JP4543492B2 - Rolled refractory section steel and method for producing the same - Google Patents
Rolled refractory section steel and method for producing the same Download PDFInfo
- Publication number
- JP4543492B2 JP4543492B2 JP2000111073A JP2000111073A JP4543492B2 JP 4543492 B2 JP4543492 B2 JP 4543492B2 JP 2000111073 A JP2000111073 A JP 2000111073A JP 2000111073 A JP2000111073 A JP 2000111073A JP 4543492 B2 JP4543492 B2 JP 4543492B2
- Authority
- JP
- Japan
- Prior art keywords
- less
- strain
- steel
- nominal
- flange
- 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
Images
Description
【０００１】
【発明の属する技術分野】
本発明は、圧延形鋼の製造方法に関し、特に、高層建築物における鉄鋼構造物の梁材に適した耐局部座屈性および耐破壊性能に優れ、且つ火災時の高温強度に優れたものの製造方法に関する。
【０００２】
【従来の技術】
今日の高層建築物には、大地震に見舞われた時、梁部材の塑性変形により地震エネルギーを吸収させ、大崩壊を回避する人的安全性を重視した限界状態設計法が適用される。建築物の梁部材には大地震の際、大きな引張り、圧縮応力が加わり局部座屈を起こし、座屈した場所から亀裂が発生し崩壊に至る場合がある。従って、限界状態設計法で使用される梁部材には優れた耐座屈性および靭性が要求される。
【０００３】
圧延形鋼の一つであるＨ形鋼は、大量にかつ安定して製造できるため、その優れた経済性とあいまって、建築・土木用の梁材として広く用いられている。これまで建築用の圧延形鋼については、特開平５−２５５８８号公報、特開平５−３４５９１５号公報に低降伏比の観点から耐震性を向上させる技術が開示されている。しかし、梁部材の局部座屈は、材料の引張強度に遥かに及ばない低歪側で生じるため、耐局部座屈性の指標としての降伏比の有効性は明確になっていない。
また、大地震の際、局部座屈と共に、問題となる梁端の破断に関する指標についても不明確である。
【０００４】
一方、圧延Ｈ形鋼の製造方法としては、非調質で低降伏比かつ優れた靭性と溶接性を備えたＨ形鋼の製造方法が特開平６−２４０３５０号公報で提案されている。Ｎｂを必須添加元素とし、熱間圧延中にオーステナイト粒を微細化し、靭性を向上させるとともに、圧延終了後、フェライトが３０％以上析出するまで、放冷し、ｔ／４（ｔ：板厚）を０．３℃／ｓ以上５℃／ｓ以下の冷却速度で、６００℃以下まで冷却し、フェライトとベイナイトを含む組織とする。
【０００５】
しかしながら本技術は、極厚Ｈ形鋼の製造を主に対象とするものと考えられ、必須元素であるＮｂはフランジ板厚中心、フィレット部の靭性を確保するために添加されていると推察され、建築梁用部材として多用される８ｍｍ以上４０ｍｍ以下の比較的薄いフランジ厚を対象とするものではない。
【０００６】
他方、建築用鋼材に対する耐火性能に関する要求も年々高まり、鋼成分および組織制御による低降伏比耐火鋼材の製造方法に関しては、例えば、特許２１３４１７６号公報に、Ｍｏを０．２〜０．７％含み、ミクロ組織が、２０〜５０％のフェライトとベイナイトの混合組織からなることを特徴とする建築用低降伏比鋼材に関する技術が記載されている。
【０００７】
また、特許１９２５４４０号公報には、Ｍｎ：０．３〜０．７％、Ｍｏ：０．５〜０．８％含み、熱間圧延を８００〜１０００℃で終了してミクロ組織をフェライト主体とすることを特徴とする耐火性の優れた建築用低降伏比鋼の製造方法が開示されている。
【０００８】
【発明が解決しようとする課題】
上述したように、Ｈ形鋼の耐局部座屈性、耐梁破断特性を向上させるための鋼組成、組織形態など材質的な指標は十分把握されおらず、また、梁部材として多用される８ｍｍ以上４０ｍｍ以下の比較的薄いフランジ厚を対象とする製造方法も明らかになっていない。更に、耐火性に優れた鋼材に関しては、建築用低降伏比鋼材として開示されてはいるものの、耐局部座屈性や耐破壊性能については検討はなされておらず、これらの特性を備えた梁部材として適切な組織形態も明らかになっていない。
【０００９】
そこで、本発明は、梁材の軸方向に作用する圧縮応力による耐局部座屈性、耐梁破断特性と材質特性の関係を把握し、大地震の際に、局部座屈を起こしにくく、かつ、梁端などで破壊しにくいため、建築構造物を倒壊から防止する性能の高い耐火性に優れた圧延形鋼を提供する。
【００１０】
【課題を解決するための手段】
本発明者らは、引張試験で得られる諸特性と、耐局部座屈性、耐梁破断特性の関係を把握することを検討した。その結果、耐局部座屈性に関してはＨ形鋼の圧縮試験における座屈発生限界歪みが、破断が生じるような高い歪領域ではなく、概ね２〜５％公称歪みであることを見出し、引張試験における２〜５％公称歪における加工硬化指数（ｎ値）、降伏伸びと良い相関にあることを把握した。
【００１１】
また、フランジ、ウエブの特性を種々変更したＨ形鋼について調査した結果、耐局部座屈性には、フランジの特性の影響が大きく、ウエブの特性は殆ど影響を与えないことも知見した。
【００１２】
そして、耐梁破断特性は、実際の破断が梁端部等の構造上の形状不連続などによる応力集中部や、溶接欠陥による破断であることから、これらを想定した解析モデルを作成し、材質特性との関係を調査した。解析モデルは、長さａ，深さｄの表面欠陥を有する断面Ａ´に対し、直角方向に荷重Ｐを負荷した場合とした。
【００１３】
断面Ａ´の平均応力σＡ´が破壊限界応力σＣ（但し、σＣ＝ＴＳと仮定）に達した場合において、正常部断面Ａ（表面切欠きがない場合の全断面）と断面Ａ´の力の釣り合い（σＡ＝σＡ´×（１−ａｄ／Ｗｔ）、（σＡ：正常部断面における応力、Ｗ：全幅、ｔ：全厚）と、応力ー歪み曲線に関するＳｗｉｆｔの式：σ＝（α／（１＋ε））｛β＋ｌｎ（１＋ε）｝ｎ（ここで、σ：公称応力、ε：公称歪、α、β：定数，ｎ：加工硬化指数）から、破壊条件式として、次式が得られる。
【００１４】
（α／（１＋ε））｛β＋ｌｎ（１＋ε）｝ｎ＝ＴＳ×（１−ａｄ／Ｗｔ）
この式に基づき、ｎ値、降伏比など材質特性を広範囲に変化させた材料を用い、表面欠陥を付与した引張試験片を作成して、引張試験を行った。その結果、破断歪みは材質特性と欠陥寸法によって整理されること、及び、許容欠陥寸法を向上させる材質因子について指針を得た。
【００１５】
本発明は以上の知見を基に更に鋼材の材質として、溶接性に優れ、耐火性に優れた特性が得られるようその成分組成についても検討を加えてなされたものである。耐火性に関しては、常温の降伏強度に対する６００℃における降伏強度の比を５５％超え、７００℃における降伏強度の比を２０％超えに設定した。
【００１６】
すなわち、本発明は、
１．質量％で、Ｃ：０．０５〜０．１８％、Ｓｉ：０．６％以下、Ｍｎ：０．６〜１．６％、Ｍｏ：０．２〜０．７％、Ｐ：０．０２０％以下、Ｓ：０．０１５％以下、Ａｌ：０．０１〜０．０５％を含有し、Ｎｂ：０．００５％未満、Ｎ：０．００８０％以下、Ｈ：４ｐｐｍ以下に規制し、更に（１）式によるＣｅｑ：０．４０％以下で残部がＦｅ及び不可避不純物よりなる鋼で、フランジ長手方向の引張特性が、降伏伸び：０．８〜３．０％、降伏比：７０％以下、及び、公称歪み２〜５％における（２）式による加工硬化指数（ｎ値）：０．２０以上である圧延耐火形鋼。
【００１７】
Ｃｅｑ＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４・・・・・・・・・（１）
ｎ＝（ｌｎσ5−ｌｎσ2）／（ｌｎε5−ｌｎε2）・・・・・・・・・（２）
σ5＝１．０５×σN5，σ2＝１．０２×σN2，ε5＝ｌｎ（１．０５），
ε2＝ｌｎ（１．０２）
但し、σ5：公称歪５％における真応力、σ2：公称歪２％における真応力、ε5：公称歪み５％における真歪、ε2：公称歪み２％における真歪、
σN5：公称歪み５％における公称応力、σN2：公称歪み２％における公称応力
ｌｎ：自然対数
とする。
【００１８】
２．鋼組成として、更に質量％で、Ｃｕ：０．６％以下、Ｎｉ：１％以下、Ｃｒ：０．５％以下の一種又は二種以上を含有する１記載の圧延耐火形鋼。
【００１９】
３．鋼組成として、更に質量％で、Ｖ：０．２％以下、Ｔｉ：０．０３％以下の一種又は二種を含有する１又は２に記載の圧延耐火形鋼。
【００２０】
４．フランジの金属組織が、軟質相のフェライト相と硬質相のベイナイト相、またはベイナイト相を含む硬質相よりなる混合組織で、軟質相の体積率が５０％超え８０％以下、平均粒径１０μｍ以上、硬質相のアスペクト比が３以下であることを特徴とする１乃至３の何れかに記載の圧延耐火形鋼。
【００２１】
５．１乃至３の何れかに記載の鋼成分を有する鋳片または鋼片を１０５０〜１３００℃以下に加熱し、Ａｒ3点以上で圧延を終了し、５℃／ｓ以下の冷却速度で、６００〜７００℃に冷却後、フランジ外面またはフランジ外面と内面の双方を冷却速度５℃／ｓ以上となるように加速冷却し、冷却停止温度５５０℃以下とすることを特徴とする圧延耐火形鋼の製造方法。
【００２２】
【発明の実施の形態】
以下、本発明で規定する成分組成、機械的特性および製造条件について、詳細に説明する。
【００２３】
１．成分組成
Ｃ：０．０５〜０．１８％
Ｃは、鋼の強度を確保し、所望の組織形態とするため、０．０５％以上添加するが、０．１８％を超えて多量に含有すると靭性あるいは溶接性が劣化するため、０．０５〜０．１８％（０．０５％以上、０．２０％以下）とする。
【００２４】
Ｓｉ：０．６％以下
Ｓｉは、脱酸のため鋼に必然的に含まれ、強度を向上させるが、０．６％を超えると鋼の焼入れ性が過度に増加し、ＨＡＺ靭性及び溶接性の観点から好ましくないため０．６％以下とする。
【００２５】
Ｍｎ：０．６〜１．６％
Ｍｎは、鋼材の強度、靭性の向上ならびに、ＦｅＳの生成抑制のため０．６％以上添加する。１．６％を超えると、鋼の焼入れ性の増加を引き起こすため、溶接時に硬化層が出現し、割れ感受性が劣化するため、０．６〜１．６％とする。
【００２６】
Ａｌ：０．０１〜０．０５％
Ａｌは、安価で強力な脱酸材であり、０．０１％以上添加するが、０．０５％を超えると鋼の清浄度が低下し溶接部の靭性が劣化するため、０．０１〜０．０５％とする。
【００２７】
Ｎ：０．００８０％以下
Ｎは、鋼中に含まれる不可避的不純物である。含有量が多くなるとＨＡＺ靭性の劣化、経時劣化、あるいは連続鋳造スラブ疵の発生を助長するため、０．００８０％以下とする。
【００２８】
Ｈ：４ｐｐｍ以下
Ｈは、鋼中に含まれる不可避的不純物である。含有量が多くなると圧延後の割れや遅れ破壊を生じるため、４ｐｐｍ以下とする。
【００２９】
Ｐ：０．０２０％以下、Ｓ：０．０１５％以下
Ｐ，Ｓは、鋼中に混入する不純物として不可避的に存在する。Ｐの低減はＨＡＺにおける粒界破壊の防止に有効なため、０．０２０％以下とする。Ｓの低減はＨＡＺにおける水素割れ防止に有効であるため、０．０１５％以下とする。
【００３０】
Ｃｅｑ：０．４０以下
Ｃｅｑ（＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４）は、０．４０を超えると、母材および溶接部における靭性が損なわれる場合があるため、０．４０以下とする。
【００３１】
本発明では、更に、機械的特性を向上させるため、Ｃｕ，Ｎｉ，Ｃｒ，Ｖ，Ｔｉの一種又は二種以上を添加することができる。
Ｃｕ：０．６％以下、Ｎｉ：１％以下、Ｃｒ：０．５％以下の一種又は二種以上
Ｃｕ，Ｎｉ，Ｃｒは、固溶強化により鋼材を強化するため、一種又は二種以上添加する。また、Ｃｕには、耐候性を向上させる効果も有する。しかし、必要以上の添加は、靭性、溶接性を低下させるため、Ｃｕ：０．６％以下、Ｎｉ：１％以下、Ｃｒ：０．５％以下とする。
【００３２】
Ｖ：０．２％以下、Ｔｉ：０．０３％以下の一種又は二種
Ｖ，Ｔｉは固溶強化とともに析出強化により、鋼材を強化するため、一種又は二種添加する。必要以上の添加は、靭性、溶接性を低下させるため、Ｖ：０．２％以下、Ｔｉ：０．０３％以下とする。
【００３３】
尚、本発明における成分組成上の特徴は、一般的に鋼材の強度及び靭性を向上させることを目的に、添加されることが多いＮｂを含有せず、不可避不純物として混入した場合でも、０．００５％未満に規制する点にある。Ｎｂが含有された場合、熱間圧延における未再結晶領域が高温側に拡大され、例えばフランジ厚が８ｍｍ以上、４０ｍｍ以下の形鋼の圧延においては、未再結晶域での大幅な圧下により、必要以上にオーステナイト粒径が微細化され、最終変態組織が微細化し、降伏点が上昇する。そのため、公称歪み：２〜５％におけるｎ値が低下し、座屈限界発生歪みは小さくなり、本発明が目的とする作用効果が得られない。
【００３４】
２．機械特性
本願発明では、機械的特性として引張特性について規定する。
【００３５】
降伏伸び：０．８〜３．０％
降伏伸びは、局部座屈に至る過程において、部材全体の変形を促進するため、局部的な座屈の発生による低歪座屈を抑え、鋼材全体としてのエネルギー吸収を大きくして耐局部座屈性を改善し、また、耐破壊性能も改善する。
【００３６】
０．８％より小さいと、その効果が不十分で、３．０％より大きいと加工硬化の生じないまま、降伏の段階で座屈が生じる可能性があるため、降伏伸びを０．８〜３．０％（０．８％以上、３．０％以下）とする。
【００３７】
降伏比：７０％以下
降伏比は、耐破壊性能に強い影響を与えるため規定する。降伏比を低下させた場合、破断歪みは増加する。降伏比７０％とした場合、引張強度５００ＭＰａ，ｎ値０．２０の鋼材で、断面積の１０％に相当する欠陥による破断歪みは約４．８％となり、建築用低降伏比鋼に関するＳＮ規格の上限降伏比８０％における破断歪みである約２．５％に対し、優れた耐破壊性能を示す。
【００３８】
従って、本発明では、降伏比７０％以下とする。尚、降伏比は引張試験で得られる応力ー歪み線図に応じて、上降伏点と引張強度の比などとして求めればよい。
【００３９】
ｎ値：０．２０以上
ｎ値は、耐局部座屈性、耐破壊性能に影響を及ぼすため、規定する。Ｈ形鋼梁の座屈は、局部座屈部の歪みが公称歪み２〜５％において生ずるため、この範囲におけるｎ値（加工硬化指数）を規定する。ｎ値が大きい場合、歪みを受けた部分の硬化領域が大きく広がり、歪みは鋼材全体に分布し,その部分の局所的変形が抑制され、耐局部座屈性が向上する。このような効果は、公称歪み２〜５％におけるｎ値を０．２０とした場合、顕著となるため、本発明では公称歪み２〜５％におけるｎ値を０．２０以上とする。
【００４０】
また、ｎ値を大きくした場合、耐破壊性能が向上する。引張り強さ：５００ＭＰａ，表面欠陥断面積率：３％と比較的、欠陥寸法が小さい場合の鋼材において、降伏比：７０％、ｎ値：０．２０の鋼材の破断歪みは約１０％であるが、降伏比：８０％、ｎ値：０．１５である鋼材の破断歪みは約６％となり、破断歪みは低下し、耐破壊性能に劣る。
【００４１】
３．組織形態
本発明に望ましい金属組織は、軟質相であるフェライトと硬質相であるベイナイト、またはベイナイトを含む硬質相（例えば、ベイナイト＋パーライト）の混合組織であり、軟質相と硬質相の混合組織とすることにより、主に、軟質相／硬質相の界面において軟質相側を降伏させながら、硬質相で全体の強度を上昇させ、降伏比を低減させる。
【００４２】
軟質相の体積率：５０％超え、８０％以下
軟質相の体積率は、フランジ長手引張試験において、降伏比７０％以下、降伏伸び０．８％以上とするため、５０％超えとする。一方、８０％を超えると引張強度が４９０Ｎ／ｍｍ2級を満足しないため、５０％超え、８０％以下とする。尚、体積率は２次元断面において観察したフェライト面積率を、体積率に等しいものと仮定した。
【００４３】
軟質相の平均粒径：１０μｍ以上
軟質相の平均粒径は、１０μｍ未満の場合、降伏応力が上昇し、降伏比が高くなるため、１０μｍ以上とする。
【００４４】
硬質相のアスペクト比：３以下
硬質相のアスペクト比が３を超えた場合、降伏伸びが低下するため、３以下とする。アスペクト比は、フランジ圧延方向に平行に切断した断面において、各硬質相の圧延方向に沿った長さと、板厚方向に沿った長さとの比として求めた。アスペクト比が大きい程、組織が圧延方向に伸長していることを示す。
４．製造方法
スラブ加熱温度：１０５０℃以上、１３００℃以下
スラブ加熱温度が１０５０℃未満の場合、熱間変形抵抗の増大により、断面形状が劣化し、圧延割れを生じ、鋳片を用いた場合は均質化が不十分となり特性が劣化する。１３００℃を超えると、結晶粒が粗大化し、靭性が劣化するため、１０５０℃以上、１３００℃以下とする。
【００４５】
圧延終了温度：Ａｒ3点以上
圧延終了温度は、Ａｒ3点未満の場合、フェライト相に歪みが蓄積され、降伏点を上昇させ、降伏比を高くし、また、硬質相のアスペクト比を増大させ、降伏伸びを低下させるため、Ａｒ3点以上とする。Ａｒ3点は、鋼成分、オーステナイト粒径、フランジ厚等によって変化し、目安として例えば、次式を用いる。Ａｒ3（℃）＝９１０−３１０Ｃ−８０Ｍｎ−２０Ｃｕ−１５Ｃｒ−５５Ｎｉ−８０Ｍｏ＋０．３５（ｔ−８），但し、ｔは板厚、フランジ厚（ｍｍ）である。
【００４６】
冷却条件
冷却はフランジ外面、あるいは外面と内面の双方から行なうが、冷却による歪み発生防止及びフランジ厚さ方向の特性の均一性の観点からは、内外面双方から冷却することが望ましい。圧延終了後、低冷却速度で７００℃以下６００℃以上に冷却し、その後、高冷却速度で引続き５５０℃以下まで冷却する２段冷却とする。
【００４７】
圧延終了後の自然放冷も含む低冷却速度による冷却は、板厚方向に均一、且つ十分な量のフェライト相と十分にアスペクト比の小さな硬質相を得るために行うもので、冷却停止温度が７００℃より高いとその後の水冷後の変態組織として、十分な量のフェライト相が得られず、一方、６００℃より低いとパーライト変態が進行し、所望の機械的特性が得られない。
【００４８】
冷却速度は５℃／ｓを超えるとフランジの厚さ方向の組織が不均一となりやすく所望の組織形態に制御することが困難となるので、５℃／ｓ以下とする。上述したように５℃／ｓ以下の冷却には自然放冷の場合も含むものとする。
【００４９】
引き続いて行う高冷却速度による冷却は、硬質相を得るためで、冷却速度が５℃／ｓより小さいと、硬質相の硬さが不十分で、所望の機械的特性が得られないため、５℃／ｓ以上とする。冷却停止温度は５５０℃より高い場合、硬質相の硬さが不十分となるため、５５０℃以下とする。
【００５０】
冷却停止温度の下限は特に規定しないが、２００℃より低いと、靭性が損なわれる可能性があるため、２００℃以上で停止し、その後、自然放冷することが望ましい。
【００５１】
尚、いずれの冷却速度もフランジ厚さ：ｔ２（図１参照）の外面側の（１／４）ｔ２において規定する。
【００５２】
本発明における形鋼のフランジ厚は、８ｍｍ以上、４０ｍｍ以下がその効果を得る上で最も望ましい。８ｍｍより薄い場合、圧延後の断面形状を良好に確保することが困難で、４０ｍｍより厚い場合は、フランジ板厚中心で所望の金属組織に制御することが難しくなる。また、強度は、その望ましいミクロ組織から、引張強度４９０Ｎ／ｍｍ2級が主たる対象となるが、限定されるわけではない。
【００５３】
【実施例】
（実施例１）
表１に示す成分組成の鋼を溶製後、連続鋳造により鋳片とした。鋼Ａ、Ｂは、仕上圧延後、フランジを水冷し、ＪＩＳＧ３１３６ ＳＮ４９０Ｂ鋼相当の機械的特性を目標とした成分組成である。鋼Ｂは、Ｎｂが添加され、本発明範囲外となっている。鋳片を１２５０℃に加熱後、圧延終了温度約８００℃とする圧延で、３００×３００×１０×１５（ｍｍ）（Ｈ×Ｂ×ｔ１×ｔ２、図１参照）のＨ形鋼とした。
【００５４】
圧延終了後、表２に示す冷却条件で冷却を行った。冷却法１は、水冷開始温度７８０℃、冷却停止温度５００℃でその後常温まで自然放冷するもので、冷却法２は、圧延後、６６０℃まで自然放冷後、水冷を開始し、４４０℃で冷却停止後、常温まで自然放冷する２段冷却法である。冷却速度はいずれの冷却法でも、水冷時のフランジ厚さ（ｔ２）の１／４で、６０℃／ｓとした。尚、冷却法１は水冷開始温度が高く、本発明範囲外と成っている。
【００５５】
冷却後、製造した各Ｈ形鋼より、引張試験片、衝撃試験片を採取し、機械的特性を調査した。図１に試験片採取位置の概略位置を示す。引張試験は、フランジ幅方向１／４の位置から圧延方向を長手方向とし、ＪＩＳＺ２２０１ １Ａ号引張試験片（平行部幅：４０ｍｍ，ゲージ長：２００ｍｍ）を３本採取し、常温における引張特性、公称歪みで２〜５％におけるｎ値を求めた。
【００５６】
さらに、フランジ幅方向１／４の位置のフランジ厚中心（１／２ｔ）から、ＪＩＳＧ０５６７に規定のＩＩ−８号試験片（平行部径：８ｍｍ，ゲージ長：４０ｍｍ）を採取し、６００℃、７００℃における引張特性を調査した。衝撃試験は板厚中心（１／２ｔ）よりＪＩＳＺ２２０２ Ｖノッチ衝撃片を３本採取し、試験温度０℃で衝撃吸収エネルギを求めた。
【００５７】
表３に引張試験、衝撃試験の結果を示す。いずれのサンプルも、引張強度、衝撃特性に関してはＳＮ４９０Ｂの規格を満足する特性がえられているが、鋼組成または冷却法のいずれか、または双方が本発明範囲外で比較例となっているサンプルＮｏ．１１、１３、１４は、降伏伸び、降伏比またはｎ値が本発明範囲外となっている。サンプルＮｏ．１２は、鋼組成、冷却法共に本発明範囲内で、優れた特性が得られている。尚、いずれのサンプルも６００℃における降伏強度は、２２０ＭＰａ以上で、常温の降伏強度の６０％以上、７００℃における降伏強度は１１０ＭＰａ以上で常温の３０％以上の良好な耐火性能を示している。
【００５８】
次にこれらの形鋼の耐局部座屈特性を評価するため、長さ５００ｍｍとした形鋼サンプルの圧縮試験により、座屈を生じる歪み（座屈発生限界歪み）を求めた。図２に圧縮試験の状況を模式的に示す。
また、耐破壊性能を評価するため、平行部に平行部断面の１０％に相当する切欠きを有する引張試験片を用い、引張試験により破断歪みを測定した。
表４に、圧縮試験、切欠き付き引張試験の結果を示す。座屈発生限界歪み、破断歪み共に鋼組成、冷却条件のいずれもが本発明範囲内となるサンプルＮｏ．１２では、比較例であるサンプルＮｏ．１１，１３，１４に対し、優れた特性となっている。尚、これらの試験におけるサンプルＮｏ．１２の特性は、４９０ＭＰａ級鋼のＡｓ ｒｏｌｌ材で得られる特性よりも優れたものとなっている。座屈発生限界歪みは、４９０ＭＰａ級鋼のＡｓ ｒｏｌｌ材では０．５１％で、５０％向上したとしても０．７７％であり、サンプルＮｏ．１２に及ばない。破断歪みは、４９０ＭＰａ級鋼のＡｓ ｒｏｌｌ材では３．２％で、５０％向上したとしても４．８％であり、サンプルＮｏ．１２に及ばない。
上述したように、Ｎｂを含有し、本発明範囲外の組成となる鋼Ｂでは、降伏伸び、降伏比、ｎ値の何れかが本発明の規定外となり、耐局部座屈特性および耐破壊性能に優れた特性は得られない。
【００５９】
【表１】
【表２】
【表３】
【表４】
（実施例２）
表５に示す鋼を溶製後、連続鋳造により鋳片とし、１２５０℃に加熱後、３００×３００×１０×１５（ｍｍ）のＨ形鋼に圧延した。圧延後、表２の冷却法２に示す製造条件で圧延、冷却を行った。冷却法２は、６６０℃まで自然放冷後水冷を開始し、４４０℃で冷却を停止し、その後常温まで自然放冷するものである。水冷時のフランジ厚さ（ｔ２）に対し、（１／４）ｔ２における冷却速度は、約６０℃／ｓであった。
【００６４】
その後、各Ｈ形鋼より、実施例１と同様に、引張試験片、衝撃試験片を採取し、機械的特性を調査した。引張試験は、フランジ幅方向１／４の位置から圧延方向を長手方向とし、ＪＩＳＺ２２０１ １Ａ号引張試験片（平行部幅：４０ｍｍ，ゲージ長：２００ｍｍ）を３本採取し、常温における引張特性、公称歪みで２〜５％におけるｎ値を求めた。
【００６５】
さらに、フランジ幅方向１／４の位置のフランジ厚中心（１／２ｔ）から、ＪＩＳＧ０５６７に規定のＩＩ−８号試験片（平行部径：８ｍｍ，ゲージ長：４０ｍｍ）を採取し、６００℃、７００℃における引張特性を調査した。衝撃試験は板厚中心（１／２ｔ）よりＪＩＳＺ２２０２ Ｖノッチ衝撃片を３本採取し、試験温度０℃で衝撃吸収エネルギを求めた。
【００６６】
表６に引張試験、衝撃試験の結果を示す。本発明範囲内の製造条件によるＮｏ．２１，２２，２３、２４、２６，２８は、引張り特性に関する本発明の規定を全て満足するが、Ｍｏ量が本発明範囲外で、少ない鋼ＧによるＮｏ．２５では、耐火性が劣っている。Ｍｏ量が本発明範囲外で、多い鋼ＩによるＮｏ．２７では衝撃特性が劣っている。
【００６７】
次に、常温における引張および衝撃特性、耐火性に関して良好な特性を示すＮｏ．１２、２１，２２，２３、２４、２６，２８について耐局部座屈特性を評価するため、長さ５００ｍｍとした形鋼サンプルの圧縮試験（図２参照）により、座屈を生じる歪み（座屈発生限界歪み）を求めた。
また、更に、耐破壊性能を評価するため、平行部に平行部断面の１０％に相当する切欠きを有する引張試験片を用い、引張試験により破断歪みを測定した。圧縮試験および切欠き付き引張試験は実施例１と同様にした。
表７に、圧縮試験、切欠き付き引張試験の結果を示す。いずれのサンプルでも座屈発生限界歪みは、同一の試験条件で得られる４９０ＭＰａ級鋼の圧延まま材で得られる０．５１％に対し５０％向上している０．７７％を更に超える良好な値が得られている。また、破断歪みも同一の試験条件で得られる４９０ＭＰａ級鋼の圧延まま材で得られる３．２％に対し５０％向上している４．８％を更に超える良好な値が得られている。
【００６８】
以上の試験結果から明らかなように、降伏伸び、降伏比およびｎ値の全てが本発明の規定を満足した場合、優れた耐局部座屈性と耐破壊性能が得られる。
【００６９】
【表５】
【表６】
【表７】
（実施例３）
表１に示す鋼Ａを溶製後、連続鋳造により鋳片とした。鋳片を１２５０℃に加熱後、圧延終了温度８００℃とする圧延で、３００×３００×１０×１５（ｍｍ）（Ｈ×Ｂ×ｔ１×ｔ２、図１参照）のＨ形鋼とした。表８に示す圧延、冷却条件により製造した。サンプルＮｏ．３２は、圧延終了後、常温まで自然放冷した。尚、自然放冷の冷却速度は、８００〜５００℃までの平均で約０．８℃／ｓであった。
これらの形鋼で、圧延、冷却条件が引張り特性、衝撃特性および耐局部座屈性、耐破壊性能に及ぼす影響を調査した。
【００７３】
表９に引張、衝撃特性の試験結果を示す。試験は、実施例１と同様に行った。
圧延、冷却条件が本願発明の規定を満足するＮ０．１２，３１，３６では、降伏伸び、降伏比、ｎ値のいずれもが、本発明で規定する範囲内で、引張強度も４９０Ｎ／ｍｍ2級を満足している。
【００７４】
一方、圧延、冷却条件が本願発明の範囲外となるＮｏ．３２，１１，３３，３４，３５，３７，３８では降伏伸び、降伏比、ｎ値のいずれかが、本発明の規定外となった。尚、高温強度は、いずれのサンプルも、６００℃における降伏強度は２２０ＭＰａ以上で常温の降伏強度の５５％以上、７００℃における降伏強度は１１０ＭＰａ以上で常温の３０％以上の良好な耐火性能を有している。
【００７５】
次に、引張強度がＳＮ４９０Ｂの規格を満足するＮｏ．１２，３１，１１，３４，３６，３７について、耐局部座屈特性を評価するため、長さ５００ｍｍとした形鋼サンプルの圧縮試験により、座屈を生じる歪み（座屈発生限界歪み）を求めた。また、更に、耐破壊性能を評価するため、平行部に平行部断面の１０％に相当する切欠きを有する引張試験片を用い、引張試験により破断歪みを測定した。圧縮試験および切欠き付き引張試験は実施例１と同様にした。
【００７６】
表１０に圧縮試験、切欠き付き引張試験の結果を示す。座屈発生限界歪みは、降伏伸び,降伏比、ｎ値の全てが本発明の規定を満足するサンプルＮｏ．１２、３１、３６に加え、ｎ値が本発明の規定を満足するサンプルＮｏ．３４はサンプルＮｏ．１１，３７と比較して座屈発生限界歪みが良好で、本発明例と同等の特性が得られ、耐局部座屈性におけるｎ値の影響の大きいことが認められた。
【００７７】
破断歪みは、降伏伸び,降伏比、ｎ値の全てが本発明の規定を満足するサンプルＮｏ．１２、３１、３６では、優れた破断歪みが得られているが、降伏伸びが小さいＮｏ．３４は破断歪みは小さく、降伏伸びが０のＮｏ．１１，３７では更に小さかった。
【００７８】
以上の試験結果から明らかなように、降伏伸び、降伏比およびｎ値の全てが本発明の規定を満足した場合、優れた耐局部座屈性と耐破壊性能が得られる。
【００７９】
【表８】
【表９】
【表１０】
（実施例４）
表１に示す成分組成の鋼を溶製後、連続鋳造により鋳片とした。鋳片を１２５０℃に加熱後、圧延終了温度８００℃とする圧延で、３００×３００×１０×１５（ｍｍ）（Ｈ×Ｂ×ｔ１×ｔ２、図１参照）のＨ形鋼とし、表１１に示す圧延、冷却条件により製造した。サンプルＮｏ．３２は、圧延終了後、常温まで自然放冷した。尚、自然放冷の冷却速度は、８００〜５００℃までの平均で約０．８℃／ｓであった。
【００８３】
これらの形鋼で、ミクロ組織が引張り特性、衝撃特性および耐局部座屈性、耐破壊性能に及ぼす影響を調査した。ミクロ組織は、フランジ幅方向１／４の位置における長手に沿った断面で、フランジ厚さ中心の光学顕微鏡組織、走査型電子顕微鏡組織を観察し、線分法により、フェライトの体積率と平均粒径を求めた。
硬質相については、その組織形態および圧延方向と板厚方向の長さを求め、その比の値として、アスペクト比を算出した。
【００８４】
表１２にミクロ組織の観察結果を示す。鋼組成、製造条件が本発明範囲内のサンプルＮｏ．１２，３１，４２はミクロ組織に関する本発明の規定を全て満足するが、サンプルＮｏ．３２，１１，１３，４１，３３，３４，１４はミクロ組織に関する本発明の規定のいずれかを満足しない。
【００８５】
次に、実施例１，２、３と同様に、引張試験、シャルピー衝撃試験を行った。
表１３にそれらの結果を示す。ミクロ組織に関する本発明の規定のいずれかを満足しないサンプルＮｏ．３２，１１，１３，４１，３３，３４，１４は、降伏伸び、降伏比およびｎ値の何れかが、本発明範囲外となる。一方、本発明例であるサンプルＮｏ．１２，３１，４２は、ミクロ組織に関する本発明の規定を満足し、降伏伸び、降伏比およびｎ値の何れもが、本発明範囲内となる。
【００８６】
更に、引張強度４９０ＭＰａ以上であるサンプルＮｏ．１２，３１，１１，４１，３４，４２，１３，１４について、耐局部座屈性、耐破壊性能を実施例１，２、３と同様な方法により求めた。
【００８７】
表１４に座屈発生限界歪みと破断歪みの測定値を示す。本発明で規定する組織形態を有するサンプルＮｏ．１２、３１，４２では両者で優れた特性がえられたのに対し、軟質相、硬質相における規定を満足しないサンプルＮｏ．１１，４１，３４，１３，１４では、何れか、又は両者の特性が劣っていた。
【００８８】
上述したように、鋼組成、製造条件が本発明の規定を満足する圧延Ｈ形鋼で得られるミクロ組織は、耐局部座屈性、耐破壊性能に優れた特性を示した。
【００８９】
【表１１】
【表１２】
【表１３】
【表１４】
【発明の効果】
上述したように、本発明の圧延耐火形鋼は、大地震の際、建築物の梁部材に負荷される大きな引張、圧縮により生じる局部座屈を起こしにくく、また、座屈した部分の亀裂や梁端の溶接欠陥による破壊に対する抵抗力が優れているため、大地震の際、梁部材の塑性変形により地震エネルギーを吸収し大崩壊を回避する限界状態設計法に最適で、大地震に対し、安全な鋼構造物を提供し、産業社会上、その効果は極めて大きい。
【図面の簡単な説明】
【図１】圧延Ｈ形鋼の引張試験片の採取位置およびミクロ組織の観察位置を示す模式図。
【図２】耐局部座屈性を評価するための圧縮試験の概要を示す図。
【図３】耐破壊性能を評価するための表面切欠き付き引張試験片（単位：ｍｍ）を示す図。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a method for producing rolled steel, and in particular, production of steel having excellent local buckling resistance and fracture resistance suitable for steel beams in high-rise buildings, and excellent high-temperature strength during a fire. Regarding the method.
[0002]
[Prior art]
In today's high-rise buildings, when a major earthquake strikes, a limit state design method that emphasizes human safety that absorbs earthquake energy by plastic deformation of beam members and avoids major collapse is applied. In the event of a large earthquake, large tensile and compressive stresses are applied to building beam members, causing local buckling, and cracking may occur from the buckled location, leading to collapse. Therefore, excellent buckling resistance and toughness are required for the beam member used in the limit state design method.
[0003]
The H-section steel, which is one of the rolled section steels, can be manufactured in a large amount and stably, and is widely used as a beam material for construction and civil engineering, combined with its excellent economic efficiency. Conventionally, regarding rolled steel shapes for construction, techniques for improving earthquake resistance from the viewpoint of a low yield ratio are disclosed in Japanese Patent Laid-Open Nos. 5-25588 and 5-345915. However, since the local buckling of the beam member occurs on the low strain side that does not reach the tensile strength of the material, the effectiveness of the yield ratio as an index of the local buckling resistance is not clear.
In addition, in the event of a major earthquake, local buckling as well as the index related to the fracture of the beam end, which is a problem, is unclear.
[0004]
On the other hand, as a method for producing rolled H-section steel, a method for producing H-section steel that is non-tempered, has a low yield ratio, and has excellent toughness and weldability is proposed in Japanese Patent Laid-Open No. 6-240350. With Nb as an essential additive element, austenite grains are refined during hot rolling to improve toughness, and after rolling, the steel is allowed to cool until 30% or more of ferrite precipitates, t / 4 (t: thickness) Is cooled to 600 ° C. or lower at a cooling rate of 0.3 ° C./s or higher and 5 ° C./s or lower to obtain a structure containing ferrite and bainite.
[0005]
However, it is considered that this technology is mainly intended for the production of extra-thick H-section steel, and Nb, an essential element, is presumed to be added to ensure the toughness of the flange plate thickness center and fillet part. It is not intended for relatively thin flange thicknesses of 8 mm or more and 40 mm or less, which are frequently used as building beam members.
[0006]
On the other hand, the demand for fire resistance performance for building steel materials has been increasing year by year. Regarding the method for producing a low yield ratio fire resistant steel material by controlling the steel components and the structure, for example, Japanese Patent No. 2134176 includes 0.2 to 0.7% of Mo. Further, a technique relating to a low yield ratio steel material for construction is described in which the microstructure is a mixed structure of 20% to 50% ferrite and bainite.
[0007]
Japanese Patent No. 1925440 includes Mn: 0.3 to 0.7%, Mo: 0.5 to 0.8%, hot rolling is finished at 800 to 1000 ° C., and the microstructure is mainly composed of ferrite. The manufacturing method of the low yield ratio steel for construction excellent in fire resistance characterized by doing is indicated.
[0008]
[Problems to be solved by the invention]
As described above, material indices such as steel composition and structure for improving local buckling resistance and beam fracture resistance of H-section steel are not fully understood, and 8 mm is often used as a beam member. A manufacturing method for a relatively thin flange thickness of 40 mm or less is not clarified. Furthermore, although steel materials with excellent fire resistance have been disclosed as low yield ratio steel materials for construction, no consideration has been given to local buckling resistance or fracture resistance, and beams with these characteristics have not been studied. The appropriate tissue form as a member has not been clarified.
[0009]
Therefore, the present invention grasps the relationship between the local buckling resistance due to the compressive stress acting in the axial direction of the beam material, the beam fracture resistance and the material characteristics, and is less likely to cause local buckling in the event of a large earthquake, and Because it is hard to break at the end of a beam, etc., it provides a rolled steel with high fire resistance and high performance that prevents building structures from collapsing.
[0010]
[Means for Solving the Problems]
The present inventors studied to grasp the relationship between various properties obtained by a tensile test, local buckling resistance, and beam fracture resistance. As a result, regarding the local buckling resistance, it was found that the buckling occurrence limit strain in the compression test of the H-shaped steel was not a high strain region in which fracture occurred, but was approximately 2 to 5% nominal strain. It was understood that there was a good correlation with the work hardening index (n value) at 2 to 5% nominal strain and the yield elongation.
[0011]
In addition, as a result of investigating H-shaped steels with variously changed flange and web characteristics, it was also found that the flange characteristics had a large effect on the local buckling resistance and the web characteristics had little effect.
[0012]
And, since the actual fracture is due to stress concentration due to structural discontinuities such as beam ends, or fracture due to weld defects, the actual fracture is created by an analytical model that assumes these factors. The relationship with characteristics was investigated. The analysis model was a case where a load P was applied in a direction perpendicular to a cross section A ′ having a surface defect of length a and depth d.
[0013]
When the average stress σA ′ of the section A ′ reaches the fracture limit stress σC (provided that σC = TS), the normal section A (all sections when there is no surface notch) and the force of the section A ′ Swift's formula for the balance (σA = σA ′ × (1-ad / Wt), (σA: stress in normal section, W: full width, t: full thickness), and stress-strain curve: σ = (α / ( 1 + ε)) {β + ln (1 + ε)} n (Where σ: nominal stress, ε: nominal strain, α, β: constant, n: work hardening index), the following equation is obtained as a conditional expression for fracture.
[0014]
(Α / (1 + ε)) {β + ln (1 + ε)} n = TS x (1-ad / Wt)
Based on this equation, a tensile test piece having a surface defect was prepared using a material whose material characteristics such as n value and yield ratio were changed in a wide range, and a tensile test was performed. As a result, we obtained guidelines for breaking strain to be organized by material properties and defect dimensions, and for material factors that improve allowable defect dimensions.
[0015]
Based on the above knowledge, the present invention has been further studied with regard to its component composition so that the steel material has excellent weldability and excellent fire resistance. Regarding the fire resistance, the ratio of the yield strength at 600 ° C. to the yield strength at room temperature was set to exceed 55%, and the ratio of the yield strength at 700 ° C. was set to exceed 20%.
[0016]
That is, the present invention
1. In mass%, C: 0.05 to 0.18%, Si: 0.6% or less, Mn: 0.6 to 1.6%, Mo: 0.2 to 0.7%, P: 0.020 %, S: 0.015% or less, Al: 0.01-0.05%, Nb: less than 0.005%, N: 0.0080% or less, H: 4 ppm or less, and Ceq according to formula (1): 0.40% or less The balance is Fe and inevitable impurities The work hardening index according to the formula (2) when the tensile properties in the longitudinal direction of the flange are yield elongation: 0.8 to 3.0%, yield ratio: 70% or less, and
[0017]
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 (1)
n = (lnσ Five -Lnσ 2 ) / (Lnε Five −lnε 2 (2)
σ Five = 1.05 × σ N5 , Σ 2 = 1.02 × σ N2 , Ε Five = Ln (1.05),
ε 2 = Ln (1.02)
Where σ Five : True stress at 5% nominal strain, σ 2 : True stress at nominal strain of 2%, ε Five : True strain at 5% nominal strain, ε 2 : True strain at nominal strain of 2%,
σ N5 : Nominal stress at 5% nominal strain, σ N2 : Nominal stress at 2% nominal strain
ln: natural logarithm
And
[0018]
2. The rolled refractory steel according to 1, further comprising, by mass%, Cu: 0.6% or less, Ni: 1% or less, and Cr: 0.5% or less as a steel composition.
[0019]
3. The rolled refractory steel according to 1 or 2, further comprising one or two of V: 0.2% or less and Ti: 0.03% or less as a steel composition.
[0020]
4). The metal structure of the flange is a mixed structure composed of a ferrite phase of a soft phase and a bainite phase of a hard phase, or a hard phase containing a bainite phase, the volume fraction of the soft phase is more than 50% and 80% or less, the average particle size is 10 μm or more, The rolled refractory steel according to any one of 1 to 3, wherein the aspect ratio of the hard phase is 3 or less.
[0021]
The slab or steel slab having the steel component according to any one of 5.1 to 3 is heated to 1050 to 1300 ° C. or less, rolling is finished at the
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the component composition, mechanical properties and production conditions defined in the present invention will be described in detail.
[0023]
1. Ingredient composition
C: 0.05 to 0.18%
C is added in an amount of 0.05% or more in order to secure the strength of the steel and to have a desired structure form. However, if contained in a large amount exceeding 0.18%, the toughness or weldability deteriorates. To 0.18% (0.05% or more and 0.20% or less).
[0024]
Si: 0.6% or less
Si is inevitably contained in the steel for deoxidation and improves the strength. However, if it exceeds 0.6%, the hardenability of the steel is excessively increased and is not preferable from the viewpoint of HAZ toughness and weldability. .6% or less.
[0025]
Mn: 0.6 to 1.6%
Mn is added in an amount of 0.6% or more in order to improve the strength and toughness of the steel material and to suppress the formation of FeS. If it exceeds 1.6%, the hardenability of the steel is increased, so that a hardened layer appears at the time of welding and crack sensitivity deteriorates, so 0.6 to 1.6%.
[0026]
Al: 0.01 to 0.05%
Al is an inexpensive and strong deoxidizer, and is added in an amount of 0.01% or more. However, if it exceeds 0.05%, the cleanliness of the steel is lowered and the toughness of the weld is deteriorated. .05%.
[0027]
N: 0.0080% or less
N is an unavoidable impurity contained in the steel. When the content is increased, the deterioration of HAZ toughness, deterioration with time, or generation of continuous cast slab flaws is promoted, so the content is made 0.0080% or less.
[0028]
H: 4 ppm or less
H is an inevitable impurity contained in the steel. If the content increases, cracks after rolling and delayed fracture occur, so the content is set to 4 ppm or less.
[0029]
P: 0.020% or less, S: 0.015% or less
P and S inevitably exist as impurities mixed in the steel. Since reduction of P is effective in preventing grain boundary fracture in HAZ, it is set to 0.020% or less. Since the reduction of S is effective for preventing hydrogen cracking in HAZ, it is set to 0.015% or less.
[0030]
Ceq: 0.40 or less
If Ceq (= C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14) exceeds 0.40, the toughness in the base metal and the welded portion may be impaired, so it is set to 0.40 or less.
[0031]
In the present invention, one or more of Cu, Ni, Cr, V, and Ti can be added in order to improve mechanical properties.
Cu: 0.6% or less, Ni: 1% or less, Cr: 0.5% or less
Cu, Ni, and Cr are added in one kind or two or more kinds in order to strengthen the steel material by solid solution strengthening. Cu also has the effect of improving weather resistance. However, excessive addition reduces the toughness and weldability, so Cu: 0.6% or less, Ni: 1% or less, and Cr: 0.5% or less.
[0032]
One or two of V: 0.2% or less and Ti: 0.03% or less
V and Ti are added singly or in combination to strengthen the steel material by solid solution strengthening and precipitation strengthening. Since addition more than necessary reduces toughness and weldability, V: 0.2% or less and Ti: 0.03% or less.
[0033]
In addition, the feature on the component composition in the present invention is that, in order to improve the strength and toughness of steel materials in general, Nb that is often added is not contained, and even when it is mixed as an unavoidable impurity, 0. It is in the point which regulates to less than 005%. When Nb is contained, the non-recrystallized region in the hot rolling is expanded to the high temperature side. For example, in the rolling of the shape steel having a flange thickness of 8 mm or more and 40 mm or less, due to the significant reduction in the non-recrystallized region, The austenite grain size becomes finer than necessary, the final transformation structure becomes finer, and the yield point rises. Therefore, the n value at a nominal strain of 2 to 5% decreases, the buckling limit occurrence strain becomes small, and the intended effect of the present invention cannot be obtained.
[0034]
2. Mechanical properties
In the present invention, the tensile property is defined as the mechanical property.
[0035]
Yield elongation: 0.8-3.0%
Yield elongation promotes the deformation of the entire member in the process leading to local buckling, thus suppressing low strain buckling due to the occurrence of local buckling, increasing the energy absorption of the steel as a whole, and local buckling resistance. Improves the fracture resistance.
[0036]
If it is less than 0.8%, the effect is insufficient, and if it is more than 3.0%, there is a possibility that buckling may occur at the yielding stage without causing work hardening. 3.0% (0.8% or more and 3.0% or less).
[0037]
Yield ratio: 70% or less
Yield ratio is specified because it has a strong influence on fracture resistance. When the yield ratio is lowered, the fracture strain increases. When the yield ratio is 70%, a steel material with a tensile strength of 500 MPa and an n value of 0.20 has a fracture strain of about 4.8% due to a defect corresponding to 10% of the cross-sectional area. Excellent fracture resistance is exhibited with respect to about 2.5%, which is a fracture strain at an upper limit yield ratio of 80%.
[0038]
Therefore, in the present invention, the yield ratio is 70% or less. The yield ratio may be obtained as the ratio of the upper yield point to the tensile strength according to the stress-strain diagram obtained in the tensile test.
[0039]
n value: 0.20 or more
The n value is specified because it affects local buckling resistance and fracture resistance. The buckling of the H-shaped steel beam defines the n value (work hardening index) in this range because the distortion of the local buckling portion occurs at a nominal strain of 2 to 5%. When the n value is large, the hardened region of the portion subjected to the strain is greatly spread, the strain is distributed throughout the steel material, local deformation of the portion is suppressed, and the local buckling resistance is improved. Such an effect becomes remarkable when the n value at a nominal strain of 2 to 5% is 0.20. Therefore, in the present invention, the n value at a nominal strain of 2 to 5% is 0.20 or more.
[0040]
Further, when the n value is increased, the fracture resistance is improved. Tensile strength: 500 MPa, surface defect cross-sectional area ratio: 3% Steel material with a relatively small defect size, yield strain: 70%, n value: 0.20, the fracture strain of steel material is about 10% However, the fracture strain of a steel material having a yield ratio of 80% and an n value of 0.15 is about 6%, the fracture strain is reduced, and the fracture resistance is poor.
[0041]
3. Organizational form
A desirable metal structure for the present invention is a mixed structure of ferrite, which is a soft phase, and bainite, which is a hard phase, or a hard phase containing bainite (for example, bainite + pearlite), and is a mixed structure of a soft phase and a hard phase. Thus, while yielding the soft phase side mainly at the soft phase / hard phase interface, the overall strength is increased in the hard phase and the yield ratio is reduced.
[0042]
Volume fraction of soft phase: more than 50%, 80% or less
In the flange longitudinal tensile test, the volume fraction of the soft phase is over 50% in order to obtain a yield ratio of 70% or less and a yield elongation of 0.8% or more. On the other hand, if it exceeds 80%, the tensile strength does not satisfy the 490 N /
[0043]
Average particle size of soft phase: 10 μm or more
When the average particle size of the soft phase is less than 10 μm, the yield stress increases and the yield ratio increases, so that the average particle size is 10 μm or more.
[0044]
Hard phase aspect ratio: 3 or less
When the aspect ratio of the hard phase exceeds 3, the yield elongation decreases, so it is set to 3 or less. The aspect ratio was determined as the ratio of the length along the rolling direction of each hard phase to the length along the plate thickness direction in a cross section cut parallel to the flange rolling direction. A larger aspect ratio indicates that the structure extends in the rolling direction.
4). Production method
Slab heating temperature: 1050 ° C or higher and 1300 ° C or lower
When the slab heating temperature is less than 1050 ° C., the cross-sectional shape is deteriorated due to an increase in hot deformation resistance, resulting in rolling cracks. When a slab is used, homogenization is insufficient and the characteristics deteriorate. If it exceeds 1300 ° C, the crystal grains become coarse and the toughness deteriorates, so that the temperature is set to 1050 ° C or higher and 1300 ° C or lower.
[0045]
Rolling end temperature: Ar3 point or higher
When the rolling end temperature is less than the Ar3 point, strain is accumulated in the ferrite phase, the yield point is increased, the yield ratio is increased, the aspect ratio of the hard phase is increased, and the yield elongation is decreased. Do not exceed the point. The Ar3 point varies depending on the steel component, austenite grain size, flange thickness, etc., and for example, the following formula is used as a guide. Ar3 (° C.) = 910-310C-80Mn-20Cu-15Cr-55Ni-80Mo + 0.35 (t-8), where t is the plate thickness and flange thickness (mm).
[0046]
Cooling condition
Cooling is performed from the outer surface of the flange, or from both the outer surface and the inner surface. From the viewpoint of preventing distortion due to cooling and uniformity of characteristics in the thickness direction of the flange, it is desirable to cool from both the inner and outer surfaces. After rolling, the cooling is performed at a low cooling rate to 700 ° C. or lower and 600 ° C. or higher, and then at a high cooling rate, cooling to 550 ° C. or lower is performed.
[0047]
Cooling at a low cooling rate, including natural cooling after the end of rolling, is performed in order to obtain a sufficient amount of ferrite phase and a hard phase with a sufficiently small aspect ratio in the thickness direction. When the temperature is higher than 700 ° C., a sufficient amount of ferrite phase cannot be obtained as a transformed structure after the subsequent water cooling. On the other hand, when the temperature is lower than 600 ° C., pearlite transformation proceeds and desired mechanical properties cannot be obtained.
[0048]
If the cooling rate exceeds 5 ° C./s, the structure in the thickness direction of the flange tends to be non-uniform, and it becomes difficult to control the structure to a desired structure, so the temperature is set to 5 ° C./s or less. As described above, the cooling at 5 ° C./s or less includes the case of natural cooling.
[0049]
The subsequent cooling at a high cooling rate is for obtaining a hard phase. If the cooling rate is less than 5 ° C./s, the hardness of the hard phase is insufficient and desired mechanical properties cannot be obtained. ℃ / s 以上。 When the cooling stop temperature is higher than 550 ° C., the hardness of the hard phase becomes insufficient, so that it is 550 ° C. or lower.
[0050]
The lower limit of the cooling stop temperature is not particularly specified, but if it is lower than 200 ° C., the toughness may be impaired. Therefore, it is desirable to stop at 200 ° C. or higher and then naturally cool.
[0051]
In addition, all cooling rates are prescribed | regulated in (1/4) t2 of the outer surface side of flange thickness: t2 (refer FIG. 1).
[0052]
The flange thickness of the shape steel in the present invention is most desirably 8 mm or more and 40 mm or less for obtaining the effect. If it is thinner than 8 mm, it is difficult to ensure a good cross-sectional shape after rolling, and if it is thicker than 40 mm, it becomes difficult to control the metal structure at the center of the flange plate thickness. Further, the strength is mainly limited to a tensile strength of 490 N /
[0053]
【Example】
Example 1
Steels having the composition shown in Table 1 were melted and then cast into slabs by continuous casting. Steels A and B have component compositions that target the mechanical properties equivalent to JISG3136 SN490B steel by cooling the flange after finishing rolling. Steel B has Nb added and is outside the scope of the present invention. The slab was heated to 1250 ° C. and then rolled to a rolling end temperature of about 800 ° C. to obtain an H-section steel of 300 × 300 × 10 × 15 (mm) (H × B × t1 × t2, see FIG. 1).
[0054]
After rolling, cooling was performed under the cooling conditions shown in Table 2. Cooling method 1 is a water cooling start temperature of 780 ° C., a cooling stop temperature of 500 ° C., and then naturally cooled to room temperature.
[0055]
After cooling, tensile test pieces and impact test pieces were sampled from each of the manufactured H-shaped steels, and the mechanical properties were investigated. FIG. 1 shows a schematic position of the specimen collection position. In the tensile test, three JISZ2201 1A tensile test pieces (parallel part width: 40 mm, gauge length: 200 mm) were sampled from the position of the flange width direction 1/4 to the rolling direction, and tensile properties at normal temperature, nominal The n value at 2 to 5% was determined in terms of strain.
[0056]
Furthermore, from the flange thickness center (1 / 2t) at the position in the flange width direction 1/4, a II-8 test piece (parallel part diameter: 8 mm, gauge length: 40 mm) defined in JISG0567 was collected, Tensile properties at 700 ° C. were investigated. In the impact test, three JISZ2202 V-notch impact pieces were sampled from the center of the plate thickness (1 / 2t), and the impact absorption energy was determined at a test temperature of 0 ° C.
[0057]
Table 3 shows the results of the tensile test and impact test. All of the samples have characteristics satisfying the SN490B standard regarding tensile strength and impact characteristics, but either or both of the steel composition and the cooling method are comparative examples outside the scope of the present invention. No. Nos. 11, 13, and 14 have yield elongation, yield ratio, or n value outside the scope of the present invention. Sample No. No. 12 has excellent characteristics within the scope of the present invention in both steel composition and cooling method. Each sample has a yield strength at 600 ° C. of 220 MPa or more, 60% or more of the yield strength at room temperature, and a yield strength at 700 ° C. of 110 MPa or more and 30% or more at room temperature.
[0058]
Next, in order to evaluate the local buckling resistance characteristics of these shape steels, a strain causing buckling (buckling generation limit strain) was obtained by a compression test of a shape steel sample having a length of 500 mm. FIG. 2 schematically shows the state of the compression test.
Further, in order to evaluate the fracture resistance performance, the fracture strain was measured by a tensile test using a tensile test piece having a notch corresponding to 10% of the cross section of the parallel part in the parallel part.
Table 4 shows the results of the compression test and the notched tensile test. Sample No. in which both the buckling occurrence limit strain and the breaking strain are within the scope of the present invention in both the steel composition and the cooling conditions. No. 12, sample No. which is a comparative example. Compared to 11, 13, and 14, the characteristics are excellent. In addition, sample No. in these tests. The characteristics of 12 are superior to those obtained with the As roll material of 490 MPa class steel. The buckling generation limit strain is 0.51% for the 490 MPa grade steel As roll material, and is 0.77% even if it is improved by 50%. Less than 12. The breaking strain of Asroll material of 490 MPa class steel is 3.2%, and even if it is improved by 50%, it is 4.8%. Less than 12.
As described above, in steel B containing Nb and having a composition outside the scope of the present invention, any of yield elongation, yield ratio, and n value is outside the scope of the present invention, and local buckling resistance and fracture resistance Excellent characteristics cannot be obtained.
[0059]
[Table 1]
[Table 2]
[Table 3]
[Table 4]
(Example 2)
The steel shown in Table 5 was melted, made into a slab by continuous casting, heated to 1250 ° C., and rolled into an H-shaped steel of 300 × 300 × 10 × 15 (mm). After rolling, rolling and cooling were performed under the production conditions shown in
[0064]
Thereafter, in the same manner as in Example 1, tensile test pieces and impact test pieces were collected from each H-shaped steel, and the mechanical properties were investigated. In the tensile test, three JISZ2201 1A tensile test pieces (parallel part width: 40 mm, gauge length: 200 mm) were sampled from the position of the flange width direction 1/4 to the rolling direction, and tensile properties at normal temperature, nominal The n value at 2 to 5% was determined in terms of strain.
[0065]
Furthermore, from the flange thickness center (1 / 2t) at the position in the flange width direction 1/4, a II-8 test piece (parallel part diameter: 8 mm, gauge length: 40 mm) defined in JISG0567 was collected, Tensile properties at 700 ° C. were investigated. In the impact test, three JISZ2202 V-notch impact pieces were sampled from the center of the plate thickness (1 / 2t), and the impact absorption energy was determined at a test temperature of 0 ° C.
[0066]
Table 6 shows the results of the tensile test and impact test. According to the manufacturing conditions within the scope of the present invention, Nos. 21, 22, 23, 24, 26, and 28 satisfy all the provisions of the present invention relating to tensile properties, but the amount of Mo is out of the scope of the present invention, and No. In 25, fire resistance is inferior. The amount of Mo is out of the scope of the present invention, and steel No. No. 27 has poor impact characteristics.
[0067]
Next, No. which shows good properties with respect to tensile and impact properties at normal temperature and fire resistance. In order to evaluate local buckling resistance characteristics of 12, 21, 22, 23, 24, 26, and 28, a strain (buckling) that causes buckling is caused by a compression test (see FIG. 2) of a section steel sample having a length of 500 mm. The generation limit strain) was determined.
Furthermore, in order to evaluate the fracture resistance, the fracture strain was measured by a tensile test using a tensile test piece having a notch corresponding to 10% of the cross section of the parallel part in the parallel part. The compression test and the notched tensile test were the same as in Example 1.
Table 7 shows the results of the compression test and the notched tensile test. In any sample, the critical strain for occurrence of buckling is a good value exceeding 0.77%, which is 50% higher than 0.51% obtained with an as-rolled material of 490 MPa class steel obtained under the same test conditions. Is obtained. In addition, the fracture strain is a good value exceeding 4.8%, which is 50% higher than the 3.2% obtained with the as-rolled 490 MPa class steel obtained under the same test conditions.
[0068]
As is apparent from the above test results, when the yield elongation, yield ratio, and n value all satisfy the provisions of the present invention, excellent local buckling resistance and fracture resistance can be obtained.
[0069]
[Table 5]
[Table 6]
[Table 7]
(Example 3)
After the steel A shown in Table 1 was melted, a slab was formed by continuous casting. The slab was heated to 1250 ° C. and then rolled to a rolling end temperature of 800 ° C. to obtain a H-section steel of 300 × 300 × 10 × 15 (mm) (H × B × t1 × t2, see FIG. 1). Manufactured under the rolling and cooling conditions shown in Table 8. Sample No. No. 32 was naturally cooled to room temperature after the end of rolling. In addition, the natural cooling rate was about 0.8 ° C./s on average from 800 to 500 ° C.
In these sections, the effects of rolling and cooling conditions on tensile properties, impact properties, local buckling resistance and fracture resistance were investigated.
[0073]
Table 9 shows the test results of tensile and impact characteristics. The test was performed in the same manner as in Example 1.
In N0.12, 31, and 36 where the rolling and cooling conditions satisfy the provisions of the present invention, the yield elongation, the yield ratio, and the n value are all within the range defined by the present invention, and the tensile strength is 490 N /
[0074]
On the other hand, the rolling and cooling conditions are outside the scope of the present invention. In 32, 11, 33, 34, 35, 37, and 38, any of yield elongation, yield ratio, and n value is out of the scope of the present invention. The high-temperature strength of each sample has good fire resistance at 600 ° C., yield strength of 220 MPa or more and 55% or more of normal temperature yield strength, and 700 ° C. yield strength of 110 MPa or more and 30% or more of normal temperature. is doing.
[0075]
Next, No. whose tensile strength satisfies the standard of SN490B. In order to evaluate the local buckling resistance of 12, 31, 11, 34, 36, and 37, a strain (buckling limit strain) that causes buckling is obtained by a compression test of a section steel sample having a length of 500 mm. It was. Furthermore, in order to evaluate the fracture resistance, the fracture strain was measured by a tensile test using a tensile test piece having a notch corresponding to 10% of the cross section of the parallel part in the parallel part. The compression test and the notched tensile test were the same as in Example 1.
[0076]
Table 10 shows the results of the compression test and the notched tensile test. The buckling occurrence limit strain is a sample No. in which the yield elongation, the yield ratio, and the n value all satisfy the provisions of the present invention. In addition to Samples Nos. 12, 31, and 36, Sample Nos. Whose n value satisfies the provisions of the present invention. 34 is a sample no. Compared with 11, 37, the buckling occurrence limit strain was good, the same characteristics as those of the examples of the present invention were obtained, and it was recognized that the influence of the n value on the local buckling resistance was large.
[0077]
The breaking strain is the sample No. in which the yield elongation, yield ratio, and n value all satisfy the provisions of the present invention. In Nos. 12, 31, and 36, excellent fracture strain was obtained, but No. No. 34 has a small breaking strain and a yield elongation of 0. 11 and 37 were even smaller.
[0078]
As is clear from the above test results, excellent local buckling resistance and fracture resistance can be obtained when the yield elongation, yield ratio, and n value all satisfy the provisions of the present invention.
[0079]
[Table 8]
[Table 9]
[Table 10]
Example 4
Steels having the composition shown in Table 1 were melted and then cast into slabs by continuous casting. The slab is heated to 1250 ° C. and then rolled to a rolling end temperature of 800 ° C. to form an H-section steel of 300 × 300 × 10 × 15 (mm) (H × B × t1 × t2, see FIG. 1). It was manufactured under the rolling and cooling conditions shown in FIG. Sample No. No. 32 was naturally cooled to room temperature after the end of rolling. In addition, the natural cooling rate was about 0.8 ° C./s on average from 800 to 500 ° C.
[0083]
The effects of the microstructure on the tensile properties, impact properties, local buckling resistance and fracture resistance of these sections were investigated. The microstructure is a cross-section along the longitudinal direction at the position of the flange width direction 1/4, and the optical microscope structure and scanning electron microscope structure at the center of the flange thickness are observed, and the volume fraction of ferrite and the average grain size are determined by the line segment method. The diameter was determined.
For the hard phase, the structure form and the length in the rolling direction and the plate thickness direction were determined, and the aspect ratio was calculated as the ratio value.
[0084]
Table 12 shows the observation results of the microstructure. Sample No. with steel composition and production conditions within the scope of the present invention. Nos. 12, 31, and 42 satisfy all the provisions of the present invention regarding the microstructure. 32, 11, 13, 41, 33, 34, 14 do not satisfy any of the provisions of the present invention relating to the microstructure.
[0085]
Next, similarly to Examples 1, 2, and 3, a tensile test and a Charpy impact test were performed.
Table 13 shows the results. Sample No. which does not satisfy any of the provisions of the present invention regarding the microstructure. For 32, 11, 13, 41, 33, 34, and 14, any of yield elongation, yield ratio, and n value is outside the scope of the present invention. On the other hand, sample no. Nos. 12, 31, and 42 satisfy the provisions of the present invention regarding the microstructure, and the yield elongation, yield ratio, and n value are all within the scope of the present invention.
[0086]
Furthermore, sample No. with a tensile strength of 490 MPa or more. With respect to 12, 31, 11, 41, 34, 42, 13, and 14, local buckling resistance and fracture resistance were determined in the same manner as in Examples 1, 2, and 3.
[0087]
Table 14 shows the measured values of buckling occurrence limit strain and breaking strain. Sample No. having the tissue morphology defined in the present invention. In Samples Nos. 12, 31, and 42, while excellent characteristics were obtained in both cases, Sample No. In 11, 41, 34, 13, and 14, either or both characteristics were inferior.
[0088]
As described above, the microstructure obtained with the rolled H-section steel whose steel composition and production conditions satisfy the provisions of the present invention exhibited excellent characteristics in local buckling resistance and fracture resistance.
[0089]
[Table 11]
[Table 12]
[Table 13]
[Table 14]
【The invention's effect】
As described above, the rolled refractory steel of the present invention is less likely to cause local buckling caused by large tension or compression applied to the beam member of the building in the event of a large earthquake, Because it has excellent resistance to fracture due to weld defects at the beam end, it is ideal for the limit state design method that absorbs seismic energy and avoids large collapse by plastic deformation of beam members in the event of a large earthquake. Providing safe steel structures, the effect on industrial society is extremely large.
[Brief description of the drawings]
FIG. 1 is a schematic view showing a sampling position of a tensile test piece of rolled H-section steel and an observation position of a microstructure.
FIG. 2 is a diagram showing an outline of a compression test for evaluating local buckling resistance.
FIG. 3 is a view showing a tensile test piece (unit: mm) with a surface notch for evaluating fracture resistance.
Claims (5)
Ｃｅｑ＝Ｃ＋Ｍｎ／６＋Ｓｉ／２４＋Ｎｉ／４０＋Ｃｒ／５＋Ｍｏ／４＋Ｖ／１４…（１）
ｎ＝（ｌｎσ５−ｌｎσ２）／（ｌｎε５−ｌｎε２）…（２）
σ５＝１．０５×σＮ５，σ２＝１．０２×σＮ２，ε５＝ｌｎ（１．０５），ε２＝ｌｎ（１．０２）
但し、σ５：公称歪５％における真応力、σ２：公称歪２％における真応力、ε５：公称歪み５％における真歪、ε２：公称歪み２％における真歪、
σＮ５：公称歪み５％における公称応力、σＮ２：公称歪み２％における公称応力
ｌｎ：自然対数In mass%, C: 0.05 to 0.18%, Si: 0.6% or less, Mn: 0.6 to 1.6%, Mo: 0.2 to 0.7%, P: 0.020 %, S: 0.015% or less, Al: 0.01-0.05%, Nb: less than 0.005%, N: 0.0080% or less, H: 4 ppm or less, and Ceq according to the formula (1): 0.40% or less with the balance being Fe and inevitable impurities, the tensile properties in the longitudinal direction of the flange are yield elongation: 0.8-3.0%, yield ratio: 70% or less And the work hardening index (n value) by (2) Formula in nominal distortion 2-5%: Rolled refractory steel which is 0.20 or more.
Ceq = C + Mn / 6 + Si / 24 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 (1)
n = (lnσ 5 −lnσ 2 ) / (lnε 5 −lnε 2 ) (2)
σ 5 = 1.05 × σ N5 , σ 2 = 1.02 × σ N2 , ε 5 = ln (1.05), ε 2 = ln (1.02)
Where σ 5 : true stress at nominal strain 5%, σ 2 : true stress at nominal strain 2%, ε 5 : true strain at nominal strain 5%, ε 2 : true strain at nominal strain 2%,
σ N5 : nominal stress at a nominal strain of 5%, σ N2 : nominal stress at a nominal strain of 2% ln: natural logarithm
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000111073A JP4543492B2 (en) | 2000-04-12 | 2000-04-12 | Rolled refractory section steel and method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2000111073A JP4543492B2 (en) | 2000-04-12 | 2000-04-12 | Rolled refractory section steel and method for producing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JP2001294984A JP2001294984A (en) | 2001-10-26 |
| JP4543492B2 true JP4543492B2 (en) | 2010-09-15 |
Family
ID=18623479
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2000111073A Expired - Fee Related JP4543492B2 (en) | 2000-04-12 | 2000-04-12 | Rolled refractory section steel and method for producing the same |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP4543492B2 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4631299B2 (en) * | 2004-03-25 | 2011-02-16 | Ｊｆｅスチール株式会社 | Low yield ratio rolled H-section steel excellent in fire resistance and manufacturing method thereof |
| JP4673822B2 (en) | 2006-11-14 | 2011-04-20 | 新日本製鐵株式会社 | Refractory steel material excellent in toughness of welded joint and method for producing the same |
| CN101680068A (en) | 2008-03-31 | 2010-03-24 | 新日本制铁株式会社 | Refractory steel material with welded joint excellent in unsusceptibility to reheat embrittlement and toughness and process for producing the same |
| JP5874290B2 (en) * | 2011-10-07 | 2016-03-02 | Ｊｆｅスチール株式会社 | Steel material for welded joints excellent in ductile crack growth characteristics and method for producing the same |
| CN110205554B (en) * | 2019-06-28 | 2021-06-01 | 东北大学 | 690 MPa-grade steel for anti-seismic, fire-resistant and weather-resistant building structure and preparation method thereof |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH036322A (en) * | 1989-06-02 | 1991-01-11 | Nippon Steel Corp | Production of low yield ratio steel products for building having excellent fire resistivity and steel material for building formed by using these steel products |
| JPH0820819A (en) * | 1994-07-12 | 1996-01-23 | Nkk Corp | Production of shape steel of low yield ratio for refractory use |
| JPH1112648A (en) * | 1997-06-26 | 1999-01-19 | Nkk Corp | Steel excellent in buckling resistance and fire resistance |
| JPH1112681A (en) * | 1997-06-26 | 1999-01-19 | Nkk Corp | Steel member having excellent buckling resisting characteristic and fire resistance |
-
2000
- 2000-04-12 JP JP2000111073A patent/JP4543492B2/en not_active Expired - Fee Related
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPH036322A (en) * | 1989-06-02 | 1991-01-11 | Nippon Steel Corp | Production of low yield ratio steel products for building having excellent fire resistivity and steel material for building formed by using these steel products |
| JPH0820819A (en) * | 1994-07-12 | 1996-01-23 | Nkk Corp | Production of shape steel of low yield ratio for refractory use |
| JPH1112648A (en) * | 1997-06-26 | 1999-01-19 | Nkk Corp | Steel excellent in buckling resistance and fire resistance |
| JPH1112681A (en) * | 1997-06-26 | 1999-01-19 | Nkk Corp | Steel member having excellent buckling resisting characteristic and fire resistance |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2001294984A (en) | 2001-10-26 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| KR101247089B1 (en) | Steel plate for line pipes and steel pipes | |
| JP4997805B2 (en) | High-strength thick steel plate, method for producing the same, and high-strength steel pipe | |
| JP5679114B2 (en) | Low yield ratio high strength hot rolled steel sheet with excellent low temperature toughness and method for producing the same | |
| JP4858221B2 (en) | High-tensile steel with excellent ductile crack initiation characteristics | |
| JP3960341B2 (en) | Thermal processing control type 590 MPa class H-section steel and manufacturing method thereof | |
| JP4252949B2 (en) | Low yield ratio high-tensile steel sheet with small acoustic anisotropy and excellent weldability, and method for producing the same | |
| JP5385760B2 (en) | Cold-formed square steel pipe with excellent earthquake resistance | |
| KR101011625B1 (en) | Welding joint exellent in toughness and control of fatigue crack initiation property | |
| JP6572876B2 (en) | Low yield ratio high tensile steel plate and method for producing the same | |
| JP6036616B2 (en) | Steel sheet for welded structure excellent in fatigue crack resistance and method for producing the same | |
| JP5045074B2 (en) | High tensile thin-walled steel sheet having low yield ratio and manufacturing method thereof | |
| JP7262288B2 (en) | High-strength low-yield-ratio thick steel plate with excellent toughness of base metal and weld heat-affected zone and small acoustic anisotropy, and its manufacturing method | |
| JP2007177325A (en) | High tensile strength thick steel plate having low yield ratio and its production method | |
| JP6988836B2 (en) | Ultra-low yield ratio high-strength thick steel sheet and its manufacturing method | |
| JP4335789B2 (en) | High-tensile steel plate with excellent weldability with small acoustic anisotropy and method for producing the same | |
| JP5368820B2 (en) | 780 MPa class low yield ratio circular steel pipe for building structure having excellent earthquake resistance and method for producing the same | |
| JP6036615B2 (en) | Steel sheet for welded structure having excellent weldability and fatigue crack propagation resistance and method for producing the same | |
| JP4543492B2 (en) | Rolled refractory section steel and method for producing the same | |
| JP6981546B2 (en) | Thick steel plate and its manufacturing method | |
| JP4848960B2 (en) | Thin-walled low-yield-ratio high-tensile steel plate and method for producing the same | |
| JP6400517B2 (en) | High strength steel material with excellent fatigue crack propagation resistance and method for producing the same | |
| JP4008378B2 (en) | Low yield ratio high strength steel with excellent toughness and weldability | |
| JP4354754B2 (en) | High-tensile steel plate with excellent base metal toughness and HAZ toughness | |
| JP3632559B2 (en) | Rolled section steel and method for producing the same | |
| JP3371744B2 (en) | Low yield ratio steel material and method of manufacturing the same |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Free format text: JAPANESE INTERMEDIATE CODE: A621 Effective date: 20070307 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20090121 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20100302 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20100325 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20100413 |
|
| A521 | Written amendment |
Free format text: JAPANESE INTERMEDIATE CODE: A523 Effective date: 20100524 |
|
| 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: 20100608 |
|
| A01 | Written decision to grant a patent or to grant a registration (utility model) |
Free format text: JAPANESE INTERMEDIATE CODE: A01 |
|
| A61 | First payment of annual fees (during grant procedure) |
Free format text: JAPANESE INTERMEDIATE CODE: A61 Effective date: 20100621 |
|
| FPAY | Renewal fee payment (event date is renewal date of database) |
Free format text: PAYMENT UNTIL: 20130709 Year of fee payment: 3 |
|
| R150 | Certificate of patent or registration of utility model |
Ref document number: 4543492 Country of ref document: JP Free format text: JAPANESE INTERMEDIATE CODE: R150 Free format text: JAPANESE INTERMEDIATE CODE: R150 |
|
| LAPS | Cancellation because of no payment of annual fees |