JP4631241B2

JP4631241B2 - High-tensile hot-dip galvanized steel sheet and high-tensile alloyed hot-dip galvanized steel sheet with excellent strength ductility balance, plating adhesion and corrosion resistance

Info

Publication number: JP4631241B2
Application number: JP2001288740A
Authority: JP
Inventors: 善継鈴木; 一章京野
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2001-09-21
Filing date: 2001-09-21
Publication date: 2011-02-16
Anticipated expiration: 2021-09-21
Also published as: JP2003096541A

Description

【０００１】
【発明の属する技術分野】
本発明は、高張力（合金化）溶融亜鉛めっき鋼板（鋼帯を含む）に係わり、特に複雑な形状にプレス成形する場合にも充分に耐え得る強度延性バランスおよびめっき密着性に優れた高張力（合金化）溶融亜鉛めっき鋼板、加えて、さらに耐食性に優れた高張力（合金化）溶融亜鉛めっき鋼板に関するものである。
【０００２】
【従来の技術】
近年、地球環境の保全という観点から、自動車の燃費改善が要求されている。さらに、衝突時に乗員を保護するため、自動車車体の安全性向上も要求されている。このような状況から、自動車車体の軽量化および自動車車体の強化が積極的に進められている。特に、自動車車体の軽量化のために、熱延鋼板および冷延鋼板等の自動車用鋼板を高強度化し、鋼板板厚を低減することが提案されている。一方、鋼板を素材とする自動車用部品の多くがプレス加工によって成形されるため、自動車用鋼板には優れたプレス成形性が要求される。また、溶融亜鉛めっき鋼板は防錆性（耐食性）に優れ、安価に製造できるため、自動車車体用防錆表面処理鋼板として多用されている。
【０００３】
鋼板を高強度化するには、Ｓｉ、Ｍｎ等の元素を添加し、固溶強化等を図る必要があるが、Ｓｉ、Ｍｎは易酸化性元素であるため、焼鈍時にＳｉ、Ｍｎ等が表面に濃化して、その表面に施される溶融亜鉛めっきの濡れ性が悪化し、めっき密着性が劣化する。
上記問題を解決するために、例えば特開平５−１７９３５６号公報や特開平５−５１６４７号公報では、Ｓｉ、Ｍｎの添加量を減らし、熱延巻取り時に焼き入れ急冷し、溶融亜鉛めっきラインにおいて、二相域で焼鈍した後、めっきする方法が提案されている。しかしながら、実際には、Ｓｉが少しでも添加されていると、めっき密着性が劣化して、めっき剥離が生じやすいため、従来は、Ｓｉ、Ｍｎ含有量が多い鋼板に、めっき密着性が良好な溶融亜鉛めっきを施すことは事実上不可能とされていた。
【０００４】
また、良好な延びと強度を両立するために、溶融亜鉛めっき鋼板の最終組織を、焼き戻しマルテンサイト、残留オーステナイトを含み、残部をフェライトと低温変態相からなる複合組織とする必要がある。そのためにはＳｉ、Ｍｎを多量に複合添加することが有効であるが、上記のようにＳｉ、Ｍｎを多量に含むとめっき密着性が劣化する。
【０００５】
【発明が解決しようとする課題】
本発明は、上記問題を解決しようとするもので、下地鋼板がＳｉ、Ｍｎを多量に含んでいても溶融亜鉛めっき密着性に優れ、かつプレス成形性等の機械的特性、強度延性バランスに優れた高張力（合金化）溶融亜鉛めっき鋼板を提供することを目的とする。加えて、さらに耐食性に優れた高張力（合金化）溶融亜鉛めっき鋼板を提供することを目的とする。
【０００６】
【課題を解決するための手段】
本発明者は、高張力溶融亜鉛めっき鋼板において、Ｓｉ、Ｍｎを多量に含有し機械的特性を維持したままの鋼板の表層への溶融亜鉛めっき密着性の劣化を阻止するための条件を鋭意調査したところ、鋼中のＭｎ／Ｓｉ質量比が比較的小さく、相対的にＳｉを多量に含有する場合でも、めっき層直下の母材表層部の酸素量が多く、かつ鋼中のＭｎ／Ｓｉ質量比とめっき層中のＡｌ、Ｓｉ濃度の関係を特定化すれば、上記目的を達成できることを見出した。
【０００７】
すなわち、本発明は、質量％でＣ：０．０５〜０．２５％、Ｓｉ：０．５０％超２．００％未満、Ｍｎ：３．５％以下、Ａｌ：０．０１〜１．０％を含み、残部がＦｅおよび不可避的不純物からなり、鋼中のＭｎ／Ｓｉ質量比：０．５以上２未満の組成と、焼き戻しマルテンサイト、残留オーステナイト、フェライトおよび低温変態相からなり、体積分率で前記焼き戻しマルテンサイトが２０％以上で、前記残留オーステナイトが２％以上の複合組織を有する鋼板上に、めっき層中のＡｌ濃度が下記の式（１）を満たし、かつめっき層中のＳｉ濃度が下記の式（２）を満たす溶融亜鉛めっき層を有するとともに、めっき層除去後の地鉄表層酸素量が０．０５ｇ／ｍ²以上であることを特徴とする強度延性バランス、めっき密着性および耐食性に優れた高張力溶融亜鉛めっき鋼板である。
【０００８】
0.67-1/50(Mn/Si)≧［めっき層中のＡｌ濃度（質量％）］≧0.37-1/50(Mn/Si)
・・・（１）
1.67-1/3(Mn/Si) ≧［めっき層中のＳｉ濃度（質量％）］≧0.167-1/30(Mn/Si)
・・・（２）
（式（１）、（２）のＭｎ／Ｓｉは鋼中のＭｎ／Ｓｉ質量比を表わす。）
【０００９】
好ましい本発明は、前記鋼板が、さらに下記の群から選択された少なくとも１種の成分を含む強度延性バランス、めっき密着性および耐食性に優れた高張力溶融亜鉛めっき鋼板である。
（第１群）質量％で１．０％以下のＣｒ、１．０％以下のＭｏおよび０．００３％以下のＢからなる群から選択された少なくとも１種。
（第２群）質量％で０．１％以下のＴｉ、０．１％以下のＮｂおよび０．１％以下のＶからなる群から選択された少なくとも１種。
（第３群）質量％で１．０％以下のＣｕおよび１．０％以下のＮｉからなる群から選択された少なくとも１種。
【００１０】
また、本発明は、質量％で、Ｃ：０．０５〜０．２５％、Ｓｉ：０．５０％超２．００％未満、Ｍｎ：３．５％以下、Ａｌ：０．０１〜１．０％を含み、残部がＦｅおよび不可避的不純物からなり、および鋼中のＭｎ／Ｓｉ質量比：０．５以上２未満で示される組成と、焼き戻しマルテンサイト、残留オーステナイト、フェライトおよび低温変態相からなり、体積分率で、前記焼き戻しマルテンサイトが２０％以上で、前記残留オーステナイトが２％以上の複合組織を有する鋼板上に、めっき層中のＡｌ濃度が下記の式（３）を満たし、かつめっき層中のＳｉ濃度が下記の式（２）を満たす合金化溶融亜鉛めっき層を有するとともに、めっき層除去後の地鉄表層酸素量が０．０５ｇ／ｍ² 以上であることを特徴とする強度延性バランス、めっき密着性および耐食性に優れた高張力合金化溶融亜鉛めっき鋼板である。
【００１１】
0.5-1/50(Mn/Si) ≧［めっき層中のＡｌ濃度（質量％）］≧0.2-1/50(Mn/Si)
・・・（３）
1.67-1/3(Mn/Si) ≧［めっき層中のＳｉ濃度（質量％）］≧0.167-1/30(Mn/Si)
・・・（２）
（式（３）、（２）のＭｎ／Ｓｉは鋼中のＭｎ／Ｓｉ質量比を表わす。）
【００１２】
好ましい本発明は、前記鋼板が、さらに下記の群から選択された少なくとも１種の成分を含む強度延性バランス、めっき密着性および耐食性に優れた高張力溶融亜鉛めっき鋼板である。
（第１群）質量％で１．０％以下のＣｒ、１．０％以下のＭｏおよび０．００３％以下のＢからなる群から選択された少なくとも１種。
（第２群）質量％で０．１％以下のＴｉ、０．１％以下のＮｂおよび０．１％以下のＶからなる群から選択された少なくとも１種。
（第３群）質量％で１．０％以下のＣｕおよび１．０％以下のＮｉからなる群から選択された少なくとも１種。
【００１３】
【発明の実施の形態】
本発明者は、Ｓｉ、Ｍｎを含有する高強度鋼鈑に溶融亜鉛めっきを施すに際し、鋼鈑の表層の結晶粒界および／または結晶粒内に酸化物を存在させておくことにより、Ｓｉ、Ｍｎが表面濃化した皮膜の形成を抑制し、溶融亜鉛との濡れ性が良好になり、不めっきの発生を抑制できることを知見し、特開平９−３１０１６３号公報に開示した。
そして、地鉄表層部に内部酸化物が存在する溶融亜鉛めっき鋼鈑（ＧＩ) および合金化溶融亜鉛めっき鋼鈑（ＧＡ）のめっき品質、機械的性質、溶接性について、さらに詳細な検討を行った結果、鋼中のＭｎ／Ｓｉ質量比、めっき層中のＡｌ濃度にも影響されることを究明した。
【００１４】
すなわち、本発明は以下の実験事実に基づいて完成されたものである。以下、鋼組成は質量分率で表す。
Ｃ：０．１０％、Ｓｉ：０．３〜２％、Ｍｎ：１．０〜３．５％、Ｐ：０．０１％、Ａｌ：０．０４％を含有する厚さ３０ｍｍのシートバーを１２５０℃で加熱し、５パスで厚さ２．３ｍｍの熱延鋼板とした後、６２０℃で巻き取った。次いで、酸洗により黒皮を除去し、１．０ｍｍまで冷間圧延し、焼鈍炉において８００〜９００℃で加熱後、６０℃−５％ＨＣｌで６秒間酸洗した。その後、溶融亜鉛めっきシミュレーターにより７８０℃で５％Ｈ₂−Ｎ₂還元性雰囲気中で焼鈍し、４６０℃の溶融亜鉛めっき浴（０．０８〜０．２５％Ａｌ−Ｚｎ）で溶融亜鉛めっきし、付着量を片面５０ｇ／ｍ²になるようにガスワイピングした。合金化は通電炉において５００℃で実施した。得られためっき鋼板のめっき密着性および機械的特性を調査した。
【００１５】
なお、めっき層直下の地鉄表層部の内部酸化物の量が０．０５〜０．５ｇ／ｍ²の範囲となるように冷間圧延後の加熱時焼鈍雰囲気を調整した。
以下、合金化した溶融亜鉛めっき鋼板をＧＡ、合金化していない溶融亜鉛めっき鋼板をＧＩで表し、また冷延鋼板をＣＲ、熱延鋼板をＨｏｔで表して、鋼中のＭｎ／Ｓｉ質量比とめっき層中のＡｌ濃度およびＳｉ濃度との関係について説明する。
【００１６】
図１に、ＧＩのめっき品質、機械的性質および溶接性に及ぼす鋼板中のＭｎ／Ｓｉ質量比とめっき層中のＡｌ濃度 (質量％）を示す。
Ｍｎ／Ｓｉ質量比が２．０以上である場合は、めっき層中のＡｌ濃度が下記式 (１）を満たす範囲であれば、めっき品質は良好となり、機械的性質には若干のばらつきが認められたが、機械的性質、溶接性ともに概ね良好となる。Ｍｎ／Ｓｉ質量比が０．５未満であると、めっき層中のＡｌ濃度を下記式（１）の範囲にしてもめっき品質の不良が生じる。Ｍｎ／Ｓｉ質量比が０．５以上２．０未満の領域では、めっき層中のＡｌ濃度が下記式（１）の範囲を超えていると、溶接不良が生じ、また、下記式（１）の範囲に満たないとめっき品質の不良が生じる。
Ｍｎ／Ｓｉ質量比が０．５以上２．０未満、かつ、めっき層中のＡｌ濃度が下記式 (１）を満たす範囲では、めっき品質が良好なものと不良のものが混在する。
0.67-1/50(Mn/Si)≧［めっき層中のＡｌ濃度（質量％）］≧0.37-1/50(Mn/Si)
・・・（１）
【００１７】
図２に、ＧＡのめっき品質、機械的性質および溶接性に及ぼすＭｎ／Ｓｉ質量比とめっき層中のＡｌ濃度 (質量％）を示す。
Ｍｎ／Ｓｉ質量比が２．０以上である場合は、めっき層中のＡｌ濃度が下記式 (３）を満たす範囲であれば、めっき品質は良好となり、機械的性質には若干のばらつきが認められたが、機械的性質は概ね良好となる。また、合金化の遅延という問題も発生しない。Ｍｎ／Ｓｉ質量比が０．５未満であると、めっき層中のＡｌ濃度を下記式（３）の範囲としてもめっき品質の不良が生じる。Ｍｎ／Ｓｉ質量比が０．５以上２．０未満の領域では、めっき層中のＡｌ濃度が下記式（３）の範囲を超えていると、合金化遅延が生じ、また、下記式（３）の範囲に満たないとめっき品質の不良が生じる。Ｍｎ／Ｓｉ質量比が０．５以上２．０未満、かつ、めっき層中のＡｌ濃度が下記式 (３）を満たす範囲では、めっき品質が良好なものと不良のものが混在する。
0.5-1/50(Mn/Si) ≧［めっき層中のＡｌ濃度（質量％）］≧0.2-1/50(Mn/Si)
・・・（３）
【００１８】
さらに、めっき層中のＡｌ濃度が、ＧＩについては上記式（１）を、ＧＡについては上記式（３）を満たすようにめっき浴中のＡｌ濃度を調整して得られたＧＩおよびＧＡについて、めっき品質、機械的性質および溶接性に及ぼす、鋼板中のＭｎ／Ｓｉ質量比とめっき層中のＳｉ濃度 (質量％）影響を調査した。その結果、図３に示すように、めっき層中のＳｉ濃度が、ＧＩ、ＧＡとも下記式（２）を満たす場合には、めっき品質の不良が生じないことがわかった。
1.67-1/3(Mn/Si) ≧［めっき層中のＳｉ濃度（質量％）］≧0.167-1/30(Mn/Si)
・・・（２）
【００１９】
上記実験結果から、鋼中のＭｎ／Ｓｉ質量比が２未満の場合、すなわちＭｎに比べて相対的にＳｉ含有量が多い場合でも、地鉄表層の酸素量が所定範囲内にあって、めっき層中のＡｌ濃度およびＳｉ濃度を特定の範囲内に調整すれば、溶融亜鉛めっき層の密着性が良好であるが、めっき層中のＡｌ濃度が特定範囲外となると溶接性の劣化や合金化の遅延が発生し、めっき層中のＳｉ濃度が外れると耐食性やめっき密着性が劣化すること、および鋼中のＭｎ／Ｓｉ質量比が特定の範囲外になると密着性が劣化することを知見し、前記式（１）および式（２）、ならびに前記式（３）および式（２）を誘導した。
【００２０】
すなわち、鋼中のＭｎ／Ｓｉ質量比とめっき層中のＡｌ濃度およびＳｉ濃度を、前記式（１）および式（２）、ならびに前記式（３）および式（２）を満足するように調整すれば、鋼中にＳｉおよびＭｎが存在しても、その鋼板表面への溶融亜鉛めっきの密着性が良好なＧＩおよびＧＡが製造できることを知見し、本発明を完成した。
【００２１】
本発明において鋼中の構成成分の含有量およびその複合組織を規定した理由は次の通りである。
Ｃ：０．０５〜０．２５％
Ｃは必要強度を得るためと残留オーステナイト等の所望の組織を得るために不可欠な成分であり、少なくとも０．０５％が必要であるが、０．２５％を超えると溶接性が悪化するため上記範囲とした。好ましくは０．０７〜０．１８％である。
【００２２】
Ｓｉ：０．５０％超２．００％未満
Ｓｉは固溶強化と所望の組織を得るために不可欠な成分であり、延性を劣化させずに高強度化を図ることを可能にする成分である。その効果は０．５０％より多くないと発揮されない。一方、２．００％以上になると、めっき密着性が劣化する。そのため上記範囲とした。好ましくは０．６〜１．６％である。
【００２３】
Ｍｎ：３．５％以下
Ｃと同様に必要強度を得るため、また鋼の焼き入れ性を向上させ所望の組織を得るために不可欠な成分であり、１％以上であれば、効果が十分発揮され、好ましい。しかし、３．５％を超えても効果が飽和しコストの上昇を招くため上記範囲とした。
【００２４】
Ａｌ：０．０１〜１．０％
Ａｌは脱酸などの目的のために添加するのが好ましい。また、延性の向上にも寄与する。所望の効果を得るためには０．０１％以上必要であり、１．０％を超えると効果が飽和し、コストの上昇を招くため上限を１．０％とした。
【００２５】
鋼中のＭｎ／Ｓｉ質量比：０．５以上２未満
めっき密着性向上効果を得るためには、鋼中のＭｎ／Ｓｉ質量比が高い方が有利である。これはめっき直前の焼鈍時に生成する表面濃化物が、Ｓｉ主体の酸化物から、溶融亜鉛との濡れ性が良好であるＳｉ−Ｍｎ系複合酸化物に変化するためである。さらに、鋼板を連続溶融亜鉛めっき設備（ＣＧＬと表す。）の通板前にあらかじめ加熱処理し、次いで、冷却後表面を酸洗処理することにより表面を活性化する場合に、鋼中のＭｎ／Ｓｉ質量比が高い方が酸化皮膜の酸洗性向上効果が得られる。これは、鋼板表面の酸化物が難酸洗性であるＳｉ主体の酸化物から酸洗性良好なＳｉ−Ｍｎ系複合酸化物に変化するためと考えられる。
【００２６】
また、鋼中のＭｎ／Ｓｉ質量比が高い方が合金化を遅延させずにすむため、溶融亜鉛めっき後、合金化処理する場合の生産性も向上する。鋼中のＭｎ／Ｓｉ質量比が０．５未満であると、めっき密着性が劣化するため、鋼中のＭｎ／Ｓｉ質量比を０．５以上と規定した。また、鋼中のＭｎ／Ｓｉ質量比が２以上になると、機械的特性のばらつきがやや大きくなる。本発明が目的とする高張力高延性めっき鋼板を得るためには、鋼中のＭｎ／Ｓｉ質量比は０．５以上２未満であるのが好ましい。より好ましいのは０．８以上２未満である。
【００２７】
さらに、本発明の高張力溶融亜鉛めっき鋼板または高張力合金化溶融亜鉛めっき鋼板は鋼板成分として、前記３群に属す元素を下記の量（質量％）で、１種以上含有していてもよい。その場合はさらに、以下の効果を有する。
第１群はＣｒ、ＭｏおよびＢからなる群から選択された少なくとも１種であり、主として焼入れ性向上に寄与する。
第２群はＴｉ、ＮｂおよびＶからなる群から選択された少なくとも１種であり、主として炭窒化物を形成し、析出強化により鋼を高強度化する作用をする。
第３群はＣｕおよびＮｉからなる群から選択された少なくとも１種であり、主としてめっき密着性の向上に寄与する。
【００２８】
Ｃｒ：１．０％以下
Ｃｒは焼き入れ性を向上し、低温変態相の生成を促進する作用を有するため必要に応じて添加する。好ましくは０．０５％以上が効果的であるが、１．０％を超えるとめっき密着性が劣化するため上限を１．０％とするのが好ましい。含有させる場合には、０．１〜０．３％とするのがより好ましい。
【００２９】
Ｍｏ：１．０％以下
ＭｏはＣｒと同様に焼き入れ性を向上し、低温変態相の生成を促進する作用を有するため必要に応じて添加する。好ましくは０．０５％以上が効果的であるが、１．０％を超えるとコスト上昇を招くため、上限は１．０％とするのが好ましい。含有させる場合には、０．０５〜０．３％とするのがより好ましい。
【００３０】
Ｂ：０．００３％以下
Ｂは焼き入れ性を向上させる作用を有するため必要に応じて添加する。但し、０．００３％を超えるとめっき密着性が劣化するため、０．００３％を上限とするのが好ましい。含有させる場合には、０．０００５〜０．００２％とするのがより好ましい。
【００３１】
Ｔｉ、Ｎｂ、Ｖ：０．１％以下
Ｔｉ、ＮｂおよびＶは炭窒化物を形成し、鋼を析出強化により高強度化する作用を有するため必要に応じて添加する。これらを添加する場合は、それぞれ０．０１％以上添加するのが好ましい。但し、０．１％を超えても過度に高強度化し、延性がかえって劣化するため、上限は０．１％とするのが好ましい。含有させる場合には、０．０２〜０．０５％とするのがより好ましい。
【００３２】
Ｃｕ：１．０％以下
Ｃｕはオーステナイト中に偏析し、必要強度を得るためと所望の組織を得るために重要であるだけでなく、めっき密着性を向上させる効果もあるため必要に応じて添加する。めっき密着性が向上する理由は現時点では明らかになっていないが、所望の効果を得るためには最低０．０１％の添加が好ましい。但し、１．０％を超えるとコストが劣化するため、上限を１．０％とするのが好ましい。含有させる場合には、０．０５〜０．４％とするのがより好ましい。
【００３３】
Ｎｉ：１．０％以下
ＮｉはＣｕと同様オーステナイト中に偏析し、必要強度を得るためと所望の組織を得るため重要であるだけでなく、めっき密着性を向上させる効果もあるので必要に応じて添加する。めっき密着性が向上する理由は現時点では明らかになっていないが、所望の効果を得るためには、最低０．０１％添加するのが好ましい。但し、１．０％を超えるとコストが劣化するため、上限を１．０％とするのが好ましい。含有させる場合には、０．０２５〜０．２％とするのがより好ましい。
なお、上記の元素以外の残部はＦｅおよび不可避的不純物である。
【００３４】
焼き戻しマルテンサイト
焼き戻しマルテンサイトは、焼き戻しにより軟質化し充分な塑性変形能を有するため、延び特性の向上に有効である。体積分率２０％未満では、延性向上効果が認められないため２０％以上とした。但し８０％を超えると鋼板の高強度化が困難となるため８０％以下が好ましい。
【００３５】
残留オーステナイト
残留オーステナイトは加工時にマルテンサイトに歪誘起変態し、局部的に加えられた加工歪みを広く分散させ、鋼板の延性を向上させる効果を有する。体積分率２％未満では延性の顕著な向上が期待できないため、２％以上であることが必要であり、５％以上であると延性向上効果がより顕著であるため好ましい。
【００３６】
上記複合組織を得る製造法は特に限定されないが、例えば、鋼板をあらかじめ（Ａｃ₃変態点−８０℃）以上に加熱した後、１０℃／秒以上の冷却速度で組織を焼き入れし、次いでＣＧＬにてＡｃ₁〜Ａｃ₃変態点の間で加熱し、５℃／秒以上の冷却速度で冷却して組織を焼き戻すことにより得られる。但し、これは１例であり、本発明が規定する成分と相を有する高張力鋼板であれば、どのような製造方法で得られたものでもよい。
【００３７】
本発明でいう低温変態相とは、マルテンサイトあるいはベイナイトを指す。
マルテンサイト、ベイナイトとも硬質相であり、組織強化によって鋼板強度を増加させる作用を有する。また、変態時に可動転位の発生を伴うため、鋼板の降伏比を低下させる作用も有する。なお、このような効果を充分に得るためには、低温変態相はマルテンサイトとするのが好ましい。本発明において低温変態相の量は特に限定されない。鋼板の強度に応じて適宜配分すればよい。
【００３８】
次に、本発明において、めっき層中のＡｌ濃度 (質量％）、Ｓｉ濃度 (質量％）、地鉄表層の酸素量（ｍｇ／ｍ²) を規定した理由を説明する。
めっき層中のＡｌ濃度
本発明において、めっき層中のＡｌ濃度の範囲が重要である。本発明者は、前述のように、Ｍｎ／Ｓｉ質量比が０．５以上で、かつ、めっき層中のＳｉ濃度が前記式（２）を満たす鋼板では、ＧＩの場合は前記式（１）、ＧＡの場合は前記式（３）の範囲内で所定のめっき層中のＡｌ濃度を確保することにより良好なめっき密着性が確保できることを知見した。ＧＩの場合は、めっき後の復熱などによる合金化反応の開始を抑制する必要があるため、ＧＡの場合よりＡｌ濃度を高めにする。また、Ｓｉ含有量が多い場合には、局所的合金化反応が多発するので、これに基づく合金化反応の開始を抑制するため、Ｍｎ／Ｓｉ質量比が低いほど、Ａｌ含有量を多くする。
【００３９】
Ａｌ濃度が前記式（１）または式（３）の左辺の値より高いと、ＧＩの場合はめっき時の初期に生成するＦｅ−Ａｌ合金層が厚いため溶接性が劣化したり、ＧＡの場合は合金化が著しく遅延する。Ａｌ濃度が前記式（１）または式（３）の右辺の値より低いと、Ｆｅ−Ａｌ合金層の生成が抑えられ、硬くて脆いΓ相がめっき初期に生成しやすくなり、めっき密着性が劣化する。したがって、良好なめっき密着性を確保するためには、ＧＩの場合は前記式（１）、ＧＡの場合は前記式（３）の範囲内に所定のＡｌ濃度を維持することが必要である。
【００４０】
めっき層中のＡｌ濃度を所定量にするための方法は特に限定されないが、例えば、めっき浴中のＡｌ量を高めにしたり、めっき時間を長くすることによりＡｌと地鉄の反応を促進してめっき層中のＡｌ濃度を高くする方法が例示される。また、本発明の鋼中成分を含有する鋼板をあらかじめ加熱し、冷却後に表面を軽く酸洗し、表面を活性化した後に、ＣＧＬに通板してもよい。これらの製造方法の例は本発明を限定するものではない。
【００４１】
めっき層中のＳｉ濃度
ＧＩの場合も、ＧＡの場合も前記式（２）の範囲内で所定のめっき層中のＳｉ濃度を確保することにより良好なめっき密着性および耐食性が確保できる。めっき層中のＳｉは、地鉄（被めっき材）からめっき層中に供給されることにより、主に酸化物として存在するものと、固溶Ｓｉがめっき層中に取り込まれたものとがあるが、Ｓｉ濃度が前記式（２）の左辺の値より高いとめっき密着性が劣化し、逆にＳｉ濃度が前記式（２）の右辺の値より低いとめっき層の耐食性が劣化する。
めっき層中のＳｉ濃度を特定量にするための方法は特に限定されないが、めっき前の鋼板表面に濃化するＳｉ量を焼鈍条件、還元性雰囲気などを制御することにより、鋼板からめっき層に取り込まれるＳｉ量を調整することができる。
【００４２】
地鉄表層の酸素量
地鉄表層の内部酸化物が存在していると地鉄のＳｉやＭｎの含有量が極めて多くても、めっき密着性が改善可能である。これは、地鉄表層が十分に内部酸化していると、めっき直前の焼鈍時のＳｉの表面濃化が抑制されるためである。一方、内部酸化が不十分であると、めっき直前の焼鈍時にＳｉの表面濃化が抑制されないため、めっき密着性が劣化する。したがって、地鉄表層に存在する内部酸化物の量を、鋼板表面単位面積当たりの質量で０．０５ｇ／ｍ²以上とする必要がある。なお、地鉄表層の内部酸化物の量が余り多すぎると、耐食性を確保するためのめっき層中のＳｉが不足してしまい、さらに、表面の荒れが発生する。したがって、地鉄表層の内部酸化物の量は、鋼板表面単位面積当たりの質量で１ｇ／ｍ²以下とすることが好ましい。
【００４３】
ここで、地鉄表層とは、めっき層との界面から１００μｍまでの深さのことを言う。また、内部酸化物とは、地鉄の結晶粒界または結晶粒内に存在する酸化物のことを言い、地鉄表面に形成されている酸化物とは区別される。そして、次のように地鉄表層の酸素量を求めることにより測定できる。すなわち、めっき層を除去した鋼板について鋼中酸素量を分析し、さらに、同様にめっき層を除去した鋼板の表裏の表層を１００μｍまで機械研磨したものについて、鋼中酸素量を分析し、これらの分析値より表層の酸化物の増量分を算出し、鋼鈑表面の単位面積当たりの量（ｇ／ｍ²）に換算することにより求められる。ここで、めっき層の除去は、例えば、２０質量％ＮａＯＨ−１０質量％トリエタノールアミン水溶液と、３５質量％過酸化水素水溶液を１９５：７の割合で混合した溶液に浸漬することにより可能である。他に酸浸漬法、アルカリ浸漬法などが用いられるが、特に限定されない。ただし、めっき層除去後の表面が酸化しないように注意する必要がある。
【００４４】
地鉄表層の内部酸化物の量を確保する方法は問わないが、例えば、ＣＧＬ通板前に、Ｆｅにとっては還元性であるが、Ｓｉ、Ｍｎなどの易酸化性元素にとっては酸化性であるような、やや高露点条件で加熱することにより、Ｓｉ、Ｍｎなどの内部酸化物を予め確保する方法、あるいは、熱間圧延工程において、高温巻き取り後の冷却中に酸化スケールから供給される酸素で地鉄を内部酸化させ、これを黒皮酸洗除去、冷間圧延後にも残存させて被めっき材とする方法が例として挙げられるが、特にこれらに限定されない。
【００４５】
ＣＧＬ（溶融亜鉛めっき）条件
本発明の溶融亜鉛めっき鋼板を製造するための鋼板のＣＧＬ条件は特に限定されず、定法により実施可能である。但し、ＣＧＬ加熱温度（二次加熱温度）が６５０℃以下であると鋼板表面の酸化皮膜が還元できず、不めっきが発生しやすくなる。一方、８５０℃以上であると、加熱時にＳｉとＭｎの表面濃化が多いため、同様に不めっきが発生しやすい。よって６５０〜８５０℃が好ましい。
【００４６】
溶融亜鉛めっき浴は、めっき層の合金化後の密着性を確保するために、Ａｌ濃度を０．０８質量％以上とすることが好ましい。但し、０．２０質量％を超えると合金化が困難になったり、得られる溶融亜鉛めっき鋼板の溶接性が劣化することがあるため、上限は０．２０質量％が好ましい。なお、前記したように、めっき層中のＡｌ濃度を本発明の範囲に調整するために、浴中のＡｌ濃度の他に、進入板温、めっき浴浸漬時間、その他の操業条件を制御する。
【００４７】
溶融亜鉛めっき浴の浴温が４４０℃以下であると、めっき浴の浴温変動により凝固点（４２０℃）を下回る箇所が出てくる可能性があり、操業上安定性に欠ける。また、４８０℃を超えると加熱保持にかかるコストがかさむ。そのため浴温は４４０〜４８０℃が好ましい。
【００４８】
合金化する場合、合金化温度が４５０℃以下であるとζ相が生成しやすくなり、ＧＡの摺動性に欠けるおそれがあるだけでなく、合金化に時間がかかるため生産性が劣化する。また、６００℃を超えるとΓ相が生成しやすくなり、ＧＡのめっき密着性に欠けるおそれがある。そのため合金化温度は４５０〜６００℃が好ましい。
【００４９】
合金化度はＦｅ拡散量が８〜１３％の範囲に収まる程度であるのが好ましい。８％未満であるとζ相が残存し、耐フレーキング性が劣化しやすく、１３％以上であるとΓ相が生成し、めっき密着性が劣化する場合がある。但し、これらの製造方法の条件は例示であり、本発明は特定の製造方法に限定されない。
【００５０】
【実施例】
以下、実施例を挙げて本発明をより具体的に説明するが、本発明はこれらの実施例により何ら限定されるものではない。
（実施例１〜９、比較例１〜４）
表１に示した化学組成（Ｃ、Ｓｉ、Ｍｎ、Ｐ、Ｓ、Ａｌ、Ｃｒ、Ｃｕ、Ｎｉ、Ｍｏ、Ｔｉ、Ｎｂ、ＶおよびＢ）のスラブ（厚さ３００ｍｍ）を１２５０℃で加熱し、熱間圧延により厚さ２．０ｍｍの熱延鋼板（鋼Ａ〜Ｉが実施例；鋼Ｊが比較例）とした後、６２０℃で巻き取った。次いで、酸洗により黒皮除去した後、必要に応じ冷間圧延を行う場合には５０％の圧下率で圧延し、加熱炉で加熱（一次加熱）した後、ＣＧＬに通板して酸洗、焼鈍、溶融亜鉛めっきおよび合金化処理を行った。冷間圧延工程の有無、一次加熱条件、めっき浴中のＡｌ濃度と合金化の有無を表２に示した。なお、一次加熱後の冷却速度は３０℃／秒、二次加熱温度は７８０℃、二次加熱後の冷却速度は１０℃／秒であり、めっき付着量は片面で５０ｇ／ｍ²ずつであった。合金化温度は４５０〜６００℃の範囲とした。
【００５１】
【表１】

【００５２】
【表２】

【００５３】
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のめっき層中のＡｌ濃度、Ｓｉ濃度を表３に、合金化度（Ｆｅ拡散量）、めっき鋼板の焼き戻しマルテンサイト、残留オーステナイト、フェライト分率および低温変態相の複合組織の体積分率、めっき層剥離後の地鉄表層酸素量、めっき密着性、耐食性および機械的特性（伸び率、引張強度）についての調査結果を表４に示した。
【００５４】
【表３】

【００５５】
【表４】

【００５６】
めっき層中のＡｌ濃度、Ｓｉ濃度は、めっき層をインヒビターを添加したＮａＯＨ、ＫＯＨなどのアルカリ、もしくはＨＣｌ、Ｈ₂ＳＯ₄などの酸で溶解し、その液をＩＣＰなどで、分析定量することにより測定した。
【００５７】
鋼板の焼き戻しマルテンサイト相の体積分率は、樹脂に埋め込んだ鋼板断面を、研磨した後、１mass％ピロ亜硫酸ナトリウムのピクラール溶液（４ｇピクリン酸／１００ｍｌエタノール）を用いて、エッチングした後、電子顕微鏡によって倍率１０００倍で観察後、画像解析によって、１００ｍｍ四方の正方形領域内に存在するマルテンサイト相の体積率とした。
【００５８】
フェライト相は、樹脂に埋め込んだ鋼板断面を研磨し、ナイタール溶液（６９mass％ＨＮＯ₃溶液３vol ％−エタノール９７vol ％）で組織をエッチングした後、光学顕微鏡で２５０倍で観察した、１００ｍｍ四方の正方形領域内の写真を画像処理することによりフェライト相の占有面積率を求め、フェライト相の体積分率とした。
【００５９】
鋼板の残留オーステナイト相の体積分率は、鋼板より採取した試験片を板厚方向の中心面まで研磨し、板厚中心面でのＸ線強度測定により求めた。すなわち、ＭｏＫαを使用し、フェライト（マルテンサイトを含む）の（２００）（２１１）各面の回折Ｘ線強度と、オーステナイトの（２００）（２２０）各面の回折Ｘ線強度を求め、フェライト（マルテンサイトを含む）の（２００）（２１１）の積分強度とオーステナイト（２００）（２２０）の積分強度の合計値に対するオーステナイト（２００）（２２０）の積分強度の比を求め、これをオーステナイト相の体積分率とした。
【００６０】
めっき密着性は、めっき鋼板にセロファンテープを貼りテープ面を９０°内に曲げ、曲げ戻しをした後、テープを剥したときの単位長さ当りのめっき剥離量を蛍光Ｘ線によりＺｎカウント数として測定し、表５の基準に照らしてランク１、２のものを良好（○）、３以上のものを不良（×）として評価した。
【００６１】

【００６２】
耐食性は、軟鋼板（ＳＰＣＣ）の溶融亜鉛めっき鋼板または合金化溶融亜鉛めっき鋼板を基準に取り、それぞれの試験片を複合腐食サイクル試験（０．５％塩水噴霧を３５℃で６Ｈｒ実施後、７０℃で６Ｈｒ乾燥し、その後４０℃で湿度９０％の湿潤状態に１２Ｈｒ保持）を６０サイクル、すなわち、６０日間施した後、最大腐食深さを比較して評価した。腐食試験後の試験片は、腐食深さ（孔食）を極値統計処理により最大腐食深さを求めた。基準の鋼板の最大腐食深さの半分以下のものを良好（○）、１．５倍以上のものを不良（×）として評価した。
【００６３】
機械的特性は、鋼板から圧延方向と直交する方向を引張方向として採取したＪＩＳ５号引張試験片を用いて降伏強さ（降伏点）ＹＰ、引張り強度ＴＳ、伸び率Ｅｌを測定した。引張強度が７８０ＭＰａ以上で、かつ伸び率が２８％以上であるものを良好とした。
【００６４】
めっき層剥離後の地鉄表層の酸素量は、めっき層を２０質量％ＮａＯＨ−１０質量％トリエタノールアミン水溶液と、３５質量％過酸化水素水溶液を１９５：７の割合で混合した溶液に浸漬することによりめっき層を除去した試料について鋼中全酸素濃度を分析し、さらに、同様にめっき層を除去した後、鋼板の表裏の表層を１００μｍまで機械研磨した試料について、板厚方向中心部の酸素濃度を分析し、鋼中全酸素濃度と板厚方向中心部のそれぞれの分析値から表層のみの酸化増量を算出し、鋼板表面の単位面積当たりの量（ｇ／ｍ²) に換算した。
【００６５】
鋼組成、鋼組織、めっき層およびめっき層剥離後の地鉄表層酸素量が本発明の範囲内のものは、いずれもめっき密着性、溶融亜鉛めっき鋼板の機械的特性が良好であった。一方、本発明の範囲外のものは、めっき密着性、機械的特性が劣っていた。
【００６６】
【発明の効果】
以上のように、本発明によれば、めっき密着性、溶融亜鉛めっき鋼板の機械的特性に優れ、さらには耐食性にも優れた高張力溶融亜鉛めっき鋼板および高張力合金化溶融亜鉛めっき鋼板が得られる。本発明の鋼板を適用することにより、自動車車体の軽量化および低燃費化が可能となり、ひいては地球環境の改善にも大きく貢献する。
【図面の簡単な説明】
【図１】溶融亜鉛めっき鋼板（ＧＩ）の鋼中のＭｎ／Ｓｉ質量比とめっき層中のＡｌ濃度との関係を表す図である。
【図２】合金化溶融亜鉛めっき鋼板（ＧＡ）の鋼中のＭｎ／Ｓｉ質量比とめっき層中のＡｌ濃度との関係を表す図である。
【図３】溶融亜鉛めっき鋼板（ＧＩ、ＧＡ）の鋼中のＭｎ／Ｓｉ含有量とめっき層中のＳｉ濃度との関係を表す図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to high-tensile (alloyed) hot-dip galvanized steel sheets (including steel strips), and particularly high tensile strength with excellent strength-ductility balance and plating adhesion that can withstand even when pressed into complex shapes. The present invention relates to a (alloyed) hot-dip galvanized steel sheet and, in addition, to a high-tensile (alloyed) hot-dip galvanized steel sheet having excellent corrosion resistance.
[0002]
[Prior art]
In recent years, there has been a demand for improvement in fuel efficiency of automobiles from the viewpoint of conservation of the global environment. Furthermore, in order to protect a passenger | crew at the time of a collision, the safety improvement of a motor vehicle body is also requested | required. Under such circumstances, the weight reduction of the automobile body and the reinforcement of the automobile body are being actively promoted. In particular, in order to reduce the weight of an automobile body, it has been proposed to increase the strength of steel sheets for automobiles such as hot-rolled steel sheets and cold-rolled steel sheets and reduce the thickness of the steel sheet. On the other hand, since many automotive parts made of steel plates are formed by press working, the automotive steel plates are required to have excellent press formability. Moreover, since the hot dip galvanized steel sheet is excellent in rust prevention (corrosion resistance) and can be manufactured at low cost, it is frequently used as a rust-proof surface-treated steel sheet for automobile bodies.
[0003]
In order to increase the strength of a steel sheet, it is necessary to add elements such as Si and Mn to enhance solid solution. However, since Si and Mn are easily oxidizable elements, Si, Mn, etc. As a result, the wettability of the hot dip galvanizing applied to the surface deteriorates and the plating adhesion deteriorates.
In order to solve the above problem, for example, in JP-A-5-179356 and JP-A-5-51647, the addition amount of Si and Mn is reduced, quenching and quenching during hot rolling is performed, and in a hot dip galvanizing line A method of plating after annealing in a two-phase region has been proposed. However, in practice, if Si is added even a little, plating adhesion deteriorates and plating peeling is likely to occur. Conventionally, plating adhesion is good for steel sheets having a high Si and Mn content. It was virtually impossible to apply hot dip galvanizing.
[0004]
In order to achieve both good elongation and strength, it is necessary that the final structure of the hot dip galvanized steel sheet includes a tempered martensite and residual austenite, and the balance is a composite structure composed of ferrite and a low-temperature transformation phase. For this purpose, it is effective to add a large amount of Si and Mn. However, if a large amount of Si and Mn is contained as described above, the plating adhesion deteriorates.
[0005]
[Problems to be solved by the invention]
The present invention is intended to solve the above problem, and even if the base steel sheet contains a large amount of Si and Mn, it has excellent hot dip galvanizing adhesion, and excellent mechanical properties such as press formability and strength ductility balance. Another object is to provide a high-tensile (alloyed) hot-dip galvanized steel sheet. In addition, an object is to provide a high-tensile (alloyed) hot-dip galvanized steel sheet that is further excellent in corrosion resistance.
[0006]
[Means for Solving the Problems]
The present inventor has intensively investigated the conditions for preventing deterioration of hot dip galvanizing adhesion to the surface layer of a steel sheet containing a large amount of Si and Mn and maintaining mechanical properties in a high-tensile hot dip galvanized steel sheet. As a result, even when the Mn / Si mass ratio in the steel is relatively small and a relatively large amount of Si is contained, the amount of oxygen in the surface layer of the base material immediately below the plating layer is large, and the Mn / Si mass in the steel It has been found that the above object can be achieved by specifying the relationship between the ratio and the Al and Si concentrations in the plating layer.
[0007]
That is, in the present invention, by mass, C: 0.05 to 0.25%, Si: more than 0.50% and less than 2.00%, Mn: 3.5% or less, Al: 0.01 to 1.0 %, With the balance being Fe and inevitable impurities, Mn / Si mass ratio in the steel: composition of 0.5 or more and less than 2, tempered martensite, residual austenite, ferrite and low-temperature transformation phase, On the steel sheet having a composite structure in which the tempered martensite is 20% or more and the retained austenite is 2% or more, the Al concentration in the plating layer satisfies the following formula (1), and the plating layer contains In addition to having a hot dip galvanized layer satisfying the following formula (2), the surface layer oxygen content after removing the plated layer is 0.05 g / m ² It is a high-tensile hot-dip galvanized steel sheet excellent in strength ductility balance, plating adhesion and corrosion resistance, characterized by the above.
[0008]
0.67-1 / 50 (Mn / Si) ≧ [Al concentration in plating layer (mass%)] ≧ 0.37-1 / 50 (Mn / Si)
(1)
1.67-1 / 3 (Mn / Si) ≧ [Si concentration in plating layer (mass%)] ≧ 0.167-1 / 30 (Mn / Si)
(2)
(Mn / Si in formulas (1) and (2) represents the mass ratio of Mn / Si in steel.)
[0009]
A preferred present invention is a high-tensile hot-dip galvanized steel sheet excellent in strength ductility balance, plating adhesion and corrosion resistance, wherein the steel sheet further contains at least one component selected from the following group.
(First Group) At least one selected from the group consisting of Cr of 1.0% or less, Mo of 1.0% or less, and B of 0.003% or less by mass%.
(Second group) At least one selected from the group consisting of Ti of 0.1% or less by mass, Nb of 0.1% or less, and V of 0.1% or less.
(Third group) At least one selected from the group consisting of 1.0% or less of Cu and 1.0% or less of Ni by mass.
[0010]
Moreover, this invention is mass%, C: 0.05-0.25%, Si: more than 0.50% and less than 2.00%, Mn: 3.5% or less, Al: 0.01-1. A composition containing 0%, the balance being Fe and inevitable impurities, and a Mn / Si mass ratio in the steel: 0.5 or more and less than 2, tempered martensite, residual austenite, ferrite and low-temperature transformation phase On a steel sheet having a composite structure in which the tempered martensite is 20% or more and the retained austenite is 2% or more in terms of volume fraction, the Al concentration in the plating layer satisfies the following formula (3): And the Si concentration in the plating layer satisfies the following formula (2) Alloying It has a hot-dip galvanized layer and the amount of oxygen in the surface layer after removing the plated layer is 0.05 g / m ² This is a high-tensile alloyed hot-dip galvanized steel sheet excellent in strength ductility balance, plating adhesion and corrosion resistance characterized by the above.
[0011]
0.5-1 / 50 (Mn / Si) ≧ [Al concentration in plating layer (mass%)] ≧ 0.2-1 / 50 (Mn / Si)
(3)
1.67-1 / 3 (Mn / Si) ≧ [Si concentration in plating layer (mass%)] ≧ 0.167-1 / 30 (Mn / Si)
(2)
(Mn / Si in formulas (3) and (2) represents the mass ratio of Mn / Si in steel)
[0012]
A preferred present invention is a high-tensile hot-dip galvanized steel sheet excellent in strength ductility balance, plating adhesion and corrosion resistance, wherein the steel sheet further contains at least one component selected from the following group.
(First Group) At least one selected from the group consisting of Cr of 1.0% or less, Mo of 1.0% or less, and B of 0.003% or less by mass%.
(Second group) At least one selected from the group consisting of Ti of 0.1% or less by mass, Nb of 0.1% or less, and V of 0.1% or less.
(Third group) At least one selected from the group consisting of 1.0% or less of Cu and 1.0% or less of Ni by mass.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The present inventor, when applying hot dip galvanizing to a high-strength steel sheet containing Si and Mn, by allowing an oxide to exist in the crystal grain boundary and / or crystal grains of the surface layer of the steel sheet, It was found in Japanese Patent Application Laid-Open No. 9-310163 that the formation of a Mn-enriched film was suppressed, the wettability with molten zinc was improved, and the occurrence of non-plating could be suppressed.
A more detailed study was conducted on the plating quality, mechanical properties, and weldability of hot-dip galvanized steel sheets (GI) and alloyed hot-dip galvanized steel sheets (GA), which have internal oxides on the surface layer of the steel. As a result, it was found that it was also affected by the Mn / Si mass ratio in the steel and the Al concentration in the plating layer.
[0014]
That is, the present invention has been completed based on the following experimental facts. Hereinafter, the steel composition is expressed by mass fraction.
A sheet bar having a thickness of 30 mm containing C: 0.10%, Si: 0.3-2%, Mn: 1.0-3.5%, P: 0.01%, Al: 0.04% After heating at 1250 ° C. to obtain a hot-rolled steel sheet having a thickness of 2.3 mm by 5 passes, the film was wound at 620 ° C. Next, the black skin was removed by pickling, cold rolled to 1.0 mm, heated at 800-900 ° C. in an annealing furnace, and then pickled at 60 ° C.-5% HCl for 6 seconds. Then, 5% H at 780 ° C by hot dip galvanizing simulator ₂ -N ₂ Annealed in a reducing atmosphere, hot dip galvanized in a hot dip galvanizing bath (0.08 to 0.25% Al—Zn) at 460 ° C., the adhesion amount was 50 g / m on one side ² Gas wiping was performed. Alloying was performed at 500 ° C. in an electric furnace. The plating adhesion and mechanical properties of the obtained plated steel sheet were investigated.
[0015]
In addition, the amount of the internal oxide in the surface layer portion of the ground metal immediately below the plating layer is 0.05 to 0.5 g / m. ² The annealing atmosphere during heating after cold rolling was adjusted so as to be in the range.
Hereinafter, the alloyed hot-dip galvanized steel sheet is represented by GA, the non-alloyed hot-dip galvanized steel sheet is represented by GI, the cold-rolled steel sheet is represented by CR, the hot-rolled steel sheet is represented by Hot, and the Mn / Si mass ratio in the steel and The relationship between the Al concentration and the Si concentration in the plating layer will be described.
[0016]
FIG. 1 shows the Mn / Si mass ratio in the steel sheet and the Al concentration (mass%) in the plating layer that affect the plating quality, mechanical properties and weldability of GI.
When the Mn / Si mass ratio is 2.0 or more, if the Al concentration in the plating layer satisfies the following formula (1), the plating quality is good and the mechanical properties slightly vary. However, both mechanical properties and weldability are generally good. When the Mn / Si mass ratio is less than 0.5, poor plating quality occurs even when the Al concentration in the plating layer is in the range of the following formula (1). In the region where the Mn / Si mass ratio is 0.5 or more and less than 2.0, if the Al concentration in the plating layer exceeds the range of the following formula (1), poor welding occurs, and the following formula (1) If it is less than this range, poor plating quality will occur.
In the range where the Mn / Si mass ratio is 0.5 or more and less than 2.0 and the Al concentration in the plating layer satisfies the following formula (1), those having good plating quality and those having poor plating are mixed.
0.67-1 / 50 (Mn / Si) ≧ [Al concentration in plating layer (mass%)] ≧ 0.37-1 / 50 (Mn / Si)
(1)
[0017]
FIG. 2 shows the Mn / Si mass ratio affecting the plating quality, mechanical properties and weldability of GA and the Al concentration (mass%) in the plating layer.
When the Mn / Si mass ratio is 2.0 or more, if the Al concentration in the plating layer satisfies the following formula (3), the plating quality is good and the mechanical properties slightly vary. However, the mechanical properties are generally good. Further, the problem of delay in alloying does not occur. When the Mn / Si mass ratio is less than 0.5, poor plating quality occurs even when the Al concentration in the plating layer is in the range of the following formula (3). In the region where the Mn / Si mass ratio is 0.5 or more and less than 2.0, if the Al concentration in the plating layer exceeds the range of the following formula (3), alloying delay occurs, and the following formula (3 If the range is not within the range, the plating quality will be poor. In the range where the Mn / Si mass ratio is 0.5 or more and less than 2.0 and the Al concentration in the plating layer satisfies the following formula (3), those having good plating quality and those having poor plating are mixed.
0.5-1 / 50 (Mn / Si) ≧ [Al concentration in plating layer (mass%)] ≧ 0.2-1 / 50 (Mn / Si)
(3)
[0018]
Further, for GI and GA obtained by adjusting the Al concentration in the plating bath so that the Al concentration in the plating layer satisfies the above formula (1) for GI and the above formula (3) for GA, The effects of Mn / Si mass ratio in the steel sheet and Si concentration (mass%) in the plating layer on the plating quality, mechanical properties and weldability were investigated. As a result, as shown in FIG. 3, it was found that when the Si concentration in the plating layer satisfies the following formula (2) for both GI and GA, the plating quality does not deteriorate.
1.67-1 / 3 (Mn / Si) ≧ [Si concentration in plating layer (mass%)] ≧ 0.167-1 / 30 (Mn / Si)
(2)
[0019]
From the above experimental results, when the Mn / Si mass ratio in the steel is less than 2, that is, even when the Si content is relatively large compared to Mn, the oxygen content of the surface layer is within a predetermined range, If the Al concentration and Si concentration in the layer are adjusted within a specific range, the adhesiveness of the hot dip galvanized layer is good, but if the Al concentration in the plated layer is outside the specific range, the weldability is deteriorated or alloyed. It was found that corrosion resistance and plating adhesion deteriorate when the Si concentration in the plating layer is removed, and that adhesion deteriorates when the Mn / Si mass ratio in the steel is outside a specific range. The above formulas (1) and (2) and the above formulas (3) and (2) were derived.
[0020]
That is, the Mn / Si mass ratio in the steel and the Al concentration and Si concentration in the plating layer are adjusted so as to satisfy the above formulas (1) and (2), and the above formulas (3) and (2). Then, even if Si and Mn existed in the steel, it was found that GI and GA having good adhesion of the hot dip galvanizing to the steel plate surface could be produced, and the present invention was completed.
[0021]
The reason why the content of the constituent components in the steel and the composite structure thereof are defined in the present invention is as follows.
C: 0.05-0.25%
C is an indispensable component for obtaining the required strength and for obtaining a desired structure such as retained austenite, and at least 0.05% is necessary. However, if it exceeds 0.25%, the weldability deteriorates, so The range. Preferably it is 0.07 to 0.18%.
[0022]
Si: more than 0.50% and less than 2.00%
Si is an indispensable component for obtaining solid solution strengthening and a desired structure, and is a component that makes it possible to increase the strength without deteriorating ductility. The effect is not exhibited unless it exceeds 0.50%. On the other hand, when it is 2.00% or more, the plating adhesion deteriorates. Therefore, the above range was adopted. Preferably it is 0.6 to 1.6%.
[0023]
Mn: 3.5% or less
Similar to C, it is an essential component for obtaining the required strength, and improving the hardenability of the steel to obtain the desired structure. If it is 1% or more, the effect is sufficiently exhibited, which is preferable. However, even if it exceeds 3.5%, the effect is saturated and the cost is increased.
[0024]
Al: 0.01 to 1.0%
Al is preferably added for the purpose of deoxidation and the like. It also contributes to the improvement of ductility. In order to obtain a desired effect, 0.01% or more is necessary. If the content exceeds 1.0%, the effect is saturated and the cost is increased, so the upper limit is made 1.0%.
[0025]
Mn / Si mass ratio in steel: 0.5 or more and less than 2
In order to obtain the plating adhesion improving effect, it is advantageous that the Mn / Si mass ratio in the steel is higher. This is because the surface concentrate produced during annealing immediately before plating changes from an Si-based oxide to an Si—Mn based complex oxide having good wettability with molten zinc. Further, when the steel sheet is preheated before passing through a continuous hot dip galvanizing facility (CGL) and then the surface is activated by pickling the surface after cooling, Mn / Si in the steel The higher the mass ratio, the better the pickling performance of the oxide film. This is presumably because the oxide on the surface of the steel sheet changes from a Si-based oxide having poor pickling properties to a Si—Mn-based composite oxide having good pickling properties.
[0026]
Moreover, since the one where the Mn / Si mass ratio in steel is higher does not delay the alloying, the productivity in the case of alloying after hot dip galvanizing is also improved. When the Mn / Si mass ratio in the steel is less than 0.5, the plating adhesion deteriorates, so the Mn / Si mass ratio in the steel is defined as 0.5 or more. Further, when the Mn / Si mass ratio in the steel is 2 or more, the variation in mechanical properties becomes slightly large. In order to obtain the high-tensile and highly ductile plated steel sheet that is the object of the present invention, the Mn / Si mass ratio in the steel is preferably 0.5 or more and less than 2. More preferred is 0.8 or more and less than 2.
[0027]
Furthermore, the high-tensile hot-dip galvanized steel sheet or the high-tensile alloyed hot-dip galvanized steel sheet of the present invention may contain one or more elements belonging to Group 3 in the following amounts (mass%) as steel plate components. . In that case, the following effects are further obtained.
The first group is at least one selected from the group consisting of Cr, Mo and B, and contributes mainly to improving the hardenability.
The second group is at least one selected from the group consisting of Ti, Nb and V, which mainly forms carbonitrides and acts to increase the strength of the steel by precipitation strengthening.
The third group is at least one selected from the group consisting of Cu and Ni, and mainly contributes to improvement of plating adhesion.
[0028]
Cr: 1.0% or less
Cr improves the hardenability and has the effect of promoting the formation of a low temperature transformation phase, so it is added as necessary. Preferably, 0.05% or more is effective, but if it exceeds 1.0%, the plating adhesion deteriorates, so the upper limit is preferably made 1.0%. When it contains, it is more preferable to set it as 0.1 to 0.3%.
[0029]
Mo: 1.0% or less
Mo, like Cr, improves the hardenability and has the effect of promoting the formation of a low-temperature transformation phase, so it is added as necessary. Preferably, 0.05% or more is effective, but if it exceeds 1.0%, the cost increases, so the upper limit is preferably made 1.0%. When contained, it is more preferably 0.05 to 0.3%.
[0030]
B: 0.003% or less
B has the effect of improving the hardenability, so is added as necessary. However, if it exceeds 0.003%, the plating adhesion deteriorates, so 0.003% is preferably the upper limit. When it contains, it is more preferable to set it as 0.0005 to 0.002%.
[0031]
Ti, Nb, V: 0.1% or less
Ti, Nb, and V form carbonitrides and have the effect of increasing the strength of steel by precipitation strengthening, so are added as necessary. When adding these, it is preferable to add 0.01% or more respectively. However, even if it exceeds 0.1%, the strength is excessively increased and ductility is deteriorated. Therefore, the upper limit is preferably set to 0.1%. When contained, it is more preferably 0.02 to 0.05%.
[0032]
Cu: 1.0% or less
Cu is segregated in austenite and is important not only for obtaining the required strength and for obtaining the desired structure, but also for improving the plating adhesion, and is added as necessary. The reason why the plating adhesion is improved is not clear at present, but in order to obtain a desired effect, the addition of at least 0.01% is preferable. However, if it exceeds 1.0%, the cost deteriorates, so the upper limit is preferably made 1.0%. When contained, it is more preferably 0.05 to 0.4%.
[0033]
Ni: 1.0% or less
Ni is segregated in austenite like Cu and is important not only for obtaining the required strength and for obtaining the desired structure, but also for improving the plating adhesion, and is added as necessary. The reason why the plating adhesion is improved is not clear at present, but in order to obtain a desired effect, it is preferable to add at least 0.01%. However, if it exceeds 1.0%, the cost deteriorates, so the upper limit is preferably made 1.0%. When it contains, it is more preferable to set it as 0.025 to 0.2%.
The balance other than the above elements is Fe and inevitable impurities.
[0034]
Tempered martensite
Tempered martensite is softened by tempering and has sufficient plastic deformability, and is therefore effective in improving elongation characteristics. If the volume fraction is less than 20%, the effect of improving ductility is not recognized, so the content was set to 20% or more. However, if it exceeds 80%, it is difficult to increase the strength of the steel sheet, so 80% or less is preferable.
[0035]
Retained austenite
Residual austenite has an effect of strain-induced transformation into martensite during processing, widely dispersing locally applied processing strain, and improving the ductility of the steel sheet. If the volume fraction is less than 2%, a significant improvement in ductility cannot be expected. Therefore, it is necessary that the volume fraction be 2% or more, and if it is 5% or more, the effect of improving the ductility is more remarkable.
[0036]
The production method for obtaining the composite structure is not particularly limited. _Three Transformation point-80 ° C) or higher, and the structure was quenched at a cooling rate of 10 ° C / second or higher. ₁ ~ Ac _Three It is obtained by heating between transformation points, cooling at a cooling rate of 5 ° C./second or more, and tempering the structure. However, this is only an example, and any high-strength steel sheet having a component and phase defined by the present invention may be used.
[0037]
The low temperature transformation phase referred to in the present invention refers to martensite or bainite.
Both martensite and bainite are hard phases and have the effect of increasing steel sheet strength by strengthening the structure. Moreover, since it involves the generation of movable dislocations during transformation, it also has the effect of reducing the yield ratio of the steel sheet. In order to sufficiently obtain such an effect, the low temperature transformation phase is preferably martensite. In the present invention, the amount of the low temperature transformation phase is not particularly limited. What is necessary is just to distribute suitably according to the intensity | strength of a steel plate.
[0038]
Next, in the present invention, the Al concentration (mass%), the Si concentration (mass%) in the plating layer, and the oxygen content (mg / m) ² Explain the reason for specifying).
Al concentration in the plating layer
In the present invention, the range of Al concentration in the plating layer is important. As described above, the inventor of the present invention has a Mn / Si mass ratio of 0.5 or more and a steel sheet in which the Si concentration in the plating layer satisfies the above formula (2). In the case of GA, it has been found that good plating adhesion can be secured by securing the Al concentration in the predetermined plating layer within the range of the formula (3). In the case of GI, since it is necessary to suppress the start of the alloying reaction due to recuperation after plating, the Al concentration is made higher than in the case of GA. Further, when the Si content is high, local alloying reactions occur frequently. Therefore, in order to suppress the initiation of the alloying reaction based on this, the Al content is increased as the Mn / Si mass ratio is lower.
[0039]
If the Al concentration is higher than the value on the left side of the formula (1) or formula (3), in the case of GI, the Fe-Al alloy layer generated at the initial stage of plating is thick, so that the weldability deteriorates or the case of GA Significantly delays alloying. When the Al concentration is lower than the value on the right side of the formula (1) or formula (3), the formation of the Fe—Al alloy layer is suppressed, and a hard and brittle Γ phase is easily generated at the initial stage of plating, and the plating adhesion is improved. to degrade. Therefore, in order to ensure good plating adhesion, it is necessary to maintain a predetermined Al concentration within the range of the formula (1) in the case of GI and the range of the formula (3) in the case of GA.
[0040]
The method for setting the Al concentration in the plating layer to a predetermined amount is not particularly limited. For example, by increasing the amount of Al in the plating bath or by increasing the plating time, the reaction between Al and the ground iron is promoted. A method for increasing the Al concentration in the plating layer is exemplified. Moreover, after heating the steel plate containing the component in steel of this invention beforehand, after cooling, the surface may be lightly pickled, and after activating the surface, you may plate through CGL. These examples of the production method are not intended to limit the present invention.
[0041]
Si concentration in the plating layer
In the case of GI and GA, good plating adhesion and corrosion resistance can be ensured by securing the Si concentration in the predetermined plating layer within the range of the formula (2). Si in the plating layer is mainly present as an oxide by being supplied from the ground iron (material to be plated) into the plating layer, and there is one in which solute Si is taken into the plating layer. However, if the Si concentration is higher than the value on the left side of the equation (2), the plating adhesion deteriorates. Conversely, if the Si concentration is lower than the value on the right side of the equation (2), the corrosion resistance of the plating layer deteriorates.
The method for setting the Si concentration in the plating layer to a specific amount is not particularly limited, but the amount of Si concentrated on the steel plate surface before plating is controlled from the steel plate to the plating layer by controlling the annealing conditions, reducing atmosphere, etc. The amount of Si taken in can be adjusted.
[0042]
Oxygen content of the surface layer
When the internal oxide of the surface iron surface layer is present, the plating adhesion can be improved even if the Si or Mn content of the ground iron is extremely high. This is because the surface concentration of Si during annealing immediately before plating is suppressed when the surface iron surface layer is sufficiently internally oxidized. On the other hand, when the internal oxidation is insufficient, the surface concentration of Si is not suppressed at the time of annealing immediately before plating, so that the plating adhesion deteriorates. Therefore, the amount of the internal oxide present in the surface layer of the steel is 0.05 g / m in mass per unit surface area of the steel plate. ² It is necessary to do it above. In addition, when there is too much quantity of the internal oxide of a surface iron surface layer, Si in the plating layer for ensuring corrosion resistance will run short, and also surface roughness will generate | occur | produce. Therefore, the amount of the internal oxide on the surface layer of the steel is 1 g / m in mass per unit surface area of the steel sheet. ² The following is preferable.
[0043]
Here, the surface iron surface layer means a depth of 100 μm from the interface with the plating layer. In addition, the internal oxide means an oxide existing in the grain boundary or in the crystal grain of the base iron, and is distinguished from the oxide formed on the surface of the base iron. And it can measure by calculating | requiring the amount of oxygen of a surface iron surface layer as follows. That is, the oxygen content in the steel was analyzed for the steel plate from which the plating layer was removed, and the oxygen content in the steel was analyzed for those obtained by mechanically polishing the front and back surfaces of the steel plate from which the plating layer was removed to 100 μm. The amount of increase in the surface oxide is calculated from the analysis value, and the amount per unit area of the steel plate surface (g / m ² ). Here, the plating layer can be removed, for example, by immersing in a solution in which a 20% by mass NaOH-10% by mass triethanolamine aqueous solution and a 35% by mass hydrogen peroxide aqueous solution are mixed at a ratio of 195: 7. . In addition, an acid dipping method, an alkali dipping method, or the like is used, but is not particularly limited. However, care must be taken not to oxidize the surface after removing the plating layer.
[0044]
There is no limitation on the method for securing the amount of internal oxide on the surface layer of the iron base. For example, it is reducible for Fe before passing through CGL, but it is oxidizable for oxidizable elements such as Si and Mn. In addition, by heating under slightly higher dew point conditions, it is possible to secure internal oxides such as Si and Mn in advance, or in the hot rolling process, with oxygen supplied from the oxide scale during cooling after high temperature winding. Examples include a method of oxidizing the base iron internally, removing the black skin by pickling, and allowing it to remain after cold rolling to obtain a material to be plated, but is not particularly limited thereto.
[0045]
CGL (hot dip galvanizing) conditions
The CGL conditions of the steel sheet for producing the hot dip galvanized steel sheet of the present invention are not particularly limited and can be carried out by a usual method. However, if the CGL heating temperature (secondary heating temperature) is 650 ° C. or lower, the oxide film on the steel sheet surface cannot be reduced, and non-plating is likely to occur. On the other hand, when the temperature is 850 ° C. or higher, the surface concentration of Si and Mn is large during heating, and thus non-plating is likely to occur. Therefore, 650-850 degreeC is preferable.
[0046]
The hot dip galvanizing bath preferably has an Al concentration of 0.08% by mass or more in order to ensure adhesion of the plated layer after alloying. However, if it exceeds 0.20% by mass, alloying may become difficult, and the weldability of the resulting hot-dip galvanized steel sheet may deteriorate, so the upper limit is preferably 0.20% by mass. As described above, in order to adjust the Al concentration in the plating layer to the range of the present invention, in addition to the Al concentration in the bath, the approach plate temperature, the plating bath immersion time, and other operation conditions are controlled.
[0047]
When the bath temperature of the hot dip galvanizing bath is 440 ° C. or lower, there is a possibility that a portion below the freezing point (420 ° C.) may appear due to the bath temperature fluctuation of the plating bath, and the operation is not stable. Moreover, when it exceeds 480 degreeC, the cost concerning heating holding will increase. Therefore, the bath temperature is preferably 440 to 480 ° C.
[0048]
In the case of alloying, if the alloying temperature is 450 ° C. or lower, the ζ phase is likely to be generated, and not only the GA slidability may be lost, but also the time required for alloying deteriorates productivity. Moreover, when it exceeds 600 degreeC, it will become easy to produce | generate a (GAMMA) phase and there exists a possibility that the plating adhesiveness of GA may be missing. Therefore, the alloying temperature is preferably 450 to 600 ° C.
[0049]
The degree of alloying is preferably such that the amount of Fe diffusion falls within the range of 8 to 13%. If it is less than 8%, the ζ phase remains and the flaking resistance is likely to deteriorate, and if it is 13% or more, the Γ phase is generated and the plating adhesion may deteriorate. However, the conditions of these manufacturing methods are examples, and the present invention is not limited to a specific manufacturing method.
[0050]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited at all by these Examples.
(Examples 1-9, Comparative Examples 1-4)
A slab (thickness 300 mm) having a chemical composition (C, Si, Mn, P, S, Al, Cr, Cu, Ni, Mo, Ti, Nb, V, and B) shown in Table 1 was heated at 1250 ° C. A hot rolled steel sheet having a thickness of 2.0 mm (steel A to I was an example; steel J was a comparative example) was hot rolled at 620 ° C. Next, after removing the black skin by pickling, if cold rolling is performed as necessary, it is rolled at a reduction rate of 50%, heated in a heating furnace (primary heating), passed through CGL and pickled. Annealing, hot dip galvanizing and alloying treatment were performed. Table 2 shows the presence or absence of the cold rolling process, the primary heating conditions, the Al concentration in the plating bath, and the presence or absence of alloying. The cooling rate after primary heating is 30 ° C./second, the secondary heating temperature is 780 ° C., the cooling rate after secondary heating is 10 ° C./second, and the amount of plating adhesion is 50 g / m on one side. ² It was one by one. The alloying temperature was in the range of 450 to 600 ° C.
[0051]
[Table 1]

[0052]
[Table 2]

[0053]
Table 3 shows the Al concentration and Si concentration in the coating layer of the obtained hot-dip galvanized steel sheet and alloyed hot-dip galvanized steel sheet, alloying degree (Fe diffusion amount), tempered martensite of the plated steel sheet, retained austenite, ferrite Table 4 shows the results of investigations on the volume fraction of the composite structure of the fraction and the low-temperature transformation phase, the amount of oxygen in the surface layer of the steel layer after peeling of the plating layer, plating adhesion, corrosion resistance, and mechanical properties (elongation rate, tensile strength). It was.
[0054]
[Table 3]

[0055]
[Table 4]

[0056]
Al concentration and Si concentration in the plating layer are determined by adding alkali to the plating layer, such as NaOH and KOH, or HCl, H ₂ SO _Four It measured by melt | dissolving with acids, etc., and analyzing and quantifying the liquid by ICP etc.
[0057]
The volume fraction of the tempered martensite phase of the steel sheet was determined by polishing the cross-section of the steel sheet embedded in the resin, etching it with a picral solution (4 g picric acid / 100 ml ethanol) of 1 mass% sodium pyrosulfite, After observation with a microscope at a magnification of 1000 times, the volume ratio of the martensite phase present in a 100 mm square area was determined by image analysis.
[0058]
The ferrite phase is obtained by polishing the cross section of the steel plate embedded in the resin, and adding a nital solution (69 mass% HNO _Three After etching the structure with 3 vol% solution-97 vol% ethanol), the area occupied by the ferrite phase was determined by image processing of a photograph in a 100 mm square area observed at 250 times with an optical microscope. Volume fraction was used.
[0059]
The volume fraction of the retained austenite phase of the steel plate was obtained by polishing a test piece collected from the steel plate to the center plane in the plate thickness direction and measuring the X-ray intensity at the plate thickness center plane. That is, using MoKα, the diffraction X-ray intensity of each surface (200) (211) of ferrite (including martensite) and the diffraction X-ray intensity of each surface (200) (220) of austenite are obtained, and ferrite ( The ratio of the integrated intensity of austenite (200) (220) to the total value of the integrated intensity of (200) (211) of martensite and the integrated intensity of austenite (200) (220) was determined, and this was calculated as the austenite phase. Volume fraction was used.
[0060]
For plating adhesion, cellophane tape is applied to a plated steel sheet, the tape surface is bent within 90 °, bent back, and the amount of plating peeled off per unit length when the tape is peeled is expressed as a Zn count by fluorescent X-rays. Based on the criteria of Table 5, those of

ranks

1 and 2 were evaluated as good (◯), and those of 3 or more were evaluated as bad (×).
[0061]

[0062]
Corrosion resistance is based on a hot-dip galvanized steel plate or alloyed hot-dip galvanized steel plate of mild steel plate (SPCC). Each test piece was subjected to a combined corrosion cycle test (0.5% salt spray was applied at 35 ° C. for 6 hours, then 70 The sample was dried at 6 ° C. for 6 hours, and then kept at 12 ° C. in a wet state of 90% humidity at 40 ° C. for 60 cycles, that is, after 60 days, the maximum corrosion depth was compared and evaluated. For the test piece after the corrosion test, the maximum corrosion depth was determined by extreme statistical processing of the corrosion depth (pitting corrosion). A steel sheet of less than half the maximum corrosion depth of the standard steel sheet was evaluated as good (◯), and a steel sheet of 1.5 times or more was evaluated as defective (×).
[0063]
For mechanical properties, yield strength (yield point) YP, tensile strength TS, and elongation El were measured using a JIS No. 5 tensile test piece taken from the steel sheet with the direction orthogonal to the rolling direction as the tensile direction. Those having a tensile strength of 780 MPa or more and an elongation of 28% or more were considered good.
[0064]
The amount of oxygen in the surface layer of the ground iron after the plating layer is peeled is immersed in a solution obtained by mixing a 20 mass% NaOH-10 mass% triethanolamine aqueous solution and a 35 mass% hydrogen peroxide aqueous solution in a ratio of 195: 7. For the sample from which the plating layer was removed, the total oxygen concentration in the steel was analyzed, and after removing the plating layer in the same manner, the oxygen in the central part in the plate thickness direction was obtained by mechanically polishing the front and back surfaces of the steel plate to 100 μm. Analyzing the concentration, calculating the amount of increase in oxidation only on the surface layer from the analytical values of the total oxygen concentration in the steel and the central part in the thickness direction, and the amount per unit area of the steel sheet surface (g / m ² ).
[0065]
The steel composition, steel structure, plated layer, and surface iron surface layer oxygen content after peeling of the plated layer were within the range of the present invention, and the plating adhesion and the mechanical properties of the hot-dip galvanized steel sheet were all good. On the other hand, those outside the scope of the present invention were inferior in plating adhesion and mechanical properties.
[0066]
【The invention's effect】
As described above, according to the present invention, a high-tensile hot-dip galvanized steel sheet and a high-tensile alloyed hot-dip galvanized steel sheet that are excellent in plating adhesion, mechanical properties of hot-dip galvanized steel sheet, and excellent in corrosion resistance are obtained. It is done. By applying the steel plate of the present invention, it is possible to reduce the weight and fuel consumption of an automobile body, and thus greatly contribute to the improvement of the global environment.
[Brief description of the drawings]
FIG. 1 is a diagram showing the relationship between the Mn / Si mass ratio in hot dip galvanized steel sheet (GI) and the Al concentration in a plating layer.
FIG. 2 is a diagram showing the relationship between the Mn / Si mass ratio in steel of a galvannealed steel sheet (GA) and the Al concentration in the plating layer.
FIG. 3 is a diagram showing the relationship between the Mn / Si content in hot dip galvanized steel sheets (GI, GA) and the Si concentration in the plating layer.

Claims

C: 0.05 to 0.25% by mass, Si: more than 0.50% and less than 2.00%, Mn: 3.5% or less, Al: 0.01 to 1.0%, the balance being Fe and unavoidable impurities, Mn / Si mass ratio in steel: 0.5 to less than 2 composition, tempered martensite, residual austenite, ferrite and low-temperature transformation phase. On the steel sheet having a composite structure in which the return martensite is 20% or more and the retained austenite is 2% or more, the Al concentration in the plating layer satisfies the following formula (1), and the Si concentration in the plating layer is In addition to the hot-dip galvanized layer satisfying the formula (2), the oxygen content of the surface layer after removal of the plated layer is 0.05 g / m ² or more. Excellent high tension melting Lead-plated steel sheet.
Record
0.67-1 / 50 (Mn / Si) ≧ [Al concentration in plating layer (mass%)] ≧
0.37-1 / 50 (Mn / Si) (1)
1.67-1 / 3 (Mn / Si) ≧ [Si concentration in plating layer (mass%)] ≧
0.167-1 / 30 (Mn / Si) (2)
(Mn / Si in formulas (1) and (2) represents the mass ratio of Mn / Si in steel.)

The high-strength hot-dip galvanized steel sheet excellent in strength ductility balance, plating adhesion and corrosion resistance according to claim 1, wherein the steel sheet further contains at least one component selected from the following group.
(First group) At least one selected from the group consisting of Cr of 1.0% or less, Mo of 1.0% or less, and B of 0.003% or less by mass%.
(Second group) At least one selected from the group consisting of Ti of 0.1% or less by mass, Nb of 0.1% or less, and V of 0.1% or less.
(Third group) At least one selected from the group consisting of 1.0% or less of Cu and 1.0% or less of Ni by mass.

C: 0.05 to 0.25% by mass, Si: more than 0.50% and less than 2.00%, Mn: 3.5% or less, Al: 0.01 to 1.0%, the balance being of Fe and unavoidable impurities, Mn / Si mass ratio in the steel: 0.5 and less than 2 composition above, tempered martensite, consists retained austenite, ferrite and low temperature transformation phases, volume fraction, the baked On the steel sheet having a composite structure in which the return martensite is 20% or more and the retained austenite is 2% or more, the Al concentration in the plating layer satisfies the following formula (3), and the Si concentration in the plating layer is A balance between strength and ductility, plating adhesion, and an alloyed hot-dip galvanized layer satisfying the following formula (2), wherein the amount of oxygen on the surface layer after removal of the plated layer is 0.05 g / m ² or more High tension with excellent corrosion resistance Alloyed hot-dip galvanized steel sheet.
Record
0.5-1 / 50 (Mn / Si) ≧ [Al concentration in plating layer (mass%)] ≧
0.2-1 / 50 (Mn / Si) (3)
1.67-1 / 3 (Mn / Si) ≧ [Si concentration in plating layer (mass%)] ≧
0.167-1 / 30 (Mn / Si) (2)
(Mn / Si in formulas (3) and (2) represents the mass ratio of Mn / Si in steel)

The high-tension alloyed hot-dip galvanized steel sheet excellent in strength ductility balance, plating adhesion and corrosion resistance according to claim 3, wherein the steel sheet further contains at least one component selected from the following group.
(First group) At least one selected from the group consisting of Cr of 1.0% or less, Mo of 1.0% or less, and B of 0.003% or less by mass%.
(Second group) At least one selected from the group consisting of Ti of 0.1% or less by mass, Nb of 0.1% or less, and V of 0.1% or less.
(Third group) At least one selected from the group consisting of 1.0% or less of Cu and 1.0% or less of Ni by mass.