JP3599594B2 - Manufacturing method of high-strength hot-dip galvanized steel sheet with excellent plating appearance - Google Patents
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【０００１】
【発明の属する技術分野】
本発明は、自動車部品を中心として建材や家電などの幅広い分野で使用される高強度溶融亜鉛めっき鋼板の製造方法に関し、特にめっき外観に優れた高強度溶融亜鉛めっき鋼板の製造方法に関するものである。
【０００２】
【従来の技術】
近年、自動車部品を初め、建材や家電部品などの幅広い分野で亜鉛系めっき鋼板が多く使用されている。これら亜鉛系めっき鋼板の中でも、塗装後の耐食性、溶接性、防活性および経済性に優れることから溶融亜鉛めっき鋼板が特に多量に使用されている。
【０００３】
更に近年、環境問題が重要視されるようになり、自動車メーカー各社では車体の軽量化による燃費の一層の向上を目的として、高強度溶融亜鉛めっき鋼板が様々な部品に対しても使用できないか検討している。
【０００４】
ところで高強度溶融亜鉛めっき鋼板を製造するためには、Ｓｉ，Ｍｎ，Ｃｒなどの強化元素を添加する必要がある。しかし、これらの元素はいずれも極めて酸化されやすい元素であり、通常の溶融めっきラインにおける還元性雰囲気内では、選択酸化されて原板の表面に濃化し、めっき濡れ性を著しく劣化させることが知られている。
【０００５】
この対策として、例えば特開平６−８１０９６号公報や特開平６−１７２９５３号公報では酸化−還元法が提案されている。また特開平５−１３２７４９号公報では表面研削法が提案されている。さらに特開平４−３３３５５２号公報ではプレめっき法が提案されている。
【０００６】
しかし、酸化−還元法では、酸化帯での硬化皮膜量および還元帯での還元量を適切に制御することが難しいため、実機製造ラインで実施することは極めて困難である。また表面研削法では、表面研削後の還元焼鈍にて再濃化が生じるため不めっき等のめっき外観劣化要因を完全に取り除くことができない。そしてまたプレめっき法は、めっき外観を改善する上で最も有効、且つ比較的簡便な方法と考えられるものの、プレめっき後に高温焼鈍を行うと効果が薄れるため、従来法ではプレ焼鈍にて材質を確保した上でプレめっきを行い、その後溶融めっきまで比較的低温を維持することが必要であった。すなわち、プレ焼鈍工程の追加による製造コストの高騰が避けられなかった。
【０００７】
【発明が解決しようとする課題】
本発明は前記従来の問題に着目してなされたものであって、その目的は、高強度鋼板を原板とした、めっき外観に優れた高強度溶融亜鉛めっき鋼板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】
本発明によれば、（ａ）鋼中にＳｉを０．０５％以上かつＭｎを１．５％以上含有する鋼板、または（ｂ）ＭｎおよびＣｒを合計で１．５％以上含有する鋼板を、浴温が４４０℃以上で且つＡｌを０．０５〜０．５％含有する溶融亜鉛めっき浴に、下記不等式（１）および（２）を満足する侵入板温Ｔ（℃）で浸漬してめっきを行うことを特徴とするめっき外観に優れた高強度溶融亜鉛めっき鋼板の製造方法が提供される。
【０００９】
３５０＋３０／ｔ≦Ｔ（℃）＜４２０＋３０／ｔ ・・・（１）
（式中、ｔ：板厚（ｍｍ））
Ｔ（℃）≦４６０ ・・・・・・（２）
また本発明によれば、前記製造方法において溶融亜鉛めっきする前に鋼板の表面に、ＮｉおよびＣｏの少なくとも１つの元素を０．２〜３．０ｇ／ｍ2プレめっきする高強度溶融亜鉛めっき鋼板の製造方法が提供される。
【００１０】
【発明の実施の形態】
本発明者らは、ＳｉやＭｎ，Ｃｒを添加して高強度化を図った鋼板において、めっき濡れ性を改善しめっき外観に優れたものが得られないか鋭意研究を重ねた結果、めっき条件および方法を適正化することによって高強度でしかもめっき外観に優れた鋼板が得られるという新たな知見を得、本発明になすに至った。
【００１１】
まず本発明の製造方法に使用する原板としては、（ａ）鋼中にＳｉを０．０５％以上かつＭｎを１．５％以上含有する鋼板、または（ｂ）ＭｎおよびＣｒを合計で１．５％以上含有する鋼板を用いる。Ｓｉは、鋼の伸びを劣化させずに強度を上げるのに有効な元素であり、その効果を発揮するためには０．０５％以上が必要である。またＭｎおよびＣｒについては、いずれも鋼の強度を上げるのに有効な元素であり、その効果を発揮するためには、ＭｎおよびＣｒを合計量で１．５％以上添加することが必要である。なお添加量の好ましい上限は３．０％である。
【００１２】
本発明の大きな特徴の一つは、めっき浴の浴温を４４０℃以上とし、且つＡｌを０．０５〜０．５％含有させる点にある。原板をめっき浴中に約２秒程度浸漬してめっきを行い、めっき外観を良好なものにするためには、浴中においてＺｎ、Ａｌ、Ｆｅの反応をある程度促進させることが必要であり、このために浴温を４４０℃以上、より好ましくは４５０℃以上とする必要がある。なお浴温上限については特に限定はないが、浴中Ｚｎの蒸発による炉内への酸化亜鉛の付着、浴中ドロスの増加およびエネルギーコスト等を考慮すると５１０℃以下、より好ましくは４８０℃以下である。
【００１３】
一方めっき浴中のＡｌ含有量が０．０５％より少ないと、合金化が進みすぎて合金層のめっき密着性および加工部の耐赤錆性が劣化する。他方Ａｌ含有量が０．５％より多いと、不めっきや合金ムラが発生しやすくなる。
【００１４】
また本発明のもう一つの大きな特徴は、前記不等式（１）および（２）を満足する浸入板温で浸漬してめっきを行う点にある。本発明者等は、原板の板厚と侵入板温とを種々変化させてめっきを行い、その関係を鋭意検討した結果、原板の板厚によって最適な侵入板温が変化することを突き止めたのである。図１は縦軸を侵入板温（℃）、横軸を板厚（ｍｍ）として、各板厚ごとに侵入板温を変えてめっきを行いその良否を示した図である。この図によれば、板厚が厚くなるほど、良好なめっきが得られるための侵入板温域は全体的に低温側に移動することがわかる。この図から板厚をｔ（ｍｍ）として、侵入板温Ｔ（℃）は、３５０＋３０／ｔ〜４２０＋３０／ｔの範囲であって、且つ４６０℃以下と定めた。侵入板温が上下限を外れた場合に不めっきが発生し、めっき外観が劣化する理由については今のところ明確ではないが、浴温と侵入板温のバランスによって、原板がめっき浴に浸漬している間のめっき層／原板界面でのＦｅ、Ｚｎ、Ａｌの反応量が変化するためではないかと推測している。
【００１５】
次に本願請求項２の発明に係る製造方法について説明する。請求項２の製造方法では、前記請求項１の製造方法において、溶融亜鉛めっきする前に鋼板の表面に、ＮｉおよびＣｏの少なくとも１つの元素を０．２〜３．０ｇ／ｍ２プレめっきする点が大きな特徴である。この製造方法によれば、めっき濡れ性を阻害するＳｉ，Ｍｎ，Ｃｒなどの元素が比較的多量に添加された場合であっても、優れためっき外観を得ることができる。プレめっきを行うことによって溶融めっき後のめっき外観が改善される理由については次のように考えられる。
【００１６】
すなわち、鋼中にＳｉ，Ｍｎ，Ｃｒ等の元素が含まれていると、高温還元雰囲気中における表面濃化によって不めっき等のめっき外観劣化が通常発生するが、このＳｉ，Ｍｎ，Ｃｒなどの原板表面への拡散はプレめっきを施した原板においても起こり、また還元焼鈍が高温で長時間になるとプレめっき層中への拡散も起こる。しかし、プレめっき層が存在するとこれがバリアーとなってＳｉ，Ｍｎ，Ｃｒなどが最表面に達することはない。このため最表面での選択酸化による濃化は発生せず、不めっき等のめっき外観の劣化は抑制できるものと考えられる。
【００１７】
プレめっきの付着量を０．２〜３．０ｇ／ｍ２とする必要があるのは、付着量が０．２ｇ／ｍ２未満ではめっき外観の改善効果が小さく、他方プレめっきの付着量が３．０ｇ／ｍ２を超えると合金化速度が遅くなって生産性が低下するのみならず、溶融めっき後のめっき外観が白っぽく、表面粗度が著しく大きくなるからである。プレめっきの好ましい付着量は、０．５〜２．０ｇ／ｍ２である。
【００１８】
プレめっき層の成分はＮｉおよびＣｏの少なくとも１つである必要がある。Ｎｉ、Ｃｏによるめっきによって、めっき反応の活性点が均一に分布するようになり、合金化反応が均一に進みやすくなるからである。なおＺｎなどの不純物元素が不可避的成分として含有されていても何ら問題はない。
【００１９】
また請求項２の製造方法では、Ｎｉ−Ｃｏによるプレめっきを請求項１の製造方法にさらに付加するものであるから、従来法のようにプレ焼鈍工程を追加せずとも、良好なめっき外観を得ることができる。
【００２０】
めっき外観は溶融めっき時に決まるものであるため、本発明の製造方法において溶融めっき後に合金化処理をさらに行ってもよい。但しプレめっきを行ったときは合金化処理をする必要がない。合金化処理の方法に関しては特に限定はなく、溶融めっきライン内の合金化炉あるいはバッチ炉など使用してもよい。
【００２１】
合金化温度については、例えば４００〜８５０℃が適切であり、好ましくは４２０〜７００℃、更に好ましくは５５０〜６５０℃の温度範囲である。合金化温度が４００℃未満では合金化速度が極めて遅く、生産性が劣化するおそれがある。他方８５０℃を超えると合金化が進み過ぎ、めっき層と原板の界面に極めて硬くて脆いΓ相が成長するため、耐パウダリング性が劣化するおそれがある。
【００２２】
本発明で使用する鋼板としては、（ａ）Ｓｉを０．０５％以上かつＭｎを１．５％以上含有する鋼板、または（ｂ）ＭｎおよびＣｒを合計で１．５％以上含有する鋼板であれば特に限定はなく、冷延鋼板および圧延鋼板のいずれであってもよい。
【００２３】
【実施例】
以下、実施例に基づいて本発明を詳細に述べる。ただし、下記実施例は本発明を制限するものではなく、前・後記の趣旨を逸脱しない範囲で変更実施することは本発明の技術的範囲に包含される。
【００２４】
原板として表１に記載の化学成分および板厚からなる未焼鈍冷延鋼板を用い、アルカリ脱脂後、Ｎ２−５％Ｈ２雰囲気にて８００℃×３分の還元焼鈍を行い、Ｚｎ−０．１３％Ａｌ浴にて表１、２のめっき条件に基づき溶融亜鉛めっきを行った（片面付着量約１００ｇ／ｍ２）。
【００２５】
一部の材料については、Ｎｉ−約１５％Ｃｏのプレめっきを電気めっきにて行った後に、上述の還元焼鈍および溶融亜鉛めっきを行った。
【００２６】
また、一部の材料については、溶融亜鉛めっき後に合金化処理を実施した（合金化めっき層中の平均Ｆｅ濃度：７〜１５％）。
【００２７】
得られた溶融亜鉛めっき鋼板および合金化溶融亜鉛めっき鋼板について、下記方法によるめっき外観の調査を行うとともに、合金化溶融亜鉛めっき鋼板については、下記方法による耐パウダリング性を調査し、表１、２に示す結果を得た。
【００２８】
（めっき外観）
めっき外観について、めっき面積１００×１００ｍｍあたりの不めっき数を目視により測定し下記基準で判定した。
◎：不めっきなし。
○：不めっき３個以内。
△：不めっき４〜１０個。
×：不めっき１１個以上あり。
【００２９】
（耐パウダリング性）
耐パウダリング性については、曲げ角６０°、曲げ半径１ｍｍのＶ型パンチおよびダイスを用いて曲げ試験を行い、曲げ内側のめっき剥離部をテープ剥離し、下記基準で目視にて評価した。
◎：めっき剥離幅が５ｍｍ未満
○：めっき剥離幅が５ｍｍ以上１０ｍｍ未満
△：めっき剥離幅が１０ｍｍ以上１５ｍｍ未満
×：めっき剥離幅が１５ｍｍ以上
（生産性）
生産性を下記基準で評価した。
◎：合金化時間が２分未満、または合金化しない
○：合金化時間が２分以上
【００３０】
【表１】
【表２】
浴温が低いＮｏ.１および侵入板温が低いＮｏ.２では、いずれも得られた鋼板のめっき外観がやや劣る。侵入板温が高いＮｏ．５および侵入板温がやや高いＮｏ．６では、いずれも得られた鋼板のめっき外観が劣る。また比較例であるＮｏ．１０では、侵入板温が低いために得られた鋼板のめっき外観が劣る。侵入板温が高いＮｏ．１１および侵入板温がやや高いＮｏ．１２では、得られた鋼板のめっき外観が劣る。侵入板温が低いＮｏ．１６では、得られた鋼板のめっき外観が劣る。侵入板温が高いＮｏ．２０では、得られた鋼板のめっき外観が劣る。侵入板温がやや低いＮo.２５では、得られた鋼板のめっきがやや劣る。
【００３３】
一方実施例であるＮｏ．７〜９ではめっき条件が適正であるため、Ｍｎ、Ｃｒを含んでいても不めっきがほとんどなく、めっき外観に優れる溶融亜鉛めっき鋼板が得られた。また生産性も良好であった。
【００３４】
めっき処理後合金化処理を行った実施例であるＮｏ．３，４，１３〜１５では、めっき条件が適正であるため、Ｓｉを含んでいても不めっきがほとんどなくめっき外観に優れ、且つ耐パウダリング性に優れた合金化溶融亜鉛めっき鋼板が得られた。また生産性も良好であった。
【００３５】
プレめっきを行った実施例であるＮｏ．１８，１９では、めっき条件およびめっき方法が適正であるため、Ｓｉを多量に含んでいても不めっきがほとんどなくめっき外観に優れた溶融亜鉛めっき鋼板が得られた。また生産性も良好であった。
【００３６】
めっき処理後合金化処理を行った実施例であるＮｏ．２２、２４ではめっき条件が適正であるため、Ｓｉを多量に含んでいても不めっきがほとんどなく、めっき外観に優れ、且つ耐パウダリング性に優れた合金化溶融亜鉛めっき鋼板が得られ、生産性も良好であった。
【００３７】
プレめっきを行った実施例であるＮｏ．２６〜２９では、めっき条件およびめっき方法が適正であるため、Ｓｉを多量に含んでいても不めっきがほとんどなくめっき外観に優れた溶融亜鉛めっき鋼板が得られ、生産性も良好であった。
【００３８】
プレめっきを行い、めっき後合金化処理を行った実施例であるＮｏ．３０では、めっき条件およびめっき方法が適正であるため、Ｓｉを多量に含んでいても不めっきがなくめっき外観に優れ、且つ耐パウダリング性に優れた合金化溶融亜鉛めっき鋼板が得られた。また生産性も良好であった。
【００３９】
【発明の効果】
本発明の製造方法によれば、原板がめっき濡れ性を阻害する元素を多量に含む高強度鋼板であっても、めっき外観に優れた溶融亜鉛めっき鋼板を製造することができる。これによって自動車用部品を初め高強度および耐食性を必要とする部品用の鋼板が効率的に生産することができる。
【００４０】
【図面の簡単な説明】
【００４１】
【図１】めっき外観に及ぼす板厚とめっき浴への侵入板温の関係を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a high-strength hot-dip galvanized steel sheet used in a wide range of fields, such as building materials and home appliances, mainly for automobile parts, and particularly to a method for manufacturing a high-strength hot-dip galvanized steel sheet having excellent plating appearance. .
[0002]
[Prior art]
2. Description of the Related Art In recent years, zinc-based plated steel sheets are widely used in a wide range of fields, such as automobile parts, building materials and home electric parts. Among these galvanized steel sheets, hot-dip galvanized steel sheets are particularly used in a large amount because of their excellent corrosion resistance, weldability, activity prevention and economic efficiency after coating.
[0003]
In recent years, environmental issues have become increasingly important, and automakers are investigating whether high-strength hot-dip galvanized steel sheets can be used for various parts in order to further improve fuel efficiency by reducing vehicle weight. are doing.
[0004]
Incidentally, in order to manufacture a high-strength galvanized steel sheet, it is necessary to add a reinforcing element such as Si, Mn, or Cr. However, all of these elements are extremely susceptible to oxidation, and are known to be selectively oxidized and concentrated on the surface of the original sheet in a reducing atmosphere in a normal hot-dip plating line, thereby significantly deteriorating the plating wettability. ing.
[0005]
As a countermeasure, for example, Japanese Patent Application Laid-Open Nos. 6-81096 and 6-172953 propose an oxidation-reduction method. Japanese Patent Application Laid-Open No. 5-132747 proposes a surface grinding method. Further, Japanese Patent Application Laid-Open No. 4-333552 proposes a pre-plating method.
[0006]
However, in the oxidation-reduction method, since it is difficult to appropriately control the amount of the cured film in the oxidation zone and the reduction amount in the reduction zone, it is extremely difficult to implement the method on an actual production line. Further, in the surface grinding method, re-concentration occurs due to reduction annealing after the surface grinding, so that it is not possible to completely remove factors of plating appearance deterioration such as non-plating. Although the pre-plating method is considered to be the most effective and relatively simple method for improving the plating appearance, the effect is reduced by performing high-temperature annealing after the pre-plating. It was necessary to perform pre-plating after securing the temperature, and then maintain a relatively low temperature until hot-dip plating. That is, an increase in manufacturing cost due to the addition of the pre-annealing step was inevitable.
[0007]
[Problems to be solved by the invention]
The present invention has been made in view of the conventional problems, and an object of the present invention is to provide a method for producing a high-strength hot-dip galvanized steel sheet having excellent plating appearance using a high-strength steel sheet as an original sheet. .
[0008]
[Means for Solving the Problems]
According to the present invention, ( a ) a steel sheet containing 0.05% or more of Si and 1.5% or more of Mn in steel, or ( b ) a steel sheet containing 1.5% or more of Mn and Cr in total. Immersed in a hot-dip galvanizing bath having a bath temperature of 440 ° C. or higher and containing 0.05 to 0.5% of Al at a penetration plate temperature T (° C.) satisfying the following inequalities (1) and (2). A method for producing a high-strength hot-dip galvanized steel sheet having excellent plating appearance characterized by performing plating is provided.
[0009]
350 + 30 / t ≦ T (° C.) <420 + 30 / t (1)
(Where t: plate thickness (mm))
T (° C.) ≦ 460 (2)
Further, according to the present invention, a high-strength hot-dip galvanized steel sheet in which at least one element of Ni and Co is pre-plated with 0.2 to 3.0 g / m 2 on the surface of the steel sheet before hot-dip galvanizing in the manufacturing method. Is provided.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The present inventors have intensively studied whether or not a steel sheet having high strength by adding Si, Mn, and Cr can be obtained by improving plating wettability and obtaining excellent plating appearance. The present inventors have obtained a new finding that a steel sheet having high strength and excellent plating appearance can be obtained by optimizing the method and the method, and have led to the present invention.
[0011]
First, as an original sheet used in the production method of the present invention, ( a ) a steel sheet containing 0.05% or more of Si and 1.5% or more of Mn in steel, or ( b ) Mn and Cr in total of 1.%. A steel sheet containing 5% or more is used. Si is an element effective for increasing the strength without deteriorating the elongation of the steel, and 0.05% or more is required to exhibit the effect. Further, Mn and Cr are both effective elements for increasing the strength of steel, and in order to exhibit the effect, it is necessary to add Mn and Cr in a total amount of 1.5% or more. . Note that a preferable upper limit of the addition amount is 3.0%.
[0012]
One of the major features of the present invention is that the bath temperature of the plating bath is 440 ° C. or higher and Al is contained at 0.05 to 0.5%. In order to perform plating by immersing the original plate in a plating bath for about 2 seconds to improve the plating appearance, it is necessary to accelerate the reaction of Zn, Al, and Fe in the bath to some extent. Therefore, the bath temperature needs to be 440 ° C. or higher, more preferably 450 ° C. or higher. The upper limit of the bath temperature is not particularly limited. However, in consideration of adhesion of zinc oxide to the inside of the furnace due to evaporation of Zn in the bath, increase in dross in the bath, energy cost, and the like, the temperature is preferably 510 ° C or lower, more preferably 480 ° C or lower. is there.
[0013]
On the other hand, when the Al content in the plating bath is less than 0.05%, alloying proceeds excessively, and the plating adhesion of the alloy layer and the red rust resistance of the processed portion deteriorate. On the other hand, when the Al content is more than 0.5%, non-plating and alloy unevenness are likely to occur.
[0014]
Another major feature of the present invention is that plating is performed by immersion at an infiltration plate temperature that satisfies the inequalities (1) and (2). The present inventors performed plating by changing the sheet thickness of the original sheet and the intruding sheet temperature in various ways, and as a result of earnestly examining the relationship, as a result, they found that the optimum intruding sheet temperature changes depending on the sheet thickness of the original sheet. is there. FIG. 1 is a diagram showing the quality of plating performed by changing the penetration plate temperature for each plate thickness, with the vertical axis representing the penetration plate temperature (° C.) and the horizontal axis representing the plate thickness (mm). According to this figure, it can be seen that as the plate thickness increases, the intruded plate temperature region for obtaining good plating moves to the lower temperature side as a whole. From this figure, assuming that the plate thickness is t (mm), the penetration plate temperature T (° C.) is in the range of 350 + 30 / t to 420 + 30 / t and 460 ° C. or less. It is not clear at this time why non-plating occurs when the penetration plate temperature deviates from the upper and lower limits, and the plating appearance deteriorates.However, due to the balance between bath temperature and penetration plate temperature, the original plate is immersed in the plating bath. It is speculated that the reaction amount of Fe, Zn, and Al at the plating layer / original plate interface during the heating may change.
[0015]
Next, a manufacturing method according to the second aspect of the present invention will be described. In the manufacturing method according to
[0016]
That is, when elements such as Si, Mn, and Cr are contained in steel, plating appearance deterioration such as non-plating usually occurs due to surface concentration in a high-temperature reducing atmosphere. Diffusion to the original plate surface also occurs in the preplated original plate, and when the reduction annealing is performed at a high temperature for a long time, diffusion into the preplated layer also occurs. However, if a pre-plated layer is present, it acts as a barrier and Si, Mn, Cr, etc., do not reach the outermost surface. For this reason, it is considered that concentration does not occur due to selective oxidation on the outermost surface, and deterioration of plating appearance such as non-plating can be suppressed.
[0017]
You need to the adhesion amount of the pre-plated with 0.2 to 3.0 g / m 2, the adhesion amount is small effect of improving the coating appearance is less than 0.2 g / m 2, the adhesion amount of the other preplating If it exceeds 3.0 g / m 2 , not only the alloying speed becomes slow and the productivity is lowered, but also the plating appearance after hot-dip plating becomes whitish and the surface roughness becomes extremely large. The preferable amount of the pre-plated coating is 0.5 to 2.0 g / m 2 .
[0018]
The component of the pre-plating layer needs to be at least one of Ni and Co. This is because, by plating with Ni and Co, the active points of the plating reaction are distributed uniformly, and the alloying reaction easily proceeds uniformly. There is no problem even if an impurity element such as Zn is contained as an unavoidable component.
[0019]
Further, in the manufacturing method of the second aspect, the pre-plating by Ni-Co is further added to the manufacturing method of the first aspect, so that a good plating appearance can be obtained without adding a pre-annealing step as in the conventional method. Obtainable.
[0020]
Since the plating appearance is determined during hot-dip plating, an alloying treatment may be further performed after hot-dip plating in the production method of the present invention. However, when pre-plating is performed, there is no need to perform alloying treatment. There is no particular limitation on the method of the alloying treatment, and an alloying furnace or a batch furnace in a hot-dip plating line may be used.
[0021]
An appropriate alloying temperature is, for example, 400 to 850 ° C, preferably 420 to 700 ° C, and more preferably 550 to 650 ° C. When the alloying temperature is lower than 400 ° C., the alloying speed is extremely slow, and there is a possibility that the productivity may be deteriorated. On the other hand, if the temperature exceeds 850 ° C., alloying proceeds excessively, and an extremely hard and brittle Γ phase grows at the interface between the plating layer and the original sheet, so that the powdering resistance may be deteriorated.
[0022]
Examples of the steel sheet used in the present invention include ( a ) a steel sheet containing 0.05% or more of Si and 1.5% or more of Mn, or ( b ) a steel sheet containing 1.5% or more of Mn and Cr in total. There is no particular limitation so long as it is a cold-rolled steel sheet or a rolled steel sheet.
[0023]
【Example】
Hereinafter, the present invention will be described in detail based on examples. However, the following embodiments do not limit the present invention, and modifications and implementations without departing from the spirit of the preceding and the following are included in the technical scope of the present invention.
[0024]
An unannealed cold-rolled steel sheet having the chemical composition and sheet thickness shown in Table 1 was used as an original sheet. After alkali degreasing, reduction annealing was performed at 800 ° C. for 3 minutes in an N 2 -5% H 2 atmosphere to obtain Zn-0. Hot-dip galvanizing was performed in a .13% Al bath under the plating conditions shown in Tables 1 and 2 (adhesion amount per side: about 100 g / m 2 ).
[0025]
For some materials, the above-described reduction annealing and hot-dip galvanizing were performed after pre-plating Ni-about 15% Co by electroplating.
[0026]
For some materials, alloying treatment was performed after hot-dip galvanizing (average Fe concentration in the alloyed plating layer: 7 to 15%).
[0027]
Regarding the obtained hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet, the plating appearance was examined by the following method, and for the alloyed hot-dip galvanized steel sheet, the powdering resistance was examined by the following method. The results shown in FIG.
[0028]
(Plating appearance)
Regarding the plating appearance, the number of non-platings per plating area of 100 × 100 mm was visually measured and judged according to the following criteria.
◎: no plating.
：: Less than 3 unplated.
Δ: Unplated 4 to 10 pieces.
X: 11 or more non-platings are present.
[0029]
(Powdering resistance)
The powdering resistance was evaluated by performing a bending test using a V-shaped punch and a die having a bending angle of 60 ° and a bending radius of 1 mm.
：: Plating peel width is less than 5 mm ○: Plating peel width is 5 mm or more and less than 10 mm △: Plating peel width is 10 mm or more and less than 15 mm ×: Plating peel width is 15 mm or more (productivity)
The productivity was evaluated according to the following criteria.
：: alloying time is less than 2 minutes or not alloyed ○: alloying time is 2 minutes or more
[Table 1]
[Table 2]
In No. 1 having a low bath temperature and No. 2 having a low intruding plate temperature, the plating appearance of the obtained steel sheet was slightly inferior. No. No. 5 and No. 5 in which the penetration plate temperature was slightly higher. In No. 6, the plating appearance of the obtained steel sheet was inferior. In addition, in Comparative Example No. In No. 10, the plating appearance of the obtained steel plate is inferior due to the low penetration plate temperature. No. No. 11 and No. 11 in which the penetration plate temperature was slightly higher. In No. 12, the plating appearance of the obtained steel sheet is inferior. No. In No. 16, the plating appearance of the obtained steel sheet is inferior. No. In No. 20, the plating appearance of the obtained steel sheet is inferior . In the case of No. 25 having a slightly lower intrusion plate temperature, plating of the obtained steel plate is slightly inferior.
[0033]
On the other hand, in Example No. In Nos. 7 to 9, since the plating conditions were appropriate, a hot-dip galvanized steel sheet having excellent plating appearance with almost no non-plating even when containing Mn and Cr was obtained. The productivity was also good.
[0034]
In Example No. 1 in which alloying treatment was performed after plating treatment. In 3,4,13-15, since the plating conditions are appropriate, an alloyed hot-dip galvanized steel sheet having excellent plating appearance and excellent powdering resistance with little non-plating even if containing Si can be obtained. Was. The productivity was also good.
[0035]
In Example No. in which pre-plating was performed. In Nos. 18 and 19, since the plating conditions and the plating method were appropriate, a hot-dip galvanized steel sheet excellent in plating appearance with almost no non-plating even if containing a large amount of Si was obtained. The productivity was also good.
[0036]
In Example No. 1 in which alloying treatment was performed after plating treatment. The plating conditions of 22 and 24 are appropriate, so that even if a large amount of Si is contained, there is almost no non-plating, and an alloyed hot-dip galvanized steel sheet having excellent plating appearance and excellent powdering resistance can be obtained and produced. The properties were also good.
[0037]
In Example No. in which pre-plating was performed. In Nos. 26 to 29, since the plating conditions and the plating method were appropriate, a hot-dip galvanized steel sheet excellent in plating appearance with almost no non-plating even if containing a large amount of Si was obtained, and the productivity was good.
[0038]
In Example No. 1 in which pre-plating was performed and alloying treatment was performed after plating. In No. 30 , since the plating conditions and the plating method were appropriate, an alloyed hot-dip galvanized steel sheet having excellent plating appearance and excellent powdering resistance was obtained without non-plating even if a large amount of Si was contained. The productivity was also good.
[0039]
【The invention's effect】
According to the production method of the present invention, a hot-dip galvanized steel sheet excellent in plating appearance can be produced even if the original sheet is a high-strength steel sheet containing a large amount of elements that inhibit plating wettability. As a result, it is possible to efficiently produce steel sheets for parts requiring high strength and corrosion resistance, such as automobile parts.
[0040]
[Brief description of the drawings]
[0041]
FIG. 1 is a diagram showing the relationship between the thickness of a sheet and the temperature of a sheet entering a plating bath, which affects the plating appearance.
Claims (2)
（ｂ）ＭｎおよびＣｒを合計で１．５％以上含有する鋼板を、
浴温が４４０℃以上で且つＡｌを０．０５〜０．５％含有する溶融亜鉛めっき浴に、下記不等式（１）および（２）を満足する侵入板温Ｔ（℃）で浸漬してめっきを行うことを特徴とするめっき外観に優れた高強度溶融亜鉛めっき鋼板の製造方法。
３５０＋３０／ｔ≦Ｔ（℃）＜４２０＋３０／ｔ ・・・（１）
（式中、ｔ：板厚（ｍｍ））
Ｔ（℃）≦４６０ ・・・・・・（２） (A) Si: 0.05% ( % is wt%, the same applies hereinafter) or more and Mn: steel containing 1.5% or more, or,
( B ) a steel sheet containing 1.5% or more of Mn and Cr in total;
Plating by dipping in a hot-dip galvanizing bath having a bath temperature of 440 ° C. or more and containing 0.05 to 0.5% of Al at a penetration plate temperature T (° C.) satisfying the following inequalities (1) and (2): A method for producing a high-strength hot-dip galvanized steel sheet having excellent plating appearance.
350 + 30 / t ≦ T (° C.) <420 + 30 / t (1)
(Where t: plate thickness (mm))
T (° C.) ≦ 460 (2)
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