JPH0790486A - Steel for structural purpose excellent in fatigue property of welded joint - Google Patents
Steel for structural purpose excellent in fatigue property of welded jointInfo
- Publication number
- JPH0790486A JPH0790486A JP24091593A JP24091593A JPH0790486A JP H0790486 A JPH0790486 A JP H0790486A JP 24091593 A JP24091593 A JP 24091593A JP 24091593 A JP24091593 A JP 24091593A JP H0790486 A JPH0790486 A JP H0790486A
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- Prior art keywords
- steel
- welding
- strength
- joint
- fatigue strength
- Prior art date
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- Butt Welding And Welding Of Specific Article (AREA)
- Arc Welding In General (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は溶接継手疲労特性の優れ
た鋼材にかかわるものであり、さらに詳しくは溶接時に
発生する残留応力を抑えた、溶接継手の疲労強度を高め
た構造用鋼に関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel material having excellent fatigue properties of welded joints, and more specifically to a structural steel with suppressed residual stress generated during welding and improved fatigue strength of welded joints. Is.
【０００２】[0002]
【従来の技術】一般に構造用鋼板母材の疲労強度は母材
強度の増加につれて増加するが、溶接された継手の疲労
強度（以下、継手疲労強度という）は母材強度を上昇さ
せても向上しないことが通説となっていた。従って構造
用高張力鋼の継手疲労強度は、低強度鋼のそれとほぼ同
じであり、疲労破壊が問題となる構造物では、高張力鋼
を用いても設計強度を上げることができず、止端処理と
呼ばれる改善処理により、高張力鋼の継手疲労強度を確
保する方法が研究されてきた。例えば、グラインダーに
よって止端を研削して止端半径を大きくする方法、ＴＩ
Ｇ溶接およびプラズマ処理によって止端部を再溶融して
上端形状を滑らかにする方法（例えば特公昭５４−３０
３８６号）、ショットピーニングによって止端部に圧縮
残留応力を発生させる方法などが代表的な止端処理方法
である。2. Description of the Related Art Generally, the fatigue strength of a base material for structural steel plates increases as the strength of the base material increases, but the fatigue strength of welded joints (hereinafter referred to as joint fatigue strength) improves even when the strength of the base material increases. It was a popular theory not to do it. Therefore, the joint fatigue strength of structural high-strength steel is almost the same as that of low-strength steel, and in structures where fatigue fracture is a problem, even if high-strength steel is used, the design strength cannot be increased and the toe A method for ensuring the joint fatigue strength of high-strength steel has been studied by an improvement treatment called treatment. For example, a method of grinding the toe with a grinder to increase the toe radius, TI
A method of remelting the toe portion by G welding and plasma treatment to smooth the upper end shape (for example, Japanese Patent Publication No. 54-30).
No. 386), a method of generating compressive residual stress at the toe portion by shot peening is a typical toe treatment method.
【０００３】構造用鋼に限定しなければ、冷延鋼板など
薄鋼板のスポット溶接継手疲労強度向上を目的とした発
明はいくつかあり、特公平３−５６３０１号、特開昭６
３−３１７６２５号、特開平３−１９９３４２号などが
提案されている。このうち、特公平３−５６３０１号で
は、スポット溶接継手のナゲット近傍の硬度分布を定め
るため、Ｔｉ又はＮｂとＢ添加、並びに未再結晶組織の
面積率を制限している。特開昭６３−３１７６２５号お
よび特開平３−１９９３４２号は、いずれも鋼板の化学
成分を規定したものであり、特開昭６３−３１７６２５
号はＴｉ，Ｎｂ，Ｂの三者共存を、特開平３−１９９３
４２号はＴｉ，Ｖ，Ｚｒなどの成分添加を提案してい
る。又溶接継手に限定しなければ、鋼板母材の疲労強度
の向上を目的としたものはいくつかあり、特に本発明の
ようにＣｕ元素を含有した鋼板に関するものでは、特公
平１−３２３０１号、特開昭６０−１５５６４２号、特
開平３−８２７０８号などが提案されている。If not limited to structural steel, there are several inventions aimed at improving the fatigue strength of spot-welded joints of thin steel sheets such as cold-rolled steel sheets, which is disclosed in Japanese Patent Publication No. 3-56301.
No. 3-317625 and Japanese Patent Laid-Open No. 3-199342 are proposed. Among these, in Japanese Examined Patent Publication No. 3-56301, in order to determine the hardness distribution near the nugget of the spot welded joint, Ti or Nb and B are added, and the area ratio of the non-recrystallized structure is limited. JP-A-63-317625 and JP-A-3-199342 both specify the chemical composition of the steel sheet.
No. 3 discloses coexistence of Ti, Nb, and B.
No. 42 proposes addition of components such as Ti, V and Zr. Further, if not limited to welded joints, there are several ones for the purpose of improving the fatigue strength of the steel sheet base material, and particularly in regard to a steel sheet containing a Cu element as in the present invention, Japanese Patent Publication No. 1-32301. JP-A-60-155642 and JP-A-3-82708 are proposed.
【０００４】又、溶接残留応力に関連した報告はいくつ
かあり、相変態の超塑性現象に着目して、低合金鋼およ
びステンレス鋼の溶接残留応力の緩和や溶接変形低減を
検討した報告が、溶接学会全国大会講演概要第３７集
ｐ．３１４−３１５、第３８集ｐ．７８−７９、第３９
集ｐ．３３８−３３９、ｐ．３４０−３４１に見られ
る。又、溶接残留応力を低減させる溶接方法としては、
マルテンサイト系ステンレス鋼溶接棒による変態膨張効
果を用いた特開昭６０−６８１７５号、熱膨張率の小さ
い溶接材料（ステンレス用）を用いた特開昭５７−１７
３７７号などが提案されている。There are several reports relating to welding residual stress. Focusing on the superplasticity phenomenon of phase transformation, a report examining relaxation of welding residual stress and reduction of welding deformation of low alloy steel and stainless steel has been reported. Welding Society National Convention Lecture Summary 37th p. 314-315, 38th p. 78-79, 39th
Collection p. 338-339, p. 340-341. In addition, as a welding method for reducing the welding residual stress,
Japanese Patent Application Laid-Open No. 60-68175, which uses the transformation expansion effect of a martensitic stainless steel welding rod, and Japanese Patent Application Laid-Open No. 57-17, which uses a welding material having a small coefficient of thermal expansion (for stainless steel).
No. 377 has been proposed.
【０００５】さらにスポット溶接継手の強度向上を目的
として、特開平２−１１５３５２号によりＣｕ，Ｐ，Ｎ
などの成分を限定し、特定の位置（ナゲット外周から板
厚と同じ距離離れた熱影響部（以下ＨＡＺという））で
の硬さが、母材硬さおよびナゲット部硬さをもとに、あ
る関係式より求められる値以上であることを満足するこ
とを特徴とする鋼板が提案されている。Further, in order to improve the strength of the spot-welded joint, JP-A-2-115352 discloses Cu, P, N.
Based on the hardness of the base metal and the hardness of the nugget part, the hardness at a specific position (heat-affected zone (hereinafter referred to as HAZ) that is the same distance from the outer periphery of the nugget as the plate thickness) is limited. A steel sheet characterized by satisfying a value equal to or more than a value obtained from a certain relational expression has been proposed.
【０００６】これらの状況に対し本発明者らは、構造用
鋼の継手疲労強度向上を検討した結果、特願平４−２９
４５４４号においてＣｕ添加の構造用鋼を開発した。す
なわち、低炭素鋼とすることにより溶接止端部の残留応
力が低減されるとともに、ＨＡＺでのＣｕ元素の微細析
出によって軟化域の発生が抑えられることを知見したも
のであった。さらに、特願平５−０１４２３３号におい
て、ＨＡＺの硬度上昇を抑えるため炭素当量Ｃｅｑを規
定した構造用鋼を提案した。Under these circumstances, the inventors of the present invention have studied the improvement of the joint fatigue strength of structural steel, and as a result, Japanese Patent Application No. 4-29.
No. 4544 developed a Cu-added structural steel. That is, it has been found that the use of the low carbon steel reduces the residual stress at the weld toe and suppresses the generation of the softened region due to the fine precipitation of Cu element in the HAZ. Furthermore, Japanese Patent Application No. 5-014233 proposes a structural steel in which a carbon equivalent Ceq is specified in order to suppress an increase in hardness of HAZ.
【０００７】[0007]
【発明が解決しようとする課題】しかし、その後さらに
継手疲労強度向上に対する要求に対して種々検討した結
果、特願平４−２９４５４４号および特願平５−０１４
２３３号において、低炭素にするほど鋼板の強度確保の
ため逆にＭｎ，Ｃｕが増加することになり、かつ連続鋳
造時の表面割れ防止のためＮｉを適量以上添加すると、
溶接熱の冷却過程においてＨＡＺの強度（高温強度）が
高くなり、室温に冷却された時の溶接残留応力が上昇し
てしまい、継手疲労強度が低下するという問題が生じる
ことがわかった。However, as a result of various studies on the demands for further improvement of the joint fatigue strength after that, Japanese Patent Application Nos. 4-294544 and 5-014.
In No. 233, the lower the carbon content, the more Mn and Cu increase to secure the strength of the steel sheet, and Ni is added in an appropriate amount to prevent surface cracking during continuous casting.
It was found that the strength (high temperature strength) of the HAZ increases during the cooling process of the welding heat, the residual welding stress increases when cooled to room temperature, and the joint fatigue strength decreases.
【０００８】一方、従来技術のうち薄鋼板に関する特公
平３−５６３０１号は、Ｔｉ又はＮｂ添加に加えて未再
結晶組織の面積率を規定しており製造コストが高くなる
とともに、特に加熱・圧延条件の調整が煩雑になる。特
開昭６３−３１７６２５号はＴｉ，Ｎｂ，Ｂの同時添加
を必須としており、又特開平３−１９９３４２号はＯが
一定値以下でかつＡｌ／Ｎ比を一定値以上にすることを
必須としており、製鋼工程での多大なコスト上昇になる
という問題がある。On the other hand, Japanese Examined Patent Publication No. 56301/1993 concerning thin steel plates among the prior art specifies the area ratio of the non-recrystallized structure in addition to the addition of Ti or Nb, which raises the manufacturing cost and especially heating / rolling. Adjustment of conditions becomes complicated. JP-A-63-317625 requires the simultaneous addition of Ti, Nb, and B, and JP-A-3-199342 requires that the O content be below a certain value and the Al / N ratio be above a certain value. However, there is a problem that the cost in the steelmaking process will increase significantly.
【０００９】又母材疲労強度向上を目的とした特公平１
−３２３０１号は耐食性の向上効果も兼ねているため、
Ｍｏ又はＣｏ，Ｎｂ又はＶ，Ｚｒ又はＢｅ，Ｃｅ又はＰ
ｂの添加を必須としており、製造コストが著しく高くな
る。特開昭６０−１５５６４２号は耐腐食疲労特性の向
上を目的としており、ＳとＰの含有量比率を規定してい
るため製鋼工程でのコストが上昇する。特開平３−８２
７０８号は、ＣとＰの含有量比率を規定しており、かつ
Ｐの含有量が高いことから、溶接性に悪影響を及ぼすと
考えられる。Japanese Patent Publication No. 1 for the purpose of improving base material fatigue strength.
-32301 also has the effect of improving corrosion resistance,
Mo or Co, Nb or V, Zr or Be, Ce or P
Since the addition of b is indispensable, the manufacturing cost becomes extremely high. Japanese Unexamined Patent Publication No. 60-155642 aims at improving the corrosion fatigue resistance, and since the content ratio of S and P is specified, the cost in the steelmaking process increases. JP-A-3-82
No. 708 stipulates the content ratio of C and P, and since the content of P is high, it is considered that weldability is adversely affected.
【００１０】又、溶接残留応力に関連した溶接学会全国
大会講演概要第３７集ｐ．３１４−３１５、第３８集
ｐ．７８−７９、第３９集ｐ．３３８−３３９、ｐ．３
４０−３４１および特開昭６０−６８１７５号は、オー
ステナイトからフェライトあるいはマルテンサイトへの
変態温度の低下を狙って溶接残留応力を低減させたもの
であるので、一般に高合金鋼が対象となって高コストは
避けられない。特開昭５７−１７３７７号も同様に高合
金材料である。又特開平２−１１５３５２号では、スポ
ット溶接継手の十字引張強度向上を目的としており、溶
接された継手の疲労強度が向上するかどうかは不明であ
る。本発明の目的は、高温強度を低下させることにより
溶接残留応力を低減して継手疲労強度を向上させた構造
用鋼を安定して提供するものである。Also, the 37th Annual Meeting of the Welding Society National Conference on Welding Residual Stress, p. 37. 314-315, 38th p. 78-79, 39th p. 338-339, p. Three
40-341 and Japanese Patent Laid-Open No. 60-68175 reduce welding residual stress with the aim of lowering the transformation temperature of austenite to ferrite or martensite, and therefore are generally targeted at high alloy steels. The cost is unavoidable. JP-A-57-17377 is also a high alloy material. Further, in Japanese Patent Laid-Open No. 2-115352, the purpose is to improve the cross tensile strength of the spot-welded joint, and it is unclear whether the fatigue strength of the welded joint is improved. An object of the present invention is to stably provide structural steel in which welding residual stress is reduced by reducing high temperature strength and joint fatigue strength is improved.
【００１１】[0011]
【課題を解決するための手段】本発明は高温強度を低く
することにより、溶接残留応力を低減して継手疲労強度
向上を狙ったものである。すなわち、本発明の要旨とす
るところは、重量％で、Ｃ：０．００１〜０．０１０
％、Ｓｉ：０．００５〜０．０５％、Ｍｎ：０．０５〜
１．００％、Ｐ≦０．０２０％、Ｓ≦０．０１０％、Ｎ
ｉ：０．３〜２．０％、Ｃｕ：０．５〜２．０％、Ａ
ｌ：０．０１０〜０．０５０％、Ｂ：０．０００１〜
０．００１０％を含有し、かつＮｉ／Ｃｕ≧０．４の組
成を有し、残部は鉄およびその他の不可避的成分からな
り、かつ下式で規定されるパラメータＡが１５以下であ
ることを特徴とする溶接継手疲労特性の優れた構造用鋼
である。 Ａ＝0.350 ＋22.8×Ｃ＋12.5×Ｓｉ＋16.8×Ｍｎ＋23.4
×Ｐ−164 ×Ｓ＋30.9×Ｎｉ−2.24×Ｃｕ−332 ×ＡｌDISCLOSURE OF THE INVENTION The present invention is aimed at improving the joint fatigue strength by reducing the residual welding stress by lowering the high temperature strength. That is, the gist of the present invention is that, in% by weight, C: 0.001 to 0.010.
%, Si: 0.005-0.05%, Mn: 0.05-
1.00%, P ≦ 0.020%, S ≦ 0.010%, N
i: 0.3 to 2.0%, Cu: 0.5 to 2.0%, A
1: 0.010 to 0.050%, B: 0.0001 to
0.0010% and having a composition of Ni / Cu ≧ 0.4, the balance consisting of iron and other unavoidable components, and the parameter A defined by the following formula is 15 or less. A structural steel with excellent welded joint fatigue characteristics. A = 0.350 + 22.8 × C + 12.5 × Si + 16.8 × Mn + 23.4
XP-164 xS + 30.9 xNi-2.24 xCu-332 xAl
【００１２】[0012]
【作用】以下に本発明を詳細に説明する。まず本発明に
おける成分限定理由を述べる。Ｃは後述する溶接止端部
近傍の硬度分布の均一化および溶接残留応力低下のため
少なくすることが望ましく、０．０１０％以下である必
要があるが、強度確保のためには０．００１％以上は必
要であるので０．００１〜０．０１０％とする。Ｓｉは
脱酸のためには不可避元素であり、０．００５％以上を
必要とするが溶接性を確保するためには少なくすること
が望ましいので含有量は０．０５％以下とする。The present invention will be described in detail below. First, the reasons for limiting the components in the present invention will be described. It is desirable to reduce C so that the hardness distribution in the vicinity of the weld toe portion, which will be described later, becomes uniform and the welding residual stress decreases, but it is necessary to be 0.010% or less, but 0.001% to secure the strength. The above is necessary, so 0.001 to 0.010% is set. Si is an unavoidable element for deoxidation and needs to be 0.005% or more, but it is desirable to reduce it to secure weldability, so the content is made 0.05% or less.
【００１３】Ｍｎは安価に強度を上げる元素として有用
であり、強度確保のため０．０５％以上は必要であるが
多くなると溶接性を損なうので含有量は０．０５〜１．
００％とする。Ｐは不純物元素であり、溶接割れ感受性
の低減や応力除去焼鈍による脆化や割れの防止を図るた
め、０．０２０％以下に限定する。Ｓは不純物元素であ
り、溶接割れ感受性の低減や応力除去焼鈍による脆化や
割れの防止を図るため、０．０１０％以下に限定する。
Ｓは低ければ低いほど靭性が向上する。[0013] Mn is useful as an element for inexpensively increasing the strength, and 0.05% or more is necessary to secure the strength, but if it increases, the weldability is impaired, so the content is 0.05-1.
00%. P is an impurity element and is limited to 0.020% or less in order to reduce the susceptibility to welding cracks and prevent embrittlement and cracking due to stress relief annealing. S is an impurity element and is limited to 0.010% or less in order to reduce the susceptibility to welding cracks and prevent embrittlement and cracking due to stress relief annealing.
The lower the S, the higher the toughness.
【００１４】Ｃｕは後述するように溶接入熱によって微
細に析出し、止端部近傍のＨＡＺの軟化を防ぐために
０．５％以上は必要であるが、多くなると溶接割れを生
じるため０．５〜２．０％とする。Ａｌは脱酸のため
０．０１０％以上必要であるが、多くなると鋼中介在物
が多くなりすぎ、鋼の靭性を低下させるため０．０５０
％を上限とする。Ｂは低Ｃ鋼材の結晶粒界を強化し、低
温での粒界割れを防止する元素として有用であり、０．
０００１％以上は必要であるが多すぎると脆化を起こす
ため、上限を０．００１０％とする。As will be described later, Cu is finely precipitated by welding heat input, and 0.5% or more is necessary to prevent softening of the HAZ in the vicinity of the toe portion, but if it increases, welding cracking occurs, so 0.5%. ~ 2.0%. Al is required to be 0.010% or more for deoxidation, but if it is increased, the amount of inclusions in the steel becomes too large and the toughness of the steel is reduced.
% Is the upper limit. B is useful as an element that strengthens the crystal grain boundaries of the low C steel material and prevents grain boundary cracking at low temperatures.
0001% or more is necessary, but if it is too much, embrittlement occurs, so the upper limit is made 0.0010%.
【００１５】Ｎｉ／Ｃｕ比は、連続鋳造時における表面
割れを防止するために必要であり、Ｃｕ濃縮部の凝固温
度を上昇させるため、Ｎｉ／Ｃｕ≧０．４となるように
Ｎｉを添加する。ただし、Ｃｕの微細析出に伴う靭性の
低下を防ぐために、Ｎｉは少なくとも０．３％以上の添
加が必要であり、又、Ｎｉの多量添加は溶接割れを生じ
るため、上限を２．０％とする。本発明では、代表的な
溶接時の冷却過程における種々の鋼板の降伏強度を検討
した結果、強度を上記成分の関数として下式Ａによって
与えた。 Ａ＝0.350 ＋22.8×Ｃ＋12.5×Ｓｉ＋16.8×Ｍｎ＋23.4×Ｐ −164 ×Ｓ＋30.9×Ｎｉ−2.24×Ｃｕ−332 ×Ａｌ ………（１）The Ni / Cu ratio is necessary to prevent surface cracks during continuous casting, and Ni is added so that Ni / Cu ≧ 0.4 in order to raise the solidification temperature of the Cu concentrated portion. . However, in order to prevent a decrease in toughness due to fine precipitation of Cu, it is necessary to add at least 0.3% or more of Ni, and addition of a large amount of Ni causes welding cracks, so the upper limit is made 2.0%. To do. In the present invention, as a result of examining the yield strength of various steel plates in a typical cooling process during welding, the strength is given by the following formula A as a function of the above components. A = 0.350 + 22.8 × C + 12.5 × Si + 16.8 × Mn + 23.4 × P−164 × S + 30.9 × Ni−2.24 × Cu−332 × Al ………… (1)
【００１６】そして溶接残留応力と高温での降伏強度
（パラメータＡ）との関係を検討した結果、図１に示す
関係を得た。図１の縦軸の残留応力は、継手疲労強度に
影響を及ぼす、溶接線に垂直な方向の止端での残留応力
である（板厚１２mm、溶接入熱１８kJ／cmのＣＯ2 溶
接）。すなわち継手疲労強度を向上させるほど溶接残留
応力が十分に小さい値であると判断される（２）式の関
係を見いだした。 Ａ≦１５ ……………………………………………（２）As a result of examining the relationship between the residual welding stress and the yield strength (parameter A) at high temperature, the relationship shown in FIG. 1 was obtained. The residual stress on the vertical axis in FIG. 1 is the residual stress at the toe in the direction perpendicular to the welding line that affects the joint fatigue strength (CO 2 welding with a plate thickness of 12 mm and welding heat input of 18 kJ / cm). That is, the relationship of the equation (2), which determines that the welding residual stress is sufficiently small to improve the joint fatigue strength, was found. A ≦ 15 ……………………………………………… (2)
【００１７】一般に高温強度には、Ｃｒ，Ｍｏなどの成
分が大きな影響を及ぼすが、本発明鋼は炭素鋼を対象と
しており、さらにＣｒ，Ｍｏは高温強度を上昇させる成
分であるので本発明鋼には不要であることから、（１）
式から外した。なお本発明におけるＮは、特開平２−１
１５３５２号に示すように加工性を高めることを目的と
して０．００５０％以下に限定するものとは異なり、継
手疲労強度に及ぼすＮの影響は小さいので、その成分範
囲は特に限定するものではない。Generally, the components such as Cr and Mo have a great influence on the high temperature strength, but the steel of the present invention is intended for carbon steel, and since Cr and Mo are the components which increase the high temperature strength, the steel of the present invention. Is unnecessary for (1)
Removed from the formula. In addition, N in the present invention is set to JP-A 2-1.
Unlike the limit of 0.0050% or less for the purpose of improving the workability as shown in No. 15352, the influence of N on the joint fatigue strength is small, and therefore its component range is not particularly limited.
【００１８】又本発明におけるＣｕは、同じく特開平２
−１１５３５２号に示すように継手引張強度向上を目的
として０．８％以上に限定するものではなく、０．５％
以上であれば継手疲労強度を著しく向上させることがで
きる。さらに特開平２−１９９３４２号に示すようにＴ
ｉ，Ｖ，Ｚｒ，Ｃａ，Ｃｒ，Ｎｉと同等の効果を示して
１．０％以下に限定するものではなく、溶接の熱によっ
てＨＡＺを析出強化するためには０．５〜２．０％の範
囲であれば継手疲労強度を著しく向上させることができ
る。加えて特公平３−５６３０１号は、鋼板の未再結晶
組織の面積率を５〜３０％と規定しているが、ＨＡＺ粗
粒域は１５００℃付近まで加熱された領域であり、溶接
前の鋼板の未再結晶組織の面積率が何％であろうともオ
ーステナイト単相に戻されるため、本発明では特に未再
結晶組織の割合など、組織を制限するものではない。Further, Cu in the present invention is the same as in JP-A-2
As shown in -115352, it is not limited to 0.8% or more for the purpose of improving the joint tensile strength, but 0.5%.
If it is above, the joint fatigue strength can be remarkably improved. Further, as shown in JP-A-2-199342, T
i, V, Zr, Ca, Cr, Ni show the same effect and are not limited to 1.0% or less, but 0.5 to 2.0% for precipitation strengthening HAZ by the heat of welding. Within the range, the joint fatigue strength can be significantly improved. In addition, Japanese Examined Patent Publication No. 3-56301 defines the area ratio of the non-recrystallized structure of the steel sheet as 5 to 30%, but the HAZ coarse grain region is a region heated up to around 1500 ° C. and before welding. Since the area ratio of the unrecrystallized structure of the steel sheet is returned to the austenite single phase, the present invention does not particularly limit the structure such as the ratio of the unrecrystallized structure.
【００１９】次に本発明の構造用鋼の継手疲労強度が向
上する理由を述べる。溶接継手においては疲労亀裂は溶
接止端で発生した後、伝播して最終破断に至るが、溶接
時に発生する残留応力（通常は引張の残留応力）が、疲
労破壊を助長させており、溶接残留応力を低減すれば継
手疲労強度が向上することは従来から知られている。引
張の溶接残留応力を生じる部分は溶接金属の他にＨＡＺ
があり、変形抵抗のなくなる力学的溶融温度（通常８０
０℃前後）以上に加熱された部分は、冷却時の収縮によ
って降伏応力レベルの引張残留応力が発生する。Next, the reason why the joint fatigue strength of the structural steel of the present invention is improved will be described. Fatigue cracks in welded joints propagate at the weld toe and then propagate to the final fracture, but the residual stress (usually tensile residual stress) generated during welding promotes fatigue fracture. It has been conventionally known that reducing stress improves joint fatigue strength. In addition to the weld metal, HAZ is the part that causes tensile welding residual stress.
The mechanical melting temperature (usually 80
In the portion heated above 0 ° C.), shrinkage during cooling causes tensile residual stress at the yield stress level.
【００２０】溶接残留応力は、通常８００℃以下の冷却
過程での体積収縮によって応力が発生し、室温に冷却さ
れた時に残留している応力のことであるが、本発明者ら
は、冷却過程で発生している応力は、その温度における
鋼材の降伏強度（高温での降伏強度）レベルであること
を見つけた。従って、８００℃以下の温度での降伏応力
が低い鋼材ほど、室温に冷却された時の残留応力は小さ
くなることがわかった。The welding residual stress is a stress that is generated by volume contraction in a cooling process at 800 ° C. or less and remains when cooled to room temperature. It was found that the stress generated in the steel is the yield strength (yield strength at high temperature) level of steel at that temperature. Therefore, it was found that the lower the yield stress at a temperature of 800 ° C. or lower, the smaller the residual stress when cooled to room temperature.
【００２１】次に、降伏応力の温度依存性に及ぼす添加
元素の影響を検討した結果、室温から８００℃までの広
範囲な温度域に渡って、（１）式に示すパラメータＡが
１５以下の鋼材は、降伏応力が低く、従って継手疲労強
度を低下させるに十分な溶接残留応力の低下が認められ
ることがわかった。溶接残留応力が継手疲労強度に及ぼ
す影響は、平均応力効果として整理される。疲労強度
は、正の平均応力（引張応力）が大きいほど小さくな
り、修正Ｇｏｏｄｍａｎ線図に従えば、引張強さの１／
２の大きさの正の平均応力が存在する鋼材の疲労強度
は、平均応力のない鋼材の疲労強度の１／２になってし
まう。引張の残留応力は平均応力として溶接止端部に作
用し疲労強度を低下させるため、残留応力の低い継手ほ
ど疲労強度が大きいことは明らかである。Next, as a result of examining the effect of the additional element on the temperature dependence of the yield stress, a steel material having a parameter A shown in the formula (1) of 15 or less over a wide temperature range from room temperature to 800 ° C. Was found to have a low yield stress, and therefore a sufficient reduction in welding residual stress to reduce the joint fatigue strength was observed. The effect of residual welding stress on joint fatigue strength is summarized as the average stress effect. Fatigue strength decreases as the positive average stress (tensile stress) increases, and according to the modified Goodman diagram,
The fatigue strength of a steel material having a positive average stress of 2 is half the fatigue strength of a steel material having no average stress. Since the residual tensile stress acts as an average stress on the weld toe and reduces the fatigue strength, it is clear that the joint with lower residual stress has a greater fatigue strength.
【００２２】本発明鋼の継手疲労強度向上効果は、上述
の残留応力低減効果が主であるが、それ以外にも、Ｃ量
を低減させてＨＡＺ硬化を防ぐこと、およびＣｕの微細
析出によってＨＡＺ軟化を防ぐことによって溶接金属お
よびＨＡＺでのひずみの集中を防止する効果も働いてい
る。特願平５−０１４２３３号ではＨＡＺの硬化を防ぐ
目的から、炭素当量Ｃｅｑを０．２以下に規定している
が、（１）式のパラメータは炭素当量を増加させる元素
を制限しているため、結果的には（１）式のみで溶接残
留応力の低減と、ＨＡＺ硬化の抑制を果たすことが可能
である。The effect of improving the joint fatigue strength of the steel of the present invention is mainly the above-mentioned residual stress reducing effect, but in addition to this, the amount of C is reduced to prevent HAZ hardening, and the fine precipitation of Cu causes the HAZ to grow. By preventing softening, it also has an effect of preventing strain concentration in the weld metal and HAZ. In Japanese Patent Application No. 5-014233, the carbon equivalent Ceq is specified to be 0.2 or less for the purpose of preventing hardening of the HAZ, but the parameter of the formula (1) limits the elements that increase the carbon equivalent. As a result, it is possible to reduce the welding residual stress and suppress the HAZ hardening only by the formula (1).
【００２３】すなわち本発明の構造用鋼は、高温での降
伏強度を低くして溶接残留応力を低減させる効果と、Ｃ
ｕの析出強化を用いてＨＡＺの硬度を均一にすることに
より塑性変形の集中を抑える効果とを程よく兼ね合わせ
て継手疲労強度を著しく向上させた鋼板である。本発明
では特に鋼板の引張強度レベルを特定していないが、こ
れは上述のＣｕ析出による強化効果を利用することによ
り鋼板素材の強度を変化させることができるためであ
る。しかし元来Ｃ含有量が少ないため、７００MPa クラ
スの強度が限界であろう。又溶接材料の強度は鋼材と同
レベルであることが望ましいが、低Ｃのため希釈され
て、止端部近傍は硬度平坦となるため、必ずしも同一強
度レベルの必要性はない。しかしＭｏ，Ｃｕなど溶接の
熱により硬化する元素が溶接材料に多量に含まれている
場合はこの限りではない。That is, the structural steel of the present invention has the effect of lowering the yield strength at high temperatures to reduce welding residual stress, and
A steel sheet in which the fatigue strength of the joint is remarkably improved by appropriately combining the effect of suppressing the concentration of plastic deformation by making the hardness of the HAZ uniform by using the precipitation strengthening of u. In the present invention, the tensile strength level of the steel sheet is not specified, but this is because the strength of the steel sheet material can be changed by utilizing the above-mentioned strengthening effect by Cu precipitation. However, since the C content is originally low, the 700 MPa class strength will be the limit. Further, it is desirable that the strength of the welding material is the same level as that of the steel material, but since it is diluted with low C and the hardness near the toe portion becomes flat, the strength level is not necessarily the same. However, this does not apply when the welding material contains a large amount of elements such as Mo and Cu that are hardened by the heat of welding.
【００２４】又、本発明は回し溶接継手のような溶接残
留応力の高い場合に特に有効であるが、隅肉継手、突合
せ継手においても疲労強度が向上する。Ｔ字隅肉継手で
は、板厚が小さいか又は入熱が小さい場合には、角変形
による曲げ応力が加わるため止端部の溶接残留応力は圧
縮となるが、この場合も本発明の鋼板の残留応力は従来
鋼より大きな圧縮の残留応力が発生し、疲労強度が向上
する。Further, although the present invention is particularly effective in the case where the welding residual stress is high such as in the case of a turn welded joint, the fatigue strength is improved also in a fillet joint and a butt joint. In the T-shaped fillet joint, when the plate thickness is small or the heat input is small, the bending residual stress due to the angular deformation causes the welding residual stress at the toe to be compressed. The residual stress causes a larger compressive residual stress than that of the conventional steel and improves the fatigue strength.
【００２５】さらに本発明では、溶接方法、すなわち入
熱の違いによる疲労強度向上効果の違いが考えられる
が、溶接では例え大入熱であっても冷却速度が遅くなる
だけで、上述の残留応力低減効果は発揮される。又、Ｈ
ＡＺではＣｕ析出が飽和することは考えられない。従っ
て入熱が大きくなるとＨＡＺの幅が大きくなり、残留応
力の低下は期待でき、Ｃｕ析出による強化機構も進行し
て、疲労強度の向上効果は大入熱であっても有効であ
る。又言うまでもなく、溶融溶接であれば、溶接方法に
関係なく疲労強度向上が期待できる。ただし、溶接入熱
および鋼板の板厚によって溶接残留応力の絶対値そのも
のは異なるため、継手疲労強度の向上効果も溶接入熱や
板厚によって異なるが、同一入熱および同一板厚であれ
ば、本発明鋼の継手疲労強度は従来鋼より向上する。Further, in the present invention, the difference in the fatigue strength improving effect due to the welding method, that is, the difference in heat input can be considered. However, in welding, even if the heat input is large, the cooling rate is slowed down, and the above-mentioned residual stress The reduction effect is exhibited. Also, H
It is unlikely that Cu precipitation will be saturated in AZ. Therefore, as the heat input increases, the width of the HAZ becomes wider, the residual stress can be expected to decrease, the strengthening mechanism by Cu precipitation also progresses, and the effect of improving fatigue strength is effective even with a large heat input. Needless to say, in the case of fusion welding, improvement in fatigue strength can be expected regardless of the welding method. However, since the absolute value of the welding residual stress itself varies depending on the welding heat input and the plate thickness of the steel sheet, the effect of improving the joint fatigue strength also differs depending on the welding heat input and the sheet thickness. The joint fatigue strength of the steel of the present invention is improved as compared with the conventional steel.
【００２６】[0026]
【実施例】表１に示す成分を有する板厚１２mmの鋼板を
製造し、この鋼材に母材強度と同レベルの強度を持つ溶
接材料を用いて入熱１８kJ／cmでＣＯ2 溶接を行って、
十字隅肉継手を製作し、室温、大気中で片振り疲労試験
（応力比Ｒ＝０）を行った。各継手の試験片形状・寸法
をそれぞれ図２に示す。比較のため、添加元素の含有量
およびパラメータＡを、本発明の範囲外に変化させた比
較鋼の例も示した。又、表中の機械的性質は室温大気中
の結果である。Example A steel plate having a plate thickness of 12 mm having the components shown in Table 1 was manufactured, and a welding material having the same level of strength as the base metal was used to perform CO 2 welding with a heat input of 18 kJ / cm. ,
A cruciform fillet joint was manufactured, and a one-sided fatigue test (stress ratio R = 0) was performed in the air at room temperature. The shape and size of the test piece of each joint are shown in FIG. For comparison, examples of comparative steels in which the content of the additional element and the parameter A are changed outside the scope of the present invention are also shown. Further, the mechanical properties in the table are results in room temperature atmosphere.
【００２７】[0027]
【表１】 [Table 1]
【００２８】疲労試験結果を合わせて表１に示す。疲労
試験結果は、試験片の破断寿命が２×１０6 回に対応す
る疲労強度で示してある。本発明鋼は比較鋼に比べて約
１０％以上継手疲労強度が向上している。本発明鋼Ｂは
引張強さが７００MPa クラス、本発明鋼Ｄは引張強さが
６００MPa の鋼板であるが、強度レベルによらず疲労強
度の向上が認められている。又、比較鋼Ｆは本発明者ら
が特願平５−０１４２３３号で発明した鋼板であるが、
本発明鋼の方がさらに大きな疲労強度を示している。The results of the fatigue test are also shown in Table 1. The fatigue test results are shown by the fatigue strength corresponding to the breaking life of the test piece of 2 × 10 6 . The steel of the present invention has improved joint fatigue strength by about 10% or more as compared with the comparative steel. The invention steel B is a steel sheet having a tensile strength of 700 MPa class and the invention steel D is a steel sheet having a tensile strength of 600 MPa, but it is recognized that the fatigue strength is improved regardless of the strength level. Comparative steel F is a steel plate invented by the present inventors in Japanese Patent Application No. 5-014233.
The steel of the present invention shows a larger fatigue strength.
【００２９】[0029]
【発明の効果】本発明にかかる構造用鋼は、継手形式、
鋼板素材の強度など、広範囲に渡り溶接継手の疲労特性
に優れている。従って疲労破壊が問題となる構造物での
使用に際し、設計・施工面で特別な配慮を必要とせず高
い疲労強度を安定して得ることが可能であり、工業的に
その効果は大きい。The structural steel according to the present invention has a joint type,
Has excellent fatigue properties for welded joints over a wide range, including the strength of steel sheet materials. Therefore, when used in a structure in which fatigue fracture is a problem, high fatigue strength can be stably obtained without requiring special consideration in design and construction, and the effect is industrially great.
【図１】本発明のパラメータＡと十字隅肉溶接継手の止
端での溶接線に垂直な方向の溶接残留応力との関係を示
した図表。FIG. 1 is a chart showing a relationship between a parameter A of the present invention and a residual welding stress in a direction perpendicular to a welding line at a toe of a cross fillet welded joint.
【図２】（ａ），（ｂ）は本発明の実施例における十字
隅肉継手の試験片形状・寸法の説明図。2 (a) and 2 (b) are explanatory views of the shape and size of a test piece of a cross fillet joint in an example of the present invention.
Claims (1)
式で規定されるパラメータＡが１５以下であることを特
徴とする溶接継手疲労特性の優れた構造用鋼。 Ａ＝0.350 ＋22.8×Ｃ＋12.5×Ｓｉ＋16.8×Ｍｎ＋23.4
×Ｐ−164 ×Ｓ＋30.9×Ｎｉ−2.24×Ｃｕ−332 ×Ａｌ1. By weight%, C: 0.001-0.010%, Si: 0.005-0.05%, Mn: 0.05-1.00%, P ≦ 0.020%, S ≦ 0.010%, Ni: 0.3 to 2.0%, Cu: 0.5 to 2.0%, Al: 0.010 to 0.050%, B: 0.0001 to 0.0010% A structure having excellent welded joint fatigue characteristics, characterized in that it contains and Ni / Cu ≧ 0.4, the balance consists of iron and other unavoidable components, and the parameter A defined by the following formula is 15 or less. For steel. A = 0.350 + 22.8 × C + 12.5 × Si + 16.8 × Mn + 23.4
XP-164 xS + 30.9 xNi-2.24 xCu-332 xAl
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24091593A JPH0790486A (en) | 1993-09-28 | 1993-09-28 | Steel for structural purpose excellent in fatigue property of welded joint |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP24091593A JPH0790486A (en) | 1993-09-28 | 1993-09-28 | Steel for structural purpose excellent in fatigue property of welded joint |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH0790486A true JPH0790486A (en) | 1995-04-04 |
Family
ID=17066559
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP24091593A Pending JPH0790486A (en) | 1993-09-28 | 1993-09-28 | Steel for structural purpose excellent in fatigue property of welded joint |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH0790486A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8650971B2 (en) | 2009-05-22 | 2014-02-18 | The University Of Electro-Communications | Slippage detection device and method |
-
1993
- 1993-09-28 JP JP24091593A patent/JPH0790486A/en active Pending
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8650971B2 (en) | 2009-05-22 | 2014-02-18 | The University Of Electro-Communications | Slippage detection device and method |
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