JP2004353022A

JP2004353022A - Hot-dip Zn-Al alloy-plated steel material and method for producing the same

Info

Publication number: JP2004353022A
Application number: JP2003150516A
Authority: JP
Inventors: Shintaro Yamanaka; 晋太郎山中; Masahiro Yamamoto; 正弘山本
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2003-05-28
Filing date: 2003-05-28
Publication date: 2004-12-16
Anticipated expiration: 2023-05-28
Also published as: JP3728298B2

Abstract

【課題】フラックス法による均一で高付着量かつ高耐食性の溶融Ｚｎ−Ａｌ系合金めっき鋼材及びその製造方法を提供する。
【解決手段】Ａｌ：０．１〜１５質量％を含み、残部がＺｎ及び不可避的不純物からなる溶融Ｚｎ−Ａｌ系合金めっき鋼材において、前記溶融Ｚｎ−Ａｌ系合金めっき層がＭｎ：０．０５〜１質量％、及び、Ｍｇ：０．１〜１５質量％を含み、そのめっき付着量が３００ｇ／ｍ^２〜１０００ｇ／ｍ^２であることを特徴とする溶融Ｚｎ−Ａｌ系合金めっき鋼材、及びその製造方法である。
【選択図】なしThe present invention provides a hot-dip Zn-Al-based alloy-plated steel material having a uniform, high adhesion amount and high corrosion resistance by a flux method, and a method for producing the same.
In a hot-dip Zn-Al-based alloy-plated steel material containing 0.1 to 15% by mass of Al and the balance being Zn and unavoidable impurities, the molten Zn-Al-based alloy-plated layer has an Mn: 0.05 to 1 wt%, and, Mg: 0.1 to 15 includes a mass%, the melting Zn-Al alloy coated steel material, characterized in that the coating weight is ^{^{300g / m 2 ~1000g / m 2}} , and The manufacturing method.
[Selection diagram] None

Description

【０００１】
【発明の属する技術分野】
本発明は、フラックス法による均一で高付着量かつ高耐食性の溶融Ｚｎ−Ａｌ系合金めっき鋼材及びその製造方法に関する。
【０００２】
【従来の技術】
従来から、送電鉄塔、橋梁、道路用資材、建築金物、建築・土木用材料等の分野においては、経済性、耐久性、作業性等の観点から溶融Ｚｎめっき鋼材が多く用いられている。また、最近ではＺｎめっきよりも耐食性に優れるとのことからＺｎ−Ａｌ合金めっきも使われつつある。これらＺｎめっきやＺｎ−Ａｌ合金めっきにおいては、通常、めっきの付着量とその耐食性は比例関係にあり、めっきが厚いほど地鉄の露出に至るまでに長時間を要すため、耐食性は向上する。すなわち、Ｚｎ−Ａｌ合金めっきの耐食性がＺｎめっきの２倍あったとしても、Ｚｎ−Ａｌ合金めっきの付着量がＺｎめっきの半分しかない場合、その耐食性は同等となる。
【０００３】
めっき付着量に影響を及ぼす因子としては、めっき浴の粘度や濡れ付着力、めっき時間、めっき温度、めっき浴からの素材の引き上げ速度、めっきのワイピング（たれきり）等が挙げられるが、これらの内、めっき浴の粘度や濡れ付着力の影響はそれほど大きくはない。また、めっき浴からの素材の引き上げ速度については、薄鋼板のめっきのような連続式においては、引き上げ速度の変更は容易であるが、フラックス式めっきのようなバッチ式のめっきにおいては、引き上げ速度の変更は難しい。めっきのワイピングについては、加工済の鋼材や溶接をした鋼材、また小物等の複雑な形状の素材をめっきする場合が多いフラックス式のめっきにおいては、均一なめっき付着量を得ることは難しく、そもそもワイピングはめっきの付着量を減少させる方向に作用するため、均一で高付着量のめっきを得るには不向きである。
【０００４】
これらの理由のため、フラックス式めっきにおいては、めっき時間とめっき浴の温度によって、めっきの付着量を制御する場合が多い。めっき時間とめっき浴の温度は、地鉄とめっきの界面に生成するＦｅ−Ｚｎ系合金層の厚みに特に大きな影響を与え、めっき時間が長いか、めっき温度が高いと合金層は厚くなり、結果としてめっきの付着量は大きくなる。ところで、この合金層の厚みは、めっき浴の組成によっても大きく異なる。例えば、浴中のＡｌ量が０．０２質量％以下であるようなＺｎめっきにおいては、めっき時間を長くするか、めっき温度を高くすることで、Ｆｅ−Ｚｎ系合金層は成長し、６００ｇ／ｍ^２程度の厚いめっきも可能である。
【０００５】
ところが、Ａｌを０．１質量％以上含むようなＺｎ−Ａｌめっき浴では、Ｆｅ−Ａｌ系合金層が初期に生成し、これがＦｅ−Ｚｎ系合金層の成長を妨げるために、めっき付着量が大きくなりにくい。このＦｅ−Ａｌ系合金層は非常に安定で、例えば５３０℃程度までめっき温度を高くしても安定で、Ｆｅ−Ｚｎ系合金層の成長を抑制するため、めっき付着量は大きくならない。比較的高濃度のＡｌを含むめっき浴の場合、例えば、質量％で、１０％以上Ａｌを含むめっき浴の場合は、めっき浴温度を高くすることで、Ｆｅ−Ａｌ系合金層自体が成長するため、めっき付着量は大きくなる。しかし、めっきが不均一、つまり、局所的に厚くなり、外観が不良となるため、製品として適さない。
【０００６】
また、めっき時間を長くしたとしても、Ｆｅ−Ｚｎ系合金層は成長しにくい。かなり長い時間、例えば、１時間程度めっき浴に浸漬したときは、めっき付着量が大きくなる場合もあるが、やはり不均一なめっきで、外観が不良となるため、製品として適さない。このように、高付着量で均一なＺｎ−Ａｌ合金めっきを得ることは困難で、これまでに十分に検討されてはいない。これまでに知られている高付着量のＺｎ−Ａｌ系合金めっきを得る方法としては次のようなものがある。例えば、通常のＡｌをほとんど含まない純Ｚｎめっきを行い、Ｆｅ−Ｚｎ系合金層を成長させた後に、Ｚｎ−Ａｌ系合金めっきを行うという２段めっき処理が一部で採用されている。しかしながら、この方法では、めっき浴を２槽有する必要があること、また、２回のめっき操作による作業時間の増加や維持管理費、設置場所の増加といった種々の欠点がある。
【０００７】
特開平５−１０６００２号公報（特許文献１）では、Ｚｎ−Ａｌ合金めっき浴中に１．５〜１０質量％の銅を添加することで、比較的厚いＺｎ−Ａｌ合金めっきが得られる方法が提案されている。しかし、この方法では、めっき浴の組成が変動しやすく、めっき品質にばらつきが出ることが懸念される。また、特開平９−２５１３４号公報（特許文献２）では、鋼材を所定のフラックス処理した後に、Ａｌ濃度１０〜２０質量％からなるＺｎめっき浴に、めっき温度４３０〜５２０℃、めっき時間０．５〜１０分の条件でめっきすることで、めっき厚み（めっき付着量）４５０ｇ／ｍ^２以上の厚めっきが得られるとされている。ところが、この方法では、Ａｌ濃度が１０質量％以下のめっき浴の場合には適用できず、また、特殊なフラックスを使用する必要があるため、汎用性がない。
【０００８】
特開平１１−３５００９５号公報（特許文献３）では、所定のフラックス処理をした後に、溶融フラックス層を有するＺｎ−Ａｌめっき浴に浸漬することで、高付着量のめっきが得られるとされている。ところが、この方法においても、Ａｌ含有量が３０〜７０質量％であるめっき浴を主対象としていることのほか、特殊なフラックスを使用しており、汎用性がないこと、また、溶融フラックス層を必要とし、その劣化に対する交換、補充に対する作業に労力を要すること、また、フラックス中に弗化物を含んでいるため作業環境の悪化が懸念されること等、種々の問題点がある。
【０００９】
さらに、特開平８−２８３９２５号公報（特許文献４）では、鋼材の表面粗度を一定の範囲内とし、さらに、めっき浴中に一定の鉄分成分を含ませることによって、高付着量で均一なＺｎ−Ａｌ−Ｓｉめっきを得られるとされている。しかしながら、この方法は、Ａｌ−Ｓｉめっきを対象としており、めっき浴温が５８０℃以上と高いため、Ｚｎを主体とするめっきの場合には不適である。
【００１０】
一方、特開平５−１１７８３０号公報（特許文献５）には、その付着量は明言されてはいないが、溶融Ｚｎ−Ａｌめっき浴に特定量のＭｎを添加することで、不めっきを防止し、かつ表面にざらつきのない溶融Ｚｎ合金めっきが得られると記載されている。しかしながら、この方法では不めっきのないのめっきを得ることは可能であるが、Ｍｎはめっきの耐食性を低下させる傾向にあるため、腐食環境の厳しい場所や長期耐久性を必要とされる場合には、適当でない。
以上のように、高付着量のＺｎ−Ａｌ合金めっきを得る方法として、数種の方法が見出されているものの、作業性や作業環境、品質、また、耐久性といった面で問題点がある。また、高付着量のめっきができたとしても、安定的に均一な合金めっきを得ることは難しい。
【００１１】
【引用文献】
（１）特許文献１（特開平５−１０６００２号公報）
（２）特許文献２（特開平９−２５１３４号公報）
（３）特許文献３（特開平１１−３５００９５号公報）
（４）特許文献４（特開平８−２８３９２５号公報）
（５）特許文献５（特開平５−１１７８３０号公報）
【００１２】
【発明が解決しようとする課題】
本発明は、このようなＺｎ−Ａｌ合金めっきにおける従来の諸問題を解決し、フラックス法による、均一で高付着量かつ高耐食性の溶融Ｚｎ−Ａｌ系合金めっき鋼材及びその製造方法を提供することを目的とする。
【００１３】
【課題を解決するための手段】
本発明者らは、上記の従来の技術が抱える問題点を解決し、種々の組成のＺｎ−Ａｌ系合金めっきについて、均一で高付着量かつ高耐食性のめっきを安定的に得る方法について鋭意検討を重ねた結果、めっき層中にＭｎ及びＭｇを複合添加することで、均一で高付着量かつ高耐食性の溶融Ｚｎ−Ａｌ系合金めっき鋼材を実現できることが分かり、本発明に至った。
【００１４】
すなわち、本発明は以下の内容を要旨とする。
（１）Ａｌ：０．１〜１５質量％を含み、残部がＺｎ及び不可避的不純物からなる溶融Ｚｎ−Ａｌ系合金めっき鋼材において、前記溶融Ｚｎ−Ａｌ系合金めっき層がＭｎ：０．０５〜１質量％、及び、Ｍｇ：０．１〜１５質量％を含み、そのめっき付着量が３００ｇ／ｍ^２〜１０００ｇ／ｍ^２であることを特徴とする溶融Ｚｎ−Ａｌ系合金めっき鋼材。
（２）前記溶融Ｚｎ−Ａｌ系合金めっき層が、さらに、Ｓｉ：０．０５〜０．２質量％含有することを特徴とする（１）に記載の溶融Ｚｎ−Ａｌ系合金めっき鋼材。
【００１５】
（３）フラックス処理をした鋼材を溶融Ｚｎ−Ａｌ系合金めっき浴に浸漬して溶融Ｚｎ−Ａｌ系合金めっき鋼材を製造する方法であって、前記溶融Ｚｎ−Ａｌ系合金めっき浴が、Ａｌ：０．１〜１５質量％、Ｍｎ：０．０５〜１質量％、及びＭｇ：０．１〜１５質量％を含有し、残部がＺｎ及び不可避的不純物からなり、該めっき浴温が４３０〜５５０℃であることを特徴とする溶融Ｚｎ−Ａｌ系合金めっき鋼材の製造方法。
（４）前記溶融Ｚｎ−Ａｌ系合金めっき浴が、さらに、Ｓｉ：０．０５〜０．２質量％含有することを特徴とする（３）に記載の溶融Ｚｎ−Ａｌ系合金めっき鋼材の製造方法にある。
【００１６】
【発明の実施の形態】
以下、本発明を詳細に説明する。
まず、本発明における鋼材のめっき層中の成分について説明する。
本発明において、めっき層中のＭｎは、Ｚｎ−Ａｌ系合金めっきの付着量を大きくし、また、めっきを均一にさせる効果があり、０．０５〜１質量％の範囲とする必要がある。Ｍｎが０．０５質量％未満ではその効果が不十分で、めっき付着量が３００ｇ／ｍ^２未満の薄く不均一なめっきとなる。逆に、１質量％を超えると、めっき層と鋼材の密着性が低下するほか、耐食性が低下する傾向にあり、さらに、多量のドロスを形成し、めっき作業に問題を生じる。好ましいＭｎの範囲は０．１〜０．５質量％、より好ましくは０．２〜０．４質量％の範囲である。
【００１７】
Ｍｇは、Ｍｎと複合添加することで、Ｚｎ−Ａｌ系合金めっき層の耐食性を低下させずに、めっき付着量を大きくさせる効果があり、０．１〜１５質量％の範囲とする必要がある。その機構については明言をし得ないが、０．１質量％未満では耐食性を向上させる効果に乏しく、１５質量％を超えると耐食性は向上するものの、めっき層が脆くなり、加工性が低下するからである。そのため、本発明におけるＭｇの範囲を０．１〜１５質量％とする。好ましい範囲は、０．５〜３質量％である。
【００１８】
Ａｌは、めっき層の耐食性を向上させる効果がある。本発明においては、めっき層中のＡｌの範囲を０．１〜１５質量％としているが、その理由は次の通りである。Ａｌが０．１質量％未満では、耐食性を向上させる効果に乏しい。また、Ａｌが０．１質量％未満では、めっき層と地鉄界面に生成する合金層はＦｅ−Ｚｎ系合金が主体であり、Ａｌが０．０５質量％を超すと、めっき層と地鉄界面に生成する合金層は非成長型のＦｅ−Ａｌ系合金層が主体である。
【００１９】
本発明においては、Ｍｎ及びＭｇによってＦｅ−Ａｌ系合金層の制御を行っているために、その下限値を０．１質量％とした。Ａｌが１５質量％を超えた場合においても、Ｍｎ及びＭｇによるＦｅ−Ａｌ系合金層の制御の効果は認められるが、外観が粗悪となる他、Ｍｎ及びＭｇの多量添加が必要となり、加工性が低下すること等の問題が生じるため、その上限値を１５質量％とした。上記の問題を解決すれば、１５質量％を超えるＡｌを含有する溶融Ｚｎ−Ａｌ系合金めっきにおいても、本発明を応用することは可能である。好ましいＡｌの範囲は、０．２〜１２質量％である。
【００２０】
本発明のめっきには、さらにＳｉを含ませることができる。Ｓｉは、めっきの耐食性及び加工性をさらに向上させる作用がある。この作用を効果的に得るには、本発明におけるＳｉの範囲を０．０５〜０．２質量％の範囲とすることが好ましい。本発明のめっき付着量は３００ｇ／ｍ^２〜１０００ｇ／ｍ^２であることが必要である。３００ｇ／ｍ^２未満では耐食性に劣る。１０００ｇ／ｍ^２より大きい場合は、めっきと鋼材の密着性が低下するため不適である。
【００２１】
本発明における被めっき材である鋼材の種類は限定されない。普通鋼、低合金鋼、高合金鋼、鋳物等、その鋼成分には限定されるものではなく、また、その形状についても、板、鋼管、形鋼、線材や、溶接やボルト等で接合した組み合わせ鋼材、ボルト、ナット等の小物等、また、鉄塔、橋梁部材等の鋼製部材にも適用でき、めっき浴に浸漬し、めっき処理が可能なものであれば何でも良い。但し、鋼成分によっては、めっき付着量に影響を与えるため、事前にめっき条件を決めておく必要がある。
【００２２】
本発明の鋼材を製造するには、まず鋼材表面を公知の方法で前処理を行う。前処理としては、例えば一般的に行われている塩酸、硫酸等による酸洗のほか、ショットブラスト、グリッドブラスト、サンドブラスト、グラインダー処理等を実施することができる。鋼材の表面が十分に清浄化されれば、これら前処理の処理条件は何ら問わない。例えば、塩酸や硫酸による酸洗の条件としては、水溶液濃度：１０〜２０質量％、浴温：常温〜８０℃、酸洗時間：５〜３０分といった例を挙げることができる。
【００２３】
次いで、フラックス処理をする。ここで言うフラックス処理とは、鋼材表面にフラックスを塗布、付着させる処理のことであり、フラックスの成分やその処理方法等については特に限定するものではなく、従来から知られている方法で良い。例えば、フラックス成分としては、塩化亜鉛、塩化アンモニウム、塩化マグネシウム、塩化リチウム、塩化錫、塩化カリウム、塩化カルシウム、塩化鉛、塩化ナトリウム、塩化アンチモン、塩化インジウム、塩化ビスマス、塩化カドミウム等の塩化物や、アルカリ金属、アルカリ土類金属のフッ化物、ケイフッ化物、フッ化水素物等を挙げることができる。
【００２４】
処理方法としては、乾式フラックス、湿式フラックス、溶融フラックス等を挙げることができる。乾式フラックスとは、前記フラックスを水溶液として、鋼材に付着させた後、乾燥し、その後めっき浴に浸漬するものである。湿式フラックスとは、前記フラックスをめっき浴上に浮遊させて、適当な厚みのフラックス層を形成させ、このフラックス層を介して鋼材をめっき浴に浸漬するものである。溶融フラックスとは、前記フラックス自体を溶融させた浴に鋼材を浸漬した後に、めっき浴に浸漬するものである。
【００２５】
フラックス処理した鋼材は、Ａｌ：０．１〜１５質量％、Ｍｎ：０．０５〜１質量％、Ｍｇ：０．１〜１５質量％、残部がＺｎ及び不可避的不純物を含有する浴温４３０〜５５０℃のＺｎ−Ａｌ系合金めっき浴に浸漬する。上記組成のめっき浴に浸漬することで、本発明の、Ａｌ：０．１〜１５質量％、Ｍｎ：０．０５〜１質量％、Ｍｇ：０．１〜１５質量％を含み、残部がＺｎ及び不可避的不純物からなる、めっき付着量が３００ｇ／ｍ^２〜１０００ｇ／ｍ^２の溶融Ｚｎ−Ａｌ系合金めっき鋼材を得ることができる。
【００２６】
めっき浴温を４３０〜５５０℃の範囲に規定した理由は、この範囲外のめっき浴温度では本発明の溶融Ｚｎ−Ａｌ系合金めっき鋼材が得られないばかりか、その他種々の問題を生じるからである。すなわち、めっき浴温が４３０℃未満では、めっき浴の流動性が低下して、不均一で外観が劣悪なめっきとなりやすく、また、めっき付着量が大きくならない。また、５５０℃を超える場合は、めっき浴中に多量のドロスが発生し、操業に困難をきたすだけでなく、このドロスが被めっき材の表面に付着し、外観が不良のめっきとなりやすい。また、めっき付着量が極度に多くなりやすい。さらに、めっき釜の寿命も短くなる。好ましいめっき温度は４５０〜５００℃の範囲である。
【００２７】
被めっき材をめっき浴に浸漬する時間は特に規定しないが、１分以上３０分以内であることが望ましい。この範囲内であれば、本発明の溶融Ｚｎ−Ａｌ系合金めっき鋼材を一層安定的に得ることができる。前記めっき浴には、さらに、Ｓｉ：０．０５〜０．２質量％含ませることができる。めっき浴中に上記範囲のＳｉを含ませることで、均一で高付着量、高耐食性、かつ密着性に優れた溶融Ｚｎ−Ａｌ系合金めっき鋼材を得ることができる。
【００２８】
また、このＺｎ−Ａｌ系合金めっき浴には、例えば、Ｆｅ、Ｐｂ、Ｃｄ、Ｓｎ、Ｃｕ、Ｓｂ、Ｂｉ、Ａｇ、Ｎｉ、Ａｓ等が不可避的不純物として混入していても問題はない。被めっき材をめっき浴へ浸漬する速度は何ら規定するものではない。例えば、鋼管の連続めっきにおけるテーラーウィルソン方式のように、鋼管をめっき浴に落下させるような速い浸漬速度でも良いし、あるいは、鉄塔部材のような大型鋼製部材をめっきする場合のように、クレーンで被めっき材を吊り上げた後、ゆっくりとめっき浴に浸漬させるような遅い浸漬速度でもよい。
【００２９】
被めっき材をめっき浴から取り出す速度も特に規定するものでない。テーラーウィルソン方式のように０．７〜２ｍ／秒程度の高速で取り出しても良いし、あるいはクレーンを用いた場合のように０．２ｍ／秒程度の低速で取り出しても良い。さらにめっき後の外観を良好にさせるため、必要に応じて水冷や湯冷による冷却を行っても良い。
以上の手順、条件で処理することで、均一で高付着量かつ高耐食性の溶融Ｚｎ−Ａｌ系合金めっき鋼材を得ることができる。
【００３０】
【実施例】
以下、本発明を実施例により、さらに詳細に説明する。
（実施例１）
大きさが５０ｍｍ×１００ｍｍ×厚さ２．３ｍｍの黒皮付き普通鋼熱延鋼材を、１５％塩酸中に３０分間浸漬した後、引き上げ、スケール残りがないことを確認した。次いで、乾式フラックス処理を行った。乾式フラックス処理は、ＺｎＣｌ_２：２００ｇ／ｌ、ＮＨ_４Ｃｌ：４０ｇ／ｌからなる液温７０℃のフラックスに鋼材を１０秒間浸漬した後に引き上げ、２００℃に設定した電気オーブンの中で５分間乾燥させる処理とした。その後、表２に示す組成のＺｎ合金めっき浴（Ｚｎ−０．２質量％Ａｌ−０．５質量％Ｍｇめっき浴、又はＺｎ−１０質量％Ａｌ−３質量％Ｍｇめっき浴を基準に、Ｍｎ、Ｓｉを添加）に２分間浸漬し、引き上げ後、湯冷して試験片を作製した。
【００３１】
このようにして得られた試験片のめっき付着量は、めっきを塩酸で溶解し、その前後の質量変化から求めた。また、塩酸溶解によって得られためっき層を溶かし込んだ溶液を用い、ＩＣＰ発光分析でそのめっき組成を分析した。また、その外観を目視観察し、下記基準で評価した。可以上の評点を合格とした。
良：表面が平滑で、めっき欠陥が全く無い。
可：凹凸がやや大きく、めっきやけが若干認められる。
劣：不めっきやピンホール、ドロス付着等が存在、又は、凹凸がやや多く、めっきやけが試験片面積の５０％以上存在する。
なお、ここでいうめっきやけとは合金層がめっき表層まで成長していることである。
【００３２】
また、９０°折り曲げ試験を行い、めっきの密着性を目視観察による下記基準で評価した。可以上の評点を合格とした。
良：加工部にめっき割れが全く無い。
可：加工部に割れが僅かに存在。
劣：割れが加工部全面に存在、又は、加工部のめっきが剥離。
【００３３】
耐食性については、塩水噴霧試験（３５℃、５％ＮａＣｌ）を２０００時間実施した後のめっきの平均腐食減量を求め、下記基準で評価し、可以上の判定であれば合格とした。
優：めっき平均腐食減量率が０．１ｇ／ｍ^２／ｈｒ未満
良：めっき平均腐食減量率が０．１〜０．５ｇ／ｍ^２／ｈｒ
可：めっき平均腐食減量率が０．５〜１．０ｇ／ｍ^２／ｈｒ
劣：めっき平均腐食減量率が１．０ｇ／ｍ^２／ｈｒ超え、又は、めっきが消耗し赤錆が発生
これらの試験結果を表１に示す。
【００３４】
【表１】

【００３５】
Ｎｏ．１〜Ｎｏ．６は、Ｚｎ−０．２質量％Ａｌ−０．５質量％Ｍｇめっき浴を基準に、Ｍｎを０．０５〜０．８質量％含ませた場合である。得られためっき層中の成分は、いずれも本発明の範囲内であり、めっき付着量、外観、密着性、耐食性のいずれも良好である。特に、めっき層がＭｎを０．１〜０．５質量％の範囲で含む場合は、さらにその性能は向上し、Ｍｎを０．３質量％含む場合は、一層その性能は良くなる。Ｎｏ．６は、Ｎｏ．４を基準にめっき層中にＳｉを０．１質量％含ませた場合であり、耐食性が向上することが分かる。Ｎｏ．７〜Ｎｏ．１０は、Ｚｎ−１０質量％Ａｌ−３質量％Ｍｇめっき浴を基準に、Ｍｎを０．１〜０．８質量％含ませた場合である。得られためっき層中の成分は、いずれも本発明の範囲内であり、特にＭｎを０．１〜０．５質量％の範囲で含む場合は、めっき付着量、外観、密着性、耐食性のいずれも良好で、Ｍｎを０．３質量％含む場合はその性能はさらに良い。
【００３６】
（比較例）
大きさが５０ｍｍ×１００ｍｍ×厚さ２．３ｍｍの黒皮付き普通鋼熱延鋼材を、１５％塩酸中に３０分間浸漬した後、引き上げ、スケール残りがないことを確認した。次いで、乾式フラックス処理を行った。乾式フラックス処理は、ＺｎＣｌ_２：２００ｇ／ｌ、ＮＨ_４Ｃｌ：４０ｇ／ｌからなる液温７０℃のフラックスに鋼材を１０秒間浸漬した後に引き上げ、２００℃に設定した電気オーブンの中で５分間乾燥させる処理とした。その後、表２に示す組成のＺｎ系合金めっき浴に２分間浸漬し、引き上げ後、湯冷して試験片を作製した。
このようにして得られた試験片のめっき付着量、外観、めっき密着性、耐食性は、実施例１と同様の方法にて評価し、結果を表２に示した。
【００３７】
【表２】

【００３８】
Ｎｏ．１１は、めっき層中にＡｌ、Ｍｎ、Ｍｇ、Ｓｉのいずれも含まないＺｎめっきをした場合である。耐食性に劣るため不適である。Ｎｏ．１２は、めっき層中にＡｌを０．４質量％含む場合である。めっき付着量が少なく（３００ｇ／ｍ^２未満）、耐食性に劣る（赤錆が発生）ため不適である。Ｎｏ．１３は、めっき層中にＡｌ：０．４質量％、Ｍｎ：０．１質量％を、Ｎｏ．１４はめっき層中にＡｌ：０．４質量％、Ｍｎ：１．０質量％を含む場合である。いずれもめっき付着量は多くなるものの、耐食性に劣る（めっき平均腐食減量が１．０ｇ／ｍ^２／ｈｒ以上）ため不適である。
【００３９】
Ｎｏ．１５は、めっき層中にＡｌ：０．４質量％、Ｍｇ：０．２質量％を、Ｎｏ．１６は、めっき層中にＡｌ：０．４質量％、Ｍｇ：１０質量％を含む場合である。いずれもめっき付着量が少なく（３００ｇ／ｍ^２未満）、耐食性に劣る（赤錆が発生）ため不適である。Ｎｏ．１７は、めっき層中にＡｌ：０．４質量％、Ｍｎ：０．１質量％、Ｍｇ：２０質量％含む場合である。めっき付着量は多く、耐食性も良好であるが、めっきの密着性に劣るため不適である。Ｎｏ．１８は、めっき層中にＡｌ：０．４質量％、Ｍｎ：２．５質量％、Ｍｇ：０．５質量％含む場合である。耐食性は良好であるが、めっき付着量が極度に多く（１０００ｇ／ｍ^２より多い）、密着性に劣るため不適である。
【００４０】
Ｎｏ．１９、Ｎｏ．２０は、それぞれ、めっき層中にＭｎ：０．１質量％、Ｍｇ：０．５質量％を含み、いずれも本発明の範囲内であるが、Ａｌのみが本発明の範囲外である場合、すなわち、Ａｌ：０．０６質量％（Ｎｏ．９）、Ａｌ：２２質量％（Ｎｏ．１０）である場合である。Ａｌが０．０６質量％の場合、めっき付着量が極度に多く（１０００ｇ／ｍ^２より多い）、さらに耐食性に劣るため不適である。また、Ａｌが２２質量％である場合は、めっきの付着量及び耐食性は良好であるが、外観が不均一で劣るため不適である。
【００４１】
（実施例２）
大きさが５０ｍｍ×１００ｍｍ×厚さ２．３ｍｍの黒皮付き普通鋼熱延鋼材を、１５％塩酸中に３０分間浸漬した後、引き上げ、スケール残りがないことを確認した。次いで、乾式フラックス処理を行った。乾式フラックス処理は、ＺｎＣｌ_２：２００ｇ／ｌ、ＮＨ_４Ｃｌ：４０ｇ／ｌからなる液温７０℃のフラックスに鋼材を１０秒間浸漬した後に引き上げ、２００℃に設定した電気オーブンの中で５分間乾燥させる処理とした。その後、表３に示す組成のＺｎ系合金めっき浴（Ｚｎ−０．２質量％Ａｌ−０．３質量％Ｍｎめっき浴を基準に、Ｍｇ、Ｓｉを添加）に２分間浸漬し、引き上げ後、湯冷して試験片を作製した。
このようにして得られた試験片のめっき付着量、外観、めっき密着性、耐食性は、実施例１と同様の方法にて評価し、結果を表３に示した。
【００４２】
【表３】

【００４３】
Ｎｏ．２１、Ｎｏ．２２、は、Ｚｎ−０．２質量％Ａｌ−０．３質量％Ｍｎめっき浴を基準に、Ｍｇを０．１〜０．５質量％含ませた場合である。得られためっき層の組成は、いずれも本発明の範囲内であり、また、めっき付着量、外観、密着性、耐食性のいずれも良好である。特に、めっき層がＭｇを０．５質量％含む場合は、さらにその性能は向上する。Ｎｏ．２３〜２５は、Ｚｎ−１０質量％Ａｌ−０．３質量％Ｍｎめっき浴を基準に、Ｍｇを０．１〜３．０質量％含ませた場合である。得られためっき層の成分は、いずれも本発明の範囲内で、特に、Ｍｇを０．５〜３．０質量％の範囲で含む場合は、めっき付着量、外観、密着性、耐食性のいずれも良好で、Ｍｇを３．０質量％含む場合はその性能はさらに良い。
【００４４】
（実施例３）
大きさが５０ｍｍ×１００ｍｍ×厚さ２．３ｍｍの黒皮付き普通鋼熱延鋼材を、１５％塩酸中に３０分間浸漬した後、引き上げ、スケール残りがないことを確認した。次いで、乾式フラックス処理を行った。乾式フラックス処理は、ＺｎＣｌ_２：２００ｇ／ｌ、ＮＨ_４Ｃｌ：４０ｇ／ｌからなる液温７０℃のフラックスに鋼材を１０秒間浸漬した後に引き上げ、２００℃に設定した電気オーブンの中で５分間乾燥させる処理とした。その後、表４に示す組成のＺｎ系合金めっき浴（Ｚｎ−０．２質量％Ａｌ−０．３質量％Ｍｎ−０．５質量％Ｍｇめっき浴）に２分間浸漬し、引き上げ後、湯冷して試験片を作製した。なお、めっき浴の温度は、４１０〜６００℃の間で種々、変化させた。また、一部の試験材は、そのめっき付着量を変化させるために、めっき浴への浸漬時間を最長９０分まで変化させた。このようにして得られた試験片のめっき付着量、外観、めっき密着性、耐食性は、実施例１と同様の方法にて評価し、結果を表４に示した。
【００４５】
【表４】

【００４６】
Ｎｏ．２６〜３２は、めっき浴温度を変えた場合である。めっき浴温が、本発明の範囲外である場合（Ｎｏ．２６および２７）、得られためっきの付着量が本発明の範囲外となり、また、外観が不良となるため不適である。めっき浴温が、本発明の範囲内の４３０〜５５０℃である場合（Ｎｏ．２８〜３２）、得られためっき組成は、いずれも本発明の範囲内であり、また、めっき付着量、外観、密着性、耐食性のいずれも良好である。特に、めっき浴温が４５０〜５５０℃の場合（Ｎｏ．２９、３０）は、いっそう良好となる。
【００４７】
Ｎｏ．３３〜３５は、めっき時間を変えて、めっき付着量を意図的に変化させた場合である。めっき時間が本発明の範囲外の３０秒（０．５分）である場合（Ｎｏ．３３）、めっき付着量が３００ｇ／ｍ^２未満となるため不適である。また、めっき時間が本発明の範囲外の９０分である場合（Ｎｏ．３４）、めっき付着量が１０００ｇ／ｍ^２より多くなり、外観及び密着性に劣るため不適である。一方、Ｎｏ．３５は、めっき時間を３０分とした場合であり、めっき付着量、外観、密着性、耐食性のいずれも良好である。
【００４８】
【発明の効果】
以上、本発明の溶融Ｚｎ−Ａｌ系合金めっき鋼材は、従来は不可能であった、フラックス法による均一で高付着量かつ高耐食性の溶融Ｚｎ−Ａｌ系合金めっき鋼材を実現したものである。すなわち、Ｚｎ−Ａｌ系合金めっき中にＭｎ及びＭｇを含ませ、めっき浴温を所定の範囲内とすることで、均一で高付着量、高耐食性かつ外観が良好な溶融Ｚｎ−Ａｌ系合金めっき鋼材を提供することができる。また、本発明の製造方法によれば、従来のめっき設備を改造することなく、めっき浴組成を変更するだけで、均一で高付着量かつ高耐食性の溶融Ｚｎ−Ａｌ系合金めっき鋼材を安価、簡便に製造することができる。このため、長期耐久性が求められる送電鉄塔、橋梁、道路用資材、建築金物等、建築・土木用材料等にこの鋼材を適用することで、これら施設のメンテナンスフリーが実現でき、産業上の価値は極めて大きい。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a hot-dip Zn—Al-based alloy-plated steel material having a uniform, high adhesion amount and high corrosion resistance by a flux method, and a method for producing the same.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in the fields of power transmission towers, bridges, road materials, building hardware, construction and civil engineering materials, hot-dip galvanized steel materials have been widely used from the viewpoints of economy, durability, workability, and the like. In recent years, Zn-Al alloy plating is being used because it has better corrosion resistance than Zn plating. In these Zn plating and Zn-Al alloy plating, the amount of plating and its corrosion resistance are generally in a proportional relationship, and the thicker the plating, the longer it takes to reach the exposure of the ground iron, the better the corrosion resistance. . That is, even if the corrosion resistance of the Zn—Al alloy plating is twice as large as that of the Zn plating, the corrosion resistance is equivalent if the amount of the Zn—Al alloy plating is only half that of the Zn plating.
[0003]
Factors affecting the plating adhesion amount include the viscosity and wet adhesion of the plating bath, the plating time, the plating temperature, the speed of lifting the material from the plating bath, the wiping of the plating, and the like. Of these, the influence of the viscosity of the plating bath and the wet adhesion is not so large. Regarding the pulling speed of the material from the plating bath, it is easy to change the pulling speed in a continuous type such as plating of a thin steel sheet, but in a batch type plating such as a flux type plating, the pulling speed is not changed. Is difficult to change. Regarding wiping of plating, it is difficult to obtain a uniform coating weight with flux-type plating, which is often used to plate processed steel materials, welded steel materials, and materials with complicated shapes such as small items. Since wiping acts in the direction of decreasing the amount of plating, it is not suitable for obtaining uniform and high-plating plating.
[0004]
For these reasons, in flux plating, the amount of plating is often controlled by the plating time and the temperature of the plating bath. The plating time and the temperature of the plating bath have a particularly large effect on the thickness of the Fe-Zn-based alloy layer generated at the interface between the base iron and the plating, and when the plating time is long or the plating temperature is high, the alloy layer becomes thick, As a result, the amount of plating increases. By the way, the thickness of the alloy layer greatly varies depending on the composition of the plating bath. For example, in Zn plating in which the amount of Al in the bath is 0.02% by mass or less, by increasing the plating time or increasing the plating temperature, the Fe-Zn-based alloy layer grows to 600 g / m ² about the thick plating is also possible.
[0005]
However, in a Zn-Al plating bath containing 0.1% by mass or more of Al, an Fe-Al-based alloy layer is initially formed, which hinders the growth of the Fe-Zn-based alloy layer. It is hard to grow. This Fe-Al-based alloy layer is extremely stable, for example, is stable even when the plating temperature is increased to about 530 ° C. Since the growth of the Fe-Zn-based alloy layer is suppressed, the amount of plating does not increase. In the case of a plating bath containing a relatively high concentration of Al, for example, in the case of a plating bath containing 10% or more Al by mass%, the Fe-Al-based alloy layer itself grows by increasing the plating bath temperature. Therefore, the amount of plating increases. However, the plating is not uniform, that is, the plating becomes locally thick and the appearance is poor, so that it is not suitable as a product.
[0006]
Further, even if the plating time is lengthened, the Fe—Zn-based alloy layer does not easily grow. When immersed in a plating bath for a considerably long period of time, for example, about one hour, the amount of plating applied may increase, but it is also unsuitable as a product due to uneven plating and poor appearance. As described above, it is difficult to obtain a uniform Zn-Al alloy plating with a high adhesion amount, and it has not been sufficiently studied so far. There are the following methods for obtaining a Zn-Al-based alloy plating with a high adhesion amount which has been known so far. For example, a two-stage plating process in which ordinary pure Zn plating containing almost no Al is performed, a Zn—Al-based alloy plating is performed after an Fe—Zn-based alloy layer is grown, is partially adopted. However, this method has various disadvantages such as the necessity of having two plating baths, an increase in work time, maintenance and management costs, and an increase in installation locations due to two plating operations.
[0007]
JP-A-5-106002 (Patent Document 1) discloses a method in which a relatively thick Zn-Al alloy plating can be obtained by adding 1.5 to 10% by mass of copper to a Zn-Al alloy plating bath. Proposed. However, in this method, the composition of the plating bath is likely to fluctuate, and there is a concern that the plating quality varies. Further, in Japanese Patent Application Laid-Open No. 9-25134 (Patent Document 2), after a steel material is subjected to a predetermined flux treatment, a plating temperature of 430 to 520 ° C. and a plating time of 0.degree. It is stated that by plating under conditions of 5 to 10 minutes, a thick plating having a plating thickness (plating adhesion amount) of 450 g / m ² or more can be obtained. However, this method cannot be applied to a plating bath having an Al concentration of 10% by mass or less, and has a lack of versatility since a special flux needs to be used.
[0008]
Japanese Patent Application Laid-Open No. 11-350095 (Patent Document 3) states that after performing a predetermined flux treatment, immersion in a Zn-Al plating bath having a molten flux layer allows plating with a high adhesion amount to be obtained. . However, also in this method, in addition to the plating bath having an Al content of 30 to 70% by mass, a special flux is used, and there is no versatility. There are various problems such as the necessity, labor for replacement and replenishment for the deterioration, and work environment deterioration due to the fact that the flux contains fluoride.
[0009]
Further, in Japanese Patent Application Laid-Open No. 8-283925 (Patent Document 4), the surface roughness of a steel material is kept within a certain range, and further, a certain iron component is contained in a plating bath, so that a high adhesion amount and uniformity are obtained. It is said that Zn-Al-Si plating can be obtained. However, this method is intended for Al-Si plating and the plating bath temperature is as high as 580 ° C. or higher, and is not suitable for plating mainly composed of Zn.
[0010]
On the other hand, Japanese Patent Application Laid-Open No. 5-117830 (Patent Document 5) does not specify the amount of deposition, but non-plating is prevented by adding a specific amount of Mn to a molten Zn-Al plating bath. It is described that a hot-dip Zn alloy plating having no surface roughness can be obtained. However, although it is possible to obtain plating free from non-plating by this method, Mn tends to reduce the corrosion resistance of the plating, so in a severely corrosive environment or when long-term durability is required. Not suitable.
As described above, although several methods have been found as methods for obtaining a Zn-Al alloy plating with a high adhesion amount, there are problems in terms of workability, work environment, quality, and durability. . Further, even if a plating with a high adhesion amount can be performed, it is difficult to stably obtain a uniform alloy plating.
[0011]
[References]
(1) Patent Document 1 (JP-A-5-106002)
(2) Patent Document 2 (Japanese Patent Application Laid-Open No. 9-25134)
(3) Patent Document 3 (Japanese Patent Application Laid-Open No. 11-350095)
(4) Patent Document 4 (Japanese Patent Laid-Open No. 8-283925)
(5) Patent Document 5 (JP-A-5-117830)
[0012]
[Problems to be solved by the invention]
The present invention solves the conventional problems in such Zn-Al alloy plating and provides a molten Zn-Al-based alloy plated steel material having a uniform, high coating weight and high corrosion resistance by a flux method, and a method for producing the same. With the goal.
[0013]
[Means for Solving the Problems]
Means for Solving the Problems The present inventors have solved the above-mentioned problems of the conventional technology, and have earnestly studied a method for stably obtaining a uniform, high coating amount and high corrosion resistance plating of Zn-Al based alloy platings of various compositions. As a result, it was found that by adding Mn and Mg in the plating layer in a composite manner, it is possible to realize a hot-dip Zn—Al-based alloy plated steel material having a uniform, high adhesion amount and high corrosion resistance.
[0014]
That is, the present invention has the following contents.
(1) In a hot-dip Zn-Al-based alloy-plated steel material containing 0.1 to 15% by mass of Al and the balance being Zn and inevitable impurities, the molten Zn-Al-based alloy-plated layer has a Mn: 0.05 to 1 wt%, and, Mg: 0.1 to 15 includes a mass%, the melting Zn-Al alloy coated steel material, characterized in that the coating weight is ^{^{300g / m 2 ~1000g / m 2}} .
(2) The hot-dip Zn-Al-based alloy-plated steel material according to (1), wherein the hot-dip Zn-Al-based alloy-plated layer further contains 0.05 to 0.2% by mass of Si.
[0015]
(3) A method for producing a hot-dip Zn-Al-based alloy-plated steel material by immersing a steel material subjected to a flux treatment in a hot-dip Zn-Al-based alloy-plating bath, wherein the hot-dip Zn-Al-based alloy-plated bath contains Al: 0.1 to 15% by mass, Mn: 0.05 to 1% by mass, and Mg: 0.1 to 15% by mass, the balance being Zn and unavoidable impurities, and the plating bath temperature being 430 to 550. C., a method for producing a hot-dip Zn—Al-based alloy-plated steel material.
(4) The production of a hot-dip Zn-Al-based alloy-plated steel material according to (3), wherein the hot-dip Zn-Al-based alloy-plating bath further contains Si: 0.05 to 0.2% by mass. In the way.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
First, the components in the plating layer of the steel according to the present invention will be described.
In the present invention, Mn in the plating layer has the effect of increasing the adhesion amount of the Zn-Al-based alloy plating and making the plating uniform, and needs to be in the range of 0.05 to 1% by mass. If the Mn content is less than 0.05% by mass, the effect is insufficient, resulting in a thin and non-uniform plating having a coating weight of less than 300 g / m ² . Conversely, if it exceeds 1% by mass, the adhesion between the plating layer and the steel material is reduced, and the corrosion resistance tends to be reduced. Further, a large amount of dross is formed, which causes a problem in the plating operation. The preferred range of Mn is 0.1 to 0.5% by mass, more preferably 0.2 to 0.4% by mass.
[0017]
Mg, when added in combination with Mn, has the effect of increasing the plating adhesion amount without deteriorating the corrosion resistance of the Zn-Al-based alloy plating layer, and needs to be in the range of 0.1 to 15% by mass. . The mechanism cannot be stated clearly, but if it is less than 0.1% by mass, the effect of improving the corrosion resistance is poor. If it exceeds 15% by mass, the corrosion resistance is improved, but the plating layer becomes brittle and the workability is reduced. It is. Therefore, the range of Mg in the present invention is set to 0.1 to 15% by mass. A preferred range is from 0.5 to 3% by mass.
[0018]
Al has an effect of improving the corrosion resistance of the plating layer. In the present invention, the range of Al in the plating layer is 0.1 to 15% by mass, for the following reason. If Al is less than 0.1% by mass, the effect of improving corrosion resistance is poor. When Al is less than 0.1% by mass, the alloy layer formed at the interface between the plating layer and the base iron is mainly composed of a Fe—Zn-based alloy. When Al exceeds 0.05% by mass, the plating layer and the base iron The alloy layer generated at the interface is mainly a non-growth type Fe-Al alloy layer.
[0019]
In the present invention, since the Fe-Al-based alloy layer is controlled by Mn and Mg, the lower limit is set to 0.1% by mass. Even when Al exceeds 15% by mass, the effect of controlling the Fe-Al-based alloy layer by Mn and Mg is recognized, but the appearance becomes poor, and a large amount of Mn and Mg must be added, and the workability is increased. Therefore, the upper limit was set to 15% by mass. If the above problems are solved, the present invention can be applied to hot-dip Zn-Al-based alloy plating containing Al exceeding 15% by mass. The preferred range of Al is 0.2 to 12% by mass.
[0020]
The plating of the present invention may further contain Si. Si has the effect of further improving the corrosion resistance and workability of the plating. To obtain this effect effectively, the range of Si in the present invention is preferably set to a range of 0.05 to 0.2% by mass. Coating weight of the present invention is required to have a ^{^{300g / m 2 ~1000g / m 2}} . If it is less than 300 g / m ² , the corrosion resistance is poor. If it is more than 1000 g / m ^2, it is not suitable because the adhesion between the plating and the steel material is reduced.
[0021]
The type of steel material to be plated in the present invention is not limited. Common steel, low alloy steel, high alloy steel, castings, etc. are not limited to their steel components, and their shapes are also joined by plates, steel pipes, shaped steels, wires, welds, bolts, etc. It can also be applied to steel materials such as combined steel materials, bolts and nuts, and steel members such as steel towers and bridge members. Any material can be used as long as it can be immersed in a plating bath and plated. However, depending on the steel composition, the amount of plating is affected, so it is necessary to determine plating conditions in advance.
[0022]
In order to manufacture the steel material of the present invention, first, the surface of the steel material is pretreated by a known method. As the pretreatment, for example, shot blasting, grid blasting, sand blasting, grinder treatment, or the like can be performed in addition to the generally performed pickling with hydrochloric acid, sulfuric acid, or the like. As long as the surface of the steel material is sufficiently cleaned, the processing conditions for these pretreatments are not limited. For example, conditions for pickling with hydrochloric acid or sulfuric acid include an aqueous solution concentration of 10 to 20% by mass, a bath temperature of normal temperature to 80 ° C., and a pickling time of 5 to 30 minutes.
[0023]
Next, a flux treatment is performed. The flux treatment referred to herein is a treatment for applying and attaching a flux to the surface of a steel material, and there is no particular limitation on the components of the flux and the treatment method, and any conventionally known method may be used. For example, the flux components include chlorides such as zinc chloride, ammonium chloride, magnesium chloride, lithium chloride, tin chloride, potassium chloride, calcium chloride, lead chloride, sodium chloride, antimony chloride, indium chloride, bismuth chloride, cadmium chloride and the like. , Alkali metal, alkaline earth metal fluorides, silicon fluorides, hydrogen fluorides and the like.
[0024]
Examples of the treatment method include a dry flux, a wet flux, and a molten flux. The dry flux means that the flux is applied as an aqueous solution to a steel material, dried, and then immersed in a plating bath. The wet flux is a method in which the flux is floated on a plating bath to form a flux layer having an appropriate thickness, and a steel material is immersed in the plating bath via the flux layer. The molten flux is obtained by immersing a steel material in a bath in which the flux itself is melted, and then immersing the steel material in a plating bath.
[0025]
The steel material subjected to the flux treatment is as follows: Al: 0.1 to 15% by mass; Mn: 0.05 to 1% by mass; Mg: 0.1 to 15% by mass; Immerse in a 550 ° C. Zn—Al-based alloy plating bath. By being immersed in the plating bath having the above composition, the composition of the present invention contains Al: 0.1 to 15% by mass, Mn: 0.05 to 1% by mass, and Mg: 0.1 to 15% by mass, with the balance being Zn. and inevitable impurities, the amount of plating adhesion can be obtained molten Zn-Al alloy coated steel ^{^{300g / m 2 ~1000g / m 2}} .
[0026]
The reason why the plating bath temperature is specified in the range of 430 to 550 ° C. is that if the plating bath temperature is out of this range, not only the hot-dip Zn—Al alloy plated steel material of the present invention cannot be obtained, but also various other problems occur. is there. That is, when the plating bath temperature is lower than 430 ° C., the fluidity of the plating bath is reduced, and the plating tends to be uneven and the appearance is poor, and the amount of plating does not increase. On the other hand, when the temperature exceeds 550 ° C., a large amount of dross is generated in the plating bath, which causes difficulties in the operation, and the dross adheres to the surface of the material to be plated, and the plating tends to be poor in appearance. In addition, the amount of plating tends to be extremely large. Furthermore, the life of the plating pot is shortened. Preferred plating temperatures are in the range of 450-500 ° C.
[0027]
The time for immersing the material to be plated in the plating bath is not particularly limited, but is preferably 1 minute or more and 30 minutes or less. Within this range, the hot-dip Zn—Al-based alloy-plated steel material of the present invention can be obtained more stably. The plating bath may further contain Si: 0.05 to 0.2% by mass. By including Si in the above range in the plating bath, a hot-dip Zn—Al-based alloy-plated steel material that is uniform and has a high adhesion amount, high corrosion resistance, and excellent adhesion can be obtained.
[0028]
Further, there is no problem even if, for example, Fe, Pb, Cd, Sn, Cu, Sb, Bi, Ag, Ni, As, or the like is mixed in the Zn-Al-based alloy plating bath as inevitable impurities. The speed at which the material to be plated is immersed in the plating bath is not specified at all. For example, as in the Taylor-Wilson method in continuous plating of steel pipes, a high immersion speed such as dropping a steel pipe into a plating bath may be used, or, as in the case of plating a large steel member such as a steel tower member, a crane. After the material to be plated is lifted by the method described above, a slow immersion speed such that the material is slowly immersed in the plating bath may be used.
[0029]
The speed at which the material to be plated is removed from the plating bath is not particularly specified. It may be taken out at a high speed of about 0.7 to 2 m / sec as in the Taylor-Wilson system, or may be taken out at a low speed of about 0.2 m / sec as in the case of using a crane. Furthermore, in order to improve the appearance after plating, cooling by water cooling or hot water cooling may be performed as necessary.
By performing the treatment under the above procedures and conditions, it is possible to obtain a hot-dip Zn—Al-based alloy-plated steel material that is uniform, has a high adhesion amount and high corrosion resistance.
[0030]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples.
(Example 1)
A hot-rolled steel plate with black scale having a size of 50 mm × 100 mm × 2.3 mm in thickness was immersed in 15% hydrochloric acid for 30 minutes, then pulled up, and it was confirmed that there was no scale residue. Next, a dry flux treatment was performed. In the dry flux treatment, the steel material is immersed in a flux composed of ZnCl ₂ : 200 g / l and NH ₄ Cl: 40 g / l at a liquid temperature of 70 ° C. for 10 seconds, then pulled up, and dried in an electric oven set at 200 ° C. for 5 minutes. The processing was performed. Thereafter, based on a Zn alloy plating bath having a composition shown in Table 2 (Zn-0.2 mass% Al-0.5 mass% Mg plating bath, or Zn-10 mass% Al-3 mass% Mg plating bath, , Si added) for 2 minutes, and after pulling up, cooling with hot water to prepare a test piece.
[0031]
The coating weight of the test piece thus obtained was determined from the change in mass before and after dissolving the plating with hydrochloric acid. The plating composition was analyzed by ICP emission spectrometry using a solution in which the plating layer obtained by dissolving hydrochloric acid was dissolved. The appearance was visually observed and evaluated according to the following criteria. A grade higher than or equal to acceptable was passed.
Good: The surface is smooth and there is no plating defect.
Acceptable: Irregularities are slightly large and plating and burns are slightly observed.
Poor: non-plating, pinholes, dross adhesion, etc. are present, or irregularities are somewhat large, and plating or injuries are present at 50% or more of the test piece area.
The term “burning” as used herein means that the alloy layer has grown to the plating surface layer.
[0032]
Further, a 90 ° bending test was performed, and the adhesion of the plating was evaluated by visual observation according to the following criteria. A grade higher than or equal to acceptable was passed.
Good: There is no plating crack in the processed part.
Acceptable: Cracks slightly exist in the processed part.
Poor: Cracks were present all over the processed part, or plating on the processed part was peeled off.
[0033]
Regarding the corrosion resistance, the average corrosion weight loss of the plating after performing the salt spray test (35 ° C., 5% NaCl) for 2000 hours was evaluated and evaluated according to the following criteria.
Excellent: Average plating weight loss rate of less than 0.1 g / m ² / hr Good: Average plating weight loss rate of 0.1 to 0.5 g / m ² / hr
Acceptable: average corrosion weight loss rate of plating is 0.5 to 1.0 g / m ² / hr
Inferior: The average corrosion weight loss rate of plating exceeded 1.0 g / m ² / hr, or the plating was consumed and red rust was generated. Table 1 shows the test results.
[0034]
[Table 1]

[0035]
No. 1 to No. No. 6 is a case where Mn is contained in an amount of 0.05 to 0.8% by mass based on a Zn-0.2% by mass Al-0.5% by mass Mg plating bath. All the components in the obtained plating layer are within the scope of the present invention, and all of the coating weight, appearance, adhesion, and corrosion resistance are good. In particular, when the plating layer contains Mn in the range of 0.1 to 0.5% by mass, the performance is further improved. When the plating layer contains 0.3% by mass of Mn, the performance is further improved. No. No. 6 is No. 4 shows the case where 0.1% by mass of Si is contained in the plating layer, which indicates that the corrosion resistance is improved. No. 7-No. No. 10 is a case where Mn is contained in an amount of 0.1 to 0.8% by mass based on a Zn-10% by mass Al-3% by mass Mg plating bath. The components in the obtained plating layer are all within the range of the present invention. In particular, when Mn is contained in the range of 0.1 to 0.5% by mass, the coating weight, appearance, adhesion, and corrosion resistance Both are good, and when Mn is contained at 0.3% by mass, the performance is further improved.
[0036]
(Comparative example)
A hot-rolled steel plate with black scale having a size of 50 mm × 100 mm × 2.3 mm in thickness was immersed in 15% hydrochloric acid for 30 minutes, then pulled up, and it was confirmed that there was no scale residue. Next, a dry flux treatment was performed. In the dry flux treatment, the steel material is immersed in a flux composed of ZnCl ₂ : 200 g / l and NH ₄ Cl: 40 g / l at a liquid temperature of 70 ° C. for 10 seconds, then pulled up, and dried in an electric oven set at 200 ° C. for 5 minutes. The processing was performed. Then, it was immersed in a Zn-based alloy plating bath having the composition shown in Table 2 for 2 minutes, pulled up, and cooled with hot water to produce a test piece.
The coating weight, appearance, plating adhesion, and corrosion resistance of the test pieces thus obtained were evaluated in the same manner as in Example 1, and the results are shown in Table 2.
[0037]
[Table 2]

[0038]
No. No. 11 is a case where Zn plating which does not contain any of Al, Mn, Mg and Si in the plating layer was performed. Unsuitable due to poor corrosion resistance. No. No. 12 is a case where 0.4% by mass of Al is contained in the plating layer. This is unsuitable because the coating weight is small (less than 300 g / m ² ) and the corrosion resistance is poor (red rust is generated). No. No. 13 contained 0.4% by mass of Al and 0.1% by mass of Mn in the plating layer. No. 14 is a case where the plating layer contains 0.4% by mass of Al and 1.0% by mass of Mn. In any case, although the plating adhesion amount is large, it is unsuitable because of poor corrosion resistance (average corrosion weight loss of plating is 1.0 g / m ² / hr or more).
[0039]
No. No. 15 contained 0.4% by mass of Al and 0.2% by mass of Mg in the plating layer. No. 16 is a case where the plating layer contains 0.4% by mass of Al and 10% by mass of Mg. All of them are unsuitable because of low plating adhesion amount (less than 300 g / m ² ) and poor corrosion resistance (generation of red rust). No. 17 is a case where the plating layer contains Al: 0.4% by mass, Mn: 0.1% by mass, and Mg: 20% by mass. Although the plating amount is large and the corrosion resistance is good, it is not suitable because of poor adhesion of the plating. No. No. 18 is a case where the plating layer contains 0.4% by mass of Al, 2.5% by mass of Mn, and 0.5% by mass of Mg. Although corrosion resistance is good, it is unsuitable because the amount of plating is extremely large (greater than 1000 g / m ² ) and the adhesion is poor.
[0040]
No. 19, no. 20 each include 0.1% by mass of Mn and 0.5% by mass of Mg in the plating layer, and both are within the scope of the present invention, but when only Al is out of the scope of the present invention, That is, this is the case where Al: 0.06% by mass (No. 9) and Al: 22% by mass (No. 10). If the Al content is 0.06% by mass, the coating weight is extremely large (greater than 1000 g / m ² ) and the corrosion resistance is poor. Further, when the content of Al is 22% by mass, the adhesion amount of the plating and the corrosion resistance are good, but the appearance is uneven and poor, which is not suitable.
[0041]
(Example 2)
A hot-rolled steel plate with black scale having a size of 50 mm × 100 mm × 2.3 mm in thickness was immersed in 15% hydrochloric acid for 30 minutes, then pulled up, and it was confirmed that there was no scale residue. Next, a dry flux treatment was performed. In the dry flux treatment, the steel material is immersed in a flux composed of ZnCl ₂ : 200 g / l and NH ₄ Cl: 40 g / l at a liquid temperature of 70 ° C. for 10 seconds, then pulled up, and dried in an electric oven set at 200 ° C. for 5 minutes. The processing was performed. Then, it was immersed for 2 minutes in a Zn-based alloy plating bath having the composition shown in Table 3 (based on the Zn-0.2% by mass Al-0.3% by mass Mn plating bath and adding Mg and Si). A test piece was prepared by cooling with hot water.
The coating weight, appearance, plating adhesion, and corrosion resistance of the test pieces thus obtained were evaluated in the same manner as in Example 1, and the results are shown in Table 3.
[0042]
[Table 3]

[0043]
No. 21, no. No. 22 is a case where Mg was contained in an amount of 0.1 to 0.5% by mass based on a Zn-0.2% by mass Al-0.3% by mass Mn plating bath. The compositions of the obtained plating layers are all within the range of the present invention, and all of the plating adhesion amount, appearance, adhesion, and corrosion resistance are good. In particular, when the plating layer contains 0.5% by mass of Mg, the performance is further improved. No. Nos. 23 to 25 are cases where Mg is contained in an amount of 0.1 to 3.0% by mass based on a Zn-10% by mass Al-0.3% by mass Mn plating bath. The components of the plating layer obtained are all within the scope of the present invention, and particularly when the content of Mg is in the range of 0.5 to 3.0% by mass, any of the plating adhesion amount, appearance, adhesion, and corrosion resistance Is good, and when Mg is contained in an amount of 3.0% by mass, the performance is further improved.
[0044]
(Example 3)
A hot-rolled steel plate with black scale having a size of 50 mm × 100 mm × 2.3 mm in thickness was immersed in 15% hydrochloric acid for 30 minutes, then pulled up, and it was confirmed that there was no scale residue. Next, a dry flux treatment was performed. In the dry flux treatment, the steel material is immersed in a flux composed of ZnCl ₂ : 200 g / l and NH ₄ Cl: 40 g / l at a liquid temperature of 70 ° C. for 10 seconds, then pulled up, and dried in an electric oven set at 200 ° C. for 5 minutes. The processing was performed. Then, it was immersed in a Zn-based alloy plating bath having the composition shown in Table 4 (Zn-0.2% by mass Al-0.3% by mass Mn-0.5% by mass Mg plating bath) for 2 minutes. Then, a test piece was prepared. The temperature of the plating bath was variously changed between 410 and 600 ° C. In addition, in some test materials, the immersion time in the plating bath was changed up to 90 minutes in order to change the amount of plating. The coating weight, appearance, plating adhesion, and corrosion resistance of the test pieces thus obtained were evaluated in the same manner as in Example 1, and the results are shown in Table 4.
[0045]
[Table 4]

[0046]
No. 26 to 32 are cases where the plating bath temperature was changed. When the plating bath temperature is out of the range of the present invention (Nos. 26 and 27), the amount of the obtained plating is out of the range of the present invention, and the appearance is poor. When the plating bath temperature is 430 to 550 ° C. within the range of the present invention (Nos. 28 to 32), the obtained plating compositions are all within the range of the present invention, and the amount of plating and the appearance , Adhesion and corrosion resistance are all good. In particular, when the plating bath temperature is 450 to 550 ° C. (Nos. 29 and 30), it becomes even better.
[0047]
No. Nos. 33 to 35 are cases in which the plating time was changed to intentionally change the amount of plating. When the plating time is 30 seconds (0.5 minutes) out of the range of the present invention (No. 33), the plating adhesion amount is less than 300 g / m ^2, which is not suitable. Further, when the plating time is 90 minutes out of the range of the present invention (No. 34), the plating adhesion amount is more than 1000 g / m ² and the appearance and the adhesion are poor, which is not suitable. On the other hand, No. No. 35 indicates a case where the plating time was 30 minutes, and all of the plating adhesion amount, appearance, adhesion, and corrosion resistance were good.
[0048]
【The invention's effect】
As described above, the hot-dip Zn-Al-based alloy-plated steel material of the present invention realizes a uniform, high-adhesion-weight, high-corrosion-resistant hot-dip Zn-Al-based alloy-plated steel material by a flux method, which was not possible in the past. That is, by including Mn and Mg in the Zn-Al-based alloy plating and setting the plating bath temperature within a predetermined range, the molten Zn-Al-based alloy plating having a uniform, high adhesion amount, high corrosion resistance and good appearance is provided. Steel material can be provided. Further, according to the production method of the present invention, without modifying the conventional plating equipment, only by changing the plating bath composition, a uniform, high coating weight and high corrosion resistance hot-dip Zn-Al-based alloy-plated steel material is inexpensive, It can be easily manufactured. For this reason, by applying this steel material to power transmission towers, bridges, road materials, building hardware, construction and civil engineering materials, etc., which require long-term durability, maintenance-free of these facilities can be realized, and industrial value Is extremely large.

Claims

Al: In a hot-dip Zn—Al-based alloy-plated steel material containing 0.1 to 15% by mass and the balance being Zn and unavoidable impurities, the molten Zn—Al-based alloy-plated layer has a Mn of 0.05 to 1% by mass. and, Mg: 0.1 to 15 includes a mass%, the melting Zn-Al alloy coated steel material, characterized in that the coating weight is ^{^{300g / m 2 ~1000g / m 2}} .

The hot-dip Zn-Al-based alloy-plated steel material according to claim 1, wherein the hot-dip Zn-Al-based alloy-plated layer further contains 0.05 to 0.2% by mass of Si.

A method for producing a hot-dip Zn-Al-based alloy-plated steel material by immersing a steel material subjected to a flux treatment in a hot-dip Zn-Al-based alloy-plating bath, wherein the hot-dip Zn-Al-based alloy-plated bath contains Al: 0.1 -15% by mass, Mn: 0.05-1% by mass, and Mg: 0.1-15% by mass, the balance consisting of Zn and unavoidable impurities, and the plating bath temperature is 430-550 ° C. A method for producing a hot-dip Zn-Al-based alloy-plated steel material, comprising:

The method for producing a hot-dip Zn-Al-based alloy plated steel material according to claim 3, wherein the hot-dip Zn-Al-based alloy plating bath further contains 0.05 to 0.2% by mass of Si.