JP2022143059A - Flux-cored wire for gas-shielded arc welding - Google Patents

Abstract

To provide a flux-cored wire for gas-shielded arc welding that gives a weld metal having good mechanical properties, generates stable arc, and is excellent in welding workability even when welding is performed under low heat input welding conditions and high-efficiency welding conditions such as high heat input and high interpass temperature.SOLUTION: A flux-cored wire for gas-shielded arc welding in which a steel outer skin is filled with flux, contains C: 0.04 to 0.10%, Si: 0.4 to 1.4%, Mn: 2.5 to 3.6%, Mo: 0.2 to less than 0.6%, Cu: 0.05 to 0.5%, Ti: 0.1 to 0.4%, and B: 0.0015 to 0.010% in mass % in terms of the total mass of the wire in the total of the steel outer skin and the flux, and further contains a total F conversion value: 0.005 to 0.10%, a total SiO2 conversion value: 0.01 to 0.2%, and a total of Na2O conversion value and K2O conversion value: 0.02 to 0.14% in mass % in terms of the total mass of the wire in the flux.SELECTED DRAWING: None

Description

The present invention can obtain a weld metal having good mechanical properties even when welding is performed under high-efficiency welding conditions, from low heat input welding conditions to high heat input and high interpass temperatures. The present invention relates to a flux-cored wire for gas-shielded arc welding, which has a stable arc, less spatter generation, and excellent welding workability even in welding.

Gas-shielded arc welding using a solid wire is frequently used as a highly efficient welding method for steel structures in the fields of shipbuilding and building steel frames. The applied welding conditions are high current and high heat input welding of 30 to 40 kJ/cm. Furthermore, if the time of each welding pass is shortened and welding is to be performed as continuously as possible, the temperature between passes becomes high. In recent years, in order to further improve welding efficiency, there is a shift to welding at a high heat input and high interpass temperature exceeding 40 kJ/cm, but it is necessary for the weld metal to have a predetermined strength and toughness. However, when welding is performed at such a high heat input and high interpass temperature, the mechanical properties of the weld metal tend to deteriorate, making it impossible to obtain sound welded joints, and using a solid wire for gas-shielded arc welding. Welding with a high current generates a large amount of spatter, which causes a problem that welding workability is remarkably deteriorated.

As a means to solve these problems, Ti-B welding consumables have been proposed as solid wires for welding that can produce weld metals with excellent mechanical properties in welding at high heat input and high interpass temperature. Some have been done. For example, Patent Document 1 proposes a welding solid wire containing one or more of C, Si, Mn, Ti and Mg or Al, and containing predetermined amounts of B, Cu, Ni, Cr, and Mo. .

Further, Patent Document 2 contains C, Si, Mn, Ti, Al, Cu, Mo, B, further contains a predetermined amount of Ni, limits N to a certain amount or less, and further contains a predetermined amount of K A solid wire for welding has been proposed. However, when the welding solid wires disclosed in Patent Documents 1 and 2 are welded under high heat input and high interpass welding conditions with a welding heat input of up to 40 kj/cm, the strength and toughness of the weld metal are Although excellent properties can be obtained, in the case of welding conditions with a low heat input of about 20 kJ/cm such as horizontal position welding, the weld metal has excessive strength and cannot satisfy the predetermined mechanical properties.

Further, in Patent Document 3, by containing appropriate amounts of C, Si, Mn, Mo, Ti, B, Cu, Ni, and Cr, welding from low heat input to high heat input and high interpass temperature can be performed. There is a disclosure of a solid wire for welding that provides the strength and toughness of the weld metal. However, even with the solid wire for welding disclosed in Patent Document 3, under welding conditions of a large heat input exceeding 40 kJ/cm and a high temperature between passes, the strength and toughness of the weld metal cannot be obtained. However, there is a problem that the amount of spatter generated increases at times.

A solid wire for gas-shielded arc welding that generates less spatter, which is a problem in welding at high current, has been developed. A technique is disclosed in which the amount of spatter generated is reduced and the wire feedability is improved by providing a liquid lubricant film on the outer peripheral surface of the solid lubricant.

In addition, Patent Document 5 discloses a solid wire for gas shielded arc welding that can reduce the amount of spatter generated by forming an alkali metal-impregnated portion impregnated with two or more types of alkali metals under the wire surface layer. there is However, high-current welding using a solid wire for gas-shielded arc welding generates a large amount of spatter itself. There was also a problem that the shape could not be improved.

On the other hand, as a flux-cored wire for gas-shielded arc welding that ensures good welding workability while ensuring the strength and toughness of the weld metal under welding conditions of large heat input and high interpass temperature, for example, Patent Document 6 and Patent Document 7 discloses a flux-cored wire that provides good welding workability and weld metal with excellent mechanical properties under welding conditions of high heat input and high interpass temperature. However, even with these flux-cored wires, there is a problem that the strength and toughness of the weld metal cannot be obtained under welding conditions of a high heat input exceeding 40 kJ/cm and a high temperature between passes. In addition, the latter method has a problem that welding defects such as slag entrainment are likely to occur because the amount of slag generated increases.

JP 2008-142726 A JP-A-2004-237361 Japanese Patent Application Laid-Open No. 2003-136281 JP 2005-169415 A JP 2009-255142 A JP-A-2005-279683 JP 2015-205303 A

Therefore, the present invention has been devised in view of the above-mentioned problems, and the welding conditions of a low heat input of about 20 kJ/cm are changed to a high heat input of 60 kJ/cm and a high interpass temperature. It is possible to obtain weld metal with good mechanical properties without welding defects even if welding is performed under highly efficient welding conditions such as , and the arc is stable even in high-current welding, and the amount of spatter generation is reduced. An object of the present invention is to provide a flux-cored wire for gas-shielded arc welding which is less and excellent in welding workability.

The present inventors have found that even if welding is performed under highly efficient welding conditions such as a low heat input welding heat input of about 20 kJ / cm to a large heat input of 60 kJ / cm and a high interpass temperature. A flux for gas-shielded arc welding that can obtain weld metal with good mechanical properties without welding defects, and has excellent welding workability such as a stable arc and little spatter even in high-current welding. The component composition of the cored wire was investigated in detail.

As a result, welding defects occur even under low heat input welding conditions of about 20 kJ/cm, high current welding conditions, and high heat input and high interpass temperature welding conditions of 60 kJ/cm. In order to achieve proper strength and stable toughness of the weld metal, it is necessary to reduce oxides, which are slag-forming agents, in the wire as much as possible, and to It was found that the transformation is effective.

In addition, by setting the amounts of Mo and B in the wire to appropriate amounts, even under the welding conditions of a large welding heat input of 60 kJ/cm and a high temperature between passes, the toughness of the weld metal is not lowered and a predetermined tensile strength can be achieved. It has been found that a weld metal having strength can be obtained.

Furthermore, it was found that the toughness of the weld metal can be further improved by adjusting the amounts of Al and Mg in the wire.

Welding workability is determined by adjusting the sum of the F conversion values of C, Ti, and metal fluorides and the sum of the Na oxide and K oxide conversion values of Na ₂ O and K ₂ O to an appropriate amount. It was found that the appearance and shape of the bead can be improved by stabilizing and reducing the amount of spatter generated and by adjusting the total amount of Si oxide equivalent to SiO ₂ to an appropriate amount.

That is, the gist of the present invention is that (1) in a flux-cored wire for gas-shielded arc welding in which a steel sheath is filled with flux, the total mass of the steel sheath and flux is C: 0.04-0.10%, Si: 0.4-1.4%, Mn: 2.5-3.6%, Mo: 0.2-0.6%, Cu: 0.05-0 .5%, Ti: 0.1 to 0.4%, B: 0.0015 to 0.010%, and further, in mass% with respect to the total mass of the wire, metal fluoride: F conversion value in the flux 0.005 to 0.10% in total, Si oxide: 0.01 to 0.2% in total converted to SiO ₂ , one or more of Na oxide and K oxide: Na ₂ O It contains 0.02 to 0.14% in total of the converted value and the K ₂ O converted value, and the balance consists of Fe in the steel outer shell, iron powder added for component adjustment, Fe content in iron alloy powder, and impurities. It is characterized by

(2) The sum of one or both of Al and Mg in terms of mass % with respect to the total mass of the wire, the sum of the steel sheath and the flux: 0.25% or less according to (1) Flux-cored wire for gas-shielded arc welding.

According to the flux-cored wire for gas shielded arc welding of the present invention, high efficiency such as high interpass temperature can be achieved from welding conditions with a low heat input of about 20 kJ / cm to a large heat input of 60 kJ / cm. It is possible to obtain a weld metal with good mechanical properties without welding defects even if welding is performed under the welding conditions of , and the arc is stable even with high current welding, the amount of spatter is small, and the appearance of the bead is improved.・It is possible to obtain high-quality welds with high efficiency, such as excellent welding workability such as good shape.

Hereinafter, the component composition and content of the flux-cored wire for gas-shielded arc welding to which the present invention is applied, and the reasons for limiting each component composition will be described. In addition, content of each component composition shall be represented by mass %, and the description regarding the mass % shall be simply described as %.

(First embodiment)
[Total C of steel skin and flux: 0.04 to 0.10%]
C has the effect of improving the strength of the weld metal. If C is less than 0.04%, sufficient strength of the weld metal cannot be obtained under welding conditions of high heat input and high temperature between passes. On the other hand, if C exceeds 0.10%, the strength of the weld metal increases and the toughness decreases. Therefore, the total content of C in the steel skin and flux should be 0.04 to 0.10%. C can be added from metal powder, alloy powder, etc. from the flux, in addition to the components contained in the steel outer sheath.

[Si: 0.4 to 1.4% in total of steel skin and flux]
Si is a deoxidizing agent and adjusts the amount of oxygen in the weld metal. Si also has the effect of improving the strength of the weld metal. If the Si content is less than 0.4%, deoxidation will be insufficient, resulting in low strength and toughness of the weld metal. On the other hand, if Si exceeds 1.4%, the strength of the weld metal becomes excessively high, and toughness cannot be stably obtained. On the other hand, if the Si content exceeds 1.4%, the amount of slag generated during welding increases, and welding defects such as slag entrainment tend to occur. Therefore, the total Si content of the steel sheath and flux should be 0.4 to 1.4%. Si can be added from metal Si, Fe--Si, Fe--Si--Mn and other alloy powders from the flux, in addition to the components contained in the steel outer sheath.

[Total Mn of steel skin and flux: 2.5 to 3.6%]
Mn has the effect of improving the toughness and strength of the weld metal under welding conditions of high heat input and high interpass temperature. If the Mn content is less than 2.5%, the strength of the weld metal is low and the toughness is low under the welding conditions of high heat input and high temperature between passes. On the other hand, if the Mn content exceeds 3.6%, the strength of the weld metal increases with low heat input welding, and toughness cannot be stably obtained. Moreover, when Mn exceeds 3.6%, the amount of slag generated during welding increases, and welding defects such as slag entrainment tend to occur. Therefore, Mn is set to 2.5 to 3.6% in total of the steel sheath and flux. Mn can be added from alloy powder such as metallic Mn, Fe--Mn, Fe--Si--Mn, etc., in addition to components contained in the steel outer shell.

[Total Mo of steel skin and flux: 0.2 to less than 0.6%]
Mo is important for ensuring the strength of the weld metal under the welding conditions of high heat input and high temperature between passes when Mn is in the range described above. If Mo is less than 0.2%, the strength of the weld metal will be low under welding conditions of high heat input and high temperature between passes. On the other hand, when the Mo content is 0.6% or more, the strength of the weld metal becomes excessively high under low heat input welding conditions, and toughness cannot be stably obtained. Therefore, the total content of Mo in the steel sheath and flux should be 0.2 to less than 0.6%. In addition, Mo can be added from the metal Mo powder from flux other than the component contained in steel outer coverings.

[Cu: 0.05 to 0.5% in total of steel skin and flux]
Cu has a precipitation strengthening action, lowers the transformation temperature, refines the structure of the weld metal, and stabilizes toughness. If Cu is less than 0.05%, this effect cannot be obtained, and stable toughness of the weld metal cannot be obtained. On the other hand, when Cu exceeds 0.5%, precipitation embrittlement occurs, the toughness of the weld metal is lowered, and hot cracking is likely to occur. Therefore, Cu is set to 0.05 to 0.5% in the total of the steel sheath and the flux. Cu can be added from metal Cu from flux, alloy powder such as Fe--Si--Cu, in addition to components contained in the steel skin and Cu plating applied to the surface of the steel skin.

[Total Ti of steel skin and flux: 0.1 to 0.4%]
Ti stabilizes the arc and acts as a deoxidizing agent, especially during high-current welding and welding at high heat input and high interpass temperature, and produces fine oxides of Ti in the weld metal. has the effect of further improving the toughness of If Ti is less than 0.1%, this effect cannot be obtained, and the arc becomes unstable and the toughness of the weld metal decreases during welding at high current and high heat input and high interpass temperature. do. On the other hand, if Ti exceeds 0.4%, the amount of precipitates of Ti increases in the weld metal and the toughness decreases. Therefore, Ti is set to 0.1 to 0.4% in total of the steel outer covering and the flux. In addition to the components contained in the steel outer shell, Ti can be added from metal Ti from flux, alloy powder such as Fe—Ti, and the like.

[Total B of steel skin and flux: 0.0015 to 0.010%]
B has the effect of suppressing the formation of intergranular ferrite formed at the grain boundaries of the weld metal under welding conditions of high heat input and high interpass temperature, thereby improving the toughness. When the B content is less than 0.0015%, the toughness of the weld metal is lowered under welding conditions of high heat input and high interpass temperature. On the other hand, when B exceeds 0.010%, hot cracking is likely to occur. Therefore, B is set to 0.0015 to 0.010% in total of the steel skin and the flux. B can be added from alloy powders such as Fe--Si--B and Fe--Mn--B in addition to components contained in the steel outer shell.

[Metal fluoride in flux: total F conversion value: 0.005 to 0.10%]
Metal fluoride has the effect of concentrating and stabilizing the arc. If the total F conversion value of the metal fluorides is less than 0.005%, this effect cannot be obtained, the arc becomes unstable, and the amount of spatter generation increases. On the other hand, if the total F conversion value of the metal fluoride exceeds 0.10%, the arc becomes strong and unstable, and the amount of spatter generation increases. Therefore, the total F conversion value of the metal fluorides contained in the flux should be 0.005 to 0.10%. In addition, the metal fluoride can be added from CaF ₂ , NaF, LiF, MgF ₂ , K ₂ SiF ₆ , Na ₃ AlF ₆ , AlF ₃ etc. from the flux, and the F conversion value is the content of F contained in them is the sum of

[Si oxide in flux: total _SiO2 conversion value: 0.01 to 0.2%]
The Si oxide in the flux has the effect of increasing the viscosity of the molten slag, improving the slag enveloping property, improving the conformability of the bead toe, and improving the bead appearance and shape. If the total SiO ₂ equivalent value of Si oxides is less than 0.01%, the conformability of the toe of the weld bead is poor, and the appearance and shape of the bead are poor. On the other hand, if the total _SiO2 conversion value of Si oxides exceeds 0.2%, the amount of oxygen in the weld metal increases and the toughness decreases. Also, if the total SiO ₂ conversion value of Si oxides exceeds 0.2%, the amount of slag increases, and welding defects such as slag entrainment tend to occur. Therefore, the total SiO ₂ conversion value of Si oxides contained in the flux should be 0.01 to 0.2%. The Si oxide can be added from silica sand, orthoclase, solid components of water glass composed of potassium silicate, etc. from the flux.

[One or more of Na oxide and K oxide in flux: 0.02 to 0.14% in total of Na ₂ O conversion value and K ₂ O conversion value]
Na oxide and K oxide have the effect of stabilizing the arc. When one or more of Na oxide and K oxide is less than 0.02% in total of Na ₂ O conversion value and K ₂ O conversion value, the arc becomes unstable and the amount of spatter generation is large. Become. On the other hand, when one or more of Na oxide and K oxide exceeds 0.14% in total of Na ₂ O conversion value and K ₂ O conversion value, the arc becomes unstable and the amount of spatter generation increases. . In addition, when one or more of Na oxide and K oxide exceeds 0.14% in total of Na ₂ O conversion value and K ₂ O conversion value, the amount of slag generated during welding increases, and slag Welding defects such as entrainment are more likely to occur. Therefore, one or more of Na oxides and K oxides contained in the flux should be 0.02 to 0.14% in terms of Na ₂ O and K ₂ O equivalents. Na oxides and K oxides can be added from solid components of water glass composed of sodium silicate and potassium silicate, powders of potassium feldspar, sodium titanate and the like.

The remainder of the flux-cored wire for gas-shielded arc welding of the present invention is Fe in the steel outer sheath, iron powder added for component adjustment, and Fe in iron alloy powder such as Fe—Si, Fe—Mn, and Fe—Ti alloy. and impurities. Impurities are not particularly specified, but from the viewpoint of hot cracking and weld metal toughness, P: 0.03% or less and S: 0.03% or less are preferable.

Although the flux filling rate is not particularly limited, it is preferably 8 to 20% with respect to the total mass of the wire from the viewpoint of productivity.

(Second embodiment)
By further including one or both of Al and Mg in the first embodiment, the toughness of the weld metal can be further improved.

[One or both of Al and Mg in total of steel skin and flux: 0.25% or less]
Al and Mg are strong deoxidizers and have the effect of reducing oxygen in the weld metal and increasing the toughness of the weld metal. However, if one or both of Al and Mg exceeds 0.25%, a violent oxidation reaction occurs in the arc during welding, resulting in a large amount of fume generation and spatter generation. Therefore, one or both of Al and Mg in the total of the steel skin and flux should be 0.25% or less. In order to obtain the effect of reducing oxygen in the weld metal and increasing the toughness of the weld metal, one or both of Al and Mg are preferably 0.05% or more. Al and Mg can be added from alloy powders such as metallic Al, Fe--Al, metallic Mg, and Al--Mg.

Hereinafter, the effects of the first embodiment and the second embodiment of the present invention will be specifically described with reference to examples.

First, JIS G3141 SPHC (C: 0.02% by mass, Si: 0.01% by mass, Mn: 0.40% by mass, P: 0.012% by mass, S: 0.010% by mass) was applied to the steel outer skin. is used to form the steel skin into a U shape, fill it with a flux filling rate of 10 to 15%, and form it into a C shape. Experimental flux-cored wires of various components shown in 1 were produced. The wire diameter of the prototype was 1.4 mm.

Using the prototype flux-cored wires shown in Table 1, spatter generation, arc stability, bead appearance/shape, presence or absence of defects by X-ray transmission test, and weld metal performance were investigated.

The amount of spatter generated was determined as a value per unit time (g/min) by measuring the weight of spatter generated when welding for 1 minute using a collection box made of copper. Sputtering was measured under condition No. 1 shown in Table 2. The average value of 5 measurements under the welding conditions of T1, and 1.5 g/min or less was considered good.

Arc stability is evaluated through continuous measurement of welding voltage fluctuation during welding and the magnitude of the fluctuation. When ±1 V with respect to the average voltage was used as a threshold, the arc was considered stable when the voltage fluctuation exceeded the threshold for less than 90% of the measurement time. On the other hand, when the voltage fluctuation exceeded the threshold for more than 10% of the measurement time, the arc was considered unstable.

The bead appearance and shape of the bead was judged to be good if there were no undercuts or overlaps that required repair at the weld bead sound part. The appearance of the bead was judged to be good when the waveforms were uniform without any partial turbulence.

Welding workability and weld metal performance were evaluated under condition No. 1 shown in Table 2. T2 (hereinafter referred to as low heat input) and condition No. Under the construction conditions of T3 (hereinafter referred to as between high heat input and high pass), a multi-layer weld metal test was performed using a test piece with a 35 ° L-shaped groove and a root gap of 7 mm with a backing metal. Arc stability and bead appearance/shape were investigated. After the welding was completed, the backing metal was removed and an X-ray transmission test was performed. In the X-ray transmission test, the test was performed based on the radiographic test method for steel welded joints shown in JIS Z 3104: 1995, and when no flaw was generated, it was regarded as no defect. Also, a tensile test piece (JIS Z2201 No. AO) and an impact test piece (JIS Z2202 No. 4) were taken from the welded metal portion to investigate the mechanical properties.

For evaluation of strength, tensile strength was 490 to 690 MPa, and for evaluation of toughness, five Charpy impact tests at 0°C were performed, and an average absorbed energy of 80 J or more and a minimum value of 60 J or more were considered good. These results are summarized in Table 3.

Wire symbols W1 to W10 in Tables 1 and 3 are examples of the present invention, and wire symbols W11 to W22 are comparative examples. The wire symbols W1 to W10, which are examples of the present invention, have appropriate amounts of C, Si, Mn, Mo, Cu, Ti, and B in the flux-cored wire, and the sum of the F conversion values of the metal fluorides in the flux, Since the sum of the SiO ₂ conversion values of Si oxides and the sum of Na ₂ O conversion values and K ₂ O conversion values of one or more of Na oxides and K oxides is appropriate, the amount of spatter generation is small. , Under both low and high heat input and high interpass temperature welding conditions, the arc is stable, the bead appearance and shape are good, there are no weld defects, the tensile strength of the weld metal and the average value of absorbed energy and Both lowest values were good.

Wire symbols W2, W5, W6, and W10, in which the total amount of one or both of Al and Mg is appropriate, are the average values of the absorbed energy of the weld metal under the welding conditions of low heat input and high heat input/high interpass temperature. of 100 J or more was obtained, which was an extremely satisfactory result.

In the comparative example, wire symbol W11 had a small amount of C, so the tensile strength of the weld metal was low under the welding conditions of large heat input and high temperature between passes. In addition, since the amount of Ti was small, the arc was unstable under the welding conditions of large heat input and high temperature between passes, and the absorbed energy of the weld metal was low. Furthermore, since the total amount of one or both of Al and Mg was large, a large amount of spatter was generated, and a large amount of fumes was also generated.

Since wire symbol W12 has a large amount of C, the tensile strength of the weld metal is high and the absorbed energy is low under both low heat input and high heat input/high interpass temperature welding conditions. In addition, since the total F-converted value of the metal fluorides was small, the amount of spatter generated was large, and the arc was unstable under both low heat input and high heat input/high interpass temperature welding conditions.

Wire symbol W13 has a small amount of Si, so the tensile strength and absorbed energy of the weld metal are low under both low heat input and high heat input/high interpass temperature welding conditions. In addition, since the amount of B was large, hot cracks occurred in the first layer under the welding conditions of low heat input and high heat input/high temperature between passes.

Wire symbol W14 contains a large amount of Si, so slag entrainment occurs under both low heat input and high heat input/high interpass temperature welding conditions, and the tensile strength of the weld metal is high and the absorbed energy is low. In addition, since the total F conversion value of metal fluorides is large, the amount of spatter generated is large, and the arc is strong and unstable under both low heat input and high heat input/high interpass temperature welding conditions.

Wire symbol W15 had a small amount of Mn, so the tensile strength and absorbed energy of the weld metal under the welding conditions of large heat input and high temperature between passes were low. In addition, since the total _SiO2 equivalent value of Si oxide is small, the weld bead toe has poor conformability under both low heat input and high heat input/high interpass temperature welding conditions, resulting in poor bead appearance and shape. rice field.

Wire symbol W16 had a large amount of Mn, so the tensile strength of the weld metal was high under low heat input welding conditions, and the minimum value of absorbed energy was low. In addition, since the Mn content was large, slag entrainment occurred under both low heat input and high heat input/high interpass temperature welding conditions. Furthermore, since the sum of the Na ₂ O conversion value and the K ₂ O conversion value of one or more of Na oxide and K oxide is small, the amount of spatter generation is large, low heat input and high heat input/high pass The arc was unstable under both welding conditions of medium temperature.

Wire symbol W17 had a low Mo content, so the tensile strength of the weld metal was low under the welding conditions of large heat input and high temperature between passes. In addition, since the amount of Ti is large, the absorbed energy of the weld metal is low under both low heat input and high heat input/high interpass temperature welding conditions.

Wire symbol W18 had a large amount of Mo, so the tensile strength of the weld metal was high under low heat input welding conditions, and the minimum value of absorbed energy was low. In addition, since the sum of the Na ₂ O conversion value and the K ₂ O conversion value of one or more of Na oxide and K oxide is large, the amount of spatter generation is large, low heat input and high heat input/high pass The arc was unstable under both low and medium temperature welding conditions, and slag entrainment occurred.

With the wire symbol W19, the Cu content was small, so the minimum value of the absorbed energy of the weld metal was low under both low heat input and high heat input/high interpass temperature welding conditions.

Wire symbol W20 has a large amount of Cu, so hot cracks occur in the first layer under both low heat input and high heat input/high interpass temperature welding conditions, and the absorbed energy of the weld metal is low. Also, since the total amount of Al and Mg was small, the effect of improving the absorbed energy was not obtained.

Since wire symbol W21 has a small amount of B, the absorbed energy of the weld metal is low under the welding conditions of large heat input and high temperature between passes.

Wire symbol W22 has a large total _SiO2 equivalent value of Si oxide, so slag entrainment occurs under both low heat input and high heat input/high interpass temperature welding conditions, and the absorbed energy of the weld metal is low. rice field.

Claims (2)

A flux-cored wire for gas-shielded arc welding in which a steel sheath is filled with flux,
% by mass of the total mass of the wire, the sum of the steel sheath and flux,
C: 0.04 to 0.10%,
Si: 0.4 to 1.4%,
Mn: 2.5-3.6%,
Mo: less than 0.2 to 0.6%,
Cu: 0.05-0.5%,
Ti: 0.1 to 0.4%,
B: contains 0.0015 to 0.010%,
In addition, in mass % with respect to the total mass of the wire, in the flux,
Metal fluoride: 0.005 to 0.10% in total F conversion value,
Si oxide: 0.01 to 0.2% in total in terms of _SiO2 ,
One or more of Na oxide and K oxide: 0.02 to 0.14% in total of Na ₂ O conversion value and K ₂ O conversion value,
1. A flux-cored wire for gas-shielded arc welding, wherein the balance consists of Fe in the steel outer sheath, iron powder added for component adjustment, Fe content in the iron alloy powder, and impurities. % by mass of the total mass of the wire, the sum of the steel sheath and flux,
The flux-cored wire for gas-shielded arc welding according to claim 1, further containing 0.25% or less of the total of one or both of Al and Mg.