JP2004107717A

JP2004107717A - ANTIDAZZLE HOT-DIP Zn-BASE PLATED STEEL SHEET SUPERIOR IN CORROSION RESISTANCE, AND MANUFACTURING METHOD THEREFOR

Info

Publication number: JP2004107717A
Application number: JP2002270937A
Authority: JP
Inventors: Takao Tsujimura; 辻村　太佳夫; Koichi Watanabe; 渡辺　幸一; Nobuhiko Yamaki; 山木　信彦; Atsushi Ando; 安藤　敦司
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 2002-09-18
Filing date: 2002-09-18
Publication date: 2004-04-08

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot-dip Zn-base plated steel sheet having an antidazzling property together with corrosion resistance. <P>SOLUTION: The antidazzle hot-dip Zn-base plated steel sheet superior in corrosion resistance has the hot-dip Zn-base plated layer which includes 1.0-6.0 mass% Mg, 4.0-22.0 mass% Al, and further one or more elements of 0.07 mass% or less Si, 0.045 mass% or less B and 0.1 mass% or less Ti, for instance as needed, wherein the surface of the hot-dip Zn-base plated layer shows the surface morphology consisting of recesses made by collision with droplets having unevenness of a complicated shape on the surface and the flat face, and has 60-degrees specular gloss of less than 150, which is prescribed in JIS Z 8741. The method for manufacturing the steel sheet is characterized by spraying water containing no such material as to enhance a heat-releasing effect, onto the surface of the plated layer of which the hot-dipped coating mass has been adjusted and which has not yet been solidified, with the use of the 2nd fluid nozzle. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、耐食性に優れた防眩性溶融Ｚｎ基めっき鋼板およびその製造法に関する。
【０００２】
【従来の技術】
溶融Ｚｎめっき鋼板は、各種塗装鋼板の原板として広く用いられる他、建材用途や、建築工事現場のデッキプレート，土木工事現場の土砂止め用仮枠などの用途では、有色塗装をせずにめっき外観のまま使用されるケースが増えている。ところが、めっき外観のまま屋外で使用した場合には、太陽光を反射して眩しすぎることがしばしばある。住宅地では住環境を悪化させ、また工事現場では作業者の目に健康上の悪影響を与えるだけでなく、眩惑感により作業の安全性にも問題を生じる。
【０００３】
このような眩しすぎるめっき外観を改善した鋼板として、めっき表面に凹凸を形成した防眩性めっき鋼板が知られている。これは、連続溶融めっきラインにおいて、めっき付着量絞り装置の直後に設けられたスプレーノズルから未凝固のめっき層表面に液体を吹き付けることにより、表面に凹凸を形成したものである。この凹凸が光を乱反射させ、防眩性が発揮される。
【０００４】
例えば、特開平８−１８８８６３号公報には、めっき層中にＦｅ，Ｍｇ，Ａｌ等を３％以下含有する溶融Ｚｎめっき鋼板の製造において、ガスワイピング直上で水スプレーを行うことによって、溶融Ｚｎめっき層の表面の平均結晶粒径を５０μｍ以下、表面粗度Ｒａを０．４〜１．０μｍにする技術が開示されている。それによると、光沢度Ｇ値が１０〜１５０の防眩性溶融Ｚｎめっき鋼板が得られている。
【０００５】
また、特開平１０−８８３１０号公報には、溶融Ｚｎ−Ａｌ系めっき鋼板の製造に際し、ガスワイピング後に特定条件下で気水スプレー冷却を行うことにより、めっき層表面に微細な凹凸を形成する技術が開示されている。この場合、６０度鏡面光沢度が１００以下の防眩性に優れた溶融Ｚｎ−Ａｌ系めっき鋼板が得られている。
【０００６】
【発明が解決しようとする課題】
発明者らは、これらの防眩性溶融Ｚｎ系めっき鋼板について品質特性を詳細に調査検討した。その結果、上記従来の方法によりめっき層に凹凸を形成させた鋼板は、めっき層が平滑な場合と比べ耐食性の低下が認められた。しかも、大きな防眩性を示す鋼板ほど耐食性が低下した。これは、凹凸の形成に起因して凹部でのめっき層の厚さが薄くなったことが原因と考えられる。特に、防眩性の高いものは凹凸が大きいため凹部のめっき層厚さがより一層薄くなり、耐食性低下も大きくなったと推察される。
【０００７】
このように上記の防眩性鋼板は、耐食性を維持する上でめっき層厚さをあまり薄くすることができない。めっき付着量が１００ｇ／ｍ^２未満では屋外での耐久性が実用上問題となる場合がある。
【０００８】
また、上記の鋼板の製造において防眩効果の高い凹凸を形成させるには、吹き付ける液体からできるだけ大きな抜熱効果を得ることが重要である。特開平８−１８８８６３号では水を勢い良く吹き付ける方法が採用され、また特開平１０−８８３１０号では抜熱効果を高めるリン酸水素アンモニウムを添加した水溶液をミスト状にして噴霧する方法が採用されている。しかし、前者は凹部でのめっき層厚さが過度に薄くなりやすいという欠点があり、後者は抜熱効果を高める物質の添加によりノズル詰まりが生じやすくコストも高くつくという欠点がある。
【０００９】
現時点において、以下の点をすべて満たす溶融Ｚｎ基めっき鋼板は見当たらない。
▲１▼建材その他の屋外用途に望まれる高い防眩性と優れた耐食性を有すること。▲２▼めっき層厚さが薄い場合（例えばめっき付着量が片面１００ｇ／ｍ^２未満、あるいはさらに片面６０ｇ／ｍ^２未満といった薄目付けのめっきの場合）においても上記▲１▼の性能を呈すること。
▲３▼溶融めっきを施したままの外観において上記▲１▼の性能を呈すること。
▲４▼抜熱効果を高めるための物質を使用しない手法により、防眩性を広い範囲（例えば６０度鏡面光沢度が５〜１５０）にコントロールできるものであること。
本発明では、その実現を目的とする。
【００１０】
【課題を解決するための手段】
発明者らは、種々のめっき組成のＺｎ基めっき鋼板を作製し、溶融めっきラインでの防眩性付与手段を検討してきた。その結果、めっき浴中に適量のＭｇとＡｌを添加したとき、未凝固のめっき層表面に水ミストを吹き付けた場合にできる表面性状が特異な形態となることを見出した。すなわち、水ミストの液滴が衝突した部分（液滴衝突痕）がわずかに凹部となるとともに、その凹部の表面には極めて光を乱反射させやすい複雑形状の凹凸が形成される。そして、液滴が衝突しなかった箇所は平滑性が維持される。このような特異な表面性状により、前記▲１▼〜▲４▼を満たす防眩性めっき鋼板が得られるのである。本発明はこれらの知見に基づいて完成したものである。
【００１１】
すなわち、上記目的は、Ｍｇ：１．０〜６．０質量％，Ａｌ：４．０〜２２．０質量％を含有する溶融Ｚｎ基めっき層の表面が、凹部表面に複雑形状の凹凸を有する液滴衝突痕と平滑な面からなる表面形態を呈し、ＪＩＳ　Ｚ　８７４１に規定される６０度鏡面光沢度が１５０未満である耐食性に優れた防眩性溶融Ｚｎ基めっき鋼板によって達成される。
また、特に、めっき付着量が鋼板片面あたり１００ｇ／ｍ^２未満であるものを提供する。
ここで、液滴衝突痕の直径は、水ミストの液滴が衝突した部分の最大径と最小径の平均をいう。
以下、本明細書において単に「光沢度」というときは、「ＪＩＳ　Ｚ　８７４１に規定される６０度鏡面光沢度」を意味する。
【００１２】
また、上記防眩性溶融Ｚｎ基めっき鋼板において、ＪＩＳ　Ｚ　２３７１に規定される塩水噴霧試験において１５００時間以上の耐赤錆発生性を示すもの、あるいはさらに、ＪＩＳ　Ｚ　８７４１に規定される６０度鏡面光沢度が６０未満であるものを提供する。
【００１３】
また、Ｚｎ基めっき層の組成として、Ｍｇ：１．０〜６．０質量％，Ａｌ：４．０〜２２．０質量％を含有し残部がＺｎおよび不可避的不純物からなるもの、あるいはＭｇ：１．０〜６．０質量％，Ａｌ：４．０〜２２．０質量％を含有し、さらにＳｉ：０．０７質量％以下，Ｂ：０．０４５質量％以下，Ｔｉ：０．１質量％以下のうち１種または２種以上を含有し、残部がＺｎおよび不可避的不純物からなるものを提供する。
【００１４】
また本発明では、上記防眩性めっき鋼板の製造法として、溶融めっき付着量の調整後、まだ凝固していないめっき層の表面に、抜熱効果を高めるための物質を添加していない水を２流体ノズルを用いて噴霧する方法を提供する。
【００１５】
【発明の実施の形態】
本発明のめっき鋼板は、その表面が特異な凹凸形態となっていることを特徴とする。
図１〜３には、後述する実施例で得られたサンプルのめっき層表面に形成された液滴衝突痕の走査型電子顕微鏡（ＳＥＭ）写真を示している。このうち図１，図３のものが本発明例の鋼板における液滴衝突痕である。
【００１６】
液滴衝突痕は、水ミストの液滴が衝突した部分であり、周囲より若干凹部になっている。その凹部には複雑な形状の凹凸が形成されていることがわかる。ミストの液滴が当たらなかった部分は平滑性が維持されている。これらの例に見られるように、本発明のめっき鋼板の表面は、めっき層表面の全体に凹凸が一様に形成されている必要はない。複雑形状の凹凸を有する液滴衝突痕と平滑な部分とが共存するという特異な表面形態を有することによって、外観上、適度な防眩性を呈するのである。
【００１７】
このような特異な表面形態を有するめっき鋼板においては、表面に分布している液滴衝突痕の密度が、外観上の防眩性に大きく影響する。すなわち、めっき層表面に衝突するミストの量をコントロールすることにより、例えば光沢度が１０以下といった非常に防眩性の高いものから、光沢度が１５０を超える防眩性の低いものまで、種々の光沢度の製品を作ることができるのである。
前記したような屋外用途を考慮した場合、光沢度が１５０未満でなければ防眩性が不十分である。
【００１８】
光沢度が１５０未満の防眩性を安定して得るには、めっき層表面に形成される直径５０μｍ以上の液滴衝突痕の分布密度（鋼板単位面積当たりの個数）を調整することによって可能になる。直径５０μｍ未満の小さい液滴衝突痕は外観上の防眩性にあまり影響しないことがわかった。このため、それらを除外して、直径５０μｍ以上の液滴衝突痕だけに着目してその分布密度を調整すればよい。分布密度と光沢度の相関は、液滴衝突痕の平均直径によって異なってくる。
特に、光沢度が６０未満の高い防眩性を安定して得るには、液滴衝突痕の平均直径を１００μｍ以上とすることが有利である。
【００１９】
以上のような特異な凹凸形態を有するＺｎ系めっき層表面を得るには、Ｍｇを適量添加したＺｎ−Ａｌ−Ｍｇ系合金めっき浴を用いる。
めっき浴のＭｇ含有量を１．０質量％以上にすると、めっき浴から引き上げて、溶融めっきの付着量を調整したのち、未凝固の状態にあるめっき層表面に水ミストを吹き付けたとき、水ミストの衝突箇所に複雑形状の凹凸を有する前述の液滴衝突痕が形成される。これは、約１質量％以上のＭｇ添加により溶融状態のめっき層における酸化膜形成能が著しく向上するためであると考えられる。
Ｍｇ含有量が６．０質量％を超えるとめっき層中に粗大なＺｎ_２Ｍｇ相が生じ、この部分で局部腐食が起こるためめっき層の耐食性が劣化する。また、めっき浴においてドロスの発生が顕著になる。このため、Ｍｇ含有量は６．０質量％以下にする必要がある。ただ、めっき条件によってはＭｇ含有量が４．０質量％を超えるとＺｎ_２Ｍｇ相が生成する傾向が強まるので、４．０質量％以下にすることがより望ましい。
【００２０】
Ａｌは、Ｍｇ添加によって生成が促進される浴中の表面酸化ドロスの生成を抑制する作用を呈する。浴中のＡｌ含有量が４．０質量％より低いとその作用は十分発揮されない。一方、Ａｌ含有量が２２質量％より高いとめっき浴中の凝固開始温度が上昇するため、めっき浴温を高くせざるを得ず、これにより合金層の発生が顕著となりめっき層が剥離しやすくなる。
なお、実操業での経済性を考慮すると、めっき浴中のＡｌ含有量は１５質量％以下にすることが好ましい。
【００２１】
以上のように、本発明の溶融Ｚｎ基めっき鋼板は、めっき層中にＭｇ：１．０〜６．０質量％，Ａｌ：４．０〜２２．０質量％を含有することを特徴とする。特に好ましいめっき層中のＭｇおよびＡｌの含有量は、Ｍｇ：１．０〜４．０質量％，Ａｌ：４．０〜１５．０質量％である。Ｍｇ，Ａｌ以外には必要に応じて種々の元素を含有してよい。ただし、「Ｚｎ基」であるからめっき層中に少なくともＺｎが５０質量％以上含まれることが必要である。
具体的なめっき層組成として、Ｍｇ：１．０〜６．０質量％好ましくは１．０〜４．０質量％，Ａｌ：４．０〜２２．０質量％好ましくは４．０〜１５．０質量％を含有し、残部がＺｎおよび不可避的不純物からなるものや、あるいは、Ｍｇ：１．０〜６．０質量％好ましくは１．０〜４．０質量％，Ａｌ：４．０〜２２．０質量％好ましくは４．０〜１５．０質量％を含有し、さらにＳｉ：０．０７質量％以下，Ｂ：０．０４５質量％以下，Ｔｉ：０．１質量％以下のうち１種または２種を含み、残部がＺｎおよび不可避的不純物からなるものを挙げることができる。
【００２２】
めっき付着量については、連続溶融めっきラインで製造しうる広い範囲が適用できる。防眩性付与のために形成した凹凸の凹部でめっき層がかなり薄くなっても、上記組成のＺｎ−Ａｌ−Ｍｇ系合金めっき層は高い耐食性を発揮する。したがって、従来は耐食性と防眩性の両立が困難であった薄目付けのめっき鋼板も、本発明の適用により提供が可能となる。例えば、めっき付着量が１００ｇ／ｍ^２未満のもの、あるいはさらに６０ｇ／ｍ^２未満の薄目付けのものにおいて、ＪＩＳ　Ｚ　２３７１に規定される塩水噴霧試験で１５００時間以上の耐赤錆発生性を示す高耐食性と、光沢度が６０未満という高い防眩性を両立させることができるのである。
【００２３】
このような高耐食性を有する防眩性めっき鋼板は、通常の連続溶融めっきラインにおいて、めっき付着量調整装置（ガスワイピングノズルなど）の直後に２流体ノズルを設けることによって比較的容易に製造することができる。すなわち、めっき原板をめっき浴に浸漬して引き上げ、溶融めっき付着量を調整したのち、まだ凝固していないめっき層の表面に２流体ノズルからミスト状の液体を噴霧する方法により製造できる。その際、噴霧する液体として、リン酸水素アンモニウム等の抜熱効果を高める物質を添加した薬液を用いることもできる。しかし、検討の結果、そのような物質を添加していない水で十分な効果が得られることが確認された。これは、Ｍｇ添加によって酸化皮膜の形成能が非常に高くなることに起因すると考えられる。なお、薬液使用の有無、あるいは薬液を使用した場合の薬液の種類により、液滴衝突痕内部の凹凸形態の差異はほとんどみられない。
【００２４】
噴霧液として、具体的には上水道の水（水道水）や不純物の少ない工業用水をそのまま使用することができる。これにより、薬剤を溶かした水溶液を使用する場合に生じていたノズル詰まりの問題が解消され、また水溶液の調製，貯蔵，温度管理，供給の手間が省かれるため、製造コストが低減できる。
【００２５】
噴霧条件については、通板速度や板幅などに応じて液滴衝突痕を形成するのに十分な水量および吹き付け圧力を確保すればよい。噴霧したミストの液滴のなかにはめっき層表面に届かずに蒸発してしまうものも多数あるため、水量や吹き付け圧力は生成する液滴衝突痕の密度に大きく影響する。
【００２６】
【実施例】
〔実施例１〕
めっき原板として板厚１．２ｍｍの弱脱酸鋼板を用い、めっき浴中のＡｌ，Ｍｇを種々変化させたＺｎ系めっき浴に約３秒浸漬したのち引き上げ、気体絞り装置にてめっき付着量を鋼板片面あたり９０ｇ／ｍ^２、または５０ｇ／ｍ^２に調整した。その直後に空気圧：２．０ｋｇｆ／ｃｍ^２，水圧：１．５ｋｇｆ／ｃｍ^２の条件で２流体ノズルからミスト状の液滴を、未凝固の状態にあるめっき層表面に噴霧した。ノズルとめっき層表面の距離は２００ｍｍであり、水量は約１５０ｍｌ／ｍｉｎであった。噴霧時間は、約１秒に相当する。噴霧液には水道水を用いた。
噴霧を終えたのち、冷却速度８℃／ｓｅｃの条件で空冷し、めっき層を完全に凝固させた。
なお、めっき浴中には、Ａｌ，Ｍｇの他、０．０１８質量％のＳｉ，０．０３０質量％のＴｉ，０．０１５質量％のＢが含まれ、残部はＺｎおよび不可避的不純物であった。
【００２７】
得られためっき鋼板試料について、めっき層表面の形態を走査型電子顕微鏡（ＳＥＭ）で観察し、以下のように評価した。
○：凹部表面に「非常に複雑な形状」の凹凸を有する液滴衝突痕と平滑な面からなる表面形態を有するもの。
△：凹部表面に「複雑な形状」の凹凸を有する液滴衝突痕と平滑な面からなる表面形態を有するもの。
×：液滴衝突痕の存在は認められるが、複雑な形状の凹凸を有していないもの。
【００２８】
各試料のめっき層表面について、光沢度計を用いてＪＩＳ　Ｚ　８４７１に規定される６０度鏡面光沢度Ｇｓを測定した。
光沢度についての評価基準は以下のとおりである。
◎：Ｇｓが６０以上１００未満
○：Ｇｓが１００以上１５０未満
△：Ｇｓが１５０以上２００未満
×：Ｇｓが２００以上
【００２９】
各めっき鋼板試料について、ＪＩＳ　Ｚ　２３７１に規定される塩水噴霧試験を実施して、目視による外観観察により赤錆の発生が認められるまでの試験時間（すなわち、耐赤錆発生性）を評価した。試験片表面に「引っかききず」は設けていない。耐食性の評価基準は以下のとおりである。
（○以上を合格とする）
◎：耐赤錆発生性が３０００時間以上
○：耐赤錆発生性が１５００時間以上３０００時間未満
△：耐赤錆発生性が５００時間以上１５００時間未満
×：耐赤錆発生性が５００時間未満
【００３０】
各めっき鋼板試料について、めっき層剥離試験を行った。１８０°密着曲げを行い、その曲げ加工部に粘着テープを貼り付け、それを剥がした際に剥離しためっき層の量を目視で評価した。粘着テープはＪＩＳ　Ｚ　１５２２で定めるセロハン粘着テープを用いた。
めっき層剥離試験結果の評価基準は以下のとおりである。
（○以上を合格とする）
◎：剥離なし
○：ごくわずかに剥離が認められる
△：一部剥離が認められる
×：全面剥離が認められる
【００３１】
また、めっき浴のドロス発生量を調べた。各組成のめっき浴をめっき温度で２４時間大気中に静置した後、表面酸化により発生したドロスの量を目視で評価した。
ドロス発生の評価基準は以下のとおりである。
（○以上を合格とする）
○：ドロス発生なし
△：ドロス発生あり
×：著しいドロス発生あり
以上の結果を表１に示す。
【００３２】
【表１】

【００３３】
本発明例であるＮｏ．１〜４，８，９は、複雑形状の凹凸を有する適正衝突痕がめっき層表面に高い密度で分布しており、めっき付着量１００ｇ／ｍ^２未満のものにおいて、６０度鏡面光沢度Ｇｓが１５０未満の防眩性と、塩水噴霧試験による耐赤錆発生性が１５００時間以上の優れた耐食性が両立できることが確かめられた。特にＮｏ．８，９はめっき付着量が５０ｇ／ｍ^２と薄いものであるが、それぞれめっき付着量９０ｇ／ｍ^２のＮｏ．１，３と同等の性能を有することがわかる。また、本発明例はいずれも加工部のめっき層の耐剥離性に優れ、ドロスの発生も良好に抑えられた。
【００３４】
これに対し、比較例のＮｏ．５はめっき層のＡｌ含有量が高いため、めっき層剥離が生じた。Ｎｏ．６はめっき浴のＭｇ含有量が高いため、ドロスの発生が著しい。Ｎｏ．７はめっき浴のＭｇ含有量が低いため、複雑形状の凹凸を有する適正衝突痕が形成されず、防眩性に劣る。また耐食性も十分でない。
【００３５】
〔実施例２〕
Ａｌ：６．２質量％，Ｍｇ：３．０質量％，Ｓｉ：０．０２３質量％を含有し、残部がＺｎおよび不可避的不純物からなる溶融めっき浴を用い、鋼板片面当たりのめっき付着量を９０ｇ／ｍ^２に調整しためっき鋼板について、水ミストの噴霧量と光沢度の関係を調べた。めっき浴組成を一定とし、ミスト噴霧量を種々変化させた以外、めっき条件は実施例１と同様である。
表２に結果を示す。
【００３６】
【表２】

【００３７】
ミスト噴霧量を変えることで光沢度が１５０を超える防眩性の低いものから、光沢度が１０以下の極めて防眩性の高いものまで、幅広い範囲で好みの外観にコントロールできることがわかる。このように広い範囲で外観がコントロールできるのは、凹部表面に複雑形状の凹凸を有する液滴衝突痕（これらは防眩性の増大に効く）と平滑な面（これは光輝性の維持に効く）からなる特異な表面形態によるところが大きい。「なお、実施例１と同様の塩水噴霧試験を行った結果、いずれも耐赤錆発生性が１５００時間以上の良好な耐食性を示した。
【００３８】
図１〜３に、液滴衝突痕についての走査型電子顕微鏡（ＳＥＭ）写真を例示する。図１は表１のＮｏ．３（本発明例）、図２は表１のＮｏ．７（比較例）、図３は表２のＤ（本発明例）のものである。
本発明例である図１，図３のものは液滴衝突痕内部に複雑形状の凹凸が形成されているのに対し、めっき浴のＭｇ含有量が少なかった図２の液滴衝突痕ではそのような複雑形状の凹凸は生じていない。
【００３９】
【発明の効果】
本発明では、従来の防眩性溶融Ｚｎ基めっき鋼板とは異なる特異な凹凸形態のめっき層表面を実現した。
本発明の防眩性めっき鋼板は、その特異な表面形態により、めっき付着量が少ないものでも安定して高耐食性が得られる。また、表面の光沢度を広い範囲でコントロールすることができ、防眩性が極めて高いものでも高耐食性が維持される。このように、めっき付着量の少ない薄目付けＺｎ基めっき鋼板においても高い防眩性と優れた耐食性を両立させることは、従来困難であったことである。
したがって、本発明は防眩性溶融Ｚｎ基めっき鋼板の普及に寄与するものである。
【図面の簡単な説明】
【図１】本発明例の溶融Ｚｎ基めっき鋼板表面に形成された液滴衝突痕の形態を表す走査型電子顕微鏡（ＳＥＭ）写真である。
【図２】本発明例の溶融Ｚｎ基めっき鋼板表面に形成された液滴衝突痕の形態を表す走査型電子顕微鏡（ＳＥＭ）写真である。
【図３】比較例の溶融Ｚｎ基めっき鋼板表面に形成された液滴衝突痕の形態を表す走査型電子顕微鏡（ＳＥＭ）写真である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an antiglare hot-dip Zn-coated steel sheet having excellent corrosion resistance and a method for producing the same.
[0002]
[Prior art]
Hot-dip galvanized steel sheet is widely used as an original sheet for various coated steel sheets, and is used for building materials, deck plates for construction work sites, temporary frames for earth and sand prevention at civil engineering work sites, etc., without plating. More cases are used as is. However, when it is used outdoors with the plating appearance, it often reflects the sunlight and is too dazzling. In a residential area, the living environment is degraded, and in a construction site, not only the health of the worker is adversely affected, but also the safety of work is caused by dazzling.
[0003]
As an example of a steel sheet having improved plating appearance that is too dazzling, an anti-glare plated steel sheet having irregularities formed on a plating surface is known. In the continuous hot-dip plating line, a liquid is sprayed onto a surface of an unsolidified plating layer from a spray nozzle provided immediately after a plating amount reducing device, thereby forming irregularities on the surface. The irregularities reflect light irregularly, and exhibit antiglare properties.
[0004]
For example, Japanese Patent Application Laid-Open No. Hei 8-18863 discloses that, in the production of a hot-dip galvanized steel sheet containing 3% or less of Fe, Mg, Al, etc. in a plating layer, hot-dip galvanizing is performed by spraying water just above gas wiping. A technique is disclosed in which the average crystal grain size on the surface of the layer is 50 μm or less and the surface roughness Ra is 0.4 to 1.0 μm. According to this, an antiglare hot-dip galvanized steel sheet having a gloss G value of 10 to 150 is obtained.
[0005]
Japanese Patent Application Laid-Open No. 10-88310 discloses a technique for forming fine irregularities on the surface of a plating layer by performing steam-water spray cooling under specific conditions after gas wiping in the production of a hot-dip Zn-Al-based plated steel sheet. Is disclosed. In this case, a hot-dip Zn-Al-based plated steel sheet having a 60-degree specular gloss of 100 or less and excellent in antiglare properties has been obtained.
[0006]
[Problems to be solved by the invention]
The inventors investigated and examined the quality characteristics of these anti-glare hot-dip Zn-coated steel sheets in detail. As a result, it was found that the steel sheet having the plating layer formed with the unevenness by the above-described conventional method had lower corrosion resistance than the case where the plating layer was smooth. Moreover, the corrosion resistance of steel sheets having greater anti-glare properties decreased. This is considered to be because the thickness of the plating layer in the concave portion was reduced due to the formation of the concave and convex portions. In particular, it is presumed that those having high anti-glare properties have large irregularities, so that the thickness of the plating layer in the concave portions is further reduced, and the corrosion resistance is greatly reduced.
[0007]
Thus, the above-mentioned anti-glare steel sheet cannot make the thickness of the plating layer too small in order to maintain the corrosion resistance. If the coating weight is less than 100 g / m ² , durability in outdoor may be a practical problem.
[0008]
In order to form irregularities having a high antiglare effect in the production of the steel plate, it is important to obtain as much heat removal effect as possible from the liquid to be sprayed. In Japanese Patent Application Laid-Open No. Hei 8-18863, a method of spraying water vigorously is adopted, and in Japanese Patent Application Laid-Open No. Hei 10-88310, a method of spraying an aqueous solution containing ammonium hydrogen phosphate, which enhances the heat removal effect, in the form of a mist is adopted. I have. However, the former has a disadvantage that the thickness of the plating layer in the concave portion tends to be excessively thin, and the latter has a disadvantage that the addition of a substance that enhances the heat removal effect causes nozzle clogging and increases the cost.
[0009]
At present, no hot-dip Zn-based plated steel sheet satisfying all of the following points has been found.
(1) Having high anti-glare properties and excellent corrosion resistance desired for building materials and other outdoor uses. (2) Even when the thickness of the plating layer is small (for example, in the case of thin plating such that the coating weight is less than 100 g / m ^{2 on} one side, or even less than 60 g / m ^{2 on} one side), the performance of the above (1) is exhibited. .
(3) To exhibit the performance of (1) in the appearance as it is after hot-dip plating.
(4) The anti-glare property can be controlled in a wide range (for example, 60-degree specular glossiness is 5-150) by a method that does not use a substance for enhancing a heat removal effect.
The present invention aims to achieve that.
[0010]
[Means for Solving the Problems]
The inventors have produced Zn-based plated steel sheets of various plating compositions and studied means for imparting antiglare properties in a hot-dip plating line. As a result, it has been found that when an appropriate amount of Mg and Al is added to the plating bath, the surface properties obtained when water mist is sprayed on the surface of the unsolidified plating layer have a unique form. That is, the portion (droplet collision mark) where the droplet of the water mist collides slightly becomes a concave portion, and the concave-convex surface has complicated irregularities which are extremely easy to diffuse light. Then, smoothness is maintained at a portion where the droplet did not collide. With such unique surface properties, an antiglare plated steel sheet satisfying the above (1) to (4) can be obtained. The present invention has been completed based on these findings.
[0011]
In other words, the object is to provide a surface of a hot-dip Zn-based plating layer containing 1.0 to 6.0% by mass of Mg and 4.0 to 22.0% by mass of Al, which has a concave-convex surface with a complicated shape. This is achieved by an anti-glare hot-dip galvanized steel sheet which has a surface morphology consisting of droplet collision marks and a smooth surface, and has a 60-degree specular glossiness of less than 150 specified in JIS Z8741 and has excellent corrosion resistance.
In particular, the present invention provides a steel sheet having a coating weight of less than 100 g / m ² per one surface of a steel sheet.
Here, the diameter of the droplet collision mark refers to the average of the maximum diameter and the minimum diameter of the portion where the droplets of the water mist collide.
Hereinafter, when simply referred to as “glossiness” in the present specification, it means “60-degree specular glossiness specified in JIS Z8741”.
[0012]
The anti-glare hot-dip Zn-based plated steel sheet has a red rust resistance of 1500 hours or more in a salt spray test specified in JIS Z 2371, or a 60-degree specular gloss specified in JIS Z 8741. Provide a degree less than 60.
[0013]
Further, as a composition of the Zn-based plating layer, a composition containing 1.0 to 6.0% by mass of Mg and 4.0 to 22.0% by mass of Al and the balance consisting of Zn and unavoidable impurities, or Mg: 1.0 to 6.0% by mass, Al: 4.0 to 22.0% by mass, Si: 0.07% by mass or less, B: 0.045% by mass or less, Ti: 0.1% by mass % Or less, with the balance comprising Zn and unavoidable impurities.
[0014]
Further, in the present invention, as a method for producing the anti-glare plated steel sheet, after adjusting the amount of hot-dip coating, on the surface of the plating layer that has not yet solidified, water containing no substance for enhancing the heat removal effect is added. A method for spraying using a two-fluid nozzle is provided.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
The plated steel sheet of the present invention is characterized in that its surface has a unique irregular shape.
FIGS. 1 to 3 show scanning electron microscope (SEM) photographs of droplet collision traces formed on the surface of a plating layer of a sample obtained in Examples described later. 1 and 3 show the droplet collision marks on the steel sheet of the present invention.
[0016]
The droplet collision mark is a portion where the droplet of the water mist collides, and is slightly recessed from the periphery. It can be seen that the concave portion has a complicated shape. The portion to which the mist droplets did not strike maintains the smoothness. As seen from these examples, the surface of the plated steel sheet of the present invention does not need to have the unevenness uniformly formed on the entire surface of the plating layer. By having a peculiar surface morphology in which a droplet collision trace having a complex irregularity and a smooth part coexist, a proper antiglare property is exhibited in appearance.
[0017]
In a plated steel sheet having such a peculiar surface morphology, the density of droplet collision traces distributed on the surface greatly affects antiglare properties in appearance. That is, by controlling the amount of mist that collides with the plating layer surface, for example, from those having a very high antiglare property such as a gloss of 10 or less to those having a low antiglare property whose gloss exceeds 150. It is possible to make products with glossiness.
In consideration of the outdoor use as described above, if the glossiness is less than 150, the antiglare property is insufficient.
[0018]
In order to stably obtain an antiglare property having a gloss of less than 150, it is possible to adjust the distribution density (number per unit area of the steel sheet) of droplet collision marks having a diameter of 50 μm or more formed on the plating layer surface. Become. It was found that a small droplet collision mark having a diameter of less than 50 μm did not significantly affect the antiglare property in appearance. Therefore, excluding them, the distribution density may be adjusted by focusing only on the droplet collision traces having a diameter of 50 μm or more. The correlation between distribution density and gloss depends on the average diameter of the droplet collision traces.
In particular, in order to stably obtain a high antiglare property having a glossiness of less than 60, it is advantageous to set the average diameter of the droplet collision marks to 100 μm or more.
[0019]
In order to obtain the surface of the Zn-based plating layer having the above-described peculiar irregularities, a Zn-Al-Mg-based alloy plating bath containing an appropriate amount of Mg is used.
When the Mg content of the plating bath is 1.0% by mass or more, the water is removed from the plating bath to adjust the amount of hot-dip coating, and then water mist is sprayed on the unsolidified plating layer surface. The above-mentioned droplet collision mark having a complicatedly shaped unevenness is formed at the mist collision location. This is considered to be due to the fact that the addition of about 1% by mass or more of Mg significantly improves the ability to form an oxide film in the molten plating layer.
If the Mg content exceeds 6.0% by mass, a coarse Zn ₂ Mg phase is generated in the plating layer, and local corrosion occurs in this portion, so that the corrosion resistance of the plating layer is deteriorated. Further, dross is remarkably generated in the plating bath. Therefore, the Mg content needs to be 6.0% by mass or less. However, depending on the plating conditions, if the Mg content exceeds 4.0% by mass, the tendency to form a Zn ₂ Mg phase increases, so it is more desirable to set the content to 4.0% by mass or less.
[0020]
Al exhibits an action of suppressing the generation of surface oxidized dross in a bath whose generation is promoted by the addition of Mg. If the Al content in the bath is lower than 4.0% by mass, the effect is not sufficiently exhibited. On the other hand, when the Al content is higher than 22% by mass, the solidification start temperature in the plating bath increases, so that the plating bath temperature must be increased, whereby the generation of the alloy layer becomes remarkable and the plating layer is easily peeled. Become.
In consideration of economical efficiency in the actual operation, the Al content in the plating bath is preferably set to 15% by mass or less.
[0021]
As described above, the hot-dip Zn-based plated steel sheet of the present invention is characterized in that the plating layer contains 1.0 to 6.0% by mass of Mg and 4.0 to 22.0% by mass of Al. . Particularly preferable contents of Mg and Al in the plating layer are Mg: 1.0 to 4.0% by mass and Al: 4.0 to 15.0% by mass. Various elements other than Mg and Al may be contained as necessary. However, since it is a "Zn group", it is necessary that at least 50% by mass or more of Zn is contained in the plating layer.
As a specific plating layer composition, Mg: 1.0 to 6.0% by mass, preferably 1.0 to 4.0% by mass, and Al: 4.0 to 22.0% by mass, preferably 4.0 to 15. 0% by mass, the balance consisting of Zn and unavoidable impurities, or Mg: 1.0 to 6.0% by mass, preferably 1.0 to 4.0% by mass, and Al: 4.0 to 4.0% by mass. 22.0% by mass, preferably 4.0 to 15.0% by mass, and Si: 0.07% by mass or less, B: 0.045% by mass or less, and Ti: 0.1% by mass or less. And those containing two or more species, the balance being Zn and unavoidable impurities.
[0022]
As for the coating weight, a wide range that can be manufactured in a continuous hot-dip plating line can be applied. Even if the plating layer is considerably thin in the concave and convex portions formed for imparting antiglare properties, the Zn-Al-Mg-based alloy plating layer having the above composition exhibits high corrosion resistance. Therefore, it is possible to provide a thin-plated steel sheet which has conventionally been difficult to achieve both corrosion resistance and anti-glare properties by applying the present invention. For example, when the coating weight is less than 100 g / m ² , or even thinner than 60 g / m ^2, a red rust resistance of 1500 hours or more is obtained in a salt spray test specified in JIS Z 2371. It is possible to achieve both corrosion resistance and high antiglare property having a glossiness of less than 60.
[0023]
Such anti-glare plated steel sheet having high corrosion resistance can be relatively easily manufactured by providing a two-fluid nozzle immediately after a coating weight adjusting device (such as a gas wiping nozzle) in a normal continuous hot-dip plating line. Can be. That is, it can be manufactured by a method in which a plating base plate is immersed in a plating bath and pulled up to adjust the amount of hot-dip coating, and then a mist-like liquid is sprayed from a two-fluid nozzle onto the surface of the plating layer that has not yet solidified. At this time, as the liquid to be sprayed, a chemical solution to which a substance that enhances the heat removal effect, such as ammonium hydrogen phosphate, can be used. However, as a result of the examination, it was confirmed that sufficient effect could be obtained with water to which such a substance was not added. This is thought to be due to the fact that the addition of Mg significantly increases the ability to form an oxide film. It should be noted that there is almost no difference in the concave and convex form inside the droplet collision trace depending on whether or not the chemical is used, or the type of the chemical when the chemical is used.
[0024]
As the spray liquid, specifically, tap water (tap water) or industrial water with less impurities can be used as it is. As a result, the problem of nozzle clogging that has occurred when using an aqueous solution in which a drug is dissolved is eliminated, and the labor for preparation, storage, temperature control, and supply of the aqueous solution is omitted, so that manufacturing costs can be reduced.
[0025]
Regarding the spraying conditions, it is sufficient to secure a sufficient amount of water and a sufficient spray pressure to form a droplet collision mark according to the passing speed, the plate width, and the like. Since many of the sprayed mist droplets do not reach the plating layer surface and evaporate, the amount of water and the spray pressure greatly affect the density of the generated droplet collision marks.
[0026]
【Example】
[Example 1]
A weakly deoxidized steel sheet having a thickness of 1.2 mm was used as a base plate for plating, immersed for about 3 seconds in a Zn-based plating bath in which Al and Mg in the plating bath were variously changed, and then lifted up. It was adjusted to steel per side 90 g / ^{m 2} or 50g / ^{m 2,.} Immediately thereafter, mist-like droplets were sprayed from a two-fluid nozzle onto the unsolidified plating layer surface under the conditions of air pressure: 2.0 kgf / cm ² and water pressure: 1.5 kgf / cm ² . The distance between the nozzle and the plating layer surface was 200 mm, and the amount of water was about 150 ml / min. The spray time corresponds to about 1 second. Tap water was used as the spray liquid.
After the spraying was completed, air-cooling was performed at a cooling rate of 8 ° C./sec to completely solidify the plating layer.
The plating bath contains, in addition to Al and Mg, 0.018% by mass of Si, 0.030% by mass of Ti, and 0.015% by mass of B, with the balance being Zn and unavoidable impurities. Was.
[0027]
About the obtained plated steel sheet sample, the form of the plating layer surface was observed with a scanning electron microscope (SEM), and evaluated as follows.
：: A surface morphology consisting of a droplet collision mark having irregularities of “very complicated shape” on the concave surface and a smooth surface.
Δ: A surface morphology consisting of a droplet collision mark having irregularities of “complex shape” on the concave surface and a smooth surface.
×: The presence of a droplet collision mark is recognized, but the sample does not have a complicated shape of irregularities.
[0028]
With respect to the plating layer surface of each sample, a 60-degree specular gloss Gs defined in JIS Z 8471 was measured using a gloss meter.
The evaluation criteria for the glossiness are as follows.
◎: Gs is 60 or more and less than 100 ：: Gs is 100 or more and less than 150 △: Gs is 150 or more and less than 200 ×: Gs is 200 or more
Each of the plated steel sheet samples was subjected to a salt spray test specified in JIS Z 2371, and the test time until occurrence of red rust was observed by visual observation of external appearance (that is, resistance to red rust generation) was evaluated. No "scratch" was provided on the surface of the test piece. The evaluation criteria for the corrosion resistance are as follows.
(Pass or more is acceptable)
：: Red rust generation resistance of 3000 hours or more ○: Red rust generation resistance of 1500 hours or more and less than 3000 hours △: Red rust generation resistance of 500 hours or more and less than 1500 hours X: Red rust resistance of 500 hours or less and less than 500 hours
Each plated steel sheet sample was subjected to a plating layer peeling test. 180 ° adhesion bending was performed, an adhesive tape was stuck on the bent portion, and the amount of the peeled plating layer when peeled off was visually evaluated. As the adhesive tape, a cellophane adhesive tape specified in JIS Z 1522 was used.
The evaluation criteria for the plating layer peeling test results are as follows.
(Pass or more is acceptable)
◎: No peeling ：: Very slight peeling is observed Δ: Partial peeling is observed ×: Full-surface peeling is observed [0031]
Further, the amount of dross generated in the plating bath was examined. After the plating baths of each composition were allowed to stand in the atmosphere at the plating temperature for 24 hours, the amount of dross generated by surface oxidation was visually evaluated.
The evaluation criteria for the dross generation are as follows.
(Pass or more is acceptable)
：: No dross generated Δ: Dross generated X: Notable dross generated The above results are shown in Table 1.
[0032]
[Table 1]

[0033]
No. 1 of the present invention example. In Nos. 1 to 4, 8, and 9, appropriate collision marks having irregularities of complicated shapes are distributed at a high density on the surface of the plating layer, and when the plating adhesion amount is less than 100 g / m ² , the 60-degree specular gloss Gs is It was confirmed that the anti-glare property of less than 150 and the excellent corrosion resistance of the red rust resistance of 1500 hours or more in the salt spray test were compatible. In particular, no. 8 and 9 are those amounts plating adhesion is thin and 50 g / ^{m 2,} but the coating weight 90 g / ^{m 2,} respectively No. It turns out that it has performance equivalent to 1,3. In addition, all of the examples of the present invention were excellent in the peeling resistance of the plated layer in the processed portion, and the generation of dross was well suppressed.
[0034]
On the other hand, in Comparative Example No. In No. 5, since the Al content of the plating layer was high, peeling of the plating layer occurred. No. In No. 6, dross is remarkably generated due to a high Mg content in the plating bath. No. In No. 7, since the Mg content of the plating bath is low, an appropriate collision mark having a complicated shape of irregularities is not formed, and the anti-glare property is poor. Also, the corrosion resistance is not sufficient.
[0035]
[Example 2]
Using a hot-dip plating bath containing 6.2% by mass of Al, 3.0% by mass of Mg, and 0.023% by mass of Si, and the balance consisting of Zn and unavoidable impurities, With respect to the plated steel sheet adjusted to 90 g / m ² , the relationship between the spray amount of water mist and the glossiness was examined. The plating conditions were the same as in Example 1, except that the plating bath composition was kept constant and the mist spray amount was varied.
Table 2 shows the results.
[0036]
[Table 2]

[0037]
It can be seen that by changing the amount of the mist spray, the desired appearance can be controlled in a wide range from a low anti-glare property having a gloss of more than 150 to an extremely high anti-glare property having a gloss of 10 or less. The appearance can be controlled in such a wide range because the droplet collision traces having complicated irregularities on the concave surface (these are effective for increasing the antiglare property) and the smooth surface (this is effective for maintaining the glittering property) )). "As a result of the same salt spray test as in Example 1, all of them showed good corrosion resistance with red rust resistance of 1500 hours or more.
[0038]
FIGS. 1 to 3 illustrate scanning electron microscope (SEM) photographs of droplet collision marks. FIG. 2 (Example of the present invention) and FIG. 7 (Comparative Example), and FIG. 3 shows D (Example of the present invention) in Table 2.
In FIGS. 1 and 3, which are examples of the present invention, complex irregularities are formed inside the droplet collision trace, whereas in the droplet collision trace of FIG. Such complicated shape irregularities are not generated.
[0039]
【The invention's effect】
In the present invention, the surface of the plating layer having a unique uneven shape different from that of the conventional anti-glare hot-dip Zn-based steel sheet is realized.
The anti-glare plated steel sheet of the present invention can achieve high corrosion resistance stably even with a small amount of plating due to its unique surface morphology. Further, the glossiness of the surface can be controlled in a wide range, and high corrosion resistance is maintained even if the antiglare property is extremely high. As described above, it has been conventionally difficult to achieve both high antiglare property and excellent corrosion resistance even in a thin-coated Zn-based plated steel sheet having a small amount of plating.
Therefore, the present invention contributes to the spread of anti-glare hot-dip Zn-coated steel sheets.
[Brief description of the drawings]
FIG. 1 is a scanning electron microscope (SEM) photograph showing the form of a droplet collision trace formed on the surface of a hot-dip Zn-plated steel sheet according to the present invention.
FIG. 2 is a scanning electron microscope (SEM) photograph showing the form of a droplet collision mark formed on the surface of a hot-dip Zn-base plated steel sheet according to the present invention.
FIG. 3 is a scanning electron microscope (SEM) photograph showing the form of a droplet collision trace formed on the surface of a hot-dip Zn-plated steel sheet of a comparative example.

Claims

The surface of the hot-dip Zn-based plating layer containing 1.0 to 6.0% by mass of Mg and 4.0 to 22.0% by mass of Al is smooth with a droplet collision mark having a complicated shape on the concave surface. An anti-glare hot-dip Zn-based steel sheet having excellent corrosion resistance, having a surface morphology consisting of various surfaces, and having a 60-degree specular glossiness defined by JIS Z # 8741 of less than 150.

A hot-dip Zn-based plating layer containing 1.0 to 4.0% by mass of Mg and 4.0 to 22.0% by mass of Al is formed with an adhesion amount of less than 100 g / m ² per one surface of the steel sheet. The plating layer surface has a surface morphology consisting of a droplet collision mark having a complex shape of irregularities on the concave surface and a smooth surface, and has excellent corrosion resistance in which the 60-degree specular glossiness specified in JIS Z8741 is less than 150. Anti-glare hot-dip Zn-based steel sheet.

The antiglare hot-dip galvanized steel sheet having excellent corrosion resistance according to claim 1 or 2, which exhibits a red rust resistance of 1500 hours or more in a salt spray test specified in JIS Z 2371.

The corrosion resistance according to claim 1 or 2, wherein the 60-degree specular glossiness specified in JIS Z # 8741 is less than 60, and the composition exhibits a red rust resistance of 1500 hours or more in a salt spray test specified in JIS Z # 2371. Excellent anti-glare hot-dip Zn-based steel sheet.

The Zn-based plating layer contains Mg: 1.0 to 6.0% by mass and Al: 4.0 to 22.0% by mass, with the balance being Zn and unavoidable impurities. Plated steel sheet.

The Zn-based plating layer contains 1.0 to 6.0% by mass of Mg and 4.0 to 22.0% by mass of Al, and further contains 0.07% by mass or less of Si and 0.045% by mass or less of B. , Ti: one or more of 0.1% by mass or less, and the balance consists of Zn and unavoidable impurities.

The plating according to any one of claims 1 to 7, wherein after adjusting the coating weight of the hot-dip plating, water to which a substance that enhances the heat removal effect has not been added is sprayed on the surface of the plating layer that has not yet solidified using a two-fluid nozzle. Steel plate manufacturing method.