JP3617234B2 - Hot-dip Zn-Al alloy plated steel sheet with excellent surface smoothness and method for producing the same - Google Patents
Hot-dip Zn-Al alloy plated steel sheet with excellent surface smoothness and method for producing the same Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、主に建材用途の塗装鋼板あるいはラミネート鋼板用の原板として用いられる、めっき表面の平滑性に優れた溶融Ｚｎ−Ａｌ合金めっき鋼板及びその製造方法に関する。
【０００２】
【従来の技術】
鋼板への溶融めっきは、主に耐食性の向上を目的として行われており、その製品は自動車、建材、家電用途を中心に広く使用されている。特に、通常の溶融亜鉛めっきにアルミニウムを添加しためっき系は耐食性に優れることから、その開発が進み、近年主に、５重量％のアルミニウムが添加された溶融Ｚｎ−Ａｌ合金めっき鋼板が広く使用されている。この溶融Ｚｎ−Ａｌ合金めっき鋼板は鋼板素地との反応層が薄いため優れた耐食性及び加工性を有している。しかし、この溶融Ｚｎ−Ａｌ合金めっき鋼板のめっき皮膜が凝固する時点における冷却方向は、鋼板面に対して垂直方向であり、このめっき鋼板表面には、放射状成長した２〜５ｍｍ大のスパングルが形成され、このスパングル粒界には凝固引け巣（以下デンツと記載）が存在する。このデンツは片面付着量が８０ｇ／ｍ２ 以上のめっき皮膜にて顕著に生成し、その深さはめっき皮膜の半分にも及ぶ。このデンツを軽減あるいは消失させるために従来より様々な検討がなされている。検討は大きく２つに分類され、１つはめっき後の冷却の制御による、もう１つは浴中への核生成元素の添加による、スパングルの微細化である。前者については、水ミストあるいは薬液ミストといった、微細化された熱媒体をまだ溶融状態にあるめっき皮膜に接触させ、これによりめっき皮膜を急冷しスパングルを微細化する方法であり、広く利用されている。後者については、特開平２−７３９５４号公報では浴中にＳｉを添加する方法、特開平５−１２５５１５号公報、特開平６−１５８２５６号公報、特開平６−１５８２５７号公報、特開平６−１５８２５８号公報及び特開平６−１５８２５９号公報では浴中にＴｉを添加する方法が開示されている。
【０００３】
【発明が解決しようとする課題】
しかしながら、上記した従来のめっき後の冷却の制御方法では、スパングルは消失するものの、水あるいは薬液をスパングル消失に十分な量をめっき皮膜に接触させると、現在一般に流通しているミストスプレーノズルによる噴霧では、熱媒体と溶融状態にあるめっき皮膜の接触に由来する微細な凹凸が生成してしまう。一方、特開平２−７３９５４号公報の技術による浴中へのＳｉの添加は、そのスパングル微細化に有効な添加方法が困難で単純にＡｌ−Ｓｉ合金の形態で添加してもスパングルの核として有効に作用する高融点のＡｌ−Ｓｉ系合金やＳｉ−Ｏ系の化合物は生成せず、逆に共晶形成に作用しスパングルが肥大することもある。また、特開平５−１２５５１５号公報、特開平６−１５８２５６号公報、特開平６−１５８２５７号公報、特開平６−１５８２５８号公報及び特開平６−１５８２５９号公報の技術による浴中へのＴｉの添加は、高融点のＡｌ−Ｔｉ系合金がスパングルの核として作用し、その結果、スパングルは少なくても１／１０程度に微細化するが、デンツの縮小効果は必ずしも十分ではなく、さらに、高融点のＡｌ−Ｔｉ系合金を定常的に被めっき物である鋼板に随伴するめっき皮膜中に供給するのも困難である。その他めっき皮膜凝固後に後加熱することによりスパングルを消失させる技術も特開昭５２−１３１９３４号公報に開示されている。この方法は効果があるが、コストがかかるうえ、実際には後加熱後の冷却が問題となる。
【０００４】
本発明の目的は、スパングル粒界のひけすが問題となる片面めっき付着量が８０ｇ／ｍ２ 以上の溶融Ｚｎ−Ａｌ合金めっき鋼板に関して、この凝固ひけすを緩和させることにより、表面平滑性の高い溶融Ｚｎ−Ａｌ合金めっき鋼板及びその製造方法を提供することにある。更には、得られた溶融Ｚｎ−Ａｌ合金めっき鋼板を原板とすることにより、表面平滑性の高い溶融Ｚｎ−Ａｌ合金めっき塗装鋼板あるいは溶融Ｚｎ−Ａｌ合金めっきラミネート鋼板を提供することにある。
【０００５】
【課題を解決するための手段】
前記課題を解決し目的を達成するために、本発明は以下に示す手段を用いている。
（１）本発明のめっき鋼板は、質量％で、Ａｌ：１〜２０％を含み、残部がＺｎ及び不可避的不純物からなる溶融Ｚｎ−Ａｌ合金めっき鋼板において、めっき皮膜表面のスパングルがうろこ状に偏心していることを特徴とする表面平滑性に優れた溶融Ｚｎ−Ａｌ合金めっき鋼板である。
【０００６】
（２）本発明のめっき鋼板は、めっき被膜表面のスパングル粒界のひけす深さＲｙが８μｍ以下であることを特徴とする上記（１）に記載の表面平滑性に優れた溶融Ｚｎ−Ａｌ合金めっき鋼板である。
【０００７】
（３）本発明のめっき鋼板の製造方法は、質量％で、Ａｌ：１〜２０％を含み、残部がＺｎ及び不可避的不純物からなり、めっき皮膜表面のスパングルがスパングルレスあるいはうろこ状に偏心している溶融Ｚｎ−Ａｌ合金めっき鋼板を製造する方法において、めっきした後のめっき皮膜の冷却方向がめっき鋼板に対して水平方向であることを特徴とする表面平滑性に優れた溶融Ｚｎ−Ａｌ合金めっき鋼板の製造方法である。
（４）本発明のめっき鋼板の製造方法は、質量％で、Ａｌ：１〜２０％を含み、残部がＺｎ及び不可避的不純物からなり、めっき皮膜表面のスパングルがスパングルレスあるいはうろこ状に偏心し、めっき皮膜表面のスパングル粒界のひけす深さＲｙが８μｍ以下である溶融Ｚｎ−Ａｌ合金めっき鋼板を製造する方法において、めっきした後のめっき皮膜の冷却方向がめっき鋼板に対して水平方向であることを特徴とする表面平滑性に優れた溶融Ｚｎ−Ａｌ合金めっき鋼板の製造方法である。
（５）本発明のめっき鋼板の製造方法は、めっき浴中に、さらに、質量％で、Ｍｇ：１％以下（０％を含む）を含むことを特徴とする、上記（３）または（４）のいずれか一方に記載の表面平滑性に優れた溶融Ｚｎ−Ａｌ合金めっき鋼板の製造方法である。
【０００８】
（６）本発明の塗装鋼板は、上記（１）または（２）に記載の溶融Ｚｎ−Ａｌ合金めっき鋼板に光沢度７０以上の塗膜を形成してなることを特徴とする溶融Ｚｎ−Ａｌ合金めっき塗装鋼板である。
【０００９】
（７）本発明のラミネート鋼板は、上記（１）または（２）に記載の溶融Ｚｎ−Ａｌ合金めっき鋼板に光沢度７０以上のフィルムのラミネート被膜を形成してなることを特徴とする溶融Ｚｎ−Ａｌ合金めっきラミネート鋼板である。
【００１０】
なお、上記（３）および（４）のスパングルレス、および上記（１），（３），（４）のスパングルがうろこ状に偏心は、各々以下のように定義する。
スパングルレス：一方向への凝固により、めっき皮膜表面の凝固粒界が消失したもの（デンツは存在しない）。
【００１１】
スパングルがうろこ状に偏心：スパングルが放射状成長せずに偏心し、めっき皮膜表面の凝固粒界が分散したもの（デンツは軽減される）。
また、上記（２）および（４）のひけす深さＲｙはＪＩＳ Ｂ ０６０１で規定され、上記（６）および（７）の光沢度はＪＩＳ Ｋ ５４００で規定されるものである。
【００１２】
【発明の実施の形態】
本発明者は、スパングル粒界のひけすが問題となる片面めっき付着量が８０ｇ／ｍ２ 以上の溶融Ｚｎ−Ａｌ合金めっき鋼板に関して、表面平滑性の高い溶融Ｚｎ−Ａｌ合金めっき鋼板を得るために、凝固ひけすを緩和させるめっき後の冷却の制御方法について、鋭意研究を重ねた。
【００１３】
その結果、めっき皮膜が凝固する時点における冷却方向を、従来の鋼板面に対して垂直方向から水平方向にすることにより、従来、放射状成長していたスパングル形状が偏心あるいは消失するという知見を得た。これにより、スパングル粒界である放射状スパングルの三重点粒界が解消、あるいはスパングル自体が消失し、この部分に生成する凝固ひけすも緩和あるいは消失する。
【００１４】
以上の知見に基づき、本発明者は、めっき浴組成を制御し、めっき皮膜が凝固する時点における冷却方向を、鋼板面に対して水平方向にして、めっき表面のスパングルの形態及びスパングル粒界のひけす深さを制御することにより、表面平滑性に優れた本発明の溶融Ｚｎ−Ａｌ合金めっき鋼板を見出し、さらに、得られた溶融Ｚｎ−Ａｌ合金めっき鋼板を原板とすることにより、表面平滑性の高い溶融Ｚｎ−Ａｌ合金めっき塗装鋼板あるいは溶融Ｚｎ−Ａｌ合金めっきラミネート鋼板を見出し、本発明を完成させた。
【００１５】
すなわち、本発明はめっき浴組成、めっき表面のスパングルの形態及びスパングル粒界のひけす深さ、及び製造条件を下記範囲に限定することにより、表面平滑性に優れた溶融Ｚｎ−Ａｌ合金めっき鋼板を得ることができ、さらに、得られた得られた溶融Ｚｎ−Ａｌ合金めっき鋼板を原板とすることにより、表面平滑性の高い溶融Ｚｎ−Ａｌ合金めっき塗装鋼板あるいは溶融Ｚｎ−Ａｌ合金めっきラミネート鋼板を得ることができる。
【００１６】
以下、本発明の成分添加理由、成分限定理由、めっき表面のスパングルの形態及びスパングル粒界のひけす深さの限定理由、及び製造条件の限定理由について説明する。
【００１７】
（１）めっき浴組成範囲
Ａｌ：１〜２０％
めっき浴中のＡｌ濃度の範囲が１〜２０％であるのは、この濃度範囲において製造されるめっき鋼板表面には放射状の共晶成長にともなう粒状組織（スパングル）とその粒界“ひけす”が生成し、この“ひけす”が、めっき鋼板およびその表面に塗装あるいはフィルムをラミネートした製品表面の外観を著しく悪化させることに基づく。
【００１８】
また、Ａｌが１％未満ではＡｌ−Ｚｎの共晶体の形成が少ないため、めっき層の耐食性は十分ではない。一方、浴中のＡｌ量が２０％を超えては、めっき−鋼界面でのＡｌとＦｅの相互拡散反応が過剰に進み加工に脆いＦｅ−Ａｌ系合金層の異常成長があり、初期のめっき密着性はもとより湿潤雰囲気下における点状赤錆の発生など、耐食性に対する弊害を招くことが考えられる。従って、Ａｌ量は１〜２０％である。
【００１９】
Ｍｇ：１％以下（０％を含む）
Ｍｇ添加量が１％以下（０％を含む）であるのは、１％を超えてＭｇを添加した場合、Ｍｇが共晶成長に作用し、放射状スパングル成長を呈しなくなるためである。
【００２０】
Ｓｉ、Ｔｉ、Ｎｉ、Ｃｏ、Ｓｂに代表される第三元素は放射状スパングル形成という機構には影響しないため、本発明では、その添加量は特に制限しないが、例えば、Ｓｉの過剰添加は皮膜の加工性低下を招く、Ｔｉの過剰添加は浴歩留まりの低下を招く、Ｓｂの過剰添加は粒界腐食を促進する、といった点を考慮した最適添加量を設定することが望ましい。
【００２１】
（２）スパングルの形態及びスパングル粒界のひけす深さ
本発明の溶融Ｚｎ−Ａｌ合金めっき鋼板は、めっき皮膜表面のスパングルが消失あるいは偏心しており、スパングル粒界のひけす深さは、ＪＩＳ Ｂ ０６０１に基づくＲｙが８μｍ以下である。
めっき表面のスパングルの形態をスパングルレス（消失）あるいは偏心状態にすることにより、図２（ａ）に示すような従来の放射状スパングルの三重点粒界が解消、あるいはスパングル自体が消失し、この部分に生成する凝固ひけすも緩和あるいは消失する。この結果、図２（ｂ）、（ｃ）に示すように、鋼板めっき表面の凹凸が平滑化される。
【００２２】
また、めっき表面のスパングル粒界のひけす深さが８μｍを超える場合には、個々のスパングルが目視で見て目立つ様になり、外観不良の問題を生じる。一方、８μｍ以下の場合は、外観不良の問題が生じない。
【００２３】
上記のめっき浴組成、めっき表面のスパングルの形態及びスパングル粒界のひけす深さに調整することにより、スパングル粒界のひけすが問題となる片面めっき付着量が８０ｇ／ｍ２ 以上の溶融Ｚｎ−Ａｌ合金めっき鋼板に関して、この凝固ひけすを緩和させて、表面平滑性の高い溶融Ｚｎ−Ａｌ合金めっき鋼板を得ることが可能となる。
【００２４】
このような特性のめっき鋼板は、以下の製造方法により製造することができる。
（３）めっき鋼板製造工程
上記の成分組成範囲に調整しためっき浴でめっきした後、めっき皮膜の冷却方向がめっき鋼板に対して水平方向となるように、鋼板冷却を制御する。
【００２５】
これは、めっき皮膜が凝固する時点における冷却方向を、従来の鋼板面に対して垂直方向から水平方向にすることにより、従来、放射状成長していためっき皮膜表面のスパングルを消失あるいは偏心させて、めっき表面の平滑性を向上させるためである。
従来方法での鋼板冷却の概念を図１（ａ）に示す。連続式溶融めっき製造ラインではめっき浴１から出ためっき鋼板はトップロール２に至る間のめっき皮膜温度が共晶温度となる領域（すなわち、めっき皮膜凝固温度域）で、冷却方向がＤ１（鋼板垂直方向）となるように冷却してめっき皮膜を凝固させる。従来技術ではこの冷却過程はいかなる方法、例えば大気放冷、空気噴霧冷却あるいはミスト噴霧冷却、においても鋼板の保有する熱量は鋼板の垂直方向かつ鋼板幅方向にほぼ均一に放出される。
【００２６】
そのため、冷却過程で凝固温度に達しためっき皮膜は最終的なスパングル数に匹敵する凝固核を起点として成長していく際に、ほぼ同心円状に広がるため、各スパングルの粒界は特定の場所に集中してしまう。よって、当然のことながら、図２（ａ）に示すような大きな引け巣が生成し、つまり、デンツを形成することとなる。
これに対してその起点から放射状に凝固成長する際に、めっき鋼板の保有する熱量を図１（ａ）に示すような鋼板垂直方向（Ｄ１）ではなく、図１（ｂ）， （ｃ）に示すように、鋼板水平方向（Ｄ２、Ｄ３）とすることにより、スパングルは凝固起点から放射状ではなく、ある特定方向に選択的に成長するようになる。この様な成長過程をとることにより、各スパングルの最終凝固部は従来の三重点から二重点あるいは線へと移行する。すなわち凝固引け巣の集中が緩和され、この結果、図２（ｂ），（ｃ）に示すように、これに基づく表面凹凸が平滑化される。
【００２７】
冷却制御のための冷熱源に関する制限はなく、空気吹き付け、炭酸ガス、窒素ガス吹き付け、ミスト冷却等の非接触式や端面に対する冷却ロール設置等の接触式が適用される。ただし、冷却方向Ｄ２の場合はめっき皮膜凝固温度域に相当する位置にて、冷却方向Ｄ３の場合はめっき皮膜凝固完了温度域に相当する位置にて、それぞれ、冷熱源を設置する必要がある。
なお、通常、凝固温度域は板厚、ラインスピード等により変動するため、冷熱源は操業条件によりその高さ方向位置を任意に変更可能な構造をとることが好ましい。
【００２８】
また、冷熱源の能力は、冷却速度Ｒ（℃／ｓｅｃ）、熱伝達係数α（ｋｃａｌ／ｋｇ／ｈｒ／℃）、鋼板の板厚をｔ（ｍｍ）、雰囲気温度をＴ０とした場合、垂直方向の冷却速度Ｒ（Ｄ１）よりも水平方向の冷却速度Ｒ（Ｄ２）、Ｒ（Ｄ３）の方が大きいことが必要である。
垂直方向の冷熱源が大気であり、これに対して水平方向の冷熱源を冷却された大気である場合は、Ｒ（Ｄ１）＝α（大気）×（３７５−Ｔ０（Ｄ１））／（７７２．２×ｔ）において、Ｒ（Ｄ２）、Ｒ（Ｄ３）＞Ｒ（Ｄ１）
すなわちＴ０（Ｄ２）、Ｔ０（Ｄ３）＜Ｔ０（Ｄ１）であることが必要である。
【００２９】
垂直方向の冷熱源が大気よりも冷却能力の高いガスである場合は、α（Ｄ２）、α（Ｄ３）＞α（Ｄ１）となる。またこのガスを冷却してＴ０（Ｄ２）、Ｔ０（Ｄ３）＜Ｔ０（Ｄ１）とし、前者との組み合わせにより、Ｒ（Ｄ２）、Ｒ（Ｄ３）＞Ｒ（Ｄ１）を満たすことが必要である。
また、冷熱源をミスト冷却あるいは直接接触冷却とする場合にも、α（Ｄ２）、α（Ｄ３）＞α（Ｄ１）＝７７２．２×ｔ×Ｒ（Ｄ１）／（３７５−Ｔ０（Ｄ１））の条件を満たすことが必要である。
【００３０】
このとき、α（Ｄ１）に対して、α（Ｄ２）あるいはα（Ｄ３）が大きくなるほど、スパングルは偏心状からスパングルレスの状態に移行する。すなわち、水平方向の冷熱源の能力が強くその雰囲気温度が低いほど、垂直方向の雰囲気温度Ｔ０（Ｄ１）が高いほど、スパングルは消失される方向に制御される。この場合、垂直方向の雰囲気温度の調節手段は特に限定されず、熱風吹き付け、赤外線加熱、誘導加熱等いかなる方法を用いてもかまわない。
【００３１】
このようにして得られためっき鋼板はスパングルが消失あるいは偏心していることが特徴であり、ひけすの深さはＪＩＳ Ｂ ０６０１に基づくＲｙが８μｍ以下（従来製造材のＲｙは１０〜１５μｍ（片面めっき付着量８０〜１５０ｇ／ｍ２ ））となる。
【００３２】
また、このめっき鋼板の表面に光沢度（ＪＩＳ Ｋ ５４００）７０以上の塗膜を塗装あるいはフィルムをラミネートした場合、従来の溶融Ｚｎ−Ａｌ合金めっき鋼板では、その後のスキンパスの有無を問わず、ひけすの透過やひけすを起点とした塗膜・フィルムの膨れ状の欠陥が生成し、製品の外観を著しく損ねていたが、本発明による溶融Ｚｎ−Ａｌ合金めっき鋼板ではこれらの欠陥の生成が著しく改善あるいは消失される。
以下に本発明の実施例を挙げ、本発明の効果を立証する。
【００３３】
【実施例】
溶融Ｚｎ−Ａｌ合金めっき鋼板は連続式溶融亜鉛めっきラインにより製造した。鋼板の板厚は０．５ｍｍとした。なお、浴中Ａｌ濃度は０．５、１．５、４．５、１８、２５重量％にそれぞれ調整した。
【００３４】
めっき鋼板の表面平滑性は、鋼板の中央部と端部より採取した試験片に対して２０×２０ｍｍの領域を粗さ測定したＲｙの平均値により評価した。スパングルの形態については目視により、放射状スパングル（通常）、偏心スパングル（偏心）及びスパングルレス（スパングル消失）に分類した。
【００３５】
得られためっき鋼板には１％相当のスキンパスを施した後、りん酸塩処理を行い、その上に厚さ５μｍのエポキシ系プライマ塗布後、厚さ２０μｍのポリエステル系塗料を塗布した。この塗装鋼板表面外観（カラー後外観）は目視により、めっき鋼板のひけすが光沢差として認識されるか否かの判定を行った。表中では、光沢差が認識されるものを×、認識されないものを○として示した。
【００３６】
また、得られためっき鋼板には１％相当のスキンパスを施した後、りん酸塩処理を行い、その上に厚さ３μｍのウレタン系接着剤を塗布後、厚さ１００μｍの塩化ビニルフィルムをラミネートした。このラミネート鋼板表面外観（ラミネート後外観）は目視により、ラミネート鋼板表面に生成する膨れの有無を判定した。表中では、膨れが認識されるものを×、認識されないものを○として示した。
【００３７】
（実施例１）
表１に示す浴中Ａｌ濃度でめっきした鋼板両端部を同表に示す条件で冷却した。すなわち、本発明例Ｎｏ．１〜５は冷却方向がＤ２（図１（ｂ）に示す鋼板水平方向）となるように２℃の空気により冷却し、比較例Ｎｏ．１〜５は常温空気により冷却方向が本発明例と同様Ｄ２となるように冷却した。従来例Ｎｏ．１〜５はＤ２方向の冷却を行わず、垂直方向（Ｄ１）の冷却のみとした。なお、水平方向の冷却は鋼板が３９０〜３７０℃の温度域にある位置にて行った。垂直方向の冷却は大気雰囲気とした。
【００３８】
結果を表１にあわせて示す。本発明例、比較例、従来例を問わず、浴中Ａｌ濃度が本発明の範囲から外れる０．５及び２５重量％の場合（本発明例Ｎｏ．１，５、比較例Ｎｏ．１，５、従来例Ｎｏ．１，５）には放射状のスパングルは観察されなかった。
【００３９】
２℃の空気により端面を冷却した本発明例Ｎｏ．２〜４の場合、水平方向の冷熱源の能力が垂直方向より強いため、スパングルは偏心し、めっきままの鋼板のＲｙは８μｍ以下となり、塗装あるいはラミネート鋼板には欠陥は観察されなかった。
【００４０】
これに対して、従来例Ｎｏ．２〜４及び常温空気により端面を冷却した比較例Ｎｏ．２〜４では、垂直方向の冷熱源の能力が水平方向より強いため、スパングルは放射状成長を呈し、めっきままの鋼板のＲｙは８μｍ超えとなり、塗装あるいはラミネート鋼板には欠陥が観察された。
（実施例２）
表２に示す浴中Ａｌ濃度でめっきした鋼板両端部を同表に示す条件で冷却した。すなわち、本発明例Ｎｏ．１〜５は冷却方向がＤ３（図１（ｃ）に示す鋼板水平方向）となるように２℃の空気により冷却し、比較例Ｎｏ．１〜５は冷却方向が本発明例と同様Ｄ３となるように常温空気により冷却した。従来例Ｎｏ．１〜５はＤ３方向の冷却を行わず、垂直方向（Ｄ１）の冷却のみとした。なお、水平方向の冷却は鋼板が３９０〜３７０℃の温度域にある位置にて行った。垂直方向は大気雰囲気とした。
【００４１】
結果を表２にあわせて示す。本発明例、比較例、従来例を問わず、浴中Ａｌ濃度が本発明の範囲から外れる０．５及び２５重量％の場合（本発明例Ｎｏ．１，５、比較例Ｎｏ．１，５、従来例Ｎｏ．１，５）には放射状のスパングルは観察されなかった。
【００４２】
２℃の空気により端面を冷却した本発明例Ｎｏ．２〜４の場合、水平方向の冷熱源の能力が垂直方向より強いため、スパングルは偏心し、めっきままの鋼板のＲｙは８μｍ以下となり、塗装あるいはラミネート鋼板には欠陥は観察されなかった。
【００４３】
これに対して、従来例Ｎｏ．２〜４及び常温空気により端面を冷却した比較例Ｎｏ．２〜４は、垂直方向の冷熱源の能力が水平方向より強いため、スパングルは放射状成長を呈し、めっきままの鋼板のＲｙは８μｍ超えとなり、塗装あるいはラミネート鋼板には欠陥が観察された。
【００４４】
（実施例３）
表３に示す浴中Ａｌ濃度でめっきした鋼板両端部を同表に示す条件で冷却した。すなわち、本発明例Ｎｏ．１〜１０は冷却方向がＤ２（図１（ｂ）に示す鋼板水平方向）となるように鋼板両端部を２℃の空気あるいは二流体ミスト（エア圧＝４ｋｇｆ／ｃｍ２ 、水圧＝１ｋｇｆ／ｃｍ２ ）により冷却した。なお、水平方向の冷却は鋼板が３９０〜３７０℃の温度域にある位置にて行った。垂直方向は２５０℃の熱風吹き付けを実施した。
【００４５】
結果を表３にあわせて示す。冷却方法を問わず、浴中Ａｌ濃度が本発明の範囲から外れる０．５及び２５重量％の場合（本発明例Ｎｏ．１，５，６，１０）には放射状のスパングルは観察されなかった。
【００４６】
２℃の空気あるいは二流体ミスト（エア圧＝４ｋｇｆ／ｃｍ２ 、水圧＝１ｋｇｆ／ｃｍ２ ）により端面を冷却し、かつ垂直方向に２５０℃の熱風吹き付けを実施した本発明例Ｎｏ．２〜４，７〜９の場合、実施例１及び２の冷却方法に比べて、水平方向の冷熱源の能力が垂直方向よりさらに強いため、スパングルは消失し、めっきままの鋼板のＲｙは１〜２μｍとさらに小さくなり、塗装あるいはラミネート鋼板には欠陥は観察されなかった。
【００４７】
【表１】
【表２】
【表３】
【発明の効果】
本発明によれば、めっき浴組成、スパングル形態及びスパングル粒界のひけす深さ、及び製造条件を特定することにより、凝固ひけすがきわめて軽減された溶融Ｚｎ−Ａｌ合金めっき鋼板を製造することが可能となり、更に、この鋼板上に光沢度あるいは平滑度の高い膜を付与した場合に、めっき鋼板由来の外観不良がきわめて軽減された製品が得られる。
【図面の簡単な説明】
【図１】従来の鋼板冷却と本発明の鋼板冷却の概念を示す図。（ａ）は従来方法での鋼板冷却の概念を示す図。（ｂ），（ｃ）は本発明の鋼板冷却の概念を示す図。
【図２】従来のめっき鋼板表面と本発明のめっき鋼板表面の顕微鏡写真とスパングル形態を示す図。
（ａ）は従来のめっき鋼板表面の顕微鏡写真と放射状スパングルの模式図。（ｂ）は本発明のめっき鋼板表面の顕微鏡写真と偏心スパングルの模式図。（ｃ）は本発明のめっき鋼板表面（スパングルレス）の顕微鏡写真。
【符号の説明】
１…めっき浴
２…トップロール[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hot-dip Zn—Al alloy-plated steel sheet having excellent smoothness on the plating surface, which is mainly used as a raw sheet for coated steel sheets or laminated steel sheets for building materials, and a method for producing the same.
[0002]
[Prior art]
Hot-dip plating on steel sheets is performed mainly for the purpose of improving corrosion resistance, and its products are widely used mainly for automobiles, building materials, and home appliances. In particular, the plating system in which aluminum is added to normal hot dip galvanizing is excellent in corrosion resistance, so its development has progressed. In recent years, hot-dip Zn-Al alloy plated steel sheets to which 5% by weight of aluminum has been added have been widely used. ing. This hot-dip Zn—Al alloy-plated steel sheet has excellent corrosion resistance and workability because the reaction layer with the steel sheet substrate is thin. However, the cooling direction at the time when the plated film of the molten Zn—Al alloy-plated steel sheet solidifies is a direction perpendicular to the steel sheet surface, and 2-5 mm large spangles that are radially grown are formed on the surface of the plated steel sheet. The spangle grain boundary has a solidification shrinkage (hereinafter referred to as “dents”). The dents are remarkably generated in a plating film having a single-side adhesion amount of 80 g / m 2 or more, and the depth reaches half of the plating film. Various studies have been made to reduce or eliminate the dents. The investigations are broadly classified into two, one is the control of cooling after plating, and the other is the refinement of spangles by adding nucleating elements to the bath. The former is a method of bringing a finely divided heat medium such as water mist or chemical mist into contact with a plating film that is still in a molten state, thereby rapidly cooling the plating film to make spangles fine and widely used. . Regarding the latter, Japanese Patent Application Laid-Open No. 2-73955 discloses a method of adding Si to the bath, Japanese Patent Application Laid-Open No. 5-125515, Japanese Patent Application Laid-Open No. 6-158256, Japanese Patent Application Laid-Open No. 6-158257, and Japanese Patent Application Laid-Open No. 6-158258. JP-A-6-158259 discloses a method of adding Ti to a bath.
[0003]
[Problems to be solved by the invention]
However, in the conventional cooling control method after plating described above, spangles disappear, but when a sufficient amount of water or chemical solution is brought into contact with the plating film, spraying by a mist spray nozzle that is currently in circulation Then, the fine unevenness | corrugation resulting from the contact of a heat carrier and the plating film in a molten state will produce | generate. On the other hand, the addition of Si to the bath by the technique of Japanese Patent Laid-Open No. 2-73954 is difficult as an addition method effective for the refinement of spangles. Even if it is simply added in the form of an Al-Si alloy, it becomes a core of spangles. A high melting point Al—Si based alloy or Si—O based compound that works effectively is not generated, and conversely, eutectic formation may occur and spangles may be enlarged. Further, Ti in the bath by the techniques of JP-A-5-125515, JP-A-6-158256, JP-A-6-158257, JP-A-6-158258 and JP-A-6-158259 is disclosed. The addition of Al-Ti alloy having a high melting point acts as a nucleus of spangles. As a result, spangles are refined to about 1/10 at least, but the reduction effect of Dents is not always sufficient, It is also difficult to supply the Al—Ti alloy having a melting point into the plating film accompanying the steel plate as the object to be plated. Another technique for eliminating spangles by post-heating after solidification of the plating film is also disclosed in JP-A-52-131934. Although this method is effective, it is costly and actually cools after post-heating.
[0004]
The object of the present invention is to reduce the solidification sink for a hot-dip Zn-Al alloy-plated steel sheet with a single-sided plating adhesion of 80 g / m 2 or more, which is a problem of sink marks at spangle boundaries. The object is to provide a high hot-dip Zn-Al alloy-plated steel sheet and a method for producing the same. Furthermore, another object of the present invention is to provide a molten Zn-Al alloy-plated coated steel sheet or a molten Zn-Al alloy-plated laminated steel sheet having high surface smoothness by using the obtained molten Zn-Al alloy-plated steel sheet as an original sheet.
[0005]
[Means for Solving the Problems]
In order to solve the above problems and achieve the object, the present invention uses the following means.
(1) The plated steel sheet of the present invention is mass%, contains Al: 1 to 20%, and in the molten Zn-Al alloy plated steel sheet, the balance being Zn and inevitable impurities, the spangle on the surface of the plating film is scaly. It is a hot-dip Zn—Al alloy-plated steel sheet having excellent surface smoothness characterized by being eccentric .
[0006]
(2) The plated Zn steel sheet according to the present invention has a surface roughness Ry of 8 μm or less at the spangle grain boundary on the surface of the plating film, and is a molten Zn—Al excellent in surface smoothness as described in (1) above Alloy-plated steel sheet.
[0007]
(3) The manufacturing method of the plated steel sheet of the present invention is mass%, contains Al: 1 to 20%, the balance is made of Zn and inevitable impurities, and the spangles on the surface of the plating film are eccentric in a spangle-less or scaly manner. In the method for producing a hot-dip Zn-Al alloy-plated steel sheet, the hot-dip Zn-Al alloy plating with excellent surface smoothness is characterized in that the cooling direction of the plating film after plating is horizontal with respect to the plated steel sheet It is a manufacturing method of a steel plate.
(4) The method for producing a plated steel sheet of the present invention is mass%, contains Al: 1 to 20%, the balance is made of Zn and inevitable impurities, and the spangle on the surface of the plating film is eccentric in a spangle-less or scaly manner. In the method for producing a hot-dip Zn-Al alloy-plated steel sheet in which the depth Ry of the spangle grain boundary on the surface of the plated film is 8 μm or less, the cooling direction of the plated film after plating is horizontal to the plated steel sheet. It is the manufacturing method of the hot-dip Zn-Al alloy plating steel plate excellent in the surface smoothness characterized by being.
(5) The method for producing a plated steel sheet according to the present invention further includes, in the plating bath, Mg: 1% or less (including 0%) in mass%, wherein the above (3) or (4) The method for producing a hot-dip Zn—Al alloy-plated steel sheet having excellent surface smoothness as described in any one of the above.
[0008]
(6) The coated steel sheet of the present invention is a molten Zn-Al characterized by forming a coating film having a glossiness of 70 or more on the molten Zn-Al alloy-plated steel sheet described in (1) or (2) above. Alloy plated steel sheet.
[0009]
(7) A laminated steel sheet according to the present invention is obtained by forming a laminated film of a film having a glossiness of 70 or more on the molten Zn-Al alloy-plated steel sheet described in (1) or (2) above. -Al alloy plated laminated steel sheet.
[0010]
The spangles of the spangles (3) and (4) and the spangles (1), (3), and (4) are defined as follows.
Spangleless: Solidified grain boundaries on the surface of the plating film disappeared by solidification in one direction (Dents does not exist).
[0011]
Spangles are eccentric in scale : Spangles are eccentric without growing radially, and solidified grain boundaries are dispersed on the plating film surface (dents are reduced).
Further, the depth Ry sinked in the above (2) and (4) is defined in JIS B 0601, and the glossiness in the above (6) and (7) is defined in JIS K 5400.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In order to obtain a hot-smooth Zn-Al alloy-plated steel sheet having high surface smoothness, the inventor of the present invention relates to a hot-dip Zn-Al alloy-plated steel sheet having a single-side plating adhesion amount of 80 g / m 2 or more in which sink marks of spangle boundaries are a problem In addition, intensive research was conducted on a method for controlling the cooling after plating to alleviate solidified sink marks.
[0013]
As a result, the cooling direction at the time when the plating film solidifies was changed from the vertical direction to the horizontal direction with respect to the conventional steel sheet surface, and the knowledge that the spangle shape that had been grown in the past was eccentric or disappeared was obtained. . As a result, the triple-point grain boundary of the radial spangle, which is the spangle grain boundary, is eliminated, or the spangle itself disappears, and the solidified sink marks generated in this part are alleviated or eliminated.
[0014]
Based on the above knowledge, the present inventor controls the plating bath composition and sets the cooling direction at the time of solidification of the plating film to the horizontal direction with respect to the steel plate surface, and the spangle shape and spangle boundary of the plating surface. By controlling the sinking depth, the hot-dip Zn-Al alloy-plated steel sheet of the present invention excellent in surface smoothness was found, and further, by using the obtained hot-dip Zn-Al alloy-plated steel sheet as the original plate, surface smoothness was achieved. The present invention has been completed by finding a hot-melted Zn-Al alloy-plated steel sheet or a hot-dip Zn-Al alloy-plated laminated steel sheet.
[0015]
That is, the present invention limits the smoothness of the hot-dip Zn-Al alloy-plated steel sheet by limiting the plating bath composition, the form of spangles on the plating surface and the depth of the spangle boundaries, and the production conditions to the following ranges. Furthermore, by using the obtained molten Zn-Al alloy-plated steel sheet as an original sheet, a hot-smooth Zn-Al alloy-plated coated steel sheet or a molten Zn-Al alloy-plated laminated steel sheet Can be obtained.
[0016]
Hereinafter, the reason for component addition, the reason for component limitation, the form of spangles on the plating surface, the reason for limiting the depth of spangle boundaries, and the reason for limitation of manufacturing conditions will be described.
[0017]
(1) Plating bath composition range Al: 1 to 20%
The range of Al concentration in the plating bath is 1 to 20% because the granular steel structure (spangle) accompanying radial eutectic growth and its grain boundary “sink” on the surface of the plated steel sheet produced in this concentration range. This “sink” is based on the remarkable deterioration of the appearance of the plated steel sheet and the surface of the product having a coating or film laminated on its surface.
[0018]
Further, if Al is less than 1%, the formation of an Al—Zn eutectic is small, so that the corrosion resistance of the plating layer is not sufficient. On the other hand, if the amount of Al in the bath exceeds 20%, the mutual diffusion reaction between Al and Fe at the plating-steel interface is excessive, and there is abnormal growth of the Fe-Al alloy layer that is brittle in processing. In addition to adhesion, it is considered to cause adverse effects on corrosion resistance such as generation of spot-like red rust in a humid atmosphere. Therefore, the Al content is 1 to 20%.
[0019]
Mg: 1% or less (including 0%)
The reason why the amount of Mg added is 1% or less (including 0%) is that when Mg exceeds 1%, Mg acts on eutectic growth and does not exhibit radial spangle growth.
[0020]
Since the third element represented by Si, Ti, Ni, Co, and Sb does not affect the mechanism of radial spangle formation, the addition amount is not particularly limited in the present invention. It is desirable to set an optimum addition amount in consideration of the fact that excessive addition of Ti causes deterioration of workability, reduction of bath yield, and excessive addition of Sb promotes intergranular corrosion.
[0021]
(2) Spangle shape and sinking depth of spangle grain boundary In the hot-dip Zn-Al alloy plated steel sheet of the present invention, the spangle on the surface of the plating film disappears or is eccentric, and the sinking depth of the spangle grain boundary is JIS Ry based on B 0601 is 8 μm or less.
By changing the form of spangles on the plating surface to spangle-less (disappearance) or eccentric state, the triple-point grain boundary of the conventional radial spangle as shown in FIG. 2 (a) is eliminated, or the spangle itself disappears. The solidified sink that forms in the film also relaxes or disappears. As a result, as shown in FIGS. 2B and 2C, the unevenness on the surface of the steel plate is smoothed.
[0022]
In addition, when the depth of the spangle grain boundary on the plating surface exceeds 8 μm, each spangle becomes conspicuous by visual observation, resulting in a problem of poor appearance. On the other hand, in the case of 8 μm or less, the problem of poor appearance does not occur.
[0023]
By adjusting the plating bath composition, the spangle shape of the plating surface, and the sinking depth of the spangled grain boundary, the molten Zn having a single-sided plating adhesion of 80 g / m 2 or more where sinking of the spangled grain boundary becomes a problem -Regarding an Al alloy-plated steel sheet, it is possible to relax this solidified sink and obtain a hot-smooth Zn-Al alloy-plated steel sheet with high surface smoothness.
[0024]
A plated steel sheet having such characteristics can be manufactured by the following manufacturing method.
(3) Plated steel plate manufacturing process After plating with the plating bath adjusted to the above component composition range, steel plate cooling is controlled so that the cooling direction of the plating film is in the horizontal direction with respect to the plated steel plate.
[0025]
This is because the cooling direction at the time when the plating film solidifies is changed from the vertical direction to the horizontal direction with respect to the conventional steel plate surface, thereby eliminating or decentering the spangle on the surface of the plating film that has been radially grown, This is to improve the smoothness of the plating surface.
The concept of steel plate cooling in the conventional method is shown in FIG. In the continuous hot dip plating production line, the plated steel sheet coming out of the
[0026]
Therefore, when the plating film that has reached the solidification temperature during the cooling process grows from a solidification nucleus comparable to the final number of spangles, it spreads almost concentrically, so the grain boundary of each spangle is located at a specific location. Concentrate. Therefore, as a matter of course, a large shrinkage nest as shown in FIG. 2A is generated, that is, dents are formed.
On the other hand, when solidifying and growing radially from the starting point, the amount of heat possessed by the plated steel sheet is not in the steel sheet vertical direction (D1) as shown in FIG. 1 (a), but in FIGS. 1 (b) and 1 (c). As shown, by setting the steel plate in the horizontal direction (D2, D3), the spangles grow selectively in a specific direction from the solidification start point instead of in a radial pattern. By taking such a growth process, the final solidified portion of each spangle moves from a conventional triple point to a double point or line. That is, the concentration of the solidification shrinkage nest is relaxed, and as a result, the surface irregularities based on this are smoothed as shown in FIGS.
[0027]
There is no restriction on the cooling heat source for cooling control, and a non-contact type such as air blowing, carbon dioxide gas, nitrogen gas blowing, mist cooling or a contact type such as installation of a cooling roll on the end surface is applied. However, it is necessary to install a cooling heat source at a position corresponding to the plating film solidification temperature range in the cooling direction D2 and at a position corresponding to the plating film solidification completion temperature range in the cooling direction D3.
In general, since the solidification temperature range varies depending on the plate thickness, line speed, etc., it is preferable that the cold heat source has a structure in which the position in the height direction can be arbitrarily changed according to the operating conditions.
[0028]
The capacity of the cold heat source is vertical when the cooling rate R (° C./sec), the heat transfer coefficient α (kcal / kg / hr / ° C.), the plate thickness of the steel sheet is t (mm), and the ambient temperature is T0. It is necessary that the horizontal cooling rates R (D2) and R (D3) are larger than the cooling rate R (D1) in the direction.
When the vertical cooling source is the air and the horizontal cooling source is the cooled air, R (D1) = α (atmosphere) × (375−T0 (D1)) / (772 .2 × t), R (D2), R (D3)> R (D1)
That is, it is necessary that T0 (D2), T0 (D3) <T0 (D1).
[0029]
When the vertical heat source is a gas having a higher cooling capacity than the atmosphere, α (D2) and α (D3)> α (D1). In addition, it is necessary to cool this gas so that T0 (D2) and T0 (D3) <T0 (D1), and satisfy R (D2) and R (D3)> R (D1) in combination with the former. .
Also, when the cooling heat source is mist cooling or direct contact cooling, α (D2), α (D3)> α (D1) = 772.2 × t × R (D1) / (375−T0 (D1) ) Must be satisfied.
[0030]
At this time, as α (D2) or α (D3) increases with respect to α (D1), the spangle moves from an eccentric state to a spangle-less state. That is, the greater the ability of the horizontal heat source, the lower the ambient temperature, and the higher the vertical ambient temperature T0 (D1), the more the spangle is controlled to disappear. In this case, the means for adjusting the atmospheric temperature in the vertical direction is not particularly limited, and any method such as hot air blowing, infrared heating, induction heating may be used.
[0031]
The plated steel sheet thus obtained is characterized by the disappearance or eccentricity of spangles, and the depth of sink is Ry of 8 μm or less based on JIS B 0601 (Ry of conventional production material is 10 to 15 μm (one side) The plating adhesion amount is 80 to 150 g / m 2 )).
[0032]
In addition, when a coated film having a gloss level (JIS K 5400) of 70 or more is applied to the surface of the plated steel sheet or a film is laminated, the conventional molten Zn-Al alloy plated steel sheet has a sink mark regardless of whether or not there is a subsequent skin pass. Swelling defects of coating films and films originating from soot transmission and sink marks were generated, and the appearance of the product was significantly impaired. However, in the hot-dip Zn-Al alloy plated steel sheet according to the present invention, these defects were generated. Significantly improved or disappeared.
Examples of the present invention will be given below to prove the effects of the present invention.
[0033]
【Example】
The hot-dip Zn-Al alloy-plated steel sheet was produced by a continuous hot-dip galvanizing line. The plate thickness of the steel plate was 0.5 mm. The Al concentration in the bath was adjusted to 0.5, 1.5, 4.5, 18, and 25% by weight, respectively.
[0034]
The surface smoothness of the plated steel sheet was evaluated by an average value of Ry obtained by measuring the roughness of a 20 × 20 mm region with respect to a test piece collected from the center and end of the steel sheet. The form of spangles was visually classified into radial spangles (normal), eccentric spangles (eccentric), and spangles (spangle disappeared).
[0035]
The obtained plated steel sheet was subjected to a skin pass equivalent to 1%, and then subjected to a phosphate treatment. After the application of an epoxy primer having a thickness of 5 μm, a polyester paint having a thickness of 20 μm was applied thereto. The appearance of the coated steel sheet surface (appearance after color) was visually determined to determine whether sink marks on the plated steel sheet were recognized as a gloss difference. In the table, the case where the gloss difference is recognized is indicated as x, and the case where the difference is not recognized is indicated as ◯.
[0036]
In addition, the obtained plated steel sheet was subjected to a skin pass equivalent to 1%, then subjected to a phosphate treatment, a 3 μm thick urethane adhesive was applied thereon, and then a 100 μm thick vinyl chloride film was laminated. did. The appearance of the laminated steel sheet surface (appearance after lamination) was determined by visual observation for the presence or absence of swelling generated on the surface of the laminated steel sheet. In the table, those in which blisters are recognized are shown as x, and those in which blisters are not recognized are shown as ◯.
[0037]
Example 1
Both ends of the steel plate plated with the Al concentration in the bath shown in Table 1 were cooled under the conditions shown in the same table. That is, the invention example No. 1 to 5 were cooled with air at 2 ° C. so that the cooling direction was D2 (the steel plate horizontal direction shown in FIG. 1B). Nos. 1 to 5 were cooled with normal temperature air so that the cooling direction was D2 as in the present invention. Conventional Example No. In Nos. 1 to 5, cooling in the D2 direction was not performed, and only cooling in the vertical direction (D1) was performed. In addition, cooling in the horizontal direction was performed at a position where the steel sheet was in a temperature range of 390 to 370 ° C. The cooling in the vertical direction was an air atmosphere.
[0038]
The results are shown in Table 1. Regardless of the present invention example, comparative example, and conventional example, when the Al concentration in the bath is 0.5 and 25% by weight outside the scope of the present invention (invention example Nos. 1 and 5, comparative example Nos. 1 and 5) No radial spangles were observed in Conventional Examples No. 1 and 5).
[0039]
Example No. of the present invention in which the end face was cooled with air at 2 ° C. In the case of 2 to 4, since the ability of the cold heat source in the horizontal direction was stronger than that in the vertical direction, the spangle was eccentric, the Ry of the as-plated steel sheet was 8 μm or less, and no defects were observed in the coated or laminated steel sheets.
[0040]
On the other hand, the conventional example No. 2 to 4 and comparative example No. in which the end face was cooled with room temperature air. In Nos. 2 to 4, since the ability of the cold heat source in the vertical direction was stronger than that in the horizontal direction, spangles exhibited radial growth, Ry of the as-plated steel sheet exceeded 8 μm, and defects were observed in the coated or laminated steel sheets.
(Example 2)
Both ends of the steel plate plated with the Al concentration in the bath shown in Table 2 were cooled under the conditions shown in the same table. That is, the invention example No. 1 to 5 were cooled with air at 2 ° C. so that the cooling direction was D3 (the horizontal direction of the steel plate shown in FIG. 1C). Nos. 1 to 5 were cooled with room temperature air so that the cooling direction was D3 as in the example of the present invention. Conventional Example No. In Nos. 1 to 5, cooling in the D3 direction was not performed, and only cooling in the vertical direction (D1) was performed. In addition, cooling in the horizontal direction was performed at a position where the steel sheet was in a temperature range of 390 to 370 ° C. The vertical direction was an air atmosphere.
[0041]
The results are shown in Table 2. Regardless of the present invention example, comparative example, and conventional example, when the Al concentration in the bath is 0.5 and 25% by weight outside the scope of the present invention (invention example Nos. 1 and 5, comparative example Nos. 1 and 5) No radial spangles were observed in Conventional Examples No. 1 and 5).
[0042]
Example No. of the present invention in which the end face was cooled with air at 2 ° C. In the case of 2 to 4, since the ability of the cold heat source in the horizontal direction was stronger than that in the vertical direction, the spangle was eccentric, the Ry of the as-plated steel sheet was 8 μm or less, and no defects were observed in the coated or laminated steel sheets.
[0043]
On the other hand, the conventional example No. 2 to 4 and comparative example No. in which the end face was cooled with room temperature air. In Nos. 2 to 4, since the ability of the cold heat source in the vertical direction was stronger than that in the horizontal direction, the spangles exhibited radial growth, the Ry of the as-plated steel sheet exceeded 8 μm, and defects were observed in the coated or laminated steel sheets.
[0044]
(Example 3)
Both ends of the steel plate plated with the Al concentration in the bath shown in Table 3 were cooled under the conditions shown in the same table. That is, the invention example No. 1 to 10 are air or two-fluid mist (air pressure = 4 kgf / cm 2 , water pressure = 1 kgf / cm) at both ends of the steel plate so that the cooling direction is D2 (the steel plate horizontal direction shown in FIG. 1B). 2 ). In addition, cooling in the horizontal direction was performed at a position where the steel sheet was in a temperature range of 390 to 370 ° C. In the vertical direction, hot air was sprayed at 250 ° C.
[0045]
The results are shown in Table 3. Regardless of the cooling method, radial spangles were not observed when the Al concentration in the bath was 0.5 and 25% by weight outside the scope of the present invention (Invention Examples No. 1, 5, 6, 10). .
[0046]
Example No. of the present invention in which the end face was cooled with air at 2 ° C. or two-fluid mist (air pressure = 4 kgf / cm 2 , water pressure = 1 kgf / cm 2 ) and hot air was blown at 250 ° C. in the vertical direction. In the case of 2-4, 7-9, since the capability of the horizontal heat source is stronger than that in the vertical direction compared to the cooling methods of Examples 1 and 2, the spangle disappears and the Ry of the as-plated steel sheet is 1 It was further reduced to ˜2 μm, and no defects were observed in the coated or laminated steel sheet.
[0047]
[Table 1]
[Table 2]
[Table 3]
【The invention's effect】
According to the present invention, a hot-dip Zn-Al alloy-plated steel sheet with extremely reduced solidification sink is manufactured by specifying the plating bath composition, spangle form and depth of spangle boundary, and manufacturing conditions. In addition, when a film having high gloss or smoothness is formed on the steel sheet, a product in which the appearance defect derived from the plated steel sheet is extremely reduced can be obtained.
[Brief description of the drawings]
FIG. 1 is a view showing the concept of conventional steel plate cooling and steel plate cooling according to the present invention. (A) is a figure which shows the concept of the steel plate cooling by the conventional method. (B), (c) is a figure which shows the concept of the steel plate cooling of this invention.
FIG. 2 is a view showing a micrograph and spangle form of a conventional plated steel sheet surface and a plated steel sheet surface of the present invention.
(A) is the microscope picture of the conventional plated steel plate surface, and the schematic diagram of a radial spangle. (B) is the microscope picture of the plated steel plate surface of this invention, and the schematic diagram of an eccentric spangle. (C) is a photomicrograph of the surface (spangle-less) of the plated steel sheet of the present invention.
[Explanation of symbols]
1 ... Plating
Claims (7)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP03765197A JP3617234B2 (en) | 1997-02-21 | 1997-02-21 | Hot-dip Zn-Al alloy plated steel sheet with excellent surface smoothness and method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP03765197A JP3617234B2 (en) | 1997-02-21 | 1997-02-21 | Hot-dip Zn-Al alloy plated steel sheet with excellent surface smoothness and method for producing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH10237613A JPH10237613A (en) | 1998-09-08 |
| JP3617234B2 true JP3617234B2 (en) | 2005-02-02 |
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| JP03765197A Expired - Fee Related JP3617234B2 (en) | 1997-02-21 | 1997-02-21 | Hot-dip Zn-Al alloy plated steel sheet with excellent surface smoothness and method for producing the same |
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| JP (1) | JP3617234B2 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| PL190116B1 (en) * | 1998-11-17 | 2005-11-30 | Grillo Werke Ag | Use of zinc alloys |
| JP4555492B2 (en) * | 2000-03-16 | 2010-09-29 | 新日本製鐵株式会社 | Hot-dip zinc-aluminum alloy plated steel sheet with excellent anti-glare properties |
| JP6216282B2 (en) * | 2014-03-31 | 2017-10-18 | 日新製鋼株式会社 | Anti-glare hot-dip Zn-based plated steel sheet and method for producing the same |
| JP6439755B2 (en) * | 2016-06-15 | 2018-12-19 | Ｊｆｅスチール株式会社 | Method for producing galvannealed steel sheet |
| KR102388565B1 (en) * | 2020-08-28 | 2022-04-20 | 포스코강판 주식회사 | Zn-Mg-Al coated steel sheets having surface spangle patterns and excellent corrosion resistance, and its manufacturing method |
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1997
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