JP3745496B2 - Manufacturing method of cold-rolled steel sheet and alloyed hot-dip galvanized steel sheet with excellent paint bake hardening performance - Google Patents
Manufacturing method of cold-rolled steel sheet and alloyed hot-dip galvanized steel sheet with excellent paint bake hardening performance Download PDFInfo
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Description
【０００１】
【発明の属する技術分野】
本発明は、塗装焼付硬化性（ＢＨ性）、常温遅時効性、成形性を兼ね備えた冷延鋼板および合金化溶融亜鉛めっき鋼板の製造方法に関するものである。
本発明が係わる冷延鋼板および合金化溶融亜鉛めっき鋼板は、自動車、家庭電気製品、建物などに使用されるものである。また、本発明が係わる冷延鋼板は、表面処理をしない狭義の冷延鋼板の他、防錆のために合金化溶融Ｚｎめっき、電気めっきなどの表面処理を施すためのめっき原板となる広義の冷延鋼板を含むものである。
【０００２】
本発明による鋼板は、強度と加工性を兼ね備えた鋼板であるので、使用に当たっては今までの鋼板より板厚を減少できること、すなわち軽量化が可能となる。したがって、地球環境保全に寄与できるものと考えられる。
【０００３】
【従来の技術】
溶鋼の真空脱ガス処理の最近の進歩により、極低炭素鋼の溶製が容易になった現在、良好な加工性を有する極低炭素鋼板の需要は益々増加しつつある。この中でも、例えば特開昭５９−３１８２７号公報などに開示されているＴｉとＮｂを複合添加した極低炭素鋼板は、極めて良好な加工性を有し、塗装焼付硬化（ＢＨ）性を兼備し、溶融亜鉛めっき特性にも優れているので、重要な位置をしめつつある。しかしながら、そのＢＨ量は通常のＢＨ鋼板のレベルを超えるものではなく、さらなるＢＨ量を付与しようとすると常温非時効性が確保できなくなるという欠点を有する。
【０００４】
一方、特開平６−０９３３７６号公報には、ＴｉやＮｂを添加せず、Ｃの添加を極めて少量にとどめることで常温遅時効性を確保し、さらにＰを活用することによって深絞り成形性を確保する技術が開示されている。しかしながら、Ｃを０．０００１〜０．００１５％の範囲に制御することは製鋼技術上困難であり、歩留り低下の原因となる。また、焼鈍後の熱処理については何ら示されておらず、ＢＨ性と遅時効性とのバランスは従来の鋼板を逸脱するものとは考えられない。
【０００５】
高ＢＨ性と常温遅時効性とを兼ね備えた鋼板に関する技術については、例えば特公平３−２２２４号公報に記載のものがある。これは極低炭素鋼に多量のＮｂとＢ、さらにはＴｉを複合添加して焼鈍後の組織をフェライト相と低温変態生成相との複合組織とし、高ｒ値、高ＢＨ、高延性および常温非時効性を兼ね備えた冷延鋼板を得るものである。しかしながら、この技術には以下のような実操業上の問題点を有することが明らかとなった。１）このような多量のＮｂ、Ｂ、さらにはＴｉを含有する成分組成の鋼では、α→γ変態点が低下するわけではなく、複合組織を得るためには極めて高い温度の焼鈍が必須となり、連続焼鈍時に板破断等のトラブルの原因となること、２）α＋γの温度領域が極めて狭いため、板幅方向に組織が変化し、結果として材質が大きくばらついたり、数℃の焼鈍温度の変化によって複合組織になる場合とならない場合があり、製造がきわめて不安定となる。
【０００６】
さらに特開平７−３００６２３号公報には、Ｎｂを添加した極低炭素冷延鋼板において焼鈍後の冷却速度を制御することによって粒界中の炭素濃度を高めて、高ＢＨと常温遅時効性との両立が可能であることが示されている。しかしながら、これによっても高ＢＨと常温遅時効性とのバランスは十分とは言えない。
【０００７】
【発明が解決しようとする課題】
上述のとおり、従来のＢＨ鋼板は、安定的な製造が困難であったり、ＢＨ量を増加させると同時に常温遅時効性が失われ、結果として長期間の常温での保存や、赤道を越える輸出が困難であるといった欠点を有していた。
そこで、本発明は、高ＢＨ性と常温遅時効性とを兼ね備えた鋼板、さらには、赤道を越えるような輸出にも耐えることのできる、塗装焼付硬化性能に優れた冷延鋼板および合金化溶融亜鉛めっき鋼板の製造方法を提供することを目的とするものである。
【０００８】
【課題を解決するための手段】
本発明者らは、上記の目標を達成するために、鋭意、研究を遂行し、以下に述べるような、従来にはない知見を得た。
すなわち、Ｐを添加した極低炭素冷延鋼板を焼鈍の後にさらに熱処理することによって、従来以上にＢＨ性と常温遅時効性とのバランスを改善することが可能であることを見出したものである。
【０００９】
本発明は、このような思想と新知見に基づいて構築されたものであり、その要旨とするところは以下のとおりである。
（１） 質量％で、
Ｃ ：０．００１４〜０．００２５％、
Ｓｉ≦１．５％、
Ｍｎ：０．０３〜２．０％、
Ｐ ：０．０１〜０．１５％、
Ｓ ≦０．０１５％、
Ａｌ：０．００５〜０．１％、
Ｎ ≦０．００４０％
を含有し、残部Ｆｅおよび不可避的不純物からなる組成のスラブを、Ａｒ3 変態点以上の温度で熱間圧延を行い、６０〜９５％の冷間圧延を施し、連続焼鈍ラインにて６５０℃以上、Ａｃ3 変態点以下の温度範囲で焼鈍し、引き続いて平均冷却速度４０℃／ｓ以上で２８０〜４５０℃の温度域まで冷却し、該温度域で１２０秒以上の熱処理を行うことを特徴とする塗装焼付硬化性能に優れた冷延鋼板の製造方法。
【００１０】
（２） さらに、質量％で、Ｂ：０．０００１〜０．００４０％を含有することを特徴とする前記（１）に記載の塗装焼付硬化性能に優れた冷延鋼板の製造方法。
（３） 質量％で、
Ｃ ：０．００１４〜０．００３０％、
Ｓｉ≦１．５％、
Ｍｎ：０．０３〜２．０％、
Ｐ ：０．０１〜０．１５％、
Ｓ ≦０．０１５％、
Ａｌ：０．００５〜０．１％、
Ｎ ≦０．００４０％
を含有し、さらに
Ｔｉ：０．００２〜０．０２％
および
Ｎｂ：０．００２〜０．０１８％
の１種または２種を、
Ｔｉ＋Ｎｂ＝０．００２〜０．０２％
となるように含有し、残部Ｆｅおよび不可避的不純物からなる組成のスラブを、Ａｒ3 変態点以上の温度で熱間圧延を行い、６０〜９５％の冷間圧延を施し、連続焼鈍ラインにて６５０℃以上、Ａｃ3 変態点以下の温度範囲で焼鈍し、引き続いて平均冷却速度４０℃／ｓ以上で２８０〜４５０℃の温度域まで冷却し、該温度域で１２０秒以上の熱処理を行うことを特徴とする塗装焼付硬化性能に優れた冷延鋼板の製造方法。
【００１１】
（４） さらに、質量％で、Ｂ：０．０００１〜０．００４０％を含有することを特徴とする前記（３）に記載の塗装焼付硬化性能に優れた冷延鋼板の製造方法。
（５） 質量％で、
Ｃ ：０．００１４〜０．００２５％、
Ｓｉ≦０．３％、
Ｍｎ：０．０３〜２．０％、
Ｐ ：０．０１〜０．１５％、
Ｓ ≦０．０１５％、
Ａｌ：０．００５〜０．１％、
Ｎ ≦０．００４０％
を含有し、残部Ｆｅおよび不可避的不純物からなる組成のスラブを、Ａｒ3 変態点以上の温度で熱間圧延を行い、６０〜９５％の冷間圧延を施し、連続溶融亜鉛めっきラインにて６５０℃以上、Ａｃ3 変態点以下の温度範囲で焼鈍し、引き続いて平均冷却速度１０℃／ｓ以上で亜鉛めっき浴温度まで冷却して、めっきした後、４７０〜５５０℃までの温度範囲で１５秒以上の熱処理を行うことを特徴とする塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法。
【００１２】
（６） 質量％で、
Ｃ ：０．００１４〜０．００２５％、
Ｓｉ≦０．３％、
Ｍｎ：０．０３〜２．０％、
Ｐ ：０．０１〜０．１５％、
Ｓ ≦０．０１５％、
Ａｌ：０．００５〜０．０７％未満、
Ｎ ≦０．００４０％、
Ｂ：０．０００１〜０．００４０％
を含有し、残部Ｆｅおよび不可避的不純物からなる組成のスラブを、Ａｒ 3 変態点以上の温度で熱間圧延を行い、６０〜９５％の冷間圧延を施し、連続溶融亜鉛めっきラインにて６５０℃以上、Ａｃ 3 変態点以下の温度範囲で焼鈍し、引き続いて平均冷却速度１０℃／ｓ以上で亜鉛めっき浴温度まで冷却して、めっきした後、４７０〜５５０℃までの温度範囲で１５秒以上の熱処理を行うことを特徴とする塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法。
（７） 質量％で、
Ｃ ：０．００１４〜０．００３０％、
Ｓｉ≦０．３％、
Ｍｎ：０．０３〜２．０％、
Ｐ ：０．０１〜０．１５％、
Ｓ ≦０．０１５％、
Ａｌ：０．００５〜０．１％、
Ｎ ≦０．００４０％
を含有し、さらに
Ｔｉ：０．００２〜０．０１５％
および
Ｎｂ：０．００２〜０．０１５％
のうち１種または２種を
Ｔｉ＋Ｎｂ＝０．００２〜０．０１５％
となるように含有し、残部Ｆｅおよび不可避的不純物からなる組成のスラブを、Ａｒ3 変態点以上の温度で熱間圧延を行い、６０〜９５％の冷間圧延を施し、連続溶融亜鉛めっきラインにて６５０℃以上、Ａｃ3 変態点以下の温度範囲で焼鈍し、引き続いて平均冷却速度１０℃／ｓ以上で亜鉛めっき浴温度まで冷却して、めっきした後、４７０〜５５０℃までの温度範囲で１５秒以上の熱処理を行うことを特徴とする塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法。
【００１３】
（８） さらに、質量％で、Ｂ：０．０００１〜０．００４０％を含有することを特徴とする前記（７）に記載の塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法。
【００１４】
【発明の実施の形態】
ここに、本発明において鋼組成および製造条件を上述のように限定する理由についてさらに説明する。
Ｃは製品のＢＨ特性および常温遅時効性さらには加工性を決定する極めて重要な元素である。Ｃが０．００１４％未満となると十分なＢＨ性が発現しないほか、製造コストが著しく増加するので、その下限を０．００１４％とする。一方、Ｃ量が０．００２５％を超えると成形性の劣化を招き、また常温非時効性が確保されなくなるので、上限を０．００２５％とする。高ＢＨ性と常温遅時効性とのバランスは、Ｃ量を０．００１６〜０．００２２％の範囲とすることがさらに好ましい。Ｔｉ、Ｎｂを含有する場合には、固溶Ｃを確保しにくくなるのでＣの上限を０．００３０％とする。Ｔｉ、Ｎｂを含有する場合には０．００１７〜０．００２４％がＣ量の好ましい範囲である。
【００１５】
Ｓｉは安価に強度を増加させる元素として知られており、その添加量は狙いとする強度レベルに応じて変化するが、添加量が１．５％超となると降伏強度が上昇しすぎてプレス成形時に面歪が生じる。また、化成処理性の低下を招くこともある。合金化溶融亜鉛めっきを施す場合には、めっき密着性の低下、合金化反応の遅延による生産性の低下などの問題が生ずるので、Ｓｉ量は０．３％以下とする。
【００１６】
ＭｎはＭｎＳを形成し熱延時のＳによる耳割れを抑制したり、熱延板組織を微細にするので、０．０３％以上添加する。さらに、Ｍｎは降伏強度をあまり増加させずに強度を増加させる有効な固溶体強化元素であり、かつ化成処理性を改善したり、溶融亜鉛めっき性を改善する効果も有する。一方、Ｍｎ量が２．０％を超えると強度が高くなりすぎたり、亜鉛めっきの密着性が阻害されたりするのでその上限を２．０％とする。
【００１７】
Ｐは本発明において最も重要な元素の一つである。すなわち、Ｐの添加は後述する焼鈍後の熱処理との組み合わせによって、高いＢＨ性と優れた常温遅時効性とを両立する効果を発現する。この観点から、Ｐは最低でも０．０１％添加しなければならない。より顕著な効果を発現させるためには、Ｐ量は０．０２５％以上とするのが好ましい。Ｐ添加の効果については必ずしも明らかではないが、次のような機構に基づくと考えられる。すなわち、ＰはＣと引力の相互作用を有しており、低温域での熱処理によりＣがＰの周辺にトラップされると思われる。ＢＨ処理（１７０℃×２０分）では、Ｐ周辺にトラップされたＣが転位を固着するためＢＨ性が発現するのに対して、常温時効性を評価するための試験であるＡＩ（Ａｇｉｎｇ Ｉｎｄｅｘ：１００℃×６０分）での熱処理ではＣがＰのトラップからはずれることができず、転位まで移動できないために常温遅時効性が発現されると思われる。また、ＰはＳｉと同様に安価に強度を上昇する元素として知られており強度を増加する必要がある場合にはさらに積極的に添加する。また、Ｐは熱延組織を微細にし、加工性を向上する効果も有する。ただし、添加量が０．１５％を超えると、降伏強度が増加し過ぎてプレス時に面形状不良を引き起こす。さらに、連続溶融亜鉛めっき時に合金化反応が極めて遅くなり、生産性が低下する。また、２次加工性も劣化する。したがって、Ｐの上限値を０．１５％とする。
【００１８】
Ｓは０．０１５％超では、熱間割れの原因となったり、加工性を劣化させるので０．１５％を上限とする。
Ａｌは脱酸調製およびＴｉを添加しない場合にはＮの固定に使用するが、０．００５％未満ではその効果が不十分である。一方、Ａｌ量が０．１％超になるとコストアップを招いたり、表面性状の劣化を招くのでその上限を０．１％とする。
【００１９】
Ｎはあまり多いと多量のＴｉ、Ｎｂ、Ａｌが必要になったり、加工性が劣化したりするので０．００４０％を上限値とする。
Ｂは２次加工脆化の防止に有効であるほか、ＡｌやＴｉでＮを固定するよりも再結晶温度が低くなるので、必要に応じて０．００４０％以下添加する。しかし、Ｂが０．０００１％未満ではその効果が発現しないので、０．０００１％を下限とする。
【００２０】
Ｔｉ、ＮｂはＮ、Ｃ、Ｓの一部を固定することにより、常温遅時効性を確保する役割を有する。さらには、熱延板の結晶粒を微細化し、製品板の加工性を良好にするので必要に応じて添加する。Ｔｉ、Ｎｂが０．００２％未満ではその添加効果が現れないのでこれを下限値とする。一方、Ｔｉ、Ｎｂの添加量が多すぎると十分なＢＨ性が発現しにくいばかりではなく、後述の熱処理によってＢＨと常温遅時効性とのバランスがむしろ劣化したりする。また再結晶温度が著しく上昇したり、亜鉛めっきの密着性も阻害される。特にＢＨ性と常温遅時効性とのバランスは、Ｔｉ、Ｎｂ量や焼鈍−冷却後の熱処理温度域の影響を受けやすいので、合金化溶融亜鉛めっきを施す場合とそうでない場合とでＴｉ、Ｎｂ量の上限を変化させる必要がある。合金化溶融亜鉛めっきを施さない場合、Ｔｉ、Ｎｂを単独で添加するとき、上限をそれぞれ０．０２％、０．０１８％とし、複合で添加する場合には、合計で０．０２％を超えないようにする。Ｔｉ、Ｎｂのより好ましい範囲は、Ｔｉ：０．００４〜０．０１５％、Ｎｂ：０．００３〜０．０１０％、Ｔｉ＋Ｎｂ＝０．００４〜０．０１５％である。また、合金化溶融亜鉛めっきを施す場合には、熱処理温度が４７０〜５５０℃の比較的高温となるので固溶ＣがＴｉやＮｂと結合してＢＨ性が低下する。従って、合金化溶融亜鉛めっきを施す場合には、Ｔｉ、Ｎｂの上限をいずれも０．０１５％、Ｔｉ＋Ｎｂの上限を０．０１５％とする。より好ましくはＴｉ：０．００４〜０．０１０％、Ｎｂ：０．００３〜０．００９％、Ｔｉ＋Ｎｂ＝０．００４〜０．０１０％である。
【００２１】
これらを主成分とする鋼にＣｕ、Ｓｎ、Ｚｎ、Ｍｏ、Ｗ、Ｃｒ、Ｎｉを合計で１％以下含有しても構わない。
次に、製造条件の限定理由について述べる。
熱間圧延に供するスラブは特に限定するものではない。すなわち、連続鋳造スラブや薄スラブキャスターなどで製造したものであればよい。また、鋳造後に直ちに熱間圧延を行う連続鋳造−直接圧延（ＣＣ−ＤＲ）のようなプロセスにも適合する。
【００２２】
熱延の仕上温度は製品板の加工性を確保するという観点からＡｒ3 変態点以上とする必要がある。
熱延後の冷却は、限定するものではないが、特に優れた加工性を必要とする場合には、圧延後１．５秒以内に冷却を開始し、巻取温度までの平均冷却速度を３０℃／ｓ以上とすることが望ましい。
【００２３】
巻取温度は特に限定しないが、ＴｉやＢを添加しないときには６５０〜８００℃とすることが望ましい。これによってＡｌＮの形成、成長が促され良好な成形性が確保される。ＴｉやＢを添加する際にはＮは巻取前に固定されるので巻取温度は室温から８００℃とすればよい。巻取温度の上限が８００℃であることは、コイル両端部での材質劣化に起因する歩留低下を防止すること、また、熱延組織の粗大化を防止する観点から決定される。
【００２４】
冷間圧延は、通常の条件でよく、焼鈍後の深絞り性を確保する目的からその圧延率は、６０％以上とする。圧下率を９５％超とすると加工性が劣化してしまうのでこれを上限とする。
連続焼鈍あるいはライン内焼鈍方式の連続溶融亜鉛めっき設備の焼鈍温度は、６５０℃以上Ａｃ3 変態点以下とする。焼鈍温度が６５０℃未満では、再結晶が完了せず、加工性が劣悪となる。一方、焼鈍温度がＡｃ3 変態点超では、変態によって加工性の低下を招く。
【００２５】
焼鈍後の冷却および熱処理条件は、本発明において極めて重要である。すなわち、これらの条件を適切にすることによって、高ＢＨ性と常温遅時効性とを兼備した鋼板を製造することが初めて可能となる。通常の連続焼鈍ラインでの製造を考慮すると、焼鈍後の熱処理温度は２８０〜４５０℃が適当な範囲でなる。これは、連続焼鈍ラインでの生産性を低下させない温度域であると共に、ＰとＣとの結合を促すのにも良好な温度域である。すなわち、２８０℃未満ではＣの拡散が不十分なためＰとＣとの結合が不十分となり常温遅時効性が発現されにくい。また、熱処理炉の温度を４５０℃超とするためには長時間を要したり、燃料コストが増加するため、著しい生産性の低下を招き現実的でない。熱処理時間は１２０秒以上行うことが必要である。２８０〜３８０℃の範囲で１５０秒以上熱処理を行うのがより好ましい。上記の温度域でＣをＰ周辺まで移動させるためには、焼鈍後少なくとも６５０℃以上の温度から急冷して、Ｃの拡散のための駆動力を大きくする必要がある。したがって、６５０℃以上の温度から熱処理温度までの範囲を４０℃／ｓ以上で冷却しなければならない。また、冷却終点温度は、室温〜熱処理温度の範囲まで一度低下させるとＣの拡散のための駆動力が大きくなり、常温遅時効性が確保されやすくなる。この温度域で徐冷してしまうとＣはＰの周りでなく結晶粒界に移動してしまい、所望のＢＨ性と常温遅時効性が得られなくなってしまう。
【００２６】
一方、合金化溶融亜鉛めっきを施す場合には、その合金化処理が４７０〜５５０℃となるため、これを活用して常温遅時効化、すなわちＰとＣとの結合を図ることができる。このような比較的高温ではＣの拡散速度は大きいので、焼鈍後の冷却は１０℃／ｓ以上とすれば十分である。
調質圧延は、常温遅時効性のさらなる向上、また、形状矯正のために圧下率２％以下の範囲で行うのがよい。圧下率が３％を超えると降伏強度が高くなったり、設備の負荷が大きくなるのでその上限は３％とする。
【００２７】
焼鈍−冷却−熱処理−（必要に応じて調質圧延）の後には、種々の表面処理を施しても構わない。
本発明によって得られる冷延鋼板はＢＨ性と常温遅時効性とのバランスに優れ、しかも加工性にも優れている。
【００２８】
【実施例】
次に本発明を実施例にて説明する。
＜実施例１＞
表１に示す組成を有する鋼を溶製し、スラブ加熱温度１２００℃、仕上温度９２０℃、巻取温度７２０℃で熱間圧延し、４．０ｍｍ厚の鋼帯とした。酸洗後、８０％の圧下率の冷間圧延を施し０．８ｍｍ厚の冷延板とし、次いで連続焼鈍設備にて加熱速度１０℃／ｓ、加熱温度７５０℃、６８０℃より３００℃までの平均冷却速度を１００℃／ｓとし、次いで３００℃にて１８０秒熱処理を行った。さらに１．０％の圧下率の調質圧延をし、ＪＩＳ Ｚ ２２０１記載の５号試験片を採取しｒ値（１５％引張）およびＡＩ、ＢＨの測定を行った。ＡＩは常温遅時効性の指標であり、値が小さいほど良好である。ＡＩが３０ＭＰａを超えると加工時にストレッチャーストレインが発生しやすい。ちなみに、ＡＩは１０％の引張予変形時の引張応力σ１を１００℃×３６００秒の熱処理を施した後、再引張を行ったときの降伏応力σ２から差し引いた値（ＡＩ（ＭＰａ）＝σ２−σ１）で評価した。ＢＨは、２％の引張予変形時の応力σ３を１７０℃×１２００秒熱処理後、再引張したときの降伏応力σ４から差し引いた値（ＢＨ（ＭＰａ）＝σ４−σ３）で評価した。
【００２９】
結果を図１、２に示す。これから明らかなようにＰの添加量を０．０１％以上とすることによって高ＢＨ性と常温遅時効性とを両立することができる。一方、Ｐ量が少ない場合には、高ＢＨは得られるが、ＡＩが３０ＭＰａを大きく超えてしまい、常温遅時効性は確保されなかった。
【００３０】
【表１】
＜実施例２＞
表２に示す組成を有する鋼を溶製し、スラブ加熱温度１１５０℃、仕上温度９３０℃、巻取温度６８０℃で熱間圧延し、３．５ｍｍ厚の鋼帯とした。酸洗後、８０％の圧下率の冷間圧延を施し０．７ｍｍ厚の冷延板とし、次いで連続焼鈍設備にて加熱速度１０℃／ｓ、加熱温度７７０℃、７００℃より各熱処理温度まで平均冷却速度を８０℃／ｓとし、次いで各熱処理温度にて１５０秒熱処理を行った。さらに１．０％の圧下率の調質圧延をし、ＪＩＳ Ｚ ２２０１記載の５号引張試験片を採取しＡＩ、ＢＨの測定を行った。
【００３２】
結果を図３に示す。これより明らかなように、焼鈍−冷却後に熱処理を行わなかったもの（●印）や２００℃または２４０℃で熱処理したものは、２８０℃以上で熱処理されたものに比べてＢＨ性と常温遅時効性が劣った。また、この温度が５００℃の場合も若干ではあるが、ＢＨとＡＩのバランスが劣化する。
【００３３】
【表２】
＜実施例３＞
表１の試料Ａ−４を実施例１と同じ条件で熱間圧延、冷間圧延を行った。次いで、連続焼鈍設備にて加熱速度１０℃／ｓ、加熱温度７５０℃とする焼鈍を行い、６８０℃より３００℃までの平均冷却速度を種々変化させた。また、連続溶融亜鉛めっきラインにて加熱速度１０℃／ｓ、加熱温度７７０℃、７００℃からめっき浴の温度４６０℃までの平均冷却速度を種々変化させたのち、めっき浴に浸漬し、再加熱して５２０℃で２０秒の合金化熱処理を行った。これらの結果を図４、５に示す。これらより、連続焼鈍ラインの場合には、冷却速度を４０℃／ｓ以上とすることで、また連続溶融亜鉛めっきラインでは、冷却速度を１０℃／ｓ以上とすることで良好なＢＨおよびＡＩ特性を得ることができる。
＜実施例４＞
表３の種々の鋼をスラブ加熱温度１２２０℃、仕上温度９２０℃、巻取温度６００℃の条件で熱間圧延し、３．８ｍｍ厚の鋼板とした。酸洗後、冷間圧延して０．７５ｍｍ厚の冷延板とし、次いで、図６に示すような熱処理パターンＡ、Ｂ、Ｃのいずれかによって熱処理を施した。熱処理の後、圧下率０．８％の調質圧延を施し、引張試験に供した。結果を表４（表３のつづき）に示す。これより、本発明の範囲で製造した鋼板は、ＢＨ、ＡＩ、ｒ値、伸び（Ｅｌ）とも良好な値を示すのに対して、本発明外のものは、ＢＨとＡＩとのバランスが著しく劣化した。
【００３５】
【表３】
【表４】
【発明の効果】
以上詳述したように、本発明により、高ＢＨ性と常温遅時効性とを兼ね備え、赤道を越えるような輸出にも耐えることのできる鋼板の製造方法を、また、強度と加工性を兼ね備え、使用に当たっては今までの鋼板より板厚を減少でき、地球環境保全に寄与できる軽量化を可能にする鋼板の製造方法を提供できるため、本発明は工業的に価値の高い発明であると言える。
【図面の簡単な説明】
【図１】Ｐ添加量とＢＨ、ＡＩとの関係を表す図である。
【図２】Ｐ添加量とｒ値との関係を表す図である。
【図３】熱処理温度を種々変化させたときのＡＩとＢＨとの関係の変化を表す図である。
【図４】連続焼鈍によって熱処理を行ったときの焼鈍後の冷却速度とＢＨ、ＡＩとの関係を表す図である。
【図５】連続溶融亜鉛めっきラインで熱処理を行ったときの冷却速度とＢＨ、ＡＩとの関係を表す図である。
【図６】実施例で用いた熱処理パターンを説明する図である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a cold-rolled steel sheet and an alloyed hot-dip galvanized steel sheet that have paint bake hardenability (BH property), room temperature slow aging property, and formability.
The cold-rolled steel sheet and the galvannealed steel sheet according to the present invention are used for automobiles, household electrical appliances, buildings and the like. Further, the cold-rolled steel sheet according to the present invention has a broad meaning to be a plating base plate for performing surface treatment such as alloyed hot-dip Zn plating and electroplating for rust prevention, in addition to a narrowly-defined cold-rolled steel sheet not subjected to surface treatment Includes cold-rolled steel sheets.
[0002]
Since the steel plate according to the present invention is a steel plate having both strength and workability, the thickness can be reduced, that is, the weight can be reduced as compared with conventional steel plates. Therefore, it is thought that it can contribute to global environmental conservation.
[0003]
[Prior art]
With the recent progress in vacuum degassing of molten steel, it has become easier to produce ultra-low carbon steel, and now the demand for ultra-low carbon steel sheets with good workability is increasing. Among these, for example, an ultra-low carbon steel sheet combined with Ti and Nb disclosed in Japanese Patent Application Laid-Open No. 59-31827 has extremely good workability and has paint bake hardening (BH) properties. Since it is also excellent in hot dip galvanizing properties, it is becoming an important position. However, the amount of BH does not exceed the level of a normal BH steel sheet, and there is a drawback that normal temperature non-aging cannot be ensured when a further amount of BH is applied.
[0004]
On the other hand, in JP-A-6-093376, Ti or Nb is not added, and the addition of C is kept to a very small amount to ensure a slow aging property at room temperature. Techniques to ensure are disclosed. However, it is difficult to control C in the range of 0.0001 to 0.0015% in terms of steelmaking technology, which causes a decrease in yield. Moreover, nothing is shown about the heat processing after annealing, and it cannot be considered that the balance between BH property and delayed aging deviates from the conventional steel plate.
[0005]
For example, Japanese Patent Publication No. 3-2224 discloses a technique related to a steel sheet having both high BH properties and room temperature slow aging. This is because ultra-low carbon steel is added with a large amount of Nb and B, and further Ti is combined to make the structure after annealing into a composite structure of ferrite phase and low-temperature transformation formation phase, high r value, high BH, high ductility and room temperature. A cold-rolled steel sheet having non-aging properties is obtained. However, it has become clear that this technology has the following operational problems. 1) In steels with component compositions containing such a large amount of Nb, B, and even Ti, the α → γ transformation point does not decrease, and in order to obtain a composite structure, extremely high temperature annealing is essential. 2) Since the temperature range of α + γ is extremely narrow, the structure changes in the width direction of the plate, resulting in large variations in the material and a change in the annealing temperature of several degrees Celsius. Depending on the case, it may or may not become a composite structure, and the production becomes extremely unstable.
[0006]
Furthermore, in JP-A-7-300623, the carbon concentration in the grain boundary is increased by controlling the cooling rate after annealing in the ultra-low carbon cold-rolled steel sheet to which Nb is added, and high BH, room temperature slow aging, It is shown that both can be achieved. However, the balance between high BH and room temperature slow aging is not sufficient.
[0007]
[Problems to be solved by the invention]
As mentioned above, the conventional BH steel sheet is difficult to manufacture stably or increases the amount of BH and at the same time loses the room temperature slow aging, resulting in long-term storage at room temperature and export exceeding the equator. Has the disadvantage of being difficult.
Therefore, the present invention is a steel sheet having both high BH properties and room temperature slow aging, and further, a cold-rolled steel sheet and an alloyed melt that can withstand exports that exceed the equator and have excellent paint bake hardening performance. The object is to provide a method for producing a galvanized steel sheet.
[0008]
[Means for Solving the Problems]
The inventors of the present invention diligently conducted research to achieve the above-described goal, and obtained the following unprecedented knowledge as described below.
That is, the present inventors have found that the balance between BH property and room temperature slow aging can be improved more than conventional by further heat-treating the ultra-low carbon cold-rolled steel sheet to which P is added after annealing. .
[0009]
The present invention has been constructed on the basis of such ideas and new findings, and the gist thereof is as follows.
(1) in mass%,
C: 0.0014 to 0.0025%,
Si ≦ 1.5%,
Mn: 0.03 to 2.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to 0.1%,
N ≦ 0.0040%
The slab containing the balance Fe and inevitable impurities is hot-rolled at a temperature not lower than the Ar 3 transformation point, subjected to 60-95% cold rolling, and 650 ° C. or higher in a continuous annealing line. , Annealing in a temperature range below the Ac 3 transformation point, subsequently cooling to a temperature range of 280 to 450 ° C. at an average cooling rate of 40 ° C./s or more, and performing a heat treatment for 120 seconds or more in the temperature range. A method for producing cold-rolled steel sheets with excellent paint bake hardening performance.
[0010]
(2) Moreover, in mass%, B: production method excellent cold-rolled steel sheet in bake hardenability properties according to (1), characterized in that it contains from 0.0001 to 0.0040%.
(3) mass%,
C: 0.0014 to 0.0030%,
Si ≦ 1.5%,
Mn: 0.03 to 2.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to 0.1%,
N ≦ 0.0040%
Further Ti: 0.002-0.02%
And Nb: 0.002 to 0.018%
1 type or 2 types of
Ti + Nb = 0.002 to 0.02%
In a continuous annealing line, a slab having a composition comprising the balance Fe and inevitable impurities is hot-rolled at a temperature equal to or higher than the Ar 3 transformation point, subjected to 60-95% cold rolling, and a continuous annealing line. Annealing in a temperature range of 650 ° C. or more and below the Ac 3 transformation point, followed by cooling to a temperature range of 280 to 450 ° C. at an average cooling rate of 40 ° C./s or more, and performing heat treatment for 120 seconds or more in the temperature range A method for producing a cold-rolled steel sheet excellent in paint bake hardening performance.
[0011]
(4) Furthermore, in mass%, B: characterized in that it contains 0.0001 to 0.0040% of (3) The method of producing excellent cold-rolled steel sheet in bake hardenability properties described.
(5) in mass%,
C: 0.0014 to 0.0025%,
Si ≦ 0.3%,
Mn: 0.03 to 2.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to 0.1%,
N ≦ 0.0040%
The slab containing the balance Fe and inevitable impurities is hot-rolled at a temperature equal to or higher than the Ar 3 transformation point, subjected to 60-95% cold rolling, and 650 in a continuous hot-dip galvanizing line. ° C. or higher, and cooled Ac 3 transformation point at a temperature range of annealing, to a zinc plating bath temperature at an average cooling rate of 10 ° C. / s or higher subsequently, after plating, 15 seconds at a temperature range of up to four hundred seventy to five hundred and fifty ° C. The manufacturing method of the galvannealed steel plate excellent in the paint bake hardening performance characterized by performing the above heat processing.
[0012]
(6) In mass%,
C: 0.0014 to 0.0025%,
Si ≦ 0.3%,
Mn: 0.03 to 2.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to less than 0.07%,
N ≦ 0.0040%,
B: 0.0001 to 0.0040%
The slab containing the balance Fe and inevitable impurities is hot-rolled at a temperature equal to or higher than the Ar 3 transformation point, subjected to 60-95% cold rolling, and 650 in a continuous hot-dip galvanizing line. ° C. or higher, and cooled Ac 3 transformation point at a temperature range of annealing, to a zinc plating bath temperature at an average cooling rate of 10 ° C. / s or higher subsequently, after plating, 15 seconds at a temperature range of up to four hundred seventy to five hundred and fifty ° C. excellent production method of galvannealed steel sheet in painting bake hardenability performance you characterized by performing the above heat treatment.
(7) in mass%,
C: 0.0014 to 0.0030%,
Si ≦ 0.3%,
Mn: 0.03 to 2.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to 0.1%,
N ≦ 0.0040%
In addition, Ti: 0.002 to 0.015%
And Nb: 0.002 to 0.015%
1 type or 2 types of Ti + Nb = 0.002 to 0.015%
The slab having the composition comprising the balance Fe and inevitable impurities is hot-rolled at a temperature equal to or higher than the Ar 3 transformation point, subjected to 60-95% cold rolling, and a continuous hot-dip galvanizing line Annealing at a temperature range of 650 ° C. or more and below the Ac 3 transformation point, followed by cooling to a galvanizing bath temperature at an average cooling rate of 10 ° C./s or more, plating, and a temperature range of 470 to 550 ° C. A method for producing an alloyed hot-dip galvanized steel sheet excellent in paint bake hardening performance, characterized by performing a heat treatment for 15 seconds or more.
[0013]
(8) Moreover, in mass%, B: Production of excellent galvannealed steel sheet bake hardenability properties according to (7), characterized in that it contains 0.0001 to 0.0040% Method.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Here, the reason why the steel composition and production conditions are limited as described above in the present invention will be further described.
C is an extremely important element that determines the BH characteristics, normal temperature slow aging property and workability of the product. When C is less than 0.0014%, sufficient BH properties are not exhibited, and the manufacturing cost is remarkably increased, so the lower limit is made 0.0014%. On the other hand, if the amount of C exceeds 0.0025%, the moldability is deteriorated and the non-aging property at room temperature is not ensured, so the upper limit is made 0.0025%. The balance between the high BH property and the room temperature slow aging is more preferably within the range of 0.0016 to 0.0022% of the C content. When Ti and Nb are contained, since it becomes difficult to ensure solid solution C, the upper limit of C is made 0.0030%. When Ti and Nb are contained, 0.0017 to 0.0024% is a preferable range of the C amount.
[0015]
Si is known as an element that increases the strength at a low cost, and the amount added varies depending on the target strength level, but if the amount exceeds 1.5%, the yield strength increases too much and press forming is performed. Sometimes surface distortion occurs. Moreover, the chemical conversion processability may be reduced. When alloying hot dip galvanizing is performed, problems such as a decrease in plating adhesion and a decrease in productivity due to a delay in the alloying reaction occur, so the Si amount is set to 0.3% or less.
[0016]
Mn forms MnS, suppresses the ear cracking due to S during hot rolling, and makes the hot rolled sheet structure fine, so 0.03% or more is added. Furthermore, Mn is an effective solid solution strengthening element that increases the strength without significantly increasing the yield strength, and also has the effect of improving the chemical conversion treatment property and the hot dip galvanizing property. On the other hand, if the amount of Mn exceeds 2.0%, the strength becomes too high or the adhesion of galvanization is hindered, so the upper limit is made 2.0%.
[0017]
P is one of the most important elements in the present invention. That is, the addition of P exhibits an effect of achieving both high BH properties and excellent room temperature slow aging properties in combination with a heat treatment after annealing described later. From this viewpoint, P must be added at a minimum of 0.01%. In order to express a more remarkable effect, the P content is preferably 0.025% or more. The effect of P addition is not necessarily clear, but is thought to be based on the following mechanism. That is, P has an interaction between C and attractive force, and it seems that C is trapped around P by heat treatment in a low temperature region. In the BH treatment (170 ° C. × 20 minutes), C trapped around P fixes dislocations and thus develops BH properties, whereas AI (Aging Index :) is a test for evaluating normal temperature aging. In the heat treatment at 100 ° C. × 60 minutes, it is considered that C cannot deviate from the trap of P and cannot move to the dislocation, so that normal temperature slow aging is exhibited. Further, P is known as an element that increases the strength at a low cost like Si, and is added more actively when the strength needs to be increased. P also has the effect of making the hot-rolled structure fine and improving workability. However, if the addition amount exceeds 0.15%, the yield strength increases excessively, causing surface shape defects during pressing. Furthermore, the alloying reaction becomes extremely slow during continuous hot dip galvanizing, and productivity is lowered. Also, the secondary workability is deteriorated. Therefore, the upper limit value of P is set to 0.15%.
[0018]
If S exceeds 0.015%, it causes hot cracking and deteriorates workability, so 0.15% is made the upper limit.
Al is used for deoxidation preparation and fixation of N when Ti is not added, but if it is less than 0.005%, its effect is insufficient. On the other hand, if the Al content exceeds 0.1%, the cost is increased or the surface properties are deteriorated, so the upper limit is made 0.1%.
[0019]
If N is too large, a large amount of Ti, Nb, and Al becomes necessary, and workability deteriorates, so 0.0040% is made the upper limit.
B is effective in preventing secondary work embrittlement, and the recrystallization temperature is lower than fixing N with Al or Ti, so 0.0040% or less is added as necessary. However, if B is less than 0.0001%, the effect is not exhibited, so 0.0001% is made the lower limit.
[0020]
Ti and Nb have a role of securing a slow aging property at room temperature by fixing a part of N, C, and S. Furthermore, since the crystal grain of a hot-rolled sheet is refined | miniaturized and the workability of a product board is made favorable, it adds as needed. If Ti and Nb are less than 0.002%, the effect of addition does not appear, so this is the lower limit. On the other hand, when the addition amount of Ti and Nb is too large, not only is sufficient BH property difficult to develop, but the balance between BH and room temperature slow aging is rather deteriorated by the heat treatment described later. Further, the recrystallization temperature is remarkably increased and the adhesion of galvanizing is also inhibited. In particular, the balance between BH properties and room temperature slow aging is easily affected by the amount of Ti and Nb and the heat treatment temperature range after annealing-cooling. It is necessary to change the upper limit of the amount. When alloying hot dip galvanization is not applied, when adding Ti and Nb alone, the upper limits are 0.02% and 0.018%, respectively, and when adding in combination, it exceeds 0.02% in total. Do not. More preferable ranges of Ti and Nb are Ti: 0.004 to 0.015%, Nb: 0.003 to 0.010%, and Ti + Nb = 0.004 to 0.015%. Further, when alloying hot dip galvanizing is performed, the heat treatment temperature becomes relatively high at 470 to 550 ° C., so that the solid solution C is combined with Ti or Nb and the BH property is lowered. Therefore, when alloying hot dip galvanizing is performed, the upper limits of Ti and Nb are both 0.015%, and the upper limit of Ti + Nb is 0.015%. More preferably, Ti is 0.004 to 0.010%, Nb is 0.003 to 0.009%, and Ti + Nb = 0.004 to 0.010%.
[0021]
You may contain 1% or less of Cu, Sn, Zn, Mo, W, Cr, and Ni in the steel which has these as a main component in total.
Next, the reasons for limiting the manufacturing conditions will be described.
The slab used for hot rolling is not particularly limited. That is, what was manufactured with the continuous casting slab, the thin slab caster, etc. should just be used. It is also compatible with processes such as continuous casting-direct rolling (CC-DR) in which hot rolling is performed immediately after casting.
[0022]
The hot rolling finishing temperature needs to be not less than the Ar 3 transformation point from the viewpoint of ensuring the workability of the product plate.
Although cooling after hot rolling is not limited, when particularly excellent workability is required, cooling is started within 1.5 seconds after rolling, and the average cooling rate up to the coiling temperature is set to 30. It is desirable to set it to at least ° C / s.
[0023]
The coiling temperature is not particularly limited, but is preferably 650 to 800 ° C. when Ti or B is not added. This promotes the formation and growth of AlN and ensures good moldability. When adding Ti or B, N is fixed before winding, so the winding temperature may be from room temperature to 800 ° C. The upper limit of the coiling temperature of 800 ° C. is determined from the viewpoint of preventing a decrease in yield due to material deterioration at both ends of the coil and preventing the hot rolled structure from becoming coarse.
[0024]
Cold rolling may be performed under normal conditions, and the rolling rate is set to 60% or more for the purpose of ensuring deep drawability after annealing. If the rolling reduction exceeds 95%, workability deteriorates, so this is the upper limit.
The annealing temperature of the continuous hot dip galvanizing equipment of the continuous annealing or in-line annealing method is set to 650 ° C. or higher and Ac 3 transformation point or lower. When the annealing temperature is less than 650 ° C., recrystallization is not completed, and the workability is deteriorated. On the other hand, if the annealing temperature exceeds the Ac 3 transformation point, the workability is lowered by the transformation.
[0025]
Cooling and heat treatment conditions after annealing are extremely important in the present invention. That is, by making these conditions appropriate, it becomes possible for the first time to manufacture a steel sheet having both high BH properties and room temperature slow aging properties. Considering production in a normal continuous annealing line, the heat treatment temperature after annealing is in a suitable range of 280 to 450 ° C. This is a temperature range that does not decrease the productivity in the continuous annealing line, and is also a good temperature range for promoting the bonding of P and C. That is, when the temperature is lower than 280 ° C., the diffusion of C is insufficient, so that the bond between P and C is insufficient, and the room temperature slow aging property is hardly exhibited. In addition, it takes a long time to increase the temperature of the heat treatment furnace to over 450 ° C., and the fuel cost increases, which leads to a significant reduction in productivity and is not realistic. The heat treatment time must be 120 seconds or longer. It is more preferable to perform the heat treatment for 150 seconds or more in the range of 280 to 380 ° C. In order to move C to the vicinity of P in the above temperature range, it is necessary to rapidly cool from a temperature of at least 650 ° C. or higher after annealing to increase the driving force for C diffusion. Therefore, the range from the temperature of 650 ° C. or higher to the heat treatment temperature must be cooled at 40 ° C./s or higher. Further, once the cooling end point temperature is lowered from the range of room temperature to the heat treatment temperature, the driving force for C diffusion increases, and normal temperature slow aging is easily secured. If it is gradually cooled in this temperature range, C moves not to the periphery of P but to the crystal grain boundary, and the desired BH property and room temperature slow aging cannot be obtained.
[0026]
On the other hand, when alloying hot dip galvanization is performed, the alloying treatment is 470 to 550 ° C., so that this can be utilized to achieve room temperature slow aging, that is, bonding between P and C. Since the diffusion rate of C is large at such a relatively high temperature, it is sufficient that the cooling after annealing is 10 ° C./s or more.
The temper rolling is preferably performed in a range of a rolling reduction of 2% or less in order to further improve the room temperature slow aging property and correct the shape. If the rolling reduction exceeds 3%, the yield strength increases and the load on the equipment increases, so the upper limit is made 3%.
[0027]
After the annealing-cooling-heat treatment- (temper rolling if necessary), various surface treatments may be performed.
The cold-rolled steel sheet obtained by the present invention has an excellent balance between BH properties and room temperature slow aging properties, and also has excellent workability.
[0028]
【Example】
Next, the present invention will be described with reference to examples.
<Example 1>
Steel having the composition shown in Table 1 was melted and hot-rolled at a slab heating temperature of 1200 ° C., a finishing temperature of 920 ° C., and a winding temperature of 720 ° C. to obtain a steel strip having a thickness of 4.0 mm. After pickling, cold rolling with a reduction rate of 80% is performed to obtain a cold-rolled sheet having a thickness of 0.8 mm, and then at a continuous annealing facility, a heating rate of 10 ° C./s, a heating temperature of 750 ° C., from 680 ° C. to 300 ° C. The average cooling rate was 100 ° C./s, and then heat treatment was performed at 300 ° C. for 180 seconds. Furthermore, temper rolling was performed at a rolling reduction of 1.0%, a No. 5 test piece described in JIS Z 2201 was taken, and the r value (15% tensile), AI, and BH were measured. AI is an index of slow aging at room temperature, and the smaller the value, the better. When AI exceeds 30 MPa, stretcher strain tends to occur during processing. Incidentally, AI is a value obtained by subtracting the tensile stress σ1 at the time of tensile pre-deformation of 10% from the yield stress σ2 when re-tensioning is performed after heat treatment at 100 ° C. × 3600 seconds (AI (MPa) = σ 2 − Evaluation was performed using σ1). BH was evaluated by a value (BH (MPa) = σ4-σ3) obtained by subtracting the stress σ3 at the time of tensile pre-deformation of 2% from the yield stress σ4 when re-tensioned after heat treatment at 170 ° C. for 1200 seconds.
[0029]
The results are shown in FIGS. As is clear from this, both high BH properties and room temperature slow aging can be achieved by adding P in an amount of 0.01% or more. On the other hand, when the amount of P is small, high BH can be obtained, but AI greatly exceeds 30 MPa, and room temperature slow aging was not ensured.
[0030]
[Table 1]
<Example 2>
Steel having the composition shown in Table 2 was melted and hot-rolled at a slab heating temperature of 1150 ° C., a finishing temperature of 930 ° C., and a winding temperature of 680 ° C. to form a steel strip having a thickness of 3.5 mm. After pickling, cold rolling with a reduction rate of 80% is performed to form a cold rolled sheet having a thickness of 0.7 mm, and then at a heating rate of 10 ° C./s, a heating temperature of 770 ° C., and 700 ° C. to each heat treatment temperature in a continuous annealing facility. The average cooling rate was 80 ° C./s, and then heat treatment was performed at each heat treatment temperature for 150 seconds. Furthermore, temper rolling was performed at a rolling reduction of 1.0%, a No. 5 tensile test piece described in JIS Z 2201 was collected, and AI and BH were measured.
[0032]
The results are shown in FIG. As is clear from this, BH property and room temperature slow aging compared with those heat-treated at 200 ° C. or 240 ° C. and those not heat-treated after annealing and cooling (marked with ●). Inferior. In addition, when the temperature is 500 ° C., the balance between BH and AI deteriorates slightly.
[0033]
[Table 2]
<Example 3>
Sample A-4 in Table 1 was hot-rolled and cold-rolled under the same conditions as in Example 1. Subsequently, annealing was performed at a heating rate of 10 ° C./s and a heating temperature of 750 ° C. in a continuous annealing facility, and the average cooling rate from 680 ° C. to 300 ° C. was variously changed. Moreover, after changing various average cooling rates from a heating rate of 10 ° C./s, a heating temperature of 770 ° C. and a heating temperature of 700 ° C. to a plating bath temperature of 460 ° C. in a continuous hot dip galvanizing line, it is immersed in the plating bath and reheated. Then, an alloying heat treatment was performed at 520 ° C. for 20 seconds. These results are shown in FIGS. From these, in the case of a continuous annealing line, good BH and AI characteristics can be obtained by setting the cooling rate to 40 ° C./s or more, and in the case of a continuous hot dip galvanizing line, setting the cooling rate to 10 ° C./s or more. Can be obtained.
<Example 4>
Various steels in Table 3 were hot-rolled under the conditions of a slab heating temperature of 1220 ° C., a finishing temperature of 920 ° C., and a coiling temperature of 600 ° C. to obtain a 3.8 mm thick steel plate. After pickling, it was cold-rolled to form a cold rolled sheet having a thickness of 0.75 mm, and then heat-treated by any one of heat treatment patterns A, B, and C as shown in FIG. After the heat treatment, temper rolling with a rolling reduction of 0.8% was performed and subjected to a tensile test. The results are shown in Table 4 (continued in Table 3). As a result, the steel sheets manufactured within the scope of the present invention show good values for BH, AI, r value, and elongation (El), while those outside the present invention have a remarkable balance between BH and AI. Deteriorated.
[0035]
[Table 3]
[Table 4]
【The invention's effect】
As described in detail above, according to the present invention, a method for producing a steel sheet that has both high BH properties and room temperature slow aging, can withstand exports that exceed the equator, and has both strength and workability, In use, the present invention can be said to be an industrially valuable invention because it can provide a method of manufacturing a steel sheet that can reduce the thickness of the steel sheet and can contribute to global environmental conservation.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the amount of P added and BH and AI.
FIG. 2 is a diagram illustrating a relationship between an addition amount of P and an r value.
FIG. 3 is a diagram showing a change in the relationship between AI and BH when various heat treatment temperatures are changed.
FIG. 4 is a diagram showing a relationship between a cooling rate after annealing and BH and AI when heat treatment is performed by continuous annealing.
FIG. 5 is a diagram showing a relationship between a cooling rate and BH and AI when heat treatment is performed in a continuous hot dip galvanizing line.
FIG. 6 is a diagram illustrating a heat treatment pattern used in an example.
Claims (8)
Ｃ ：０．００１４〜０．００２５％、
Ｓｉ≦１．５％、
Ｍｎ：０．０３〜２．０％、
Ｐ ：０．０１〜０．１５％、
Ｓ ≦０．０１５％、
Ａｌ：０．００５〜０．１％、
Ｎ ≦０．００４０％
を含有し、残部Ｆｅおよび不可避的不純物からなる組成のスラブを、Ａｒ3 変態点以上の温度で熱間圧延を行い、６０〜９５％の冷間圧延を施し、連続焼鈍ラインにて６５０℃以上、Ａｃ3 変態点以下の温度範囲で焼鈍し、引き続いて平均冷却速度４０℃／ｓ以上で２８０〜４５０℃の温度域まで冷却し、該温度域で１２０秒以上の熱処理を行うことを特徴とする塗装焼付硬化性能に優れた冷延鋼板の製造方法。In mass%,
C: 0.0014 to 0.0025%,
Si ≦ 1.5%,
Mn: 0.03 to 2.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to 0.1%,
N ≦ 0.0040%
The slab containing the balance Fe and inevitable impurities is hot-rolled at a temperature not lower than the Ar 3 transformation point, subjected to 60-95% cold rolling, and 650 ° C. or higher in a continuous annealing line. , Annealing in a temperature range below the Ac 3 transformation point, subsequently cooling to a temperature range of 280 to 450 ° C. at an average cooling rate of 40 ° C./s or more, and performing a heat treatment for 120 seconds or more in the temperature range. A method for producing cold-rolled steel sheets with excellent paint bake hardening performance.
Ｃ ：０．００１４〜０．００３０％、
Ｓｉ≦１．５％、
Ｍｎ：０．０３〜２．０％、
Ｐ ：０．０１〜０．１５％、
Ｓ ≦０．０１５％、
Ａｌ：０．００５〜０．１％、
Ｎ ≦０．００４０％
を含有し、さらに
Ｔｉ：０．００２〜０．０２％
および
Ｎｂ：０．００２〜０．０１８％
の１種または２種を、
Ｔｉ＋Ｎｂ＝０．００２〜０．０２％
となるように含有し、残部Ｆｅおよび不可避的不純物からなる組成のスラブを、Ａｒ3 変態点以上の温度で熱間圧延を行い、６０〜９５％の冷間圧延を施し、連続焼鈍ラインにて６５０℃以上、Ａｃ3 変態点以下の温度範囲で焼鈍し、引き続いて平均冷却速度４０℃／ｓ以上で２８０〜４５０℃の温度域まで冷却し、該温度域で１２０秒以上の熱処理を行うことを特徴とする塗装焼付硬化性能に優れた冷延鋼板の製造方法。In mass%,
C: 0.0014 to 0.0030%,
Si ≦ 1.5%,
Mn: 0.03 to 2.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to 0.1%,
N ≦ 0.0040%
Further Ti: 0.002-0.02%
And Nb: 0.002 to 0.018%
1 type or 2 types of
Ti + Nb = 0.002 to 0.02%
In a continuous annealing line, a slab having a composition comprising the balance Fe and inevitable impurities is hot-rolled at a temperature equal to or higher than the Ar 3 transformation point, subjected to 60-95% cold rolling, and a continuous annealing line. Annealing in a temperature range of 650 ° C. or more and below the Ac 3 transformation point, followed by cooling to a temperature range of 280 to 450 ° C. at an average cooling rate of 40 ° C./s or more, and performing heat treatment for 120 seconds or more in the temperature range A method for producing a cold-rolled steel sheet excellent in paint bake hardening performance.
Ｃ ：０．００１４〜０．００２５％、
Ｓｉ≦０．３％、
Ｍｎ：０．０３〜２．０％、
Ｐ ：０．０１〜０．１５％、
Ｓ ≦０．０１５％、
Ａｌ：０．００５〜０．１％、
Ｎ ≦０．００４０％
を含有し、残部Ｆｅおよび不可避的不純物からなる組成のスラブを、Ａｒ3 変態点以上の温度で熱間圧延を行い、６０〜９５％の冷間圧延を施し、連続溶融亜鉛めっきラインにて６５０℃以上、Ａｃ3 変態点以下の温度範囲で焼鈍し、引き続いて平均冷却速度１０℃／ｓ以上で亜鉛めっき浴温度まで冷却して、めっきした後、４７０〜５５０℃までの温度範囲で１５秒以上の熱処理を行うことを特徴とする塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法。In mass%,
C: 0.0014 to 0.0025%,
Si ≦ 0.3%,
Mn: 0.03 to 2.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to 0.1%,
N ≦ 0.0040%
The slab containing the balance Fe and inevitable impurities is hot-rolled at a temperature equal to or higher than the Ar 3 transformation point, subjected to 60-95% cold rolling, and 650 in a continuous hot-dip galvanizing line. ° C. or higher, and cooled Ac 3 transformation point at a temperature range of annealing, to a zinc plating bath temperature at an average cooling rate of 10 ° C. / s or higher subsequently, after plating, 15 seconds at a temperature range of up to four hundred seventy to five hundred and fifty ° C. The manufacturing method of the galvannealed steel plate excellent in the paint bake hardening performance characterized by performing the above heat processing.
Ｃ ：０．００１４〜０．００２５％、
Ｓｉ≦０．３％、
Ｍｎ：０．０３〜２．０％、
Ｐ ：０．０１〜０．１５％、
Ｓ ≦０．０１５％、
Ａｌ：０．００５〜０．０７％未満、
Ｎ ≦０．００４０％、
Ｂ：０．０００１〜０．００４０％
を含有し、残部Ｆｅおよび不可避的不純物からなる組成のスラブを、Ａｒ 3 変態点以上の温度で熱間圧延を行い、６０〜９５％の冷間圧延を施し、連続溶融亜鉛めっきラインにて６５０℃以上、Ａｃ 3 変態点以下の温度範囲で焼鈍し、引き続いて平均冷却速度１０℃／ｓ以上で亜鉛めっき浴温度まで冷却して、めっきした後、４７０〜５５０℃までの温度範囲で１５秒以上の熱処理を行うことを特徴とする塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法。 % By mass
C: 0.0014 to 0.0025%,
Si ≦ 0.3%,
Mn: 0.03 to 2.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to less than 0.07%,
N ≦ 0.0040%,
B: 0.0001 to 0.0040%
The slab containing the balance Fe and inevitable impurities is hot-rolled at a temperature equal to or higher than the Ar 3 transformation point, subjected to 60-95% cold rolling, and 650 in a continuous hot-dip galvanizing line. ° C. or higher, and cooled Ac 3 transformation point at a temperature range of annealing, to a zinc plating bath temperature at an average cooling rate of 10 ° C. / s or higher subsequently, after plating, 15 seconds at a temperature range of up to four hundred seventy to five hundred and fifty ° C. excellent production method of galvannealed steel sheet in painting bake hardenability performance you characterized by performing the above heat treatment.
Ｃ ：０．００１４〜０．００３０％、
Ｓｉ≦０．３％、
Ｍｎ：０．０３〜２．０％、
Ｐ ：０．０１〜０．１５％、
Ｓ ≦０．０１５％、
Ａｌ：０．００５〜０．１％、
Ｎ ≦０．００４０％
を含有し、さらに
Ｔｉ：０．００２〜０．０１５％
および
Ｎｂ：０．００２〜０．０１５％
のうち１種または２種を
Ｔｉ＋Ｎｂ＝０．００２〜０．０１５％
となるように含有し、残部Ｆｅおよび不可避的不純物からなる組成のスラブを、Ａｒ3 変態点以上の温度で熱間圧延を行い、６０〜９５％の冷間圧延を施し、連続溶融亜鉛めっきラインにて６５０℃以上、Ａｃ3 変態点以下の温度範囲で焼鈍し、引き続いて平均冷却速度１０℃／ｓ以上で亜鉛めっき浴温度まで冷却して、めっきした後、４７０〜５５０℃までの温度範囲で１５秒以上の熱処理を行うことを特徴とする塗装焼付硬化性能に優れた合金化溶融亜鉛めっき鋼板の製造方法。In mass%,
C: 0.0014 to 0.0030%,
Si ≦ 0.3%,
Mn: 0.03 to 2.0%,
P: 0.01 to 0.15%,
S ≦ 0.015%,
Al: 0.005 to 0.1%,
N ≦ 0.0040%
And further Ti: 0.002 to 0.015%
And Nb: 0.002 to 0.015%
1 type or 2 types of Ti + Nb = 0.002 to 0.015%
The slab having the composition comprising the balance Fe and inevitable impurities is hot-rolled at a temperature equal to or higher than the Ar 3 transformation point, subjected to 60-95% cold rolling, and a continuous hot-dip galvanizing line Annealing at a temperature range of 650 ° C. or more and below the Ac 3 transformation point, followed by cooling to a galvanizing bath temperature at an average cooling rate of 10 ° C./s or more, plating, and a temperature range of 470 to 550 ° C. A method for producing an alloyed hot-dip galvanized steel sheet excellent in paint bake hardening performance, characterized by performing a heat treatment for 15 seconds or more.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP10172497A JP3745496B2 (en) | 1997-04-18 | 1997-04-18 | Manufacturing method of cold-rolled steel sheet and alloyed hot-dip galvanized steel sheet with excellent paint bake hardening performance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP10172497A JP3745496B2 (en) | 1997-04-18 | 1997-04-18 | Manufacturing method of cold-rolled steel sheet and alloyed hot-dip galvanized steel sheet with excellent paint bake hardening performance |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH10298662A JPH10298662A (en) | 1998-11-10 |
| JP3745496B2 true JP3745496B2 (en) | 2006-02-15 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP10172497A Expired - Fee Related JP3745496B2 (en) | 1997-04-18 | 1997-04-18 | Manufacturing method of cold-rolled steel sheet and alloyed hot-dip galvanized steel sheet with excellent paint bake hardening performance |
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| JP (1) | JP3745496B2 (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3912014B2 (en) * | 2001-02-05 | 2007-05-09 | Ｊｆｅスチール株式会社 | Alloyed hot-dip galvanized steel sheet and method for producing the same |
| KR100723180B1 (en) * | 2005-05-03 | 2007-05-30 | 주식회사 포스코 | Cold rolled steel sheet having good formability and process for producing the same |
| KR20070038730A (en) | 2005-10-06 | 2007-04-11 | 주식회사 포스코 | The precipitation hardening cold rolled steel sheet having excellent yield ratios, and the method for manufacturing the same |
| JP4904887B2 (en) * | 2006-03-30 | 2012-03-28 | Ｊｆｅスチール株式会社 | Method for adjusting bake hardenability of ultra-low carbon steel containing Nb |
| KR101042434B1 (en) * | 2007-10-29 | 2011-06-16 | 현대제철 주식회사 | A cold rolledsteel sheet and method for manufacturing the same |
| JP5556483B2 (en) * | 2010-08-03 | 2014-07-23 | 新日鐵住金株式会社 | Continuous annealing method for steel sheet using continuous annealing furnace |
| JP5920281B2 (en) * | 2013-05-08 | 2016-05-18 | Ｊｆｅスチール株式会社 | Alloyed hot-dip galvanized steel sheet and method for producing the same |
| CN116121656A (en) * | 2022-12-21 | 2023-05-16 | 本钢板材股份有限公司 | Bake-hardening steel plate for electrogalvanizing and production method thereof |
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1997
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| JPH10298662A (en) | 1998-11-10 |
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