JP2004060051A

JP2004060051A - Surface treating composition for plated steel member having excellent corrosion resistance after heating and environmental suitability, method for producing plated steel member, and plated steel member

Info

Publication number: JP2004060051A
Application number: JP2003156515A
Authority: JP
Inventors: Masato Nakazawa; 仲澤　眞人; Takaharu Maekawa; 前川　敬治; Minoru Hattori; 服部　実; Takashi Fujimoto; 藤本　貴士
Original assignee: Nippon Denko Co Ltd; Nippon Steel Corp
Current assignee: Nippon Denko Co Ltd; Nippon Steel Corp
Priority date: 2002-06-05
Filing date: 2003-06-02
Publication date: 2004-02-26

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plated steel member at a low cost, which can widely be applied to use for house appliances/building materials/automobiles or the like, has excellent corrosion resistance after heating and has no elution of hexavalent chromium being an environmental load substance at all. <P>SOLUTION: In the method for producing a plated steel member having excellent corrosion resistance after heating and environmental suitability, a composition comprising partially reduced chromic acid, a phosphoric compound and a nitric compound as essential components, and having the relations in the following inequalities (I) to (III) among the reduction ratio of chromium (X) in the partially reduced chromic acid and the concentration in a bath of each component is applied to a plated steel member, and drying is performed: inequality (I) is 85(%)≤X; inequality (II) is Y≤1.9 provided that Y=(HNO<SB>3</SB>/CrO<SB>3</SB>)+(H<SB>3</SB>PO<SB>4</SB>/CrO<SB>3</SB>); and inequality (III) is Y≥4.5-X/25. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、家電・建材・自動車等の用途に広く適用可能であって、加熱後の耐食性に優れ、かつ環境負荷物質である６価クロムの溶出がゼロであるめっき鋼材と、該めっき鋼材の製造方法、ならびに、これらに用いる加熱後耐食性、環境適合性に優れためっき鋼材用表面処理組成物に関する。
【０００２】
【従来の技術】
【特許文献１】特開平０６−１７９９８１号公報
【特許文献２】特開平０７−２１３９９４号公報
【特許文献３】特開平０８−３３７８８４号公報
【特許文献４】特開２０００−２１９９７６号公報
【０００３】
家電・建材製品や自動車部材用のめっき鋼材においては、防錆性の向上を目的としてクロメート処理が施される場合がある。これらのうち、加工時や使用時に高温にさらされるもの、例えば、自動車マフラー、暖房機器、ブラウン管ヒートシュリンクバンドなどに用いられる素材については、さらに耐熱性、加熱後耐食性が要求される。一方、昨今の環境問題への関心の高まりや国内外の法規制、自主規制により、素材からの６価クロムの溶出をなくすことが要求されている。これらの要求に答えるためには、
（Ａ）クロメートと同等の耐食性、耐熱性を有する３価クロム処理
（Ｂ）クロメートと同等の耐食性、耐熱性を有する非クロム処理
の少なくともいずれかを、できるだけ安価に提供する必要がある。
【０００４】
クロメート処理はそれ自体、めっき鋼板の耐食性、耐熱性を高度に達成しうるものである。しかしそれ以外にも、めっきの種類や用途に応じて、耐熱、耐食に関する従来技術が複数あり、例えば、特開平０６−１７９９８１号公報、特開平０７−２１３９９４号公報、特開平０８−３３７８８４号公報、特開２０００−２１９９７６号公報などが例示できる。このうち特開平０６−１７９９８１号公報には、めっき鋼板にクロメート処理を行い、このうえにシリカとアルカリ金属酸化物からなるセラミック皮膜を設けた耐熱、耐食性鋼板が開示されている。特開平０７−２１３９９４号公報には、Ａｌ−Ｚｎ　合金めっきまたはＡｌめっき鋼板の表面に、化成処理層を介して、ストロンチウムクロメートを含有するＰＥＳ　などの樹脂層を設けた塗装鋼板が開示されている。また、特開平０８−３３７８８４号公報には、Ａｌ−Ｚｎ　合金めっきまたはＡｌめっき鋼板を、クロム還元率が３０〜７０％の部分還元クロム酸と、りん酸、シリカ、ホスホン酸からなる組成物で表面処理して得られる耐食性、耐熱性に優れたクロメート処理鋼板が開示されている。特開２０００−２１９９７６号公報では、亜鉛合金めっき鋼板の表面に、クロメートを含有せず、チオカルボニル基含有化合物等を含有する水ガラスの皮膜層を設けた、非クロム型耐熱鋼板が開示されている。
【０００５】
【発明が解決しようとする課題】
しかしながら、これらの従来技術には課題がある。
まず特開平０６−１７９９８１号公報、およびこれに類する技術においては、クロメート処理として塗布型クロメートを使用すると６価Ｃｒの溶出が避けられず、電解型クロメートを使用すると、加熱後耐食性が塗布型クロメート処理に及ばない。また、２層皮膜処理であるため、製造上の制約もある。特開平０７−２１３９９４号公報の技術においては、３層皮膜処理であるうえ、高価な耐熱性樹脂を厚膜で塗布する必要があることから、きわめてコストが高く、汎用に適さない。また、ストロンチウムクロメートを含有するため６価Ｃｒの溶出も見られる。特開平０８−３３７８８４号公報の技術は、クロム還元率が３０〜７０％であるため、加熱後耐食性には優れるものの、６価Ｃｒの溶出は避けられない。特開２０００−２１９９７６号公報の技術は、クロムを含有しないため６価Ｃｒ溶出の問題は無いが、加熱後耐食性がクロメートには及ばず、また水ガラスはクロメートほどは安価でない。
【０００６】
すなわち、従来技術においては、加熱後耐食性を確保しつつ６価クロムの溶出が無く、しかも製造が容易で皮膜コストも安いものは見られない。
本発明の目的は、家電・建材・自動車等の用途に広く適用可能であって、加熱後の耐食性に優れ、かつ環境負荷物質である６価クロムの溶出がゼロであるめっき鋼材として、上記でのべた
（Ａ）クロメートと同等の耐食性、耐熱性を有する３価クロム処理
を施しためっき鋼材を安価に提供することである。
【０００７】
【課題を解決するための手段】
本発明者らは、上記課題を解決すべく鋭意検討を重ねた。この結果、まず６価クロムの溶出ゼロに関しては、クロム還元率が８５％以上であるような部分還元クロム酸を用いたうえ、浴中にりん酸化合物および硝酸化合物を、クロム酸の還元率および添加量に応じた特定割合だけ添加した組成物を作成する。これをめっき鋼板に塗布し、乾燥することにより、めっき表面をエッジングさせつつ残存６価クロムを還元し、オール３価クロムの皮膜として成膜させるという手段で解決出来る目処を得た。
【０００８】
また、加熱後耐食性については、上記組成物に添加するりん酸化合物および硝酸化合物の合計添加量に上限を設けること、組成物にさらに無機分散体を添加することにより、６価クロメート同等以上の性能が得られることを見出し、本発明を完成するに至った。
【０００９】
本発明は、以下の（１）〜（７）より成る。
（１）　　部分還元クロム酸、りん酸化合物、硝酸化合物を必須成分とし、かつ、部分還元クロム酸のクロム還元率（Ｘ，　％）、部分還元クロム酸の浴中濃度（ＣｒＯ_３換算）、りん酸化合物の浴中濃度（Ｈ_３ＰＯ_４　換算）、硝酸化合物の浴中濃度（ＨＮＯ_３換算）の間に、下式（Ｉ）〜（ＩＩＩ）の関係を有する加熱後耐食性、環境適合性に優れためっき鋼材用表面処理組成物。
８５（％）　　≦　Ｘ　　　　　　　　　　　　　　　　（Ｉ）
Ｙ　＝　（ＨＮＯ_３／ＣｒＯ_３）　＋　（Ｈ_３ＰＯ_４／ＣｒＯ_３）　としたとき
Ｙ≦　　１．　９　　　　　　　　　　　　　　　　　　　　（ＩＩ）
Ｙ≧　４．５　−　　Ｘ／２５　　　　　　　　　　（ＩＩＩ）
（２）　　浴中にさらに無機分散体を含有する前記（１）記載の加熱後耐食性、環境適合性に優れためっき鋼材用表面処理組成物。
（３）　　浴中にさらに潤滑剤を含有する前記（１）または（２）記載の加熱後耐食性、環境適合性に優れためっき鋼材用表面処理組成物。
（４）　　前記（１）〜（３）記載の表面処理用組成物をめっき鋼材に塗布し、乾燥することを特徴とする加熱後耐食性、環境適合性に優れためっき鋼材の製造方法。
（５）　　めっき鋼材の表面に、Ｃｒ，　Ｐ，　Ｎを必須成分として含有し、かつ、Ｃｒ付着量（Ｃｒ，　ｍｇ／ｍ^２）、Ｐ付着量（Ｐ，　ｍｇ／ｍ^２）、Ｎ付着量（Ｎ，　ｍｇ／ｍ^２）および６価クロム溶出量（Ｄ，ｐｐｍ）が下式（ＩＶ）、（Ｖ）の関係を満足する皮膜を　Ｃｒ　付着量として１０〜３００ｍｇ／ｍ^２有することを特徴とする加熱後耐食性、環境適合性に優れためっき鋼材。
（Ｐ／Ｃｒ）＋　（Ｎ／Ｃｒ）≦　１．　２　　（ＩＶ）
Ｄ　　＝　　０　　　　　　　　　　　　　（Ｖ）
（６）　　皮膜中に更に無機分散体を含有することを特徴とする前記（５）記載の加熱後耐食性、環境適合性に優れためっき鋼材。
（７）　　皮膜中にさらに潤滑剤を含有することを特徴とする前記（５）または（６）記載の加熱後耐食性、環境適合性に優れためっき鋼材。
【００１０】
【発明の実施の形態】
以下、本発明を詳述する。
まず、前記（１）は本発明のめっき鋼材の製造に用いる表面処理組成物を規定したものである。（Ｉ）式は必須成分である部分還元クロム酸のクロム還元率の範囲を規定したものである。クロム還元率が８５％未満では、６価クロムの溶出が見られる。
（ＩＩ）、（ＩＩＩ）式は、組成物中の硝酸化合物、りん酸化合物と部分還元クロム酸の比率を規定している。（ＩＩ）式が満足されないと、加熱後耐食性が不良となる。一方、（ＩＩＩ）式が満足されないと、６価Ｃｒ　の溶出が見られる。以上、（Ｉ）〜（ＩＩＩ）式の関係を図示したのが図１である。本発明の組成物は、図１の太線で示した範囲内の浴組成のものである。
【００１１】
前記（２）は、組成物への添加により、めっき鋼板の性能をさらに高度なものとすることができる浴中添加物として、無機分散体を規定している。無機分散体としてはシリカ、アルミナ、チタニア、ジルコニア等の無機系ゾルが例示でき、特に、シリカの添加は耐食性の向上に効果がある。無機分散体の粒子径は膜厚に比べて小さく、かつ浴中で容易に凝集しない程度に大きければ良いが、通常５〜３００ｎｍ程度である。耐食性向上の観点からは小さいほうが好ましい。またその形状は、球形ではなく、扁平なものであっても良い。
組成物中への無機分散体の添加量は特に規定しないが、耐食性向上の目的であれば、無機物／全皮膜　　の重量比率で０．２　以上の添加が望ましく、一方、成膜性を阻害しない上限を考慮すると、無機物／全皮膜　　の重量比率で　０．６　　以下の添加が望ましい。
【００１２】
前記（３）は、組成物への添加により、めっき鋼板の性能をさらに高度なものとすることができる浴中添加物として、潤滑剤を規定している。潤滑剤としては、有機潤滑剤、例えばポリエチレンワックス、ポリオレフィンワックス、パラフィンワックス、マイクロワックス、フルオロカーボン類、モンタンワックス、カルナバワックス、ステアリン酸およびその化合物、あるいは、無機潤滑剤、例えばグラファイト、ＭｏＳ，ＢＮなどが使用可能である。潤滑剤の粒径は膜厚に比べてやや大きくても良く、通常、０．０５〜１ミクロン程度のものが適する。潤滑剤を部分還元クロム酸水溶液中に安定に分散させるには、粒子表面を界面活性剤や保護コロイドで被覆することが有効であり、特にノニオン系もしくはアニオン系の界面活性剤や保護コロイドが有効である。例をあげれば、ポリアルキレングリコール系活性剤、アルキルフェノール系活性剤、アルキルベンゼンスルフォン酸塩、セルロース、ポリエチレングリコール、ポリビニルアルコール、脂肪酸石鹸、スルフォン酸系活性剤、りん酸系活性剤などがある。組成物中への潤滑剤の添加量は特に規定しないが、潤滑性を有意に改善するには、潤滑剤／全皮膜　　の重量比率で０．０２以上の添加が望ましく、一方、成膜性を阻害しない上限を考慮すると、無機物／全皮膜の重量比率で０．３　以下の添加が望ましい。
【００１３】
前記（４）は、本発明のめっき鋼材の製造方法を規定したものである。具体的には、前記（１）〜（３）の組成物を、めっき鋼材に塗布、乾燥することによるものである。組成物の濃度や塗布方式、乾燥方式は、めっき鋼材の形態や種類、望む付着量に合わせて適宜選択することが可能である。たとえばコイルへの塗布においては、ロールコーターによる塗布、スプレー＋リンガーロールによる塗布、浸漬＋　エアナイフ絞りによる塗布などが例示できる。また、乾燥はブロアー乾燥、熱風炉や直火炉による乾燥、誘導加熱方式による乾燥などが例示できる。乾燥では水分が十分蒸散して成膜がすすめばよく、乾燥板温としてはおおよそ６０℃程度以上であれば良い。乾燥時間も数秒あれば十分である。
【００１４】
前記（５）は、前記（４）の方法で製造されためっき鋼材の表面皮膜構造および皮膜性能を規定したものである。Ｃｒ付着量が１０ｍｇ／ｍ^２未満では耐食性が不十分であり、３００ｍｇ／ｍ^２超では飽和する。
（ＩＶ）式は、前記（Ｉ）〜（ＩＩＩ）式の浴組成範囲の組成物を塗布、乾燥することにより製造された表面処理めっき鋼材の、表面皮膜の組成範囲を規定している。以下に、（ＩＶ）式に用いるＣｒ、Ｐ、Ｎ付着量の測定方法について述べる。
【００１５】
供試材のＣｒ、Ｐ付着量は、重量法により検量線を作成したのち、蛍光Ｘ線により測定した。その手順は以下の通りである。板厚０．８ｍｍ　の亜鉛めっき鋼板を１４０ｍｍ　×１４０ｍｍ　に切断したもの１０枚程度準備し、それぞれ重量を化学天秤で０．１ｍｇ　のオーダーまで正確に測定する。つぎに、本発明組成物のうち表１に示すＬと、コロイダルシリカとを、ＣｒＯ_３：　ＳｉＯ_２＝１：３となるように混合した組成物を準備する。すなわち、混合後の組成物の構成比は全体として、
ＣｒＯ_３：ＨＮＯ_３：Ｈ_３ＰＯ_４　：ＳｉＯ_２　　＝　１．００　：０．３５：１．００：３．００　　　　　　（Ａ）
となる。これを重量測定済みの上記亜鉛めっき鋼板の片面に均一塗布する。この際、組成物の水希釈率や塗布条件等を変えて、付着量が０．２　〜３ｇ／ｍ^２程度の範囲で異なる４〜７水準のもの（以下、各サンプルとよぶ）を作成する。塗布、乾燥後の亜鉛めっき鋼板の重量を再び化学天秤で測定し、重量増から組成物の全付着量（ｇ／ｍ^２）を各サンプルごとに算出する。
【００１６】
ここで、組成物の構成比が標記（Ａ）であることから、全付着量に対するＣｒ，　Ｐの重量比率（ｗｔ％）は以下のように算出される。
Ｃｒ＝　９．７２　（ｗｔ％）　　　Ｐ＝　５．９１　（ｗｔ％）　　　　　　　（Ｂ）
この値を上記で求めた各サンプルごとの全付着量（ｇ／ｍ^２）に乗じることにより、各サンプルにおけるＣｒ，　Ｐ　の付着量（ｍｇ／ｍ^２）が算出される。
【００１７】
つぎに、各サンプルを３５ｍｍ×３５ｍｍに切断し、各１６枚の小片サンプルとする。これを蛍光Ｘ線分析装置（理学電機工業製、ＲＩＸ２０００）で分析する。Ｘ線管のターゲットはＲｈ、印加条件は５０ｋＶ，５０ｍＡ、測定面積は２０ｍｍφとした。測定元素はＣｒ，　Ｐとし、それぞれのＸ線強度（ｋｃｐｓ）を測定する。小片サンプル１６枚の平均値をもって、各サンプルのＣｒ，　Ｐ　の強度（ｋｃｐｓ）とした。
【００１８】
最後に、上記で求めた各サンプルのＣｒ，　Ｐの強度（ｋｃｐｓ）と、さきに算出した各サンプルごとのＣｒ，　Ｐの付着量（ｍｇ／ｍ^２）とを相関させて直線近似することにより、蛍光Ｘ線におけるＣｒ，　Ｐの検量線とする。以後はこの検量線を用いて、未知サンプルのＣｒ，　Ｐの蛍光Ｘ線強度（ｋｃｐｓ）から換算して、それぞれのＣｒ，　Ｐ付着量（ｍｇ／ｍ^２）を求めた。
【００１９】
一方、Ｎ付着量については、蛍光Ｘ線の感度が低く正確な定量ができないことから、Ｘ線光電子分光法（ＸＰＳ）によりＮ／Ｃｒの比率を求め、先に求めたＣｒ付着量とかけあわせてＮ付着量を算出する。ＸＰＳによりＮ／Ｃｒの元素比率を求める時には、アルゴンスパッタリングを行いながら測定を行い（いわゆる深さ分析）、汚染物質であるＣが減少して組成が安定するところを起点、めっき金属が現れて皮膜成分であるＣｒ、Ｎの強度がノイズレベルまで減少するところを終点として、その間のＣｒ、Ｎの元素比率（ａｔｍ％）を積算することにより求める。
【００２０】
（Ｖ）式は、上記表面皮膜の６価クロム溶出率がゼロであることを規定している。６価クロム溶出率（Ｄ，ｐｐｍ）は以下の手順で求めた。表裏両面に皮膜処理されためっき鋼板から５０ｍｍ×６０ｍｍのサンプルをｎ数＝５枚ずつ切り出す。すなわち、サンプル総表面積が３００ｃｍ^２となるようにする。これを沸騰状態にある水５００ｃｃ　中に、サンプルどうしが重ならないよう注意しながら浸漬し、３０分後に取り出す。抽出液が常温に戻ってから、希硫酸とジフェニルカルバジド水溶液を少量添加したのち、比色分析により溶出６価Ｃｒの濃度を定量する。いわゆるジフェニルカルバジド法による分析である。
【００２１】
前記（６）、（７）はそれぞれ、前記（２）、（３）の組成物を用いて製造した、さらに高度な性能を有するめっき鋼材である。
【００２２】
次に本発明に使用可能な原料、材料について述べる。
部分還元クロム酸　　としては、無水クロム酸、（重）クロム酸カリウム、（重）クロム酸ナトリウム、（重）クロム酸アンモニウム、クロム酸バリウム、クロム酸ストロンチウムなどのクロム酸、クロム酸塩、重クロム酸塩を出発物質としてデンプン、アルコール、過酸化水素等で部分還元したクロム酸を用いることができる。
本発明におけるりん酸化合物としては、正りん酸、ポリリン酸、硝酸化合物としては硝酸が好ましい。
【００２３】
本発明に使用する組成物は、必須成分および添加物を所定の割合で混合するだけで得られる。混合の順序は特に規定するものではないが、大スケールで安定的に組成物を得るためには、部分還元クロム酸とりん酸化合物、硝酸化合物をあらかじめ混合して保管し、必要時にこれを、無機分散体や潤滑剤と混ぜ合わせても良い。
【００２４】
本発明が適用可能なめっき鋼材としては、電気めっき、溶融めっき、蒸着めっき、無電解めっき、溶融塩電解めっき等の方法により作成された各種めっき鋼材があげられる。たとえば、亜鉛めっき鋼材、アルミニウムめっき鋼材、亜鉛とニッケル、鉄、アルミニウム、クロム、チタン、マグネシウム、マンガン、コバルト、錫、鉛などの１種または２種以上の金属との合金めっき鋼材さらにこれらのめっき層に他の金属および／またはシリカ、アルミナ、チタニア、ジルコニア等の無機物、および／または有機化合物を意図的に含有させた、もしくは不純物として含有するめっき鋼材、さらには、上述の２種類以上のめっきを複層有するめっき鋼材などがある。
【００２５】
【実施例】
次に、本発明を実施例を用いて非限定的に説明する。
実施例１
（１）供試した鋼材
下記のめっき鋼板を用いた。
ＥＧ（電気亜鉛めっき鋼板）：板厚０．８ｍｍ　の軟鋼板に片面あたり２０ｇ／ｍ^２の亜鉛めっきを電析させた鋼板
（２）組成物
表１に示す浴記号Ａ〜Ｚ、ＡＡ〜ＡＥの部分還元クロム酸を用いて、組成物を作成した。この際、添加物としてコロイダルシリカを、部分還元クロム酸に対して重量比が、ＣｒＯ_３：ＳｉＯ_２＝１：３となるように添加した。
（３）表面処理
上記（２）の組成物をロールコーターで供試板両面に塗布し、熱風乾燥炉で到達板温９０℃となるよう乾燥した。乾燥皮膜のＣｒ付着量は蛍光Ｘ線で測定した。
（４）性能評価試験
（４−１）溶出６価Ｃｒ（ｐｐｍ）の測定
表裏両面に皮膜処理された供試板から５０ｍｍ×６０ｍｍのサンプルをｎ数＝５枚ずつ切り出した。これを沸騰状態にある水５００ｃｃ　中に、サンプルどうしが重ならないよう注意しながら浸漬し、３０分後に取り出した。抽出液が常温に戻ってから、その４０ｃｃに対して、希硫酸８ｃｃとジフェニルカルバジド水溶液２ｃｃを添加したのち、比色分析により溶出６価Ｃｒの濃度を定量した。
（４−２）　Ｃｒ　、Ｐ、Ｎ付着量
供試材のＣｒ、Ｐ付着量は、重量法により検量線を作成したのち、蛍光Ｘ線により測定した。Ｎ付着量は、Ｘ線光電子分光法によりＮ／　Ｃｒ比率を求めた後、上記で求めたＣｒ付着量を用いて算出した。いずれも手順は既述の通りである。
（４−３）　　加熱後耐食性
供試板を誘導加熱方式により、５０℃／ｓｅｃで６００℃まで加熱したのち、約２分間で常温まで空冷した。均熱部分から１５０ｍｍ　×７０ｍｍのサイズのサンプルを切り出して、その端面と裏面をテープシールしたのち、塩水噴霧試験（５％　ＮａＣｌ，　３５　℃）を７２時間行い、白錆発生面積率を測定した。
【００２６】
結果を表２に示す。前述の（Ｉ）〜（ＩＩＩ）式を満たす本発明の組成物を用いると、それにより得られためっき鋼板は６価Ｃｒの溶出が無く、しかも優れた加熱後耐食性を有することがわかる。また、その皮膜組成は、前式（ＩＶ）を満足することがわかる。
【００２７】
実施例２
（１）供試しためっき鋼材
以下のめっき鋼板を用いた。
ＧＩ（溶融亜鉛めっき鋼板）：板厚０．８ｍｍ　の軟鋼板に片面あたり６０ｇ／ｍ^２の溶融亜鉛めっきを施した鋼板。
ＺＬ（電気亜鉛−　ニッケル合金めっき鋼板）：板厚１．０ｍｍ　の軟鋼板に片面あたり２０ｇ／ｍ^２の亜鉛−ニッケル合金めっき（Ｎｉ１０ｗｔ％）　を電析させた鋼板。
ＡＬ（溶融アルミニウムめっき鋼板）：板厚１．６ｍｍ　の軟鋼板に片面あたり５０ｇ／ｍ^２の溶融アルミニウムめっきを施した鋼板。
なお、めっき中には合金元素としてシリコンを８ｗｔ％含有している。
ＥＧ（電気亜鉛めっき鋼板）：板厚０．８ｍｍ　の軟鋼板に片面あたり２０ｇ／ｍ^２の亜鉛めっきを電析させた鋼板
（２）組成物
表１に示す浴記号Ｌ、Ｍ，Ｑ，Ｙ、Ｚ、ＡＡの部分還元クロム酸を用いて、組成物を作成した。添加物として「シリカ」と記載されたものは、コロイダルシリカを、部分還元クロム酸に対して重量比がＣｒＯ_３：ＳｉＯ_２＝１：５となるように添加した。「潤滑剤」と記載のものは、ポリエチレンワックスを、部分還元クロム酸に対して重量比が、ＣｒＯ_３：ワックス＝１：０．１　となるように添加した。
（３）表面処理
上記（２）の組成物をロールコーターで供試板両面に塗布し、熱風乾燥炉で到達板温９０　℃となるよう乾燥した。乾燥皮膜のＣｒ付着量は蛍光Ｘ線で測定した。（４）性能評価試験
（４−１）溶出６価Ｃｒ（ｐｐｍ）の測定
（４−２）　Ｃｒ　、Ｐ、Ｎ付着量
（４−３）　　加熱後耐食性
いずれも実施例１と同様に評価した。
（４−４）　　動摩擦係数
動摩擦係数の測定はいわゆる平板摺動試験により行った。すなわち、供試材を幅３０ｍｍ、長さ３００ｍｍ　に切り出し、表面が平滑なＣｒめっき鋼製の平面圧子（接触面積３０ｍｍ×２０ｍｍ）　により、両面を押さえ圧　５ｋｇｆ／ｃｍ^２（油圧シリンダ径５０ｍｍのため押さえ荷重Ｐに換算して９８ｋｇｆ）で押さえ、引き抜き速度２０ｍｍ／ｍｉｎで供試材の中央部分８０ｍｍを引き抜いた時の平均引き抜き荷重（Ｆ）を測定して、動摩擦係数をμ＝Ｆ／２Ｐとして算出した。測定は供試材を毎回変更して３回行い、その平均値を求めた。
（４−５）　　一次防錆性
１５０ｍｍ　×７０ｍｍのサイズのサンプルを切り出して、その端面と裏面をテープシールしたのち、塩水噴霧試験（５％　ＮａＣｌ，　３５℃）　を７２時間行い、白錆発生面積率を測定した。
【００２８】
結果を表３に示す。前述の（Ｉ）〜（ＩＩＩ）式を満たす本発明の組成物を用いると、各種めっき鋼板は６価Ｃｒの溶出が無く、しかも優れた加熱後耐食性を有することがわかる。また、その皮膜組成は、前式（ＩＶ）を満足する。無機分散体としてシリカを添加したものは、無添加のものより、一次防錆性に優れる。潤滑剤を添加したものについては、動摩擦係数が低く、優れた潤滑性を示す。
【００２９】
【表１】

【００３０】
【表２】

【００３１】
【表３】

【００３２】
【発明の効果】
本発明により、家電・建材・自動車等の用途に広く適用可能であって、加熱後の耐食性に優れ、かつ環境負荷物質である６価クロムの溶出がゼロであるめっき鋼材を安価に提供することができる。したがって、工業的にきわめて価値が高い発明であるといえる。
【図面の簡単な説明】
【図１】本発明組成物のクロム還元率と組成の範囲を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention is widely applicable to applications such as home appliances, building materials, and automobiles, has excellent corrosion resistance after heating, and has no elution of hexavalent chromium as an environmentally hazardous substance. The present invention relates to a production method, and a surface treatment composition for a plated steel material having excellent corrosion resistance after heating and environmental compatibility used in the production method.
[0002]
[Prior art]
[Patent Document 1] Japanese Patent Application Laid-Open No. 06-179981 [Patent Document 2] Japanese Patent Application Laid-Open No. 07-213994 [Patent Document 3] Japanese Patent Application Laid-Open No. 08-337844 [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-219776 ]
Chromate treatment may be applied to plated steel materials for home appliances, building materials and automobile members in order to improve rust prevention. Among them, materials exposed to high temperatures during processing and use, for example, materials used for automobile mufflers, heating equipment, cathode ray tube heat shrink bands, and the like, are required to further have heat resistance and corrosion resistance after heating. On the other hand, due to the recent rising interest in environmental issues, domestic and foreign laws and regulations, and voluntary regulations, it is required to eliminate elution of hexavalent chromium from materials. To answer these requests,
It is necessary to provide at least one of (A) a trivalent chromium treatment having the same corrosion resistance and heat resistance as chromate and (B) a non-chromium treatment having the same corrosion resistance and heat resistance as chromate.
[0004]
The chromate treatment itself can achieve a high level of corrosion resistance and heat resistance of the plated steel sheet. However, in addition to the above, there are a plurality of conventional techniques relating to heat resistance and corrosion resistance depending on the type and use of plating, for example, JP-A-06-179981, JP-A-07-213994, and JP-A-08-33784. And JP-A-2000-219776 can be exemplified. Among them, Japanese Patent Application Laid-Open No. 06-179981 discloses a heat-resistant and corrosion-resistant steel sheet in which a plated steel sheet is subjected to a chromate treatment, and a ceramic coating made of silica and an alkali metal oxide is provided thereon. JP-A-07-213994 discloses a coated steel sheet in which a resin layer such as PES containing strontium chromate is provided on the surface of an Al-Zn alloy-plated or Al-plated steel sheet via a chemical conversion treatment layer. . Japanese Patent Application Laid-Open No. 08-337884 discloses that an Al—Zn alloy-plated or Al-plated steel sheet is formed from a composition comprising a partially reduced chromic acid having a chromium reduction ratio of 30 to 70%, phosphoric acid, silica, and phosphonic acid. A chromate-treated steel sheet having excellent corrosion resistance and heat resistance obtained by surface treatment is disclosed. Japanese Patent Application Laid-Open No. 2000-219776 discloses a non-chromium heat-resistant steel sheet in which a surface layer of a zinc alloy-plated steel sheet is provided with a coating layer of water glass not containing chromate but containing a thiocarbonyl group-containing compound or the like. I have.
[0005]
[Problems to be solved by the invention]
However, these conventional techniques have problems.
First, in Japanese Patent Application Laid-Open No. 06-179981 and a technique similar thereto, elution of hexavalent Cr is inevitable when a coating type chromate is used as a chromate treatment, and when an electrolytic type chromate is used, the corrosion resistance after heating is reduced. It does not extend to processing. In addition, since it is a two-layer coating process, there are restrictions on manufacturing. The technique disclosed in Japanese Patent Application Laid-Open No. 07-213994 is extremely expensive and is not suitable for general use because it requires a three-layer film treatment and also requires the application of an expensive heat-resistant resin in a thick film. In addition, since strontium chromate is contained, elution of hexavalent Cr is also observed. In the technique disclosed in Japanese Patent Application Laid-Open No. 08-337844, the chromium reduction ratio is 30 to 70%, so that the corrosion resistance after heating is excellent, but the elution of hexavalent Cr is inevitable. The technique disclosed in Japanese Patent Application Laid-Open No. 2000-219776 has no problem of elution of hexavalent Cr because it does not contain chromium, but its corrosion resistance after heating is not as good as chromate, and water glass is not as inexpensive as chromate.
[0006]
That is, in the prior art, there is not found any one in which hexavalent chromium is not eluted while ensuring corrosion resistance after heating, and the production is easy and the film cost is low.
An object of the present invention is to provide a plated steel material which is widely applicable to applications such as home appliances, building materials, and automobiles, has excellent corrosion resistance after heating, and has zero elution of hexavalent chromium, which is an environmentally hazardous substance. An object of the present invention is to provide inexpensively a plated steel material that has been subjected to a trivalent chromium treatment and has the same corrosion resistance and heat resistance as the solid (A) chromate.
[0007]
[Means for Solving the Problems]
The present inventors have intensively studied to solve the above-mentioned problems. As a result, first, with respect to zero elution of hexavalent chromium, a partially reduced chromic acid having a chromium reduction rate of 85% or more was used, and a phosphate compound and a nitric acid compound were added to the bath to reduce the chromic acid reduction rate. A composition is prepared by adding a specific ratio according to the amount added. This was applied to a plated steel sheet and dried to obtain a target that could be solved by reducing the remaining hexavalent chromium while edging the plated surface and forming a film of all trivalent chromium.
[0008]
With respect to the corrosion resistance after heating, by setting an upper limit on the total amount of the phosphate compound and the nitric acid compound added to the composition, and by further adding an inorganic dispersion to the composition, a performance equal to or higher than hexavalent chromate can be obtained. Was obtained, and the present invention was completed.
[0009]
The present invention includes the following (1) to (7).
(1) Partially reduced chromic acid, a phosphoric acid compound, and a nitric acid compound are essential components, and the chromium reduction ratio of partially reduced chromic acid (X,%), the concentration of partially reduced chromic acid in a bath (in terms of CrO ₃ ), The relationship between the acid compound concentration in the bath (in terms of H ₃ PO ₄ ) and the nitric acid compound concentration in the bath (in terms of HNO ₃ ) has the following formulas (I) to (III). Excellent surface treatment composition for plated steel.
85 (%) ≤ X (I)
When Y = (HNO ₃ / CrO ₃ ) + (H ₃ PO ₄ / CrO ₃ ), Y ≦ 1. 9 (II)
Y ≧ 4.5−X / 25 (III)
(2) The surface treatment composition for a plated steel material according to the above (1), further comprising an inorganic dispersion in the bath, which is excellent in corrosion resistance after heating and environmental compatibility.
(3) The surface treatment composition for a plated steel material according to the above (1) or (2), further comprising a lubricant in a bath, which is excellent in corrosion resistance after heating and environmental compatibility.
(4) A method for producing a plated steel material having excellent corrosion resistance after heating and environmental compatibility, wherein the composition for surface treatment according to the above (1) to (3) is applied to a plated steel material and dried.
(5) Cr, P, and N are contained as essential components on the surface of the plated steel material, and the Cr adhesion amount (Cr, mg / m ² ), the P adhesion amount (P, mg / m ² ), and the N adhesion amount (N, mg / m ² ) and a film whose hexavalent chromium elution amount (D, ppm) satisfies the following formulas (IV) and (V) have a Cr adhesion amount of 10 to 300 mg / m ^2. Plating steel with excellent corrosion resistance after heating and environmental compatibility.
(P / Cr) + (N / Cr) ≦ 1. 2 (IV)
D = 0 (V)
(6) The plated steel material having excellent corrosion resistance after heating and environmental compatibility according to the above (5), wherein the coating further contains an inorganic dispersion.
(7) The plated steel material having excellent corrosion resistance after heating and environmental compatibility according to the above (5) or (6), further comprising a lubricant in the film.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
First, (1) defines a surface treatment composition used for producing the plated steel material of the present invention. Formula (I) defines the range of the chromium reduction rate of the partially reduced chromic acid, which is an essential component. When the chromium reduction ratio is less than 85%, elution of hexavalent chromium is observed.
Formulas (II) and (III) define the ratio of the nitrate compound, the phosphate compound and the partially reduced chromic acid in the composition. If the formula (II) is not satisfied, the corrosion resistance after heating becomes poor. On the other hand, if the formula (III) is not satisfied, elution of hexavalent Cr 2 is observed. FIG. 1 shows the relationship between the expressions (I) to (III). The composition of the present invention has a bath composition within the range shown by the thick line in FIG.
[0011]
The above (2) defines an inorganic dispersion as an additive in a bath that can further enhance the performance of a plated steel sheet by adding it to the composition. Examples of the inorganic dispersion include inorganic sols such as silica, alumina, titania, and zirconia. In particular, the addition of silica is effective in improving corrosion resistance. The particle diameter of the inorganic dispersion may be small as compared with the film thickness and large enough not to easily aggregate in the bath, but is usually about 5 to 300 nm. From the viewpoint of improving the corrosion resistance, a smaller one is preferable. Further, the shape may be flat, instead of spherical.
The amount of the inorganic dispersion added to the composition is not particularly specified, but for the purpose of improving corrosion resistance, it is desirable to add 0.2 or more by weight of inorganic substance / total coating, while not impairing the film forming property. Considering the upper limit, it is desirable to add 0.6 or less by weight of inorganic substance / total coating.
[0012]
The above (3) specifies a lubricant as an additive in a bath that can further enhance the performance of a plated steel sheet by adding it to the composition. Examples of the lubricant include organic lubricants such as polyethylene wax, polyolefin wax, paraffin wax, micro wax, fluorocarbons, montan wax, carnauba wax, stearic acid and compounds thereof, and inorganic lubricants such as graphite, MoS, BN, etc. Can be used. The particle size of the lubricant may be slightly larger than the film thickness, and usually, a particle size of about 0.05 to 1 micron is suitable. In order to stably disperse the lubricant in the partially reduced chromic acid aqueous solution, it is effective to coat the particle surface with a surfactant or a protective colloid, particularly a nonionic or anionic surfactant or a protective colloid is effective. It is. Examples include polyalkylene glycol-based activators, alkylphenol-based activators, alkylbenzene sulfonates, cellulose, polyethylene glycol, polyvinyl alcohol, fatty acid soaps, sulfonic acid-based activators, and phosphoric acid-based activators. The amount of the lubricant to be added to the composition is not particularly specified, but in order to significantly improve the lubricity, it is desirable to add a lubricant / total coating weight ratio of 0.02 or more. Considering the upper limit not hindering, it is desirable to add 0.3 or less by weight of inorganic substance / total coating.
[0013]
The above (4) specifies the method for producing a plated steel material of the present invention. Specifically, the composition of (1) to (3) is applied to a plated steel material and dried. The concentration of the composition, the application method, and the drying method can be appropriately selected according to the form and type of the plated steel material and the desired amount of adhesion. For example, in the application to the coil, application by a roll coater, application by spray + ringer roll, application by dipping + air knife drawing, and the like can be exemplified. Examples of the drying include blower drying, drying using a hot air oven or a direct fire oven, and drying using an induction heating method. In the drying, it is sufficient that the moisture is sufficiently evaporated to form a film, and the drying plate temperature may be about 60 ° C. or more. A few seconds are sufficient for the drying time.
[0014]
The above (5) defines the surface film structure and the film performance of the plated steel material manufactured by the method (4). If the amount of Cr attached is less than 10 mg / m ² , the corrosion resistance is insufficient, and if it exceeds 300 mg / m ^2, it is saturated.
The formula (IV) defines the composition range of the surface coating of the surface-treated plated steel material produced by applying and drying the composition having the bath composition range of the formulas (I) to (III). Hereinafter, a method for measuring the amounts of Cr, P, and N used in equation (IV) will be described.
[0015]
The amounts of Cr and P adhered to the test material were measured by X-ray fluorescence after preparing a calibration curve by a gravimetric method. The procedure is as follows. Approximately 10 galvanized steel sheets each having a thickness of 0.8 mm cut into a size of 140 mm x 140 mm are prepared, and the weight of each sheet is accurately measured to the order of 0.1 mg using an analytical balance. Next, among the compositions of the present invention, a composition is prepared by mixing L shown in Table 1 and colloidal silica so that CrO ₃ : SiO ₂ = 1: 3. That is, the composition ratio of the composition after mixing as a whole,
CrO ₃ : HNO ₃ : H ₃ PO ₄ : SiO ₂ = 1.00: 0.35: 1.00: 3.00 (A)
It becomes. This is uniformly applied to one surface of the galvanized steel plate whose weight has been measured. At this time, by changing the water dilution ratio of the composition, the application conditions, and the like, 4 to 7 levels (hereinafter, referred to as samples) having different adhesion amounts in the range of about 0.2 to 3 g / m ² are prepared. . The weight of the galvanized steel sheet after application and drying is measured again with an analytical balance, and the total adhesion amount (g / m ² ) of the composition is calculated for each sample from the weight increase.
[0016]
Here, since the composition ratio of the composition is the title (A), the weight ratio (wt%) of Cr and P to the total adhesion amount is calculated as follows.
Cr = 9.72 (wt%) P = 5.91 (wt%) (B)
By multiplying this value by the total adhesion amount (g / m ² ) of each sample obtained above, the adhesion amount of Cr and P (mg / m ² ) in each sample is calculated.
[0017]
Next, each sample is cut into 35 mm x 35 mm to obtain 16 small piece samples. This is analyzed with a fluorescent X-ray analyzer (RIX2000, manufactured by Rigaku Corporation). The target of the X-ray tube was Rh, the application conditions were 50 kV, 50 mA, and the measurement area was 20 mmφ. The elements to be measured are Cr and P, and the respective X-ray intensities (kcps) are measured. The average value of 16 small piece samples was used as the Cr (P) intensity (kcps) of each sample.
[0018]
Finally, a linear approximation is made by correlating the Cr (P) intensity (kcps) of each sample obtained above with the Cr (P) adhesion amount (mg / m ² ) of each sample previously calculated. , And a calibration curve for Cr and P in fluorescent X-rays. Thereafter, using this calibration curve, the Cr and P adhesion amounts (mg / m ² ) of each of the unknown samples were calculated by converting from the fluorescent X-ray intensity (kcps) of Cr and P of the unknown sample.
[0019]
On the other hand, since the sensitivity of fluorescent X-rays was low and accurate quantification was not possible, the N / Cr ratio was determined by X-ray photoelectron spectroscopy (XPS), and the N / Cr ratio was multiplied by the previously determined Cr deposition amount. To calculate the N adhesion amount. When the element ratio of N / Cr is determined by XPS, measurement is performed while performing argon sputtering (so-called depth analysis), and starting from the point where the contaminant C is reduced and the composition is stabilized, the plating metal appears and the film is formed. It is determined by integrating the element ratios (atm%) of Cr and N between the points where the intensity of the components Cr and N decreases to the noise level as the end point.
[0020]
Formula (V) specifies that the hexavalent chromium elution rate of the surface coating is zero. Hexavalent chromium elution rate (D, ppm) was determined by the following procedure. A sample of 50 mm × 60 mm is cut out from a plated steel sheet having a film treatment on both the front and back surfaces, where n = 5. That is, the total surface area of the sample is set to 300 cm ² . This is immersed in 500 cc of boiling water, taking care not to overlap the samples, and taken out after 30 minutes. After the extract has returned to room temperature, a small amount of dilute sulfuric acid and an aqueous solution of diphenylcarbazide are added, and the concentration of the eluted hexavalent Cr is quantified by colorimetric analysis. The analysis is based on the so-called diphenylcarbazide method.
[0021]
The above (6) and (7) are plated steel materials having higher performance, respectively, manufactured using the compositions of the above (2) and (3).
[0022]
Next, the raw materials and materials that can be used in the present invention will be described.
Examples of the partially reduced chromic acid include chromic anhydride, potassium (di) chromate, sodium (di) chromate, ammonium (di) chromate, barium chromate, strontium chromate and the like, chromate, dichromate Chromic acid partially reduced with starch, alcohol, hydrogen peroxide or the like can be used as an acid salt as a starting material.
As the phosphoric acid compound in the present invention, orthophosphoric acid and polyphosphoric acid are preferable, and as the nitric acid compound, nitric acid is preferable.
[0023]
The composition used in the present invention can be obtained only by mixing essential components and additives in a predetermined ratio. The order of mixing is not particularly specified, but in order to obtain a composition stably on a large scale, partially reduced chromic acid, a phosphate compound, and a nitrate compound are mixed in advance and stored, and when necessary, It may be mixed with an inorganic dispersion or a lubricant.
[0024]
Examples of the plated steel material to which the present invention can be applied include various types of plated steel materials prepared by a method such as electroplating, hot dipping, vapor deposition plating, electroless plating, and molten salt electroplating. For example, galvanized steel, aluminum-plated steel, alloy-plated steel with zinc and one or more metals such as nickel, iron, aluminum, chromium, titanium, magnesium, manganese, cobalt, tin, lead, and the like. A plated steel material in which the layer intentionally contains or contains an impurity and / or an inorganic compound such as silica, alumina, titania, and zirconia, and / or an organic compound, and further, two or more types of plating described above. And a plated steel material having a plurality of layers.
[0025]
【Example】
Next, the present invention will be described by way of non-limiting examples.
Example 1
(1) Tested steel materials The following plated steel sheets were used.
EG (Electro-galvanized steel sheet): Steel sheet obtained by depositing 20 g / m ² per side of galvanized mild steel sheet having a thickness of 0.8 mm (2) Composition Bath symbols AZ, AA-AE shown in Table 1 A composition was prepared using the partially reduced chromic acid of At this time, colloidal silica was added as an additive so that the weight ratio to the partially reduced chromic acid was CrO ₃ : SiO ₂ = 1: 3.
(3) Surface treatment The composition of the above (2) was applied to both surfaces of the test plate with a roll coater, and dried in a hot-air drying oven to reach a plate temperature of 90 ° C. The amount of Cr attached to the dried film was measured by X-ray fluorescence.
(4) Performance Evaluation Test (4-1) Measurement of Elution Hexavalent Cr (ppm) From the test plate coated on both front and back surfaces, 50 mm × 60 mm samples were cut out by n = 5 each. This was immersed in 500 cc of boiling water, taking care not to overlap the samples, and was taken out after 30 minutes. After the extract was returned to room temperature, 8 cc of dilute sulfuric acid and 2 cc of diphenylcarbazide aqueous solution were added to 40 cc of the extract, and the concentration of the eluted hexavalent Cr was quantified by colorimetric analysis.
(4-2) Cr, P, and N Adhesion Amounts of Cr and P of the test material were measured by X-ray fluorescence after preparing a calibration curve by a gravimetric method. The N adhesion amount was calculated by using the Cr adhesion amount obtained above after obtaining the N / Cr ratio by X-ray photoelectron spectroscopy. In each case, the procedure is as described above.
(4-3) After Heating The corrosion-resistant test plate was heated to 600 ° C. at 50 ° C./sec by an induction heating method, and then air-cooled to room temperature in about 2 minutes. A sample having a size of 150 mm × 70 mm was cut out from the soaking part, and the end face and the back face were tape-sealed. Then, a salt spray test (5% NaCl, 35 ° C.) was performed for 72 hours to measure a white rust generation area ratio.
[0026]
Table 2 shows the results. When the composition of the present invention that satisfies the above-mentioned formulas (I) to (III) is used, it can be seen that the plated steel sheet obtained therefrom has no elution of hexavalent Cr and has excellent corrosion resistance after heating. Further, it is understood that the film composition satisfies the above formula (IV).
[0027]
Example 2
(1) The plated steel sheet below the plated steel material tested was used.
GI (hot-dip galvanized steel sheet): A steel sheet obtained by subjecting a mild steel sheet having a thickness of 0.8 mm to hot-dip galvanizing at 60 g / m ² per side.
ZL (Electric zinc-nickel alloy plated steel sheet): A steel sheet obtained by depositing a zinc-nickel alloy plating (Ni 10 wt%) of 20 g / m ² per side on a mild steel sheet having a thickness of 1.0 mm.
AL (Hot-dip aluminized steel sheet): A steel sheet in which a mild steel sheet having a thickness of 1.6 mm is subjected to hot-dip aluminum plating at 50 g / m ² per side.
The plating contains 8 wt% of silicon as an alloy element.
EG (Electro-galvanized steel sheet): Steel sheet having a thickness of 0.8 mm and galvanized at 20 g / m ² per side electrodeposited on a mild steel sheet (2) Composition Bath symbols L, M, Q, Y shown in Table 1 , Z, and AA, the composition was prepared using partially reduced chromic acid. Those described as "silica" as additives, colloidal silica, the weight ratio to the partial reduction of chromic acid is CrO 3: _SiO 2 = 1: was added to a _5. For those described as “lubricant”, polyethylene wax was added so that the weight ratio to the partially reduced chromic acid was CrO ₃ : wax = 1: 0.1.
(3) Surface treatment The composition of the above (2) was applied to both sides of the test plate with a roll coater, and dried in a hot air drying oven so that the plate temperature reached 90 ° C. The amount of Cr attached to the dried film was measured by X-ray fluorescence. (4) Performance evaluation test (4-1) Measurement of dissolved hexavalent Cr (ppm) (4-2) Cr, P, and N adhesion amounts (4-3) Corrosion resistance after heating All were evaluated in the same manner as in Example 1. .
(4-4) Dynamic friction coefficient The dynamic friction coefficient was measured by a so-called flat plate sliding test. That is, the test material is cut into a width of 30 mm and a length of 300 mm, and a flat surface indenter (contact area: 30 mm × 20 mm) made of a Cr-plated steel having a smooth surface has a pressing pressure of 5 kgf / cm ^{2 on} both sides. The average pulling load (F) when 80 mm was pulled out at the center of the test material at a pulling speed of 20 mm / min was measured by pressing down at 98 kgf) in terms of the pressing load P, and the dynamic friction coefficient was set as μ = F / 2P. Calculated. The measurement was performed three times while changing the test material every time, and the average value was obtained.
(4-5) Primary rust preventive property A sample having a size of 150 mm x 70 mm was cut out, and the end face and the back face were tape-sealed. Then, a salt spray test (5% NaCl, 35 ° C) was performed for 72 hours to obtain a white rust generation area. The rate was measured.
[0028]
Table 3 shows the results. When the composition of the present invention that satisfies the above formulas (I) to (III) is used, it is understood that various plated steel sheets have no elution of hexavalent Cr and have excellent corrosion resistance after heating. Further, the film composition satisfies the above formula (IV). The one in which silica is added as an inorganic dispersion is more excellent in primary rust prevention than the one in which silica is not added. The lubricant added has a low dynamic friction coefficient and exhibits excellent lubricity.
[0029]
[Table 1]

[0030]
[Table 2]

[0031]
[Table 3]

[0032]
【The invention's effect】
According to the present invention, it is possible to provide a low-cost plated steel material that is widely applicable to home appliances, building materials, automobiles, and the like, has excellent corrosion resistance after heating, and has zero elution of hexavalent chromium, which is an environmentally hazardous substance. Can be. Therefore, it can be said that the invention is extremely valuable industrially.
[Brief description of the drawings]
FIG. 1 is a graph showing the chromium reduction ratio and the composition range of the composition of the present invention.

Claims

Partially reduced chromic acid, a phosphoric acid compound, and a nitric acid compound are essential components, and the chromium reduction rate of the partially reduced chromic acid (X,%), the concentration of the partially reduced chromic acid in the bath (in terms of CrO ₃ ), A plating excellent in corrosion resistance after heating and environmental compatibility having a relationship of the following formulas (I) to (III) between the bath concentration (H ₃ PO ₄ conversion) and the nitric acid compound bath concentration (HNO ₃ conversion). Surface treatment composition for steel materials.
85 (%) ≤ X (I)
When Y = (HNO ₃ / CrO ₃ ) + (H ₃ PO ₄ / CrO ₃ ), Y ≦ 1. 9 (II)
Y ≧ 4.5−X / 25 (III)

The surface treatment composition for a plated steel material according to claim 1, further comprising an inorganic dispersion in the bath, which is excellent in corrosion resistance after heating and environmental compatibility.

The surface treatment composition for plated steel material according to claim 1 or 2, further comprising a lubricant in the bath.

4. A method for producing a plated steel material having excellent corrosion resistance after heating and environmental compatibility, wherein the composition for surface treatment according to claim 1 is applied to a plated steel material and dried.

Cr, P, and N are contained as essential components on the surface of the plated steel material, and the Cr adhesion amount (Cr, mg / m ² ), the P adhesion amount (P, mg / m ² ), and the N adhesion amount (N, mg / m ² ) and a film whose hexavalent chromium elution amount (D, ppm) satisfies the relationship of the following formulas (IV) and (V) is 10 to 300 mg / m ² as a Cr adhesion amount. Plated steel with excellent post-corrosion resistance and environmental compatibility.
(P / Cr) + (N / Cr) ≦ 1. 2 (IV)
D = 0 (V)

The plated steel material according to claim 5, further comprising an inorganic dispersion in the coating, the coating having excellent corrosion resistance after heating and environmental compatibility.

The plated steel material having excellent corrosion resistance after heating and environmental compatibility according to claim 5 or 6, wherein the coating further contains a lubricant.