JP2004195543A - Steel wire for gas shielded arc welding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welding wire which can maintain a stable feeding performance even in such critical working conditions that the feeding speed of the welding wire increases or the temperature of the welding wire increases as is the case with the gas shielded arc welding under a high heat input and high interpass temperature. <P>SOLUTION: The steel wire material of the welding wire comprises C:0.005-0.09 mass%, Si:0.50-1.2 mass%, Mn:1.50-2.2 mass%, Ti:0.15-0.30 mass%, B:0.0005-0.0035 mass%, Cu:≤0.50 mass%, S:0.005-0.025 mass% and the balance Fe with unavoidable impurities. The surface of the welding wire is covered by a solid lubricant layer of 0.2-1.0 g per the steel wire material of 10 kg, and the surface of the solid lubricant layer is coated with a lubricant of 0.2-1.8 g per the steel wire material of 10 kg. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

［Mn］：鋼素線のMn含有量（質量％）
［Si］：鋼素線のSi含有量（質量％）
［Ni］：鋼素線のNi含有量（質量％）
［Cr］：鋼素線のCr含有量（質量％）
［Mo］：鋼素線のMo含有量（質量％）
［Ｋ］：鋼素線のＫ含有量（質量％）
［Ｓ］：鋼素線のＳ含有量（質量％）
［Ti］：鋼素線のTi含有量（質量％）
［Al］：鋼素線のAl含有量（質量％）
また第２の好適態様として、固形潤滑剤層が、前記したMoＳ₂ ，Ｋ化合物および銅粉に加えてグラファイト：５〜20質量％を含有することが好ましい。
１または２に記載のガスシールドアーク溶接用鋼ワイヤ。
【００１５】
また第３の好適態様として、鋼素線の実測表面積Ｓ₀ （mm² ）と理論表面積Ｓ_a （mm² ）とを用いて下記の (3)式から算出される実表面積比Ｓが0.01〜3.0 ％の範囲内を満足することが好ましい。
Ｓ＝ 100×（Ｓ₀ −Ｓ_a ）／Ｓ_a ・・・ (3)
Ｓ ：実表面積比（％）
Ｓ₀ ：実測表面積（mm² ）
Ｓ_a ：理論表面積（mm² ）
また第４の好適態様として、鋼素線の表面に、平均厚さ 0.5μｍ以上のCuめっき層を形成することが好ましい。
【００１６】
【発明の実施の形態】
まず、本発明の溶接ワイヤの素材となる鋼素線の成分を限定した理由について説明する。
Ｃ： 0.005〜0.09質量％
Ｃは、溶接金属の強度を確保するために重要な成分であるが、溶融メタルの粘性を低下させ流動性を向上させる作用を有する元素である。Ｃ含有量が 0.005質量％未満では、溶接金属の強度を確保できない。一方、 0.09質量％を超えると、溶接を行なう際に溶融メタルの挙動が不安定となり、スパッタが多量に発生する。しかも不安定な短絡現象が起こり、 溶接ワイヤの送給性を阻害する。したがって、Ｃは 0.005〜0.09質量％の範囲内を満足する必要がある。
【００１７】
Si：0.50〜1.2 質量％
Siは、脱酸作用を有し、 溶接金属の脱酸のためには不可欠な元素である。Si含有量が0.50質量％未満では、溶接を行なう際に溶滴および溶融池が揺動し、スパッタが多量に発生する。しかも不安定な短絡現象が起こり、溶接ワイヤの送給性を阻害する。一方、 1.2質量％を超えると、溶接金属の靭性が低下する。したがって、Siは0.50〜1.2 質量％の範囲内を満足する必要がある。
【００１８】
Mn：1.50〜2.2 質量％
Mnは、Siと同様に脱酸作用を有し、 溶融メタルの脱酸のためには不可欠な元素である。Mn含有量が1.50質量％未満では、溶接を行なう際に溶融池が揺動して、スパッタが多量に発生するばかりでなく、溶融メタルの脱酸が不足し、溶接金属にブローホールが発生しやすくなる。しかも不安定な短絡現象が起こり、溶接ワイヤの送給性を阻害する。一方、 2.2質量％を超えると、溶接金属の靭性が低下する。したがって、Mnは1.50〜2.2 質量％の範囲内を満足する必要がある。
【００１９】
Ti：0.15〜0.30質量％
Tiは、脱酸剤として作用し、 さらに溶接金属の強度，靭性を増加させる元素である。しかもアークを安定させて、スパッタを減少させる効果も有する。Ti含有量が0.15質量％未満では、これらの効果が発揮されない上に、スラグ中に十分な量のTi酸化物を形成させることができないので、スラグの剥離性が向上しない。一方、 0.30質量％を超えると、ガスシールドアーク溶接を行なう際に溶滴が粗大となり、大粒のスパッタを発生させるとともに、溶接金属の靭性が著しく低下する。したがって、Tiは0.15〜0.30質量％の範囲内を満足する必要がある。
【００２０】
Ｂ：0.0005〜0.0035質量％
Ｂは、溶接金属の粒界フェライトの粗大化を抑制して組織を微細化し、靭性を向上させるのに有効である。Ｂ含有量が0.0005質量％未満では、これらの効果が発揮されない。一方、0.0035質量％を超えると、高温割れが生じやすくなる。したがって、Ｂは0.0005〜0.0035質量％の範囲内を満足する必要がある。
【００２１】
Cu：0.50質量％以下
Cuは、溶接ワイヤの表面に形成されるCuめっき層から主に溶接金属中に移行する元素であるが、Cuめっきを施さない場合にも溶接ワイヤ中に不可避的不純物として含有される。しかしCu含有量（すなわちCuめっき層中のCu含有量と溶接ワイヤ中のCu含有量との合計）が0.50質量％を超えると、溶接ビードに割れが生じやすくなる。したがって、Cuは0.50質量％以下に限定した。
【００２２】
Ｓ： 0.005〜0.025 質量％
Ｓは、製鋼および鋳造工程で不可避的に混入する元素である。Ｓ含有量が 0.005質量％未満では、平滑なビードが形成されず、ハンピングビードが生じやすくなる。一方、 0.025質量％を超えると、溶接金属の高温割れが発生しやすくなる。したがって、Ｓは 0.005〜0.025 質量％の範囲内を満足する必要がある。
【００２３】
また本発明では、鋼素線は、上記した組成に加えてMo：0.50質量％以下，Ni：2.0質量％以下およびCr：0.30質量％以下のうちの１種または２種以上を含有し、かつ下記の (1)式から算出されるＣＥ値が0.45以上、 (2)式から算出されるＫＥＱ値が0.02〜0.10の範囲内を満足することが好ましい。

［Mn］：鋼素線のMn含有量（質量％）
［Si］：鋼素線のSi含有量（質量％）
［Ni］：鋼素線のNi含有量（質量％）
［Cr］：鋼素線のCr含有量（質量％）
［Mo］：鋼素線のMo含有量（質量％）
［Ｋ］：鋼素線のＫ含有量（質量％）
［Ｓ］：鋼素線のＳ含有量（質量％）
［Ti］：鋼素線のTi含有量（質量％）
［Al］：鋼素線のAl含有量（質量％）
つまりMo，NiおよびCrは、いずれも溶接金属の強度を増加させ、かつ耐候性を向上させる成分であり、必要に応じて添加すれば良い。ただし各元素とも僅かな添加量で、これらの効果を発揮するから、特に下限を設ける必要はない。しかし過剰に添加すると溶接金属の靭性低下を招くので、これらの元素を添加する場合は、Mo：0.50質量％以下，Ni： 2.0質量％以下およびCr：0.30質量％以下とするのが好ましい。
【００２４】
また (1)式から算出されるＣＥ値は炭素当量と呼ばれるものであり、ＣＥ値が0.45未満では、大入熱かつ高パス間温度の条件で溶接を行なう場合に、十分な強度の溶接金属が得られない。したがって、ＣＥ値は0.45以上とするのが好ましい。一方、 ＣＥ値が 0.8を超えると、溶接金属の耐割れ性と靭性が低下する。そのため、ＣＥ値は 0.8以下とするのが一層好ましい。
【００２５】
次に、 (2)式から算出されるＫＥＱ値はビード形状を劣化させる元素の添加量を評価する指標である。つまりＫおよびＳは、Ti，SiおよびAlの含有量と関連させて添加するのが好ましいので、その指標としてＫＥＱ値が0.02〜0.10の範囲内を満足するように添加するのが好ましい。ＫＥＱ値がこの範囲を外れると、ハンピングビードが生じやすくなる。
【００２６】
なおAlは、脱酸剤として、横向き溶接におけるアーク安定剤として作用し、さらに溶接金属の強度，靭性を向上させる元素である。しかし0.50質量％を超えると、溶接金属の靭性を低下させる。したがって、Alは0.50質量％以下とするのが好ましい。
上記した鋼素線の成分以外の残部は、Feおよび不可避的不純物である。たとえばＯあるいはＮが代表的な不可避的不純物であり、鋼材を溶製する段階や鋼素線を製造する段階で不可避的に混入する。 Ｏは 0.020質量％以下，Ｎは 0.010質量％以下に低減するのが好ましい。 特にＯは、溶接に際して溶滴を微細化する効果を有するので、0.0020〜0.0080質量％とするのが一層好ましい。
【００２７】
次に、本発明の溶接ワイヤの製造方法について説明する。 なお、鋼素線の表面に形成される固形潤滑剤層あるいは潤滑剤層については、溶接ワイヤの製造工程にあわせて説明する。
転炉または電気炉等を用いて、上記した組成を有する溶鋼を溶製する。この溶鋼の溶製方法は、特定の技術に限定せず、従来から知られている技術を使用する。次いで、得られた溶鋼を、連続鋳造法や造塊法等によって鋼材（たとえばビレット等）を製造する。 この鋼材を加熱した後、熱間圧延を施し、さらに乾式の冷間圧延（すなわち伸線）を施して鋼素線を製造する。 熱間圧延や冷間圧延の操業条件は、特定の条件に限定せず、所望の寸法形状の鋼素線を製造する条件であれば良い。
【００２８】
さらに鋼素線は、焼鈍−酸洗−銅めっき−伸線加工−潤滑剤塗布の工程を順次施して、所定の製品すなわち溶接ワイヤとなる。
なお焼鈍を施す前に、あらかじめ鋼素線の表面にカリウム塩溶液を塗布しておくのが好ましい。カリウム塩溶液としては、クエン酸３カリウム水溶液，炭酸カリウム水溶液，水酸化カリウム水溶液等を使用するのが好ましい。また、塗布した後のカリウム塩濃度は、Ｋに換算した値で 0.5〜3.0 体積％とするのが好ましい。
【００２９】
このようにして表面にカリウム塩溶液を塗布した鋼素線を焼鈍することによって、生成される内部酸化層中にＫが安定して保持される。一方、ＫをCuめっき層中に保持させる方法や単に塗布するだけの方法では、Cuめっきや鋼素線の変色等の問題が発生しやすい。しかも熱的に不安定であるから、Ｋによる低スパッタ化の効果が小さくなる。
【００３０】
焼鈍は鋼素線の軟化およびＫの付与を目的として行なうものであり、 650〜950 ℃の温度範囲で、かつ水蒸気を含む窒素ガス雰囲気中で行なうのが好ましい。すなわち焼鈍温度が 650℃未満では、内部酸化の進行が遅くなる。一方、 950℃を超えると内部酸化の進行が速すぎて内部酸化量の調整が困難となる。
焼鈍雰囲気は、内部酸化を進行させる観点から、露点０℃以下、酸素濃度 200体積ppm 以下とするのが好ましい。表面にカリウム塩溶液を塗布した鋼素線を、このような焼鈍雰囲気で焼鈍することによって、その表面から酸化が進行して、表層部が内部酸化される。この内部酸化層にＫが確実に保持される。
【００３１】
なお、焼鈍時間および焼鈍温度は、カリウム塩溶液の塗布条件（たとえば塗布量，カリウム塩濃度，鋼素線の直径等）に応じて設定するのが好ましい。さらに鋼素線中のＫ含有量が0.0003〜0.0030質量％，Ｏ含有量が0.0020〜0.0080質量％となるように、焼鈍時間や焼鈍温度を設定するのが好ましい。
このようにして焼鈍を施した鋼素線は、酸洗した後で、その表面にCuめっきを施すのが好ましい。Cuめっき層の厚さは 0.5μｍ以上とするのが好ましい。
【００３２】
すなわち大電流で連続溶接を行なう場合は、給電不良により溶接ワイヤの送給が阻害されやすい。これに対して、Cuめっき層の厚さを 0.5μｍ以上とすることによって、給電不良に起因する溶接ワイヤの送給の不安定化を防止できる。より好ましくは 0.8μｍ以上である。このようにCuめっきを厚目付とすることによって、給電チップの損耗を低減する効果も得られる。
【００３３】
さらに、鋼素線の実表面積比Ｓが0.01〜3.00％の範囲内を満足することが好ましい。実表面積比Ｓは下記の (3)式で算出される値である。
Ｓ＝ 100×（Ｓ₀ −Ｓ_a ）／Ｓ_a ・・・ (3)
Ｓ ：実表面積比（％）
Ｓ₀ ：実測表面積（mm² ）
Ｓ_a ：理論表面積（mm² ）
ここで表面積とは、後述する潤滑剤を塗布する前の状態の表面積を意味する。したがって、溶接ワイヤの素材である鋼素線の表面積を指す。ただし鋼素線にCuめっきを施した場合は、Cuめっき層を含めた鋼素線の表面積である。
【００３４】
さらに鋼素線の実測表面積Ｓ₀ （mm² ）とは、走査型電子顕微鏡（いわゆるＳＥＭ）による 400倍の観察面に鋼素線が占める面積を指す。また鋼素線の理論表面積Ｓ_a （mm² ）とは、同様の観察面で鋼素線を円柱として計算した表面積を指す。
したがって鋼素線の実表面積比Ｓは、潤滑剤を塗布する前の鋼素線表面の凹凸の大きさを表わすことになる。つまり実表面積比Ｓが増大すると、凹凸が大きくなり、潤滑剤が付着する面積が増加することを意味している。逆に実表面積比Ｓが減少すると、潤滑剤が付着する面積が縮小することを意味している。溶接を行なう際に給電の安定化を図るためには、鋼素線の表面を平滑にする（すなわち実表面積比Ｓを小さくする）ことが好ましく、実表面積比Ｓを3.0 ％以下とすることが好ましい。一方、 実表面積比Ｓが0.01％未満では、鋼素線の表面に潤滑剤を塗布したときに、その付着量が不足しやすい。潤滑剤を過剰に塗布すると、鋼素線の表面に潤滑剤を付着させることは可能であるが、溶接を行なうにあたって送給ローラーでスリップするので送給が不安定になる。したがって、鋼素線の実表面積比Ｓは0.01〜3.0 ％の範囲内を満足することが好ましい。
【００３５】
このようにしてCuめっきを施した鋼素線を伸線、塗布する工程を利用して、表面に、MoＳ₂ ：15〜70質量％，Ｋ化合物：２〜25質量％，伸線工程で発生する銅粉：70質量％以下からなる固形潤滑剤層を形成する。この固形潤滑剤層は、鋼素線10kgあたり 0.2〜1.0 ｇとする。
溶接電流 400Ａで１分以上の連続溶接を行なうと、給電チップは 500℃以上の温度になる。このような高温では、脂肪酸エステルや潤滑油は分解するので潤滑性を維持できない。そこで本発明者らは種々の潤滑剤を検討した結果、高温でも潤滑性を維持するものとして、MoＳ₂ ，Ｋ化合物，銅粉が有効であることを見出した。ただしMoＳ₂ ：15〜70質量％，Ｋ化合物：２〜25質量％，伸線工程で発生する銅粉：70質量％以下の範囲内を満足する必要がある。この範囲を外れると、大入熱かつ高パス間温度でガスシールドアーク溶接を行なうにあたって、潤滑性を維持できず、溶接ワイヤの送給速度が著しく変動するので送給が不安定になる。
【００３６】
なおMoＳ₂ の含有量は、好ましくは15〜50質量％である。さらにグラファイトを５〜20質量％含有すると、高温の給電チップでの潤滑性が向上するので一層好ましい。
またＫ化合物としてステアリン酸カリウムを使用すると、高温の潤滑性が向上するので好ましい。
【００３７】
一方、 Cuめっき後の伸線工程で発生する銅粉は、コンジットチューブでの摩擦を低減する効果がある。固形潤滑剤層の銅粉量が70質量％を超えると、溶接を行なう際に給電チップで焼き付きが発生して、瞬間的に溶接ワイヤの送給が停止する。その結果、アークが不安定になる。したがって、固形潤滑剤層中の銅粉の含有量は70質量％以下に限定した。なお、固形潤滑剤層中の銅粉が５質量％未満では、溶接ワイヤを送給する際の抵抗を十分に軽減できないので、銅粉の含有量を５質量％以上とするのが好ましい。
【００３８】
Ｋは、前記した通り、アークを安定化し、溶接ワイヤの送給を安定化する働きがある。Ｋ化合物としては、ステアリン酸カリウムが好ましい。固形潤滑剤層中のＫ化合物が２質量％未満では、アーク安定化による溶接ワイヤ送給の安定化の効果がなく、70質量％を超えて添加すると、固形潤滑剤による送給性向上の効果がなくなる。したがって、固形潤滑剤層中のＫ化合物の含有量は２〜70質量％とした。
【００３９】
また、固形潤滑剤の付着量が鋼素線10kgあたり 0.2ｇ未満では、溶接ワイヤを送給する際の抵抗を軽減する効果が得られない。一方、鋼素線10kgあたり 1.0ｇを超えると、給電チップ内面に固形潤滑剤が付着蓄積されて溶接ワイヤの送給を阻害する。したがって、固形潤滑剤の付着量は鋼素線10kgあたり 0.2〜1.0 ｇの範囲内を満足する必要がある。
【００４０】
さらに、溶接を行なう際の溶接ワイヤの送給抵抗を軽減して、送給を安定化させるために、この固形潤滑剤層の表面に室温（25℃）で液体の脂肪酸エステルまたは潤滑油を塗布する。あるいは脂肪酸エステルと潤滑油との混合物を塗布しても良い。このようにして脂肪酸エステルおよび／または潤滑油からなる潤滑剤層を形成する。この潤滑剤層が鋼素線10kgあたり 0.2ｇ未満では、溶接ワイヤを送給する際の抵抗を軽減する効果が得られない。一方、鋼素線10kgあたり 1.8ｇを超えると、溶接を行なうにあたって溶接ワイヤが送給ローラーでスリップし、送給速度が著しく変動するので送給が不安定になる。したがって、潤滑剤層は鋼素線10kgあたり 0.2〜1.8 ｇの範囲内を満足する必要がある。
【００４１】
このようにして脂肪酸エステルおよび／または潤滑油を塗布して潤滑剤層を形成することによって、MoＳ₂ による鋼素線の変色と劣化を防止する効果も得られる。
【００４２】
【実施例】
連続鋳造によって製造されたビレットを熱間圧延して、直径 5.5〜7.0mm の線材とした。次いで冷間圧延（すなわち伸線）によって直径 2.0〜2.8mm の鋼素線とした。
この鋼素線を、露点−２℃以下，酸素濃度 200体積ppm 以下，二酸化炭素濃度0.1体積％以下の窒素雰囲気中で焼鈍した。焼鈍温度は 750〜950 ℃とした。焼鈍の後、鋼素線に酸洗を施し、必要に応じて鋼素線の表面にCuめっきを施した。さらに冷間で伸線加工（湿式伸線）を施して、直径 1.4〜1.6mm の溶接ワイヤを製造した。この冷間の伸線加工には湿式伸線を用いたが、その一部にMoＳ₂ ，ＢＮ，グラファイト，金属石鹸，あるいはＫ化合物からなる乾式伸線を加えることによって、高温潤滑性物質を溶接ワイヤの表面に付着させた。その高温潤滑性物質の付着量は、乾式伸線数，ダイススケジュール，ダイス形状を変更することによって調整した。
【００４３】
鋼素線の成分およびCuめっき層の厚さを表１，２に示す。なお表１，２中に示した鋼素線中のCu量は、Cuめっき層中のCuを含めた値である。さらに各鋼素線の表面に形成した固形潤滑剤層と潤滑剤層の成分を表３，４に示す。
【００４４】
【表１】

【００４５】
【表２】

【００４６】
【表３】

【００４７】
【表４】

【００４８】
これらの溶接ワイヤを使用して、表５に示す条件でガスシールドアーク溶接を行ない、溶接継手を作製した。開先形状は図１に示す通り、レ型開先（開先角度θ＝35°，ルートギャップＲ＝８mm）とし、鋼板１はＪＩＳ規格SM490Cの鋼板（厚さｔ＝32mm，幅Ｗ＝200mm ）を使用した。なお、シールドガスとして炭酸ガスを使用した。
【００４９】
【表５】

【００５０】
このようにしてガスシールドアーク溶接を行ないながら、溶接ワイヤの送給性，スパッタの発生量，給電チップの損耗度を下記の要領で調査した。
(a) 溶接ワイヤの送給性
ガスシールドアーク溶接を行ないながら溶接ワイヤの送給抵抗をロードセルで測定し、その平均値が29.4Ｎ以下（＝３kgf 以下）を良（○），29.4Ｎ超え（＝３kgf 超え）〜53.9Ｎ以下（＝5.5kgf以下）を可（△），53.9Ｎ超え（＝5.5kgf超え）を不可（×）として評価した。
(b) スパッタの発生量
Cu製捕集容器内でガスシールドアーク溶接を行ないながら、飛散したスパッタを回収して重量を測定し、スパッタの発生量が溶接時間１分あたり 2.0ｇ以下を良（○）， 2.0ｇ超え〜 3.0ｇ以下を可（△）， 3.0ｇ超えを不可（×）として評価した。
(c) 給電チップの損耗度
ガスシールドアーク溶接が終了した後、使用した給電チップ先端の内径を測定し、その最大値と最小値を用いて下記の (4)式から算出される楕円化率が２％以下を良（○），２％超え〜５％以下を可（△），５％超えを不可（×）として評価した。
【００５１】
楕円化率（％）＝ 100×（Ｄ_max −Ｄ_min ）／Ｄ_min ・・・ (4)
Ｄ_max ：給電チップ先端の最大内径（mm）
Ｄ_min ：給電チップ先端の最小内径（mm）
このようにして評価した結果を表６，７に示す。
【００５２】
【表６】

【００５３】
【表７】

【００５４】
またガスシールドアーク溶接の終了後、得られた溶接継手の溶接金属から引張試験片（ＪＩＳ規格Z2201 に準拠したＡ１号試験片）とシャルピー衝撃試験片（ＪＩＳ規格Z2202 に準拠した２mmＶノッチ試験片）を採取し、それぞれ引張試験（室温）およびシャルピー衝撃試験（０℃）を行なった。こうして得られた引張強さ（MPa ）とシャルピー吸収エネルギー（Ｊ）を表８，９に示す。なお、溶接金属の強度については、引張強さが490MPa以上を良（○），490MPa未満を不可（×）として評価した。靭性については、０℃における吸収エネルギーが 100Ｊ以上を良（○）， 100Ｊ未満を不可（×）として評価した。
【００５５】
【表８】

【００５６】
【表９】

【００５７】
表６，７から明らかなように、溶接ワイヤの送給抵抗は、発明例が26.5〜53.9Ｎであったのに対して、比較例では35.3〜94.1Ｎであった。スパッタの発生量は、発明例が1.47〜3.10ｇ／分であったのに対して、比較例では2.02〜5.24ｇ／分であった。給電チップの楕円化率は、発明例が 1.7〜4.8 ％であったのに対して、比較例では 2.9〜8.5 ％であった。つまり発明例の溶接ワイヤは、その送給抵抗，スパッタの発生量，給電チップの楕円化率が、いずれも比較例に比べて優れており、溶接ワイヤの送給性に優れていることが確かめられた。
【００５８】
また表８，９から明らかなように、発明例の溶接ワイヤを用いて得られた溶接金属の引張強さは491MPa以上、溶接金属の０℃におけるシャルピー吸収エネルギーは 100〜130 Ｊであったのに対して、比較例では34〜65Ｊであった。つまり発明例の溶接ワイヤを用いて得られた溶接金属の強度および靭性は、比較例に比べて優れていることが確かめられた。
【００５９】
【発明の効果】
軟鋼， 490Ｎ／mm² 級高張力鋼あるいは 590Ｎ／mm² 級高張力鋼のガスシールドアーク溶接を大入熱かつ高パス間温度で行なう際に、本発明の溶接ワイヤを用いることによって、溶接ワイヤの優れた送給性が得られ、安定した溶接が可能となる。その結果、強度および靭性に優れた溶接金属を有する溶接継手を安定して得ることができる。
【図面の簡単な説明】
【図１】開先形状を示す断面図である。
【符号の説明】
１ 鋼板
２ 当て金[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention, mild steel, 490 N / mm ² class high strength steel, 590N / mm ² class high strength steel gas shielded arc welding steel wire for use in the gas shielded arc welding (hereinafter, referred to as welding wire) relates, Particularly, the present invention relates to a welding wire used for gas shielded arc welding at a large heat input and a high interpass temperature.
[0002]
[Prior art]
Normally, in gas shielded arc welding, welding is performed by feeding a welding wire having a diameter of 0.6 to 1.6 mm as a consumable electrode at a speed of about 20 m / min. In order to maintain good weldability, it is essential to feed the welding wire stably. Therefore, the feedability of the welding wire has been improved by applying a Cu plating to the surface of the steel wire or using a welding wire coated with lubricating oil.
[0003]
Further, in order to further improve the welding efficiency in gas shielded arc welding, a technique for performing welding at a large heat input and a high interpass temperature has been studied in recent years. For example, gas shielded arc welding of 490 N / mm2 class ² high-strength steel sheet with a welding heat input of 40 kJ / cm and a temperature of about 350 ° C. near the welding line is performed. However, when gas shielded arc welding is performed under such a condition of large heat input and high inter-pass temperature, not only the strength of the weld metal decreases but also the toughness deteriorates.
[0004]
Therefore, in order to improve the properties of the weld metal, a welding wire (so-called solid wire) composed of a steel wire with an increased Mn content by adding Ti and B has been used. The use of such a welding wire improves the strength of the weld metal and stabilizes the weldability. As a result, when performing gas shielded arc welding, it is possible to increase the feeding speed of the welding wire and increase the welding current. In other words, it is possible to increase the welding wire feed speed by about 1.5 times compared to the normal feed speed and increase the welding current from the normal current value (= about 300A) to about 400A for welding. It is.
[0005]
In such high-speed and large-current welding, the amount of heat input increases and the temperature between passes increases, so that it is necessary to stably supply the welding wire. However, when performing gas shielded arc welding under conditions of large heat input and high interpass temperature, the conventionally known Cu plating and lubricating oil can stably maintain the feedability of the welding wire at a high level. It is difficult to do. Therefore, various techniques for improving the feedability of a welding wire used under conditions of large heat input and high inter-pass temperature have been studied.
[0006]
For example, Japanese Unexamined Patent Publication No. Hei 5-23731 discloses that a wire made of polytetrafluoroethylene, MoS ₂ , graphite and a mineral is held on the surface of a steel wire as a material to improve the feedability of a welding wire. The technology is disclosed.
Japanese Patent Application Laid-Open No. 11-217578 discloses a technique for improving the feedability of a welding wire by holding a lubricant such as MoS ₂ or WS ₂ , an ester or a petroleum braze on the surface of a steel wire as a material. Is disclosed.
[0007]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 5-23731 [Patent Document 2]
JP 11-217578 A
[Problems to be solved by the invention]
However, in the technology disclosed in Japanese Patent Application Laid-Open Nos. Hei 5-23731 and Hei 11-217578, when applied to gas shielded arc welding with a large current using a welding robot, the feeding of the welding wire is still performed. It is inevitable that stability cannot be maintained and the welding operation is hindered.
[0009]
Accordingly, an object of the present invention is to increase the feeding speed of a welding wire, such as gas shielded arc welding performed under conditions of large heat input and high interpass temperature, such as high current welding using a welding robot, It is an object of the present invention to provide a welding wire capable of obtaining a stable feeding property even when used under severe conditions where the temperature of the welding wire rises.
[0010]
[Means for Solving the Problems]
The present inventors have conducted intensive research on the phenomenon that the feedability of a welding wire becomes unstable when performing gas shielded arc welding with a large current using a welding robot. As a result, it was found that the composition of the steel strand as the material, the composition and the amount of the lubricant applied to the steel strand had a great effect.
[0011]
First, regarding the components of the steel wire, short-circuiting at the time of welding and reduction of the feed resistance of the welding wire are achieved by containing a predetermined amount of C, Si, Mn, Ti and B. As a result, even when the feeding speed of the welding wire is increased, the stability of the feeding of the welding wire can be maintained, so that a stable arc can be obtained.
In addition, when performing gas shielded arc welding with a welding current of about 400 A, the tip temperature of the power supply tip exceeds 550 ° C, so that conventionally known lubricating oils and ester-based lubricants are exposed to high temperatures. Decompose. Therefore, these lubricating oils and ester-based lubricants cannot maintain lubricity at high temperatures. Therefore, even if the temperature of the welding wire rises as the temperature of the power supply tip rises, the welding wire can be fed by applying a solid lubricant containing a heat-stable inorganic material and MoS ₂ and K compounds. Maintain feeding. As a result, a highly stable arc can be obtained.
[0012]
That is, the present invention relates to a welding steel wire used in gas shielded arc welding, wherein C: 0.005 to 0.09% by mass, Si: 0.50 to 1.2% by mass, Mn: 1.50 to 2.2% by mass, Ti: 0.15 to 0.30% by mass. %, B: 0.0005 to 0.0035% by mass, Cu: 0.50% by mass or less, S: 0.005 to 0.025% by mass, and MoS ₂ : 15 on the surface of a steel wire having a composition consisting of Fe and unavoidable impurities. 7070 mass%, K compound: 2-25 mass%, copper powder: 0.2-1.0 g per 10 kg of steel wire, containing 70 mass% or less, and fatty acid ester on the surface of the solid lubricant layer And / or a steel layer for gas shielded arc welding having a lubricant layer of lubricating oil in an amount of 0.2 to 1.8 g per 10 kg of steel wire.
[0013]
In the above-mentioned invention, as a first preferred embodiment, in addition to the above-described composition, the steel wire is one or more of Mo: 0.50% by mass or less, Ni: 2.0% by mass or less, and Cr: 0.30% by mass or less. It is preferable to contain two or more kinds, and to satisfy a CE value calculated from the following formula (1) of 0.45 or more and a KEQ value calculated from the following formula (2) within a range of 0.02 to 0.10.
[0014]

[Mn]: Mn content (mass%) of steel strand
[Si]: Si content of steel wire (% by mass)
[Ni]: Ni content of steel wire (mass%)
[Cr]: Cr content of steel wire (% by mass)
[Mo]: Mo content of steel wire (% by mass)
[K]: K content of steel wire (% by mass)
[S]: S content of steel strand (% by mass)
[Ti]: Ti content of steel strand (% by mass)
[Al]: Al content of steel wire (mass%)
As a second preferred embodiment, the solid lubricant layer preferably contains 5 to 20% by mass of graphite in addition to the above-mentioned MoS ₂ , K compound and copper powder.
3. The steel wire for gas shielded arc welding according to 1 or 2.
[0015]
As a third preferred embodiment, the actual surface area ratio S calculated from the following equation (3) using the measured surface area S ₀ (mm ² ) and the theoretical surface area S _a (mm ² ) of the steel strand is 0.01 to 0.01. It is preferable to satisfy the range of 3.0%.
S = 100 × (S ₀ −S _a ) / S _a (3)
S: actual surface area ratio (%)
S ₀ : measured surface area (mm ² )
S _a : Theoretical surface area (mm ² )
As a fourth preferred embodiment, it is preferable to form a Cu plating layer having an average thickness of 0.5 μm or more on the surface of the steel wire.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
First, the reason why the composition of the steel strand as the material of the welding wire of the present invention is limited will be described.
C: 0.005 to 0.09 mass%
C is an important component for securing the strength of the weld metal, but is an element having an effect of reducing the viscosity of the molten metal and improving the fluidity. If the C content is less than 0.005% by mass, the strength of the weld metal cannot be secured. On the other hand, if it exceeds 0.09% by mass, the behavior of the molten metal during welding becomes unstable, and a large amount of spatter is generated. In addition, an unstable short-circuit phenomenon occurs, impeding the feedability of the welding wire. Therefore, C must satisfy the range of 0.005 to 0.09% by mass.
[0017]
Si: 0.50 to 1.2 mass%
Si has a deoxidizing effect and is an indispensable element for deoxidizing weld metal. If the Si content is less than 0.50% by mass, the droplet and the molten pool fluctuate during welding, and a large amount of spatter is generated. In addition, an unstable short-circuit phenomenon occurs, which hinders the feedability of the welding wire. On the other hand, if it exceeds 1.2% by mass, the toughness of the weld metal decreases. Therefore, Si must satisfy the range of 0.50 to 1.2% by mass.
[0018]
Mn: 1.50 to 2.2 mass%
Mn has a deoxidizing effect like Si, and is an essential element for deoxidizing molten metal. If the Mn content is less than 1.50% by mass, the molten pool swings when performing welding, causing not only a large amount of spatter but also insufficient deoxidation of the molten metal and blowholes in the weld metal. It will be easier. In addition, an unstable short-circuit phenomenon occurs, which hinders the feedability of the welding wire. On the other hand, if it exceeds 2.2% by mass, the toughness of the weld metal decreases. Therefore, Mn needs to satisfy the range of 1.50 to 2.2% by mass.
[0019]
Ti: 0.15 to 0.30 mass%
Ti is an element that acts as a deoxidizing agent and further increases the strength and toughness of the weld metal. Moreover, it has the effect of stabilizing the arc and reducing spatter. If the Ti content is less than 0.15% by mass, these effects are not exhibited, and a sufficient amount of Ti oxide cannot be formed in the slag, so that the slag removability is not improved. On the other hand, if it exceeds 0.30% by mass, droplets become coarse when performing gas shielded arc welding, large spatters are generated, and the toughness of the weld metal is significantly reduced. Therefore, Ti needs to satisfy the range of 0.15 to 0.30% by mass.
[0020]
B: 0.0005 to 0.0035 mass%
B is effective in suppressing the coarsening of grain boundary ferrite of the weld metal to refine the structure and improve the toughness. If the B content is less than 0.0005% by mass, these effects are not exhibited. On the other hand, if it exceeds 0.0035% by mass, hot cracking is likely to occur. Therefore, B needs to satisfy the range of 0.0005 to 0.0035% by mass.
[0021]
Cu: 0.50 mass% or less
Cu is an element that mainly migrates into the weld metal from the Cu plating layer formed on the surface of the welding wire, but is included as an unavoidable impurity in the welding wire even when Cu plating is not performed. However, when the Cu content (that is, the sum of the Cu content in the Cu plating layer and the Cu content in the welding wire) exceeds 0.50% by mass, cracks tend to occur in the weld bead. Therefore, Cu was limited to 0.50% by mass or less.
[0022]
S: 0.005 to 0.025 mass%
S is an element inevitably mixed in the steel making and casting processes. When the S content is less than 0.005% by mass, a smooth bead is not formed, and a humping bead is easily generated. On the other hand, if it exceeds 0.025% by mass, hot cracking of the weld metal tends to occur. Therefore, S must satisfy the range of 0.005 to 0.025% by mass.
[0023]
Further, in the present invention, the steel strand contains one or more of Mo: 0.50% by mass or less, Ni: 2.0% by mass or less, and Cr: 0.30% by mass or less, in addition to the above composition, and It is preferable that the CE value calculated from the following equation (1) satisfies the range of 0.45 or more, and the KEQ value calculated from the equation (2) satisfies the range of 0.02 to 0.10.

[Mn]: Mn content (mass%) of steel strand
[Si]: Si content of steel wire (% by mass)
[Ni]: Ni content of steel wire (mass%)
[Cr]: Cr content of steel wire (% by mass)
[Mo]: Mo content of steel wire (% by mass)
[K]: K content of steel wire (% by mass)
[S]: S content of steel strand (% by mass)
[Ti]: Ti content of steel strand (% by mass)
[Al]: Al content of steel wire (mass%)
That is, Mo, Ni and Cr are components that increase the strength of the weld metal and improve the weather resistance, and may be added as needed. However, these effects are exhibited with a small amount of each element, so that it is not particularly necessary to set lower limits. However, if added in excess, the toughness of the weld metal is reduced. Therefore, when these elements are added, it is preferable that the content of Mo is 0.50% by mass or less, the content of Ni is 2.0% by mass or less and the content of Cr is 0.30% by mass or less.
[0024]
The CE value calculated from the equation (1) is called a carbon equivalent. When the CE value is less than 0.45, when welding is performed under conditions of large heat input and high interpass temperature, a weld metal having sufficient strength is used. Can not be obtained. Therefore, the CE value is preferably set to 0.45 or more. On the other hand, if the CE value exceeds 0.8, the crack resistance and toughness of the weld metal decrease. Therefore, the CE value is more preferably set to 0.8 or less.
[0025]
Next, the KEQ value calculated from the equation (2) is an index for evaluating the addition amount of the element that deteriorates the bead shape. That is, since K and S are preferably added in relation to the contents of Ti, Si and Al, they are preferably added so that the KEQ value satisfies the range of 0.02 to 0.10. If the KEQ value is out of this range, a humping bead tends to occur.
[0026]
Al is an element that acts as a deoxidizing agent, acts as an arc stabilizer in transverse welding, and further improves the strength and toughness of the weld metal. However, if it exceeds 0.50% by mass, the toughness of the weld metal is reduced. Therefore, the content of Al is preferably set to 0.50% by mass or less.
The balance other than the components of the above-mentioned steel wires is Fe and inevitable impurities. For example, O or N is a typical inevitable impurity, and is inevitably mixed in a step of melting a steel material or a step of manufacturing a steel wire. O is preferably reduced to 0.020% by mass or less, and N is preferably reduced to 0.010% by mass or less. In particular, O has the effect of making the droplets fine during welding, so it is more preferable to set O to 0.0020 to 0.0080% by mass.
[0027]
Next, a method for manufacturing a welding wire according to the present invention will be described. The solid lubricant layer or the lubricant layer formed on the surface of the steel wire will be described in accordance with the manufacturing process of the welding wire.
Using a converter or an electric furnace, molten steel having the above composition is produced. The method for smelting molten steel is not limited to a specific technique, and a conventionally known technique is used. Next, a steel material (for example, a billet or the like) is manufactured from the obtained molten steel by a continuous casting method, an ingot making method, or the like. After the steel material is heated, it is subjected to hot rolling, and further to dry cold rolling (that is, wire drawing) to produce a steel strand. The operating conditions of the hot rolling and the cold rolling are not limited to specific conditions, and may be any conditions as long as a steel wire having a desired size and shape is manufactured.
[0028]
Further, the steel wire is subjected to the steps of annealing, pickling, copper plating, wire drawing, and lubricant application in order to obtain a predetermined product, that is, a welding wire.
It is preferable to apply a potassium salt solution to the surface of the steel wire before annealing. As the potassium salt solution, it is preferable to use an aqueous solution of tripotassium citrate, an aqueous solution of potassium carbonate, an aqueous solution of potassium hydroxide, or the like. The potassium salt concentration after the application is preferably 0.5 to 3.0% by volume in terms of K.
[0029]
By annealing the steel wire coated with the potassium salt solution on the surface in this manner, K is stably retained in the generated internal oxide layer. On the other hand, a method of holding K in the Cu plating layer or a method of simply applying K is likely to cause problems such as Cu plating and discoloration of the steel wire. In addition, since it is thermally unstable, the effect of reducing sputtering by K is reduced.
[0030]
Annealing is performed for the purpose of softening the steel wire and imparting K, and is preferably performed in a temperature range of 650 to 950 ° C. and in a nitrogen gas atmosphere containing steam. That is, if the annealing temperature is lower than 650 ° C., the progress of internal oxidation is slow. On the other hand, if the temperature exceeds 950 ° C., the progress of internal oxidation is too fast, and it becomes difficult to adjust the amount of internal oxidation.
The annealing atmosphere preferably has a dew point of 0 ° C. or less and an oxygen concentration of 200 vol ppm or less from the viewpoint of promoting internal oxidation. By annealing a steel wire having a surface coated with a potassium salt solution in such an annealing atmosphere, oxidation proceeds from the surface and the surface layer is internally oxidized. K is reliably held in this internal oxide layer.
[0031]
The annealing time and the annealing temperature are preferably set according to the application conditions of the potassium salt solution (for example, the application amount, the potassium salt concentration, the diameter of the steel wire, etc.). Further, it is preferable to set the annealing time and the annealing temperature so that the K content in the steel wire is 0.0003 to 0.0030% by mass and the O content is 0.0020 to 0.0080% by mass.
It is preferable that the steel wire annealed in this way be subjected to pickling and then subjected to Cu plating on its surface. The thickness of the Cu plating layer is preferably 0.5 μm or more.
[0032]
That is, when performing continuous welding with a large current, feeding of the welding wire is likely to be hindered due to poor power supply. On the other hand, by setting the thickness of the Cu plating layer to 0.5 μm or more, it is possible to prevent the feeding of the welding wire from becoming unstable due to the power feeding failure. It is more preferably at least 0.8 μm. By making the Cu plating thicker, an effect of reducing the wear of the power supply chip can be obtained.
[0033]
Further, it is preferable that the actual surface area ratio S of the steel strand satisfies the range of 0.01 to 3.00%. The actual surface area ratio S is a value calculated by the following equation (3).
S = 100 × (S ₀ −S _a ) / S _a (3)
S: actual surface area ratio (%)
S ₀ : measured surface area (mm ² )
S _a : Theoretical surface area (mm ² )
Here, the surface area means the surface area before applying a lubricant described later. Therefore, it refers to the surface area of the steel wire which is the material of the welding wire. However, when the steel wire is plated with Cu, it is the surface area of the steel wire including the Cu plating layer.
[0034]
Further, the measured surface area S ₀ (mm ² ) of the steel wire refers to the area occupied by the steel wire on a 400-times observation surface by a scanning electron microscope (so-called SEM). The theoretical surface area S _a (mm ² ) of the steel strand refers to the surface area calculated using the steel strand as a cylinder on the same observation surface.
Therefore, the actual surface area ratio S of the steel wire represents the size of the irregularities on the surface of the steel wire before the lubricant is applied. That is, when the actual surface area ratio S increases, the irregularities increase, and the area to which the lubricant adheres increases. Conversely, when the actual surface area ratio S decreases, it means that the area to which the lubricant adheres decreases. In order to stabilize the power supply during welding, it is preferable to smooth the surface of the steel wire (that is, to reduce the actual surface area ratio S), and to set the actual surface area ratio S to 3.0% or less. preferable. On the other hand, when the actual surface area ratio S is less than 0.01%, when the lubricant is applied to the surface of the steel wire, the amount of the lubricant tends to be insufficient. If the lubricant is applied excessively, it is possible to attach the lubricant to the surface of the steel wire, but the feeding becomes unstable because the feed roller slips when performing welding. Therefore, it is preferable that the actual surface area ratio S of the steel wire satisfies the range of 0.01 to 3.0%.
[0035]
Using the process of drawing and applying the Cu-plated steel wire, MoS ₂ : 15 to 70% by mass, K compound: 2 to 25% by mass, generated in the drawing process Copper powder: A solid lubricant layer composed of 70% by mass or less is formed. The solid lubricant layer is 0.2 to 1.0 g per 10 kg of steel wire.
When continuous welding is performed for 1 minute or more with a welding current of 400 A, the temperature of the power supply tip becomes 500 ° C. or more. At such a high temperature, the fatty acid ester and the lubricating oil decompose, so that lubricity cannot be maintained. The present inventors have studied various lubricants and have found that MoS ₂ , K compounds, and copper powder are effective in maintaining lubricity even at high temperatures. However MoS _2: 15 to 70 wt%, K compound: 2 to 25 wt%, copper powder produced by drawing process: it is necessary to satisfy the range 70 wt% or less. Outside of this range, when performing gas shielded arc welding at a large heat input and a high interpass temperature, lubricity cannot be maintained, and the feeding speed of the welding wire fluctuates significantly, so that feeding becomes unstable.
[0036]
The content of MoS ₂ is preferably 15 to 50% by mass. Further, when graphite is contained in an amount of 5 to 20% by mass, lubricity in a high-temperature power supply tip is improved, which is more preferable.
Use of potassium stearate as the K compound is preferable because lubricity at high temperatures is improved.
[0037]
On the other hand, copper powder generated in the wire drawing step after Cu plating has an effect of reducing friction in the conduit tube. If the amount of copper powder in the solid lubricant layer exceeds 70% by mass, seizure occurs at the power supply tip when performing welding, and the supply of the welding wire is instantaneously stopped. As a result, the arc becomes unstable. Therefore, the content of the copper powder in the solid lubricant layer was limited to 70% by mass or less. If the copper powder in the solid lubricant layer is less than 5% by mass, the resistance at the time of feeding the welding wire cannot be sufficiently reduced, so that the content of the copper powder is preferably 5% by mass or more.
[0038]
As described above, K has a function of stabilizing the arc and stabilizing the feeding of the welding wire. As the K compound, potassium stearate is preferable. When the K compound in the solid lubricant layer is less than 2% by mass, the effect of arc stabilization does not have the effect of stabilizing the feeding of the welding wire, and when it exceeds 70% by mass, the effect of improving the feedability by the solid lubricant is obtained. Disappears. Therefore, the content of the K compound in the solid lubricant layer is set to 2 to 70% by mass.
[0039]
If the amount of the solid lubricant attached is less than 0.2 g per 10 kg of the steel wire, the effect of reducing the resistance when feeding the welding wire cannot be obtained. On the other hand, if the weight exceeds 1.0 g per 10 kg of the steel wire, the solid lubricant adheres and accumulates on the inner surface of the power supply tip, and the feeding of the welding wire is obstructed. Therefore, it is necessary that the amount of the solid lubricant adhered falls within the range of 0.2 to 1.0 g per 10 kg of the steel wire.
[0040]
Furthermore, in order to reduce the feed resistance of the welding wire during welding and stabilize the feed, a liquid fatty acid ester or lubricating oil is applied to the surface of this solid lubricant layer at room temperature (25 ° C). I do. Alternatively, a mixture of a fatty acid ester and a lubricating oil may be applied. Thus, a lubricant layer composed of the fatty acid ester and / or the lubricating oil is formed. If the lubricant layer is less than 0.2 g per 10 kg of the steel wire, the effect of reducing the resistance when feeding the welding wire cannot be obtained. On the other hand, if the weight exceeds 1.8 g per 10 kg of the steel wire, the welding wire slips at the feed roller when performing welding, and the feeding speed fluctuates remarkably, so that feeding becomes unstable. Therefore, the lubricant layer must satisfy the range of 0.2 to 1.8 g per 10 kg of the steel wire.
[0041]
By forming the lubricant layer by applying the fatty acid ester and / or the lubricating oil in this manner, an effect of preventing discoloration and deterioration of the steel wire by MoS ₂ can be obtained.
[0042]
【Example】
The billet produced by continuous casting was hot-rolled into a wire having a diameter of 5.5 to 7.0 mm. Next, a steel wire having a diameter of 2.0 to 2.8 mm was formed by cold rolling (that is, drawing).
The steel wire was annealed in a nitrogen atmosphere having a dew point of −2 ° C. or less, an oxygen concentration of 200 vol ppm or less, and a carbon dioxide concentration of 0.1 vol% or less. The annealing temperature was 750-950 ° C. After annealing, the steel wire was pickled and, if necessary, the surface of the steel wire was plated with Cu. Further, cold drawing was performed (wet drawing) to produce a welding wire with a diameter of 1.4 to 1.6 mm. Wet wire drawing was used for the cold wire drawing, but a high temperature lubricating substance was welded by adding dry wire drawing of MoS ₂ , BN, graphite, metal soap, or K compound to a part of it. Attached to the surface of the wire. The adhesion amount of the high-temperature lubricating substance was adjusted by changing the number of dry drawing, the die schedule, and the die shape.
[0043]
Tables 1 and 2 show the components of the steel wire and the thickness of the Cu plating layer. The amount of Cu in the steel wire shown in Tables 1 and 2 is a value including Cu in the Cu plating layer. Tables 3 and 4 show the components of the solid lubricant layer and the lubricant layer formed on the surface of each steel wire.
[0044]
[Table 1]

[0045]
[Table 2]

[0046]
[Table 3]

[0047]
[Table 4]

[0048]
Using these welding wires, gas shielded arc welding was performed under the conditions shown in Table 5 to produce welded joints. As shown in FIG. 1, the groove shape is a groove shape (groove angle θ = 35 °, root gap R = 8 mm), and the steel plate 1 is a JIS standard SM490C steel plate (thickness t = 32 mm, width W = 200 mm). )It was used. Note that carbon dioxide gas was used as a shielding gas.
[0049]
[Table 5]

[0050]
While performing gas shielded arc welding in this manner, the feedability of the welding wire, the amount of spatter generated, and the degree of wear of the power supply tip were investigated in the following manner.
(a) Feedability of welding wire While performing gas shielded arc welding, the feed resistance of the welding wire was measured with a load cell, and the average value was 29.4 N or less (= 3 kgf or less) as good (○), exceeding 29.4 N ( = 3 kgf or more and 53.9 N or less (= 5.5 kgf or less) were evaluated as acceptable (△), and those exceeding 53.9 N (= 5.5 kgf) were evaluated as unacceptable (x).
(b) Spatter generation
While performing gas shielded arc welding in a Cu collection vessel, the scattered spatter was collected and weighed, and the amount of spatter generated was better than 2.0 g per minute of welding time per minute (good), exceeding 2.0 g ~ It was evaluated as 3.0 g or less as acceptable (△) and exceeding 3.0 g as unacceptable (x).
(c) Degree of wear of power supply tip After gas shield arc welding is completed, measure the inner diameter of the tip of the power supply tip used, and use the maximum and minimum values to calculate the ellipticity calculated from the following equation (4). Was evaluated as good (○) when it was 2% or less, acceptable (を) when it exceeded 2% to 5% or less, and unacceptable (x) when it exceeded 5%.
[0051]
Ellipticity (%) = 100 × (D _max −D _min ) / D _min (4)
D _max : maximum inner diameter (mm) of the tip of the power supply tip
D _min : Minimum inner diameter of the tip of the power supply tip (mm)
Tables 6 and 7 show the results of the evaluation.
[0052]
[Table 6]

[0053]
[Table 7]

[0054]
After gas shielded arc welding is completed, a tensile test piece (A1 test piece according to JIS Z2201) and a Charpy impact test piece (2 mm V notch test piece according to JIS Z2202) are obtained from the weld metal of the obtained welded joint. Were subjected to a tensile test (room temperature) and a Charpy impact test (0 ° C.), respectively. Tables 8 and 9 show the tensile strength (MPa) and Charpy absorbed energy (J) thus obtained. With respect to the strength of the weld metal, a tensile strength of 490 MPa or more was evaluated as good (不可), and a tensile strength of less than 490 MPa was evaluated as unacceptable (×). Regarding toughness, the absorption energy at 0 ° C. of 100 J or more was evaluated as good (○) and less than 100 J was evaluated as unacceptable (×).
[0055]
[Table 8]

[0056]
[Table 9]

[0057]
As is clear from Tables 6 and 7, the feed resistance of the welding wire was 26.5 to 53.9 N in the inventive example, but 35.3 to 94.1 N in the comparative example. The amount of spatter generated was 1.47-3.10 g / min in the invention example, while it was 2.02-5.24 g / min in the comparative example. The ellipticity of the power supply chip was 1.7 to 4.8% in the invention example, and 2.9 to 8.5% in the comparative example. In other words, it was confirmed that the welding wire of the invention example was superior in the feed resistance, the amount of spatter generated, and the ellipticity of the power supply tip as compared with the comparative example, and was excellent in the feedability of the welding wire. Was done.
[0058]
Further, as is clear from Tables 8 and 9, the tensile strength of the weld metal obtained using the welding wire of the invention example was 491 MPa or more, and the Charpy absorbed energy at 0 ° C. of the weld metal was 100 to 130 J. On the other hand, it was 34 to 65 J in the comparative example. That is, it was confirmed that the strength and toughness of the weld metal obtained using the welding wire of the invention example were superior to those of the comparative example.
[0059]
【The invention's effect】
Mild steel, gas shielded arc welding of 490 N / mm ² class high strength steel or 590N / mm ² class high strength steel when carried out at a temperature between large heat input and high-pass, by using a welding wire of the present invention, the welding wire Excellent feedability can be obtained, and stable welding can be performed. As a result, a welded joint having a weld metal excellent in strength and toughness can be stably obtained.
[Brief description of the drawings]
FIG. 1 is a sectional view showing a groove shape.
[Explanation of symbols]
1 Steel plate 2 Cover

Claims (5)

A welding steel wire used in gas shielded arc welding, wherein C: 0.005 to 0.09% by mass, Si: 0.50 to 1.2% by mass, Mn: 1.50 to 2.2% by mass, Ti: 0.15 to 0.30% by mass, B: 0.0005 ～0.0035 mass%, Cu: 0.50 mass% or less, S: 0.005 to 0.025 containing mass%, MoS on the surface of the steel element wire having the balance consisting of Fe and unavoidable impurities _2: 15-70 wt%, K-compound: 2 to 25% by mass, copper powder: 0.2 to 1.0 g per 10 kg of the steel wire having a solid lubricant layer containing 70% by mass or less, and fatty acid ester and / or A steel wire for gas shielded arc welding, comprising a lubricant layer comprising a lubricating oil in an amount of 0.2 to 1.8 g per 10 kg of the steel wire. The steel strand contains, in addition to the composition, one or more of Mo: 0.50% by mass or less, Ni: 2.0% by mass or less, and Cr: 0.30% by mass or less, and the following (1) The steel wire for gas shielded arc welding according to claim 1, wherein the CE value calculated from the equation satisfies 0.45 or more, and the KEQ value calculated from the equation (2) satisfies the range of 0.02 to 0.10.

[Mn]: Mn content (mass%) of steel strand
[Si]: Si content of steel wire (% by mass)
[Ni]: Ni content of steel wire (mass%)
[Cr]: Cr content of steel wire (% by mass)
[Mo]: Mo content of steel wire (% by mass)
[K]: K content of steel wire (% by mass)
[S]: S content of steel strand (% by mass)
[Ti]: Ti content of steel strand (% by mass)
[Al]: Al content of steel wire (mass%) 3. The steel wire for gas shielded arc welding according to claim 1, wherein the solid lubricant layer contains 5 to 20% by mass of graphite in addition to the MoS ₂ , the K compound, and the copper powder. 4. The actual surface area ratio S calculated from the following equation (3) using the measured surface area S ₀ (mm ² ) and the theoretical surface area S _a (mm ² ) of the steel strand satisfies the range of 0.01 to 3.0%. The steel wire for gas shielded arc welding according to claim 1, 2 or 3, wherein:
S = 100 × (S ₀ −S _a ) / S _a (3)
S: actual surface area ratio (%)
S ₀ : measured surface area (mm ² )
S _a : Theoretical surface area (mm ² ) The steel wire for gas shielded arc welding according to claim 1, wherein a Cu plating layer having an average thickness of 0.5 μm or more is formed on a surface of the steel wire.

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