Ar-CO2 mixed gas shielded arc welding flux-cored wire

Abstract

To provide a flux-cored wire for Ar-CO2 mixed gas shielded arc welding that achieves superior workability in all-position circumferential welding of steel pipes and yields welded metal with superior strength and toughness.SOLUTION: A flux-cored wire for Ar-CO2 mixed gas shielded arc welding includes, in terms of percentage by mass% of the total wire, the following elements in a combined total of the steel coating and flux, 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 Nb and V: 0.01-0.1%, and further includes, in the flux, TiO2 equivalent value: 3-8%, Al2O3 equivalent value: 0.02-0.3%, SiO2 equivalent value: 0.1-0.6%, ZrO2 equivalent value: 0.25-0.65%, Na2O equivalent value and K2O equivalent value: 0.05-0.2%, Mg: 0.1-0.8%, F equivalent value: 0.05-0.25%, and Bi equivalent value: 0.001-0.01%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a flux-cored wire for Ar-CO2 mixed gas shielded arc welding, which has good arc stability, less spatter generation, particularly good slag detachment property and no welding defects, and excellent strength and low-temperature toughness of the weld metal in the all-position circumferential welding of steel pipes.

Background Art

[0002] The flux-cored wire for gas shielded arc welding is a rutile-based flux-cored wire for welding, which has extremely excellent welding efficiency and welding workability in all-position welding, and is applied in a wide range of fields such as shipbuilding, bridges, offshore structures, steel structures, etc. For example, in recent years, natural gas and oil field development on the seabed have advanced, and the laying of pipelines has increased. Therefore, in the all-position circumferential welding of pipelines, a flux-cored wire for gas shielded arc welding that enables high-efficiency construction is used.

[0003] Since pipelines are laid on the ground, seabed, cold regions, etc., extremely high reliability is required due to harsh usage environments, and high quality is also required in the welded parts. In the all-position circumferential welding that constitutes such pipelines, for example, in Patent Document 1, a technique of a flux-cored wire that can obtain good welding workability in all-position welding by defining a fluorine compound containing Na and K is disclosed. However, Bi is not added to the disclosed technique of Patent Document 1, and the addition amount of Zr oxide is also small, so the slag detachment property is poor and welding defects such as slag entrainment occur. In addition, since Nb and V are not added, there is a problem that the strength of the weld metal of the steel pipe cannot be stably obtained.

[0004] In Patent Document 2, a technique of a flux-cored wire that can obtain a weld metal with good welding workability and low-temperature toughness in all-position welding by optimizing the components of the slag component, alloy component and deoxidizer is disclosed. However, Nb and V are not added to the disclosed technique of Patent Document 2, and there is a problem that the strength of the weld metal of the steel pipe cannot be stably obtained. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2016-131985 [Patent Document 2] Japanese Patent Publication No. 2018-153853 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] 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. [Means for solving the problem]

[0007] 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.

[0008] As a result, we found that by using a slag component consisting mainly of metal oxides with TiO2 as the main component and fluorine compounds, 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.

[0009] In other words, the gist of the present invention is a flux-cored wire for Ar-CO2 mixed gas shielded arc welding, wherein the steel sheath is filled with flux, and the total mass of the steel sheath and flux, in mass %, 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 contains Nb and V in total or in combination: 0.01~0.1%, and further, in mass %, the flux contains Ti oxide converted to TiO2. The material is characterized by containing the following: total calculated values: 3-8%, total Al oxide equivalent values: 0.02-0.3%, total Si oxide equivalent values: 0.1-0.6%, total Zr oxide equivalent values: 0.25-0.65%, one or more of Na oxide, Na fluoride, K oxide, and K fluoride: 0.05-0.2% (total of Na2O and K2O equivalent values), Mg: 0.1-0.8%, total F equivalent values ​​of fluorine compounds: 0.05-0.25%, total Bi equivalent values ​​of one or both of Bi oxides: 0.001-0.01%, with the remainder consisting of Fe from the steel shell, Fe content from iron powder, iron alloy powder, and impurities. [Effects of the Invention]

[0010] 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. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 shows the groove shape of a steel pipe used in weld metal testing. [Modes for carrying out the invention]

[0012] 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 %.

[0013] [Total carbon 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.

[0014] [Total Si content of steel shell and flux: 0.1-0.6%] Si contributes to improved weldability by improving the appearance and shape of the weld bead as part of the 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 yield in the weld metal results 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.

[0015] [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 in the steel sheath, Mn can be added from alloy powders such as metallic Mn, Fe-Mn, and Fe-Si-Mn from the flux.

[0016] [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 weld metal becomes excessively strong, 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 in the flux.

[0017] [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.

[0018] [Total Ti content of steel shell and flux: 0.05~0.25%] Ti has the effect of refining the structure of the weld metal and improving the low-temperature toughness. However, if the Ti content is less than 0.05%, the low-temperature toughness of the weld metal will decrease. On the other hand, if the Ti content exceeds 0.25%, precipitation strengthening will occur 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 in the steel outer skin and the flux should be 0.05 - 0.25%. In addition to the components contained in the steel outer skin, Ti can be added from metallic Ti, alloy powders such as Fe-Ti, etc. in the flux.

[0019] [The total of steel outer skin and flux: B: 0.002 - 0.015%] Adding a small amount of B can suppress the formation of grain boundary ferrite in the weld metal and has the effect of improving the low-temperature toughness of the weld metal. However, if the B content is less than 0.002%, the low-temperature toughness of the weld metal will decrease. On the other hand, if the B content exceeds 0.015%, the low-temperature toughness of the weld metal will decrease and hot cracking is likely to occur in the weld metal. Therefore, the total B content in the steel outer skin and the flux should be 0.002 - 0.015%. B can be added from alloy powders such as B, Fe-B, Fe-Mn-B, etc. in the total of the steel outer skin and the flux.

[0020] [The total of steel outer skin and flux: Al: 0.05% or less] Al remains in the weld metal as an oxide and reduces the toughness of the weld metal. Especially when the Al content exceeds 0.05%, the low-temperature toughness of the weld metal will decrease. Therefore, the Al content should be 0.05% or less. Note that Al is not an essential element and its content may be 0%.

[0021] [The total of one or both of Nb and V in the total of steel outer skin 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.

[0022] [Total Ti oxide content in flux (TiO2 equivalent): 3-8%] Titanium oxide contributes to arc stabilization during welding, improves bead shape, and enhances welding workability. Furthermore, in all-position circumferential welding, titanium oxide adjusts the viscosity and melting point of the molten slag, preventing metal sagging. However, if the total TiO2 equivalent value of titanium 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 titanium oxide exceeds 8%, the arc is stable and spatter generation is low, but the excess titanium oxide remaining in the weld metal reduces low-temperature toughness. Therefore, the total TiO2 equivalent value of titanium oxide contained in the flux should be between 3% and 8%. Titanium oxide is added from the flux as rutile, titanium oxide, titanium slag, ilmenite, etc.

[0023] [Total Al oxide content in flux (equivalent 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 equivalent value 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 equivalent value exceeds 0.3%, excess Al oxide remains in the weld metal, reducing its low-temperature toughness. Therefore, the total Al oxide equivalent value of Al oxide contained in the flux should be between 0.02% and 0.3%. Al oxides can be added from the flux, such as alumina.

[0024] [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.

[0025] [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 O2 equivalent value of Zr oxides 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 O2 equivalent value of Zr oxides exceeds 0.65%, slag detachability will deteriorate. Therefore, the total Zr O2 equivalent value of Zr oxides 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.

[0026] [One or more of the following in the flux: Na oxide, Na fluoride, K oxide, and K fluoride: 0.05-0.2% in total, based on Na2O and K2O equivalent values] 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, 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, 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 0.05-0.2% in terms of Na2O equivalent and K2O equivalent should be 0.05-0.2%. 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 as either Si oxides or Na compounds.

[0027] [Mg in flux: 0.1-0.8%] Magnesium (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. 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.

[0028] [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 fluorine compounds is less than 0.05%, the arc becomes unstable. On the other hand, if the total F equivalent value of 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 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 total amount of F contained in them.

[0029] [Total Bi equivalent value of one or both of the Bi 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 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 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 Bi and Bi oxide contained in the flux should be between 0.001% and 0.01%. Bi and Bi oxide are added in the form of metallic Bi or Bi oxide, etc.

[0030] 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 powders such as Fe-Mn and Fe-Si alloys, and impurities. While there are no specific restrictions on impurities, it is preferable that P: 0.03% or less and S: 0.03% or less from the viewpoint of high-temperature cracking and toughness of the weld metal. Furthermore, while there are no specific restrictions on the flux filling rate, it is preferable to set it to 8-20% of the total wire mass from the viewpoint of productivity.

[0031] 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. [Examples]

[0032] The effects of the present invention will be specifically described below with reference to examples.

[0033] First, using SPCC as specified in JIS G 3141:2017 for the steel sheath, the steel sheath was formed into a U-shape during the forming process. Then, the seams of the steel sheath were welded to create a seamless wire. This wire was then pipe-formed and drawn to produce 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%.

[0034] [Table 1]

[0035] Using the prototype flux-cored wire shown in Table 1, we evaluated the weldability and mechanical properties of the weld metal in all-position circumferential welding of steel pipes.

[0036] Weld metal testing was performed after automatic welding of steel pipes specified in JIS G 3106:2015, using the groove shape shown in Figure 1, under the welding conditions shown in Table 2.

[0037] [Table 2]

[0038] The welding workability was assessed visually by examining the arc stability, spatter generation, bead appearance and shape, slag detachability, and the presence or absence of molten metal dripping during automatic welding of steel pipes. The presence or absence of weld cracks was also investigated.

[0039] (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.

[0040] (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.

[0041] (Bead shape / 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.

[0042] (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.

[0043] (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.

[0044] (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.

[0045] (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.

[0046] (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.

[0047] [Table 3]

[0048] 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.

[0049] In the comparative example, wire symbol W17 had a low carbon content, resulting in low tensile strength of the weld metal. Furthermore, the low total TiO2 equivalent value of the Ti oxides led 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.

[0050] 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 resulted in poor bead appearance and shape, as well as metal sagging.

[0051] Wire symbol W19 had a low Si content, resulting in poor bead appearance and shape.

[0052] 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 resulted in poor bead appearance and shape, as well as metal sagging.

[0053] Wire symbol W21 had a low Mn content, resulting in low absorbed energy of the weld metal and poor bead appearance and shape. Furthermore, the high total Zr oxide equivalent value resulted in poor slag release properties.

[0054] Wire symbol W22 had a high manganese content, resulting in high tensile strength of the weld metal and low absorbed energy. However, the combined Na2O and K2O equivalent values ​​were low, leading to an unstable arc, high spatter generation, and poor bead appearance and shape.

[0055] Wire symbol W23 had a low copper 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.

[0056] Wire symbol W24 had a high copper content, resulting in high tensile strength of the weld metal and low absorbed energy. However, it also had a high magnesium content, leading to a large amount of spatter generation.

[0057] Wire symbol W25 had a low Ni content, resulting in a low absorbed energy of the weld metal. Additionally, the low total F equivalent value of the fluorine compounds led to an unstable arc.

[0058] Wire symbol W26 has a high nickel content, which caused hot cracking in the weld metal. Furthermore, the high total F equivalent value of fluorine compounds resulted in an unstable arc, excessive spatter, poor bead appearance and shape, and metal sagging.

[0059] 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.

[0060] Wire symbol W28 had a high Ti content, resulting in high tensile strength of the weld metal and low absorbed energy. However, the low total SiO2 equivalent value of the Si oxide resulted in poor bead appearance and shape.

[0061] Wire symbol W29 had a low B content, resulting in a low absorbed energy of the weld metal.

[0062] Wire symbol W30 has a high proportion of B, resulting in low energy absorption by the weld metal and the occurrence of hot cracking.

[0063] Wire symbol W31 has a high Al content, resulting in a low absorbed energy of the weld metal.

[0064] Wire symbol W32 had a low tensile strength in the weld metal because the sum of one or both of Nb and V was low.

[0065] Wire symbol W33 had a high sum of either Nb or V, or both, resulting in a low absorbed energy of the weld metal.

[0066] Wire symbol W34 had a high total value of Ti oxides converted to TiO2, resulting in a low absorbed energy of the weld metal.

[0067] Wire symbol W35 had a high total Al oxide equivalent value (Al2O3), resulting in a low absorbed energy of the weld metal.

[0068] 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.

[0069] Wire symbol W37 had a low Mg content, resulting in a low absorbed energy of the weld metal.

[0070] Wire symbol W38 indicates that the sum of the Bi equivalent values ​​for one or both of Bi and Bi oxide is high, resulting in a low absorbed energy of the weld metal and the occurrence of cracks in the weld metal.

Claims

[Claim 1] Ar-CO2 is a steel shell filled with flux. 2 In flux-cored wire for mixed gas shielded arc welding, 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 Ti oxide TiO 2 Total converted value: 3-8% Al oxide 2 O 3 Total converted value: 0.02-0.3% SiO 2 Total converted value: 0.1-0.6% Zr oxide ZrO 2 Total converted value: 0.25-0.65% One or more of the following: Na oxides, Na fluorides, K oxides, and K fluorides: Na 2 O equivalent value and K 2 The total O equivalent value is 0.05-0.2%. 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%. The remainder consists of Fe of the steel outer skin, Fe content of iron powder and ferroalloy powder, and impurities, and is characterized by Ar-CO 2 A wire with flux for shielded arc welding with a mixed gas.

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