JP2005029840A - High strength steel for welded structure excellent in both of base metal toughness and weld part haz toughness, and its production method - Google Patents
High strength steel for welded structure excellent in both of base metal toughness and weld part haz toughness, and its production method Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 53
- 239000010959 steel Substances 0.000 title claims abstract description 53
- 239000010953 base metal Substances 0.000 title claims abstract description 31
- 238000004519 manufacturing process Methods 0.000 title claims description 16
- 238000010438 heat treatment Methods 0.000 claims abstract description 15
- 239000000203 mixture Substances 0.000 claims abstract description 8
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 6
- 239000012535 impurity Substances 0.000 claims abstract description 4
- 229910052742 iron Inorganic materials 0.000 claims abstract description 3
- 239000000463 material Substances 0.000 claims description 32
- 238000001816 cooling Methods 0.000 claims description 23
- 238000003466 welding Methods 0.000 claims description 18
- 229910000746 Structural steel Inorganic materials 0.000 claims description 17
- 238000001953 recrystallisation Methods 0.000 claims description 13
- 230000001186 cumulative effect Effects 0.000 claims description 10
- 238000005098 hot rolling Methods 0.000 claims description 10
- 230000009467 reduction Effects 0.000 claims description 10
- 229910000859 α-Fe Inorganic materials 0.000 claims description 10
- 229910001566 austenite Inorganic materials 0.000 claims description 9
- 238000003303 reheating Methods 0.000 claims description 6
- 238000005496 tempering Methods 0.000 claims description 3
- 229910052748 manganese Inorganic materials 0.000 abstract description 3
- 229910052757 nitrogen Inorganic materials 0.000 abstract description 3
- 229910052799 carbon Inorganic materials 0.000 abstract 1
- 229910052698 phosphorus Inorganic materials 0.000 abstract 1
- 229910052761 rare earth metal Inorganic materials 0.000 abstract 1
- 150000002910 rare earth metals Chemical class 0.000 abstract 1
- 239000002245 particle Substances 0.000 description 21
- 230000000694 effects Effects 0.000 description 17
- 238000005096 rolling process Methods 0.000 description 16
- 238000000034 method Methods 0.000 description 10
- 230000007423 decrease Effects 0.000 description 8
- 150000003568 thioethers Chemical class 0.000 description 6
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 5
- 150000004767 nitrides Chemical class 0.000 description 5
- 230000009466 transformation Effects 0.000 description 5
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 4
- 238000005516 engineering process Methods 0.000 description 4
- 150000001247 metal acetylides Chemical class 0.000 description 4
- 229910052760 oxygen Inorganic materials 0.000 description 4
- 239000001301 oxygen Substances 0.000 description 4
- 239000000126 substance Substances 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 3
- 229910052715 tantalum Inorganic materials 0.000 description 3
- 229910052726 zirconium Inorganic materials 0.000 description 3
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 2
- 229910001563 bainite Inorganic materials 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 230000003749 cleanliness Effects 0.000 description 2
- 238000004581 coalescence Methods 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 238000011084 recovery Methods 0.000 description 2
- 238000009628 steelmaking Methods 0.000 description 2
- 238000005728 strengthening Methods 0.000 description 2
- 238000004220 aggregation Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 239000002826 coolant Substances 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000008034 disappearance Effects 0.000 description 1
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- 238000002474 experimental method Methods 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000010309 melting process Methods 0.000 description 1
- 229910052750 molybdenum Inorganic materials 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 229910052758 niobium Inorganic materials 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000019086 sulfide ion homeostasis Effects 0.000 description 1
- 230000001629 suppression Effects 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、建築、橋梁、造船、海洋構造物、ラインパイプ、建設機械などの溶接構造物として広く利用可能な、母材靭性と溶接部ＨＡＺ靭性の両方に優れた４９０ＭＰａ級の引張強度を有する溶接構造物用鋼およびその製造方法に関するものである。
【０００２】
【従来の技術】
建築、橋梁、造船、海洋構造物など溶接構造物の脆性破壊防止の観点から、母材の靭性だけでなく、溶接部からの脆性破壊の発生抑制、すなわち、使用される鋼板のＨＡＺ靱性の向上に関する研究が数多く報告されてきた。一般に、母材靭性の確保のためには最終のフェライト粒径を小さくすることが肝要であり、必要靭性レベルにより普通圧延、制御圧延、さらには制御圧延＋加速冷却が利用されてきた。その基本はＡｌＮやＴｉＮなどの高温で安定な窒化物をピニング粒子として用いて、母材の加熱オーステナイト（γ）粒径を微細化した上で、さらに圧延によりオーステナイト中にフェライトの核生成サイトを多数導入し、最終フェライト粒径を微細にすることにある。
【０００３】
したがって、このような母材の製造方法では、当然ながら窒化物の種類により熱間圧延前の再加熱温度を変える必要が生じたり、加熱γ粒径の変動から最終のフェライト粒径にも変化が生じ、結果的に、母材靭性にバラツキが生じることがしばしば起こる。一方、溶接部ＨＡＺ靭性も加熱γ粒径が入熱量によって異なることから、要求靭性値が高いほどその値を小さくする必要があるにも関わらず、近年では加熱γ粒径が大きくなる条件、すなわち溶接施工能率の向上の観点から、大入熱溶接（およそ２０ｋＪ／ｍｍ以下）や超大入熱溶接（２０〜１５０ｋＪ／ｍｍ）が実施される場合が増加している。大入熱溶接と超大入熱溶接の鋼板への影響の差異は、高温での滞留時間の差異に起因しており、特に超大入熱溶接ではその時間が極めて長時間であるために、結晶粒径が著しく粗大化する領域が広く、靱性の低下が著しくなる点にある。
【０００４】
以上のような母材靭性のバラツキと溶接部ＨＡＺ靭性の入熱依存性の問題点を回避する抜本的な方法として、母材組織および溶接部ＨＡＺ組織の加熱γ粒径を強力なピニング粒子によって制御し、両者の高温での粒成長を顕著に抑制することが考えられる。これが実現できた場合は、母材靭性の安定性はもとより入熱が大きくなった場合にも溶接部ＨＡＺ靱性を十分に向上させることができる。また、母材の加熱γ粒径が著しく微細になる場合には、従来の制御圧延や加速冷却を用いることなく普通圧延でも同程度のフェライト粒径と母材靭性を付与できる可能性が出てくることから、本技術の確立は工業的価値が高い。
【０００５】
加熱γ粒径のピニング効果が最も期待できる粒子として、高温でも溶解しにくい酸化物や硫化物が考えられる。例えば、酸化物の導入方法としては鋼の溶製工程においてＴｉなどの脱酸元素を単独に添加する方法があるが、多くの場合に溶鋼保持中に酸化物の凝集合体がおこり粗大な酸化物の生成をもたらすことによりかえって鋼の清浄度を損ない靱性を低下させてしまうことが知られている。そのため、複合脱酸法などさまざまな工夫がなされているが、従来知られている方法では、高温での母材の加熱γ粒径を例えば１２５０℃付近において５０μｍ程度に微細化させるほどの技術は現時点では確立できていない。同様に、さらには溶接入熱が大きい場合の結晶粒粗大化を完全に阻止しうるほどの技術もできていない。
【０００６】
【発明が解決しようとする課題】
本発明者らは、従来以上にピニング粒子を微細分散させることを鋭意検討し、母材の加熱γ粒径を微細化し、同時に大入熱あるいは超大入熱溶接においても溶接部ＨＡＺ組織の加熱γ粒径を微細化し、母材靭性と溶接部ＨＡＺ靭性の両方に優れた高強度溶接構造用鋼の製造技術の確立を課題とした。
【０００７】
【課題を解決するための手段】
上記課題を解決するための本発明の要旨は、以下の通りである。
（１） 質量％で
Ｃ ：０．０１〜０．２０％
Ｓｉ ：０．０２〜０．５０％
Ｍｎ ：０．３〜２．０％
Ｐ ：≦０．０３％
Ｓ ：０．０００１〜０．０３０％
Ａｌ ：０．０００５〜０．０５％
Ｔｉ ：０．００３〜０．０５０％
Ｎ ：０．００１〜０．０１０％
ＲＥＭ：０．０００１〜０．０５０％
を含み、残部が鉄および不可避的不純物からなり、加熱γ粒径が最大でも５０μｍ以下であることを特徴とする母材靭性と溶接部ＨＡＺ靭性の両方に優れた高強度溶接構造用鋼。
（２） 質量％で、
Ｃｕ：０．０５〜１．５％
Ｎｉ：０．０５〜５．０％
Ｃｒ：０．０２〜１．５％
Ｍｏ：０．０２〜１．５０％
Ｖ ：０．０１〜０．１０％
Ｎｂ：０．０００１〜０．２０％
Ｚｒ：０．０００１〜０．０５０％
Ｔａ：０．０００１〜０．０５０％
Ｂ ：０．０００３〜０．００５０％
のうち１種または２種以上を含有することを特徴とする（１）記載の母材靭性と溶接部ＨＡＺ靭性の両方に優れた高強度溶接構造用鋼。
（３） 母材の最終のフェライト粒径が再加熱温度によらず３０μｍ以下であることを特徴とする（１）または（２）記載の母材靭性と溶接部ＨＡＺ靭性の両方に優れた高強度溶接構造用鋼。
（４） 溶接部ＨＡＺ組織の加熱γ粒径（旧オーステナイト粒径）が溶接入熱によらず２００μｍ以下であることを特徴とする（１）〜（３）のいずれか１項記載の母材靭性と溶接部ＨＡＺ靭性の両方に優れた高強度溶接構造用鋼。
（５） （１）または（２）記載の鋼と同一成分を有する鋼塊をＡｃ３点以上、１３５０℃以下に加熱後、再結晶温度域で熱間圧延した後、自然冷却することを特徴とする母材靭性と溶接部ＨＡＺ靭性の両方に優れた高強度溶接構造用鋼の製造方法。
（６） （１）または（２）記載の鋼と同一成分を有する鋼塊をＡｃ３点以上、１３５０℃以下に加熱後、再結晶温度域で熱間圧延し、さらに未再結晶温度域において累積圧下率で４０〜９０％の熱間圧延をした後、自然冷却することを特徴とする母材靭性と溶接部ＨＡＺ靭性の両方に優れた高強度溶接構造用鋼の製造方法。
（７） （１）または（２）記載の鋼と同一成分を有する鋼塊をＡｃ３点以上、１３５０℃以下に加熱後、再結晶温度域で熱間圧延し、さらに未再結晶温度域において累積圧下率で４０〜９０％の熱間圧延をした後、１〜６０℃／ｓｅｃの冷却速度で０〜６００℃まで冷却することを特徴とする母材靭性と溶接部ＨＡＺ靭性の両方に優れた高強度溶接構造用鋼の製造方法。
（８） （１）または（２）記載の鋼と同一成分を有する鋼塊をＡｃ３点以上、１３５０℃以下に加熱後、再結晶温度域で熱間圧延し、さらに未再結晶温度域において累積圧下率で４０〜９０％の熱間圧延をした後、１〜６０℃／ｓｅｃの冷却速度で０〜６００℃まで冷却し、引き続いて３００℃〜Ａｃ１点に加熱して焼戻し熱処理することを特徴とする母材靭性と溶接部ＨＡＺ靭性の両方に優れた高強度溶接構造用鋼の製造方法。
【０００８】
【発明の実施の形態】
ＲＥＭは、従来から強脱酸剤、脱硫剤として鋼の清浄度を高めることで、溶接熱影響部の靱性を向上させることが知られている。また、ＲＥＭを含有する酸化物の分散を制御して、母材靭性および溶接部ＨＡＺ靱性の両方を向上させる技術として用いた例が特開２００３−４９２３７号公報に記載されている。
本発明者らは、そのようなＲＥＭの強脱酸剤あるいは強力な硫化物生成能に着目するとともに、従来広く用いられてきたＴｉＮとの組合せによって、母材およびＨＡＺ組織を今まで以上に微細化できる余地があると考えた。
【０００９】
以下、本発明に関して詳細に説明する。
本発明者らは、Ｔｉを添加し弱脱酸した溶鋼中にＲＥＭを添加した場合の酸化物の状態とＴｉＮ量を系統的に調べた。その結果、Ｓｉ、Ｍｎによる脱酸後に、Ｔｉ添加、ＲＥＭ添加の順に添加した場合に、あるいはＴｉ添加とＲＥＭ添加を同時に行い、さらに平衡状態になった状態で再度ＲＥＭを添加することで、ＲＥＭの酸化物あるいは硫化物が極めて微細に、かつ高密度に生成されることを見出した。その粒子径は０．００５〜０．５μｍ、粒子数は鋼中に１ｍｍ２当たり１００００個以上であり、これらの存在は溶接部ＨＡＺ組織において強力なピニング力を有していることが確認された。さらに、ＴｉＮ量に注目した場合に、ＲＥＭ添加鋼では従来にない微細分散が認められ、これが母材の加熱γ粒径の微細化に上記ＲＥＭ酸化物（あるいは硫化物）とともに有効に作用し、母材加熱γ粒径が最大でも５０μｍ程度であることが判明した。
【００１０】
本発明は以上のような加熱γ粒径の微細化によって達成される母材靭性と溶接部ＨＡＺ靱性の両方に優れた鋼材に関するものであり、加熱γ粒径の変化を極力抑えた画期的な技術である。すなわち、本発明の特徴は、母材の加熱γ粒径（旧オーステナイト粒径）が再加熱温度によらず５０μｍ以下であり、さらに溶接部ＨＡＺ組織の加熱γ粒径（旧オーステナイト粒径）が溶接入熱によらず２００μｍ以下であり、これらのミクロ組織を反映して、母材靭性と溶接部ＨＡＺ靭性の両方に優れた高強度溶接構造用鋼を提供できる点にある。しかも、本技術を用いれば母材の製造条件の一つである再加熱温度によらず最終フェライト粒径を３０μｍ以下に安定して作り込むことができる。
【００１１】
本発明におけるＲＥＭの添加方法であるが、既に述べたように、最初に、Ｓｉ、Ｍｎを添加後、まず、Ｔｉを添加し溶鋼中の酸素量を調整した後、少量のＲＥＭを徐々に添加するか、あるいは、Ｔｉと少量のＲＥＭを同時に添加した後に、最終段階で再度ＲＥＭを添加する。最適なＲＥＭの添加量は、Ｔｉ添加後、溶鋼中に存在する酸素量などに依存するが、実験では、その時の酸素濃度はＴｉ添加量とＲＥＭ添加までの時間に依存し、ＴｉとＲＥＭ添加量を適正な範囲で制御すれば良い。なお、最終的なＲＥＭ添加時の溶存酸素量は０．１〜５０ｐｐｍ程度が適量である。下限の０．１ｐｐｍは微細なＲＥＭ酸化物（あるいはＲＥＭ硫化物）ができる最小の量であり、５０ｐｐｍを超えると粗大なＲＥＭ酸化物ができるようになり、ピニング力が弱くなることからこれを限度とした。
【００１２】
以下、本発明の成分の限定理由について述べる。
Ｃ：Ｃは鋼における母材強度を向上させる基本的な元素として欠かせない元素であり、その有効な下限として０．０１％以上の添加が必要であるが、０．２０％を越える過剰の添加では、鋼材の溶接性や靱性の低下を招くので、その上限を０．２０％とした。
Ｓｉ：Ｓｉは製鋼上脱酸元素として必要な元素であり、鋼中に０．０２％以上の添加が必要であるが、０．５％を越えるとＨＡＺ靱性を低下させるのでそれを上限とする。
Ｍｎ：Ｍｎは、母材の強度および靱性の確保に必要な元素であるが、２．０％を越えるとＨＡＺ靱性を著しく阻害するが、逆に０．３％未満では、母材の強度確保が困難になるために、その範囲を０．３〜２．０％とする。
【００１３】
Ｐ：Ｐは鋼の靱性に影響を与える元素であり、０．０３％を越えて含有すると鋼材の母材だけでなくＨＡＺの靱性を著しく阻害するのでその含有される上限を０．０３％とした。
Ｓ：Ｓは０．０３０％を越えて過剰に添加されると粗大な硫化物の生成の原因となり、靱性を阻害するが、その含有量が０．０００１％未満になると、粒内フェライトの生成に有効なＭｎＳ等の硫化物生成量が著しく低下するために、０．０００１〜０．０３０％をその範囲とする。
【００１４】
Ａｌ：Ａｌは通常脱酸剤として添加されるが、本発明においては、０．０５％越えて添加されるとＲＥＭの添加の効果を阻害するために、これを上限とする。また、ＲＥＭの酸化物を安定に生成するためには０．０００５％は必要であり、これを下限とした。
Ｔｉ：Ｔｉは、脱酸剤として、さらには窒化物形成元素としてし結晶粒の細粒化に効果を発揮する元素であるが、多量の添加は炭化物の形成による靱性の著しい低下をもたらすために、その上限を０．０５０％にする必要があるが、所定の効果を得るためには０．００３％以上の添加が必要であり、その範囲を０．００３〜０．０５０％とする。
【００１５】
Ｎ：Ｎは本来不純物として取り扱うべきものであるが、この量が適正範囲の場合においては、極めて強力なＴｉＮのピニング効果を現出させることから、０．００１〜０．０１０％とした。下限値はピニング効果を発揮するための最小量であり、上限値はＨＡＺ靭性を阻害するために規定した。
【００１６】
ＲＥＭ：ＲＥＭは硫化物を生成することにより伸長ＭｎＳの生成を抑制し、鋼材の板厚方向の特性、特に耐ラメラティアー性を改善する。さらにＲＥＭの介在物を通して強力なピニング効果を有していることから、本発明の重要な元素である。ＲＥＭは０．０００１％未満では、十分な効果が得られないので下限値を０．０００１％にした。逆に、０．０５０％を超えるとＲＥＭの粗大酸化物個数が増加し、超微細な酸化物あるいは硫化物の個数が低下するため、その上限を０．０５０％とする。
【００１７】
なお、本発明においては、上記の基本成分に、強度および靱性を改善する元素として、Ｃｕ、Ｎｉ、Ｃｒ、Ｍｏ、Ｖ、Ｎｂ、Ｚｒ、Ｔａ、Ｂの中で、１種または２種以上の元素を必要に応じて添加することができる。
【００１８】
Ｃｕ：Ｃｕは、靱性を低下させずに強度の上昇に有効な元素であるが、０．０５％未満では効果がなく、１．５％を越えると鋼片加熱時や溶接時に割れを生じやすくする。従って、その含有量を０．０５〜１．５％以下とする。
Ｎｉ：Ｎｉは、靱性および強度の改善に有効な元素であり、その効果を得るためには０．０５％以上の添加が必要であるが、５．０％以上の添加では溶接性が低下するために、その上限を５．０％とする。
Ｃｒ：Ｃｒは析出強化による鋼の強度を向上させるために、０．０２％以上の添加が有効であるが、多量に添加すると、焼入れ性を上昇させ、ベイナイト組織を生じさせ、靱性を低下させる。従って、その上限を１．５％とする。
【００１９】
Ｍｏ：Ｍｏは、焼入れ性を向上させると同時に、炭窒化物を形成し強度を改善する元素であり、その効果を得るためには、０．０２％以上の添加が必要になるが、１．５０％を越えた多量の添加は必要以上の強化とともに、靱性の著しい低下をもたらすために、その範囲を０．０２〜０．５０％以下とする。
Ｖ：Ｖは、炭化物、窒化物を形成し強度の向上に効果がある元素であるが、０．０１％以下の添加ではその効果がなく、０．１０％を越える添加では、逆に靱性の低下を招くために、その範囲を０．０１〜０．１０％以下とする。
Ｎｂ：Ｎｂは、炭化物、窒化物を形成し強度の向上に効果がある元素であるが、０．０００１％以下の添加ではその効果がなく、０．２０％を越える添加では、靱性の低下を招くために、その範囲を０．０００１〜０．２０％以下とする。
Ｚｒ、Ｔａ：ＺｒとＴａもＮｂと同様に炭化物、窒化物を形成し強度の向上に効果がある元素であるが、０．０００１％以下の添加ではその効果がなく、０．０５０％を越える添加では、逆に靱性の低下を招くために、その範囲を０．０００１〜０．０５０％以下とする。
【００２０】
Ｂ：Ｂは一般に、固溶すると焼入れ性を増加させるが、またＢＮとして固溶Ｎを低下させ、溶接熱影響部の靱性を向上させる元素である。従って、０．０００３％以上の添加でその効果を利用できるが、過剰の添加は、靱性の低下を招くために、その上限を０．００５０％とする。
【００２１】
上記の成分を含有する鋼は、製鋼工程で溶製後、連続鋳造などを経て再加熱、圧延、冷却処理を施される。この場合、以下の点を限定した。
熱間圧延・制御圧延ともに、鋼塊をオーステナイト化するためにＡｃ３点以上の温度に加熱する必要がある。しかし、１３５０℃を超えて加熱すると、熱源コストの増大が生じることから、加熱温度は１３５０℃以下とした。
次いで、熱間圧延・制御圧延ともに、再結晶温度域で圧延することによりオーステナイト粒径を小さくすることが必要である。また、制御圧延を用いて、強度上昇と靭性向上を図る場合には、さらに未再結晶温度域で圧延することによりオーステナイト粒内に変形帯を導入し、フェライト変態核を導入することが有効である。未再結晶域での累積圧下率が４０％未満では変形帯が十分に形成されないので、未再結晶域で累積圧下率の下限値を４０％とした。しかし、累積圧下率が９０％を超えると、母材シャルピー試験の吸収エネルギーの低下が著しくなるために、上限を９０％にした。
【００２２】
自然放冷（空冷）よりさらに強度を上昇させるためには加速冷却が必要である。しかしながら、冷却速度が１℃／ｓｅｃ未満では、十分な強度を得ることができない。逆に、冷却速度が６０℃／ｓｅｃ超ではベイナイト主体組織が生成するため母材の靭性が低下する。したがって、冷却速度を１〜６０℃／ｓｅｃに限定した。本発明においては、母材の強度を得るために変態が終了するまで加速冷却を継続する必要がある。このため、冷却停止温度の上限を６００℃とした。６００℃超の停止温度では変態が終了しないために、十分な強度が得られない。通常、加速冷却は水を冷却媒体として用いる。それ故、実際上の冷却停止温度の下限は０℃となるので、下限値を０℃とした。
【００２３】
加速冷却後の焼戻し熱処理は回復による母材組織の靭性向上を目的としたものであるから、加熱温度は逆変態が生じない温度域であるＡｃ１点以下でなければならない。回復は転位の消滅・合体により格子欠陥密度を減少させるものであり、これを実現するためには３００℃以上に加熱することが必要である。このため、加熱温度の下限を３００℃とした。上限は変態点以下であるため、Ａｃ１点を上限とした。
【００２４】
【実施例】
次に、本発明の実施例について述べる。
表１の化学成分を有する鋼塊を表２に示す熱間圧延および熱処理を行い鋼板とした後、母材靭性と溶接入熱が１０ｋＪ／ｍｍの大入熱溶接および５０ｋＪ／ｍｍの超大入熱溶接を付与し、それぞれの旧γ粒径を測定するとともに、ＨＡＺ靭性を評価した。靭性はそれぞれ母材が−１００℃、溶接部ＨＡＺ靭性が−２０℃におけるシャルピー吸収エネルギーにより評価した。
【００２５】
鋼１〜１５と５−Ｎｏ．２は本発明の例を示したものである。表２から明らかなように、本発明の鋼板は化学成分と製造条件の各要件を満足しており、加熱γ粒径が５０μｍ以下の微細組織を呈しており、これを反映して母材靭性は１００Ｊ以上ときわめて良好な値となっている。さらに、１０ｋＪ／ｍｍの大入熱溶接および５０ｋＪ／ｍｍの超大入熱溶接のＨＡＺ靭性もＨＡＺの加熱γ粒径が２００μｍ以下となっていることから、ほぼ母材並みの１００Ｊ以上の高靭性を有していることがわかる。
【００２６】
それに対し、鋼１７〜２８および、２−Ｎｏ．３と３−Ｎｏ．２は本発明方法から逸脱した比較例を示したものである。すなわち、鋼１６、１７、１８、１９、２０、２２、２３、２４、２８は基本成分あるいは選択元素の内いずれかの元素が、発明の用件を越えて添加されている例であり、本発明の重要な部分であるＴｉ量、Ｎ量あるいはＲＥＭ量は満たしているものの、靱性劣化要因となる元素が過剰に添加された事により、母材靭性の劣化およびＨＡＺ靱性の劣化がいずれも助長されている。鋼２１、２４、２６、２７ではＡｌ、Ｔｉ、Ｎ、ＲＥＭが下限値より小さい場合に相当し、加熱γ粒径が母材、ＨＡＺで共に粗大化している。以上の比較例ではいずれも母材靭性と溶接部ＨＡＺ靱性は低いレベルにあり、特にＨＡＺ靭性の劣化代が大きい。
比較例２−Ｎｏ．３と３−Ｎｏ．２は本発明の２と３と化学成分が同じであるが、製造条件が満たされていない例であり、前者が累積圧下量が小さい場合に、後者が冷却速度が小さい場合にそれぞれ相当し、ＨＡＺ靭性は比較的良好であるにも関わらず、母材靱性の劣化が起きている。
【００２７】
【表１】
【表２】
【表３】
【発明の効果】
本発明の化学成分および製造方法に限定し、Ｔｉ量、Ｎ量、ＲＥＭ量をそれぞれ適切に添加することで、母材の加熱γ粒径を微細化することができ、さらに溶接入熱に関わらずＨＡＺの加熱γ粒径も微細化することができ、この二つの効果により母材靭性と溶接部ＨＡＺ靱性の両者に優れた高強度溶接構造用鋼の製造が可能となる。その結果、建築、橋梁、造船、海洋構造物、ラインパイプ、建設機械などの鋼構造物の脆性破壊に対する安全性が大幅に向上し、産業上の効果は著しく大きい。[0001]
BACKGROUND OF THE INVENTION
The present invention can be widely used as a welded structure such as a building, a bridge, a shipbuilding, an offshore structure, a line pipe, and a construction machine, and has a tensile strength of 490 MPa class excellent in both base metal toughness and welded portion HAZ toughness. The present invention relates to steel for welded structures and a method for producing the same.
[0002]
[Prior art]
From the viewpoint of preventing brittle fracture of welded structures such as buildings, bridges, shipbuilding, and offshore structures, not only the toughness of the base metal but also the suppression of the occurrence of brittle fracture from the welded part, that is, the improvement of the HAZ toughness of the steel sheet used Many studies have been reported. In general, it is important to reduce the final ferrite grain size in order to ensure the toughness of the base metal. Depending on the required toughness level, normal rolling, controlled rolling, and controlled rolling + accelerated cooling have been used. The basics are that high-temperature stable nitrides such as AlN and TiN are used as pinning particles, the heated austenite (γ) grain size of the base material is refined, and further, the ferrite nucleation sites are formed in the austenite by rolling. It is to introduce a large number and make the final ferrite grain size fine.
[0003]
Therefore, in such a manufacturing method of the base material, it is natural that the reheating temperature before hot rolling needs to be changed depending on the type of nitride, or the final ferrite particle size changes due to the variation of the heated γ particle size. Often results in variations in the base material toughness. On the other hand, the weld HAZ toughness also varies depending on the amount of heat input, so that the higher the required toughness value, the smaller the value needs to be reduced in recent years. From the viewpoint of improving the welding work efficiency, cases where large heat input welding (approximately 20 kJ / mm or less) and super large heat input welding (20 to 150 kJ / mm) are increasing. The difference in the effect of high heat input welding and super high heat input welding on the steel sheet is due to the difference in residence time at high temperatures, and especially in super high heat input welding, the time is extremely long. The area where the diameter is remarkably coarsened is wide and the toughness is remarkably lowered.
[0004]
As a drastic method to avoid the above-mentioned variation in the base metal toughness and the heat input dependency of the welded part HAZ toughness, the heated γ grain size of the base metal structure and the welded part HAZ structure is determined by strong pinning particles. It is conceivable to control and remarkably suppress the grain growth at both high temperatures. If this can be realized, the weld HAZ toughness can be sufficiently improved not only in the stability of the base metal toughness but also in the case where the heat input becomes large. In addition, when the heated γ grain size of the base material becomes extremely fine, there is a possibility that the same ferrite grain size and base material toughness can be imparted even with ordinary rolling without using conventional controlled rolling or accelerated cooling. Therefore, the establishment of this technology has high industrial value.
[0005]
Oxides and sulfides that are difficult to dissolve even at high temperatures can be considered as the particles that are most expected to have the pinning effect of the heated γ particle diameter. For example, as a method for introducing an oxide, there is a method in which a deoxidizing element such as Ti is added alone in the steel melting process. In many cases, however, the oxide is a coarse oxide due to aggregation and coalescence of the oxide during holding of the molten steel. On the other hand, it is known that the cleanliness of the steel is impaired and the toughness is lowered by causing the formation of. For this reason, various devices such as a composite deoxidation method have been devised. However, in a conventionally known method, a technique for reducing the heating γ particle size of a base material at a high temperature to, for example, about 50 μm in the vicinity of 1250 ° C. It has not been established at this time. Similarly, there is no technology that can completely prevent the coarsening of the crystal grains when the welding heat input is large.
[0006]
[Problems to be solved by the invention]
The present inventors diligently studied to finely disperse pinning particles more than before, refined the heating γ particle size of the base material, and at the same time, heated γ of the weld zone HAZ structure even in high heat input or super high heat input welding. The aim was to establish a manufacturing technology for high-strength welded structural steel that was refined in particle size and excellent in both base metal toughness and weld zone HAZ toughness.
[0007]
[Means for Solving the Problems]
The gist of the present invention for solving the above problems is as follows.
(1) C: 0.01 to 0.20% by mass%
Si: 0.02 to 0.50%
Mn: 0.3 to 2.0%
P: ≦ 0.03%
S: 0.0001 to 0.030%
Al: 0.0005 to 0.05%
Ti: 0.003 to 0.050%
N: 0.001 to 0.010%
REM: 0.0001 to 0.050%
A high-strength welded structural steel excellent in both base metal toughness and weld zone HAZ toughness, characterized in that the balance is iron and inevitable impurities, and the heated γ grain size is at most 50 μm or less.
(2) By mass%
Cu: 0.05 to 1.5%
Ni: 0.05-5.0%
Cr: 0.02 to 1.5%
Mo: 0.02 to 1.50%
V: 0.01-0.10%
Nb: 0.0001 to 0.20%
Zr: 0.0001 to 0.050%
Ta: 0.0001 to 0.050%
B: 0.0003 to 0.0050%
The high strength welded structural steel excellent in both the base metal toughness and the welded portion HAZ toughness described in (1), characterized by containing one or more of them.
(3) The final ferrite grain size of the base material is 30 μm or less regardless of the reheating temperature, and is excellent in both the base material toughness and the welded portion HAZ toughness described in (1) or (2) Strength welded structural steel.
(4) The base material according to any one of (1) to (3), wherein the heated γ particle size (old austenite particle size) of the weld zone HAZ structure is 200 μm or less regardless of welding heat input. High strength welded structural steel with excellent toughness and weld zone HAZ toughness.
(5) A steel ingot having the same composition as the steel described in (1) or (2) is heated to a temperature of Ac 3 or higher and 1350 ° C. or lower, then hot-rolled in a recrystallization temperature range, and then naturally cooled. The manufacturing method of the high strength welded structural steel excellent in both the base material toughness and the welded part HAZ toughness.
(6) A steel ingot having the same composition as the steel described in (1) or (2) is heated to Ac 3 points or more and 1350 ° C. or less, then hot-rolled in the recrystallization temperature range, and further in the non-recrystallization temperature range A method for producing high-strength welded structural steel excellent in both base metal toughness and welded portion HAZ toughness, characterized by natural cooling after hot rolling at a cumulative rolling reduction of 40 to 90%.
(7) After heating the steel ingot having the same component as the steel described in (1) or (2) to Ac 3 points or more and 1350 ° C. or less, it is hot-rolled in the recrystallization temperature range, and further in the non-recrystallization temperature range After hot rolling with a cumulative rolling reduction of 40 to 90%, cooling to 0 to 600 ° C. at a cooling rate of 1 to 60 ° C./sec. A method for manufacturing high strength welded structural steel.
(8) After heating the steel ingot having the same component as the steel described in (1) or (2) to Ac 3 points or more and 1350 ° C. or less, it is hot-rolled in the recrystallization temperature range, and further in the non-recrystallization temperature range After hot rolling with a cumulative rolling reduction of 40 to 90%, it is cooled to 0 to 600 ° C. at a cooling rate of 1 to 60 ° C./sec, and subsequently heated to 300 ° C. to Ac 1 point for tempering heat treatment. A method for producing high-strength welded structural steel excellent in both base metal toughness and weld zone HAZ toughness.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
REM is known to improve the toughness of the heat affected zone by increasing the cleanliness of steel as a strong deoxidizer and desulfurizer. Japanese Patent Application Laid-Open No. 2003-49237 discloses an example in which dispersion of an oxide containing REM is controlled to improve both base metal toughness and welded portion HAZ toughness.
The present inventors pay attention to such a strong deoxidizer of REM or a strong sulfide generation ability, and by combining with TiN that has been widely used conventionally, the base material and the HAZ structure are made finer than ever. I thought there was room for it.
[0009]
Hereinafter, the present invention will be described in detail.
The present inventors systematically investigated the state of oxide and the amount of TiN when REM was added to molten steel that was weakly deoxidized by adding Ti. As a result, after deoxidation with Si and Mn, Ti addition and REM addition were added in this order, or Ti addition and REM addition were performed at the same time, and REM was added again in an equilibrium state. It was found that the oxides or sulfides were produced very finely and with high density. The particle diameter is 0.005 to 0.5 μm, and the number of particles is 10,000 or more per 1 mm 2 in the steel, and the presence of these has been confirmed to have a strong pinning force in the welded HAZ structure. . Further, when attention is paid to the amount of TiN, the REM-added steel has a fine dispersion that is not found in the prior art, and this effectively acts together with the REM oxide (or sulfide) in the refinement of the heated γ grain size of the base material, It was found that the base material heated γ particle size was about 50 μm at the maximum.
[0010]
The present invention relates to a steel material excellent in both the base metal toughness and the welded portion HAZ toughness achieved by the refinement of the heated γ grain size as described above, and is an epoch-making that suppresses changes in the heated γ grain size as much as possible. Technology. That is, the feature of the present invention is that the heated γ particle size (old austenite particle size) of the base material is 50 μm or less regardless of the reheating temperature, and the heated γ particle size (old austenite particle size) of the weld HAZ structure is Regardless of the welding heat input, it is 200 μm or less, and reflects the microstructure and can provide a high-strength welded structural steel excellent in both base metal toughness and welded portion HAZ toughness. Moreover, if this technique is used, the final ferrite particle size can be stably formed to 30 μm or less regardless of the reheating temperature which is one of the manufacturing conditions of the base material.
[0011]
Although it is the addition method of REM in this invention, as already stated, after adding Si and Mn first, after adding Ti first and adjusting the oxygen amount in molten steel, a small amount of REM is gradually added. Alternatively, after adding Ti and a small amount of REM at the same time, REM is added again at the final stage. The optimal amount of REM added depends on the amount of oxygen present in the molten steel after Ti addition, but in the experiment, the oxygen concentration at that time depends on the amount of Ti added and the time until REM addition, and the addition of Ti and REM The amount may be controlled within an appropriate range. In addition, about 0.1-50 ppm is a suitable amount for the dissolved oxygen amount at the time of final REM addition. The lower limit of 0.1 ppm is the minimum amount that can produce fine REM oxide (or REM sulfide), and if it exceeds 50 ppm, coarse REM oxide can be produced and the pinning force becomes weak, so this is the limit. It was.
[0012]
Hereinafter, the reasons for limiting the components of the present invention will be described.
C: C is an indispensable element as a basic element for improving the strength of the base metal in steel, and as an effective lower limit, addition of 0.01% or more is necessary, but an excess exceeding 0.20% Addition causes a decrease in the weldability and toughness of the steel material, so the upper limit was made 0.20%.
Si: Si is an element necessary as a deoxidizing element in steelmaking, and 0.02% or more is necessary to be added to the steel. However, if it exceeds 0.5%, the HAZ toughness is lowered, so that is the upper limit. .
Mn: Mn is an element necessary for securing the strength and toughness of the base material. However, if it exceeds 2.0%, the HAZ toughness is remarkably inhibited, but if it is less than 0.3%, the strength of the base material is secured. Therefore, the range is made 0.3 to 2.0%.
[0013]
P: P is an element that affects the toughness of steel, and if it exceeds 0.03%, not only the base material of steel but also the toughness of HAZ is significantly inhibited, so the upper limit of its content is 0.03%. did.
S: When S is added excessively over 0.030%, coarse sulfides are formed and toughness is inhibited. When the content is less than 0.0001%, intragranular ferrite is formed. Since the amount of sulfides such as MnS that is effective for reducing significantly decreases, 0.0001 to 0.030% is made the range.
[0014]
Al: Al is usually added as a deoxidizer, but in the present invention, if added over 0.05%, the effect of the addition of REM is inhibited, so this is made the upper limit. Further, 0.0005% is necessary to stably generate the REM oxide, and this is set as the lower limit.
Ti: Ti is an element that is effective as a deoxidizer and further as a nitride-forming element, and is effective in reducing the grain size. However, the addition of a large amount causes a significant decrease in toughness due to the formation of carbides. The upper limit needs to be 0.050%, but in order to obtain a predetermined effect, 0.003% or more must be added, and the range is made 0.003 to 0.050%.
[0015]
N: N should originally be handled as an impurity, but when this amount is within an appropriate range, a very strong pinning effect of TiN appears, so the content was made 0.001 to 0.010%. The lower limit value is the minimum amount for exhibiting the pinning effect, and the upper limit value is specified to inhibit the HAZ toughness.
[0016]
REM: REM suppresses the generation of elongated MnS by generating sulfides, and improves the properties in the thickness direction of the steel material, particularly the lamellar resistance. Furthermore, since it has a strong pinning effect through the inclusion of REM, it is an important element of the present invention. If the REM is less than 0.0001%, a sufficient effect cannot be obtained, so the lower limit is set to 0.0001%. Conversely, if it exceeds 0.050%, the number of coarse oxides in REM increases and the number of ultrafine oxides or sulfides decreases, so the upper limit is made 0.050%.
[0017]
In the present invention, one or more of Cu, Ni, Cr, Mo, V, Nb, Zr, Ta, and B are included as elements for improving the strength and toughness in the basic component. Elements can be added as needed.
[0018]
Cu: Cu is an element effective in increasing the strength without reducing toughness, but if it is less than 0.05%, it is not effective, and if it exceeds 1.5%, it tends to cause cracking when heating the steel slab or welding. To do. Therefore, the content is made 0.05 to 1.5% or less.
Ni: Ni is an element effective for improving toughness and strength. To obtain the effect, 0.05% or more of addition is necessary. However, addition of 5.0% or more lowers weldability. Therefore, the upper limit is made 5.0%.
Cr: Cr is effective to add 0.02% or more to improve the strength of steel by precipitation strengthening, but if added in a large amount, the hardenability is increased, the bainite structure is generated, and the toughness is reduced. . Therefore, the upper limit is made 1.5%.
[0019]
Mo: Mo is an element that improves hardenability and at the same time forms carbonitride to improve strength. To obtain the effect, addition of 0.02% or more is necessary. The addition of a large amount exceeding 50% brings about a remarkable decrease in toughness as well as an unnecessarily strengthening, so the range is made 0.02 to 0.50% or less.
V: V is an element that forms carbides and nitrides and is effective in improving the strength. However, the addition of 0.01% or less has no effect, and the addition exceeding 0.10%, on the other hand, exhibits toughness. In order to bring about a fall, the range is made 0.01 to 0.10% or less.
Nb: Nb is an element that forms carbides and nitrides and is effective in improving the strength. However, the addition of 0.0001% or less has no effect, and the addition exceeding 0.20% reduces toughness. Therefore, the range is made 0.0001 to 0.20% or less.
Zr, Ta: Zr and Ta are elements that form carbides and nitrides as well as Nb and are effective in improving the strength. However, addition of 0.0001% or less has no effect and exceeds 0.050%. Addition, on the contrary, causes a decrease in toughness, so the range is made 0.0001 to 0.050% or less.
[0020]
B: In general, B is an element that increases the hardenability when dissolved, but lowers the dissolved N as BN and improves the toughness of the heat affected zone. Therefore, the effect can be utilized by addition of 0.0003% or more, but excessive addition causes a decrease in toughness, so the upper limit is made 0.0050%.
[0021]
The steel containing the above components is subjected to reheating, rolling, and cooling through continuous casting after melting in the steelmaking process. In this case, the following points were limited.
In both hot rolling and controlled rolling, it is necessary to heat the steel ingot to a temperature of 3 or more points in order to austenite. However, if heating exceeds 1350 ° C., the heat source cost increases, so the heating temperature is set to 1350 ° C. or lower.
Next, in both hot rolling and controlled rolling, it is necessary to reduce the austenite grain size by rolling in the recrystallization temperature range. In addition, when using controlled rolling to increase strength and improve toughness, it is effective to introduce a deformation band into the austenite grains by rolling in the non-recrystallization temperature range and introduce ferrite transformation nuclei. is there. If the cumulative reduction rate in the non-recrystallized region is less than 40%, the deformation band is not sufficiently formed. Therefore, the lower limit value of the cumulative reduction rate in the non-recrystallized region is set to 40%. However, if the cumulative rolling reduction exceeds 90%, the absorbed energy in the base metal Charpy test is significantly reduced, so the upper limit was made 90%.
[0022]
Accelerated cooling is required to increase the strength further than natural cooling (air cooling). However, if the cooling rate is less than 1 ° C./sec, sufficient strength cannot be obtained. On the contrary, when the cooling rate exceeds 60 ° C./sec, the toughness of the base material decreases because a bainite main structure is generated. Therefore, the cooling rate was limited to 1-60 ° C./sec. In the present invention, it is necessary to continue accelerated cooling until the transformation is completed in order to obtain the strength of the base material. For this reason, the upper limit of the cooling stop temperature was set to 600 ° C. Since the transformation does not end at a stop temperature exceeding 600 ° C., sufficient strength cannot be obtained. Usually, accelerated cooling uses water as a cooling medium. Therefore, since the lower limit of the actual cooling stop temperature is 0 ° C., the lower limit is set to 0 ° C.
[0023]
Since the tempering heat treatment after accelerated cooling is intended to improve the toughness of the base metal structure by recovery, the heating temperature must be Ac 1 point or less, which is a temperature range in which reverse transformation does not occur. Recovery reduces the lattice defect density by the disappearance and coalescence of dislocations. In order to realize this, heating to 300 ° C. or higher is necessary. For this reason, the minimum of heating temperature was 300 degreeC. Since the upper limit is equal to or lower than the transformation point, Ac 1 point was set as the upper limit.
[0024]
【Example】
Next, examples of the present invention will be described.
A steel ingot having the chemical composition shown in Table 1 is subjected to hot rolling and heat treatment as shown in Table 2 to obtain a steel plate, followed by a large heat input welding with a base metal toughness and welding heat input of 10 kJ / mm and a super high heat input of 50 kJ / mm. Welding was applied, the respective prior γ grain sizes were measured, and the HAZ toughness was evaluated. Toughness was evaluated by Charpy absorbed energy when the base material was −100 ° C. and the weld HAZ toughness was −20 ° C.
[0025]
Steels 1-15 and 5-No. 2 shows an example of the present invention. As is apparent from Table 2, the steel sheet of the present invention satisfies the requirements of chemical components and production conditions, and exhibits a microstructure with a heated γ grain size of 50 μm or less, reflecting the toughness of the base metal. Is a very good value of 100 J or more. Furthermore, the HAZ toughness of 10 kJ / mm high heat input welding and 50 kJ / mm super high heat input welding also has a high toughness of 100 J or more, which is almost the same as that of the base material, because the HAZ heated γ grain size is 200 μm or less. You can see that it has.
[0026]
In contrast, steels 17-28 and 2-No. 3 and 3-No. 2 shows a comparative example deviating from the method of the present invention. That is, steels 16, 17, 18, 19, 20, 22, 23, 24, and 28 are examples in which any of the basic components or selected elements is added beyond the requirements of the invention. Although the amount of Ti, N, or REM, which is an important part of the invention, is satisfied, the deterioration of the base metal toughness and the HAZ toughness are all promoted by adding excessive elements that cause toughness deterioration. Has been. In steels 21, 24, 26, and 27, this corresponds to the case where Al, Ti, N, and REM are smaller than the lower limit values, and the heated γ grain size is coarsened by both the base material and HAZ. In all of the above comparative examples, the base metal toughness and the welded portion HAZ toughness are at a low level, and the deterioration margin of the HAZ toughness is particularly large.
Comparative Example 2-No. 3 and 3-No. 2 is an example in which the chemical components are the same as 2 and 3 of the present invention, but the production conditions are not satisfied, and the former corresponds to the case where the cumulative reduction amount is small and the latter corresponds to the case where the cooling rate is small, respectively. Although the HAZ toughness is relatively good, the base material toughness is deteriorated.
[0027]
[Table 1]
[Table 2]
[Table 3]
【The invention's effect】
By limiting to the chemical components and the production method of the present invention and appropriately adding Ti amount, N amount, and REM amount, respectively, the heated γ particle size of the base material can be made finer, and further, it is related to welding heat input. The heated γ grain size of HAZ can also be made finer, and by these two effects, it is possible to produce a high strength welded structural steel excellent in both base metal toughness and welded portion HAZ toughness. As a result, safety against brittle fracture of steel structures such as buildings, bridges, shipbuilding, offshore structures, line pipes and construction machinery is greatly improved, and the industrial effect is remarkably great.
Claims (8)
Ｃ ：０．０１〜０．２０％
Ｓｉ ：０．０２〜０．５０％
Ｍｎ ：０．３〜２．０％
Ｐ ：≦０．０３％
Ｓ ：０．０００１〜０．０３０％
Ａｌ ：０．０００５〜０．０５％
Ｔｉ ：０．００３〜０．０５０％
Ｎ ：０．００１〜０．０１０％
ＲＥＭ：０．０００１〜０．０５０％
を含み、残部が鉄および不可避的不純物からなり、加熱γ粒径が最大でも５０μｍ以下であることを特徴とする母材靭性と溶接部ＨＡＺ靭性の両方に優れた高強度溶接構造用鋼。C by mass: 0.01 to 0.20%
Si: 0.02 to 0.50%
Mn: 0.3 to 2.0%
P: ≦ 0.03%
S: 0.0001 to 0.030%
Al: 0.0005 to 0.05%
Ti: 0.003 to 0.050%
N: 0.001 to 0.010%
REM: 0.0001 to 0.050%
A high-strength welded structural steel excellent in both base metal toughness and weld zone HAZ toughness, characterized in that the balance is iron and inevitable impurities, and the heated γ grain size is at most 50 μm or less.
Ｃｕ：０．０５〜１．５％
Ｎｉ：０．０５〜５．０％
Ｃｒ：０．０２〜１．５％
Ｍｏ：０．０２〜１．５０％
Ｖ ：０．０１〜０．１０％
Ｎｂ：０．０００１〜０．２０％、
Ｚｒ：０．０００１〜０．０５０％
Ｔａ：０．０００１〜０．０５０％
Ｂ ：０．０００３〜０．００５０％
のうち１種または２種以上を含有することを特徴とする請求項１記載の母材靭性と溶接部ＨＡＺ靭性の両方に優れた高強度溶接構造用鋼。% By mass
Cu: 0.05 to 1.5%
Ni: 0.05-5.0%
Cr: 0.02 to 1.5%
Mo: 0.02 to 1.50%
V: 0.01-0.10%
Nb: 0.0001 to 0.20%,
Zr: 0.0001 to 0.050%
Ta: 0.0001 to 0.050%
B: 0.0003 to 0.0050%
The high strength welded structural steel excellent in both base metal toughness and weld zone HAZ toughness according to claim 1, comprising one or more of them.
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| JP2008248292A (en) * | 2007-03-29 | 2008-10-16 | Nippon Steel Corp | High strength steel for welded structure having excellent surface crack resistance, and method for producing the same |
| JP2009242849A (en) * | 2008-03-31 | 2009-10-22 | Jfe Steel Corp | Method for producing high toughness steel |
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| CN109868342B (en) * | 2019-03-28 | 2020-02-07 | 北京科技大学 | Method for improving toughness of high-carbon-equivalent steel plate welding heat affected zone by using rare earth |
| CN111893240A (en) * | 2020-07-28 | 2020-11-06 | 北京科技大学 | Method for improving welding performance of Nb and Ti microalloyed steel by using rare earth |
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| JP2008248292A (en) * | 2007-03-29 | 2008-10-16 | Nippon Steel Corp | High strength steel for welded structure having excellent surface crack resistance, and method for producing the same |
| JP2009242849A (en) * | 2008-03-31 | 2009-10-22 | Jfe Steel Corp | Method for producing high toughness steel |
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