JP2004181530A - Welded joint having excellent fatigue strength characteristic - Google Patents
Welded joint having excellent fatigue strength characteristic Download PDFInfo
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- JP2004181530A JP2004181530A JP2003386203A JP2003386203A JP2004181530A JP 2004181530 A JP2004181530 A JP 2004181530A JP 2003386203 A JP2003386203 A JP 2003386203A JP 2003386203 A JP2003386203 A JP 2003386203A JP 2004181530 A JP2004181530 A JP 2004181530A
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Abstract
Description
本発明は、疲労強度特性に優れた溶接継手に関し、詳しくは疲労が問題となる鋼構造物もしくは疲労設計が施される鋼構造物に用いて好適な溶接継手に関する。溶接される鋼材としては、例えば車両および鉄道の通行による繰り返し荷重を受ける橋梁用鋼材などが挙げられる。鋼材の形態としては特に問わないが、構造部材として用いられ、疲労強度特性が要求される厚鋼板および形鋼が好ましい。 The present invention relates to a welded joint having excellent fatigue strength characteristics, and more particularly to a welded joint suitable for use in a steel structure in which fatigue is a problem or a steel structure to be subjected to fatigue design. Examples of the steel material to be welded include a steel material for a bridge that is subjected to a repeated load due to traffic of a vehicle and a railway. The form of the steel material is not particularly limited, but a thick steel plate and a shaped steel used as a structural member and required to have fatigue strength characteristics are preferable.
橋梁などの鋼構造物の設計においては、大型化とそれに伴う軽量化の目的から使用鋼材の高強度化が求められている。しかし疲労強度は、鋼材については引張強さの増加と共に上昇するが、溶接継手では引張強さが増加しても向上しない。このため、溶接鋼構造物では、高強度鋼材を用いても設計強度を上げることが困難になるという問題があった。この高強度鋼材の溶接継手で疲労強度が向上しない原因としては、引張残留応力が引張強さに比例して大きくなることが挙げられている。 In the design of steel structures such as bridges, it is required to increase the strength of steel materials used for the purpose of increasing the size and accompanying weight reduction. However, the fatigue strength of steel materials increases with an increase in tensile strength, but does not improve with an increase in tensile strength of a welded joint. For this reason, in a welded steel structure, there was a problem that it was difficult to increase the design strength even when using a high-strength steel material. The reason why the fatigue strength is not improved by this high-strength steel welded joint is that the residual tensile stress increases in proportion to the tensile strength.
引張残留応力を低減させる方法として、溶接後の化粧溶接により引張残留応力を低減させる手法（特許文献１参照）、溶接後塑性変形により引張残留応力を低減させる手法（特許文献２参照）、ハンマーピーニングにより圧縮残留応力を導入する手法（特許文献３参照）、溶接金属の変態膨張を利用して圧縮残留応力を導入する手法（特許文献４参照）などが開示されている。 As a method of reducing the residual tensile stress, a method of reducing the residual tensile stress by decorative welding after welding (see Patent Document 1), a method of reducing the residual tensile stress by plastic deformation after welding (see Patent Document 2), hammer peening (See Patent Document 3), a method of introducing compressive residual stress using transformation expansion of a weld metal (see Patent Document 4), and the like.
一方、溶接継手の疲労強度は応力集中を緩和することによっても向上することが知られている。溶接ビードを研削することにより応力集中を緩和する手法（特許文献５参照）、溶接金属の成分調整により溶接止端部半径と接触角度を大きくして応力集中を緩和する手法（特許文献６参照）が開示されている。
しかし、特許文献１、２、３、５に開示されている手法では、溶接後の各工程において大きな労力を要するという問題がある。また、特許文献４に開示されている手法では、高価な合金元素を多く添加した溶接材料を用いるため経済的な面で問題がある。また、特許文献６に開示されている手法では、溶接される鋼材の組成により溶接金属の組成が変化し、鋼種によっては良好な止端形状が得られない可能性がある。
However, the techniques disclosed in
前記従来技術の諸問題に鑑み、本発明は、溶接後に何らの処置も施すことなく、経済的に、かつ鋼種によらず適用可能な、疲労強度特性に優れた溶接継手を提供することを目的とする。 In view of the above-mentioned problems of the prior art, an object of the present invention is to provide a welded joint having excellent fatigue strength characteristics that can be applied economically and without depending on the type of steel without performing any treatment after welding. And
本発明者らは溶接継手の疲労強度特性について研究し、その結果、次の点を明らかにした。なお、以下で「鋼材」には「溶接金属」を含まない。 The present inventors have studied the fatigue strength characteristics of a welded joint, and as a result, have clarified the following points. In the following, “steel material” does not include “weld metal”.
(1)鋼材の厚さに対する溶接ビード幅の比率が0.2 以下になるとビード止端部の応力集中が小さくなり、疲労強度特性が向上する。 (1) When the ratio of the width of the weld bead to the thickness of the steel material is 0.2 or less, the stress concentration at the bead toe becomes small, and the fatigue strength characteristics are improved.
(2)上記(1)の傾向は、鋼材の厚さに対する溶接ビード高さの比率が0.3 以下である場合に顕著になる。 (2) The above tendency (1) becomes remarkable when the ratio of the weld bead height to the thickness of the steel material is 0.3 or less.
(3)上記(1)の場合で、かつ溶接ビード近傍の鋼材表面粗さがJIS B 0601:2000のRa6.3μｍ以下であると、さらに疲労特性が向上する。ここで、溶接ビード近傍とは、溶接線中央を中心とした鋼材の厚さ×0.7以下の幅の領域で、かつ溶接ビードを含まない領域をいう。 (3) In the case of (1) above, if the surface roughness of the steel material near the weld bead is 6.3 μm or less in JIS B 0601: 2000, the fatigue characteristics are further improved. Here, the vicinity of the weld bead refers to a region having a width of not more than 0.7 times the thickness of the steel material centered on the center of the weld line and not including the weld bead.
(4)上記(1)〜(3)の場合で、かつ溶接金属と鋼材の強度比率が1.3 以下であると、さらに疲労強度特性が向上する。 (4) In the above cases (1) to (3) and when the strength ratio between the weld metal and the steel material is 1.3 or less, the fatigue strength characteristics are further improved.
(5)上記(1)〜(4)の場合で、鋼材が高強度（降伏強さ≧685MPa）で、かつ溶接金属と鋼材の降伏強さ比率が1.0以下であると、さらに疲労強度特性が向上する。 (5) In the above cases (1) to (4), if the steel material has a high strength (yield strength ≧ 685 MPa) and the yield strength ratio between the weld metal and the steel material is 1.0 or less, the fatigue strength characteristics are further improved. improves.
(6)上記(1)〜(5)の場合で、かつ鋼材が低炭素ベイナイト組織であると、さらに疲労強度特性が向上する。 (6) In the above cases (1) to (5) and when the steel material has a low carbon bainite structure, the fatigue strength characteristics are further improved.
本発明は、これらの知見に基づき、さらに検討を重ねてなされたものであり、その要旨は以下のとおりである。 The present invention has been further studied based on these findings, and the gist is as follows.
〔１〕 鋼材の厚さに対する溶接ビード幅の比率が0.2 以下であり、かつ前記鋼材の厚さに対する溶接ビード高さの比率が0.3 以下であることを特徴とする疲労強度特性に優れた溶接継手。 [1] A welded joint excellent in fatigue strength characteristics, wherein a ratio of a weld bead width to a thickness of a steel material is 0.2 or less, and a ratio of a weld bead height to a thickness of the steel material is 0.3 or less. .
〔２〕 前記鋼材の表面粗さが前記溶接ビード近傍でJIS B 0601:2000のRa6.3μｍ以下であることを特徴とする〔１〕記載の疲労強度特性に優れた溶接継手。 [2] The welded joint having excellent fatigue strength characteristics according to [1], wherein the steel material has a surface roughness of 6.3 μm or less in JIS B 0601: 2000 in the vicinity of the weld bead.
〔３〕 前記鋼材の降伏強さに対する溶接金属の降伏強さの比率が1.3 以下であることを特徴とする〔１〕または〔２〕に記載の疲労強度特性に優れた溶接継手。 [3] The welded joint according to [1] or [2], wherein the ratio of the yield strength of the weld metal to the yield strength of the steel material is 1.3 or less.
〔４〕 鋼材の降伏強さに対する溶接金属の降伏強さの比率が1.0以下で、かつ鋼材の降伏強さが685MPa以上であることを特徴とする〔１〕または〔２〕に記載の疲労強度特性に優れた溶接継手。 [4] The fatigue strength according to [1] or [2], wherein the ratio of the yield strength of the weld metal to the yield strength of the steel material is 1.0 or less, and the yield strength of the steel material is 685 MPa or more. Welded joint with excellent properties.
〔５〕 前記鋼材の組成が質量％でＣ：0.03％以下、Si：0.5 ％以下、Mn：1.0 〜2.0 ％、Ｂ：0.0003〜0.0050％、Ｎ：0.0050％以下を含有し、かつTi：0.005 〜0.20％、Nb：0.005 〜0.20％のうちから選ばれた１種又は２種を含有し、残部Fe及び不可避的不純物からなり、前記鋼材の組織がべイナイト単相であることを特徴とする〔１〕〜〔４〕のいずれかに記載の疲労強度特性に優れた溶接継手。 [5] The steel material contains, by mass%, C: 0.03% or less, Si: 0.5% or less, Mn: 1.0 to 2.0%, B: 0.0003 to 0.0050%, N: 0.0050% or less, and Ti: 0.005%. 0.20.20%, Nb: 0.00500.20%, containing one or two selected from the group consisting of the balance of Fe and unavoidable impurities, wherein the structure of the steel material is a single phase of bainite. A welded joint having excellent fatigue strength characteristics according to any one of [1] to [4].
〔６〕 前記鋼材の組成がさらに質量％でCu：0.7 〜2.0 ％、Ｖ：0.005 〜0.2 ％、Ni：2.0 ％以下、Cr：0.5 ％以下、Mo：0.5 ％以下、Ｗ：0.5 ％以下、Zr：0.5 ％以下のうちから選ばれた１種又は２種以上を含有することを特徴とする〔５〕記載の疲労強度特性に優れた溶接継手。 [6] The composition of the steel material is further by mass: Cu: 0.7 to 2.0%, V: 0.005 to 0.2%, Ni: 2.0% or less, Cr: 0.5% or less, Mo: 0.5% or less, W: 0.5% or less, Zr: A welded joint excellent in fatigue strength characteristics according to [5], characterized by containing one or more selected from 0.5% or less.
本発明によれば、疲労が問題となる溶接鋼構造物もしくは疲労設計が施される溶接鋼構造物に使用される鋼材の溶接継手において、溶接後に何らの処置も行わなくても２×10６回疲労強度が190MPa以上となる溶接継手を製造できるという産業上有益な効果を奏する。 According to the present invention, in a welded joint of a steel material used for a welded steel structure in which fatigue is a problem or a welded steel structure to be subjected to fatigue design, 2 × 10 6 can be used without any treatment after welding. This has an industrially beneficial effect that a welded joint having a cyclic fatigue strength of 190 MPa or more can be manufactured.
本発明でいう疲労強度特性に優れた溶接継手とは、応力比０の繰り返し負荷条件において、疲労特性が、日本鋼構造協会の疲労設計指針における強度等級Ａ以上（２×10６回疲労強度が190MPa以上）の特性を有する溶接継手を意味する。 A welded joint having excellent fatigue strength characteristics as referred to in the present invention means that, under repeated loading conditions with a stress ratio of 0, the fatigue characteristics have a strength class A or higher (2 × 10 6 times fatigue strength) in the fatigue design guideline of the Japan Steel Structure Association. 190MPa or more).
本発明は、鋼材の厚さに対する溶接ビード幅の比率を0.2 以下とし、かつ鋼材の厚さに対する溶接ビード高さの比率を0.3 以下とすることにより、溶接継手の応力集中を抑制し、何らの溶接後処理をも施すことなく、疲労強度特性を向上させるものである。なお、図１に溶接ビード幅ｗおよび溶接ビード高さｈの定義を示す。ただし、ｔは鋼材の厚さを示す。 The present invention suppresses the stress concentration of the welded joint by controlling the ratio of the weld bead width to the thickness of the steel material to 0.2 or less and the ratio of the weld bead height to the thickness of the steel material to 0.3 or less. It is intended to improve the fatigue strength characteristics without performing post-welding treatment. FIG. 1 shows the definitions of the weld bead width w and the weld bead height h. Here, t indicates the thickness of the steel material.
以下に、本発明要件の限定理由を説明する。
（鋼材の厚さに対する溶接ビード幅の比率ｗ/ｔが0.2 以下）
鋼材の厚さに対する溶接ビード幅の比率ｗ/ｔが0.5 未満の領域では溶接ビード幅が狭くなると応力集中が減少する。この応力集中の減少は、ｗ/ｔが0.2 以下の条件で顕著になり、疲労特性向上に有効に作用する。よって、鋼材の厚さに対する溶接ビード幅の比率ｗ/ｔを0.2 以下とした。
The reasons for limiting the requirements of the present invention will be described below.
(Ratio w / t of weld bead width to steel thickness is 0.2 or less)
In a region where the ratio w / t of the weld bead width to the thickness of the steel material is less than 0.5, the stress concentration decreases as the weld bead width decreases. This reduction in stress concentration becomes remarkable under the condition that w / t is 0.2 or less, and effectively acts to improve fatigue characteristics. Therefore, the ratio w / t of the weld bead width to the thickness of the steel material is set to 0.2 or less.
（鋼材の厚さに対する溶接ビード高さの比率ｈ/ｔが0.3 以下）
鋼材の厚さに対する溶接ビード高さの比率ｈ/ｔは、鋼材の厚さに対する溶接ビード幅の比率ｗ/ｔが0.1 以下であれば応力集中に影響を及ぼさないが、ｗ/ｔが0.1 超の場合には、ｈ/ｔが0.3 を超えると応力集中が増加する。よって、鋼材の厚さに対する溶接ビード高さの比率ｈ/ｔを0.3 以下とした。
(Ratio h / t of weld bead height to steel thickness is 0.3 or less)
The ratio h / t of the weld bead height to the thickness of the steel material does not affect the stress concentration if the ratio w / t of the weld bead width to the thickness of the steel material is 0.1 or less, but w / t exceeds 0.1. In the case of (1), when h / t exceeds 0.3, the stress concentration increases. Therefore, the ratio h / t of the weld bead height to the thickness of the steel material is set to 0.3 or less.
（溶接ビード近傍の鋼材表面粗さがRa6.3μｍ以下）
溶接ビード近傍（溶接線中央を中心とした鋼材の厚さ×0.7以下の幅の領域で、かつ溶接ビードを含まない領域）の鋼材表面粗さをRa6.3μｍ以下とすることにより、上記ビード形状が満足されている場合（ｗ/ｔ≦0.2 、かつｈ/ｔ≦0.3 の場合）には、応力集中が更に緩和され、疲労強度特性に有利に働くため、溶接ビード近傍の鋼材表面粗さをRa6.3μｍ以下とすることを好適要件とした。ここで、表面粗さがRa6.3μｍ以下である領域は鋼材表面全域でなくてもよく、溶接線中央を中心とした鋼材の厚さ×0.7以下の幅の領域で、かつ溶接ビードを含まない領域が、機械加工などで所定の粗さ以下になっていればよい。なお、Raの定義はJIS B 0601：2000による。また「溶接線」の定義はJIS Z 3001:1999 による。
(Steel surface roughness near the weld bead is Ra6.3μm or less)
By setting the surface roughness of the steel material in the vicinity of the weld bead (in the area of the thickness of the steel material centered on the center of the welding line x 0.7 or less and not including the weld bead) to Ra6.3 μm or less, the above bead shape Is satisfied (when w / t ≦ 0.2 and h / t ≦ 0.3), the stress concentration is further relaxed and the fatigue strength characteristics are favored, so that the steel surface roughness near the weld bead is reduced. Ra is preferably set to 6.3 μm or less. Here, the region where the surface roughness is Ra6.3 μm or less may not be the entire surface of the steel material, and is a region having a width of 0.7 mm or less of the thickness of the steel material centered on the center of the welding line and does not include a weld bead. It is sufficient that the region has a predetermined roughness or less by machining or the like. The definition of Ra is based on JIS B 0601: 2000. The definition of "welding line" is based on JIS Z 3001: 1999.
（鋼材の降伏強さに対する溶接金属の降伏強さの比率が1.3 以下）
鋼材の降伏強さに対する溶接金属の降伏強さの比率を1.3 以下にすることにより、上記溶接ビード形状が満足されている場合（ｗ／ｔ≦0.2 、かつｈ／ｔ≦0.3 の場合）には、降伏強さの差による溶接ビード止端部への応力集中が抑制されるため、鋼材の降伏強さに対する溶接金属の降伏強さの比率が1.3 以下であることを好適要件とした。
(The ratio of the yield strength of the weld metal to the yield strength of the steel material is 1.3 or less)
By making the ratio of the yield strength of the weld metal to the yield strength of the steel material 1.3 or less, when the above-mentioned weld bead shape is satisfied (w / t ≦ 0.2 and h / t ≦ 0.3), Since the concentration of stress at the weld bead toe due to the difference in yield strength is suppressed, the ratio of the yield strength of the weld metal to the yield strength of the steel material is preferably 1.3 or less.
（鋼材の降伏強さに対する溶接金属の降伏強さの比率が1.0以下で、かつ鋼材の降伏強さが685MPa以上）
鋼材の降伏強さに対する溶接金属の降伏強さの比率を1.0以下とすることにより、前記溶接ビード形状を満足する溶接継手の場合（ｗ/ｔ≦0.2 、かつｈ/ｔ≦0.3 の場合）、引張残留応力の低減に伴う疲労強度向上が見込める。ただし、この効果は、鋼材の降伏強さが685MPa以上である場合に大きく発現する。
(The ratio of the yield strength of the weld metal to the yield strength of the steel material is 1.0 or less, and the yield strength of the steel material is 685 MPa or more)
By making the ratio of the yield strength of the weld metal to the yield strength of the steel material 1.0 or less, in the case of a welded joint that satisfies the weld bead shape (when w / t ≦ 0.2 and h / t ≦ 0.3), Fatigue strength improvement can be expected due to reduction of tensile residual stress. However, this effect is significantly exhibited when the yield strength of the steel material is 685 MPa or more.
（鋼材の組織がべイナイト単相）
鋼材がベイナイト単相組織の場合、フェライト＋パーライト組織の場合と比べて組織の均質性が高いために溶接ビード止端部への応力集中が抑制されるため、鋼材の組織がべイナイト単相であることを好適要件とした。
(Steel structure is bainite single phase)
When the steel material has a bainite single-phase structure, the concentration of stress on the weld bead toe is suppressed because the structure is more homogeneous than in the case of the ferrite + pearlite structure. There was a favorable requirement.
次に、鋼材の好適な組成について説明する。組成の成分含有量の単位は質量％とし、％と略記する。 Next, a preferred composition of the steel material will be described. The unit of the component content of the composition is mass% and is abbreviated as%.
（Ｃ：0.03％以下）
Ｃは、冷却速度に依存せずにベイナイト単相組織とするために0.03％以下とする。すなわち、0.03％より多く含有すると、組織に炭化物を含むパーライトが出現し始めるため、材質の均質性が損なわれ、溶接金属と鋼材の降伏強さ比率が1.3 超となり、疲労強度が向上しにくくなる。また、Ｃの増大はマルテンサイトを局部的に生成しやすくするほか、硬さが上昇して靭性の劣化を招くことになる。従って、Ｃは0.03％以下とする。なお、Ｃ含有量を低くすることによって、本発明の効果が減少することはないが、実用的には、製鋼上のコストやNb、Ｖ等による析出強化効果を利用することを勘案すると、Ｃ含有量は0.005 ％以上とすることが好ましい。
(C: 0.03% or less)
C is set to 0.03% or less in order to form a bainite single phase structure without depending on the cooling rate. In other words, if the content exceeds 0.03%, pearlite containing carbides starts to appear in the structure, which impairs the homogeneity of the material, the yield strength ratio between the weld metal and the steel material exceeds 1.3, and it is difficult to improve the fatigue strength. . In addition, an increase in C makes it easier to locally generate martensite, and also increases hardness to cause deterioration in toughness. Therefore, C is set to 0.03% or less. Although the effect of the present invention is not reduced by lowering the C content, practically, considering the cost of steelmaking and the use of precipitation strengthening effect by Nb, V, etc., The content is preferably at least 0.005%.
（Si：0.5 ％以下）
Siは脱酸のため混入するが、多すぎるとベイナイト組織の生成を抑制すると共に、靭性も劣化させるので0.5 ％以下とする。なお、脱酸および強度確保のために0.02％以上含有することが好ましい。
(Si: 0.5% or less)
Si is mixed in for deoxidation, but if it is too much, the formation of bainite structure is suppressed and the toughness is deteriorated. In addition, it is preferable to contain 0.02% or more for deoxidation and ensuring strength.
（Mn：1.0 〜2.0 ％）
Mnは、ベイナイト単相組織とするために1.0 ％以上が好ましく、一方、2.0 ％を超えると、硬さが上昇して靭性が劣化するので、1.0 〜2.0 ％とする。
(Mn: 1.0-2.0%)
Mn is preferably 1.0% or more in order to form a bainite single phase structure. On the other hand, if it exceeds 2.0%, the hardness increases and the toughness deteriorates.
（Ｂ：0.0003〜0.0050％）
Ｂは広い冷却速度範囲に亘ってオーステナイト粒界からのフェライト生成を抑制するため、安定してベイナイト組織を得るのに不可欠の成分である。その効果はＮが十分に固定された場合に0.0003％以上で現れ、一方、0.0050％を超える含有では効果が飽和してコスト上不利になる。よって0.0003〜0.0050％とした。
(B: 0.0003-0.0050%)
B is a component indispensable for obtaining a bainite structure stably because it suppresses ferrite generation from austenite grain boundaries over a wide cooling rate range. The effect appears at 0.0003% or more when N is sufficiently fixed. On the other hand, when the content exceeds 0.0050%, the effect is saturated and the cost is disadvantageous. Therefore, it was made 0.0003 to 0.0050%.
（Ｎ：0.0050％以下）
Ｎは、少ないほどＢによる効果がよく現れ、またＨＡＺ（Heat Affected Zone：溶接熱影響部）靭性の面からも少ないことが望ましい。また、ＨＡＺでは固定されたＮが再固溶して靭性劣化の原因となる。これらのことから、Ｎは0.0050％以下とした。
(N: 0.0050% or less)
It is desirable that the smaller N is, the better the effect of B is and the smaller the N is in terms of HAZ (Heat Affected Zone: heat affected zone) toughness. Further, in the HAZ, the fixed N re-dissolves to cause toughness degradation. For these reasons, N is set to 0.0050% or less.
以上の元素はそれぞれ単独で含有するのが好ましい。さらに必要に応じて次のTi、Nbのうち１種または２種を含有してもよい。 It is preferable that each of the above elements is contained alone. Further, if necessary, one or two of the following Ti and Nb may be contained.
（Ti：0.005 〜0.20％）
Tiは、炭化物や窒化物の析出物を形成することにより、鋼材製造時のオーステナイト粒の成長を抑制して細粒化に寄与すると共に、ＨＡＺの結晶粒粗大化も抑制しＨＡＺの靭性を向上する効果がある。さらに、Ｎを固定して前記したＢによる効果を助長する。また、Tiそのものは固溶してべイナイト変態を促進する。これらの効果を得るには、0.005 ％以上の含有が好ましい。一方、過度の含有は、靭性を劣化するため、0.20％以下とする。
(Ti: 0.005 to 0.20%)
Ti suppresses the growth of austenite grains during steel production by forming precipitates of carbides and nitrides and contributes to grain refinement, and also suppresses HAZ crystal grain coarsening and improves HAZ toughness. Has the effect of doing Further, N is fixed to promote the effect of B described above. Further, Ti itself forms a solid solution to promote bainite transformation. In order to obtain these effects, the content is preferably 0.005% or more. On the other hand, excessive content degrades toughness, so the content is made 0.20% or less.
（Nb：0.005 〜0.20％）
Nbは、べイナイト変態を促進すると共に、析出強化および靭性の向上にも有効である。これらの効果を得るためには、0.005 ％以上の含有が好ましいが、0.20％を超えると，焼入れ組織が針状化して靭性が劣化する傾向にあるため、0.20％以下とする。
(Nb: 0.005 to 0.20%)
Nb promotes bainite transformation and is also effective for strengthening precipitation and improving toughness. In order to obtain these effects, the content is preferably 0.005% or more. However, if it exceeds 0.20%, the quenched structure tends to become acicular and the toughness tends to be deteriorated.
また、さらに、必要に応じて次のＶ、Cu、Ni、Cr、Mo、Ｗ、Zrのうち１種または２種以上を含有してもよい。 Further, if necessary, one or more of the following V, Cu, Ni, Cr, Mo, W, and Zr may be contained.
（Cu：0.7 〜2.0 ％）
Cuは、析出強化効果が利用できる成分である。析出強化を用いるためには、0.7 ％以上の含有が好ましいが、2.0 ％を超えて含有すると、析出強化が過多となり靭性が急激に劣化する。このため、0.7 〜2.0 ％とする。
(Cu: 0.7-2.0%)
Cu is a component that can utilize the precipitation strengthening effect. In order to use precipitation strengthening, the content is preferably 0.7% or more, but if it exceeds 2.0%, the precipitation strengthening becomes excessive and the toughness rapidly deteriorates. Therefore, it is set to 0.7 to 2.0%.
（Ｖ：0.005 〜0.2 ％）
Ｖは固溶と析出強化効果が利用できる成分であるが、この効果を得るためには、0.005 ％以上の含有が好ましい。一方、0.2 ％を超える含有は、べイナイト組織の生成を抑制するため、0.2 ％以下とする。
(V: 0.005 to 0.2%)
V is a component that can utilize the effects of solid solution and precipitation strengthening, but in order to obtain this effect, the content is preferably 0.005% or more. On the other hand, if the content exceeds 0.2%, the formation of a bainite structure is suppressed, so the content is made 0.2% or less.
（Ni：2.0 ％以下）
Niは、強度および靭性を向上させ、またCuを含有した場合には圧延時のCu割れを防止するのに有効であるが、高価である上、過剰に含有してもその効果が飽和するため、2.0 ％以下とすることが好ましい。なお、0.05％未満では上記効果が不十分であるため、0.05％以上とすることが好ましい。
(Ni: 2.0% or less)
Ni is effective in improving strength and toughness, and when Cu is contained, is effective in preventing Cu cracking during rolling, but is expensive, and its effect is saturated even if contained excessively. , 2.0% or less. Note that if the content is less than 0.05%, the above effect is insufficient. Therefore, the content is preferably set to 0.05% or more.
（Cr：0.5 ％以下）
Crは強度を向上させる効果があるが、0.5 ％を超えると溶接部靭性が劣化するため、0.5 ％以下とすることが好ましい。なお、0.05％未満では上記効果が不十分であるため、0.05％以上とすることが好ましい。
(Cr: 0.5% or less)
Cr has an effect of improving the strength, but if it exceeds 0.5%, the toughness of the welded portion is deteriorated. Note that if the content is less than 0.05%, the above effect is insufficient. Therefore, the content is preferably set to 0.05% or more.
（Mo：0.5 ％以下）
Moは、常温および高温での強度を向上させる効果があるが、0.5 ％を超えると、溶接の作業性が劣化するため、0.5 ％以下とすることが好ましい。なお。0.05％未満では上記効果が不十分であるため、0.05％以上とすることが好ましい。
(Mo: 0.5% or less)
Mo has the effect of improving the strength at room temperature and high temperature, but if it exceeds 0.5%, the workability of welding is deteriorated. Therefore, it is preferable that Mo be 0.5% or less. In addition. If the content is less than 0.05%, the above effect is insufficient, so that the content is preferably 0.05% or more.
（Ｗ：0.5 ％以下）
Ｗは、高温での強度を向上させする効果があるが，高価である上、0.5 ％を超えると、靭性が劣化するため、0.5 ％以下とすることが好ましい。なお、0.05％未満では上記効果が不十分であるため、0.05％以上とすることが好ましい。
(W: 0.5% or less)
W has the effect of improving the strength at high temperatures, but is expensive, and if it exceeds 0.5%, the toughness deteriorates. Therefore, it is preferable that W is 0.5% or less. Note that if the content is less than 0.05%, the above effect is insufficient. Therefore, the content is preferably set to 0.05% or more.
（Zr：0.5 ％以下）
Zrは、強度を向上させる効果に加えて、亜鉛メッキを施した際の割れを防止する効果があるが、0.5 ％を超えると溶接継手の靭性が劣化するため、0.5 ％以下とすることが好ましい。なお、0.05％未満では上記効果が不十分であるため、0.05％以上とすることが好ましい。
(Zr: 0.5% or less)
Zr has the effect of preventing cracking when galvanized, in addition to the effect of improving the strength. However, if it exceeds 0.5%, the toughness of the welded joint deteriorates, so Zr is preferably made 0.5% or less. . Note that if the content is less than 0.05%, the above effect is insufficient. Therefore, the content is preferably set to 0.05% or more.
本発明の溶接継手を製造する方法について述べると、鋼材は、通常の製鋼法で溶製し凝固させた鋼素材を厚板圧延法あるいは形鋼圧延法等により圧延成形して製造することができる。この鋼材から本発明の溶接継手を製造する溶接法は特に限定されるものではなく、得られる溶接ビード形状が本発明要件を満たすような溶接条件を設定しうるものであれば、ＳＡＷ（Submerged Arc Welding：サブマージドアーク溶接）、ＣＯ２（ガスシールド）溶接、レーザ溶接、電子ビーム溶接等々の何れを用いてもよいが、なかでも狭開先での溶接施工が可能で溶接ビードの幅や高さを比較的小さいものとなしうるレーザ溶接や電子ビーム溶接のような高エネルギービーム溶接を採用するほうが好ましい。 Describing the method for manufacturing the welded joint of the present invention, steel material can be manufactured by rolling and forming a steel material melted and solidified by a normal steel making method by a thick plate rolling method or a shape steel rolling method. . The welding method for producing the welded joint of the present invention from this steel material is not particularly limited, and a SAW (Submerged Arc) can be used as long as the obtained weld bead shape can set welding conditions that satisfy the requirements of the present invention. Welding: submerged arc welding), CO 2 (gas shield) welding, laser welding, electron beam welding, etc. may be used, but welding can be performed with a narrow groove, and the width and height of the weld bead can be used. It is more preferable to employ high energy beam welding such as laser welding or electron beam welding which can make the size relatively small.
鋼材として、表１に示す組成および機械的性質を有する鋼板を用いて、表２に示す溶接法にて同表に示す溶接ビード形状を有する突合せ溶接継手を作製した。これら溶接継手からJIS Z 3103-1987 に準拠した疲れ試験片を採取し、疲労試験に供した。疲労試験の応力比（＝最低荷重／最高荷重）は０とし、200 万回疲労強度を求めた。なお、降伏強さ、引張強さは、図２に示す形状の引張試験片３を用い、JIS Z 2241に則って測定した。なお、試験片は図１に試験片３として示す位置から採取した。すなわち、試験片３全体が溶接金属２からなるように、また、引張方向が紙面に垂直な方向になるように採取した。鋼板表面粗さは、触針式表面粗さ測定器を用いて測定した。測定にあたり、カットオフ値：2.5mm、評価長さ：12.5mmとし、触針の形状は、先端の半径２μｍ、円すいのテーパ角は６０度とした。
Using a steel plate having the composition and mechanical properties shown in Table 1 as a steel material, a butt welded joint having a weld bead shape shown in the table was produced by a welding method shown in Table 2. Fatigue test specimens based on JIS Z 3103-1987 were collected from these welded joints and subjected to a fatigue test. The stress ratio (= minimum load / maximum load) in the fatigue test was set to 0, and the fatigue strength was calculated 2 million times. In addition, the yield strength and the tensile strength were measured according to JIS Z 2241 using a
表２に各試験の結果を示す。本発明の範囲内である発明例の溶接継手は、日本鋼構造協会の疲労設計指針における強度等級Ａ以上（２×10６回疲労強度が190MPa以上）の良好な特性を有している。一方、本発明を外れる比較例は、同設計指針におけるＤ等級以上のレベル（２×10６回疲労強度が100MPa以上）にとどまっており、Ａ等級には達していない。 Table 2 shows the results of each test. The welded joints of the invention examples within the scope of the present invention have good properties of strength class A or more (2 × 10 6 fatigue strength of 190 MPa or more) according to the fatigue design guidelines of the Japan Steel Structure Association. On the other hand, the comparative examples deviating from the present invention are at the level of D class or higher (2 × 10 6 fatigue strength is 100 MPa or higher) in the design guideline, and do not reach the A class.
本発明は、疲労が問題となる溶接鋼構造物もしくは疲労設計が施される溶接鋼構造物のすべてに利用することができる。 INDUSTRIAL APPLICATION This invention can be utilized for all the welded steel structures in which fatigue becomes a problem, or the welded steel structures to which fatigue design is performed.
１ 溶接継手
２ 溶接金属
３ 引張試験片
ｔ 鋼材の厚さ（または鋼板板厚）
ｗ 溶接ビード幅
ｈ 溶接ビード高さ
DESCRIPTION OF SYMBOLS 1 Weld joint 2
w Weld bead width h Weld bead height
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Cited By (4)
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| JP2007239049A (en) * | 2006-03-09 | 2007-09-20 | Kobe Steel Ltd | High yield ratio high tensile strength steel plate having excellent fatigue crack propagation suppression and toughness in weld heat affected zone |
| JP2007239042A (en) * | 2006-03-09 | 2007-09-20 | Kobe Steel Ltd | High yield ratio high tensile strength steel sheet having excellent fatigue crack propagation suppression and toughness in weld heat affected zone |
| US8653403B2 (en) | 2009-12-04 | 2014-02-18 | Nippon Steel & Sumitomo Metal Corporation | Butt-welded joint and method for manufacturing same |
| US8992109B2 (en) | 2009-12-04 | 2015-03-31 | Nippon Steel & Sumitomo Metal Corporation | Butt-welded joint of welded structure, and method for manufacturing the same |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| JP2007239049A (en) * | 2006-03-09 | 2007-09-20 | Kobe Steel Ltd | High yield ratio high tensile strength steel plate having excellent fatigue crack propagation suppression and toughness in weld heat affected zone |
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| US8653403B2 (en) | 2009-12-04 | 2014-02-18 | Nippon Steel & Sumitomo Metal Corporation | Butt-welded joint and method for manufacturing same |
| US8992109B2 (en) | 2009-12-04 | 2015-03-31 | Nippon Steel & Sumitomo Metal Corporation | Butt-welded joint of welded structure, and method for manufacturing the same |
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| JP4513311B2 (en) | 2010-07-28 |
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