JP3879266B2 - Alloyed hot-dip galvanized steel sheet excellent in formability and manufacturing method thereof - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、自動車車体部品等のプレス加工が施される用途に好適な、加工時の耐めっき剥離性の良好な合金化溶融亜鉛めっき鋼板およびその製造方法に関する。
【０００２】
【従来の技術】
近年、家電、建材、及び自動車の産業分野においては溶融亜鉛めっき鋼板が大量に使用されているが、とりわけ経済性、防錆機能、塗装後の性能が優れている合金化溶融亜鉛めっき鋼板が広く用いられている。合金化溶融亜鉛めっき鋼板は、溶融亜鉛めっき鋼板を合金化処理温度に加熱し、Ｚｎめっき層をＦｅ−Ｚｎ合金化して製造される。めっき層は Ｆｅ−Ｚｎ金属間化合物よりなり、その平均のＦｅ含有量は通常８〜１２重量％である。
【０００３】
合金化溶融亜鉛めっき鋼板のプレス成形性（以下、単に「成形性」とも記す）は、めっき層を有さない鋼板に比較して劣るとされている。それは表面のめっき層が成形時の鋼板の変形を妨げるのが原因とされている。また、プレス加工時に、パウダリング（めっき層が粉末状に剥離する不良現象）やフレーキング（プレス加工に際してめっき層が薄片状になって剥離する不良現象）が発生するとめっき表面での摺動性が悪くなり鋼板のダイス孔への流入抵抗が増すことも成形性が損なわれる原因となる。
【０００４】
特開平４−２０２７８６号公報および特開平４−２０２７８７号公報には、亜鉛系めっき鋼板、特に合金化溶融亜鉛めっき鋼板の上に複数のＦｅ系合金電気めっき層を設け、表面の物性を変化させることによって、成形時に生じ易いめっき層の亀裂発生を防止し、電着塗装性と成形性を向上させる技術が開示されている。しかしながらここに開示されている技術では、溶融めっき層の上に多層の電気めっき層を設ける必要があるために製造コストが高くなり生産性も阻害されるという問題があった。
【０００５】
特開平８−１５８０６６号公報には、めっき層の上にＦｅ−Ｎｉ−Ｏ系の酸化物皮膜を表面に有する、プレス成形性、溶接性、接着性および化成処理性に優れた亜鉛系めっき鋼板が開示されている。この方法は上記の金属元素を１０〜１５００ｍｇ／ｍ2 と酸素を０．５〜３０％含有する酸化物で構成される皮膜をめっき層表面に備えるものである。しかしながらここに開示されている鋼板においても成形性の改善効果は十分ではない。
【０００６】
【発明が解決しようとする課題】
合金化溶融亜鉛めっき鋼板の成形性を冷間圧延鋼板並に改善するにはめっき層の表面に厚い金属めっきを施すのが有効である。本発明者らの研究によれば、金属めっき皮膜の付着量が２０００ｍｇ／ｍ2 以上であれば冷間圧延鋼板にほぼ近いレベルまで成形性を向上させることができる。金属めっき皮膜の付着量が２０００ｍｇ／ｍ2 よりも少なくなると成形性改善効果が少なくなり、１００ｍｇ／ｍ2 未満では殆ど効果がなくなり、金属めっき皮膜を備えない合金化溶融亜鉛めっき鋼板と同等レベルにまで低下することが判明した。しかしながら２０００ｍｇ／ｍ2 以上の厚い金属めっきを生産性良くしかも経済的に施すのは容易ではない。
【０００７】
本発明の目的は、上記の問題点を解決し、低コストで効率的に製造できる、成形性に優れた合金化溶融亜鉛めっき鋼板およびその製造方法を提供することにある。
【０００８】
【課題を解決するための手段】
本発明者らは、合金化溶融亜鉛めっき鋼板の成形性を母材鋼板（例えば、焼鈍済みの冷間圧延鋼板や熱間圧延鋼板など）並に改善するには、プレス成形する際のめっき層表面での金型との摺動性が大きく影響していることに着目し、めっき層表面の摺動性を改善する方法について鋭意研究を重ねた結果、以下のような知見を得た。
【０００９】
ａ．合金化溶融亜鉛めっきの表面形状は、めっき層表面のＦｅ−Ｚｎ結晶粒の平均結晶粒径を５μｍ以下とすることで摺動性が改善される。めっき層表面の結晶粒が微細になることでめっき層表面が滑らかになり、プレス加工される際のめっき層表面と金型との接触が緊密になるなどの作用により、プレス時に使用される潤滑油などによる潤滑効果が改善されるためと推測される。
【００１０】
ｂ．めっき層の摺動性を向上させるためにはその表面を潤滑油の保持性が優れる表面状態にするのがよい。合金化溶融亜鉛めっき層表面においては、酸化亜鉛をめっき層表面に備えるものが好適である。酸化亜鉛は親油性を有しており、プレス時に鋼板と金型との界面に潤滑油を保持する作用があるものと考えられる。合金化溶融亜鉛めっき層表面には、合金化処理時の高温加熱に伴い、一般的に、付着量がＺｎ含有量として２０〜６０ｍｇ／ｍ2 の酸化皮膜が自然発生的に存在している。しかしながら摺動性を向上させるには上記付着量では不足であり、さらに多くの酸化亜鉛を備えているものがよい。
【００１１】
ｃ．めっき層が金型に対して相対的に軟質である場合には両者間での摺動抵抗が大きくなり、めっき層のフレーキングが発生しやすくなるとともに成形性が損なわれる。
【００１２】
前述の酸化亜鉛に加えて、めっき層表面に硬質な金属を備えたものはめっき層の摺動性が更に良好である。この金属の付着量は比較的少量でよく、金属と酸化亜鉛が最表面に共存（混在）した状態のものがよい。金属としては、作業の容易さからＦｅ、Ｃｏ、Ｎｉの内の１種または２種以上が好適である。
【００１３】
ｄ．金属イオンを含有した溶液による電気めっき法、置換めっき法などの方法によりめっき層を処理すると、金属元素は、電気伝導度が小さく、また、金属イオン溶解のしにくい酸化皮膜上には析出せず、酸化亜鉛皮膜の欠陥部分（酸化皮膜に生じるピンホールや酸化皮膜の薄い部分等）に析出する傾向を有する。このため、上記の方法により処理すれば、金属と酸化亜鉛が共存（混在）した皮膜を備えさせることができる。これにより、適度の摺動性とプレス成形性とを兼ね備えためっき鋼板を得ることができる。
【００１４】
本発明はこれらの新たに得られた知見を基にして完成されたものであり、その要旨は下記の（１）に記載の合金化溶融亜鉛めっき鋼板、または、（２）に記載のその製造方法にある。
【００１５】
（1）Ｆｅを７〜１５重量％含有し、表面の平均結晶粒径が５μｍ以下である合金化溶融亜鉛めっき層の上に、Ｚｎ量が１００〜１０００ｍｇ／ｍ2である酸化亜鉛と、Ｆｅ、Ｃｏ、Ｎｉの内の１種または２種以上の金属を合計で１０〜１０００ｍｇ／ｍ2とを含有する表面皮膜を有することを特徴とする成形性に優れた合金化溶融亜鉛めっき鋼板。
【００１６】
（2）母材鋼板に有効Ａｌ濃度が０．０８０〜０．２０重量％である溶融亜鉛めっき浴を用いてめっきし、めっき付着量を調整し、２０〜７０℃／秒の加熱速度で４９０℃〜５５０℃に加熱して合金化処理した後、陽極酸化および／または酸化性雰囲気ガス中での保持によりＺｎ量が１００〜１０００ｍｇ／ｍ2である酸化亜鉛をめっき層表面に備えさせる処理と、Ｆｅ、Ｃｏ、Ｎｉの内の１種または２種以上の金属イオンを含有する溶液を用いて該金属を合計で１０〜１０００ｍｇ／ｍ2付着させる処理とを施すことを特徴とする上記（1）に記載の成形性に優れた合金化溶融亜鉛めっき鋼板の製造方法。
【００１７】
【発明の実施の形態】
本発明の実施に際し、その形態や条件の範囲およびそれを設定した理由について以下に述べる。
【００１８】
溶融めっきの母材は、冷延鋼板が好ましいが、表面の酸化皮膜を除去した熱延鋼板でも構わない。製造設備は一般に使用されるものであり、アルカリ溶液などによる脱脂を行った後、還元焼鈍し、溶融めっきした後、合金化処理を施して合金化溶融亜鉛めっき鋼板を製造する。
【００１９】
めっき層の化学組成は、Ｆｅを７〜１５重量％含有し、残部は実質的にＺｎよりなる。めっき層中のＦｅ含有量が１５重量％を超えると、パウダリング性が著しく劣化するので良くない。好ましくは１３重量％以下である。Ｆｅ含有量が７重量％未満では表層にη−Ｚｎが残存することが多くなり、以降の塗装性、溶接性が不良となり良くない。
【００２０】
合金化溶融亜鉛めっき層の表層部のＦｅ−Ｚｎ合金層の平均結晶粒径が５μｍを超えるとめっき層と金型との間の摩擦抵抗が増し、めっき層表面に後述の酸化亜鉛皮膜を備えさせても耐フレーキング性に対する改善効果が発揮されない。このため表面の平均結晶粒径は５μｍ以下とする。平均結晶粒径は小さいほど好ましい。通常の手段でも平均結晶粒径を０．５μｍ程度にまで小さくすることは可能である。
【００２１】
本発明におけるめっき層表層部の平均結晶粒径は、表層のＦｅ−Ｚｎ合金が搬送用のロールへの接触などにより機械的に押しつぶされていない部分を走査型電子顕微鏡で１０００倍以上の倍率で観察し、画像処理してそれぞれの結晶粒径を面積が等価な円として換算した場合に直径と仮定して算出した平均値である。
【００２２】
上述の合金化溶融亜鉛めっき層の上には、Ｚｎ量が１００〜１０００ｍｇ／ｍ2 である酸化亜鉛と、Ｆｅ、Ｃｏ、Ｎｉの内の１種または２種以上を合計で１０〜１０００ｍｇ／ｍ2 とを含有する皮膜を備える。
【００２３】
酸化亜鉛には、潤滑油との親和性が高く、単位面積当たりの油付着量を増し摺動面での油膜切れを生じ難くする作用がある。表面酸化のＺｎ量が１００ｍｇ／ｍ2 に満たない場合には上記の作用が不十分であり、めっき鋼板の成形性が改善されない。このため、酸化亜鉛の付着量はＺｎ量で１００ｍｇ／ｍ2 以上とする。好ましくは２００ｍｇ／ｍ2 以上である。
【００２４】
酸化亜鉛の付着量がＺｎで１０００ｍｇ／ｍ2 を超えると摺動性を改善する効果が飽和する。また、経済的な手段では１０００ｍｇ／ｍ2 を超えるような大量の酸化物を表面に備えさせることは困難であるので、酸化亜鉛はＺｎ量で１０００ｍｇ／ｍ2 以下とする。好ましくは５００ｍｇ／ｍ2 以下である。
【００２５】
酸化亜鉛と混在させる金属の種類をＦｅ、Ｃｏ、Ｎｉの内の１種または２種以上に限定するのは、これらの金属が摺動性を改善する効果に優れることと、酸化皮膜上に付着させるのが容易な金属であるからである。これらの金属の付着量が（２種以上である場合にはその合計で）１０ｍｇ／ｍ2 に満たない場合には、金型との金属接触が生じた際の摺動性を改善することができない。好ましくは２００ｍｇ／ｍ2 以上とするのがよい。
【００２６】
これらの金属の付着量が１０００ｍｇ／ｍ2 を超えると、金属が酸化亜鉛を覆い尽くし、表面に共存する酸化亜鉛が少なくなり、保油性が不足して成形性の改善が不十分となる。これを避けるために金属の付着量は１０００ｍｇ／ｍ2 以下とする。好ましくは７００ｍｇ／ｍ2 以下である。
【００２７】
酸化亜鉛中のＺｎ含有量は、測定用試料を３重量％以上の重クロム酸アンモニウム溶液とアンモニア水溶液の混合水溶液でｐＨ１０以上の溶液中に、溶出したＺｎ酸化物をＺｎ量として検出測定した値を酸化亜鉛中のＺｎ量として規定する。上記混合溶液ではクロム酸イオンが亜鉛金属に対するインヒビターとして作用するのでＺｎは溶解しない。Ｆｅ、Ｃｏ、Ｎｉ等の金属元素はアルカリ性溶液では溶解しないので、表面に存在する酸化亜鉛のみを選択的に溶解させることができる。
【００２８】
酸化亜鉛の形態はＺｎＯ、ＺｎＯ化合物、Ｚｎ（ＯＨ）2 、Ｚｎ（ＯＨ）2 化合物など表面には多種存在するが、重クロム酸アンモニウム溶液のアンモニア水溶液中にはすべて溶解する。これらの酸化物および水酸化物はいずれも保油性があるものと考えるため、酸化物に含有されているＺｎ量にて、酸化亜鉛量を規定するものである。
【００２９】
本発明の鋼板は以下に述べる方法で効率的に製造できる。
母材鋼板をアルカリ脱脂した後、十分な還元雰囲気中で６００℃以上に加熱しする還元加熱を施す。母材が冷間圧延ままの未焼鈍材であるために焼鈍を必要とする場合には再結晶温度以上に加熱して還元焼鈍を施す。
【００３０】
還元加熱（または還元焼鈍）時の雰囲気の露点は、−６０〜−２０℃の範囲にするのがよい。さらには、水素濃度が６〜１２体積％、残部が窒素である雰囲気の場合には、露点を−４０〜−２０℃の範囲に保持することが好ましい。還元加熱（または還元焼鈍）後にはめっき浴温度近傍の温度に冷却し、めっき浴に浸漬し、引き上げてガスワイピング等の方法で付着量を調整した後、合金化処理する。
【００３１】
溶融めっき浴に含有されるＡｌは、溶融めっき時の界面での合金化を抑制する作用がある。めっき浴のＡｌ含有量は、有効Ａｌ（全Ａｌ重量％−全Ｆｅ重量％）として、０．０８０重量％以上とするのが好ましい。
【００３２】
合金化反応の初期に生成する合金相であるζ相（ＦｅＺｎ13）が安定であるため、有効Ａｌが０．０８０重量％に満たない場合には、初期に形成されたζ相が粗大に成長し、その形態が表面に残存するので、表層のＦｅ−Ｚｎ合金の平均結晶粒径を小さくすることが困難である。めっき浴の有効Ａｌ濃度は０．２０重量％を上限とするのがよい。０．２０重量％を超えてＡｌ濃度を高めると、合金化が遅延し、生産性が低下するおそれがある。
【００３３】
合金化処理する条件を制御することにより、表面のＦｅ−Ｚｎ合金の平均結晶粒径を５μｍ以下とする。これは、めっき付着量を調整した後、めっき浴温度よりもやや低温になった鋼板を、４９０℃〜５５０℃、より好ましくは５００℃〜５３０℃の合金化処理温度領域に急速加熱し、保持時間を調整して皮膜のＦｅ含有量を７〜１５重量％にする。合金化処理温度への加熱速度は２０℃／秒以上、より好ましくは３０℃／秒以上で、７０℃／秒以下の範囲で行うのが良い。
【００３４】
しかしながら、めっき層表面のＦｅ−Ｚｎ合金の平均結晶粒径を小さくする方法は上述の方法に限定される必要はない。合金化時のＦｅ−Ｚｎ合金の核発生頻度を高めることに関しては、めっき前の母材表面を酸化させたり（還元焼鈍時に還元鉄が生成され、反応性が高くなる）、Ｆｅ系めっきやＮｉ系めっきなどの前処理を母材に施し、Ｆｅ−Ｚｎ合金化反応の初期から表面を活性化させておくことにより、合金化のヒートパターンを変化させることなく、表層Ｆｅ−Ｚｎ合金を細粒化させることが可能である。
【００３５】
めっき層表面に酸化亜鉛とＦｅ、Ｃｏ、Ｎｉの内の１種以上の金属とを共存させる方法は、合金化処理後のめっき層表面に酸化処理を施して所定量の酸化亜鉛を付着させた後に上記金属を付着させる方法と、合金化処理後のめっき層に所定量の上記金属を付着させた後、表面に存在する亜鉛または酸化亜鉛をさらに酸化させて酸化亜鉛量を所定の範囲にする方法があるがいずれの方法でも構わない。
【００３６】
合金化が終了しためっき層の表面には酸化亜鉛皮膜が自然発生的に生じている。酸化亜鉛量を更に増して所定の範囲にするための酸化亜鉛処理方法としては、鋼板をｐＨ４〜１０の溶液中で陽極酸化する方法が容易であり好適である。鋼板を、水蒸気を飽和量含む窒素ガス、酸素ガスなどの混合ガスからなる１００〜３５０℃の酸化性ガス中で保持する処理などでも良い。
【００３７】
合金化処理後または酸化亜鉛処理後の鋼板に、Ｆｅ、Ｃｏ、Ｎｉの内の１種または２種以上を合計で１０〜１０００ｍｇ／ｍ2 付着させる。これらの金属の付着方法としては、ｐＨ２〜４程度の酸性溶液中にＦｅイオン、Ｎｉイオン、Ｃｏイオンなどを溶解した液中に２〜３０秒程度浸漬し、置換めっきする方法が、コスト的には有利である。
【００３８】
しかしながら金属元素の付着方法は置換めっき法に限定される必要はなく、ｐＨ２〜ｐＨ４程度の、上記金属イオンを含有する酸性溶液等の処理液中で電解処理して上記金属元素を酸化亜鉛が付着していない部分や付着量が少ない部分などに電析させる電気めっき方法など、任意の方法を用いることができる。付着量を制御するには所定量の電気量を通電する電気めっき方法が好ましい。
【００３９】
本発明では、酸化亜鉛皮膜内に生じているピンホールや、酸化亜鉛皮膜が薄い部分に金属元素が析出するので、金属皮膜と酸化亜鉛皮膜が混在して共存する表面皮膜が得られる。共存状態は皮膜発生条件を調整することで可能である。
【００４０】
本発明の方法では、上述したように、合金化処理しためっき層表面に所定量の金属を付着させ、その後にあらためて酸化亜鉛被覆処理してもよい。この場合の酸化皮膜処理方法は前述のと同様の方法で良い。これにより、Ｆｅ、Ｎｉ、Ｃｏ等の金属は酸化されないで亜鉛が選択的に酸化されて酸化亜鉛量を所定の範囲にすることができる。
【００４１】
本発明の鋼板の母材となる合金化溶融亜鉛めっき鋼板は、公知の一般的な、合金化溶融亜鉛めっき鋼板製造設備を使用することにより容易に製造できる。誘導加熱方式の合金化炉を備えた設備を用いればさらに容易である。
【００４２】
【実施例】
厚さが０．７５ｍｍの極低炭素鋼を素材とする冷間圧延鋼板に、溶融めっきシミュレータにより、付着量が３０〜７０ｇ／ｍ2 の溶融亜鉛めっきを施した。めっき浴の有効Ａｌ濃度は０．１２重量％であった。この亜鉛めっき鋼板を誘導加熱方式により、加熱速度を１０〜１００℃／秒まで変化させて４８０℃〜５５０℃に加熱し、保持時間を５〜４０秒間とし、めっき層のＦｅ含有量が７〜１５重量％、表面のＦｅ−Ｚｎ合金の平均結晶粒径が１〜１０μｍの合金化溶融亜鉛めっき鋼板を得た。合金化処理後の冷却過程の鋼板温度が１００〜３５０℃の間に、水蒸気を飽和させた大気中での酸化処理を施して酸化亜鉛の付着量を種々の値に調整した。得られた鋼板の平均結晶粒径は、測定個所２０以上のめっき層表面を観察し、倍率２０００倍で写真を撮影し、画像処理してそれぞれの結晶粒径を面積が等価な円として換算した直径の平均値として求めた。
【００４３】
これらの鋼板表面に、めっき浴組成がＦｅイオン、ＮｉイオンおよびＣｏイオンの内の１種以上を１０〜１００ｇ／リットル含有し、ｐＨ２〜ｐＨ４、温度が５０℃である硫酸浴中で、電流密度１〜１０Ａ／ｄｍ2 の条件で電気めっきし、付着量が片面当たり１００〜２０００ｍｇ／ｍ2 のＦｅ、Ｎｉ、Ｃｏの１種以上の金属を付着させた。
【００４４】
上記と同一の化学組成およびめっき層を有する合金化溶融亜鉛めっき鋼板試料を、硫酸溶液中にＮｉ、Ｆｅ、Ｃｏの硫酸塩を溶解した置換めっき浴中に１〜３０秒間浸漬させる置換めっきを行い、金属元素を１０００ｍｇ／ｍ2 以下の範囲で付着させた。
【００４５】
これらの金属の付着量は以下の方法で測定した。ＮｉおよびＣｏは塩酸酸性溶液中でめっき層と共に溶解して溶液分析によって測定し、Ｆｅは付着処理をおこなう前後での鋼板の重量変化を測定する重量法によって測定した。
【００４６】
金属に被覆されずに鋼板表面に露出している酸化亜鉛のＺｎ量は、重クロム酸アンモニウム含有アンモニア水溶液中に、酸化亜鉛を溶解し、Ｚｎとして検出した。
【００４７】
得られた鋼板の摺動性を以下の方法で評価した。
図１は溝型に鋼板を曲げ成形する際の成形力から鋼板の摩擦係数を評価する摺動性評価装置の概念を示す斜視図である。この装置により測定した摩擦係数により鋼板の摺動性を評価した。試験片１はしわ押さえビード４からの力を受けてダイス面２に押し付けられている。押し金具５の形状は直方体状である。押し金具５の下降に伴って試験片１はダイス面２としわ押さえビード４との間で摺動しつつ平行な溝状の開口部であるダイス溝３に引き込まれる。試験片の摺動性に応じて押し金具５の圧入力が変化するので、圧入力としわ押さえ荷重との関係から試験片の摩擦係数を測定することができる。
【００４８】
試験片１の寸法は幅３０ｍｍ、長さ２７０ｍｍとし、ビードの断面寸法は半径５ｍｍの半円形とした。ダイス面２、しわ押さえビード４および押し金具５の表面は、６００＃の研磨紙で研磨したものを用い、試験片１の両面には潤滑剤として防錆油を片面あたり、２．５ｇ／ｍ2 塗布し、押し金具３の圧入速度は６０ｍｍ／分とした。しわ押さえ荷重は、７５０、１０００、１２５０、１５００ｋｇｆの４条件とし、それぞれの場合の押し金具５の圧入力の最大値を求め、しわ押さえ荷重の増分（ｄＰ）と押し金具圧入力の最大荷重の増分（ｄＦ）とから、摩擦係数（μ）をμ＝ｄＦ／２ｄＰなる式により計算して求め、μの値にしたがって摺動性を下記の基準で評価した。
【００４９】
◎：μが０．２４以下（極めて良好）、
○：０．２４超０．２８以下○（良好）、
△：０．２８超０．３２以下△（不良）、
×：０．３２超（極めて不良）。
得られた鋼板の成形性は以下の方法で評価した。厚さ０．７５ｍｍ、直径６０ｍｍφの試験片を外径３４ｍｍのポンチ、孔径３５．５ｍｍダイスを用いて円筒に成形するカップ絞り試験を行い、しわ押さえ力（ＢＨＦ）を変化させ、ワレ発生境界を調査した。工具研磨：研磨紙＃６００で研磨、成形速度６０ｍｍ／分、市販の防錆油を０．５ｇ／ｍ2 塗布した状態で、亀裂が発生する直前のＢＨＦの値にて評価した。
【００５０】
上記合金化溶融亜鉛めっき鋼板と同一の化学組成を有する焼鈍済みの冷間圧延鋼板では、上記と同様のカップ絞り試験をおこなった際のしわ押さえ力は３５００Ｋｇｆであり、酸化亜鉛や金属付着処理をおこなわない合金化溶融亜鉛めっきそのままの鋼板では、２０００Ｋｇｆが境界であった。このため得られためっき鋼板の成形性は以下の基準で評価した。
【００５１】
３０００Ｋｇｆでワレ発生の生じないもの・・・極めて良好（◎）、
２５００以上３０００Ｋｇｆ未満・・・良好（○）、
２０００以上３０００Ｋｇｆ未満・・・やや不良（△）、
２０００Ｋｇｆ未満・・・不良（×）。
各種の試験結果を表１に示した。
【００５２】
【表１】
表１からわかるように、本発明の規定する条件を満たしている試験番号１〜１５は、いずれも良好な摺動性と成形性を示した。中でも好ましい範囲である酸化亜鉛付着量が２００〜１０００ｍｇ／ｍ2 、金属付着量が２００〜７００ｍｇ／ｍ2 であった試験番号２、３、５、９および１１〜１３は極めて良好であった。
【００５４】
これに対し、めっき層表面の平均結晶粒径が本発明の規定する範囲外であった試験番号２１および２２、金属付着量が１０ｍｇ／ｍ2 に満たなかった試験番号２４および２８〜３０などはいずれの特性とも好ましくなかった。酸化亜鉛中の亜鉛量が本発明の規定する範囲に満たなかった試験番号２５〜２７および３１〜３４は成形性がよくなかった。なかでも、金属付着量とＺｎ量が共に本発明の規定する下限よりも少なかった試験番号２３は、特に良くなかった。
【００５５】
【発明の効果】
本発明の合金化溶融亜鉛めっき鋼板は、滑らかなめっき層表面に金型との摺動抵抗が少なく潤滑油の保持性に優れた表面皮膜を有するので、優れた摺動性と成形性を兼ね備えている。また本発明の鋼板は、低コストで効率的に製造できる。従って本発明の鋼板は自動車車体用鋼板などの用途に極めて好適である
【図面の簡単な説明】
【図１】摺動性評価装置の概念を示す斜視図である。
【符号の説明】
１・・・試験片、２・・・ダイス面、３・・・ダイス溝、４・・・しわ押さえビード、５・・・押し金具。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an alloyed hot-dip galvanized steel sheet having good plating peel resistance at the time of processing, and a method for producing the same, suitable for applications in which press working of automobile body parts and the like is performed.
[0002]
[Prior art]
In recent years, hot-dip galvanized steel sheets have been used in large quantities in the industrial fields of home appliances, building materials, and automobiles. Especially, alloyed hot-dip galvanized steel sheets that are excellent in economic efficiency, rust prevention function, and performance after painting are widely used. It is used. The alloyed hot-dip galvanized steel sheet is manufactured by heating a hot-dip galvanized steel sheet to an alloying treatment temperature and forming a Zn plating layer into an Fe—Zn alloy. A plating layer consists of a Fe-Zn intermetallic compound, The average Fe content is 8 to 12 weight% normally.
[0003]
The press formability (hereinafter, also simply referred to as “formability”) of the alloyed hot-dip galvanized steel sheet is inferior to that of a steel sheet having no plating layer. This is because the surface plating layer prevents the deformation of the steel sheet during forming. In addition, when powdering (defect phenomenon in which the plating layer peels off in powder form) or flaking (defect phenomenon in which the plating layer becomes exfoliated during pressing process) occurs during press working, the slidability on the plating surface Worsening and increasing the inflow resistance to the die hole of the steel sheet also causes the formability to be impaired.
[0004]
In JP-A-4-202786 and JP-A-4-202787, a plurality of Fe-based alloy electroplating layers are provided on a zinc-based plated steel sheet, particularly an alloyed hot-dip galvanized steel sheet, to change the physical properties of the surface. Thus, a technique for preventing cracking of a plating layer that easily occurs during molding and improving electrodeposition coating property and formability is disclosed. However, the technique disclosed herein has a problem that the manufacturing cost is increased and the productivity is hindered because it is necessary to provide a multi-layered electroplating layer on the hot dipping layer.
[0005]
JP-A-8-158066 discloses a galvanized steel sheet having an Fe-Ni-O-based oxide film on the surface of a plating layer and excellent in press formability, weldability, adhesion and chemical conversion treatment. Is disclosed. In this method, a coating layer composed of an oxide containing 10 to 1500 mg / m 2 of the metal element and 0.5 to 30% of oxygen is provided on the surface of the plating layer. However, even in the steel sheet disclosed here, the effect of improving formability is not sufficient.
[0006]
[Problems to be solved by the invention]
In order to improve the formability of the alloyed hot-dip galvanized steel sheet as well as the cold-rolled steel sheet, it is effective to apply a thick metal plating to the surface of the plating layer. According to the study by the present inventors, the formability can be improved to a level almost close to that of a cold-rolled steel sheet when the amount of the metal plating film deposited is 2000 mg / m 2 or more. If the adhesion amount of the metal plating film is less than 2000 mg / m 2, the effect of improving the formability is reduced, and if it is less than 100 mg / m 2 , the effect is almost lost, and is equivalent to the galvannealed steel sheet without the metal plating film. It turned out to be reduced. However, it is not easy to apply a thick metal plating of 2000 mg / m 2 or more with good productivity and economically.
[0007]
An object of the present invention is to provide an alloyed hot-dip galvanized steel sheet excellent in formability and a method for producing the same, which can solve the above problems and can be efficiently produced at low cost.
[0008]
[Means for Solving the Problems]
In order to improve the formability of an alloyed hot-dip galvanized steel sheet as much as that of a base steel sheet (for example, a cold-rolled steel sheet or a hot-rolled steel sheet that has been annealed), the plating layer at the time of press forming Focusing on the fact that the slidability with the mold on the surface has a great influence, the following findings were obtained as a result of intensive studies on methods for improving the slidability of the plating layer surface.
[0009]
a. The slidability of the surface shape of the alloyed hot dip galvanizing is improved by setting the average crystal grain size of the Fe—Zn crystal grains on the surface of the plating layer to 5 μm or less. Lubricant used during pressing due to the fact that the surface of the plating layer becomes smooth as the crystal grains on the surface of the plating layer become finer, and the contact between the plating layer surface and the mold becomes tight during pressing. This is presumably because the lubricating effect of oil or the like is improved.
[0010]
b. In order to improve the slidability of the plating layer, it is preferable that the surface thereof be in a surface state in which the lubricating oil retention is excellent. On the surface of the alloyed hot dip galvanized layer, one having zinc oxide on the surface of the plated layer is suitable. Zinc oxide has lipophilicity and is considered to have an action of retaining lubricating oil at the interface between the steel plate and the mold during pressing. In general, an oxide film having an adhesion amount of 20 to 60 mg / m 2 as a Zn content spontaneously exists on the surface of the alloyed hot-dip galvanized layer with high-temperature heating during the alloying treatment. However, the amount of adhesion is insufficient to improve the slidability, and it is preferable to have more zinc oxide.
[0011]
c. When the plating layer is relatively soft with respect to the mold, the sliding resistance between the two becomes large, flaking of the plating layer is likely to occur, and the moldability is impaired.
[0012]
In addition to the aforementioned zinc oxide, those having a hard metal on the surface of the plating layer have better sliding properties of the plating layer. The amount of the metal attached may be relatively small, and the metal and zinc oxide coexist on the outermost surface (mixed). As the metal, one or more of Fe, Co, and Ni are preferable from the viewpoint of ease of work.
[0013]
d. When the plating layer is treated by a method such as electroplating or displacement plating with a solution containing metal ions, the metal element does not deposit on the oxide film which has low electrical conductivity and is difficult to dissolve metal ions. , The zinc oxide film has a tendency to deposit on defective portions (pinholes generated in the oxide film, thin portions of the oxide film, etc.). For this reason, if it processes by said method, the film | membrane which a metal and zinc oxide coexisted (mixed) can be provided. Thereby, the plated steel plate which has moderate slidability and press formability can be obtained.
[0014]
The present invention has been completed on the basis of these newly obtained findings, the gist of which is the alloyed hot-dip galvanized steel sheet described in (1) below or the production thereof described in (2). Is in the way.
[0015]
(1) On an alloyed hot-dip galvanized layer containing 7 to 15% by weight of Fe and having an average surface grain size of 5 μm or less, zinc oxide having a Zn content of 100 to 1000 mg / m 2 , Fe An alloyed hot-dip galvanized steel sheet excellent in formability, characterized by having a surface film containing 10 or 1000 mg / m 2 of one or more metals of Co, Ni in total.
[0016]
(2) The base steel plate is plated using a hot dip galvanizing bath having an effective Al concentration of 0.080 to 0.20% by weight, the amount of plating is adjusted, and the heating rate is 20 to 70 ° C./second. A treatment in which the surface of the plating layer is provided with zinc oxide having a Zn amount of 100 to 1000 mg / m 2 by anodization and / or holding in an oxidizing atmosphere gas after heating to 550 ° C. to 550 ° C. above, wherein the subjecting Fe, Co, and one or a total of the metal with a solution containing two or more metal ions 10 to 1000 mg / m 2 adhered to the processing of the Ni (1 The manufacturing method of the galvannealed steel plate excellent in the formability as described in).
[0017]
DETAILED DESCRIPTION OF THE INVENTION
In carrying out the present invention, the scope of the form and conditions and the reason for setting it will be described below.
[0018]
The hot-plated steel plate is preferably a cold-rolled steel plate, but may be a hot-rolled steel plate from which the surface oxide film has been removed. Manufacturing equipment is generally used, and after degreasing with an alkaline solution or the like, reduction annealing, hot dip plating, and alloying treatment are performed to manufacture an alloyed hot dip galvanized steel sheet.
[0019]
The chemical composition of the plating layer contains 7 to 15% by weight of Fe, and the balance is substantially made of Zn. If the Fe content in the plating layer exceeds 15% by weight, the powdering property is remarkably deteriorated, which is not good. Preferably it is 13 weight% or less. If the Fe content is less than 7% by weight, η-Zn often remains on the surface layer, and the subsequent paintability and weldability become poor, which is not good.
[0020]
When the average crystal grain size of the Fe—Zn alloy layer in the surface layer portion of the alloyed hot-dip galvanized layer exceeds 5 μm, the frictional resistance between the plated layer and the mold increases, and the surface of the plated layer is provided with a zinc oxide film to be described later. Even if it makes it, the improvement effect with respect to anti-flaking property is not exhibited. For this reason, the average crystal grain size of the surface is 5 μm or less. The smaller the average crystal grain size, the better. It is possible to reduce the average crystal grain size to about 0.5 μm by ordinary means.
[0021]
The average crystal grain size of the surface layer portion of the plating layer in the present invention is such that the portion of the surface layer where the Fe-Zn alloy is not mechanically crushed by contact with a transporting roll or the like with a scanning electron microscope at a magnification of 1000 times or more. It is an average value calculated by assuming a diameter when observing and image processing and converting each crystal grain size into a circle with an equivalent area.
[0022]
On the galvannealed layer described above, a zinc oxide Zn amount is 100~1000mg / m 2, Fe, Co , 10~1000mg / m in total one or two or more of the Ni And a film containing 2 .
[0023]
Zinc oxide has a high affinity with the lubricating oil, and has the effect of increasing the amount of oil adhered per unit area and making it difficult to cause an oil film breakage on the sliding surface. When the amount of Zn in the surface oxidation is less than 100 mg / m 2 , the above action is insufficient and the formability of the plated steel sheet is not improved. For this reason, the amount of zinc oxide deposited is 100 mg / m 2 or more in terms of Zn. Preferably it is 200 mg / m 2 or more.
[0024]
When the adhesion amount of zinc oxide exceeds 1000 mg / m 2 with Zn, the effect of improving the slidability is saturated. In addition, since it is difficult to provide a surface with a large amount of oxide exceeding 1000 mg / m 2 by economical means, the amount of zinc oxide is set to 1000 mg / m 2 or less. Preferably it is 500 mg / m 2 or less.
[0025]
The reason for limiting the type of metal mixed with zinc oxide to one or more of Fe, Co, and Ni is that these metals are excellent in improving the slidability and adhere to the oxide film. This is because it is a metal that is easy to cause. When the adhesion amount of these metals is less than 10 mg / m 2 (in the case of two or more kinds), the slidability when metal contact with the mold occurs can be improved. Can not. Preferably it is 200 mg / m 2 or more.
[0026]
When the adhesion amount of these metals exceeds 1000 mg / m 2 , the metal covers the zinc oxide, the zinc oxide coexisting on the surface is reduced, the oil retention is insufficient, and the moldability is insufficiently improved. In order to avoid this, the adhesion amount of the metal is set to 1000 mg / m 2 or less. Preferably it is 700 mg / m 2 or less.
[0027]
The Zn content in zinc oxide is a value obtained by detecting and measuring the eluted Zn oxide as a Zn amount in a solution having a pH of 10 or more in a mixed aqueous solution of ammonium bichromate solution and ammonia aqueous solution of 3% by weight or more. Is defined as the amount of Zn in zinc oxide. In the above mixed solution, since chromate ions act as an inhibitor for zinc metal, Zn does not dissolve. Since metal elements such as Fe, Co, and Ni are not dissolved in an alkaline solution, only zinc oxide present on the surface can be selectively dissolved.
[0028]
There are various forms of zinc oxide on the surface such as ZnO, ZnO compounds, Zn (OH) 2 , Zn (OH) 2 compounds, etc., but they are all dissolved in an aqueous ammonia solution of ammonium dichromate. Since these oxides and hydroxides are considered to have oil retaining properties, the amount of zinc oxide is defined by the amount of Zn contained in the oxide.
[0029]
The steel sheet of the present invention can be efficiently produced by the method described below.
After the base steel sheet is degreased with alkali, reduction heating is performed by heating to 600 ° C. or higher in a sufficient reducing atmosphere. When the base material is an unannealed material as it is cold-rolled, when annealing is required, it is heated above the recrystallization temperature and subjected to reduction annealing.
[0030]
The dew point of the atmosphere during reduction heating (or reduction annealing) is preferably in the range of −60 to −20 ° C. Furthermore, in an atmosphere where the hydrogen concentration is 6 to 12% by volume and the balance is nitrogen, it is preferable to keep the dew point in the range of −40 to −20 ° C. After reductive heating (or reductive annealing), it is cooled to a temperature in the vicinity of the plating bath temperature, dipped in the plating bath, pulled up, adjusted for adhesion by a method such as gas wiping, and then alloyed.
[0031]
Al contained in the hot dipping bath has an action of suppressing alloying at the interface during hot dipping. The Al content of the plating bath is preferably 0.080 wt% or more as effective Al (total Al wt%-total Fe wt%).
[0032]
Since the ζ phase (FeZn 13 ), which is an alloy phase generated early in the alloying reaction, is stable, when the effective Al is less than 0.080% by weight, the initially formed ζ phase grows coarsely. However, since the form remains on the surface, it is difficult to reduce the average crystal grain size of the surface Fe—Zn alloy. The effective Al concentration of the plating bath is preferably 0.20% by weight. If the Al concentration exceeds 0.20% by weight, alloying is delayed, and productivity may be reduced.
[0033]
By controlling the alloying conditions, the average grain size of the surface Fe—Zn alloy is set to 5 μm or less. This is because, after adjusting the amount of plating, the steel sheet, which is slightly lower than the plating bath temperature, is rapidly heated to the alloying treatment temperature range of 490 ° C to 550 ° C, more preferably 500 ° C to 530 ° C, and held. The time is adjusted so that the Fe content of the film is 7 to 15% by weight. The heating rate to the alloying treatment temperature is 20 ° C./second or more, more preferably 30 ° C./second or more and 70 ° C./second or less.
[0034]
However, the method for reducing the average crystal grain size of the Fe—Zn alloy on the plating layer surface need not be limited to the above-described method. Regarding increasing the frequency of nucleation of the Fe-Zn alloy during alloying, the surface of the base material before plating is oxidized (reduced iron is generated during reduction annealing, and the reactivity is increased), Fe-based plating and Ni The surface layer Fe-Zn alloy is finely grained without changing the heat pattern of alloying by applying pretreatment such as plating to the base material and activating the surface from the beginning of the Fe-Zn alloying reaction. It is possible to make it.
[0035]
In the method in which zinc oxide and at least one of Fe, Co, and Ni coexist on the surface of the plating layer, the plating layer surface after the alloying treatment is subjected to oxidation treatment to adhere a predetermined amount of zinc oxide. A method of attaching the metal later, and a predetermined amount of the metal deposited on the plated layer after the alloying treatment, and further oxidizing the zinc or zinc oxide present on the surface to bring the zinc oxide amount into a predetermined range There are methods, but any method is acceptable.
[0036]
A zinc oxide film is spontaneously formed on the surface of the plated layer after the alloying is completed. As a zinc oxide treatment method for further increasing the amount of zinc oxide to a predetermined range, a method of anodizing a steel plate in a solution having a pH of 4 to 10 is easy and preferable. The process etc. which hold | maintain a steel plate in 100-350 degreeC oxidizing gas which consists of mixed gas, such as nitrogen gas and oxygen gas containing a water vapor | saturation amount may be sufficient.
[0037]
A total of 10 to 1000 mg / m 2 of Fe, Co, or Ni is adhered to the steel plate after the alloying treatment or the zinc oxide treatment. As a method for attaching these metals, a method of immersing in a solution in which Fe ions, Ni ions, Co ions, etc. are dissolved in an acidic solution having a pH of about 2 to 4 for about 2 to 30 seconds and performing displacement plating is cost effective. Is advantageous.
[0038]
However, the deposition method of the metal element need not be limited to the displacement plating method, and zinc oxide is deposited on the metal element by electrolytic treatment in a treatment solution such as an acidic solution containing the metal ions having a pH of about 2 to 4. Any method can be used, such as an electroplating method in which electrodeposition is performed on a portion that is not formed or a portion with a small amount of adhesion. In order to control the amount of adhesion, an electroplating method in which a predetermined amount of electricity is applied is preferable.
[0039]
In the present invention, since the metal element is deposited in the pinholes generated in the zinc oxide film or the portion where the zinc oxide film is thin, a surface film in which the metal film and the zinc oxide film coexist can be obtained. The coexistence state is possible by adjusting the film generation conditions.
[0040]
In the method of the present invention, as described above, a predetermined amount of metal may be adhered to the surface of the alloyed plating layer, and then zinc oxide coating may be performed again. In this case, the oxide film treatment method may be the same as described above. Thereby, metals, such as Fe, Ni, and Co, are not oxidized, but zinc is selectively oxidized and the amount of zinc oxide can be made into a predetermined range.
[0041]
The alloyed hot-dip galvanized steel sheet used as the base material of the steel sheet of the present invention can be easily manufactured by using a known general alloyed hot-dip galvanized steel sheet manufacturing facility. It is even easier if equipment equipped with an induction heating type alloying furnace is used.
[0042]
【Example】
A cold-rolled steel sheet made of ultra-low carbon steel having a thickness of 0.75 mm was subjected to hot dip galvanization with an adhesion amount of 30 to 70 g / m 2 by a hot dip plating simulator. The effective Al concentration of the plating bath was 0.12% by weight. This galvanized steel sheet is heated to 480 ° C. to 550 ° C. by changing the heating rate to 10 to 100 ° C./second by induction heating method, the holding time is 5 to 40 seconds, and the Fe content of the plating layer is 7 to An alloyed hot-dip galvanized steel sheet having an average grain size of 1 to 10 μm and a surface Fe—Zn alloy of 15% by weight was obtained. While the steel plate temperature in the cooling process after the alloying treatment was 100 to 350 ° C., the amount of zinc oxide deposited was adjusted to various values by performing an oxidation treatment in the atmosphere saturated with water vapor. The average crystal grain size of the obtained steel sheet was obtained by observing the surface of the plating layer at 20 or more measurement points, taking a photograph at a magnification of 2000 times, and performing image processing to convert each crystal grain size as a circle with an equivalent area. It calculated | required as an average value of a diameter.
[0043]
In these sulfuric acid baths, the plating bath composition contains 10 to 100 g / l of one or more of Fe ions, Ni ions and Co ions,
[0044]
Substitution plating is performed in which an alloyed hot-dip galvanized steel sheet sample having the same chemical composition and plating layer as described above is immersed in a substitution plating bath in which a sulfate of Ni, Fe, Co is dissolved in a sulfuric acid solution for 1 to 30 seconds. The metal element was deposited in the range of 1000 mg / m 2 or less.
[0045]
The adhesion amount of these metals was measured by the following method. Ni and Co were dissolved together with the plating layer in a hydrochloric acid acidic solution and measured by solution analysis, and Fe was measured by a weight method that measures a change in the weight of the steel sheet before and after the adhesion treatment.
[0046]
The Zn amount of zinc oxide exposed on the steel sheet surface without being coated with metal was detected as Zn dissolved in an aqueous ammonium dichromate solution containing ammonia.
[0047]
The slidability of the obtained steel sheet was evaluated by the following method.
FIG. 1 is a perspective view showing a concept of a slidability evaluation apparatus that evaluates a friction coefficient of a steel sheet from a forming force when the steel sheet is bent into a groove mold. The slidability of the steel sheet was evaluated based on the friction coefficient measured by this apparatus. The test piece 1 is pressed against the
[0048]
The test piece 1 had a width of 30 mm and a length of 270 mm, and the bead had a cross-sectional dimension of a semicircle with a radius of 5 mm. The surfaces of the
[0049]
A: μ is 0.24 or less (very good),
○: More than 0.24 and 0.28 or less ○ (good),
Δ: More than 0.28 and less than 0.32 Δ (defect),
X: More than 0.32 (very poor).
The formability of the obtained steel sheet was evaluated by the following method. A cup squeeze test was conducted in which a test piece having a thickness of 0.75 mm and a diameter of 60 mmφ was formed into a cylinder using a punch with an outer diameter of 34 mm and a hole diameter of 35.5 mm, and the wrinkle holding force (BHF) was changed to change the crack occurrence boundary. investigated. Tool polishing: Polished with abrasive paper # 600, with a molding speed of 60 mm / min, and with a commercially available rust preventive oil applied at 0.5 g / m 2 , evaluation was performed using the BHF value immediately before the occurrence of cracks.
[0050]
In an annealed cold-rolled steel sheet having the same chemical composition as the above alloyed hot-dip galvanized steel sheet, the wrinkle holding force when a cup squeezing test similar to the above is performed is 3500 kgf, and zinc oxide or metal adhesion treatment is performed. In the steel plate as it was without galvannealing, 2000 Kgf was the boundary. For this reason, the formability of the obtained plated steel sheet was evaluated according to the following criteria.
[0051]
No cracking at 3000 kgf ... very good (◎),
2500 or more and less than 3000 kgf ... good (◯),
2000 or more and less than 3000 kgf ... Somewhat bad (△),
Less than 2000 kgf ... defect (x).
Various test results are shown in Table 1.
[0052]
[Table 1]
As can be seen from Table 1, Test Nos. 1 to 15 satisfying the conditions defined by the present invention all showed good slidability and moldability. Particularly preferable zinc oxide coating weight of 200 to 1000 mg / m 2 range,
[0054]
On the other hand, test numbers 21 and 22 in which the average crystal grain size on the surface of the plating layer was outside the range defined by the present invention, test numbers 24 and 28 to 30 in which the metal adhesion amount was less than 10 mg / m 2 , etc. None of these characteristics was desirable. Test numbers 25 to 27 and 31 to 34, in which the amount of zinc in zinc oxide was less than the range defined by the present invention, had poor moldability. Especially, the test number 23 in which both the metal adhesion amount and the Zn amount were less than the lower limit defined by the present invention was not particularly good.
[0055]
【The invention's effect】
The alloyed hot-dip galvanized steel sheet of the present invention has a surface coating that has a low sliding resistance with the mold and excellent lubricating oil retention on the surface of the smooth plating layer. ing. Moreover, the steel plate of this invention can be manufactured efficiently at low cost. Accordingly, the steel sheet of the present invention is extremely suitable for applications such as automobile body steel sheets.
FIG. 1 is a perspective view showing a concept of a slidability evaluation apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Test piece, 2 ... Die surface, 3 ... Die groove, 4 ... Wrinkle holding bead, 5 ... Press metal fittings.
Claims (2)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP22043998A JP3879266B2 (en) | 1998-08-04 | 1998-08-04 | Alloyed hot-dip galvanized steel sheet excellent in formability and manufacturing method thereof |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP22043998A JP3879266B2 (en) | 1998-08-04 | 1998-08-04 | Alloyed hot-dip galvanized steel sheet excellent in formability and manufacturing method thereof |
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| JP3879266B2 true JP3879266B2 (en) | 2007-02-07 |
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| JP3582504B2 (en) * | 2001-08-31 | 2004-10-27 | 住友金属工業株式会社 | Hot-press plated steel sheet |
| WO2003035922A1 (en) * | 2001-10-23 | 2003-05-01 | Sumitomo Metal Industries, Ltd. | Method for press working, plated steel product for use therein and method for producing the steel product |
| WO2004094684A1 (en) | 2003-04-23 | 2004-11-04 | Sumitomo Metal Industries, Ltd. | Hot press formed product and method for production thereof |
| JP2006051543A (en) | 2004-07-15 | 2006-02-23 | Nippon Steel Corp | Hot press method for high strength automotive member made of cold rolled or hot rolled steel sheet, or al-based plated or zn-based plated steel sheet, and hot pressed parts |
| JP4630099B2 (en) * | 2005-03-25 | 2011-02-09 | 株式会社神戸製鋼所 | Hot-dip hot-dip galvanized steel sheet with excellent phosphatability and post-coating corrosion resistance and method for producing the same |
| JP5540459B2 (en) * | 2006-03-01 | 2014-07-02 | Ｊｆｅスチール株式会社 | Alloy hot-dip galvanized steel sheet |
| JP5009035B2 (en) * | 2007-04-17 | 2012-08-22 | 新日本製鐵株式会社 | Manufacturing method of high-tensile alloyed hot-dip galvanized steel sheet with excellent appearance |
| JP5239570B2 (en) * | 2007-09-04 | 2013-07-17 | Ｊｆｅスチール株式会社 | Galvanized steel sheet |
| JP6493472B2 (en) * | 2017-09-05 | 2019-04-03 | 新日鐵住金株式会社 | Manufacturing method of hot press-formed member |
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