JP4534362B2 - Hot-rolled high-tensile steel plate with excellent chemical conversion and corrosion resistance and method for producing the same - Google Patents
Hot-rolled high-tensile steel plate with excellent chemical conversion and corrosion resistance and method for producing the same Download PDFInfo
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Description
【0001】
【発明の属する技術分野】
本発明は、プレス加工により製造される自動車の足回り部品やホイールディスクなどの使途に供して好適な、引張強度が 590〜980 MPa レベルで、延性、伸びフランジ性などの成形性および表面性状に優れ、さらには化成処理性および耐食性にも優れる熱延高張力鋼板およびその製造方法に関するものである。
【0002】
【従来の技術】
熱延鋼板は、一般に、連続鋳造した鋳片をそのまま、あるいはその後1200℃以上の温度に加熱してから、粗圧延および仕上圧延の2段階の熱間圧延によって製造される。
特に引張強度が 590〜980 MPa レベルの高張力鋼板は、強度確保のため、Siを 0.5〜2.5 mass%程度含有する鋼を用いる。この場合、熱間圧延中にSiの酸化スケールが鋼表面を覆うため、これが製品にSiスケール疵を残す原因となる。
このため、通常、粗圧延および仕上圧延の圧延前には高圧水を用いたデスケーリングが行なわれるが、このデスケーリングが不十分でスケールの取れ残りがあると、圧延時にスケールが噛み込まれてスケール疵となる。このスケール疵は、外観を損ねるだけでなく、たとえ酸洗でスケールを完全に除去したとしても表面に凹凸が残るため、疲労特性など表面の切り欠き状欠陥に影響を受ける特性値は低下する。
【0003】
また、自動車の足回り部品やホイールディスクは、耐食性の観点から化成処理が施されるが、表面に凹凸が残存していると化成処理皮膜の生成が均一でなくなるため、化成処理後に外観不良が生じたり、化成処理後の耐食性が低下する。
このようなスケール残りや表面の凹凸は、特にSiを多量に添加した高張力鋼板の製造時に顕著に現れる。
【0004】
そこで、このようなスケール残りに起因した障害を軽減するため、例えば特公昭60−1085号公報には、Siを0.10〜4.00mass%含有する鋼スラブを熱間圧延するに際し、鋳片温度が1000℃以上の時に、吐出圧:8〜25 MPaの高圧水ジェットによるデスケーリングを累積時間にして0.04秒以上施す技術が開示されている。
また、特開平4−238620号公報には、難剥離性スケール鋼種を熱間圧延するに際し、仕上圧延前に、単位散布面積当たりの衝突圧が 0.2 MPa以上、0.4 MPa 以下で、かつ流量が 0.1リットル/(min・mm2)以上、0.2 リットル/(min・mm2)以下の高水圧スプレーを鋼板表面に噴射する技術が開示されている。
さらに、特開平7−70649 号には、仕上ミル入側での温度をSi量に応じて制御し、単位面積当たりの衝突圧が 5.0〜30.0 kgf/mm2(49〜294 MPa)の高水圧でデスケーリングを行う技術が開示されている。
【0005】
【発明が解決しようとする課題】
しかしながら、上記特公昭60−1085号公報に開示の技術では、1000℃以上という高温の仕上圧延入側温度(FET)を確保する必要があるため、加熱炉から高温で鋼片を抽出しなければならず、原単位が悪化したり、スケールロスが増加するという問題があった。加えて、圧下率やデスケーリングの時間に種々の制約が加わるため、圧延作業が煩雑になるという問題もあった。
また、上記特開平4−238620号公報に開示の技術では、大部分のスケールは剥離されるものの、高Si鋼で形成される地金に食い込むようなスケールは除去されずに残る場合があり、スケール疵を完全には回避することは難しいという問題があった。
さらに、上記特開平7−70649 号公報に開示の技術では、仕上圧延の入側温度(FET)をSi量に応じて制御する必要があるため、圧延作業が煩雑になるだけでなく、この方法によって添加可能となるSi量の上限は1.0 mass%程度であり、Siをより多く含有する高Si含有鋼には適用できないという問題があった。
【0006】
また、これらの従来技術によって、0.5 mass%以上のSiを含有する鋼板を製造した場合、鋼板表面の平均粗さがせいぜい2μm 程度のものしか得られず、満足いくほどの疲労特性や化成処理性を得ることかできないという問題もあった。
さらに、仕上圧延の入側で高圧水によるデスケーリングを施す方法は、水の散布角度や水温の管理が難しく、季節要因による変動が大きいことや、鋼板の幅中央とエッジ付近では高圧水による冷却速度が異なるため、材料特性のバラツキが生じることも問題となっていた。
【0007】
本発明は、上記の実状に鑑み開発されたもので、Siを 0.5mass%以上含有する鋼板であっても、スケール疵の発生を効果的に防止すると共に、鋼板の表面粗さを低減し、ひいては優れた化成処理および耐食性が得られる熱延高張力鋼板を、その有利な製造方法と共に提案することを目的とする。
【0008】
【課題を解決するための手段】
さて、発明者らは、上記の目的を達成すべく鋭意研究を重ねた結果、鋼板の結晶粒を微細化すれば、特にデスケーリングを施さなくても、スケール残りやスケール疵の発生が効果的に抑制され、その結果、表面性状ひいては化成処理および耐食性が著しく改善されることの知見を得た。
本発明は、上記の知見に立脚するものである。
【0009】
すなわち、本発明の要旨構成は次のとおりである。
1.C:0.01〜0.20mass%、
Si:0.5 〜2.5 mass%、
Mn:1.0 〜3.0 mass%、
P:0.05mass%以下、
Al:0.01〜0.1 mass%、
S:0.005 mass%以下および
Ti:0.05〜0.35mass%
を、Ti(mass%)とC(mass%)とが次式
−1.4 ≧ log(Ti×C)≧−1.8
を満足する範囲において含有し、残部はFeおよび不可避的不純物の組成になり、平均結晶粒径が 3.0μm 以下で、かつ表面粗さが算術平均粗さRaで 1.5μm 以下であることを特徴とする化成処理性および耐食性に優れる熱延高張力鋼板。
【0010】
2.上記1において、鋼組織が、フェライト、パーライト、ベイナイト、マルテンサイトおよび残留オーステナイトのうちから選んだ2種類以上の複合組織であることを特徴とする化成処理性および耐食性に優れる熱延高張力鋼板。
【0011】
3.C:0.01〜0.20mass%、
Si:0.5 〜2.5 mass%、
Mn:1.0 〜3.0 mass%、
P:0.05mass%以下、
Al:0.01〜0.1 mass%、
S:0.005 mass%以下および
Ti:0.05〜0.35mass%
を、Ti(mass%)とC(mass%)とが次式
−1.4 ≧ log(Ti×C)≧−1.8
を満足する範囲において含有し、残部はFeおよび不可避的不純物の組成になる鋼スラブを、1150℃以下に加熱し、粗圧延後、1050℃以下で仕上圧延を開始し、仕上圧延第1スタンドでの圧延速度を 400 m/min以上、圧下率を80%以上とし、仕上圧延の最終圧下を表面粗さ(Ra)が3μm 以下の圧延ロールで行い、(Ar3+150 ℃)〜(Ar3+50℃) で仕上圧延を終了し、ついで20℃/s以上の冷却速度で600 ℃以下まで冷却後、 600〜350 ℃の温度範囲で巻き取ることを特徴とする化成処理性および耐食性に優れる熱延高張力鋼板の製造方法。
【0012】
【発明の実施の形態】
以下、本発明を具体的に説明する。
まず、本発明において鋼の成分組成を上記の範囲に限定した理由について説明する。
C:0.01〜0.20mass%
Cは、安価な強化成分であり、所望の鋼板強度に応じて必要量を含有させる。しかしながら、含有量が0.01mass%に満たないと結晶粒が粗大化し、本発明で目標とする平均結晶粒径: 3.0μm 以下を達成できなくなり、一方0.20mass%を超えると加工性が低下するだけでなく、溶接性も低下するので、Cは0.01〜0.20mass%の範囲に限定した。より好ましくは0.05〜0.15mass%の範囲である。
【0013】
−1.4 ≧ log(Ti×C)≧−1.8
但し、このCは、後述するTiとの関連において、次式の関係
−1.4 ≧ log(Ti×C)≧−1.8
を満足しないと、スラブ加熱時におけるオーステナイト粒径が微細とならず、その後の粗圧延、仕上圧延による結晶粒の微細化が促進されないため、最終的に3.0 μm 以下の結晶粒径を得ることができず、化成処理性および耐食性の向上が期待できない。従って、Cは、Tiとの関連で、上掲式を満足する範囲で含有させることが重要である。なお、式中のC、Tiはmass%表示した値である。
【0014】
Si:0.5 〜2.5 mass%
Siは、固溶強化成分として強度−伸びバランスを改善しつつ、強度の上昇に有効に寄与する。この効果は、Si量が 0.5mass%以上で発現するが、過剰な添加は、その効果が飽和するだけでなく、むしろ延性や表面性状を劣化を招くので、Siは 0.5〜2.5 mass%の範囲に限定した。好ましくは 1.0〜2.0 mass%の範囲である。
【0015】
Mn:1.0 〜3.0 mass%
Mnは、Ar3変態点を低下させる作用を通じて結晶粒の微細化に寄与し、また、第2相のマルテンサイト化および残留オーステナイト化を進展させる作用を通じて、強度−延性バランスおよび強度−疲労強度バランスを高める効果がある。さらに、Mnは有害な固溶SをMnSとして無害化する作用も有する。これらの効果は1.0 mass%以上の添加で発現するが、多量の添加は鋼を硬質化し、かえって強度−延性バランスを劣化させる。従って、Mn量は 1.0〜3.0 mass%好ましくは1.0〜2.0 mass%の範囲に限定した。
【0016】
P:0.05mass%以下
Pは、強化成分として有用であり、所望の鋼板強度に応じて添加するが、過剰に添加すると粒界に偏析して脆化の原因となり、また溶接性を低下させる。従って、Pは0.05mass%以下で含有させるものとした。好ましくは 0.001〜0.03mass%である。
【0017】
Al:0.01〜0.10mass%
Alは、脱酸等の目的で添加する。この目的のためには0.01mass%以上の添加が必要であるが、0.10mass%を超えて添加してもコストアップになるばかりか、表面欠陥の原因ともなるので、Alは0.01〜0.10mass%好ましくは0.02〜0.07mass%の範囲で添加することが好ましい。
【0018】
S:0.005 mass%以下
Sは、鋼中のMnと反応してA系介在物(JIS G 0555に記載のように加工によって粘性変形したもの(硫化物など))を生成し、伸びフランジ性や疲労強度を低下させる有害な元素である。従って、Sは 0.005 mass %以下、より好ましくは0.002 mass%以下に制限した。
【0019】
Ti:0.05〜0.35mass%
Tiは、TiCとして存在して、スラブ加熱段階でのオーステナイト粒を微細化するのに有効に作用する。このような作用を発揮させるためには、少なくとも0.05mass%の含有が必要であるが、0.35mass%を超えると、効果が飽和し含有量に見合う効果が期待できない。従って、Tiは0.05〜0.35mass%の範囲に限定した。より好ましくは0.10〜0.25mass%である。
【0020】
以上、鋼板の成分組成範囲について説明したが、本発明では、鋼の平均結晶粒径および表面粗さを所定の範囲に制限することが重要である。
(1) 平均結晶粒径≦3.0 μm
化成処理時にはリン酸塩溶液への浸漬時に表面が電解により活性化するが、その際、粒界は選択的にエッチングされ、粒界が化成処理皮膜の基となって化成処理性が向上する。そのためには、結晶粒界が多いほどすなわち結晶粒径が小さいほど有利である。また、微細粒とすることにより、強度−延性バランス、強度−穴拡げバランスも良好となる。従って、本発明では、鋼板の全厚にわたる平均結晶粒径を 3.0μm 以下に制限したのである。
【0021】
(2) 表面粗さ(Ra)≦ 1.5μm 以下
表面粗さを算術平均粗さRaで 1.5μm 以下とするのは、表面粗さが 1.5μm より大きくなると、耐食性や化成処理性が低下するためである。なお、表面粗さを 0.5μm 未満としても格段に化成処理性や耐食性が向上せず、また0.5 μm 未満に管理することは実機において困難な場合があるため表面粗さ(Ra)は 0.5μm 以上とすることが好ましい。
ここに、かような鋼板表面粗さは、結晶粒径と仕上圧延機のロール粗度により調整される。よって、鋼板表面粗度を本発明の範囲内に調整するためには、仕上圧延機のロール粗度を3μm 以下に管理することが必要である。
なお、この熱延板の表面粗さについては、従来特に考慮が払われてなく、一般的な表面粗さは2〜5μm 程度であった。
【0022】
図1に、鋼板の平均結晶粒径と表面粗さが化成処理性に及ぼす影響について調べた結果を示す。
同図に示したとおり、平均結晶粒径が 3.0μm 以下で、かつ表面粗さ(Ra)が 1.5μm 以下の場合に良好な化成処理性が得られている。
【0023】
上記したように、結晶粒を微細化することにより化成処理性が向上し、ひいては耐食性が向上するメカニズムについて、その詳細は不明であるが、次のとおりと考えられる。
一般に、結晶粒界には析出物や介在物などが集積し易いため、錆などの起点となり易い。しかしながら、結晶粒の微細化により結晶粒界が増加すると、粒界面積当たりの不純物濃度が低下するため、相対的に錆の発生が抑制されることが、理由の1つとして考えられる。
また、かような結晶粒の微細化によって、脱スケール性が大幅に改善される。その理由は、明確に解明されたわけではないが、次のように考えている。
脱スケールは通常、塩酸溶液に浸漬し行われる。その際、結晶粒界はエッチングされ易いため、結晶粒が微細化され結晶粒界面積が増加することにより、表面スケールの剥離を容易にするものと考えられる。
【0024】
さらに、本発明では、鋼組織は、フェライト、パーライト、ベイナイト、マルテンサイトおよび残留オーステナイトのうちから選んだ2種類以上の複合組織とすることが好ましい。
というのは、かような複合組織は、伸び−穴拡げバランスに優れ、また疲労特性にも優れており、熱延高張力鋼板として必要な材料特性をバランスよく備えた組織だからである。
【0025】
次に、本発明の製造条件について説明する。
(1) 熱延前における鋼スラブの加熱温度:1150℃以下
熱延前の加熱温度は、粗圧延、仕上圧延後の結晶粒径に大きな影響を与えるため重要である。本発明では、加熱時にTiCを定量析出させ、微細なTiCにより結晶粒の成長を抑制することが必要である。
図2に、加熱温度およびTi, C量(mass%)と、得られる熱延板の粒径との関係について調べた結果を示す。なお、Ti, C量(mass%)については log(Ti×C)で示すものとする。ここに、同図の実験に供した鋼の組成は、Si:1.4 mass%, Mn:1.8 mass%, P:0.02mass%, S:0.001 mass%およびAl:0.05mass%を基本組成として含有し、CとTiをそれぞれC:0.01〜0.2 mass%, Ti:0.05〜0.35mass%の範囲で種々に変化させた鋼であり、かかる組成になる鋼スラブ(厚さ:260 mm)を、スラブ加熱温度:1000〜1300℃、圧延終了温度:900 ℃、仕上板厚:3.0mm 、巻取り温度:450 ℃の条件で製造したものである。
同図に示したとおり、平均結晶粒径を 3.0μm 以下とするにはTiとC量との関係において、加熱温度を1150℃以下とする必要があることが分かる。
なお、得られる鋼スラブが、上記したような再加熱材ではなく、連続鋳造後直ちに熱間粗圧延に供されるいわゆる直送圧延材である場合には、かようなスラブ加熱は必ずしも行う必要はなく、そのまま熱間粗圧延に供しても良い。
【0026】
(2) 仕上圧延開始温度:1050℃以下
粗圧延後、仕上圧延前には、通常、吐出圧:約5〜20 MPa程度のデスケーリングが行われる。本発明では特に仕上圧延前のデスケーリングを高圧水で行なう必要はなく、上記のような通常の条件たとえば吐出圧:5〜20 MPa程度のデスケーリングでよい。
ここに、仕上圧延における圧延開始温度を1050℃以下としたのは、次の理由による。
仕上圧延開始温度が1050℃よりも高いと、圧延により導入された歪が回復し、粒が成長粗大化して、最終的に 3.0μm 以下の結晶粒を得ることが困難となり、また厚いスケールが生成し、それが圧延時に鋼板の内部へ入り込み、かみ込みスケールとなって表面性状を劣化させる。
【0027】
(3) 仕上圧延第1スタンドにおける圧延速度≧400 m/min 、圧下率≧80%
仕上圧延時における圧延速度および圧下率は、フェライト粒径を 3.0μm 以下にする上で重要である。特に仕上圧延第1スタンドにおける圧延速度が 400 m/minを下回る遅い圧延速度となると、仕上圧延でのスタンド間(通常7スタンド)での滞留時間が長くなるため圧延による導入された結晶粒への歪みが回復し、また粒成長が促進されるため、圧延中に結晶粒が粗大化し、微細なγ粒を得ることができなくなる。
また、この第1スタンドにおける圧下率が80%より小さいと、粒への歪みが小さく、オーステナイト粒を微細にすることができない。
【0028】
図3に、仕上圧延第1スタンドにおける圧延速度および圧下率と熱延板の結晶粒径との関係について調べた結果を示す。
ここに、同図の実験に供した鋼の組成は、C:0.09mass%,Si:1.4 mass%,Mn:1.8 mass%,P:0.02mass%,S:0.001 mass%,Al:0.05mass%およびTi:0.18mass%を含有し、残部は実質的にFeの組成になる鋼であり、かかる組成の鋼スラブ(厚さ:260 mm)を、スラブ加熱温度:1050℃、圧延終了温度:900 ℃、仕上板厚:3.0 mm、巻取り温度:450 ℃の条件で製造したものである。
なお、仕上圧延第1スタンドにおける圧延速度は 100〜800 m/min 、圧下率は70, 80, 90%とした。
同図より明らかなように、仕上圧延第1スタンドにおける圧延速度を 400 m/min以上、圧下率を80%以上とすることによって、平均結晶粒径を 3.0μm 以下とすることができた。
【0029】
(4) 仕上圧延終了温度:(Ar3+150 ℃)〜(Ar3+50℃)
仕上圧延終了温度が(Ar3+50℃) 未満では、表層部のフェライト粒が粗大となり、一方(Ar3+150 ℃)を超えると、鋼板全体の組織が粗大化して、伸びや穴拡げ性などの加工性が低下するためである。
なお、仕上圧延の最終圧下は、前述したように鋼板の表面粗さ(Ra)を 1.5μm以下とするため、表面粗さ(Ra)が3μm 以下の圧延ロールで行う必要がある。
【0030】
(5) 仕上圧延終了後、巻取りまでの冷却速度:20℃/s以上
仕上圧延終了後の冷却速度は20℃/s以上とする必要である。というのは、圧延終了後の冷却速度が20℃/sより遅い場合には、圧延終了時に微細化しているオーステナイト組織が冷却中に粗大化し、変態後得られる製品板の組織が粗大化して、本発明で所望する 3.0μm 以下の組織が得られなくなるからである。
【0031】
(6) 巻取り温度:600 〜350 ℃
巻取り温度を 600〜350 ℃としたのは、巻取り温度が 600℃を超えると粗大なセメンタイトが生成して、強度−延性バランスが低下し、一方 350℃未満ではコイル全体での温度制御が困難となり、均一な材料特性を得ることができなくなるからである。
上記の巻取り後、通常の酸洗を施して製品とする。
【0032】
【実施例】
表1に示す成分組成になる鋼スラブを、表2に示す種々の条件で処理し、板厚:3.0 mmの熱延鋼板とした。
得られた熱延鋼板を酸洗後、平均結晶粒径、表面粗さおよび金属組織を調査した。また、これら熱延鋼板の機械的特性を調査した。さらに、化成処理性および耐食性についても調査した。
これらの結果を表3に示す。
【0033】
なお、熱延鋼板の結晶粒径は、板厚断面を(2%硝酸+エチルアルコール)溶液でエッチング後、EBSD(Electron Back Scattering Diffraction) で隣接する結晶粒界が15°以上である大傾角粒界を全板厚にわたり測定して、平均結晶粒界を求めた。
表面粗さは、JIS B 0601の規定に準拠し、カットオフ値や測定範囲は基準値を用いて測定し、算術平均粗さ(Ra)を求めた。
【0034】
また、化成処理性は、70×150 mmの試験片を切り出し、リン酸塩処理を行って評価した。すなわち、リン酸塩液中に浸漬後の外観、結晶サイズ、P比を測定した。
ここに、外観とは、化成処理皮膜が均一に形成されているかどうかの評価で、均一な場合を◎、不均一な場合を×で表した。
また、結晶サイズとは、化成処理後の表面を1000倍で電子顕微鏡観察して、化成処理被膜の平均結晶粒径を測定したもので、このサイズが10μm 以下であれば化成処理性が良好といえる。
さらに、P比とは、X線回折により測定した、Phosphophyllite(=Zn2Fe(PO4)2 ・4H2O)の(100)面からのピーク強度(P)と Hopeite(=Zn3Fe(PO4)2・4H2O)の(020)面からのピーク強度(H)を、次式{P/(P+H)}に代入して求めた値で、この値が0.85以上であれば化成処理性に優れているといえる。
そして、本発明では、上記した外観、結晶サイズおよびP比の全てが良好な場合に、化成処理性に優れると評価した。
【0035】
さらに、耐食性は、70×150 mmの試験片を切り出し、 0.5%NaCl水溶液に8時間浸漬後、大気中に16時間放置する合計24時間の処理を1サイクルとして、30サイクル後の腐食による最大侵食深さを測定することによって、評価した。最大侵食深さが 0.1mm以下であれば、耐食性に優れるといえる。
また、穴拡げ率:λ(%)は、日本鉄鋼連盟規格(JFS T1001)に従い、次式のようにして求めた。
λ={(Dh −D0 )/D0 }× 100 (%)
ここで、D0 :初期穴径(10mm)
Dh :試験により破断した後の穴径(mm)
【0036】
【表1】
【0037】
【表2】
【0038】
【表3】
【0039】
No.2〜6はいずれも、成分組成は本発明の範囲を満足しているが、製造条件が本発明範囲を逸脱した結果、結晶粒径や表面粗さが本発明の適正範囲から外れ、その結果、化成処理性や耐食性が大幅に劣化している。
また No.16〜21はいずれも、成分組成が本発明の適正範囲を外れているため、製造方法は適正でも結晶粒径が微細化せず、表面粗さ、化成処理性および耐食性に劣っている。
これに対し、本発明に従い得られた発明例(No.1および7〜15)はいずれも、TS×El≧18000 (MPa・%)、TS×λ≧65000 (MPa・%)という優れた特性を有するだけでなく、化成処理性および耐食性にも優れていた。
【0040】
【発明の効果】
かくして、本発明によれば、Siを 0.5mass%以上含有する高張力鋼においても、従来のように粗圧延や仕上圧延の前に高圧水を用いてデスケーリングを施す必要なしに、スケール残りやスケール疵の発生を効果的に防止して、鋼板の表面性状を著しく改善することができ、ひいては化成処理性および耐食性を格段に向上させることができる。
【図面の簡単な説明】
【図1】 鋼板の平均結晶粒径と表面粗さが化成処理性に及ぼす影響を示した図である。
【図2】 加熱温度およびTi, C量が、熱延板の結晶粒径に及ぼす影響を、加熱温度と log(Ti×C)との関係で示した図である。
【図3】 仕上圧延第1スタンドにおける圧延速度および圧下率が、熱延板の結晶粒径に及ぼす影響を示した図である。[0001]
BACKGROUND OF THE INVENTION
The present invention is suitable for use in automobile undercarriage parts and wheel discs manufactured by press working, has a tensile strength of 590 to 980 MPa level, and has formability such as ductility and stretch flangeability, and surface properties. The present invention relates to a hot-rolled high-tensile steel sheet excellent in chemical conversion processability and corrosion resistance, and a method for producing the same.
[0002]
[Prior art]
Generally, a hot-rolled steel sheet is manufactured by two-stage hot rolling including rough rolling and finish rolling after continuously casting a slab as it is or after heating to a temperature of 1200 ° C. or higher.
In particular, for high-tensile steel sheets with a tensile strength of 590 to 980 MPa, steel containing about 0.5 to 2.5 mass% of Si is used to ensure strength. In this case, the Si oxide scale covers the steel surface during hot rolling, which causes Si scale defects to remain in the product.
For this reason, normally, descaling using high-pressure water is performed before rolling in rough rolling and finish rolling. However, if this descaling is insufficient and there is a residual scale, the scale is bitten during rolling. Scale 疵. This scale wrinkle not only deteriorates the appearance, but even if the scale is completely removed by pickling, unevenness remains on the surface, so that the characteristic value affected by notch defects on the surface such as fatigue characteristics is lowered.
[0003]
Also, undercarriage parts and wheel discs of automobiles are subjected to chemical conversion treatment from the viewpoint of corrosion resistance.However, if irregularities remain on the surface, the formation of a chemical conversion treatment film will not be uniform, resulting in poor appearance after chemical conversion treatment. Or corrosion resistance after chemical conversion treatment decreases.
Such scale residue and surface irregularities are particularly prominent during the production of high-tensile steel sheets containing a large amount of Si.
[0004]
Therefore, in order to alleviate the obstacle caused by such scale residue, for example, Japanese Patent Publication No. 60-1085 discloses a slab temperature of 1000 slab when hot rolling a steel slab containing 0.10 to 4.00 mass% of Si. A technique is disclosed in which descaling with a high-pressure water jet with a discharge pressure of 8 to 25 MPa is performed for a cumulative time of 0.04 seconds or more when the temperature is higher than or equal to ° C.
Further, in JP-A-4-238620, when hot-removable scale steel grade is hot rolled, before finish rolling, the impact pressure per unit spray area is 0.2 MPa or more and 0.4 MPa or less and the flow rate is 0.1. A technique is disclosed in which a high water pressure spray of liter / (min · mm 2 ) or more and 0.2 liter / (min · mm 2 ) or less is sprayed on the surface of a steel sheet.
Further, Japanese Patent Application Laid-Open No. 7-70649 discloses that the temperature at the finishing mill entry side is controlled in accordance with the amount of Si, and the high water pressure with a collision pressure per unit area of 5.0 to 30.0 kgf / mm 2 (49 to 294 MPa). A technique for performing descaling is disclosed.
[0005]
[Problems to be solved by the invention]
However, in the technique disclosed in the above Japanese Patent Publication No. 60-1085, it is necessary to secure a high temperature finish rolling entry temperature (FET) of 1000 ° C. or higher, so that the steel slab must be extracted from the heating furnace at a high temperature. However, there was a problem that the basic unit deteriorated and the scale loss increased. In addition, since various restrictions are imposed on the rolling reduction and descaling time, there is a problem that the rolling operation becomes complicated.
Moreover, in the technique disclosed in the above Japanese Patent Laid-Open No. 4-238620, although most of the scale is peeled off, the scale that bites into the bare metal formed of high Si steel may remain without being removed. There was a problem that it was difficult to completely avoid scale dredging.
Furthermore, in the technique disclosed in the above-mentioned JP-A-7-70649, it is necessary to control the finishing rolling entry temperature (FET) in accordance with the amount of Si. The upper limit of the amount of Si that can be added is about 1.0 mass%, and there is a problem that it cannot be applied to a high Si content steel containing more Si.
[0006]
In addition, when steel sheets containing 0.5 mass% or more of Si are produced by these conventional techniques, only an average roughness of the steel sheet surface of about 2 μm can be obtained, and satisfactory fatigue properties and chemical conversion properties can be obtained. There was also a problem that could not be obtained.
Furthermore, the method of descaling with high-pressure water on the entrance side of finish rolling is difficult to control the water spray angle and water temperature, and there are large fluctuations due to seasonal factors, and cooling with high-pressure water near the center and edge of the steel sheet. Since the speeds are different, the variation in material characteristics has also been a problem.
[0007]
The present invention was developed in view of the above situation, and even if it is a steel sheet containing 0.5 mass% or more of Si, while effectively preventing the generation of scale flaws, the surface roughness of the steel sheet is reduced, As a result, an object of the present invention is to propose a hot-rolled high-tensile steel sheet that can provide excellent chemical conversion treatment and corrosion resistance together with its advantageous production method.
[0008]
[Means for Solving the Problems]
Now, as a result of intensive studies to achieve the above-mentioned object, the inventors have succeeded in generating scale residue and scale wrinkles, even without performing descaling, if the crystal grains of the steel sheet are refined. As a result, the present inventors have found that the surface properties, and thus the chemical conversion treatment and the corrosion resistance are remarkably improved.
The present invention is based on the above findings.
[0009]
That is, the gist configuration of the present invention is as follows.
1. C: 0.01-0.20 mass%,
Si: 0.5-2.5 mass%,
Mn: 1.0-3.0 mass%
P: 0.05 mass% or less,
Al: 0.01-0.1 mass%,
S: 0.005 mass% or less and
Ti: 0.05-0.35mass%
Ti (mass%) and C (mass%) are expressed by the following formula: −1.4 ≧ log (Ti × C) ≧ −1.8
The balance is the composition of Fe and inevitable impurities, the average crystal grain size is 3.0 μm or less, and the surface roughness is 1.5 μm or less in terms of arithmetic average roughness Ra. Hot-rolled high-tensile steel sheet with excellent chemical conversion and corrosion resistance.
[0010]
2. A hot-rolled high-tensile steel sheet excellent in chemical conversion treatment property and corrosion resistance, wherein the steel structure is a composite structure of two or more selected from ferrite, pearlite, bainite, martensite and retained austenite.
[0011]
3. C: 0.01-0.20 mass%,
Si: 0.5-2.5 mass%,
Mn: 1.0-3.0 mass%
P: 0.05 mass% or less,
Al: 0.01-0.1 mass%,
S: 0.005 mass% or less and
Ti: 0.05-0.35mass%
Ti (mass%) and C (mass%) are expressed by the following formula: −1.4 ≧ log (Ti × C) ≧ −1.8
The steel slab containing Fe and the inevitable impurities is heated to 1150 ° C or less after the rough rolling, and finish rolling is started at 1050 ° C or less after the rough rolling. rolling speed 400 m / min or more, the reduction ratio was 80% or more, subjected to final reduction of finish rolling surface roughness (Ra) of the following rolling rolls 3μm, (Ar 3 +150 ℃) ~ (Ar 3 +50 Hot rolling with excellent chemical conversion treatment and corrosion resistance, characterized in that finish rolling is finished at ℃) and then cooled to 600 ℃ or less at a cooling rate of 20 ℃ / s or more and then wound up in a temperature range of 600 to 350 ℃. Manufacturing method of high-tensile steel plate.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described below.
First, the reason why the composition of steel is limited to the above range in the present invention will be described.
C: 0.01 ~ 0.20mass%
C is an inexpensive reinforcing component and contains a necessary amount according to the desired steel plate strength. However, if the content is less than 0.01 mass%, the crystal grains become coarse and the average grain size targeted by the present invention: 3.0 μm or less cannot be achieved. On the other hand, if it exceeds 0.20 mass%, the workability is reduced. Moreover, since weldability also falls, C was limited to the range of 0.01 to 0.20 mass%. More preferably, it is the range of 0.05-0.15 mass%.
[0013]
−1.4 ≧ log (Ti × C) ≧ −1.8
However, in relation to Ti, which will be described later, this C is a relation of the following formula: −1.4 ≧ log (Ti × C) ≧ −1.8
Otherwise, the austenite grain size during slab heating does not become fine, and the refinement of crystal grains by subsequent rough rolling and finish rolling is not promoted, so that a crystal grain size of 3.0 μm or less may eventually be obtained. It is not possible to improve the chemical conversion and corrosion resistance. Therefore, it is important that C is contained in a range satisfying the above formula in relation to Ti. In the formula, C and Ti are values expressed in mass%.
[0014]
Si: 0.5 to 2.5 mass%
Si contributes effectively to an increase in strength while improving the strength-elongation balance as a solid solution strengthening component. This effect is exhibited when the Si content is 0.5 mass% or more, but excessive addition not only saturates the effect, but also causes deterioration of ductility and surface properties, so Si is in the range of 0.5 to 2.5 mass%. Limited to. Preferably it is the range of 1.0-2.0 mass%.
[0015]
Mn: 1.0-3.0 mass%
Mn contributes to the refinement of crystal grains through the action of lowering the Ar 3 transformation point, and the strength-ductility balance and the strength-fatigue strength balance through the action of martensite formation and retained austenite formation in the second phase. There is an effect to increase. Furthermore, Mn also has an effect of detoxifying harmful solid solution S as MnS. These effects are manifested by addition of 1.0 mass% or more, but addition of a large amount hardens the steel and, on the contrary, deteriorates the strength-ductility balance. Therefore, the amount of Mn is limited to the range of 1.0 to 3.0 mass%, preferably 1.0 to 2.0 mass%.
[0016]
P: 0.05 mass% or less P is useful as a reinforcing component and is added depending on the desired steel plate strength. However, if added excessively, it segregates at the grain boundaries and causes embrittlement, and also deteriorates weldability. Therefore, P is contained at 0.05 mass% or less. Preferably it is 0.001-0.03 mass%.
[0017]
Al: 0.01-0.10mass%
Al is added for the purpose of deoxidation and the like. For this purpose, it is necessary to add 0.01 mass% or more, but adding more than 0.10 mass% not only increases costs but also causes surface defects, so Al is 0.01 to 0.10 mass%. Preferably, it is added in the range of 0.02 to 0.07 mass%.
[0018]
S: 0.005 mass% or less S reacts with Mn in steel to produce A-type inclusions (those that are viscously deformed by processing as described in JIS G 0555 (sulfides, etc.)). It is a harmful element that reduces fatigue strength. Therefore, S is limited to 0.005 mass% or less, more preferably 0.002 mass% or less.
[0019]
Ti: 0.05-0.35mass%
Ti exists as TiC and effectively acts to refine the austenite grains in the slab heating stage. In order to exert such an action, it is necessary to contain at least 0.05 mass%. However, if it exceeds 0.35 mass%, the effect is saturated and an effect commensurate with the content cannot be expected. Therefore, Ti was limited to the range of 0.05 to 0.35 mass%. More preferably, it is 0.10 to 0.25 mass%.
[0020]
Although the component composition range of the steel sheet has been described above, in the present invention, it is important to limit the average crystal grain size and surface roughness of the steel to a predetermined range.
(1) Average crystal grain size ≤3.0 μm
During the chemical conversion treatment, the surface is activated by electrolysis when immersed in the phosphate solution. At that time, the grain boundary is selectively etched, and the chemical conversion treatment property is improved by using the grain boundary as a base of the chemical conversion treatment film. For that purpose, the more the crystal grain boundaries, that is, the smaller the crystal grain size, the more advantageous. Moreover, by using fine particles, the strength-ductility balance and the strength-hole expansion balance are also improved. Therefore, in the present invention, the average crystal grain size over the entire thickness of the steel sheet is limited to 3.0 μm or less.
[0021]
(2) Surface roughness (Ra) ≤ 1.5 μm or less The surface roughness is 1.5 μm or less in terms of arithmetic average roughness Ra because the corrosion resistance and chemical conversion treatment properties decrease when the surface roughness exceeds 1.5 μm. It is. Note that even if the surface roughness is less than 0.5 μm, the chemical conversion properties and corrosion resistance are not significantly improved, and it may be difficult to manage to less than 0.5 μm in actual machines, so the surface roughness (Ra) is 0.5 μm or more. It is preferable that
Here, such steel sheet surface roughness is adjusted by the crystal grain size and the roll roughness of the finish rolling mill. Therefore, in order to adjust the steel sheet surface roughness within the range of the present invention, it is necessary to manage the roll roughness of the finish rolling mill to 3 μm or less.
The surface roughness of the hot-rolled sheet has not been particularly considered so far, and the general surface roughness is about 2 to 5 μm.
[0022]
In FIG. 1, the result of having investigated about the influence which the average crystal grain diameter and surface roughness of a steel plate have on a chemical conversion treatment property is shown.
As shown in the figure, good chemical conversion properties are obtained when the average crystal grain size is 3.0 μm or less and the surface roughness (Ra) is 1.5 μm or less.
[0023]
As described above, the chemical conversion processability is improved by refining the crystal grains, and as a result, the details of the mechanism by which the corrosion resistance is improved are unknown, but are considered as follows.
In general, precipitates and inclusions are likely to accumulate at the crystal grain boundaries, so that they are likely to be the starting point of rust and the like. However, when the grain boundaries increase due to the refinement of the crystal grains, the impurity concentration per grain interface area decreases, so that the generation of rust is relatively suppressed.
Moreover, the descalability is greatly improved by such refinement of crystal grains. The reason is not clearly clarified, but I think as follows.
Descaling is usually performed by dipping in a hydrochloric acid solution. At that time, since the crystal grain boundary is easily etched, it is considered that the crystal scale is refined and the interface area of the crystal grain is increased, thereby facilitating peeling of the surface scale.
[0024]
Furthermore, in the present invention, the steel structure is preferably two or more types of composite structures selected from ferrite, pearlite, bainite, martensite and retained austenite.
This is because such a composite structure is excellent in stretch-hole expansion balance and fatigue characteristics, and is a structure having a well-balanced material characteristic necessary for a hot-rolled high-tensile steel sheet.
[0025]
Next, the manufacturing conditions of the present invention will be described.
(1) Heating temperature of steel slab before hot rolling: 1150 ° C or less The heating temperature before hot rolling is important because it greatly affects the grain size after rough rolling and finish rolling. In the present invention, it is necessary to quantitatively precipitate TiC during heating and to suppress the growth of crystal grains with fine TiC.
In FIG. 2, the result of having investigated about the relationship between heating temperature, Ti, C amount (mass%), and the particle size of the hot-rolled sheet obtained is shown. In addition, about Ti and C amount (mass%), it shall show with log (TixC). Here, the composition of the steel used in the experiment of the figure contains Si: 1.4 mass%, Mn: 1.8 mass%, P: 0.02 mass%, S: 0.001 mass% and Al: 0.05 mass% as the basic composition. Steel and slabs (thickness: 260 mm) with such compositions are obtained by variously changing C and Ti in the range of C: 0.01 to 0.2 mass% and Ti: 0.05 to 0.35 mass%, respectively. It is manufactured under the conditions of temperature: 1000 to 1300 ° C., rolling end temperature: 900 ° C., finished plate thickness: 3.0 mm, and winding temperature: 450 ° C.
As shown in the figure, it can be seen that the heating temperature needs to be 1150 ° C. or less in relation to Ti and C content in order to make the average crystal grain size 3.0 μm or less.
In addition, when the obtained steel slab is not a reheated material as described above but a so-called direct-rolled material that is subjected to hot rough rolling immediately after continuous casting, such slab heating is not necessarily performed. Alternatively, it may be subjected to hot rough rolling as it is.
[0026]
(2) Finishing rolling start temperature: 1050 ° C. or less After rough rolling, before finishing rolling, descaling is usually performed at a discharge pressure of about 5 to 20 MPa. In the present invention, descaling prior to finish rolling need not be performed with high-pressure water, and the normal conditions as described above, for example, descaling of about 5 to 20 MPa may be used.
Here, the reason why the rolling start temperature in finish rolling is set to 1050 ° C. or lower is as follows.
When the finish rolling start temperature is higher than 1050 ° C, the strain introduced by rolling is recovered, the grains grow and become coarse, and it becomes difficult to finally obtain crystal grains of 3.0 μm or less, and a thick scale is formed. However, it enters the inside of the steel plate during rolling and becomes a bite scale, which deteriorates the surface properties.
[0027]
(3) Rolling speed at finish stand 1st stand ≧ 400 m / min, rolling reduction ≧ 80%
The rolling speed and rolling reduction during finish rolling are important for reducing the ferrite grain size to 3.0 μm or less. In particular, when the rolling speed at the first finish rolling stand is lower than 400 m / min, the residence time between the stands in the finish rolling (usually 7 stands) becomes longer, so that Since strain is recovered and grain growth is promoted, crystal grains become coarse during rolling, and fine γ grains cannot be obtained.
Moreover, when the rolling reduction in this 1st stand is smaller than 80%, the distortion to a grain is small and an austenite grain cannot be made fine.
[0028]
In FIG. 3, the result of having investigated about the relationship between the rolling speed | rate and rolling reduction in the finish rolling 1st stand, and the crystal grain diameter of a hot-rolled sheet is shown.
Here, the composition of the steel used in the experiment of the figure is: C: 0.09 mass%, Si: 1.4 mass%, Mn: 1.8 mass%, P: 0.02 mass%, S: 0.001 mass%, Al: 0.05 mass% And Ti: 0.18 mass%, and the balance is a steel having a substantially Fe composition. A steel slab (thickness: 260 mm) having such a composition is heated to a slab heating temperature of 1050 ° C. and a rolling end temperature of 900. It was manufactured under the conditions of ℃, finishing plate thickness: 3.0 mm, winding temperature: 450 ℃.
The rolling speed in the first finish rolling stand was 100 to 800 m / min, and the rolling reduction was 70, 80, 90%.
As is clear from the figure, the average crystal grain size could be reduced to 3.0 μm or less by setting the rolling speed in the first finish rolling stand to 400 m / min or more and the rolling reduction to 80% or more.
[0029]
(4) finish rolling temperature: (Ar 3 +150 ℃) ~ (Ar 3 + 50 ℃)
The finish rolling temperature is lower than (Ar 3 + 50 ℃), the surface layer portion ferrite grains become coarse, and whereas the (Ar 3 +150 ℃) exceeding, a whole steel sheet microstructure is coarsened, such as elongation and hole expandability This is because workability is lowered.
Note that the final rolling of the finish rolling needs to be performed with a rolling roll having a surface roughness (Ra) of 3 μm or less in order to set the surface roughness (Ra) of the steel sheet to 1.5 μm or less as described above.
[0030]
(5) Cooling rate after finishing rolling to winding: 20 ° C./s or more The cooling rate after finishing rolling needs to be 20 ° C./s or more. This is because when the cooling rate after rolling is slower than 20 ° C./s, the austenite structure refined at the end of rolling becomes coarse during cooling, and the structure of the product plate obtained after transformation becomes coarse. This is because the desired texture of 3.0 μm or less cannot be obtained in the present invention.
[0031]
(6) Winding temperature: 600 to 350 ℃
The coiling temperature is set to 600-350 ° C. When the coiling temperature exceeds 600 ° C, coarse cementite is formed, and the strength-ductility balance is lowered. This is because it becomes difficult and uniform material properties cannot be obtained.
After the above winding, normal pickling is performed to obtain a product.
[0032]
【Example】
Steel slabs having the composition shown in Table 1 were processed under various conditions shown in Table 2 to obtain hot-rolled steel sheets having a plate thickness of 3.0 mm.
After pickling the obtained hot-rolled steel sheet, the average crystal grain size, surface roughness and metal structure were investigated. In addition, the mechanical properties of these hot-rolled steel sheets were investigated. Furthermore, the chemical conversion property and the corrosion resistance were also investigated.
These results are shown in Table 3.
[0033]
The crystal grain size of the hot-rolled steel sheet is a large-angle grain whose cross-section is etched with a (2% nitric acid + ethyl alcohol) solution and the adjacent grain boundary is 15 ° or more by EBSD (Electron Back Scattering Diffraction). The boundary was measured over the entire plate thickness to determine the average grain boundary.
The surface roughness was in accordance with the provisions of JIS B 0601, the cut-off value and measurement range were measured using reference values, and the arithmetic average roughness (Ra) was obtained.
[0034]
Further, the chemical conversion treatment property was evaluated by cutting out a 70 × 150 mm test piece and performing a phosphate treatment. That is, the appearance, crystal size, and P ratio after immersion in the phosphate solution were measured.
Here, the appearance is an evaluation of whether or not the chemical conversion film is uniformly formed. The uniform case is indicated by ◎, and the non-uniform case is indicated by ×.
In addition, the crystal size is obtained by observing the surface after chemical conversion treatment with an electron microscope at a magnification of 1000 and measuring the average crystal grain size of the chemical conversion treatment film. If this size is 10 μm or less, the chemical conversion treatment property is good. I can say that.
Furthermore, the P ratio is the peak intensity (P) from the (100) plane of Phosphophyllite (= Zn 2 Fe (PO 4 ) 2 .4H 2 O) measured by X-ray diffraction and Hopeite (= Zn 3 Fe ( PO 4 ) 2 · 4H 2 O) is a value obtained by substituting the peak intensity (H) from the (020) plane into the following equation {P / (P + H)}. It can be said that it is excellent in processability.
And in this invention, when all the above-mentioned external appearance, crystal | crystallization size, and P ratio were favorable, it evaluated that it was excellent in chemical conversion treatment property.
[0035]
Furthermore, the corrosion resistance is the maximum erosion due to corrosion after 30 cycles, with a 70 x 150 mm test piece cut out, immersed in 0.5% NaCl aqueous solution for 8 hours, and left in the atmosphere for 16 hours for a total of 24 hours. Evaluation was made by measuring the depth. If the maximum erosion depth is 0.1 mm or less, it can be said that the corrosion resistance is excellent.
Further, the hole expansion ratio: λ (%) was obtained by the following formula according to the Japan Iron and Steel Federation standard (JFS T1001).
λ = {(D h −D 0 ) / D 0 } × 100 (%)
Where D 0 : initial hole diameter (10 mm)
D h : Hole diameter (mm) after breaking by test
[0036]
[Table 1]
[0037]
[Table 2]
[0038]
[Table 3]
[0039]
In any of No. 2 to 6, the component composition satisfies the scope of the present invention, but as a result of the manufacturing conditions deviating from the scope of the present invention, the crystal grain size and surface roughness deviate from the appropriate range of the present invention. As a result, chemical conversion property and corrosion resistance are greatly deteriorated.
In addition, since No. 16 to 21 all have component compositions outside the appropriate range of the present invention, the crystal grain size does not become fine even if the manufacturing method is appropriate, and the surface roughness, chemical conversion treatment property and corrosion resistance are inferior. Yes.
In contrast, the invention examples obtained according to the present invention (No. 1 and 7 to 15) all have excellent characteristics of TS × El ≧ 18000 (MPa ·%) and TS × λ ≧ 65000 (MPa ·%). In addition, it was excellent in chemical conversion treatment and corrosion resistance.
[0040]
【The invention's effect】
Thus, according to the present invention, even in a high-strength steel containing 0.5 mass% or more of Si, it is possible to remove the remaining scale without using descaling using high-pressure water before rough rolling or finish rolling as in the past. The generation of scale wrinkles can be effectively prevented, and the surface properties of the steel sheet can be remarkably improved. As a result, chemical conversion properties and corrosion resistance can be significantly improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing the influence of the average crystal grain size and surface roughness of a steel sheet on chemical conversion properties.
FIG. 2 is a graph showing the influence of heating temperature and Ti, C amount on the crystal grain size of a hot-rolled sheet in relation to the heating temperature and log (Ti × C).
FIG. 3 is a view showing the influence of the rolling speed and rolling reduction in the first finish rolling stand on the crystal grain size of a hot-rolled sheet.
Claims (3)
Si:0.5 〜2.5 mass%、
Mn:1.0 〜3.0 mass%、
P:0.05mass%以下、
Al:0.01〜0.1 mass%、
S:0.005 mass%以下および
Ti:0.05〜0.35mass%
を、Ti(mass%)とC(mass%)とが次式
−1.4 ≧ log(Ti×C)≧−1.8
を満足する範囲において含有し、残部はFeおよび不可避的不純物の組成になり、平均結晶粒径が 3.0μm 以下で、かつ表面粗さが算術平均粗さRaで 1.5μm 以下であることを特徴とする化成処理性および耐食性に優れる熱延高張力鋼板。C: 0.01-0.20 mass%,
Si: 0.5-2.5 mass%,
Mn: 1.0-3.0 mass%
P: 0.05 mass% or less,
Al: 0.01-0.1 mass%,
S: 0.005 mass% or less and
Ti: 0.05-0.35mass%
Ti (mass%) and C (mass%) are expressed by the following formula: −1.4 ≧ log (Ti × C) ≧ −1.8
The balance is the composition of Fe and inevitable impurities, the average crystal grain size is 3.0 μm or less, and the surface roughness is 1.5 μm or less in terms of arithmetic average roughness Ra. Hot-rolled high-tensile steel sheet with excellent chemical conversion and corrosion resistance.
Si:0.5 〜2.5 mass%、
Mn:1.0 〜3.0 mass%、
P:0.05mass%以下、
Al:0.01〜0.1 mass%、
S:0.005 mass%以下および
Ti:0.05〜0.35mass%
を、Ti(mass%)とC(mass%)とが次式
−1.4 ≧ log(Ti×C)≧−1.8
を満足する範囲において含有し、残部はFeおよび不可避的不純物の組成になる鋼スラブを、1150℃以下に加熱し、粗圧延後、1050℃以下で仕上圧延を開始し、仕上圧延第1スタンドでの圧延速度を 400 m/min以上、圧下率を80%以上とし、仕上圧延の最終圧下を表面粗さ(Ra)が3μm 以下の圧延ロールで行い、(Ar3+150 ℃)〜(Ar3+50℃) で仕上圧延を終了し、ついで20℃/s以上の冷却速度で600 ℃以下まで冷却後、 600〜350 ℃の温度範囲で巻き取ることを特徴とする化成処理性および耐食性に優れる熱延高張力鋼板の製造方法。C: 0.01-0.20 mass%,
Si: 0.5-2.5 mass%,
Mn: 1.0-3.0 mass%
P: 0.05 mass% or less,
Al: 0.01-0.1 mass%,
S: 0.005 mass% or less and
Ti: 0.05-0.35mass%
Ti (mass%) and C (mass%) are expressed by the following formula: −1.4 ≧ log (Ti × C) ≧ −1.8
The steel slab containing Fe and the inevitable impurities is heated to 1150 ° C or less after the rough rolling, and finish rolling is started at 1050 ° C or less after the rough rolling. rolling speed 400 m / min or more, the reduction ratio was 80% or more, subjected to final reduction of finish rolling surface roughness (Ra) of the following rolling rolls 3μm, (Ar 3 +150 ℃) ~ (Ar 3 +50 Hot rolling with excellent chemical conversion treatment and corrosion resistance, characterized in that finish rolling is finished at ℃) and then cooled to 600 ℃ or less at a cooling rate of 20 ℃ / s or more and then wound up in a temperature range of 600 to 350 ℃. Manufacturing method of high-tensile steel plate.
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Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS601085B2 (en) * | 1981-07-13 | 1985-01-11 | 川崎製鉄株式会社 | Descaling method during hot rolling of Si-containing steel |
JPH04238620A (en) * | 1991-01-08 | 1992-08-26 | Kawasaki Steel Corp | Method for descaling in hot rolling |
JPH0770649A (en) * | 1993-09-02 | 1995-03-14 | Kawasaki Steel Corp | Production of hot rolled steel sheet excellent in stretch-flange formability, ductility and surface property |
JPH09137249A (en) * | 1995-11-10 | 1997-05-27 | Kawasaki Steel Corp | Hot rolled hightensile strength steel plate excellent in fatigue characteristic and workability and its production |
JPH09263883A (en) * | 1996-03-28 | 1997-10-07 | Kobe Steel Ltd | High strength hot rolled steel plate excellent in pitting corrosion resistance and workability, high strength galvanized steel plate, and their production |
JPH09263884A (en) * | 1996-03-28 | 1997-10-07 | Kobe Steel Ltd | High strength hot rolled steel plate excellent in pitting corrosion resistance and crushing resistance, high strength galvanized steel plate, and their production |
JPH11189839A (en) * | 1997-12-26 | 1999-07-13 | Nippon Steel Corp | High strength steel plate with high dynamic deformation resistance, and its production |
JPH11193439A (en) * | 1997-12-26 | 1999-07-21 | Nippon Steel Corp | Steel plate combining good workability with high strength and having high dynamic deformation resistance, and its production |
JP2000212686A (en) * | 1999-01-19 | 2000-08-02 | Kawasaki Steel Corp | High tensile strength hot dip galvanized steel sheet excellent in workability and its production |
-
2001
- 2001-02-02 JP JP2001026847A patent/JP4534362B2/en not_active Expired - Fee Related
Patent Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS601085B2 (en) * | 1981-07-13 | 1985-01-11 | 川崎製鉄株式会社 | Descaling method during hot rolling of Si-containing steel |
JPH04238620A (en) * | 1991-01-08 | 1992-08-26 | Kawasaki Steel Corp | Method for descaling in hot rolling |
JPH0770649A (en) * | 1993-09-02 | 1995-03-14 | Kawasaki Steel Corp | Production of hot rolled steel sheet excellent in stretch-flange formability, ductility and surface property |
JPH09137249A (en) * | 1995-11-10 | 1997-05-27 | Kawasaki Steel Corp | Hot rolled hightensile strength steel plate excellent in fatigue characteristic and workability and its production |
JPH09263883A (en) * | 1996-03-28 | 1997-10-07 | Kobe Steel Ltd | High strength hot rolled steel plate excellent in pitting corrosion resistance and workability, high strength galvanized steel plate, and their production |
JPH09263884A (en) * | 1996-03-28 | 1997-10-07 | Kobe Steel Ltd | High strength hot rolled steel plate excellent in pitting corrosion resistance and crushing resistance, high strength galvanized steel plate, and their production |
JPH11189839A (en) * | 1997-12-26 | 1999-07-13 | Nippon Steel Corp | High strength steel plate with high dynamic deformation resistance, and its production |
JPH11193439A (en) * | 1997-12-26 | 1999-07-21 | Nippon Steel Corp | Steel plate combining good workability with high strength and having high dynamic deformation resistance, and its production |
JP2000212686A (en) * | 1999-01-19 | 2000-08-02 | Kawasaki Steel Corp | High tensile strength hot dip galvanized steel sheet excellent in workability and its production |
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