JP2015214749A - MOLTEN Al-Zn-BASED PLATED SHEET STEEL, AND PRODUCTION METHOD THEREOF - Google Patents
MOLTEN Al-Zn-BASED PLATED SHEET STEEL, AND PRODUCTION METHOD THEREOF Download PDFInfo
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- 229910018137 Al-Zn Inorganic materials 0.000 claims abstract description 81
- 229910018573 Al—Zn Inorganic materials 0.000 claims abstract description 81
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Abstract
Description
本発明は、塗装後耐食性に優れた溶融Ａｌ−Ｚｎ系めっき鋼板、及びその製造方法に関するものである。 The present invention relates to a molten Al—Zn plated steel sheet having excellent post-coating corrosion resistance and a method for producing the same.
溶融Ａｌ−Ｚｎ系めっき鋼板、例えば亜鉛系めっき層中にＡｌを質量％で２５〜９０％含有する溶融Ａｌ−Ｚｎ系めっき鋼板は、溶融亜鉛めっき鋼板に比べて優れた耐食性を示す。
一般的に、この溶融Ａｌ−Ｚｎ系めっき鋼板は、スラブを熱間圧延若しくは冷間圧延した薄鋼板を下地鋼板として用い、該下地鋼板を連続式溶融めっきラインの焼鈍炉にて再結晶焼鈍及び溶融めっき処理を行うことによって製造される。この形成されたＡｌ−Ｚｎ系めっき層は、下地鋼板との界面に存在する合金相と、その上に存在する上層とを備える。
さらに、上層は、主として、Ａｌがデンドライト凝固し、Ｚｎを過飽和に含有したデンドライト凝固部分（α−Ａｌ相）と、残りのデンドライト間隙の部分（Ｚｎリッチ相）からなる。このデンドライト凝固部分はめっき層の膜厚方向に積層している。この上層の特徴的な皮膜構造により、表面からの腐食進行経路が複雑になり腐食が容易に下地鋼板に到達しにくくなる。これにより、溶融Ａｌ−Ｚｎ系めっき鋼板は、めっき層の厚みが同一の溶融亜鉛めっき鋼板に比べ優れた耐食性を有する。
A molten Al—Zn-based plated steel sheet, for example, a molten Al—Zn-based plated steel sheet containing 25 to 90% by mass of Al in a zinc-based plated layer exhibits excellent corrosion resistance as compared with a hot-dip galvanized steel sheet.
Generally, this molten Al-Zn-based plated steel sheet uses a thin steel sheet obtained by hot rolling or cold rolling a slab as a base steel sheet, and the base steel sheet is recrystallized and annealed in an annealing furnace of a continuous hot-dip plating line. It is manufactured by performing a hot dipping process. The formed Al—Zn-based plating layer includes an alloy phase present at the interface with the base steel plate and an upper layer present thereon.
Furthermore, the upper layer is mainly composed of a dendrite solidified portion (α-Al phase) in which Al is dendrite solidified and contains Zn in a supersaturated state, and a remaining dendrite gap portion (Zn rich phase). This dendrite solidified portion is laminated in the film thickness direction of the plating layer. This characteristic film structure of the upper layer complicates the corrosion progress path from the surface and makes it difficult for the corrosion to easily reach the base steel plate. Thereby, the hot-dip Al-Zn-based plated steel sheet has excellent corrosion resistance as compared with a hot-dip galvanized steel sheet having the same plating layer thickness.
なお、めっき浴には、不可避的不純物や、鋼板やめっき浴中の機器等から溶出するＦｅを含有し、その他、過度の合金相成長を抑制するためのＳｉが添加されることが通常である。めっき浴において、Ｓｉは合金相に金属間化合物の形、あるいは上層に金属間化合物、固溶体若しくは単体の形で存在している。そして、このＳｉの働きにより、溶融Ａｌ−Ｚｎ系めっき鋼板の界面の合金相成長が抑えられ、合金相厚さは約１〜５μｍ程度となっている。めっき層厚が同一ならば、合金相が薄いほど耐食性向上に効果のある上層が厚くなるので、合金相の成長を抑制することは耐食性の向上に寄与することになる。また、合金相は上層よりも固く、加工時にクラックの起点として作用することから、合金相の成長抑制はクラックの発生を減少させ、曲げ加工性を向上させる効果をもたらすことにもなる。そして、発生したクラック部は下地鋼板が露出しており耐食性に劣るので、合金相の成長を抑制し、クラックの発生を抑制することは曲げ加工部耐食性をも向上させることになる。 The plating bath contains inevitable impurities and Fe eluted from the steel plate and the equipment in the plating bath, etc. In addition, it is usual that Si for suppressing excessive alloy phase growth is added. . In the plating bath, Si is present in the alloy phase in the form of an intermetallic compound, or in the upper layer in the form of an intermetallic compound, a solid solution, or a simple substance. And, by the action of Si, the growth of the alloy phase at the interface of the molten Al—Zn-based plated steel sheet is suppressed, and the alloy phase thickness is about 1 to 5 μm. If the plating layer thickness is the same, the thinner the alloy phase, the thicker the upper layer that is effective in improving the corrosion resistance. Therefore, suppressing the growth of the alloy phase contributes to improving the corrosion resistance. In addition, since the alloy phase is harder than the upper layer and acts as a starting point of cracks during processing, the suppression of the growth of the alloy phase reduces the occurrence of cracks and also brings about the effect of improving bending workability. And since the base steel plate is exposed and the crack part which generate | occur | produced is inferior to corrosion resistance, suppressing the growth of an alloy phase and suppressing generation | occurrence | production of a crack will also improve bending part corrosion resistance.
このように耐食性に優れる溶融Ａｌ−Ｚｎ系めっき鋼板は、長期間屋外に曝される屋根や壁などの建材分野を中心に需要が伸び、近年は、自動車分野においても使用されるようになってきた。特に自動車分野においては、地球温暖化対策の一環で車体を軽量化して燃費を向上させＣＯ２排出量を削減することが求められている。このため、高強度鋼板の使用による軽量化と、鋼板の耐食性向上によるゲージダウンが強く望まれている。しかし、溶融Ａｌ−Ｚｎ系めっき鋼板を自動車分野、特に外板パネルに用いようとした場合に次の問題がある。 Thus, the demand for molten Al—Zn-based plated steel sheets having excellent corrosion resistance has been increased mainly in the field of building materials such as roofs and walls exposed to the outdoors for a long period of time, and in recent years, they have also been used in the automobile field. It was. Particularly in the automobile field, as a part of global warming countermeasures, it is required to reduce the body weight to improve fuel efficiency and reduce CO 2 emissions. For this reason, weight reduction by use of a high-strength steel plate and gauge down by the corrosion resistance improvement of a steel plate are strongly desired. However, there are the following problems when trying to use the molten Al—Zn-based plated steel sheet in the automobile field, particularly in the outer panel.
溶融Ａｌ−Ｚｎ系めっき鋼板を自動車外板パネルとして使用する場合、該めっき鋼板は連続式溶融めっき設備でめっきまで施した状態で自動車メーカー等に供され、そこでパネル部品形状に加工された後に化成処理、さらに電着塗装、中塗り塗装、上塗り塗装の自動車用総合塗装が施されることが一般的である。しかしながら、溶融Ａｌ−Ｚｎ系めっき鋼板を用いた外板パネルは、塗膜に損傷が生じた際、上述したα−Ａｌ相とＺｎリッチ相の二相から成る独特なめっき相構造に起因して、傷部を起点にＺｎの優先溶解（Ｚｎリッチ相の選択腐食）が塗膜／めっき界面で発生する。これが塗装健全部の奥深くに向けて進行して大きな塗膜膨れを起こす結果、十分な耐食性（塗装後耐食性）を確保できない場合があった。 When using a hot-dip Al-Zn-based plated steel sheet as an automobile outer panel, the plated steel sheet is supplied to an automobile manufacturer, etc. in a state where it has been subjected to plating with a continuous hot-dip plating facility, and after being processed into a panel part shape, it is then formed into a chemical. In general, a general coating for automobiles including electrodeposition coating, intermediate coating, and top coating is applied. However, the outer panel using the molten Al-Zn-based plated steel sheet is caused by the unique plated phase structure composed of the two phases of the α-Al phase and the Zn-rich phase when the coating film is damaged. The preferential dissolution of Zn (selective corrosion of the Zn-rich phase) occurs at the coating film / plating interface starting from the scratch. As a result of this proceeding deeper into the coating-sound part and causing a large swelling of the coating film, sufficient corrosion resistance (corrosion resistance after coating) may not be ensured.
一方、溶融Ａｌ−Ｚｎ系めっき鋼板を建屋の屋根材や壁材として建材分野で用いた場合もまた、塗装後耐食性が問題となっている。屋根材や壁材として使用される場合は、溶融めっき鋼板は一般的に下塗り塗装、上塗り塗装を施した状態で建築会社等に供され、必要なサイズに剪断してから使用される。このため、必然的に塗装がされていない鋼板端面が露出し、ここを起点にエッジクリープと呼ばれる塗膜膨れが発生することがある。溶融Ａｌ−Ｚｎ系めっき鋼板の場合、自動車外板パネルの場合と同様に、鋼板端面部を起点に塗膜／めっき界面におけるＺｎリッチ相の選択腐食が起こる結果、溶融Ｚｎめっきに比べて著しく大きなエッジクリープを生じて塗装後耐食性が劣ることがあった。 On the other hand, when a molten Al—Zn-based plated steel sheet is used in the building material field as a roofing material or a wall material of a building, corrosion resistance after painting is also a problem. When used as a roofing material or a wall material, a hot-dip plated steel sheet is generally provided to a construction company or the like in a state where a base coat or top coat is applied, and is used after being sheared to a required size. For this reason, the end surface of the steel plate which is not necessarily coated is exposed, and the swelling of the coating film called edge creep may occur from this point. In the case of a hot-dip Al-Zn-based plated steel sheet, as in the case of an automobile outer panel, as a result of selective corrosion of the Zn-rich phase at the coating film / plating interface starting from the end face of the steel sheet, it is significantly larger than hot-dip Zn plating. Edge creep may occur, resulting in poor corrosion resistance after painting.
上記問題を解決すべく、例えば特許文献１には、めっき組成にＭｇ、又はさらにＳｎ等を添加し、めっき層中にＭｇ２Ｓｉ、ＭｇＺｎ２、Ｍｇ２Ｓｎ等のＭｇ化合物を形成させることで、鋼板端面からの赤錆発生を改善した溶融Ａｌ−Ｚｎ系めっき鋼板が開示されている。
しかしながら、特許文献１に開示される溶融Ａｌ−Ｚｎ系めっき鋼板に塗装を施した場合、後に塗膜に損傷が生じたときの耐食性（塗装後耐食性）は、依然として解消されていなかった。
In order to solve the above problem, for example, in Patent Document 1, Mg or Sn is further added to the plating composition, and Mg compounds such as Mg 2 Si, MgZn 2 and Mg 2 Sn are formed in the plating layer. In addition, a molten Al-Zn-based plated steel sheet that has improved the occurrence of red rust from the end face of the steel sheet is disclosed.
However, when the molten Al-Zn-based plated steel sheet disclosed in Patent Document 1 is coated, the corrosion resistance (corrosion resistance after painting) when the coating film is damaged later has not been eliminated.
また、溶融Ａｌ−Ｚｎ系めっき鋼板は、建材や家電分野に塗装を施さず使用される場合もある。なかでも、壁材や家電製品の背面板等に使用される場合には、めっき鋼板の表面が人目に曝されることになるので、高い外観品位が求められる。外観品位とは、主に、異物付着や不めっき、傷等の欠陥有無の他に、模様や色調のムラのないことをいう。後者の模様や色調については、溶融Ａｌ−Ｚｎ系めっき鋼板が無塗装で使用される場合により強く求められる品位である。そのため、塗装鋼板として使用する溶融Ａｌ−Ｚｎ系めっき鋼板の全てが、無塗装で用いられる用途（壁材、家電製品の背面板等）に適用できるわけではなく、外観品位のさらなる向上についても望まれていた。
さらに、溶融Ａｌ−Ｚｎ系めっき鋼板の場合、めっきの成分組成によって、めっき後の表面が徐々に黒色に変化（黒変）することがあった。例えば、特許文献１に示されたＳｎを添加した溶融Ａｌ−Ｚｎ系めっき鋼板でも、黒変が発生する場合があり、無塗装で使用する用途に全ての溶融Ａｌ−Ｚｎ系めっき鋼板を適用することができないという問題があった。
また、連続式溶融めっきラインの溶融めっき処理において、めっき浴中の成分管理は連続操業性の点で重要であり、めっき浴のドロスの生成量が多くなると前記成分管理が難しくなるという問題があった。
Moreover, the fusion | melting Al-Zn type plated steel plate may be used without performing a coating in the building material and household appliance field | areas. Especially, when it is used for a wall material, a back plate of home appliances, and the like, the surface of the plated steel sheet is exposed to the human eye, so a high appearance quality is required. The appearance quality mainly means that there is no unevenness in the pattern and color tone in addition to the presence or absence of foreign matter adhesion, non-plating, scratches and the like. About the latter pattern and color tone, it is a quality demanded more strongly when the molten Al—Zn-based plated steel sheet is used without coating. For this reason, not all of the molten Al-Zn-based plated steel sheets used as coated steel sheets can be applied to applications that are used without coating (wall materials, back plates of household electrical appliances, etc.), and further improvement in appearance quality is also expected. It was rare.
Furthermore, in the case of a molten Al—Zn-based plated steel sheet, the surface after plating may gradually change to black (blackening) depending on the component composition of plating. For example, even a molten Al—Zn-based plated steel sheet added with Sn shown in Patent Document 1 may cause blackening, and all the molten Al—Zn-based plated steel sheets are applied to applications that are used without coating. There was a problem that I could not.
In addition, in the hot dip plating process of a continuous hot dip plating line, the management of components in the plating bath is important in terms of continuous operability, and there is a problem that the above component management becomes difficult as the amount of dross generated in the plating bath increases. It was.
本発明は、かかる事情に鑑みてなされたものであって、連続操業性の低下を招くことなく、優れた塗装後耐食性を有する溶融Ａｌ−Ｚｎ系めっき鋼板及びその製造方法を提供することを目的とする。 The present invention has been made in view of such circumstances, and an object thereof is to provide a molten Al-Zn-based plated steel sheet having excellent post-coating corrosion resistance without incurring a decrease in continuous operability and a method for producing the same. And
本発明者らは、上記の課題を解決すべく、鋭意研究を重ねた。その結果、めっき層中に、Ａｌに加えて、Ｂｉを特定量含有させ、さらに、Ｍｇ、Ｃａ及びＳｒからなる群より選択される一種以上を特定量含有させることにより、従来にない優れた塗装後耐食性が得られることを見出した。また、その際にめっき浴におけるドロスが増加することもなく、良好な操業性が得られた。
さらに、必要に応じて、めっき層のビッカース硬度を特定の範囲にすることで、めっき層を軟質化し、加工性を改善することにより加工部耐食性を向上できることを見出した。
The inventors of the present invention have made extensive studies to solve the above problems. As a result, in addition to Al, the plating layer contains a specific amount of Bi, and further contains a specific amount of one or more selected from the group consisting of Mg, Ca, and Sr. It has been found that post-corrosion resistance can be obtained. Further, at that time, dross in the plating bath did not increase, and good operability was obtained.
Furthermore, it was found that the corrosion resistance of the processed part can be improved by softening the plated layer and improving the workability by setting the Vickers hardness of the plated layer within a specific range as necessary.
本発明は、上記知見に基づきなされたものであり、その要旨は以下の通りである。
［１］質量％で、Ａｌ：２５〜９０％及びＢｉ：０．０１〜０．１％を含有し、さらに、Ｍｇ、Ｃａ及びＳｒからなる群より選択される一種以上を合計で０．０１〜１０％含有しためっき層を有することを特徴とする溶融Ａｌ−Ｚｎ系めっき鋼板。
The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] In mass%, Al: 25 to 90% and Bi: 0.01 to 0.1% are contained, and at least one selected from the group consisting of Mg, Ca and Sr is 0.01 in total A molten Al-Zn-based plated steel sheet having a plating layer containing 10% to 10%.
［２］前記めっき層が、質量％で、さらにＺｎ：１０〜７５％を含有することを特徴とする上記［１］に記載の溶融Ａｌ−Ｚｎ系めっき鋼板。 [2] The molten Al—Zn-based plated steel sheet according to the above [1], wherein the plated layer further contains Zn: 10 to 75% by mass%.
［３］前記めっき層が、質量％で、さらにＳｉ：０．１〜１０％を含有することを特徴とする上記［１］又は［２］に記載の溶融Ａｌ−Ｚｎ系めっき鋼板。 [3] The molten Al—Zn-based plated steel sheet according to the above [1] or [2], wherein the plating layer further contains Si: 0.1 to 10% by mass%.
［４］前記めっき層のＡｌ含有量が４５〜７０質量％であることを特徴とする上記［１］〜［３］のいずれかに記載の溶融Ａｌ−Ｚｎ系めっき鋼板。 [4] The Al-Zn-based plated steel sheet according to any one of [1] to [3], wherein the Al content of the plating layer is 45 to 70% by mass.
［５］前記めっき層のビッカース硬度が、平均で５０〜１００Ｈｖであることを特徴とする上記［１］〜［４］のいずれかに記載の溶融Ａｌ−Ｚｎ系めっき鋼板。 [5] The molten Al—Zn-based plated steel sheet according to any one of the above [1] to [4], wherein the plating layer has an average Vickers hardness of 50 to 100 Hv.
［６］連続式の溶融めっき設備において、質量％で、Ａｌ：２５〜９０％及びＢｉ：０．０１〜０．１％を含有し、さらにＭｇ、Ｃａ及びＳｒからなる群より選択される一種以上を合計で０．０１〜１０％を含有し、残部がＺｎ及び不可避的不純物からなるめっき浴中に、下地鋼板を浸漬させて溶融めっきを施すことを特徴とする溶融Ａｌ−Ｚｎ系めっき鋼板の製造方法。 [6] In a continuous hot dip plating facility, in mass%, Al: 25 to 90% and Bi: 0.01 to 0.1%, and further selected from the group consisting of Mg, Ca and Sr A hot-dip Al-Zn-based plated steel sheet, which comprises 0.01 to 10% in total and the remaining steel sheet is immersed in a plating bath consisting of Zn and inevitable impurities and is subjected to hot-dip plating. Manufacturing method.
［７］前記めっき浴が、質量％で、Ｚｎを１０〜７５％を含有することを特徴とする上記［６］に記載の溶融Ａｌ−Ｚｎ系めっき鋼板。 [7] The molten Al—Zn-based plated steel sheet according to [6], wherein the plating bath contains 10% to 75% by mass of Zn.
［８］前記めっき浴が、質量％でＳｉ：０．１〜１０％を含有することを特徴とする上記［６］又は［７］に記載の溶融Ａｌ−Ｚｎ系めっき鋼板。 [8] The molten Al—Zn-based plated steel sheet according to the above [6] or [7], wherein the plating bath contains Si: 0.1 to 10% by mass.
［９］前記溶融めっき後の鋼板を２５０〜３７５℃の温度で５〜６０秒間保持することを特徴とする上記［６］〜［８］のいずれかに記載の溶融Ａｌ−Ｚｎ系めっき鋼板。 [9] The hot-dip Al—Zn-based plated steel sheet according to any one of [6] to [8], wherein the hot-plated steel sheet is held at a temperature of 250 to 375 ° C. for 5 to 60 seconds.
［１０］前記溶融めっき後の鋼板を３００〜３７５℃で５〜６０秒間保持することを特徴とする上記［９］に記載の溶融Ａｌ−Ｚｎ系めっき鋼板。 [10] The hot-dip Al—Zn-plated steel sheet according to [9], wherein the hot-plated steel sheet is held at 300 to 375 ° C. for 5 to 60 seconds.
本発明によれば、連続操業性の低下を招くことなく、耐食性、特に塗装後耐食性に優れた溶融Ａｌ−Ｚｎ系めっき鋼板が得られる。そして、本発明の溶融Ａｌ−Ｚｎ系めっき鋼板を高強度鋼板とすることによって、自動車分野において、軽量化と優れた耐食性の両立が可能となる。また、建材分野で屋根材や壁材として使用することにより、建屋寿命の延命が可能となる。 ADVANTAGE OF THE INVENTION According to this invention, the molten Al-Zn type plated steel plate excellent in corrosion resistance, especially the corrosion resistance after a coating is obtained, without causing the fall of continuous operativity. And by making the molten Al-Zn-based plated steel sheet of the present invention a high-strength steel sheet, it is possible to achieve both weight reduction and excellent corrosion resistance in the automobile field. In addition, the life of the building can be extended by using it as a roofing material or wall material in the building material field.
以下、本発明について具体的に説明する。尚、以下の説明において、めっき層、及びめっき浴の組成を示す各元素の含有量の単位はいずれも「質量％」であり、以下、特に断らない限り単に「％」で示す。 Hereinafter, the present invention will be specifically described. In the following description, the unit of the content of each element indicating the composition of the plating layer and the plating bath is “mass%”, and hereinafter, it is simply indicated by “%” unless otherwise specified.
先ず始めに、本発明で最も重要である、溶融Ａｌ−Ｚｎ系めっき鋼板による塗装後耐食性の改善方法について説明する。
本発明の溶融Ａｌ−Ｚｎ系めっき鋼板は、めっき層中に、Ａｌに加えて、Ｂｉを０．０１〜０．１％含有し、さらに、Ｍｇ、Ｃａ、Ｓｒからなる群より選択される一種以上を合計で０．０１〜１０％含有する。めっき層中に、Ｂｉ、並びに、Ｍｇ、Ｃａ及びＳｒのうちの少なくとも一種の元素を特定量含有することで、本発明で課題とする塗装後耐食性の改善が可能となる。
First, a method for improving post-coating corrosion resistance using a molten Al—Zn-based plated steel sheet, which is most important in the present invention, will be described.
The molten Al—Zn-based plated steel sheet of the present invention contains 0.01 to 0.1% Bi in addition to Al in the plating layer, and is further selected from the group consisting of Mg, Ca, and Sr. The total content is 0.01 to 10%. By containing a specific amount of Bi and at least one element of Mg, Ca, and Sr in the plating layer, it is possible to improve the post-coating corrosion resistance, which is an object of the present invention.
Ｂｉを含まない従来の溶融Ａｌ−Ｚｎ系めっき鋼板のめっき層が大気に触れると、すぐにα−Ａｌ相の周囲に緻密、且つ安定なＡｌ２Ｏ３の酸化膜が形成される。この酸化膜による保護作用によってα−Ａｌ相の溶解性はＺｎリッチ相の溶解性に比べ非常に低くなる。この結果、従来のＡｌ−Ｚｎ系めっき鋼板を下地に用いた塗装鋼板は、塗膜に損傷が生じた場合、傷部を起点に塗膜／めっき界面でＺｎリッチ相の選択腐食を起こし、塗装健全部の奥深くに向けて進行して大きな塗膜膨れを起こすことから、塗装後耐食性が劣る。一方、Ｂｉを含有した溶融Ａｌ−Ｚｎ系めっき鋼板を下地に用いた塗装鋼板の場合、Ｂｉが、上述したα−Ａｌ相の周囲に形成するＡｌ酸化膜を破壊し、α−Ａｌ相の溶解性を上げ、α−Ａｌ相とＺｎリッチ相の両方が溶解するめっき層の均一腐食が起こる。このため、従来のＡｌ−Ｚｎ系めっき鋼板を下地に用いた塗装鋼板の場合に問題となるＺｎリッチ相の選択腐食を抑制できる。その結果、めっき層に特定量のＢｉを含有させた溶融Ａｌ−Ｚｎ系めっき鋼板は優れた塗装後耐食性を示す。
さらに、めっき層中にＭｇ、Ｃａ及びＳｒからなる群より選択される元素の中から一種以上を含有させることで、腐食により生成した腐食生成物中にこれらの元素が取り込まれ、腐食生成物が安定化される。この結果、鋼板の腐食を早期に抑えることができる。
以上のことから、本発明の溶融Ａｌ−Ｚｎ系めっき鋼板は、優れた塗装後耐食性を実現できる。
As soon as the plating layer of the conventional molten Al—Zn plated steel sheet not containing Bi is exposed to the atmosphere, a dense and stable Al 2 O 3 oxide film is formed around the α-Al phase. Due to the protective action of the oxide film, the solubility of the α-Al phase is very low compared to the solubility of the Zn-rich phase. As a result, when the coated steel sheet using the conventional Al-Zn-based plated steel sheet as a base is damaged in the coating film, it causes selective corrosion of the Zn-rich phase at the coating film / plating interface starting from the scratch. The corrosion resistance after painting is inferior because it progresses deeper into the healthy part and causes a large swelling of the coating film. On the other hand, in the case of a coated steel plate using a molten Al—Zn-based plated steel plate containing Bi as a base, Bi breaks the Al oxide film formed around the α-Al phase described above, and dissolves the α-Al phase. The plating layer in which both the α-Al phase and the Zn-rich phase are dissolved causes uniform corrosion. For this reason, the selective corrosion of the Zn rich phase which becomes a problem in the case of a coated steel sheet using a conventional Al—Zn-based plated steel sheet as a base can be suppressed. As a result, a molten Al—Zn-based plated steel sheet containing a specific amount of Bi in the plating layer exhibits excellent post-coating corrosion resistance.
Furthermore, by including one or more elements selected from the group consisting of Mg, Ca and Sr in the plating layer, these elements are taken into the corrosion products generated by the corrosion, and the corrosion products are Stabilized. As a result, corrosion of the steel sheet can be suppressed at an early stage.
From the above, the molten Al—Zn plated steel sheet of the present invention can realize excellent post-coating corrosion resistance.
次に、本発明の対象とする溶融Ａｌ−Ｚｎ系めっき鋼板のめっき層の組成について説明する。
前記めっき層中のＢｉ含有量を、０．０１〜０．１％としたのは次の理由からである。Ｂｉが０．０１％未満の場合は、上記に示したＺｎリッチ相の選択腐食を抑制可能とするＡｌ酸化膜の破壊が起こらないため、塗装後耐食性の向上は望めない。逆に、Ｂｉが０．１％超えの場合には、Ａｌ酸化膜の破壊が激しく起こり、めっき層全体の溶解性が過度に上昇する。この結果、めっき層を均一腐食させても、その溶解速度が大きくなるため、大きな膨れ幅を生じ、塗装後耐食性が劣化する。よって、優れた塗装後耐食性を安定的に得るためには、Ｂｉの含有量を０．０１〜０．１％の範囲とする必要があり、０．０１〜０．０５％の範囲とすることが好ましい。
また、前記めっき層中のＢｉ含有量は、１．０％以下、好ましくは０．５％以下で塗装を施さず使用する場合に表面外観が問題とならない。さらに、好ましくは０．１％以下、より好ましくは０．０５％以下とすることで、めっき表面の黒変することがなく、外観品位に特に優れる。そのため、塗装後耐食性と優れためっきの外観品位を両立する観点からは、めっき層中のＢｉ含有量を、０．０１〜０．１％とする必要があり、０．０１〜０．０５％とすることがより好ましい。
Next, the composition of the plating layer of the hot-dip Al—Zn plated steel sheet that is the subject of the present invention will be described.
The Bi content in the plating layer is set to 0.01 to 0.1% for the following reason. When Bi is less than 0.01%, the Al oxide film capable of suppressing the selective corrosion of the Zn-rich phase described above does not occur, so that improvement in corrosion resistance after coating cannot be expected. On the contrary, when Bi exceeds 0.1%, the Al oxide film is severely destroyed, and the solubility of the entire plating layer is excessively increased. As a result, even if the plating layer is uniformly corroded, the dissolution rate is increased, resulting in a large swollen width and deterioration of the corrosion resistance after coating. Therefore, in order to stably obtain excellent post-coating corrosion resistance, the Bi content needs to be in the range of 0.01 to 0.1%, and should be in the range of 0.01 to 0.05%. Is preferred.
Further, the Bi content in the plating layer is 1.0% or less, preferably 0.5% or less, and the surface appearance does not become a problem when used without coating. Furthermore, by making it 0.1% or less, more preferably 0.05% or less, the plating surface is not blackened, and the appearance quality is particularly excellent. Therefore, from the viewpoint of achieving both corrosion resistance after coating and excellent plating appearance quality, the Bi content in the plating layer needs to be 0.01 to 0.1%, and 0.01 to 0.05%. More preferably.
前記めっき層中のＭｇ、Ｃａ及びＳｒからなる群より選択される一種以上の合計含有量を０．０１〜１０％としたのは次の理由からである。Ｍｇ、Ｃａ及びＳｒからなる群より選択される一種以上の合計含有量が０．０１％未満の場合には、腐食生成物に取り込まれるＭｇ、Ｃａ、Ｓｒの量が少なく、腐食生成物の安定化が望めない。一方、前記合計含有量が１０％を超える場合には、腐食生成物の安定化効果が飽和するだけでなく、製造コストの上昇が生じることとなる。さらに、前記合計含有量が１０％を超える場合には、後述するとおり、めっき浴中のドロス生成量が増大し、連続操業性が劣ることとなる。
また、めっき層中の各成分の含有量はめっき浴中の各成分の含有量とほぼ一致する。このため、めっき層中のＭｇ、Ｃａ及びＳｒの含有量は、めっき浴中の成分管理で調整される。めっき浴中においてＭｇ、Ｃａ及びＳｒからなる群より選択される一種以上の合計含有量が多くなると、めっき浴のドロスの生成量が多くなり、成分管理が難しくなるといった問題が生じる。よって、めっき浴の組成管理の観点からは、前記めっき層中のＭｇ、Ｃａ及びＳｒからなる群より選択される一種以上の合計含有量を０．０１〜５％の範囲とすることが好ましく、０．０１〜３％の範囲とすることがより好ましく、０．０１〜１％の範囲とすることが特に好ましい。
なお、安定して連続操業を行うためには、前記ドロス生成量を可能な限り低減することが好ましい。特に、単位時間当たりの浴面のドロス生成量が、同時間中に製造した溶融Ａｌ−Ｚｎ系めっき鋼板の総めっき付着量（めっき処理により、めっき浴から持ち出されためっき浴量）の１０％未満であることが好ましく、５％未満であることがより好ましい。このような範囲にドロス生成量を制御することは、めっき浴中のＭｇ、Ｃａ及びＳｒからなる群より選択される一種以上の合計含有量を前述した好適範囲にすることで可能となる。
The reason why the total content of one or more selected from the group consisting of Mg, Ca and Sr in the plating layer is set to 0.01 to 10% is as follows. When the total content of one or more selected from the group consisting of Mg, Ca and Sr is less than 0.01%, the amount of Mg, Ca and Sr taken into the corrosion product is small, and the corrosion product is stable. I can't expect it. On the other hand, when the total content exceeds 10%, not only the stabilization effect of the corrosion product is saturated, but also the production cost is increased. Furthermore, when the total content exceeds 10%, as described later, the amount of dross generated in the plating bath increases and the continuous operability is deteriorated.
Further, the content of each component in the plating layer substantially matches the content of each component in the plating bath. For this reason, the content of Mg, Ca and Sr in the plating layer is adjusted by component management in the plating bath. When the total content of one or more selected from the group consisting of Mg, Ca and Sr in the plating bath increases, the amount of dross generated in the plating bath increases and component management becomes difficult. Therefore, from the viewpoint of the composition management of the plating bath, it is preferable that the total content of one or more selected from the group consisting of Mg, Ca and Sr in the plating layer is in the range of 0.01 to 5%. A range of 0.01 to 3% is more preferable, and a range of 0.01 to 1% is particularly preferable.
In addition, in order to perform a continuous operation stably, it is preferable to reduce the dross generation amount as much as possible. In particular, the amount of dross generation on the bath surface per unit time is 10% of the total plating adhesion amount of the molten Al—Zn-plated steel sheet produced during the same time (the amount of plating bath taken out of the plating bath by the plating process). Is preferably less than 5%, and more preferably less than 5%. It is possible to control the dross generation amount within such a range by setting the total content of one or more selected from the group consisting of Mg, Ca and Sr in the plating bath to the above-described preferable range.
なお、前記めっき層中にＭｇ、Ｃａ及びＳｒからなる群より選択される元素を複合で含有する場合も、単独で含有する場合と同じ効果が得られるが、実際の操業の点から、めっき浴組成を安定かつ容易に管理するべく、含有させる元素数を少なくすること、具体的には、Ｍｇ、Ｃａ又はＳｒを単独で含有させることが好ましい。 In addition, when the element selected from the group consisting of Mg, Ca, and Sr is contained in the plating layer in the composite, the same effect as the case of containing it alone is obtained, but from the point of actual operation, the plating bath In order to manage the composition stably and easily, it is preferable to reduce the number of elements to be contained, specifically, Mg, Ca or Sr alone.
さらに、塗装後耐食性とめっきの外観品位とを、操業上の煩雑さを招くことなく高いレベルで実現できる点から、前記めっき層中の、Ｍｇ、Ｃａ及びＳｒからなる群より選択される一種以上の合計含有量に対するＢｉの含有量（Ｂｉの含有量／Ｍｇ、Ｃａ及びＳｒからなる群より選択される一種以上の合計含有量）が、０．００２〜２の範囲であることが好ましく、０．００２〜１の範囲であることがより好ましい。Ｍｇ、Ｃａ及びＳｒからなる群より選択される一種以上の合計含有量に対するＢｉの含有量が０．００２未満の場合、塗装後耐食性の低下を招くおそれがあり、一方Ｂｉの含有量が２を超えると、めっきの外観品位低下や操業上の問題が発生するおそれがある。 Furthermore, from the point which can implement | achieve corrosion resistance after coating and the external appearance quality of plating at a high level, without causing the complexity of operation, 1 or more types selected from the group which consists of Mg, Ca, and Sr in the said plating layer The Bi content relative to the total content of Bi (the Bi content / one or more total content selected from the group consisting of Mg, Ca and Sr) is preferably in the range of 0.002 to 2, A range of 0.002 to 1 is more preferable. If the Bi content relative to the total content of one or more selected from the group consisting of Mg, Ca and Sr is less than 0.002, the corrosion resistance after coating may be reduced, while the Bi content is 2. If it exceeds, there is a risk that the appearance quality of the plating deteriorates and operational problems occur.
本発明の溶融Ａｌ−Ｚｎ系めっき鋼板は、めっき層中にＡｌを２５〜９０％含有する溶融Ａｌ−Ｚｎ系めっき鋼板である。さらに、耐食性と操業面のバランスから、めっき層中のＡｌ含有量の好ましい範囲は４５〜７０％であり、より好ましい範囲は５０〜６０％である。めっき層中のＡｌが２５％以上で、下地鋼板との界面に存在する合金相の上に存在する上層に、上述したＡｌのデンドライト凝固が起こる。これによって、上層は、主として、Ａｌがデンドライト凝固し、Ｚｎを過飽和に含有したデンドライト凝固部分（α−Ａｌ相）と、残りのデンドライト間隙の部分（Ｚｎリッチ相）からなる。さらに、デンドライト凝固部分はめっき層の膜厚方向に積層した、耐食性に優れる構造をとる。このようなめっき層構造を安定的に得るには、Ａｌを４５％以上にすることが好ましい。一方、Ａｌが９０％超えでは、Ｆｅに対して犠牲防食作用をもつＺｎ量が少ないため、鋼素地が露出した場合に耐食性が劣化する。一般的に、めっきの付着量が少ないほど鋼素地が露出しやすいため、付着量が少なくても十分な耐食性が得られるようにするには、Ａｌを７０％以下にすることが好ましい。また、Ａｌ−Ｚｎ系の溶融めっきでは、Ａｌ含有量の増加に伴い、めっき浴の温度（以下、浴温度と称す）が高くなるため、操業面での問題が懸念されるが、前記Ａｌ含有量であれば、浴温度が適度であり問題はない。 The molten Al—Zn-based plated steel sheet of the present invention is a molten Al—Zn-based plated steel sheet containing 25 to 90% of Al in the plating layer. Furthermore, from the balance between corrosion resistance and operation, the preferable range of the Al content in the plating layer is 45 to 70%, and the more preferable range is 50 to 60%. The Al dendrite solidification described above occurs in the upper layer existing on the alloy phase existing at the interface with the base steel plate when Al in the plating layer is 25% or more. Thus, the upper layer mainly consists of a dendrite solidified portion (α-Al phase) in which Al is dendrite solidified and contains Zn in a supersaturated state, and a remaining dendrite gap portion (Zn rich phase). Furthermore, the dendrite solidified portion has a structure excellent in corrosion resistance, laminated in the film thickness direction of the plating layer. In order to stably obtain such a plating layer structure, it is preferable to make Al 45% or more. On the other hand, if Al exceeds 90%, the amount of Zn having a sacrificial anticorrosive action against Fe is small, and therefore the corrosion resistance is deteriorated when the steel substrate is exposed. In general, the smaller the amount of plating, the easier the steel substrate is exposed. Therefore, in order to obtain sufficient corrosion resistance even if the amount of adhesion is small, Al is preferably made 70% or less. Moreover, in Al—Zn-based hot dipping, as the Al content increases, the temperature of the plating bath (hereinafter referred to as “bath temperature”) increases, so there are concerns about operational problems. If it is an amount, the bath temperature is moderate and there is no problem.
本発明の溶融Ａｌ−Ｚｎ系めっき鋼板に用いられる下地鋼板の種類については、特に限定はされない。例えば、酸洗脱スケールした熱延鋼板若しくは鋼帯、又は、それらを冷間圧延して得られた冷延鋼板若しくは鋼帯を用いることができる。 There is no particular limitation on the type of base steel sheet used in the hot-dip Al—Zn-based plated steel sheet of the present invention. For example, a hot-rolled steel plate or steel strip that has been pickled and descaled, or a cold-rolled steel plate or steel strip obtained by cold rolling them can be used.
なお、本発明のめっき鋼板は、めっき層中にＺｎを１０〜７５％含有することが好ましく、３０〜５５％含有することがより好ましく、４０〜５０％含有することが特に好ましい。Ｚｎが１０％以上で、めっきがＦｅに対して十分な犠牲防食作用を示すため、鋼素地が露出した場合に耐食性が十分に得られる。一方、７５％以下とすることで、過剰な犠牲防食作用を防ぎ、めっき層の溶解の促進による耐食性の劣化を防ぐ。 In addition, it is preferable that the plated steel plate of this invention contains 10-75% of Zn in a plating layer, It is more preferable to contain 30-55%, It is especially preferable to contain 40-50%. Since Zn is 10% or more and the plating exhibits a sufficient sacrificial anticorrosive action for Fe, corrosion resistance is sufficiently obtained when the steel substrate is exposed. On the other hand, by making it 75% or less, excessive sacrificial anticorrosive action is prevented, and deterioration of corrosion resistance due to promotion of dissolution of the plating layer is prevented.
また、本発明のめっき鋼板は、めっき層中にＳｉを０．１〜１０％含有することが好ましい。Ｓｉは下地鋼板との界面に形成する界面合金相の成長を抑制し、耐食性や加工性の向上を目的にめっき浴中に添加され、めっき層に含有される。具体的には、溶融Ａｌ−Ｚｎ系めっき鋼板の場合、めっき浴中にＳｉを含有させめっき処理を行うと、鋼板がめっき浴中に浸漬されると同時に鋼板表面のＦｅと浴中のＡｌやＳｉが合金化反応し、Ｆｅ-Ａｌ系及び／又はＦｅ−Ａｌ−Ｓｉ系の化合物を形成する。このＦｅ−Ａｌ−Ｓｉ系の化合物の形成により、界面合金相の成長が抑制される。めっき浴中のＳｉ含有量を０．１％以上とすることで界面合金相の十分な成長抑制が可能となる。一方、めっき浴中のＳｉ含有量が１０％以下の場合、製造しためっき層中にクラックの伝播経路となり加工性を低下させるＳｉ相として析出し難くなるので、めっき浴中のＳｉ含有量は１０％以下とすることが好ましい。よって、めっき浴中のＳｉ含有量の好適範囲は、０．１〜１０％である。Ａｌ−Ｚｎ系めっき鋼板の場合、めっき層の組成がめっき浴組成とほぼ同等となるため、めっき層中のＳｉ含有量はめっき浴中のＳｉ含有量の好適範囲と同等で０．１〜１０％であることが好ましい。 Moreover, it is preferable that the plated steel plate of this invention contains 0.1 to 10% of Si in a plating layer. Si is added to the plating bath for the purpose of suppressing the growth of the interfacial alloy phase formed at the interface with the base steel sheet and improving the corrosion resistance and workability, and is contained in the plating layer. Specifically, in the case of a molten Al—Zn-based plated steel sheet, when Si is contained in the plating bath and plating is performed, the steel sheet is immersed in the plating bath and at the same time Fe on the steel sheet surface and Al in the bath Si undergoes an alloying reaction to form Fe-Al and / or Fe-Al-Si compounds. Formation of this Fe—Al—Si compound suppresses the growth of the interface alloy phase. By making the Si content in the plating bath 0.1% or more, it is possible to sufficiently suppress the growth of the interface alloy phase. On the other hand, when the Si content in the plating bath is 10% or less, it becomes difficult to precipitate as an Si phase which becomes a propagation path of cracks in the manufactured plating layer and deteriorates workability. Therefore, the Si content in the plating bath is 10 % Or less is preferable. Therefore, the suitable range of Si content in a plating bath is 0.1 to 10%. In the case of an Al—Zn-based plated steel sheet, since the composition of the plating layer is almost equivalent to the plating bath composition, the Si content in the plating layer is equivalent to the preferred range of the Si content in the plating bath and is 0.1 to 10 % Is preferred.
さらに、前記めっき層は、Ｍｎ、Ｖ、Ｃｒ、Ｍｏ、Ｔｉ、Ｎｉ、Ｃｏ、Ｓｂ、Ｚｒ及びＢからなる群より選ばれる一種又は二種以上の元素を、合計で０．０１〜１０％含有することが好ましい。腐食生成物の安定性を向上させ、腐食の進行を遅延させる効果を発揮できるためである。 Further, the plating layer contains 0.01 to 10% in total of one or more elements selected from the group consisting of Mn, V, Cr, Mo, Ti, Ni, Co, Sb, Zr and B. It is preferable to do. This is because the stability of the corrosion product can be improved and the effect of delaying the progress of corrosion can be exhibited.
なお、めっき層の成分組成は、例えば、めっき層を塩酸等に浸漬して溶解させ、その溶解液をＩＣＰ発光分光分析や原子吸光分析を行うことで確認することができる。この方法はあくまでも一例であり、めっき層の成分組成を正確に定量できる方法であればどのような方法でも良く、特に限定するものではない。 The component composition of the plating layer can be confirmed by, for example, immersing and dissolving the plating layer in hydrochloric acid or the like, and performing ICP emission spectroscopic analysis or atomic absorption analysis on the solution. This method is merely an example, and any method may be used as long as the component composition of the plating layer can be accurately quantified, and the method is not particularly limited.
また、本発明の溶融Ａｌ−Ｚｎ系めっき鋼板は、前記めっき層のビッカース硬度を、平均で５０〜１００Ｈｖとすることが好ましい。ビッカース硬度を上記範囲とすることで、優れた加工後耐食性を実現できるからである。
具体的には、前記めっき層のビッカース硬度を平均で１００Ｈｖ以下と軟質にすることで、曲げなどの加工を行った際、めっき層が下地鋼板に追従し、クラックの発生を抑制でき、その結果として、曲げ加工部においても平板部と同程度の耐食性を確保できる。また、前記ビッカース硬度の下限を５０Ｈｖとすることで、成形加工時にめっき層が金型等に凝着するのを防止する。
Moreover, it is preferable that the molten Al-Zn type plated steel sheet of this invention sets the Vickers hardness of the said plating layer to 50-100Hv on an average. This is because by setting the Vickers hardness within the above range, excellent post-processing corrosion resistance can be realized.
Specifically, by making the Vickers hardness of the plating layer as soft as 100 Hv or less on average, when processing such as bending, the plating layer follows the base steel plate, and the generation of cracks can be suppressed. As a result, the same degree of corrosion resistance as that of the flat plate portion can be secured in the bent portion. Further, by setting the lower limit of the Vickers hardness to 50 Hv, it is possible to prevent the plating layer from adhering to a mold or the like during the molding process.
こで、前記めっき層の平均ビッカース硬度については、例えば、溶融Ａｌ−Ｚｎ系めっき鋼板のめっき層断面を研磨した後、マイクロビッカース硬度計を用いて、めっき層の上層側の任意の箇所を断面方向から低荷重で数点測定し、平均を算出することで得られる。
測定点数の上下限は特に定めないが、測定の精度の観点から、１０点以上が好ましく、より多いほど好ましい。この方法はあくまでも一例であり、めっき層の平均ビッカース硬度を正確に定量できる方法であればどのような方法でも良く、特に限定するものではない。
また、低荷重の上下限については特に定めないが、適正な荷重よりも大きいと圧痕が大きくなることで下地鋼板の硬さの影響を受けやすくなる。よって下地鋼板の影響を避ける観点から、５０ｇｆ以下とすることが好ましく、１０ｇｆ以下とすることがより好ましい。
Here, with respect to the average Vickers hardness of the plating layer, for example, after polishing the plating layer cross section of the molten Al-Zn-based plated steel sheet, using a micro Vickers hardness meter, It is obtained by measuring several points with low load from the direction and calculating the average.
The upper and lower limits of the number of measurement points are not particularly defined, but from the viewpoint of measurement accuracy, 10 points or more are preferable, and the more is more preferable. This method is merely an example, and any method may be used as long as it can accurately quantify the average Vickers hardness of the plating layer, and is not particularly limited.
Further, the upper and lower limits of the low load are not particularly defined, but if the load is larger than an appropriate load, the indentation becomes large, so that it is easily affected by the hardness of the base steel plate. Therefore, from the viewpoint of avoiding the influence of the base steel plate, it is preferably 50 gf or less, and more preferably 10 gf or less.
さらに、本発明の溶融Ａｌ−Ｚｎ系めっき鋼板のめっき層の付着量は片面あたり３５〜１５０ｇ／ｍ２であることが好ましい。３５ｇ／ｍ２以上であれば優れた耐食性が得られ、１５０ｇ／ｍ２以下であれば優れた加工性が得られる。また、より優れた耐食性及び加工性を得る点からは、前記付着量を、４０〜１１０ｇ／ｍ２とすることが好ましく、４０〜８０ｇ／ｍ２とすることがより好ましい。 Furthermore, it is preferable that the adhesion amount of the plating layer of the hot-dip Al—Zn-based plated steel sheet of the present invention is 35 to 150 g / m 2 per side. If it is 35 g / m 2 or more, excellent corrosion resistance is obtained, and if it is 150 g / m 2 or less, excellent workability is obtained. Further, more excellent from the viewpoint of obtaining a corrosion resistance and workability, the adhesion amount is preferably to 40~110g / m 2, and more preferably to 40 and 80 g / m 2.
次に、本発明の溶融Ａｌ−Ｚｎ系めっき鋼板の製造方法について説明する。
本発明の溶融Ａｌ−Ｚｎ系めっき鋼板は、連続式溶融めっき設備で製造され、めっき浴の組成管理以外は、全て常用の方法で行うことができる。
Next, the manufacturing method of the fusion | melting Al-Zn type plated steel plate of this invention is demonstrated.
The hot-dip Al—Zn-based plated steel sheet of the present invention is manufactured by a continuous hot-dip plating facility, and all can be performed by a conventional method except for the composition management of the plating bath.
めっき浴中のＡｌ含有量は２５〜９０％、Ｂｉ：０．０１〜０．１％とし、加えて、Ｍｇ、Ｃａ及びＳｒからなる群より選択される一種以上を合計で０．０１〜１０％含有させる。このような組成のめっき浴を用いることにより、上述しためっき層の構成を具える溶融Ａｌ−Ｚｎ系めっき鋼板を製造できる。その際、前述の通り、めっき層にＦｅに対する犠牲防職能を十分に付与するため、めっき浴中にＺｎを１０％以上含有させること、また界面合金相の成長を抑制するために、めっき浴中にＳｉを０．１〜１０％含有させることが好ましい。 The Al content in the plating bath is 25 to 90% and Bi: 0.01 to 0.1%. In addition, at least one selected from the group consisting of Mg, Ca and Sr is 0.01 to 10 in total. % Content. By using a plating bath having such a composition, a molten Al—Zn-based plated steel sheet having the above-described configuration of the plating layer can be produced. At that time, as described above, in order to sufficiently impart the sacrificial protective ability against Fe to the plating layer, in order to contain 10% or more of Zn in the plating bath, and to suppress the growth of the interface alloy phase, It is preferable to contain 0.1 to 10% of Si.
なお、めっき浴中に上述したＡｌ、Ｚｎ、Ｓｉ、Ｂｉ、Ｍｇ、Ｃａ、Ｓｒ以外にも例えばＭｎ、Ｖ、Ｃｒ、Ｍｏ、Ｔｉ、Ｎｉ、Ｃｏ、Ｓｂ、Ｚｒ、Ｂ等の何らかの元素を添加することは、本発明の効果が損なわれない限り可能である。特に、Ｍｎ、Ｖ、Ｃｒ、Ｍｏ、Ｔｉ、Ｎｉ、Ｃｏ、Ｓｂ、Ｚｒ及びＢから選ばれる一種又は二種以上の元素を合計で０．０１〜１０％をめっき浴中に含有させることが、前述の通り、製造した溶融Ａｌ−Ｚｎ系めっき鋼板の耐食性を向上させるため好ましい。 In addition to the above-described Al, Zn, Si, Bi, Mg, Ca, and Sr, some elements such as Mn, V, Cr, Mo, Ti, Ni, Co, Sb, Zr, and B are added to the plating bath. This is possible as long as the effects of the present invention are not impaired. In particular, a total of 0.01 to 10% of one or more elements selected from Mn, V, Cr, Mo, Ti, Ni, Co, Sb, Zr and B is contained in the plating bath. As described above, it is preferable because the corrosion resistance of the manufactured molten Al—Zn-based plated steel sheet is improved.
さらに、加工性に優れる溶融Ａｌ−Ｚｎ系めっき鋼板を得るためには、連続式溶融めっき設備で溶融めっきを施した後、冷却した鋼板を２５０〜３７５℃の温度で５〜６０秒間保持することが好ましい。この場合、溶融めっき設備にさらにバッチ式加熱設備を組み合わせて製造する場合に比べて、効率的なＡｌ−Ｚｎ系めっき鋼板の製造が可能となる。 Furthermore, in order to obtain a hot-dip Al—Zn-based plated steel sheet having excellent workability, after the hot-dip plating is performed with a continuous hot-dip plating facility, the cooled steel sheet is held at a temperature of 250 to 375 ° C. for 5 to 60 seconds. Is preferred. In this case, it is possible to manufacture an efficient Al—Zn-based plated steel sheet as compared with the case of manufacturing a combination of a hot-dip plating facility and a batch-type heating facility.
前記鋼板を、２５０〜３７５℃の温度で５〜６０秒間保持する（温度保持工程）理由としては、この工程によって、めっき層が急冷により非平衡に凝固することがなく、めっき層中に導入された歪が解放され、Ａｌ−Ｚｎ系めっきにおいてＡｌリッチ相（α−Ａｌ相）とＺｎリッチ相の二相分離が促進されるため、めっき層の軟質化を実現できる。その結果、鋼板の加工性の向上が可能となり、また、軟質化が実現されためっき層は、従来の硬質のめっき層に比べ、加工時に発生するクラックの数や幅が減少することで、加工部の耐食性の改善が可能となる。 The reason why the steel sheet is held at a temperature of 250 to 375 ° C. for 5 to 60 seconds (temperature holding process) is that the plating layer is not solidified in a non-equilibrium state by rapid cooling and is introduced into the plating layer by this process. Since the strain is released and the two-phase separation of the Al-rich phase (α-Al phase) and the Zn-rich phase is promoted in Al—Zn-based plating, softening of the plating layer can be realized. As a result, it is possible to improve the workability of the steel sheet, and the plating layer that has been made softer reduces the number and width of cracks that occur during processing compared to conventional hard plating layers. The corrosion resistance of the part can be improved.
なお、前記保持温度が２５０℃以上、かつ前記保持時間が５秒以上の場合には、溶融めっき層の硬化が早くなりすぎず、十分に歪の解放や、Ａｌリッチ相（α−Ａｌ相）とＺｎリッチ相の分離が進むため、所望の加工性が得られる。一方、前記保持温度が３７５℃以下であれば、温度保持工程前の冷却が十分となり、連続式溶融めっき設備内の溶融めっき浴から搬出されためっき後の鋼帯がロールへ接触したときにめっきがロールに付着せず、めっき層の一部が剥がれるメタルピックアップが生じることがなく好ましい。さらに、前記保持時間が６０秒以下の場合は、保持時間が長すぎることがなく、連続式溶融めっき設備での製造に適する。
また、より優れた加工性を実現する点からは、前記温度保持工程におけるめっき鋼板の保持温度は、３００〜３７５℃であることが好ましく、３５０〜３７５℃であることがより好ましい。さらに、連続式溶融めっき設備における製造性（温度保持工程にかかるコスト）を考慮すると、めっき鋼板の保持時間は、５〜３０秒であることが好ましく、５〜２０秒であることがより好ましい。
When the holding temperature is 250 ° C. or higher and the holding time is 5 seconds or longer, the hot dip plated layer does not cure too quickly, and the strain is sufficiently released or the Al rich phase (α-Al phase). Since the separation of the Zn-rich phase proceeds, the desired workability can be obtained. On the other hand, if the holding temperature is 375 ° C. or lower, the cooling before the temperature holding step is sufficient, and the plating is performed when the steel strip after plating carried out from the hot dipping bath in the continuous hot dipping equipment comes into contact with the roll. Is preferable because it does not adhere to the roll and a metal pickup in which a part of the plating layer is peeled off does not occur. Furthermore, when the holding time is 60 seconds or less, the holding time is not too long and is suitable for production in a continuous hot dip plating facility.
Moreover, from the point which implement | achieves the outstanding workability, it is preferable that the holding temperature of the plated steel plate in the said temperature holding process is 300-375 degreeC, and it is more preferable that it is 350-375 degreeC. Furthermore, considering the manufacturability (cost required for the temperature holding step) in the continuous hot dip plating facility, the holding time of the plated steel sheet is preferably 5 to 30 seconds, and more preferably 5 to 20 seconds.
また、上述した温度保持工程の前に、溶融めっきを施した後の鋼板を３７５℃以下まで冷却することが好ましい。３７５℃以下まで冷却することにより、メタルピックアップが生じることがない。
上記のように、めっき浴の組成管理とめっき後の温度保持工程を組み合わせることで、塗装後耐食性に優れるとともに、良好な加工性により加工部耐食性にも優れた溶融Ａｌ−Ｚｎ系めっき鋼板を、連続的な溶融めっき設備で効率的に製造することができる。
Moreover, it is preferable to cool the steel plate after hot-plating to 375 degrees C or less before the temperature holding process mentioned above. The metal pickup does not occur by cooling to 375 ° C. or lower.
As described above, by combining the composition management of the plating bath and the temperature holding step after plating, while being excellent in corrosion resistance after coating, a molten Al-Zn-based plated steel sheet excellent in processed part corrosion resistance due to good workability, It can be efficiently manufactured with continuous hot dipping equipment.
次に、本発明を実施例に基づき具体的に説明する。
（サンプル１〜２４）
サンプルとなる全ての溶融Ａｌ−Ｚｎ系めっき鋼板について、常法で製造した板厚０．８ｍｍの冷延鋼板を下地鋼板として用い、連続式溶融めっき設備によって、めっき浴の浴温を６００℃、めっき付着量を片面あたり５０ｇ／ｍ２、すなわち両面で１００ｇ／ｍ２の条件で溶融めっき処理を施した。また、一部の溶融Ａｌ−Ｚｎ系めっき鋼板は、連続式溶融めっき設備において、めっき処理を施し冷却した後、表１に示す保持温度及び保持時間の条件で温度保持を行った。
Next, the present invention will be specifically described based on examples.
(Samples 1-24)
About all the molten Al-Zn-based plated steel sheets used as samples, a cold rolled steel sheet having a thickness of 0.8 mm manufactured by a conventional method is used as a base steel sheet, and the bath temperature of the plating bath is 600 ° C by a continuous hot-dip plating facility. The hot dip coating was performed under the condition that the amount of plating was 50 g / m 2 per side, that is, 100 g / m 2 on both sides. Further, some of the hot-dip Al—Zn-plated steel sheets were subjected to plating treatment in a continuous hot-dip plating facility, cooled, and then held at the holding temperature and holding time conditions shown in Table 1.
（１）めっき層の組成
サンプルとなる溶融Ａｌ−Ｚｎ系めっき鋼板を、それぞれ１００ｍｍΦに打ち抜き、塩酸に浸漬してめっき層を溶解させた後、溶解液の組成をＩＣＰ発光分光分析で定量化することで確認した。各サンプルの組成を表１に示す。
(1) Composition of plating layer Each molten Al-Zn-based plated steel sheet as a sample is punched to 100 mmΦ, immersed in hydrochloric acid to dissolve the plating layer, and then the composition of the solution is quantified by ICP emission spectrometry. I confirmed that. The composition of each sample is shown in Table 1.
（２）塗装後耐食性の評価
サンプルとなる溶融Ａｌ−Ｚｎ系めっき鋼板をそれぞれ９０ｍｍ×７０ｍｍのサイズに剪断後、自動車外板用塗装処理と同様に、化成処理としてリン酸亜鉛処理を行った後、電着塗装、中塗り、及び上塗り塗装を施した。ここで、リン酸亜鉛処理、電着塗装、中塗り塗装及び上塗り塗装は以下に示す条件で行った。
○リン酸亜鉛処理：日本パーカライジング社製の脱脂剤：ＦＣ−Ｅ２００１、表面調整剤：ＰＬ−Ｘ、及び化成処理剤：ＰＢ−ＡＸ３５Ｍ（温度：３５℃）を用いて、化成処理液の遊離フッ素濃度を２００質量ｐｐｍ、化成処理液の浸漬時間を１２０秒の条件で化成処理を施した。
○電着塗装：関西ペイント社製の電着塗料：ＧＴ−１００を用いて、膜厚が１５μｍとなるように電着塗装を施した。
○中塗り塗装：関西ペイント社製の中塗り塗料：ＴＰ−６５−Ｐを用いて、膜厚が３０μｍとなるようにスプレー塗装を施した。
○上塗り塗装：関西ペイント社製の中塗り塗料：Ｎｅｏ６０００を用いて、膜厚が３０μｍとなるようにスプレー塗装を施した。
その後、図１に示すとおり、評価面の端部５ｍｍ、及び非評価面（背面）をテープでシール処理を行った後、評価面の中央にカッターナイフでめっき鋼板の地鉄に到達する深さまで、長さ６０ｍｍ、中心角９０°のクロスカット傷を加えたものを塗装後耐食性の評価用サンプルとした。
上記評価用サンプルを用いて図２に示すサイクルで腐食促進試験を実施した。腐食促進試験を湿潤からスタートし、６０サイクル及び／又は１２０サイクル後まで行った後、傷部からの塗膜膨れが最大である部分の塗膜膨れ幅（最大塗膜膨れ幅）を測定し、塗装後耐食性を下記の基準で評価した。評価結果を表１に示す。
（６０サイクル後の評価基準）
○：最大塗膜膨れ幅≦１．０ｍｍ
△：１．０ｍｍ＜最大塗膜膨れ幅≦１．５ｍｍ
×：最大塗膜膨れ幅＞１．５ｍｍ
（１２０サイクル後の評価基準）
◎：最大塗膜膨れ幅≦２．０ｍｍ
○：２．０ｍｍ＜最大塗膜膨れ幅≦２．５ｍｍ
△：２．５ｍｍ＜最大塗膜膨れ幅≦３．０ｍｍ
×：最大塗膜膨れ幅＞３．０ｍｍ
(2) Evaluation of corrosion resistance after painting After the molten Al-Zn-based plated steel sheet as a sample was sheared to a size of 90 mm x 70 mm, respectively, and after the zinc phosphate treatment as a chemical conversion treatment, similar to the coating treatment for automobile outer plates Electrodeposition coating, intermediate coating, and top coating were applied. Here, the zinc phosphate treatment, electrodeposition coating, intermediate coating, and top coating were performed under the following conditions.
○ Zinc phosphate treatment: Defluorinating agent manufactured by Nihon Parkerizing Co., Ltd .: FC-E2001, surface conditioner: PL-X, and chemical conversion treatment agent: PB-AX35M (temperature: 35 ° C.) Chemical conversion treatment was performed under the conditions of a concentration of 200 mass ppm and an immersion time of the chemical conversion solution of 120 seconds.
Electrodeposition coating: Electrodeposition coating manufactured by Kansai Paint Co., Ltd .: Using GT-100, electrodeposition coating was applied so that the film thickness was 15 μm.
○ Intermediate coating: Using Kansai Paint Co., Ltd., intermediate coating: TP-65-P, spray coating was applied to a film thickness of 30 μm.
○ Top coating: Spray coating was performed using an intermediate coating paint: Neo6000 manufactured by Kansai Paint Co., Ltd. so that the film thickness was 30 μm.
Thereafter, as shown in FIG. 1, after the end of the
A corrosion acceleration test was performed in the cycle shown in FIG. 2 using the sample for evaluation. The corrosion acceleration test is started from wet and after 60 cycles and / or after 120 cycles, the film swelling width (maximum film swelling width) of the portion where the film swelling from the scratch is maximum is measured, The corrosion resistance after painting was evaluated according to the following criteria. The evaluation results are shown in Table 1.
(Evaluation criteria after 60 cycles)
○: Maximum swollen width of coating film ≦ 1.0 mm
Δ: 1.0 mm <maximum paint film swelling width ≦ 1.5 mm
×: Maximum coating film swelling width> 1.5 mm
(Evaluation criteria after 120 cycles)
A: Maximum paint film swell width ≦ 2.0 mm
A: 2.0 mm <maximum coating film swelling width ≦ 2.5 mm
Δ: 2.5 mm <maximum paint film swell width ≦ 3.0 mm
×: Maximum coating film swelling width> 3.0 mm
（３）めっきの外観品位
サンプルとなる溶融Ａｌ−Ｚｎ系めっき鋼板について、めっき処理を施した後１時間以内に、雰囲気：大気、温度：２０℃、相対湿度：５０％に調節した恒温恒湿槽内に入れた。以後、９０日間放置した後、サンプルを取り出しめっき表面の目視観察を行い、下記の基準で外観品位を評価した。評価結果を表１に示す。
○：黒変が認められない
△：黒変は認められるが、塗装を施さない用途で特に問題にならない
×：黒変が塗装を施さない用途で問題になる
(3) Appearance quality of plating With respect to a hot-dip Al—Zn-based plated steel sheet as a sample, the constant temperature and humidity were adjusted to atmosphere: air, temperature: 20 ° C., and relative humidity: 50% within 1 hour after plating. Placed in the tank. Thereafter, after leaving for 90 days, the sample was taken out and visually observed on the plating surface, and the appearance quality was evaluated according to the following criteria. The evaluation results are shown in Table 1.
○: Blackening is not recognized Δ: Blacking is recognized, but there is no particular problem in applications where no coating is applied. ×: Blackening is a problem in applications where coating is not applied.
（４）めっき層のビッカース硬度
溶融Ａｌ−Ｚｎ系めっき鋼板の一部のサンプルについて、めっき層断面を研磨した後、マイクロビッカース硬度計を用いて、めっき層の上層側の任意の箇所を断面方向から荷重５ｇｆで各２０点ずつビッカース硬度を測定した。測定した２０点の平均値をめっき層の硬度として算出した。算出結果を表１に示す。
(4) Vickers hardness of the plating layer For some samples of the molten Al-Zn-based plated steel sheet, after polishing the plating layer cross section, using a micro Vickers hardness tester, the arbitrary portion on the upper layer side of the plating layer in the cross-sectional direction From the above, Vickers hardness was measured at 20 points each with a load of 5 gf. The average value of the measured 20 points was calculated as the hardness of the plating layer. The calculation results are shown in Table 1.
（５）加工部耐食性評価
溶融Ａｌ−Ｚｎ系めっき鋼板の一部のサンプルについて、同板厚の板を内側に４枚挟んで１８０°曲げの加工（４Ｔ曲げ）を施した後、曲げの外側にＪＩＳ Ｚ ２３７１−２０００に準拠した塩水噴霧試験を行った。各サンプルの赤錆が発生するまでの時間を測定し、以下の基準により評価した。
○：赤錆発生時間≧４０００時間
×：赤錆発生時間＜４０００時間
(5) Processed part corrosion resistance evaluation About some samples of the molten Al-Zn-based plated steel sheet, four plates of the same thickness are sandwiched inside and subjected to 180 ° bending (4T bending), and then the outside of the bending Were subjected to a salt spray test in accordance with JIS Z 2371-2000. The time until red rust occurred in each sample was measured and evaluated according to the following criteria.
○: Red rust occurrence time ≧ 4000 hours ×: Red rust occurrence time <4000 hours
（６）連続操業性
各サンプルの溶融Ａｌ−Ｚｎ系めっき鋼板の製造における、浴面のドロス生成量により連続操業性を評価した。浴面ドロスを全量除去してから１時間の間に生成したドロスを汲み上げて質量を測定することで、ドロス生成量を得た。同時間中に製造した溶融Ａｌ−Ｚｎ系めっき鋼板のめっき付着量の合計量に対する前記ドロス量の割合（ドロス量／めっき付着量の合計量×１００（％））を算出し、以下の基準により評価した。
○：ドロス生成量がめっき付着量の５％未満
△：ドロス生成量がめっき付着量の５％以上１０％未満
×：ドロス生成量がめっき付着量の１０％以上
(6) Continuous operability Continuous operability was evaluated based on the amount of dross generated on the bath surface in the production of the molten Al-Zn-based plated steel sheet of each sample. The dross generation amount was obtained by pumping up the dross generated during 1 hour after removing all the bath surface dross and measuring the mass. The ratio of the dross amount to the total amount of the coating amount of the molten Al—Zn-plated steel sheet produced during the same time (the amount of dross / the total amount of the coating amount × 100 (%)) was calculated, and the following criteria were used. evaluated.
○: Dross generation amount is less than 5% of plating adhesion amount Δ: Dross generation amount is 5% or more and less than 10% of plating adhesion amount ×: Dross generation amount is 10% or more of plating adhesion amount
表１より、本発明例のサンプルでは、比較例のサンプルとは異なり、６０サイクル後の最大塗膜膨れ幅が１．０ｍｍ以下、又は、１２０サイクル後の最大塗膜膨れ幅が３．０ｍｍ以下であったことから、塗装後耐食性に優れた溶融Ａｌ−Ｚｎ系めっき鋼板が得られたことがわかる。また、本発明例のサンプルの中において、Ｂｉ含有量を適切な範囲に制御することで、優れた外観品位と塗装後耐食性との両立が可能な溶融Ａｌ−Ｚｎ系めっき鋼板が得られることがわかる。さらに本発明例においてはドロス生成量がめっき付着量の１０％未満であったことから、連続操業性に優れることがわかる。
また、めっき後に２５０〜３７５℃で５秒以上の温度保持を行い、めっき層のビッカース硬度が平均で５０〜１００Ｈｖの範囲であるサンプルについては、温度保持を行わなかったサンプルに比べて、加工後耐食性に優れることがわかる。
From Table 1, the sample of the present invention is different from the sample of the comparative example in that the maximum film swell width after 60 cycles is 1.0 mm or less, or the maximum film swell width after 120 cycles is 3.0 mm or less. Therefore, it can be seen that a molten Al—Zn plated steel sheet having excellent corrosion resistance after coating was obtained. Moreover, in the sample of the present invention example, by controlling the Bi content to an appropriate range, a molten Al—Zn-based plated steel sheet capable of achieving both excellent appearance quality and corrosion resistance after coating can be obtained. Recognize. Furthermore, in the example of this invention, since the dross production | generation amount was less than 10% of the plating adhesion amount, it turns out that it is excellent in continuous operativity.
In addition, after the plating, the temperature is maintained at 250 to 375 ° C. for 5 seconds or more, and the sample whose Vickers hardness of the plated layer is in the range of 50 to 100 Hv on average is compared with the sample that was not subjected to the temperature maintenance. It turns out that it is excellent in corrosion resistance.
本発明の溶融Ａｌ−Ｚｎ系めっき鋼板は、塗装後耐食性に優れ、自動車、家電、建材の分野等、広範な分野で適用できる。特に自動車分野において、高強度鋼板に適用すると、自動車の軽量化と高耐食性を達成する表面処理鋼板として使用できる。
The molten Al—Zn-based plated steel sheet of the present invention has excellent post-coating corrosion resistance and can be applied in a wide range of fields such as automobiles, home appliances, and building materials. In particular, in the automobile field, when applied to a high-strength steel sheet, it can be used as a surface-treated steel sheet that achieves weight reduction and high corrosion resistance of the automobile.
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