JP3906827B2 - Steel wire for carbon dioxide shielded arc welding and welding method using the same - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a carbon dioxide shielded arc welding steel wire (hereinafter referred to as a welding steel wire) and a welding method using the same, and is particularly stable when used in a positive polarity (ie, a welding steel wire is a negative electrode). The present invention relates to a welding steel wire that can achieve spray transfer, which is a suitable droplet transfer form, suppresses the occurrence of spatter, has an excellent bead shape, and is excellent in manufacturability, and a welding method using the same.

Gas shielded arc welding using CO ₂ gas as the 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) in which a mixed gas of Ar gas and CO ₂ gas (mixing ratio of CO ₂ : 2 to 40% by volume) is a shielding gas is a fine method 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 high-speed welding. Therefore, mixed gas arc welding is used in fields that require high-quality welding.

However the cost of Ar gas, because it is expensive and 5 times the CO ₂ gas, in the actual welding is by reducing the amount of Ar gas, a mixed gas obtained by the mixing ratio of CO ₂ gas and 50 vol% or more 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 coarser than ordinary mixed gas arc welding ( CO ₂ mixing ratio of shielding gas: 2 to 40% by volume). A small 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. When a mixed gas consisting of Ar-5 to 25% by volume CO ₂ is used, the droplets are fine, and the droplet growth in the peak period and the droplet transfer in the base period are efficient due to the powerful downward plasma stream. I can do it well. 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. During the base period, the droplets are always suspended from the tip of the welding wire, 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 welding steel wire with positive polarity, which is the greatest feature of the present invention. 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.

  In JP 63-281796, there is no description about the polarity, but in the case of the reverse polarity used in ordinary carbon dioxide shielded arc welding, the addition of REM can increase the spatter of large grains due to arc contraction and repulsion. It is known that adding REM does not provide an arc stabilizing effect. On the other hand, in the case of positive polarity, an additive element (that is, Al) necessary for the stabilization of the arc, which is a feature of the present invention, and an element that decreases the spraying effect of droplet transfer and the arc stabilization effect in the positive polarity (that is, O). ), And no disclosure of elements (ie, O, Al) that reduce the yield of REM in steelmaking, and no disclosure of important technology regarding the interaction of additive elements such as REM, Al, O. For this reason, the technique disclosed in Japanese Patent Application Laid-Open No. 63-281796 cannot provide a sufficient arc stabilization effect in carbon dioxide shielded arc welding and excellent manufacturability of steel wires.

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. In the case of using a shielding gas whose main component is CO ₂ gas ( 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. In carbon dioxide shielded arc welding using a shield gas mainly composed of CO ₂ gas, 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 ordinary carbon dioxide shielded arc welding, a shield gas in which Ar gas and CO ₂ gas are mixed ( CO ₂ mixing ratio: 2 to 40% by volume) is used. In the present invention, CO ₂ gas is used as a main component (ie, A shielding gas having a CO ₂ mixing ratio of more than 60% by volume) is used. Therefore, the 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 using a welding steel wire as a negative electrode, stable transfer of droplets becomes 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, and stable transfer of droplets becomes possible.
(c) REM is added to the steel wire of the steel wire for welding, and the arc generation point at the cathode is concentrated and stabilized by defining not only the contents of Al, O and Ca but also the interrelationship of these elements. It becomes possible to make it.

(d) Adjust the REM, O, Ca, Ti, Zr, and Al content of the steel wire of the steel wire for welding so that the E value calculated by the following equation (1) is 0.00 or more. As a result, it is possible to improve the REM yield at the steel making stage where the steel material of the steel wire is melted, and to improve the workability to ensure excellent manufacturability.
E = [REM] + ([Ti] + [Zr] + [Al]) / 5-9 × ([O] + [Ca]) (1)
[REM]: Rare earth element content of steel wire (mass%)
[O]: O content (mass%) of steel wire
[Ti]: Ti content of steel wire (mass%)
[Zr]: Zr content (% by mass) of steel wire
[Al]: Al content (mass%) of steel wire
[Ca]: Ca content (mass%) of steel wire
That is, the present invention is a welding steel wire used for positive carbon dioxide shielded arc welding, and C: 0.20 mass% or less, Si: 0.05-2.5 mass%, Mn: 0.25-3.5 mass%, REM: 0.010 -0.100 mass%, Al: 0.02-3.00 mass%, O: 0.0010-0.0050 mass%, Ca: 0.0050 mass% or less, P: 0.05 mass% or less, S: 0.05 mass% or less, and as necessary Ti: 0.02-0.50 mass%, Zr: 0.02-0.50 mass%, Cr: 0.02-3.0 mass%, Ni: 0.05-3.0 mass%, Mo: 0.05-1.5 mass%, Cu: 0.05-3.0 mass%, B: 0.0005 to 0.015 wt%, Mg: 0.001 to 0.2 wt%, Nb: 0.005 to 0.5 wt% or V: 0.005 to 0.5 wt%, the balance being Fe and inevitable impurities, and the above formula (1) It is a steel wire for carbon dioxide gas shielded arc welding which consists of a steel strand whose E value computed by above is 0.00 or more.

In the invention of the steel wire for carbon dioxide shielded arc welding described above, the steel wire preferably has an E value calculated by the formula ( 1) of 0.05 or more.
In addition, the present invention uses the above-described carbon steel wire for shielded arc welding, shields the arc point with a shielding gas having a CO ₂ mixing ratio of 60% by volume or more in a mixed gas of Ar and CO _2, and has positive polarity. This is a carbon dioxide shielded arc welding method for performing welding.

In the carbon dioxide shielded arc welding method described above, it is preferable that the CO ₂ concentration of the shielding gas is 100% by volume.
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, it is possible to achieve ultra-low sputtering, which has been impossible in positive carbon dioxide shielded arc welding, improve the bead shape, and enable stable thick steel plate joint welding.

First, the reason why the steel wire component of the steel wire for carbon dioxide shielded arc welding of the present invention (that is, the steel wire for welding) is limited 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, if the C content exceeds 0.20% by mass, not only the behavior of droplets and molten metal becomes unstable in positive polarity welding, but also the toughness of the weld metal is reduced. 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: 0.010 to 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 welding steel wire is a plus electrode), adding REM to the steel wire will cause arc concentration and will not have the effect of reducing spatter. . However, in carbon dioxide shielded arc welding of positive polarity (that is, a welding steel wire is a negative electrode), it is an indispensable element for stabilizing droplet transfer. Droplet transfer can be further stabilized by the combined addition with Al described later. If the REM content is less than 0.010% 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 0.010 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 together Ce and La, it is preferable to use the mixture obtained by mixing within the range of Ce: 45-80 mass% and La: 10-45 mass% previously.

Al: 0.02 to 3.00 mass%
Al is an element that acts as a strong deoxidizer and increases 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. In the reverse polarity carbon dioxide shielded arc welding, there is no clear effect of stabilizing the droplet transfer. However, in the positive polarity carbon dioxide shielded arc welding, the effect of stabilizing the droplet transfer is high in welding at 350 A or higher current. Prominently demonstrated. On the other hand, in low current welding, the number of short circuit transitions can be increased to achieve uniform droplet transfer and improved bead shape. It also has the effect of reducing the REM oxidation loss in the manufacturing stage of welding steel wires due to its affinity with O. When Al is less than 0.02% by mass, such an effect cannot be obtained. On the other hand, when Al exceeds 3.00 mass%, the crystal grain of a weld metal will coarsen and toughness will fall remarkably. Therefore, Al needs to satisfy the range of 0.02-3.00 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 0.0 05 0 % by 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. However, if the O content exceeds 0.0 05 0 wt%, the effect of REM addition that the stabilization of the arc in the high current welding positive polarity is lost, swinging droplet sputtering is a large amount of generated increases . The O is violently react with REM in steel making step of melting the steel of the steel element wires have the function of forming a slag, the O content exceeds 0.0 05 0 wt%, the yield of REM It drops significantly. Therefore, O is set to 0.0 0.05 mass% or less. However, if the O content is less than 0.0010% by mass, the effect of adding O cannot be sufficiently obtained. Therefore, it is necessary to be 0.0010 to 0.0050 wt%.

Ca: 0.0050 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 0.0050% by mass, the effect of REM addition, which stabilizes the arc in high current welding, is impaired. Therefore, Ca needs to be 0.0050 mass% or less.

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, and to improve workability and ensure excellent manufacturability, the following equation (1) is used: The calculated E value needs to satisfy equation (2).
E = [REM] + ([Ti] + [Zr] + [Al]) / 5-9 × ([O] + [Ca]) (1)
[REM]: Rare earth element content of steel wire (mass%)
[O]: O content (mass%) of steel wire
[Ti]: Ti content of steel wire (mass%)
[Zr]: Zr content (% by mass) of steel wire
[Al]: Al content (mass%) of steel wire
[Ca]: Ca content (mass%) of steel wire
E ≧ 0.00 ・ ・ (2)
When Zr is not added to the steel wire, E value is calculated with [Zr] = 0 in the equation (1).

Furthermore, in the present invention, in addition to the above-described composition, the steel wire preferably contains one or two of Ti: 0.02 to 0.50 mass% and Zr: 0.02 to 0.50 mass%. The reason will be described.
Ti and Zr are elements that both 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. If Ti is less than 0.02 mass% and Zr is less than 0.02 mass%, this effect cannot be obtained. On the other hand, when Ti exceeds 0.50 mass% or Zr exceeds 0.50 mass%, the droplets become coarse and a large amount of large spatter is generated. Therefore, when Ti and Zr 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 the E value calculated by the formula (1) is 0.05 or more. Preferably there is.

In addition to the above-described components, the following elements can be added to the steel strand in the present invention.
K: 0.0001 to 0.015 mass%
K is an element that spreads the arc in positive polarity carbon dioxide shielded arc welding and enables spray transfer of the droplets even at a low current, and has the effect of 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.
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, N, which is a typical inevitable impurity inevitably mixed in the stage of melting a steel material or the stage of manufacturing a steel wire, is preferably reduced 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 if CO ₂ gas is used alone (that is, 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 250 to 450 A, welding voltage is 27 to 38 V (increase with current), 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 A range of 5 to 40 kJ / cm is preferable. There are no particular restrictions on the type of steel to be welded (ie, steel plate), but rolled steel (SM material) for Si-Mn welded structures specified in JIS standard G3106 and steel for building structures 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 plated with copper 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 at the steelmaking stage and the REM content obtained from the analysis of the steel wire. The results are shown in Tables 4 and 5. Tables 4 and 5 also show the E value calculated using the equation (1) and the copper plating thickness of the steel wire.

As is apparent from Tables 1-5, the examples of the invention, the O content 0.0010 to 0.0 05 0 wt%, the Al content is set to 0.02 to 3.00 wt%, and since the E value 0.00 or more, in Comparative Example Compared to REM yield. Among the inventive examples, in particular, the wire numbers 5 to 16 had an O content of 0.0100% by mass or less and an E value of 0.05 or more, so the REM yield was remarkably improved.
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 amount was evaluated as good (◯) when the spatter generation amount was 0.3 g / min or less, acceptable (Δ) when exceeding 0.3 g / min to 0.6 g / min or less (x) when exceeding 0.6 g / min. The results are as shown in Tables 6 and 7.

The bead shape was evaluated by visually observing the bead and assuming that a smooth bead was good (◯), a non-uniform bead was acceptable (Δ), and a humping bead was unacceptable (×). The results are shown in Tables 6 and 7.
The conditions for positive carbon dioxide shielded arc welding are shown in Table 8.

As apparent from Table 6, in the invention examples, a high current at high heat input positive carbon dioxide shielded arc welding, whereas the spatter generation rate was 0. 21 ~0.54g / min, In the comparative example in which the steel wire component was outside the scope of the present invention, the amount of spatter generated was 2.22 to 4.22 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 addition, as apparent from Tables 6 and 7, the bead shape was superior in the inventive examples.

Claims (4)

Steel wire for welding used for positive carbon dioxide shielded arc welding, C: 0.20 mass% or less, Si: 0.05 to 2.5 mass%, Mn: 0.25 to 3.5 mass%, rare earth element: 0.010 to 0.100 mass% , Al: 0.02 to 3.00% by mass, O: 0.0010 to 0.0050% by mass, Ca: 0.0050% by mass or less, P: 0.05% by mass or less, S: 0.05% by mass or less, and Ti: 0.02 to 0.50 mass%, Zr: 0.02-0.50 mass%, Cr: 0.02-3.0 mass%, Ni: 0.05-3.0 mass%, Mo: 0.05-1.5 mass%, Cu: 0.05-3.0 mass%, B: 0.0005-0.015 mass %, Mg: 0.001 to 0.2% by mass, Nb: 0.005 to 0.5% by mass or V: 0.005 to 0.5% by mass, the balance being Fe and inevitable impurities, and calculated by the following formula (1) A steel wire for carbon dioxide shielded arc welding, comprising a steel wire having an E value of 0.00 or more.
E = [REM] + ([Ti] + [Zr] + [Al]) / 5-9 × ([O] + [Ca]) (1)
[REM]: Rare earth element content of steel wire (mass%)
[O]: O content (mass%) of steel wire
[Ti]: Ti content of steel wire (mass%)
[Zr]: Zr content (% by mass) of steel wire
[Al]: Al content (mass%) of steel wire
[Ca]: Ca content (mass%) of steel wire Before SL (1) carbon dioxide gas shielded arc welding steel wire of claim 1, E value calculated is equal to or made of steel element wires is 0.05 or more expression. Using the steel wire for carbon dioxide shielded arc welding according to claim 1 or 2, the arc point is shielded with a shielding gas having a CO ₂ mixing ratio of 60% by volume or more in a mixed gas of Ar and CO _2, and positive polarity A carbon dioxide shielded arc welding method characterized in that welding is performed at a temperature. Carbon dioxide shielded arc welding method according to claim 3, CO ₂ concentration of the shielding gas being 100% by volume.