Carbon dioxide gas shielded arc welding wire and welding method

Abstract

Provided are: a carbon dioxide gas shielded arc welding wire capable of improving detachability of slag adhered to a bead surface after welding, while maintaining toughness of a weld metal; and a welding method using the welding wire. This welding wire is for use in carbon dioxide gas shielded arc welding performed with positive polarity, and has a chemical composition containing, in mass%, 0.200% or less of C, 0.05-2.50% of Si, 0.25-3.50% of Mn, 0.050% or less of P, 0.050% or less of S, 0.02-3.00% of Al, 0.0100% or less of O (oxygen), 0.0050% or less of Ca, and 0.010-0.100% of REM. In the REM, Nd is contained in an amount of 0.0015-0.0200%, and the remaining portion is Fe and unavoidable impurities. This carbon dioxide gas shielded arc welding method uses the welding wire and involves performing welding with a positive polarity by using, as a shield gas, a gas having a CO2 concentration of 60 vol% or more.

Description

Carbon dioxide shielded arc welding wire and welding method

[0001] The present invention relates to a wire for carbon dioxide gas shielded arc welding (hereinafter also simply referred to as "welding wire") and a welding method using the same. In particular, the present invention relates to a welding wire and a welding method using the same that can achieve spray transfer, which is considered to be the most stable form of droplet transfer, in positive polarity welding in which the welding wire is the negative electrode, suppress the generation of spatter, and have excellent defect resistance. In this specification, "x to y" representing a range of numerical values, etc. means not less than x and not more than y, and includes the boundary value.

[0002] Carbon dioxide (CO ) is used as a shielding gas. ２ ) gas, carbon dioxide shielded arc welding is ２ Because gas is inexpensive and it is an efficient welding method, it is widely used for welding steel materials. In particular, with the rapid spread of automatic welding, it is used in various fields such as shipbuilding, architecture, bridges, automobiles, construction, machinery, etc. In the shipbuilding, architecture, and bridge fields, it is often used for high-current multi-layer welding of thick plates.

[0003] In addition, Ar gas and CO ２ Mixed gas with gas (CO ２ A welding method using a shielding gas with a mixture ratio of 2 to 40% by volume (so-called mixed-gas shielded arc welding) enables fine spray transfer of metal droplets smaller than the diameter of the welding wire. This droplet spray transfer is the most superior droplet transfer mode, producing less spatter, excellent weld bead shape, and is known to be suitable for high-speed welding. For this reason, mixed-gas shielded arc welding is used in fields requiring high-quality welding.

[0004] However, the cost of Ar gas is ２ Therefore, in actual welding work, the amount of Ar gas used is reduced to CO ２ Gas is 100% by volume, or CO ２ It is considered preferable to use a mixed gas with a gas mixture ratio of 60% by volume or more.

[0005] Such CO ２When a shielding gas with a gas mixture ratio of 60% by volume or more is used, coarse droplets 10 to 20 times larger than those in gas-shielded arc welding with a mixture ratio of 2 to 40% by volume hang from the tip of the welding wire and are transferred while swaying due to the arc force. This phenomenon is known as globule transfer. When such globule transfer occurs, a large amount of spatter occurs due to short circuits with the base material (i.e., steel sheet) and re-arcing, resulting in an unstable bead shape. Especially in high-speed welding, there are problems such as an uneven bead shape (so-called humping bead) and poor removability of the slag formed on the bead surface.

[0006] To address this problem, Patent Documents 1 and 2 disclose that adding rare earth elements (REM) reduces CO ２ It is also disclosed that the bead shape is stabilized in gas-shielded arc welding using a shielding gas whose main component is carbon dioxide (mixture ratio: 60% by volume or more). However, there is no disclosure about the problem of poor slag removability due to the slag formed on the bead surface in carbon dioxide-shielded arc welding tightly covering the bead surface.

[0007] In addition, Patent Document 3 discloses a method for producing a ferroelectric liquid containing Ar+2% O. ２ It is disclosed that the toughness of the weld is improved by adding Nd and Sm among the REMs to the welding wire components of ferritic stainless steel used in MIG welding using gas. However, there is no disclosure about the welding workability in carbon dioxide gas shielded arc welding.

[0008] JP 2005-046877 A JP 2005-046879 A JP 63-212089 A

[0009] The present invention aims to solve the above-mentioned problems and to provide a wire for carbon dioxide-shielded arc welding that can improve the removability of slag adhering to the bead surface after welding while maintaining the toughness of the weld metal, and a welding method using the same.

[0010] In order to solve the above problems, the inventors have conducted extensive research into the components contained in welding wire, and as a result have found that adding Nd to steel wire for carbon dioxide gas shielded arc welding can improve slag removability.

[0011] The present invention was completed based on these findings and further investigations. The gist of the present invention is as follows. [1] A welding wire used in positive carbon dioxide gas shielded arc welding, the welding wire having a chemical composition, in mass%, of C: 0.200% or less, Si: 0.05% to 2.50%, Mn: 0.25% to 3.50%, P: 0.050% or less, S: 0.050% or less, Al: 0.02% to 3.00%, O (oxygen): 0.0100% or less, Ca: 0.0050% or less, rare earth elements: 0.010% to 0.100%, and among the rare earth elements, Nd: 0.0015% to 0.0200%, and optionally at least one selected from a first group: Ti: 0.02% to 0.50%, and Zr: 0.001% to 0.500%, [2] A wire for carbon dioxide gas shielded arc welding, characterized in that it contains at least one element selected from the following group: a second group: at least one selected from Cu: 0.02% to 3.00%, Ni: 0.02% to 3.00%, Cr: 0.02% to 3.00%, Mo: 0.02% to 1.50%, B: 0.0001% to 0.0150%, and Mg: 0.001% to 0.200%, and a third group: at least one selected from Nb: 0.001% to 0.500%, and V: 0.001% to 0.500%, with the balance being Fe and unavoidable impurities. ２ [3] A carbon dioxide gas shielded arc welding wire used in a carbon dioxide gas shielded arc welding method using a shielding gas with a concentration of 60% by volume or more. [4] A carbon dioxide gas shielded arc welding method using the welding wire described in [1] or [2] above, wherein the shielding gas is CO ２ A carbon dioxide gas shielded arc welding method characterized by performing welding with positive polarity using a gas having a concentration of 60% by volume or more.

[0012] According to the present invention, by adding Nd to the welding wire in carbon dioxide gas shielded arc welding, it is possible to improve the removability of slag adhering to the bead surface after welding, which is an industrially significant advantage.

[0013] 1 is a schematic cross-sectional view showing a groove shape and a schematic cross-sectional view showing multiple layers of weld metal formed in the groove portion.

[0014] The embodiments relating to the constituent features of the present invention will be specifically described below.

[0015] [Welding Wire] First, the welding wire used in the positive carbon dioxide gas shielded arc welding method according to this embodiment will be described. Hereinafter, "%" in the chemical composition means "mass %".

[0016] [Chemical Composition of Welding Wire] The basic chemical composition of the welding wire is C: 0.200% or less, Si: 0.05% to 2.50%, Mn: 0.25% to 3.50%, P: 0.050% or less, S: 0.050% or less, Al: 0.02% to 3.00%, and O (oxygen): 0.0100% or less. Furthermore, it contains Ca: 0.0050% or less, rare earth elements: 0.010% to 0.100%, and among the rare earth elements, Nd: 0.0015% to 0.0200%, with the balance being Fe and unavoidable impurities.

[0017] Next, examples of optional compositions include compositions that fall into the following three groups. The welding wire according to this embodiment contains at least one group of elements selected from the groups shown below. The first group is a group of elements that are strong deoxidizers and increase the strength of the weld metal, and includes at least one of Ti: 0.02% to 0.50% and Zr: 0.001% to 0.500%. The second group is a group of elements that increase the strength of the weld metal and improve its weather resistance. The elements in the second group include at least one of Cu: 0.02% to 3.00%, Ni: 0.02% to 3.00%, Cr: 0.02% to 3.00%, Mo: 0.02% to 1.50%, B: 0.0001% to 0.0150%, and Mg: 0.001% to 0.200%. The third group is a group of elements that improve the strength and toughness of the weld metal and improve the arc stability, and is at least one of Nb: 0.001% to 0.500% and V: 0.001% to 0.500%.

[0018] [Reasons for Limiting Composition] The reasons for limiting each of the welding wire compositions are as follows.

[0019] [Basic Composition] [C: 0.200% or Less] C is an element necessary for ensuring the strength of the weld metal, and has the effect of reducing the viscosity of the molten metal and improving its fluidity. However, if the C content exceeds 0.200%, not only does the behavior of the droplets and molten metal become unstable during positive polarity welding, but the toughness of the weld metal also decreases. Therefore, the C content is limited to 0.200% or less. On the other hand, if the C content is reduced excessively, the strength of the weld metal cannot be ensured. Therefore, the C content is preferably 0.003% to 0.200%. Furthermore, 0.010% to 0.100% is more preferable.

[0020] [Si: 0.05% to 2.50%] Si has a deoxidizing effect and is an essential element for deoxidizing the molten metal. If the Si content is less than 0.05%, the molten metal is not sufficiently deoxidized, resulting in blow defects in the weld metal. On the other hand, if the Si content exceeds 2.50%, the toughness of the weld metal is significantly reduced. Therefore, the Si content must be within the range of 0.05% to 2.50%. Furthermore, in order to suppress arc spread in positive carbon dioxide gas shielded arc welding and increase the number of droplet transfers, 0.25% or more is preferable. Therefore, the Si content is preferably 0.25% to 2.50%. More preferably, it is 0.50% to 2.50%.

[0021] [Mn: 0.25% to 3.50%] Mn, like Si, has a deoxidizing effect and is an essential element for deoxidizing the molten metal. If the Mn content is less than 0.25%, the molten metal will not be sufficiently deoxidized, resulting in the formation of blowholes in the weld metal. On the other hand, if the Mn content exceeds 3.50%, the toughness of the weld metal will decrease. Therefore, the Mn content must be within the range of 0.25% to 3.50%. Note that, in order to promote the deoxidation of the molten metal and prevent the formation of blowholes, a Mn content of 0.45% or more is preferable. Therefore, the Mn content is preferably 0.45% to 3.50%. A more preferable range is 0.65% to 3.50%.

[0022] [P: 0.050% or Less] P is an element that lowers the melting point of steel, improves electrical resistivity, and enhances melting efficiency. Furthermore, it also acts to refine droplets and stabilize the arc during positive-polarity carbon dioxide gas-shielded arc welding. However, if the P content exceeds 0.050%, the viscosity of the molten metal during positive-polarity carbon dioxide gas-shielded arc welding significantly decreases, the arc becomes unstable, and small spatter increases. Furthermore, the risk of hot cracking of the weld metal increases. Therefore, the P content is set to 0.050% or less. Preferably, it is set to 0.030% or less. On the other hand, because it takes a long time to reduce P during the steelmaking stage of melting steel material for steel wire, 0.002% or more is preferred from the perspective of improving productivity. Therefore, the P content is preferably set to 0.002% to 0.030%. More preferably, it is set to 0.002% to 0.015%.

[0023] [S: 0.050% or Less] S reduces the viscosity of the molten metal, promotes the detachment of droplets suspended at the tip of the welding wire, and stabilizes the arc in positive-polarity carbon dioxide gas-shielded arc welding. S also has the effect of widening the arc in positive-polarity carbon dioxide gas-shielded arc welding, reducing the viscosity of the molten metal, and smoothing the bead. However, if the S content exceeds 0.050%, small spatter increases and the toughness of the weld metal decreases. Therefore, the S content is set to 0.050% or less. Preferably, it is set to 0.020% or less. On the other hand, since it takes a long time to reduce the S content during the steelmaking stage of melting the steel material for the steel wire, 0.002% or more is preferable from the perspective of improving productivity. Therefore, the S content is preferably set to 0.002% to 0.020%. More preferably, it is set to 0.002% to 0.010%.

[0024] [Al: 0.02% to 3.00%] Al acts as a strong deoxidizer and increases the strength of the weld metal. Furthermore, deoxidizing the molten metal reduces viscosity and stabilizes bead shape (i.e., suppresses humping bead). In reverse-polarity CO2-shielded arc welding, no clear effect on stabilizing droplet transfer is observed. However, in positive-polarity CO2-shielded arc welding, a significant effect on stabilizing droplet transfer is exhibited at high-current welding of 350 A or more. Meanwhile, in low-current welding, increasing the number of short-circuit transfers can achieve uniform droplet transfer and improved bead shape. Furthermore, due to its affinity with O (oxygen), Al also has the effect of reducing oxidation loss of rare earth elements (REM) during the manufacturing stage of the welding wire. If Al is less than 0.02%, this effect cannot be obtained. On the other hand, if Al is more than 3.00%, the crystal grains of the weld metal become coarse, significantly reducing toughness. Therefore, Al must be within the range of 0.02% to 3.00%, preferably 0.02% to 2.80%, and more preferably 0.02% to 2.60%.

[0025] [O (oxygen): 0.0100% or less] O (oxygen) destabilizes the arc point generated in droplets suspended at the tip of the welding wire during positive carbon dioxide gas shielded arc welding, thereby miniaturizing the droplets. However, if the O (oxygen) content exceeds 0.0100%, the effect of adding REM to stabilize the arc during positive high-current welding is lost, causing increased droplet oscillation and resulting in the generation of large amounts of spatter. Therefore, the O (oxygen) content is limited to 0.0100% or less. Preferably, it is 0.0001% to 0.0050%, and more preferably, it is 0.0001% to 0.0025%.

[0026] [Ca: 0.0050% or less] Ca is mixed into molten steel as an impurity during steelmaking and casting, or into steel wire as an impurity during wiredrawing. In positive carbon dioxide gas shielded arc welding, if the Ca content exceeds 0.0050%, the effect of adding REM, i.e., stabilizing the arc during high-current welding, is impaired. Therefore, the Ca content is limited to 0.0050% or less. The Ca content is preferably 0.0001% to 0.0025%, and more preferably 0.0001% to 0.0010%.

[0027] [Rare Earth Elements (REM): 0.010% to 0.100%] REM is an element effective for refining inclusions during steelmaking and casting and improving the toughness of weld metal. However, in conventional reverse-polarity (i.e., welding wire as the positive electrode) carbon dioxide-shielded arc welding, adding REM to a steel wire causes arc concentration, preventing the reduction of spatter. However, in positive-polarity carbon dioxide-shielded arc welding, REM is an essential element for stabilizing droplet transfer. Adding REM in combination with Al as described above can further stabilize droplet transfer. If the REM content is less than 0.010%, this droplet transfer stabilization effect cannot be achieved. On the other hand, if the REM content exceeds 0.100%, cracks may occur during the welding wire manufacturing process or the toughness of the weld metal may decrease. Therefore, the REM content must be within the range of 0.010% to 0.100%. The content is preferably 0.025% to 0.050%, and more preferably 0.030% to 0.040%.

[0028] Here, REM is a collective term for 17 elements from Period 4 to Period 6 of Group 3 of the Periodic Table, excluding the actinides. For the above-mentioned purposes, in this embodiment, it is preferable to use 15 lanthanide elements with atomic numbers 57 to 71. Nd will be described later. Ce and La are also suitable. Ce and La may be added alone or in combination. When adding both Ce and La, it is preferable to use a mixture obtained by previously mixing Ce and La in mass ratios within the ranges of Ce: 45% to 80% and La: 10% to 45%, respectively. Furthermore, the REM content in this embodiment is the sum of the contents of the above-mentioned REM elements.

[0029] [Nd: 0.0015% to 0.0200%] Nd is one of the REM elements (atomic number 60). Nd is an element that stabilizes droplet transfer in positive carbon dioxide gas shielded arc welding, and also an element that improves the removability of slag adhering to the bead surface after welding. In particular, ２ A stable effect can be achieved even at a concentration of 60% by volume or more.

[0030] Here, Nd can be analyzed separately from the above-mentioned REM by JIS K 0116 (emission spectroscopy). Nd can be added by directly adding it to molten steel that will become the wire material.

[0031] If the Nd content in the welding wire is less than 0.0015%, the slag removability decreases. On the other hand, if it exceeds 0.0200%, the toughness of the weld metal deteriorates. Therefore, the Nd content needs to be within the range of 0.0015% to 0.0200%. Preferably, it is 0.0020% to 0.0200%, and more preferably, it is 0.0025% to 0.0200%. Note that the "Nd content" referred to here refers to the Nd content relative to the entire welding wire.

[0032] [First Group of Optional Compositions] Ti and Zr, which are elements in the first group, both act as strong deoxidizers and increase the strength of the weld metal. Furthermore, these elements have the effect of deoxidizing the molten metal, reducing its viscosity and stabilizing the bead shape (i.e., suppressing humping beads). Because of these effects, Ti and Zr are effective elements in high-current welding of 350 A or more, and are preferably added as needed. If the Ti content is less than 0.02% or the Zr content is less than 0.001%, the above effects cannot be obtained. On the other hand, if the Ti content exceeds 0.50% or the Zr content exceeds 0.500%, the droplets become coarse and a large amount of large spatter is generated. Therefore, if Ti and Zr are contained, it is preferable to limit the Ti content to 0.02% to 0.50% and the Zr content to 0.001% to 0.500%. At least one of Ti and Zr may be included. The more preferable ranges of Ti and Zr are 0.05% to 0.50% for Ti and 0.005% to 0.500% for Zr.

[0033] [Second Group of Optional Compositions] As described above, the second group consists of Cu, Ni, Cr, Mo, B, and Mg, all of which are elements that increase the strength and weather resistance of the weld metal. The preferred contents of these elements are Cu: 0.02% to 3.00%, Ni: 0.02% to 3.00%, Cr: 0.02% to 3.00%, Mo: 0.02% to 1.50%, B: 0.0001% to 0.0150%, and Mg: 0.001% to 0.200%. If these contents are too small, the above-described effects cannot be achieved. On the other hand, excessive addition of these elements can result in a decrease in the toughness of the weld metal. Therefore, when elements from the second group are contained, it is preferable that the contents satisfy the above ranges. Furthermore, at least one of these elements may be contained. More preferred ranges are Cu: 0.02% to 0.20%, Ni: 0.02% to 2.50%, Cr: 0.03% to 0.20%, Mo: 0.03% to 1.00%, B: 0.0010% to 0.0100%, and Mg: 0.001% to 0.010%.

[0034] [Third Group of Optional Compositions] Nb and V, which belong to the third group, are elements that improve the strength and toughness of the weld metal and improve the arc stability. The preferred contents of these elements are Nb: 0.001% to 0.500% and V: 0.001% to 0.500%. If the contents are small, these effects cannot be obtained. On the other hand, excessive addition of these elements leads to a decrease in the toughness of the weld metal. Therefore, when Nb or V of the third group is contained, it is preferable that the above-mentioned ranges are satisfied. At least one of these elements may be contained. More preferred ranges are Nb: 0.001% to 0.450% and V: 0.001% to 0.450%.

[0035] [Remainder Composition] The balance other than the above-described composition is Fe and unavoidable impurities. For example, N, a typical unavoidable impurity that is inevitably mixed in during the process of melting steel or manufacturing steel strands, is preferably reduced to 0.0200% or less. More preferably, it is reduced to 0.0100% or less. Examples of other unavoidable impurities include H, Zn, Re, Co, Sb, Sn, and Bi, and a total of 0.01% or less is acceptable. Note that the inclusion of the optional elements described above at or below the lower limit is acceptable as long as it does not impair the effects of this embodiment. Furthermore, elements other than these may be contained as long as the basic composition and optional composition described above are satisfied, and such embodiments are also within the technical scope of the present invention.

[0036] [Method of Manufacturing Welding Wire] Here, a method of manufacturing welding wire will be described. Molten steel having the above-described composition is melted in a converter, electric furnace, or the like, and then the steel material (e.g., billet, etc.) produced by continuous casting is hot-rolled and then cold-rolled (e.g., wire-drawing) to form a steel wire having a diameter of 1.0 to 2.8 mm. Here, the hot-rolling and cold-rolling only need to produce a steel wire having a predetermined size and shape, so the setting conditions for the rolling, etc. are not particularly limited. The steel wire after rolling is sequentially subjected to the steps of annealing, pickling, Cu plating, and wire-drawing to form a welding wire having a predetermined wire diameter. The diameter of the welding wire is preferably 0.8 mm to 1.6 mm.

[0037] [CO₂ Shielded Arc Welding Method and Shielding Gas] Next, a carbon dioxide shielded arc welding method will be described. In the carbon dioxide shielded arc welding method according to this embodiment, CO₂ is used as the shielding gas. ２ Gas is used as 100% by volume, or CO ２ When the gas is mixed with Ar gas, CO ２ A mixed gas with a gas mixture ratio of 60% by volume or more is used.

[0038] This is because the use of Ar gas, which is expensive, can be reduced and CO ２ This is to increase the gas mixture ratio. ２ Generally, when there is a large amount of gas, the bead shape tends to become unstable. In this respect, the bead shape can be stabilized by adding REM to the welding wire according to the present embodiment. ２ In order to suppress the formation of slag on the bead surface due to the gas, Nd is added to the welding wire according to the present embodiment, thereby improving slag removability. As a result, in the carbon dioxide gas shielded arc welding method according to the present embodiment, CO ２ Even when a gas with a concentration of 60% by volume or more is used, the bead shape is stable and welding can be performed with good slag removability.

[0039] [Groove Shape] FIG. 1 shows an example of a groove shape in the carbon dioxide gas shielded arc welding method according to this embodiment.

[0040] The groove shape includes, but is not limited to, a V-groove, an I-groove, a V-groove, etc. Fig. 1 shows an example of a V-groove in which steel materials 1 are butted together at a groove angle θ, a backing metal 2 is placed at the bottom of the groove, and a gap G is formed between the bottoms of the steel materials.

[0041] The groove angle θ is not particularly limited, but from the viewpoint of construction efficiency, it is preferably 25° or less (including 0°). The gap G is also not particularly limited, but from the viewpoint of construction efficiency, it is preferably in the range of 0 mm to 20 mm.

[0042] [Steel Material] In the case of thick steel plates used in steel structures such as buildings and ships, the steel materials applied in this embodiment include rolled steel materials for welded structures (SM materials) specified in JIS G3106 and rolled steel materials for building structures (SN materials) specified in JIS G3136. Examples of steel grades include 490 MPa-class steel materials, 550 MPa-class steel materials, 590 MPa-class steel materials, and 780 MPa-class steel materials. Furthermore, the plate thickness t of the steel material is not particularly limited. When welding thick steel plates in the range of 10 mm to 150 mm, multi-layer welding is also possible.

[0043] Next, an example of the chemical composition of the steel material is shown below. The chemical composition of the steel material to be used preferably contains, in mass %, C: 0.04% to 0.15%, Si: 0.05% to 1.00%, Mn: 0.50% to 2.50%, P: 0.030% or less, S: 0.020% or less, Al: 0.050% or less, O (oxygen): 0.010% or less, N: 0.010% or less, with the balance being Fe and unavoidable impurities.

[0044] Furthermore, it is preferable that the steel contains at least one element selected from the group consisting of Cu: 1.00% or less, Ni: 2.00% or less, Cr: 1.00% or less, Mo: 1.00% or less, Nb: 0.20% or less, V: 0.20% or less, Ti: 0.050% or less, Sn: 0.005% or less, Pb: 0.050% or less, REM: 0.050% or less, and B: 0.0030% or less as an optional composition. The optional composition is determined in consideration of strength, toughness, etc., according to the intended use of the steel material.

[0045] [Other Welding Conditions] Next, other welding conditions will be described.

[0046] [Welding current I: 240 A to 450 A] If the welding current I is lower than 240 A, the arc pressure will be low, resulting in slag inclusion and incomplete fusion due to unmelted slag. On the other hand, if the welding current I is higher than 450 A, sagging due to convection of the weld metal, i.e., overlapping, will occur. Therefore, the welding current I is preferably set to 240 A to 450 A. More preferably, it is set to 240 A to 400 A, and even more preferably, it is set to 240 A to 350 A.

[0047] [Welding voltage V: 27 V to 38 V] If the welding voltage V is lower than 27 V, the arc cannot be maintained stably, resulting in unstable welding. On the other hand, if the welding voltage V is higher than 38 V, the arc spreads and the arc heat is dispersed, making it difficult to melt the slag and making slag entrapment more likely to occur. Therefore, the welding voltage V is preferably set to 27 V to 38 V. More preferably, it is set to 28 V to 37 V, and even more preferably, it is set to 29 V to 36 V.

[0048] [Welding Speed ​​S: 20 cm / min to 250 cm / min] If the welding speed S is less than 20 cm / min, even with the appropriate current and voltage, excessive weld metal is produced, resulting in dripping of the weld metal. On the other hand, if the welding speed S is greater than 250 cm / min, sufficient heat is not applied, and the slag cannot be melted, resulting in slag inclusion. Therefore, the welding speed S is preferably set to 20 cm / min to 250 cm / min. More preferably, it is set to 30 cm / min to 200 cm / min, and even more preferably, it is set to 40 cm / min to 150 cm / min.

[0049] [Welding heat input Q: 4 kJ / cm to 40 kJ / cm] If the welding heat input Q is less than 4 kJ / cm, welding defects such as insufficient fusion and penetration are likely to occur. On the other hand, if it exceeds 40 kJ / cm, the mechanical properties of the joint will deteriorate. Therefore, the welding heat input Q is preferably 4 kJ / cm to 40 kJ / cm. More preferably, it is 6 kJ / cm to 40 kJ / cm, and even more preferably, it is 7 kJ / cm to 40 kJ / cm.

[0050] [Welding Wire Extension Length L: 15 mm to 30 mm] The extension length L (mm) is the length from the tip of the contact tip of the welding nozzle to the tip of the welding wire, and when the arc length is added, it is the length from the tip of the contact tip to the base material, and is one of the important welding conditions that directly affects the welding current. If the extension length is less than 15 mm, spatter occurs and welding becomes unstable. On the other hand, if the extension length exceeds 30 mm, the penetration depth becomes unstable and welding defects are likely to occur. Therefore, it is preferable that the welding wire extension length L be 15 mm to 30 mm.

[0051] [Multi-Layer Welding] In this embodiment, as shown in Fig. 2, a backing metal 2 can be used at the bottom of the groove to form the weld metal 3 by multi-layer welding. In this embodiment, the welding conditions for each layer and each pass from the first layer to the final layer are set appropriately within the range of welding conditions described above. The number of layers of the multi-layer weld metal 3 depends on the plate thickness t of the steel material 1, the groove angle θ, the gap G, and the like, but as described above, if the plate thickness t is 10 mm to 150 mm, approximately 1 to 20 layers are preferable. Furthermore, with regard to the number of passes, although multiple passes may be performed per layer, 1 to 200 passes are preferable.

[0052] [Welding Polarity] The welding polarity is positive (the steel is positive and the welding wire is negative). This is because positive polarity improves the efficiency of welding, especially in the case of a narrow groove shape with a small groove angle θ and a small gap G. In a narrow groove, the arc tends to be directed toward the groove surface, making it difficult to melt the bottom of the groove. However, by welding with positive polarity using the REM-added welding wire of this embodiment, the arc tends to concentrate at the groove bottom, allowing the groove bottom to be stably and sufficiently melted. Furthermore, in a narrow groove, spatter tends to adhere to the groove surface. However, by welding with positive polarity using the REM-added welding wire of this embodiment, the generation of spatter is reduced, and spatter adhesion to the groove surface is reduced. This eliminates the need for spatter removal after welding.

[0053] An example of an evaluation test when positive polarity carbon dioxide gas shielded arc welding was performed using the welding wire according to the present invention will be described below.

[0054] The compositions of the welding wires used in the evaluation and the evaluation results of slag removability are shown in Tables 1-1 and 1-2.

[0055] To evaluate slag removability, the slag coverage rate was measured after striking the bead surface with a chisel after welding. A slag coverage rate (%) of 20% or more and 100% or less was evaluated as "poor," and a rate of less than 20% was evaluated as "excellent." The slag coverage rate (%) was calculated using the following formula (1): Slag coverage rate (%) = area covered by slag (mm ２ ) / bead surface area (mm２ ) x 100 ... (1)

[0056] The specifications and welding conditions for carbon dioxide gas shielded arc welding are as follows: The steel material specifications and dimensions are SM490B, with a plate thickness of 12 mm, a plate width of 75 mm, and a plate length of 500 mm. The shielding gas specifications are CO ２ The gas was 100% by volume or 80% by volume with the remainder being Ar gas, and the gas flow rate was 25 L / min.

[0057] The welding conditions were as follows: welding current I = 320 A, welding voltage V = 30.8 V, welding speed S = 120 cm / min, extension length L = 25 mm, welding wire diameter = 1.195 mm, welding heat input Q = 4.9 kJ / cm, an inverter power supply was used as the welding power source, and the polarity was positive.

[0058]

[0059]

[0060] As is clear from Tables 1-1 and 1-2, in the inventive examples in which the composition of the welding wire was within the range specified in the present invention, the slag removability after welding was "excellent," while in the comparative examples in which the composition of the welding wire was outside the range specified in the present invention, the slag removability was "poor."

[0061] 1 Steel material 2 Backing metal 3 Weld metal (multilayer) θ Groove angle G Gap t Steel plate thickness

Claims

1. A welding wire used in positive carbon dioxide gas shielded arc welding, the welding wire having a chemical composition, in mass %, of C: 0.200% or less, Si: 0.05% to 2.50%, Mn: 0.25% to 3.50%, P: 0.050% or less, S: 0.050% or less, Al: 0.02% to 3.00%, O (oxygen): 0.0100% or less, Ca: 0.0050% or less, rare earth elements: 0.010% to 0.100%, and among the rare earth elements, Nd: 0.0015% to 0.0200%, and optionally a first group; at least one selected from Ti: 0.02% to 0.50% and Zr: 0.001% to 0.500%; At least one selected from Cu: 0.02% to 3.00%, Ni: 0.02% to 3.00%, Cr: 0.02% to 3.00%, Mo: 0.02% to 1.50%, B: 0.0001% to 0.0150%, and Mg: 0.001% to 0.200%, and a third group; A wire for carbon dioxide gas shielded arc welding, characterized by containing at least one element selected from the group consisting of Nb: 0.001% to 0.500% and at least one element selected from V: 0.001% to 0.500%, with the balance being Fe and unavoidable impurities.

2. CO ２ 2. The wire for carbon dioxide gas shielded arc welding according to claim 1, which is used in a carbon dioxide gas shielded arc welding method using a shielding gas having a concentration of 60% by volume or more.

3. A carbon dioxide gas shielded arc welding method using the welding wire according to claim 1 or 2, wherein CO is used as the shielding gas. ２ A carbon dioxide gas shielded arc welding method characterized by performing welding with positive polarity using a gas having a concentration of 60% by volume or more.

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