JP2004232091A - Method for producing steel material for structural use excellent in earthquake-proof characteristic - Google Patents
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本発明は、耐震性を要求される建築構造物、橋梁等構造物の強度部材に用いて好適な構造用鋼材に係り、とくに高変形速度においても高い破壊靱性を有する構造用鋼材に関する。本発明でいう、耐震性とは、大地震の震源に近くおけるような高変形速度の変形においても高い破壊靱性を有することをいう。また、本発明の鋼材とは、鋼板、形鋼を含むものとする。 The present invention relates to a structural steel material suitable for use as a strength member of a structure such as a building or a bridge requiring earthquake resistance, and more particularly to a structural steel material having high fracture toughness even at a high deformation rate. The seismic resistance as used in the present invention means that it has high fracture toughness even at a high deformation rate of deformation close to the epicenter of a large earthquake. Further, the steel material of the present invention includes a steel plate and a shaped steel.
1981年の新耐震設計法の改正により、建築分野では、大地震時には鋼材の塑性変形を許容し、地震エネルギーを吸収して構造物の倒壊を防止するという設計概念が適用されている。新耐震設計法が適用される建築構造物の鋼材は、降伏後の変形能を表すパラメータである降伏比（ＹＲ）が低いことが要求されている。このような要求に対し、例えば、特許文献１、特許文献２には、低降伏比を有する建築用鋼材が提案されている。 With the revision of the New Seismic Design Law in 1981, a design concept has been applied in the building field that allows plastic deformation of steel in the event of a large earthquake and absorbs seismic energy to prevent collapse of structures. Steel materials of building structures to which the new seismic design method is applied are required to have a low yield ratio (YR), which is a parameter representing the deformability after yielding. In response to such a requirement, for example, Patent Documents 1 and 2 propose a building steel material having a low yield ratio.
しかし、活断層タイプの地震で震源に非常に近い場合には、揺れの速度が非常に速く、建物に対し歪速度にして10-1〜10ｓ-1の高速変形（振動）が加えられるといわれている。一般に、高速変形下では降伏比は高くなる傾向にあり、上記したような高速変形においては低降伏比が確保できなくなることが推察される。また、最近の直下型地震（1995年、阪神大震災) においては、震源地近くの鋼構造物が脆性破壊により損傷を受けている。震源地近くの鋼構造物のように、高速変形を受ける鋼構造物に使用する鋼材は、脆性破壊を防止し鋼構造物の損傷を防ぐために、高速変形下でも高い破壊靱性を有することが必要となる。 However, if very close to the epicenter in the active fault type of earthquake, very fast speed of shaking, high-speed deformation of the strain rate for building 10 -1 ~10s -1 (vibration) is said to be added ing. In general, the yield ratio tends to increase under high-speed deformation, and it is presumed that a low yield ratio cannot be secured in high-speed deformation as described above. In addition, in the recent direct earthquake (1995, Great Hanshin Earthquake), steel structures near the epicenter were damaged by brittle fracture. Steel materials used in steel structures that undergo high-speed deformation, such as steel structures near the epicenter, must have high fracture toughness even under high-speed deformation to prevent brittle fracture and prevent damage to the steel structure It becomes.
しかし、一般に限界CTOD等の破壊靱性値は、変形速度の増加に伴い低下することが知られており、高変形速度において欠陥の存在を前提とした場合、従来の建築構造用鋼では脆性破壊の発生自体を完全に抑制することは非常に困難となる。そこで、脆性破壊の発生を許容したうえで、その亀裂の伝播を阻止する性能を有する鋼材が、特許文献３に提案されている。特許文献３に記載された鋼材は、鋼材を構成する外表面のうち少なくとも２つの外表面に関して表層から全厚みの10〜33％の範囲内の平均フェライト粒径が３μm 以下の超細粒組織であることを特徴とする鋼材である。 However, it is generally known that the fracture toughness value, such as the critical CTOD, decreases with an increase in the deformation rate. It is very difficult to completely suppress the occurrence itself. Therefore, Patent Document 3 proposes a steel material having a performance of preventing the propagation of a crack while allowing the occurrence of brittle fracture. The steel material described in Patent Document 3 has an ultrafine grain structure in which at least two of the outer surfaces constituting the steel material have an average ferrite grain size of 3 μm or less within a range of 10 to 33% of the total thickness from the surface layer from the surface layer. A steel material characterized by the following.
また、従来から、鋼材にNi、Mo等の高価な合金元素を添加し焼入焼戻等の熱処理を施してシャルピー衝撃特性や破壊靱性を向上させ、脆性破壊の発生を防止することは従来から実施されているが、鋼材自体の価格が高くなり経済的に不利となる。 Also, conventionally, it has been difficult to improve the Charpy impact properties and fracture toughness by adding expensive alloying elements such as Ni and Mo to steel materials and to perform heat treatment such as quenching and tempering to prevent the occurrence of brittle fracture. Although it is being implemented, the price of the steel itself increases, which is economically disadvantageous.
また、特許文献４には、高価な合金元素を添加することなく、Ｖ、Ｎを含有させてオーステナイト中にVNを核としてフェライトを析出させ、微細パーライト組織とすることによりシャルピー衝撃特性を向上させた耐震性に優れた極厚Ｈ形鋼が開示されている。
しかしながら、特許文献３に記載された技術では、鋼構造物内に多くの脆性亀裂が残存することになり、その後の建築鋼構造物の安全性に問題を残すことになる。さらに、建築鋼構造物では、鋼材に耐火被覆が施されており、発生した脆性亀裂を発見し、補修するために耐火被覆を剥がす必要があり、経済的に不利となる。また、特許文献４に記載された技術では、耐震性を考慮して、極厚Ｈ形鋼の靱性向上を図っているが、高速変形下での動的破壊靱性については全く考慮されていない。 However, according to the technique described in Patent Literature 3, many brittle cracks remain in the steel structure, and a problem remains in the safety of the building steel structure thereafter. Further, in a building steel structure, a fire-resistant coating is applied to a steel material, and it is necessary to remove the fire-resistant coating in order to find a brittle crack that has occurred and repair it, which is economically disadvantageous. Further, in the technology described in Patent Document 4, the toughness of an extremely thick H-section steel is improved in consideration of earthquake resistance, but dynamic fracture toughness under high-speed deformation is not considered at all.
本発明は、上記した従来技術の問題を有利に解決し、高価な合金元素を多量に添加することなく、高速変形下で優れた破壊靱性を有する耐地震特性に優れる構造用鋼材、好ましくは鋼板の製造方法を提供することを目的とする。 The present invention advantageously solves the above-mentioned problems of the prior art, without adding a large amount of expensive alloying elements, and has excellent fracture toughness under high-speed deformation. It is an object of the present invention to provide a method for producing the same.
本発明者らは、上記課題を達成するため、鋭意実験、研究を行った。 The present inventors have conducted intensive experiments and researches in order to achieve the above object.
その結果、
（１）ＶおよびＮを含有させ、圧延中およびその後の冷却中にVNを析出させると、析出したVNを核としてフェライトが析出し、微細なフェライト＋パーライト組織となること、さらに、
（２）フェライト粒内に、適正量のVNを、適正な大きさと適正な密度で析出・分散させることにより、亀裂先端での変形が均一化し、シャルピー衝撃試験吸収エネルギーが同一であっても高速変形時に高い破壊靱性値を有すること、
（３）Ａr3変態点以下の温度でフェライト粒内に析出するVN析出物量が多いほど、高速変形時に高い破壊靱性を示すこと、
を見い出した。なお、本発明でいうＡr3変態点（℃）は、次式で計算される値を用いるものとする。
as a result,
(1) When VN is contained and VN is precipitated during rolling and subsequent cooling, ferrite precipitates with the precipitated VN as a nucleus, resulting in a fine ferrite + pearlite structure.
(2) Precipitating and dispersing an appropriate amount of VN in an appropriate size and an appropriate density in ferrite grains, thereby uniformizing the deformation at the crack tip and achieving high speed even if the Charpy impact test absorption energy is the same. Have a high fracture toughness value during deformation,
(3) The higher the amount of VN precipitates precipitated in ferrite grains at a temperature below the Ar 3 transformation point, the higher the fracture toughness during high-speed deformation;
I found The Ar 3 transformation point (° C.) used in the present invention uses a value calculated by the following equation.
Ａr3（℃）＝910 ＋273 Ｃ＋25Si−74Mn−56Ni−16Cr−9Mo −5Cu −1620Nb
（ここに、Ｃ、Si、Mn、Ni、Cr、Mo、Cu、Nbは各元素の含有量（重量％）で、含まれない元素の場合には、０として計算する。）
また、さらに、本発明者らは、
（４）上記した組織を有する鋼板の多層盛溶接継手の熱影響部は、母材と同様に高速変形時に高い破壊靱性値を示すこと、
を見い出した。
Ar 3 (° C) = 910 +273 C + 25Si-74Mn-56Ni-16Cr-9Mo-5Cu-1620Nb
(Here, C, Si, Mn, Ni, Cr, Mo, Cu, and Nb are the contents (% by weight) of each element. In the case of an element that is not included, calculation is made as 0.)
In addition, the present inventors furthermore,
(4) The heat-affected zone of the multi-pass welded joint of a steel sheet having the above-described structure exhibits a high fracture toughness value at the time of high-speed deformation, similar to the base metal;
I found
本発明は、上記した知見に基づき、さらに検討を加え構成されたものである。 The present invention has been made by further study based on the above findings.
すなわち、本発明は、重量％で、Ｖ：0.04〜0.15％、Ｎ：0.0050〜0.0150％を含む鋼素材（スラブ）を、1350℃以下に加熱したのち、圧延終了温度をＡr3変態点以上とする熱間圧延を施し、その後0.09〜１℃/sの冷却速度で冷却することにより、鋼材の降伏比を80％以下、変形速度１〜1000mm/sの高速変形下での０℃における限界ＣＴＯＤ値を0.1mm 以上とすることを特徴とする耐地震特性に優れた構造用鋼材の製造方法、好ましくは構造用鋼板の製造方法であり、また、本発明は、重量％で、Ｖ：0.04〜0.15％、Ｎ：0.0050〜0.0150％を含む鋼素材を、1050℃〜1350℃に加熱したのち、圧延終了温度を950 ℃以上とする熱間圧延を施し、ついで３℃/s以上の冷却速度でＡr3変態点で冷却し、その後0.09〜１℃/sの冷却速度で冷却してもよく、また、本発明は、重量％で、Ｖ：0.04〜0.15％、Ｎ：0.0050〜0.0150％を含む鋼素材を、1350℃以下に加熱し、圧延終了温度を950 ℃以上とする第１段の熱間圧延を施したのち、熱間圧延を一時中断し、Ａr3変態点まで３℃/s以上の冷却速度で冷却し、ついで第２段の熱間圧延を施し所定の板厚としたのち0.09〜１℃/sの冷却速度で冷却してもよい。 That is, the present invention heats a steel material (slab) containing, by weight%, V: 0.04 to 0.15% and N: 0.0050 to 0.0150% to 1350 ° C. or lower, and then sets the rolling end temperature to the Ar 3 transformation point or higher. Hot rolling, and then cooling at a cooling rate of 0.09 to 1 ° C / s, the yield ratio of steel is 80% or less, and the critical CTOD at 0 ° C under high-speed deformation at a deformation rate of 1 to 1000 mm / s. The present invention relates to a method for producing a structural steel material having excellent seismic resistance, preferably a method for producing a structural steel sheet, characterized in that the value is 0.1 mm or more. A steel material containing 0.15%, N: 0.0050 to 0.0150% is heated to 1050 ° C to 1350 ° C, then hot-rolled to a rolling end temperature of 950 ° C or more, and then at a cooling rate of 3 ° C / s or more. cooled in Ar 3 transformation point, may be cooled at a cooling rate of subsequent from .09 to 1 ° C. / s, also the present invention, in weight%, : 0.04 to 0.15%, N: 0.0050 to 0.0150%, steel material is heated to 1350 ° C or lower, and the first stage hot rolling is performed at a rolling end temperature of 950 ° C or higher. Temporarily suspended, cooled to the Ar 3 transformation point at a cooling rate of 3 ° C./s or more, then subjected to the second stage of hot rolling to a predetermined thickness, and then cooled at a cooling rate of 0.09 to 1 ° C./s. You may.
また、本発明では、鋼素材（スラブ）を、重量％で、Ｃ：0.04〜0.18％、Si：0.60％以下、Mn：0.80〜1.80％、Ｐ：0.030 ％以下、Ｓ：0.015 ％以下、Ｖ：0.04〜0.15％、Ｎ：0.0050〜0.0150％を含み、さらに、Al：0.005 〜0.050 ％およびTi：0.005 〜0.050 ％のうちの１種または２種を含有し、かつ次（１）式
Ｃeq＝Ｃ＋Si/24 ＋Mn/6＋Ｖ/14 ＋Ni/40 ＋Cr/5＋Mo/4 ……（１）
（ここで、Ｃ、Si、Mn、Ｖ、Ni、Cr、Mo：各元素の含有量（重量％））で定義されるＣeqが0.34〜0.48％であり、残部Feおよび不可避的不純物からなる組成とするのが好ましい。また、上記組成に加えてさらに、重量％で、Cu：0.05〜0.60％、Ni：0.05〜0.60％、Cr：0.05〜0.50％、Mo：0.02〜0.20％のうちから選ばれた１種または２種以上を含有してもよく、および／またはさらに重量％で、Nb：0.003 〜0.030 ％を含有してもよく、および／または、さらに重量％で、Ｂ：0.0002〜0.0020％、REM ：0.0010〜0.0200％、Ca：0.0010〜0.010 ％のうちから選ばれた１種または２種以上を含有してもよい。
Further, in the present invention, the steel material (slab) is expressed in terms of% by weight: C: 0.04 to 0.18%, Si: 0.60% or less, Mn: 0.80 to 1.80%, P: 0.030% or less, S: 0.015% or less, V: : 0.04 to 0.15%, N: 0.0050 to 0.0150%, further contains one or two of Al: 0.005 to 0.050% and Ti: 0.005 to 0.050%, and the following equation (1): Ceq = C + Si / 24 + Mn / 6 + V / 14 + Ni / 40 + Cr / 5 + Mo / 4 …… (1)
(Where Ceq defined by C, Si, Mn, V, Ni, Cr, and Mo: the content (% by weight) of each element) is 0.34 to 0.48%, and the composition is the balance of Fe and unavoidable impurities. It is preferred that In addition to the above composition, one or two selected from the group consisting of Cu: 0.05 to 0.60%, Ni: 0.05 to 0.60%, Cr: 0.05 to 0.50%, and Mo: 0.02 to 0.20% by weight. Or more, and / or further by weight, Nb: 0.003 to 0.030%, and / or, further by weight, B: 0.0002 to 0.0020%, REM: 0.0010 to One or two or more selected from 0.0200% and Ca: 0.0010 to 0.010% may be contained.
本発明によれば、高価な合金元素を多量に添加することなく、１〜1000mm/sの高速変形において母材および溶接熱影響の０℃における限界ＣＴＯＤが0.1mm 以上を有する鋼材が得られる。本発明の構造用鋼材は、高速変形を受けても破壊靱性の劣化が少なく、耐震性に優れた鋼材として利用でき産業上格段の効果を奏する。 According to the present invention, it is possible to obtain a steel material having a critical CTOD of 0.1 mm or more at 0 ° C due to the influence of the base metal and welding heat at a high speed deformation of 1 to 1000 mm / s without adding a large amount of expensive alloying elements. INDUSTRIAL APPLICABILITY The structural steel material of the present invention can be used as a steel material excellent in earthquake resistance with little deterioration in fracture toughness even when subjected to high-speed deformation, and has a remarkable industrial effect.
本発明では、鋼中にＶ、Ｎを含有させ、圧延中および圧延後冷却中にオーステナイト組織中にVNを析出させ、VNを核としてフェライトを析出させることにより微細なフェライト＋パーライト組織として、さらに変態後にもフェライト粒内にVNを析出させることによりフェライト粒内に一定量のVNを、適正な大きさと適正な密度で析出・分散させる。 In the present invention, V and N are contained in steel, VN is precipitated in an austenite structure during rolling and cooling after rolling, and a fine ferrite + pearlite structure is formed by precipitating ferrite with VN as a nucleus. By depositing VN in the ferrite grains even after the transformation, a certain amount of VN is precipitated and dispersed in the ferrite grains with an appropriate size and an appropriate density.
まず、本発明における化学組成の限定理由を説明する。 First, the reasons for limiting the chemical composition in the present invention will be described.
Ｖ：0.04〜0.15％
Ｖは、鋼の強度を高める作用を有し、母材の強度および靱性を確保するうえで、本発明において不可欠の元素である。Ｖは、鋼中でVNとしてオーステナイト中に析出し、フェライトの析出核として作用し、結晶粒を微細化する。さらに、VNはフェライト中に析出し、亀裂先端の変形を均一化する。これにより、シャルピー衝撃特性に比べ高速変形時の破壊靱性をより向上させる効果を有する。このような効果は0.04％以上の含有で認められるが、0.15％を超える含有は、母材靱性および溶接性を劣化させる。このため、Ｖは0.04〜0.15％の範囲に限定した。なお、好ましい範囲は、0.05〜0.10％である。
V: 0.04 to 0.15%
V has an effect of increasing the strength of steel, and is an essential element in the present invention for securing the strength and toughness of the base material. V precipitates in steel as VN in austenite, acts as a ferrite precipitation nucleus, and refines crystal grains. Furthermore, VN precipitates in the ferrite and makes the deformation of the crack tip uniform. This has the effect of further improving the fracture toughness during high-speed deformation as compared to the Charpy impact characteristics. Such an effect is recognized at a content of 0.04% or more, but a content of more than 0.15% deteriorates base material toughness and weldability. For this reason, V is limited to the range of 0.04 to 0.15%. In addition, a preferable range is 0.05 to 0.10%.
Ｎ：0.0050〜0.0150％
Ｎは、Ｖと結合しVNを形成し、母材の強度、靱性および高速変形時の破壊靱性値を向上させる。そのためには、0.0050％以上の含有が必要であるが、0.0150％を超えて含有すると母材靱性および溶接性が大きく低下する。このため、Ｎは0.0050〜0.0150％の範囲に限定した。なお、好ましくは、0.0060〜0.0120％である。
N: 0.0050-0.0150%
N combines with V to form VN, and improves the strength, toughness, and fracture toughness during high-speed deformation of the base material. For this purpose, the content of 0.0050% or more is necessary, but if it exceeds 0.0150%, the base material toughness and weldability are greatly reduced. For this reason, N was limited to the range of 0.0050 to 0.0150%. In addition, Preferably, it is 0.0060-0.0120%.
VN析出物：0.02〜0.07％
VN析出物は、オーステナイト中に析出しフェライト変態核として作用し、結晶粒を微細化するとともに、オーステナイトがフェライトに変態した後にフェライト中に析出して、亀裂先端の変形を均一化する。これにより、シャルピー衝撃特性に比べ高速変形時の破壊靱性をより向上させる効果を有する。これらの効果は、0.02％以上の析出が必要である。なお、上記したＶ、Ｎの範囲内では析出するVNは0.07％より多く析出しないため、0.07％を上限とした。
VN precipitates: 0.02 to 0.07%
The VN precipitates precipitate in austenite and act as ferrite transformation nuclei, refine crystal grains, and precipitate in ferrite after austenite is transformed into ferrite, thereby making the crack tip uniform in deformation. This has the effect of further improving the fracture toughness during high-speed deformation as compared to the Charpy impact characteristics. These effects require a precipitation of 0.02% or more. In the range of V and N described above, since VN precipitated does not precipitate more than 0.07%, the upper limit is set to 0.07%.
Ｃ：0.04〜0.18％
Ｃは、鋼の強度を増加させる元素であり、耐震性を考慮した構造用鋼材では、引張強さが 500 MPa以上であることが好ましく、このためにＣを0.04％以上含有することが好ましい。しかし、0.18％を超えると溶接熱影響部の靱性を劣化させる。このため、Ｃは0.04〜0.18％の範囲とするのが好ましい。なお、より好ましくは溶接性および強度確保の点から0.08〜0.16％である。
C: 0.04 to 0.18%
C is an element that increases the strength of steel, and a structural steel material considering seismic resistance preferably has a tensile strength of 500 MPa or more, and therefore preferably contains 0.04% or more of C. However, when it exceeds 0.18%, the toughness of the heat affected zone is deteriorated. For this reason, C is preferably in the range of 0.04 to 0.18%. In addition, it is more preferably 0.08 to 0.16% from the viewpoint of ensuring weldability and strength.
Si：0.60％以下
Siは、鋼の強度上昇に有効な元素であるが、多量添加すると溶接熱影響部の靱性を劣化させる。このため、0.60％を上限とするのが好ましい。なお、Siは、0.20％未満では、強度上昇の効果が少ないため、より好ましくは0.20〜0.60％の範囲である。
Si: 0.60% or less
Si is an element effective for increasing the strength of steel, but when added in a large amount, it deteriorates the toughness of the heat affected zone. Therefore, the upper limit is preferably set to 0.60%. If the content of Si is less than 0.20%, the effect of increasing the strength is small. Therefore, the content is more preferably in the range of 0.20 to 0.60%.
Mn：0.80〜1.80％
Mnは、鋼の強度を増加させる有効な元素であり、強度確保の観点から0.80％以上含有するのが好ましい。しかし、1.80％を超えると、組織がベイナイト等の低温変態生成物を主体とする組織となり、母材靱性が劣化する。このため、Mnは0.80〜1.80％の範囲とするのが好ましい。
Mn: 0.80-1.80%
Mn is an effective element for increasing the strength of steel, and is preferably contained at 0.80% or more from the viewpoint of securing the strength. However, if it exceeds 1.80%, the structure becomes a structure mainly composed of a low-temperature transformation product such as bainite, and the toughness of the base material deteriorates. For this reason, Mn is preferably set in the range of 0.80 to 1.80%.
Ｐ：0.030 ％以下
Ｐは、母材、溶接熱影響部の靱性を劣化させ、また溶接割れ性を高めるため、できるだけ低減するのが好ましく、上限を0.030 ％とするのが望ましい。なお、より好ましくは0.010 ％以下である。
P: not more than 0.030% P is preferably reduced as much as possible in order to degrade the toughness of the base material and the weld heat affected zone and to enhance the weld cracking property, and it is desirable that the upper limit be 0.030%. It is more preferably at most 0.010%.
Ｓ：0.015 ％以下
Ｓは、非金属介在物を形成し靱性、延性を劣化させるため、できるだけ低減するのが好ましく、上限を0.015 ％以下とするのが望ましい。なお、より好ましくは0.010 ％以下である。
S: 0.015% or less Since S forms nonmetallic inclusions and deteriorates toughness and ductility, it is preferable to reduce S as much as possible, and it is desirable to set the upper limit to 0.015% or less. It is more preferably at most 0.010%.
Al：0.005 〜0.050 ％およびTi：0.005 〜0.050 ％のうちの１種または２種
AlおよびTiは、いずれも脱酸剤として作用するため、AlおよびTiのうち１種または２種添加できる。脱酸のためには、Al、Tiは、いずれも0.005 ％以上の添加を必要とするが、0.050 ％を超えると脱酸効果は飽和し非金属介在物が増加し鋼の清浄度が低下する。このため、Alは0.005 〜0.050 ％、Tiは0.005 〜0.050 ％の範囲とするのが好ましい。
One or two of Al: 0.005 to 0.050% and Ti: 0.005 to 0.050%
Since Al and Ti both act as deoxidizing agents, one or two of Al and Ti can be added. For deoxidation, both Al and Ti need to be added in an amount of 0.005% or more. However, when the content exceeds 0.050%, the deoxidizing effect is saturated, nonmetallic inclusions increase, and the cleanliness of the steel decreases. . Therefore, it is preferable that Al is in the range of 0.005 to 0.050% and Ti is in the range of 0.005 to 0.050%.
さらに、Tiは、高温まで安定な微細析出物を形成し、圧延加熱時のオーステナイト粒の粗大化を抑制する。それにより、圧延後のフェライト粒が微細化され、母材の強度・靱性が向上する。さらに、溶接加熱時にも、高温まで安定な微細Ti析出物がオーステナイト粒の粗大化を抑制し、溶接熱影響部の高靱化が達成される。このため、脱酸剤としてAlのみを添加した場合には、オーステナイト粒の粗大化抑制効果溶接熱影響部の高靱化効果を持たせる意味でTiを0.005 〜0.015 ％の範囲で含有させることが好ましい。 Further, Ti forms fine precipitates that are stable up to high temperatures, and suppresses austenite grain coarsening during rolling heating. Thereby, the ferrite grains after rolling are refined, and the strength and toughness of the base material are improved. Further, even during welding heating, fine Ti precipitates that are stable up to a high temperature suppress coarsening of austenite grains, and toughening of the weld heat affected zone is achieved. For this reason, when only Al is added as a deoxidizing agent, Ti may be contained in the range of 0.005 to 0.015% in the sense that the effect of suppressing the coarsening of austenite grains and the effect of increasing the toughness of the heat affected zone are obtained. preferable.
Cu：0.05〜0.60％、Ni：0.05〜0.60％、Cr：0.05〜0.50％、Mo：0.02〜0.20％のうちから選ばれた１種または２種以上
Cu、Ni、Cr、Moはいずれも強度を増加させる元素であり、本発明ではCu、Ni、Cr、Moのうちから選ばれた1 種または2 種以上を必要に応じ添加できる。しかし、Cu、Ni、Cr、Moは、それぞれ0.05％、0.05％、0.05％、0.02％未満では、上記した効果が認められない。一方、Cuは多量に添加すると熱間加工性を劣化させるため、多量添加の場合には等量のNiと同時に添加するのが望ましいが、Niを0.60％を超えて添加すると製造コストが高くなり経済的に不利となる。このため、Cu、Niの上限は0.60％とするのが好ましい。また、Cr、Moは、それぞれ0.50％、0.20％を超えると溶接性や靱性を劣化させるため、それぞれ0.50％、0.20％を上限とした。
Cu: 0.05 to 0.60%, Ni: 0.05 to 0.60%, Cr: 0.05 to 0.50%, Mo: 0.02 to 0.20%
Cu, Ni, Cr, and Mo are all elements that increase the strength, and in the present invention, one or more selected from Cu, Ni, Cr, and Mo can be added as necessary. However, Cu, Ni, Cr, and Mo do not have the above-mentioned effects when they are less than 0.05%, 0.05%, 0.05%, and 0.02%, respectively. On the other hand, if Cu is added in a large amount, the hot workability is deteriorated. Therefore, in the case of a large addition, it is desirable to add Cu at the same time as the same amount of Ni. However, if Ni is added in excess of 0.60%, the production cost increases. Economically disadvantaged. Therefore, the upper limits of Cu and Ni are preferably set to 0.60%. Further, if Cr and Mo exceed 0.50% and 0.20%, respectively, the weldability and toughness are degraded, so the upper limits are 0.50% and 0.20%, respectively.
Nb：0.003 〜0.030 ％
Nbは、Ａr3変態点を低下させ、VNのオーステナイト中での析出を促進させ、さらにNb化合物の析出とNb化合物による結晶粒の細粒化により強度と靱性をともに向上させる効果を有する。この効果を得るためには、Nbを0.003 ％以上含有する必要がある。一方、0.030 ％を超える含有は、溶接性および溶接熱影響部の靱性を劣化させる。このため、Nbは0.003 〜0.030 ％の範囲とするのが好ましい。なお、好ましくは0.005 〜0.025 ％である。
Nb: 0.003 to 0.030%
Nb has an effect of lowering the Ar 3 transformation point, promoting precipitation of VN in austenite, and improving both strength and toughness by precipitation of Nb compounds and refinement of crystal grains by the Nb compounds. In order to obtain this effect, it is necessary to contain Nb at 0.003% or more. On the other hand, if the content exceeds 0.030%, the weldability and the toughness of the weld heat affected zone deteriorate. Therefore, Nb is preferably set in the range of 0.003 to 0.030%. Preferably, the content is 0.005 to 0.025%.
Ｂ：0.0002〜0.0020％、REM ：0.0010〜0.0200％、Ca：0.0010〜0.010 ％のうちから選ばれた１種または２種以上
Ｂ、REM 、Caは、いずれも圧延後のフェライト粒を微細にする作用を有しており、必要に応じＢ、REM 、Caのうちから選ばれた１種または２種以上を添加できる。
B: 0.0002-0.0020%, REM: 0.0010-0.0200%, Ca: 0.0010-0.010% One or more kinds selected from B, REM, and Ca make ferrite grains fine after rolling. It has an action, and one or more selected from B, REM, and Ca can be added as necessary.
Ｂは、圧延中にBNとして析出し、圧延後のフェライト結晶粒を微細化する。この結晶粒の微細化は、0.0002％以上の添加で認められるが、0.0020％を超える添加は靱性を劣化させる。このことから、Ｂは0.0002〜0.0020％の範囲に限定するのが好ましい。 B precipitates as BN during rolling and refines the ferrite crystal grains after rolling. The refinement of the crystal grains is observed at an addition of 0.0002% or more, but an addition exceeding 0.0020% deteriorates the toughness. For this reason, B is preferably limited to the range of 0.0002 to 0.0020%.
REM 、Caは、高温で安定な析出物として鋼中に微細分散し、圧延時のオーステナイト粒の粗大化を抑制する。それにより、圧延後のフェライト粒を微細化する。さらに、溶接加熱時にも、オーステナイト粒の粗大化を抑制し、溶接熱影響部の組織を微細化する。このために、REM 、Caは0.0010％以上の添加を必要とするが、REM が0.0200％、Caが0.010 ％を超えると鋼の清浄度が低下し、靱性が劣化する。このため、REM は0.0010〜0.0200％、Caは0.0010〜0.010 ％の範囲に限定するのが望ましい。 REM and Ca finely disperse in the steel as stable precipitates at high temperatures, and suppress coarsening of austenite grains during rolling. Thereby, the ferrite grains after rolling are refined. Furthermore, even during welding heating, coarsening of austenite grains is suppressed, and the structure of the weld heat affected zone is refined. For this purpose, REM and Ca need to be added in an amount of 0.0010% or more. However, if REM exceeds 0.0200% and Ca exceeds 0.010%, the cleanliness of the steel decreases and the toughness deteriorates. For this reason, it is desirable to limit the REM to the range of 0.0010 to 0.0200% and the Ca to the range of 0.0010 to 0.010%.
Ｃeq：0.34〜0.48％
Ｃeqは次（１）式で定義する。
Ceq: 0.34 to 0.48%
Ceq is defined by the following equation (1).
Ｃeq＝Ｃ＋Si/24 ＋Mn/6＋Ｖ/14 ＋Ni/40 ＋Cr/5＋Mo/4 ……（１）
ここで、Ｃ、Si、Mn、Ｖ、Ni、Cr、Moは各元素の含有量（重量％）である。
Ceq = C + Si / 24 + Mn / 6 + V / 14 + Ni / 40 + Cr / 5 + Mo / 4 (1)
Here, C, Si, Mn, V, Ni, Cr, and Mo are the contents (% by weight) of each element.
なお、各元素の含有量は、合金元素として添加される以外に不可避的に混入することにより鋼中に含有されるものをも含むものとする。 In addition, the content of each element shall include what is contained in steel by being inevitably mixed in addition to being added as an alloying element.
（１）式に記載された元素が含有されない場合には、その元素の含有量を０として計算するものとする。 When the element described in the formula (1) is not contained, the content of the element is calculated as 0.
Ｃeqが0.34％未満では、母材の強度、および溶接熱影響部軟化部の強度を確保することが困難となり、一方、0.48％を超えると溶接割れ感受性が高くなり、溶接熱影響部の靱性が低下する。このようなことからＣeqは0.34〜0.48％の範囲とするのが望ましい。 If Ceq is less than 0.34%, it is difficult to secure the strength of the base material and the strength of the softened part of the weld heat affected zone, while if it exceeds 0.48%, the susceptibility to weld cracking increases, and the toughness of the weld heat affected zone becomes poor. descend. For this reason, Ceq is desirably in the range of 0.34 to 0.48%.
本発明の鋼材の組織について説明する。 The structure of the steel material of the present invention will be described.
本発明の鋼材は、フェライト＋パーライト組織で、フェライトの結晶粒度がJIS G 0552で規定される結晶粒度番号で５番以上で、フェライト粒の面積率が50〜100 ％であり、該フェライト粒内に粒子径５〜200nm のVN析出物が106 〜1010個／mm3 の範囲で析出分散した組織を有する。 The steel material of the present invention has a ferrite + pearlite structure, the grain size of ferrite is 5 or more in the grain size number specified in JIS G 0552, the area ratio of the ferrite grains is 50 to 100%, Has a structure in which VN precipitates having a particle size of 5 to 200 nm are precipitated and dispersed in a range of 10 6 to 10 10 particles / mm 3 .
フェライトの結晶粒度：JIS G 0552で規定される結晶粒度番号で５番以上
フェライトの結晶粒度がJIS G 0552で規定される結晶粒度で５番未満では、靱性の低下が著しいため、フェライトの結晶粒度は粒度番号で５番以上とした。
Ferrite grain size: No. 5 or more in the grain size number specified in JIS G 0552 If the grain size of the ferrite is less than 5 in the grain size specified in JIS G 0552, the toughness is remarkably reduced. Is 5 or more in particle size number.
フェライトの面積率：50〜100 ％
フェライトの面積率が50％未満では、母材の靱性が低下し、高速変形時に亀裂先端の変形が不均一となり、高速変形下での破壊靱性が劣化する。このため、フェライトの面積率は50％以上に限定した。
Ferrite area ratio: 50-100%
If the area ratio of ferrite is less than 50%, the toughness of the base material decreases, the deformation of the crack tip becomes uneven during high-speed deformation, and the fracture toughness under high-speed deformation deteriorates. For this reason, the area ratio of ferrite was limited to 50% or more.
粒子径５〜200nm のVN析出物：106 〜1010個／mm3
フェライト粒内に析出する粒子径が200nm を超える粗大なVN析出物は、破壊の基点となりやすく靱性を劣化させるため、本発明では、フェライト粒内に析出するVN析出物の大きさを200nm 以下に限定した。フェライト中に析出した粒子径200nm 以下のVN析出物は、亀裂先端の変形を均一化する。一方、５nm未満の大きさの微細なVN析出物は、上記したVN析出物の変形均一化効果を有している可能性はあるが、電子顕微鏡による分析測定が困難となるため５nmをVN析出物の大きさの下限とした。５nm未満のVN析出物は存在していてもよいのは言うまでもない。さらに、粒子径５〜200nm の範囲のVN析出物の分散密度は、106 〜1010個／mm3 の範囲に限定する。粒子径５〜200nm のVN析出物の分散密度が106 個／mm3 未満では、変形均一化効果が少なく、一方、1010個／mm3 を超えると過度の析出物の存在により靱性が劣化する。なお、亀裂先端の変形的均一化を促進する観点から粒子径100 〜200nm の範囲のVN析出物の分散密度を105 個／mm3 以下とするのが好ましい。
VN precipitate having a particle size of 5 to 200 nm: 10 6 to 10 10 particles / mm 3
In the present invention, the size of the VN precipitates deposited in the ferrite grains is reduced to 200 nm or less, because coarse VN precipitates having a diameter of more than 200 nm precipitated in the ferrite grains are likely to serve as a starting point of fracture and deteriorate toughness. Limited. VN precipitates having a particle diameter of 200 nm or less precipitated in the ferrite make the deformation at the crack tip uniform. On the other hand, fine VN precipitates having a size of less than 5 nm may have the effect of uniformizing the deformation of the VN precipitates described above, but it becomes difficult to analyze and measure them with an electron microscope. The lower limit of the size of the object. It goes without saying that VN precipitates of less than 5 nm may be present. Further, the dispersion density of VN precipitates having a particle size in the range of 5 to 200 nm is limited to the range of 10 6 to 10 10 particles / mm 3 . If the dispersion density of VN precipitates having a particle diameter of 5 to 200 nm is less than 10 6 / mm 3 , the effect of uniformizing deformation is small, while if it exceeds 10 10 / mm 3 , the toughness is deteriorated due to the presence of excessive precipitates. I do. Incidentally, the dispersion density of VN precipitates in the range from the viewpoint of the particle diameter 100 to 200 nm to facilitate the deformation uniformity of crack tip preferably 10 5 cells / mm 3 or less.
上記した組成と組織とすることにより、鋼材は、降伏比80％以下、変形速度１〜1000mm/sの高速変形下での０℃における限界ＣＴＯＤ値が0.1mm 以上を有する耐地震特性に優れた構造用鋼材となる。降伏比が80％を超えると地震時の塑性変形能が低下し、構造物としての安全性が低下する。また、変形速度１〜1000mm/sの高速変形下での０℃における限界ＣＴＯＤ値が0.1mm 未満では、大地震時におけるような高速変形を受けた場合に脆性亀裂を発生させやすくなり、構造物の安全性が低下する。なお、本発明における限界ＣＴＯＤ値は、１ＴＣＴ試験片または３点曲げ試験片を用いて、WES 1108-1995 規格またはASTM E 1290 、BS 7448 に準拠した破壊靱性試験にて測定した値を使用するものとする。 With the above composition and structure, the steel material is excellent in seismic resistance having a yield ratio of 80% or less and a critical CTOD value at 0 ° C of 0.1 mm or more under high-speed deformation at a deformation speed of 1 to 1000 mm / s. It becomes a structural steel material. When the yield ratio exceeds 80%, the plastic deformability during an earthquake decreases, and the safety as a structure decreases. If the critical CTOD value at 0 ° C. under a high-speed deformation at a deformation speed of 1 to 1000 mm / s is less than 0.1 mm, a brittle crack is easily generated when subjected to a high-speed deformation as in a large earthquake. The safety of is reduced. In the present invention, the critical CTOD value uses a value measured by a fracture toughness test based on WES 1108-1995 standard or ASTM E 1290, BS 7448 using a 1 TCT test piece or a three-point bending test piece. And
ついで、上記した鋼材の製造方法について説明する。 Next, a method for manufacturing the above-described steel material will be described.
上記した組成のうちいずれかの組成を有する鋼素材（スラブ）を通常公知の溶製、凝固方法により作製し、該鋼素材（スラブ）を所定の加熱温度に加熱したのち熱間圧延を施し所定寸法の鋼材（鋼板）とする。 A steel material (slab) having any one of the above-described compositions is prepared by a commonly known melting and solidifying method, and the steel material (slab) is heated to a predetermined heating temperature, and then subjected to hot rolling to obtain a predetermined material. Dimensions of steel material (steel plate).
鋼素材（スラブ）の加熱温度は、1350℃以下とする。 The heating temperature of the steel material (slab) is 1350 ° C or less.
加熱温度が1350℃を超えると結晶粒が粗大化するうえ、加熱炉の損耗が著しくなるため、加熱温度は1350℃以下に限定する。なお、過熱温度の下限については特に限定されないが、後述するようにAr3 変態点以上の温度で圧延することが可能なように加熱する必要がある。 If the heating temperature exceeds 1350 ° C., the crystal grains become coarse and the heating furnace becomes significantly worn. Therefore, the heating temperature is limited to 1350 ° C. or less. The lower limit of the superheating temperature is not particularly limited, but it is necessary to perform heating so that rolling can be performed at a temperature equal to or higher than the Ar 3 transformation point as described later.
上記加熱温度に加熱された鋼素材( スラブ) は、ついでＡr3変態点以上の温度を圧延終了温度とする熱間圧延を施され、製品厚さの鋼素材( 鋼板) とされる。圧延終了温度がＡr3変態点未満では、２相域圧延となるため靱性が劣化したり材質の異方性が強くなる。このため、熱間圧延の圧延終了温度はＡr3変態点以上とするのが望ましい。 The steel material (slab) heated to the above-mentioned heating temperature is then subjected to hot rolling with a temperature equal to or higher than the Ar 3 transformation point as a rolling end temperature, thereby obtaining a steel material (steel plate) having a product thickness. If the rolling end temperature is lower than the Ar 3 transformation point, the rolling is in the two-phase region, so that the toughness is deteriorated and the material anisotropy is increased. For this reason, it is desirable that the rolling end temperature of the hot rolling be equal to or higher than the Ar 3 transformation point.
なお、粒子径100 〜200nm のVN析出物の密度を105 個／mm3 未満とするには、熱間圧延の圧延終了温度を950 ℃以上とし、圧延終了後３℃/s以上の冷却速度でＡr3変態点まで冷却し、その後空冷、好ましくは0.09℃/s以上１℃/s以下の冷却速度で冷却、するのがよい。熱間圧延の終了温度が950 ℃未満では、亀裂先端の均一化にあまり効果のない粒子径の大きいVNが圧延中に多量に析出する。このため、熱間圧延の圧延終了温度は950 ℃以上とするのが好ましい。また、圧延終了後Ａr3変態点までの冷却速度が３℃/s未満では、オーステナイト中に析出するVNが増加し、結果として亀裂先端の均一化があまり効果がない粒子径の大きなVNが増加するため、所望のVN析出物の分散が得られない。また、Ａr3変態点以下の温度での冷却は、空冷でよいが、厚鋼板で空冷とすると、冷却速度が遅くなり、VN析出物の好適な分散が得られなくなる懸念がある場合には、１℃/s以下の冷却速度で冷却、するのがよい。 In order to reduce the density of VN precipitates having a particle diameter of 100 to 200 nm to less than 10 5 / mm 3 , the rolling end temperature of hot rolling is set to 950 ° C. or more, and the cooling rate is set to 3 ° C./s or more after the end of rolling. To cool to the Ar 3 transformation point, and then air cooling, preferably at a cooling rate of 0.09 ° C./s or more and 1 ° C./s or less. If the end temperature of the hot rolling is lower than 950 ° C., a large amount of VN having a large particle diameter, which is not so effective in making the crack tip uniform, precipitates during the rolling. For this reason, the rolling end temperature of the hot rolling is preferably set to 950 ° C. or higher. If the cooling rate from the end of rolling to the transformation point of Ar 3 is less than 3 ° C./s, the amount of VN precipitated in austenite increases, and as a result, the VN with a large particle size, which does not have much effect on the uniformity of the crack tip, increases. Therefore, the desired dispersion of the VN precipitate cannot be obtained. In addition, cooling at a temperature equal to or lower than the Ar 3 transformation point may be air cooling, but if air cooling is performed using a thick steel plate, the cooling rate is reduced, and there is a concern that a suitable dispersion of VN precipitates may not be obtained. It is preferable to cool at a cooling rate of 1 ° C./s or less.
また、圧延終了温度を950 ℃以上として、圧延終了後にＡr3変態点まで３℃/s以上の冷却速度で冷却するとオーステナイト中のVNが少なめとなり、フェライト粒径あが大きめとなる場合がある。このような場合は、圧延終了温度を950 ℃以上とする第１段の熱間圧延を施したのち、熱間圧延を一時中断し、Ａr3変態点まで３℃/s以上の冷却速度で冷却し、ついで第２段の熱間圧延を施し所定の板厚としたのち空冷0.09℃/s以上１℃/s以下の冷却速度で冷却）してもよい。ここで、Ａr3変態点以下の温度での第２段の熱間圧延は、２相域圧延となるため、加工歪が残留するような強圧下の加工とすると靱性が劣化したり、材質の異方性が強くなる。このため、２相域の圧延での圧下率は20％以下に留めるのが好ましい。また、第２段の熱間圧延終了後の冷却は、空冷でよいが、厚鋼板で空冷とすると、冷却速度が遅くなり、VN析出物の好適な分散が得られなくなる懸念がある場合には、0.09℃/s以上１℃/s以下の冷却速度で冷却するのがよい。 Further, when the rolling end temperature is set to 950 ° C. or higher and cooling is performed at a cooling rate of 3 ° C./s or more to the Ar 3 transformation point after the end of rolling, VN in austenite becomes smaller and the ferrite grain size may become larger. In such a case, the first stage of hot rolling at 950 ° C. or higher is performed, and then the hot rolling is temporarily interrupted and cooled to the Ar 3 transformation point at a cooling rate of 3 ° C./s or higher. Then, a second stage of hot rolling may be performed to obtain a predetermined thickness, and then air cooling may be performed at a cooling rate of 0.09 ° C./s or more and 1 ° C./s or less). Here, since the second-stage hot rolling at a temperature equal to or lower than the Ar 3 transformation point is a two-phase region rolling, if the processing is performed under high pressure such that the processing strain remains, the toughness is deteriorated, and the material quality is deteriorated. The anisotropy increases. For this reason, it is preferable that the rolling reduction in the rolling in the two-phase region is kept to 20% or less. In addition, the cooling after the end of the second-stage hot rolling may be air-cooled.However, if air-cooling is performed with a thick steel plate, the cooling rate is reduced, and there is a concern that a suitable dispersion of VN precipitates may not be obtained. It is preferable to cool at a cooling rate of 0.09 ° C./s or more and 1 ° C./s or less.
（実施例１）
表１に示す組成の鋼を転炉で溶製し、連続鋳造法で240 〜310mm のスラブとした。これらスラブを表２に示す熱間圧延条件と、冷却条件で所定板厚の厚鋼板製品とした。これら厚鋼板について、組織観察、VN析出物の析出量および粒径分布、および引張特性、シャルピー衝撃特性、破壊靱性の機械的特性を調査した。
(Example 1)
Steel having the composition shown in Table 1 was melted in a converter, and slabs of 240 to 310 mm were formed by continuous casting. These slabs were made into thick steel products having a predetermined thickness under the hot rolling conditions and cooling conditions shown in Table 2. With respect to these steel plates, microstructure observation, precipitation amount and particle size distribution of VN precipitates, and tensile properties, Charpy impact properties, and mechanical properties of fracture toughness were investigated.
組織観察は、光学顕微鏡および電子顕微鏡により行い、フェライトの面積率、結晶粒度を測定した。結晶粒度の測定は、JIS G 0552の規定に準拠して、フェライトの面積率は画像処理装置により行った。 Microstructure observation was performed with an optical microscope and an electron microscope, and the area ratio and crystal grain size of ferrite were measured. The crystal grain size was measured in accordance with JIS G 0552, and the area ratio of ferrite was measured by an image processing device.
引張試験は、板厚50mm未満の鋼板については1/2t部から、板厚50mm未満の鋼板については1/4t部から、圧延方向にJIS 4 号引張試験片を採取し、変形速度0.03mm/sの静的変形と、変形速度１〜1000mm/sの高速変形における強度および降伏比を求めた。 For the tensile test, a JIS No. 4 tensile test piece was sampled in the rolling direction from a 1 / 2t section for a steel sheet with a thickness of less than 50 mm and from a 1 / 4t section for a steel sheet with a thickness of less than 50 mm, and a deformation rate of 0.03 mm / The strength and the yield ratio in static deformation of s and high-speed deformation at a deformation speed of 1 to 1000 mm / s were determined.
シャルピー衝撃試験は、板厚50mm未満の鋼板については1/2t部から、板厚50mm未満の鋼板については1/4t部から、圧延方向にJIS 4 号衝撃試験片を採取し、０℃における吸収エネルギーvE0 と破面遷移温度vTrsを求めた。 For Charpy impact test, a JIS No. 4 impact test specimen was sampled in the rolling direction from a 1 / 2t section for a steel sheet with a thickness of less than 50mm and from a 1 / 4t section for a steel sheet with a thickness of less than 50mm, and absorbed at 0 ° C. Energy vE 0 and fracture surface transition temperature vTrs were determined.
破壊靱性試験は、板厚50mm未満の鋼板については1/2t部から、板厚50mm未満の鋼板については1/4t部から、圧延方向にWES 1108-1995 の規定に準拠した１ＴＣＴコンパクト破壊靱性試験片を採取し、WES 1108-1995 の規定に準拠して、変形速度0.03mm/sの静的変形と、変形速度１〜1000mm/sの高速変形における破壊靱性値（限界ＣＴＯＤ）を、試験温度０℃で求めた。 Fracture toughness test: 1TCT compact fracture toughness test in accordance with WES 1108-1995 in the rolling direction, starting from 1 / 2t section for steel sheets with thickness less than 50mm and from 1 / 4t section for steel sheets with thickness less than 50mm Samples were taken and the fracture toughness (critical CTOD) at static deformation at a deformation rate of 0.03 mm / s and high-speed deformation at a deformation rate of 1 to 1000 mm / s were determined in accordance with the provisions of WES 1108-1995. Determined at 0 ° C.
これらの結果を表２および３に示す。 The results are shown in Tables 2 and 3.
本発明範囲の厚鋼板（本発明例）は、高速変形においても０℃における限界ＣＴＯＤが0.1mm 以上の優れた破壊靱性を有しており、高速変形における降伏比も80％以下となり、高速変形下でも高い変形能を有していることがわかる。一方、本発明の範囲を外れる比較例は、１〜1000mmの高速変形において０℃における限界ＣＴＯＤが0.1mm 以上を安定して有することはなく、変形速度が高くなると限界ＣＴＯＤが低下し、破壊靱性が劣化している。
（実施例２）
表２に示す鋼板No. ５、No.11 、No.15 、No.17 、No.19 、No.23 、No.25 を用い、入熱25kJ/cm のCO2 溶接により、開先形状をＶ型開先とする多層盛溶接継手を作製した。
Thick steel sheets within the scope of the present invention (examples of the present invention) have excellent fracture toughness having a critical CTOD at 0 ° C of 0.1 mm or more even at high speed deformation, a yield ratio at high speed deformation of 80% or less, and a high speed deformation. It can be seen that it has high deformability even below. On the other hand, the comparative examples out of the range of the present invention show that the critical CTOD at 0 ° C. at a high-speed deformation of 1 to 1000 mm does not stably have a value of 0.1 mm or more, and the higher the deformation speed, the lower the critical CTOD and the lower the fracture toughness. Has deteriorated.
(Example 2)
Using steel plates No. 5, No. 11, No. 15, No. 17, No. 19, No. 23 and No. 25 shown in Table 2, the groove shape was formed by CO 2 welding with a heat input of 25 kJ / cm. A multilayer welded joint having a V-shaped groove was prepared.
これら溶接継手について、シャルピー衝撃特性および破壊靱性を調査した。なお、ノッチ位置は、フュージョンライン（BOND) およびフュージョンラインから１mmの熱影響部（HAZ １mm）とした。 The Charpy impact characteristics and fracture toughness of these welded joints were investigated. The notch position was a fusion line (BOND) and a heat affected zone (HAZ 1 mm) 1 mm from the fusion line.
シャルピー衝撃試験は、板厚50mm未満の鋼板については1/2t部から、板厚50mm以上の鋼板については1/4t部から、圧延方向にJIS 4 号衝撃試験片を採取し、０℃における吸収エネルギーvE0 と破面遷移温度vTrsを求めた。 For Charpy impact test, JIS No. 4 impact test specimens were sampled in the rolling direction from a 1 / 2t section for steel sheets with a thickness of less than 50mm and from a 1 / 4t section for steel sheets with a thickness of 50mm or more, and absorbed at 0 ° C. Energy vE 0 and fracture surface transition temperature vTrs were determined.
破壊靱性試験は、板厚50mm未満の鋼板については1/2t部から、板厚50mm以上の鋼板については1/4t部から、圧延方向にWES 1108-1995 の規定に準拠した１ＴＣＴコンパクト破壊靱性試験片を採取し、WES 1108-1995 の規定に準拠して、変形速度0.03mm/sの静的変形と、変形速度１〜1000mm/sの高速変形における破壊靱性値（限界ＣＴＯＤ）を、試験温度０℃で求めた。 Fracture toughness test: 1TCT compact fracture toughness test in accordance with WES 1108-1995 in the rolling direction, starting from 1 / 2t section for steel sheets with thickness less than 50mm and from 1 / 4t section for steel sheets with thickness of 50mm or more. Samples were taken and the fracture toughness (critical CTOD) at static deformation at a deformation rate of 0.03 mm / s and high-speed deformation at a deformation rate of 1 to 1000 mm / s were determined in accordance with the provisions of WES 1108-1995. Determined at 0 ° C.
それらの結果を表４に示す。 Table 4 shows the results.
本発明例は、ノッチ位置がBONDおよびHAZ １mmともに、静的変形および高速変形における限界ＣＴＯＤが0.1mm 以上の優れた破壊靱性を有している。このように、本発明の鋼板は溶接継手部も優れた高速変形下における破壊靱性を有している。一方、本発明の範囲を外れる比較例は、変形速度が高くなると限界ＣＴＯＤ0.1mm 未満と低下し、破壊靱性が劣化している。 The present invention example has excellent fracture toughness with a critical CTOD of 0.1 mm or more in both static deformation and high-speed deformation at both the notch position of BOND and 1 mm of HAZ. Thus, the steel sheet of the present invention also has excellent fracture toughness under high-speed deformation at the welded joint. On the other hand, in the comparative examples out of the range of the present invention, as the deformation rate increases, the critical CTOD decreases to less than 0.1 mm, and the fracture toughness deteriorates.
Claims (7)
Ｃ：0.04〜0.18％、 Si：0.60％以下、
Mn：0.80〜1.80％、 Ｐ：0.030 ％以下、
Ｓ：0.015 ％以下、 Ｖ：0.04〜0.15％、
Ｎ：0.0050〜0.0150％を含み、さらに、
Al：0.005 〜0.050 ％およびTi：0.005 〜0.050 ％のうちの１種または２種を含有し、かつ下記（１）式で定義されるＣeqが0.34〜0.48％であり、残部Feおよび不可避的不純物からなる組成であることを特徴とする請求項１ないし３のいずれかに記載の構造用鋼材の製造方法。
記
Ｃeq＝Ｃ＋Si/24 ＋Mn/6＋Ｖ/14 ＋Ni/40 ＋Cr/5＋Mo/4 ……（１）
ここで、Ｃ、Si、Mn、Ｖ、Ni、Cr、Mo：各元素の含有量（重量％） The steel material is, in weight%,
C: 0.04 to 0.18%, Si: 0.60% or less,
Mn: 0.80-1.80%, P: 0.030% or less,
S: 0.015% or less, V: 0.04-0.15%,
N: 0.0050 to 0.0150%,
Al: one or two of 0.005 to 0.050% and Ti: 0.005 to 0.050%, and Ceq defined by the following formula (1) is 0.34 to 0.48%, and the balance Fe and unavoidable impurities The method for producing a structural steel material according to any one of claims 1 to 3, wherein the composition comprises:
Note Ceq = C + Si / 24 + Mn / 6 + V / 14 + Ni / 40 + Cr / 5 + Mo / 4 ... (1)
Here, C, Si, Mn, V, Ni, Cr, Mo: Content of each element (% by weight)
Cu：0.05〜0.60％、Ni：0.05〜0.60％、Cr：0.05〜0.50％、Mo：0.02〜0.20％のうちから選ばれた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４に記載の構造用鋼材の製造方法。 Wherein the composition further comprises
5. The composition according to claim 4, wherein one or more selected from Cu: 0.05 to 0.60%, Ni: 0.05 to 0.60%, Cr: 0.05 to 0.50%, and Mo: 0.02 to 0.20%. 3. The method for producing a structural steel material according to item 1.
Nb：0.003 〜0.030 ％を含有することを特徴とする請求項４または５に記載の構造用鋼材の製造方法。 Wherein the composition further comprises
The method for producing a structural steel material according to claim 4 or 5, wherein Nb is contained in an amount of 0.003 to 0.030%.
Ｂ：0.0002〜0.0020％、REM ：0.0010〜0.0200％、Ca：0.0010〜0.010 ％のうちから選ばれた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４ないし６のいずれかに記載の構造用鋼材の製造方法。 Wherein the composition further comprises
B: 0.0002 to 0.0020%, REM: 0.0010 to 0.0200%, Ca: 0.0010 to 0.010%, one or more selected from the group consisting of: Method for manufacturing structural steel materials.
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