JP3921136B2 - High strength and high ductility hot dip galvanized steel sheet with excellent burring workability and manufacturing method thereof - Google Patents
High strength and high ductility hot dip galvanized steel sheet with excellent burring workability and manufacturing method thereof Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、自動車、建材、家電製品などに適するバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板及びその製造方法に関する。
【０００２】
【従来の技術】
自動車のクロスメンバーやサイドメンバー等の部材は、近年の燃費軽量化の動向に対応すべく軽量化が検討されており、材料面では、薄肉化しても強度および衝突安全性が確保されるという観点から鋼板の高強度化が進められている。しかしながら、材料の成形性は強度が上昇するのに伴って劣化するので、上記部材の軽量化を実現するには、成形性と高強度の両方を満足する鋼板を製造する必要がある。
【０００３】
成形性を表す指標としては、引張り試験の際の伸び（Ｅｌ．）が用いられ、この値が高いことが成形性の指標の一つとして用いられている。また、強度としては、引張り試験の際の最大応力である引張強さ（ＴＳ）がその値として用いられており、これらの積（ＴＳ×Ｅｌ．）が２１０００（ＭＰａ・％）を上回る鋼板が高強度かつ高延性鋼板として知られている。これらの特性を有する鋼板としては、特開平１−２３０７１５号公報や特開平２−２１７４２５号公報に開示されているような残留オーステナイトを含む鋼板がある。
【０００４】
これら残留オーステナイトを含む鋼板は、その成分元素として、ＣとＳｉおよびＭｎのみを基本的な合金元素とし、冷延鋼板の場合、二相域で焼鈍後、３００〜４５０℃程度の温度範囲でベイナイト変態を行うことを特徴とする熱処理により、残留オーステナイトを金属中に含む鋼板であり、これら鋼板は残留オーステナイトを含む組織を作るために、特開平０５−１７１３４４号公報や特開平０５−１９５１４３号公報で開示しているように、ＳｉまたはＡｌを含有させる必要がある。
【０００５】
これらの鋼板は、金属組織に含まれている残留オーステナイトをプレス成形時に、応力誘起変態により、マルテンサイトに変態させることで優れた延性を得ていることから、特開平１０−１３０７７６号公報や特開平４−９８８５９号公報に開示されているように、残留オーステナイトの安定性の向上と体積率増加に着目した研究が数多く行われてきた。
【０００６】
【発明が解決しようとする課題】
しかしながら、これらの鋼板は、軟質なフェライトと硬質な残留オーステナイトを含む不均一な組織であり、これら両相の境界が微少ボイドの生成を誘起し、バーリング加工性に劣るという問題を有していた。
【０００７】
また、自動車用鋼板の高性能化を反映して、耐食性および外観向上を目的に自動車部材のめっき化が進んでいるが、現在は、車内に装着される特定の部材を除いて、多くの部材に、溶融亜鉛めっき鋼板が使用されている。
【０００８】
しかしながら、これら鋼板はＳｉを多量に含むため、鋼板表面が酸化し易く、溶融亜鉛めっきの際に微少不めっきを生じる、合金化後の加工部においてめっき密着性が劣る等の問題がある。
【０００９】
これらの問題を解決するための手段としては、例えば、特開平３−２８３５９号公報や特開平３−６４４３７号公報には鋼板表面に、０．００２〜２．０ｇ／ｍ2程度のＮｉ、Ｃｕ、Ｃｏ、Ｆｅの単独または複合めっきを行うことで、めっき性を改善しているが、この方法では、溶融亜鉛めっきライン前段に新たにめっき設備を設けるか、もしくは、あらかじめ電気めっきラインにおいてめっき処理を行わねばならず、大幅なコストアップを招くという問題を有していた。
【００１０】
あるいは、特開平１１−３０９９４４号公報や特開平１１−１４１４２３号公報に開示されているように、鋼中に０．０１〜２．０％程度のＮｉ、Ｃｕ、Ｃｏを単独あるいは複合添加することで、めっき性を改善している。しかしながら、鋼中へＮｉ、Ｃｕ、Ｃｏ等の高価な元素の添加を必要とするため、コスト高を招くという問題を有していた。
【００１１】
本発明は上記課題を解決し、バーリング加工性に優れた高強度高延性合金化溶融亜鉛めっき鋼板ならびにバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板およびその製造法を提供することを目的とする。
【００１２】
【課題を解決するための手段】
本発明者等は、種々検討を行った結果、めっき性に関しては、鋼中にＭｇ、Ｚｒ、Ｃａ、Ｙ、Ｈｆ、ランタノイド族の元素群中から１種または２種以上を合計で０．００１〜１％を添加することで、高強度鋼板の溶融亜鉛めっき濡れ性確保および合金化めっきにおける合金化促進を見出した。この効果は、鋼中のこれら元素の含有量を０．００１％以上とすることで発揮される。
【００１３】
また、鋼中に主相としてベイナイトを体積分率で５０〜９７％含有し、第２相として残留オーステナイトを３〜５０％未満含有し、残部フェライト（体積率で４７％以下）とすることで、バーリング加工性に優れた高強度高延性鋼板が製造可能であることを見出した。
【００１４】
本発明は、上記知見に基づいて完成されたもので、その要旨とするところは以下の通りである。
［１］ 鋼板が質量％で、
Ｃ：０．０００１〜０．３％、
Ｓｉ：０．００１〜４％（ただし、０．１％未満を除く）、
Ｍｎ：０．００１〜３％、
Ａｌ：０．００１〜４％、
Ｍｏ：０．００１〜４％、
Ｐ：０．０００１〜０．３％、
Ｓ：０．０１％以下
を含有し、Ｍｇ、Ｚｒ、Ｃａ、Ｙ、Ｈｆおよびランタノイド族の元素群中から１種または２種以上を合計で０．００１〜１％含有し、残部がＦｅ及び不可避的不純物からなり、鋼板のミクロ組織が体積分率で、主相としてベイナイトを５０〜９７％、第２相として残留オーステナイトを３〜５０％未満含有し、残部フェライトからなり、該フェライトの平均粒径が１０μｍ以下であり、前記鋼板の表面に、質量％で、
Ａｌ：０．００１〜０．５％、
Ｆｅ：５〜２０％を含有し、残部がＺｎ及び不可避不純物からなるめっき層を有することを特徴とするバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板。
［２］ 鋼板が質量％で、
Ｃ：０．０００１〜０．３％、
Ｓｉ：０．００１〜４％（但し、０．１％未満を除く）、
Ｍｎ：０．００１〜３％、
Ａｌ：０．００１〜４％、
Ｍｏ：０．００１〜４％、
Ｐ：０．０００１〜０．３％、
Ｓ：０．０１％以下
を含有し、Ｍｇ、Ｚｒ、Ｃａ、Ｙ、Ｈｆおよびランタノイド族の元素群中から１種または２種以上を合計で０．００１〜１％含有し、残部がＦｅ及び不可避的不純物からなり、鋼板のミクロ組織が体積分率で、主相としてベイナイトを５０〜９７％、第２相として残留オーステナイトを３〜５０％未満含有し、残部フェライトからなり、該フェライトの平均粒径が１０μｍ以下であり、前記鋼板の表面に、質量％で、
Ａｌ：０．００１〜０．５％、
Ｆｅ：５％未満を含有し、残部がＺｎ及び不可避不純物からなるめっき層を有することを特徴とするバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板。
［３］ さらに、鋼中に質量％で、
Ｎｉ：０．００１〜４％、
Ｃｕ：０．００１〜４％、
Ｃｒ：０．００１〜４％、
Ｃｏ：０．００１〜４％
の１種又は２種以上を含有することを特徴とする［１］又は［２］に記載のバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板。
［４］ めっき層中のＣｕ含有率（質量％）と鋼中のＣｕ含有率（質量％）の比をａ、めっき層中のＮｉ含有率（質量％）と鋼中のＮｉ含有率（質量％）の比をｂとすると、０．０００１≦ａ＋ｂ≦０．２を満たすことを特徴とする［３］記載のバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板。
［５］ さらに、鋼中に質量％で、Ｎｂ、Ｔｉ、Ｖの１種または２種以上を合計で０．００１〜１％含有することを特徴とする［１］〜［４］のいずれか１項に記載のバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板。
［６］ さらに、鋼中に質量％で、
Ｂ：０．０００１〜０．１％を含有することを特徴とする［１］〜［５］のいずれか１項に記載のバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板。
［７］ めっき鋼板の垂直断面において、めっき層／鋼板界面から１０μｍ以内の鋼中に、内部酸化物であるＭｇＯ、ＣａＯ、ＺｒＯ２、ＣｅＯ２、Ｌａ２Ｏ３、ＨｆＯ２、ＴｉＯ２、Ｙ２Ｏ３、ＳｉＯ２、ＭｎＯ、およびＡｌ２Ｏ３の１種または２種以上の合計を面積率で０．１％以上含むことを特徴とする［１］〜［６］のいずれか１項に記載のバーリング加工性に優れた高強度溶融亜鉛めっき鋼板。
［８］ めっき鋼板の垂直断面において、めっき層／鋼板界面からＭｇＯ、ＣａＯ、ＺｒＯ２、ＣｅＯ２、Ｌａ２Ｏ３、ＨｆＯ２、ＴｉＯ２、Ｙ２Ｏ３、ＳｉＯ２、ＭｎＯ、およびＡｌ２Ｏ３の１種または２種以上の内部酸化物が存在する最大深さまでの範囲における鋼板中に、内部酸化物であるＭｇＯ、ＣａＯ、ＺｒＯ２、ＣｅＯ２、Ｌａ２Ｏ３、ＨｆＯ２、ＴｉＯ２、Ｙ２Ｏ３、ＳｉＯ２、ＭｎＯ、およびＡｌ２Ｏ３の１種または２種以上が面積率で１％以上含まれることを特徴とする［１］〜［７］のいずれか１項に記載のバーリング加工性に優れた高強度溶融亜鉛めっき鋼板。
［９］ さらに、めっき層が質量％で、
Ｍｎ：０．００１〜２％、
を含有し、残部がＺｎ及び不可避不純物からなるめっき層を有する溶融亜鉛めっき鋼板であって、
鋼のＳｉ含有率：Ｘ（質量％）、Ｍｎ含有率：Ｙ（質量％）及びＡｌ含有率：Ｚ（質量％）、並びにめっき層のＡｌ含有率：Ａ（質量％）及びＭｎ含有率：Ｂ（質量％）が、下記（１）式を満たすことを特徴とする［１］〜［８］のいずれか１項に記載のバーリング加工性に優れた高強度溶融亜鉛めっき鋼板。
【００１５】
３−（Ｘ＋Ｙ／１０＋Ｚ／３）−１２．５×（Ａ−Ｂ）≧０・・・（１）
［１０］ 更にめっき層が、質量％で、
Ｃａ：０．００１〜０．１％、
Ｍｇ：０．００１〜３％、
Ｓｉ：０．００１〜０．１％、
Ｍｏ：０．００１〜０．１％、
Ｗ：０．００１〜０．１％、
Ｚｒ：０．００１〜０．１％、
Ｃｓ：０．００１〜０．１％、
Ｒｂ：０．００１〜０．１％、
Ｋ ：０．００１〜０．１％、
Ａｇ：０．００１〜５％、
Ｎａ：０．００１〜０．０５％、
Ｃｄ：０．００１〜３％、
Ｃｕ：０．００１〜３％、
Ｎｉ：０．００１〜０．５％、
Ｃｏ：０．００１〜１％、
Ｌａ：０．００１〜０．１％、
Ｔｌ：０．００１〜８％、
Ｎｄ：０．００１〜０．１％、
Ｙ ：０．００１〜０．１％、
Ｉｎ：０．００１〜５％、
Ｂｅ：０．００１〜０．１％、
Ｃｒ：０．００１〜０．０５％、
Ｐｂ：０．００１〜１％、
Ｈｆ：０．００１〜０．１％、
Ｔｃ：０．００１〜０．１％、
Ｔｉ：０．００１〜０．１％、
Ｇｅ：０．００１〜５％、
Ｔａ：０．００１〜０．１％、
Ｂ ：０．００１〜０．１％、
の１種または２種以上を含有することを特徴とする［１］〜［９］のいずれか１項に記載のバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板。
［１１］ ［１］〜［１０］のいずれか１項に記載の成分からなる鋳造スラブを鋳造まま、あるいは、一旦冷却した後に再度加熱し、熱延後巻き取った熱延鋼板を酸洗後冷延し、その後、（Ａｃ１＋１００）（℃）以上（Ａｃ３＋１００）（℃）以下で焼鈍した後に、０．１℃／秒以上の冷却速度で６５０〜８００℃の温度域に冷却し、引き続いて１〜１００℃／秒の冷却速度で、Ｚｎめっき浴温度〜（Ｚｎめっき浴温度＋１００）（℃）まで冷却した後、３５０〜（Ｚｎめっき浴温度＋１００）（℃）の温度域で後続のめっき浴の浸漬時間を含めて１〜３０００秒間保持した後、Ｚｎめっき浴に浸漬して、その後、室温まで冷却することを特徴とするバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板の製造方法。
［１２］ Ｚｎめっき浴に浸漬した後、浴温〜（Ｚｎめっき浴温度＋１００）（℃）の温度範囲で１〜３００秒間の保持を行い、室温まで冷却することを特徴とする［１１］記載のバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板の製造方法。
［１３］ 鋳造スラブを１１５０〜１２５０℃に加熱し、１０００℃までの圧延率を５０％以上とし、仕上げ温度を８５０℃以上として熱延後、６５０℃以下で巻き取ることを特徴とする［１１］又は［１２］記載のバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板の製造方法。
【００１６】
【発明の実施の形態】
本発明の要旨は、主相としてベイナイトを体積分率で（以下、同じ）５０〜９７％含有し、第２相として残留オーステナイトを３〜５０％未満含有し、残部フェライトからなるバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板およびその製造方法である。
【００１７】
まず、ミクロ組織について説明する。
【００１８】
高強度溶融亜鉛めっき鋼板のバーリング加工性は、製品に含まれるベイナイトとフェライトの体積分率に左右される。ベイナイトの体積率が５０％未満ではその効果がほとんど表れないことから、本発明では下限値を５０％以上とした。一方、延性確保のためにはベイナイトは９７％以下であることが必要である。
【００１９】
残部組織であるフェライトの体積率が４７％以上となると、フェライトと残留オーステナイトの界面面積が多くなり、微少ボイドの生成が顕著となり、バーリング加工性に劣る。このことから、残部フェライトの体積率は４７％未満が望ましい。さらには、３５％以下とすることが望ましい。
【００２０】
本発明に係る高強度溶融亜鉛めっき鋼板の延性は、第２相である残留オーステナイトの体積分率に左右される。金属組織に含まれている残留オーステナイトは応力を受けていない状態では、安定に存在するものの、変形が加えられるとマルテンサイトに変態し、変態誘起塑性により優れた延性が得られる。しかしながら、その体積分率が３％未満では、その効果がほとんど表れないことから下限値を３％以上とした。一方、残留オーステナイトの体積分率が５０％以上になると、極端に著しい成形を加えた場合、成形後多量のマルテンサイトが存在することとなり、二次加工性や衝撃特性に問題を生じる事があるので、本発明では、その上限値を５０％未満とした。
【００２１】
また、主相であるベイナイト、第２相の残留オーステナイトおよび残部組織であるフェライト以外の不可避相として、マルテンサイト、パーライト、炭化物、窒化物、硫化物および酸化物の１種又は２種以上の合計を体積分率で１０％以下含有するものも、本発明の範囲内とする。
【００２２】
さらに、鋼板に含まれる残部フェライトの平均粒径を１０μｍ以下とすることで、優れたバーリング加工性が得られる。ただし、この効果が顕著になるのは平均粒径が７μｍ以下であることから、平均粒径は７μｍ以下が望ましい。一方、平均粒径の下限は特に定めることなく本発明の効果を得ることができる。
【００２３】
なお、上記ミクロ組織の各相、フェライト、ベイナイト、残留オーステナイト、マルテンサイト、酸化物相および残部組織の同定、存在位置の観察および平均粒径（平均円相当径）と占積率の測定は、ナイタール試薬および特開昭５９ー２１９４７３号公報に開示された試薬により鋼板圧延方向断面または圧延直角方向断面を腐食して５００倍〜２００００倍の光学顕微鏡、走査型電子顕微鏡および透過型電子顕微鏡観察により定量化が可能である。また、めっき層／鋼板界面近傍の内部酸化物の形態および同定は、走査型顕微鏡、透過電子顕微鏡およびＥＰＭＡを用いて行い、最大深さについては、５００〜２００００倍で２０〜５０視野を観察し、その中で０．０５μｍ以上の内部酸化物が存在する最大値を最大深さとした。
【００２４】
次に、本発明における鋼板成分の限定理由について述べる。
【００２５】
本発明者等は、質量％で、Ｃ：０．０００１〜０．３％、Ｓｉ：０．００１〜０．１％未満、Ｍｎ：０．００１〜３％、Ａｌ：０．１〜４％、Ｍｏ：０．００１〜４％、Ｐ：０．０００１〜０．３％、Ｓ：０．０１％以下を含有し、残部Ｆｅおよび不可避不純物より成る鋳造スラブを鋳造まま、あるいは、一旦冷却した後に再度加熱し、熱延後巻き取った熱延鋼板を酸洗後冷延し、その後（Ａｃ１＋１００）（℃）以上１０００℃以下で焼鈍し、０．１〜５０℃／秒の冷却速度で６５０〜８００℃の温度域に冷却し、引き続いて１〜１００℃／秒の冷却速度で、Ｚｎめっき浴温度〜（Ｚｎめっき浴温度＋１００）（℃）まで冷却した後、３５０〜（Ｚｎめっき浴温度＋１００）（℃）の温度域で後続のめっき浴の浸漬時間を含めて１〜３０００秒間保持した後、Ｚｎめっき浴に浸漬して、その後室温まで冷却した。さらに、一部の試料についてはＺｎめっき浴に同条件で浸漬後、Ｚｎめっき浴温度〜５５０℃で５〜６０秒間保持することで合金化処理を行った後、３５０℃までの温度範囲を０．５〜１００℃／秒の冷却速度で冷却し、その後室温まで冷却した。
【００２６】
上記の試験を行い、めっき表面の欠陥発生率に基づき外観を５段階評価した。その結果、鋼板成分を上記範囲とすることで、外観欠陥のほとんど生じない評点５〜４を得ることが解った。
【００２７】
評点５〜４はそれぞれめっきの外観は不めっきの発生状況を目視にて判断した。
【００２８】
評価指標は、以下の通りである。
【００２９】
評点５：不めっきは、ほとんどなし。（面積率で０．１％以下）
評点４：不めっきは、微少。（面積率で０．１％超３％以下）
評点３：不めっきは、少。（面積率で３％超５％以下）
評点２：不めっきは、多数。（面積率で５％超５０％以下）
評点１：めっき塗れず。（面積率で５０％超）
めっき付着量については、特に制約は設けないが、耐食性の観点から片面の付着量が５ｇ／ｍ2以上であることが望ましい。本発明の溶融亜鉛めっき鋼板上に塗装性、耐食性、溶接性を改善する目的で上層めっきを施すことや、各種処理、例えば、クロメート処理、りん酸塩処理、潤滑性向上処理、溶接性向上処理を施しても本発明を逸脱するものではない。
【００３０】
めっき層中Ａｌ量を０．００１〜０．５％の範囲内としたのは、０．００１％未満では、ドロス発生が顕著で良好な外観が得られないこと、０．５％を超えてＡｌを添加すると合金化反応を著しく抑制してしまい、合金化溶融亜鉛めっき層を形成することが困難となるためである。
【００３１】
さらに、合金化処理を施すことによってよってめっき層中にＦｅが取り込まれ、塗装性やスポット溶接性に優れた高強度高延性溶融亜鉛めっき鋼板を得ることができる。めっき層中のＦｅ量が２０質量％を超えるとめっき自体の密着性を損ない、加工の際めっき層が破壊、脱落し金型に付着することで、成形時の疵の原因となる。一方、スポット溶接性を良好にするためにはＦｅ量を５％以上にすることが望ましい。従って、合金化処理を行う場合、めっき層中のＦｅ量の範囲は５〜２０質量％とする。
【００３２】
また、合金化処理を行わない場合めっき層中のＦｅ量が５質量％未満でも、合金化により得られるスポット溶接を除く効果である耐食性と延性や加工性は良好である。
【００３３】
さらに、めっき層中Ｃｕ含有率（質量％）と鋼中Ｃｕ含有率（質量％）の比をａ（＝めっき層中Ｃｕ含有率／鋼中Ｃｕ含有率）、めっき層中Ｎｉ含有率（質量％）と鋼中Ｎｉ含有率（質量％）の比をｂ（＝めっき層中Ｎｉ含有率／鋼中Ｎｉ含有率）とすると、これらが０．０００１≦ａ＋ｂ≦０．２を満たすことにより、さらに優れためっき外観が得られる。ａ＋ｂが０．０００１より小さいと本発明の効果が発揮されず、０．２を超えるような合金中への過度の添加は、経済的に好ましくないため、前記の範囲を満たすことが好ましい。
【００３４】
なお、上記のａとｂの関係は、本発明者らが実験を行い、新たに見出した式である。
【００３５】
さらに、めっき層中Ｍｎ量を０．００１〜２質量％の範囲とすることで不めっきが抑制され、良好な外観のめっきが得られるうえ、耐食性を向上できる。この効果が顕在化するのは、めっき層中Ｍｎ量が０．００１質量％以上の範囲であることから、下限を０．００１質量％以上とする。Ｍｎが上限の２質量％を超えるとＭｎを含有するドロス発生が顕著となり、めっき外観が著しく低下する。
【００３６】
この効果は、鋼のＳｉ含有率：Ｘ（質量％）、鋼のＭｎ含有率：Ｙ（質量％）、鋼のＡｌ含有率：Ｚ（質量％）、めっき層のＡｌ含有率：Ａ（質量％）、めっき層のＭｎ含有率：Ｂ（質量％）が、下記（１）式を満たすことで、さらに良好な外観のめっきが得られるうえ、耐食性を向上できることが明らかとなった。
【００３７】
３−（Ｘ＋Ｙ／１０＋Ｚ／３）−１２．５×（Ａ−Ｂ）≧０・・・（１）
さらに、めっき層中に、質量％で、Ｃａ、Ｍｇ、Ｓｉ、Ｍｏ、Ｗ、Ｚｒ、Ｃｓ、Ｒｂ、Ｋ、Ａｇ、Ｎａ、Ｃｄ、Ｃｕ、Ｎｉ、Ｃｏ、Ｌａ、Ｔｌ、Ｎｄ、Ｙ、Ｉｎ、Ｂｅ、Ｃｒ、Ｐｂ、Ｈｆ、Ｔｃ、Ｔｉ、Ｇｅ、Ｔａ、Ｖ、Ｂの１種または２種以上を含有することで、さらに良好な外観のめっきが得られることおよび合金化が促進できることを見出した。
【００３８】
めっき層中のＣａ量を０．００１〜０．１質量％、Ｍｇ量を０．００１〜３質量％、Ｓｉ量を０．００１〜０．１％、Ｍｏ量を０．００１〜０．１％、Ｗ量を０．００１〜０．１％、Ｚｒ量を０．００１〜０．１％、Ｃｓ量を０．００１〜０．１％、Ｒｂ量を０．００１〜０．１％、Ｋ量を０．００１〜０．１％、Ａｇ量を０．００１〜５％、Ｎａ量を０．００１〜０．０５％、Ｃｄ量を０．００１〜３％、Ｃｕ量を０．００１〜３％、Ｎｉ量を０．００１〜０．５％、Ｃｏ量を０．００１〜１％、Ｌａ量を０．００１〜０．１％、Ｔｌ量を０．００１〜８％、Ｎｄ量を０．００１〜０．１％、Ｙ量を０．００１〜０．１％、Ｉｎ量を０．００１〜５％、Ｂｅ量を０．００１〜０．１％、Ｃｒ量を０．００１〜０．０５％、Ｐｂ量を０．００１〜１％、Ｈｆ量を０．００１〜０．１％、Ｔｃ量を０．００１〜０．１％、Ｔｉ量を０．００１〜０．１％、Ｇｅ量を０．００１〜５％、Ｔａ量を０．００１〜０．１％、Ｖ量を０．００１〜０．２％、Ｂ量を０．００１〜０．１％としたのは、この範囲において不めっきが発生せず、良好な外観のめっきが得られるためである。含有量がそれぞれの上限を超えると、それぞれの成分を含有するドロスの生成する、あるいは、めっき浴中にてＺｎ化合物が析出し、めっき層中に取り込まれることにより、めっき外観が著しく低下する。
【００３９】
次に、本発明に於ける鋼板成分の限定理由について述べる。
【００４０】
Ｃ：オーステナイト安定化元素であり、二相域加熱時およびベイナイト変態温度域でフェライトからオーステナイト中へと移動し、オーステナイト中に濃化することでオーステナイトを安定化させる。その結果、室温においてもオーステナイトが安定化することとなり、変態誘起塑性により優れた延性が確保される。Ｃが０．０００１質量％未満だと３％以上の残留オーステナイトを確保するのが困難であることから、その下限値を０．０００１質量％とした。一方では、Ｃが０．３質量％を超えると溶接が困難となることから、その上限を０．３質量％とした。
【００４１】
Ｓｉ：Ｓｉは強化元素であるのに加え、セメンタイトに固溶しないことから、セメンタイト析出を遅らせ、オーステナイトがフェライトとセメンタイトへ分解するのを遅らせる。この間に、オーステナイト中へとＣを濃化させることが可能となり、室温でもオーステナイトが存在し得る。ただし、０．００１質量％未満だとその効果は発揮しない。一方、４％を超えると溶接性が悪化することから、その上限を４質量％とした。
【００４２】
Ｍｎ：Ｍｎは強度確保に必要な元素であり、０．００１質量％未満では、強化効果が発現しないことから下限を０．００１質量％とした。一方、３質量％を超えると延性に悪影響を及ぼすことから３質量％を上限値とした。
【００４３】
Ａｌ：Ａｌは、脱酸材として用いられるのに加え、セメンタイトに固溶しないことから、セメンタイト析出を遅らせ、オーステナイトがフェライトとセメンタイトへ分解するのを遅らせる。この間に、オーステナイト中へとＣを濃化させることが可能となり、室温でもオーステナイトが存在し得る。ただし、０．００１質量％未満だとその効果は発揮しない。一方、４％を超えると溶接性が悪化することから、その上限を４質量％とした。
【００４４】
Ｍｏ：Ｍｏは、セメンタイト析出およびパーライト変態を遅らせることから、残留オーステナイトの確保に重要である。ただし、０．００１質量％未満だとその効果を発揮しない。一方、４％を超えると延性に悪影響を及ぼすことから、上限値を４質量％とした。
【００４５】
Ｐ：Ｐを０．０００１質量％未満とすることは、経済的に不利であることからこの値を下限値とした。一方、０．３質量％を超える量の添加では、溶接性ならびに製造時および熱延時の製造性に悪影響を及ぼす。このことから上限値を、０．３質量％とした。
【００４６】
Ｓ：Ｓは、溶接性ならびに製造時および熱延時の製造性に悪影響を及ぼす。このことから、その上限値を０．０１質量％以下とした。
【００４７】
Ｍｇ、Ｚｒ、Ｃａ、Ｙ、Ｈｆ、および、Ｌａ、Ｃｅなどのランタノイド族などの元素は、ＡｌおよびＳｉの酸化物形態を外部酸化から内部酸化へと変化させ、濡れ性の向上と合金化促進を引き起こす。詳細なメカニズムは不明であるが、鋼板中に存在する固溶Ｍｇ、Ｚｒ、Ｃａ、Ｙ、Ｈｆ、および、Ｌａ、Ｃｅなどのランタノイド族などの元素が、冷間圧延後の焼鈍において、鋼板内部にて酸化することで、ＡｌおよびＳｉの酸化物形態の変化を引き起こしたものと考えられる。この効果は、この元素群中から１種または２種以上を合計で０．００１質量％未満の添加では効果が少ないことから、その下限を０．００１質量％とした。一方で、過剰な添加は熱延および鋳造時の製造性の低下ならびに製品の延性の低下を招くことから、その上限を１質量％とした。
【００４８】
さらに、本発明が対象とする鋼板は、強度の更なる向上を目的に、Ｎｉ、Ｃｕ、Ｃｒ、Ｃｏの１種または２種以上を含有できる。
【００４９】
Ｎｉ：Ｎｉは、めっき性向上と強化に有効な元素である。ただし、０．００１質量％未満であるとその効果が発揮されないことから、その下限値を０．００１質量％とした。一方、４質量％を超える添加は延性に悪影響を及ぼすとともに、コスト高を招き経済的に不利となることから、上限値を４質量％とした。
【００５０】
Ｃｕ：Ｃｕは、めっき性向上と強化に有効な元素である。ただし、０．００１質量％未満であるとその効果が発揮されないことから、その下限値を０．００１質量％とした。一方、４質量％を超える添加は延性に悪影響を及ぼすとともに熱延時の製造性に悪影響を及ぼすことから、上限値を４質量％とした。
【００５１】
Ｃｒ：Ｃｒは、強化元素である。ただし、０．００１質量％未満であるとその効果が発揮されないことから、その下限値を０．００１質量％とした。一方、４質量％を超える添加は延性に悪影響を及ぼすことから、上限値を４質量％とした。
【００５２】
Ｃｏ：Ｃｏは、強化元素である。ただし、０．００１質量％未満であるとその効果が発揮されないことから、その下限値を０．００１質量％とした。一方、４質量％を超える添加は延性に悪影響を及ぼすとともに、コスト高を招き経済的に不利となることから、上限値を４質量％とした。
【００５３】
さらに、本発明が対象とする鋼板は、強度の更なる向上を目的に、強炭化物形成元素であるＮｂ、Ｔｉ、Ｖの１種または２種以上を含有できる。
【００５４】
これらの元素は、微細な炭化物、窒化物または炭窒化物を形成することから、鋼板の強化には極めて有効であることから、必要に応じて１種または２種類以上を合計で０．００１質量％以上添加できるものとした。一方で、多量の添加は、延性の劣化や残留オーステナイト中へのＣの濃化を妨げることから、その添加の上限を、１種または２種類以上の合計を１質量％とした。
【００５５】
Ｂもまた必要に応じて添加できる。Ｂは、０．０００１質量％以上の添加で粒界の強化や鋼材の強度化に有効であるが、その添加量が０．１質量％を超えると、その効果が飽和するばかりでなく、必要以上に鋼板強度を増加させ、加工性を低下させることから、その上限を０．１質量％とした。
【００５６】
さらに、めっき鋼板の垂直断面において、めっき層／鋼板界面から１０μｍまでの範囲における鋼中に、内部酸化物であるＭｇＯ、ＣａＯ、ＺｒＯ２、ＣｅＯ２、Ｌａ２Ｏ３、ＨｆＯ２、ＴｉＯ２、Ｙ２Ｏ３、ＳｉＯ２、ＭｎＯおよびＡｌ２Ｏ３の１種または２種以上の合計が面積率で０．１％以上存在すると、ＳｉＯ２、ＭｎＯ又はＡｌ２Ｏ３の形態が外部酸化から内部酸化へと変化することにより、更なる濡れ性の向上と合金化の促進が得られる。一方、合金化促進のためにはこれらの内部酸化物の合計が面積率で５０％以下であることが好ましいが、合金化処理を行わない場合には、これらの内部酸化物の１種又は２種以上の合計の面積率が５０％以上であったとしても、合金化により得られるスポット溶接を除く効果である耐食性と延性や加工性は良好である。また、内部酸化物であるＭｇＯ、ＣａＯ、ＺｒＯ２、ＣｅＯ２、Ｌａ２Ｏ３、ＨｆＯ２、ＴｉＯ２およびＹ２Ｏ３の存在により、ＳｉＯ ２ 、ＭｎＯ又はＡｌ ２ Ｏ ３ の内部酸化物は均一に分散されることから、穴拡げ性の向上にも寄与する。
【００５７】
これら内部酸化物はフェライト、残留オーステナイトおよびベイナイトの各相の粒界のみならず、これら相の粒内へも形成され、内部酸化物を均一に分散させることから、バーリング加工性の向上へも有効である。
【００５８】
また、めっき鋼板の垂直断面においてめっき層／鋼板界面から内部酸化物であるＭｇＯ、ＣａＯ、ＺｒＯ２、ＣｅＯ２、Ｌａ２Ｏ３、ＨｆＯ２、ＴｉＯ２、Ｙ２Ｏ３、ＳｉＯ２、ＭｎＯ又はＡｌ２Ｏ３が存在する最大深さまでの範囲における鋼板組織中に、これらの酸化物の１種または２種以上の合計が面積率で１％以上含まれると、更なる濡れ性の向上と合金化の促進が得られる。この効果は、面積率で１％以上となると顕在化することからこの範囲が好ましい。面積率で５％以上とすることが、さらに好ましい。一方、これらの内部酸化物の面積率が５０％超になるとめっき層と鋼板の間の元素拡散を阻害してしまい、合金化が遅れる。このことから合金化促進のためには、内部酸化物の面積率は５０％以下であることが好ましい。しかしながら、合金化処理を行わない場合には、内部酸化物の面積率が５０％以上であったとしても、合金化により得られるスポット溶接を除く効果である耐食性と延性や加工性は良好である。また、内部酸化物であるＭｇＯ、ＣａＯ、ＺｒＯ２、ＣｅＯ２、Ｌａ２Ｏ３、ＨｆＯ２、ＴｉＯ２およびＹ２Ｏ３により、ＳｉＯ ２ 、ＭｎＯ又はＡｌ ２ Ｏ ３ の内部酸化物は均一に分散されることから、穴拡げ性の向上にも寄与する。
【００５９】
また、これら内部酸化物はフェライト、残留オーステナイトおよびベイナイトの各相の粒界のみならず、これら相の粒内へも形成され、内部酸化物を均一に分散させることから、バーリング加工性の向上へも有効である。
【００６０】
尚、上述したような鋼板中に存在する酸化物の同定・観察や面積率測定は、ＥＰＭＡやＦＥ−ＳＥＭなどを用いて行うことができる。本発明に当たっては、２０００〜２００００倍で５０視野以上を測定し、画像解析により面積率を求めた。また、酸化物の同定には、抽出レプリカ試料を作成してＴＥＭ、ＥＰＭＡおよびＥＢＳＰを用いた。また、ここでいう、ＭｎＯ、Ａｌ2Ｏ3、ＳｉＯ2は、他の原子を含む複合酸化物であったり、欠陥を多く含む場合があるが、元素分析及び構造同定からもっとも近いものを見つけて判別した。面積率測定は、ＥＰＭＡやＦＥ−ＳＥＭなどを用い各成分の面分析を行うことで求めることができる。この場合には、個々の正確な構造の同定は難しいものの、上述した構造解析の結果と併せて形態やその組成から判断し得る。その後面分析の画像解析から各面積率を求めることができる。
【００６１】
以上のような組織と特性を有する鋼板の製造方法について述べる。
【００６２】
上記成分組成の要件を満足する成分組成の鋳造スラブを鋳造まま、あるいは、一旦冷却した後に再度加熱し、熱延後巻き取った熱延鋼板を酸洗後冷延し、その後、（Ａｃ１＋１００）（℃）以上で焼鈍する。
【００６３】
冷延鋼板の連続焼鈍では、主相であるベイナイトの体積率を５０％以上とするため（Ａｃ１＋１００）（℃）以上に加熱する。この時の加熱温度が、（Ａｃ１＋１００）（℃）より低いと、フェライト体積率が多くなりすぎてしまいベイナイト体積率を５０％以上とすることができず、バーリング加工性に劣る。同時に、加熱温度を（Ａｃ１＋１００）（℃）以上にすることで、フェライト粒径を小さくすることができ、更なる、バーリング加工性の向上を引き起こす。この効果は、加熱温度を（Ａｃ１＋１００）（℃）以上にすることで発揮される。ただし、この効果が顕著になるのは加熱温度が（Ａｃ３−５０）（℃）以上であることから、（Ａｃ３−５０）（℃）以上が望ましい。一方、加熱温度の上限は特に定めることなく本発明の効果を得ることができる。しかしながら、焼鈍温度の過剰な高温化は粒界酸化相生成が促進されるうえ、製造コストの上昇をまねくために、焼鈍温度の上限は（Ａｃ３＋１００）（℃）以下とする。
【００６４】
焼鈍の保持時間が短すぎると、未溶解炭化物が残存する可能性が高く、残留オーステナイト体積率が少なくなるため、１０秒以上とすることが望ましい。一方、保持時間が長すぎると、結晶粒が粗大化する可能性が高くなり強度−延性バランスが悪くなるため、その上限は１０００秒とすることが好ましい。
【００６５】
その後、１次冷却として０．１℃／秒以上の冷却速度で６５０〜８００℃の温度域に冷却し、引き続いて２時冷却として１〜１００℃／秒の冷却速度で、めっき浴温度〜（めっき浴温度＋１００）（℃）まで冷却した後、３５０〜（めっき浴温度＋１００）（℃）の温度域で、めっき浴の侵漬時間を含めて１〜３０００秒間保持する。
【００６６】
これは、二相域に加熱して生成させたオーステナイトをパーライトに変態させることなく、ベイナイト変態まで維持し、３５０〜（Ｚｎめっき浴温度＋１００）（℃）の温度域を１〜３０００秒間かけて通過させることで、その組織をフェライト（＋ベイナイト）＋残留オーステナイトとして所定の特性を得るためである。
【００６７】
焼鈍後、６５０〜８００℃までの１次冷却速度が０．１℃／秒未満ではフェライト変態が顕著となり、フェライト体積率５０％を超えてしまい好ましくないことから、その下限値を０．１℃／秒とした。その上限は、特に定めないが、過度に冷却速度を大きくすることは、過剰な設備投資を招く。このことから、上限は１００℃／秒以下が望ましい。しかしながら、この値を越えたとしても、本発明で示す効果は発揮される。
【００６８】
また、その後、めっき浴温度〜（めっき浴温度＋１００）（℃）までの２次冷却速度が１℃／秒未満では、冷却途中でオーステナイトがパーライトへと変態してしまうため、残留オーステナイトが残らず望ましくない。また、２次冷却速度が１００℃／秒より速いと、板幅方向での冷却終点温度がばらつくこととなり、均一な鋼板の製造ができなくなるので好ましくない。
【００６９】
めっき浴浸漬前の保持温度を３５０〜（Ｚｎめっき浴温度＋１００）（℃）としたのは、この温度域にてベイナイト変態が起こり、残留オーステナイトを室温まで残すためである。３５０℃未満では、二相域に加熱して生成させたオーステナイトがマルテンサイト変態を起こしてしまい残留オーステナイトが残らないため、下限温度を３５０℃とした。一方、保持温度が（Ｚｎめっき浴温度＋１００）（℃）より高いと、二相域に加熱して生成させたオーステナイトがパーライトへと変態する、あるいは、オーステナイト中からセメンタイトが析出するため、オーステナイトがベイナイトへと分解してしまうことから、その上限温度を（Ｚｎめっき浴温度＋１００）（℃）とした。
【００７０】
Ｚｎめっき浴浸漬時間を含めた前記の保持時間が１秒未満では鋼板をめっき浴へ浸漬する時間が十分でないので好ましくなく、３０００秒を超えると設備が巨大になりすぎ、不経済となるため好ましくないので、前記の保持時間は１〜３０００秒間とした。
【００７１】
めっき浴浸漬後の選択的に行う合金化処理において、保持温度を浴温〜（Ｚｎめっき浴温度＋１００）（℃）としたのは、この温度より高いと、オーステナイトがパーライトへと変態する、あるいは、オーステナイト中からセメンタイトが析出するため、オーステナイトがベイナイトへと分解してしまうことから、その上限温度を（Ｚｎめっき浴温度＋１００）（℃）とした。保持温度が浴温より低いと合金化に長時間の時間を要するので、下限温度を浴温とした。
【００７２】
浴浸漬後、浴温〜（めっき浴温度＋１００）（℃）の温度範囲での保持を行わなくても、本発明に記載のバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板を得ることができる。
【００７３】
Ｚｎめっき浴温度から、又はＺｎめっき浸漬後の保持温度から室温までの冷却速度は特に規定するものではないが、これらの温度から、３５０℃までの冷却速度を０．５℃／秒以上とすると、この温度域での冷却速度がこれより遅いと、ベイナイト変態が進行しすぎてしまい必要以上にオーステナイトが安定化してしまう、あるいは、セメンタイトが析出してしまい残留オーステナイトが分解し、適正な変態誘起塑性が得られなくなるので、冷却速度の下限値を０．５℃／秒以上とすることが好ましい。一方、この温度範囲での冷却速度が１００℃／秒を超えて、冷却したとしても、材質上はなんら問題を生じないが、過度に冷却速度を上げることは、製造コスト高を招くこととなるので、上限を１００℃／秒とすることが好ましい。
【００７４】
酸化物を制御し、濡れ性と合金化の向上を図るためには、熱延段階から温度加工履歴を制御することが望ましい。まず、鋳片の加熱温度を１１５０〜１２５０℃として、１０００℃までの圧延率を５０％以上とし、仕上げ温度を８５０℃以上として、巻取りを６５０℃以下とすることで、表面酸化層をできるだけ均一に形成させるとともに、焼鈍時のＳｉ酸化物形成を抑制すべくＭｇ、Ｚｒ、Ｃａ、Ｙ、Ｈｆ、および、Ｌａ、Ｃｅなどのランタノイド族などの元素を固溶状態にしておくことが望ましい。さらには、鋼板内部に存在する内部酸化物であるＭｇＯ、ＣａＯ、ＺｒＯ２、ＣｅＯ２、Ｌａ２Ｏ３、ＨｆＯ２、ＴｉＯ２、Ｙ２Ｏ３、ＳｉＯ２、ＭｎＯおよびＡｌ２Ｏ３により、Ｓｉ酸化物形成が抑制される。
【００７５】
また、仕上げ圧延後のデスケには高圧デスケや強酸洗を行い、熱延で形成した酸化相をできるだけ除去することが望ましい。冷延後の焼鈍では、Ｓｉの外部酸化を抑制する目的から７５０℃以上の温度域まで５℃／ｓ以上で昇温することが望ましい。
【００７６】
また、本発明のバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板の素材は、通常の製鉄工程である精錬、製鋼、鋳造、熱延、冷延工程を経て製造されることを原則とするが、その一部あるいは全部を省略して製造されるものでも、本発明に係わる条件を満足する限り、本発明の効果を得ることができる。
【００７７】
また、めっき密着性をさらに向上させるために、焼鈍前に鋼板に、Ｎｉ、Ｃｕ、Ｃｏ、Ｆｅの単独あるいは複数より成るめっきを施しても本発明を逸脱するものではない。
【００７８】
さらには、めっき前の焼鈍については、「脱脂酸洗後、非酸化雰囲気にて加熱し、Ｈ2及びＮ2を含む還元雰囲気にて焼鈍後、めっき浴温度近傍まで冷却し、めっき浴に浸漬」というゼンジマー法、「焼鈍時の雰囲気を調節し、最初、鋼板表面を酸化させた後、その後還元することによりめっき前の清浄化を行った後にめっき浴に浸漬」という全還元炉方式、あるいは、「鋼板を脱脂酸洗した後、塩化アンモニウムなどを用いてフラックス処理を行って、めっき浴に浸漬」というフラックス法等があるが、いずれの条件で処理を行ったとしても本発明の効果は発揮できる。
【００７９】
なお、焼鈍後、切削を行い鋼板表面の酸化物を除去した後、めっき浴に浸漬させ、めっきを施したとしても本発明の効果を得ることができる。
【００８０】
【実施例】
以下実施例によって本発明をさらに詳細に説明する。
【００８１】
表１に成分組成を記載したスラブを熱延、酸洗、冷延し、１ｍｍ厚とした。熱間圧延において、１０００℃までの圧延率を７０％とした。その後、各鋼の成分（質量％）よって下記式に従ってＡｃ１とＡｃ３変態温度を計算により求めた。
【００８２】
Ａｃ１＝７２３−１０．７×Ｍｎ（％）＋２９．１×Ｓｉ（％）。
【００８３】
Ａｃ３＝９１０−２０３×Ｃ（％） １／２ ＋４４．７×Ｓｉ（％）＋３１．５×Ｍｏ（％）−３０×Ｍｎ（％）−１１×Ｃｒ（％）＋４００×Ａｌ（％）
これらのＡｃ１とＡｃ３変態温度から計算される焼鈍温度に１０℃／ｓで１０％Ｈ２−Ｎ２雰囲気で昇温・保定した後、１〜５℃／秒の冷却速度で６８０〜７５０℃まで１次冷却し、その後、５〜１０℃／秒の冷却速度でめっき浴温度まで２次冷却し、浴組成を種々に変化させた４６０℃の溶融亜鉛めっき浴に３秒間浸漬することでめっきを行った。この際のめっき付着量は、片面４０ｇ／ｍ２とした。
【００８４】
この後、一部の鋼板については、めっき浴温度〜６００℃の温度範囲で２０秒間保持を行った後、３５０℃までの温度域を３〜１０℃／秒の冷却速度で冷却後、室温まで冷却した。製造条件の詳細を表２、表３（表２の続き１）および表４（表２の続き２）に示す。
【００８５】
めっき表面外観におけるドロス巻き込みの状況の目視観察および不めっき部面積の測定によりめっき性を評価した。作製しためっき層中濃度測定は、アミン系インヒビターを入れた５％塩酸でめっき層を溶かした後、ＩＣＰ発光分析法を用いて行った。
【００８６】
これらめっきを施した鋼板から、ＪＩＳ５号試験片を採取し、ゲージ長さ５０ｍｍ、引張り試験速度１０ｍｍ／分で常温引張り試験を行った。
【００８７】
バーリング加工性を示す指標となる穴拡げ性は、直径１０ｍｍの円形穴を、クリアランスが１２％となる条件にて打ち抜き、かえりがダイ側となるようにし、６０°円錐ポンチにて成形し、穴拡げ率λ（％）により評価した。強度−バーリング加工性バランス（ＴＳ×λ）が５００００（ＭＰａ・％）を超えるものを、バーリング加工性に優れた高強度鋼板とした。
【００８８】
残留オーステナイト体積率Ｖγの測定は、めっき層／鋼板界面より板厚の７／１６内層を化学研磨後、Ｍｏ管球を用いたＸ線回折で、フェライトの（２００）の回折強度Ｉα（２００）、フェライトの（２１１）の回折強度Ｉα（２１１）とオーステナイトの（２２０）の回折強度Ｉγ（２２０）および（３１１）の回折強度Ｉγ（３１１）の強度比より求めた。
【００８９】
Ｖγ（体積％）＝０．２５×｛Ｉγ（２２０）／（１．３５×Ｉα（２００）
＋Ｉγ（２２０））
＋Ｉγ（２２０）／（０．６９×Ｉα（２１１）＋Ｉγ（２２０））
＋Ｉγ（３１１）／（１．５×Ｉα（２００）＋Ｉγ（３１１））
＋Ｉγ（３１１）／（０．６９×Ｉα（２１１）＋Ｉγ（３１１））｝
酸化物の体積率と分布については、研磨を行った後、ＳＥＭおよびＥＰＭＡを用いて観察することで測定を行った。
【００９０】
表５、表６（表５の続き１）、表７（表５の続き２）、表８（表５の続き３）、表９（表５の続き４）および表１０（表５の続き５）に機械特性、めっき特性等を示す。表５〜表１０（表５の続き５）に示すように、鋼板成分としてＭｇ、Ｚｒ、Ｃａ、Ｙ、Ｈｆ、Ｌａ−Ｃｅを含むものおよびめっき層／鋼板界面より、１０μｍ以内の鋼中にＭｇＯ、ＣａＯ、ＺｒＯ2、ＣｅＯ2、Ｌａ2Ｏ3、ＨｆＯ2、ＴｉＯ2、Ｙ2Ｏ3を面積率で０．１％以上含むものは、不めっきもなく良好なめっき性が得られている。
【００９１】
鋼板の成分が所定の範囲であったとしても、製造条件および鋼板組織が所定の要件を満たさないものは、ベイナイト分率が低く、強度−バーリング加工性バランス（ＴＳ×λ）が５００００（ＭＰａ・％）未満となりバーリング加工性に劣る。さらには、残留オーステナイト分率が低くなり、強度−延性バランス（ＴＳ×Ｅｌ．）も２１０００（ＭＰａ・％）未満となり、強度−延性バランスに劣る。
【００９２】
製造条件が本発明を満たすものであっても、成分範囲が所定の要件を満たさないものは、本発明の効果を得ることができない。
【００９３】
【表１】
【表２】
【表３】
【表４】
【表５】
【表６】
【表７】
【表８】
【表９】
【表１０】
【発明の効果】
本発明により、良好なめっき性が得られ、バーリング加工性に優れ、強度−延性バランス（ＴＳ×Ｅｌ．）も２１０００（ＭＰａ・％）を超える良好な溶融亜鉛めっき鋼板が得られた。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high strength and high ductility hot dip galvanized steel sheet excellent in burring workability suitable for automobiles, building materials, home appliances, and the like, and a method for producing the same.
[0002]
[Prior art]
Lightweight automotive cross members and side members are being studied to meet the recent trend of lighter fuel consumption, and in terms of materials, the strength and collision safety can be ensured even if they are made thinner. Since then, the strength of steel sheets has been increasing. However, since the formability of the material deteriorates as the strength increases, it is necessary to manufacture a steel sheet that satisfies both the formability and high strength in order to reduce the weight of the member.
[0003]
As an index representing formability, elongation (El.) During a tensile test is used, and a high value is used as one of the moldability indices. Further, as the strength, the tensile strength (TS) which is the maximum stress in the tensile test is used as the value, and a steel plate having a product (TS × El.) Exceeding 21000 (MPa ·%) is used. It is known as a high strength and high ductility steel sheet. As a steel plate having these characteristics, there is a steel plate containing retained austenite as disclosed in JP-A-1-230715 and JP-A-2-217425.
[0004]
These steel sheets containing retained austenite have only C, Si, and Mn as their constituent elements, and in the case of cold-rolled steel sheets, bainite in a temperature range of about 300 to 450 ° C. after annealing in a two-phase region. Steel sheets containing residual austenite in the metal by heat treatment characterized by performing transformation.05-171344As disclosed in Japanese Patent Laid-Open No. 2005-195143 and Japanese Patent Laid-Open No. 05-195143, it is necessary to contain Si or Al.
[0005]
These steel sheets obtain excellent ductility by transforming the retained austenite contained in the metal structure into martensite by stress-induced transformation at the time of press forming. Therefore, JP-A-10-130776 and As disclosed in Japanese Laid-Open Patent Publication No. 4-988859, many studies have focused on improving the stability and increasing the volume ratio of retained austenite.
[0006]
[Problems to be solved by the invention]
However, these steel sheets have a non-uniform structure containing soft ferrite and hard retained austenite, and the boundary between these two phases induces the formation of minute voids and has a problem of poor burring workability. .
[0007]
Reflecting the high performance of automotive steel plates, the plating of automotive parts is progressing for the purpose of improving corrosion resistance and appearance. Currently, there are many members except for specific parts that are installed in cars. In addition, a hot dip galvanized steel sheet is used.
[0008]
However, since these steel plates contain a large amount of Si, the surface of the steel plate is likely to be oxidized, causing a slight non-plating during hot dip galvanization, and poor plating adhesion in the processed part after alloying.
[0009]
As means for solving these problems, for example, in Japanese Patent Laid-Open No. 3-28359 and Japanese Patent Laid-Open No. 3-64437, 0.002 to 2.0 g / m on the steel plate surface.2Plating properties are improved by performing single or composite plating of Ni, Cu, Co, and Fe. However, in this method, a new plating facility is provided in front of the hot dip galvanizing line, or electric plating is performed in advance. There was a problem that a plating process had to be performed in the plating line, resulting in a significant cost increase.
[0010]
Alternatively, as disclosed in JP-A-11-309944 and JP-A-11-141423, about 0.01 to 2.0% of Ni, Cu, or Co is added to the steel alone or in combination. Therefore, the plating property is improved. However, since it is necessary to add expensive elements such as Ni, Cu, and Co to the steel, there is a problem that the cost is increased.
[0011]
An object of the present invention is to solve the above-mentioned problems and to provide a high-strength and high-ductility galvannealed steel sheet excellent in burring workability, a high-strength high-ductility hot-dip galvanized steel sheet excellent in burring workability, and a method for producing the same. And
[0012]
[Means for Solving the Problems]
As a result of various studies, the present inventors have found that the plating property is 0.001 in total from one or more of Mg, Zr, Ca, Y, Hf, and lanthanoid group elements in steel. By adding ˜1%, it was found that hot-dip galvanizing wettability of a high-strength steel sheet was ensured and alloying was promoted in alloying plating. This effect is exhibited when the content of these elements in the steel is 0.001% or more.
[0013]
Further, by containing 50 to 97% of bainite as a main phase in the steel in a volume fraction and containing less than 3 to 50% of retained austenite as the second phase, the balance ferrite (volume ratio of 47% or less) is used. The present inventors have found that a high-strength, high-ductility steel sheet excellent in burring workability can be produced.
[0014]
The present invention has been completed based on the above findings, and the gist thereof is as follows.
[1] The steel sheet is mass%,
C: 0.0001 to 0.3%,
Si: 0.001 to 4%(However, excluding less than 0.1%),
Mn: 0.001 to 3%,
Al: 0.001 to 4%,
Mo: 0.001 to 4%,
P: 0.0001 to 0.3%,
S: 0.01% or less
A total of 0.001 to 1% of Mg, Zr, Ca, Y, Hf and lanthanoid group elements, with the balance being Fe and inevitable impurities, Is the volume fraction, bainite as the main phase is 50-97%, as the second phaseResidualContaining less than 3-50% austenite, consisting of the remaining ferrite,The average particle size of the ferrite is 10 μm or less,On the surface of the steel sheet,
Al: 0.001 to 0.5%,
A high-strength, high-ductility hot-dip galvanized steel sheet excellent in burring workability, characterized by comprising a plating layer containing Fe: 5 to 20%, the balance being Zn and inevitable impurities.
[2] The steel sheet is mass%,
C: 0.0001 to 0.3%,
Si: 0.001 to 4%(However, excluding less than 0.1%),
Mn: 0.001 to 3%,
Al: 0.001 to 4%,
Mo: 0.001 to 4%,
P: 0.0001 to 0.3%,
S: 0.01% or less
A total of 0.001 to 1% of Mg, Zr, Ca, Y, Hf and lanthanoid group elements, with the balance being Fe and inevitable impurities, Is the volume fraction, bainite as the main phase is 50-97%, as the second phaseResidualContaining less than 3-50% austenite, consisting of the remaining ferrite,The average particle size of the ferrite is 10 μm or less,On the surface of the steel sheet,
Al: 0.001 to 0.5%,
A high-strength, high-ductility hot-dip galvanized steel sheet excellent in burring workability, comprising Fe: less than 5% and the balance having a plating layer composed of Zn and inevitable impurities.
[3] Furthermore, in mass% in steel,
Ni: 0.001 to 4%,
Cu: 0.001 to 4%,
Cr: 0.001 to 4%,
Co: 0.001 to 4%
One or more ofContainsIt is characterized by [1]Or [2]A high strength and high ductility hot dip galvanized steel sheet excellent in burring workability as described in 1.
[4] The ratio of the Cu content (mass%) in the plating layer and the Cu content (mass%) in the steel is a, the Ni content (mass%) in the plating layer and the Ni content (mass%) in the steel. If the ratio is b, 0.0001 ≦ a + b ≦ 0.2 is satisfied [3] High strength and high ductility hot dip galvanized steel sheet with excellent burring workability.
[5Furthermore, the steel contains 0.001 to 1% in total of one or more of Nb, Ti, and V in mass%, [1] to [1]4] The high intensity | strength high ductility hot dip galvanized steel plate excellent in burring workability of any one of these.
[6] Furthermore, in mass% in steel,
B: containing 0.0001 to 0.1% [1] to [1]5] The high intensity | strength high ductility hot dip galvanized steel plate excellent in burring workability of any one of these.
[7] In the vertical cross section of the plated steel sheet, in the steel within 10 μm from the plating layer / steel sheet interface,Is an internal oxideMgO, CaO, ZrO2, CeO2, La2O3, HfO2TiO2, Y2O3, SiO2, MnO, and Al2O3[1] to [1], wherein the total of one or more of the above is contained in an area ratio of 0.1% or more.6] The high intensity | strength hot-dip galvanized steel plate excellent in burring workability of any one of.
[8] In the vertical section of the plated steel plate, MgO, CaO, ZrO from the plating layer / steel plate interface2, CeO2, La2O3, HfO2TiO2, Y2O3, SiO2, MnO, and Al2O3In the steel sheet in the range up to the maximum depth where one or more internal oxides exist,Is an internal oxideMgO, CaO, ZrO2, CeO2, La2O3, HfO2TiO2, Y2O3, SiO2, MnO, and Al2O31 type or 2 types or more are contained by 1% or more by area ratio [1]-[7] The high intensity | strength hot-dip galvanized steel plate excellent in burring workability of any one of.
[9Furthermore, the plating layer is mass%,
Mn: 0.001-2%,
Is a hot dip galvanized steel sheet having a plating layer consisting of Zn and inevitable impurities,
Steel Si content: X (mass%), Mn content: Y (mass%) and Al content: Z (mass%), and Al content of plating layer: A (mass%) and Mn content: B (% by mass) satisfies the following formula (1): [1] to [1]8] The high intensity | strength hot-dip galvanized steel plate excellent in burring workability of any one of.
[0015]
3- (X + Y / 10 + Z / 3) -12.5 × (A−B) ≧ 0 (1)
[10] Further, the plating layer is in mass%,
Ca: 0.001 to 0.1%,
Mg: 0.001 to 3%,
Si: 0.001 to 0.1%,
Mo: 0.001 to 0.1%,
W: 0.001 to 0.1%,
Zr: 0.001 to 0.1%,
Cs: 0.001 to 0.1%,
Rb: 0.001 to 0.1%,
K: 0.001 to 0.1%,
Ag: 0.001 to 5%,
Na: 0.001 to 0.05%,
Cd: 0.001 to 3%
Cu: 0.001 to 3%,
Ni: 0.001 to 0.5%,
Co: 0.001-1%,
La: 0.001 to 0.1%,
Tl: 0.001-8%
Nd: 0.001 to 0.1%,
Y: 0.001 to 0.1%
In: 0.001 to 5%,
Be: 0.001 to 0.1%,
Cr: 0.001 to 0.05%,
Pb: 0.001 to 1%,
Hf: 0.001 to 0.1%,
Tc: 0.001 to 0.1%,
Ti: 0.001 to 0.1%,
Ge: 0.001 to 5%,
Ta: 0.001 to 0.1%,
B : 0.001 to 0.1%,
The high-strength and high-ductility hot-dip galvanized steel sheet excellent in burring workability according to any one of [1] to [9], characterized by containing one or more of the following.
[11] After pickling the hot-rolled steel sheet that has been cast after the cast slab made of the component according to any one of [1] to [10] or is heated again after being cooled, and pickled after hot-rolling Cold-rolled and then annealed at (Ac1 + 100) (° C.) or higher and (Ac3 + 100) (° C.) or lower, and then cooled to a temperature range of 650 to 800 ° C. at a cooling rate of 0.1 ° C./second or higher. After cooling to Zn plating bath temperature to (Zn plating bath temperature + 100) (° C.) at a cooling rate of ˜100 ° C./sec, the subsequent plating bath in the temperature range of 350 to (Zn plating bath temperature + 100) (° C.) The method for producing a high strength and high ductility hot dip galvanized steel sheet excellent in burring workability, characterized in that it is held for 1 to 3000 seconds including the immersion time and then immersed in a Zn plating bath and then cooled to room temperature. .
[12] The method according to [11], wherein after being immersed in a Zn plating bath, holding is performed for 1 to 300 seconds in a temperature range of bath temperature to (Zn plating bath temperature +100) (° C.) and cooling to room temperature. Of high strength and high ductility hot dip galvanized steel sheet with excellent burring workability.
[13] The cast slab is heated to 1150 to 1250 ° C., the rolling rate up to 1000 ° C. is set to 50% or higher, the finishing temperature is set to 850 ° C. or higher, and then rolled at 650 ° C. or lower. ] Or the manufacturing method of the high intensity | strength high ductility hot dip galvanized steel plate excellent in the burring workability of [12] description.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The gist of the present invention is that the main phase contains 50 to 97% of bainite by volume fraction (hereinafter the same), and the second phase.ResidualA high-strength, high-ductility hot-dip galvanized steel sheet containing 3 to 50% of austenite and excellent in burring workability composed of the remaining ferrite, and a method for producing the same.
[0017]
First, the microstructure will be described.
[0018]
The burring workability of a high-strength hot-dip galvanized steel sheet depends on the volume fraction of bainite and ferrite contained in the product. Since the effect hardly appears when the volume fraction of bainite is less than 50%, the lower limit is set to 50% or more in the present invention. On the other hand, in order to ensure ductility, the bainite needs to be 97% or less.
[0019]
When the volume fraction of ferrite, which is the remaining structure, is 47% or more, the interface area between ferrite and retained austenite increases, the formation of minute voids becomes remarkable, and the burring workability is poor. For this reason, the volume fraction of the remaining ferrite is desirably less than 47%. Furthermore, it is desirable to set it as 35% or less.
[0020]
The ductility of the high-strength hot-dip galvanized steel sheet according to the present invention depends on the volume fraction of retained austenite that is the second phase. Residual austenite contained in the metal structure exists stably in a state where it is not subjected to stress, but when deformed, it transforms into martensite, and excellent ductility is obtained by transformation-induced plasticity. However, when the volume fraction is less than 3%, the effect hardly appears, so the lower limit is set to 3% or more. On the other hand, when the volume fraction of retained austenite is 50% or more, when extremely remarkable molding is performed, a large amount of martensite exists after molding, which may cause problems in secondary workability and impact characteristics. Therefore, in the present invention, the upper limit value is set to less than 50%.
[0021]
Moreover, as a unavoidable phase other than the main phase bainite, the second phase retained austenite and the remaining structure ferrite, one or more of martensite, pearlite, carbide, nitride, sulfide and oxide Are contained within the scope of the present invention.
[0022]
Furthermore, the outstanding burring workability is acquired because the average particle diameter of the remainder ferrite contained in a steel plate shall be 10 micrometers or less. However, this effect becomes remarkable because the average particle size is 7 μm or less, and the average particle size is preferably 7 μm or less. On the other hand, the lower limit of the average particle diameter is not particularly defined, and the effects of the present invention can be obtained.
[0023]
In addition, each phase of the above microstructure, ferrite, bainite,ResidualIdentification of austenite, martensite, oxide phase and remaining structure, observation of existing positions, and measurement of average particle diameter (average equivalent circle diameter) and space factor are disclosed in Nital reagent and JP-A-59-219473. It can be quantified by observation with an optical microscope, a scanning electron microscope, and a transmission electron microscope at a magnification of 500 to 20000 times by corroding the cross section in the rolling direction of the steel sheet or the cross section in the direction perpendicular to the rolling direction. Also, near the plating layer / steel plate interfaceinternalOxide morphology and identification are performed using a scanning microscope, transmission electron microscope and EPMA, and the maximum depth is observed at 20 to 50 fields at 500 to 20000 times, in which 0.05 μm or more is observed.internalThe maximum value where oxides exist was defined as the maximum depth.
[0024]
Next, the reasons for limiting the steel plate components in the present invention will be described.
[0025]
The present inventors, in mass%, C: 0.0001 to 0.3%, Si: 0.001 to less than 0.1%, Mn: 0.001 to 3%, Al: 0.1 to 4% , Mo: 0.001 to 4%, P: 0.0001 to 0.3%, S: 0.01% or less, and the cast slab composed of the remaining Fe and unavoidable impurities is cast or cooled once Later, it was heated again, the hot-rolled steel sheet wound up after hot rolling was pickled and cold-rolled, then annealed at (Ac1 + 100) (° C.) to 1000 ° C., and 650 at a cooling rate of 0.1 to 50 ° C./second. After cooling to a temperature range of ˜800 ° C., followed by cooling at a cooling rate of 1 to 100 ° C./second from Zn plating bath temperature to (Zn plating bath temperature + 100) (° C.), 350 to (Zn plating bath temperature) +100) (° C.) 1 to 300 including the immersion time of the subsequent plating bath After holding seconds, then immersed in a Zn plating bath, and then cooled to room temperature. Further, some samples were immersed in a Zn plating bath under the same conditions and then alloyed by holding at a Zn plating bath temperature of 550 ° C. for 5 to 60 seconds, and then the temperature range up to 350 ° C. was reduced to 0. Cooled at a cooling rate of 5 to 100 ° C./second, and then cooled to room temperature.
[0026]
Said test was done and the external appearance was evaluated in five steps based on the defect occurrence rate of the plating surface. As a result, it was found that by setting the steel plate component in the above range, scores 5 to 4 with almost no appearance defects were obtained.
[0027]
Ratings 5 to 4 were made by visually observing the appearance of non-plating for the appearance of plating.
[0028]
The evaluation index is as follows.
[0029]
Score 5: Almost no plating. (Area ratio is 0.1% or less)
Score 4: Non-plating is very small. (Area ratio is over 0.1% and 3% or less)
Score 3: Less plating. (Area ratio is more than 3% and less than 5%)
Score 2: Many non-plating. (Area ratio is more than 5% and less than 50%)
Score 1: Not plated. (Over 50% in area ratio)
There are no particular restrictions on the plating adhesion amount, but the adhesion amount on one side is 5 g / m from the viewpoint of corrosion resistance.2The above is desirable. For the purpose of improving paintability, corrosion resistance and weldability on the hot dip galvanized steel sheet of the present invention, various treatments such as chromate treatment, phosphate treatment, lubricity improvement treatment, weldability improvement treatment The present invention does not depart from the present invention.
[0030]
The reason why the Al content in the plating layer is within the range of 0.001 to 0.5% is that if it is less than 0.001%, dross generation is remarkable and a good appearance cannot be obtained, exceeding 0.5% When Al is added, the alloying reaction is remarkably suppressed, and it becomes difficult to form an alloyed hot-dip galvanized layer.
[0031]
Further, by applying the alloying treatment, Fe is taken into the plating layer, and a high-strength and high-ductility hot-dip galvanized steel sheet excellent in paintability and spot weldability can be obtained. If the amount of Fe in the plating layer exceeds 20% by mass, the adhesion of the plating itself is impaired, and the plating layer breaks and falls off during processing and adheres to the mold, thereby causing defects during molding. On the other hand, in order to improve spot weldability, it is desirable that the Fe content be 5% or more. Therefore, when alloying is performed, the range of the amount of Fe in the plating layer is 5 to 20% by mass.
[0032]
Further, when the alloying treatment is not performed, even if the amount of Fe in the plating layer is less than 5% by mass, the corrosion resistance, ductility and workability, which are the effects excluding spot welding obtained by alloying, are good.
[0033]
Further, the ratio of the Cu content (mass%) in the plating layer and the Cu content (mass%) in the steel is a (= Cu content in the plating layer / Cu content in the steel), Ni content (mass in the plating layer). %) And the Ni content (mass%) in the steel as b (= Ni content in the plating layer / Ni content in the steel), when these satisfy 0.0001 ≦ a + b ≦ 0.2, Further, an excellent plating appearance can be obtained. When a + b is less than 0.0001, the effect of the present invention is not exhibited, and excessive addition to the alloy exceeding 0.2 is not economically preferable, so that the above range is preferably satisfied.
[0034]
The above relationship between a and b is an expression newly found by the inventors through experiments.
[0035]
Furthermore, non-plating is suppressed by making the amount of Mn in a plating layer into the range of 0.001-2 mass%, and favorable external appearance plating can be obtained, and corrosion resistance can be improved. This effect becomes apparent because the Mn content in the plating layer is in the range of 0.001% by mass or more, so the lower limit is made 0.001% by mass or more. When Mn exceeds 2 mass% of the upper limit, dross generation containing Mn becomes remarkable, and the plating appearance is remarkably deteriorated.
[0036]
The effect is that the Si content of the steel: X (mass%), the Mn content of the steel: Y (mass%), the Al content of the steel: Z (mass%), the Al content of the plating layer: A (mass) %) And the Mn content of the plating layer: B (mass%) satisfying the following formula (1), it is clear that plating with a better appearance can be obtained and the corrosion resistance can be improved.
[0037]
3- (X + Y / 10 + Z / 3) -12.5 × (A−B) ≧ 0 (1)
Further, in the plating layer, in mass%, Ca, Mg, Si, Mo, W, Zr, Cs, Rb, K, Ag, Na, Cd, Cu, Ni, Co, La, Tl, Nd, Y, In By containing one or more of Be, Cr, Pb, Hf, Tc, Ti, Ge, Ta, V, and B, it is possible to obtain plating with a better appearance and to promote alloying. I found it.
[0038]
The amount of Ca in the plating layer is 0.001 to 0.1% by mass, the amount of Mg is 0.001 to 3% by mass, the amount of Si is 0.001 to 0.1%, and the amount of Mo is 0.001 to 0.1%. %, W amount 0.001-0.1%, Zr amount 0.001-0.1%, Cs amount 0.001-0.1%, Rb amount 0.001-0.1%, K amount 0.001-0.1%, Ag amount 0.001-5%, Na amount 0.001-0.05%, Cd amount 0.001-3%, Cu amount 0.001 -3%, Ni amount 0.001-0.5%, Co amount 0.001-1%, La amount 0.001-0.1%, Tl amount 0.001-8%, Nd amount 0.001 to 0.1%, Y amount 0.001 to 0.1%, In amount 0.001 to 5%, Be amount 0.001 to 0.1%, Cr amount 0.001 ~ 0.05%, Pb amount is 0.00 -1%, Hf amount 0.001-0.1%, Tc amount 0.001-0.1%, Ti amount 0.001-0.1%, Ge amount 0.001-5%, The Ta amount is 0.001 to 0.1%, the V amount is 0.001 to 0.2%, and the B amount is 0.001 to 0.1%. This is because plating with a good appearance can be obtained. When the content exceeds each upper limit, dross containing each component is generated, or a Zn compound is precipitated in the plating bath and taken into the plating layer, so that the plating appearance is remarkably deteriorated.
[0039]
Next, the reasons for limiting the steel plate components in the present invention will be described.
[0040]
C: An austenite stabilizing element that moves from ferrite to austenite during two-phase heating and bainite transformation temperature range, and stabilizes austenite by concentrating in austenite. As a result, austenite is stabilized even at room temperature, and excellent ductility is ensured by transformation-induced plasticity. When C is less than 0.0001% by mass, 3% or moreResidualSince it is difficult to ensure austenite, the lower limit was set to 0.0001% by mass. On the other hand, if C exceeds 0.3 mass%, welding becomes difficult, so the upper limit was made 0.3 mass%.
[0041]
Si: In addition to Si being a strengthening element, Si does not dissolve in cementite, so it delays cementite precipitation and delays the decomposition of austenite into ferrite and cementite. During this time, it becomes possible to concentrate C into austenite, and austenite can exist even at room temperature. However, if it is less than 0.001% by mass, the effect is not exhibited. On the other hand, if it exceeds 4%, the weldability deteriorates, so the upper limit was made 4% by mass.
[0042]
Mn: Mn is an element necessary for ensuring the strength, and if it is less than 0.001% by mass, the reinforcing effect is not exhibited, so the lower limit was made 0.001% by mass. On the other hand, if it exceeds 3% by mass, the ductility is adversely affected, so 3% by mass was made the upper limit.
[0043]
Al: In addition to being used as a deoxidizer, Al does not dissolve in cementite, so it delays cementite precipitation and delays the decomposition of austenite into ferrite and cementite. During this time, it becomes possible to concentrate C into austenite, and austenite can exist even at room temperature. However, if it is less than 0.001% by mass, the effect is not exhibited. On the other hand, if it exceeds 4%, the weldability deteriorates, so the upper limit was made 4% by mass.
[0044]
Mo: Mo is important for securing retained austenite because it delays cementite precipitation and pearlite transformation. However, if it is less than 0.001% by mass, the effect is not exhibited. On the other hand, if it exceeds 4%, the ductility is adversely affected, so the upper limit was made 4% by mass.
[0045]
P: Setting P to less than 0.0001 mass% is economically disadvantageous, so this value was set as the lower limit. On the other hand, the addition exceeding 0.3% by mass adversely affects weldability and manufacturability during production and hot rolling. Therefore, the upper limit value was set to 0.3% by mass.
[0046]
S: S adversely affects weldability and manufacturability during production and hot rolling. For this reason, the upper limit value was set to 0.01% by mass or less.
[0047]
Elements such as Mg, Zr, Ca, Y, Hf, and lanthanoids such as La and Ce change the oxide form of Al and Si from external oxidation to internal oxidation, improving wettability and promoting alloying cause. Although the detailed mechanism is unknown, elements such as solute Mg, Zr, Ca, Y, Hf, and lanthanoid groups such as La and Ce that are present in the steel sheet are formed in the steel sheet during annealing after cold rolling. It is considered that the oxidation of Al and Si caused changes in the oxide form. Since this effect is less effective when one or two or more of these element groups are added in a total amount of less than 0.001% by mass, the lower limit is set to 0.001% by mass. On the other hand, excessive addition causes a decrease in manufacturability during hot rolling and casting and a decrease in the ductility of the product, so the upper limit was set to 1% by mass.
[0048]
Furthermore, the steel plate targeted by the present invention can contain one or more of Ni, Cu, Cr, and Co for the purpose of further improving the strength.
[0049]
Ni: Ni is an element effective for improving and strengthening the plating property. However, if the amount is less than 0.001% by mass, the effect is not exhibited, so the lower limit was set to 0.001% by mass. On the other hand, addition exceeding 4% by mass has an adverse effect on ductility and increases costs and is economically disadvantageous. Therefore, the upper limit is set to 4% by mass.
[0050]
Cu: Cu is an element effective for improving plating ability and strengthening. However, if the amount is less than 0.001% by mass, the effect is not exhibited, so the lower limit was set to 0.001% by mass. On the other hand, addition exceeding 4% by mass adversely affects ductility and adversely affects manufacturability during hot rolling, so the upper limit was set to 4% by mass.
[0051]
Cr: Cr is a strengthening element. However, if the amount is less than 0.001% by mass, the effect is not exhibited, so the lower limit was set to 0.001% by mass. On the other hand, since addition exceeding 4 mass% has a bad influence on ductility, the upper limit was made 4 mass%.
[0052]
Co: Co is a strengthening element. However, if the amount is less than 0.001% by mass, the effect is not exhibited, so the lower limit was set to 0.001% by mass. On the other hand, addition exceeding 4% by mass has an adverse effect on ductility and increases costs and is economically disadvantageous. Therefore, the upper limit is set to 4% by mass.
[0053]
Furthermore, the steel plate targeted by the present invention can contain one or more of Nb, Ti and V, which are strong carbide forming elements, for the purpose of further improving the strength.
[0054]
Since these elements form fine carbides, nitrides, or carbonitrides, and are extremely effective for strengthening steel sheets, one or two or more of these elements may be added in a total amount of 0.001 mass if necessary. % Can be added. On the other hand, addition of a large amount prevents deterioration of ductility and concentration of C in retained austenite, so the upper limit of addition was set to 1% by mass in one or more types.
[0055]
B can also be added as needed. B is effective for strengthening grain boundaries and strengthening steel by adding 0.0001% by mass or more. However, when the added amount exceeds 0.1% by mass, the effect is not only saturated but also necessary. Since the steel sheet strength is increased and the workability is lowered as described above, the upper limit is set to 0.1% by mass.
[0056]
Furthermore, in the vertical cross section of the plated steel sheet, in the steel in the range from the plating layer / steel sheet interface to 10 μm,Is an internal oxideMgO, CaO, ZrO2, CeO2, La2O3, HfO2TiO2, Y2O3, SiO2, MnO and Al2O3When the total of one or more of these is 0.1% or more by area ratio, SiO2, MnO or Al2O3By changing the form from external oxidation to internal oxidation, further improvement in wettability and promotion of alloying can be obtained. On the other hand, in order to promote alloying, theseinternalThe total oxide is preferably 50% or less in terms of area ratio, but when the alloying treatment is not performed, these oxidesinternalEven if the total area ratio of one kind or two or more kinds of oxides is 50% or more, the corrosion resistance, ductility and workability which are the effects excluding spot welding obtained by alloying are good. Also,Is an internal oxideMgO, CaO, ZrO2, CeO2, La2O3, HfO2TiO2And Y2O3Due to the presence ofSiO 2 , MnO or Al 2 O 3 ofSince the internal oxide is uniformly dispersed, it contributes to improvement of hole expansibility.
[0057]
theseinternalThe oxide is ferrite,ResidualInternal oxidation occurs not only in the grain boundaries of each phase of austenite and bainite but also in the grains of these phases.objectIs uniformly dispersed, which is effective in improving burring workability.
[0058]
Also, from the plating layer / steel plate interface in the vertical section of the plated steel plateIs an internal oxideMgO, CaO, ZrO2, CeO2, La2O3, HfO2TiO2, Y2O3, SiO2, MnO or Al2O3If the total of one or more of these oxides is contained in an area ratio of 1% or more in the steel sheet structure in the range up to the maximum depth in which there is, the further improvement in wettability and the promotion of alloying can be achieved. can get. Since this effect becomes apparent when the area ratio is 1% or more, this range is preferable. More preferably, the area ratio is 5% or more. Meanwhile, theseinternalWhen the area ratio of the oxide exceeds 50%, element diffusion between the plating layer and the steel sheet is inhibited, and alloying is delayed. Therefore, in order to promote alloying, the area ratio of the internal oxide is preferably 50% or less. However, when the alloying treatment is not performed, even if the area ratio of the internal oxide is 50% or more, the corrosion resistance, ductility and workability, which are the effects excluding spot welding obtained by alloying, are good. . Also,Is an internal oxideMgO, CaO, ZrO2, CeO2, La2O3, HfO2TiO2And Y2O3BySiO 2 , MnO or Al 2 O 3 ofSince the internal oxide is uniformly dispersed, it contributes to improvement of hole expansibility.
[0059]
Also theseinternalThe oxide is ferrite,ResidualInternal oxidation occurs not only in the grain boundaries of each phase of austenite and bainite but also in the grains of these phases.objectIs uniformly dispersed, which is effective in improving burring workability.
[0060]
Note that identification / observation and area ratio measurement of the oxides present in the steel sheet as described above can be performed using EPMA, FE-SEM, or the like. In the present invention, 50 fields or more were measured at 2000 to 20000 times, and the area ratio was determined by image analysis. For identification of oxides, extraction replica samples were prepared and TEM, EPMA, and EBSP were used. Also, here, MnO, Al2OThree, SiO2May be a complex oxide containing other atoms or a lot of defects, but it was determined by finding the closest one from elemental analysis and structural identification. The area ratio measurement can be obtained by performing surface analysis of each component using EPMA, FE-SEM, or the like. In this case, although it is difficult to identify an individual accurate structure, it can be determined from the form and the composition thereof together with the result of the structural analysis described above. Thereafter, each area ratio can be obtained from image analysis of surface analysis.
[0061]
A method for producing a steel sheet having the above structure and characteristics will be described.
[0062]
A cast slab having a component composition that satisfies the above-described component composition is cast as it is, or once cooled and then heated again, the hot-rolled steel sheet wound up after hot rolling is pickled and cold-rolled, and then (Ac1 + 100) ( ° C) or more.
[0063]
In the continuous annealing of the cold-rolled steel sheet, it is heated to (Ac1 + 100) (° C.) or more so that the volume fraction of bainite as the main phase is 50% or more. If the heating temperature at this time is lower than (Ac1 + 100) (° C.), the ferrite volume fraction increases too much, and the bainite volume fraction cannot be made 50% or more, resulting in poor burring workability. At the same time, by setting the heating temperature to (Ac1 + 100) (° C.) or higher, the ferrite particle size can be reduced, and further burring workability is improved. This effect is exhibited by setting the heating temperature to (Ac1 + 100) (° C.) or higher. However, this effect becomes remarkable because the heating temperature is (Ac3-50) (° C) or higher, and (Ac3-50) (° C) or higher is desirable. On the other hand, the effect of the present invention can be obtained without particularly setting the upper limit of the heating temperature. However, an excessive increase in the annealing temperature promotes the formation of a grain boundary oxidation phase and increases the manufacturing cost. Therefore, the upper limit of the annealing temperature is set to (Ac3 + 100) (° C.) or less.
[0064]
If the holding time of annealing is too short, there is a high possibility that undissolved carbide remains,ResidualSince the austenite volume fraction decreases, it is desirable that the austenite volume ratio be 10 seconds or longer. On the other hand, if the holding time is too long, there is a high possibility that the crystal grains become coarse and the balance between strength and ductility deteriorates. Therefore, the upper limit is preferably set to 1000 seconds.
[0065]
Thereafter, the primary cooling is performed at a cooling rate of 0.1 ° C./second or more to a temperature range of 650 to 800 ° C., and the cooling at a cooling rate of 1 to 100 ° C./second is performed as a two-hour cooling. After cooling to the plating bath temperature +100) (° C.), the temperature is maintained at 350 to (plating bath temperature +100) (° C.) for 1 to 3000 seconds including the immersion time of the plating bath.
[0066]
This maintains the bainite transformation without transforming the austenite generated by heating in the two-phase region to pearlite, and the temperature range of 350 to (Zn plating bath temperature +100) (° C.) is taken for 1 to 3000 seconds. This is to obtain predetermined characteristics by passing the structure as ferrite (+ bainite) + retained austenite.
[0067]
After annealing, if the primary cooling rate from 650 to 800 ° C. is less than 0.1 ° C./second, ferrite transformation becomes remarkable and exceeds 50% of the ferrite volume ratio, so the lower limit is set to 0.1 ° C. Per second. The upper limit is not particularly defined, but excessively increasing the cooling rate causes excessive capital investment. Therefore, the upper limit is desirably 100 ° C./second or less. However, even if this value is exceeded, the effects shown in the present invention are exhibited.
[0068]
After that, when the secondary cooling rate from the plating bath temperature to (plating bath temperature + 100) (° C.) is less than 1 ° C./second, austenite is transformed into pearlite during cooling, so that residual austenite does not remain. Not desirable. On the other hand, when the secondary cooling rate is faster than 100 ° C./sec, the cooling end point temperature in the plate width direction varies, and it becomes impossible to produce a uniform steel plate.
[0069]
The reason why the holding temperature before immersion in the plating bath is set to 350 to (Zn plating bath temperature + 100) (° C.) is that bainite transformation occurs in this temperature range, and residual austenite remains at room temperature. When the temperature is lower than 350 ° C., the austenite generated by heating in the two-phase region causes martensitic transformation and no residual austenite remains, so the lower limit temperature was set to 350 ° C. On the other hand, if the holding temperature is higher than (Zn plating bath temperature +100) (° C.), the austenite generated by heating in the two-phase region is transformed into pearlite, or cementite precipitates from the austenite, so the austenite Since it decomposes into bainite, the upper limit temperature was set to (Zn plating bath temperature + 100) (° C.).
[0070]
If the holding time including the Zn plating bath immersion time is less than 1 second, it is not preferable because the time for immersing the steel sheet in the plating bath is not sufficient, and if it exceeds 3000 seconds, the equipment becomes excessively large and uneconomical. Therefore, the holding time was set to 1 to 3000 seconds.
[0071]
In the alloying treatment that is selectively performed after immersion in the plating bath, the holding temperature is set to the bath temperature to (Zn plating bath temperature + 100) (° C.). If the temperature is higher than this temperature, austenite is transformed into pearlite, or Since cementite is precipitated from austenite, austenite is decomposed into bainite. Therefore, the upper limit temperature is set to (Zn plating bath temperature + 100) (° C.). If the holding temperature is lower than the bath temperature, it takes a long time for alloying, so the lower limit temperature was taken as the bath temperature.
[0072]
After the bath immersion, the high strength and high ductility hot dip galvanized steel sheet having excellent burring workability described in the present invention can be obtained without holding in the temperature range of bath temperature to (plating bath temperature +100) (° C.). Can do.
[0073]
Although the cooling rate from the Zn plating bath temperature or the holding temperature after immersion in the Zn plating to the room temperature is not particularly specified, when the cooling rate from these temperatures to 350 ° C. is 0.5 ° C./second or more. If the cooling rate in this temperature range is slower than this, the bainite transformation will proceed too much and the austenite will be stabilized more than necessary, or cementite will precipitate and the residual austenite will decompose, leading to proper transformation induction. Since plasticity cannot be obtained, the lower limit value of the cooling rate is preferably 0.5 ° C./second or more. On the other hand, even if the cooling rate in this temperature range exceeds 100 ° C./second, the material does not cause any problem, but excessively increasing the cooling rate leads to an increase in manufacturing cost. Therefore, the upper limit is preferably set to 100 ° C./second.
[0074]
In order to control oxides and improve wettability and alloying, it is desirable to control the temperature processing history from the hot rolling stage. First, by setting the heating temperature of the slab to 1150 to 1250 ° C., the rolling rate up to 1000 ° C. to 50% or more, the finishing temperature to 850 ° C. or more, and winding to 650 ° C. or less, the surface oxide layer can be as much as possible. It is desirable to form elements such as Mg, Zr, Ca, Y, Hf, and lanthanoids such as La and Ce in a solid solution state in order to form them uniformly and suppress Si oxide formation during annealing. Furthermore, it exists inside the steel plate.Is an internal oxideMgO, CaO, ZrO2, CeO2, La2O3, HfO2TiO2, Y2O3, SiO2, MnO and Al2O3Thereby, Si oxide formation is suppressed.
[0075]
Further, it is desirable to remove the oxidized phase formed by hot rolling as much as possible by performing high pressure deske and strong pickling on the deske after the finish rolling. In the annealing after cold rolling, it is desirable to raise the temperature at 5 ° C./s or more up to a temperature range of 750 ° C. or more for the purpose of suppressing external oxidation of Si.
[0076]
In principle, the material of the high strength and high ductility hot dip galvanized steel sheet with excellent burring workability according to the present invention is manufactured through refining, steelmaking, casting, hot rolling, and cold rolling processes, which are ordinary steelmaking processes. However, even if it is manufactured by omitting part or all of it, the effects of the present invention can be obtained as long as the conditions according to the present invention are satisfied.
[0077]
Further, in order to further improve the plating adhesion, the present invention does not depart from the present invention even if the steel plate is plated with Ni, Cu, Co, or Fe alone or before the annealing.
[0078]
Furthermore, regarding the annealing before plating, “after degreasing pickling, heating in a non-oxidizing atmosphere,2And N2After annealing in a reducing atmosphere containing, cool down to near the plating bath temperature and immerse in the plating bath `` by adjusting the atmosphere during annealing, first oxidizing the steel sheet surface, then reducing it A total reduction furnace method called “Immerse in plating bath after cleaning before plating” or “Flux treatment after degreasing and pickling the steel plate and then using ammonium chloride etc. and soaking in plating bath” The effect of the present invention can be exhibited regardless of the conditions.
[0079]
In addition, even if it cut | disconnects after annealing and removes the oxide of the steel plate surface, it is immersed in a plating bath and the effect of this invention can be acquired.
[0080]
【Example】
Hereinafter, the present invention will be described in more detail by way of examples.
[0081]
The slab whose component composition is listed in Table 1 was hot rolled, pickled, and cold rolled to a thickness of 1 mm. In hot rolling, the rolling rate up to 1000 ° C. was set to 70%. Then, Ac1 and Ac3 transformation temperature was calculated | required by calculation according to the following formula with the component (mass%) of each steel.
[0082]
Ac1 = 723-10.7 × Mn (%) + 29.1 × Si (%).
[0083]
Ac3 = 910−203 × C (%) 1/2 + 44.7 × Si (%) + 31.5 × Mo (%) − 30 × Mn (%) − 11 × Cr (%) + 400 × Al (%)
The annealing temperature calculated from these Ac1 and Ac3 transformation temperatures is 10% H at 10 ° C./s.2-N2After temperature rising and holding in the atmosphere, primary cooling to 680-750 ° C. at a cooling rate of 1-5 ° C./second, followed by secondary cooling to the plating bath temperature at a cooling rate of 5-10 ° C./second, Plating was performed by immersing in a hot-dip galvanizing bath at 460 ° C. with various changes in the bath composition for 3 seconds. In this case, the plating adhesion amount is 40 g / m on one side2It was.
[0084]
Then, about some steel plates, after hold | maintaining for 20 second in the temperature range of plating bath temperature -600 degreeC, the temperature range to 350 degreeC is cooled by the cooling rate of 3-10 degreeC / second, and it reaches room temperature. Cooled down. Details of the production conditions are shown in Table 2, Table 3 (Continuation 1 of Table 2) and Table 4 (Continuation 2 of Table 2).
[0085]
The plating property was evaluated by visual observation of the state of dross entrainment on the plating surface appearance and measurement of the area of the non-plated part. The concentration in the prepared plating layer was measured using ICP emission analysis after dissolving the plating layer with 5% hydrochloric acid containing an amine-based inhibitor.
[0086]
JIS No. 5 test specimens were collected from these plated steel plates and subjected to a room temperature tensile test at a gauge length of 50 mm and a tensile test speed of 10 mm / min.
[0087]
Hole expandability, which is an indicator of burring workability, is to punch a circular hole with a diameter of 10 mm under the condition that the clearance is 12%, make the burr on the die side, and mold it with a 60 ° conical punch. Evaluation was made based on the spread rate λ (%). One having a strength-burring workability balance (TS × λ) exceeding 50000 (MPa ·%) was defined as a high-strength steel plate excellent in burring workability.
[0088]
The residual austenite volume fraction Vγ is measured by X-ray diffraction using a Mo tube after chemically polishing the 7/16 inner layer of the plate thickness from the plating layer / steel plate interface, and the diffraction intensity Iα (200) of ferrite (200). The diffraction intensity Iα (211) of ferrite (211) and the diffraction intensity Iγ (220) of austenite (220) and the diffraction intensity Iγ (311) of (311) were obtained from the intensity ratio.
[0089]
Vγ (volume%) = 0.25 × {Iγ (220) / (1.35 × Iα (200)
+ Iγ (220))
+ Iγ (220) / (0.69 × Iα (211) + Iγ (220))
+ Iγ (311) / (1.5 × Iα (200) + Iγ (311))
+ Iγ (311) / (0.69 × Iα (211) + Iγ (311))}
The volume ratio and distribution of the oxide were measured by observing with SEM and EPMA after polishing.
[0090]
Table 5, Table 6 (continued from Table 5), Table 7 (continued from Table 5), Table 8 (continued from Table 5), Table 9 (continued from Table 5) and Table 10 (continued from Table 5) 5) shows mechanical characteristics, plating characteristics, etc. As shown in Table 5 to Table 10 (continuation 5 of Table 5), those containing Mg, Zr, Ca, Y, Hf, La-Ce as steel plate components and steel within 10 μm from the plating layer / steel plate interface MgO, CaO, ZrO2, CeO2, La2OThree, HfO2TiO2, Y2OThreeIn which the area ratio is 0.1% or more, there is no unplating and good plating properties are obtained.
[0091]
Even if the components of the steel sheet are within a predetermined range, those whose manufacturing conditions and steel sheet structure do not satisfy the predetermined requirements have a low bainite fraction and a strength-burring workability balance (TS × λ) of 50000 (MPa · %) And is inferior in burring workability. Furthermore, the retained austenite fraction is lowered, the strength-ductility balance (TS × El.) Is also less than 21000 (MPa ·%), and the strength-ductility balance is inferior.
[0092]
Even if the production conditions satisfy the present invention, the effect of the present invention cannot be obtained if the component range does not satisfy the predetermined requirements.
[0093]
[Table 1]
[Table 2]
[Table 3]
[Table 4]
[Table 5]
[Table 6]
[Table 7]
[Table 8]
[Table 9]
[Table 10]
【The invention's effect】
According to the present invention, a good hot dip galvanized steel sheet having good plating properties, excellent burring workability, and a strength-ductility balance (TS × El.) Exceeding 21000 (MPa ·%) was obtained.
Claims (13)
Ｃ：０．０００１〜０．３％、
Ｓｉ：０．００１〜４％（但し、０．１％未満を除く）、
Ｍｎ：０．００１〜３％、
Ａｌ：０．００１〜４％、
Ｍｏ：０．００１〜４％、
Ｐ：０．０００１〜０．３％、
Ｓ：０．０１％以下
を含有し、Ｍｇ、Ｚｒ、Ｃａ、Ｙ、Ｈｆおよびランタノイド族の元素群中から１種または２種以上を合計で０．００１〜１％含有し、残部がＦｅ及び不可避的不純物からなり、鋼板のミクロ組織が体積分率で、主相としてベイナイトを５０〜９７％含有し、第２相として残留オーステナイトを３〜５０％未満含有し、残部フェライトからなり、該フェライトの平均粒径が１０μｍ以下であり、前記鋼板の表面に、質量％で、
Ａｌ：０．００１〜０．５％、
Ｆｅ：５〜２０％を含有し、残部がＺｎ及び不可避的不純物からなるめっき層を有することを特徴とするバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板。The steel plate is mass%,
C: 0.0001 to 0.3%,
Si: 0.001 to 4% (excluding less than 0.1%) ,
Mn: 0.001 to 3%,
Al: 0.001 to 4%,
Mo: 0.001 to 4%,
P: 0.0001 to 0.3%,
S: 0.01% or less, Mg, Zr, Ca, Y, Hf and one or more of the lanthanoid group elements contained in a total amount of 0.001 to 1%, the balance being Fe and It consists of inevitable impurities, the microstructure of the steel sheet is volume fraction, contains 50 to 97% bainite as the main phase, contains less than 3 to 50% residual austenite as the second phase, and consists of the remaining ferrite, The average particle diameter is 10 μm or less, and the surface of the steel sheet is in mass%,
Al: 0.001 to 0.5%,
A high-strength and high-ductility hot-dip galvanized steel sheet excellent in burring workability, characterized by comprising a plating layer containing Fe: 5 to 20% and the balance being Zn and inevitable impurities.
Ｃ：０．０００１〜０．３％、
Ｓｉ：０．００１〜４％（但し、０．１％未満を除く）、
Ｍｎ：０．００１〜３％、
Ａｌ：０．００１〜４％、
Ｍｏ：０．００１〜４％、
Ｐ：０．０００１〜０．３％、
Ｓ：０．０１％以下
を含有し、Ｍｇ、Ｚｒ、Ｃａ、Ｙ、Ｈｆ、ランタノイド族の元素群中から１種または２種以上を合計で０．００１〜１％含有し、残部がＦｅ及び不可避的不純物からなり、鋼板のミクロ組織が体積分率で、主相としてベイナイトを５０〜９７％、第２相として残留オーステナイトを３〜５０％未満含有し、残部フェライトからなり、該フェライトの平均粒径が１０μｍ以下であり、前記鋼板の表面に、質量％で、
Ａｌ：０．００１〜０．５％、
Ｆｅ：５％未満を含有し、残部がＺｎ及び不可避不純物からなるめっき層を有することを特徴とするバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板。The steel plate is mass%,
C: 0.0001 to 0.3%,
Si: 0.001 to 4% (excluding less than 0.1%) ,
Mn: 0.001 to 3%,
Al: 0.001 to 4%,
Mo: 0.001 to 4%,
P: 0.0001 to 0.3%,
S: 0.01% or less, Mg, Zr, Ca, Y, Hf, lanthanoid group of one or more from 0.001 to 1% in total, with the balance being Fe and It consists of inevitable impurities, the microstructure of the steel sheet is volume fraction, contains 50 to 97% bainite as the main phase, contains less than 3 to 50% residual austenite as the second phase, and consists of the remaining ferrite, the average of the ferrite The particle size is 10 μm or less, and on the surface of the steel plate,
Al: 0.001 to 0.5%,
A high-strength, high-ductility hot-dip galvanized steel sheet excellent in burring workability, comprising Fe: less than 5% and the balance having a plating layer composed of Zn and inevitable impurities.
Ｎｉ：０．００１〜４％、
Ｃｕ：０．００１〜４％、
Ｃｒ：０．００１〜４％、
Ｃｏ：０．００１〜４％
の１種又は２種以上を含有することを特徴とする請求項１又は２に記載のバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板。Furthermore, in steel,
Ni: 0.001 to 4%,
Cu: 0.001 to 4%,
Cr: 0.001 to 4%,
Co: 0.001 to 4%
The high strength and high ductility hot dip galvanized steel sheet excellent in burring workability according to claim 1 or 2 , characterized by containing one or more of the following.
Ｂ：０．０００１〜０．１％を含有することを特徴とする請求項１〜５のいずれか１項に記載のバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板。Furthermore, in steel,
B: 0.0001-0.1% is contained, The high intensity | strength high ductility hot dip galvanized steel plate excellent in burring workability of any one of Claims 1-5 characterized by the above-mentioned.
Ｍｎ：０．００１〜２％、
を含有し、残部がＺｎ及び不可避不純物からなるめっき層を有する溶融亜鉛めっき鋼板であって、
鋼板のＳｉ含有率：Ｘ（質量％）、Ｍｎ含有率：Ｙ（質量％）及びＡｌ含有率：Ｚ（質量％）、並びにめっき層のＡｌ含有率：Ａ（質量％）及びＭｎ含有率：Ｂ（質量％）が、下記（１）式を満たすことを特徴とする請求項１〜８のいずれか１項に記載のバーリング加工性に優れた高強度溶融亜鉛めっき鋼板。
３−（Ｘ＋Ｙ／１０＋Ｚ／３）−１２．５×（Ａ−Ｂ）≧０・・・（１）Furthermore, the plating layer is mass%,
Mn: 0.001-2%,
Is a hot dip galvanized steel sheet having a plating layer consisting of Zn and inevitable impurities,
Si content of steel sheet: X (mass%), Mn content: Y (mass%) and Al content: Z (mass%), and Al content of plating layer: A (mass%) and Mn content: B (mass%) satisfy | fills following (1) Formula, The high intensity | strength hot-dip galvanized steel plate excellent in burring workability of any one of Claims 1-8 characterized by the above-mentioned.
3- (X + Y / 10 + Z / 3) -12.5 × (A−B) ≧ 0 (1)
Ｃａ：０．００１〜０．１％、
Ｍｇ：０．００１〜３％、
Ｓｉ：０．００１〜０．１％、
Ｍｏ：０．００１〜０．１％、
Ｗ：０．００１〜０．１％、
Ｚｒ：０．００１〜０．１％、
Ｃｓ：０．００１〜０．１％、
Ｒｂ：０．００１〜０．１％、
Ｋ ：０．００１〜０．１％、
Ａｇ：０．００１〜５％、
Ｎａ：０．００１〜０．０５％、
Ｃｄ：０．００１〜３％、
Ｃｕ：０．００１〜３％、
Ｎｉ：０．００１〜０．５％、
Ｃｏ：０．００１〜１％、
Ｌａ：０．００１〜０．１％、
Ｔｌ：０．００１〜８％、
Ｎｄ：０．００１〜０．１％、
Ｙ ：０．００１〜０．１％、
Ｉｎ：０．００１〜５％、
Ｂｅ：０．００１〜０．１％、
Ｃｒ：０．００１〜０．０５％、
Ｐｂ：０．００１〜１％、
Ｈｆ：０．００１〜０．１％、
Ｔｃ：０．００１〜０．１％、
Ｔｉ：０．００１〜０．１％、
Ｇｅ：０．００１〜５％、
Ｔａ：０．００１〜０．１％、
Ｂ ：０．００１〜０．１％、
の１種または２種以上を含有することを特徴とする請求項１〜９のいずれか１項に記載のバーリング加工性に優れた高強度高延性溶融亜鉛めっき鋼板。Furthermore, the plating layer is mass%,
Ca: 0.001 to 0.1%,
Mg: 0.001 to 3%,
Si: 0.001 to 0.1%,
Mo: 0.001 to 0.1%,
W: 0.001 to 0.1%,
Zr: 0.001 to 0.1%,
Cs: 0.001 to 0.1%,
Rb: 0.001 to 0.1%,
K: 0.001 to 0.1%,
Ag: 0.001 to 5%,
Na: 0.001 to 0.05%,
Cd: 0.001 to 3%
Cu: 0.001 to 3%,
Ni: 0.001 to 0.5%,
Co: 0.001-1%,
La: 0.001 to 0.1%,
Tl: 0.001-8%
Nd: 0.001 to 0.1%,
Y: 0.001 to 0.1%
In: 0.001 to 5%,
Be: 0.001 to 0.1%,
Cr: 0.001 to 0.05%,
Pb: 0.001 to 1%,
Hf: 0.001 to 0.1%,
Tc: 0.001 to 0.1%,
Ti: 0.001 to 0.1%,
Ge: 0.001 to 5%,
Ta: 0.001~0.1%,
B : 0.001 to 0.1%,
The high strength and high ductility hot dip galvanized steel sheet excellent in burring workability according to any one of claims 1 to 9, wherein the steel sheet contains one or more of the following.
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