JP7855536B2 - Ar-CO2 mixed gas shielded arc welding flux-cored wire - Google Patents

Description

The present invention relates to a flux-cored wire for Ar-CO2 mixed gas shielded arc welding, which provides good arc stability, low spatter generation, particularly good slag detachability, no welding defects, and excellent strength and low-temperature toughness of the weld metal in _all -position circumferential welding of steel pipes.

Flux-cored wires for gas shielded arc welding, particularly rutile-type flux-cored wires offering superior welding efficiency and workability in all-position welding, are widely used in various fields such as shipbuilding, bridges, offshore structures, and steel structures. For example, in recent years, the development of natural gas and oil fields on the seabed has progressed, leading to an increase in pipeline construction. Therefore, flux-cored wires for gas shielded arc welding, enabling highly efficient construction in all-position welding of pipelines, are being used.

Because pipelines are laid on land, underwater, and in cold regions, they require extremely high reliability due to harsh operating environments, and high quality is also required for welds. For example, Patent Document 1 discloses a flux-cored wire technology that achieves good weldability in all positions by specifying a fluorine compound containing Na and K. However, the technology disclosed in Patent Document 1 does not contain Bi and has a small amount of Zr oxide, resulting in poor slag detachability and welding defects such as slag inclusion. Furthermore, the lack of Nb and V means that the strength of the weld metal of steel pipes cannot be consistently obtained.

Patent Document 2 discloses a flux-cored wire technology that achieves good weldability and low-temperature toughness in all-position welding by optimizing the slag, alloy, and deoxidizing agent components. However, the technology disclosed in Patent Document 2 does not include Nb and V, resulting in the problem that the strength of the weld metal for steel pipes cannot be consistently obtained.

Japanese Patent Publication No. 2016-131985 Japanese Patent Publication No. 2018-153853

Therefore, the present invention has been made to solve the above-mentioned problems, and aims to provide a flux-cored wire for Ar- _CO2 mixed gas shielded arc welding that exhibits good arc stability in all-position circumferential welding of steel pipes, generates little spatter, has particularly good slag detachability and no welding defects, and has excellent strength and low-temperature toughness of the weld metal.

The inventors of the present invention conducted various studies on flux-cored wire for Ar- _CO2 mixed gas shielded arc welding in order to obtain a weld metal that exhibits good arc stability, low spatter generation, particularly good slag detachability, no welding defects, and good strength and low-temperature toughness at -60°C in all-position circumferential welding of steel pipes.

As a result, we found that by using a slag component consisting mainly of a metal oxide with _TiO2 as the main component and a fluorine compound, along with an alloy component containing optimal amounts of Nb and V, and a deoxidizing agent, we could obtain a weld metal with good weldability, slag detachability, strength, and low-temperature toughness in all-position welding of steel pipes.

In other words, the gist of the present invention is a flux-cored wire for Ar- _CO2 mixed gas shielded arc welding, in which flux is filled into a steel sheath, and the total mass of the steel sheath and flux, in mass % of the total mass of the wire, contains C: 0.03-0.08%, Si: 0.1-0.6%, Mn: 1.5-2.8%, Cu: 0.01-0.5%, Ni: 0.5-1.5%, Ti: 0.05-0.25%, B: 0.002-0.015%, Al: 0.05% or less, and the total of one or both of Nb and V: 0.01-0.1%, and further, in mass % of the total mass of the wire, the flux contains the total value of Ti oxide in terms of _TiO2 : 3-8%, the total value of Al _{oxide in terms of Al2O3 :} 0.02-0.3%, and Si oxide in terms of SiO The material contains the following components: total equivalent values of ₂ : 0.1-0.6%, total equivalent values of Zr oxides (ZrO2 ₎ : 0.25-0.65%, one or more of Na oxides, Na fluorides, K oxides, and K fluorides: 0.05-0.2% in total equivalent values of _Na2O and _K2O , Mg: 0.1-0.8%, total equivalent values of fluorine compounds (F): 0.05-0.25%, total equivalent values of Bi and Bi oxides (one or both): 0.001-0.01%, with the remainder consisting of Fe from the steel shell, Fe from iron powder, Fe from iron alloy powder, and impurities.

According to the flux-cored wire for Ar- _CO2 mixed gas shielded arc welding to which the present invention is applied, arc stability is good in all-position circumferential welding of steel pipes, spatter generation is low, slag detachability is particularly good with no slag inclusion, and a weld metal with good strength and low-temperature toughness is obtained. Therefore, the present invention makes it possible to improve welding efficiency and the quality of the weld metal.

Figure 1 shows the groove shape of a steel pipe used in weld metal testing.

The following describes the component composition and content of flux-cored wire for Ar- _CO2 mixed gas shielded arc welding to which the present invention is applied, as well as the reasons for limiting the composition of each component. The content of each component will be expressed as a mass % relative to the total mass of the flux-cored wire, and when expressing the mass %, it will simply be written as %.

[Total C content of steel shell and flux: 0.03–0.08%]
Carbon (C) has the effect of improving the strength of the weld metal. However, if the C content is less than 0.03%, the strength of the weld metal will be low. On the other hand, if the C content exceeds 0.08%, the strength of the weld metal will be excessive, and its low-temperature toughness will decrease. Therefore, the total C content of the steel sheath and flux should be between 0.03% and 0.08%. In addition to the components contained in the steel sheath, C can be added from metal powders and alloy powders in the flux.

[Total Si content of steel shell and flux: 0.1–0.6%]
Si contributes to improved weldability by enhancing the appearance and shape of the weld bead through partial formation as weld slag during welding. However, if the Si content is less than 0.1%, the effect of improving the appearance and shape of the weld bead is not sufficiently obtained. On the other hand, if the Si content exceeds 0.6%, the excess Si remains in the weld metal, resulting in excessive strength and a decrease in the low-temperature toughness of the weld metal. Therefore, the total Si content of the steel sheath and flux should be between 0.1% and 0.6%. In addition to the components contained in the steel sheath, Si can be added from the flux using alloy powders such as metallic Si, Fe-Si, and Fe-Si-Mn.

[Total Mn content of steel shell and flux: 1.5–2.8%]
Like Si, manganese (Mn) contributes to improved welding workability by improving the appearance and shape of the weld bead as part of the weld slag during welding. Furthermore, Mn retains in the weld metal, increasing its strength and low-temperature toughness. However, if the Mn content is less than 1.5%, the bead appearance and shape are poor, and the low-temperature toughness of the weld metal decreases. On the other hand, if the Mn content exceeds 2.8%, an excessive amount of Mn is retained in the weld metal, resulting in excessively high weld metal strength and decreased low-temperature toughness. Therefore, the total Mn content of the steel sheath and flux should be between 1.5% and 2.8%. In addition to components contained in the steel sheath, Mn can be added from alloy powders such as metallic Mn, Fe-Mn, and Fe-Si-Mn from the flux.

[Total Cu content of steel shell and flux: 0.01–0.5%]
Cu refines the microstructure of the weld metal, increasing its strength and low-temperature toughness. However, if the Cu content is less than 0.01%, the strength and low-temperature toughness of the weld metal decrease. On the other hand, if the Cu content exceeds 0.5%, the strength of the weld metal becomes excessive, and its low-temperature toughness decreases. Therefore, the total Cu content of the steel sheath and flux should be between 0.01% and 0.5%. Cu can be added from the Cu plating applied to the surface of the steel sheath, as well as from alloy powders such as metallic Cu, Cu-Zr, and Fe-Si-Cu from the flux.

[Total Ni content of steel shell and flux: 0.5–1.5%]
Ni has the effect of improving the low-temperature toughness of weld metal. However, if the Ni content is less than 0.5%, the low-temperature toughness of the weld metal decreases. On the other hand, if the Ni content exceeds 1.5%, the weld metal becomes more susceptible to hot cracking. Therefore, the total Ni content of the steel sheath and flux should be between 0.5% and 1.5%. In addition to the components contained in the steel sheath, Ni can be added from metallic Ni, Fe-Ni, and other alloy powders from the flux.

[Total Ti of steel shell and flux: 0.05–0.25%]
Ti has the effect of refining the microstructure of the weld metal and improving its low-temperature toughness. However, if the Ti content is less than 0.05%, the low-temperature toughness of the weld metal decreases. On the other hand, if the Ti content exceeds 0.25%, precipitation strengthening occurs due to the precipitation of carbides, resulting in excessive strength of the weld metal and a decrease in low-temperature toughness. Therefore, the total Ti content of the steel sheath and flux should be between 0.05% and 0.25%. In addition to components contained in the steel sheath, Ti can be added from metallic Ti, Fe-Ti, and other alloy powders from the flux.

[Total of steel shell and flux: B: 0.002–0.015%]
Adding B in small amounts suppresses the formation of grain boundary ferrites in the weld metal and improves the low-temperature toughness of the weld metal. However, if B is less than 0.002%, the low-temperature toughness of the weld metal decreases. On the other hand, if B exceeds 0.015%, the low-temperature toughness of the weld metal decreases, and the weld metal becomes more susceptible to hot cracking. Therefore, the total amount of B in the steel sheath and flux should be between 0.002% and 0.015%. B, Fe-B, Fe-Mn-B, and other alloy powders can be added to the total amount in the steel sheath and flux.

[Total Al content of steel shell and flux: 0.05% or less]
Al (Al) remains in the weld metal as an oxide, reducing its toughness. In particular, if the Al content exceeds 0.05%, the low-temperature toughness of the weld metal decreases. Therefore, the Al content should be 0.05% or less. Note that Al is not an essential element, and its content may be 0%.

[Total of Nb and V (either one or both) in the steel shell and flux: 0.01–0.1%]
Nb and V have the effect of improving the strength of the weld metal through solid solution strengthening. However, if the sum of one or both Nb and V is less than 0.01%, the strength of the weld metal will decrease. On the other hand, if the sum of one or both Nb and V exceeds 0.1%, carbides and nitrides will precipitate, resulting in low-temperature toughness. Therefore, the sum of one or both Nb and V in the steel shell and flux should be between 0.01% and 0.1%. In addition to the components contained in the steel shell, Nb and V are also present in trace amounts in Ti oxides such as rutile, titanium slag, and ilmenite in the flux, so carefully selected components from the steel shell and oxides should be used.

[Total Ti oxide content in flux (in _TiO2 equivalent): 3-8%]
Ti oxide contributes to arc stabilization during welding, improves bead shape, and enhances welding workability. Furthermore, in all-position circumferential welding, Ti oxide adjusts the viscosity and melting point of the molten slag, preventing metal sagging. However, if the total _TiO2 equivalent value of Ti oxide is less than 3%, the arc becomes unstable, spatter generation increases, bead appearance and shape deteriorate, and the low-temperature toughness of the weld metal decreases. Also, if the total _TiO2 equivalent value is less than 3%, metal sagging occurs in all-position circumferential welding, resulting in poor bead appearance and shape. On the other hand, if the total _TiO2 equivalent value of Ti oxide exceeds 8%, the arc is stable and spatter generation is low, but the excess Ti oxide remaining in the weld metal reduces low-temperature toughness. Therefore, the total _TiO2 equivalent value of Ti oxide contained in the flux should be between 3% and 8%. Furthermore, Ti oxides are added from the flux as rutile, titanium oxide, titanium slag, ilmenite, etc.

[Total Al oxide content in flux _{, converted to Al₂O₃ :} 0.02–0.3%]
Al oxides adjust the viscosity and convection of the molten slag during welding, and are particularly effective in preventing metal sagging in all-position circumferential welding. However, if the total Al oxide content (in _Al₂O₃ equivalent ₎ is less than 0.02%, metal sagging will occur, resulting in poor bead appearance and shape. On the other hand, if the total Al oxide content (in _Al₂O₃ equivalent ₎ exceeds 0.3%, excess Al oxide remains in the weld metal, reducing its low-temperature toughness. Therefore, the total Al oxide content (in _{Al₂O₃ equivalent} ) in the flux should be between 0.02% and 0.3%. Al oxides can be added from the flux using alumina, etc.

[Total _SiO2 equivalent value of Si oxide in the flux: 0.1–0.6%]
Si oxides improve slag coverage by adjusting the viscosity and convection of molten slag, and also smooth the shape of the weld bead toe. However, if the total _SiO2 equivalent value of Si oxides is less than 0.1%, slag coverage decreases, the weld bead toe becomes convex, and the weld bead appearance deteriorates. On the other hand, if the total _SiO2 equivalent value of Si oxides exceeds 0.6%, the strength of the weld metal becomes excessive, and the low-temperature toughness decreases. Therefore, the total _SiO2 equivalent value of Si oxides contained in the flux should be between 0.1% and 0.6%. Si oxides can be added from the flux using silica sand, zircon sand, sodium silicate, etc.

[Total Zr oxide content in flux (equivalent to _ZrO2) : 0.25–0.65%]
Zr oxides have the effect of adjusting the viscosity and convection of molten slag, and in particular preventing metal sagging in all-position circumferential welding. However, if the total Zr _oxide equivalent value is less than 0.25%, metal sagging will occur in all-position circumferential welding, resulting in poor bead appearance and shape. On the other hand, if the total Zr _oxide equivalent value exceeds 0.65%, slag detachability will deteriorate. Therefore, the _total Zr oxide equivalent value of Zr oxide contained in the flux should be between 0.25% and 0.65%. Zr oxides can be added from zircon sand, zirconium oxide, etc., from the flux.

[One or more of the following in the flux: Na oxide, Na fluoride, K oxide, and K fluoride: 0.05-0.2% in total, calculated as _Na₂O and _K₂O equivalents]
Na oxides, Na fluorides, K oxides, and K fluorides act as arc stabilizers and slag-forming agents. If one or more of these substances are present in the flux at a total of less than 0.05% in terms of _Na₂O equivalent and _K₂O equivalent values, the arc becomes unstable, spatter generation increases, and the bead appearance deteriorates. On the other hand, if one or more of these substances are present at a total of more than 0.2% in terms of _Na₂O equivalent and _K₂O equivalent values, slag detachability deteriorates, and the metal tends to sag during full-position circumferential welding. Therefore, the amount of one or more of these substances in the flux at a total of 0.05% to 0.2% in terms of _Na₂O equivalent and _K₂O equivalent values is set to 0.05% to 0.2%. Furthermore, sodium oxides, sodium fluorides, potassium oxides, and potassium fluorides can be _added as solid components of water glass consisting of sodium silicate _and potassium silicate, such as NaF, _Na₃AlF₆ , _K₂SiF₆ , _{and K₂ZrF₆} . While sodium silicate and similar substances are also present in the aforementioned Si oxides, new effects have been discovered by extracting the Si oxide component and the Na compound component separately and limiting the range of each component. In other words, sodium silicate and similar substances are not predominantly present in either the Si oxide or Na compound components.

[Mg in flux: 0.1–0.8%]
Mg acts as a strong deoxidizer, reducing oxygen in the weld metal and improving its low-temperature toughness. However, if the Mg content is less than 0.1%, the low-temperature toughness of the weld metal decreases. On the other hand, if the Mg content exceeds 0.8%, oxidation reactions are accelerated in the arc during welding, leading to increased spatter generation. Therefore, the Mg content in the flux should be between 0.1% and 0.8%. Mg can be added to the flux in the form of metallic Mg or alloy powders such as Al-Mg.

[Total F equivalent value of fluorine compounds in the flux: 0.05–0.25%]
Fluorine compounds have the effect of stabilizing the arc. However, if the total F equivalent value of the fluorine compounds is less than 0.05%, the arc becomes unstable. On the other hand, if the total F equivalent value of the fluorine compounds exceeds 0.25%, the arc becomes unstable and spatter generation increases. Furthermore, in all-position circumferential welding, metal dripping is more likely to occur, resulting in poor bead appearance and shape. Therefore, the total F equivalent value of the fluorine compounds contained in the flux should be between 0.05% and 0.25%. Note that fluorine compounds can be added as sodium fluoride, potassium zirconate fluoride, etc., and the F equivalent value is the sum of the F content contained in them.

[Total Bi equivalent value of one or both of the Bi and Bi oxides in the flux: 0.001–0.01%]
Bi improves the slag detachability formed on the weld metal surface. If the Bi equivalent value of either or both of Bi and Bi oxide is less than 0.001%, the effect of promoting slag detachment is insufficient, resulting in poor slag detachability and slag inclusion. On the other hand, if the Bi equivalent value of either or both of Bi and Bi oxide exceeds 0.01%, hot cracking of the weld metal becomes more likely, and low-temperature toughness decreases. Therefore, the Bi equivalent value of either or both of the Bi and Bi oxide contained in the flux should be between 0.001% and 0.01%. Note that Bi and Bi oxide are added in the form of metallic Bi or Bi oxide, etc.

The remainder of the flux-cored wire for Ar- _CO2 mixed gas shielded arc welding according to the present invention consists of Fe in the steel sheath, iron powder added for composition adjustment, Fe content of iron alloy powder such as Fe-Mn and Fe-Si alloy, and impurities. While there are no specific restrictions on impurities, from the viewpoint of preventing hot cracking and maintaining the toughness of the weld metal, it is preferable that P: 0.03% or less and S: 0.03% or less. Furthermore, while there are no specific restrictions on the flux filling rate, from the viewpoint of productivity, it is preferable that it be 8 to 20% of the total wire mass.

The flux-cored wire for Ar- _CO2 mixed gas shielded arc welding of the present invention has a structure in which a steel sheath is formed into a pipe shape and flux is filled inside. The wires can be broadly classified into two types: wires with no seams in the steel sheath, which are obtained by welding the joints of the formed steel sheaths, and wires with seams in the steel sheath, which are obtained by not welding the joints of the steel sheaths. In the present invention, either cross-sectional structure of wire can be used, but wires with no seams in the steel sheath are more preferable because they allow for heat treatment aimed at reducing the total amount of hydrogen in the wire, and because there is no moisture absorption of flux after manufacturing, the amount of diffusible hydrogen in the weld metal can be reduced, thereby improving resistance to low-temperature cracking.

The effects of the present invention will be specifically described below with reference to examples.

First, using SPCC as specified in JIS G 3141:2017, a steel sheath was formed into a U-shape during the molding process. After welding the seams of the steel sheaths, a seamless wire was produced by pipe manufacturing and drawing, resulting in prototype flux-cored wires with various components shown in Table 1. The wire diameter was 1.2 mm. The flux filling rate was 10-18%.

Using the prototype flux-cored wire shown in Table 1, the weldability and mechanical properties of the weld metal were evaluated in circumferential welding of steel pipes in all positions.

The weld metal test was performed after automatic welding of steel pipes, using steel pipes specified in JIS G 3106:2015 with the groove shape shown in Figure 1, under the welding conditions shown in Table 2.

The welding workability was assessed visually during automatic steel pipe welding, evaluating arc stability, spatter generation, bead appearance and shape, slag detachability, and the presence or absence of molten metal drip. The presence or absence of weld cracks was also investigated.

(Arc stability)
It is preferable that there is little variation in the arc length generated between the wire tip and the base material during welding. Low variation in arc length was defined as stable, and high variation as unstable. Arc stability was judged visually during automatic steel pipe welding.

(Spatter occurrence status)
It is preferable to have a low amount of spatter generated during welding. A low amount of spatter generated during welding was considered good, and a high amount of spatter generated was considered poor. The spatter generation status was judged visually during automatic welding of steel pipes.

(Bead shape and appearance)
It is preferable that the weld metal bead height is flat and the bead width is uniform. A bead shape with a flat bead height and uniform bead width was considered good, while a bead shape with a high bead height, a convex shape, and an uneven bead width was considered poor. In terms of bead appearance, a uniform appearance without partial wave irregularities was considered good. The bead shape and appearance were judged visually during automatic welding of steel pipes.

(Slag detachability)
After welding, when the slag formed on the bead surface was struck with a chipping hammer, it was considered good if the slag cracked and could then be easily removed.

(Metal drip)
During welding, if no molten metal dripped from the molten body, it was recorded as "none," and if molten metal dripped, it was recorded as "yes." The presence or absence of metal dripping was visually judged during each pass of welding.

(Weld crack)
During automatic welding of steel pipes, if even one hot crack was observed on the bead surface, it was classified as "present." The presence or absence of hot cracks was visually determined after each pass of welding.

(Welding defects)
Before taking mechanical test specimens, welding defects such as slag inclusion were assessed by radiographic testing as specified in JIS Z 3104:1995 to determine the presence or absence of welding defects.

(mechanical properties)
Mechanical testing of the weld metal was performed in accordance with JIS Z 3111:2005, by taking tensile and impact test specimens from the center of the plate thickness direction. Toughness was evaluated using a Charpy impact test at -60°C, with an average absorbed energy of 60 J or higher for each of the three repeated tests considered good. For tensile testing, a tensile strength of 650-750 MPa was considered good. These results are summarized in Table 3.

Wire symbols W1 to W16 in Tables 1 and 3 represent examples of the present invention, while wire symbols W17 to W38 represent comparative examples. Wire symbols W1 to W16, which are examples of the present invention, show extremely satisfactory results, such as stable arcs in all _- position circumferential welding _{with low} spatter generation, _{good bead} appearance _and shape, good _slag detachability, no metal dripping, no weld cracks, no welding defects, and good values for the tensile strength and absorbed energy of the weld metal in the weld metal test.

In the comparative example, wire symbol W17 had a low carbon content, resulting in low tensile strength of the weld metal. Furthermore, the total _TiO2 equivalent value of the Ti oxide was low, leading to a low absorbed energy of the weld metal. Additionally, the arc was unstable, resulting in high spatter generation and poor bead appearance and shape.

Wire symbol W18 had a high carbon content, resulting in high tensile strength of the weld metal and low absorbed energy. However, the low total Al oxide equivalent value ( _{Al₂O₃ )} led to poor bead appearance and shape, as well as metal sagging.

Wire symbol W19 had a low Si content, resulting in poor bead appearance and shape.

Wire symbol W20 had a high Si content, resulting in high tensile strength of the weld metal and low absorbed energy. However, the low total Zr oxide equivalent value ( _ZrO2) led to poor bead appearance and shape, as well as metal sagging.

Wire symbol W21 had a low manganese content, resulting in low absorbed energy of the weld metal and poor bead appearance and shape. Furthermore, the high total Zr oxide content (equivalent to _ZrO2) resulted in poor slag release properties.

Wire symbol W22 had a high manganese content, resulting in high tensile strength of the weld metal and low absorbed energy. However, the combined values of _Na₂O and _K₂O were low, leading to an unstable arc, high spatter generation, and poor bead appearance and shape.

Wire symbol W23 had a low Cu content, resulting in low tensile strength of the weld metal and low absorbed energy. Furthermore, the high sum of _Na₂O and _K₂O equivalent values led to poor slag release and metal sagging.

Wire symbol W24, due to its high Cu content, exhibited high tensile strength in the weld metal and low absorbed energy. However, its high Mg content resulted in a large amount of spatter generation.

Wire symbol W25 had a low Ni content, resulting in a low absorbed energy of the weld metal. Furthermore, the low total F equivalent value of the fluorine compounds led to an unstable arc.

Wire symbol W26 has a high Ni content, resulting in hot cracking of the weld metal. Furthermore, the high total F equivalent value of the fluorine compounds led to an unstable arc, excessive spatter, poor bead appearance and shape, and metal sagging.

Wire symbol W27 had a low Ti content, resulting in a low absorbed energy of the weld metal. Furthermore, the combined Bi equivalent value of either Bi or Bi oxide was low, leading to poor slag release and slag inclusion.

Wire symbol W28 had a high Ti content, resulting in high tensile strength of the weld metal and low absorbed energy. However, the total _SiO2 equivalent value of Si oxide was low, resulting in poor bead appearance and shape.

Wire symbol W29 had a low B value, resulting in a low absorbed energy of the weld metal.

Wire symbol W30 has a high proportion of B, resulting in a low energy absorption value for the weld metal and the occurrence of hot cracking.

Wire symbol W31 had a high Al content, resulting in a low absorbed energy of the weld metal.

Wire symbol W32 had a low tensile strength in the weld metal because the sum of Nb and/or V was low.

Wire symbol W33 had a high sum of either Nb or V, resulting in a low absorbed energy of the weld metal.

Wire symbol W34 had a high total value of Ti oxides converted to _TiO2 , resulting in a low absorbed energy of the weld metal.

Wire symbol W35 had a high total Al oxide equivalent value ( _{Al₂O₃ )} , resulting in a low absorbed energy of the weld metal.

Wire symbol W36 has a high total _SiO2 equivalent value for Si oxide, resulting in high tensile strength of the weld metal and low absorbed energy.

Wire symbol W37 had a low Mg content, resulting in a low absorbed energy of the weld metal.

Wire symbol W38 indicates a high sum of Bi equivalent values for either Bi or Bi oxide, resulting in a low absorbed energy in the weld metal and the formation of cracks in the weld metal.

Claims (1)

In a flux-cored wire for Ar- _CO2 mixed gas shielded arc welding, which has a steel outer sheath filled with flux,
As a mass percentage of the total wire mass, the sum of the steel sheath and flux,
C: 0.03-0.08%,
Si: 0.1-0.6%,
Mn: 1.5-2.8%,
Cu: 0.01 to 0.5%,
Ni: 0.5-1.5%,
Ti: 0.05-0.25%,
B: Contains 0.002 to 0.015%,
Al: 0.05% or less,
The total amount of Nb and V, or either one or both, is 0.01 to 0.1%.
Furthermore, in mass % of the total wire mass, the flux contains
Total Ti oxide equivalent value: _3-8 %
Total Al oxide content in _{Al₂O₃ equivalent} : 0.02–0.3%
Total _SiO2 equivalent value of Si oxide: 0.1–0.6%
Total Zr oxide content in _ZrO2 equivalent: 0.25–0.65%
One or more of the following: sodium oxides, sodium fluorides, potassium oxides, and potassium fluorides: 0.05 to 0.2% in total, based on the values of _Na₂O and _K₂O .
Mg: 0.1-0.8%,
Total F equivalent value of fluorine compounds: 0.05–0.25%
The total Bi equivalent value of either or both Bi and Bi oxides contains 0.001 to 0.01%.
Ar- _CO2 mixed gas shielded arc welding flux-cored wire, characterized in that the remainder consists of Fe from the steel outer sheath, iron powder, Fe content from iron alloy powder, and impurities.