JP3654194B2 - High-strength steel material with excellent strain aging resistance and its manufacturing method - Google Patents
High-strength steel material with excellent strain aging resistance and its manufacturing method Download PDFInfo
- Publication number
- JP3654194B2 JP3654194B2 JP2001019741A JP2001019741A JP3654194B2 JP 3654194 B2 JP3654194 B2 JP 3654194B2 JP 2001019741 A JP2001019741 A JP 2001019741A JP 2001019741 A JP2001019741 A JP 2001019741A JP 3654194 B2 JP3654194 B2 JP 3654194B2
- Authority
- JP
- Japan
- Prior art keywords
- less
- steel
- strain aging
- strength
- content
- 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)
Description
【０００１】
【発明の属する技術分野】
本発明は、引張強さが７６０ＭＰａ以上の耐歪み時効特性に優れた高張力鋼材に関し、より詳しくは天然ガスや原油を輸送するラインパイプや各種圧力容器などの溶接構造物を製造するのに使用して好適な鋼材（鋼板、鋼管、形鋼、棒鋼など）とその製造方法に関する。
【０００２】
【従来の技術】
天然ガスや原油を長距離輸送するパイプラインにおいて、輸送コストの低減は普遍的なニーズであり、操業圧力の上昇による輸送効率の改善が必要とされている。操業圧力を高めるには、従来からの強度グレードのラインパイプの肉厚を増加させる方法が考えられる。しかし、この方法は、現地での溶接施工能率を低下させる他、構造物の質量増加による施工効率の低下を生じさせる問題がある。
【０００３】
これに対し、ラインパイプの素材自体を高強度化して肉厚の増大を制限するニーズが高まっており、現在、ＡＰＩ（米国石油協会）においてＸ８０グレード（引張強さ６２０ＭＰａ以上）鋼が規格化され、実用に供されてきた。
【０００４】
さらに、高強度なラインパイプ用材としては、特開平８−１９９２９２号公報および同８−２６９５４６号公報に示されるように、Ｍｎ含有量を高めに設定したＸ１００グレード（引張強さ７６０ＭＰａ以上）超級の高強度鋼がある。
【０００５】
しかし、ラインパイプの主力であるＵＯＥ鋼管に代表される大径の溶接鋼管やＥＲＷ鋼管に代表される中小径の溶接鋼管は、素材の鋼板の管状への成形が室温下、すなわち冷間加工でおこなわれ、いわゆる加工歪みが生じるため、素材の鋼板に高性能な材料（鋼）からなるものを用いても、製品の溶接鋼管では素材の鋼板の特性が保持されない可能性がある。
【０００６】
また、冷間加工に供せられない鋼材においても、溶接時や熱処理時に生じる熱歪み、および構造部材として長期間使用される間に生ずる歪みなどの歪みが部分的に蓄えられる場合がある。
【０００７】
こうした歪みは、５％以下の小さな歪み量であるが、歪んだ鋼材がさらに長期間使用される場合には、歪み時効による鋼材の劣化に留意する必要がある。
【０００８】
なお、歪み時効は、鋼材が室温下で長期間使用されることによって生ずるが、コーティング処理などのために鋼材が１００〜２５０℃に加熱されることによって促進する。
【０００９】
歪み時効による鋼材の劣化は、引張強さが３９２ＭＰａ以上や４９０ＭＰａ以上級の従来から多用されている鋼材においてもある程度生ずることは知られているが、歪み時効処理材のシャルピー衝撃試験などにより実用上ほとんど問題のないことが確認されている。
【００１０】
これに対し、引張強さが６２０ＭＰａ以上の前述したＸ８０グレード鋼級以上の高強度鋼においては、歪み時効による鋼材の劣化についての系統的な調査がされていないのが現状である。特に、シャルピー特性などの靭性低下だけではなく、引張試験時の一様伸びの低下など、加工硬化特性に対する対策を講じる必要がある。
【００１１】
しかし、一般に、金属材料は高強度化するほど伸び、延性、特に一様伸び特性が低下するため、歪み時効処理に伴う加工硬化に起因する特性劣化の対策が必要になると考えられている。
【００１２】
本発明者が、引張強さ７６０ＭＰａ以上の種々の溶接構造用鋼材について検討した結果、多くの溶接構造用鋼材で、歪み量３％の冷間加工後、２５０℃に１時間保持後空冷する時効処理後に、靭性および加工硬化特性の劣化が生じることが判明した。特に、一様伸びについては、著しい低下が生じる場合があり、構造部材としての安全性を損なう可能性があった。しかしながら、こうした高強度鋼の問題に対し、耐歪み時効特性を向上させて構造用材料としての安全性を高める技術は、皆無といっていいほどなかった。
【００１３】
【発明が解決しようとする課題】
本発明は、上記のような実状に鑑みてなされたもので、その目的は、引張強さが７６０ＭＰａ以上の耐歪み時効特性と溶接部靭性に優れた高張力鋼材、より具体的には良好な靭性と溶接性を有するとともに、その溶接部の靭性に優れ、例えば、３％歪み時効処理後の一様伸び率が歪み時効処理前の一様伸び率の０．６倍以上というような歪み時効処理後においても優れた加工硬化特性と低温靭性を有する溶接鋼管などの溶接構造用物の素材として用いて好適な鋼板に代表される高強度鋼材とその製造法を提供することにある。
【００１４】
【課題を解決するための手段】
本発明者は、上記の課題を達成するために、引張強さが７６０ＭＰａ以上の溶接構造物用の高強度鋼材の高靭化、溶接性の向上および耐歪み時効特性の向上に対し、種々検討を行った結果、以下のことを知見した。
（ａ）歪み時効の直接の原因となるＮとＣの含有量、および高強度鋼材の歪み時効を促進するＳｉ、ＰおよびＯ（酸素）の含有量を制限、具体的には式「Ａ＝50Ｎ＋Ｃ＋0.3Si＋10(Ｐ＋Ｏ)（ここで、各元素記号は鋼中に含まれる各元素の含有量（質量％）を意味する）」で定義されるＡ値が０．３５以下になるように各元素の含有量を後述する範囲内において調整すれば、歪み時効後の低温靭性と一様伸びが向上する。
（ｂ）Ｎｂ、ＴｉおよびＡｌは、引張強さ７６０ＭＰａ以上の高強度鋼材の歪み時効特性を軽減させる作用を有し、少なくともＮｂ、Ｔｉ、Ａｌの３元素を必須成分として添加するとともに、式「Ｂ＝(50Ｎ＋Ｃ＋10Ｏ)／(4Nb＋10Ti＋2sol.Al)（ここで、各元素記号は鋼中に含まれる各元素の含有量（質量％）を意味する）」で定義されるＢ値が１．６以下になるように各元素の含有量を後述する範囲内において調整すれば、時効特性感受性が低下し、歪み時効による劣化が抑制される。
（ｃ）そして、後述する組成範囲内において上記の両式を満たす場合には、溶接性と靭性並びにその溶接部の靭性に優れ、３％の歪み時効処理後の一様伸び率が歪み時効処理前の一様伸び率の０．６倍以上という優れた加工硬化特性と良好な低温靭性を有する溶接鋼管などの溶接構造用物の素材として用いて好適な鋼板に代表される高強度鋼材が得られる。
（ｄ）また、鋼板に代表される上記の高強度鋼材は、素材の鋼を９５０〜１２００℃に加熱後、仕上温度８５０〜６５０℃で熱間圧延を終了し、５００℃を下回らない温度域から３００℃以下にまで４℃／秒以上の冷却速度で加速冷却することにより、上記３％の歪み時効処理後の一様伸び率が歪み時効処理前の一様伸び率の０．６倍以上という優れた加工硬化特性を有する製品を安定して製造可能である。
【００１５】
上記の知見に基づいて完成させた本発明の要旨は、下記（１）、（２）の耐歪み時効特性に優れた高強度鋼材、下記（３）の高強度鋼材の製造方法、下記（４）の耐歪み時効特性に優れた高強度溶接鋼管および下記（５）の高強度溶接鋼管の製造方法にある。
（１）化学組成が、質量％で、Ｃ：０．０１〜０．１０％、Ｓｉ：０．１５％以下、Ｍｎ：１．００〜２．５０％、Ｐ：０．０１０％以下、Ｓ：０．００５％以下、Ｎｂ：０．００５〜０．０６％、Ｔｉ：０．００４〜０．０２５％、ｓｏｌ．Ａｌ：０．０５％以下、Ｎ：０．００５０％以下、Ｏ(酸素)：０．００３％以下、Ｃｕ：０〜１．５％、Ｎｉ：０〜２．５％、Ｍｏ：０〜０．８０％、Ｃｒ：０〜１．０％、Ｖ：０〜０．１％、Ｚｒ：０〜０．０３％、Ｃａ：０〜０．００３０％及びＢ：０〜０．００２％並びに残部がＦｅ及び不純物であって、下記の(1)式で定義されるＡ値が０．３５以下、(2)式で定義されるＢ値が１．６以下の鋼からなり、引張強さが７６０ＭＰａ以上である耐歪み時効特性に優れた高強度鋼材。
【００１６】
Ａ＝50Ｎ＋Ｃ＋0.3Si＋10(Ｐ＋Ｏ) ・・・・・・・・・ (1)
Ｂ＝(50Ｎ＋Ｃ＋10Ｏ)／(4Nb＋10Ti＋2sol.Al) ・・・・ (2)
ここで、(1)式と(2)式中の元素記号は鋼中に含まれる各元素の含有量（質量％）を意味する。
（２）鋼材が、鋼板である上記（１）に記載の高強度鋼材。
（３）質量％で、Ｃ：０．０１〜０．１０％、Ｓｉ：０．１５％以下、Ｍｎ：１．００〜２．５０％、Ｐ：０．０１０％以下、Ｓ：０．００５％以下、Ｎｂ：０．００５〜０．０６％、Ｔｉ：０．００４〜０．０２５％、ｓｏｌ．Ａｌ：０．０５％以下、Ｎ：０．００５０％以下、Ｏ(酸素)：０．００３％以下、Ｃｕ：０〜１．５％、Ｎｉ：０〜２．５％、Ｍｏ：０〜０．８０％、Ｃｒ：０〜１．０％、Ｖ：０〜０．１％、Ｚｒ：０〜０．０３％、Ｃａ：０〜０．００３０％及びＢ：０〜０．００２％並びに残部がＦｅ及び不純物であって、下記の(1)式で定義されるＡ値が０．３５以下、(2)式で定義されるＢ値が１．６以下の鋼を、９５０〜１２００℃に加熱後、熱間圧延をおこなって仕上温度８５０〜６５０℃で圧延を終了し、５００℃を下回らない温度域から３００℃以下の温度にまで４℃／秒以上の冷却速度で加速冷却する引張強さ７６０ＭＰａ以上の耐歪み時効特性に優れた高強度鋼材の製造法。
【００１７】
Ａ＝50Ｎ＋Ｃ＋0.3Si＋10(Ｐ＋Ｏ) ・・・・・・・・・ (1)
Ｂ＝(50Ｎ＋Ｃ＋10Ｏ)／(4Nb＋10Ti＋2sol.Al) ・・・・ (2)
ここで、(1) 式と(2) 式中の元素記号は鋼中に含まれる各元素の含有量（質量％）を意味する。
（４）母材部が、上記（２）に記載の高強度鋼板である耐歪み時効特性に優れた高強度溶接鋼管。
（５）上記（２）に記載の高強度鋼板を、６００℃以下の温度域で管状に成形し、その突き合わせ部を溶接接合する耐歪み時効特性に優れた高強度溶接鋼管の製造方法。
【００１８】
【発明の実施の形態】
以下、本発明を上記のように定めた理由について詳しく説明する。なお、以下の説明において、「％」は特に断らない限り「質量％」を意味する。
【００１９】
まず、鋼の化学組成について説明する。
【００２０】
Ｃ：０．０１〜０．１０％
Ｃは、母材の強度を確保する目的で含有させるが、０．０１％未満では焼入性が不足で引張強さ７６０ＭＰａ以上の確保が難しく、また母材の靭性も十分ではない。一方、０．１０％を超えて含有させると、母材の靭性および溶接性、さらにはその溶接熱影響部の靭性が低下するだけでなく、耐歪み時効特性の劣化が生ずる。よって、Ｃ含有量は０．０１〜０．１０％とした。好ましい範囲は０．０１〜０．０６％である。
【００２１】
Ｓｉ：０．１５％以下
Ｓｉは、脱酸剤として通常添加されるが、その含有量が０．１５％を超えると母材およびその溶接部ともに靭性低下をもたらすだけでなく、耐歪み時効特性も低下する。よって、Ｓｉ含有量は０．１５％以下とした。好ましい上限は０．１０％である。
【００２２】
Ｍｎ：１．００〜２．５０％
Ｍｎは、鋼の焼入性を向上させ、強度を高めるために添加含有させるが、その含有量が１．００％未満では、所望の強度を確保することが困難である。一方、２．５０％を超えて含有させると、母材およびその溶接部ともに靭性低下を招く。よって、Ｍｎ含有量は１．００〜２．５０％とした。なお、溶接部の靭性を向上させる観点からはＭｎは少ない方が望ましく、Ｍｎ含有量の好ましい範囲は１．００〜１．９０％、より好ましい範囲は１．００〜１．７０％である。
【００２３】
Ｐ：０．０１０％以下
Ｐは、不純物元素であり、母材およびその溶接熱影響部の低温靭性を損なうだけでなく、溶接性をも低下させ、さらに耐歪み時効特性も低下させる。したがって、Ｐ含有量は低ければ低いほどよいが、過度な低減はコスト上昇を招くことと、０．０１０％までであれば特に問題ないことから、その上限を０．０１０％とした。好ましい上限は０．００５％である。
【００２４】
Ｓ：０．００５％以下
Ｓは、上記のＰと同様の不純物元素であり、母材およびその溶接熱影響部の低温靭性を損なうだけでなく、溶接性をも低下させる。したがって、Ｓ含有量は、上記のＰと同様に、低ければ低いほどよいが、過度な低減はコスト上昇を招くことと、０．００５％までであれば特に問題ないことから、その上限を０．００５％とした。好ましい上限は０．００２％である。
【００２５】
Ｎｂ：０．００５〜０．０６％
Ｎｂは、母材の組織を微細化させて高強度鋼の靭性を大幅に向上させるだけでなく、耐歪み時効特性に有害な元素のＣ、Ｎと結合してこれらの元素を安定化させ、耐歪み時効特性を向上させる効果がある。しかし、その含有量が０．００５％未満では前記の効果が得られず、逆に０．０６％を超えて含有させると母材の溶接性を損なうだけでなく、靭性および耐歪み時効特性をもかえって低下させる。よって、Ｎｂ含有量は０．００５〜０．０６％とした。好ましい範囲は０．００５〜０．０３％、より好ましい範囲は０．００５〜０．０２％である。
【００２６】
Ｔｉ：０．００４〜０．０２５％
Ｔｉは、耐歪み時効特性に有害な元素のＣ、Ｎと結合してこれらの元素を安定化させ、耐歪み時効特性を大幅に向上させるだけでなく、母材およびその溶接熱影響部の組織を微細化させて高強度鋼の母材とその溶接熱影響部の低温靭性を向上させる効果がある。しかし、その含有量が０．００４％未満では前記の効果が得られず、逆に０．０２５％を超えて含有させると耐歪み時効特性を損なうだけでなく、溶接性および靭性をもかえって低下させる。よって、Ｔｉ含有量は０．００４〜０．０２５％とした。好ましい範囲は０．００４〜０．０１５％である。
【００２７】
ｓｏｌ．Ａｌ：０．０５％以下
Ａｌは、脱酸剤として添加されるが、耐歪み時効特性に有害な元素のＮと結合して安定化させ、耐歪み時効特性を大幅に向上させる効果がある。このＡｌによる耐歪み時効特性の向上効果は極微量のｓｏｌ．Ａｌ含有量で得られるが、その効果は０．００２％以上のｓｏｌ．Ａｌ含有量で顕著になる。しかし、その含有量がｓｏｌ．Ａｌ含有量で０．０５％を超えると、溶接部の靭性が劣化するだけでなく、耐歪み時効特性や溶接性がかえって低下する。よって、ｓｏｌ．Ａｌ含有量は０．０５％以下とした。好ましい上限は０．０３％である。
【００２８】
Ｎ：０．００５０％以下
Ｎは、耐歪み時効特性に極めて有害な不純物元素であり、その含有量が０．００５０％を超えると、母材およびその溶接部の靭性低下が著しくなるだけでなく、他の耐歪み時効特性向上対策を講じても良好な耐歪み時効特性が得られなくなる。よって、Ｎ含有量は０．００５０％以下とした。なお、Ｎ含有量は低ければ低いほど望ましく、好ましい上限は０．００３０％である。
【００２９】
Ｏ（酸素）：０．００３％以下
Ｏは、上記のＮと同様に、耐歪み時効特性に極めて有害な不純物元素であり、その含有量が０．００３％を超えると、母材およびその溶接部の靭性低下が著しくなるだけでなく、他の耐歪み時効特性向上対策を講じても良好な耐歪み時効特性が得られなくなる。よって、Ｏ含有量は０．００３％以下とした。なお、Ｏ含有量は低ければ低いほど望ましく、好ましい上限は０．００２０％、より好ましい上限は０．００１５％である。
【００３０】
以下の各元素は添加しなくもよいが、下記の範囲内で添加含有させれば、耐歪み時効特性を損なうことなく、母材および溶接熱影響部の強度、靭性および耐食性などを向上させることができる。このため、より厚肉の鋼板や強度の高い高強度鋼材などを製造する際には、必要に応じてこれら元素の１種以上を添加してもよい。
【００３１】
Ｃｕ：
Ｃｕは、焼入性を向上させ、溶接性をあまり損なうことなく母材を強靭化する作用を有し、その効果は０．１％以上の含有量で顕著になる。しかし、１．５％を超えて含有させると、母材およびその溶接部の靭性を損なうだけでなく、熱間延性を大きく低下させる場合がある。このため、添加する場合のＣｕ含有量は０．１〜１．５％とするのがよい。
【００３２】
Ｎｉ：
Ｎｉは、高強度鋼の低温靭性、脆性亀裂伝播停止性能および溶接性を改善する作用を有し、その効果は０．２０％以上の含有量で顕著になる。しかし、２．５％を超えて含有させると、焼入れ−焼戻し処理によって過度の残留オーステナイトが生成し、降伏強さが低下する場合がある。このため、添加する場合のＮｉ含有量は０．２０〜２．５％とするのがよい。
【００３３】
Ｃｒ：
Ｃｒは、焼入性を向上させるとともに、焼戻し処理時の析出強化によって強度および靭性を向上させる作用を有し、その効果は０．１０％以上の含有量で顕著になる。しかし、１．０％を超えて含有させると、強度を過度に高め、母材およびその溶接部の靭性を損なう。このため、添加する場合のＣｒ含有量は０．１０〜１．０％とするのがよい。
【００３４】
Ｍｏ：
Ｍｏは、焼入性を向上させるとともに、固溶強化によって強度および靭性を向上させる他、Ｎｂとの複合添加時には組織の微細化を促進すると同時に適度な残留オーステナイトを鋼中に分散させて耐歪み脆化特性を向上させる作用を有し、その効果は０．１０％以上の含有量で顕著になる。しかし、０．８０％を超えて含有させると、強度を過度に高め、母材およびその溶接部の靭性を損なう。このため、添加する場合のＭｏ含有量は０．１０〜０．８０％とするのがよい。
【００３５】
Ｖ：
Ｖは、焼入性を向上させ、強度および靭性を向上させる他、耐歪み時効特性に有害な元素を安定化して耐歪み時効特性をも向上させる作用を有し、その効果は０．００５％以上の含有量で顕著になる。しかし、０．１％を超えて含有させると、強度を過度に高め、母材およびその溶接部の靭性を損なう。このため、添加する場合のＶ含有量は０．００５〜０．１％とするのがよい。
【００３６】
Ｃａ：
Ｃａは、鋼中の介在物の形態を制御し、母材およびその溶接部の靭性や耐食性を向上させる他、耐歪み時効特性に有害な元素を安定化して耐歪み時効特性をも向上させる作用を有し、その効果は０．０００５％の含有量で顕著になる。しかし、０．００３０％を超えて含有させると、鋼の清浄度が低下し、母材およびその溶接部の靭性が低下するだけでなく、耐歪み時効特性も低下する。このため、添加する場合のＣａ含有量は０．０００５〜０．００３０％とするのがよい。
【００３７】
Ｚｒ：
Ｚｒは、鋼中の介在物の形態を制御し、母材およびその溶接部の靭性や耐食性を向上させる他、耐歪み時効特性に有害な元素を安定化して耐歪み時効特性を向上させる作用をも有し、その効果は０．００５％の含有量で顕著になる。しかし、０．０３％を超えて含有させると、鋼の清浄度が低下し、母材およびその溶接部の靭性が低下するだけでなく、耐歪み時効特性も低下する。このため、添加する場合のＺｒ含有量は０．００５〜０．０３％とするのがよい。
【００３８】
Ｂ：
Ｂは、焼入性を向上させ、強度および靭性を向上させる作用を有し、その効果は０．０００３％以上の含有量で顕著になる。しかし、０．００３％を超えて含有させると、強度を過度に高め、母材およびその溶接部の靭性を損なう。このため、添加する場合のＢ含有量は０．０００３〜０．００３％とするのがよい。
【００３９】
Ｃ、Ｓｉ、Ｐ、Ｎｂ、Ｔｉ、Ａｌ、ＮおよびＯの関係：
これら元素の含有量は、上記の範囲内において、下記の(1)式で定義されるＡ値が０．３５以下、(2)式で定義されるＢ値が１．６以下となる含有量でなければならない。すなわち、Ａ値が０．３５を超えるか、またはＢ値が１．６を超えると、歪み時効感受性が増大し、所望の耐歪み時効特性が確保できない。このことは、後述する実施例の結果からも明らかである。なお、Ｂ値の好ましい上限は０．８０である。
【００４０】
Ａ＝50Ｎ＋Ｃ＋0.3Si＋10(Ｐ＋Ｏ) ・・・・・・・・・ (1)
Ｂ＝(50Ｎ＋Ｃ＋10Ｏ)／(4Nb＋10Ti＋2sol.Al) ・・・・ (2)
ここで、(1) 式と(2) 式中の元素記号は鋼中に含まれる各元素の含有量（質量％）を意味する。
【００４１】
次に、製造方法について説明する。
【００４２】
素材鋼の加熱温度：
加熱温度が１２００℃を超えると、その後の熱間圧延後に、歪み時効に有害な元素を安定化できず、より良好な耐歪み時効特性の確保が困難になると同時に、構造用鋼材としての良好な低温靭性を確保することも難しくなる。また、９５０℃未満では目的とする７６０ＭＰａ以上の引張強さを安定して確保することが難しくなる。このため、素材鋼の加熱温度は９５０〜１２００℃とするのが望ましい。
【００４３】
熱間圧延の仕上温度：
圧延仕上温度が８５０℃を超えると、仕上げ圧延後直ちに水冷（直接焼入れ）したとしても、所望の低温靭性を安定して確保することが難しくなる。また、６５０℃未満では目的とする７６０ＭＰａ以上の引張強さを安定して確保することが難しくなる。このため、熱間圧延の仕上温度は６５０〜８５０℃とするのが望ましい。好ましい範囲は７００〜８００℃である。
【００４４】
水冷（加速冷却）開始温度：
直接焼入れ時の水冷開始温度が５００℃を下回ると、圧延仕上温度が８５０〜６５０℃の範囲であっても、良好な強度および低温靭性を安定して確保することが難しくなるだけでなく、より良好な耐歪み時効特性の確保も困難になる。このため、水冷開始温度は５００℃以上とするのがの望ましい。
【００４５】
加速冷却速度：
熱間圧延後の加速冷却は、鋼中の残留オーステナイトの分解を防ぎ、耐歪み時効特性をより一層向上させるのに必要であるが、４℃／秒未満の冷却速度では残留オーステナイトの分解を十分に防ぐことができず、耐歪み時効特性をより一層向上させることが困難になる。このため、加速冷却速度は４℃／秒以上とするのがの望ましい。好ましくは１０℃／秒以上とするのがより望ましい。なお、加速冷却速度は、速ければ速いほどよく、上限は特に定める必要はないが、あまり速くするとコスト増になりやすいので、１００℃／秒以下とするのがよい。
【００４６】
加速冷却の停止温度：
加速冷却時の冷却停止温度が３００℃を超えると、目的とする７６０ＭＰａ以上の引張強さ、および所望の靭性を確保することが難しくなるだけでなく、歪み時効脆化の抑制に有効な適量の残留オーステナイトが分解し、より良好な耐歪み時効特性の確保も困難になる。このため、加速冷却の停止温度は３００℃以下とするのがの望ましい。なお、加速冷却停止後、室温になるまでの間の冷却には何らの制約もなく、空冷または徐冷などすればよい。
【００４７】
さらに、溶接鋼管の製造方法について説明する。
【００４８】
本発明の溶接鋼管は、上記条件のもとに製造された鋼板を管状に成形し、その突き合わせ部を溶接接合して製造されるが、その際、鋼板の管状への成形は、６００℃以下の温度域でおこなう必要がある。これは、成形温度が６００℃を超えると、硬質相の機能を低下させる恐れがあるためである。
【００４９】
鋼板の管状への成形は、成形後の鋼管外径をＤ（ｍｍ）、肉厚（鋼板板厚）をｔ（ｍｍ）とした場合、（ｔ／Ｄ）値が０．１以下になるように成形するのが望ましい。これは、（ｔ／Ｄ）値が０．１を超えると、靭性と耐歪み時効脆化特性が劣化し、所望の靭性と耐歪み時効脆化特性が確保しにくくなるためである。
【００５０】
以下、本発明を実施例に基づいて説明する。
【００５１】
【実施例】
表１に示す化学組成を有する１４種類の鋼からなるスラブを準備した。
【００５２】
【表１】
【００５３】
【表２】
【００５４】
採取した各試験片は、引張試験とシャルピー衝撃試験に供し、母材の降伏強さ（ＭＰａ）、引張強さ（ＭＰａ）、一様伸び率（％）および破面遷移温度（ｖＴｓ：℃）を調べる一方、−３０℃におけるＨＡＺのシャルピー吸収エネルギー（ｖＥ−３０℃：Ｊ）を調べた。
【００５５】
また、各鋼板の一部には、歪み量が１．５％と３．０％の引張歪みを付与した後、２５０℃に１時間加熱保持する歪み時効処理をおこない、この歪み時効処理後の各鋼板からＪＩＳ Ｚ ２２０１に規定される４号試験片とＪＩＳ Ｚ ２２０２規定されるＶノッチ試験片を採取して引張試験とシャルピー衝撃試験に供し、一様伸び率（％）と破面遷移温度（ｖＴｓ：℃）を調べ、これらの調査結果を表２に併せて示した。
【００５６】
表２に示す結果からわかるように、鋼の化学組成と製造条件が本発明で規定する範囲内である試番１〜１１の鋼板は、いずれも歪み時効処理前の引張強さが７６２ＭＰａ以上と高く、一様伸び率が３．９％以上、ｖＴｓが−７８℃以下、ＨＡＺのｖＥ−３０℃が１４８Ｊ以上と良好であるだけでなく、３．０％の歪み時効処理後の一様伸び率が歪み時効処理前の６０％以上の値を保っている。
【００５８】
これに対し、前述した(2) 式で定義されるＢ値が本発明で規定する上限値の１．６を超える試番１６や、同じく(1) 式で定義させるＡ値が本発明で規定する上限値の０．４４を超える試番１７の鋼板など、鋼の化学組成が本発明で規定する範囲を外れる試番１６〜２０の鋼板は、３．０％の歪み時効処理後の一様伸び率が、いずれも、歪み時効処理前の９〜３７％と悪い。
【００５９】
【発明の効果】
本発明の高強度鋼材、たとえば鋼板は、耐歪み時効特性に優れており、耐歪み時効特性が良好な高強度溶接鋼管のような溶接構造物を得るのに使用して好適で、産業上極めて有用である。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-strength steel material excellent in strain aging characteristics having a tensile strength of 760 MPa or more, and more specifically for producing welded structures such as line pipes and various pressure vessels for transporting natural gas and crude oil. The present invention relates to a steel material (steel plate, steel pipe, shape steel, bar steel, etc.) suitable for use and a method for producing the same.
[0002]
[Prior art]
In pipelines for long-distance transportation of natural gas and crude oil, reduction of transportation costs is a universal need, and improvement in transportation efficiency is required by increasing operating pressure. In order to increase the operating pressure, a method of increasing the thickness of a conventional strength grade line pipe can be considered. However, this method has a problem in that, in addition to reducing the welding efficiency in the field, the construction efficiency is reduced due to an increase in the mass of the structure.
[0003]
On the other hand, there is a growing need to limit the increase in wall thickness by increasing the strength of the material of the line pipe itself. Currently, API (American Petroleum Institute) standardizes X80 grade (tensile strength of 620 MPa or more) steel. Have been put to practical use.
[0004]
Furthermore, as a high-strength line pipe material, as disclosed in JP-A-8-199292 and 8-269546, the X100 grade (tensile strength of 760 MPa or more) super-class with a high Mn content is set. There is high strength steel.
[0005]
However, large-diameter welded steel pipes such as UOE steel pipes, which are the mainstays of line pipes, and medium- and small-diameter welded steel pipes represented by ERW steel pipes, are formed at room temperature, that is, by cold working. Since so-called processing distortion occurs, even if a material made of a high-performance material (steel) is used as the material steel plate, the welded steel pipe of the product may not retain the properties of the material steel plate.
[0006]
Further, even in a steel material that is not subjected to cold working, there may be a partial accumulation of distortion such as thermal distortion that occurs during welding or heat treatment and distortion that occurs during long-term use as a structural member.
[0007]
Such a strain is a small strain amount of 5% or less. However, when a strained steel material is used for a longer period of time, it is necessary to pay attention to deterioration of the steel material due to strain aging.
[0008]
Strain aging occurs when the steel material is used at room temperature for a long time, but is accelerated by heating the steel material to 100 to 250 ° C. for coating treatment or the like.
[0009]
It is known that the deterioration of steel materials due to strain aging occurs to some extent even in steel materials that have been used frequently in the past with tensile strengths of 392 MPa or more and 490 MPa or more. It has been confirmed that there is almost no problem.
[0010]
On the other hand, in the above-described high-strength steel of the above-described X80 grade steel grade having a tensile strength of 620 MPa or more, there is currently no systematic investigation on the deterioration of the steel material due to strain aging. In particular, it is necessary to take measures against work-hardening properties such as a reduction in uniform elongation during tensile testing as well as a reduction in toughness such as Charpy properties.
[0011]
However, in general, the higher the strength of a metal material, the lower the elongation and ductility, particularly the uniform elongation characteristic. Therefore, it is considered that measures against characteristic deterioration due to work hardening accompanying strain aging treatment are required.
[0012]
As a result of studying various welded structural steel materials having a tensile strength of 760 MPa or more by the present inventor, many welded structural steel materials are cold-worked with a strain amount of 3%, held at 250 ° C. for 1 hour, and then air-cooled. It has been found that after aging treatment, degradation of toughness and work hardening properties occurs. In particular, the uniform elongation may be significantly reduced, which may impair the safety as a structural member. However, there has been almost no technology for improving the safety as a structural material by improving the strain aging resistance to the problem of high strength steel.
[0013]
[Problems to be solved by the invention]
The present invention has been made in view of the actual situation as described above, and the purpose thereof is a high-tensile steel material excellent in strain aging resistance and weld toughness having a tensile strength of 760 MPa or more, and more specifically good. It has toughness and weldability and is excellent in toughness of the welded part. For example, strain aging such that the uniform elongation after 3% strain aging treatment is 0.6 times or more of the uniform elongation before strain aging treatment An object of the present invention is to provide a high-strength steel material typified by a steel plate suitable for use as a material for a welded structure such as a welded steel pipe having excellent work-hardening characteristics and low-temperature toughness even after treatment, and a method for producing the same.
[0014]
[Means for Solving the Problems]
The present inventors, in order to attain the aforementioned object, the tensile strength is high Toughness of high strength steel material for welded structures above 760 MPa, to improve improved and resistance to strain age characteristics of weldability, various As a result of the examination, the following was found.
(A) the content of direct causative N and C strain aging, and Si to promote strain aging of the high strength steel material, limit the contents of P and O (oxygen), in particular the expression "A = 50N + C + 0.3Si + 10 (P + O) (where each symbol represents the content (% by mass) of each element contained in the steel) so that the A value is 0.35 or less. If the element content is adjusted within the range described later, low temperature toughness and uniform elongation after strain aging are improved.
(B) Nb, Ti and Al has an effect to reduce the strain aging characteristic above a tensile strength of 760MPa high strength steel material, at least Nb, Ti, as well as added as an essential component 3 elements Al, formula B value defined by “B = (50N + C + 10O) / (4Nb + 10Ti + 2sol.Al) (where each element symbol means the content (mass%) of each element contained in the steel)” is 1.6 or less If the content of each element is adjusted within the range described below, the aging characteristic sensitivity is lowered, and deterioration due to strain aging is suppressed.
(C) And when satisfy | filling both said formulas in the composition range mentioned later, it is excellent in weldability, toughness, and the toughness of the welded part, and the uniform elongation after 3% strain aging treatment is strain aging treatment. High strength steel materials typified by steel sheets suitable for use as welded structural materials such as welded steel pipes with excellent work hardening characteristics of 0.6 times or more of the previous uniform elongation and good low temperature toughness are obtained. It is done.
(D) Moreover, said high-strength steel materials represented by a steel plate are the temperature range which finishes hot rolling at the finishing temperature of 850-650 degreeC after heating the raw material steel to 950-1200 degreeC, and is not less than 500 degreeC. To 300 ° C. or less at an accelerated cooling rate of 4 ° C./second or more, the uniform elongation after the strain aging treatment of 3% is 0.6 times or more of the uniform elongation before the strain aging treatment. It is possible to stably manufacture products having excellent work-hardening characteristics.
[0015]
The gist of the present invention completed based on the above findings is the following (1), (2) high strength steel materials excellent in strain aging characteristics, the following (3) manufacturing method of high strength steel materials, (4 ) In a high strength welded steel pipe excellent in strain aging characteristics and a high strength welded steel pipe in the following (5).
(1) The chemical composition is mass%, C: 0.01 to 0.10%, Si: 0.15% or less, Mn: 1.00 to 2.50%, P: 0.010% or less, S : 0.005% or less, Nb: 0.005 to 0.06%, Ti: 0.004 to 0.025%, sol. Al: 0.05% or less, N: 0.0050% or less, O (oxygen): 0.003% or less, Cu: 0 to 1.5%, Ni: 0 to 2.5%, Mo: 0 to 0 .80%, Cr: 0~1.0%, V: 0~0.1%, Zr: 0~0.03%, Ca: 0~0.0030% and B: 0 to 0.002% and the balance there a Fe and impurities, a value of 0.35 or less which is defined by the following equation (1), B value defined by equation (2) becomes 1.6 or less in the steel, the tensile strength A high-strength steel material excellent in strain aging resistance that is 760 MPa or more.
[0016]
A = 50N + C + 0.3Si + 10 (P + O) (1)
B = (50N + C + 10O) / (4Nb + 10Ti + 2sol.Al) (2)
Here, the element symbols in the formulas (1) and (2) mean the content (mass%) of each element contained in the steel.
(2) The high-strength steel material according to (1), wherein the steel material is a steel plate.
(3) By mass%, C: 0.01 to 0.10%, Si: 0.15% or less, Mn: 1.00 to 2.50%, P: 0.010% or less, S: 0.005 %, Nb: 0.005 to 0.06%, Ti: 0.004 to 0.025%, sol. Al: 0.05% or less, N: 0.0050% or less, O (oxygen): 0.003% or less, Cu: 0 to 1.5%, Ni: 0 to 2.5%, Mo: 0 to 0 .80%, Cr: 0~1.0%, V: 0~0.1%, Zr: 0~0.03%, Ca: 0~0.0030% and B: 0 to 0.002% and the balance Is a steel having Fe and impurities, the A value defined by the following formula (1) is 0.35 or less, and the B value defined by the formula (2) is 1.6 or less. After heating, hot rolling is performed to finish rolling at a finishing temperature of 850 to 650 ° C., and tensile strength is accelerated and cooled at a cooling rate of 4 ° C./second or higher from a temperature range not lower than 500 ° C. to a temperature of 300 ° C. or lower A method for producing a high-strength steel material having excellent strain aging characteristics of 760 MPa or more.
[0017]
A = 50N + C + 0.3Si + 10 (P + O) (1)
B = (50N + C + 10O) / (4Nb + 10Ti + 2sol.Al) (2)
Here, the element symbols in the formulas (1) and (2) mean the content (mass%) of each element contained in the steel.
(4) A high-strength welded steel pipe having a base material portion that is the high-strength steel sheet according to (2) and excellent in strain aging resistance.
(5) A method for producing a high-strength welded steel pipe excellent in strain aging resistance, in which the high-strength steel sheet according to (2) is formed into a tubular shape in a temperature range of 600 ° C. or less and the butt portion is welded.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the reason why the present invention is defined as described above will be described in detail. In the following description, “%” means “% by mass” unless otherwise specified.
[0019]
First, the chemical composition of steel will be described.
[0020]
C: 0.01 to 0.10%
C is contained for the purpose of securing the strength of the base material. However, if it is less than 0.01%, the hardenability is insufficient, and it is difficult to secure a tensile strength of 760 MPa or more, and the toughness of the base material is not sufficient. On the other hand, if the content exceeds 0.10%, not only the toughness and weldability of the base metal, but also the toughness of the heat affected zone of the base metal is deteriorated, and the strain aging resistance is deteriorated. Therefore, the C content is set to 0.01 to 0.10%. A preferable range is 0.01 to 0.06%.
[0021]
Si: 0.15% or less Si is normally added as a deoxidizer, but also the content results in a decrease in toughness in the base metal and both its weld exceeds 0.15%, resistance to strain age The characteristics are also degraded. Therefore, the Si content is set to 0.15 % or less . A preferable upper limit is 0.10%.
[0022]
Mn: 1.00-2.50%
Mn is added and added to improve the hardenability of the steel and increase the strength. However, if the content is less than 1.00%, it is difficult to ensure the desired strength. On the other hand, if the content exceeds 2.50%, both the base metal and its welded part cause a decrease in toughness. Therefore, the Mn content is set to 1.00 to 2.50%. In addition, from the viewpoint of improving the toughness of the welded portion, it is desirable that the amount of Mn is small. A preferable range of the Mn content is 1.00 to 1.90%, and a more preferable range is 1.00 to 1.70%.
[0023]
P: 0.010% or less P is an impurity element, which not only impairs the low-temperature toughness of the base metal and its weld heat-affected zone, but also reduces weldability and further reduces strain aging resistance. Therefore, the lower the P content, the better. However, excessive reduction leads to an increase in cost and there is no particular problem if it is up to 0.010%, so the upper limit was made 0.010%. A preferable upper limit is 0.005%.
[0024]
S: 0.005% or less S is an impurity element similar to P described above, and not only impairs the low temperature toughness of the base metal and its weld heat affected zone, but also reduces weldability. Accordingly, the S content is preferably as low as the above P, but excessive reduction causes an increase in cost and there is no particular problem if it is up to 0.005%. 0.005%. A preferable upper limit is 0.002%.
[0025]
Nb: 0.005 to 0.06%
Nb not only significantly refines the toughness of high-strength steel by refining the microstructure of the base metal, but also stabilizes these elements by combining with elements C and N harmful to strain aging resistance, It has the effect of improving strain aging resistance. However, if the content is less than 0.005%, the above effects cannot be obtained. Conversely, if the content exceeds 0.06%, not only the weldability of the base metal is impaired, but also toughness and strain aging resistance are obtained. On the contrary, it lowers. Therefore, the Nb content is set to 0.005 to 0.06%. A preferable range is 0.005 to 0.03%, and a more preferable range is 0.005 to 0.02%.
[0026]
Ti: 0.004 to 0.025%
Ti combines with elements C and N, which are harmful to the strain aging resistance, to stabilize these elements and greatly improve the strain aging resistance, as well as the structure of the base material and its weld heat affected zone. Is effective in improving the low-temperature toughness of the base material of high-strength steel and its weld heat-affected zone. However, if the content is less than 0.004%, the above effect cannot be obtained. Conversely, if the content exceeds 0.025%, not only the strain aging characteristics are impaired, but also the weldability and toughness are lowered. Let Therefore, the Ti content is set to 0.004 to 0.025%. A preferred range is 0.004 to 0.015%.
[0027]
sol. Al: 0.05% or less Al is added as a deoxidizing agent, but has an effect of greatly improving the strain aging resistance by combining and stabilizing N, which is an element harmful to the strain aging resistance. The effect of improving strain aging resistance by Al is extremely small. Although obtained with an Al content, the effect is sol. It becomes remarkable with the Al content. However, its content is sol. When the Al content exceeds 0.05%, not only the toughness of the welded portion is deteriorated, but also the strain aging characteristics and weldability are lowered. Therefore, sol. The Al content was 0.05% or less. A preferable upper limit is 0.03%.
[0028]
N: 0.0050% or less N is an impurity element extremely harmful to strain aging resistance. When the content exceeds 0.0050%, not only does the toughness of the base metal and its welded part significantly decrease, but also N Even if other measures for improving the strain aging characteristics are taken, good strain aging characteristics cannot be obtained. Therefore, the N content is set to 0.0050% or less. The N content is preferably as low as possible, and the preferable upper limit is 0.0030%.
[0029]
O (oxygen): 0.003% or less O is an impurity element that is extremely harmful to the strain aging resistance as in the case of N described above, and if its content exceeds 0.003%, the base material and its weld Not only does the toughness of the part deteriorate significantly, but even if other measures for improving the anti-strain aging characteristics are taken, good anti-strain aging characteristics cannot be obtained. Therefore, the O content is set to 0.003% or less. The lower the O content, the better. The preferable upper limit is 0.0020%, and the more preferable upper limit is 0.0015%.
[0030]
The following elements do not have to be added, but if added and contained within the following ranges, the strength, toughness, corrosion resistance, etc. of the base metal and the weld heat affected zone should be improved without impairing the strain aging resistance characteristics. Can do. For this reason, when manufacturing a thicker steel plate or a high-strength steel material with high strength, one or more of these elements may be added as necessary.
[0031]
Cu:
Cu has the effect of improving the hardenability and toughening the base material without significantly impairing the weldability, and the effect becomes significant when the content is 0.1% or more. However, if the content exceeds 1.5%, not only the toughness of the base metal and its welded portion is impaired, but also the hot ductility may be greatly reduced. For this reason, when added, the Cu content is preferably 0.1 to 1.5%.
[0032]
Ni:
Ni has the effect | action which improves the low temperature toughness of a high strength steel, a brittle crack propagation stop performance, and weldability, The effect becomes remarkable by content 0.20% or more. However, if the content exceeds 2.5%, excessive retained austenite may be generated by quenching and tempering treatment, and yield strength may be reduced. For this reason, when Ni is added, the Ni content is preferably 0.20 to 2.5%.
[0033]
Cr:
Cr has an effect of improving hardenability and improving strength and toughness by precipitation strengthening during tempering, and the effect becomes remarkable when the content is 0.10% or more. However, if the content exceeds 1.0%, the strength is excessively increased and the toughness of the base metal and its welded portion is impaired. For this reason, when Cr is added, the Cr content is preferably 0.10 to 1.0%.
[0034]
Mo:
Mo improves hardenability and improves strength and toughness by solid solution strengthening, and also promotes refinement of the structure when combined with Nb, and at the same time, disperses appropriate retained austenite in the steel to prevent strain. It has the effect of improving the embrittlement characteristics, and the effect becomes remarkable when the content is 0.10% or more. However, if the content exceeds 0.80%, the strength is excessively increased and the toughness of the base material and its welded portion is impaired. For this reason, when Mo is added, the Mo content is preferably 0.10 to 0.80%.
[0035]
V:
V improves hardenability, improves strength and toughness, stabilizes elements harmful to strain aging characteristics, and improves strain aging characteristics, and the effect is 0.005%. It becomes remarkable with the above content. However, if the content exceeds 0.1%, the strength is excessively increased and the toughness of the base metal and its welded portion is impaired. For this reason, when V is added, the V content is preferably 0.005 to 0.1%.
[0036]
Ca:
Ca controls the form of inclusions in the steel and improves the toughness and corrosion resistance of the base material and its welds, and also stabilizes elements harmful to the strain aging characteristics and improves the strain aging characteristics. The effect becomes remarkable at a content of 0.0005%. However, if the content exceeds 0.0030%, the cleanliness of the steel is lowered, not only the toughness of the base metal and its welded portion is lowered, but also the strain aging resistance is lowered. For this reason, when Ca is added, the Ca content is preferably 0.0005 to 0.0030%.
[0037]
Zr:
Zr controls the form of inclusions in steel and improves the toughness and corrosion resistance of the base metal and its welds, as well as stabilizing elements that are harmful to the strain aging characteristics and improving the strain aging characteristics. The effect becomes remarkable at a content of 0.005%. However, if the content exceeds 0.03%, the cleanliness of the steel is lowered, not only the toughness of the base metal and its welded portion is lowered, but also the strain aging resistance is lowered. Therefore, the Zr content when added is preferably 0.005 to 0.03%.
[0038]
B:
B has the effect of improving hardenability and improving strength and toughness, and the effect becomes significant when the content is 0.0003% or more. However, if the content exceeds 0.003%, the strength is excessively increased and the toughness of the base material and its welded portion is impaired. Therefore, the B content when added is preferably 0.0003 to 0.003%.
[0039]
Relationship between C, Si, P, Nb, Ti, Al, N and O:
Within these ranges, the content of these elements is such that the A value defined by the following formula (1) is 0.35 or less and the B value defined by the formula (2) is 1.6 or less. Must. That is, if the A value exceeds 0.35 or the B value exceeds 1.6, the strain aging sensitivity increases, and a desired strain aging resistance characteristic cannot be ensured. This is also clear from the results of Examples described later. In addition , the preferable upper limit of B value is 0.80.
[0040]
A = 50N + C + 0.3Si + 10 (P + O) (1)
B = (50N + C + 10O) / (4Nb + 10Ti + 2sol.Al) (2)
Here, the element symbols in the formulas (1) and (2) mean the content (mass%) of each element contained in the steel.
[0041]
Next, a manufacturing method will be described.
[0042]
Heating temperature of material steel:
When the heating temperature exceeds 1200 ° C., elements that are harmful to strain aging cannot be stabilized after the subsequent hot rolling, and it becomes difficult to ensure better strain aging resistance characteristics. It also becomes difficult to ensure low temperature toughness. Moreover, if it is less than 950 degreeC, it will become difficult to ensure the target tensile strength of 760 MPa or more stably. For this reason, it is desirable that the heating temperature of the material steel is 950 to 1200 ° C.
[0043]
Hot rolling finishing temperature:
When the rolling finishing temperature exceeds 850 ° C., it is difficult to stably secure desired low temperature toughness even if water cooling (direct quenching) is performed immediately after finish rolling. Moreover, if it is less than 650 degreeC, it will become difficult to ensure the target tensile strength of 760 MPa or more stably. For this reason, it is desirable that the finishing temperature of the hot rolling is 650 to 850 ° C. A preferred range is 700-800 ° C.
[0044]
Water cooling (accelerated cooling) start temperature:
When the water cooling start temperature during direct quenching is less than 500 ° C, not only is it difficult to stably ensure good strength and low temperature toughness even if the rolling finishing temperature is in the range of 850 to 650 ° C, but more It is also difficult to ensure good strain aging characteristics. For this reason, it is desirable that the water cooling start temperature is 500 ° C. or higher.
[0045]
Accelerated cooling rate:
Accelerated cooling after hot rolling is necessary to prevent the decomposition of residual austenite in steel and further improve the strain aging characteristics, but at a cooling rate of less than 4 ° C / second, sufficient decomposition of residual austenite is sufficient. Therefore, it is difficult to further improve the strain aging characteristics. For this reason, the accelerated cooling rate is desirably 4 ° C./second or more. It is more desirable to set it at 10 ° C./second or more. The faster the accelerated cooling rate, the better. The upper limit is not particularly required, but if it is made too fast, the cost tends to increase, so it is preferable to set it at 100 ° C./second or less.
[0046]
Accelerated cooling stop temperature:
When the cooling stop temperature during accelerated cooling exceeds 300 ° C., it is difficult not only to ensure the target tensile strength of 760 MPa or more and the desired toughness, but also an appropriate amount effective for suppressing strain aging embrittlement. As a result, the retained austenite is decomposed, and it becomes difficult to secure better strain aging characteristics. For this reason, it is desirable that the accelerated cooling stop temperature be 300 ° C. or lower. In addition, there is no restriction | limiting in the cooling until it becomes room temperature after stopping accelerated cooling, What is necessary is just to carry out air cooling or slow cooling.
[0047]
Furthermore, the manufacturing method of a welded steel pipe is demonstrated.
[0048]
The welded steel pipe of the present invention is manufactured by forming a steel plate manufactured under the above conditions into a tubular shape and welding and joining the butted portions. At that time, the forming of the steel plate into a tubular shape is 600 ° C. or less. It is necessary to perform in the temperature range. This is because if the molding temperature exceeds 600 ° C., the function of the hard phase may be lowered.
[0049]
In forming a steel plate into a tubular shape, when the outer diameter of the steel pipe after forming is D (mm) and the thickness (steel plate thickness) is t (mm), the (t / D) value is 0.1 or less. It is desirable to mold it. This is because if the (t / D) value exceeds 0.1, the toughness and strain aging embrittlement resistance deteriorate, and it becomes difficult to ensure the desired toughness and strain aging embrittlement resistance.
[0050]
Hereinafter, the present invention will be described based on examples.
[0051]
【Example】
Slabs consisting of 14 types of steel having the chemical composition shown in Table 1 were prepared.
[0052]
[Table 1]
[0053]
[Table 2]
[0054]
Each collected specimen is subjected to a tensile test and a Charpy impact test, and the yield strength (MPa), tensile strength (MPa), uniform elongation (%), and fracture surface transition temperature (vTs: ° C) of the base material. On the other hand, the Charpy absorbed energy (vE- 30 ° C . : J) of HAZ at −30 ° C. was examined.
[0055]
In addition, a part of each steel sheet was subjected to a strain aging treatment in which a strain amount of 1.5% and 3.0% was applied, and then heated and maintained at 250 ° C. for 1 hour. Sample No. 4 specified in JIS Z 2201 and V-notch test piece specified in JIS Z 2202 were taken from each steel plate and subjected to tensile test and Charpy impact test. Uniform elongation (%) and fracture surface transition temperature (VTs: ° C.) was examined, and the results of these investigations are also shown in Table 2.
[0056]
As can be seen from the results shown in Table 2, all of the steel plates Nos. 1 to 11 in which the chemical composition and production conditions of the steel are within the range defined in the present invention have a tensile strength before strain aging treatment of 762 MPa or more. The uniform elongation is 3.9% or more, vTs is −78 ° C. or less, HAZ vE −30 ° C. is 148 J or more, and it is uniform after 3.0% strain aging treatment. The elongation rate is maintained at 60% or more before the strain aging treatment.
[0058]
On the other hand, the B value defined by the above-described equation (2) exceeds the upper limit of 1.6 defined by the present invention, and the A value defined by the equation (1) is also defined by the present invention. including steel Run No. 17 that exceeds the 0.44 upper limit value, the steel sheet of Run No. 16 to 20 deviate from the ranges chemical composition of the steel is specified by the present invention, 3.0% uniform after strain aging treatment Elongation rate is all bad, 9-37% before strain aging treatment.
[0059]
【The invention's effect】
The high-strength steel material of the present invention, for example, a steel plate, is excellent in strain aging characteristics, and is suitable for use in obtaining a welded structure such as a high-strength welded steel pipe having good strain aging characteristics. Useful.
Claims (5)
Ａ＝50Ｎ＋Ｃ＋0.3Si＋10(Ｐ＋Ｏ) ・・・・・・・・・・ (1)
Ｂ＝(50Ｎ＋Ｃ＋10Ｏ)／(4Nb＋10Ti＋2sol.Al) ・・・・ (2)
ここで、(1)式と(2)式中の元素記号は鋼中に含まれる各元素の含有量（質量％）を意味する。Chemical composition is mass%, C: 0.01-0.10%, Si: 0.15% or less, Mn: 1.00-2.50%, P: 0.010% or less, S: 0.0. 005% or less, Nb: 0.005 to 0.06%, Ti: 0.004 to 0.025%, sol. Al: 0.05% or less, N: 0.0050% or less, O (oxygen): 0.003% or less, Cu: 0 to 1.5%, Ni: 0 to 2.5%, Mo: 0 to 0 .80%, Cr: 0~1.0%, V: 0~0.1%, Zr: 0~0.03%, Ca: 0~0.0030% and B: 0 to 0.002% and the balance there a Fe and impurities, a value of 0.35 or less which is defined by the following equation (1), B value defined by equation (2) becomes 1.6 or less in the steel, the tensile strength A high-strength steel material excellent in strain aging resistance that is 760 MPa or more.
A = 50N + C + 0.3Si + 10 (P + O) (1)
B = (50N + C + 10O) / (4Nb + 10Ti + 2sol.Al) (2)
Here, the element symbols in the formulas (1) and (2) mean the content (mass%) of each element contained in the steel.
Ａ＝50Ｎ＋Ｃ＋0.3Si＋10(Ｐ＋Ｏ) ・・・・・・・・・・ (1)
Ｂ＝(50Ｎ＋Ｃ＋10Ｏ)／(4Nb＋10Ti＋2sol.Al) ・・・・ (2)
ここで、(1)式と(2)式中の元素記号は鋼中に含まれる各元素の含有量（質量％）を意味する。In mass%, C: 0.01 to 0.10%, Si: 0.15% or less, Mn: 1.00 to 2.50%, P: 0.010% or less, S: 0.005% or less, Nb: 0.005-0.06%, Ti: 0.004-0.025%, sol. Al: 0.05% or less, N: 0.0050% or less, O (oxygen): 0.003% or less, Cu: 0 to 1.5%, Ni: 0 to 2.5%, Mo: 0 to 0 .80%, Cr: 0~1.0%, V: 0~0.1%, Zr: 0~0.03%, Ca: 0~0.0030% and B: 0 to 0.002% and the balance Is a steel having Fe and impurities, the A value defined by the following formula (1) is 0.35 or less, and the B value defined by the formula (2) is 1.6 or less. After heating, hot rolling is performed to finish rolling at a finishing temperature of 850 to 650 ° C., and tensile strength is accelerated and cooled at a cooling rate of 4 ° C./second or higher from a temperature range not lower than 500 ° C. to a temperature of 300 ° C. or lower. A method for producing a high-strength steel material excellent in strain aging resistance of 760 MPa or more.
A = 50N + C + 0.3Si + 10 (P + O) (1)
B = (50N + C + 10O) / (4Nb + 10Ti + 2sol.Al) (2)
Here, the element symbols in the formulas (1) and (2) mean the content (mass%) of each element contained in the steel.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001019741A JP3654194B2 (en) | 2001-01-29 | 2001-01-29 | High-strength steel material with excellent strain aging resistance and its manufacturing method |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2001019741A JP3654194B2 (en) | 2001-01-29 | 2001-01-29 | High-strength steel material with excellent strain aging resistance and its manufacturing method |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2002220634A JP2002220634A (en) | 2002-08-09 |
| JP3654194B2 true JP3654194B2 (en) | 2005-06-02 |
Family
ID=18885567
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2001019741A Expired - Fee Related JP3654194B2 (en) | 2001-01-29 | 2001-01-29 | High-strength steel material with excellent strain aging resistance and its manufacturing method |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3654194B2 (en) |
Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101044161B1 (en) | 2003-06-12 | 2011-06-24 | 제이에프이 스틸 가부시키가이샤 | Low yield ratio, high strength, high toughness, thick steel plate and welded steel pipe |
| JP4507745B2 (en) * | 2003-07-31 | 2010-07-21 | Ｊｆｅスチール株式会社 | Low yield ratio high strength high toughness steel pipe excellent in strain aging resistance and manufacturing method thereof |
| JP4507746B2 (en) * | 2003-07-31 | 2010-07-21 | Ｊｆｅスチール株式会社 | Low yield ratio high strength high toughness steel pipe excellent in strain aging resistance and method for producing the same |
| JP4507747B2 (en) * | 2003-07-31 | 2010-07-21 | Ｊｆｅスチール株式会社 | Low yield ratio high strength high toughness steel pipe excellent in strain aging resistance and method for producing the same |
| JP4696615B2 (en) | 2005-03-17 | 2011-06-08 | 住友金属工業株式会社 | High-tensile steel plate, welded steel pipe and manufacturing method thereof |
| JP5028761B2 (en) * | 2005-07-19 | 2012-09-19 | Ｊｆｅスチール株式会社 | Manufacturing method of high strength welded steel pipe |
| JP5069863B2 (en) * | 2005-09-28 | 2012-11-07 | 株式会社神戸製鋼所 | 490 MPa class low yield ratio cold-formed steel pipe excellent in weldability and manufacturing method thereof |
| JP5217773B2 (en) * | 2007-09-19 | 2013-06-19 | Ｊｆｅスチール株式会社 | High-strength welded steel pipe for low temperature having a tensile strength of 570 MPa or more and 760 MPa or less excellent in weld heat-affected zone toughness and method for producing the same |
| CN104789863B (en) * | 2015-03-20 | 2017-01-18 | 宝山钢铁股份有限公司 | X80 pipeline steel with good anti-strain aging property, pipeline pipe and manufacturing method of pipeline pipe |
-
2001
- 2001-01-29 JP JP2001019741A patent/JP3654194B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JP2002220634A (en) | 2002-08-09 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP4811166B2 (en) | Manufacturing method of super high strength welded steel pipe exceeding tensile strength 800MPa | |
| JP5217556B2 (en) | High strength steel pipe for low temperature excellent in buckling resistance and weld heat affected zone toughness and method for producing the same | |
| JP3996824B2 (en) | Steel for liquid phase diffusion bonding with excellent low temperature transformation cracking resistance | |
| JP5509923B2 (en) | Method for producing high-tensile steel sheet having a tensile strength of 1100 MPa or more for laser welding or laser-arc hybrid welding | |
| EP3276024B1 (en) | Thick steel plate for structural pipes or tubes, method of producing thick steel plate for structural pipes or tubes, and structural pipes and tubes. | |
| WO2009125863A1 (en) | High-strength steel plate excellent in low-temperature toughness, steel pipe, and processes for production of both | |
| JPH10237583A (en) | High tensile strength steel and its production | |
| JP2013204103A (en) | High strength welded steel pipe for low temperature use having superior buckling resistance, and method for producing the same, and method for producing steel sheet for high strength welded steel pipe for low temperature use having superior buckling resistance | |
| WO2008007737A1 (en) | Bend pipe and process for producing the same | |
| JP2008144199A (en) | Ferritic stainless steel for automobile exhaust gas passage member, and welded steel pipe | |
| JP2007260715A (en) | Method for producing superhigh strength welded steel pipe | |
| EP3276025B1 (en) | Steel plate for structural pipe, method for producing steel plate for structural pipe, and structural pipe | |
| JP5407478B2 (en) | High-strength thick steel plate with excellent toughness of heat-affected zone of single layer large heat input welding and method for producing the same | |
| JP2018053281A (en) | Rectangular steel tube | |
| JP5157066B2 (en) | A method for producing a high-strength, high-toughness thick steel plate excellent in cut cracking resistance and DWTT characteristics. | |
| JP2006233263A (en) | Method for producing high strength welded steel tube having excellent low yield ratio and weld zone toughness | |
| JP2007260716A (en) | Method for producing ultrahigh strength welded steel pipe having excellent deformability | |
| JP3770106B2 (en) | High strength steel and its manufacturing method | |
| KR102002241B1 (en) | Steel plate for structural pipes or tubes, method of producing steel plate for structural pipes or tubes, and structural pipes and tubes | |
| KR20210099627A (en) | High-strength steel products and their manufacturing method | |
| KR19980703593A (en) | Welding coefficient with excellent fatigue strength | |
| JP3654194B2 (en) | High-strength steel material with excellent strain aging resistance and its manufacturing method | |
| JP5028761B2 (en) | Manufacturing method of high strength welded steel pipe | |
| JP5505487B2 (en) | High-strength, high-tough steel plate with excellent cut crack resistance and DWTT properties | |
| JP2001335884A (en) | High strength thick steel plate excellent in ctod(crack tip opening displacement) characteristic, and its manufacturing method |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20040317 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20040330 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20040531 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20040616 |
|
| RD02 | Notification of acceptance of power of attorney |
Free format text: JAPANESE INTERMEDIATE CODE: A7422 Effective date: 20040616 |
|
| A02 | Decision of refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A02 Effective date: 20040810 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20041005 |
|
| A911 | Transfer of reconsideration by examiner before appeal (zenchi) |
Free format text: JAPANESE INTERMEDIATE CODE: A911 Effective date: 20041026 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20041214 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20050107 |
|
| 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: 20050208 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20050221 |
|
| R150 | Certificate of patent or registration of utility model |
Free format text: JAPANESE INTERMEDIATE CODE: R150 Ref document number: 3654194 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20080311 Year of fee payment: 3 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20090311 Year of fee payment: 4 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20100311 Year of fee payment: 5 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20100311 Year of fee payment: 5 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20110311 Year of fee payment: 6 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20120311 Year of fee payment: 7 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130311 Year of fee payment: 8 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130311 Year of fee payment: 8 |
|
| 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: 20130311 Year of fee payment: 8 |
|
| 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: 20140311 Year of fee payment: 9 |
|
| S533 | Written request for registration of change of name |
Free format text: JAPANESE INTERMEDIATE CODE: R313533 |
|
| R350 | Written notification of registration of transfer |
Free format text: JAPANESE INTERMEDIATE CODE: R350 |
|
| LAPS | Cancellation because of no payment of annual fees |