JP5669684B2 - Flux-cored wire for horizontal fillet gas shielded arc welding - Google Patents

Description

The present invention relates to a flux cored wire for horizontal fillet gas shield arc welding of a steel plate (hereinafter referred to as a primer coated steel plate) obtained by coating mild steel and 490 to 590 MPa class high strength steel with a shop primer (mainly inorganic zinc primer).

  In recent years, the ratio of fillet welding of primer-coated steel sheets is high in the field of shipbuilding and marine vessels, and there is still a strong demand for improvement in welding materials in order to improve the welding efficiency. In addition, in order to comply with PSPC (coating standard for coated steel sheets), emphasis is placed on the state of steel plates after welding and coating conditions such as spatter adhesion and shot blasting after assembly by high-speed welding.

  When primer-coated steel sheets are welded especially by horizontal fillet welding, spatter generation increases, pit resistance, bead shape, and bead appearance deterioration are problems. Flux-cored wire for gas shield arc welding to improve these problems. Various proposals have been made.

Regarding the pit resistance of the flux-filled wire for horizontal fillet gas shielded arc welding of the primer coated steel sheet, the slag-based wire mainly composed of ZrO ₂ —SiO ₂ from the conventional slag-based wire mainly composed of TiO ₂ (for example, Patent Document 1 and Patent Document 2) are the mainstream. However, these wires have ZrO ₂ as the main component of the slag forming agent, so that pit resistance can be obtained by vigorous stirring action of the molten pool with a strong arc force by ZrO ₂ , but the conventional TiO ₂ is mainly used. There is a problem that spatter is more likely to occur than slag-based wires.

In the case of a slag wire mainly composed of TiO ₂ , although the amount of spatter generated is reduced, the slag becomes thick and the pit resistance is inferior. When trying to improve the pit resistance in these wires, the viscosity of the slag changes, the bead shape becomes poor, and the slag peelability may deteriorate. However, in the wire developed in the two-electrode horizontal fillet gas shielded arc welding method, the pit resistance is excellent even in the case of a slag-based wire mainly composed of TiO ₂ (for example, Patent Document 3 and Patent Document 4). reference).

  However, even in the techniques disclosed in Patent Document 3 and Patent Document 4, when the primer coated steel sheet has a large primer film thickness, there is a problem that the amount of spatter generated is large and pit generation cannot be prevented.

Japanese Patent Laid-Open No. 11-5193 JP 2000-42787 A JP 2009-190042 A JP 2010-194571 A

  In view of such problems, the present invention provides excellent pit resistance even when used for horizontal fillet welding of a primer coated steel sheet having a large primer film thickness, and generates a small amount of spatter, and has a bead shape and a bead appearance. An object of the present invention is to provide a flux-cored wire for horizontal fillet gas shielded arc welding with good welding workability such as excellent welding workability.

The gist of the present invention is a flux-cored wire for horizontal fillet gas shield arc welding in which a steel outer shell is filled with a flux, in mass% with respect to the total mass of the wire,
TiO ₂ conversion value of Ti oxide: 0.5 to 2.5%,
SiO ₂ conversion value of Si oxide: 0.1 to 0.5%,
ZrO ₂ conversion value of Zr oxide: 0.1 to 0.5%,
C: 0.03-0.10%,
Si: 0.4 to 0.85%,
Mn: 1.5-3.0%
And Mn / Si: 3.0-4.5,
Al: 0.2 to 0.5%,
Mg: 0.1 to 0.4%
And Al + Mg: 0.5-0.8%
FeO equivalent value of Fe oxide: 0.1 to 1.0%,
One or of the sum of _{K 2} O conversion value of terms of Na ₂ O values or K compounds of Na compound: 0.05% to 0.2%,
F conversion value of fluorine compound: 0.02 to 0.1%,
The total of the slag forming agents containing fluorine compounds is 1.5 to 3.5%, and the balance is Fe content of steel outer shell, Fe content in alloy iron, iron powder and inevitable impurities.

  Moreover, it exists in the fluxed wire for horizontal fillet gas shield arc welding characterized by containing 0.005-0.035% of the total of 1 type or 2 types of Bi conversion value of metal Bi or Bi oxide.

  According to the flux-filled wire for horizontal fillet gas shielded arc welding of the present invention, excellent pit resistance is obtained in horizontal fillet welding and the amount of spatter generated even when the primer coating steel sheet is thick. Since the welding workability is good such that the bead shape and the bead appearance are excellent, the welding efficiency can be improved and the quality of the welded portion can be improved.

In order to solve the above-mentioned problems, the inventors made various types of wires and examined the details. As a _result, the wire mainly composed of ZrO 2 -SiO _{2 system,} may ZrO ₂ -SiO 2 -TiO spatter arc becomes rough collapsed balance of components ₂ is increased, also deteriorates the slag encapsulated is there.

By using TiO ₂ as the main component, it is possible to prevent the arc from becoming rough and to obtain a vigorous stirring action of the molten pool with a strong arc force by ZrO ₂ and a uniform slag encapsulation state even if the amount of slag generation is reduced. Therefore, it is possible to easily release the primer combustion gas from the molten pool to the outside and prevent the generation of pits. Also, considering the fact that SiO ₂ can adjust the viscosity of the molten slag to suppress excessive retreat of the molten pool due to arc force and prevent the bead from becoming convex, the amount of SiO ₂ —ZrO ₂ is made appropriate. Thus, the present inventors have found that even when the slag forming agent is reduced to form a very low slag wire, the pit resistance is good and the slag can be uniformly encapsulated.

Al or Mg acts as a deoxidizer when added as a metal, and has the effect of adjusting the yield of Si or Mn to the weld metal, and partly as an oxide such as Al ₂ O ₃ or MgO during melting It is involved in the slag encapsulation as a slag agent. However, when added as Al ₂ O ₃ or MgO, the slag is not encapsulated uniformly and the slag peelability is poor, so it is not added as an oxide, and Al and Mg are added mainly as a deoxidizer. I found it desirable.

Furthermore, by limiting the total of Mn / Si, Al and Mg and the FeO equivalent value of Fe oxide, and the total of slag formers containing fluorine compounds, sufficient slag encapsulation, slag peelability, pit resistance and It was found that mechanical performance was obtained and that the primer coated steel sheet was applicable to thick fillet welding with a thick primer.
In the present invention, the component design of the flux-cored wire for horizontal fillet gas shielded arc welding is performed based on the above-mentioned matters newly found by the present inventors.

  The reason for limiting the component composition and content of the flux cored wire for horizontal fillet gas shielded arc welding of the present invention will be described below. In addition, content of each component composition is shown by the mass% with respect to the wire total mass.

[TiO ₂ converted value of Ti oxides 0.5 to 2.5%
TiO ₂ is rutile of Ti oxide, titanium oxide, titanium sodium is added titanium slag, ilmenite and the like. These have the effect of encapsulating the entire bead uniformly. Further, there is an effect that the arc is sustained and stabilized to reduce the amount of spatter generated. If the TiO ₂ equivalent value of the Ti oxide is less than 0.5%, the amount of slag generated is insufficient and the beads cannot be encapsulated uniformly, so that the slag seizes on the bead surface and the bead appearance becomes poor. Further, the effect of stabilizing the arc is lost and the amount of spatter generated increases. On the other hand, if it exceeds 2.5%, the arc is stabilized and the amount of spatter generated decreases, but the slag becomes thick and the viscosity of the slag increases and pits are likely to occur. Therefore, the TiO ₂ equivalent value of the Ti oxide is 0.5 to 2.5%, preferably 1.2 to 2.1%.

[SiO ₂ converted value of Si oxide: 0.1% to 0.5%]
SiO ₂ is added from silica sand, zircon sand, silica sand soda, etc., and has an action of increasing the viscosity of the molten slag and improving the slag peelability. When the SiO ₂ equivalent value of the Si oxide is less than 0.1%, the slag encapsulation state is poor and the slag peelability is poor, and the bead shape and bead appearance are also poor. On the other hand, when the SiO ₂ equivalent value of the Si oxide exceeds 0.5%, the amount of spatter generated increases. Further, the bead toe (lower plate side) is swollen, the bead shape and the bead appearance are poor, and pits and gas grooves are easily generated. Therefore, the SiO ₂ equivalent value of the Si oxide is set to 0.1 to 0.5%.

[ZrO ₂ converted value of Zr oxide: 0.1 to 0.5%]
ZrO ₂ is added from zircon sand, zirconium oxide, and the like, and stirs the molten pool with a strong arc force to easily release the primer combustion gas from the molten pool to the outside and prevent the generation of pits. Moreover, it has the effect | action which raises slag encapsulation and smoothes a bead shape. If the ZrO ₂ conversion value of the Zr oxide is less than 0.1%, the bead shape is not smooth, the bead shape becomes convex, the slag peelability becomes poor, and pits are generated. On the other hand, if the ZrO ₂ conversion value of the Zr oxide exceeds 0.5%, the bead shape tends to be convex. Therefore, the ZrO ₂ conversion value of the Zr oxide is 0.1 to 0.5%.

[C: 0.03-0.10%]
C is added from C containing a small amount of steel alloy and Fe-Si, Fe-Mn, Fe-Si-Mn, and other iron alloys to obtain the strength and toughness of the weld metal required for welded structures. Added. If C is less than 0.03, the toughness of the weld metal decreases. On the other hand, if it exceeds 0.10%, the strength of the weld metal increases and the toughness decreases. Therefore, C is 0.03 to 0.10%.

[Si: 0.4 to 0.85%]
Si is added from a steel outer shell, metal Si, Fe—Si, Fe—Si—Mn, and the like, and is added to act as a deoxidizer to ensure the strength and toughness of the weld metal. If Si is less than 0.4%, deoxidation is insufficient and pits are generated. Moreover, the strength and toughness of the weld metal are reduced. On the other hand, if it exceeds 0.85%, the strength of the weld metal increases and the toughness decreases. Therefore, Si is 0.4 to 0.85%.

[Mn: 1.5 to 3.0%]
Mn is added from a steel outer shell, metal Mn, Fe—Mn, Fe—Si—Mn, and the like, and acts as a deoxidizer and is added to ensure the strength and toughness of the weld metal. If Mn is less than 1.5%, deoxidation is insufficient and pits are generated. Moreover, the strength of the weld metal is low and the toughness is also reduced. On the other hand, if it exceeds 3.0%, the strength of the weld metal increases and the toughness decreases. Therefore, Mn is 1.5 to 3.0%.

[Mn / Si: 3.0 to 4.5]
Mn / Si affects the viscosity of the weld metal. As Mn / Si increases, the viscosity of the weld metal decreases. Conversely, when Mn / Si decreases, the viscosity of the weld metal increases. When the viscosity of the weld metal is lowered, the gas generated from the weld metal is quickly released, so that the pit resistance can be improved. When Mn / Si is less than 3.0, the amount of Mn with respect to Si decreases, and the toughness of the weld metal deteriorates. On the other hand, if it exceeds 4.5, the viscosity of the weld metal becomes too low and the bead shape becomes convex. Therefore, Mn / Si is set to 3.0 to 4.5.

[Al: 0.2 to 0.5%]
Al is added from steel outer shell, metal Al, Fe-Al, Al-Mg alloy, etc., and acts as a deoxidizer and becomes Al oxide during melting to increase the viscosity of slag, horizontal fillet welding Therefore, it has the effect of suppressing the retreat of the molten pool and maintaining sufficient slag encapsulation. If Al is less than 0.2%, the bead becomes convex and undercut or slag burn-in occurs on the upper leg. On the other hand, if it exceeds 0.5%, the bead shape is not smooth and the toe portion is swollen, and pits are likely to occur. Moreover, solidification unevenness of the molten slag occurs, resulting in poor slag peelability. Therefore, Al is 0.2 to 0.5%.

[Mg: 0.1 to 0.4%]
Mg is added from metal Mg, Al—Mg alloy or the like and acts as a strong deoxidizer to prevent pits. If Mg is less than 0.1%, there is no effect as a deoxidizer and pits are generated. On the other hand, if it exceeds 0.4%, the arc becomes rough and the amount of spatter generated increases. Therefore, Mg is 0.1 to 0.4%.

[Al + Mg: 0.5 to 0.8%]
Al and Mg act as deoxidizers as described above. If the total of Al and Mg is less than 0.5%, the deoxidizer has no effect and the strength and toughness of the weld metal decrease. On the other hand, if it exceeds 0.8%, the arc becomes rough and the amount of spatter generated increases, and the slag encapsulation becomes defective and pits are likely to occur.

[FeO equivalent value of Fe oxide: 0.1 to 1.0%]
Fe oxides such as FeO and Fe ₂ O ₃ adjust the viscosity and solidification temperature of the molten slag, eliminate the swelling of the bead toes, and improve the compatibility with the lower plate. If the FeO equivalent value of the Fe oxide is less than 0.1%, the shape of the bead toe portion becomes poor. On the other hand, if it exceeds 1.0%, the slag encapsulation state becomes poor, the slag peelability is poor, the bead toe ends are swelled, the bead shape and the bead appearance are also poor, and the amount of fumes generated is further increased. Therefore, the FeO equivalent value of the Fe oxide is 0.1 to 1.0%.

[Total of one or two of Na ₂ K converted value and K ₂ O converted value: 0.05 to 0.2%]
Na and K are added from potassium feldspar, a solid component of water glass made of sodium silicate or potassium silicate, or a fluorine compound such as sodium fluoride or potassium silicate, not only acting as an arc stabilizer but also a slag forming agent. As a result, it suppresses a rapid increase in viscosity during the solidification process of the molten slag, thereby improving the pit resistance and providing a smooth bead shape. When the total of one or two of Na ₂ K converted value and K ₂ O converted value of Na and K compound is less than 0.05%, large spatters occur frequently, and pits and gas grooves are likely to be generated. Becomes a rough surface and the bead shape and bead appearance are poor. On the other hand, if it exceeds 0.2%, the slag peelability, the bead shape and the bead appearance become poor, and the amount of spatter and fume generation increases. Accordingly, the total of one or two of the Na ₂ O equivalent value and the K ₂ O equivalent value of the Na and K compounds is 0.05 to 0.2%.

[F conversion value of fluorine compound: 0.02 to 0.1%]
F is added from sodium fluoride, potassium silicofluoride, or the like, and has the effect of improving the directivity of the arc to form a stable molten pool and adjusting the viscosity of the slag to improve the pit resistance. If the F-converted value of the fluorine compound is less than 0.02%, the arc becomes unstable, and the slag has a high viscosity and pits are likely to occur. On the other hand, if it exceeds 0.1%, the viscosity of the slag decreases and a thin slag that is difficult to remove remains on the upper leg portion of the bead, resulting in poor slag peelability, and the bead shape becomes convex. Therefore, the F conversion value of the fluorine compound is 0.02 to 0.1%.

[Total of slag forming agents including fluorine compounds: 1.5 to 3.5%]
The slag forming agent has the effect of adjusting the bead appearance. If the total amount of slag forming agents including fluorine compounds is less than 1.5%, the amount of slag produced is insufficient and slag encapsulation cannot be made uniform, and the slag is seized and the slag removability deteriorates. Further, the arc becomes rough and the amount of spatter generated increases. On the other hand, if it exceeds 3.5%, the arc is stabilized and spatter is reduced, but the amount of slag generation is large and the slag becomes thick, and pits are likely to be generated.

The slag forming agent includes a fluorine compound, and means the total of TiO ₂ , SiO ₂ , ZrO ₂ , K ₂ O, Na ₂ O, Al ₂ O ₃ , FeO, Fe ₂ O ₃ , MgO, and the like.

[Total of one or two of Bi converted values of metal Bi or Bi oxide: 0.005 to 0.035%]
Bi is added by metal Bi, oxidized Bi, or the like, and has an effect of improving the slag removability, giving gloss to the bead surface and improving the bead appearance. If the total of one or two of the Bi converted values of the metal Bi and Bi oxide is less than 0.005%, the effect cannot be obtained, and if it exceeds 0.035%, the slag on the upper part of the bead flows, The entire surface cannot be encapsulated with slag, and the bead appearance is poor. Therefore, the total of one or two of Bi converted values of one or both of metal Bi and Bi oxide is 0.005 to 0.035%.
As mentioned above, although the reason for limitation of the constituent requirements of the flux cored wire for horizontal fillet gas shielded arc welding of the present invention has been described, the other wire components include the Fe content in the steel outer sheath, the Fe content in the alloy iron, iron powder, and Inevitable impurities.

  Further, the flux cored wire for horizontal fillet gas shielded arc welding of the present invention has the above-described limited flux in the total mass of the wire in the outer shell of mild steel and low alloy steel with good wire drawing workability after flux filling. On the other hand, after filling about 8 to 18%, the diameter is reduced to a predetermined wire diameter (0.9 to 1.6 mm) by hole die drawing or roller die. It should be noted that any seamless or seam type wire without a gap penetrating the steel outer shell can be applied.

  Hereinafter, the effect of the present invention will be described in more detail with reference to examples.

  The SPCC described in JIS G3141 was used as a steel outer shell, and after filling with flux, the diameter was reduced (intermediate annealing was performed once for softening and dehydrogenation of the outer shell), and the flux filling rate shown in Table 1 was 13.5. Various types of seamless-type flux-cored wires having no through-holes in a steel outer shell of ˜15.0% and a wire diameter of 1.4 mm were manufactured.

表１に示す試作ワイヤを用いて、無機ジンクプライマ塗布鋼板のＴ字すみ肉試験体を用いて自動溶接機で水平すみ肉溶接試験を行った。試験体は鋼種ＳＭ４９０Ｂ、板厚１２ｍｍ、試験体長さ６００ｍｍであって、プライマ塗装鋼板のプライマ膜厚は約３５〜４５μｍでＴ字すみ肉試験体の下板および立板端面にもプライマ塗装がある。これらの鋼板を加圧しながら下板と立板の間隙がない状態で仮付け溶接して試験体とした。

Using the prototype wire shown in Table 1, a horizontal fillet welding test was conducted with an automatic welder using a T-shaped fillet specimen of an inorganic zinc primer coated steel sheet. The specimen is steel type SM490B, the thickness is 12 mm, the specimen length is 600 mm, the primer coating steel sheet has a primer film thickness of about 35 to 45 μm, and primer coating is also provided on the bottom plate and vertical plate end face of the T-shaped fillet specimen. . While these steel plates were pressed, they were tack welded in a state where there was no gap between the lower plate and the standing plate to obtain test specimens.

The welding conditions are welding current 320 to 330 A (power polarity DC +), arc voltage 32 to 33 V, welding speed 50 cm / min, wire protrusion length (contact tip-base material distance) 25 mm, shield gas CO ₂ gas (gas flow rate) 25 liters / min), simultaneous welding on both sides was performed twice, and the number of pits generated, bead shape, bead appearance, slag peelability, and spatter generation state were examined.

  Note that the amount of pits generated was 1 / m or less.

Moreover, the strength and toughness of the weld metal were subjected to a weld metal test according to JIS Z 3111, and a tensile test and an impact test were performed. The welding conditions were a welding current of 300 A, an arc voltage of 31 V, a welding speed of 30 cm / min, a shielding gas CO ₂ gas (gas flow rate of 25 liters / min), and an interpass temperature of 150 ± 10 ° C. As for the strength of the weld metal test, the tensile strength was 510 to 630 MPa, and the impact test was 0 ° C. and the absorbed energy was 60 J or more. The results are summarized in Table 2.

In Table 1 and Table 2, the wire No. 1 to 10 are examples of the present invention, wire Nos. 11 to 26 are comparative examples. Wire No. which is an example of the present invention. 1 to 10 are TiO ₂ converted value, SiO ₂ converted value, ZrO ₂ converted value, C, Si, Mn, ratio of Mn and Si, Al, Mg, total of Al and Mg, FeO converted value, Na ₂ O converted Value and K ₂ O converted value, F converted value, and total slag forming agent containing fluorine compound are appropriate, so the number of pits and spatter generation is small, and the bead shape, bead appearance and slag peelability are good. In addition, the tensile strength and absorbed energy of the weld metal were good, and the result was extremely satisfactory. Wire No. containing an appropriate amount of Bi. 2, 3, 6, 7 and wire no. No. 8 had very good slag peelability.

Wire No. being compared No. 11 had a small TiO ₂ conversion value, so the slag generation amount was insufficient, the slag was seized on the bead surface, the bead appearance was poor, the arc was unstable, and the amount of spatter generated was large. Moreover, since there is much Si, the absorbed energy of the weld metal was low.

Wire No. No. 12 had many TiO ₂ conversion values, so pits occurred frequently. Moreover, since there are many Bi conversion values, the slag encapsulation was poor and the bead appearance was poor.

Wire No. No. 13 had a low SiO ₂ conversion value, so the slag encapsulation was poor and the slag peelability, bead shape and bead appearance were poor. Moreover, since Mn was small, pits were generated, the tensile strength of the weld metal was low, and the absorbed energy was also low.

Wire No. No. 14 had a large SiO ₂ conversion value, so that the amount of spatter was large, pits and gas grooves were generated, the bead toe (lower plate side) was swollen, and the bead shape and bead appearance were also poor. Moreover, since Mn / Si was low, the absorbed energy of the weld metal was low.

Wire No. No. 15 has a small ZrO ₂ conversion value, and thus has a convex bead shape and poor slag peelability, and pits were generated. Moreover, since there was much Mg, the arc became rough and the amount of spatter generation was large.

Wire No. 16, since the terms of ZrO ₂ value is large, the bead shape becomes convex. In addition, since the total amount of slag forming agents including fluorine compounds is large, the amount of slag produced is large and the slag becomes thick, resulting in frequent pits.

Wire No. In No. 17, since there was little Si, pits occurred, the tensile strength of the weld metal was low, and the absorbed energy was also low. Moreover, since there were few Bi conversion values, slag encapsulation property was bad and bead appearance and slag peelability were somewhat poor.
Wire No. No. 18 had a poor bead shape because of high Mn / Si. Moreover, pits were generated because the F-converted value was small.

  Wire No. No. 19 had a large amount of Al, so that the toe end of the bead swelled and the bead shape became poor, the solidified unevenness of the molten slag occurred, the slag peelability was poor, and pits were frequently generated. Moreover, since Mn is large, the tensile strength of the weld metal was high and the absorbed energy was low.

  Wire No. In No. 20, since the total amount of Al and Mg was small, the tensile strength of the weld metal was low and the absorbed energy was also low. Moreover, since there were many F conversion values, slag peelability and bead shape were unsatisfactory.

  Wire No. No. 21 had a large sum of Al and Mg, so the amount of spatter was large, the slag encapsulation was poor, the bead appearance was poor, and pits occurred frequently. Moreover, since there were few FeO conversion values, the shape of the bead toe part was unsatisfactory.

  Wire No. Since No. 22 had many FeO conversion values, the slag encapsulation was poor and the bead appearance, bead shape, and slag peelability were poor. Moreover, since there was little Mg, the pit generate | occur | produced.

Wire No. In No. 23, since the total of Na ₂ O converted value and K ₂ O converted value was small, a large amount of spatter was generated, pits were frequently generated, and the bead shape and bead appearance were poor. Moreover, since there is much C, the tensile strength of the weld metal was high and the absorbed energy was low.
Wire No. No. 24 had a large sum of Na ₂ O converted value and K ₂ O converted value, so the slag peelability, bead shape and bead appearance were poor, and the amount of spatter was large. Moreover, since there is little C, the absorbed energy of the weld metal was low.

  Wire No. In No. 25, since the total amount of slag forming agents containing fluorine compounds was small, the amount of spatter generation was large, the amount of slag generation was insufficient, the slag encapsulation was poor, and the slag was seized, resulting in poor slag removability. Moreover, since Al was little, the bead became convex and the shape was poor, undercut was generated, and the bead appearance was also poor.

Claims (2)

In a filleted wire for horizontal fillet gas shielded arc welding in which a steel outer shell is filled with flux,
TiO ₂ conversion value of Ti oxide: 0.5 to 2.5%,
SiO ₂ conversion value of Si oxide: 0.1 to 0.5%,
ZrO ₂ conversion value of Zr oxide: 0.1 to 0.5%,
C: 0.03-0.10%,
Si: 0.4 to 0.85%,
Mn: 1.5-3.0%
And Mn / Si: 3.0-4.5,
Al: 0.2 to 0.5%,
Mg: 0.1 to 0.4%
And Al + Mg: 0.5-0.8%
FeO equivalent value of Fe oxide: 0.1 to 1.0%,
One or of the sum of _{K 2} O conversion value of terms of Na ₂ O values or K compounds of Na compound: 0.05% to 0.2%,
F conversion value of fluorine compound: 0.02 to 0.1%,
The total of the slag forming agent containing a fluorine compound is 1.5 to 3.5%, and the balance is Fe content of steel outer shell, Fe content in alloy iron, iron powder and inevitable impurities. Flux-cored wire for fillet gas shielded arc welding.   The flux cored wire for horizontal fillet gas shielded arc welding according to claim 1, characterized in that it contains 0.005 to 0.035% of one or two of Bi equivalent values of metal Bi or Bi oxide. .