Flux-cored wire for gas-shielded arc welding

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

[Technical Field]

[0001] The present invention relates to a flux-cored wire for gas-shielded arc welding that can produce weld metal with good mechanical properties even when welding under conditions ranging from low heat input to high-efficiency welding conditions of high heat input and high interpass temperatures, and that produces a stable arc even when welding with a high current, with little spatter and excellent welding workability. [Background technology]

[0002] In fields such as shipbuilding and steel construction, gas-shielded arc welding (GAW) using solid wires is widely used as a highly efficient welding method for steel structures. The welding conditions typically require high currents and high heat inputs of 30–40 kJ / cm. Furthermore, shortening the time between each welding pass and attempting to weld continuously results in high interpass temperatures. In recent years, to further improve welding efficiency, there has been a shift toward welding with high heat inputs exceeding 40 kJ / cm and high interpass temperatures. However, the weld metal must still possess a certain level of strength and toughness. However, welding with such high heat inputs and high interpass temperatures tends to degrade the mechanical properties of the weld metal, resulting in poor weld joint quality. Furthermore, welding with high currents using GAW solid wires also generates a large amount of spatter, significantly degrading welding workability.

[0003] As a means for solving these problems, several Ti-B based welding materials have been proposed as solid welding wires that can produce weld metals with excellent mechanical properties in welding with large heat inputs and high interpass temperatures. For example, Patent Document 1 proposes a solid welding wire that contains C, Si, Mn, Ti, and one or more of Mg and Al, and also contains predetermined amounts of B, Cu, Ni, Cr, and Mo.

[0004] Furthermore, Patent Document 2 proposes a welding solid wire containing C, Si, Mn, Ti, Al, Cu, Mo, and B, further containing a predetermined amount of Ni, limiting N to a certain amount or less, and further containing a predetermined amount of K. However, while the welding solid wires disclosed in Patent Documents 1 and 2 can obtain weld metals with excellent strength and toughness when welded under high heat input and high interpass welding conditions with a welding heat input of up to 40 kJ / cm, under low heat input welding conditions with a welding heat input of about 20 kJ / cm, such as horizontal position welding, the weld metals cannot satisfy predetermined mechanical properties, such as excessive strength.

[0005] Furthermore, Patent Document 3 discloses a welding solid wire that contains appropriate amounts of C, Si, Mn, Mo, Ti, B, Cu, Ni, and Cr, thereby ensuring strength and toughness of the weld metal even when welding is performed with low to high heat input and high interpass temperatures. However, even the welding solid wire disclosed in Patent Document 3 has the problem that, under welding conditions with a high heat input and high interpass temperatures, where the welding heat input exceeds 40 kJ / cm, the strength and toughness of the weld metal cannot be obtained, and the amount of spatter generated during welding increases.

[0006] Solid wires for gas-shielded arc welding that generate less spatter, which is a problem in high-current welding, have been developed. For example, Patent Document 4 discloses a technology that contains rare earth elements, has a solid lubricant on the wire surface, and further has a liquid lubricant coating on the outer circumferential surface of the solid lubricant, thereby reducing the amount of spatter generated and improving wire feedability.

[0007] Furthermore, 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, beneath the wire surface. However, in high-current welding using a solid wire for gas-shielded arc welding, a large amount of spatter is generated, so even if wire feedability is improved, the amount of spatter generated cannot be sufficiently reduced, and the bead appearance and shape cannot be improved.

[0008] On the other hand, as a flux-cored wire for gas-shielded arc welding that ensures the strength and toughness of the weld metal under welding conditions of high heat input and high interpass temperatures while providing good welding workability, Patent Documents 6 and 7, for example, disclose flux-cored wires that provide good welding workability under welding conditions of high heat input and high interpass temperatures and that produce weld metal with excellent mechanical properties. However, even these flux-cored wires have the problem that they do not provide the strength and toughness of the weld metal under welding conditions of high heat input exceeding 40 kJ / cm and high interpass temperatures. In addition, the latter also generates a large amount of slag, which increases the likelihood of welding defects such as slag entrapment. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-142726 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-237361 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-136281 [Patent Document 4] Japanese Patent Application Laid-Open No. 2005-169415 [Patent Document 5] Japanese Patent Application Laid-Open No. 2009-255142 [Patent Document 6] Japanese Patent Application Laid-Open No. 2005-279683 [Patent Document 7] Japanese Patent Application Laid-Open No. 2015-205303 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention has been devised in view of the above-mentioned problems, and has as its object to provide a flux-cored wire for gas-shielded arc welding which is capable of producing a weld metal having good mechanical properties without producing weld defects even when welding is performed under welding conditions ranging from a low heat input of about 20 kJ / cm to a high heat input of 60 kJ / cm with high interpass temperatures, and which has a stable arc even when welding with a high current, with little spatter and excellent welding workability. [Means for solving the problem]

[0011] The present inventors have conducted detailed studies on the component composition of a flux-cored wire for gas-shielded arc welding, which is capable of producing weld metal with good mechanical properties without generating weld defects even when welding is performed under welding conditions ranging from low heat input of about 20 kJ / cm to high heat input of 60 kJ / cm with high interpass temperatures, and which has excellent welding workability, such as a stable arc and little spatter even when welding with a high current.

[0012] As a result, it was found that in order to achieve the appropriate strength and stable toughness of the weld metal without generating welding defects even under low heat input welding conditions of approximately 20 kJ / cm, high current welding conditions, and high heat input and high interpass temperature welding conditions of 60 kJ / cm, it is effective to minimize the amount of oxides, which are slag-forming agents in the wire, and to optimize the amounts of the alloy components C, Si, Mn, Cu, and Ti.

[0013] Furthermore, it was discovered that by adjusting the amounts of Mo and B in the wire to an appropriate level, it is possible to obtain weld metal with a predetermined tensile strength without reducing the toughness of the weld metal, even under welding conditions with a large heat input of 60 kJ / cm and a high interpass temperature.

[0014] Furthermore, it was also found that the toughness of the weld metal can be further improved by adjusting the amounts of Al and Mg in the wire to an appropriate level.

[0015] In addition, it was found that welding workability can be improved by stabilizing the arc and reducing the amount of spatter generated by adjusting the total F-equivalent values of C, Ti, and metal fluorides, and the total Na2O-equivalent and K2O-equivalent values of Na oxides and K oxides to an appropriate amount, and that the bead appearance and shape can be improved by adjusting the total SiO2-equivalent value of Si oxides to an appropriate amount.

[0016] That is, the gist of the present invention is (1) a flux-cored wire for gas shielded arc welding, which is made by filling a steel sheath with flux, and the total mass of the steel sheath and the flux is, in mass % relative to the total mass of the wire, C: 0.04 to 0.10%, Si: 0.58 to 1.02%, Mn: 3.08 The flux contains, in mass % relative to the total mass of the wire, metal fluorides: F-equivalent total 0.005-0.10%, silicon oxides: SiO2-equivalent total 0.01-0.2%, one or more of sodium oxides and potassium oxides: Na2O-equivalent total and K2O-equivalent total 0.02-0.14%, with the remainder consisting of iron from the steel sheath, iron powder added to adjust the composition, iron content of iron alloy powder, and impurities.

[0017] (2) The flux-cored wire for gas-shielded arc welding according to (1) further contains, in mass % relative to the total mass of the wire, 0.25% or less of one or both of Al and Mg in total, based on the total mass of the steel sheath and flux. [Effects of the Invention]

[0018] The flux-cored wire for gas-shielded arc welding of the present invention can produce weld metal with good mechanical properties without weld defects, even when welding is performed under welding conditions ranging from a low heat input of about 20 kJ / cm to a high heat input of 60 kJ / cm and high interpass temperatures, and can also produce high-quality welds with high efficiency, such as excellent welding workability, with a stable arc even at high currents, little spatter, and good bead appearance and shape. DETAILED DESCRIPTION OF THE INVENTION

[0019] The composition and content of the flux-cored wire for gas-shielded arc welding according to the present invention, and the reasons for limiting each component will be described below. The content of each component will be expressed in mass %, and the mass % will be simply expressed as %.

[0020] (First embodiment) [Total of steel sheath and flux: C: 0.04~0.10%] Carbon has the effect of improving the strength of the weld metal. If the carbon content is less than 0.04%, sufficient weld metal strength cannot be obtained under welding conditions of large heat input and high interpass temperatures. On the other hand, if the carbon content exceeds 0.10%, the strength of the weld metal increases but its toughness decreases. Therefore, the total carbon content of the steel sheath and flux should be 0.04 to 0.10%. In addition to being a component contained in the steel sheath, carbon can also be added from the flux, metal powder, alloy powder, etc.

[0021] [Si content in total of steel sheath and flux: 0.4-1.4%] Si is a deoxidizer that adjusts the oxygen content of the weld metal. It also has the effect of improving the strength of the weld metal. If the Si content is less than 0.4%, deoxidation is insufficient, resulting in low weld metal strength and reduced toughness. On the other hand, if the Si content exceeds 1.4%, the strength of the weld metal becomes excessively high, and toughness cannot be consistently achieved. Furthermore, if the Si content exceeds 1.4%, the amount of slag generated during welding increases, making welding defects such as slag inclusion more likely to occur. Therefore, the total Si content of the steel sheath and flux should be 0.4 to 1.4%. In addition to being a component contained in the steel sheath, Si can also be added from the flux via metallic Si, Fe-Si, Fe-Si-Mn, or other alloy powders.

[0022] [Mn content in steel sheath and flux: 2.5-3.6%] Mn improves the toughness and strength of weld metal under welding conditions with high heat input and high interpass temperatures. If the Mn content is less than 2.5%, the strength of the weld metal decreases under welding conditions with high heat input and high interpass temperatures, resulting in a decrease in toughness. On the other hand, if the Mn content exceeds 3.6%, the strength of the weld metal increases during low heat input welding, but toughness cannot be consistently achieved. Furthermore, if the Mn content exceeds 3.6%, the amount of slag generated during welding increases, making welding defects such as slag inclusion more likely to occur. Therefore, the total Mn content of the steel sheath and flux should be 2.5 to 3.6%. In addition to the components contained in the steel sheath, Mn can also be added from metallic Mn, Fe-Mn, Fe-Si-Mn, and other alloy powders.

[0023] [Mo content of steel sheath and flux: less than 0.2-0.6%] Mo is important for ensuring the strength of the weld metal under welding conditions of high heat input and high interpass temperatures when the Mn content is within the aforementioned range. If the Mo content is less than 0.2%, the strength of the weld metal will be low under welding conditions of high heat input and high interpass temperatures. On the other hand, if the Mo content is 0.6% or more, the strength of the weld metal will be excessively high under welding conditions of low heat input, and toughness will not be consistently obtained. Therefore, the total Mo content of the steel sheath and flux should be 0.2 to less than 0.6%. In addition to being a component contained in the steel sheath, Mo can also be added from metallic Mo powder from the flux.

[0024] [Cu content in steel sheath and flux: 0.05-0.5%] Cu has a precipitation strengthening effect, lowering the transformation temperature and refining the structure of the weld metal, thereby stabilizing toughness. If Cu is less than 0.05%, this effect is not obtained, and stable weld metal toughness cannot be obtained. On the other hand, if Cu exceeds 0.5%, precipitation embrittlement occurs, reducing the toughness of the weld metal and making it more susceptible to hot cracking. Therefore, the total Cu content of the steel sheath and flux is set to 0.05 to 0.5%. Cu can be added from the components contained in the steel sheath, the Cu plating applied to the steel sheath surface, metallic Cu from the flux, and alloy powder such as Fe-Si-Cu.

[0025] [Ti: 0.1-0.4% in total for steel sheath and flux] Ti stabilizes the arc and acts as a deoxidizer, especially during high-current welding and high-heat-input / high-interpass-temperature welding. It also produces fine Ti oxides in the weld metal, further improving the toughness of the weld metal. If Ti is less than 0.1%, this effect is not achieved, resulting in an unstable arc and reduced toughness of the weld metal during high-current welding and high-heat-input / high-interpass-temperature welding. On the other hand, if Ti exceeds 0.4%, Ti precipitates increase in the weld metal, reducing toughness. Therefore, the total Ti content of the steel sheath and flux should be 0.1-0.4%. In addition to being a component of the steel sheath, Ti can also be added from metallic Ti or alloy powders such as Fe-Ti from the flux.

[0026] [B: 0.0015~0.010% in total for steel sheath and flux] B has the effect of suppressing the formation of grain boundary ferrite at the grain boundaries of the weld metal and improving toughness under welding conditions of high heat input and high interpass temperatures. If B is less than 0.0015%, the toughness of the weld metal decreases under welding conditions of high heat input and high interpass temperatures. On the other hand, if B exceeds 0.010%, hot cracking becomes more likely to occur. Therefore, the total B content of the steel sheath and flux should be 0.0015 to 0.010%. In addition to the components contained in the steel sheath, B can also be added from alloy powders such as Fe-Si-B and Fe-Mn-B.

[0027] [Metal fluorides in flux: Total F equivalent value: 0.005 to 0.10%] Metal fluorides have the effect of concentrating and stabilizing the arc. If the total F-equivalent value of the metal fluorides is less than 0.005%, this effect is not obtained, resulting in an unstable arc and increased spatter generation. On the other hand, if the total F-equivalent value of the metal fluorides exceeds 0.10%, the arc becomes strong and unstable, resulting in increased spatter generation. Therefore, the total F-equivalent value of the metal fluorides contained in the flux should be 0.005-0.10%. Note that metal fluorides can be added from the flux using CaF2, NaF, LiF, MgF2, K2SiF6, Na3AlF6, AlF3, etc., and the F-equivalent value is the total F content contained in them.

[0028] [Si oxide in flux: Total SiO2 equivalent: 0.01-0.2%] Silicon oxides in flux increase the viscosity of the molten slag, improving slag encapsulation and improving bead toe adhesion, resulting in improved bead appearance and shape. If the total SiO2 equivalent of silicon oxides is less than 0.01%, the weld bead toe adhesion will be poor, resulting in poor bead appearance and shape. On the other hand, if the total SiO2 equivalent of silicon oxides exceeds 0.2%, the oxygen content in the weld metal will increase, reducing toughness. Furthermore, if the total SiO2 equivalent of silicon oxides exceeds 0.2%, the amount of slag will increase, making welding defects such as slag entrapment more likely to occur. Therefore, the total SiO2 equivalent of silicon oxides contained in the flux should be 0.01-0.2%. Silicon oxides can be added from the solid components of the flux, such as silica sand, orthoclase, and potassium silicate water glass.

[0029] [One or more of sodium oxides and potassium oxides in the flux: 0.02 to 0.14% in total of Na2O equivalent and K2O equivalent] Na oxide and K oxide have the effect of stabilizing the arc. If the total of one or more of the Na oxides and K oxides is less than 0.02% in terms of Na2O and K2O, the arc becomes unstable and the amount of spatter increases. On the other hand, if the total of one or more of the Na oxides and K oxides exceeds 0.14% in terms of Na2O and K2O, the arc becomes unstable and the amount of spatter increases. Furthermore, if the total of one or more of the Na oxides and K oxides exceeds 0.14%, the amount of slag generated during welding increases, making welding defects such as slag inclusion more likely to occur. Therefore, the total of one or more of the Na oxides and K oxides contained in the flux should be 0.02-0.14% in terms of Na2O and K2O. Na oxide and K oxide can be added as powders of solid components of water glass made from sodium silicate and potassium silicate, potassium feldspar, sodium titanate, etc.

[0030] The remainder of the flux-cored wire for gas-shielded arc welding of the present invention is Fe in the steel sheath, iron powder added for adjusting the composition, Fe content in iron alloy powder such as Fe-Si, Fe-Mn, and Fe-Ti alloy, and impurities. Although the impurities are not particularly specified, from the viewpoints of hot cracking and toughness of the weld metal, it is preferable that P is 0.03% or less and S is 0.03% or less.

[0031] The flux filling rate is not particularly limited, but is preferably 8 to 20% of the total mass of the wire from the viewpoint of productivity.

[0032] (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.

[0033] [Al and / or Mg content in the steel sheath and flux combined: 0.25% or less] Al and Mg are strong deoxidizers that reduce oxygen in the weld metal and increase its toughness. However, if either or both of them exceed 0.25%, a violent oxidation reaction occurs in the arc during welding, resulting in increased fume and spatter generation. Therefore, the total content of either or both of Al and Mg in the steel sheath and flux must be 0.25% or less. To reduce oxygen in the weld metal and increase its toughness, it is preferable that either or both of Al and Mg be 0.05% or more. Al and Mg can be added from alloy powders such as metallic Al, Fe-Al, metallic Mg, and Al-Mg. [Example]

[0034] The effects of the first and second embodiments of the present invention will be specifically described below using examples.

[0035] First, JIS G3141 SPHC (C: 0.02 mass%, Si: 0.01 mass%, Mn: 0.40 mass%, P: 0.012 mass%, S: 0.010 mass%) was used for the steel sheath, which was formed into a U-shape and then filled with flux at a filling rate of 10 to 15% to form it into a C-shape.The joints of the steel sheath were then welded to form a pipe and drawn to produce flux-cored wires with the various compositions shown in Table 1.The diameter of the prototype wire was 1.4 mm.

[0036] [Table 1]

[0037] Using the prototype flux-cored wires shown in Table 1, the amount of spatter generated, arc stability, bead appearance and shape, the presence or absence of defects by X-ray transmission testing, and weld metal performance were investigated.

[0038] The amount of spatter generated was determined as a value per unit time (g / min) by measuring the weight of spatter generated during 1 minute of welding using a copper collection box. The spatter measurement was the average value of five measurements taken under the welding conditions of Condition No. T1 shown in Table 2, and a value of 1.5g / min or less was considered good.

[0039] Arc stability is evaluated by continuously measuring welding voltage fluctuations during welding and measuring the magnitude of those fluctuations. When the threshold is set at ±1V from the average voltage, the arc is deemed stable if the voltage fluctuation exceeds the threshold for less than 90% of the measurement time. On the other hand, the arc is deemed unstable if the voltage fluctuation exceeds the threshold for more than 10% of the measurement time.

[0040] Bead appearance and shape: The bead shape was judged to be good if there were no undercuts or overlaps that required adjustment in the sound part of the weld bead. The bead appearance was judged to be good if there was no partial disturbance in the waveform and it was uniform.

[0041] Weldability and weld metal performance were evaluated by conducting multi-pass weld metal tests using specimens with a 35° V groove, a 7mm root gap, and backing metal under the conditions shown in Table 2 (low heat input) and (high heat input, high interpass). The arc stability and bead appearance and shape were examined. After welding, the backing metal was removed and an X-ray examination was conducted. X-ray examination was conducted based on the radiographic testing method for steel welded joints specified in JIS Z 3104:1995. A defect-free condition was determined when no defects were detected. Tensile test specimens (JIS Z2201 A0) and impact test specimens (JIS Z2202 4) were also taken from the weld metal to examine its mechanical properties.

[0042] Strength was evaluated as tensile strength of 490 to 690 MPa, and toughness was evaluated as Charpy impact tests were conducted at 0°C on five specimens, with an average absorbed energy of 80 J or more and a minimum of 60 J or more being considered good. The results are summarized in Table 3.

[0043] [Table 2]

[0044] [Table 3]

[0045] In Tables 1 and 3, wires W1 to W10 are examples of the present invention, and wires W11 to W22 are comparative examples. The wires W1 to W10, which are examples of the present invention, have appropriate contents of C, Si, Mn, Mo, Cu, Ti, and B in the flux-cored wires, and appropriate amounts of the total F-equivalent value of metal fluorides, the total SiO2-equivalent value of Si oxides, and the total Na2O-equivalent value and K2O-equivalent value of one or more sodium oxides and potassium oxides in the flux. As a result, the amount of spatter generated was small, and under both low heat input and high heat input / high interpass temperature welding conditions, the arc was stable, the bead appearance and shape were good, there were no weld defects, and the average and minimum values of the tensile strength and absorbed energy of the weld metal were good.

[0046] In addition, wires W2, W5, W6 and W10, which have appropriate amounts of Al and / or Mg, achieved an average absorbed energy of 100 J or more in the weld metal under both low heat input and high heat input / high interpass temperature welding conditions, which were extremely satisfactory results.

[0047] In the comparative example, wire W11 had a low carbon content, resulting in low tensile strength of the weld metal under welding conditions of high heat input and high interpass temperature. Also, because it had a low titanium content, the arc was unstable under welding conditions of high heat input and high interpass temperature, resulting in low absorbed energy of the weld metal. Furthermore, because it had a high total of either or both of aluminum and magnesium, it generated a large amount of spatter and fumes.

[0048] Wire symbol W12 has a high carbon content, so the tensile strength of the weld metal was high and the absorbed energy was low under both low heat input and high heat input / high interpass temperature welding conditions. In addition, the total F-equivalent value of the metal fluorides was low, so the amount of spatter was high and the arc was unstable under both low heat input and high heat input / high interpass temperature welding conditions.

[0049] Wire symbol W13 has a low Si content, so the tensile strength and absorbed energy of the weld metal were low under both low heat input and high heat input / high interpass temperature welding conditions. Also, because it has a high B content, hot cracking occurred in the first layer under both low heat input and high heat input / high interpass temperature welding conditions.

[0050] Wire W14 has a high Si content, so slag inclusion occurred under both low heat input and high heat input / high interpass temperature welding conditions, the tensile strength of the weld metal was high, and the absorbed energy was low.In addition, because the total F-equivalent value of metal fluorides was high, there was a lot of spatter generation, and the arc was strong and unstable under both low heat input and high heat input / high interpass temperature welding conditions.

[0051] Wire W15 has a low Mn content, so the tensile strength and absorbed energy of the weld metal under welding conditions of high heat input and high interpass temperature were low. Also, because the total SiO2 equivalent value of Si oxide was low, the weld bead toe did not conform well under both low heat input and high heat input and high interpass temperature welding conditions, resulting in poor bead appearance and shape.

[0052] Wire symbol W16 has a high Mn content, which resulted in high tensile strength of the weld metal under low heat input welding conditions and a low minimum absorbed energy. Also, because of the high Mn content, slag inclusion occurred under both low heat input and high heat input / high interpass temperature welding conditions. Furthermore, because the total Na2O equivalent and K2O equivalent values of one or more of sodium oxides and potassium oxides was low, the amount of spatter generated was high, and the arc was unstable under both low heat input and high heat input / high interpass temperature welding conditions.

[0053] Wire symbol W17 has a low Mo content, so the tensile strength of the weld metal was low under welding conditions of high heat input and high interpass temperature. Also, because it has a high Ti content, the absorbed energy of the weld metal was low under welding conditions of low heat input and high heat input and high interpass temperature.

[0054] Wire symbol W18 has a high content of Mo, so the tensile strength of the weld metal was high under low heat input welding conditions, and the minimum absorbed energy was low. In addition, because the total Na2O equivalent value and K2O equivalent value of one or more types of sodium oxide and potassium oxide was high, the amount of spatter was large, and the arc was unstable under both low heat input and high heat input / high interpass temperature welding conditions, resulting in slag inclusion.

[0055] Wire symbol W19 has a low Cu content, so the minimum absorbed energy of the weld metal was low under both low heat input and high heat input / high interpass temperature welding conditions.

[0056] Wire W20 contains a lot of Cu, so hot cracking occurred 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 was low. Also, because the total amount of Al and Mg was low, no effect of improving absorbed energy was obtained.

[0057] Wire symbol W21 has a low B content, so the absorbed energy of the weld metal was low under welding conditions of large heat input and high interpass temperature.

[0058] Wire symbol W22 has a high total SiO2 equivalent value of Si oxides, so slag inclusion occurred under both low heat input and high heat input / high interpass temperature welding conditions, and the absorbed energy of the weld metal was low.

Claims

1. A flux-cored wire for gas shielded arc welding, which is made by filling a steel outer sheath with flux, The total mass of the steel sheath and flux is expressed as a percentage by mass of the total wire mass. C: 0.04-0.10%, Si: 0.58-1.02%, Mn: 3.08-3.6%, Mo: 0.2 to less than 0.6% Cu: 0.05-0.5%, Ti: 0.1 to 0.4%, B: 0.0015 to 0.010%; Furthermore, in the flux, in mass % relative to the total mass of the wire, Metal fluorides: 0.005 to 0.10% in total F converted value, Si oxide: SiO 2 The total conversion value is 0.01 to 0.2%, One or more of sodium oxide and potassium oxide: Na 2 O conversion value and K 2 Contains 0.02 to 0.14% in total converted to O, A flux-cored wire for gas-shielded arc welding, the balance of which consists of iron from the steel sheath, iron powder added for adjusting the composition, iron content of iron alloy powder, and impurities.

2. The total mass of the steel sheath and flux is expressed as a percentage by mass of the total wire mass.

2. The flux-cored wire for gas-shielded arc welding according to claim 1, further comprising: 0.25% or less of either or both of Al and Mg in total.

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