rust and black rust occurred on the entire surface
2: Significant white rust and black rust occurred on the entire surface
1: Red rust occurred
[0042]
[Table 1]
[Example 2]
The coated steel sheet manufactured under the same conditions as in Example 1 was subjected to a chemical conversion treatment in-line in a continuous hot-dip plating facility. The chemical conversion treatment conditions were as follows: a treatment liquid in which an acrylic emulsion resin and chromic acid were mixed at a ratio of resin solid content: Cr amount = 100: 1 (mass ratio), and a Cr adhesion amount in terms of metal chromium of 40 mg /
[0044]
The surface-treated steel sheet manufactured as described above was charged into a batch annealing facility, and heat-treated under the temperature conditions shown in Table 2.
For the surface-treated steel sheet after the heat treatment, the workability and the corrosion resistance of the processed portion were evaluated by the following methods. Table 2 shows the results.
(1) Workability
The surface-treated steel sheet was bent by 0T, and the crack at the tip of the 0T bending was observed, and evaluated according to the following criteria.
No cracks were observed even when observed with a 5:20 loupe.
4: Cracks were not observed when visually observed, but cracks were observed when observed with a 20-power loupe.
3: Cracks are observed by visual observation.
2: A large opening crack is observed by visual observation.
1: A crack accompanied by peeling has occurred.
[0045]
(2) Corrosion resistance of processed part
After the surface-treated steel sheet was bent by 3T, it was placed in a wet test machine at 50 ° C. and 98% RH or higher, and the state of rust generation from the bent portion after 2,000 hours had passed was evaluated.
5: No abnormality
4: Some white rust and black rust occurred
3: Mild white rust and black rust occurred on the entire surface
2: Significant white rust and black rust occurred on the entire surface
1: Red rust occurred
[0046]
[Table 2]
FIG. 1 shows the relationship between the holding time and the workability in the heat treatment of the plating film for each of the test materials of Example 1 and Example 2, and from this result, the holding time was defined as the range of the present invention. It can be seen that the workability is remarkably improved by doing so.
FIG. 2 shows the evaluation results of the workability and the corrosion resistance of the processed part of each test material of Example 1. According to the present invention, a surface-treated steel sheet having both excellent workability and corrosion resistance of the processed part is obtained. You can see that it is.
[0048]
[Example 3]
The coated steel sheet manufactured under the same conditions as in Example 1 was subjected to a chemical conversion treatment in-line in a continuous hot-dip plating facility. Chemical conversion treatment conditions are as follows: Cr adhesion amount in terms of chromium metal is 20 mg / m2Then, the surface of the plated steel sheet was subjected to a chromate treatment and dried at 80 ° C., and a treatment liquid containing a urethane emulsion resin was applied to the upper layer and dried at 120 ° C.
[0049]
The surface-treated steel sheet manufactured in this manner was charged into a batch annealing facility, and heat-treated under the temperature conditions shown in Table 3.
For the surface-treated steel sheet after the heat treatment, the workability and the corrosion resistance of the processed portion were evaluated by the following methods. Table 3 shows the results.
(1) Workability
The surface-treated steel sheet was bent by 2T, cracks at the tip of the 2T bending were observed, and evaluated according to the following criteria.
No crack is observed even when observed with a 5:20 loupe.
4: Cracks were not observed when visually observed, but cracks were observed when observed with a 20-fold loupe.
3: Cracks are observed by visual observation.
2: A large opening crack is observed by visual observation.
1: A crack accompanied by peeling has occurred.
[0050]
(2) Corrosion resistance of processed part
After the surface-treated steel sheet was bent by 3T, it was placed in a wet tester at 50 ° C. and 98% RH or higher, and the state of rust generation from the bent portion after lapse of 2,000 hours was observed and evaluated according to the following criteria.
5: No abnormality
4: Some white rust and black rust occurred
3: Mild white rust and black rust occurred on the entire surface
2: Significant white rust and black rust occurred on the entire surface
1: Red rust occurred
[0051]
[Table 3]
【The invention's effect】
As described above, the surface-treated steel sheet of the present invention has extremely excellent workability even though it is a surface-treated steel sheet using a hot-dip Al-Zn-based plated steel sheet having an Al content of 20 to 95 mass% in a plating film as a base steel sheet. It has corrosion resistance in the processed part. Moreover, according to the manufacturing method of the present invention, such a surface-treated steel sheet can be manufactured stably and with high productivity.
[Brief description of the drawings]
FIG. 1 is a graph summarizing the relationship between the holding time and the workability in heat treatment of a plating film for each test material of Example 1 and Example 2.
FIG. 2 is a graph showing the evaluation results of workability and corrosion resistance of a processed portion of each test material of Example 1.
Claims (11)
前記溶融Ａｌ−Ｚｎ系めっき鋼板のめっき皮膜は、めっき金属が完全に凝固した状態から１３０〜１８０℃の温度に下記(1)式で規定されるｔ１（ｈｒ）の時間内に昇温加熱した後、１３０〜１８０℃の温度範囲に７時間以上３０時間以内で且つ下記(2 ′ ) 式で規定されるｔ２（ｈｒ）よりも短かい時間保持する熱処理を経て得られためっき皮膜であり、
前記化成処理皮膜はクロメート処理によるＣｒを金属クロム換算で０．１ｍｇ／ｍ２以上１００ｍｇ／ｍ２未満含むことを特徴とする加工性と加工部耐食性に優れた表面処理鋼板。
ｔ１＝（Ｔ−３０）／１０ …… (1)
ｔ ２ ＝（２００−Ｔ）／２ …… (2 ′ )
但し Ｔ：昇温加熱する最高加熱温度（℃）A surface-treated steel sheet having a chemical conversion treatment film on the surface of a hot-dip Al-Zn-based plated steel sheet having an Al content of 20 to 95 mass% in a plating film,
The plating film of the hot-dip Al—Zn-based plated steel sheet is heated and heated to a temperature of 130 to 180 ° C. within a time t 1 (hr) defined by the following formula (1) from a state in which the plated metal is completely solidified. After that, the plating film obtained through a heat treatment that is maintained in a temperature range of 130 to 180 ° C. for 7 hours to 30 hours and shorter than t 2 (hr) defined by the following formula (2 ′ ) Yes,
The chemical conversion film excellent surface treated steel sheet in workability and the processing unit corrosion, characterized in that it comprises less than 100mg / m 2 0.1mg / m 2 or more reckoned as metal chromium to Cr by chromate treatment.
t 1 = (T−30) / 10 (1)
t 2 = (200−T) / 2 (2 ′ )
However, T: maximum heating temperature for heating (℃)
溶融めっきされためっき金属が完全に凝固しためっき皮膜に対して、１３０〜１８０℃の温度に下記(1)式で規定されるｔ１（ｈｒ）の時間内に昇温加熱した後、１３０〜１８０℃の温度範囲に７時間以上３０時間以内で且つ下記(2 ′ ) 式で規定されるｔ２（ｈｒ）よりも短かい時間保持する熱処理を実施する工程と、
ｔ１＝（Ｔ−３０）／１０ …… (1)
ｔ ２ ＝（２００−Ｔ）／２ …… (2 ′ )
但し Ｔ：昇温加熱する最高加熱温度（℃）
めっき皮膜面にクロメート処理によるＣｒを金属クロム換算で０．１ｍｇ／ｍ２以上１００ｍｇ／ｍ２未満含む化成処理皮膜を形成させる工程とを有することを特徴とする加工性と加工部耐食性に優れた表面処理鋼板の製造方法。A method for producing a surface-treated steel sheet having a chemical conversion treatment film on the surface of a hot-dip Al-Zn-based plated steel sheet having an Al content of 20 to 95 mass% in a plating film,
After the hot-dip plating metal is completely solidified, the plating film is heated to a temperature of 130 to 180 ° C. within a time t 1 (hr) defined by the following equation (1), and then heated to a temperature of 130 to 180 ° C. Performing a heat treatment in a temperature range of 180 ° C. for 7 hours to 30 hours and for a time shorter than t 2 (hr) defined by the following formula (2 ′ ) ;
t 1 = (T−30) / 10 (1)
t 2 = (200−T) / 2 (2 ′ )
However, T: maximum heating temperature for heating (℃)
The Cr by chromate treatment on the plating film surface has excellent workability and the processing unit corrosion, characterized in that a step of forming a chemical conversion film containing less than 0.1 mg / m 2 or more 100 mg / m 2 reckoned as metal chromium Manufacturing method of surface treated steel sheet.
(1) 化成処理皮膜の形成前
(2) 化成処理皮膜の形成後The heat treatment of the plating film, the following (1), the manufacturing method of the excellent surface-treated steel sheet in workability and the processing portion corrosion resistance according to claim 6, characterized in that at least one stage of (2).
(1) Before formation of chemical conversion coating
(2) After formation of chemical conversion coating
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| JP2005264188A (en) * | 2004-03-16 | 2005-09-29 | Nippon Steel Corp | HOT DIP Zn-Al ALLOY PLATED STEEL HAVING EXCELLENT BENDABILITY, AND ITS MANUFACTURING METHOD |
| KR20120016180A (en) * | 2005-09-01 | 2012-02-22 | 신닛뽄세이테쯔 카부시키카이샤 | Hot dip zn-al based alloy plated steel product excellent in bending workability and method for production thereof |
| JP2008156729A (en) * | 2006-12-26 | 2008-07-10 | Nisshin Steel Co Ltd | Zn-Al-BASED PLATING-COATED STEEL SHEET EXCELLENT IN UNBENDING RESISTANCE, AND ITS PRODUCTION METHOD |
| JP6704669B1 (en) * | 2019-08-29 | 2020-06-03 | Ｊｆｅ鋼板株式会社 | Hot-dip Al-Zn alloy plated steel sheet having excellent corrosion resistance in worked part and method for producing the same |
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