JP6149698B2 - Welding method with excellent heat-affected zone toughness - Google Patents
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Description
本発明は、靭性に優れた熱影響部を得るための溶接方法に関するものである。 The present invention relates to the welding of how to obtain a heat-affected zone with excellent toughness.
橋梁や船舶に使用される鋼板、建築物に使用される形鋼、およびエネルギー輸送に使用される鋼管等（以下、鋼材という）を溶接して構築する溶接構造物において、高強度の鋼材を使用するための様々な技術が開発されている。一方で、これらの鋼材の強度を高めることによって、その他の機械的特性の劣化（たとえば靭性低下等）を引き起こし、ひいては溶接構造物全体の耐震性や耐久性に悪影響を及ぼすことが知られている。 High-strength steel materials are used in welded structures constructed by welding steel plates used for bridges and ships, steel shapes used for buildings, and steel pipes used for energy transportation (hereinafter referred to as steel materials). Various technologies have been developed for this purpose. On the other hand, increasing the strength of these steel materials is known to cause deterioration of other mechanical properties (for example, toughness reduction) and thus adversely affect the earthquake resistance and durability of the entire welded structure. .
したがって、溶接構造物に用いる高強度の鋼材に要求される機械的諸特性は厳しくなっており、とりわけ溶接部（たとえば溶接金属、熱影響部等）の靭性に対する要求は極めて厳格である。溶接部の中でも熱影響部は、溶接によって必然的に発生する熱が鋼材に影響を及ぼす部位であり、機械的諸特性を向上した高強度の鋼材であっても、熱影響部という限られた部位の靭性が局所的に低下するという問題がある。 Accordingly, mechanical properties required for high-strength steel materials used for welded structures are becoming stricter, and in particular, the requirements for the toughness of welded parts (for example, weld metal, heat affected zone, etc.) are extremely strict. Among the welded parts, the heat-affected zone is a part where heat inevitably generated by welding affects the steel material, and even a high-strength steel material with improved mechanical properties is limited to a heat-affected zone. There exists a problem that the toughness of a site | part falls locally.
そこで、熱影響部の靭性低下を抑制する溶接技術が検討されている。
たとえば特許文献１、２には、鋼材にTiやREMを添加して、微細な硫化物や酸化物を分散させることによって、ピンニング効果を発揮させ、オーステナイト粒（以下、γ粒という）の粗大化を抑制する技術が開示されている。つまり熱影響部のγ粒径の増大を防止して、熱影響部の靭性を確保する技術である。
Then, the welding technique which suppresses the toughness fall of a heat affected zone is examined.
For example, in
特許文献３、４には、鋼材にBを添加することによって、旧γ結晶粒界から析出するフェライトの粗大化を抑制し、Caを添加することによって、Ca酸化物を核としてγ粒内に微細なフェライトを生成させて、熱影響部の靭性を確保する技術が開示されている。
また特許文献５には、細径の溶接ワイヤを使用して溶込みを深くすることによって、溶接入熱を低減し、熱影響部のγ粒径の増大を防止して、熱影響部の靭性を確保する技術が開示されている。
In
Further,
これらの技術は、いずれも鋼材に合金元素を添加して、靭性低下の原因となるγ粒の粗大化を防止するものである。しかし、鋼材の成分設計（たとえば合金元素の添加量を増加する、添加する合金元素の種類を増やす等）のみでは、鋼材の高強度化と、熱影響部の靭性向上とを両立させることは困難である。 In any of these techniques, an alloying element is added to a steel material to prevent the coarsening of γ grains, which causes a decrease in toughness. However, it is difficult to achieve both high strength of the steel and improved toughness of the heat-affected zone only by the component design of the steel (for example, increasing the amount of alloy elements added, increasing the types of alloy elements to be added, etc.) It is.
本発明は、従来の技術の問題点を解消し、鋼材を溶接するにあたって、靭性に優れた熱影響部を得ることができる溶接方法を提供することを目的とする。 The present invention is to solve the problems of the prior art, when welding the steel, and to provide a welding how you can get HAZ excellent in toughness.
本発明者は、高強度の鋼材に開先を設けて、溶接することによって生じる熱影響部の靭性を向上する技術について検討した。そして、開先周辺部のみの成分を局所的に変更することは困難であることから、鋼材全体の成分を設計するという従来の技術では、局所的な熱影響部の靭性向上と全体の強度向上とを両立させて顕著な効果を得ることは期待できないことが分かった。 This inventor examined the technique which improves the toughness of the heat affected zone which arises by providing a groove | channel in high strength steel materials and welding. And since it is difficult to locally change the components only in the periphery of the groove, the conventional technique of designing the components of the entire steel material improves the toughness of the local heat-affected zone and improves the overall strength. It was found that it is not possible to expect a remarkable effect by combining
そこで本発明者らは、開先の周辺部に適正な金属組織を生成させる技術を詳細に研究した。その結果、鋼材に開先を設けて、さらに開先とその周辺部に予め冷間で歪み（以下、予歪みという）を付与して溶接の熱によって生成するγ結晶粒を微細化することによって、局所的に金属組織を調整した後に、溶接を行なうことによって、熱影響部の靭性を改善できることを見出した。 Therefore, the present inventors have studied in detail a technique for generating an appropriate metal structure in the periphery of the groove. As a result, by providing a groove in the steel material, and further applying a strain (hereinafter referred to as pre-strain) to the groove and its peripheral portion in advance to refine the γ crystal grains generated by the heat of welding. It has been found that the toughness of the heat-affected zone can be improved by performing welding after locally adjusting the metallographic structure.
本発明は、このような知見に基づいてなされたものである。
すなわち本発明は、開先を設けた鋼材の溶接方法において、開先を設けた後に、開先およびその周辺部に予め冷間で予歪みとして下記の(1)式で算出される相当塑性ひずみεを５〜20％付与して窪みを形成し、その後に、溶接を行なう溶接方法である。
相当塑性ひずみε（％）＝1.15×ln（１−ｒ） ・・・(1)
圧下率ｒ＝Δｈ／ｈ 0 ・・・(2)
ｈ 0 ：予歪みを付与する前の鋼材の厚み（mm）
Δｈ：予歪みを付与することによる減厚量（mm）
The present invention has been made based on such knowledge.
That is, according to the present invention, in the method for welding a steel material provided with a groove, after the groove is provided, the equivalent plastic strain calculated by the following equation (1) as a pre- strain in the cold and the peripheral portion in advance is cold. In this welding method, 5 to 20% of ε is applied to form a recess, and then welding is performed.
Equivalent plastic strain ε (%) = 1.15 × ln (1-r) (1)
Reduction ratio r = Δh / h 0 (2)
h 0 : Thickness (mm) of the steel before pre-straining
Δh: Thickness reduction by applying pre-strain (mm)
本発明によれば、鋼材を溶接するにあたって、靭性に優れた熱影響部を得ることができるので、産業上格段の効果を奏する。 According to the present invention, when a steel material is welded, a heat-affected zone having excellent toughness can be obtained.
本発明は、鋼材（たとえば鋼板、形鋼、鋼管等）に開先を設けて溶接を行なうにあたって、鋼材に切削加工を施して開先を設け、次いで、開先とその周辺部に冷間で予歪みを付与した後に、溶接を行なうものである。
鋼材に予歪みを付与した後に、開先を設ける切削加工を施す場合は、開先の切削加工によって摩擦熱が発生し、予歪みを付与して微細化させたγ結晶粒が再び粗粒に変化する惧れがある。したがって、開先を設けた後に予歪みを付与する手順を採用する。
In the present invention, when a groove is provided on a steel material (for example, a steel plate, a shape steel, a steel pipe, etc.) and welding is performed, the steel material is cut to provide a groove, and then the groove and its peripheral part are cold. After pre-strain is applied, welding is performed.
After applying a pre-distortion in the steel material, if you facilities cutting providing the groove, the frictional heat is generated by cutting of the groove, gamma crystal grains were refined by applying a prestrain again crude There is a risk of changing to grains. Therefore, we adopt the procedure for applying a pre-distortion after providing the groove.
以下では、開先を設けた後に予歪みを付与する例について説明する。
開先とその周辺部に冷間で予歪みを付与することによって、当該部位の溶接の熱によって生成するγ結晶粒を微細化する。つまり、予歪みによって鋼材の初期組織を局所的（すなわち開先とその周辺部）に微細化できるので、後述する溶接における熱が熱影響部をγ相へ逆変態させる際の核生成サイトを増加させ、粗大なγ結晶粒の生成を抑制する。その結果、熱影響部の靭性を改善できる。
Below, the example which provides a pre-strain after providing a groove | channel is demonstrated.
By applying a pre-strain to the groove and its peripheral part in a cold state, the γ crystal grains generated by the heat of welding at the part are refined. In other words, the initial structure of the steel material can be refined locally (that is, the groove and its surroundings) by pre-straining, increasing the number of nucleation sites when the heat in welding described later reversely transforms the heat-affected zone to the γ phase. To suppress the formation of coarse γ crystal grains. As a result, the toughness of the heat affected zone can be improved.
予歪みが小さすぎると、γ結晶粒が微細化せず、熱影響部の靭性改善に寄与しない。したがって、予歪みは５％以上とする。一方で、予歪みが大きすぎると、加工硬化の作用で靭性の低下を招く。したがって、予歪みは20％以下とする。ここで予歪みの好適範囲の下限値と上限値は、下記の(1)式で算出される相当塑性ひずみε（％）を意味する。 If the pre-strain is too small, the γ crystal grains are not refined and do not contribute to the improvement of the toughness of the heat affected zone. Therefore, the prestrain than 5%. On the other hand, if the pre-strain is too large, the toughness is reduced due to work hardening. Accordingly, the following prestrain 20%. Here, the lower limit value and the upper limit value of the preferred range of pre-strain mean equivalent plastic strain ε (%) calculated by the following equation (1).
予歪みを付与する手段は、図１に示すように、鋼材の厚みを冷間で減厚する加工（たとえばプレス加工、パンチ加工等）とし、板厚方向に変形させることが好ましい。その理由は、簡便な手段で、所定の部位に予歪みを付与できるからである。無論、幅方向でも同等の効果が得られる。なお図１は、鋼材１にＩ開先を設け、次いで予歪みを付与した例を示す断面図である。
相当塑性ひずみε（％）＝1.15×ln（１−ｒ） ・・・(1)
圧下率ｒ＝Δｈ／ｈ0 ・・・(2)
ｈ0：予歪みを付与する前の鋼材の厚み（mm）
Δｈ：予歪みを付与することによる減厚量（mm）
予歪みを付与するために減厚すると鋼材に窪みが生じるが、図１に示すように、鋼材１の片面に窪み２を形成するように減厚することが好ましい。その理由は、両面に窪みを形成するよりも、簡素な装置で予歪みを付与できるからである。ただし鋼材１の両面に窪みを形成しても、本発明の効果を損ねる惧れはない。その場合は、上記の(2)式中のΔｈは、両面の減厚量の合計とする。
As shown in FIG. 1, it is preferable that the means for applying the pre-strain is a process for reducing the thickness of the steel material cold (for example, press process, punch process, etc.) and is deformed in the plate thickness direction. The reason is that a pre-strain can be imparted to a predetermined part by simple means. Of course, the same effect can be obtained in the width direction. FIG. 1 is a cross-sectional view showing an example in which an I groove is provided in the
Equivalent plastic strain ε (%) = 1.15 × ln (1-r) (1)
Reduction ratio r = Δh / h 0 (2)
h 0 : Thickness (mm) of the steel before pre-straining
Δh: Thickness reduction by applying pre-strain (mm)
When the thickness is reduced in order to impart pre-strain, a dent is generated in the steel material, but it is preferable to reduce the thickness so as to form a
窪み２の端部と開先４の突き合わせ面との距離Ｌ（mm）が小さすぎると、予歪みを付与する部位３（以下、予歪み領域という）が狭くなり、γ結晶粒が微細化されていない領域にも熱影響部が広がるので、熱影響部の靭性改善に寄与しない。一方で、距離Ｌが大きすぎると、予歪み領域３が広くなり、加工硬化の作用で靭性の低下を招く。したがって、窪み２の端部と開先４の突き合わせ面との距離Ｌは0.8ｈ0〜1.2ｈ0（mm）の範囲内が好ましい。
If the distance L (mm) between the end of the
開先の形状は特に限定せず、種々の形状の開先（たとえばＩ開先、Ｙ開先、Ｖ開先等）に本発明を適用できる。
また、溶接法は特に限定せず、アーク溶接（たとえばサブマージアーク溶接、ガスシールドアーク溶接等）、エレクトロスラグ溶接、ガス溶接、高エネルギービーム溶接（たとえばレーザ溶接等）、抵抗溶接、圧接等の広く普及している溶接法に本発明を適用できる。つまり、溶接後に熱影響部が形成される一般的な溶接法に本発明を適用して、熱影響部の靭性を改善することが可能である。また、溶接止端部における圧縮残留応力の影響で、疲労強度の向上にも効果を奏する。
The shape of the groove is not particularly limited, and the present invention can be applied to grooves having various shapes (for example, I groove, Y groove, V groove, etc.).
Also, the welding method is not particularly limited, and a wide range of arc welding (eg, submerged arc welding, gas shielded arc welding, etc.), electroslag welding, gas welding, high energy beam welding (eg, laser welding, etc.), resistance welding, pressure welding, etc. The present invention can be applied to popular welding methods. That is, it is possible to improve the toughness of the heat affected zone by applying the present invention to a general welding method in which the heat affected zone is formed after welding. In addition, the effect of compressive residual stress at the weld toe portion is also effective in improving fatigue strength.
いずれの溶接法を採用しても、入熱が小さすぎると、十分な溶込みが得られず、溶接金属に種々の欠陥が生じ易くなる。一方で、入熱が大きすぎると、予歪み領域３の外側（すなわちγ結晶粒が微細化されていない領域）にも熱影響部広がるので、熱影響部の靭性改善に寄与しない。したがって、溶接による入熱は、1.5〜8.0kJ／mmの範囲内が好ましい。
鋼材の鋼種も特に限定せず、一般の炭素鋼から、低炭素鋼、ＴＭＣＰ鋼をはじめ、合金元素を添加した合金鋼（たとえば高張力鋼、耐摩耗鋼、建築用耐火鋼等）まで、種々の鋼材に本発明を適用できる。ただし、既に説明した通り、高強度鋼（たとえば引張強さ400MPa以上）に適用すれば、熱影響部の靭性改善について多大な効果が得られるので好ましい。
Regardless of which welding method is employed, if the heat input is too small, sufficient penetration cannot be obtained, and various defects are likely to occur in the weld metal. On the other hand, if the heat input is too large, the heat-affected zone spreads outside the pre-strained region 3 (that is, the region where the γ crystal grains are not refined), and thus does not contribute to the improvement of the toughness of the heat-affected zone. Therefore, the heat input by welding is preferably in the range of 1.5 to 8.0 kJ / mm.
There is no particular limitation on the steel type of the steel material, and it ranges from general carbon steel to low-carbon steel, TMCP steel, and alloy steel added with alloying elements (for example, high-tensile steel, wear-resistant steel, architectural fire-resistant steel, etc.) The present invention can be applied to these steel materials. However, as already described, it is preferable to apply to high-strength steel (for example, tensile strength of 400 MPa or more) because a great effect can be obtained for improving the toughness of the heat affected zone.
さらに、TiN等の介在物によるピンニング効果を利用して熱影響部の靭性を高めた鋼材に適用すれば、靭性向上の効果がより一層向上するので好ましい。Ti：0.005〜0.030質量％、N：0.002〜0.008質量％を含有する鋼材に本発明を適用すれば、ピンニング効果を発揮させることができる。 Furthermore, it is preferable to apply to a steel material whose toughness of the heat affected zone is increased by utilizing the pinning effect due to inclusions such as TiN because the effect of improving the toughness is further improved. If the present invention is applied to a steel material containing Ti: 0.005 to 0.030 mass% and N: 0.002 to 0.008 mass%, the pinning effect can be exhibited.
表１に示す成分を有する鋼板（厚みｈ0：15mm）の端部にＹ開先を設け、さらに上面側から押圧して予歪みを付与した後に、図２に示すように、互いに付き合わせて溶接を行なった。 A Y-groove is provided at the end of a steel plate (thickness h 0 : 15 mm) having the components shown in Table 1, and after applying pre-strain by pressing from the upper side, as shown in FIG. Welding was performed.
予歪みを付与するために窪み２を形成する部位は、図２に示すように、開先４の突き合わせ面から距離Ｌ（＝18mm）までの部位とし、減厚量Δｈを種々変化させた。そのΔｈとｈ0を用いて(1)式から算出した相当塑性ひずみεを表２、３に示す。図２中の５は溶接金属、８は熱影響部を示す。
As shown in FIG. 2, the part where the
溶接は、サブマージアーク溶接、ガスシールドアーク溶接、レーザ溶接の３種類で行なった。溶接条件は表２、３に示す通りである。
得られた溶接継手から、図３に示すように、シャルピー衝撃試験片６を採取し、ＪＩＳ規格Z3111に準拠してシャルピー衝撃試験（−10℃）を行なった。シャルピー衝撃試験片６のノッチ７はＶノッチとし、ノッチ７に占める溶接金属５と鋼材１との比率が１：１となるような位置に板厚貫通方向に設けた。その結果を表２、３に示す。
Welding was performed by three types: submerged arc welding, gas shielded arc welding, and laser welding. The welding conditions are as shown in Tables 2 and 3.
As shown in FIG. 3, a Charpy
表２、３に示す発明例のうち、予歪みとして相当塑性歪み２％を付与して、サブマージアーク溶接を行なった例は、予歪みが小さいので、粗大なγ粒が残留した。その結果、吸収エネルギーVＥ-10の平均値が29Ｊであり、予歪みを付与しない比較例（VＥ-10の平均値：27Ｊ）に比べて、靭性が僅かに改善された。
その他の発明例は、いずれも予歪みとして相当塑性歪み５〜20％を付与したので、γ粒径が小さく、靭性が大幅に改善された。
Among the inventive examples shown in Tables 2 and 3, the example in which the equivalent plastic strain of 2% was applied as the pre-strain and the submerged arc welding was performed had a small pre-strain, so that coarse γ grains remained. As a result, the average value of absorbed energy V E -10 was 29 J, and the toughness was slightly improved as compared with the comparative example (average value of V E -10 : 27 J) in which no pre-strain was applied.
In all other invention examples, the equivalent plastic strain of 5 to 20% was given as a pre-strain, so the γ grain size was small and the toughness was greatly improved.
１ 鋼材
２ 窪み
３ 予歪み領域
４ 開先
５ 溶接金属
６ シャルピー衝撃試験片
７ ノッチ
８ 熱影響部
DESCRIPTION OF
Claims (1)
相当塑性ひずみε（％）＝1.15×ln（１−ｒ） ・・・(1)
圧下率ｒ＝Δｈ／ｈ 0 ・・・(2)
ｈ 0 ：予歪みを付与する前の鋼材の厚み（mm）
Δｈ：予歪みを付与することによる減厚量（mm） In the welding method for steel having a groove, after providing the groove, the equivalent plastic strain ε calculated the at GMA and (1) below as a prestrain previously cold at its peripheral portion 5 A welding method characterized by forming a recess by applying ~ 20% , and then performing welding.
Equivalent plastic strain ε (%) = 1.15 × ln (1-r) (1)
Reduction ratio r = Δh / h 0 (2)
h 0 : Thickness (mm) of the steel before pre-straining
Δh: Thickness reduction by applying pre-strain (mm)
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