JP2005046878A - Steel wire for carbon dioxide gas-shielded arc welding, and welding method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a welding wire which can realize spray transfer of droplets, reduce generation of spattering even when high heat input welding is performed, and obtain an excellent bead shape in a carbon dioxide gas-shielded arc welding using shield gas consisting mainly of gaseous carbon dioxide, and a welding method using the welding wire. <P>SOLUTION: Welding is performed with positive polarity by using a steel wire for carbon dioxide gas-shielded arc welding containing, by mass, ≤ 0.20% C, 0.05-2.5% Si, 0.25-3.5% Mn, 0.0010-0.0080% O, 0.015-0.100% rare earth elements, ≤ 0.05% P and ≤ 0.05% S, and formed of steel strands with the D-value of ≥ 0.00, which is calculated by the formula: D = [REM] - 9 × [O] + 0.5. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a steel wire for carbon dioxide shielded arc welding (hereinafter referred to as a steel wire for welding) and a welding method using the same, which can provide a spray transfer which is the most stable form of droplet transfer, and particularly for welding. Even if the steel wire is used on the positive electrode (ie, negative electrode) side, spray transfer can be obtained, and as a result, the generation of spatters can be suppressed, and an excellent bead shape can be obtained, and a welding method using the same About.

Gas shielded arc welding using CO ₂ gas as a shielding gas is widely used for welding steel materials because CO ₂ gas is inexpensive and is an efficient welding method. In particular, due to the rapid spread of automatic welding, it is used in various fields such as shipbuilding, architecture, bridges, automobiles and construction machinery. It is often used for high-current multilayer welding of thick plates in the fields of shipbuilding, construction, and bridges, and is often used for fillet welding of thin plates in the fields of automobiles and construction machinery.

A welding method (so-called mixed gas arc welding) using a mixed gas of Ar gas and CO ₂ gas (mixing ratio of CO ₂ : 2 to 40% by volume) as a shielding gas is fine in which droplets are smaller than the diameter of the welding wire. Spray transfer is possible. It is known that the spray transfer of the droplet is the best among the droplet transfer modes, the generation of spatter is small, the weld bead shape is excellent, and it is suitable for improving the welding speed. Therefore, mixed gas arc welding is used in fields that require high-quality welding.

However, the cost of Ar gas is five times higher than that of CO ₂ gas, so in actual welding work, the amount of Ar gas used is reduced, and the mixed gas with a CO ₂ gas mixing ratio of 50% by volume or more is used. Is often used as a shielding gas. When a shielding gas having a CO ₂ gas mixing ratio of 50% by volume or more is used, it is 10 to 20 times as coarse as mixed gas arc welding (shielding gas CO ₂ mixing ratio: 2 to 40% by volume). The droplet hangs on the tip of the welding wire and moves while swinging by the arc force (so-called globule transfer). When such globule transition occurs, a large amount of short circuit with the base material (that is, steel plate) and spatter due to re-arcing occur, and the bead shape is not stable. Particularly in high-speed welding, there is a problem that the bead shape tends to be uneven (so-called humping bead).

In order to solve this problem, Japanese Patent Laid-Open No. 6-218574 discloses a method of reducing the amount of spatter generated by adding K. However, with this technique, when the welding speed is increased or when the CO ₂ in the shielding gas is increased to 50% by volume or more, the effect of reducing the amount of spatter generation and stabilizing the bead shape is not necessarily obtained.

Japanese Patent Laid-Open Nos. 7-47473 and 7-290241 propose a carbon dioxide pulse arc welding method in which one pulse is generated within the transition time of one droplet to reduce spatter. These techniques, using a mixed gas consisting of Ar-5 to 25 vol% CO ₂ as a shielding gas, and performs welding at 1 droplet per pulse. That is, in the case of using a mixed gas of Ar-5 to 25 vol% CO _2, the droplet is fine, droplet transfer in droplet growth and the base period in the peak period powerful downward plasma airflow Can be done efficiently. In addition, the time required to form one droplet is as short as 1 to 2 ms, and even if one droplet does not move in one pulse, a large droplet hangs at the tip of the welding wire if it moves in the next pulse. The effect of reducing spatter is exhibited by the pulse.

However, a carbon dioxide gas shielded arc using a shielding gas (CO ₂ mixing ratio of shielding gas: 50% by volume or more) containing CO ₂ as a main component disclosed in JP-A-7-47473 and JP-A-7-290241 The droplets in welding are coarse, the downward plasma stream is weak, and droplet transfer occurs in the first half of the pulse peak period. In carbon dioxide shielded arc pulse welding, droplets grow from the middle to the latter half of the peak period, and the droplets always hang from the tip of the welding wire during the base period, and the droplets move to the steel plate side in the first half of the next peak period. Is considered ideal. The period for forming one droplet is as long as 10 to 20 ms. If one droplet does not move in one pulse, it moves in the next pulse, but during that time a coarse droplet hangs on the tip of the welding wire. Therefore, a large amount of coarse spatter is generated due to a short circuit or the like. In the carbon dioxide shielded arc welding method, the droplet transfer interval is unstable, and it is difficult to stably generate one pulse in accordance with the transfer time of one droplet.

  Further, the present inventors have developed a “MAG welding steel wire and a MAG welding method using the same” disclosed in Japanese Patent Application Laid-Open No. 2002-144081 prior to the present invention. However, this technology is intended for low current welding of thin steel sheets with gaps in the weld (ie, 250 A or less), and high current welding (ie, over 250 A) in carbon dioxide shielded arc welding provides a sufficient arc stabilization effect. I can't.

  Japanese Patent Laid-Open No. 63-281796 discloses an arc stabilization technique for carbon dioxide shielded arc welding by adding rare earth elements (hereinafter referred to as REM). However, Japanese Patent Laid-Open No. 63-281796 does not disclose the use of a steel wire for welding, which is the greatest feature of the present invention, with positive polarity. Usually, in carbon dioxide shielded arc welding, where the welding steel wire is positive, droplets that are coarser than those in the case of reverse polarity (that is, the welding steel wire is a positive electrode) are formed, and are coarse due to a large short circuit. Spattering occurs. In addition, since the transition of the droplets is rough, the bead shape is uneven, the heat generation on the steel sheet side is small, and the penetration is shallow, so that welding defects due to overlap are likely to occur. Therefore, there is usually no idea of using a welding steel wire on the positive electrode side in carbon dioxide shielded arc welding, and carbon dioxide shielded arc welding is performed with a reverse polarity.

  However, JP 63-281796 does not describe the polarity, but in the case of the reverse polarity used in normal carbon dioxide shielded arc welding, the addition of REM increases the size of spatter due to arc contraction and repulsion. The arc stabilization effect is not obtained even when REM is added. On the other hand, in the case of positive polarity, additional elements (that is, P, S) necessary for the stabilization of the arc, which is a feature of the present invention, and elements that reduce spraying of the droplet transfer and the arc stabilization effect in the positive polarity ( In other words, there is no disclosure of important technologies relating to O) and disclosure of elements (ie O) that reduce the yield of REM in steelmaking, and sufficient arc stabilization effects in carbon dioxide shielded arc welding and excellent steel wire manufacturability Cannot be obtained.

As described above, when a shielding gas in which the mixing ratio of CO ₂ gas to Ar gas exceeds 40% by volume is used compared to the case of using a normal mixed gas (CO ₂ mixing ratio: 2 to 40% by volume). Coarse droplets are suspended from the tip of the welding steel wire and swayed by the arc force. As a result, high-speed welding has a problem that irregular short-circuiting with a base material (that is, a steel plate) or spatter due to re-arcing increases and the bead shape becomes unstable. When using a shielding gas containing CO ₂ gas as a main component (CO ₂ mixing ratio: more than 40% by volume), it is necessary to achieve spray transfer of droplets in order to solve such a problem.

However, with a normal mixed gas (CO ₂ mixing ratio: 2 to 40% by volume), spray transfer of droplets is possible, but CO ₂ gas is the main component (CO ₂ mixing ratio: over 40% by volume). With the shielding gas, it was extremely difficult to achieve spray transfer.
JP-A-6-218574 JP 7-47473 A Japanese Patent Laid-Open No. 7-290241 Japanese Patent Laid-Open No. 2002-144081 JP 63-281796 A

The present invention has been developed in view of the above problems, and in carbon dioxide shielded arc welding using a shielding gas containing CO ₂ gas as a main component, spray transfer of droplets is possible and high heat input welding can be performed. It aims at providing the steel wire for welding which can obtain not only the spatter generation | occurrence | production but the outstanding manufacturability, and the welding method using the same.

In normal carbon dioxide shielded arc welding, shield gas (mixing ratio of CO ₂ : 2 to 40% by volume) in which Ar gas, O ₂ and CO ₂ gas are mixed is mainly used. In the present invention, CO ₂ gas is used. Is used as a main component (ie, CO ₂ mixing ratio: more than 60% by volume). Therefore, carbon dioxide shielded arc welding in the present invention refers to carbon dioxide shielded arc welding using a shield gas in which Ar gas and CO ₂ gas are mixed so that the mixing ratio of CO ₂ is 60% by volume or more.

In the carbon dioxide shielded arc welding using a shielding gas which is a mixed gas of Ar gas and CO ₂ gas and has CO ₂ as a main component (that is, the mixing ratio of CO ₂ exceeds 60% by volume), We have intensively studied the technology that enables spray transfer of droplets, reduces spatter generation, and improves bead shape. As a result, the following knowledge was obtained. The present invention has been made based on these findings.

  (a) By performing positive polarity welding with the welding steel wire as the negative electrode, the droplets are coarse, but stable transfer is possible.

  (b) By adding REM to the steel wire of the steel wire for welding, arc breakage in the low voltage region can be prevented, stable transfer of droplets can be achieved, and penetration can be ensured to smooth the beads. Is possible.

  (c) By adding REM to the steel wire of the steel wire for welding and further specifying the contents of P, S, and O, it becomes possible to concentrate and stabilize the arc generation point in the cathode.

  (d) By adjusting the REM content and O content of the steel wire of the welding steel wire so that the D value calculated by the following formula (1) is 0.00 or more, the steel material of the steel wire It is possible to improve the REM yield at the steelmaking stage where the steel is melted and to ensure excellent manufacturability.

D = [REM] −9 × [O] +0.5 (1)
[REM]: Rare earth element content of steel wire (mass%)
[O]: O content (mass%) of steel wire
That is, the present invention is a steel wire for welding used for positive carbon dioxide shielded arc welding, C: 0.20 mass% or less, Si: 0.05-2.5 mass%, Mn: 0.25-3.5 mass%, O: 0.0010- 0.0080% by mass, rare earth element: 0.015 to 0.100% by mass, P: 0.05% by mass or less, S: 0.05% by mass or less, and D value calculated by the following formula (1) is 0.00 or more This is a steel wire for carbon dioxide shielded arc welding consisting of a wire.

D = [REM] −9 × [O] +0.5 (1)
[REM]: Rare earth element content of steel wire (mass%)
[O]: O content (mass%) of steel wire
In the carbon dioxide shielded arc welding method, the present invention includes C: 0.20 mass% or less, Si: 0.05-2.5 mass%, Mn: 0.25-3.5 mass%, O: 0.0010-0.0080 mass%, rare earth element: 0.015-0.100. Steel for carbon dioxide shielded arc welding consisting of a steel wire having a mass%, P: 0.05 mass% or less, S: 0.05 mass% or less, and a D value calculated by the following formula (1) of 0.00 or more Carbon dioxide shielded arc welding method that uses a wire, shields the arc point using a mixed gas in which CO ₂ , O ₂ and Ar are mixed to make the CO ₂ concentration 60% by volume or more, and welding is performed with positive polarity It is.

D = [REM] −9 × [O] +0.5 (1)
[REM]: Rare earth element content of steel wire (mass%)
[O]: O content (mass%) of steel wire
In the invention of the carbon dioxide shielded arc welding method described above, the CO ₂ concentration of the mixed gas is preferably 100% by volume (JIS K1106).

  In addition, the steel wire for welding which consists of a steel strand here refers to the wire (what is called a solid wire) which does not incorporate the welding flux and mainly has the steel strand used as a raw material. Further, the present invention can be applied to a solid wire in which the surface of a steel wire is plated or a lubricant is applied without any trouble.

  According to the present invention, since it is possible to achieve spray transfer, which has been impossible in positive carbon dioxide shielded arc welding, it is possible to reduce spatter generation and improve the bead shape, enabling stable thick steel plate joint welding. Become.

  First, the reasons for limiting the components of the steel wire of the steel wire for carbon dioxide shielded arc welding of the present invention (ie, the steel wire for welding) will be described.

C: 0.20 mass% 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 the fluidity. However, when the C content exceeds 0.20% by mass, not only the behavior of the droplets and the molten metal becomes unstable, but also the toughness of the weld metal is lowered. Therefore, C is 0.20% by mass or less. On the other hand, if the C content is excessively reduced, the strength of the weld metal cannot be ensured. Therefore, it is preferable to set it as 0.003-0.20 mass%. In addition, 0.01-0.10 mass% is still more preferable.

Si: 0.05-2.5 mass%
Si has a deoxidizing action and is an indispensable element for deoxidizing molten metal. When the Si content is less than 0.05% by mass, deoxidation of the molten metal is insufficient, and blow defects occur in the weld metal. On the other hand, if it exceeds 2.5% by mass, the toughness of the weld metal is significantly reduced. Therefore, Si needs to satisfy the range of 0.05-2.5 mass%. Further, in order to suppress the spread of the arc in the positive polarity (that is, the negative electrode of the welding steel wire) carbon dioxide shielded arc welding and increase the number of times of droplet transfer, 0.25% by mass or more is desirable. Therefore, it is preferable to set it as 0.25-2.5 mass%.

Mn: 0.25 to 3.5% by mass
Mn has a deoxidizing action similar to Si and is an indispensable element for deoxidizing molten metal. When the Mn content is less than 0.25% by mass, deoxidation of the molten metal is insufficient, and blow holes are generated in the weld metal. On the other hand, if it exceeds 3.5% by mass, the toughness of the weld metal decreases. Therefore, Mn needs to satisfy the range of 0.25 to 3.5% by mass. In order to promote deoxidation of molten metal and prevent blowholes, 0.45% by mass or more is desirable. Therefore, it is preferable to set it as 0.45-3.5 mass%.

REM: 0.015-0.100 mass%
REM is an effective element for refinement of inclusions during steelmaking and casting and to improve the toughness of weld metal. However, in carbon dioxide shielded arc welding with normal reverse polarity (ie, the steel wire for welding is a plus electrode), the addition of REM in the steel wire causes concentration of the arc, and the effect of reducing spatter cannot be obtained. . However, in positive polarity carbon dioxide shielded arc welding, it is an indispensable element for stabilizing droplet transfer. If the REM content is less than 0.015% by mass, this droplet transfer stabilization effect cannot be obtained. On the other hand, if it exceeds 0.100% by mass, cracks occur in the manufacturing process of the welding steel wire, and the toughness of the weld metal decreases. Therefore, REM needs to satisfy the range of 0.015 to 0.100 mass%. In addition, Preferably it is 0.025-0.050 mass%.

  Here, REM is a general term for elements belonging to Group 3 of the periodic table. In the present invention, it is preferable to use an element having an atomic number of 57 to 71, and Ce and La are particularly preferable. When Ce and La are added to the steel strand, Ce or La may be added alone, or Ce and La may be used in combination. In addition, when adding Ce and La, it is preferable to use the mixture (for example, misch metal) obtained by mixing beforehand in the range of Ce: 45-80 mass% and La: 10-45 mass%.

P: 0.05% by mass or less P is an element that lowers the melting point of steel, improves electrical resistivity, and improves melting efficiency. Further, in the positive polarity carbon dioxide shielded arc welding, the droplets are refined to stabilize the arc. However, if the P content exceeds 0.05% by mass, the viscosity of the molten metal is significantly reduced in positive polarity carbon dioxide shielded arc welding, the arc becomes unstable, and small-particle spatter increases. In addition, the risk of hot cracking of the weld metal increases. Therefore, P is set to 0.05% by mass or less. In addition, Preferably it is 0.03 mass% or less. On the other hand, since it takes a long time to reduce P in the steelmaking stage where the steel material of the steel wire is melted, 0.002% by mass or more is desirable from the viewpoint of improving productivity. Therefore, it is preferable to set it as 0.002-0.03 mass%.

S: 0.05% by mass or less S reduces the viscosity of the molten metal, promotes the detachment of the droplet suspended from the tip of the welding steel wire, and stabilizes the arc in positive carbon dioxide shielded arc welding. S also has the effect of smoothing the bead by spreading the arc in positive carbon dioxide shielded arc welding and lowering the viscosity of the molten metal. However, when the S content exceeds 0.05% by mass, the spatter of small grains increases and the toughness of the weld metal decreases. Therefore, S is set to 0.05% by mass or less. In addition, Preferably it is 0.02 mass% or less. On the other hand, since it takes a long time to reduce S in the steelmaking stage where the steel material of the steel wire is melted, 0.002% by mass or more is desirable from the viewpoint of improving productivity. Therefore, it is preferable to set it as 0.002-0.02 mass%.

O: 0.0010 to 0.0080 mass%
O has the effect of destabilizing an arc point generated in a droplet suspended from the tip of a welding steel wire in positive carbon dioxide shielded arc welding, and making the droplet finer. If the O content is less than 0.0010% by mass, such an effect cannot be obtained. On the other hand, if it exceeds 0.0080% by mass, the effect of REM addition, which stabilizes the arc in positive current welding, is impaired, and the fluctuation of droplets increases and a large amount of spatter is generated. O also has the effect of reacting violently with REM to form slag at the steelmaking stage where the steel wire is melted. If the O content exceeds 0.0080% by mass, the yield of REM decreases significantly. To do. Therefore, O needs to satisfy the range of 0.0010-0.0080 mass%. In addition, Preferably it is 0.0010-0.0050 mass%.

  Furthermore, in order to achieve REM yield improvement and uniform distribution in the steelmaking stage where the steel material of the steel wire is melted, the D value calculated by the following equation (1) using the REM content and O content: However, it is necessary to satisfy equation (2).

D = [REM] −9 × [O] +0.5 (1)
[REM]: REM content of steel wire (mass%)
[O]: O content (mass%) of steel wire
D ≧ 0.00 (2)
The D value is preferably D ≧ 0.05.

  In addition to the above-described components, the following elements can be added to the steel strand in the present invention.

Ca: 0.003 mass% or less
Ca is mixed into the molten steel as an impurity during steelmaking and casting, or mixed into the steel strand as an impurity during wire drawing. In positive carbon dioxide shielded arc welding, if the Ca content exceeds 0.003 mass%, the effect of REM addition, which stabilizes the arc in high-current welding, and the effect of refinement of droplets by addition of O are impaired. Therefore, Ca is preferably 0.003% by mass or less.

K: 0.0001 to 0.015 mass%
K has the effect of spreading the arc in positive polarity carbon dioxide shielded arc welding, promoting a reduction in spray transfer current, and miniaturizing the droplets. Therefore, it is added to the steel wire as necessary. When the K content is less than 0.0001% by mass, this effect cannot be obtained. On the other hand, if it exceeds 0.015% by mass, the arc length becomes long, the droplet suspended on the tip of the steel wire for welding becomes unstable, and the amount of spatter increases. Therefore, K preferably satisfies the range of 0.0001 to 0.015 mass%. In addition, Preferably it is 0.0003-0.003 mass%.

  In addition, since K has a low boiling point of about 760 ° C., if K is added in the steelmaking stage in which the steel material of the steel wire is melted, the yield is remarkably lowered. Therefore, it is preferable that K is stably contained in the welding steel wire by applying a potassium salt solution to the surface of the steel wire and annealing in the manufacturing stage of the welding steel wire.

  Further, in the present invention, in addition to the above-described composition, the steel wire contains one or more of Ti: 0.02-0.50 mass%, Zr: 0.02-0.50 mass%, and Al: 0.02-3.00 mass%. It is preferable to do. The reason will be described.

  Ti, Zr, and Al are elements that act as strong deoxidizers and increase the strength of the weld metal. Furthermore, there exists an effect which stabilizes a bead shape (namely, suppresses a humping bead) by reducing a viscosity by deoxidation of molten metal. Because of this effect, it is an effective element for high current welding at 350 A or more, and it is added as necessary. This effect cannot be obtained if Ti is less than 0.02 mass%, Zr is less than 0.02 mass%, and Al is less than 0.02 mass%. On the other hand, when Ti exceeds 0.50% by mass, Zr exceeds 0.50% by mass, or Al exceeds 3.00% by mass, the droplets become coarse and large spatters are generated. Therefore, when Ti, Zr, and Al are contained, it is preferable to satisfy the ranges of Ti: 0.02 to 0.50 mass%, Zr: 0.02 to 0.50 mass%, and Al: 0.02 to 3.00 mass%.

  Furthermore, the effects of the present invention are not reduced by adding the following elements as necessary.

Cr: 0.02 to 3.0 mass%, Ni: 0.05 to 3.0 mass%, Mo: 0.05 to 1.5 mass%, Cu: 0.05 to 3.0 mass%, B: 0.0005 to 0.015 mass%, Mg: 0.001 to 0.2 mass%
Cr, Ni, Mo, Cu, B, and Mg are all elements that increase the strength of the weld metal and improve the weather resistance. When the content of these elements is very small, such an effect cannot be obtained. On the other hand, when it adds excessively, the fall of the toughness of a weld metal will be caused. Therefore, when Cr, Ni, Mo, Cu, B, and Mg are contained, Cr: 0.02 to 3.0 mass%, Ni: 0.05 to 3.0 mass%, Mo: 0.05 to 1.5 mass%, Cu: 0.05 to 3.0 mass% B: 0.0005 to 0.015% by mass, Mg: 0.001 to 0.2% by mass is preferably satisfied.

Nb: 0.005 to 0.5 mass%, V: 0.005 to 0.5 mass%
Nb and V are elements that improve the strength and toughness of the weld metal and improve the stability of the arc. When the content of these elements is very small, such an effect cannot be obtained. On the other hand, when it adds excessively, the fall of the toughness of a weld metal will be caused. Therefore, when Nb and V are contained, it is preferable to satisfy the ranges of Nb: 0.005 to 0.5% by mass and V: 0.005 to 0.5% by mass.

  The balance other than the components of the steel strand described above is Fe and inevitable impurities. For example, it is preferable to reduce N, which is a typical inevitable impurity inevitably mixed at the stage of melting a steel material or the stage of manufacturing a steel wire, to 0.020% by mass or less.

  Next, the manufacturing method of the steel wire for welding of this invention is demonstrated.

  Using a converter or an electric furnace, molten steel having the above composition is produced. The melting method of the molten steel is not limited to a specific technique, and a conventionally known technique is used. Next, a steel material (for example, a billet) is manufactured from the obtained molten steel by a continuous casting method, an ingot-making method, or the like. After this steel material is heated, hot rolling is performed, and dry cold rolling (that is, wire drawing) is further performed to manufacture a steel strand. The operating conditions for hot rolling and cold rolling are not limited to specific conditions, and may be any conditions as long as they produce a steel wire having a desired size and shape.

  Further, the steel wire is sequentially subjected to annealing, pickling, copper plating, wire drawing, and lubricant application as necessary to form a predetermined product, that is, a steel wire for welding.

  In positive carbon dioxide shielded arc welding, the arc is likely to become unstable due to power feeding failure as compared with welding with reverse polarity. However, by applying copper plating with a thickness of 0.6 μm or more to the surface of the steel wire, it is possible to prevent arc destabilization due to poor power feeding of the welding steel wire. In addition, it is more preferable that the thickness of the copper plating is 0.8 μm or more because the effect of preventing power feeding failure is remarkably exhibited. By making the copper plating thicker in this way, there is also an effect that the wear of the power supply tip can be reduced.

  However, when the Cu content of the steel wire for welding, including the Cu content in the steel strand, exceeds 3.0% by mass, the toughness of the weld metal is significantly reduced. Therefore, it is preferable that the Cu content of the steel wire for welding (that is, the sum of the Cu content of the steel strand and the Cu content of the copper plating) is 3.0% by mass or less.

  When carbon dioxide shielded arc welding is performed using the welding steel wire thus manufactured, in order to increase the stability of the power feeding and stably maintain the spray transfer of the droplets, The flatness (that is, the actual surface area / theoretical surface area) is preferably less than 1.01. The flatness of the welding steel wire can be maintained in a range of less than 1.01 by strictly controlling the dies in the wire drawing.

  In order to improve the feedability of the welding steel wire, lubricating oil may be applied to the surface of the welding steel wire (that is, the surface of the steel wire or the surface of the copper plating). The application amount of the lubricating oil is preferably within a range of 0.35 to 1.7 g per 10 kg of the welding steel wire.

  In the process of manufacturing a welding steel wire, various impurities adhere to the surface of the welding steel wire. In particular, when the amount of solid impurities deposited is suppressed to 0.01 g or less per 10 kg of the welding steel wire, the power feeding stability is further improved.

  Suitable welding conditions for performing positive polarity carbon dioxide shielded arc welding using the welding steel wire thus manufactured will be described below.

As the shielding gas, a mixed gas of Ar and CO ₂ is used. The mixing ratio of CO ₂ in the shielding gas is 60% by volume or more. Even when CO ₂ gas is used alone (ie, CO ₂ mixing ratio: 100% by volume) as a shielding gas, positive carbon dioxide shielded arc welding can be performed without hindrance.

  Welding current is 270 to 450 A, welding voltage is 27 to 38 V, welding speed is 20 to 250 cm / min, protrusion length is 15 to 30 mm, wire diameter is 0.8 to 1.6 mm, welding heat input is 5 to 40 kJ / cm Within the range of is preferable. The steel type of the base material (ie, steel plate) to be welded is not particularly limited. However, Si-Mn rolled steel for welded structure (SM material) specified in JIS standard G3106 and steel for building structure specified in JIS standard G3136. It is preferable to apply to (SN material). When welding thick steel plates with a thickness of 10 mm or more, multilayer welding is also possible.

  The billet manufactured by continuous casting was hot-rolled into a wire having a diameter of 5.5 to 7.0 mm by adjusting the components at the steelmaking stage. Subsequently, the steel strand having a diameter of 2.0 to 2.8 mm was formed by cold rolling (that is, wire drawing), and 2 to 30% by mass of a 3 potassium citrate aqueous solution was applied to 30 to 50 g per 1 kg of the steel strand.

  The components of the obtained steel strand are shown in Tables 1-3.

  Thereafter, these steel wires were annealed in a nitrogen atmosphere with a dew point of −2 ° C. or lower, an oxygen concentration of 200 vol ppm or lower, and a carbon dioxide concentration of 0.1 vol% or lower. At this time, the K content of the steel wire was adjusted to a predetermined range by adjusting the diameter of the steel wire, the concentration of the tripotassium citrate aqueous solution, the annealing time, and the annealing temperature.

  After annealing in this way, the steel strand was pickled, and then the surface of the steel strand was subjected to copper plating as necessary. Furthermore, cold drawing was performed (dry drawing) to produce a steel wire for welding with a diameter of 0.8 to 1.6 mm. Furthermore, 0.4 to 0.8 g of lubricating oil was applied to the surface of the welding steel wire per 10 kg of the welding steel wire.

  The REM yield was calculated using the amount of REM added in the steelmaking stage and the REM content obtained from the analysis of the steel wire. The result is combined with Tables 1-3, and is shown.

  As is apparent from Tables 1 to 3, since the inventive example had an O content of 0.0080 mass% or less and a D value of 0.00 or more, the REM yield was improved as compared with the comparative example. Among the invention examples, in particular, the wire numbers 3 to 30 had an O content of 0.0050 mass% or less and a D value of 0.05 or more, so the REM yield was remarkably improved and maintained at 50% or more.

  Positive carbon dioxide shielded arc welding was performed using these welding steel wires, and the entire amount of spatter generated during welding was collected and the weight thereof was measured. The spatter generation rate was evaluated as good (◯) when the amount of spatter was 0.4 g / min or less, acceptable (Δ) when exceeding 0.4 g / min to 0.6 g / min or less (×) when exceeding 0.6 g / min. The results are as shown in Tables 4-5.

  Table 6 shows the conditions of positive carbon dioxide shielded arc welding.

  As is apparent from Tables 4 to 5, in the inventive examples, the amount of spatter generated in the positive carbon dioxide shielded arc welding with high current and high heat input was 0.19 to 0.52 g / min. In the comparative example in which the component of the line is out of the range of the present invention, the amount of spatter generated was 2.54 to 3.54 g / min. Therefore, in the present invention, it was confirmed that spray transfer of droplets was obtained and the amount of spatter generated could be reduced. In particular, when the REM content of the steel wire was 0.025 mass% or more and the O content was 0.0080 mass% or less, the amount of spatter generated could be further reduced.

Claims (3)

Steel wire for welding used for positive carbon dioxide shielded arc welding, C: 0.20 mass% or less, Si: 0.05-2.5 mass%, Mn: 0.25-3.5 mass%, O: 0.0010-0.0080 mass%, rare earth Element: 0.015 to 0.100% by mass, P: 0.05% by mass or less, S: 0.05% by mass or less, and a D value calculated by the following formula (1) is 0.00 or more. Characteristic steel wire for carbon dioxide shielded arc welding.
D = [REM] −9 × [O] +0.5 (1)
[REM]: Rare earth element content of steel wire (mass%)
[O]: O content (mass%) of steel wire In the carbon dioxide shielded arc welding method, C: 0.20 mass% or less, Si: 0.05 to 2.5 mass%, Mn: 0.25 to 3.5 mass%, O: 0.0010 to 0.0080 mass%, rare earth element: 0.015 to 0.100 mass%, P: A steel wire for carbon dioxide shielded arc welding comprising 0.05 mass% or less and S: 0.05 mass% or less and comprising a steel wire having a D value calculated by the following formula (1) of 0.00 or more, A carbon dioxide gas shielded arc welding method characterized in that arc points are shielded by using a mixed gas in which CO ₂ , O ₂ and Ar are mixed to have a CO ₂ concentration of 60% by volume or more, and welding is performed with positive polarity. .
D = [REM] −9 × [O] +0.5 (1)
[REM]: Rare earth element content of steel wire (mass%)
[O]: O content (mass%) of steel wire Carbon dioxide shielded arc welding method according to claim 2, the CO ₂ concentration of the mixed gas being 100% by volume.