JP3843057B2

JP3843057B2 - Hot-dip galvanized steel sheet with excellent appearance quality and manufacturing method of galvanized steel sheet

Info

Publication number: JP3843057B2
Application number: JP2002308404A
Authority: JP
Inventors: 和彦本田; 久芳小松; 崇平田
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2002-10-23
Filing date: 2002-10-23
Publication date: 2006-11-08
Anticipated expiration: 2022-10-23
Also published as: JP2004143506A

Description

【０００１】
【発明の属する技術分野】
本発明は、溶融めっき鋼板に係わり、更に詳しくは優れた外観品位を有し、種々の用途、例えば建材用や自動車用鋼板として適用できるめっき鋼板に関するものである。
【０００２】
【従来の技術】
耐食性の良好なめっき鋼板としては溶融Ｚｎ−Ａｌめっき鋼板、溶融Ａｌめっき鋼板がある。これらの溶融めっき鋼板は、通常、鋼板を脱脂後、無酸化炉にて予熱し、表面の清浄化および材質確保のために還元炉にて還元焼鈍を行い、溶融亜鉛浴に浸漬し、付着量制御することによって製造される。その特徴として、耐食性およびめっき密着性等に優れることから、建材用途等を中心として広く使用されている。
【０００３】
溶融めっき鋼板は一般に光沢を有し、美麗である一方で、僅かな疵や模様などの欠陥が目立ちやすいという欠点がある。これら欠陥は性能上問題ない場合でも、外観品位を低下させるため、商品価値の低下に繋がる。こうした欠陥を目立たせないためには、光を乱反射させ光沢を抑えることが有効である。
【０００４】
光沢を抑える１つの手段として、ダルスキンパス圧延を行うことは有効であるが、ダルスキンパス圧延では、光沢は２００程度までしか低減できず、この程度の光沢ではかえって疵や模様などが目立ってしまい外観品位を向上できない。
【０００５】
溶融亜鉛めっき鋼板の光沢を１００以下に抑える技術が知られている（例えば特許文献１および２）。これらはいずれも溶融めっき後、めっき凝固温度以上の温度で気水スプレーを行うことにより、めっき層表面の結晶粒径と表面粗度を制御し光沢を低下させる技術である。
【０００６】
【特許文献１】
特開平８−１８８８６３号公報
【特許文献２】
特開平１０−８８３１０号公報
【０００７】
【発明が解決しようとする課題】
しかし、上記技術では気水スプレーを行う設備が必要となるため、そのスペースがない場合は採用できない。またこうした設備設置により生産コストが上昇する問題も生じる。
【０００８】
さらにこうした技術は、凹凸部でめっき厚に大きな差ができるため、めっき付着量が大きい領域で適用しないと、凹部の耐食性が十分確保できなくなる問題が生じる。
【０００９】
そこで、本発明は、上記問題点を解決して、外観品位に優れた溶融亜鉛めっき鋼板を提供するものである。
【００１０】
【課題を解決するための手段】
本発明者らは、外観品位に優れた溶融めっき鋼板について鋭意研究を重ねた結果、めっき鋼板表面に形状を制御した微小且つ複数の凹部を設けることにより溶融めっき鋼板の外観品位を向上させることができることを見いだして本発明をなした。
【００１１】
すなわち、本発明の要旨とするところは、以下のとおりである。
【００１２】
（１）Ａｌ：２２〜７０質量％、Ｓｉ：０．５〜３質量％を含有し、残部がＺｎおよび不可避的不純物からなる亜鉛めっき層を有する溶融亜鉛めっき鋼板において、該めっき鋼板表面に微小且つ複数の独立した凹部を、
（１）直径ｄが１〜１００μｍ
（２）凹部深さｈが０．５〜５０μｍ
（３）凹部による板表面の占有率を３０〜９９％
（４）凹部の体積の合計が１ｍ²あたり１０⁵μｍ³〜１０⁷μｍ³
を満足するように設けた、ＪＩＳ−Ｚ−８７４１の６０度鏡面光沢度測定方法により測定した光沢度が１００以下で、かつ、画像解析によるドロスや疵等に起因する大きさ０ . ５ｍｍ以上の外観不良部の数が 1 ｍ ² 中に１０個未満であることを特徴とする外観品位に優れた溶融めっき鋼板。
【００１３】
（２）Ａｌ：２２〜９０質量％、Ｍｇ：２〜１０質量％、Ｓｉ：０．５〜１０質量％を含有し、残部がＺｎおよび不可避的不純物からなる亜鉛めっき層を有する溶融亜鉛めっき鋼板において、該めっき鋼板表面に微小且つ複数の独立した凹部を、
（１）直径ｄが１〜１００μｍ
（２）凹部深さｈが０．５〜５０μｍ
（３）凹部による板表面の占有率を３０〜９９％
（４）凹部の体積の合計が１ｍ²あたり１０⁵μｍ³〜１０⁷μｍ³
を満足するように設けた、ＪＩＳ−Ｚ−８７４１の６０度鏡面光沢度測定方法により測定した光沢度が１００以下で、かつ、画像解析によるドロスや疵等に起因する大きさ０ . ５ｍｍ以上の外観不良部の数が 1 ｍ ² 中に１０個未満であることを特徴とする外観品位に優れた溶融めっき鋼板。
【００１４】
（３）Ｓｉ：２〜１５質量％を含有し、残部がＡｌおよび不可避的不純物からなるＡｌめっき層を有する溶融Ａｌめっき鋼板において、該めっき鋼板表面に微小且つ複数の独立した凹部を、
（１）直径ｄが１〜１００μｍ
（２）凹部深さｈが０．５〜５０μｍ
（３）凹部による板表面の占有率を３０〜９９％
（４）凹部の体積の合計が１ｍ²あたり１０⁵μｍ³〜１０⁷μｍ³
を満足するように設けた、ＪＩＳ−Ｚ−８７４１の６０度鏡面光沢度測定方法により測定した光沢度が１００以下で、かつ、画像解析によるドロスや疵等に起因する大きさ０ . ５ｍｍ以上の外観不良部の数が 1 ｍ ² 中に１０個未満であることを特徴とする外観品位に優れた溶融めっき鋼板。
【００１５】
（４）Ｓｉ：２〜１５質量％、Ｍｇ：１〜１５質量％を含有し、残部がＡｌおよび不可避的不純物からなるＡｌめっき層を有する溶融Ａｌめっき鋼板において、該めっき鋼板表面に微小且つ複数の独立した凹部を、
（１）直径ｄが１〜１００μｍ
（２）凹部深さｈが０．５〜５０μｍ
（３）凹部による板表面の占有率を３０〜９９％
（４）凹部の体積の合計が１ｍ²あたり１０⁵μｍ³〜１０⁷μｍ³
を満足するように設けた、ＪＩＳ−Ｚ−８７４１の６０度鏡面光沢度測定方法により測定した光沢度が１００以下で、かつ、画像解析によるドロスや疵等に起因する大きさ０ . ５ｍｍ以上の外観不良部の数が 1 ｍ ² 中に１０個未満であることを特徴とする外観品位に優れた溶融めっき鋼板。
【００１６】
（５）前記（１）乃至（４）項のいずれかに記載の溶融めっき鋼板のめっき層に、更に、質量％で、Ｃａ：０．０１〜０．５％、Ｂｅ：０．０１〜０．２％、Ｔｉ：０．０００１〜０．２％、Ｃｕ：０．１〜１．０％、Ｎｉ：０．００１〜０．２％、Ｃｏ：０．０１〜０．３％、Ｃｒ：０．０００１〜０．２％、Ｍｎ：０．０１〜０．５％、Ｂ：０．００１〜０．１％から選ばれる一種または二種以上を含有することを特徴とする外観品位に優れた溶融めっき鋼板。
【００１８】
（６）ロール表面に微小且つ複数の凸部を、
（１）直径ｄが１〜２００μｍ
（２）凸部高さｈが０．５〜１００μｍ
（３）凸部によるロール表面の占有率を３０〜９５％
として設けることを特徴とするスキンパスロールを使用してスキンパス圧延を行うことを特徴とする上記（１）乃至（５）項のいずれかに記載の外観品位に優れた溶融めっき鋼板の製造方法。
【００１９】
【発明の実施の形態】
以下に本発明を詳細に説明する。
【００２０】
本発明において溶融めっき鋼板とは鋼板上にＺｎ−Ａｌ−Ｓｉめっき層を付与したもの、Ｚｎ−Ａｌ−Ｍｇ−Ｓｉめっき層を付与したもの、Ａｌ−Ｓｉめっき層を付与したもの、およびＡｌ−Ｍｇ−Ｓｉめっき層を付与したものである。
【００２１】
Ａｌ：２２〜７０質量％、Ｓｉ：０．５〜３質量％、残部がＺｎおよび不可避的不純物からなるめっき層においてＡｌ組成を２２〜７０質量％に限定した理由は、２２質量％未満のＡｌ量では耐食性を向上させる効果が十分でないためであり、７０質量％を超えると耐食性を向上させる効果が飽和するためである。
【００２２】
Ｓｉ組成を０．５〜３質量％に限定した理由は、０．５質量％未満ではめっき中のＦｅ−Ａｌ合金層の成長を抑制させる効果が十分でなく、めっき密着性を向上させる効果が不十分であるためであり、３質量％を超えると密着性を向上させる効果が飽和するためである。
【００２３】
Ａｌ：２２〜９０質量％、Ｍｇ：２〜１０質量％、Ｓｉ：０．５〜１０質量％、残部がＺｎおよび不可避的不純物からなるめっき層においてＡｌ組成を２２〜９０質量％に限定した理由は、２２質量％未満のＡｌ量では耐食性が十分向上しないためであり、９０質量％を超えると耐食性を向上させる効果が飽和するためである。
【００２４】
Ｍｇ組成を２〜１０質量％に限定した理由は、２質量％未満では耐食性を向上させる効果が不十分であるためであり、１０質量％を超えるとめっき浴が酸化しやすくなり、めっき浴表面にＭｇの酸化物が多量に発生しめっきが困難となるためである。
【００２５】
Ｓｉ組成を０．５〜１０質量％に限定した理由は、０．５質量％未満ではめっき中のＦｅ−Ａｌ合金層の成長を抑制させる効果が十分でないためであり、１０質量％を超えるとめっきの耐食性が低下するためである。
【００２６】
Ｓｉ：２〜１５質量％、残部がＡｌおよび不可避的不純物からなるめっき層においてＳｉ組成を２〜１５質量％に限定した理由は、２質量％未満および１５質量％を超えたＳｉ量ではめっき浴の融点が十分低下しないためである。
【００２７】
Ｓｉ：２〜１５質量％、Ｍｇ：１〜１５質量％、残部がＡｌおよび不可避的不純物からなるめっき層においてＳｉ組成を２〜１５質量％に限定した理由は、２質量％未満および１５質量％を超えたＳｉ量ではめっき浴の融点が十分低下しないためにめっきが困難となるためである。
【００２８】
Ｍｇ組成を１〜１５質量％に限定した理由は、１質量％未満では耐食性を向上させる効果が不十分であるためであり、１５質量％を超えるとめっき浴が酸化しやすくなり、めっき浴表面にＭｇの酸化物が多量に発生しめっきが困難となるためである。
【００２９】
更に外観品位を向上させるためＣａ、Ｂｅ、Ｔｉ、Ｃｕ、Ｎｉ、Ｃｏ、Ｃｒ、Ｍｎ、Ｂの一種または二種以上の元素を添加する。これらの元素を添加し、外観品位が向上する理由は、めっき凝固時にこれらの元素の金属間化合物が結晶核となり、めっき組織の結晶を微細化する働きがあるためであると考えられる。
【００３０】
外観品位を向上させる効果は、Ｃａ、Ｂｅ、Ｔｉ、Ｃｕ、Ｎｉ、Ｃｏ、Ｃｒ、Ｍｎ、Ｂにおいて各々０．０１、０．０１、０．０００１、０．１、０．００１、０．０１、０．０００１、０．０１、０．００１質量％以上でその効果が顕著になり始め、それ以上の添加ではほぼ効果が飽和する。しかし添加量が多くなるとめっき後の外観が粗雑になり、例えばドロス、酸化物の付着などにより外観不良が発生するため、各元素の上限は、Ｃａ、Ｂｅ、Ｔｉ、Ｃｕ、Ｎｉ、Ｃｏ、Ｃｒ、Ｍｎ、Ｂにおいて各々０．５、０．２、０．２、１．０、０．２、０．３、０．２、０．５、０．１質量％である。
【００３１】
またＦｅ、Ｐｂ、Ｓｎ、Ｓｂ、Ｂｉ等の不可避的不純物は元素の総量を０．５質量％以内含有してもよい。
【００３２】
めっき付着量についても、特に制約は設けないが、耐食性の観点から片面１０ｇ／ｍ²以上、加工性の観点からすると片面２５０ｇ／ｍ²以下であることが望ましい。なお、下地の鋼板としては、熱延鋼板、冷延鋼板共に使用できるが、特にＴｉ、Ｎｂ、Ｂなどを添加した極低炭素系の鋼板は加工性が優れており望ましい。
【００３３】
本発明において、めっき鋼板表面は、表面に微小且つ複数の独立した凹部を、
（１）直径ｄが１〜１００μｍ
（２）凹部深さｈが０．５〜５０μｍ
（３）凹部による板表面の占有率を３０〜９９％
（４）凹部の体積の合計が１ｍ²あたり１０⁵μｍ³〜１０⁷μｍ³
を満足するように設け、ＪＩＳ−Ｚ−８７４１の６０度鏡面光沢度測定方法により測定した光沢度が１００以下で、かつ、画像解析によるドロスや疵等に起因する大きさ０ . ５ｍｍ以上の外観不良部の数が 1 ｍ ² 中に１０個未満である。
【００３４】
ここで凹部直径ｄとはめっき鋼板表面に垂直に投影した面積の最大直径、凹部深さｈはめっき鋼板平面部から凹部の最大深さをいう。
【００３５】
凹部の直径ｄを１〜１００μｍに限定した理由は、１μｍ未満では外観品位を向上する効果が見られないためであり、１００μｍを超えると外観品位が低下するためである。望ましくは、１〜８０μｍである。
【００３６】
凹部の深さｈを０．５〜５０μｍに限定した理由は、０．５μｍ未満では外観品位を向上する効果が見られないためであり、５０μｍを超えると外観品位が低下するためである。望ましくは、０．５〜４０μｍである。
【００３７】
凹部による板表面の占有率を３０〜９０％に限定した理由は、３０％未満では外観品位を向上する効果が見られないためであり、９０％を超えると凹部同士が互いに連絡して、外観品位が低下するためである。望ましくは、３０〜８０％である。
【００３８】
ここで凹部による板表面の占有率とは、板表面を占める凹部の割合のことである。本発明において凹部とは、周りの平坦部と比較して、直径１〜１００μｍ、深さ０．５〜５０μｍ凹んだ部分のことである。凹部は、あるものは独立しており、あるものは相互に連絡している状態で存在することもあるが、凹部同士が互いに連絡している場合、それぞれの凹部の直径と深さを持つ半球を仮想し、その半球を１つの独立した凹部とみなして、その直径と深さを使用した。
【００３９】
一方、本発明において平坦部とは直径１μｍ未満、または深さ０．５μｍ未満凹んだ部分、および通常うねりと分類される波長０．８ｍｍ以上の領域の凹凸を含むその他の部分である。
【００４０】
従って、本特許で規定された凹部の体積の合計を計算すると、１ｍｍ²あたり約１０⁵μｍ³〜１０⁷μｍ³となる。
【００４１】
本特許においてＪＩＳ−Ｚ−８７４１の６０度鏡面光沢度測定方法により測定した光沢度を１００以下に限定した理由は、光沢度が１００を超えると僅かな疵や模様などの欠陥が目立ち、外観品位が低下するためである。望ましくは６０以下である。
【００４２】
本発明において、めっき鋼板の製造方法については特に限定するところはなく、通常の無酸化炉方式の溶融めっき法が適用できる。表面に凹部をつける方法についても特に限定するところはなく、規定の凹部を得られればどんな方法を用いても構わない。
【００４３】
最も制御しやすい方法は、めっき後のスキンパス圧延において
ロール表面に微小且つ複数の凸部を、
（１）直径ｄが１〜２００μｍ
（２）凸部高さｈが０．５〜１００μｍ
（３）凸部によるロール表面の占有率を３０〜９５％
を満足するように設けたスキンパスロールを使用してスキンパス圧延を行う方法である。上記ロールを使用し、スキンパス圧延圧下率を適切に制御することによって、外観品位に優れためっき鋼板を得ることができる。
【００４４】
更にＷｃａを小さくしたスキンパスロールに上記凸部を設け、スキンパス圧延を行うとめっき外観品位が優れるだけでなく、塗装後の鮮映性も優れためっき鋼板を得ることが可能となる。
【００４５】
【実施例】
以下、実施例により本発明を更に詳細に説明する。
【００４６】
（実施例１）
まず、厚さ２．０ｍｍの冷延鋼板を準備し、これを連続式溶融めっきラインの前処理炉にて焼鈍し、浴中のＡｌ量、Ｍｇ量、Ｓｉ量を変化させた６００〜６６０℃の溶融亜鉛めっき浴で３秒溶融めっきを行った後、Ｎ₂ガスワイピングで表１に示すめっき付着量に調整し、ロール凸部、圧延圧下率を変化させたスキンパス圧延を行った。得られためっき鋼板のめっき層中組成と表面凹部の分布を表１に示す。凹部直径ｄと凹部深さｈは、３次元粗度計を使用して任意に１００点測定し、それぞれの平均値を使用した．凹部による板表面の占有率は、２×２ｍｍの範囲を３次元粗度計で測定し、測定面積に占める凹部の面積の割合を求めた。
【００４７】
光沢度はＪＩＳ−Ｚ−８７４１の６０度鏡面光沢度測定方法により測定し、以下に示す評点づけで判定した。評点は３以上を合格とした。
５：５０未満
４：５０以上８０未満
３：８０以上１００未満
２：１００以上２００未満
１：２００以上
【００４８】
外観品位は、画像解析装置を使用して、ドロスや疵等に起因する大きさ０．５ｍｍ以上の外観不良部の数を数え、以下に示す評点づけで判定した。評点は３を合格とした。
３：１ｍ²中に１０個未満
２：１ｍ²中に１０個以上１００個未満
１：１ｍ²中に１００個以上
【００４９】
密着性は、２Ｔ曲げ試験後の溶融めっき鋼板にセロハンテープを貼り、その後引き剥がし、めっきが剥離しなかった場合を○、めっきが剥離した場合を×とした。
【００５０】
評価結果を表１に示す。
【００５１】
番号１、１９はめっき中のＳｉ％が本発明の範囲外であるためめっき密着性が不合格となった。番号９、２７は凹部の直径と深さが本発明の範囲外であるため光沢度と外観品位が不合格となった。番号１０、２８は凹部の深さが本発明の範囲外であるため光沢度と外観品位が不合格となった。番号１３、３１は凹部の直径が本発明の範囲外であるため外観品位が不合格となった。番号１４、１８、３２、３６は凹部による板表面の占有率が本発明の範囲外であるため光沢度と外観品位が不合格となった。これら以外はいずれも、光沢度、外観品位共に良好な結果となった。
【００５２】
（実施例２）
まず、厚さ２．０ｍｍの冷延鋼板を準備し、これを連続式溶融めっきラインの前処理炉にて焼鈍し、浴中のＭｇ量、Ｓｉ量を変化させた６００〜６６０℃の溶融Ａｌめっき浴で３秒溶融めっきを行った後、Ｎ₂ガスワイピングで表２に示すめっき付着量に調整し、ロール凸部、圧延圧下率を変化させたスキンパス圧延を行った。得られためっき鋼板のめっき層中組成と表面凹部の分布を表１に示す。凹部直径ｄと凹部深さｈは、３次元粗度計を使用して任意に１００点測定し、それぞれの平均値を使用した。凹部による板表面の占有率は、２×２ｍｍの範囲を３次元粗度計で測定し、測定面積に占める凹部の面積の割合を求めた。
【００５３】
光沢度はＪＩＳ−Ｚ−８７４１の６０度鏡面光沢度測定方法により測定し、以下に示す評点づけで判定した。評点は３以上を合格とした。
５：５０未満
４：５０以上８０未満
３：８０以上１００未満
２：１００以上２００未満
１：２００以上
【００５４】
外観品位は、画像解析装置を使用して、ドロスや疵等に起因する大きさ０．５ｍｍ以上の外観不良部の数を数え、以下に示す評点づけで判定した。評点は３を合格とした。
３：１ｍ²中に１０個未満
２：１ｍ²中に１０個以上１００個未満
１：１ｍ²中に１００個以上
【００５５】
密着性は、２Ｔ曲げ試験後の溶融めっき鋼板にセロハンテープを貼り、その後引き剥がし、めっきが剥離しなかった場合を○、めっきが剥離した場合を×とした。
【００５６】
評価結果を表２に示す。
【００５７】
番号１、１９はめっき中のＳｉ％が本発明の範囲外であるためめっき密着性が不合格となった。番号９、２７は凹部の直径と深さが本発明の範囲外であるため光沢度と外観品位が不合格となった。番号１０、２８は凹部の深さが本発明の範囲外であるため光沢度と外観品位が不合格となった。番号１３、３１は凹部の直径が本発明の範囲外であるため外観品位が不合格となった。番号１４、１８、３２、３６は凹部による板表面の占有率が本発明の範囲外であるため光沢度と外観品位が不合格となった。これら以外はいずれも、光沢度、外観品位共に良好な結果となった。
【００５８】
（実施例３）
まず、厚さ２．０ｍｍの冷延鋼板を準備し、これを連続式溶融めっきラインの前処理炉にて焼鈍し、浴中の添加元素量を変化させた６００〜６６０℃の溶融亜鉛めっき浴で３秒溶融めっきを行った後、Ｎ₂ガスワイピングで表３に示すめっき付着量に調整し、ロール粗度、圧延圧下率を変化させたスキンパス圧延を行った。得られためっき鋼板のめっき層中組成と表面凹部の分布を表３に示す。凹部直径ｄと凹部深さｈは、３次元粗度計を使用して任意に１００点測定し、それぞれの平均値を使用した。凹部による板表面の占有率は、２×２ｍｍの範囲を３次元粗度計で測定し、測定面積に占める凹部の面積の割合を求めた。
【００５９】
光沢度はＪＩＳ−Ｚ−８７４１の６０度鏡面光沢度測定方法により測定測定し、以下に示す評点づけで判定した．評点は３以上を合格とした。
５：５０未満
４：５０以上８０未満
３：８０以上１００未満
２：１００以上２００未満
１：２００以上
【００６０】
外観品位は、画像解析装置を使用して、ドロスや疵等に起因する大きさ０．５ｍｍ以上の外観不良部の数を数え、以下に示す評点づけで判定した．評点は３を合格とした。
３：１ｍ²中に１０個未満
２：１ｍ²中に１０個以上１００個未満
１：１ｍ²中に１００個以上
【００６１】
評価結果を表３に示す。
【００６２】
本発明品はいずれも、光沢度、外観品位共に良好な結果となった。
【００６３】
（実施例４）
まず、厚さ２．０ｍｍの冷延鋼板を準備し、これを連続式溶融めっきラインの前処理炉にて焼鈍し、浴中の添加元素量を変化させた６００〜６６０℃の溶融Ａｌめっき浴で３秒溶融めっきを行った後、Ｎ₂ガスワイピングで表４に示すめっき付着量に調整し、ロール粗度、圧延圧下率を変化させたスキンパス圧延を行った．得られためっき鋼板のめっき層中組成と表面凹部の分布を表４に示す．凹部直径ｄと凹部深さｈは、３次元粗度計を使用して任意に１００点測定し、それぞれの平均値を使用した。凹部による板表面の占有率は、２×２ｍｍの範囲を３次元粗度計で測定し、測定面積に占める凹部の面積の割合を求めた。
【００６４】
光沢度はＪＩＳ−Ｚ−８７４１の６０度鏡面光沢度測定方法により測定測定し、以下に示す評点づけで判定した。評点は３以上を合格とした．
５：５０未満
４：５０以上８０未満
３：８０以上１００未満
２：１００以上２００未満
１：２００以上
【００６５】
外観品位は、画像解析装置を使用して、ドロスや疵等に起因する大きさ０．５ｍｍ以上の外観不良部の数を数え、以下に示す評点づけで判定した。評点は３を合格とした。
３：１ｍ²中に１０個未満
２：１ｍ²中に１０個以上１００個未満
１：１ｍ²中に１００個以上
【００６６】
評価結果を表４に示す。
【００６７】
本発明品はいずれも、光沢度、外観品位共に良好な結果となった。
【００６８】
【表１】

【００６９】
【表２】

【００７０】
【表３】

【００７１】
【表４】

【００７２】
【発明の効果】
本発明によれば、めっき鋼板表面に形状を制御した微小且つ複数の凹凸を設けることで、溶融めっき鋼板の光沢度、外観品位を向上させることができ、また、塗装後の鮮映性も優れたものとすることができるという顕著な効果を奏する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a hot-dip galvanized steel sheet, and more particularly, to a galvanized steel sheet that has excellent appearance quality and can be applied as a steel sheet for various uses such as building materials and automobiles.
[0002]
[Prior art]
Examples of the plated steel sheet having good corrosion resistance include a molten Zn-Al plated steel sheet and a molten Al plated steel sheet. These hot-dip galvanized steel sheets are usually preheated in a non-oxidizing furnace after degreasing the steel sheet, subjected to reduction annealing in a reducing furnace to clean the surface and secure the material, immersed in a molten zinc bath, Manufactured by controlling. As its features, it is excellent in corrosion resistance, plating adhesion, etc., it is widely used mainly for building materials.
[0003]
While the hot dip plated steel sheet is generally glossy and beautiful, it has a defect that defects such as slight wrinkles and patterns are easily noticeable. Even if these defects are not problematic in terms of performance, the appearance quality is degraded, leading to a decrease in commercial value. In order to make these defects inconspicuous, it is effective to suppress the gloss by irregularly reflecting light.
[0004]
Although it is effective to perform dal skin pass rolling as one means to suppress gloss, the dar skin pass rolling can only reduce the gloss to about 200, and this level of luster makes the appearance of wrinkles and patterns conspicuous. The quality cannot be improved.
[0005]
A technique for suppressing the gloss of a hot-dip galvanized steel sheet to 100 or less is known (for example, Patent Documents 1 and 2). These are techniques for reducing the gloss by controlling the crystal grain size and surface roughness of the plating layer surface by spraying with air and water at a temperature equal to or higher than the plating solidification temperature after hot dipping.
[0006]
[Patent Document 1]
JP-A-8-188863 [Patent Document 2]
JP-A-10-88310 [0007]
[Problems to be solved by the invention]
However, since the above technique requires a facility for spraying water, it cannot be used if there is no space. In addition, the installation of such equipment also raises the problem of increased production costs.
[0008]
Furthermore, since such a technique can make a large difference in the plating thickness at the concavo-convex portion, there arises a problem that the corrosion resistance of the concave portion cannot be sufficiently secured unless it is applied in a region where the plating adhesion amount is large.
[0009]
Then, this invention solves the said problem and provides the hot dip galvanized steel plate excellent in the external appearance quality.
[0010]
[Means for Solving the Problems]
As a result of intensive research on hot-dip plated steel sheets with excellent appearance quality, the present inventors can improve the appearance quality of hot-dip plated steel sheets by providing minute and multiple recesses whose shapes are controlled on the surface of the plated steel sheets. The present invention was made by finding what can be done.
[0011]
That is, the gist of the present invention is as follows.
[0012]
(1) In a hot-dip galvanized steel sheet having a galvanized layer containing Al: 22 to 70% by mass, Si: 0.5 to 3% by mass, the balance being Zn and inevitable impurities, And a plurality of independent recesses,
(1) Diameter d is 1 to 100 μm
(2) Concave depth h is 0.5 to 50 μm
(3) Occupancy ratio of plate surface by recess is 30 to 99%
(4) The total volume of the recesses is 10 ⁵ μm ³ to 10 ⁷ μm ³ per 1 m ^2.
The glossiness measured by the 60-degree specular gloss measurement method of JIS-Z-8741 is 100 or less , and the size is 0.5 mm or more due to dross or wrinkles by image analysis . A hot-dip galvanized steel sheet having excellent appearance quality, wherein the number of appearance defects is less than 10 in 1 m ² .
[0013]
(2) Hot dip galvanized steel sheet having a galvanized layer containing Al: 22 to 90% by mass, Mg: 2 to 10% by mass, Si: 0.5 to 10% by mass, the balance being Zn and inevitable impurities In the galvanized steel sheet surface, a plurality of minute and independent recesses,
(1) Diameter d is 1 to 100 μm
(2) Concave depth h is 0.5 to 50 μm
(3) Occupancy ratio of plate surface by recess is 30 to 99%
(4) The total volume of the recesses is 10 ⁵ μm ³ to 10 ⁷ μm ³ per 1 m ^2.
The glossiness measured by the 60-degree specular gloss measurement method of JIS-Z-8741 is 100 or less , and the size is 0.5 mm or more due to dross or wrinkles by image analysis . A hot-dip galvanized steel sheet having excellent appearance quality, wherein the number of appearance defects is less than 10 in 1 m ² .
[0014]
(3) Si: In a molten Al-plated steel sheet having an Al plating layer containing 2 to 15% by mass and the balance being Al and inevitable impurities, a minute and a plurality of independent recesses are formed on the surface of the plated steel sheet.
(1) Diameter d is 1 to 100 μm
(2) Concave depth h is 0.5 to 50 μm
(3) Occupancy ratio of plate surface by recess is 30 to 99%
(4) The total volume of the recesses is 10 ⁵ μm ³ to 10 ⁷ μm ³ per 1 m ^2.
The glossiness measured by the 60-degree specular gloss measurement method of JIS-Z-8741 is 100 or less , and the size is 0.5 mm or more due to dross or wrinkles by image analysis . A hot-dip galvanized steel sheet having excellent appearance quality, wherein the number of appearance defects is less than 10 in 1 m ² .
[0015]
(4) In a molten Al plated steel sheet having an Al plated layer containing Si: 2 to 15% by mass, Mg: 1 to 15% by mass, and the balance being Al and inevitable impurities, the surface of the plated steel sheet is minute and plural. Independent recesses,
(1) Diameter d is 1 to 100 μm
(2) Concave depth h is 0.5 to 50 μm
(3) Occupancy ratio of plate surface by recess is 30 to 99%
(4) The total volume of the recesses is 10 ⁵ μm ³ to 10 ⁷ μm ³ per 1 m ^2.
The glossiness measured by the 60-degree specular gloss measurement method of JIS-Z-8741 is 100 or less , and the size is 0.5 mm or more due to dross or wrinkles by image analysis . A hot-dip galvanized steel sheet having excellent appearance quality, wherein the number of appearance defects is less than 10 in 1 m ² .
[0016]
(5) The plating layer of the hot-dip galvanized steel sheet according to any one of (1) to (4) above, and further in mass%, Ca: 0.01 to 0.5%, Be: 0.01 to 0 0.2%, Ti: 0.0001-0.2%, Cu: 0.1-1.0%, Ni: 0.001-0.2%, Co: 0.01-0.3%, Cr: Excellent appearance quality characterized by containing one or more selected from 0.0001 to 0.2%, Mn: 0.01 to 0.5%, B: 0.001 to 0.1% Hot dip galvanized steel sheet.
[0018]
(6) Minute and plural convex portions on the roll surface,
(1) Diameter d is 1 to 200 μm
(2) Convex height h is 0.5 to 100 μm
(3) Occupancy ratio of roll surface by convex part is 30 to 95%
The method for producing a hot-dip galvanized steel sheet having excellent appearance quality according to any one of (1) to (5) above , wherein skin pass rolling is performed using a skin pass roll characterized by being provided as
[0019]
DETAILED DESCRIPTION OF THE INVENTION
The present invention is described in detail below.
[0020]
In the present invention, the hot dip plated steel sheet is a steel sheet provided with a Zn—Al—Si plating layer, a Zn—Al—Mg—Si plating layer, an Al—Si plating layer, and an Al— An Mg-Si plating layer is applied.
[0021]
Al: 22 to 70% by mass, Si: 0.5 to 3% by mass, and the balance is limited to 22 to 70% by mass in the plating layer composed of Zn and inevitable impurities. This is because the effect of improving the corrosion resistance is not sufficient in the amount, and when it exceeds 70% by mass, the effect of improving the corrosion resistance is saturated.
[0022]
The reason why the Si composition is limited to 0.5 to 3% by mass is that if it is less than 0.5% by mass, the effect of suppressing the growth of the Fe—Al alloy layer during plating is not sufficient, and the effect of improving the plating adhesion is achieved. This is because it is insufficient, and when it exceeds 3% by mass, the effect of improving the adhesion is saturated.
[0023]
Al: 22 to 90% by mass, Mg: 2 to 10% by mass, Si: 0.5 to 10% by mass, the reason why the Al composition is limited to 22 to 90% by mass in the plating layer consisting of Zn and inevitable impurities as the balance This is because the corrosion resistance is not sufficiently improved when the amount of Al is less than 22% by mass, and the effect of improving the corrosion resistance is saturated when it exceeds 90% by mass.
[0024]
The reason why the Mg composition is limited to 2 to 10% by mass is that if it is less than 2% by mass, the effect of improving the corrosion resistance is insufficient, and if it exceeds 10% by mass, the plating bath tends to be oxidized, and the surface of the plating bath This is because a large amount of Mg oxide is generated and plating becomes difficult.
[0025]
The reason why the Si composition is limited to 0.5 to 10% by mass is that when the content is less than 0.5% by mass, the effect of suppressing the growth of the Fe—Al alloy layer during plating is not sufficient. This is because the corrosion resistance of the plating is lowered.
[0026]
The reason why the Si composition was limited to 2 to 15% by mass in the plating layer consisting of Si: 2 to 15% by mass and the balance being Al and inevitable impurities is that the plating bath is less than 2% by mass and exceeds 15% by mass. This is because the melting point of does not decrease sufficiently.
[0027]
The reason why the Si composition was limited to 2 to 15% by mass in the plating layer consisting of Si: 2 to 15% by mass, Mg: 1 to 15% by mass and the balance being Al and inevitable impurities is less than 2% by mass and 15% by mass This is because, if the amount of Si exceeds 1, the melting point of the plating bath does not sufficiently decrease, so that plating becomes difficult.
[0028]
The reason why the Mg composition is limited to 1 to 15% by mass is that if it is less than 1% by mass, the effect of improving the corrosion resistance is insufficient, and if it exceeds 15% by mass, the plating bath is easily oxidized, and the surface of the plating bath This is because a large amount of Mg oxide is generated and plating becomes difficult.
[0029]
Further, in order to improve the appearance quality, one or more elements of Ca, Be, Ti, Cu, Ni, Co, Cr, Mn, and B are added. The reason why the appearance quality is improved by adding these elements is thought to be because the intermetallic compounds of these elements become crystal nuclei during plating solidification and have a function of refining the crystals of the plating structure.
[0030]
The effect of improving the appearance quality is 0.01, 0.01, 0.0001, 0.1, 0.001, 0.01 for Ca, Be, Ti, Cu, Ni, Co, Cr, Mn, and B, respectively. , 0.0001, 0.01, 0.001% by mass or more, the effect starts to become remarkable, and if it is added more than that, the effect is almost saturated. However, when the addition amount increases, the appearance after plating becomes rough. For example, appearance defects occur due to dross, oxide adhesion, etc., so the upper limit of each element is Ca, Be, Ti, Cu, Ni, Co, Cr , Mn, and B are 0.5, 0.2, 0.2, 1.0, 0.2, 0.3, 0.2, 0.5, and 0.1% by mass, respectively.
[0031]
Inevitable impurities such as Fe, Pb, Sn, Sb and Bi may contain the total amount of elements within 0.5% by mass.
[0032]
The plating adhesion amount is not particularly limited, but is preferably 10 g / m ² or more on one side from the viewpoint of corrosion resistance and 250 g / m ² or less on one side from the viewpoint of workability. As the underlying steel plate, both hot-rolled steel plates and cold-rolled steel plates can be used. In particular, ultra-low carbon steel plates to which Ti, Nb, B, etc. are added are excellent in workability and desirable.
[0033]
In the present invention, the surface of the plated steel plate has minute and plural independent recesses on the surface,
(1) Diameter d is 1 to 100 μm
(2) Concave depth h is 0.5 to 50 μm
(3) Occupancy ratio of plate surface by recess is 30 to 99%
(4) The total volume of the recesses is 10 ⁵ μm ³ to 10 ⁷ μm ³ per 1 m ^2.
Provided so as to satisfy glossiness as measured by 60 degree specular gloss measurement method of JIS-Z-8741 is at 100 or less, the size due to dross and scratches by image analysis 0. 5 mm or more appearance The number of defective parts is less than 10 in 1 m ² .
[0034]
Here, the recess diameter d is the maximum diameter of the area projected perpendicularly to the surface of the plated steel sheet, and the recess depth h is the maximum depth of the recess from the flat surface of the plated steel sheet.
[0035]
The reason why the diameter d of the recess is limited to 1 to 100 μm is that the effect of improving the appearance quality is not seen if it is less than 1 μm, and the appearance quality is lowered if it exceeds 100 μm. Desirably, it is 1-80 micrometers.
[0036]
The reason why the depth h of the recess is limited to 0.5 to 50 μm is that when the depth is less than 0.5 μm, the effect of improving the appearance quality is not seen, and when it exceeds 50 μm, the appearance quality is lowered. Desirably, it is 0.5-40 micrometers.
[0037]
The reason why the occupancy ratio of the plate surface by the recesses is limited to 30 to 90% is that the effect of improving the appearance quality is not seen if it is less than 30%. This is because the quality deteriorates. Desirably, it is 30 to 80%.
[0038]
Here, the occupancy ratio of the plate surface by the recesses is the ratio of the recesses occupying the plate surface. In this invention, a recessed part is a part 1-100 micrometers in diameter and the recessed part 0.5-50 micrometers deep compared with the surrounding flat part. Some recesses are independent and some may exist in communication with each other, but when the recesses are in communication with each other, a hemisphere having the diameter and depth of each recess , And the hemisphere was regarded as one independent recess and its diameter and depth were used.
[0039]
On the other hand, in the present invention, the flat portion is a portion recessed with a diameter of less than 1 μm or a depth of less than 0.5 μm, and other portions including irregularities in a region having a wavelength of 0.8 mm or more, which is usually classified as waviness.
[0040]
Accordingly, when the total volume of the recesses defined in this patent is calculated, it is about 10 ⁵ μm ³ to 10 ⁷ μm ³ per 1 mm ² .
[0041]
In this patent, the glossiness measured by the 60-degree specular gloss measurement method of JIS-Z-8741 is limited to 100 or less. When the glossiness exceeds 100, defects such as slight wrinkles and patterns are conspicuous, and the appearance quality. This is because of a decrease. Desirably, it is 60 or less.
[0042]
In the present invention, the method for producing a plated steel sheet is not particularly limited, and a normal non-oxidizing furnace type hot dipping method can be applied. There is no particular limitation on the method for forming the concave portion on the surface, and any method may be used as long as a predetermined concave portion can be obtained.
[0043]
The most controllable method is to form minute and multiple protrusions on the roll surface in skin pass rolling after plating.
(1) Diameter d is 1 to 200 μm
(2) Convex height h is 0.5 to 100 μm
(3) Occupancy ratio of roll surface by convex part is 30 to 95%
The skin pass rolling is performed using a skin pass roll provided so as to satisfy the above. By using the above roll and appropriately controlling the skin pass rolling reduction ratio, a plated steel sheet having excellent appearance quality can be obtained.
[0044]
Furthermore, when the above-mentioned convex part is provided on a skin pass roll having a smaller Wca and skin pass rolling is performed, it is possible to obtain a plated steel sheet that not only has excellent plating appearance quality but also excellent sharpness after coating.
[0045]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[0046]
Example 1
First, a cold-rolled steel sheet having a thickness of 2.0 mm was prepared, and this was annealed in a pretreatment furnace of a continuous hot dip plating line, and the Al amount, Mg amount, and Si amount in the bath were changed to 600 to 660 ° C. After performing hot dip galvanizing for 3 seconds in a hot dip galvanizing bath, the amount of plating adhesion shown in Table 1 was adjusted by N ₂ gas wiping, and skin pass rolling was performed by changing the roll protrusion and rolling reduction ratio. Table 1 shows the composition in the plating layer and the distribution of the surface recesses of the obtained plated steel sheet. The recess diameter d and the recess depth h were measured arbitrarily at 100 points using a three-dimensional roughness meter, and the average value of each was used. The occupancy ratio of the plate surface by the recesses was measured in a 2 × 2 mm range with a three-dimensional roughness meter, and the ratio of the area of the recesses to the measurement area was determined.
[0047]
The glossiness was measured by a JIS-Z-8741 60-degree specular gloss measurement method, and was determined by the following rating. A score of 3 or more was accepted.
5: Less than 50 4:50 or more but less than 80 3:80 or more but less than 100 2: 100 or more but less than 200 1: 200 or more
The appearance quality was determined by counting the number of defective appearance parts having a size of 0.5 mm or more caused by dross, wrinkles, etc. using an image analysis device, and rating as shown below. A score of 3 was accepted.
3: 1m ² in the 10 fewer than 2: 1m less than 100 or 10 or more during the ² 1: 100 or more during the 1m ² [0049]
For adhesion, a cellophane tape was applied to the hot-dip plated steel sheet after the 2T bending test, and then peeled off. The case where the plating was not peeled off was marked with ◯, and the case where the plating was peeled off was marked with x.
[0050]
The evaluation results are shown in Table 1.
[0051]
Nos. 1 and 19 failed in plating adhesion because Si% during plating was out of the range of the present invention. In Nos. 9 and 27, the diameter and depth of the recesses were outside the range of the present invention, so the glossiness and appearance quality were rejected. In Nos. 10 and 28, the depth of the recesses was outside the range of the present invention, so the glossiness and appearance quality were unacceptable. Nos. 13 and 31 failed in appearance quality because the diameter of the recess was outside the range of the present invention. In Nos. 14, 18, 32, and 36, the occupancy ratio of the plate surface by the recesses was outside the range of the present invention, so the glossiness and appearance quality were rejected. In all other cases, the gloss and appearance quality were good.
[0052]
(Example 2)
First, a cold rolled steel sheet having a thickness of 2.0 mm is prepared, and this is annealed in a pretreatment furnace of a continuous hot dip plating line, and 600 to 660 ° C. molten Al in which the amount of Mg and Si in the bath is changed. After performing hot dip plating for 3 seconds in the plating bath, skin pass rolling was performed by adjusting the plating adhesion amount shown in Table 2 by N ₂ gas wiping, and changing the roll protrusion and rolling reduction ratio. Table 1 shows the composition in the plating layer and the distribution of the surface recesses of the obtained plated steel sheet. The recess diameter d and the recess depth h were measured arbitrarily at 100 points using a three-dimensional roughness meter, and the average value of each was used. The occupancy ratio of the plate surface by the recesses was measured in a 2 × 2 mm range with a three-dimensional roughness meter, and the ratio of the area of the recesses to the measurement area was determined.
[0053]
The glossiness was measured by a JIS-Z-8741 60-degree specular gloss measurement method, and was determined by the following rating. A score of 3 or more was accepted.
5: Less than 50 4:50 or more but less than 80 3:80 or more but less than 100 2: 100 or more but less than 200 1: 200 or more
The appearance quality was determined by counting the number of defective appearance parts having a size of 0.5 mm or more caused by dross, wrinkles, etc. using an image analysis device, and rating as shown below. A score of 3 was accepted.
3: 1m ² in the 10 fewer than 2: 1m less than 100 or 10 or more during the ² 1: 100 or more during the 1m ² [0055]
For adhesion, a cellophane tape was applied to the hot-dip plated steel sheet after the 2T bending test, and then peeled off. The case where the plating was not peeled off was marked with ◯, and the case where the plating was peeled off was marked with x.
[0056]
The evaluation results are shown in Table 2.
[0057]
Nos. 1 and 19 failed in plating adhesion because Si% during plating was out of the range of the present invention. In Nos. 9 and 27, the diameter and depth of the recesses were outside the range of the present invention, so the glossiness and appearance quality were rejected. In Nos. 10 and 28, the depth of the recesses was outside the range of the present invention, so the glossiness and appearance quality were unacceptable. Nos. 13 and 31 failed in appearance quality because the diameter of the recess was outside the range of the present invention. In Nos. 14, 18, 32, and 36, the occupancy ratio of the plate surface by the recesses was outside the range of the present invention, so the glossiness and appearance quality were rejected. In all other cases, the gloss and appearance quality were good.
[0058]
Example 3
First, a cold-rolled steel sheet having a thickness of 2.0 mm is prepared, and this is annealed in a pretreatment furnace of a continuous hot-dip plating line, and a hot-dip galvanizing bath at 600 to 660 ° C. in which the amount of additive elements in the bath is changed. After performing hot dip plating for 3 seconds, skin pass rolling was performed by adjusting the plating adhesion amount shown in Table 3 by N ₂ gas wiping and changing the roll roughness and rolling reduction ratio. Table 3 shows the composition in the plating layer and the distribution of the surface recesses of the obtained plated steel sheet. The recess diameter d and the recess depth h were measured arbitrarily at 100 points using a three-dimensional roughness meter, and the average value of each was used. The occupancy ratio of the plate surface by the recesses was measured in a 2 × 2 mm range with a three-dimensional roughness meter, and the ratio of the area of the recesses to the measurement area was determined.
[0059]
The glossiness was measured and measured by the JIS-Z-8741 60-degree specular glossiness measuring method, and judged by the following scoring. A score of 3 or more was accepted.
5: Less than 50 4:50 or more but less than 80 3:80 or more but less than 100 2: 100 or more but less than 200 1: 200 or more
Appearance quality was judged by using the image analysis device to count the number of appearance defects with a size of 0.5 mm or more caused by dross, wrinkles, etc., and rating as shown below. A score of 3 was accepted.
3: 1m ² in the 10 fewer than 2: 1m less than 100 or 10 or more during the ² 1: 100 or more during the 1m ² [0061]
The evaluation results are shown in Table 3.
[0062]
All of the products of the present invention were good in both glossiness and appearance quality.
[0063]
Example 4
First, a cold rolled steel sheet having a thickness of 2.0 mm is prepared, and this is annealed in a pretreatment furnace of a continuous hot dip plating line, and a 600 to 660 ° C. hot dip Al plating bath in which the amount of additive elements in the bath is changed. after in was carried out for 3 seconds dip plating, and adjusted to coating weight shown in Table 4 with N ₂ gas wiping was performed roll roughness, a skin pass rolling with varied rolling reduction rate. Table 4 shows the composition of the plated steel sheet and the distribution of surface recesses in the plated steel sheet. The recess diameter d and the recess depth h were measured arbitrarily at 100 points using a three-dimensional roughness meter, and the average value of each was used. The occupancy ratio of the plate surface by the recesses was measured in a 2 × 2 mm range with a three-dimensional roughness meter, and the ratio of the area of the recesses to the measurement area was determined.
[0064]
The glossiness was measured and measured by the 60-degree specular gloss measurement method of JIS-Z-8741, and was determined by the following rating. A score of 3 or higher was accepted.
5: Less than 50 4:50 or more but less than 80 3:80 or more but less than 100 2: 100 or more but less than 200 1: 200 or more
The appearance quality was determined by counting the number of defective appearance parts having a size of 0.5 mm or more caused by dross, wrinkles, etc. using an image analysis device, and rating as shown below. A score of 3 was accepted.
3: 1m ² in the 10 fewer than 2: 1m less than 100 or 10 or more during the ² 1: 100 or more during the 1m ² [0066]
The evaluation results are shown in Table 4.
[0067]
All of the products of the present invention were good in both glossiness and appearance quality.
[0068]
[Table 1]

[0069]
[Table 2]

[0070]
[Table 3]

[0071]
[Table 4]

[0072]
【The invention's effect】
According to the present invention, it is possible to improve the glossiness and appearance quality of the hot-dip plated steel sheet by providing minute and multiple irregularities with a controlled shape on the surface of the plated steel sheet, and excellent sharpness after painting. There is a remarkable effect that it can be used.

Claims

In a hot-dip galvanized steel sheet having a galvanized layer containing Al: 22 to 70% by mass, Si: 0.5 to 3% by mass, and the balance being Zn and inevitable impurities, the surface of the plated steel sheet is minute and plural. An independent recess,
(1) Diameter d is 1 to 100 μm
(2) Concave depth h is 0.5 to 50 μm
(3) Occupancy ratio of plate surface by recess is 30 to 99%
(4) The total volume of the recesses is 10 ⁵ μm ³ to 10 ⁷ μm ³ per 1 m ^2.
The glossiness measured by the 60-degree specular gloss measurement method of JIS-Z-8741 is 100 or less , and the size is 0.5 mm or more due to dross or wrinkles by image analysis . A hot-dip galvanized steel sheet having excellent appearance quality, wherein the number of appearance defects is less than 10 in 1 m ² .

In the hot dip galvanized steel sheet having a galvanized layer containing Al: 22 to 90% by mass, Mg: 2 to 10% by mass, Si: 0.5 to 10% by mass, and the balance being Zn and inevitable impurities, Minute and multiple independent recesses on the surface of the plated steel sheet
(1) Diameter d is 1 to 100 μm
(2) Concave depth h is 0.5 to 50 μm
(3) Occupancy ratio of plate surface by recess is 30 to 99%
(4) The total volume of the recesses is 10 ⁵ μm ³ to 10 ⁷ μm ³ per 1 m ^2.
The glossiness measured by the 60-degree specular gloss measurement method of JIS-Z-8741 is 100 or less , and the size is 0.5 mm or more due to dross or wrinkles by image analysis . A hot-dip galvanized steel sheet having excellent appearance quality, wherein the number of appearance defects is less than 10 in 1 m ² .

Si: In a hot-dip Al-plated steel sheet containing 2 to 15% by mass and the balance having an Al-plated layer made of Al and inevitable impurities, the surface of the plated steel sheet has a plurality of minute and independent recesses.
(1) Diameter d is 1 to 100 μm
(2) Concave depth h is 0.5 to 50 μm
(3) Occupancy ratio of plate surface by recess is 30 to 99%
(4) The total volume of the recesses is 10 ⁵ μm ³ to 10 ⁷ μm ³ per 1 m ^2.
The glossiness measured by the 60-degree specular gloss measurement method of JIS-Z-8741 is 100 or less , and the size is 0.5 mm or more due to dross or wrinkles by image analysis . A hot-dip galvanized steel sheet having excellent appearance quality, wherein the number of appearance defects is less than 10 in 1 m ² .

In a hot-dip Al-plated steel sheet containing Si: 2 to 15% by mass, Mg: 1 to 15% by mass, and the balance being an Al-plated layer made of Al and inevitable impurities, the surface of the plated steel sheet is minute and plural . The recess
(1) Diameter d is 1 to 100 μm
(2) Concave depth h is 0.5 to 50 μm
(3) Occupancy ratio of plate surface by recess is 30 to 99%
(4) The total volume of the recesses is 10 ⁵ μm ³ to 10 ⁷ μm ³ per 1 m ^2.
The glossiness measured by the 60-degree specular gloss measurement method of JIS-Z-8741 is 100 or less , and the size is 0.5 mm or more due to dross or wrinkles by image analysis . A hot-dip galvanized steel sheet having excellent appearance quality, wherein the number of appearance defects is less than 10 in 1 m ² .

The plating layer of the hot-dip galvanized steel sheet according to any one of claims 1 to 4, further in mass%, Ca: 0.01 to 0.5%, Be: 0.01 to 0.2%, Ti: 0 0.0001-0.2%, Cu: 0.1-1.0%, Ni: 0.001-0.2%, Co: 0.01-0.3%, Cr: 0.0001-0.2 %, Mn: 0.01 to 0.5%, B: One or more selected from 0.001 to 0.1%, a hot-dip galvanized steel sheet having excellent appearance quality.

Minute and multiple protrusions on the roll surface,
(1) Diameter d is 1 to 200 μm
(2) Convex height h is 0.5 to 100 μm
(3) Occupancy ratio of roll surface by convex part is 30 to 95%
The method for producing a hot-dip galvanized steel sheet having excellent appearance quality according to any one of claims 1 to 5, wherein skin pass rolling is performed using a skin pass roll.