JP3581862B2 - Method for producing hot-dip Al-Zn-based plated steel sheet - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、めっき皮膜中のＡｌ含有量が２０〜９５ｍａｓｓ％である溶融Ａｌ−Ｚｎ系めっき鋼板の製造方法に関する。
【０００２】
【従来の技術】
５５％Ａｌ−Ｚｎ系めっき鋼板に代表される、めっき皮膜中にＡｌを２０〜９５ｍａｓｓ％含有する溶融Ａｌ−Ｚｎ系めっき鋼板（以下、「５５％Ａｌ−Ｚｎ系めっき鋼板」を例に説明する）は、特公昭４６−７１６１号に示されるように溶融亜鉛めっき鋼板に較べて優れた耐食性を示すことから、近年、建材分野を中心に需要が増加しつつある。
この５５％Ａｌ−Ｚｎ系めっき鋼板は、酸洗脱スケールした熱延鋼板又はこれをさらに冷間圧延して得られた冷延鋼板を下地鋼板とし、連続式溶融めっき設備において以下のようにして製造される。
【０００３】
連続式溶融めっき設備では、下地鋼板は還元性雰囲気に保持された焼鈍炉内で所定温度に加熱され、焼鈍と同時に鋼板表面に付着する圧延油等の除去、酸化膜の還元除去が行われた後、下端がめっき浴に浸漬されたスナウト内を通って所定濃度のＡｌを含有した溶融亜鉛めっき浴中に浸漬される。めっき浴に浸漬された鋼板はシンクロールを経由してめっき浴の上方に引き上げられた後、めっき浴上に配置されたガスワイピングノズルから鋼板の表面に向けて加圧した気体を噴射することによりめっき付着量が調整され、次いで冷却装置により冷却され、所定のめっき皮膜が形成された５５％Ａｌ−Ｚｎ系めっき鋼板が得られる。
【０００４】
連続式溶融めっき設備における焼鈍炉の熱処理条件及び雰囲気条件、めっき浴組成やめっき後の冷却速度等の操業条件は、所望のめっき品質や材質を確保するために所定の管理範囲で精度よく管理される。
上記のようにして製造された５５％Ａｌ−Ｚｎ系めっき鋼板のめっき皮膜は、主としてＺｎを過飽和に含有したＡｌがデンドライト凝固した部分と、残りのデンドライト間隙の部分からなっており、デンドライトはめっき皮膜の膜厚方向に積層している。このような特徴的な皮膜構造により、５５％Ａｌ−Ｚｎ系めっき鋼板は優れた耐食性を示す。
【０００５】
また、めっき浴には通常１．５ｍａｓｓ％程度のＳｉが添加されているが、このＳｉの働きにより、５５％Ａｌ−Ｚｎ系めっき鋼板はめっき皮膜／下地鋼板界面の合金相成長が抑えられ、合金相厚さは約１〜２μｍ程度である。この合金相が薄ければ薄いほど優れた耐食性を示す特徴的な皮膜構造の部分が多くなるので、合金相の成長抑制は耐食性の向上に寄与する。
通常、めっき浴には不可避的不純物、鋼板やめっき浴中の機器等から溶出するＦｅ、合金相抑制のためのＳｉが含まれるが、それら以外にも何らかの元素が添加されている場合もあり、合金相やめっき皮膜中にはそれら元素が合金或いは単体の形で存在している。
【０００６】
【発明が解決しようとする課題】
上述したように５５％Ａｌ−Ｚｎ系めっき鋼板は優れた耐食性を有する反面、機械的特性、特に伸び特性が他のめっき鋼板、例えばめっき皮膜中にＡｌを５ｍａｓｓ％程度含有する溶融Ａｌ−Ｚｎ系めっき鋼板（以下、「５％Ａｌ−Ｚｎ系めっき鋼板」という）に較べて劣る傾向があり、このため厳しい加工を行う用途には使用しにくい難点がある。一方、５％Ａｌ−Ｚｎ系めっき鋼板は伸び特性に優れているため加工が容易であるものの、５５％Ａｌ−Ｚｎ系めっき鋼板に較べて耐食性に劣っており、このため最近では５５％Ａｌ−Ｚｎ系めっき鋼板への置き替えが行われようになりつつある。
【０００７】
上述したように５５％Ａｌ−Ｚｎ系めっき鋼板は伸び特性値が小さいために、同程度の加工を行った場合でも同一めっき皮膜厚の５％Ａｌ−Ｚｎ系めっき鋼板に較べて加工性に劣る傾向がある。そのため折り曲げ等の加工を行うと、加工の程度によっては被加工部のめっき鋼板部分に亀裂が生じ、使用上大きな問題となる場合がある。
このような問題に対して、例えば特公昭６１−２８７４８号では５５％Ａｌ−Ｚｎ系めっき鋼板に所定の熱処理を施すことによってその延性を改善する方法が示されている。しかしながら、本発明者らが実験などにより確認したところによれば、このような熱処理をバッチ処理によりめっき鋼板コイルに対して実施した場合、熱処理中にコイル内の鋼板間に焼付き（密着）が発生し、この結果、製品であるめっき鋼板の美麗な表面外観が著しく損なわれるという問題を生じることが判った。
【０００８】
また、特公昭５３−９１７６号には合金化溶融亜鉛めっき鋼板をバッチ焼鈍によって４００〜４８０℃に加熱する際に、加熱雰囲気を微酸化性にして鋼板間での焼付けを防止する方法が示されているが、５５％Ａｌ−Ｚｎ系めっき鋼板のバッチ加熱を上記温度範囲で実施すると鋼板間での焼付けの発生は避けられない。したがって本発明の目的は、５５％Ａｌ−Ｚｎ系めっき鋼板に代表される、めっき皮膜中のＡｌ含有量が２０〜９５ｍａｓｓ％である溶融Ａｌ−Ｚｎ系めっき鋼板であって、伸び特性が優れしかも美麗なめっき表面外観を有するめっき鋼板を安定して製造することができる溶融Ａｌ−Ｚｎ系めっき鋼板の製造方法を提供することにある。
【０００９】
【課題を解決するための手段】
上記課題の解決のために、本発明者らは実用製品としての優れためっき表面外観を確保するという観点から、５５％Ａｌ−Ｚｎ系めっき鋼板の伸び特性を向上させ、且つ美麗なめっき表面外観を得るための最適な製造方法について鋭意検討を行った。その結果、５５％Ａｌ−Ｚｎ系めっき鋼板を連続溶融めっきラインで製造する際に、めっき表面粗さＲａが０．２０μｍ以上のめっき皮膜を形成させるとともに、コイル巻取り時の巻取り張力を３．０ｋｇ／ｍｍ２以下にし、次いで、タイトコイルバッチ加熱によりコイル最高温度部の到達板温が３００℃未満となるような条件で加熱処理することにより、加熱処理による伸び特性の適切な改善が図られるとともに、コイル内のめっき鋼板間の焼付けが適切に防止され、伸び特性に優れ且つ美麗なめっき表面外観を有する５５％Ａｌ−Ｚｎ系めっき鋼板を製造できることが判った。
【００１０】
すなわち、本発明の溶融Ａｌ−Ｚｎ系めっき鋼板の製造方法は以下のような特徴を有する。
【００１１】
［１］ めっき皮膜中のＡｌ含有量が２０〜９５ｍａｓｓ％である溶融Ａｌ−Ｚｎ系めっき鋼板の製造方法であって、めっき金属が凝固した後の溶融Ａｌ−Ｚｎ系めっき鋼板を加熱処理することにより伸び特性の改善を図る方法において、
めっき表面粗さＲａが０．２０μｍ以上のめっき皮膜が形成された溶融Ａｌ−Ｚｎ系めっき鋼板をコイル巻取り張力３．０ｋｇ／ｍｍ２以下で巻き取った後、タイトコイルバッチ加熱によりコイル最高温度部の到達板温が３００℃未満となるような条件で加熱処理することを特徴とする溶融Ａｌ−Ｚｎ系めっき鋼板の製造方法。
【００１２】
[2] 上記 [1] の製造方法において、コイルをタイトコイルバッチ加熱又はオープンコイルバッチ加熱により加熱処理する際の加熱雰囲気中の酸素濃度が２０体積％以上であることを特徴とする溶融Ａｌ−Ｚｎ系めっき鋼板の製造方法。
【００１３】
【発明の実施の形態】
本発明が製造の対象とするめっき鋼板は、めっき皮膜中にＡｌを２０〜９５ｍａｓｓ％含有する溶融Ａｌ−Ｚｎ系めっき鋼板であり、また、めっき皮膜のより好ましい成分組成は、Ａｌ：４５〜６５ｍａｓｓ％、Ｓｉ：０．７〜２．０ｍａｓｓ％、Ｆｅ：１０ｍａｓｓ％未満、残部が不可避的不純物を含む実質的なＺｎであり、このような組成の場合に特に優れた耐食性を発揮する。
また、溶融Ａｌ−Ｚｎ系めっき鋼板のめっき付着量は特に限定されないが、一般に片面当たり３０〜１２０ｇ／ｍ２程度が適当である。
【００１４】
本発明法では、連続溶融めっきラインにおいて鋼板面にめっき表面粗さＲａが０．２０μｍ以上の溶融Ａｌ−Ｚｎ系めっき皮膜を形成するとともに、この溶融Ａｌ−Ｚｎ系めっき鋼板をコイル巻取り張力３．０ｋｇ／ｍｍ２以下で巻き取り、次いで、タイトコイルバッチ加熱によりコイル最高温度部の到達板温が３００℃未満となるような条件で加熱処理する。
【００１５】
ここで、溶融Ａｌ−Ｚｎ系めっき鋼板のめっき表面粗さＲａを０．２０μｍ以上とするのは、めっき表面粗さＲａが０．２０μｍ未満ではめっき鋼板をコイルに巻き取った際にめっき鋼板どうしの接触面積が大きくなり、タイトコイルバッチ加熱の際にめっき鋼板間に焼付きが発生し、製品としての使用に耐え得るめっき表面外観が得られなくなるためである。但し、めっき表面粗さＲａの値があまり大きいとめっき表面の凹凸感が大きくなり、めっき表面外観が劣化する傾向がある。このためめっき表面粗さＲａは２．０μｍ以下とすることが好ましい。
【００１６】
めっき表面粗さＲａを支配する要因としては、鋼板のめっき浴中への侵入板温、めっき浴温度、めっき浴組成などの他に、スパングルを形成させるめっき鋼板にあってはめっき後の冷却速度などが、スパングル模様を目立たなくさせるめっき鋼板にあってはめっき後の調質圧延の条件などが挙げられ、したがって、これらを適宜調整することによりめっき表面粗さＲａが０．２０μｍ以上のめっき皮膜を得ることができる。
【００１７】
また、連続溶融めっきラインにおいてめっき鋼板をコイルに巻取る際に、コイル巻取り張力を３．０ｋｇ／ｍｍ２以下とするのは、巻取り張力が３．０ｋｇ／ｍｍ２を超えるとコイル内でのめっき鋼板間の接触力が大きくなり、タイトコイルバッチ加熱時にめっき鋼板間に焼付きが発生し、製品としての使用に耐え得るめっき表面外観が得られなくなるためである。但し、コイル巻取り張力があまり低いとコイル状態に保持する力が弱まり、コイルの変形若しくは潰れが発生しやすい。このためコイル巻取り張力は０．３ｋｇ／ｍｍ２以上とすることが好ましい。
【００１８】
連続溶融めっきラインから取り出されためっき鋼板のコイルは、タイトコイルバッチ加熱によりコイル最高温度部の到達板温が３００℃未満、好ましくは２００℃以下となるような条件で加熱処理される。この加熱処理において、コイル最高温度部の到達板温が３００℃以上であるとめっき表面の粘性低下が発生してめっき鋼板間に焼付きが発生し、製品としての使用に耐え得るめっき表面外観が得られない。また、加熱温度の下限については、コイル最低温度部の到達板温が１００℃以上、好ましくは１５０℃以上となるようにすることが適当である。コイル最低温度部の到達板温が１００℃未満では加熱による伸び特性の改善効果が十分に得られない。
【００１９】
また、加熱保持時間は５分以上、２４時間以下とすることが適当である。加熱保持時間が５分未満では十分な伸び特性改善効果が得られず、一方、２４時間を超えるとめっき鋼板間の焼付きが発生しやすくなる。
図１に、本発明で行うタイトコイルバッチ加熱の代表的な昇温・保持・冷却温度パターンを示す。
【００２０】
また、タイトコイルバッチ加熱を行う際の加熱雰囲気は、空気、Ｎ２，Ｈ２又はＮ２−Ｈ２などの各雰囲気とすることができる。但し、雰囲気が酸素を含んでいると、加熱中にめっき皮膜表層に薄い酸化膜が形成され、この酸化膜が鋼板間の焼付けの防止に有利に作用する。このような観点から加熱処理の雰囲気は酸素を２０体積％以上含むことが好ましい。
【００２３】
本発明法により製造されるめっき鋼板は、めっき表面にスパングルを形成してもよいし、またスパングル模様を目立たなくさせるようにしてもよい。一般に、めっき表面にスパングルを有するめっき鋼板はその外観性から裸使用する用途に、また、めっき表面のスパングル模様を目立たなくさせためっき鋼板は塗装下地用途に、それぞれ適している。
めっき表面のスパングル模様を目立たなくさせるには、常法に従ってめっき後に調質圧延などを実施すればよい。
【００２４】
【実施例】
常法で製造した冷延鋼板（板厚０．５ｍｍ）を連続式溶融めっき設備に通板し、５５mass％Ａｌ−１．５mass％Ｓｉ−Ｚｎめっき浴を用いて溶融めっきを行って溶融Ａｌ−Ｚｎ系めっき鋼板を製造し、これをコイルに巻き取った。溶融めっきラインのラインスピードは１６０ｍ／ｓｅｃとし、片面めっき付着量はめっき鋼板間でのバラツキが７５〜９０ｇ／ｍ２の範囲内に収まるようにした。次いで、めっき鋼板コイルをタイトコイルバッチ加熱により種々の条件で加熱処理し、溶融Ａｌ−Ｚｎ系めっき鋼板の製品とした。
【００２５】
得られた製品について、下記の方法に基づいて焼付け発生の有無、めっき表面外観及び伸び特性を評価した。その結果を、溶融めっき条件、タイトコイルバッチ加熱条件、めっき皮膜の構成とともに表１及び表２に示す。
なお、表１に示す各実施例（本発明例及び比較例）では、タイトコイルバッチ加熱前に調質圧延を実施することによりめっき表面のスパングル模様を目立たなくさせためっき鋼板を、また表２に示す各実施例（本発明例及び比較例）ではめっき表面にスパングルを有するめっき鋼板を、それぞれ製造した。
【００２６】
（１） 焼付けの発生の有無
加熱処理後のコイル巻き戻し時において、めっき鋼板どうしが剥がれる際に発生する音の有無により、下記の通り焼付け発生の有無を評価した。
無し：コイル巻き戻し時にバリバリという音が発生しない。
発生：コイル巻き戻し時にバリバリという音が発生する。
【００２７】
（２） めっき表面外観
加熱処理後のめっき鋼板の表面外観を目視観察し、下記の通りに評価した。
良い：めっき表面は加熱処理前と変化がなく、美麗なめっき表面外観を有する。
悪い：コイル総面積の１％以上の部分に、めっき鋼板間の焼付けによるめっき剥離又は溶着が発生し、劣悪なめっき表面外観を有する。
【００２８】
（３） 伸び特性
ＪＩＳ Ｚ ２２０１（１９９８）金属材料引張試験片に規定されている５号試験片を用いて、ＪＩＳ Ｚ ２２４１（１９９８）金属材料引張試験方法により試験を行い、破断時全伸びにより評価した。具体的な評価方法としては、加熱処理を行う前のめっき鋼板の破断時全伸びに対する破断時全伸びの増加量（％）で評価を行った。
【００２９】
【表１】
【表２】
【発明の効果】
以上述べたように本発明法によれば、５５％Ａｌ−Ｚｎ系めっき鋼板に代表される、めっき皮膜中のＡｌ含有量が２０〜９５ｍａｓｓ％である溶融Ａｌ−Ｚｎ系めっき鋼板であって、伸び特性が優れしかも美麗なめっき表面外観を有するめっき鋼板を安定して製造することができる。
【図面の簡単な説明】
【図１】本発明で行うタイトコイルバッチ加熱の代表的な昇温・保持・冷却温度パターンを示す説明図[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a hot-dip Al-Zn-based plated steel sheet having an Al content in a plating film of 20 to 95 mass%.
[0002]
[Prior art]
A hot-dip Al-Zn coated steel sheet containing 20 to 95 mass% of Al in a plating film typified by a 55% Al-Zn coated steel sheet (hereinafter, a "55% Al-Zn coated steel sheet" will be described as an example. ) Shows superior corrosion resistance as compared to hot-dip galvanized steel sheet as shown in JP-B-46-7161, and in recent years the demand has been increasing mainly in the field of building materials.
The 55% Al-Zn-based plated steel sheet is a pickled and descaled hot-rolled steel sheet or a cold-rolled steel sheet obtained by further cold-rolling the hot-rolled steel sheet as a base steel sheet. Manufactured.
[0003]
In the continuous hot-dip plating equipment, the base steel sheet was heated to a predetermined temperature in an annealing furnace maintained in a reducing atmosphere, and simultaneously with annealing, removal of rolling oil and the like adhering to the steel sheet surface and reduction of the oxide film were performed. Thereafter, the lower end is immersed in a hot-dip galvanizing bath containing a predetermined concentration of Al through a snout immersed in the plating bath. After the steel sheet immersed in the plating bath is lifted above the plating bath via the sink roll, by injecting pressurized gas toward the surface of the steel plate from the gas wiping nozzle arranged on the plating bath The coating weight is adjusted, and then cooled by a cooling device to obtain a 55% Al-Zn-based plated steel sheet on which a predetermined plating film is formed.
[0004]
The operating conditions such as the heat treatment conditions and atmosphere conditions of the annealing furnace in the continuous hot-dip plating equipment, the plating bath composition and the cooling rate after plating are precisely controlled within a predetermined control range in order to ensure the desired plating quality and material. You.
The plating film of the 55% Al—Zn-based plated steel sheet manufactured as described above mainly includes a portion in which Al containing Zn in a supersaturated state is dendrite solidified and a portion of the remaining dendrite gap, and the dendrite is plated. Laminated in the thickness direction of the film. With such a characteristic coating structure, the 55% Al-Zn plated steel sheet exhibits excellent corrosion resistance.
[0005]
Usually, about 1.5 mass% of Si is added to the plating bath. By the action of the Si, the 55% Al-Zn-based plated steel sheet suppresses the alloy phase growth at the interface between the plating film and the base steel sheet. The alloy phase thickness is about 1-2 μm. The thinner the alloy phase, the greater the number of characteristic film structures exhibiting excellent corrosion resistance. Therefore, suppressing the growth of the alloy phase contributes to the improvement of the corrosion resistance.
Usually, the plating bath contains unavoidable impurities, Fe eluted from a steel plate or equipment in the plating bath, and Si for suppressing an alloy phase, but other elements may be added with some elements, These elements are present in the alloy phase or the plating film in the form of an alloy or a simple substance.
[0006]
[Problems to be solved by the invention]
As described above, a 55% Al-Zn-based plated steel sheet has excellent corrosion resistance, but has mechanical properties, particularly elongation properties, of other plated steel sheets, for example, a molten Al-Zn-based steel sheet containing about 5 mass% of Al in a plating film. It tends to be inferior to a plated steel sheet (hereinafter, referred to as a “5% Al—Zn-based plated steel sheet”), and thus has a difficulty in being used in applications where severe processing is performed. On the other hand, although the 5% Al-Zn coated steel sheet has excellent elongation properties and is easy to process, it is inferior in corrosion resistance as compared with the 55% Al-Zn coated steel sheet. Replacement with Zn-based plated steel sheets is beginning to be performed.
[0007]
As described above, the 55% Al-Zn coated steel sheet has a small elongation characteristic value, so that even when the same processing is performed, the workability is inferior to that of the 5% Al-Zn coated steel sheet having the same plating film thickness. Tend. Therefore, when processing such as bending is performed, cracks may occur in the plated steel plate portion of the processed portion depending on the degree of processing, which may cause a serious problem in use.
To cope with such a problem, for example, Japanese Patent Publication No. 61-28748 discloses a method of improving the ductility by subjecting a 55% Al-Zn-based plated steel sheet to a predetermined heat treatment. However, the present inventors have confirmed through experiments and the like that when such a heat treatment is performed on a plated steel sheet coil by batch processing, seizure (adhesion) occurs between the steel sheets in the coil during the heat treatment. It has been found that this causes a problem that the beautiful surface appearance of the plated steel sheet as a product is significantly impaired.
[0008]
In addition, Japanese Patent Publication No. 53-9176 discloses a method in which when a galvannealed steel sheet is heated to 400 to 480 ° C. by batch annealing, the heating atmosphere is slightly oxidized to prevent seizure between the steel sheets. However, if batch heating of a 55% Al—Zn-based plated steel sheet is performed in the above temperature range, occurrence of seizure between the steel sheets cannot be avoided. Therefore, an object of the present invention is a hot-dip Al-Zn coated steel sheet having an Al content in a plating film of 20 to 95 mass%, represented by a 55% Al-Zn coated steel sheet, and having excellent elongation characteristics. It is an object of the present invention to provide a method for manufacturing a hot-dip Al-Zn-based coated steel sheet that can stably manufacture a coated steel sheet having a beautiful plated surface appearance.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have improved the elongation characteristics of a 55% Al—Zn-based plated steel sheet and have a beautiful plated surface appearance from the viewpoint of securing an excellent plated surface appearance as a practical product. Intensive study was carried out on the most suitable manufacturing method for obtaining the product. As a result, when a 55% Al—Zn-based plated steel sheet is manufactured by a continuous hot-dip plating line, a plating film having a plating surface roughness Ra of 0.20 μm or more is formed, and the winding tension at the time of coil winding is reduced to 3%. 0.0kg / mm 2 or less, and then heat treatment under conditions such that the ultimate plate temperature at the highest temperature portion of the coil is less than 300 ° C. by tight coil batch heating. It was also found that baking between plated steel sheets in the coil was appropriately prevented, and a 55% Al-Zn-based plated steel sheet having excellent elongation characteristics and a beautiful plated surface appearance could be produced.
[0010]
That is, the method for producing a hot-dip Al-Zn plated steel sheet of the present invention has the following features.
[0011]
[1] A method for producing a hot-dip Al-Zn-based coated steel sheet having an Al content of 20 to 95 mass% in a plating film, wherein the hot-dip processing of the hot-dip Al-Zn-based coated steel sheet after the plating metal has solidified. In the method of improving the elongation characteristics by
After winding a molten Al—Zn-based plated steel sheet having a plating film having a plating surface roughness Ra of 0.20 μm or more at a coil winding tension of 3.0 kg / mm 2 or less, the maximum coil temperature is obtained by heating a tight coil batch. A method for producing a hot-dip Al-Zn-based plated steel sheet, comprising performing a heat treatment under conditions such that the ultimate sheet temperature of the part is less than 300 ° C.
[0012]
In the production method [2] above [1], melting the oxygen concentration in the heating atmosphere in the heat treatment of the coil by tight coil batch heating or open coil batch heating is characterized in that 20% by volume or more Al- A method for producing a Zn-based plated steel sheet.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
The plated steel sheet to be manufactured by the present invention is a hot-dip Al-Zn-based plated steel sheet containing 20 to 95 mass% of Al in a plating film, and a more preferable component composition of the plating film is Al: 45 to 65 mass. %, Si: 0.7 to 2.0 mass%, Fe: less than 10 mass%, and the balance is substantially Zn containing unavoidable impurities. In such a composition, particularly excellent corrosion resistance is exhibited.
The coating weight of the hot-dip Al-Zn-based plated steel sheet is not particularly limited, but generally about 30 to 120 g / m 2 per one side is appropriate.
[0014]
According to the method of the present invention , a hot-dip Al-Zn-based plating film having a plating surface roughness Ra of 0.20 µm or more is formed on a steel sheet surface in a continuous hot-dip coating line, and the hot-dip Al-Zn-based steel sheet is coiled with a tension of 3 After winding at a pressure of 0.0 kg / mm 2 or less, heat treatment is performed by tight coil batch heating under conditions such that the ultimate plate temperature at the highest temperature portion of the coil is less than 300 ° C.
[0015]
Here, the reason why the plating surface roughness Ra of the hot-dip Al—Zn-based plated steel sheet is 0.20 μm or more is that when the plating surface roughness Ra is less than 0.20 μm, the plated steel sheets are wound together when coiled. This is because the contact area becomes large and seizure occurs between the plated steel sheets during tight coil batch heating, and a plated surface appearance that can withstand use as a product cannot be obtained. However, if the value of the plating surface roughness Ra is too large, the unevenness of the plating surface becomes large and the plating surface appearance tends to deteriorate. Therefore, the plating surface roughness Ra is preferably set to 2.0 μm or less.
[0016]
Factors that control the plating surface roughness Ra include the penetration temperature of the steel sheet into the plating bath, the temperature of the plating bath, the composition of the plating bath, and the cooling rate after plating for plated steel sheets that form spangles. However, in the case of a plated steel sheet that makes a spangle pattern inconspicuous, conditions of temper rolling after plating are given, and accordingly, a plating film having a plating surface roughness Ra of 0.20 μm or more can be obtained by appropriately adjusting these conditions. Can be obtained.
[0017]
Further, when the plated steel sheet is wound on the coil in the continuous hot-dip plating line, the coil winding tension is set to 3.0 kg / mm 2 or less because the winding tension exceeds 3.0 kg / mm 2 in the coil. This is because the contact force between the plated steel sheets becomes large, seizure occurs between the plated steel sheets during heating of the tight coil batch, and a plated surface appearance that can withstand use as a product cannot be obtained. However, if the coil winding tension is too low, the force for holding the coil in a weak state weakens, and the coil is likely to be deformed or crushed. For this reason, the coil winding tension is preferably set to 0.3 kg / mm 2 or more.
[0018]
The coil of the plated steel sheet taken out of the continuous hot-dip galvanizing line is subjected to heat treatment by tight coil batch heating under conditions such that the ultimate sheet temperature at the coil maximum temperature portion is less than 300 ° C, preferably 200 ° C or less. In this heat treatment, if the ultimate plate temperature of the coil maximum temperature portion is 300 ° C. or higher, the viscosity of the plated surface decreases, seizure occurs between the plated steel plates, and the plated surface appearance that can withstand use as a product is obtained. I can't get it. It is appropriate that the lower limit of the heating temperature is set so that the ultimate plate temperature at the lowest temperature portion of the coil is 100 ° C. or higher, preferably 150 ° C. or higher. If the ultimate plate temperature at the lowest temperature portion of the coil is less than 100 ° C., the effect of improving the elongation characteristics by heating cannot be sufficiently obtained.
[0019]
It is appropriate that the heating and holding time is 5 minutes or more and 24 hours or less. If the heating holding time is less than 5 minutes, a sufficient elongation property improving effect cannot be obtained, while if it exceeds 24 hours, seizure between the plated steel sheets tends to occur.
FIG. 1 shows a typical temperature rise / hold / cooling temperature pattern of tight coil batch heating performed in the present invention.
[0020]
The heating atmosphere for performing the tight coil batch heating may be any atmosphere such as air, N 2 , H 2, or N 2 -H 2 . However, if the atmosphere contains oxygen, a thin oxide film is formed on the surface of the plating film during heating, and this oxide film works advantageously to prevent burning between steel sheets. From such a viewpoint, it is preferable that the atmosphere of the heat treatment contain 20% by volume or more of oxygen.
[0023]
In the plated steel sheet manufactured by the method of the present invention, spangles may be formed on the plating surface, or the spangle pattern may be made inconspicuous. In general, a plated steel sheet having a spangle on the plating surface is suitable for use in which the spangle is unobtrusive because of its appearance, and a plated steel sheet in which the spangle pattern on the plating surface is inconspicuous is suitable for use as a coating base.
In order to make the spangle pattern on the plating surface inconspicuous, temper rolling or the like may be performed after plating according to a conventional method.
[0024]
【Example】
A cold-rolled steel sheet (sheet thickness 0.5 mm) manufactured by a usual method is passed through a continuous hot-dip plating equipment, and hot-dip plating is performed by using a 55 mass% Al-1.5 mass% Si-Zn plating bath. A Zn-based plated steel sheet was manufactured and wound on a coil. The line speed of the hot-dip plating line was set to 160 m / sec, and the single-sided plating adhesion amount was set so that the variation between the plated steel sheets was within the range of 75 to 90 g / m 2 . Next, the plated steel sheet coil was subjected to heat treatment under various conditions by tight coil batch heating to obtain a product of a molten Al-Zn-based plated steel sheet.
[0025]
The obtained product was evaluated for the occurrence of baking, the plating surface appearance, and the elongation characteristics based on the following methods. The results are shown in Tables 1 and 2, together with the hot-dip plating conditions, tight coil batch heating conditions, and the configuration of the plating film.
In addition, in each Example (Example of the present invention and Comparative Example) shown in Table 1, a tempered rolling was performed before heating the tight coil batch to obtain a plated steel sheet in which the spangle pattern on the plating surface was made inconspicuous. In each of Examples (Examples of the present invention and Comparative Examples), plated steel sheets each having a spangle on the plating surface were manufactured.
[0026]
(1) Presence or absence of seizure The presence or absence of seizure was evaluated as follows based on the presence or absence of sound generated when the plated steel sheets peeled off during coil rewinding after the heat treatment.
None: No crunching sound is generated when the coil is rewound.
Occurrence: A crunch sound is generated when the coil is rewound.
[0027]
(2) Plating Surface Appearance The surface appearance of the plated steel sheet after the heat treatment was visually observed and evaluated as follows.
Good: The plating surface has no change from that before the heat treatment and has a beautiful plating surface appearance.
Poor: Plating exfoliation or welding occurs due to baking between plated steel sheets in a portion of 1% or more of the total coil area, resulting in poor plated surface appearance.
[0028]
(3) Elongation characteristics Using a No. 5 test piece specified in JIS Z 2201 (1998) metal material tensile test piece, a test was performed according to JIS Z 2241 (1998) metal material tensile test method, and the total elongation at break was measured. evaluated. As a specific evaluation method, evaluation was performed based on the increase (%) of the total elongation at break relative to the total elongation at break of the plated steel sheet before performing the heat treatment.
[0029]
[Table 1]
[Table 2]
【The invention's effect】
As described above, according to the method of the present invention, there is provided a hot-dip Al-Zn-based coated steel sheet represented by a 55% Al-Zn-based coated steel sheet, the Al content of which is 20 to 95 mass% in a plating film, A plated steel sheet having excellent elongation properties and a beautiful plated surface appearance can be stably manufactured.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a typical heating / holding / cooling temperature pattern of tight coil batch heating performed in the present invention.
Claims (2)
めっき表面粗さＲａが０．２０μｍ以上のめっき皮膜が形成された溶融Ａｌ−Ｚｎ系めっき鋼板をコイル巻取り張力３．０ｋｇ／ｍｍ２以下で巻き取った後、タイトコイルバッチ加熱によりコイル最高温度部の到達板温が３００℃未満となるような条件で加熱処理することを特徴とする溶融Ａｌ−Ｚｎ系めっき鋼板の製造方法。A method for producing a hot-dip Al-Zn coated steel sheet having an Al content of 20 to 95 mass% in a plating film, wherein the hot-dip hot-dip Al-Zn-based coated steel sheet after the solidification of the plated metal has an elongation property. How to improve
After winding a molten Al—Zn-based plated steel sheet having a plating film having a plating surface roughness Ra of 0.20 μm or more at a coil winding tension of 3.0 kg / mm 2 or less, the maximum coil temperature is obtained by heating a tight coil batch. A method for producing a hot-dip Al-Zn-based plated steel sheet, comprising performing a heat treatment under conditions such that the ultimate sheet temperature of the part is less than 300 ° C.
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| JP2000389988A JP3581862B2 (en) | 2000-12-22 | 2000-12-22 | Method for producing hot-dip Al-Zn-based plated steel sheet |
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| JP2000389988A JP3581862B2 (en) | 2000-12-22 | 2000-12-22 | Method for producing hot-dip Al-Zn-based plated steel sheet |
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| JP3581862B2 true JP3581862B2 (en) | 2004-10-27 |
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| JP4932376B2 (en) * | 2006-08-02 | 2012-05-16 | 新日本製鐵株式会社 | High-strength hot-dip galvanized steel sheet with excellent plating properties and method for producing the same |
| JP5686438B2 (en) * | 2011-06-22 | 2015-03-18 | 株式会社淀川製鋼所 | Al-Zn alloy plated steel sheet and method and apparatus for manufacturing the same |
| WO2020111879A1 (en) | 2018-11-30 | 2020-06-04 | 주식회사 포스코 | Steel sheet plated with al-fe alloy for hot press forming having excellent corrosion resistance and heat resistance, hot press formed part, and manufacturing method therefor |
| KR102227111B1 (en) | 2018-11-30 | 2021-03-12 | 주식회사 포스코 | Hot press formed part, and manufacturing method thereof |
| KR102180811B1 (en) * | 2018-12-03 | 2020-11-20 | 주식회사 포스코 | A hot press formed part having excellent resistance against hydrogen embrittlement, and manufacturing method thereof |
| JP6704669B1 (en) * | 2019-08-29 | 2020-06-03 | Ｊｆｅ鋼板株式会社 | Hot-dip Al-Zn alloy plated steel sheet having excellent corrosion resistance in worked part and method for producing the same |
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