WO2022004032A1 - Gas shielded arc welding method, structure object production method, and shielding gas - Google Patents

Abstract

Provided is a gas shielded arc welding method with which arc stability is high and incomplete fusion can be suppressed, regardless of the conditions of a welding material, a welding base material, and the like. Also provided are a structure object production method using the welding method, and a shielding gas to be used in the welding method. The shielding gas to be used in the gas shielded arc welding contains, with respect to the total volume of the shielding gas, between 0.5 % by volume and 2.0 % by volume inclusive of CO₂, and between 0.5 % by volume and 3.0 % by volume inclusive of H₂, the remainder being Ar and unavoidable impurities. When [CO₂] represents the CO₂ content in percentage by volume with respect to the total volume of the shielding gas, and [H₂] represents the H₂ content in percentage by volume with respect to the total volume of the shielding gas, the shielding gas satisfies formula (1) and formula (2). (1): 1.30 ≤ [CO₂] + [H₂] ≤ 4.40 (2): 0.35 ≤ [H₂]/([CO₂] + [H₂]) ≤ 0.74

Description

Gas shield arc welding method, structure manufacturing method and shield gas

The present invention relates to a gas shielded arc welding method for welding using a shield gas containing Ar as a main component, a structure manufacturing method, and a shield gas.

In gas shielded arc welding, a shield gas is used to protect the molten metal (hereinafter, also referred to as a molten pool) from the adverse effects of nitrogen and oxygen in the atmosphere. The composition of the shield gas is variously optimized depending on the steel type of the welding wire and the welding base material (hereinafter, also simply referred to as “base material” or “work”) used, and the application of the structure to be manufactured. For example, when high alloy steel such as stainless steel is used as a welding wire, Ar is mainly used for the purpose of suppressing the oxygen content of the weld metal after welding and ensuring excellent mechanical performance, especially toughness. As a component, it is common to use a mixed gas containing a _{small amount of O 2} or CO _{2 as a shield gas.}

As described above, when a mixed gas containing Ar as a main component is used as a shield gas, it is possible to secure excellent toughness by increasing the content of Ar in the shield gas. On the other hand, there is a problem that the penetration performance is inferior and welding defects such as poor fusion occur. This is due to the low potential gradient of Ar, and the higher the ratio of Ar in the shield gas, the easier it is for the arc to spread, the smaller the current density, and the force that pushes down the molten pool (hereinafter also referred to as the arc force). ) Decreases.

In order to solve such a problem, Patent Document 1 discloses a flux-containing wire made of a metal oxide, a carbonate, a metal fluoride and a metal powder with a stainless steel or nickel alloy as an outer skin. the flux-cored wire according to Reference 1, as a flux component, a TiO ₂ 5 ~ 10% by weight relative to the total wire weight, the SiO ₂ 0 ~ 1.5 wt%, the carbonate 0.1-1 wt% It is characterized by containing 1 to 30% by weight of a metal powder mixture having a metal fluoride content of 0.05 to 0.5% by weight in terms of the amount of fluorine and a silicon content of 0.1 to 1.5% by weight. Then, by using the flux-cored wire, even when welding is performed with the shield gas composition set to 80% Ar + 20% CO ₂ , welding is possible in the same manner as when _{100% CO 2 shield gas is used, and defects are found.} It is disclosed that it does not occur.

Further, in Patent Document 2, a mug for welding high Cr steel containing 8% by weight or more and 13% by weight or less of Cr using a solid wire containing 8% by weight or more and 13% by weight or less of Cr. Welding shield gas is disclosed. Specifically, the shield gas for MAG welding has one layer and one pass, and the ratio of the thickness H1 of the pair of base materials and the groove distance W1 between these base materials is 0.4 or less. This is for welding a narrow groove having a tip angle θ1 of 10 ° or less. Further, Patent Document 2 is characterized in that the shield gas is composed of a three-kind mixed gas of carbon dioxide gas of 17% by volume or less, helium gas of 30% by volume or more and 80% by volume or less, and the balance of argon gas. It is disclosed that the penetration is improved.

Japanese Patent Application Laid-Open No. 2001-25893 Japanese Patent Application Laid-Open No. 2013-46932

However, Patent Document 1 assumes only a shield gas having an Ar gas of 80% or less, and does not consider the toughness of the weld metal. Further, the welding material used is limited to the flux-cored wire, and no consideration is given to the solid wire.
For example, when a wire containing flux is used, the flux itself contains a large amount of an oxide having a low work function, and this oxide acts as a cathode point for emitting electrons, so that high arc stability can be obtained.
On the other hand, when a solid wire is used, the higher the ratio of Ar in the shield gas, the more difficult it is for the cathode point to be formed on the surface of the molten metal, so that arc deflection occurs frequently and the arc becomes unstable. Therefore, when a solid wire is used, fusion failure is more likely to occur in a high Ar atmosphere than when a flux-cored wire is used.

The shield gas described in Patent Document 2 is _{composed of a three-kind mixed gas of carbon dioxide gas (CO 2} ), helium gas (He) and argon gas (Ar), and the content of He gas is 30 to 30. The composition is 80% by volume, and He gas occupies most of the shield gas.
However, He gas is known to be in short supply worldwide these days, and since it is a high-cost gas, it cannot be said to be a gas that can be used for general purposes. Further, the welding condition to which the shield gas described in Patent Document 2 is applied is one layer and one pass, and the ratio of the thickness H1 of the pair of base materials and the groove distance W1 between these base materials is 0.4 or less. , The groove angle θ1 is limited to welding to narrow grooves of 10 ° or less. Therefore, there is a demand for the development of a welding method capable of performing welding without using He gas and without particularly limiting the welding conditions.

The present invention has been made in view of the above problems, and has Ar as a main component, which is a general-purpose gas, and has high arc stability regardless of conditions such as the type and shape of the welding material and the welding base material. It is an object of the present invention to provide a gas shielded arc welding method capable of suppressing fusion defects, a method for manufacturing a structure using the welding method, and a shield gas used in the welding method.

As a result of diligent research to solve the above problems, the present inventors have reduced the amount of molecular gas having oxygen atoms such as _{CO 2} and O _{2, which is a shield gas containing Ar as a main component, and CO.} It has been found that it is effective to use a shield gas in which the contents of ₂ and H _{2 and their relative ratios are appropriately controlled.}

That is, the above object of the present invention is achieved by the configuration of the following [1] according to the gas shielded arc welding method.

[1] A gas shielded arc welding method in which a welding wire is used as an electrode and a shield gas is flowed through a welded region of a welding base material for welding.
The shield gas is based on the total volume of the shield gas.
CO ₂ : 0.5% by volume or more and 2.0% by volume or less, and
H ₂ : 0.5% by volume or more and 3.0% by volume or less,
Contains,
The rest is Ar and unavoidable impurities,
When the content of the _{CO 2} with respect to the total volume of the shield gas _{is [CO 2} ] by volume% and the content of the _{H 2} with respect to the total volume of the shield gas _{is [H 2} ] by volume, the following formula (1). ) And the gas shielded arc welding method, which is characterized by satisfying the formula (2).
1.30 ≤ [CO ₂ ] + [H ₂ ] ≤ 4.40 ... (1)
0.35 ≤ [H ₂ ] / ([CO ₂ ] + [H ₂ ]) ≤ 0.74 ... (2)

Further, preferred embodiments of the present invention relating to the gas shielded arc welding method relate to the following [2] to [6].

[2] The gas shielded arc welding method according to [1], wherein the content of Ar with respect to the total volume of the shield gas is [Ar] in% by volume, and the following formula (3) is satisfied.
57.0 ≤ 0.5 x [Ar] +1.5 x [CO ₂ ] +10 x [H ₂ ] ≤ 80.0 ... (3)

[3] The welding wire is used with respect to the total mass of the welding wire.
Cr: 18% by mass or more and 28.5% by mass or less, and
Ni: 8.0% by mass or more and 37.0% by mass or less,
Contains,
The gas shielded arc welding method according to [1] or [2], which has a structure having a ferrite percentage of 15.3% or less based on a DeLong organization chart.

[4] The welding wire is used with respect to the total mass of the welding wire.
C: 0.20% by mass or less (including 0% by mass),
Si: 1.00% by mass or less (including 0% by mass),
Mn: 4.8% by mass or less (including 0% by mass),
P: 0.03% by mass or less (including 0% by mass),
S: 0.03% by mass or less (including 0% by mass),
Cu: 4.0% by mass or less (including 0% by mass),
Mo: 4.0% by mass or less (including 0% by mass),
Nb: 1.0% by mass or less (including 0% by mass), and
N: 0.30% by mass or less (including 0% by mass),
The gas shielded arc welding method according to [3].

[5] The welded region of the welding base material has a groove and has a groove.
The groove has one type of groove shape selected from V type, Les type, I type, K type, X type, J type and U type.
The gas shielded arc welding method according to any one of [1] to [4], wherein the groove angle of the groove is 0 to 90 °.

[6] The gas flow rate Q of the shield gas is 10 to 30 (liters / minute) or less.
The protrusion length L of the welding wire is 10 to 30 (mm) or less, and the welding wire has a protrusion length L of 10 to 30 (mm) or less.
Described in any one of [1] to [5], wherein the ratio of the gas flow rate Q (liters / minute) to the protrusion length L (mm) satisfies the following formula (4). Gas shield arc welding method.
0.5 ≤ Q / L ≤ 2.2 ... (4)

Further, the above object of the present invention is achieved by the configuration of the following [7] relating to the method for manufacturing a structure.

[7] A method for manufacturing a structure manufactured by gas shielded arc welding using a welding wire and a shield gas.
The shield gas is based on the total volume of the shield gas.
CO ₂ : 0.5% by volume or more and 2.0% by volume or less, and
H ₂ : 0.5% by volume or more and 3.0% by volume or less,
Contains,
The rest is Ar and unavoidable impurities,
When the content of the _{CO 2} with respect to the total volume of the shield gas _{is [CO 2} ] by volume% and the content of the _{H 2} with respect to the total volume of the shield gas _{is [H 2} ] by volume, the following formula (1). ) And a method for manufacturing a structure, which is characterized by satisfying the formula (2).
1.30 ≤ [CO ₂ ] + [H ₂ ] ≤ 4.40 ... (1)
0.35 ≤ [H ₂ ] / ([CO ₂ ] + [H ₂ ]) ≤ 0.74 ... (2)

Further, the above object of the present invention is achieved by the configuration of the following [8] relating to the shield gas.

[8] Gas shield gas used for arc welding, which is a shield gas.
For the total volume of shield gas
CO ₂ : 0.5% by volume or more and 2.0% by volume or less, and
H ₂ : 0.5% by volume or more and 3.0% by volume or less,
Contains,
The rest is Ar and unavoidable impurities,
When the content of the _{CO 2} with respect to the total volume of the shield gas _{is [CO 2} ] by volume% and the content of the _{H 2} with respect to the total volume of the shield gas _{is [H 2} ] by volume, the following formula (1). ) And the shield gas characterized by satisfying the formula (2).
1.30 ≤ [CO ₂ ] + [H ₂ ] ≤ 4.40 ... (1)
0.35 ≤ [H ₂ ] / ([CO ₂ ] + [H ₂ ]) ≤ 0.74 ... (2)

According to the gas shielded arc welding method according to the present invention, arc stability is high and fusion failure can be suppressed regardless of conditions such as the type and shape of the welding material and the welding base material. Further, according to the method for manufacturing a structure according to the present invention, it is possible to manufacture a good joint in which the occurrence of fusion defects is suppressed.

FIG. 1 is an organizational chart of DeLong when the vertical axis is nickel equivalent (%) and the horizontal axis is chromium equivalent (%). FIG. 2 is a schematic view showing an example of a welding apparatus that can be used in the present invention. FIG. 3 shows the test No. Sample No. in T1 It is a drawing substitute photograph which shows the cross section of the weld metal of B1 (welding current 150A). FIG. 4 shows the test No. Sample No. in T16. It is a drawing substitute photograph which shows the cross section of the weld metal of B16 (welding current 150A). FIG. 5 is a drawing substitute photograph showing the appearance of the bead of the test plate welded by the method of the present invention. FIG. 6 is a drawing substitute photograph showing a cross section of the weld metal of the test plate welded by the method of the present invention.

Hereinafter, embodiments for carrying out the present invention will be described in detail. The present invention is not limited to the embodiments described below. Further, in the specification, "-" is used to mean that the numerical values described before and after the value are included as the lower limit value and the upper limit value.

[Gas shield arc welding method]
The gas shielded arc welding method according to the present invention is a method in which a consumable electrode (hereinafter, also referred to as a welding wire) is supplied via a welding torch and welding is performed while the shield gas is allowed to flow in the welded region of the welding base material. Become. Since the present invention also relates to the shield gas used in the above welding method, first, the shield gas according to the present invention will be described.

[Shielding gas]
The shield gas according to the present invention contains CO ₂ (carbon dioxide) and H ₂ (hydrogen), and the balance is composed of Ar (argon) and unavoidable impurities. As mentioned above, the shield gas is used to protect the molten metal from the adverse effects of atmospheric nitrogen and oxygen, while the shield gas contains molecular gases having oxygen atoms such as _{CO 2} and O _2. If so, oxygen atoms contained in the shield gas enter the molten metal. In order to secure the excellent toughness of the weld metal, which is the premise of the present invention, it is a condition that the weld metal has low oxygen. Therefore, the shield gas according to the present invention contains Ar gas, which is a general-purpose inert gas, as a main component while minimizing the amount of molecular gas having an oxygen atom.

Further, as described above, the shield gas, which is dominated by Ar gas, has a problem that fusion failure occurs due to arc instability and decrease in arc force due to arc deflection. On the other hand, in the present invention, the low oxygen content of the weld metal is maintained by appropriately controlling the contents of _{CO 2} gas and H _{2 gas and using Ar gas of 95% by volume or more as the balance.} While maintaining arc stability and arc force, it is possible to achieve suppression of fusion defects.
As will be described later, the CO ₂ gas is a gas that contributes to arc stability, and the H ₂ gas is a gas that contributes to arc force. Hereinafter, each gas composition and an appropriate range will be described in detail.

<CO ₂ : 0.5% by volume or more and 2.0% by volume or less>
CO ₂ easily dissociates into atoms in the arc and takes dissociation heat from the arc, which contributes to the contraction effect of the arc. The ratio of the potential gradient of _{CO 2} when air is 1 is 1.5. In addition, the dissociated O (oxygen atom) reacts with the deoxidizing element on the molten pool to form an oxide on the surface of the molten pool, and this oxide acts as a cathode point to suppress arc deflection and arc. Is stable. However, when the dissociated O enters the molten metal, the amount of oxygen in the weld metal may increase as a result, so that CO ₂ in the shield gas needs to be appropriately controlled.
If the CO ₂ content is less than 0.5% by volume, the arc stabilizing effect cannot be mainly ensured. Therefore, the CO ₂ content in the shield gas is 0.5% by volume or more, preferably 0.6% by volume or more, and more preferably 0.9% by volume or more with respect to the total volume of the shield gas. ..

On the other hand, if the CO ₂ content exceeds 2.0% by volume and is excessively contained, the droplet transfer becomes a globule transfer form due to the mixing of oxygen into the molten metal and excessive arc contraction, and as a result, The arc tends to be unstable. Therefore, the CO ₂ content in the shield gas shall be 2.0% by volume or less with respect to the total volume of the shield gas. Further, when the CO ₂ content in the shield gas is preferably 1.5% by volume or less, more preferably 1.1% by volume or less with respect to the total volume of the shield gas, oxygen entering the molten metal is further suppressed. Therefore, more excellent toughness can be ensured.

When the shield gas _{contains CO 2} , C (carbon) or CO (carbon monoxide) is generated at the time of dissociation, and the action of reducing O adsorbed on the surface of the molten pool works. Although it is a molecular gas, it can suppress oxygen entering the molten metal as much as possible. Such an _{effect of CO 2} cannot be replaced by a molecular gas having another oxygen atom, for example, O _{2 which is mentioned as a general-purpose one for welding.} This is because when the shielding gas contains O _2, after dissociation of O _2, O is adsorbed on the molten pool surface without being reduced, is because oxygen from entering into the molten metal, as a result, the weld metal There are adverse effects such as an increase in the amount of oxygen and deterioration of the glossiness of the bead surface after welding. _{Therefore, in the present invention, CO 2} is selected as a molecular gas having an oxygen atom that ensures arc stability while suppressing an increase in oxygen content of the weld metal and maintaining a good bead appearance.

<H ₂ : 0.5% by volume or more and 3.0% by volume or less>
H ₂ is a molecule having a higher potential gradient than other molecules, and the ratio of the potential gradient of _{H 2 when air is 1 is set to 10.} This is because _{the dissociation voltage of H 2} is extremely low, and a large amount of dissociation heat is taken away, which greatly contributes to the contraction effect of the arc. In addition, H ₂ has a reducing effect and also has an effect of suppressing oxygen entering the molten metal. When containing H ₂ content is less than 0.5% by volume, the arc austerity effect can not be obtained, the current density decreases, because the arc force decreases, fusion failure. Therefore, the H ₂ content in the shield gas is 0.5% by volume or more, preferably 0.8% by volume or more, and more preferably 1.0% by volume or more with respect to the total volume of the shield gas. ..

On the other hand, when the H ₂ content exceeds 3.0% by volume, the austerity effect of the arc works excessively, so that the droplet transfer becomes a globule transfer form. Globule transition is a phenomenon in which droplets are pushed up by an arc force and coarse droplets having a wire diameter or larger are irregularly separated, so that the arc becomes unstable. Therefore, the H ₂ content in the shield gas is 3.0% by volume or less, preferably 2.8% by volume or less, based on the total volume of the shield gas.

<Remaining: Ar and unavoidable impurities>
(Ar: 95% by volume or more and 98.5% by volume or less)
Ar gas is also called an inert gas or a noble gas because Ar is a monatomic molecule and has a property of not forming a stable chemical bond. In welding, the larger the proportion of Ar gas, that is, the inert gas contained in the shield gas, the more oxygen and the like entering the molten metal from the shield gas can be suppressed, and the welding metal can be reduced in oxygen. can. Therefore, the shield gas according to the present invention contains the above CO ₂ and H ₂ , and the balance is Ar and unavoidable impurities, and the Ar content is not particularly limited. When the Ar content is 95% by volume or more, the oxygen content of the weld metal can be lowered and excellent toughness can be ensured. Therefore, the Ar content in the shield gas is preferably 95% by volume or more, more preferably more than 95% by volume, and further preferably 96% by volume or more with respect to the total volume of the shield gas. ..

On the other hand, when the Ar content is 98.5% by volume or less, it is possible to prevent the potential gradient of the arc, that is, the voltage per unit distance from becoming low, and the arc length and the spread of the arc at an appropriate arc voltage. Can be maintained properly and the current density can be increased. As a result, it is possible to suppress a decrease in arc force and prevent the occurrence of fusion failure. In addition, it is possible to prevent the deflection of the arc due to the instability of the cathode point, and the arc is stabilized. Therefore, the Ar content in the shield gas is preferably 98.5% by volume or less, more preferably 98.1% by volume or less, based on the total volume of the shield gas.
The ratio of the potential gradient of Ar when air is 1 is 0.5.

(Inevitable impurities)
Examples of the unavoidable impurities that can be contained in the shield gas according to the present invention include oxygen, nitrogen, water and the like. Of the above unavoidable impurities, the smaller the oxygen content, the better, and if the O ₂ content in the shield gas is 0.02% by volume or less with respect to the total volume of the shield gas, the effect of the present invention is hindered. No. Further, the content of other unavoidable impurities is also better as it is smaller, and if the content _{of each component other than O 2} in the shield gas is 0.03% by volume or less with respect to the total volume of the shield gas, respectively. , Does not interfere with the effect of the present invention. The total amount of unavoidable impurities contained in the shield gas is preferably 0.05% by volume or less, more preferably 0.03% by volume or less, based on the total volume of the shield gas. ..

<1.30 ≤ [CO ₂ ] + [H ₂ ] ≤ 4.40>
As described above _{, both CO 2} and H ₂ are components that contribute to the arc contraction effect and have the effect of improving the arc stability. Therefore, in the present invention, the optimum range of the total amount thereof is also limited. do.
_{When the CO 2} content with respect to the total volume of the shield gas is [CO ₂ ] by volume% and the H ₂ content is [H ₂ ] by volume%, [CO ₂ ] + [H ₂ ] is less than 1.30. If there is, one or both of the effect of suppressing fusion failure and the effect of improving arc stability due to the arc contraction effect cannot be obtained.
On the other hand, when [CO ₂ ] + [H ₂ ] exceeds 4.40, the austerity effect of the arc becomes excessive and arc instability occurs.

Therefore, the CO ₂ content and the H ₂ content shall satisfy the following formula (1). The value obtained by [CO ₂ ] + [H ₂ ] is preferably 1.50 or more, more preferably 1.90 or more, and preferably 4.30 or less, 3.90. The following is more preferable.

1.30 ≤ [CO ₂ ] + [H ₂ ] ≤ 4.40 ... (1)

<0.35 ≤ [H ₂ ] / ([CO ₂ ] + [H ₂ ]) ≤ 0.74>
Since H ₂ greatly contributes to the arc austerity effect, the present invention also limits the optimum range for the ratio of the _{H 2} content to the total amount of _{the CO 2} content and the H _{2 content.} That is, _{the total amount of the CO 2} content and the H ₂ content satisfies the above formula (1), and _{the ratio of H 2 to} the total amount satisfies the following formula (2). Only in certain cases, the effect of suppressing fusion defects and the arc stability, which are the effects of the present invention, are exhibited.

If _{the ratio of the H 2} content to the total amount of the _{CO 2} content and the H ₂ content is less than 0.35, the arc austerity effect is small and fusion failure may occur.
On the other hand, when the above ratio exceeds 0.74, _{the arc stabilizing effect of CO 2} is not exhibited, and the droplet transfer becomes a globule transfer form due to the excessive arc contraction effect, so that the arc becomes more unstable. .. Therefore, the CO ₂ content and the H ₂ content shall satisfy the following formula (2). The value obtained by [H ₂ ] / ([CO ₂ ] + [H ₂ ]) is preferably 0.40 or more, more preferably 0.47 or more, and 0.70 or less. It is preferably 0.67 or less, and more preferably 0.67 or less.

0.35 ≤ [H ₂ ] / ([CO ₂ ] + [H ₂ ]) ≤ 0.74 ... (2)

<57.0 ≤ 0.5 x [Ar] + 1.5 x [CO ₂ ] + 10 x [H ₂ ] ≤ 80.0>
As described above, in the present invention, _{by appropriately controlling the CO 2} content, H ₂ content, and Ar content in the shield gas, the occurrence of fusion defects can be suppressed and the arc stability can be improved. Can be improved. The effect of each of these gases on suppressing fusion defects and improving arc stability is determined by the potential gradient ratio when air is 1.

0.5 when the Ar content with respect to the total volume of the shield gas is [Ar] by volume, the CO ₂ content is [CO ₂ ] by volume, and the H ₂ content is [H _{2] by volume. × [Ar] + 1.5 × [} CO 2] + 10 × [H 2] value obtained by 57.0 above, with the range of 80.0 or less, obtained by both arc stringency effect, the arc stabilizing effect be able to.
Therefore, in the present invention, it is preferable to satisfy the following formula (3). The value obtained by 0.5 × [Ar] + 1.5 × [CO ₂ ] + 10 × [H ₂ ] is more preferably 59.0 or more, further preferably 63.0 or more. It is more preferably 79.0 or less, and further preferably 78.0 or less.

57.0 ≤ 0.5 x [Ar] +1.5 x [CO ₂ ] +10 x [H ₂ ] ≤ 80.0 ... (3)

The shield gas according to the present invention _{is a mixed gas in which the CO 2} content and the H ₂ content are appropriately controlled and the balance is composed of Ar and unavoidable impurities. It is preferable to use a gas cylinder (hereinafter, also referred to as a gas cylinder) in which the gas is enclosed, or a method in which these gases are mixed and used using a gas mixer. A method of ejecting the mixed gas from one nozzle using a mixer is more preferable.
On the other hand, in the method of mixing in the vicinity of the molten metal using the double shield gas method using two nozzles on the outside and the inside, the composition of the gas becomes non-uniform, and the effect of the present invention may not work. .. Further, in the double shield gas method, for example, when the outside is Ar and the inside is CO ₂ or H ₂ gas, the active gas is locally present, which may adversely affect the familiarity and glossiness. There can be sex. Therefore, it is desirable not to use the method of mixing in the vicinity of the molten metal because the effect of the present invention may not be fully exhibited.

Next, a preferable form of the welding wire used in combination with the shield gas used in the gas shielded arc welding method according to the present invention will be described.

[Welding wire]
The form of the welding wire used in the welding method according to the present invention is not particularly limited, and may be a solid wire or a flux-cored wire.
The solid wire is a wire-like wire having a solid wire cross section. The surface of the solid wire may or may not be copper-plated, but it may be in either form.

The flux-cored wire is composed of a tubular outer skin and a flux filled inside the outer skin. The flux-cored wire may be in either a seamless type having no seam on the outer skin or a seam type having a seam on the outer skin. Further, the flux-cored welding wire may or may not be copper-plated on the wire surface (outside of the outer skin). The material of the outer skin is not particularly limited, and may be mild steel or stainless steel, and the composition with respect to the total mass of the weld wire can be selected according to the required characteristics of the welded structure, and is not particularly limited.

Hereinafter, preferred embodiments of the welding wire that can be used in the present invention will be described in detail. When the welding wire shown below is a flux-cored wire, the total mass of the welding wire refers to the total mass of the components in the outer skin and the flux. Examples of the outer skin include ordinary steel, SUH409L (JIS G 4312: 2001), SUS430, SUS304L, SUS316L, SUS310S (all JIS G 4305: 2012) and the like.

<Cr: 18% by mass or more and 28.5% by mass or less, Ni: 8.0% by mass or more and 37.0% by mass or less>
Cr is a component that improves the corrosion resistance of the weld metal. Further, Ni is a component that stabilizes the austenite structure of the weld metal and improves the toughness at low temperatures, and is a component that is added in a fixed amount for the purpose of adjusting the crystallization amount of the ferrite structure.
In the present invention, the welding wire is preferably austenitic stainless steel. The Cr content and Ni content in the welding wire are both JIS Z3321: 2013 (stainless steel filler rod for welding, solid wire and steel strip) or JIS Z3323: 2007 (stainless steel arc welding flux-containing wire and wire and steel strip). It is preferably within the range specified by the filler rod). Specifically, the Cr content in the welding wire is preferably 18% by mass or more and 28.5% by mass or less with respect to the total mass of the welding wire.
The Ni content in the welding wire is preferably 8.0% by mass or more and 37.0% by mass or less with respect to the total mass of the welding wire.

FIG. 1 is an organizational chart of DeLong when the vertical axis is nickel equivalent (%) and the horizontal axis is chromium equivalent (%). Based on the DeLong structure diagram shown in FIG. 1 defined by JIS Z3119-2017, the weld wire has a structure of 15.3% or less in a ferrite percentage, and austenitic base material is used to shield the weld wire. Even when hydrogen is contained in the gas, it is preferable because it can suppress the occurrence of cracks in the weld metal. In the welding wire that can be used in the present invention, the region exceeding the range of nickel equivalent and chromium equivalent shown in the DeLong organization chart shown in FIG. 1 is based on the straight line shown in the DeLong organization chart. Is extrapolated and applied.
Further, based on the DeLong structure diagram, the weld wire has a structure consisting only of austenite, or a structure consisting of austenite and ferrite and having a structure having a ferrite percentage of 15.3% or less. It is preferable because it can further prevent cracking of the weld metal.

Further, the welding wire that can be used in the present invention contains C, Si, Mn, P, S, Cu, Mo, Nb and N as optional elements in addition to the above-mentioned Cr and Ni. You may. As described above, the steel grade of the welding wire suitable for combination with the shield gas according to the present invention is austenitic stainless steel. Therefore, the preferred range of the content of these arbitrary elements is JIS Z3321: 2013 (stainless steel filler rod for welding, solid wire and steel strip) or JIS Z3323: 2007 (wire and filler rod containing stainless steel arc welding flux). It is preferable that the content is not more than the maximum value of the content of each element specified in 1. Further, it is more preferable that the welding wire contains these optional elements and the balance is Fe and unavoidable impurities.

Hereinafter, a more preferable numerical range of the component amount of the welding wire that can be used in the present invention will be specifically described together with the reason for the limitation.

<C: 0.20% by mass or less (including 0% by mass)>
C is a component that affects the strength or corrosion resistance of the weld metal, and the lower the C content in the weld wire, the better the corrosion resistance. Therefore, the smaller the C content in the weld wire, the more preferably 0% by mass. May be. When the welded wire contains C as an optional element in order to adjust the mechanical performance of the obtained weld metal, specifically, the C content in the welded wire is 0.20 mass with respect to the total mass of the wire. % Or less is more preferable.

<Si: 1.00% by mass or less (including 0% by mass)>
Si is an element that is a component that improves the strength of the weld metal, but on the other hand, it is also a component that deteriorates the toughness, so the Si content in the weld wire may be 0% by mass. When the welding wire contains Si as an arbitrary element in order to adjust the mechanical performance of the obtained weld metal, specifically, the Si content in the welding wire is 1.00 mass with respect to the total mass of the wire. % Or less is more preferable.

<Mn: 4.8% mass or less (including 0%)>
Mn is a component that improves the strength of the weld metal, but in the present invention, the Mn content in the weld wire may be 0% by mass. When the welded wire contains Mn as an optional element in order to adjust the mechanical performance of the obtained weld metal, specifically, the Mn content in the welded wire is 4.8 mass with respect to the total weight of the wire. % Or less is more preferable.

<P: 0.03% mass or less (including 0%)>
<S: 0.03% mass or less (including 0%)>
As the content of P and S in the weld metal increases, the crack resistance decreases. Therefore, the smaller the P content and the S content in the weld wire, the more preferable, and the P and S may be 0% by mass. Specifically, the P content and the S content in the welded wire are more preferably 0.03% by mass or less with respect to the total mass of the wire.

<Cu: 4.0% mass or less (including 0%)>
Cu is a component that improves the strength and corrosion resistance of the weld metal, but in the present invention, the Cu content in the welded wire may be 0% by mass. When Cu is contained as an optional element in the welding wire in order to adjust the mechanical performance and corrosion resistance of the obtained weld metal, or when Cu plating is applied to the surface for the purpose of improving the electrical conductivity during welding. Specifically, the total Cu content in the welded wire and plated is more preferably 4.0% by mass or less with respect to the total mass of the wire.

<Mo: 4.0% mass or less (including 0%)>
Mo is a component that improves high-temperature strength and corrosion resistance, but on the other hand, it is also a component that promotes σ embrittlement, so that the Mo content in the weld wire may be 0% by mass. When the welded wire contains Mo as an optional element in order to adjust the mechanical performance and corrosion resistance of the obtained weld metal, specifically, the Mo content in the welded wire is 4 with respect to the total mass of the welded wire. More preferably, it is 0.0% by mass or less.

<Nb: 1.0% by mass or less (including 0%)>
Nb has the effect of stabilizing C by forming carbides, and is a component that suppresses the formation of Cr oxides and improves corrosion resistance. The carbides referred to here also include complex compounds containing C such as charcoal sulfides and charcoal nitrides. On the other hand, when Nb is contained in the welding wire more than necessary, a low melting point compound is generated at the grain boundaries and the crack resistance is deteriorated. Therefore, the Nb content in the welding wire is 0% by mass. You may. When the welding wire contains Nb as an optional element in order to adjust the corrosion resistance of the obtained weld metal, specifically, the Nb content in the welding wire is 1.0% by mass with respect to the total mass of the welding wire. The following is preferable. As a substitute for Nb, Ti may be contained in the same range as Nb.

<N: 0.30% by mass or less (including 0%)>
N is a component that penetrates into the crystal structure and solid-solves to improve the strength and pitting corrosion resistance. On the other hand, since N also causes pore defects such as blow holes and pits in the weld metal, the N content in the weld wire may be 0% by mass. When the welded wire contains N as an optional element in order to adjust the mechanical performance and porcelain resistance of the obtained weld metal, specifically, the N content in the welded wire is relative to the total mass of the welded wire. It is preferably 0.30% by mass or less.

The welding wire that can be used in the gas shielded arc welding method according to the present invention contains V, Sn, Na, Co, Ca, Li, Sb, W, As and the like as unavoidable impurities in addition to the above elements. Will be done. When each element listed as the unavoidable impurity is contained in the welding wire as an oxide, O is also contained as an impurity.

[Welding equipment]
Next, a welding apparatus that can be used in the gas shielded arc welding method according to the present invention will be described. The welding device is not particularly limited as long as it is a welding device that performs gas shielded arc welding, and a welding device used for conventional gas shielded arc welding can be used. For example, a semi-automatic welding device, an automatic welding device using a mobile carriage, a welding robot system, and the like can be mentioned.

FIG. 2 is a schematic view showing an example of a welding apparatus that can be used in the present invention.
For example, as shown in FIG. 2, in the welding device 1, a welding torch 11 is attached to the tip thereof, and a robot 10 for moving the welding torch 11 along a welding line of a work W and a welding wire are supplied to the welding torch 11. It is provided with a wire supply unit (not shown) and a welding power supply unit 30 that supplies a current to the consumable electrode via the wire supply unit to generate an arc between the consumable electrode and the material to be welded. Further, the welding device includes a robot control unit 20 that controls the robot operation for moving the welding torch 11, and further includes a teaching pendant 40 that serves as an interface for inputting a command from the operator to the robot control unit 20. ..

Further, various conditions applicable to the gas shielded arc welding method according to the present invention will be described in detail.

(Welding torch)
The posture of the welding torch may be perpendicular to the base metal or may be tilted. When the welding torch is tilted toward the opposite side of the welding progress direction, the angle formed by the vertical line with respect to the base metal and the torch is called the advance angle, and when the welding torch is tilted toward the welding progress direction, the vertical line with respect to the base metal is tilted. The angle formed by the torch is called the receding angle. By adding a forward angle to the welding torch, it is possible to more effectively improve the shielding property during arc welding. Further, by providing a receding angle to the electrode, the rear side of the bead can be shielded, so that the oxidation reaction of the bead immediately after welding can be suppressed. In the present invention, the conditions of the forward angle and the receding angle may be changed as necessary in order to obtain proper penetration on the weld line and a good bead shape.

<Shield gas flow rate Q: 10 to 30 (liters / minute)>
The shield gas flow rate Q contributes to the shielding property for protecting the molten metal from the atmosphere. When the shield gas flow rate Q is 10 (liters / minute) or more, sufficient shielding properties can be ensured. Further, when the shield gas flow rate Q is 30 (liters / minute) or less, the gas flow suppresses turbulence and becomes a stable laminar flow. Therefore, from the viewpoint of ensuring the shielding property, the shield gas flow rate Q is preferably 10 to 30 (liters / minute), and from the viewpoint of further ensuring the familiarity and glossiness of the beads, the shield gas flow rate Q is 15. More preferably, it is ~ 25 (liters / minute).

<Welding wire protrusion length L: 10 to 30 mm>
The protruding length L of the weld wire also contributes to the shielding property for protecting the molten metal from the atmosphere. When the protruding length L of the welding wire is 30 mm or less, it is possible to suppress the change in the gas composition due to the entrainment of the atmosphere and secure sufficient shielding property. Further, when the protrusion length L of the welding wire is 10 mm or more, damage to the contact tip and the shield nozzle due to arc heat can be suppressed. Therefore, from the viewpoint of ensuring the shielding property and suppressing the damage to the device, the protrusion length L of the welding wire is preferably 10 to 30 mm, and the arc stability is ensured after suppressing the thermal damage and ensuring the weldability for a long time. From the viewpoint of further ensuring the familiarity and gloss of the bead, the protrusion length L of the weld wire is more preferably 15 to 20 mm.

<0.5 ≤ shield gas flow rate Q / welding wire protrusion length L ≤ 2.2>
In the present invention, it is preferable to appropriately control the shield gas flow rate Q and the protrusion length L of the welding wire, and control the ratio of the shield gas flow rate Q to the protrusion length L. When the Q / L is 0.5 or more, a more preferable shielding property can be secured, and when the Q / L is 2.2 or less, the gas flow can protect the arc region in a more stable laminar flow state. Therefore, the ratio of the shield gas flow rate Q to the protrusion length L preferably satisfies the following equation (4).

0.5 ≤ Q / L ≤ 2.2 ... (4)

<Groove shape / groove angle>
In the gas shielded arc welding method according to the present invention, the groove shape of the welding base material is not particularly limited, but is selected from, for example, V type, Les type, I type, K type, X type, J type and U type. It can be one type of groove shape.
Further, the groove angle is not limited, but the groove angle is preferably 0 ° or more because an I-shaped groove shape can be applied. On the other hand, when the groove angle is 90 ° or less, it is preferable because the consumption amount of the welding wire and the shield gas can be appropriately adjusted. Therefore, the groove angle is preferably 0 to 90 °.

[Manufacturing method of structure]
The present invention also relates to a method for manufacturing a structure manufactured by gas shielded arc welding using a welding wire and a shield gas whose composition is controlled as described above. It is also preferable that the composition of the welding wire is controlled as described above.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples, and the present invention is modified to the extent that it can be adapted to the gist of the present invention. It is possible, and all of them are included in the technical scope of the present invention.

Welding was performed according to the welding test method and welding conditions shown below, and the melting performance, familiarity, glossiness and droplet transfer were evaluated by the methods shown below.

<Welding test method and welding conditions>
One-layer, one-pass bead-on-plate welding was performed on the base metal of stainless steel using shield gases having various compositions under various welding conditions. The details of the welding conditions commonly used in the examples of the present invention and the comparative examples are shown in Table 1 below, and the composition of the shield gas is shown in Table 2 below. The arc length shown in Table 1 was adjusted by appropriately changing the voltage adjustment volume of the welding power supply so that the arc was photographed using a high-speed video camera and the reference length was 6 mm. An appropriate filter was applied to the lens of the high-speed video camera used so that arc light could be observed.
In addition, the arc stability was evaluated by observing the droplet transfer during welding, and the melting performance, familiarity and glossiness were evaluated by observing the beads obtained by welding as a sample. The measurement methods and evaluation criteria for each evaluation method are shown in Tables 3 to 9 below. Welding conditions other than those shown in Table 1 below are shown in Table 10 below, and the evaluation results are shown in Table 11 below.

[Test method and evaluation criteria]
<Melting performance test method when welding current is 100A>
The low current welding condition with a welding current of 100 A is a condition usually applied to difficult welding postures such as vertical welding and upward welding. Welding in such a posture usually has a very slow welding speed, so that the heat input to the weld is high, and thus fusion defect defects are unlikely to occur. In this embodiment, downward welding is simply used.

<Melting performance evaluation criteria when the welding current is 100A>
The melting performance was evaluated by measuring the bead width and the bead height and calculating the ratio of the bead width to the bead height (bead width / bead height). When the welding current is 100 A, if the value obtained by (bead width / bead height) is 2.3 or more, it is judged that the occurrence of fusion failure can be prevented even when performing groove construction, and the result is passed. And said.

<Melting performance test method when welding current is 150A>
The high current welding condition with the welding current of 150 A is a condition applied to downward welding, and the bead shape obtained in this test is important.

<Melting performance evaluation criteria when the welding current is 150A>
The bead width and the bead height were measured and the ratio of the bead width to the bead height (bead width / bead height) was calculated in the same manner as when the welding current was 100 A. When the welding current was 150 A and the value obtained by (bead width / bead height) was 3.3 or more, it was judged that the occurrence of fusion failure could be prevented, and the result was accepted. The evaluation method is shown in Table 3 below. The bead width and bead height were measured with calipers.

If the flank angle is 90 ° or more, which will be shaped like a fillet joint in the construction of the next pass, it is possible to melt the weld toe to create a joint without fusion defects. Therefore, if the value obtained by (bead width / bead height) is within the above range as a range in which defects can be prevented with a margin, it is accepted.

<Familiarity evaluation test method / evaluation criteria>
Regarding the familiarity, the sensory evaluation was performed both when the welding current was set to 100 A and when the welding current was set to 150 A. The familiarity at each welding current is evaluated on a 5-point scale from 1 to 5, and the total of the familiarity score when the welding current is 100A and the familiarity score when the welding current is 150A is comprehensively evaluated. And said. The evaluation criteria for familiarity are shown in Table 4 below, and the evaluation criteria for comprehensive evaluation of familiarity are shown in Table 5 below.

<Glossiness evaluation test method / evaluation criteria>
The glossiness was also evaluated as a sensory evaluation when the welding current was 100 A and when the welding current was 150 A. The glossiness at each welding current is evaluated in three stages of 1 to 3, and the total of the glossiness score when the welding current is 100A and the glossiness score when the welding current is 150A is comprehensively evaluated. And said. The evaluation criteria for glossiness are shown in Table 6 below, and the evaluation criteria for comprehensive evaluation of glossiness are shown in Table 7 below.

<Evaluation test method / evaluation criteria for droplet transfer>
The droplet transfer was observed with a high-speed video camera both when the welding current was 100 A and when the welding current was 150 A, and the droplet transfer at each welding current was evaluated in three stages of 1 to 3. Further, the arc stability was comprehensively evaluated based on the score of droplet transfer when the welding current was 100 A and the score of droplet transfer when the welding current was 150 A. The evaluation criteria for droplet transfer are shown in Table 8 below, and the evaluation criteria for comprehensive evaluation of arc stability are shown in Table 9 below.

〔Evaluation results〕
As shown in Tables 10 to 12 below, Test No. T1 to T13 have a melting performance because the composition of the shield gas is within the range of the present invention and the formulas (1) and (2) obtained by _{the CO 2} content and the H _{2 content are satisfied.} Excellent results were obtained in all of the items of arc stability, familiarity and glossiness.

FIG. 3 shows the test No. Sample No. in T1 It is a drawing substitute photograph which shows the cross section of the weld metal of B1 (welding current 150A). FIG. 3 shows an example in which the melting performance test is passed. Test No. In T1 (Sample No. B1), the welding current was 150 A, the value obtained by (bead width / bead height) was 5.2, and the flank angle was 155 °. In the construction in which such a smooth bead toe is formed, it was judged that the resistance to the fusion defect is extremely good.

Also, the test No. For T2 to T13, the test No. As with T1, excellent melting performance could be obtained. In addition, gas No. Test No. using G1. Of T1 to T6, especially the test No. In T1 to T3, T5 and T6, since the protrusion length L of the weld wire is in the more preferable range of the present invention, excellent arc stability can be obtained without changing the gas composition due to the entrainment of the atmosphere. rice field.

Test No. using different gases. Of T7 to T13, the test No. T7, T8, T11 and T12 are excellent arcs because the values obtained by the formula (2) using _{the CO 2} content and the H _{2 content in the shield gas exceed the more preferable lower limit value of the present invention.} I was able to obtain stability.
In addition, the test No. _{Since the CO 2} content in the shield gas of T13 is within the range of the present invention and is high, excellent arc stability could be obtained.

On the other hand, the test No. In T14, the H ₂ content in the shield gas exceeds the upper limit of the range of the present invention, and also exceeds the upper limits specified in the formulas (1) and (2) obtained by _{the CO 2} content and the H _{2 content.} Therefore, the arc stability was lowered.

Test No. _{Since the CO 2} content in the shield gas of T15 is less than the lower limit of the range of the present invention and exceeds the upper limit specified in the formula (2) obtained by _{the CO 2} content and the H _{2 content, the melting performance of T15 is high.} Became low.

Test No. In T16, the H ₂ content in the shield gas is less than the lower limit of the range of the present invention, and is also less than the lower limit specified in the formulas (1) and (2) obtained by _{the CO 2} content and the H _{2 content.} Therefore, the melting performance was low.

FIG. 4 shows the test No. Sample No. in T16. It is a drawing substitute photograph which shows the cross section of the weld metal of B16 (welding current 150A). FIG. 4 shows an example in which the melting performance test fails. Test No. In T16 (Sample No. B16), the welding current was 150 A, the value obtained by (bead width / bead height) was 3.2, and the flank angle was 125 °. When constructing the next welding path after such a bead toe is formed, if the arc does not hit the toe, a fusion defect may occur, so it is a judgment with a margin. It was judged as rejected.

Test No. No. 17 has a _{melting performance because the CO 2} content in the shield gas exceeds the upper limit of the range of the present invention and is less than the lower limit specified in the formula (2) obtained by _{the CO 2} content and the H _{2 content.} Became low.

Test No. Reference numeral 18 is that the H ₂ content in the shield gas is less than the lower limit of the range of the present invention, and is also less than the lower limit specified in the formulas (1) and (2) obtained by _{the CO 2} content and the H _{2 content.} Therefore, the melting performance was low.

FIG. 5 is a drawing substitute photograph showing the appearance of the bead of the test plate welded by the method of the present invention. Further, FIG. 6 is a drawing substitute photograph showing a cross section of the weld metal of the test plate shown in FIG. In the test plates shown in FIGS. 5 and 6, SUS304L having a plate thickness of 12 mm is used as a welding base material, the groove angle is 45 °, and the above test No. This is a three-layer, three-pass vertical welding performed under the conditions of T1. As shown in FIGS. 5 and 6, the joint obtained by the method of the present invention was able to obtain sufficient penetration and a smooth bead shape.

Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to such examples. It is clear that a person skilled in the art can come up with various modifications or modifications within the scope of the claims, which naturally belong to the technical scope of the present invention. Understood. Further, each component in the above-described embodiment may be arbitrarily combined as long as the gist of the invention is not deviated.

This application is based on the Japanese patent application filed on June 29, 2020 (Japanese Patent Application No. 2020-111997), the contents of which are incorporated herein by reference.

1 Welding device 10 Robot 11 Welding torch 20 Robot control unit 30 Welding power supply unit 40 Teaching pendant

Claims (8)

1. It is a gas shielded arc welding method that uses a welding wire as an electrode and welds while flowing a shield gas to the welded area of the welding base material.
   The shield gas is based on the total volume of the shield gas.
   CO ₂ : 0.5% by volume or more and 2.0% by volume or less, and
   H ₂ : 0.5% by volume or more and 3.0% by volume or less,
   Contains,
   The rest is Ar and unavoidable impurities,
   When the content of the _{CO 2} with respect to the total volume of the shield gas _{is [CO 2} ] by volume% and the content of the _{H 2} with respect to the total volume of the shield gas _{is [H 2} ] by volume, the following formula (1). ) And the gas shielded arc welding method, which is characterized by satisfying the formula (2).
   1.30 ≤ [CO ₂ ] + [H ₂ ] ≤ 4.40 ... (1)
   0.35 ≤ [H ₂ ] / ([CO ₂ ] + [H ₂ ]) ≤ 0.74 ... (2)
2. The gas shielded arc welding method according to claim 1, wherein when the content of Ar with respect to the total volume of the shield gas is [Ar] in% by volume, the following formula (3) is satisfied.
   57.0 ≤ 0.5 x [Ar] +1.5 x [CO ₂ ] +10 x [H ₂ ] ≤ 80.0 ... (3)
3. The welding wire is used with respect to the total mass of the welding wire.
   Cr: 18% by mass or more and 28.5% by mass or less, and
   Ni: 8.0% by mass or more and 37.0% by mass or less,
   Contains,
   The gas shielded arc welding method according to claim 1 or 2, wherein the ferrite percentage has a structure of 15.3% or less based on the organization chart of DeLong.
4. The welding wire is based on the total mass of the welding wire.
   C: 0.20% by mass or less (including 0% by mass),
   Si: 1.00% by mass or less (including 0% by mass),
   Mn: 4.8% by mass or less (including 0% by mass),
   P: 0.03% by mass or less (including 0% by mass),
   S: 0.03% by mass or less (including 0% by mass),
   Cu: 4.0% by mass or less (including 0% by mass),
   Mo: 4.0% by mass or less (including 0% by mass),
   Nb: 1.0% by mass or less (including 0% by mass), and
   N: 0.30% by mass or less (including 0% by mass),
   The gas shielded arc welding method according to claim 3, wherein the method is characterized by the above.
5. The welded area of the weld base material has a groove and has a groove.
   The groove has one type of groove shape selected from V type, Les type, I type, K type, X type, J type and U type.
   The gas shielded arc welding method according to claim 1 or 2, wherein the groove angle of the groove is 0 to 90 °.
6. The gas flow rate Q of the shield gas is 10 to 30 (liters / minute) or less,
   The protrusion length L of the welding wire is 10 to 30 (mm) or less, and the welding wire has a protrusion length L of 10 to 30 (mm) or less.
   The gas shielded arc welding method according to claim 1 or 2, wherein the ratio of the gas flow rate Q (liters / minute) to the protrusion length L (mm) satisfies the following formula (4).
   0.5 ≤ Q / L ≤ 2.2 ... (4)
7. It is a manufacturing method of a structure manufactured by gas shielded arc welding using a welding wire and a shield gas.
   The shield gas is based on the total volume of the shield gas.
   CO ₂ : 0.5% by volume or more and 2.0% by volume or less, and
   H ₂ : 0.5% by volume or more and 3.0% by volume or less,
   Contains,
   The rest is Ar and unavoidable impurities,
   When the content of the _{CO 2} with respect to the total volume of the shield gas _{is [CO 2} ] by volume% and the content of the _{H 2} with respect to the total volume of the shield gas _{is [H 2} ] by volume, the following formula (1). ) And a method for manufacturing a structure, which is characterized by satisfying the formula (2).
   1.30 ≤ [CO ₂ ] + [H ₂ ] ≤ 4.40 ... (1)
   0.35 ≤ [H ₂ ] / ([CO ₂ ] + [H ₂ ]) ≤ 0.74 ... (2)
8. Gas shield gas used for arc welding,
   For the total volume of shield gas
   CO ₂ : 0.5% by volume or more and 2.0% by volume or less, and
   H ₂ : 0.5% by volume or more and 3.0% by volume or less,
   Contains,
   The rest is Ar and unavoidable impurities,
   When the content of the _{CO 2} with respect to the total volume of the shield gas _{is [CO 2} ] by volume% and the content of the _{H 2} with respect to the total volume of the shield gas _{is [H 2} ] by volume, the following formula (1). ) And the shield gas characterized by satisfying the formula (2).
   1.30 ≤ [CO ₂ ] + [H ₂ ] ≤ 4.40 ... (1)
   0.35 ≤ [H ₂ ] / ([CO ₂ ] + [H ₂ ]) ≤ 0.74 ... (2)

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