Welding wire, welding method, and method for manufacturing weld metal

Abstract

Provided is a welding wire capable of improving electrodeposition coating properties and achieving both of resistance to loss of an electrodeposition coating part and pore defect resistance after electrodeposition coating. The welding wire comprises, with respect to the total mass of the welding wire, 0.010-0.100 mass% C, 0.15-0.50 mass% Si, 1.70-3.00 mass% Mn, and 0.01-0.17 mass% Ti, Al being 0.10 mass% or less (including 0 mass%), Cr being 1.00 mass% or less (including 0 mass%), Mo being 0.50 mass% or less (including 0 mass%), P being 0.030 mass% or less (including 0 mass%), S being 0.0300 mass% or less (including 0 mass%), Cu being 0.50 mass% or less (including 0 mass%), O being 0.0100 mass% or less (including 0 mass%), and N being 0.0100 mass% or less (including 0 mass%), with the remainder being Fe and unavoidable impurities.

Description

Welding wire, welding method, and method for producing weld metal

[0001] The present invention relates to a welding wire used in gas-shielded arc welding, a welding method using the welding wire, and a method for producing a weld metal using the welding wire.

[0002] Automotive suspension parts are exposed to moisture from the road surface, and therefore require technology to prevent rusting of suspension parts. Generally, when manufacturing parts, the parts are arc-welded and then electro-deposition-coated to form an anti-rust coating on the surface, thereby preventing rusting of the suspension parts. However, after welding, welding slag (hereinafter simply referred to as "slag"), which has low electrical conductivity, is generated on the bead surface, and depending on the condition of the slag, it may inhibit the formation of the anti-rust coating (hereinafter simply referred to as "coating" or "electro-deposition coating").

[0003] Generally, the following methods are used: after welding, the slag remaining on the bead surface is mechanically removed, followed by electrodeposition coating; or, alternatively, electrodeposition coating is performed while the slag remains on the bead surface. If electrodeposition coating is performed while the slag remains on the bead surface, it becomes difficult to form a sufficient coating film, resulting in variations in the quality of the rust prevention properties of the finished parts. Furthermore, removing the slag mechanically increases the burden on the worker. Therefore, from the perspectives of quality and workload, it is preferable to minimize the amount of slag generated during arc welding.

[0004] As mentioned above, electrodeposition paintability is an extremely important performance factor that affects the quality and workload in welding of automobile parts. Therefore, as an arc welding method that can improve electrodeposition paintability, 80% Ar-20% CO is used because it generates very little slag. ２ The most commonly used welding method is a mixed gas welding method.

[0005] Furthermore, various wires have been developed that have improved electrodeposition coatability by adjusting the composition of specific components in the wire. For example, Patent Document 1 discloses a solid wire in which the contents of C, Si, Mn, Ti, Al, Sn, P, S, B, Cr, Ni, Mo, Nb, V, Cu, etc. in the wire are controlled, and the values ​​obtained by a formula using the contents of specific elements are controlled. Furthermore, Patent Document 2 discloses an ultra-low silicon welding wire in which the contents of C, Si, Mn, P, and S in the wire are controlled. Here, ultra-low silicon welding wire refers to a wire with an Si content of 0.1 mass% or less.

[0006] Japanese Patent Publication No. 2021-3717 Japanese Patent Publication No. 2019-81195

[0007] Recently, from the viewpoint of high-speed welding and cost reduction of shielding gas, carbon dioxide gas has been used or CO2 gas in mixed gas has been used. ２ There is an increasing demand for an increased gas mixture ratio. However, shielding gas is not only used for the purpose of blocking the atmosphere, but the type of shielding gas also has a significant effect on the arc state, various properties of the weld metal, and the properties and amount of slag produced. For this reason, in the welding using the solid wire described in Patent Document 1, ２ When using a shielding gas with a gas mixture ratio exceeding 20% ​​or when using the ultra-low silicon welding wire described in Patent Document 2, CO ２ If the gas content is increased, there is a risk that the desired "resistance to pore defects" and "various performances against electrodeposition coating" may not be obtained.

[0008] Specifically, CO in the shielding gas ２In a strong oxidizing atmosphere with a gas content exceeding 20%, the amount of slag increases and changes. Furthermore, if the wire contains a small amount of deoxidizing elements, deoxidation is insufficient during welding, making porosity defects more likely to occur. Here, porosity refers to pits or blowholes. Furthermore, if electrodeposition coating is performed after welding using a conventional wire while leaving slag on the bead, even if electrodeposition coating is possible, the slag may become thick in some areas or the slag shape may cause the paint film to become unstable. As a result, for example, when a conventional wire is used to weld automobile suspension parts, after electrodeposition coating, the slag is likely to peel off due to vibrations or impacts on the electrodeposition coating film, resulting in the entire paint coating being removed and the rust prevention properties being reduced. In this specification, the ability of the paint film to resist removal after electrodeposition coating is referred to as "electrodeposition coating chipping resistance."

[0009] The present invention has been made in view of the above problem, and is a method for producing a gas containing carbon dioxide or CO ２ The present invention aims to provide a welding wire that can improve electrodeposition coating properties even when a mixed gas having a gas mixing ratio of more than 20% is used as a shielding gas, and that can achieve both resistance to electrodeposition coating chipping and resistance to porosity defects after electrodeposition coating, a welding method using the welding wire, and a method for producing weld metal using the welding wire.

[0010] The above object of the present invention is achieved by the following configuration [1] relating to a welding wire.

[0011] [1] The welding wire contains, relative to the total mass of the welding wire, C: 0.010 mass% or more and 0.100 mass% or less, Si: 0.15 mass% or more and 0.50 mass% or less, Mn: 1.70 mass% or more and 3.00 mass% or less, Ti: 0.01 mass% or more and 0.17 mass% or less, Al: 0.10 mass% or less (inclusive of 0 mass%), Cr: 1.00 mass% or less (inclusive of 0 mass%), Mo: 0.50 mass% or less (inclusive of 0 mass%), P: 0.030 mass% or less (inclusive of 0 mass%), S: 0.0300 mass% or less (inclusive of 0 mass%), Cu: 0.50 mass% or less (inclusive of 0 mass%), O: 0.0100 mass% or less (inclusive of 0 mass%), N: 0.0100 mass% or less (inclusive of 0 mass%), A welding wire, the balance of which is Fe and unavoidable impurities.

[0012] Preferred embodiments of the present invention relating to the welding wire relate to the following [2] to [4].

[0013] [2] The welding wire according to [1], wherein the value F1 calculated by the following formula (1) is 55 or more, where the Si content in the wire is [Si] in mass% relative to the total mass of the wire, the Ti content in the wire is [Ti] in mass% relative to the total mass of the wire, the Cr content in the wire is [Cr] in mass% relative to the total mass of the wire, the Mn content in the wire is [Mn] in mass% relative to the total mass of the wire, and the Mo content in the wire is [Mo] in mass% relative to the total mass of the wire. Formula (1): F1 = 200 x (3.0 x [Si] + 0.3 x [Ti] + 5.0 x [Cr]) / (1.2 x [Mn] + 1.8 x [Mo])

[0014] [3] The welding wire according to [1] or [2], characterized in that, when the O content in the wire is expressed as [O] in mass % relative to the total mass of the wire, the Si content in the wire is expressed as [Si] in mass % relative to the total mass of the wire, the Ti content in the wire is expressed as [Ti] in mass % relative to the total mass of the wire, the Cr content in the wire is expressed as [Cr] in mass % relative to the total mass of the wire, the Mn content in the wire is expressed as [Mn] in mass % relative to the total mass of the wire, the Mo content in the wire is expressed as [Mo] in mass % relative to the total mass of the wire, the Al content in the wire is expressed as [Al] in mass % relative to the total mass of the wire, and the C content in the wire is expressed as [C] in mass % relative to the total mass of the wire, the value F2 calculated by the following formula (2) is 40.00 or less, and the value F3 calculated by the following formula (3) is 8.50 or less. Formula (2): F2=5×[C] / ([Cr]+5×[Mo]) Formula (3): F3=10000×[O] / (15×[Si]+3×[Mn]+12×[Ti]+20×[Al]+15×[Cr]+2×[Mo])

[0015] [4] The welding wire according to any one of [1] to [3], wherein the value F4 calculated by the following formula (4) is 0.25 or more and 6.0 or less, where the S content in the wire is [S] in mass % with respect to the total mass of the wire, the Si content in the wire is [Si] in mass % with respect to the total mass of the wire, the Mn content in the wire is [Mn] in mass % with respect to the total mass of the wire, the Ti content in the wire is [Ti] in mass % with respect to the total mass of the wire, and the Al content in the wire is [Al] in mass % with respect to the total mass of the wire. Formula (4): F4 = 500 × [S] / (5 × [Si] + [Mn] / 10 + [Ti] + [Al])

[0016] The above object of the present invention is achieved by the following configuration [5] relating to the welding method.

[0017] [5] A welding method, characterized by performing gas-shielded arc welding using the welding wire according to any one of [1] to [4].

[0018] A preferred embodiment of the present invention relating to a welding method relates to the following [6].

[0019] [6] The welding method according to [5], characterized in that the steel plates are gas-shielded arc-welded while the feeding of the welding wire is alternately switched between a forward feeding period and a reverse feeding period.

[0020] The above object of the present invention is achieved by the following configuration [7] relating to a method for producing a weld metal.

[0021] [7] A method for producing a weld metal, characterized in that the welding wire according to any one of [1] to [4] is used to produce a weld metal by gas-shielded arc welding.

[0022] According to the present invention, carbon dioxide or CO ２ The present invention provides a welding wire that can improve electrodeposition coating properties even when a mixed gas having a gas mixing ratio of more than 20% is used as a shielding gas, and can achieve both resistance to electrodeposition coating chipping after electrodeposition coating and resistance to porosity defects, a welding method using the welding wire, and a method for producing weld metal using the welding wire.

[0023] The inventors of the present invention have found that carbon dioxide or CO ２ In the case of using a mixed gas with a gas mixing ratio of more than 20% as a shielding gas, when electrodeposition coating is performed with slag remaining on the bead after welding, even if good electrodeposition coatability is obtained, the slag is likely to peel off and chip off the entire coating film after electrodeposition coating depending on the state of the slag. Therefore, the present inventors conducted extensive research and found that by appropriately controlling the content of certain alloy components in the wire, it is possible to improve not only electrodeposition coatability but also resistance to electrodeposition coating chipping and resistance to porosity defects. Furthermore, it was found that by controlling the value obtained by a specific formula using the contents of Si, Ti, Cr, Mn, and Mo in the wire, it is possible to appropriately adjust the shape of the slag and improve resistance to electrodeposition coating chipping.

[0024] Hereinafter, a mode for carrying out the present invention (hereinafter referred to as "the present embodiment") will be described in detail. Note that the present invention is not limited to the embodiment described below, and can be carried out with any modifications within the scope of the gist of the present invention.

[0025] In this specification, the content of each component in the wire means mass % relative to the total mass of the welding wire unless otherwise specified, and the ratio of gas components in the shielding gas is expressed in volume %.

[0026] [Welding Wire] The form of the welding wire according to this embodiment is not particularly limited as long as the content of each element in the wire is within the range of the present invention. For example, both solid wire and flux-cored wire for gas-shielded arc welding can be applied to the present invention, but solid wire is preferred. In this specification, these wires are collectively referred to as "welding wire" or "wire."

[0027] Hereinafter, the specific components in the wire and the reasons for limiting the numerical values ​​of their contents will be described in more detail.

[0028] <C: 0.010% by Mass or More and 0.100% by Mass or Less> C is a component that has a deoxidizing effect and also has the effect of increasing the strength of the weld metal. Since single-pass welding is applied in the welding of thin plates, there is no risk of strength reduction due to reheating, as in the case of multi-pass welding, and it is possible to obtain strength equal to or greater than that of the base material. If the C content in the wire is less than 0.010% by mass, it becomes difficult to obtain the minimum required strength of mild steel. Therefore, the C content in the wire is set to 0.010% by mass or more, preferably 0.015% by mass or more, more preferably 0.020% by mass or more, and even more preferably 0.030% by mass or more, relative to the total mass of the wire. On the other hand, if the C content in the wire exceeds 0.100% by mass, the deoxidizing effect becomes large, the arc becomes unstable, making it difficult to obtain sufficient shielding properties, and spatter and fumes are likely to be generated. Therefore, a lower C content is preferable within a range that ensures the desired strength of the weld metal. Therefore, the C content in the wire is set to 0.100 mass% or less, preferably 0.090 mass% or less, more preferably 0.080 mass% or less, and even more preferably 0.065 mass% or less, relative to the total mass of the wire.

[0029] <Si: 0.15% by mass or more and 0.50% by mass or less> Si is a component that has a deoxidizing effect and also has the effect of improving the conformity of the weld bead. Furthermore, by appropriately controlling the Si content in the wire, it is possible to reduce slag dripping and achieve a smooth bead shape at the weld toe. If the Si content in the wire is less than 0.15% by mass, the deoxidizing effect in the molten metal cannot be sufficiently obtained, and there is a risk of porosity defects remaining in the weld metal. Furthermore, if the Si content in the wire is less than 0.15% by mass, spatter is likely to occur. Therefore, in this embodiment, by including Si in the wire at a predetermined content, the amount of spatter generated during welding can be reduced. Furthermore, if the Si content in the wire is 0.15% by mass or more, the viscosity of the molten slag increases, improving the uniformity of the slag toe on the weld bead, thereby improving the resistance to electrodeposition coating chipping. Therefore, the Si content in the wire is set to 0.15 mass % or more, preferably 0.17 mass % or more, more preferably 0.19 mass % or more, and even more preferably 0.25 mass % or more, based on the total mass of the wire. ２ is a non-conductive glassy oxide, and if the Si content in the wire exceeds 0.50 mass%, it turns into an oxide and remains as slag on the weld bead, making it difficult to form a good electrodeposition coating film and deteriorating electrodeposition paintability. Therefore, the Si content in the wire is set to 0.50 mass% or less, preferably 0.48 mass% or less, more preferably 0.45 mass% or less, and even more preferably 0.40 mass% or less, based on the total mass of the wire.

[0030] <Mn: 1.70% by Mass or More and 3.00% by Mass or Less> Mn is an important component for ensuring the desired strength of the weld metal. In the wire according to this embodiment, the C and Si contents in the wire are limited to predetermined ranges in order to improve welding workability, resistance to blowhole defects, and resistance to electrodeposition coating chipping. Therefore, in order to obtain sufficient strength of the weld metal, it is necessary to appropriately control the Mn content. If the Mn content in the wire is less than 1.70% by mass, it becomes difficult to obtain not only sufficient strength of the weld metal but also good resistance to blowhole defects. Therefore, the Mn content in the wire is set to 1.70% by mass or more, preferably 1.75% by mass or more, more preferably 1.80% by mass or more, and even more preferably 1.90% by mass or more, based on the total mass of the wire. On the other hand, if the Mn content in the wire exceeds 3.00% by mass, excessive deoxidation occurs, the amount of oxygen in the molten pool decreases, and the viscosity and surface tension of the molten metal increase, making it difficult to obtain a good bead shape. Furthermore, an increase in the Mn content reduces the viscosity of the molten slag, making the slag more likely to drip, resulting in poor uniformity of the slag toe on the weld bead and poor resistance to electrodeposition coating chipping. Therefore, the Mn content in the wire is set to 3.00 mass% or less, preferably 2.50 mass% or less, more preferably 2.30 mass% or less, and even more preferably 2.00 mass% or less, based on the total mass of the wire.

[0031] <Ti: 0.01% by mass or more and 0.17% by mass or less> Ti is a strong deoxidizing element that preferentially forms oxides through deoxidation. Therefore, like Mn and Si, Ti is an element that significantly contributes to the composition of slag. Furthermore, by incorporating Ti in combination with Si into the wire, the viscosity of the molten slag can be increased, thereby reducing the slag's tendency to drip. If the Ti content in the wire is less than 0.01% by mass, a good slag shape cannot be obtained, and the resistance to electrodeposition coating chipping deteriorates. Therefore, the Ti content in the wire is set to 0.01% by mass or more, preferably 0.015% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.025% by mass or more, based on the total mass of the wire. On the other hand, if the Ti content in the wire exceeds 0.17% by mass, excessive deoxidation occurs, the amount of slag generated increases, and the slag becomes thicker, which may cause the slag to peel off, resulting in a deterioration in resistance to electrodeposition coating chipping. Furthermore, excessive deoxidation results in a deterioration in the bead shape. Therefore, the Ti content in the wire is set to 0.17% by mass or less, preferably 0.15% by mass or less, more preferably 0.13% by mass or less, and even more preferably 0.08% by mass or less, based on the total mass of the wire.

[0032] <Al: 0.10% by mass or less (including 0% by mass)> Al is an element that has a strong deoxidizing effect and affects the yield of Si, Mn, and Ti in the weld metal. Furthermore, Al is a strong deoxidizing element and has the effect of changing the physical properties of the slag. If the Al content in the wire exceeds 0.10% by mass, the slag may be easily deoxidized, especially when carbon dioxide or CO ２In a strongly oxidizing atmosphere using a mixed gas with a gas mixing ratio of more than 20% as a shielding gas, the amount of slag increases, thick slag is formed, and resistance to chipping of the electrodeposition coating deteriorates. Therefore, the Al content in the wire is set to 0.10 mass% or less, preferably 0.09 mass% or less, more preferably 0.08 mass% or less, and even more preferably 0.07 mass% or less, based on the total mass of the wire. When Al is contained in the wire, the Al content in the wire is set to 0.001 mass% or more, more preferably 0.005 mass% or more, based on the total mass of the wire.

[0033] <Cr: 1.00% by Mass or Less (Including 0% by Mass)> The inclusion of Cr in the wire can enhance the mechanical properties of the weld metal. The Cr content in the wire can be adjusted appropriately depending on the required strength of the weld metal. In this embodiment, however, as long as the strength can be ensured by other elements, the wire does not need to contain Cr, and the Cr content may be 0% by mass. Furthermore, Cr not only has a deoxidizing effect and improves resistance to porosity defects, but also increases the viscosity of molten slag, appropriately controls the slag shape, and further improves resistance to electrodeposition coating chipping. When Cr is included in the wire to improve the mechanical properties of the weld metal or the resistance to electrodeposition coating chipping, taking into account the balance with other elements that enhance the mechanical properties in this embodiment, the Cr content in the wire is preferably 0.10% by mass or more, more preferably 0.15% by mass or more, and even more preferably 0.20% by mass or more, relative to the total mass of the wire. If the Cr content in the wire exceeds 1.00 mass%, the strength will be excessive in lap fillet welding of 440 to 980 MPa class steel plates used in automotive suspension parts, making it difficult to form weld metal with suitable strength. Therefore, the Cr content in the wire is set to 1.00 mass% or less, preferably 0.70 mass% or less, more preferably 0.55 mass% or less, and even more preferably 0.40 mass% or less, relative to the total mass of the wire.

[0034] <Mo: 0.50% by mass or less (including 0% by mass)> The inclusion of Mo in the wire can have the effect of improving the mechanical properties of the weld metal. The Mo content in the wire can be adjusted appropriately depending on the required strength of the weld metal. However, in this embodiment, if strength can be ensured with other elements, Mo need not be contained in the wire, and it may be 0% by mass. Note that when Mo is contained in the wire for the purpose of improving the mechanical properties of the weld metal, taking into consideration the balance with the other elements that improve the mechanical properties in this embodiment, the Mo content in the wire is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more, relative to the total mass of the wire. If the Mo content in the wire exceeds 0.50% by mass, the strength will be excessive in lap fillet welding of 440 to 980 MPa-class steel plates used in automotive suspension parts, making it difficult to form weld metal with appropriate strength. Furthermore, if the wire contains too much Mo, the slag tends to drip and sufficient resistance to electrodeposition coating chipping cannot be obtained. Therefore, the Mo content in the wire is set to 0.50 mass% or less, preferably 0.40 mass% or less, more preferably 0.35 mass% or less, and even more preferably 0.25 mass% or less, based on the total mass of the wire.

[0035] <P: 0.030% by mass or less (including 0% by mass)> P is an element that reduces the cracking resistance of the weld metal, and the lower the P content in the wire, the better. If the P content in the wire exceeds 0.030% by mass, the required cracking resistance cannot be obtained. Therefore, the P content in the wire is set to 0.030% by mass or less, preferably 0.025% by mass or less, and more preferably 0.020% by mass or less, relative to the total mass of the wire.

[0036] <S: 0.0300% by Mass or Less (Including 0% by Mass)> S is an element that has the effect of aggregating slag and affecting the surface tension of the weld metal, thereby improving the weld bead conformability and bead shape. On the other hand, when the S content in the wire is changed while keeping the slag amount constant, the slag aggregates and increases in thickness as the S content increases. Therefore, from the viewpoint of electrodeposition paintability, a lower S content in the wire is preferable. If the S content in the wire exceeds 0.0300% by mass, it becomes difficult to uniformly form a thin slag on the weld metal, which may result in an insufficient electrodeposition paint coating, resulting in the desired electrodeposition paintability being lost, or the slag may peel off, resulting in poor resistance to electrodeposition paint chipping. Therefore, the S content in the wire is set to 0.0300% by mass or less, preferably 0.0250% by mass or less, more preferably 0.0200% by mass or less, and even more preferably 0.0150% by mass or less, based on the total mass of the wire. In addition, when S is contained in the wire, if the S content in the wire is 0.0010% by mass or more, the effect of improving the conformity of the weld bead and the bead shape can be obtained. Therefore, the S content in the wire is preferably 0.0010% by mass or more, and more preferably 0.0030% by mass or more, relative to the total mass of the wire.

[0037] <Cu: 0.50% by mass or less (including 0% by mass)> By including Cu in the wire, the mechanical properties of the weld metal can be improved. Furthermore, by applying a Cu-containing plating to the surface of the wire, the electrical conductivity of the wire can be improved. When Cu is included in the wire to achieve these effects, taking into consideration the balance with other elements in this embodiment, the Cu content in the wire is preferably 0.03% by mass or more, and more preferably 0.05% by mass or more, relative to the total mass of the wire. If the Cu content in the wire exceeds 0.50% by mass, the strength becomes excessive in lap fillet welding of 440 to 980 MPa-class steel sheets used in automotive suspension parts, making it difficult to form weld metal with suitable strength. Therefore, the Cu content in the wire is set to 0.50% by mass or less, preferably 0.42% by mass or less, and more preferably 0.35% by mass or less, relative to the total mass of the wire. In this specification, the Cu content includes not only the Cu content contained in the bulk of the wire, but also the Cu content in the plating formed on the surface of the wire.

[0038] <O: 0.0100% by mass or less (including 0% by mass)> O is not an essential component in the wire of this embodiment, but is an element that affects the amount of slag generated and the resistance to porosity defects. Therefore, a low O content in the wire is preferable. If the O content in the wire exceeds 0.0100% by mass, an appropriate amount of slag generated and excellent resistance to porosity defects cannot be obtained. Therefore, the O content in the wire is set to 0.0100% by mass or less, preferably 0.0085% by mass or less, more preferably 0.0075% by mass or less, and even more preferably 0.0050% by mass or less, relative to the total mass of the wire. Although the lower limit of the O content in the wire is not particularly specified, it is substantially set to, for example, 0.0005% by mass or more.

[0039] <N: 0.0100% by mass or less (including 0% by mass)> N is an element that has the effect of improving the strength and fatigue resistance of the weld metal. Controlling the N content to a certain content or less improves blowhole defect resistance. When N is contained in the wire to achieve these effects, taking into consideration the balance with other elements in this embodiment, the N content in the wire is preferably 0.0035% by mass or more, and more preferably 0.0050% by mass or more, relative to the total mass of the wire. If the N content in the wire exceeds 0.0100% by mass, not only will excellent blowhole defect resistance not be achieved, but spatter will increase and the bead shape will deteriorate. Therefore, the N content in the wire is set to 0.0100% by mass or less, preferably 0.0090% by mass or less, more preferably 0.0085% by mass or less, and even more preferably 0.0080% by mass or less, relative to the total mass of the wire. While the lower limit of the N content in the wire is not particularly specified, it is practically, for example, 0.0005% by mass or more.

[0040] In this embodiment, by specifying the content of the above-mentioned specific elements in the wire, it is possible to improve electrodeposition coatability and to achieve both resistance to electrodeposition coating chipping after electrodeposition coating and resistance to pore defects. Furthermore, by controlling the value calculated by the following formula using the content of the above-mentioned specific elements, it is possible to further improve the above-mentioned effects.

[0041] Hereinafter, preferred ranges of values ​​calculated by predetermined formulas using the contents of each component contained in the wire and the reasons for limiting the numerical values ​​will be described. In the following formulas (1) to (6), [Si] is the Si content in the wire expressed as mass% with respect to the total mass of the wire, [Ti] is the Ti content in the wire expressed as mass% with respect to the total mass of the wire, [Cr] is the Cr content in the wire expressed as mass% with respect to the total mass of the wire, [Mn] is the Mn content in the wire expressed as mass% with respect to the total mass of the wire, [Mo] is the Mo content in the wire expressed as mass% with respect to the total mass of the wire, [O] is the O content in the wire expressed as mass% with respect to the total mass of the wire, [Al] is the Al content in the wire expressed as mass% with respect to the total mass of the wire, [C] is the C content in the wire expressed as mass% with respect to the total mass of the wire, and [S] is the S content in the wire expressed as mass% with respect to the total mass of the wire.

[0042] <Value F1 Calculated by Formula (1): 55 or More> By adjusting the ratio of the contents of Si, Ti, Cr, Mn, and Mo in the wire, the viscosity of the slag can be appropriately controlled, thereby making the slag less likely to drip and further preventing the slag from becoming excessively thick and peeling off the electrodeposition coating. That is, by setting the value F1 calculated by the following formula (1) to 55 or more, the electrodeposition coating chipping resistance can be further improved. Therefore, the value F1 calculated by the following formula (1) is preferably 55 or more, more preferably 78 or more, and even more preferably 150 or more. Furthermore, although there is no particular upper limit, from the viewpoint of welding workability, the value F1 is preferably 400 or less, more preferably 350 or less, and even more preferably 300 or less. Formula (1): F1=200×(3.0×[Si]+0.3×[Ti]+5.0×[Cr]) / (1.2×[Mn]+1.8×[Mo])

[0043] The present inventors have also found that controlling the values ​​calculated by the following formulas (2) and (3) within appropriate ranges further improves porosity defect resistance. Porosity defects in weld metal can be caused by the following factors: (A) zinc contained in the coating of the galvanized steel sheet; and (B) oxygen contained in the molten metal. Regarding (A), the zinc contained in the coating of the galvanized steel sheet itself may become trapped in the weld metal as bubbles, or the zinc may vaporize, causing the arc to become unstable, inhibiting the shielding gas, and allowing nitrogen to enter the molten metal, resulting in porosity defects. Therefore, the present inventors have considered that, to further improve porosity defect resistance, ensuring arc stability can suppress the entrainment of zinc vapor, while increasing the viscosity of the molten metal to suppress the inflow of molten metal directly below the arc can suppress the penetration of zinc vapor into the weld metal. Furthermore, regarding (B), the present inventors have considered that appropriately controlling the alloying elements contained in the wire can promote deoxidation of the molten metal and further improve porosity defect resistance. Details are explained below.

[0044] <Value F2 calculated by Equation (2): 40.00 or less> By appropriately controlling the C content in the wire, arc stability can be improved. However, excessive C content in the wire can cause spattering and other issues, making the arc unstable and more likely to entrain zinc vapor. Furthermore, by appropriately controlling the Cr and Mo content in the wire, the viscosity of the molten metal can be increased, suppressing the inflow of molten metal directly below the arc. This makes it easier to discharge zinc vapor directly below the arc, thereby suppressing the intrusion of zinc vapor into the molten metal. That is, by setting the value F2 calculated by the following Equation (2) to 40.00 or less, the resistance to porosity defects can be further improved. Therefore, the value F2 calculated by the following Equation (2) is preferably 40.00 or less, more preferably 18.00 or less, and even more preferably 5.00 or less. Furthermore, although the lower limit is not particularly limited, from the viewpoint of welding workability, the value F2 is preferably 0.15 or more, more preferably 0.30 or more, and even more preferably 0.50 or more. Formula (2): F2=5×[C] / ([Cr]+5×[Mo])

[0045] <Value F3 calculated by formula (3): 8.50 or less> By appropriately controlling the content of each alloy element relative to the oxygen content in the wire, it is possible to suppress oxygen contamination from the wire into the molten metal, promote deoxidation of the molten metal, and further suppress porosity defects. That is, by setting the value F3 calculated by the following formula (3) to 8.50 or less, it is possible to further improve porosity defect resistance. Therefore, the value F3 calculated by the following formula (3) is preferably set to 8.50 or less, more preferably set to 5.10 or less, and even more preferably set to 4.20 or less. Furthermore, although the lower limit is not particularly limited, from the viewpoint of welding workability, the value F3 is preferably set to 0.30 or more, more preferably set to 0.50 or more, and even more preferably set to 1.00 or more. Formula (3): F3=10000×[O] / (15×[Si]+3×[Mn]+12×[Ti]+20×[Al]+15×[Cr]+2×[Mo])

[0046] In the wire according to the present embodiment, it is further preferable that values ​​F4 to F6 calculated by the following formulas (4) to (6) based on the contents of S, Si, Mn, Ti, and Al are adjusted to be within their respective preferred ranges. The preferred ranges of values ​​F4 to F6 and the reasons for limiting their numerical values ​​are explained below.

[0047] <F4 Value Calculated by Formula (4): 0.25 or More and 6.0 or Less> When the F4 value calculated by Formula (4) is 0.25 or more, the surface tension of the molten metal can be prevented from becoming too high, resulting in a stable bead shape. Therefore, the F4 value calculated by Formula (4) is preferably 0.25 or more, more preferably 0.35 or more, and even more preferably 0.50 or more. On the other hand, when the F4 value calculated by Formula (4) is 6.0 or less, the deoxidizing effect is improved, further improving resistance to pore defects. Furthermore, by suppressing excessive slag aggregation, slag peeling can be suppressed, thereby further improving resistance to electrodeposition coating chipping. Therefore, the F4 value calculated by Formula (4) is preferably 6.0 or less, more preferably 4.5 or less, and even more preferably 3.0 or less. Formula (4): F4=500×[S] / (5×[Si]+[Mn] / 10+[Ti]+[Al])

[0048] <Value F5 Calculated by Formula (5): 0.85 or Less> When combined with Ti, Al disperses slag appropriately and prevents excessive slag thickness. Si is an element effective in aligning the slag toes. By appropriately adjusting the ratio of the Ti and Al contents to the Si content in the wire, the amount of slag generated can be controlled, further preventing the electrodeposition coating from peeling off along with the slag. In other words, setting the value calculated by the following formula (5) to 0.85 or less can further improve the resistance to electrodeposition coating chipping. Therefore, the value F5 calculated by the following formula (5) is preferably 0.85 or less, and more preferably 0.65 or less. Furthermore, while the lower limit is not particularly limited, it is preferably 0.02 or more, and more preferably 0.08 or more, from the viewpoint of welding workability. Formula (5): F5 = ([Ti] + 1.5 × [Al]) / [Si]

[0049] <F6 Calculated by Formula (6): 15 to 105> By appropriately adjusting the ratio of Mn to Ti in the wire, the amount of slag generated can be controlled, and the electrodeposition coating can be prevented from peeling off along with the slag. That is, when the value F6 calculated by Formula (6) is 15 or greater, the electrodeposition coating chip resistance can be further improved. Therefore, the value F6 calculated by Formula (6) is preferably 15 or greater, and more preferably 20 or greater. On the other hand, when the value F6 calculated by Formula (6) is 105 or less, the viscosity of the molten slag can be prevented from becoming too low, better slag toe alignment can be achieved, and the electrodeposition coating chip resistance can be further improved. Therefore, the value F5 calculated by Formula (6) is preferably 105 or less, more preferably 80 or less, and even more preferably 50 or less. Formula (6): F6 = [Mn] / [Ti]

[0050] The welding wire according to this embodiment specifies the contents of C, Si, Mn, Ti, Al, Cr, Mo, P, S, Cu, O, and N in the wire, preferably the values ​​calculated by the above formulas (1) to (6). However, the welding wire may contain Ni or B within a range not exceeding a predetermined content. The upper limits of the Ni and B contents and the reasons for the limitations will be explained below.

[0051] <Ni: 0.50% by mass or less (including 0% by mass)> Although Ni is not an essential component of the wire of this embodiment, it can be contained in the wire for the purpose of improving the strength of the weld metal. The Ni content can be adjusted appropriately depending on the required strength, as long as it does not exceed the specified upper limit. When the welding wire according to this embodiment is used for lap fillet welding of 440 to 980 MPa-class steel plates used in automotive suspension parts and Ni is contained in the wire, the Ni content is preferably 0.50% by mass or less, and more preferably 0.40% by mass or less, relative to the total mass of the wire. By suppressing the Ni content in the wire as described above, a balance is achieved with the other elements that enhance the mechanical properties of this embodiment, and excessive strength of the weld metal can be suppressed.

[0052] <B: 0.0100% by mass or less (including 0% by mass)> The inclusion of B in the wire can enhance the mechanical properties of the weld metal. The B content can be adjusted appropriately depending on the required strength, as long as it does not exceed the specified upper limit. When the welding wire according to this embodiment is used for lap fillet welding of 440 to 980 MPa-class steel plates used in automotive suspension parts and B is contained in the wire, the B content is preferably 0.0100% by mass or less, and more preferably 0.0080% by mass or less, relative to the total mass of the wire. By suppressing the B content in the wire as described above, a balance is achieved with the other elements that enhance the mechanical properties in this embodiment, and excessive strength of the weld metal can be suppressed.

[0053] <Balance: Fe and Inevitable Impurities> The balance of the wire components in this embodiment is Fe and inevitable impurities. Examples of inevitable impurities include K, Na, Ca, Zr, Nb, V, Li, Bi, and As. The content of each of these inevitable impurities is preferably 0.0500% by mass or less, more preferably 0.0100% by mass or less, and even more preferably 0.0080% by mass or less, relative to the total mass of the wire. Furthermore, the total content of these inevitable impurities is preferably 0.50% by mass or less, and even more preferably 0.10% by mass or less, relative to the total mass of the wire.

[0054] (Wire Diameter) In the present embodiment, the diameter of the welding wire is not particularly limited, but a wire having a diameter specified in welding material standards such as AWS or JIS can be used.

[0055] (Type of Wire) In the present embodiment, the type of wire is not limited as long as the contents of C, Si, Mn, Ti, Al, Cr, Mo, P, S, Cu, O, and N in the wire are controlled within the specified ranges. However, in general, in the welding of automotive undercarriage parts, from the viewpoint of improving quality and work efficiency, a welding material that produces less welding slag and can reduce the slag removal work is required. Therefore, it is preferable that the oxide content in the wire is low. Therefore, a solid wire is preferable.

[0056] [Method for Manufacturing Welding Wire] The welding wire according to this embodiment is not particularly limited in its manufacturing method, and no special manufacturing conditions are required, and it can be manufactured by a conventional method. Specifically, in the case of solid wire, first, steel containing the above-mentioned alloy elements in specified contents is melted to obtain an ingot. Next, the ingot is subjected to hot forging or the like as needed, followed by hot rolling and cold wire drawing to form a wire. Thereafter, the obtained wire is annealed at a temperature of about 500 to 900°C as needed, pickled, copper plated as needed, and further subjected to finish wire drawing as needed to obtain a target wire diameter. Thereafter, a lubricant is applied as needed, and the welding wire can be manufactured.

[0057] [Welding Method] The welding method according to this embodiment is a method of performing gas-shielded arc welding using the welding wire according to the above-described embodiment. In addition, in the welding method according to this embodiment, it is preferable to gas-shielded arc-weld the steel plates while alternately switching the feeding of the welding wire between a forward feeding period and a reverse feeding period.

[0058] (Shielding Gas) In the welding method according to the present embodiment, the shielding gas to be used is not particularly limited. ２ It is preferable to use a mixed gas having a gas content of, for example, more than 20%, more preferably 99.0% or more, even more preferably 99.5% or more, and even more preferably 99.8% or more, and it is particularly preferable to use carbon dioxide gas. ２ The gas is composed of CO and impurities, and the impurities are preferably 0.5% or less, and more preferably about 0.2%. ２ The gas other than the gas can be selected appropriately, and specifically, Ar gas or the like can be mentioned from the viewpoint of easy availability on the market.

[0059] (Welding conditions) In the present embodiment, the steel material to be welded and the welding position are not particularly limited, but for example, when manufacturing automobile suspension parts, the welding wire according to the present embodiment can be suitably used in lap fillet welding of 440 to 980 MPa class steel plates. The welding conditions in this case are also not particularly limited, and general conditions used for welding using a wire can be applied.

[0060] (Feed Control Method) The feed control method is a method of welding steel plates while alternately switching the feed of the welding wire between a forward feed period and a reverse feed period. The feed control method can be further classified into a "short-circuit feed control method" and a "short-circuit suppression feed control method." The short-circuit feed control method is a type of welding based on a short-circuit transition mode in which the feed speed of the welding wire is alternately switched between a forward feed period and a reverse feed period, thereby generating a short-circuit period and an arc period. The short-circuit suppression feed control method is a type of welding based on a globule transition mode in which the feed speed of the welding wire is alternately switched between a forward feed period and a reverse feed period, thereby suppressing the generation of a short-circuit period. The short-circuit suppression feed control method has a pulse waveform in which the welding current alternates between a high-current period and a low-current period based on a phase related to the wire tip position (hereinafter referred to as the "wire position phase"). Here, the wire position phase is preferably within a range of 0 to 360°, with the forward feed period and the reverse feed period being one cycle, and with 0° being the closest to the tip side and 180° being the closest to the base metal side. In the welding method according to this embodiment, it is preferable to use a short-circuit suppression type feed control method, and it is more preferable to select the wire position phase at which the high current period ends from the range of 100 to 150° and the wire position phase at which the high current period starts from the range of 300 to 360°. By using the short-circuit suppression type feed control method and applying this condition, it is possible to obtain a weld bead with a better appearance and improve welding workability. It is also possible to suppress the occurrence of porosity defects.

[0061] [Method for Producing Weld Metal] The method for producing weld metal according to this embodiment is a method for producing weld metal while supplying shielding gas using the welding wire according to the embodiment. When using the method for producing weld metal according to this embodiment, there is no particular limitation on the welding method other than using the welding wire according to this embodiment, but the welding method according to the embodiment can be used.

[0062] Hereinafter, examples of the welding wire according to the present embodiment and comparative examples will be described.

[0063] [Gas-shielded arc welding] (Preparation of welding wire) Solid wires with a diameter of 1.2 mm were prepared from ingots containing various alloying elements.

[0064] (Gas-shielded arc welding) Next, gas-shielded arc welding was carried out using the obtained welding wire while controlling the feeding of the welding wire. The welding conditions and the conditions for controlling the feeding are shown in Table 1 below.

[0065]

[0066] [Evaluation Tests] Welded joints obtained using the wires of the invention examples and comparative examples were evaluated for resistance to electrodeposition coating chipping, electrodeposition coating properties, and resistance to pore defects.

[0067] (Electrodeposition Coating Chipping Resistance) Electrodeposition coating chipping resistance correlates with the shape of the slag at the weld. Specifically, when slag drips, the slag thickens at the dripping location, making the slag more likely to peel off and deteriorating the electrodeposition coating chipping resistance. Therefore, the electrodeposition coating chipping resistance was evaluated by observing the shape of the slag at the weld. Specifically, the weld was observed from the front, and the difference (distance d) between the maximum and minimum distances from the vertical upper end of the slag (the end on the upper plate side) to the lower end was measured. The width of the weld metal in the vertical direction (weld width D) was also measured. The ratio (d / D) of the distance d to the weld width D was then calculated. That is, a small value of the ratio (d / D) indicates small slag chipping and good electrodeposition coating chipping resistance. The evaluation criteria for electrodeposition coating defect resistance were as follows: a ratio (d / D) of 0.35 or less was rated as ⊚ (best), a ratio of more than 0.35 but less than 0.53 was rated as ◯ (good), and a ratio of 0.53 or more was rated x (poor).

[0068] (Electrodeposition Coatability) Electrodeposition coatability was evaluated by applying electrodeposition coating to the welded joint after welding and visually observing the surface of the bead. As the evaluation criteria for electrodeposition coatability, when the electrodeposition coating covered the entire surface of the bead, it was evaluated as ○ (good). When poor coating was observed even partially, it was evaluated as × (poor).

[0069] (Porosity Defect Resistance) Porosity defect resistance was evaluated in terms of pit resistance and blowhole resistance. Pit resistance was evaluated by visually observing the surface of the bead after welding using a galvanized steel sheet as the base material to confirm the presence or absence of pits. Blowhole resistance was evaluated by observing blowholes using a radiographic test. As the evaluation criteria for pit resistance, a case in which no pits occurred on the bead was evaluated as ○ (good). A case in which pits occurred on the bead was evaluated as × (poor). As the evaluation criteria for blowhole resistance, a case in which there were zero blowholes measuring 0.7 mm or more in the direction of the weld line and 0.7 mm or more in the direction perpendicular to the weld line was evaluated as ⊚ (best), a case in which there were 1 to 3 blowholes of the above sizes was evaluated as ○ (good), and a case in which there were 4 or more blowholes of the above sizes was evaluated as × (poor).

[0070] Furthermore, as the evaluation criteria for the overall evaluation of pore defect resistance, a sample that was x (poor) in at least one of the evaluation results for pit resistance or blowhole resistance was evaluated as x (poor). A sample that was o (good) in both pit resistance and blowhole resistance was evaluated as o (good), and a sample that was o (good) in pit resistance and ⊚ (best) in blowhole resistance was evaluated as ⊚ (best).

[0071] The contents of each component contained in the welding wire used are shown in Tables 2 and 3 below, and values ​​F1 to F6 calculated using these contents according to formulas (1) to (6) are shown in Table 4 below. The results of each evaluation test are also shown in Table 5 below.

[0072] In Table 4 below, formulas (1) to (6) are as follows: Formula (1): F1=200×(3.0×[Si]+0.3×[Ti]+5.0×[Cr]) / (1.2×[Mn]+1.8×[Mo]) Formula (2): F2=5×[C] / ([Cr]+5×[Mo]) Formula (3): F3=10000×[O] / (15×[Si]+3×[Mn]+12×[Ti]+20×[Al]+15×[Cr]+2×[Mo]) Formula (4): F4=500×[S] / (5×[Si]+[Mn] / 10+[Ti]+[Al]) Formula (5): F5=([Ti]+1.5×[Al]) / [Si] Formula (6): F6=[Mn] / [Ti]

[0073] However, in the above formulas (1) to (6), [Si] is a value representing the Si content in the wire expressed as mass% with respect to the total mass of the wire, [Ti] is a value representing the Ti content in the wire expressed as mass% with respect to the total mass of the wire, [Cr] is a value representing the Cr content in the wire expressed as mass% with respect to the total mass of the wire, [Mn] is a value representing the Mn content in the wire expressed as mass% with respect to the total mass of the wire, [Mo] is a value representing the Mo content in the wire expressed as mass% with respect to the total mass of the wire, [O] is a value representing the O content in the wire expressed as mass% with respect to the total mass of the wire, [Al] is a value representing the Al content in the wire expressed as mass% with respect to the total mass of the wire, [C] is a value representing the C content in the wire expressed as mass% with respect to the total mass of the wire, and [S] is a value representing the S content in the wire expressed as mass% with respect to the total mass of the wire.

[0074] In the column for the content of each component in Table 2 below, "-" indicates that the component was not added or was below the detection limit. Furthermore, when the content of each element used in formulas (1) to (6) was "-", the content of that element was set to 0 (zero) to calculate F1 to F6.

[0075]

[0076]

[0077]

[0078]

[0079] As shown in Tables 2 to 5 above, Invention Examples Nos. 1 to 22, in which the content of each component in the welding wire was within the range specified in the present invention, were excellent in electrodeposition paintability, and were able to achieve both resistance to electrodeposition paint chipping and resistance to porosity defects.

[0080] On the other hand, in Comparative Example No. 1, the Si content in the wire was less than the lower limit specified in the present invention, and the Ti content exceeded the upper limit specified in the present invention, so the resistance to electrodeposition coating chipping and pore defect resistance were poor.

[0081] In Comparative Example No. 2, the Si content and Mn content in the wire were less than the lower limit values ​​specified in the present invention, and the Ti content exceeded the upper limit specified in the present invention, so the resistance to electrodeposition coating chipping and resistance to pore defects were poor.

[0082] In Comparative Example No. 3, the Si content and Mn content in the wire were less than the lower limit values ​​specified in the present invention, and therefore the resistance to chipping of the electrodeposition coating and the resistance to pore defects were poor.

[0083] In Comparative Example No. 4, the Si content in the wire was less than the lower limit specified in the present invention, and therefore the resistance to chipping of the electrodeposition coating was poor.

[0084] In Comparative Example No. 5, the Ti content in the wire was less than the lower limit specified in the present invention, and therefore the resistance to chipping of the electrodeposition coating was poor.

[0085] In Comparative Example No. 6, the Mo content in the wire exceeded the upper limit specified in the present invention, and therefore the resistance to chipping of the electrodeposition coating was poor.

[0086] Although various embodiments have been described above, 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 conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any manner as long as they do not deviate from the spirit of the invention.

[0087] This application is based on a Japanese patent application filed on March 8, 2024 (Patent Application No. 2024-036102) and a Japanese patent application filed on February 3, 2025 (Patent Application No. 2025-016384), the contents of which are incorporated by reference into this application.

Claims

1. The welding wire contains, relative to the total mass of the wire, C: 0.010 mass% or more and 0.100 mass% or less, Si: 0.15 mass% or more and 0.50 mass% or less, Mn: 1.70 mass% or more and 3.00 mass% or less, Ti: 0.01 mass% or more and 0.17 mass% or less, Al: 0.10 mass% or less (inclusive of 0 mass%), Cr: 1.00 mass% or less (inclusive of 0 mass%), Mo: 0.50 mass% or less (inclusive of 0 mass%), P: 0.030 mass% or less (inclusive of 0 mass%), S: 0.0300 mass% or less (inclusive of 0 mass%), Cu: 0.50 mass% or less (inclusive of 0 mass%), O: 0.0100 mass% or less (inclusive of 0 mass%), N: 0.0100 mass% or less (inclusive of 0 mass%), A welding wire, the balance of which is Fe and unavoidable impurities.

2. The welding wire according to claim 1, wherein the value F1 calculated by the following formula (1) is 55 or more, where the Si content in the wire is expressed as [Si] in mass% relative to the total mass of the wire, the Ti content in the wire is expressed as [Ti] in mass% relative to the total mass of the wire, the Cr content in the wire is expressed as [Cr] in mass% relative to the total mass of the wire, the Mn content in the wire is expressed as [Mn] in mass% relative to the total mass of the wire, and the Mo content in the wire is expressed as [Mo] in mass% relative to the total mass of the wire. Formula (1): F1 = 200 x (3.0 x [Si] + 0.3 x [Ti] + 5.0 x [Cr]) / (1.2 x [Mn] + 1.8 x [Mo]).

3. The welding wire according to claim 1, wherein the O content in the wire is expressed as [O] in mass % relative to the total mass of the wire, the Si content in the wire is expressed as [Si] in mass % relative to the total mass of the wire, the Ti content in the wire is expressed as [Ti] in mass % relative to the total mass of the wire, the Cr content in the wire is expressed as [Cr] in mass % relative to the total mass of the wire, the Mn content in the wire is expressed as [Mn] in mass % relative to the total mass of the wire, the Mo content in the wire is expressed as [Mo] in mass % relative to the total mass of the wire, the Al content in the wire is expressed as [Al] in mass % relative to the total mass of the wire, and the C content in the wire is expressed as [C] in mass % relative to the total mass of the wire, Formula (2): F2=5×[C] / ([Cr]+5×[Mo]) Formula (3): F3=10000×[O] / (15×[Si]+3×[Mn]+12×[Ti]+20×[Al]+15×[Cr]+2×[Mo]) 4. The welding wire according to claim 1, wherein the value F4 calculated by the following formula (4) is 0.25 or more and 6.0 or less, where the S content in the wire is [S] in mass% relative to the total mass of the wire, the Si content in the wire is [Si] in mass% relative to the total mass of the wire, the Mn content in the wire is [Mn] in mass% relative to the total mass of the wire, the Ti content in the wire is [Ti] in mass% relative to the total mass of the wire, and the Al content in the wire is [Al] in mass% relative to the total mass of the wire. Formula (4): F4 = 500 x [S] / (5 x [Si] + [Mn] / 10 + [Ti] + [Al]) 5. A welding method characterized by gas-shielded arc welding using the welding wire according to any one of claims 1 to 4.

6. A welding method according to claim 5, characterized in that the steel plates are gas-shielded arc-welded while the welding wire is fed alternately between a forward feed period and a reverse feed period.

7. A method for producing weld metal, characterized in that the welding wire according to any one of claims 1 to 4 is used to produce weld metal by gas-shielded arc welding.