JP3684031B2 - Building steel with excellent fire resistance and method for producing the same - Google Patents
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Description
【０００１】
【発明の属する技術分野】
本発明は、建築、土木等の分野において、各種建造物に用いる鋼材およびその製造方法に関し、特に、７００℃における高温強度の優れた耐火性を有する建築用鋼材およびその製造方法に係るものである。
【０００２】
【従来の技術】
建築、土木などの分野における各種建築用鋼材として、ＪＩＳ等で規格化された鋼材等が広く利用されている。
ところで、ビルや事務所、住居、立体駐車場などの建築物に前記の鋼材を用いる場合は、火災における安全性を確保するため、十分な耐火被覆を施すことが義務づけられており、建築関係諸法令では、火災時に鋼材温度が３５０℃以上にならないように規定されている。
【０００３】
すなわち、前記鋼材は３５０℃程度で耐力が常温時の２／３程度になり、必要な強度を下回るためである。鋼材を建造物に利用する場合、火災時において鋼材の温度が３５０℃に達しないように耐火被覆を施して使用される。そのため、鋼材費用に対し耐火被覆工費が高額になり、建設コストが大幅に上昇することが避けられない。
【０００４】
最近、上記の課題を解決するため、例えば特開平２−７７５２３号公報が開示されている。しかしながら特開平２−７７５２３号公報は、相当量のＭｏとＮｂを添加した鋼で、６００℃の耐力が常温耐力の７０％以上を確保するものであるが、７００℃での耐力は示されていない。すなわち、この例のように６００℃程度の高温強度を確保した鋼はすでに市場でも使用されているが、７００℃での高温強度を確保できる実用鋼の製造は困難であった。
【０００５】
【発明が解決しようとする課題】
前述のように建築物に鋼材を利用する場合、通常の鋼では、高温強度が低いため無被覆や軽被覆で利用することができず、割高な耐火被覆を施さなければならなかった。また、新しく開発された鋼でも、耐火温度は６００℃までの保証が限界であり、７００℃に耐える鋼材の開発が望まれていた。
本発明の目的は、７００℃で高温強度が優れた建築用鋼材及びその製造方法を提供することにある。
【０００６】
【課題を解決するための手段】
本発明は、前述の課題を克服し、目的を達成するもので、その具体的手段を以下に示す。
（１）質量比で、
Ｃ ：０．０１〜０．０５％、 Ｓｉ：０．３０％以下、
Ｍｎ：１．０〜１．５％、 Ｐ ：０．０１％以下、
Ｓ ：０．０１％以下、 Ｍｏ：０．７〜１．０％、
Ｎｂ：０．００５〜０．０５％、Ｔｉ：０．００５〜０．０２％、
Ａｌ：０．１０％以下、 Ｎ ：０．００１〜０．００６％
を含有し、残部Ｆｅおよび不可避的不純物からなるベイナイト組織であり、合金元素の積で下記式ＤB の値が０．５〜０．６からなることを特徴とする、常温ＹＳが３２５Ｎ／ mm 2 以上で、７００℃でのＹＳが常温規格値の２／３以上の耐火性の優れた建築用鋼。
ＤB ＝ 0.258√C (1+0.3Si)(1+1.5Mn)(1+3.8Mo)(1+12Nb)
（各元素の量はmass％）
【０００７】
（２）質量比で、
Ｃ ：０．０１〜０．０５％、 Ｓｉ：０．３０％以下、
Ｍｎ：１．０〜１．５％、 Ｐ ：０．０１％以下、
Ｓ ：０．０１％以下、 Ｍｏ：０．７〜１．０％、
Ｎｂ：０．００５〜０．０５％、Ｔｉ：０．００５〜０．０２％、
Ａｌ：０．１０％以下、 Ｎ ：０．００１〜０．００６％
を含有し、さらに
Ｎｉ：０．０５〜０．５％、 Ｃｕ：０．０５〜０．５％、
Ｃｒ：０．０５〜０．５％、 Ｖ ：０．０１〜０．０５％、
Ｃａ：０．０００５〜０．００３％、ＲＥＭ：０．００１〜０．００５％
のうち一種または二種以上を含有し、残部Ｆｅおよび不可避的不純物からなるベイナイト組織であり、合金元素の積で下記式ＤB の値が０．５〜０．６からなることを特徴とする、常温ＹＳが３２５Ｎ／ mm 2 以上で、７００℃でのＹＳが常温規格値の２／３以上の耐火性の優れた建築用鋼。
ＤB ＝ 0.258√C (1+0.3Si)(1+1.5Mn)(1+3.8Mo)(1+0.2Ni)(1+0.2Cu)
(1+0.9Cr)(1+12Nb)(1+0.8V)
（各元素の量はmass％）
【０００８】
（３）上記 (1)記載の鋼を１１００℃〜１３００℃に再加熱後、熱間塑性加工を８５０〜１０００℃で終了し、８００〜５００℃の平均冷却速度が０．２〜１．０℃/secで常温まで冷却して、ミクロ組織をベイナイトとすることを特徴とする、常温ＹＳが３２５Ｎ／ mm 2 以上で、７００℃でのＹＳが常温規格値の２／３以上の耐火性の優れた建築用鋼の製造方法。
（４）上記 (2)記載の鋼を１１００℃〜１３００℃に再加熱後、熱間塑性加工を８５０〜１０００℃で終了し、８００〜５００℃の平均冷却速度が０．２〜１．０℃/secで常温まで冷却して、ミクロ組織をベイナイトとすることを特徴とする、常温ＹＳが３２５Ｎ／ mm 2 以上で、７００℃でのＹＳが常温規格値の２／３以上の耐火性の優れた建築用鋼の製造方法。
【０００９】
【発明の実施の形態】
本発明者らはすでに、６００℃の高温強度が優れた鋼を見いだし、主に建築分野で使用されているが、市場ではさらに高温（７００℃）に耐える鋼への極めて強い要求がある。
この場合でも、建築用鋼としての溶接性や低ＹＲ等の特性は従来と同じように具備する必要があるため、７００℃の高温強度が優れた鋼を得ることは極めて難しい課題であった。
【００１０】
この課題を解決するため、本発明者らは鋭意検討し、４９０Ｎ／mm2 級の強度を有する鋼はミクロ組織をベイナイト一相として、相当量のＭｏを添加する方法が有効な手段であることを見いだした。
ミクロ組織をベイナイト一相とする方法として、圧延後のγからαへの変態中の急冷や再加熱で一旦γ域まで加熱し、その後冷却時に冷却速度を早める方法が一般的である。
このように、冷却速度を早めた場合、γからのベイナイトの生成はかなり低温側で起き、生成するベイナイトは微細となり、強度やＹＲ（降伏強度／引張強度）が増加し、問題となる。
【００１１】
本発明者らは鋭意検討し、鋼成分を低Ｃ＋（適正な合金成分範囲）として、圧延後の冷却速度を適正範囲にコントロールすることにより、ミクロ組織をベイナイト一相として低降伏比とし、高温強度も優れた特性を有する鋼とすることができた。
【００１２】
まず、ミクロ組織をベイナイト一相とするためには、圧延における過度の細粒化は適切でなく、８５０℃〜１０００℃の圧延終了が不可欠である。また、圧延後の冷却速度も緩やかにする必要があり、０．２〜１．０℃/secで常温まで冷却する必要がある。
【００１３】
更に、ミクロ組織のベイナイト一相化のため、合金元素の役割が重要である。
本発明者らは鋭意検討し、ベイナイト一相化のためには、従来の焼入性指数だけでは不十分であり、ＣやＭｏ，Ｎｂの役割が大きく、Ｖにも同様の効果があることを見出だし、これを下記式（各元素の量はmass％）で規定するＤB パラメーターとした。すなわち、ＤB パラメーター値が０．５以上でミクロ組織がベイナイトとなることを知見した。
本発明鋼は高温で圧延を終了するため、Ｎｂは固溶状態として残り、冷却時にベイナイト組織とする働きを持っており、この効果を従来の焼入性パラメーターに取り込み、ＤB パラメーターとして有効なものとした。しかしながら、ＤB パラメーター値が０．６を超える場合は強度が高すぎるため、その値が０．５〜０．６が良好な範囲である。
【００１５】
また、Ｃは本発明鋼では特徴的な元素であるが、極めて狭い範囲にコントロールする必要があり、０．０１〜０．０５％が適正範囲である。これ未満のＣ量では強度が不足し、この範囲を超えると降伏比が増加し、強度も高すぎるためである。
【００１６】
なお、この場合のＮｂの適正量は０．００５〜０．０５％である。これ未満では効果が少なく、これを超えると添加量に対し効果の度合いが少なく、溶接部の靭性も害する。
【００１７】
また、７００℃の高温強度を確保するためには、ミクロ組織をベイナイト一相とするだけでは不十分であり、Ｍｏの適正量の添加が必須である。
本発明者らは鋭意検討し、Ｍｏの適正値は０．７〜１．０％であることを突き止めた。０．７％未満では効果が少なく、１．０％超では経済性を失するためである。
【００１８】
次に、本発明にかかわるその他の成分元素とその添加量について説明する。 Ｓｉは焼入性を向上し、ミクロ組織をベイナイト化するが、過度の添加は靭性の劣化を招くため、０．３％以下が適正範囲である。
Ｍｎは鋼の強度向上のため最も有効な元素であるが、過度の添加は溶接性を劣化させるので、１．０〜１．５％が適正範囲である。
【００１９】
Ｐ，Ｓは不純物元素であり、少ないほど好ましいが、０．０１％以下であれば本発明の特徴を損なう恐れがないので、それぞれ０．０１％以下を適正範囲とした。
Ｔｉは溶接部の靭性向上のため必要であるが、過度の添加はＴｉＣを形成して靭性を大きく劣化させるので、０．００５〜０．０２％が適正範囲である。
【００２０】
Ａｌは脱酸元素として使用されるが、過度の添加は鋼の清浄性を損なうため、０．１％以下の添加が適正範囲である。
Ｎは高温強度を高める働きがあるが、過度の添加はスラブ鋳造時の表面割れの原因となるため、０．００１〜０．００６％が適正範囲である。
【００２１】
以上、これらの基本成分で本発明の特性を発揮できるが、以下の元素を選択的に添加することで、より大きな効果が期待できる。
Ｎｉは強度・靭性を向上させ、ミクロ組織のベイナイト化に効果を発揮する重要な元素であるが、多量の添加は経済性を失し、少ないと効果がないため、０．０５〜０．５％が適正範囲である。
ＣｕはＮｉと同等のミクロ組織のベイナイト化に効果があるが、多すぎるとＣｕの析出物を生成し、ＹＲを増加させ、少なすぎると効果がないため、０．０５〜０．５％が適正範囲である。
【００２２】
ＣｒはＭｎ，Ｍｏについでミクロ組織のベイナイト化に効果があるが、多すぎると溶接部靭性を害するので、適正範囲は０．０５〜０．５％である。
ＶはＮｂと同様に、ミクロ組織のベイナイト化に効果があるが、多量の添加は溶接部靭性を損なうため、０．０１〜０．０５％が適正範囲である。
Ｃａ，ＲＥＭは不純物であるＳと結合し、靭性の向上や溶接部の拡散水素による割れを防止する働きを有するが、多すぎると却って悪影響となるので、それぞれ０．０００５〜０．００３％、０．００１〜０．００５％が適正範囲である。
【００２３】
鋼成分とともに鋼の再加熱および圧延、冷却にかかる条件が重要である。
前述のＭｏ，Ｃｕ，Ｎｂの複合添加による７００℃強度の増加をはかるためには、再加熱時にこれらの元素を十分に溶体化させる必要があり、このため、再加熱温度の下限を１１００℃とする。また、再加熱温度が高過ぎるとオーステナイト粒が粗大化し、低温靭性が劣化するので、その上限は１３００℃にせねばならない。
【００２４】
さらに、圧延終了温度を８５０℃以上の高温とする理由は、圧延中にＭｏの炭化物やＮｂの炭窒化物を析出させないためであり、γ域でＭｏが析出すると析出物サイズが大きくなり高温強度が著しく低下する。また、１０００℃を超える温度域での圧延終了では、靭性が極度に低下するため、１０００℃が圧延終了温度の上限である。
【００２５】
圧延後の冷却速度を０．２〜１．０℃/secとする理由は、ミクロ組織をベイナイト一相とするためであり、０．２℃/sec未満ではベイナイトが生成せず、また１．０℃/secを超えるとＹＲが増加し、８０％を超えるためである。
【００２６】
【実施例】
転炉、連続鋳造、厚板工程で種々の鋼を製造し、常温強度、高温強度などを調査した。表１の No.１〜 No.１５に本発明鋼を、 No.１６〜 No.２０に比較鋼の化学成分を示す。また表２に、本発明鋼と比較鋼について、加熱、圧延冷却条件別に機械的特性を示す。
【００２７】
【表１】
【表２】
本発明鋼 No.１〜 No.１５の例では、常温の強度は４９０Ｎ／mm2 級鋼の強度レベルを満足し、７００℃のＹＳも規格強度の２／３（２１７Ｎ／mm2 ）以上の良好な値である。さらに、溶接性指数（ＰCM）も０．１６以下の良好（通常０．２０以下が良好とされる）な値であった。
【００３０】
これに対し、比較鋼 No.１６では、Ｃ量やＤB の値が低すぎたため、常温の強度が４９０Ｎ／mm2 級鋼の強度レベルを満足できず、７００℃の強度も不十分であった。
比較鋼 No.１７では、Ｃ量やＤB の値が高すぎたため、７００℃の強度は高い値が得られたが、常温の強度が４９０Ｎ／mm2 級鋼の強度を超える値であった。比較鋼 No.１８では、Ｎｂが添加されておらず、ＤB の値も低いため、常温の強度と７００℃の強度が不十分であった。
比較鋼 No.１９では、各々の成分は規制範囲となっているが、ＤB の値が低いため、常温の強度と７００℃の強度が不十分であった。
比較鋼 No.２０では、Ｍｎ量やＤB の値が高すぎたため、７００℃の強度は高い値が得られたが、常温の強度が４９０Ｎ／mm2 級鋼の強度を超える値であった。
【００３１】
【発明の効果】
本発明の化学成分および製造法で製造した鋼材は、常温の耐力（ＹＳ）が３２５Ｎ／mm2 以上で、７００℃のＹＳが常温規格値の２／３以上等の特性を備えており、溶接性も良好である、等の建築用耐火鋼材として必要な特性を兼ね備えており、従来にない全く新しい鋼材である。[0001]
BACKGROUND OF THE INVENTION
TECHNICAL FIELD The present invention relates to a steel material used in various buildings in the fields of construction, civil engineering, and the like, and a method for producing the same, and particularly relates to a steel material for construction having excellent fire resistance at a high temperature strength at 700 ° C. .
[0002]
[Prior art]
As various construction steel materials in the fields of construction, civil engineering, etc., steel materials standardized by JIS etc. are widely used.
By the way, when using the steel materials described above for buildings such as buildings, offices, residences, and multistory parking lots, it is obliged to provide sufficient fireproof coatings to ensure safety in fire. The law stipulates that the temperature of a steel material does not exceed 350 ° C during a fire.
[0003]
That is, the steel material has a proof stress of about 2/3 at room temperature at about 350 ° C., which is lower than the required strength. When steel is used for a building, it is used with a fireproof coating so that the temperature of the steel does not reach 350 ° C. during a fire. For this reason, it is inevitable that the cost of fireproof coating will be higher than the cost of steel materials, and the construction cost will rise significantly.
[0004]
Recently, for example, Japanese Patent Laid-Open No. 2-77523 has been disclosed in order to solve the above problems. However, Japanese Patent Application Laid-Open No. 2-77523 is a steel to which a considerable amount of Mo and Nb is added, and the proof stress at 600 ° C. ensures 70% or more of the normal temperature proof strength, but the proof strength at 700 ° C. is shown. Absent. That is, as in this example, steel having a high temperature strength of about 600 ° C. has already been used in the market, but it has been difficult to produce a practical steel capable of ensuring a high temperature strength at 700 ° C.
[0005]
[Problems to be solved by the invention]
As described above, when steel is used for a building, normal steel cannot be used with no coating or light coating because the high-temperature strength is low, and an expensive fireproof coating has to be applied. Further, even in newly developed steel, the limit of the fireproof temperature to 600 ° C. is the limit, and the development of a steel material that can withstand 700 ° C. has been desired.
An object of the present invention is to provide an architectural steel material having excellent high-temperature strength at 700 ° C. and a method for producing the same.
[0006]
[Means for Solving the Problems]
The present invention overcomes the above-mentioned problems and achieves the object, and specific means thereof will be described below.
(1) By mass ratio,
C: 0.01 to 0.05%, Si: 0.30% or less,
Mn: 1.0 to 1.5%, P: 0.01% or less,
S: 0.01% or less, Mo: 0.7-1.0%,
Nb: 0.005-0.05%, Ti: 0.005-0.02%,
Al: 0.10% or less, N: 0.001 to 0.006%
Containing a bainite structure the balance being Fe and inevitable impurities, the value of the formula D B by the product of the alloy elements, characterized in that it consists of 0.5 to 0.6, room temperature YS is 325N / mm A steel with excellent fire resistance that is 2 or more and YS at 700 ° C. is 2/3 or more of the normal temperature standard value .
D B = 0.258√C (1 + 0.3Si) (1 + 1.5Mn) (1 + 3.8Mo) (1 + 12Nb)
(The amount of each element is mass%)
[0007]
(2) By mass ratio,
C: 0.01 to 0.05%, Si: 0.30% or less,
Mn: 1.0 to 1.5%, P: 0.01% or less,
S: 0.01% or less, Mo: 0.7-1.0%,
Nb: 0.005-0.05%, Ti: 0.005-0.02%,
Al: 0.10% or less, N: 0.001 to 0.006%
Ni: 0.05 to 0.5%, Cu: 0.05 to 0.5%,
Cr: 0.05-0.5%, V: 0.01-0.05%,
Ca: 0.0005-0.003%, REM: 0.001-0.005%
Containing one or two or more of a bainite structure that the balance Fe and unavoidable impurities, the value of the formula D B by the product of the alloy element is characterized in that it consists of 0.5 to 0.6 Building steel with excellent fire resistance having a normal temperature YS of 325 N / mm 2 or more and a YS at 700 ° C. of 2/3 or more of the normal temperature standard value .
D B = 0.258√C (1 + 0.3Si) (1 + 1.5Mn) (1 + 3.8Mo) (1 + 0.2Ni) (1 + 0.2Cu)
(1 + 0.9Cr) (1 + 12Nb) (1 + 0.8V)
(The amount of each element is mass%)
[0008]
(3) After reheating the steel described in (1) above to 1100 ° C to 1300 ° C, the hot plastic working is finished at 850 to 1000 ° C, and the average cooling rate at 800 to 500 ° C is 0.2 to 1.0. It is cooled to room temperature at ℃ / sec, and the microstructure is bainite . The room temperature YS is 325 N / mm 2 or more, and the YS at 700 ℃ is 2/3 or more of the room temperature standard value . An excellent method of manufacturing architectural steel.
(4) After reheating the steel described in (2) above to 1100 ° C to 1300 ° C, the hot plastic working is finished at 850 to 1000 ° C, and the average cooling rate at 800 to 500 ° C is 0.2 to 1.0. It is cooled to room temperature at ℃ / sec, and the microstructure is bainite . The room temperature YS is 325 N / mm 2 or more, and the YS at 700 ℃ is 2/3 or more of the room temperature standard value . An excellent method of manufacturing architectural steel.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
The present inventors have already found a steel having excellent high-temperature strength at 600 ° C. and are mainly used in the construction field, but there is a very strong demand for steel that can withstand higher temperatures (700 ° C.) in the market.
Even in this case, it is necessary to provide weldability, low YR, and other properties as architectural steel as in the conventional case, so obtaining a steel having excellent high-temperature strength at 700 ° C. was an extremely difficult task.
[0010]
In order to solve this problem, the present inventors have intensively studied, and for steel having a strength of 490 N / mm 2 class, a method of adding a considerable amount of Mo with a microstructure of bainite as one phase is an effective means. I found.
As a method of making the microstructure into a bainite one-phase, a method of once heating to the γ region by rapid cooling or reheating during the transformation from γ to α after rolling and then increasing the cooling rate during cooling is common.
Thus, when the cooling rate is increased, the formation of bainite from γ occurs on the considerably low temperature side, the bainite generated becomes fine, and the strength and YR (yield strength / tensile strength) increase, which causes a problem.
[0011]
The present inventors have intensively studied, the steel component is set to low C + (appropriate alloy component range), and the cooling rate after rolling is controlled to an appropriate range, so that the microstructure becomes a low yield ratio with a bainite phase and a high temperature. It was possible to obtain a steel having excellent strength.
[0012]
First, in order to make the microstructure a bainite phase, excessive fine graining in rolling is not appropriate, and the end of rolling at 850 ° C. to 1000 ° C. is essential. Moreover, it is necessary to make the cooling rate after rolling gentle, and it is necessary to cool to room temperature at 0.2 to 1.0 ° C./sec.
[0013]
Furthermore, the role of alloying elements is important for making the microstructure bainite one phase.
The present inventors have intensively studied, and the conventional hardenability index alone is not sufficient for bainite phase formation, the role of C, Mo, Nb is large, and V has the same effect. the saw onsets, which following formula (the amount of each element is mass%) was D B parameters specified in. That it was found that D B parameter value microstructure is bainite at 0.5 or more.
Since the steel of the present invention to terminate the rolling at high temperatures, Nb remaining as a solid solution state, has the function of a bainite structure upon cooling, captures this effect in a conventional hardenability parameter, effective as D B parameters It was supposed to be. However, if D B parameter value exceeds 0.6 the strength it is too high, the value is 0.5 to 0.6 is a good range.
[0015]
C is a characteristic element in the steel of the present invention, but must be controlled within a very narrow range, and 0.01 to 0.05% is an appropriate range. If the C amount is less than this, the strength is insufficient, and if it exceeds this range, the yield ratio increases and the strength is too high.
[0016]
In this case, the appropriate amount of Nb is 0.005 to 0.05%. If it is less than this, the effect is small, and if it exceeds this, the degree of the effect is small with respect to the added amount, and the toughness of the welded portion is also impaired.
[0017]
Moreover, in order to ensure a high temperature strength of 700 ° C., it is not sufficient to make the microstructure be a bainite single phase, and an appropriate amount of Mo must be added.
The present inventors diligently studied and found that the appropriate value of Mo is 0.7 to 1.0%. If the content is less than 0.7%, the effect is small, and if it exceeds 1.0%, the economy is lost.
[0018]
Next, other component elements related to the present invention and the addition amount thereof will be described. Si improves hardenability and bainites the microstructure. However, excessive addition causes deterioration of toughness, so 0.3% or less is an appropriate range.
Mn is the most effective element for improving the strength of steel, but excessive addition degrades weldability, so 1.0 to 1.5% is an appropriate range.
[0019]
P and S are impurity elements and are preferably as small as possible. However, if they are 0.01% or less, there is no fear of impairing the characteristics of the present invention.
Ti is necessary for improving the toughness of the welded portion, but excessive addition forms TiC and greatly deteriorates the toughness, so 0.005 to 0.02% is an appropriate range.
[0020]
Al is used as a deoxidizing element, but excessive addition impairs the cleanliness of the steel, so addition of 0.1% or less is an appropriate range.
N has a function of increasing the high-temperature strength, but excessive addition causes surface cracks during slab casting, so 0.001 to 0.006% is an appropriate range.
[0021]
As described above, the characteristics of the present invention can be exhibited with these basic components, but a greater effect can be expected by selectively adding the following elements.
Ni is an important element that improves strength and toughness and exerts an effect on the bainite of the microstructure. However, a large amount of addition loses economic efficiency, and if it is small, there is no effect. % Is the appropriate range.
Cu is effective in forming a bainite microstructure that is equivalent to Ni. However, if it is too much, Cu precipitates are generated, and if it is too little, there is no effect. It is an appropriate range.
[0022]
Cr is effective for bainite of the microstructure after Mn and Mo, but if it is too much, the toughness of the weld is damaged, so the appropriate range is 0.05 to 0.5%.
V, like Nb, is effective for bainite of the microstructure, but adding a large amount impairs the toughness of the weld zone, so 0.01 to 0.05% is an appropriate range.
Ca and REM combine with S, which is an impurity, to have an effect of improving toughness and preventing cracking due to diffusion hydrogen in the welded portion. 0.001 to 0.005% is an appropriate range.
[0023]
The conditions concerning the reheating, rolling and cooling of the steel together with the steel components are important.
In order to increase the strength at 700 ° C. by the combined addition of Mo, Cu, and Nb, it is necessary to sufficiently dissolve these elements during reheating. For this reason, the lower limit of the reheating temperature is 1100 ° C. To do. Further, if the reheating temperature is too high, the austenite grains become coarse and the low temperature toughness deteriorates, so the upper limit must be 1300 ° C.
[0024]
Furthermore, the reason why the rolling end temperature is set to a high temperature of 850 ° C. or more is to prevent precipitation of Mo carbide and Nb carbonitride during rolling. When Mo precipitates in the γ region, the precipitate size increases and the high temperature strength is increased. Is significantly reduced. Further, at the end of rolling in a temperature range exceeding 1000 ° C., the toughness is extremely lowered, so 1000 ° C. is the upper limit of the rolling end temperature.
[0025]
The reason for setting the cooling rate after rolling to 0.2 to 1.0 ° C./sec is to make the microstructure a single phase of bainite, and if it is less than 0.2 ° C./sec, bainite is not generated. This is because if it exceeds 0 ° C./sec, YR increases and exceeds 80%.
[0026]
【Example】
Various steels were manufactured in the converter, continuous casting, and thick plate processes, and room temperature strength and high temperature strength were investigated. In Table 1, No. 1 to No. 15 show the steel of the present invention, and No. 16 to No. 20 show the chemical composition of the comparative steel. Table 2 shows mechanical properties of the steel of the present invention and the comparative steel according to heating and rolling cooling conditions.
[0027]
[Table 1]
[Table 2]
In the examples of the inventive steels No. 1 to No. 15, the strength at normal temperature satisfies the strength level of 490 N / mm 2 grade steel, and YS at 700 ° C. is 2/3 (217 N / mm 2 ) or more of the standard strength. Good value. Furthermore, the weldability index (P CM ) was a good value of 0.16 or less (usually 0.20 or less is considered good).
[0030]
In contrast, in Comparative Steel No.16, because the value of the C amount and D B was too low, normal temperature strength can not be satisfied the intensity level of 490 N / mm 2 class steel, also insufficient strength of 700 ° C. It was.
In Comparative steel No.17, because the value of the C amount and D B is too high, although the strength is high value of 700 ° C. obtained, normal temperature strength is a value that exceeds the strength of 490 N / mm 2 class steel . In Comparative steel No.18, Nb has not been added, since lower values of D B, the strength of the cold strength and 700 ° C. was insufficient.
In Comparative steel No.19, although each of the components has a restricted range, the value of D B is low, the strength of the normal temperature strength and 700 ° C. was insufficient.
In Comparative steel No.20, because the value of the Mn content and D B is too high, although the strength is high value of 700 ° C. obtained, normal temperature strength is a value that exceeds the strength of 490 N / mm 2 class steel .
[0031]
【The invention's effect】
The steel material manufactured by the chemical composition and the manufacturing method of the present invention has properties such as normal temperature proof stress (YS) of 325 N / mm 2 or more, 700 ° C. YS of 2/3 or more of the normal temperature standard value, etc. It is a completely new steel material that has unprecedented properties and has the characteristics necessary for a fire-resistant steel material for construction, such as good properties.
Claims (4)
Ｃ ：０．０１〜０．０５％、
Ｓｉ：０．３０％以下、
Ｍｎ：１．０〜１．５％、
Ｐ ：０．０１％以下、
Ｓ ：０．０１％以下、
Ｍｏ：０．７〜１．０％、
Ｎｂ：０．００５〜０．０５％、
Ｔｉ：０．００５〜０．０２％、
Ａｌ：０．１０％以下、
Ｎ ：０．００１〜０．００６％
を含有し、残部Ｆｅおよび不可避的不純物からなるベイナイト組織であり、合金元素の積で下記式ＤB の値が０．５〜０．６からなることを特徴とする、常温ＹＳが３２５Ｎ／ mm 2 以上で、７００℃でのＹＳが常温規格値の２／３以上の耐火性の優れた建築用鋼。
ＤB ＝ 0.258√C (1+0.3Si)(1+1.5Mn)(1+3.8Mo)(1+12Nb)
（各元素の量はmass％） By mass ratio,
C: 0.01-0.05%,
Si: 0.30% or less,
Mn: 1.0 to 1.5%
P: 0.01% or less,
S: 0.01% or less,
Mo: 0.7 to 1.0%,
Nb: 0.005 to 0.05%,
Ti: 0.005 to 0.02%,
Al: 0.10% or less,
N: 0.001 to 0.006%
Containing a bainite structure the balance being Fe and inevitable impurities, the value of the formula D B by the product of the alloy elements, characterized in that it consists of 0.5 to 0.6, room temperature YS is 325N / mm A steel with excellent fire resistance that is 2 or more and YS at 700 ° C. is 2/3 or more of the normal temperature standard value .
D B = 0.258√C (1 + 0.3Si) (1 + 1.5Mn) (1 + 3.8Mo) (1 + 12Nb)
(The amount of each element is mass%)
Ｃ ：０．０１〜０．０５％、
Ｓｉ：０．３０％以下、
Ｍｎ：１．０〜１．５％、
Ｐ ：０．０１％以下、
Ｓ ：０．０１％以下、
Ｍｏ：０．７〜１．０％、
Ｎｂ：０．００５〜０．０５％、
Ｔｉ：０．００５〜０．０２％、
Ａｌ：０．１０％以下、
Ｎ ：０．００１〜０．００６％
を含有し、さらに
Ｎｉ：０．０５〜０．５％、
Ｃｕ：０．０５〜０．５％、
Ｃｒ：０．０５〜０．５％、
Ｖ ：０．０１〜０．０５％、
Ｃａ：０．０００５〜０．００３％、
ＲＥＭ：０．００１〜０．００５％
のうち一種または二種以上を含有し、残部Ｆｅおよび不可避的不純物からなるベイナイト組織であり、合金元素の積で下記式ＤB の値が０．５〜０．６からなることを特徴とする、常温ＹＳが３２５Ｎ／ mm 2 以上で、７００℃でのＹＳが常温規格値の２／３以上の耐火性の優れた建築用鋼。
ＤB ＝ 0.258√C (1+0.3Si)(1+1.5Mn)(1+3.8Mo)(1+0.2Ni)(1+0.2Cu)
(1+0.9Cr)(1+12Nb)(1+0.8V)
（各元素の量はmass％） By mass ratio,
C: 0.01-0.05%,
Si: 0.30% or less,
Mn: 1.0 to 1.5%
P: 0.01% or less,
S: 0.01% or less,
Mo: 0.7 to 1.0%,
Nb: 0.005 to 0.05%,
Ti: 0.005 to 0.02%,
Al: 0.10% or less,
N: 0.001 to 0.006%
Ni: 0.05-0.5%
Cu: 0.05 to 0.5%,
Cr: 0.05 to 0.5%,
V: 0.01 to 0.05%,
Ca: 0.0005 to 0.003%,
REM: 0.001 to 0.005%
Containing one or two or more of a bainite structure that the balance Fe and unavoidable impurities, the value of the formula D B by the product of the alloy element is characterized in that it consists of 0.5 to 0.6 Building steel with excellent fire resistance having a normal temperature YS of 325 N / mm 2 or more and a YS at 700 ° C. of 2/3 or more of the normal temperature standard value .
D B = 0.258√C (1 + 0.3Si) (1 + 1.5Mn) (1 + 3.8Mo) (1 + 0.2Ni) (1 + 0.2Cu)
(1 + 0.9Cr) (1 + 12Nb) (1 + 0.8V)
(The amount of each element is mass%)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP15688397A JP3684031B2 (en) | 1996-06-18 | 1997-06-13 | Building steel with excellent fire resistance and method for producing the same |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP8-156875 | 1996-06-18 | ||
| JP15687596 | 1996-06-18 | ||
| JP15688397A JP3684031B2 (en) | 1996-06-18 | 1997-06-13 | Building steel with excellent fire resistance and method for producing the same |
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| Publication Number | Publication Date |
|---|---|
| JPH1068044A JPH1068044A (en) | 1998-03-10 |
| JP3684031B2 true JP3684031B2 (en) | 2005-08-17 |
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| JP15688397A Expired - Fee Related JP3684031B2 (en) | 1996-06-18 | 1997-06-13 | Building steel with excellent fire resistance and method for producing the same |
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