JP2004244665A - High-strength and high-ductility steel plate and its manufacturing method - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、建材、家電製品、自動車などに適する延性に優れた高強度高延性鋼板および及びその製造方法に関する。なお、本発明の鋼板は熱延鋼板、冷延鋼板，Ｚｎめっき鋼板、合金化Ｚｎめっき鋼板を含むものである。
【０００２】
【従来の技術】
高強度鋼板は、建材、家電製品、自動車など広範囲に使用されている。近年、特に自動車車体において軽量化や衝突安全性の向上の観点から、高強度鋼板が用いられるようになってきた。しかし、高強度ゆえ、加工性が強度と共に劣化してしまう。高強度鋼板の延性を向上させるためには、複合組織の活用が挙げられる。すなわち、軟質なフェライト相と第２相として硬質のマルテンサイト相を複合させたＤｕａｌ−Ｐｈａｓｅ鋼（ＤＰ鋼）、または、第２相として加工により硬質のマルテンサイトに変態するオーステナイト相を複合させた残留オーステナイト鋼が開発されてきた。しかし、それ以降、高延性に対する画期的な技術は開発されておらず、高強度化と更なる延性向上をこれら複合組織化以上に達成される技術はない。
【０００３】
本発明者らの一部は特許文献１および特許文献２等にＲＥＭを含有するＤＰ鋼又はＴＲＩＰ鋼に溶融Ｚｎめっきを施した溶融Ｚｎめっき鋼板を開示した。しかし、特許文献１および特許文献２に開示された発明は上述した複合組織化による高延性化を亜鉛めっき鋼板で実現する技術であり、更なる延性の向上を図るような技術ではない。
【０００４】
【特許文献１】
特願２００１−３０４０３４号
【特許文献２】
特願２００１−３０４０３６号
【０００５】
【発明が解決しようとする課題】
本発明は、上記課題を解決し、さらなる高延性化を達成する高強度鋼板及びその製造方法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】
本発明者らは、種々検討を行った結果、鋼中の酸化物および硫化物を制御することで種々の鋼種の高延性化が可能であることを見出した。これまでにも、介在物を制御して加工性を向上させる技術は開示されているが、そのほとんどが局部伸び向上に関するものであり、均一伸びを向上させるものではなかった。すなわち、Ｒｅｍおよび／またはＹを添加して酸化物および硫化物の形態を制御することで均一伸びが向上する技術を見出した。
【０００７】
ここで、ＲＥＭはＲｅｒａ Ｅａｒｔｈ Ｍｅｔａｌの略でＬａから始まるランタノイド系の元素を示す。工業的はミッシュメタルの形で添加されることがおおく、この場合には中でもＬａおよびＣｅの含有が主体となる。
【０００８】
また、この効果は、冷延や熱延、めっきといった異なる製品についても有効で、式（１）および（２）を満たすことで均一伸びの向上が達成される。
【０００９】
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）質量％で、
Ｃ ：０．０００１〜０．３％、
Ｓｉ：０．００１〜２．５％、
Ｍｎ：０．０１〜３％、
Ｐ ：０．０００１〜０．３％、
Ａｌ：０．０００１〜４％、
Ｓ ：０．０００１〜０．１％、
Ｎ ：０．０００１〜０．３％、
Ｏ ：０．０００１〜０．１％、
を含有し、
Ｒｅｍ：０．０００５〜０．３％、
Ｙ ：０．０００５〜０．３％、
Ｔｉ：０．００１〜１％、
Ｚｒ：０．００１〜１％、
Ｈｆ：０．００１〜１％、
Ｃａ：０．０００１〜１％、
の１種または２種以上を式（１）および（２）を満たす範囲で含有し、残部Ｆｅ及び不可避不純物からなることを特徴とする高強度高延性鋼板。
【００１０】
（Ｔｉ／４８＋Ｚｒ／９１＋Ｈｆ／１７８＋Ｃａ／４０）／（Ｒｅｍ／１４０＋Ｙ／８９）＝０〜２０ …（１）
（Ｏ／１６＋Ｓ／３２＋Ｎ／１４） ／（Ｒｅｍ／１４０＋Ｙ／８９）＝０〜１０ …（２）
（２）鋼板のミクロ組織が、主相としてフェライト又はフェライト及びベイナイトを面積分率で５０〜９７％含有し、第２相としてマルテンサイト、オーステナイトの一方又は両方を、面積分率で合計３〜５０％未満含むことを特徴とする（１）記載の高強度高延性鋼板。
（３）ＲｅｍまたはＹの酸化物および／または硫化物が
平均粒子径ｄ：０．０１〜１０．０μｍ、
密度ρ：１平方ｍｍあたり１０７〜１０９個、
平均粒子径ｄと主相平均粒径ｄｍとの比ｄ／ｄｍ； １０−４〜１００、
を満たす分布形態を有することを特徴とする（１）又は（２）記載の高強度高延性鋼板。
（４）さらに質量％で、
Ｃｒ：０．００１〜５％、
Ｍｏ：０．００１〜５％、
Ｎｉ：０．００１〜５％、
Ｃｕ：０．００１〜５％、
Ｃｏ：０．００１〜５％、
Ｗ ：０．００１〜５％、
の１種又は２種以上を含有することを特徴とする（１）〜（３）のいずれか１項に記載記載の高強度高延性鋼板。
（５）さらに質量％で、
Ｎｂ：０．００１〜１％、
Ｖ ：０．００１〜１％、
Ｔａ：０．００１〜１％、
の１種又は２種以上を含有することを特徴とする（１）〜（４）のいずれか１項に記載の高強度高延性鋼板。
（６）さらに質量％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項に記載の高強度高延性鋼板。
（７）鋼板の表面にＺｎめっきが施されていることを特徴とする（１）〜（６）のいずれか１項に記載の高強度高延性鋼板。
（８）溶鋼に、Ａｌ、Ｔｉ、Ｓｉ、Ｍｎの１種以上を添加して脱酸した後、Ｒｅｍおよび／またはＹを添加し、（１）、（４）〜（６）の何れか１項に記載の成分からなる溶鋼に調整した後０．１〜５ｍ／ｍｉｎ の鋳造速度で鋳込み、その鋼片を鋳造まま又は一旦７００℃以下に冷却した後に、１１５０〜１２８０℃に加熱し、１１５０〜１２８０℃に加熱し、続いて熱延を行う際に、１０００℃以上の圧延時の１パス当たり圧下率を３０％以下とすることを特徴とする高強度高延性鋼板の製造方法。
【００１１】
【発明の実施の形態】
以下、本発明を詳細に説明する。
【００１２】
発明者らは、質量％で、Ｃ：０．０００１〜０．３％、Ｓｉ：０．００１〜２．５％、Ｍｎ：０．０１〜３％、Ｐ：０．００１〜０．３％、Ａｌ：０．０００１〜４％、Ｓ：０．０００１〜０．０３％、Ｎ：０．０００１〜０．０３％、Ｏ：０．０００１〜０．０５％を含有し、さらに、Ｒｅｍ、Ｙ、Ｔｉ、Ｚｒ、Ｈｆ，Ｃａの１種又は２種以上を含有する種々の溶綱を鋳造速度およびＲｅｍ、Ｙ、Ｔｉ、Ｚｒ、Ｈｆ，Ｃａの添加タイミングを変化させて鋳造して、熱延鋼板、冷延鋼板およびめっき鋼板を作製した。それらの鋼板の引張り試験を行い、機械的性質を比較評価した。
【００１３】
その結果、Ｒｅｍ、Ｙの添加に伴う酸化物および硫化物の形態制御により均一伸びおよび破断延性が向上することを見出した。
【００１４】
すなわち、鋼板の成分でＲｅｍ、Ｙ、Ｔｉ、Ｚｒ，ＨｆおよびＣａの添加量の関係が次の２つの式を満たすことで均一伸びおよび破断延性が向上する。
【００１５】
（Ｔｉ／４８＋Ｚｒ／９１＋Ｈｆ／１７８＋Ｃａ／４０）／（Ｒｅｍ／１４０＋Ｙ／８９）＝０〜２０ …（１）
（Ｏ／１６＋Ｓ／３２＋Ｎ／１４） ／（Ｒｅｍ／１４０＋Ｙ／８９）＝０〜１０ …（２）
本発明では、Ｒｅｍおよび／またはＹの酸化物および／または硫化物の形態を制御することで複合組織化による高延性化に加えてさらに延性を向上させることを目的としている。したがって、（１）式にあるように他の酸化物および／または硫化物形成元素との関係が重要で、ＲｅｍおよびＹ以外の元素添加量との比率が大きいことが形態制御には重要であることを見出した。また、（２）式では酸素および／またはＳと窒素の関係も形態制御には必要不可欠で、これら元素との比も形態制御には重要であることも併せて見出した。すなわち、上記２式を満たし、ＲｅｍおよびＹの酸化物および硫化物が下記の形態をとることが延性向上に重要である。
平均粒子径ｄ：０．０１〜１０．０μｍ
密度ρ：１平方ｍｍあたり１０７〜１０９個
平均粒子径ｄと主相平均粒径ｄｍとの比ｄ／ｄｍ； １０−４〜１００
すなわち、Ｒｅｍ，Ｙの酸化物および硫化物を活用して他の延性に悪影響を及ぼすアルミナやシリカ、ＭｎＳ等の介在物を軽減することで、破断延性のみならず均一伸びをも向上させることができることを見出した。
【００１６】
ここで、上述したような酸化物および硫化物の同定・観察や面積率測定は、光学顕微鏡、ＥＰＭＡやＦＥ−ＳＥＭなどを用いて行うことができる。本発明においては、５００〜２００００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を用いたり、ＥＢＳＰ、ＥＤＸおよびＥＰＭＡを用いた。また、ここでいう、Ｒｅｍ，Ｙの酸化物および硫化物は、他の原子を含む複合物であったり、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Ｒｅｍ，Ｙを主体とした化合物で、例えば、Ｙ２Ｏ３，Ｌａ２Ｏ３，Ｃｅ２Ｏ３，ＣｅＯ２，Ｌａ２Ｓ３，ＬａＳ，Ｃｅ２Ｓ３，ＣｅＳ，Ｃｅ３Ｓ４などの複合あるいは単独の化合物である。面積率測定は、上記形態観察や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面積率を求めることができる。
【００１７】
次に、鋼板のミクロ組織について述べる。基本的には、上記酸化物および硫化物を制御することで、いずれの鋼板組織においてもその延性向上効果を得ることができる。しかし、鋼板の延性自体を十分に確保する目的から、主相をフェライト相とするのが望ましい。しかし、さらに高強度化を指向する場合にはベイナイト相を含んでも良いが、延性を確保する観点から主相としては、フェライトの単独相、又はフェライト及びベイナイトの複合相（本明細書中「フェライト又はフェライト及びベイナイト」と表記する場合も特段断らない限り同様の意味である）を、面積分率で５０％以上含むことが望ましい。フェライト及びベイナイトの複合相とする場合も、フェライトは延性を確保するために、面積分率で５０％以上含有することが好ましい。一方、高強度化と高延性をバランスさせるためには、フェライト又はフェライト及びベイナイトを面積分率で９７％以下とすることが好ましい。
【００１８】
さらに高強度と高延性を両立させるため、残留オーステナイトおよび／またはマルテンサイトを含む複合組織とすることも望ましい。高強度と高延性のために、残留オーステナイト相および／またはマルテンサイトは、面積分率で合計３％以上含有することが好ましいが面積分率が合計５０％以上になると脆化傾向を示すので５０％未満とすることが好ましい。
【００１９】
上記の他にミクロ組織の残部組織として、炭化物、窒化物、硫化物、酸化物の１又は２以上を面積分率５％以下で含有する場合も本発明の範囲とする鋼板である。
【００２０】
なお、上記ミクロ組織の各相、フェライト、ベイナイト、オーステナイト、マルテンサイト、界面酸化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５９−２１９４７３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〜１００００倍の光学顕微鏡およびＳＥＭ観察により定量化が可能である。
【００２１】
次に、本発明における鋼板成分の好適な範囲の限定理由について述べる。
【００２２】
Ｃは、良好な強度延性バランスを確保するための第２相の面積分率を十分確保する目的で添加する元素である。特に第２相がオーステナイトである場合には、面積分率のみならずその安定性向上にも寄与して延性を大きく向上させる。強度および各第２相の面積分率を確保するために下限を０．０００１質量％（以下、同じ）とし、溶接性を保持可能な上限として０．３質量％とした。
【００２３】
Ｓｉは、主相であるフェライト生成を促進させることおよび強度延性バランスを劣化させる炭化物の生成を抑制する目的で添加する元素であり、その下限を０．００１質量％とした。また、過剰添加は溶接性およびめっき濡れ性に悪影響を及ぼす。このため、上限を２．５質量％とした。
【００２４】
Ｍｎは、めっき濡れ性および密着性の制御に加えて、高強度化の目的で添加する。また、マルテンサイトやオーステナイトなどの第２相を含む場合には、強度低下と延性劣化の１つの原因である炭化物析出やパーライト生成を抑制する目的で添加する。これらのことから、０．０１質量％以上とした。一方では、第２相がオーステナイトの場合に延性向上に寄与するベイナイト変態を遅滞させることや溶接性を劣化させることから３質量％を上限とした。
【００２５】
Ｐ量を０．０００１〜０．０５質量％の範囲としたのは、０．０００１質量％以上で強化効果が現れることや極低化は経済的にも不利であることからこれを下限とした。また、０．３質量％を上限としたのは、これを超える量の添加では、溶接性や鋳造時や熱延時の製造性に悪影響を及ぼすためである。
【００２６】
Ａｌは、Ｒｅｍ，Ｙの酸化物および硫化物を制御する上で重要な脱酸添加元素である。Ｒｅｍ，Ｙ添加前の酸素量を制御して、これら元素の酸化物および硫化物形態を制御する目的から、０．０００１質量％以上の添加とした。一方過剰添加は溶接性およびめっき濡れ性を損なうため４％を上限とした。
【００２７】
ＳはＲｅｍ，Ｙの硫化物を制御する観点から添加量を０．０００１〜０．１質量％の範囲とした。また、Ｒｅｍ，Ｙ添加の延性改善効果を得るために上述の式（２）を満たす範囲での添加とした。一方で、極低化は経済的にも不利である。また、０．１質量％を超える量の添加では、溶接性や鋳造時や熱延時の製造性に悪影響を及ぼすだけでなく、本発明のＲｅｍ，Ｙ添加効果が認められなくなることからこれを上限とした。
【００２８】
ＮはＣ同様良好な強度延性バランスを確保するための第２相の面積分率を十分確保するためや、Ｒｅｍ，Ｙの酸化物および硫化物形成に影響するＴｉ，Ｚｒ，Ｈｆと窒化物を形成してＲｅｍ，Ｙの酸化物および硫化物形成を間接的に促す役割がある元素であるために下限を０．０００１％とし、さらに上記理由から式（２）を満たす範囲とした。一方で、溶接性を保持可能な上限として０．３質量％とした。
【００２９】
ＯはＳと同様にＲｅｍ，Ｙの酸化物を制御する観点から添加量を０．０００１〜０．１質量％の範囲とした。また、Ｒｅｍ，Ｙ添加の延性改善効果を得るために上述の式（２）を満たす範囲での添加とした。一方で、極低化は経済的にも不利である。また、０．１質量％を超える量の添加では、延性や溶接性や鋳造時や熱延時の製造性に悪影響を及ぼすだけでなく、本発明のＲｅｍ，Ｙ添加効果が認められなくなることからこれを上限とした。
【００３０】
Ｒｅｍ、Ｙは、本発明における酸化物および硫化物の形態制御による延性改善に重要な元素である。これらの元素を主成分とする酸化物および硫化物を形成させることで破断延性および均一伸びを向上させることができる。このため、それぞれ０．０００５％を下限とした。また一方で過剰添加は鋳造性や熱間加工性などの製造性および鋼板製品の延性を低下させるため、それぞれ０．３質量％を上限とした。
【００３１】
Ｔｉ，Ｚｒ，Ｈｆ，ＣａはＡｌ同様、Ｒｅｍ，Ｙの酸化物および硫化物を制御する上で重要な脱酸添加元素であるが、添加量と添加タイミングによっては、Ｒｅｍ，Ｙの酸化物および硫化物の良好な形態形成を阻害する。阻害しない範囲として、それぞれ０．０００１質量％以上１％以下とし、更に上記式（１）を満たす添加とした。
【００３２】
さらに、本発明が対象とする鋼は、強度のさらなる向上を目的としてＣｒ、Ｍｏ，Ｎｉ、Ｃｕ、Ｃｏ、Ｗの１種または２種以上を含有できる。
【００３３】
Ｃｒは、強化目的および炭化物生成の抑制の目的から添加する元素で、０．００１質量％以上とし、５質量％を超える量の添加では、加工性に悪影響を及ぼすため、これを上限とした。
【００３４】
Ｍｏは、強度延性バランスを劣化させる炭化物やパーライトの生成を抑制する目的で添加できる元素であり、良好な強度延性バランスを得るために重要な添加元素である。その下限を０．００１質量％とした。また、過剰添加は、延性劣化を招くことから、上限を５％とした。
【００３５】
Ｎｉは、組織強化の目的で０．００１質量％以上とし、５質量％を超える量の添加では、加工性に悪影響を及ぼすため、これを上限とした。
【００３６】
Ｃｕは、強化目的で０．００１質量％以上の添加とし、５質量％を超える量の添加では、加工性に悪影響を及ぼす。
【００３７】
Ｃｏは、強度延性バランスの向上のため、０．００１質量％以上の添加とした。一方、高価な元素であるため多量添加は経済性を損なうため、５質量％以下にすることが望ましい。
【００３８】
Ｗ量を０．００１〜５質量％の範囲としたのは、０．００１質量％以上で強化効果が現れること、５質量％を上限としたのは、これを超える量の添加では、加工性に悪影響を及ぼすためである。
【００３９】
さらに、本発明が対象とする鋼は、強度のさらなる向上を目的として強炭化物形成元素であるＮｂ，Ｖ、Ｔａの１種または２種以上を含有できる。
【００４０】
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して、鋼板の強化に極めて有効であるため、必要に応じて１種または２種以上をそれぞれ０．００１質量％以上の添加とした。一方で、延性劣化や残留オーステナイト中へのＣの濃化を阻害することから、それぞれの添加量の上限として１質量％とした。
【００４１】
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高強度化に有効ではあるが、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上昇させ、加工性が低下するため、上限を０．１質量％とした。
【００４２】
不可避的不純物として、例えばＳｎなどがあるがこれら元素をＳｎ≦０．０１質量％以下の範囲で含有しても本発明の効果を損なうものではない。
【００４３】
本発明の鋼板は、熱延鋼板、冷延鋼板、亜鉛めっき鋼板および合金化亜鉛めっき鋼板についてその効果の発現を見出したものである。
【００４４】
これらの鋼板を製造する場合には、所定の成分に調整された溶鋼を最終的に成分調整するにあたり、Ｒｅｍ，Ｌａ，Ｙを添加する前にはＡｌ，Ｔｉ、Ｓｉ、Ｍｎなどの強脱酸元素で十分に溶鋼中の酸素を低下させておく必要がある。その後、Ｒｅｍ，Ｌａ，Ｙの１種又は２種以上を添加して鋳造するが、鋳造速度としては０．１〜５ｍ／ｍｉｎが望ましい。この様に精錬および鋳造方法を制御することでＲｅｍ，Ｌａ，Ｙを主成分とする酸化物および硫化物の形態を制御して、延性向上効果を出現させるものであり、脱酸元素の添加順序は本発明において重要である。
【００４５】
鋳造速度は０．０１ｍ／ｍｉｎより遅いかまたは５ｍ／ｍｉｎより速いとＲｅｍやＹの酸化物および／または硫化物形態が延性向上に寄与する形態とならずに延性向上硬化が得られない。
【００４６】
その後、鋳造ままもしくは一旦７００℃以下まで冷却した後、鋼片を再加熱して熱延を行う。鋳造ままの鋼片をそのまま加熱して熱延することは加熱原単位の減少になり好ましく、また鋼片を７００℃以下まで冷却することはスラブ表面の手入れの必要な場合には好ましい。
【００４７】
このとき、粒界酸化相の多量生成を抑制するために加熱温度を１１５０℃以上または１２８０℃以下とすることが望ましい。加熱温度が１１５０℃以上の高温になると全面に比較的均一に酸化スケールが形成され粒界酸化は抑制される傾向に有る。また、１１５０℃より低温加熱では熱延での変形抵抗が高くなり、傷や割れ発生の原因にもなる。一方、加熱温度が１２８０℃を超えると酸化スケールが多量発生したり粒径の粗大化を招くため、上記の範囲とすることが好ましい。また、１０００℃以上の圧延時の１パス当たり圧下率を３０％以下とすることで、熱間での割れを防止することおよび延性向上に寄与する酸化物および／または硫化物形態を形成させることができる。
【００４８】
この時、熱延完了温度は鋼の化学成分によって決まるＡｒ３ 変態温度以上で行うのが一般的であるが、Ａｒ３ から１０℃程度低温までであれば最終的な鋼板の特性を劣化させない。また、冷却後の巻取温度は鋼の化学成分によって決まるベイナイト変態開始温度以上とすることで、冷延時の荷重を必要以上に高めることがさけられるが、冷延の全圧下率が小さい場合にはこの限りでなく、鋼のベイナイト変態温度以下で巻き取られても最終的な鋼板の特性を劣化させない。
【００４９】
その後、必要に応じ、冷延後焼鈍したり、さらにめっき工程を経ることで各種の最終製品とする。冷延の全圧下率は、最終板厚と冷延荷重の関係から設定されるが、５０％以上であれば製品での良好な強度延性のバランスを得やすい。
【００５０】
【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。
【００５１】
製鋼段階は、Ａｌ、Ｔｉ，Ｓｉ，Ｍｎで先に脱酸した後にＲｅｍ、Ｙを添加し、最終的に表１、表２（表１のつづき）に示すような組成の溶鋼に調整し、０．０５〜３ｍ／ｍｉｎで鋳造した。鋳造後の鋼片を鋳造まま又は７００℃以下に冷却した後、１０２０〜１２５０℃に加熱し、１０００℃以上での圧下率を１０〜３０％ととしてＡｒ３ 変態温度以上で熱延を完了し、９００℃で巻き取った鋼帯を酸洗後、各試験に供した。各製品はすべて１．４ｍｍ厚とした。冷延およびめっき鋼板用の熱延原板は３ｍｍとし、１．４ｍｍに冷延後、冷延用は連続焼鈍に、めっき用は溶融亜鉛めっき工程にてそれぞれ製品を作成した。
【００５２】
表３、表４（表３のつづき）に示すように、発明鋼は均一伸びおよび全伸びの値が同様の成分・組織構成・強度を有する比較鋼に比べて２〜５％程度高い値を示す。
【００５３】
また、表５、表６（表５のつづき）に幾つかの鋼材について、鋳造速度および熱延の加熱温度を変化させた場合の機械的特性およびＲｅｍ，Ｙの酸化物および硫化物形態に及ぼす影響を示す。鋳造速度が速くなると介在物密度が大きくなり、遅くなると介在物密度が小さくなってしまう。その結果、延性改善効果が十分でないことが分かる。また、加熱温度が低い場合には、十分な強度が得られない。
【００５４】
【表１】
【表２】
【表３】
【表４】
【表５】
【表６】
【発明の効果】
本発明により、鋼成分を特定の範囲とし、それらの量的関係を特定の関係式を満足するように調整することにより延性に優れた高強度高延性鋼板を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-strength and high-ductility steel sheet excellent in ductility suitable for building materials, home appliances, automobiles, and the like, and a method for producing the same. The steel sheet of the present invention includes a hot rolled steel sheet, a cold rolled steel sheet, a Zn plated steel sheet, and an alloyed Zn plated steel sheet.
[0002]
[Prior art]
High-strength steel sheets are used in a wide range of building materials, home appliances, automobiles and the like. In recent years, high-strength steel sheets have come to be used from the viewpoint of reducing weight and improving collision safety, particularly in automobile bodies. However, due to the high strength, the workability deteriorates with the strength. In order to improve the ductility of a high-strength steel plate, utilization of a composite structure is mentioned. That is, a dual-phase steel (DP steel) in which a soft ferrite phase and a hard martensite phase are combined as the second phase, or an austenite phase that is transformed into hard martensite by processing as the second phase. Residual austenitic steel has been developed. However, since then, no epoch-making technology for high ductility has been developed, and there is no technology that can achieve higher strength and further improvement of ductility than these composite structures.
[0003]
Some of the present inventors disclosed a hot-dip Zn-plated steel sheet obtained by applying hot-dip Zn plating to DP steel or TRIP steel containing REM in Patent Document 1 and Patent Document 2. However, the invention disclosed in Patent Document 1 and Patent Document 2 is a technique for realizing the above-described high ductility by the composite structure using a galvanized steel sheet, and is not a technique for further improving the ductility.
[0004]
[Patent Document 1]
Japanese Patent Application No. 2001-304034 [Patent Document 2]
Japanese Patent Application No. 2001-304036
[Problems to be solved by the invention]
An object of this invention is to provide the high strength steel plate which solves the said subject and achieves further high ductility, and its manufacturing method.
[0006]
[Means for Solving the Problems]
As a result of various studies, the present inventors have found that high ductility of various steel types can be achieved by controlling oxides and sulfides in the steel. Until now, techniques for controlling inclusions to improve workability have been disclosed, but most of them have been related to improvement of local elongation and have not improved uniform elongation. That is, the present inventors have found a technique in which uniform elongation is improved by adding Rem and / or Y to control the form of oxide and sulfide.
[0007]
Here, REM is an abbreviation for Rera Earth Metal and represents a lanthanoid element starting from La. Industrially, it is added in the form of misch metal. In this case, the inclusion of La and Ce is the main component.
[0008]
This effect is also effective for different products such as cold rolling, hot rolling, and plating, and uniform elongation can be improved by satisfying the formulas (1) and (2).
[0009]
The present invention has been completed based on the above findings, and the gist thereof is as follows.
(1) In mass%,
C: 0.0001 to 0.3%,
Si: 0.001 to 2.5%,
Mn: 0.01 to 3%
P: 0.0001 to 0.3%,
Al: 0.0001 to 4%
S: 0.0001 to 0.1%,
N: 0.0001 to 0.3%
O: 0.0001 to 0.1%
Containing
Rem: 0.0005 to 0.3%,
Y: 0.0005 to 0.3%
Ti: 0.001 to 1%,
Zr: 0.001 to 1%,
Hf: 0.001 to 1%,
Ca: 0.0001 to 1%,
A high-strength, high-ductility steel sheet containing one or more of the above in a range satisfying the formulas (1) and (2) and comprising the balance Fe and inevitable impurities.
[0010]
(Ti / 48 + Zr / 91 + Hf / 178 + Ca / 40) / (Rem / 140 + Y / 89) = 0-20 (1)
(O / 16 + S / 32 + N / 14) / (Rem / 140 + Y / 89) = 0-10 (2)
(2) The microstructure of the steel sheet contains ferrite or ferrite and bainite as a main phase in an area fraction of 50 to 97%, and one or both of martensite and austenite as a second phase in a total area of 3 to 3 The high-strength and high-ductility steel sheet according to (1), comprising less than 50%.
(3) Rem or Y oxide and / or sulfide has an average particle diameter d: 0.01 to 10.0 μm,
Density ρ: 10 7 to 10 9 per square mm,
Ratio d / dm of average particle diameter d and main phase average particle diameter dm; 10 −4 to 10 0 ,
The high-strength and highly ductile steel sheet according to (1) or (2), having a distribution form satisfying
(4) Furthermore, in mass%,
Cr: 0.001 to 5%,
Mo: 0.001 to 5%,
Ni: 0.001 to 5%,
Cu: 0.001 to 5%,
Co: 0.001-5%
W: 0.001 to 5%,
The high-strength and high-ductility steel sheet according to any one of (1) to (3), comprising one or more of the following.
(5) Furthermore, in mass%,
Nb: 0.001 to 1%,
V: 0.001 to 1%,
Ta: 0.001 to 1%,
The high-strength and high-ductility steel sheet according to any one of (1) to (4), characterized by containing one or more of the following.
(6) The high-strength and highly ductile steel sheet according to any one of (1) to (5), further containing, by mass%, B: 0.0001 to 0.1%.
(7) The high strength and high ductility steel plate according to any one of (1) to (6), wherein the surface of the steel plate is Zn-plated.
(8) After adding one or more of Al, Ti, Si, and Mn to the molten steel for deoxidation, Rem and / or Y is added, and any one of (1), (4) to (6) After adjusting to molten steel consisting of the components described in the section, casting is performed at a casting speed of 0.1 to 5 m / min, and the steel piece is cast as it is or once cooled to 700 ° C. or lower, and then heated to 1150 to 1280 ° C. A method for producing a high-strength, high-ductility steel sheet, characterized in that when heated to 1280 ° C and subsequently hot rolled, the rolling reduction per pass during rolling at 1000 ° C or higher is 30% or less.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
[0012]
The inventors, in mass%, C: 0.0001 to 0.3%, Si: 0.001 to 2.5%, Mn: 0.01 to 3%, P: 0.001 to 0.3% Al: 0.0001 to 4%, S: 0.0001 to 0.03%, N: 0.0001 to 0.03%, O: 0.0001 to 0.05%, and Rem, Various types of molten steel containing one or more of Y, Ti, Zr, Hf, and Ca are cast while changing the casting speed and the addition timing of Rem, Y, Ti, Zr, Hf, and Ca. A rolled steel sheet, a cold rolled steel sheet and a plated steel sheet were produced. The steel sheets were subjected to a tensile test, and the mechanical properties were compared and evaluated.
[0013]
As a result, it was found that uniform elongation and fracture ductility were improved by controlling the form of oxide and sulfide accompanying the addition of Rem and Y.
[0014]
That is, uniform elongation and fracture ductility are improved when the relationship between the amounts of Rem, Y, Ti, Zr, Hf and Ca added by the components of the steel sheet satisfies the following two expressions.
[0015]
(Ti / 48 + Zr / 91 + Hf / 178 + Ca / 40) / (Rem / 140 + Y / 89) = 0-20 (1)
(O / 16 + S / 32 + N / 14) / (Rem / 140 + Y / 89) = 0-10 (2)
An object of the present invention is to further improve ductility in addition to increasing ductility by complex structure by controlling the form of oxides and / or sulfides of Rem and / or Y. Therefore, the relationship with other oxides and / or sulfide-forming elements is important as shown in the formula (1), and it is important for form control that the ratio of the addition amount of elements other than Rem and Y is large. I found out. In addition, in the formula (2), the relationship between oxygen and / or S and nitrogen is also indispensable for form control, and the ratio with these elements is also important for form control. That is, it is important for improving ductility that the above two formulas are satisfied and the oxides and sulfides of Rem and Y take the following form.
Average particle diameter d: 0.01-10.0 μm
Density [rho: 1 square mm per 107 to 109 on the average ratio d / dm between the particle diameter d and the main phase average particle diameter dm; 10 -4 to 10 0
In other words, by utilizing the oxides and sulfides of Rem and Y and reducing inclusions such as alumina, silica, and MnS that adversely affect other ductility, not only fracture ductility but also uniform elongation can be improved. I found out that I can do it.
[0016]
Here, identification / observation and area ratio measurement of the oxides and sulfides described above can be performed using an optical microscope, EPMA, FE-SEM, or the like. In the present invention, 50 fields or more were measured at 500 to 20000 times, and the area ratio was determined by image analysis. For identification of oxides, an extracted replica sample was prepared and TEM was used, or EBSP, EDX, and EPMA were used. In addition, the oxides and sulfides of Rem and Y mentioned here may be composites containing other atoms or contain many defects, but Rem and Y are mainly used from elemental analysis and structural identification. Compound, for example, Y 2 O 3 , La 2 O 3 , Ce 2 O 3 , CeO 2 , La 2 S 3 , LaS, Ce 2 S 3 , CeS, Ce 3 S 4 and the like or a single compound . The area ratio measurement can be obtained by performing surface analysis of each component using the above form observation, 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 surface area ratio can be obtained from image analysis of surface analysis.
[0017]
Next, the microstructure of the steel sheet will be described. Basically, by controlling the oxides and sulfides, the effect of improving ductility can be obtained in any steel sheet structure. However, it is desirable that the main phase is a ferrite phase in order to sufficiently ensure the ductility of the steel sheet. However, in order to further increase the strength, a bainite phase may be included. However, from the viewpoint of ensuring ductility, the main phase may be a single phase of ferrite or a composite phase of ferrite and bainite (in this specification, “ferrite Or “ferrite and bainite” unless otherwise specified) is preferably contained in an area fraction of 50% or more. Even when a composite phase of ferrite and bainite is used, it is preferable that the ferrite is contained in an area fraction of 50% or more in order to ensure ductility. On the other hand, in order to balance the increase in strength and the high ductility, it is preferable that ferrite or ferrite and bainite have an area fraction of 97% or less.
[0018]
Furthermore, in order to achieve both high strength and high ductility, it is also desirable to have a composite structure containing retained austenite and / or martensite. For high strength and high ductility, the retained austenite phase and / or martensite is preferably contained in an area fraction of 3% or more in total. However, if the area fraction becomes 50% or more in total, an embrittlement tendency is exhibited. It is preferable to make it less than%.
[0019]
In addition to the above, the steel sheet within the scope of the present invention also includes one or more of carbides, nitrides, sulfides, and oxides with an area fraction of 5% or less as the remaining structure of the microstructure.
[0020]
In addition, each phase of the above microstructure, ferrite, bainite, austenite, martensite, interfacial oxidation phase and the remaining structure are identified, the location is observed, and the average particle diameter (average equivalent circle diameter) and space factor are measured by Nital. The reagent and the reagent disclosed in Japanese Patent Application Laid-Open No. 59-219473 can be quantified 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 with an optical microscope and SEM observation at 500 times to 10,000 times.
[0021]
Next, the reason for limiting the preferable range of the steel plate component in the present invention will be described.
[0022]
C is an element added for the purpose of sufficiently securing the area fraction of the second phase for securing a good strength ductility balance. In particular, when the second phase is austenite, the ductility is greatly improved by contributing not only to the area fraction but also to the stability thereof. In order to secure the strength and the area fraction of each second phase, the lower limit was set to 0.0001 mass% (hereinafter the same), and the upper limit capable of maintaining weldability was set to 0.3 mass%.
[0023]
Si is an element added for the purpose of accelerating the formation of ferrite as the main phase and suppressing the formation of carbides that deteriorate the strength-ductility balance, and the lower limit was set to 0.001% by mass. Further, excessive addition has an adverse effect on weldability and plating wettability. For this reason, the upper limit was made 2.5 mass%.
[0024]
Mn is added for the purpose of increasing the strength in addition to controlling the plating wettability and adhesion. When a second phase such as martensite or austenite is included, it is added for the purpose of suppressing carbide precipitation and pearlite formation, which are one cause of strength reduction and ductility deterioration. From these things, it was set as 0.01 mass% or more. On the other hand, when the second phase is austenite, the upper limit is 3% by mass because the bainite transformation that contributes to the improvement of ductility is delayed and the weldability is deteriorated.
[0025]
The amount of P was set in the range of 0.0001 to 0.05 mass% because the strengthening effect appears at 0.0001 mass% or more and the extremely low is economically disadvantageous. . The reason why the upper limit is 0.3% by mass is that the addition exceeding this amount adversely affects weldability and manufacturability during casting and hot rolling.
[0026]
Al is a deoxidizing element important for controlling oxides and sulfides of Rem and Y. In order to control the amount of oxygen before the addition of Rem and Y to control the oxide and sulfide forms of these elements, the addition was made 0.0001% by mass or more. On the other hand, excessive addition impairs weldability and plating wettability, so 4% was made the upper limit.
[0027]
S was added in an amount of 0.0001 to 0.1% by mass from the viewpoint of controlling the sulfides of Rem and Y. Further, in order to obtain the effect of improving the ductility of the addition of Rem and Y, the addition was made within the range satisfying the above-mentioned formula (2). On the other hand, extremely low is also economically disadvantageous. In addition, the addition exceeding 0.1% by mass not only adversely affects weldability and manufacturability during casting or hot rolling, but also prevents the Rem and Y addition effects of the present invention from being recognized. It was.
[0028]
N, like C, has sufficient area fraction of the second phase to ensure a good balance of strength and ductility, and Ti, Zr, Hf and nitride that affect the formation of oxides and sulfides of Rem and Y. The lower limit was made 0.0001% because it is an element that has the role of indirectly promoting the formation of oxides and sulfides of Rem and Y, and further, the range satisfying the formula (2) for the above reason. On the other hand, the upper limit for maintaining weldability was set to 0.3% by mass.
[0029]
O was added in the range of 0.0001 to 0.1% by mass from the viewpoint of controlling the oxides of Rem and Y as in S. Further, in order to obtain the effect of improving the ductility of the addition of Rem and Y, the addition was made within the range satisfying the above-mentioned formula (2). On the other hand, extremely low is also economically disadvantageous. In addition, addition of more than 0.1% by mass not only adversely affects ductility, weldability, manufacturability during casting or hot rolling, but also the Rem and Y addition effects of the present invention are not recognized. Was the upper limit.
[0030]
Rem and Y are elements important for improving ductility by controlling the form of oxides and sulfides in the present invention. The fracture ductility and uniform elongation can be improved by forming oxides and sulfides containing these elements as main components. For this reason, 0.0005% was made into the minimum, respectively. On the other hand, excessive addition lowers the manufacturability such as castability and hot workability, and the ductility of the steel sheet product, so the upper limit was 0.3% by mass.
[0031]
Ti, Zr, Hf, and Ca, like Al, are important deoxidizing elements for controlling the oxides and sulfides of Rem and Y, but depending on the amount and timing of addition, the oxides of Rem and Y and Inhibits good morphogenesis of sulfides. The range of not inhibiting is 0.0001% by mass or more and 1% or less, respectively, and the addition satisfies the above formula (1).
[0032]
Furthermore, the steel targeted by the present invention can contain one or more of Cr, Mo, Ni, Cu, Co, and W for the purpose of further improving the strength.
[0033]
Cr is an element added for the purpose of strengthening and suppressing the formation of carbides, and is 0.001% by mass or more, and if added in an amount exceeding 5% by mass, the workability is adversely affected, so this was made the upper limit.
[0034]
Mo is an element that can be added for the purpose of suppressing the formation of carbide and pearlite that deteriorates the strength and ductility balance, and is an important additive element for obtaining a good strength and ductility balance. The lower limit was 0.001% by mass. Moreover, excessive addition causes ductility deterioration, so the upper limit was made 5%.
[0035]
Ni is made 0.001% by mass or more for the purpose of strengthening the structure, and if added in an amount exceeding 5% by mass, the workability is adversely affected, so this was made the upper limit.
[0036]
Cu is added in an amount of 0.001% by mass or more for the purpose of strengthening, and if added in an amount exceeding 5% by mass, the workability is adversely affected.
[0037]
Co was added in an amount of 0.001% by mass or more in order to improve the strength ductility balance. On the other hand, since it is an expensive element, the addition of a large amount impairs the economy, so it is desirable to make it 5% by mass or less.
[0038]
The amount of W in the range of 0.001 to 5% by mass is that the strengthening effect appears at 0.001% by mass or more, and the upper limit of 5% by mass is the workability when the amount exceeds this. This is to adversely affect
[0039]
Furthermore, the steel targeted by the present invention can contain one or more of Nb, V and Ta, which are strong carbide forming elements, for the purpose of further improving the strength.
[0040]
These elements form fine carbides, nitrides or carbonitrides, and are extremely effective for strengthening steel sheets. Therefore, one or more elements are added in amounts of 0.001% by mass or more as required. It was. On the other hand, since it inhibits ductile deterioration and concentration of C in retained austenite, the upper limit of each addition amount is set to 1% by mass.
[0041]
B can also be added as needed. B is effective for strengthening grain boundaries and increasing the strength of steel by adding 0.0001% by mass or more. However, when the amount of addition 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.
[0042]
Inevitable impurities include, for example, Sn, but even if these elements are contained in the range of Sn ≦ 0.01 mass% or less, the effect of the present invention is not impaired.
[0043]
The steel sheet of the present invention has been found to exhibit its effect with respect to hot-rolled steel sheets, cold-rolled steel sheets, galvanized steel sheets, and galvannealed steel sheets.
[0044]
When these steel plates are manufactured, in the final adjustment of the molten steel adjusted to a predetermined component, strong deoxidation such as Al, Ti, Si, Mn, etc. is performed before adding Rem, La, Y. It is necessary to sufficiently reduce oxygen in the molten steel with elements. Thereafter, one or more of Rem, La, and Y are added and cast, and the casting speed is preferably 0.1 to 5 m / min. In this way, by controlling the refining and casting method, the form of oxides and sulfides containing Rem, La, and Y as main components is controlled, and the effect of improving ductility appears. Is important in the present invention.
[0045]
If the casting speed is slower than 0.01 m / min or faster than 5 m / min, the form of oxide and / or sulfide of Rem or Y does not contribute to the improvement of ductility and ductile improvement hardening cannot be obtained.
[0046]
Thereafter, as cast or once cooled to 700 ° C. or lower, the steel slab is reheated and hot rolled. It is preferable to heat and heat-roll the as-cast steel slab as it is to reduce the heating unit, and to cool the steel slab to 700 ° C. or less is preferable when the slab surface needs to be maintained.
[0047]
At this time, it is desirable to set the heating temperature to 1150 ° C. or higher or 1280 ° C. or lower in order to suppress a large amount of grain boundary oxidized phases. When the heating temperature is higher than 1150 ° C., an oxide scale is relatively uniformly formed on the entire surface, and grain boundary oxidation tends to be suppressed. Further, when the heating is performed at a temperature lower than 1150 ° C., the deformation resistance in hot rolling becomes high, which may cause scratches and cracks. On the other hand, when the heating temperature exceeds 1280 ° C., a large amount of oxide scale is generated or the particle size becomes coarse, so the above range is preferable. Moreover, by making the rolling reduction per pass at the time of rolling at 1000 ° C. or more 30% or less, forming an oxide and / or sulfide form contributing to preventing hot cracking and improving ductility. Can do.
[0048]
At this time, the hot rolling ending temperature is carried out in more than Ar3 transformation temperature determined by the chemical composition of steel is generally not degrade the properties of the final steel sheet so long from Ar 3 to 10 ° C. about cold. In addition, the coiling temperature after cooling is higher than the bainite transformation start temperature determined by the chemical composition of the steel, so that the load during cold rolling can be increased more than necessary, but when the total rolling reduction of cold rolling is small Is not limited to this, and even if the steel sheet is wound at a temperature lower than the bainite transformation temperature of the steel, the properties of the final steel sheet are not deteriorated.
[0049]
After that, if necessary, it is annealed after cold rolling or further through a plating process to obtain various final products. The total rolling reduction of cold rolling is set from the relationship between the final plate thickness and the cold rolling load, but if it is 50% or more, it is easy to obtain a good balance of strength ductility in the product.
[0050]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
[0051]
In the steelmaking stage, Rem and Y are added after deoxidizing with Al, Ti, Si, Mn first, and finally adjusted to the molten steel having the composition shown in Table 1 and Table 2 (continued in Table 1), Casting was performed at 0.05 to 3 m / min. After the cast steel slab is cast or cooled to 700 ° C. or lower, it is heated to 1020 to 1250 ° C., and the rolling at 1000 ° C. or higher is set to 10 to 30%, and the hot rolling is completed at the Ar 3 transformation temperature or higher. The steel strip wound up at 900 ° C. was pickled and then subjected to each test. Each product was 1.4 mm thick. The cold-rolled and hot-rolled sheet for the plated steel sheet was 3 mm, and after cold-rolling to 1.4 mm, the product for cold-rolling was made by continuous annealing, and the product for plating was made by a hot dip galvanizing process.
[0052]
As shown in Tables 3 and 4 (continued in Table 3), the inventive steel has a uniform elongation and a value of about 2 to 5% higher than the comparative steel having the same composition, structure, and strength in the values of uniform elongation and total elongation Show.
[0053]
Tables 5 and 6 (continued in Table 5) affect the mechanical properties and the oxide and sulfide forms of Rem and Y when the casting speed and the heating temperature of hot rolling are changed for some steel materials. Show the impact. Inclusion density increases as the casting speed increases, and inclusion density decreases as the casting speed increases. As a result, it can be seen that the effect of improving ductility is not sufficient. Further, when the heating temperature is low, sufficient strength cannot be obtained.
[0054]
[Table 1]
[Table 2]
[Table 3]
[Table 4]
[Table 5]
[Table 6]
【The invention's effect】
According to the present invention, it is possible to obtain a high-strength and high-ductility steel sheet having excellent ductility by adjusting the steel components within a specific range and adjusting their quantitative relationship to satisfy a specific relational expression.
Claims (8)
Ｃ ：０．０００１〜０．３％、
Ｓｉ：０．００１〜２．５％、
Ｍｎ：０．０１〜３％、
Ｐ ：０．０００１〜０．３％、
Ａｌ：０．０００１〜４％、
Ｓ ：０．０００１〜０．１％、
Ｎ ：０．０００１〜０．３％、
Ｏ ：０．０００１〜０．１％、
を含有し、
Ｒｅｍ：０．０００５〜０．３％、
Ｙ ：０．０００５〜０．３％、
Ｔｉ：０．０００１〜１％、
Ｚｒ：０．０００１〜１％、
Ｈｆ：０．０００１〜１％、
Ｃａ：０．０００１〜１％、
の１種または２種以上を式（１）および（２）を満たす範囲で含有し、残部Ｆｅ及び不可避不純物からなることを特徴とする高強度高延性鋼板。
（Ｔｉ／４８＋Ｚｒ／９１＋Ｈｆ／１７８＋Ｃａ／４０）／（Ｒｅｍ／１４０＋Ｙ／８９）＝０〜２０ …（１）
（Ｏ／１６＋Ｓ／３２＋Ｎ／１４） ／（Ｒｅｍ／１４０＋Ｙ／８９）＝０〜１０ …（２）% By mass
C: 0.0001 to 0.3%,
Si: 0.001 to 2.5%,
Mn: 0.01 to 3%
P: 0.0001 to 0.3%,
Al: 0.0001 to 4%
S: 0.0001 to 0.1%,
N: 0.0001 to 0.3%
O: 0.0001 to 0.1%
Containing
Rem: 0.0005 to 0.3%,
Y: 0.0005 to 0.3%
Ti: 0.0001 to 1%
Zr: 0.0001 to 1%,
Hf: 0.0001 to 1%
Ca: 0.0001 to 1%,
A high-strength, high-ductility steel sheet containing one or more of the above in a range satisfying the formulas (1) and (2) and comprising the balance Fe and inevitable impurities.
(Ti / 48 + Zr / 91 + Hf / 178 + Ca / 40) / (Rem / 140 + Y / 89) = 0-20 (1)
(O / 16 + S / 32 + N / 14) / (Rem / 140 + Y / 89) = 0-10 (2)
平均粒子径ｄ：０．０１〜１０．０μｍ、
密度ρ：１平方ｍあたり１０７〜１０９個、
平均粒子径ｄと主相平均粒径ｄｍとの比ｄ／ｄｍ； １０−４〜１００、
を満たす分布形態を有することを特徴とする請求項１又は２記載の高強度高延性鋼板。The oxide and / or sulfide of Rem or Y
Average particle diameter d: 0.01-10.0 μm,
Density ρ: 10 7 to 10 9 per square meter,
Ratio d / dm of average particle diameter d and main phase average particle diameter dm; 10 −4 to 10 0 ,
The high-strength and highly ductile steel sheet according to claim 1, wherein the steel sheet has a distributed form satisfying
Ｃｒ：０．００１〜５％、
Ｍｏ：０．００１〜５％、
Ｎｉ：０．００１〜５％、
Ｃｕ：０．００１〜５％、
Ｃｏ：０．００１〜５％、
Ｗ ：０．００１〜５％、
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１〜３のいずれか１項に記載記載の高強度高延性鋼板。Furthermore, in mass%,
Cr: 0.001 to 5%,
Mo: 0.001 to 5%,
Ni: 0.001 to 5%,
Cu: 0.001 to 5%,
Co: 0.001-5%
W: 0.001 to 5%,
The high-strength, high-ductility steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains one or more of the following.
Ｎｂ：０．００１〜１％、
Ｖ ：０．００１〜１％、
Ｔａ：０．００１〜１％、
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１〜４のいずれか１項に記載の高強度高延性鋼板。In addition,
Nb: 0.001 to 1%,
V: 0.001 to 1%,
Ta: 0.001 to 1%,
The high-strength and highly ductile steel sheet according to any one of claims 1 to 4, characterized by containing one or more of the following.
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