JP3941173B2 - Manufacturing method of hot-rolled steel sheet with excellent scale adhesion and corrosion resistance - Google Patents
Manufacturing method of hot-rolled steel sheet with excellent scale adhesion and corrosion resistance Download PDFInfo
- Publication number
- JP3941173B2 JP3941173B2 JP19973997A JP19973997A JP3941173B2 JP 3941173 B2 JP3941173 B2 JP 3941173B2 JP 19973997 A JP19973997 A JP 19973997A JP 19973997 A JP19973997 A JP 19973997A JP 3941173 B2 JP3941173 B2 JP 3941173B2
- Authority
- JP
- Japan
- Prior art keywords
- scale
- less
- steel sheet
- hot
- steel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Landscapes
- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は、足廻り部品やバンパーなどの自動車部品、鉄骨建材、鋼管やドラム缶などに使われる熱延鋼板の製造方法に係わり、さらに詳しくは、酸洗処理などの脱スケール処理を施すことなく加工が可能である、耐食性に優れた熱延鋼板の製造方法に関する。
【０００２】
【従来の技術】
熱延鋼板は、鋼板表面にスケールが付いたまま加工されて使用される場合がある。熱間圧延したままの鋼板には表面に酸化スケール（以下単にスケールと記す）が形成されている。このスケールはその後の成形加工（曲げ加工、絞り加工等）時に剥離することがある。スケールが部分的に剥離すると製品の外観品質が損なわれ、剥離したスケールは鋼材を成形加工する時の作業性を悪くする。このため、成形加工を伴い、かつ、外観品質が必要な用途に用いる場合には、鋼自体の成形性を向上させた鋼板に、酸洗やショットブラストなど別工程による脱スケール処理を施して使用される。他方、経済性を追及する観点から、脱スケール処理を施さなくても加工できる、スケールの密着性に優れた熱延鋼板の開発が望まれている。
【０００３】
また、製品の耐食性が特に重要な場合には、めっき鋼板を用いたり重防食塗装を施すなどの方法があるが、これらの方法はいずれもコストがかかる。このため、鋼自体の耐食性が優れた鋼板の開発が望まれており、例えば、特開昭５４−９１１３号公報には、Ｃｕ、Ｐ、Ｎｉを添加した鋼板が提案されている。しかし、この鋼板の耐食性改善効果には限界がある。また、通常の熱延鋼板と同様に、スケールの密着性がよくない場合には、製品の外観や加工時の作業性が阻害される。
【０００４】
スケールの密着性は、その組成、構造、厚さ等に影響される。薄くて緻密なスケールは密着性が優れる。薄くて緻密なスケール層を得るには、鋼を高温の酸化性雰囲気に曝さないことが重要である。スケールの密着性を改善するために、熱間圧延後の鋼を急速に冷却したり、非酸化性の雰囲気中で冷却する等の方法が提案されている。
【０００５】
特開昭６１−１９４１１２号公報には、０．０４〜０．５重量％のＳｉを添加した鋼片を、Ａｒ3 ＋５０℃以下の温度で熱間圧延した後、４０℃／秒以上の冷却速度で冷却して５００℃〜３６０℃で巻き取ることによりスケールを薄くして、スケールの密着性に優れた熱延鋼板を得る方法が記載されている。しかしＳｉを含有する鋼では、スラブが加熱される段階で、地鉄とスケールとの界面にＦｅ2ＳｉＯ4（ファイヤライト）とＦｅＯからなる低融点の共晶化合物が生成し、地鉄とスケールの双方に食い込む。このため、仕上圧延前までの高圧水などによるスケール除去が完全におこなえず、部分的にスケールが残ったまま仕上圧延される場合が生じる。この部分には、結果的に厚いスケールが残るため、スケールの密着性はよくない。
【０００６】
熱間圧延鋼板の成形性は、熱間圧延で生じる圧延歪を十分に回復し、結晶粒を大きくし、パーライトやセメンタイトを成長させることにより良好になる。このため、熱間圧延後の鋼板を高温で巻取るとその成形性は改善される。スケールの密着性を改善するために熱間圧延時の鋼板の巻取温度を低くする方法では、熱延鋼板自体の成形性を改善するが難しいのが問題である。
【０００７】
特開昭５９−２２２５３３号公報には、熱間圧延して７００〜５５０℃で巻き取った後、窒素ガスまたはＡｒガスからなる非酸化性雰囲気中で３５０℃まで冷却する熱延鋼板の製造方法が提案されている。さらに特開昭６２−１３６５２９号公報には、熱間圧延後２０〜４０℃／秒の冷却速度で冷却して５５０℃以下で巻き取った後、前記公報と同様に非酸化性雰囲気中で３５０℃まで冷却する熱延綱板の製造方法が提案されている。しかし、これらの方法は巻取り後の冷却を非酸化性雰囲気中でおこなう方法であり、大気を遮断して雰囲気を調整する設備が必要になるので、経済性や生産性が阻害される。
【０００８】
このように、従来の提案では鋼板のスケール密着性と耐食性および成形性とを両立させて経済的に製造する方法は開示されていない。
【０００９】
【発明が解決しようとする課題】
本発明は、スケール密着性、耐食性、および成形性に優れた熱延鋼板の製造方法を提供することを目的とする。
【００１０】
【課題を解決するための手段】
本発明の要旨は、下記の (1) 〜 (4) に示す、スケール密着性と耐食性に優れた熱延鋼板の製造方法にある。
【００１１】
(1) 重量％で、Ｃ：０．２％以下、Ｓｉ：０．０８％以下、Ｍｎ：０．０５〜２％、Ｐ：０．０１〜０．０６％、Ｓ：０．０１５％以下、Ａｌ：０．１〜１％、Ｃｕ：０．１〜０．５％およびＮｉ：０．０１〜０．３％を含有し、残部が鉄および不可避不純物からなる鋼の仕上圧延を１１００℃以下で開始して９００℃以下で終了し、仕上圧延後の鋼板に対して仕上圧延終了後２秒以内に強制冷却を開始し、少なくとも７００℃までは冷却速度３０℃／秒以上で急冷した後、６５０〜５５０℃で巻取り、５５０〜４００℃の間を平均２０℃／時以下の冷却速度で徐冷する工程を含むことを特徴とするスケール密着性と耐食性に優れた熱延鋼板の製造方法。
(2) 鋼の化学成分として、さらに、重量％で、Ｎｂ：０．１％以下、Ｔｉ：０．１％以下およびＣｒ：１％以下のうちの１種以上を含有することを特徴とする、上記(1)のスケール密着性と耐食性に優れた熱延鋼板の製造方法。
(3) 鋼の化学成分として、さらに、重量％で、Ｂ：０．００５％以下を含有することを特徴とする、上記(1)又は(2)のスケール密着性と耐食性に優れた熱延鋼板の製造方法。
(4) 鋼の化学成分として、さらに、重量％で、Ｃａ：０．００４％以下を含有することを特徴とする、上記(1)〜(3)のいずれかのスケール密着性と耐食性に優れた熱延鋼板の製造方法。
【００１２】
上記の課題を解決するための本発明の基になっている考え方を以下に記す。
【００１３】
(１) 鋼中のＡｌ含有量がスケールの密着性に影響する。Ａｌ含有量を特定範囲に調整した鋼の仕上圧延とその後の冷却条件を選択して熱間圧延すれば、密着性に優れたスケール層が得られる。さらに、Ａｌと、Ｃｕ、Ｐ、Ｎｉとを共に含有させた鋼では、熱間圧延ままの鋼板の耐食性が一段と向上する。
【００１４】
本発明者等は、種々の割合でＡｌを含有させた鋼からなる厚さ２４０ｍｍのスラブを１２２０℃に加熱して粗圧延をおこない、仕上圧延を１０５０℃で開始して８６０℃で終了し、仕上圧延終了から１秒後に３０℃／秒の冷却速度で冷却を開始し、６００℃で巻取り、その鋼板コイルを５５０〜４００℃の間を２０℃／時の冷却速度で徐冷して、厚さ２．３ｍｍ、幅１２５０ｍｍの熱延鋼板を得た。鋼の化学組成を表１に示した。
【００１５】
【表１】
これらの熱延鋼板のスケール厚さ、密着性および耐食性を、以下の方法で評価した。
【００１７】
スケールの密着性は、曲げ試験片に内側曲げ半径が板厚の１．５倍の９０度曲げ試験をおこなった後、曲げ部外側のスケールが剥離した部分の面積率を求めた。スケール剥離面積率が２％以下の場合はスケールの密着性が良好と判断される。表１には、その結果を、スケール剥離面積率が２％以下のものを「○」、２％を超えるものを「×」で表示した。
【００１８】
耐食性は、スケールが付着したままの鋼板から得た幅３０ｍｍ、長さ７０ｍｍの試験片に、「３５℃の５％食温水を６時間噴霧→湿度９５％以上の室温雰囲気中で１２時間保持→５０℃の乾燥雰囲気中で６時間保持」を１サイクルとする腐食試験を１２０サイクルおこない、試験片表面に認められる腐食部分の赤錆を除去した後、板厚方向への腐食深さの最大値をマイクロメータで測定して評価した。最大腐食深さが１．５ｍｍ以下の場合は耐食性が良好と判断される。表１には、その結果を、最大腐食深さが１．５ｍｍ以下のものを「○」、１．５ｍｍを超え１．８ｍｍ以下のものを「△」、１．８ｍｍを超えるものを「×」で表示した。
【００１９】
表１に示されているように、Ａｌ含有量が高い鋼▲１▼、▲２▼、▲４▼および▲５▼は、スケール密着性が良好である。これに対し、Ａｌ含有量が少ない鋼▲３▼はスケールの密着性がよくない。また、Ａｌと微量のＣｕ、Ｐ、Ｎｉを共に含有している鋼▲１▼および▲２▼の耐食性は一段と優れている。
【００２０】
Ａｌを含有させることにより鋼板を加工した時のスケールの密着性が向上する機構は、未だ不明な部分が多いが、以下のように推測される。スケールと地鉄の界面には、スラブ加熱または熱間圧延時にＡｌの濃化により形成されたと考えられる、ＦｅＡｌ2０4を主体とするＡｌとＦｅとの複合酸化物層が形成されている。この複合酸化物は地鉄との密着性が優れているＦｅ3０4と同じ結晶構造（スピネル構造）を持っている。このために、この複合酸化物層はスケール層との整合性が高いだけではなく、地鉄との整合性も比較的良好であり、結果的にスケール層と地鉄の密着性の向上に寄与しているのではないかと考えられる。
【００２１】
仕上圧延前でのスケールの除去性は、Ｓｉ含有率が高い鋼と異なり、Ａｌの含有率が高くても問題がなく良好である。これは、ＦｅＡｌ2Ｏ4とＦｅＯの共晶化合物の融点が高く、通常のスラブ加熱温度では、この複合酸化物層は溶融状態にはならない。このため、複合酸化物層がスケールや地鉄界面に食い込むことがないからであると考えられる。
【００２２】
鋼板の耐食性が、微量のＣｕ、Ｐ、Ｎｉなどに加えて、Ａｌを含有させることで一段と向上するのは、Ｃｕ、Ｐ、Ｎｉなどを含有することで形成される緻密な皮膜状の腐食生成物の安定性が、安定なＡｌ系の酸化物と共存することによって、さらに増すことによるものであると考えられる。
【００２３】
(２) スケール層の大半を占めるＦｅＯは、５６０℃以下でＦｅとＦｅ3Ｏ4に共析変態する性質がある。このため、鋼板の温度が５６０℃以下になると、地鉄素地表面にはＦｅとＦｅ3Ｏ4層とが形成される。
【００２４】
鋼との密着性に優れるＦｅＡｌ2Ｏ4を主とする複合酸化物層は、Ａｌ含有量が制限されているために、鋼板素地の表面全体を覆う訳ではないので、部分的に複合酸化物層で覆われない領域、すなわちスケールの密着性が十分に改善されていない領域も存在する。しかし、上述のＦｅＯの共析変態で生じるＦｅ3Ｏ4層は、ＦｅＡｌ2Ｏ4複合酸化物層の上のみならず、複合酸化物層が形成されなかった鋼板素地表面をも覆う。これによりスケール層と地鉄との密着力が更に強固になる。
【００２５】
また、この変態時にはＦｅ3Ｏ4の間にＦｅが析出し、あたかもＦｅの楔がＦｅ3Ｏ4を固定するような形態になる。このこともスケールの密着性改善に寄与しているものと推測される。上述のＦｅＯの共析変態は、５５０〜４００℃の温度範囲で特に促進される。従って熱間圧延された鋼板をこの温度範囲に滞留させることで、鋼板の界面に一様にＦｅ3Ｏ4層を生じさせ、スケールの密着性を更に改善することができる。
【００２６】
熱間圧延鋼板の成形性を改善するためにコイルの巻取温度をある程度高めても、上述の共析変態の効果を活用すればスケールの密着性を良好なレベルに保つことができる。
【００２７】
【発明の実施の形態】
以下、本発明の実施の形態について詳細に説明する。
【００２８】
(Ａ) 鋼の化学組成
Ｃ：鋼板の強度を確保するために使用される。しかし、その含有量が０．２％を超えると、鋼板表面に多量のセメンタイト（Ｆｅ3Ｃ ）が生じるので、スケールの密着性のみならず鋼板の加工性や溶接性も損なわれる。従ってＣの含有量は０．２％以下とする。鋼板の成形性が重要な場合にはＣ含有量は低い方が好ましく、０．００１％程度の極低炭素でも本発明は有効である。しかし極低炭素領域までＣを低下させるのは経済的でないためＣ含有量の下限は０．０１％とするのが好ましい。
【００２９】
Ｓｉ：製鋼時の脱酸剤として用いられる。また、鋼板の強度を高める安価な元素としても広く用いられる。しかしＳｉは、高温域ではＦｅとＳｉの低融点の共晶化合物を形成し、熱間圧延前のデスケーリング不良や、鋼板を成形、加工する時のスケールの密着性不良などの問題を起こす。このためＳｉ含有量は低いほど好ましく、０．０８％を上限とする。好ましくは０．０４％以下とする。また、鋼板の強度よりも成形性を重視する用途などの場合には、Ｓｉを用いなくても良い。
【００３０】
Ｍｎ：鋼板の強度を確保するとともに、鋼中に不純物として存在するＳをＭｎＳとして固定し、熱間圧延中に生じるおそれがある割れを抑制する作用がある。Ｍｎ含有量が０．０５％未満の場合にはこの割れ抑制の効果が得られず、一方、２％を超えて含有させてもその作用が飽和するうえ、スケールの密着性を劣化させる。このためＭｎの含有量は０．０５〜２％とする。
【００３１】
Ｐ：緻密な腐食皮膜を生成して耐食性を高める作用を有しているが、Ｐの含有量が０．０１％に満たない場合にはその効果が不十分である。一方、０．０６％を超えて含有させるとスケールの密着性が劣化する。このため、Ｐ含有量は０．０１〜０．０６％とする。
【００３２】
Ａｌ：従来は、主として製鋼時に脱酸剤として用いられており、その効果は、０．１％に満たない量で十分に発揮される。しかしＡｌは、本発明では、熱延鋼板のスケールの密着性を改善するうえで最も重要な元素である。すなわち、Ａｌを多量に含有させた鋼では、スラブ加熱時または熱間圧延中に、鋼に固溶しているＡｌがスケールと鋼表面との界面に濃化され、ＦｅとＡｌの複合酸化物層が形成される。これによりスケールの密着性が改善される。Ａｌ含有量が０．１％に満たない場合にはその効果が弱いので、Ａｌ含有量の下限は０．１％とする。他方、Ａｌの含有量が増すにつれて、密着性向上効果が飽和するうえ経済性を損なう。このため、その上限を１％とする。
【００３３】
Ｃｕ：耐食性を向上させるための主要な成分である。Ｃｕを含有する鋼では鋼の表面に緻密な腐食皮膜が生成して耐食性が改善される。Ｃｕの含有量が０．１％に満たない場合には前記作用による耐食性向上の効果を得ることができない。他方、Ｃｕを０．５％を超えて含有させても、耐食性改善効果が飽和するばかりでなくスケール密着性も劣化する。このため、Ｃｕ含有量は０．１〜０．５％とする。
【００３４】
Ｎｉ：Ｃｕ添加にともなって生じるおそれがある鋼の熱間加工性の低下を抑制する作用があるほか、耐食性を向上させる効果も有する。これらの効果を得るにはＮｉを０．０１以上含有させる必要がある。他方、Ｎｉを０．３％を超えて含有させても、前記作用が飽和するうえ経済性も損なわれる。このため、Ｎｉ含有量は０．０１〜０．３％とする。
【００３５】
本発明が目的としている熱延鋼板は、基本的には、上述の元素とＦｅとで構成されるが、さらに、鋼板の強度や成形性を必要とする場合には以下に述べる元素を含有させてもよい。
【００３６】
高強度の熱延鋼板を必要とする場合にはＮｂ、Ｔｉ、Ｖ、Ｃｒ、Ｍｏの内の１種以上を含有させてもよい。Ｎｂ、ＴｉおよびＶは、鋼のフェライト地に炭窒化物として析出して鋼板の強度を高めるが、０．００５％未満ではその効果が弱い。このため、これらの元素を含有させる場合には、いずれの元素の場合でも０．００５％以上とするのが好ましい。過剰に含有させてもその効果が飽和し経済性を損なうので、その上限は、ＮｂおよびＴｉについては０．１％、Ｖについては０．２％とするのが望ましい。
【００３７】
ＣｒとＭｏは変態強化を通じて強度を高めるが、０．０１％未満ではその効果が弱い。このため、これらの元素を含有させる場合には、いずれの元素の場合でも０．０１％以上とするのが好ましい。Ｃｒは１％、Ｍｏは０．５％がそれぞれの元素が強度に有効に寄与する含有量の上限である。このため、これらの元素の含有量の上限は、Ｃｒについては１％、Ｍｏについては０．５％とするのがよい。
【００３８】
成形性がより優れた熱延鋼板を必要とする場合にはＢを含有させるのが望ましい。Ｂには鋼のＡｒ3 変態点を下げる作用を通じて鋼板の降伏強度を低め、加工性を改善する効果が期待できる。その効果を発揮するには０．００１％以上含有させるのが好ましい。０．００５％を超えると成形性改善の効果が飽和する。したがってＢの上限は０．００５％とするのが望ましい。
【００３９】
曲げ性などがより優れた熱延鋼板を必要とする場合には、介在物の形態を制御する目的でＣａ、Ｚｒまたは希土類元素を含有させるのがよい。曲げ性改善の効果を得るには、Ｃａの場合は０．０００２％以上、Ｚｒの場合は０．０１％以上、希土類元素の場合は０．００２％以上含有させるのが好ましい。他方、Ｃａの場合は０．００４％、Ｚｒの場合は０．０５％、希土類元素の場合は０．０５％を超えて含有させると、逆に鋼中の介在物が多くなって加工性が劣化する。このため、これらの元素の含有量の上限は、Ｃａでは０．００４％、Ｚｒでは０．０５％、希土類元素では０．０５％とする。介在物の形態制御はこれらの元素の内のいずれか１種を含有させればよいが、２種以上を複合して含有させてもかまわない。
【００４０】
上記の成分以外はＦｅおよび不可避的不純物である。不可避的不純物としてのＳは、熱間圧延前のスラブ加熱時および熱間圧延中に鋼の表面に濃化してスケールの密着性を損なうことがある。Ｓ含有量が０．０１５％以下であればスケール密着性に及ぼす悪影響は少ない。このため、Ｓは０．０１５％以下にすることが好ましい。
【００４１】
（Ｂ）熱延鋼板の製造条件
本発明では、前項（Ａ）に記載した組成の鋼からなるスラブを熱間圧延する。その際の冷却条件を特定することで、鋼板の成形性とスケールの密着性がさらに改善される。熱間圧延時の仕上圧延は、１１００℃以下で開始し、９００℃以下で終了させ、仕上圧延終了後２秒以内に注水冷却を開始し、少なくとも７００℃までは冷却速度３０℃／秒以上で急冷し、５５０℃以下で巻き取る。
【００４２】
仕上圧延前のスラブ加熱はおこなってもよいし、これを省略して粗圧延しても良い。また、スラブが薄い場合などでは粗圧延を省略してもかまわない。通常、粗圧延及び仕上圧延前には高圧水などによってスケールを除去する。スケールが十分に除去されないまま仕上圧延を行うと、残ったスケールが圧延によって鋼板に押し込まれ、噛み込みスケールとして鋼板表面に残存する。このため、熱間圧延終了後のこの部分のスケールが厚くなる。スケールの密着性に優れた熱延鋼板を製造するためには、仕上圧延前にスケールを十分に除去しておくことが必要である。
【００４３】
鋼の熱間変形抵抗は温度が高いほど低くなり、鋼板の材料特性は仕上圧延温度が高い方がよいので、仕上圧延温度は高いのが望ましい。しかし、スラブの加熱温度を高くするのはコストがかかるので、通常は、仕上圧延開始温度は１１５０℃以下、仕上圧延終了温度は９５０℃以下でおこなわれる。他方、スケールは、鋼の温度が高くなると指数関数的に速く成長し、その厚みが増すと剥離し易くなる。このため、スケールの密着性を改善するには、鋼板が高温に曝される時間をできるだけ短くするのがよい。
【００４４】
これらの観点から、本発明では、仕上圧延は１１００℃以下で開始し、９００℃以下で終了する。仕上圧延の終了温度は好ましくは８６０℃以下である。仕上圧延の開始と終了の温度の下限は、それぞれ９００℃および７５０℃とするのが好ましい。スケールの密着性を向上させる観点からは仕上温度は低い方が好ましいが、仕上温度をこれ以上低くすると圧延機への負荷が過大になり圧延が困難になる。
【００４５】
さらに本発明では、仕上圧延終了後２秒以内に冷却を開始し、少なくとも７００℃までは３０℃／秒以上の冷却速度で冷却する。好ましくは１秒以内に冷却を開始する。冷却方法は、通常おこなわれている冷却水を用いたスプレー冷却方法、ラミナーフローによる冷却方法でもよいが、高圧水を噴射するなどのさらなる冷却促進手段を用いるのが望ましい。
【００４６】
７００℃まで冷却した後、６５０〜５５０℃で巻取る。鋼板自体の成形性を向上させるには高温で巻取るのがよいが、巻取温度が６５０℃を超えると、スケールが厚くなり密着性が低下する。他方、巻取温度が５５０℃に満たない場合には、鋼板自体の成形性が損なわれるうえ、以下に述べる理由でスケールの密着性改善効果が十分には得られない。
【００４７】
巻取り後のコイルは、５５０〜４００℃の温度区間の平均冷却速度を２０℃／時以下にして冷却される。５６０℃以下では、４ＦｅＯ→Ｆｅ3Ｏ4＋Ｆｅの反応式で示される共析変態が生じる。５５０〜４００℃の温度区間の平均冷却速度を２０℃／時以下とし、上記の共析変態を十分に進行させ、鋼板素地表面のスケールをＦｅ3Ｏ4が主体になったスケールにすることで、スケールの密着性をさらに向上させる。巻取温度が５５０℃未満、または、巻取った後のコイルの冷却速度が２０℃／時を超える場合は、４ＦｅＯ→Ｆｅ3Ｏ4＋Ｆｅ共析変態が十分に進まずスケール密着性が低下する。また、巻取温度が６５０℃を超えると、スケールの生成量が多くなりスケール密着性が低下する。
【００４８】
巻取後のコイルの冷却速度は、熱間圧延直後に巻取った高温状態のコイルを密集して保管したり、保温カバー等の放熱防止装置を用いて調整する等の方法を適宜用いればよい。
【００４９】
【実施例】
表２に、試験に用いた鋼の化学組成を示す。
【００５０】
【表２】
鋼Ａ〜Ｍは本発明が規定する化学組成範囲にある鋼であり、鋼Ｎ〜Ｗは、比較例として選定した、本発明が規定する化学組成範囲から外れるものである。上記の化学組成からなる鋼の２４０ｍｍ厚のスラブを１２２０℃に加熱し、粗圧延し、仕上圧延し、注水冷却して巻取り、冷却して板厚２．３ｍｍの鋼板を得た。巻取り後のコイルの冷却速度は、適宜保温カバーを用いて調整した。これらの鋼板の機械的性質、スケール密着性および耐食性を、以下に述べる方法で評価した。
【００５２】
引張試験は、ＪＩＳ−Ｚ−２２０１に規定される５号試験片を用いて評価した。曲げ試験は、幅５０ｍｍ、長さ１２０ｍｍの試験片を採取してＪＩＳ−Ｚ−２２４８に規定される方法で、曲げ半径：板厚の１．５倍、曲げ角度９０度にておこなった。この曲げ試験片の曲げ部の外側に粘着テープを貼り付けて浮いたスケールを除去したのち、曲げ部外側の拡大写真を撮影してスケールが剥離している部分の面積率を測定し、スケール剥離面積率が２％以下の場合を良好とした。表３には、スケール剥離面積率が２％以下のものを「○」、２％を超えるものを「×」で表示した。
【００５３】
耐食性については、鋼板から幅３０ｍｍ、長さ７０ｍｍの試験片を切り出し、「塩水噴霧（５％食塩水、３５℃×６時間保持）→湿潤保持（湿度：９５％以上、温度：室温で１２時間保持）→乾燥（５０℃×６時間保持）」を１サイクルとする腐食試験を行い、１２０サイクル試験後の試験片表面の最大腐食深さをマイクロメータで測定し、最大腐食探さが１．５ｍｍ以下の場合を良好とした。表３には、各試験片の最大腐食深さが１．５ｍｍ以下のものを「○」、１．５ｍｍを超え１．８ｍｍ以下のものを「△」、１．８ｍｍを超えるものを「×」で表示した。
【００５４】
熱延条件および各種の性能評価結果を表３に併せて示す。
【００５５】
【表３】
表３に示されているように、本発明が規定する条件の範囲内で製造された鋼板は、スケール密着性と耐食性に優れていた。また、ＴＳ×Ｅｌの値が１６９０以上の範囲にあり、強度に見合った良好な延性が得られた。
【００５７】
他方、Ａｌ含有量が本発明の規定を下回る鋼Ｎ、Ｏを用いた試番１４、１５は、スケール密着性と耐食性がよくなかった。Ｓｉ、Ｐ、Ｓ、Ｍｎの内のいずれかの元素の含有量が本発明が規定する範囲から外れている鋼Ｐ、Ｑ、Ｒ、Ｓを用いた試番１６〜１９では、スケール密着性がよくなかった。Ｃｕ、Ｐ、Ｎｉの内のいずれかが本発明が規定する範囲から外れた鋼Ｔ、Ｕ、Ｖを用いた試番２０〜２２では、耐食性がよくなかった。ＡｌとＣｕ含有量が共に本発明が規定する範囲から外れた鋼Ｗを用いた試番２３では、スケール密着性と耐食性が共によくなかった。製造条件が本発明が規定する範囲から外れた試番２４〜２８および３０でも、スケール密着性が低下した。
【００５８】
また、巻取温度が本発明が規定する範囲よりも低かった試番２９では、スケール密着性と耐食性は良好であったが、ＴＳ×Ｅｌの値が低く、強度に見合った良好な延性が得られなかった。
【００５９】
【発明の効果】
本発明の方法により、スケールが付着した状態で成形加工してもスケールが剥離せず、鋼板自体の成形性が良好で、耐食性が優れた熱延鋼板が製造できる。本発明の方法は、特定の化学組成と製造条件の組み合わる方法であるので、容易かつ経済的に実施できる。本発明の方法による鋼板は、耐食性に優れるうえ、加工時のスケール剥離によるプレス金型の手入れ頻度が低減されるので、加工性にも優れる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing hot rolled steel sheets used for automobile parts such as undercarriage parts and bumpers, steel frame building materials, steel pipes and drums, and more specifically, processing without descaling such as pickling. It is related with the manufacturing method of the hot-rolled steel plate excellent in corrosion resistance.
[0002]
[Prior art]
A hot-rolled steel sheet may be processed and used with a scale on the surface of the steel sheet. An oxide scale (hereinafter simply referred to as scale) is formed on the surface of the hot-rolled steel sheet. This scale may be peeled off during the subsequent forming process (bending process, drawing process, etc.). When the scale is partially peeled, the appearance quality of the product is impaired, and the peeled scale deteriorates workability when forming the steel material. For this reason, when used for applications that require forming processing and require appearance quality, the steel sheet with improved formability of the steel itself is used after being descaled in a separate process such as pickling or shot blasting. Is done. On the other hand, from the perspective of pursuing economic efficiency, there is a demand for the development of a hot-rolled steel sheet excellent in scale adhesion that can be processed without being descaled.
[0003]
In addition, when the corrosion resistance of the product is particularly important, there are methods such as using a plated steel plate or applying a heavy anticorrosion coating, but these methods are all costly. For this reason, development of a steel plate with excellent corrosion resistance of the steel itself is desired. For example, JP-A No. 54-9113 proposes a steel plate to which Cu, P, and Ni are added. However, the effect of improving the corrosion resistance of this steel sheet is limited. Further, as in the case of ordinary hot-rolled steel sheets, when the adhesion of the scale is not good, the appearance of the product and workability during processing are hindered.
[0004]
Scale adhesion is affected by its composition, structure, thickness, and the like. Thin and dense scales have excellent adhesion. In order to obtain a thin and dense scale layer, it is important not to expose the steel to a high temperature oxidizing atmosphere. In order to improve the adhesion of the scale, methods such as rapidly cooling the steel after hot rolling or cooling in a non-oxidizing atmosphere have been proposed.
[0005]
In JP-A-61-194112, a steel slab containing 0.04 to 0.5% by weight of Si is hot-rolled at a temperature of Ar 3 + 50 ° C. or lower and then cooled at 40 ° C./second or higher. A method is described in which a scale is thinned by cooling at a speed and winding at 500 ° C. to 360 ° C. to obtain a hot-rolled steel sheet having excellent scale adhesion. However, in steel containing Si, when the slab is heated, a low-melting eutectic compound composed of Fe 2 SiO 4 (firelite) and FeO is formed at the interface between the base iron and the scale, and the base iron and the scale are formed. Bite into both. For this reason, scale removal with high-pressure water or the like before finish rolling cannot be performed completely, and finish rolling may occur with the scale remaining partially. As a result, a thick scale remains in this portion, so the adhesion of the scale is not good.
[0006]
The formability of the hot-rolled steel sheet is improved by sufficiently recovering the rolling strain generated by hot rolling, increasing the crystal grains, and growing pearlite and cementite. For this reason, when the hot-rolled steel sheet is wound at a high temperature, its formability is improved. In the method of lowering the coiling temperature of the steel sheet during hot rolling in order to improve the adhesion of the scale, it is difficult to improve the formability of the hot rolled steel sheet itself.
[0007]
Japanese Patent Application Laid-Open No. 59-222533 discloses a method for producing a hot-rolled steel sheet that is hot-rolled and wound at 700 to 550 ° C. and then cooled to 350 ° C. in a non-oxidizing atmosphere composed of nitrogen gas or Ar gas. Has been proposed. Furthermore, Japanese Patent Laid-Open No. 62-136529 discloses that after hot rolling, the steel sheet is cooled at a cooling rate of 20 to 40 ° C./second and wound at 550 ° C. or lower, and then in a non-oxidizing atmosphere as in the above publication. A method for producing a hot-rolled steel sheet that is cooled to ° C has been proposed. However, these methods are methods in which cooling after winding is performed in a non-oxidizing atmosphere, and equipment for shutting off the air and adjusting the atmosphere is required, so that economical efficiency and productivity are hindered.
[0008]
As described above, the conventional proposal does not disclose a method for economically producing the steel sheet with both scale adhesion, corrosion resistance, and formability.
[0009]
[Problems to be solved by the invention]
An object of this invention is to provide the manufacturing method of the hot-rolled steel plate excellent in scale adhesiveness, corrosion resistance, and formability.
[0010]
[Means for Solving the Problems]
Gist of the present invention are shown in the following (1) to (4), in the manufacturing method of the excellent hot rolled steel sheet scale adhesion and corrosion resistance.
[0011]
(1) By weight, C: 0.2% or less, Si: 0.08% or less, Mn: 0.05-2%, P: 0.01-0.06%, S: 0.015% or less , Al: 0.1 to 1%, Cu: 0.1 to 0.5% and Ni: 0.01 to 0.3%, the finish rolling of steel consisting of iron and unavoidable impurities at 1100 ° C After starting at the following and ending at 900 ° C. or less, forcibly cooling the finished steel plate within 2 seconds after finishing rolling, and rapidly cooling to at least 700 ° C. at a cooling rate of 30 ° C./second or more. Manufacturing a hot-rolled steel sheet excellent in scale adhesion and corrosion resistance, comprising a step of winding at 650 to 550 ° C. and gradually cooling between 550 and 400 ° C. at an average cooling rate of 20 ° C./hour or less. Method.
(2) as the chemical composition of steel, further, by weight%, Nb: 0.1% or less, Ti: 0.1% or less and Cr: characterized in that it contains one or more of the 1% or less (1) A method for producing a hot-rolled steel sheet having excellent scale adhesion and corrosion resistance.
(3) Hot rolling excellent in scale adhesion and corrosion resistance as described in (1) or (2) above, wherein the chemical composition of steel further contains B: 0.005% or less by weight%. A method of manufacturing a steel sheet.
(4) as the chemical composition of steel, further, by weight%, Ca: characterized by containing 0.004% or less, excellent in any of the scale adhesion and corrosion resistance of the above (1) to (3) A method for producing hot rolled steel sheets.
[0012]
The idea on which the present invention is based to solve the above problems will be described below.
[0013]
(1) Al content in steel affects scale adhesion. If finish rolling of steel with the Al content adjusted to a specific range and subsequent cooling conditions are selected and hot rolling is performed, a scale layer having excellent adhesion can be obtained. Furthermore, in steel containing both Al, Cu, P, and Ni, the corrosion resistance of the hot-rolled steel sheet is further improved.
[0014]
The present inventors heated a slab having a thickness of 240 mm made of steel containing Al at various ratios to 1220 ° C. to perform rough rolling, finish rolling was started at 1050 ° C. and ended at 860 ° C., 1 second after the finish rolling is completed, cooling is started at a cooling rate of 30 ° C./second, winding is performed at 600 ° C., and the steel sheet coil is gradually cooled between 550 and 400 ° C. at a cooling rate of 20 ° C./hour, A hot-rolled steel sheet having a thickness of 2.3 mm and a width of 1250 mm was obtained. The chemical composition of the steel is shown in Table 1.
[0015]
[Table 1]
The scale thickness, adhesion and corrosion resistance of these hot-rolled steel sheets were evaluated by the following methods.
[0017]
For the adhesion of the scale, the area ratio of the part where the scale on the outer side of the bent part was peeled was determined after a bending test piece was subjected to a 90-degree bending test in which the inner bending radius was 1.5 times the plate thickness. When the scale peeling area ratio is 2% or less, it is judged that the adhesion of the scale is good. In Table 1, the results are indicated by “◯” when the scale peeled area ratio is 2% or less, and by “X” when the ratio exceeds 2%.
[0018]
Corrosion resistance was determined by spraying a test piece having a width of 30 mm and a length of 70 mm obtained from a steel plate with the scales attached to it, spraying 5% hot water at 35 ° C. for 6 hours → holding in a room temperature atmosphere with a humidity of 95% or more for 12 hours → After 120 cycles of corrosion test with “1 hour hold in dry atmosphere at 50 ° C.” performed to remove red rust of the corroded portion found on the surface of the test piece, the maximum value of the corrosion depth in the plate thickness direction Evaluation was made by measuring with a micrometer. When the maximum corrosion depth is 1.5 mm or less, it is judged that the corrosion resistance is good. In Table 1, the results are shown as “◯” when the maximum corrosion depth is 1.5 mm or less, “△” when 1.5 mm or more and 1.8 mm or less, and “×” when 1.8 mm or less. Is displayed.
[0019]
As shown in Table 1, steels (1), (2), (4), and (5) with high Al content have good scale adhesion. On the other hand, steel (3) with a small Al content does not have good scale adhesion. Moreover, the corrosion resistance of steels {circle around (1)} and {circle around (2)} containing both Al and trace amounts of Cu, P, and Ni are much better.
[0020]
The mechanism for improving the adhesion of the scale when processing the steel sheet by containing Al is still unclear, but is presumed as follows. A composite oxide layer of Al and Fe mainly composed of FeAl 2 0 4 is formed at the interface between the scale and the ground iron, which is considered to have been formed by concentration of Al during slab heating or hot rolling. This composite oxide has the same crystal structure (spinel structure) as Fe 3 0 4, which has excellent adhesion to the ground iron. For this reason, this composite oxide layer not only has a high compatibility with the scale layer, but also has a relatively good compatibility with the ground iron, and as a result contributes to the improvement of the adhesion between the scale layer and the ground iron. It is thought that it is doing.
[0021]
Unlike steel with a high Si content, the removability of the scale before finish rolling is satisfactory without any problem even if the Al content is high. This is because the eutectic compound of FeAl 2 O 4 and FeO has a high melting point, and at a normal slab heating temperature, this composite oxide layer does not enter a molten state. For this reason, it is considered that the complex oxide layer does not bite into the scale or the iron-iron interface.
[0022]
The corrosion resistance of steel sheets is further improved by containing Al in addition to trace amounts of Cu, P, Ni, etc. The formation of dense film-like corrosion formed by containing Cu, P, Ni, etc. It is considered that the stability of the product is further increased by coexisting with a stable Al-based oxide.
[0023]
(2) FeO occupying most of the scale layer has the property of eutectoid transformation into Fe and Fe 3 O 4 at 560 ° C. or lower. Therefore, the temperature of the steel sheet is 560 ° C. or less, in the base steel matrix surface Fe and Fe 3 O 4 layer is formed.
[0024]
The composite oxide layer mainly composed of FeAl 2 O 4 that has excellent adhesion to steel does not cover the entire surface of the steel sheet substrate because the Al content is limited, so the composite oxide is partially There are also areas that are not covered with layers, i.e. areas where the adhesion of the scale has not been sufficiently improved. However, the Fe 3 O 4 layer generated by the eutectoid transformation of FeO described above covers not only the FeAl 2 O 4 composite oxide layer but also the steel sheet substrate surface on which the composite oxide layer is not formed. This further strengthens the adhesion between the scale layer and the ground iron.
[0025]
Further, during this transformation, Fe is precipitated between Fe 3 O 4 , and the Fe wedge is fixed as if Fe 3 O 4 is fixed. It is speculated that this also contributes to the improvement of the adhesion of the scale. The above eutectoid transformation of FeO is particularly promoted in the temperature range of 550 to 400 ° C. Therefore, by retaining the hot-rolled steel sheet in this temperature range, the Fe 3 O 4 layer can be uniformly formed at the interface of the steel sheet, and the adhesion of the scale can be further improved.
[0026]
Even if the coil winding temperature is increased to some extent in order to improve the formability of the hot-rolled steel sheet, the adhesion of the scale can be maintained at a good level by utilizing the above eutectoid transformation effect.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail.
[0028]
(A) Steel chemical composition C: Used to ensure the strength of the steel sheet. However, if the content exceeds 0.2%, a large amount of cementite (Fe 3 C) is generated on the surface of the steel sheet, so that not only the adhesion of the scale but also the workability and weldability of the steel sheet are impaired. Accordingly, the C content is 0.2% or less. When the formability of the steel sheet is important, the C content is preferably low, and the present invention is effective even with extremely low carbon of about 0.001%. However, since it is not economical to lower C to the extremely low carbon region, the lower limit of the C content is preferably 0.01%.
[0029]
Si: Used as a deoxidizer during steelmaking. It is also widely used as an inexpensive element that increases the strength of steel sheets. However, Si forms a low-melting eutectic compound of Fe and Si at high temperatures, causing problems such as descaling failure before hot rolling and poor adhesion of scale when forming and processing a steel sheet. For this reason, Si content is so preferable that it is low, and makes 0.08% an upper limit. Preferably it is 0.04% or less. In addition, Si may not be used in applications where the formability is more important than the strength of the steel sheet.
[0030]
Mn: While securing the strength of the steel sheet, S present as an impurity in the steel is fixed as MnS, and has the effect of suppressing cracks that may occur during hot rolling. When the Mn content is less than 0.05%, the effect of suppressing cracking cannot be obtained. On the other hand, the content exceeding 2% saturates the action and deteriorates the adhesion of the scale. For this reason, content of Mn shall be 0.05-2%.
[0031]
P: Although it has the effect | action which produces | generates a dense corrosion film and improves corrosion resistance, when the content of P is less than 0.01%, the effect is inadequate. On the other hand, if the content exceeds 0.06%, the adhesion of the scale deteriorates. For this reason, the P content is set to 0.01 to 0.06%.
[0032]
Al: Conventionally, it is mainly used as a deoxidizer during steelmaking, and the effect is sufficiently exhibited in an amount of less than 0.1%. However, Al is the most important element in the present invention for improving the adhesion of the scale of the hot-rolled steel sheet. That is, in steel containing a large amount of Al, during slab heating or during hot rolling, Al dissolved in the steel is concentrated at the interface between the scale and the steel surface, and a composite oxide of Fe and Al A layer is formed. This improves the adhesion of the scale. Since the effect is weak when the Al content is less than 0.1%, the lower limit of the Al content is set to 0.1%. On the other hand, as the Al content increases, the effect of improving the adhesion is saturated and the economy is impaired. For this reason, the upper limit is made 1%.
[0033]
Cu: A main component for improving the corrosion resistance. In steel containing Cu, a dense corrosion film is formed on the surface of the steel and the corrosion resistance is improved. When the Cu content is less than 0.1%, the effect of improving the corrosion resistance by the above action cannot be obtained. On the other hand, even if Cu is contained exceeding 0.5%, not only the corrosion resistance improving effect is saturated but also the scale adhesion is deteriorated. For this reason, Cu content shall be 0.1-0.5%.
[0034]
Ni: In addition to the effect of suppressing the hot workability of steel that may occur with the addition of Cu, it also has the effect of improving corrosion resistance. In order to obtain these effects, it is necessary to contain 0.01 or more of Ni. On the other hand, even if Ni is contained in an amount exceeding 0.3%, the above-described action is saturated and economical efficiency is also impaired. For this reason, the Ni content is set to 0.01 to 0.3%.
[0035]
The hot-rolled steel sheet intended by the present invention is basically composed of the above-described elements and Fe. However, when the strength and formability of the steel sheet are required, the elements described below are contained. May be.
[0036]
When a high-strength hot-rolled steel sheet is required, one or more of Nb, Ti, V, Cr, and Mo may be contained. Nb, Ti and V are precipitated as carbonitrides on the ferrite ground of the steel to increase the strength of the steel sheet, but the effect is weak at less than 0.005%. For this reason, when these elements are contained, the content is preferably 0.005% or more in any case. Even if contained excessively, the effect is saturated and the economic efficiency is impaired. Therefore, the upper limit is preferably 0.1% for Nb and Ti, and 0.2% for V.
[0037]
Cr and Mo increase the strength through transformation strengthening, but the effect is weak at less than 0.01%. For this reason, when these elements are contained, the content is preferably 0.01% or more for any element. Cr is 1%, and Mo is 0.5% is the upper limit of the content in which each element contributes effectively to the strength. For this reason, the upper limit of the content of these elements is preferably 1% for Cr and 0.5% for Mo.
[0038]
When a hot-rolled steel sheet with better formability is required, it is desirable to contain B. B can be expected to have the effect of lowering the yield strength of the steel sheet and improving workability by lowering the Ar3 transformation point of the steel. In order to exhibit the effect, it is preferable to contain 0.001% or more. If it exceeds 0.005%, the effect of improving formability is saturated. Therefore, the upper limit of B is preferably 0.005%.
[0039]
When a hot-rolled steel sheet with better bendability is required, Ca, Zr or a rare earth element is preferably contained for the purpose of controlling the form of inclusions. In order to obtain the effect of improving bendability, it is preferable to contain 0.0002% or more for Ca, 0.01% or more for Zr, and 0.002% or more for rare earth elements. On the other hand, when Ca is contained in an amount of 0.004%, Zr is 0.05%, and rare earth elements are contained in excess of 0.05%, the inclusions in the steel increase and the workability is increased. to degrade. For this reason, the upper limit of the content of these elements is 0.004% for Ca, 0.05% for Zr, and 0.05% for rare earth elements. In order to control the form of inclusions, any one of these elements may be contained, but two or more kinds may be contained in combination.
[0040]
Other than the above components are Fe and inevitable impurities. S as an unavoidable impurity may be concentrated on the surface of the steel during slab heating before hot rolling and during hot rolling to impair the adhesion of the scale. If the S content is 0.015% or less, there is little adverse effect on the scale adhesion. For this reason, S is preferably 0.015% or less.
[0041]
(B) Manufacturing conditions for hot-rolled steel sheet In the present invention, a slab made of steel having the composition described in (A) above is hot-rolled. By specifying the cooling conditions at that time, the formability of the steel sheet and the adhesion of the scale are further improved. Finish rolling at the time of hot rolling starts at 1100 ° C. or less, ends at 900 ° C. or less, starts cooling with water injection within 2 seconds after finishing rolling, and at a cooling rate of 30 ° C./second or more until at least 700 ° C. Quickly cool and wind up at 550 ° C or lower.
[0042]
Slab heating before finish rolling may be performed, or this may be omitted and rough rolling may be performed. Further, when the slab is thin, rough rolling may be omitted. Usually, the scale is removed with high-pressure water or the like before rough rolling and finish rolling. When finish rolling is performed without sufficiently removing the scale, the remaining scale is pushed into the steel plate by rolling, and remains on the steel plate surface as a biting scale. For this reason, the scale of this part after completion | finish of hot rolling becomes thick. In order to produce a hot-rolled steel sheet having excellent scale adhesion, it is necessary to sufficiently remove the scale before finish rolling.
[0043]
The hot deformation resistance of steel becomes lower as the temperature is higher, and the material properties of the steel sheet are preferably higher at the finish rolling temperature. Therefore, it is desirable that the finish rolling temperature is higher. However, since it is expensive to raise the heating temperature of the slab, the finish rolling start temperature is usually 1150 ° C. or lower and the finish rolling end temperature is 950 ° C. or lower. On the other hand, the scale grows exponentially fast as the temperature of the steel increases, and tends to peel off as its thickness increases. For this reason, in order to improve the adhesion of the scale, it is preferable to shorten the time during which the steel sheet is exposed to a high temperature as much as possible.
[0044]
From these viewpoints, in the present invention, finish rolling starts at 1100 ° C. or lower and ends at 900 ° C. or lower. The finishing temperature of finish rolling is preferably 860 ° C. or lower. The lower limit of the temperature at the start and end of finish rolling is preferably 900 ° C. and 750 ° C., respectively. From the viewpoint of improving the adhesion of the scale, it is preferable that the finishing temperature is low. However, if the finishing temperature is further reduced, the load on the rolling mill becomes excessive and rolling becomes difficult.
[0045]
Furthermore, in the present invention, cooling is started within 2 seconds after finishing rolling, and cooling is performed at a cooling rate of 30 ° C./second or more up to at least 700 ° C. Cooling is preferably started within 1 second. The cooling method may be a conventional spray cooling method using cooling water or a laminar flow cooling method, but it is desirable to use further cooling promoting means such as jetting high-pressure water.
[0046]
After cooling to 700 ° C, it is wound up at 650-550 ° C. In order to improve the formability of the steel sheet itself, it is preferable to wind at a high temperature. However, if the winding temperature exceeds 650 ° C., the scale becomes thick and the adhesiveness decreases. On the other hand, when the coiling temperature is less than 550 ° C., the formability of the steel sheet itself is impaired, and the effect of improving the adhesion of the scale cannot be sufficiently obtained for the reasons described below.
[0047]
The coil after winding is cooled by setting the average cooling rate in the temperature range of 550 to 400 ° C. to 20 ° C./hour or less. Below 560 ° C., the eutectoid transformation shown by the reaction formula of 4FeO → Fe 3 O 4 + Fe occurs. By setting the average cooling rate in the temperature range of 550 to 400 ° C. to 20 ° C./hour or less, sufficiently progressing the above eutectoid transformation, and making the scale of the steel sheet substrate surface mainly composed of Fe 3 O 4 , Further improve the adhesion of the scale. When the coiling temperature is less than 550 ° C. or the coil cooling rate after winding is over 20 ° C./hour, the 4FeO → Fe 3 O 4 + Fe eutectoid transformation does not proceed sufficiently and the scale adhesion decreases. . On the other hand, when the coiling temperature exceeds 650 ° C., the amount of scale generated increases and the scale adhesion deteriorates.
[0048]
The coil cooling rate after winding may be appropriately determined by using a method of closely storing a coil in a high temperature state wound immediately after hot rolling or adjusting it using a heat dissipation prevention device such as a heat insulating cover. .
[0049]
【Example】
Table 2 shows the chemical composition of the steel used in the test.
[0050]
[Table 2]
Steels A to M are steels in the chemical composition range defined by the present invention, and steels N to W are out of the chemical composition range defined by the present invention, selected as a comparative example. A 240 mm-thick slab of steel having the above chemical composition was heated to 1220 ° C., roughly rolled, finish-rolled, cooled by pouring water, wound and cooled to obtain a steel plate having a thickness of 2.3 mm. The coil cooling rate after winding was appropriately adjusted using a heat insulating cover. The mechanical properties, scale adhesion and corrosion resistance of these steel plates were evaluated by the methods described below.
[0052]
The tensile test was evaluated using the No. 5 test piece prescribed | regulated to JIS-Z-2201. The bending test was performed by taking a test piece having a width of 50 mm and a length of 120 mm and by a method defined in JIS-Z-2248 at a bending radius of 1.5 times the plate thickness and a bending angle of 90 degrees. After removing the floating scale by applying an adhesive tape to the outside of the bending part of this bending test piece, take an enlarged photo of the outside of the bending part and measure the area ratio of the part where the scale is peeled off. The case where the area ratio was 2% or less was considered good. In Table 3, “○” indicates that the scale peeled area ratio is 2% or less, and “×” indicates that the ratio exceeds 2%.
[0053]
For corrosion resistance, a test piece having a width of 30 mm and a length of 70 mm was cut out from the steel sheet, and “salt spray (5% saline, 35 ° C. × 6 hours hold) → wet hold (humidity: 95% or more, temperature: room temperature for 12 hours) Holding) → Drying (50 ° C x 6 hours holding) "is performed as a cycle, and the maximum corrosion depth on the surface of the test piece after 120 cycles is measured with a micrometer. The following cases were considered good. In Table 3, “◯” indicates that the maximum corrosion depth of each test piece is 1.5 mm or less, “Δ” indicates that the maximum corrosion depth is 1.5 mm or more and 1.8 mm or less, and “×” indicates that the test piece exceeds 1.8 mm. Is displayed.
[0054]
Table 3 also shows hot rolling conditions and various performance evaluation results.
[0055]
[Table 3]
As shown in Table 3, the steel sheet produced within the range defined by the present invention was excellent in scale adhesion and corrosion resistance. Moreover, the value of TS × El was in the range of 1690 or more, and good ductility corresponding to the strength was obtained.
[0057]
On the other hand, the test numbers 14 and 15 using steels N and O whose Al content is less than that of the present invention did not have good scale adhesion and corrosion resistance. In trial numbers 16 to 19 using steels P, Q, R, and S in which the content of any element of Si, P, S, and Mn is outside the range defined by the present invention, the scale adhesion is low. It was not good. Corrosion resistance was not good in test numbers 20 to 22 using steels T, U, and V in which any one of Cu, P, and Ni deviated from the range defined by the present invention. In Sample No. 23 using steel W in which both Al and Cu contents were out of the range defined by the present invention, both the scale adhesion and the corrosion resistance were not good. Even in the case of trial numbers 24 to 28 and 30 where the manufacturing conditions deviated from the range defined by the present invention, the scale adhesion was lowered.
[0058]
Further, in the trial number 29 in which the coiling temperature was lower than the range specified by the present invention, the scale adhesion and the corrosion resistance were good, but the TS × El value was low, and good ductility corresponding to the strength was obtained. I couldn't.
[0059]
【The invention's effect】
By the method of the present invention, a hot-rolled steel sheet can be produced that does not peel off even if it is formed with the scale attached, has good formability of the steel sheet itself, and has excellent corrosion resistance. Since the method of the present invention is a method of combining a specific chemical composition and production conditions, it can be carried out easily and economically. The steel plate according to the method of the present invention is excellent in corrosion resistance and also excellent in workability because the frequency of care of the press die due to scale peeling during processing is reduced.
Claims (4)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP19973997A JP3941173B2 (en) | 1997-07-25 | 1997-07-25 | Manufacturing method of hot-rolled steel sheet with excellent scale adhesion and corrosion resistance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP19973997A JP3941173B2 (en) | 1997-07-25 | 1997-07-25 | Manufacturing method of hot-rolled steel sheet with excellent scale adhesion and corrosion resistance |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH1143724A JPH1143724A (en) | 1999-02-16 |
| JP3941173B2 true JP3941173B2 (en) | 2007-07-04 |
Family
ID=16412832
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP19973997A Expired - Fee Related JP3941173B2 (en) | 1997-07-25 | 1997-07-25 | Manufacturing method of hot-rolled steel sheet with excellent scale adhesion and corrosion resistance |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3941173B2 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100419080B1 (en) * | 1999-09-28 | 2004-02-18 | 제이에프이 엔지니어링 가부시키가이샤 | Hot-rolled steel sheet having high tensile strength and method for production thereof |
| DE102013004905A1 (en) * | 2012-03-23 | 2013-09-26 | Salzgitter Flachstahl Gmbh | Zunderarmer tempered steel and process for producing a low-dispersion component of this steel |
| JP5799913B2 (en) * | 2012-08-02 | 2015-10-28 | 新日鐵住金株式会社 | Hot rolled steel sheet with excellent scale adhesion and method for producing the same |
| WO2020065372A1 (en) * | 2018-09-25 | 2020-04-02 | Arcelormittal | High strength hot rolled steel having excellent scale adhesivness and a method of manufacturing the same |
| CN115382906A (en) * | 2022-08-25 | 2022-11-25 | 湖南华菱湘潭钢铁有限公司 | Production method of atmospheric corrosion resistant steel plate |
-
1997
- 1997-07-25 JP JP19973997A patent/JP3941173B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH1143724A (en) | 1999-02-16 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP2005528519A5 (en) | ||
| KR20010023573A (en) | High strength thin steel sheet, high strength galvannealed steel sheet and manufacturing method thereof | |
| JP3610883B2 (en) | Method for producing high-tensile steel sheet with excellent bendability | |
| JP2576894B2 (en) | Hot-dip galvanized high-tensile cold-rolled steel sheet excellent in press formability and method for producing the same | |
| JP3941173B2 (en) | Manufacturing method of hot-rolled steel sheet with excellent scale adhesion and corrosion resistance | |
| JP3322157B2 (en) | Method for producing ferritic stainless steel strip containing Cu | |
| JP2003155541A (en) | High strength hot rolled steel sheet having excellent corrosion resistance and stretch-flanging property, and production method therefor | |
| JP5051886B2 (en) | Method for producing cold-rolled steel sheet and plated steel sheet | |
| JPS6235463B2 (en) | ||
| JPH1036939A (en) | Hot rolled steel and production of hot rolled steel sheet | |
| JPH1081919A (en) | Production of steel sheet for two-piece can, excellent in non-earing characteristic and surface roughing resistance | |
| JP3347152B2 (en) | Method for producing cold-rolled high-strength hot-dip galvanized steel sheet with excellent resistance to pitting corrosion | |
| JPS6115929B2 (en) | ||
| JP2812770B2 (en) | Manufacturing method of alloyed hot-dip galvanized cold-rolled steel sheet for deep drawing with excellent bake hardenability and powdering resistance | |
| JP3842897B2 (en) | Manufacturing method of high workability hot-rolled high-tensile steel sheet with excellent shape freezing property | |
| JPH0466653A (en) | Manufacture of hot-dip galvanized steel sheet for high working excellent in surface property | |
| JPS6249323B2 (en) | ||
| JP2660640B2 (en) | Manufacturing method of alloyed hot-dip galvanized cold-rolled steel sheet for deep drawing with excellent bake hardenability and powdering resistance | |
| JPH0234793A (en) | Production of high-strength hot-rolled steel sheet to be worked having excellent scale adhesion | |
| JPH10212560A (en) | Hot rolled steel sheet excellent in scale adhesion and corrosion resistance and its production | |
| JP2689810B2 (en) | Method for manufacturing high strength hot rolled steel sheet with excellent surface properties | |
| JPH05230543A (en) | Production of high strength cold rolled steel sheet excellent in baking hardenability and deep drawability | |
| JP3257715B2 (en) | Method for producing high-strength galvannealed steel sheet for high working with excellent plating adhesion | |
| JP3016333B2 (en) | Cold drawn steel sheet for deep drawing excellent in corrosion resistance and method for producing the same | |
| JP2660639B2 (en) | Manufacturing method of galvannealed cold-rolled steel sheet with excellent deep drawability |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20040623 |
|
| RD02 | Notification of acceptance of power of attorney |
Free format text: JAPANESE INTERMEDIATE CODE: A7422 Effective date: 20040625 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20050524 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20060718 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20060907 |
|
| A02 | Decision of refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A02 Effective date: 20061212 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20070125 |
|
| A911 | Transfer of reconsideration by examiner before appeal (zenchi) |
Free format text: JAPANESE INTERMEDIATE CODE: A911 Effective date: 20070214 |
|
| TRDD | Decision of grant or rejection written | ||
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 Effective date: 20070313 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20070326 |
|
| R150 | Certificate of patent or registration of utility model |
Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20110413 Year of fee payment: 4 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120413 Year of fee payment: 5 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120413 Year of fee payment: 5 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130413 Year of fee payment: 6 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130413 Year of fee payment: 6 |
|
| S111 | Request for change of ownership or part of ownership |
Free format text: JAPANESE INTERMEDIATE CODE: R313111 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130413 Year of fee payment: 6 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20140413 Year of fee payment: 7 |
|
| LAPS | Cancellation because of no payment of annual fees |