Flux-cored wire for gas shield arc welding

Abstract

To provide a flux-cored wire for gas shield arc welding which is excellent in slag peelability when being subjected to high heat input welding, is less in fume generation and sputter generation, and has good mechanical property of weld metal.SOLUTION: A flux-cored wire for gas shield arc welding contains, in mass% to the total mass of a steel sheath, 0.02% or less C in the steel sheath, contains, in mass% to the total mass of a wire, 0.01 to 0.08% C, 0.4 to 1.4% Si, 1.5 to 3.0% Mn, 0.05 to 0.5% Cu, 0.1 to 0.3% Ti, 0.10 to 0.80% Mg, and 0.015% or less S, and further contains, in the flux, in mass% to the total mass of the wire, 0.005 to 0.10% metal fluoride in the total of an F conversion value, 0.01 to 0.2% Si oxide in the total of an SiO2 conversion value, 0.01 to 0.10% K oxide in the total of a K2O conversion value, and 0.01% or less Na oxide in the total of an Na2O conversion value.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a flux-cored wire for gas shielded arc welding of 490-550 MPa grade steel, which is excellent in slag detachability particularly when welding with a large heat input, has a small amount of fume generation and spatter generation, and can obtain a weld metal having good mechanical properties even under welding conditions of large heat input and high inter-pass temperature.

Background Art

[0002] In the fields of shipbuilding and construction steel structures, in order to improve welding efficiency, a gas shielded arc welding method in a large heat input range has been conventionally used. In large heat input welding using a solid wire for gas shielded arc welding, the welding efficiency can be increased because the welding deposition rate per hour can be increased. However, there are problems such as poor welding workability, such as unstable arcs, a large amount of spatter generation, and poor bead appearance and shape.

[0003] On the other hand, in large heat input welding using a flux-cored wire for gas shielded arc welding, in addition to the problem of a large amount of fume generation, the amount of slag generation also increases, so there are problems such as welding defects such as slag entrainment and poor slag detachability.

[0004] Patent Document 1 discloses a flux-cored wire that can obtain a weld metal having appropriate strength and toughness at large heat input welding, and further at large heat input and high inter-pass temperature, with stable arcs, a small amount of fume generation, and a small amount of spatter generation. However, there was a problem that Mg was not contained in an appropriate amount and the slag detachability was poor.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Therefore, the present invention has been devised in view of the above-described problems, and is a flux-cored wire for gas shielded arc welding of 490 to 550 MPa grade steel, which is particularly excellent in slag detachability when welding with a large heat input, has a small amount of fume generation and spatter generation, and further has good mechanical properties even under welding conditions of large heat input and high inter-pass temperature. An object of the present invention is to provide a flux-cored wire for gas shielded arc welding that can obtain a weld metal.

Means for Solving the Problems

[0007] The present inventors have obtained a weld metal having appropriate strength and toughness for flux-cored wires for gas shielded arc welding with a large heat input in 490 to 550 MPa grade steel, and further with a large heat input and high inter-pass temperature. In particular, they have excellent slag detachability, a small amount of fume generation and spatter generation, a stable arc, excellent bead shape and appearance, and can prevent welding defects. The component composition of the flux-cored wire for gas shielded arc welding that can obtain good welding workability was examined in detail.

[0008] As a result, it has been found that by reducing the contents of C in the steel sheath, S in the wire, and Na oxide, the amount of fume generation can be reduced even under welding conditions with a large heat input.

[0009] It has also been found that by setting the content of Mg to an appropriate amount, the slag detachability becomes good.

[0010] Regarding other welding workability, by setting the total of C, Ti, the F conversion value of metal fluoride, and the total of the K2O conversion value of K oxide in the wire to an appropriate amount, the arc is stabilized and the amount of spatter generation is reduced. By setting the total of the SiO2 conversion value of silicon oxide to an appropriate amount, it has been found that the bead shape and appearance are improved.

[0011] Furthermore, in order to achieve appropriate strength and stable toughness of the weld metal even under welding conditions with high heat input, it was found that oxides, which are slag formers in the wire, should be reduced as much as possible, and appropriate quantification of the respective contents of alloying elements C, Si, Mn, Cu, Ti, and Mg is effective. Also, by setting the contents of Mo and B in the wire to appropriate amounts, it was found that high strength can be achieved without reducing the toughness of the weld metal even under welding conditions with high heat input and high interpass temperature.

[0012] That is, the gist of the present invention is a flux-cored wire for gas shielded welding obtained by filling a flux into a steel sheath, wherein C in the steel sheath is contained at 0.02% by mass or less based on the total mass of the steel sheath, and in terms of mass% based on the total mass of the wire, the total of the steel sheath and the flux contains C: 0.01 to 0.08%, Si: 0.4 to 1.4%, Mn: 1.5 to 3.0%, Cu: 0.05 to 0.5%, Ti: 0.1 to 0.3%, Mg: 0.10 to 0.80%, S: 0.015% or less, and further, in terms of mass% based on the total mass of the wire, the flux contains metal fluorides: 0.005 to 0.10% in total in terms of F conversion value, SiO2: 0.01 to 0.2% in total in terms of SiO2 conversion value, K2O: 0.01 to 0.10% in total in terms of K2O conversion value, Na2O: 0.01% or less in total in terms of Na2O conversion value, and the balance consists of Fe of the steel sheath, iron powder added for component adjustment, Fe components of ferroalloys, and unavoidable impurities.

[0013] Also, it is further characterized in that, in terms of mass% based on the total mass of the wire, the total of the steel sheath and the flux contains Mg: 0.10 to 0.50%.

[0014] Furthermore, it is characterized in that, in terms of mass% based on the total mass of the wire, the total of the steel sheath and the flux further contains Mo: 0.5% or less and B: 0.010% or less.

Advantages of the Invention

[0015] According to the flux-cored wire for gas shielded arc welding to which the present invention having the above-described configuration is applied, when welding steel of 490 to 550 MPa grade, it is excellent in slag detachability particularly when welding with a large heat input, the amount of fume generation and the amount of spatter generation are small, the arc stability is good, the bead appearance and shape are excellent, the amount of slag generation is small and welding defects can be prevented, etc., and the welding workability is good. Furthermore, even under welding construction conditions of a large heat input and a high inter-pass temperature, the strength and toughness of the weld metal can be sufficiently ensured, and a high-quality weld metal with high efficiency can be obtained.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, the components of the flux-cored wire for gas shielded arc welding to which the present invention is applied and the reasons for limiting the composition will be described. The content of each component composition is expressed in mass%, and the description regarding the mass% will be simply described as %.

[0017] [C in the steel sheath is 0.02% or less by mass% with respect to the total mass of the steel sheath] By setting C in the steel sheath to 0.02% or less with respect to the total mass of the steel sheath, in CO2 gas shielded arc welding, the droplet rupture phenomenon occurring during droplet transfer is suppressed, the molten pool and the arc state are stabilized, and the amount of spatter generation and the amount of fume generation are reduced. On the other hand, when C in the steel sheath exceeds 0.02%, an intense oxidation reaction occurs in the arc during welding, resulting in an increase in the amount of fume generation and the amount of spatter generation. Therefore, C in the steel sheath with respect to the total mass of the steel sheath is 0.02% or less.

[0018] Hereinafter, the content of each component is shown in mass% with respect to the total mass of the flux-cored wire, and the description regarding the mass% will be simply described as %.

[0019] [C: 0.01 to 0.08% in total of the steel sheath and the flux] C has the effect of improving the strength of the weld metal. If C is less than 0.01%, sufficient strength of the weld metal cannot be obtained. On the other hand, if C exceeds 0.08%, the strength of the weld metal becomes excessively high and the toughness decreases. Therefore, the total of the steel outer skin and the flux should have C in the range of 0.01% to 0.08%. Note that C can be added not only from the components contained in the steel outer skin but also from metal powder, alloy powder, etc. in the flux.

[0020] [The total of the steel outer skin and the flux should have Si: 0.4 - 1.4%] Si is a deoxidizer and adjusts the oxygen content of the weld metal. Also, Si has the effect of improving the strength of the weld metal. If Si is less than 0.4%, deoxidation is insufficient, the strength of the weld metal is low, and the toughness decreases. On the other hand, if Si exceeds 1.4%, the strength of the weld metal becomes excessively high and the toughness decreases. Also, if Si exceeds 1.4%, the amount of slag generated during welding increases, and welding defects such as slag entrapment are likely to occur. Therefore, the total of the steel outer skin and the flux should have Si in the range of 0.4% to 1.4%. Note that Si can be added not only from the components contained in the steel outer skin but also from alloy powders such as metallic Si, Fe - Si, Fe - Si - Mn, etc. in the flux.

[0021] [The total of the steel outer skin and the flux should have Mn: 1.5 - 3.0%] Mn has the effect of improving the strength and toughness of the weld metal. If Mn is less than 1.5%, the strength of the weld metal decreases and the toughness decreases. On the other hand, if Mn exceeds 3.0%, the strength of the weld metal becomes excessively high and the toughness decreases. Also, if Mn exceeds 3.0%, the amount of slag generated during welding increases, and welding defects such as slag entrapment are likely to occur. Therefore, the total of the steel outer skin and the flux should have Mn in the range of 1.5% to 3.0%. Note that Mn can be added not only from the components contained in the steel outer skin but also from alloy powders such as metallic Mn, Fe - Mn, Fe - Si - Mn, etc. in the flux.

[0022] [The total of the steel outer skin and the flux should have Cu: 0.05 - 0.5%] Cu has the effect of precipitation strengthening, lowering the transformation temperature, refining the structure of the weld metal, and stabilizing toughness. If the content of Cu is less than 0.05%, this effect cannot be obtained, and stable toughness of the weld metal cannot be achieved. On the other hand, if it exceeds 0.5%, precipitation embrittlement occurs, the toughness of the weld metal decreases, and hot cracks are likely to occur in the weld. Therefore, the total of the steel outer skin and the flux is set to 0.05 - 0.5%. In addition to the component contained in the steel outer skin and the Cu plating applied to the surface of the steel outer skin, Cu can be added from metallic Cu in the flux, alloy powders such as Fe - Si - Cu, etc.

[0023] [The total of the steel outer skin and the flux: Ti: 0.1 - 0.3%] Ti has the effect of stabilizing the arc during welding with a large heat input and during welding construction with a large heat input and high inter - pass temperature, acting as a deoxidizer, and generating fine oxides of Ti in the weld metal to further improve the toughness of the weld metal. If the content of 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 with a large heat input and during welding construction with a large heat input and high inter - pass temperature. On the other hand, if Ti exceeds 0.3%, the precipitates of Ti in the weld metal increase and the toughness decreases. Therefore, the total of the steel outer skin and the flux is set to 0.1 - 0.3%. In addition to the component contained in the steel outer skin, Ti can be added from metallic Ti in the flux, alloy powders such as Fe - Ti, etc.

[0024] [The total of the steel outer skin and the flux: Mg: 0.10 - 0.80%] Mg is a strong deoxidizer, which has the effect of reducing oxygen in the weld metal and improving the toughness of the weld metal. It also has the effect of changing the precipitation form of the slag and improving the slag detachability. If the content of Mg is less than 0.10%, deoxidation is insufficient and the toughness of the weld metal decreases. Also, if the content of Mg is less than 0.10%, the precipitation form of the slag does not change and the slag detachability deteriorates. On the other hand, if Mg exceeds 0.80%, intense oxidation reaction occurs in the arc during welding, resulting in an increase in the amount of fume generation and spatter generation. Therefore, the total of the steel outer skin and the flux for Mg is set to 0.10 - 0.80%. In addition, Mg can be added from metallic Mg, alloy powders such as Al - Mg, etc.

[0025] Furthermore, the slag detachability can be improved by reducing Mg, and preferably Mg is set to 0.10 to 0.50%.

[0026] [In total of the steel outer skin and the flux, S: 0.015% or less] S exists as an impurity in the metal powder and alloy iron in the steel outer skin and the flux, and has the effect of slightly reducing the surface tension of the droplet. When S is 0.015% or less, the droplet during welding becomes larger, so that the evaporation of the metal in the arc atmosphere can be suppressed and the generation of fume can be inhibited. On the other hand, when S exceeds 0.015%, especially during welding with large heat input and welding at large heat input and high inter-pass temperature, the droplet becomes smaller and the surface area of the droplet becomes larger, so that the metal evaporates in the arc atmosphere and the amount of fume generated increases. Therefore, S in total of the steel outer skin and the flux is set to 0.015% or less.

[0027] [In total of the metal fluorides in the flux: 0.005 to 0.10% in terms of F conversion value] The metal fluoride has the effect of concentrating and stabilizing the arc. If the total F conversion value of the metal fluoride is less than 0.005%, this effect cannot be obtained, the arc is unstable, and the amount of spatter generated increases. On the other hand, if the total F conversion value of the metal fluoride exceeds 0.10%, the arc becomes unstable and the amount of spatter generated increases. Therefore, the total F conversion value of the metal fluoride contained in the flux is set to 0.005 to 0.10%. The metal fluoride can be added from CaF2, NaF, LiF, MgF2, K2SiF6, Na3AlF6, AlF3, etc. in the flux, and the F conversion value is the total of the F contents contained therein.

[0028] [In total of the silicon oxides in the flux: 0.01 to 0.2% in terms of SiO2 conversion value] The SiO₂ in the flux can increase the viscosity of the molten slag, improve the slag coating property, enhance the adaptability at the bead stop end, and improve the bead appearance and shape. If the total SiO₂ equivalent value of the SiO₂ is less than 0.01%, the adaptability at the stop end of the weld bead will deteriorate, and the bead appearance and shape will worsen. On the other hand, if the total SiO₂ equivalent value of the SiO₂ exceeds 0.2%, the amount of slag will increase, and welding defects such as slag entrapment are likely to occur. Therefore, the total SiO₂ equivalent value of the SiO₂ contained in the flux should be 0.01 - 0.2%. Note that the SiO₂ can be added from the solid components of water glass composed of silicon, orthoclase, and potassium silicate in the flux.

[0029] [K oxide in the flux: total K₂O equivalent value is 0.01 - 0.10%] The K oxide has the effect of stabilizing the arc. If the total K₂O equivalent value of the K oxide is less than 0.01%, the arc will become unstable and the amount of spatter generated will increase. On the other hand, if the total K₂O equivalent value of the K oxide exceeds 0.10%, the arc will be unstable and the amount of spatter generated will increase. Also, if the total K₂O equivalent value of the K oxide exceeds 0.10%, the amount of slag generated during welding will increase, and welding defects such as slag entrapment are likely to occur. Therefore, the total K₂O equivalent value of the K oxide contained in the flux should be 0.01 - 0.10%. Note that the K oxide can be added from the solid components of water glass composed of potassium silicate, powders such as orthoclase, etc.

[0030] [Na oxide: total Na₂O equivalent value is 0.01% or less] If the total Na₂O equivalent value of the Na oxide exceeds 0.01%, the amount of fume generated will increase especially during welding with a large heat input and welding construction at a large heat input and high inter-pass temperature. Therefore, the total Na₂O equivalent value of the Na oxide should be 0.01% or less. Note that the Na oxide is not an essential component and its content may be 0%.

[0031] [Total of steel outer skin and flux: Mo is 0.5% or less] Mo is important for ensuring the strength of the weld metal under welding conditions with high heat input and high interpass temperature. However, when Mo exceeds 0.5%, the strength of the weld metal becomes excessively high and toughness cannot be stably obtained. Therefore, the total of Mo in the steel sheath and the flux should be 0.5% or less. Note that Mo can be added not only as a component contained in the steel sheath but also as alloy powder such as metallic Mo from the flux.

[0032] [For the total of the steel sheath and the flux, B: 0.010% or less] B has the effect of suppressing the formation of grain boundary ferrite formed at the grain boundaries of the weld metal and improving toughness under welding conditions with high heat input and high interpass temperature. However, when B exceeds 0.010%, the grain boundaries become embrittled, toughness decreases, and hot cracks are likely to occur. Therefore, the total of B in the steel sheath and the flux should be 0.010% or less. Note that B can be added not only as a component contained in the steel sheath but also as alloy powder such as Fe - Si - B and Fe - Mn - B.

[0033] The flux - cored wire for 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. As types of wires, they can be roughly classified into a wire without a seam in the steel sheath obtained by welding the seam of the formed steel sheath and a wire with a seam in the steel sheath without welding the seam of the steel sheath. In the present invention, wires with any cross - sectional structure can be adopted. However, for a wire with a seam in the steel sheath, when the strength of the weld metal increases, cold cracks are likely to occur, so it is necessary to use raw materials with a low moisture content. On the other hand, a wire without a seam in the steel sheath can be heat - treated for the purpose of reducing the total hydrogen content in the wire, and since there is no moisture absorption of the flux after manufacturing, the diffusible hydrogen content of the weld metal can be reduced and the cold crack resistance can be improved, so it is more preferable.

[0034] As other components of the flux-cored wire for gas-shielded arc welding of the present invention, for the purpose of reducing the oxygen in the weld metal, Al may be contained in an amount of 0.15% or less. The balance is Fe of the steel sheath, iron powder added for component adjustment, Fe component of ferroalloy powders such as Fe-Si, Fe-Mn, Fe-Ti alloys, and inevitable impurities. Although no particular regulations are made for the inevitable impurities, from the viewpoints of hot cracking and toughness of the weld metal, it is preferably P: 0.05% or less. Also, the flux filling rate is not particularly limited, but from the viewpoint of productivity, it is preferably 8 to 20% with respect to the total mass of the wire.

Examples

[0035] Hereinafter, the effects of the present invention will be specifically described with reference to examples.

[0036] Using a steel sheath having the chemical components shown in Table 1, the steel sheath was formed into a U shape, filled with a flux filling rate of 10 to 15% and formed into a C shape, and then the joints of the steel sheath were welded to form a pipe, drawn, and a flux-cored wire having various components shown in Table 2 was trial-produced. The wire diameter of the trial-produced wire was 1.4 mm.

[0037]

Table 1

[0038]

Table 2

[0039] Using the trial-produced flux-cored wire shown in Table 2, investigations were conducted on slag detachability, fume generation amount, spatter generation amount, arc stability, bead appearance / shape, presence or absence of hot cracking, presence or absence of defects by X-ray transmission test, and mechanical properties.

[0040] The amount of fume generated was determined as the value per hour (mg / min) by measuring the weight of the fume generated during welding for 1 minute in accordance with JIS Z 3930. The measurement of the fume was taken as the average value of three measurements under the construction conditions of Condition No. T1 shown in Table 3, and a value of 600 mg / min or less was considered good.

[0041] The amount of spatter generated was determined as the value per hour (g / min) by measuring the weight of the spatter generated during welding for 1 minute using a copper collection box. The measurement of the spatter was taken as the average value of five measurements under the construction conditions of Condition No. T1 shown in Table 3, and a value of 1.5 g / min or less was considered good.

[0042] For welding workability and weld metal properties, a multi-layer bead weld metal test was conducted using a test piece with a 35° bevel groove, a root gap of 8 mm, and a backing strip under the construction conditions of Condition No. T2 shown in Table 3. The slag detachability, arc stability, bead appearance / shape, and presence of hot cracks during welding were visually inspected. After welding, the backing strip was removed and an X-ray penetration test was performed. Also, tensile test pieces (A0 size) and impact test pieces (V-notch test pieces) were taken from the weld metal part to investigate the mechanical properties.

[0043] Slag detachability was considered good when cracks appeared in the slag and it could be easily removed after tapping the slag on the bead surface with a chipping hammer after welding. Also, when cracks easily appeared in the slag and it could be easily removed after lightly hitting the slag on the bead surface with a chipping hammer, it was considered extremely good.

[0044] Arc stability was considered stable when the variation in the length of the arc generated between the wire tip and the steel plate was small.

[0045] Bead appearance / shape was considered good when the beads were beautiful and uniform.

[0046] The presence of hot cracks was determined as "present" if even one crack was observed on the bead surface after each pass welding in the weld metal test.

[0047] In the X-ray transmission test, the test was conducted based on the radioactivity transmission test of steel welded joints specified in JIS Z3104:1995, and the case where no slag entrapment or the like occurred in the welded part was defined as "non-defective".

[0048] For the evaluation of the mechanical properties of the weld metal, the tensile strength was considered good in the range of 490 to 690 MPa, and for toughness, five Charpy impact tests were conducted at 0 °C each. The average value of the absorbed energy being 80 J or more and the minimum value being 60 J or more were considered good. The results are summarized in Table 4.

[0049]

Table 3

[0050]

Table 4

[0051] The wire symbols W1 to W10 in Table 2 and Table 4 are examples of the present invention, and the wire symbols W11 to W21 are comparative examples. For the wire symbols W1 to W10 which are examples of the present invention, the contents of C in the steel outer skin, C, Si, Mn, Cu, Ti, Mg, and S in the flux-containing wire are appropriate amounts, and the total of the F-converted values of metal fluorides in the flux, the total of the SiO2-converted values of silicon oxides, the total of the K2O-converted values of potassium oxides, and the total of the Na2O-converted values of sodium oxides are appropriate amounts. Therefore, even under the welding construction conditions of large heat input, the slag detachability is good, the amount of fume generation and the amount of spatter generation are small, the arc is stable, the bead appearance and shape are good, there are no welding defects, and both the average value and the minimum value of the tensile strength and absorbed energy of the weld metal are good, resulting in satisfactory results.

[0052] In addition, since Mg is in the range of 0.10 to 0.50% for W1 to W3, W5, and W7 to W10, the slag detachability is extremely good, resulting in very satisfactory results.

[0053] In the comparative example, since the wire symbol W11 had a high C content in the steel outer skin symbol F4, the amount of fume generation and the amount of spatter generation were large. Also, since it had a high Ti content, the absorbed energy of the weld metal was low.

[0054] Since the wire symbol W12 had a low C content in the flux-cored wire, the strength of the weld metal was low. Also, since the total K2O conversion value of the K oxide was high, the arc became unstable, the amount of spatter generation was large, and slag entrapment occurred in the welded part.

[0055] Since the wire symbol W13 had a high C content in the flux-cored wire, the strength of the weld metal became excessively high and the absorbed energy was low. Also, since it had a high S content, the amount of fume generation was large.

[0056] Since the wire symbol W14 had a low Si content, the strength of the weld metal was low and the absorbed energy was also low. Also, since it had a high Mg content, the amount of fume generation and the amount of spatter generation were large.

[0057] Since the wire symbol W15 had a high Si content, the strength of the weld metal became excessively high, the absorbed energy was also low, and slag entrapment occurred in the welded part. Furthermore, since the total F conversion value of the metal fluoride was low, the arc became unstable and the amount of spatter generation was large.

[0058] Since the wire symbol W16 had a low Mn content, the strength of the weld metal was low and the absorbed energy was also low. Also, since the total F conversion value of the metal fluoride was high, the arc was unstable and the amount of spatter generation was large.

[0059] Since the wire symbol W17 had a high Mn content, the strength of the weld metal became excessively high, the absorbed energy was also low, and slag entrapment occurred in the welded part. Furthermore, since the total SiO2 conversion value of the Si oxide was low, the bead appearance and shape were poor.

[0060] Since the wire symbol W18 had less Cu, the absorbed energy of the weld metal was low. Also, since the total SiO2 equivalent value of the Si oxide was high, slag entrainment occurred.

[0061] Since the wire symbol W19 had a lot of Cu, the absorbed energy of the weld metal was low, and hot cracks occurred in the welded part. Also, since the total K2O equivalent value of the K oxide was small, the arc became unstable and the amount of spatter generation was large.

[0062] Since the wire symbol W20 had less Ti, the arc became unstable and the absorbed energy of the weld metal was low. Also, since the total Na2O equivalent value of the Na oxide was high, the amount of fume generation was large.

[0063] Since the wire symbol W21 had less Mg, the absorbed energy of the weld metal was low and the slag detachability was poor.

Example

[0064] Using a steel outer skin with the chemical composition shown in Table 1 in the same manner as in Example 1, the steel outer skin was formed into a U shape, filled with a flux filling rate of 10 - 15% and formed into a C shape, and then the seam of the steel outer skin was welded to form a pipe, drawn, and a flux-cored wire with various components shown in Table 5 was prototyped. The prototyped wire diameter was 1.4 mm.

[0065]

Table 5

[0066] Using the prototyped flux-cored wire shown in Table 5, investigations were conducted on slag detachability, amount of fume generation, amount of spatter generation, arc stability, bead appearance / shape, presence or absence of hot cracks, presence or absence of defects by X-ray transmission test, and weld metal performance.

[0067] The amount of fume generated was determined as the value per hour (mg / min) by measuring the weight of the fume generated during welding for 1 minute in accordance with JIS Z 3930. The measurement of the fume was taken as the average value of three measurements under the construction conditions of Condition No. T1 shown in Table 3, and a value of 600 mg / min or less was considered good.

[0068] The amount of spatter generated was determined as the value per hour (g / min) by measuring the weight of the spatter generated during welding for 1 minute using a copper collection box. The measurement of the spatter was taken as the average value of five measurements under the construction conditions of Condition No. T1 shown in Table 3, and a value of 1.5 g / min or less was considered good.

[0069] For the welding workability and the properties of the weld metal, a multi-layer bead weld metal test was carried out using a test piece with a backing bar, a 35° bevel groove, and a root gap of 8 mm under the construction conditions of Condition No. T3 shown in Table 3. The slag detachability, arc stability, bead appearance / shape, and the presence or absence of hot cracks during welding were visually inspected. After welding, the backing bar was removed and an X-ray penetration test was performed. Also, tensile test pieces (A0 size) and impact test pieces (V-notch test pieces) were taken from the weld metal part to investigate the mechanical properties.

[0070] Regarding the slag detachability, it was considered good when cracks appeared in the slag and it could be easily removed later when the slag formed on the bead surface after welding was struck with a chipping hammer. Also, it was considered extremely good when cracks easily appeared in the slag and it could be easily removed later when the slag formed on the bead surface was lightly struck with a chipping hammer.

[0071] Regarding the arc stability, it was considered stable when the variation in the length of the arc generated between the wire tip and the steel plate was small.

[0072] Regarding the bead appearance / shape, it was considered good when the beads were beautiful and uniform.

[0073] Regarding the presence or absence of hot cracks, in the weld metal test, if even one crack was observed on the bead surface after each pass welding, it was considered "present".

[0074] In the X-ray transmission test, the test was conducted based on the radioactivity transmission test of steel welded joints shown in JIS Z3104:1995, and the case where no slag entrainment or the like occurred in the welded part was defined as "defect-free".

[0075] For the evaluation of the mechanical properties of the weld metal, five tensile strength tests were carried out with values ranging from 520 to 720 MPa, and five Charpy impact tests were carried out at 0 °C. The average value of the absorbed energy was required to be 80 J or more, and the minimum value was required to be 60 J or more. The results are summarized in Table 6.

[0076]

Table 6

[0077] The wire symbols W22 to W26 in Tables 5 and 6 are examples of the present invention, and the wire symbols W27 to W31 are comparative examples. For the wire symbols W22 to W26 which are examples of the present invention, the contents of C in the steel sheath, C, Si, Mn, Cu, Ti, Mg, S, Mo, and B in the flux-containing wire are appropriate amounts, and the total of the F-converted values of metal fluorides in the flux, the total of the SiO2-converted values of silicon oxides, the total of the K2O-converted values of potassium oxides, and the total of the Na2O-converted values of sodium oxides are appropriate amounts. Therefore, even under the welding construction conditions of large heat input and high interpass temperature, the slag detachability is good, the amount of fume generation and the amount of spatter generation are small, the arc is stable, the bead appearance and shape are good, there are no welding defects, and both the average value and the minimum value of the tensile strength and absorbed energy of the weld metal are good, resulting in satisfactory results.

[0078] In addition, since Mg in W22 to W25 is in the range of 0.10 to 0.50%, the slag detachability is extremely good, resulting in very satisfactory results.

[0079] For wire symbol W27 in the comparative examples, since the amount of Cu is small, the absorbed energy of the weld metal is low. Also, although the amount of B is appropriate, the effect of improving the absorbed energy of the weld metal could not be obtained.

[0080] Since the wire symbol W28 had a high sulfur content, the amount of fume generated was large. Also, since it had a high molybdenum content, the strength of the weld metal became excessively high and the absorbed energy was also low. Although the boron content was appropriate, the effect of improving the absorbed energy of the weld metal was not obtained.

[0081] Since the wire symbol W29 had a high magnesium content, the amount of fume generated and the amount of spatter generated were large. Also, since it had a high boron content, the absorbed energy of the weld metal was low and hot cracking occurred in the welded part.

[0082] Since the wire symbol W30 had a low silicon content, the strength of the weld metal was low and the absorbed energy was also low. Also, since the total value of the Na2O conversion of sodium oxide was high, the amount of fume generated was large. Although the molybdenum and boron contents were appropriate, the effect of improving the strength and absorbed energy of the weld metal was not obtained.

[0083] Since the wire symbol W31 had a low manganese content, the strength of the weld metal was low and the absorbed energy was also low. Although the molybdenum and boron contents were appropriate, the effect of improving the strength and absorbed energy of the weld metal was not obtained.

Claims

1. In a flux-cored wire for gas shielded welding obtained by filling a flux into a steel sheath, C in the steel sheath is contained in an amount of 0.02% or less by mass based on the total mass of the steel sheath, and in terms of mass% based on the total mass of the wire, the total of the steel sheath and the flux, C: 0.01 to 0.08%, Si: 0.4 to 1.4%, Mn: 1.5 to 3.0%, Cu: 0.05 to 0.5%, Ti: 0.1 to 0.3%, Mg: 0.10 to 0.80% is contained, S: 0.015% or less, Furthermore, in terms of mass% based on the total mass of the wire, in the flux, Metal fluoride: The total of the F-converted values is 0.005 to 0.10%, Silicon oxide: SiO 2 in terms of the total conversion value, 0.01 to 0.2%, K Oxide: K 2 It contains 0.01 to 0.10% in terms of the total value in terms of O conversion value, Na oxide: Na 2 The total value in terms of O conversion is 0.01% or less, The balance consists of Fe of the steel sheath, iron powder added for component adjustment, Fe content of ferroalloys, and inevitable impurities, and is a flux-cored wire for gas shielded arc welding.

2. In terms of mass% based on the total mass of the wire, the total of the steel sheath and the flux, Mg: 0.10 to 0.50% The flux-cored wire for gas shielded arc welding according to claim 1, characterized in that.

3. In terms of mass% based on the total mass of the wire, the total of the steel sheath and the flux, Mo: 0.5% or less, B: 0.010% or less The flux-cored wire for gas shielded arc welding according to claim 1 or claim 2, further characterized by containing.

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