Flux-cored wire and method for manufacturing welded joint

Abstract

To provide a flux-cored wire and a method for manufacturing a weld joint using the flux-cored wire which can obtain weld metal excellent in welding workability, and low temperature toughness and resistance to cold cracking.SOLUTION: A flux-cored wire has a steel-made outer skin and a flux filling the inside of the steel-made outer skin, has a predetermined chemical component, and contains predetermined amounts of the total of a TiO2 conversion value of a Ti oxide, the total of an SiO2 conversion value of an Si oxide, the total of a ZrO2 conversion value of a Zr oxide, the total of an Al2O3 conversion value of an Al oxide, the total of one or more kinds of fluorides of K2SiF6, K2ZrF6, NaF, Na3AlF6, CaF2 and MgF2, the total of one or more kinds of Na-containing compounds of an Na oxide, NaF and Na3AlF6, and the total of one or more kinds of K-containing compounds of a K oxide, K2SiF6 and K2ZrF6. A predetermined X value is 0.10-160.00.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a method for making a flux-cored wire and a welded joint. [Background technology]

[0002] In recent years, there has been an increasing demand for larger and lighter construction and industrial machinery, and as a result, ultra-high tensile steel plates such as 690 MPa class steel are being used. Various studies have been conducted on wires for welding ultra-high tensile steel plates.

[0003] For example, Patent Document 1 describes the wire containing, in mass % relative to the total mass, C: 0.02-0.09%, Si: 0.2-0.6%, Mn: 1.5-3.3%, Ni: 1.5-3.5%, Mo: 0.21-0.5%, Ti: 0.01-0.1%, B: 0.002-0.015%, Al: 0.05% or less, Nb: 0.015% or less, V: 0.015% or less, TiO2 equivalent value: 3-8%, SiO2 equivalent value ... and Nb: 0.015% or less. The publication discloses a flux-cored wire for Ar-CO2 mixed gas shielded arc welding, comprising: 0.1-0.5% Ar; 0.3-0.8% Mg; 0.05-0.5% F-equivalent value of fluorine compounds; 0.05-0.2% total of one or two of the Na-equivalent value and the K-equivalent value in the fluorine compounds; 0.05-0.2% total of Na2O and K2O; 0.05-0.2% ZrO2-equivalent value: 0.2% or less; and 0.1% or less Al2O3-equivalent value. The wire of Patent Document 1 has good welding workability in all positions when welding high-tensile steel with a 0.2% yield strength of 690 MPa or more used in steel structures, etc., and can produce a weld metal with excellent low-temperature cracking resistance and low-temperature toughness.

[0004] Patent Document 2 also discloses a flux-cored wire having a steel sheath and flux filled inside the steel sheath, the flux containing fluorides totaling 0.11% or more in F conversion value, Ti oxides totaling 4.30 to 7.50% in TiO2 conversion, oxides totaling 0.30 to 2.40% by mass, and carbonates totaling 0 to 0.60% by mass, the Ca oxide content totaling CaO conversion is less than 0.20% by mass, the CaF2 content is less than 0.50%, chemical components are within a predetermined range, the Z value is 2.00% or less, the V value is 5.0 or more and 27.0 or less, and Ceq is 0.30 to 1.00% or less. The wire of Patent Document 2 has high strength and high toughness, is excellent in resistance to low-temperature cracking, can produce welds with good bead shapes, can significantly reduce the amount of spatter generated during welding, and can increase the viscosity of the molten metal during welding.

[0005] Flux-cored wires are also disclosed in Patent Documents 3-13. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-209901 A [Patent Document 2] International Publication No. 2018 / 087812 [Patent Document 3] Patent No. 6432715 [Patent Document 4] International Publication No. 2017 / 154122 [Patent Document 5] International Publication No. 2017 / 154120 [Patent Document 6] JP 2019-42782 A [Patent Document 7] JP 2019-25525 A [Patent Document 8] JP 2019-25524 A [Patent Document 9] JP 2018-192520 A [Patent Document 10] International Publication No. 2019 / 142835 [Patent Document 11] International Publication No. 2017 / 038610 [Patent Document 12] International Publication No. 2017 / 038609 [Patent Document 13] International Publication No. 2016 / 060208 Summary of the Invention [Problem to be solved by the invention]

[0007] As disclosed in Patent Documents 1 and 2, in order to improve the welding workability, it is effective to make the wire contain Ti oxide. On the other hand, if the wire contains Ti oxide, the amount of oxygen in the weld metal increases, and the low-temperature toughness of the weld metal cannot be ensured. Therefore, in order to achieve both welding workability and low-temperature toughness of the weld metal, it is necessary to reduce the oxygen content of the weld metal. In addition, the weld metal is required to have resistance to low-temperature cracking, and it is also necessary to reduce the amount of diffused hydrogen.

[0008] However, although the wires of Patent Documents 1 to 13 can produce weld metals with excellent properties, recent demands currently call for further improvements in the low-temperature toughness and low-temperature cracking resistance of the weld metal, as well as in welding workability (particularly vertical weldability).

[0009] Therefore, an object of the present disclosure is to provide a flux-cored wire that can provide a weld metal that is excellent in low-temperature toughness and low-temperature cracking resistance as well as in welding workability (particularly vertical weldability), and a method for manufacturing a welded joint using the flux-cored wire. [Means for solving the problem]

[0010] The means for solving the problems include the following aspects. <1> A flux-cored wire for welding comprising a steel sheath and flux filled inside the steel sheath, The chemical components, excluding oxides, fluorides, nitrides, and metal carbonates, are, in mass% relative to the total mass of the flux-cored wire, C: 0.020~0.100%, Si: 0.20 to 0.80%, Mn: 1.50-3.50%, P: 0 to 0.030%, S: 0~0.030%, Cu: 0.005 to 1.000%, Ni: 0.10-5.00%, Cr: 0~1.000%, Mo: 0~1.000%, Cr+Mo: 0.005~1.000%, Nb: 0 to 0.0150%, V: 0 to 0.0150%, Mg: 0-1.00%, Al: 0 to 0.100%, Ca: 0-0.100%, Ti: 0 to 0.100%, B: 0~0.0100%, REM: 0~0.100%, Bi: 0 to 0.050%, and The balance is Fe and impurities. The total TiO2 equivalent value of Ti oxides is 3.00 to 8.00%, The total amount of silicon oxides converted into SiO2 is 0.10 to 0.50%. The total Zr oxide content in terms of ZrO2 is 0 to 0.80%. The total Al2O3 equivalent value of aluminum oxide is 0 to 0.80%. Contains one or more fluorides of K2SiF6, K2ZrF6, NaF, Na3AlF6, CaF2, and MgF2, the total of which is 0.10 to 2.00%, Contains one or more Na-containing compounds selected from Na oxide, NaF, and Na3AlF6, the total of which (Na oxide is calculated as Na2O) is 0.01 to 2.00%, Contains one or more K-containing compounds selected from K oxide, K2SiF6, and K2ZrF6, the total of which (K oxide is calculated as K2O) is 0.01 to 2.00%, The flux-cored wire has an X value calculated by the following formula A of 0.10 to 160.00. X=(8×CaF2+5×MgF2+5×NaF+5×K2SiF6+5×K2ZrF6+Na3AlF6) / (SiO2+Al2O3+ZrO2+0.5×MgO+CaO+0.5×Na2O+0.5×K2O+MnO2+FeO)...Formula A In formula A, CaF2, MgF2, NaF, K2SiF6, K2ZrF6, and Na3AlF6 are the contents of the compounds represented by each chemical formula in mass% relative to the total mass of the flux-cored wire. SiO2 represents the total of the SiO2 equivalent value of Si oxide, Al2O3 represents the total of the Al2O3 equivalent value of Al oxide, ZrO2 represents the total of the ZrO2 equivalent value of Zr oxide, MgO represents the total of the MgO equivalent value of Mg oxide, CaO represents the total of the CaO equivalent value of Ca oxide, Na2O represents the total of the Na2O equivalent value of Na oxide, K2O represents the total of the K2O equivalent value of K oxide, MnO2 represents the total of the MnO2 equivalent value of Mn oxide, and FeO represents the total of the FeO equivalent value of Fe oxide. In addition, the SiO2 equivalent value, the Al2O3 equivalent value, the ZrO2 equivalent value, the MgO equivalent value, the CaO equivalent value, the Na2O equivalent value, the K2O equivalent value, the MnO2 equivalent value, and the FeO equivalent value in Formula A are expressed in mass% with respect to the total mass of the flux-cored wire. <2> Contains one or more Mg-containing compounds, either Mg oxide or MgF2, with the total amount (Mg oxide is calculated as MgO) being 0.01-2.00% <1> The flux-cored wire according to claim 1. <3> Ceq calculated by the following formula B is 0.300 to 0.750 <1> or <2> The flux-cored wire according to claim 1. Ceq=[C]+[Si] / 24+[Mn] / 6+[Ni] / 40+[Cr] / 5+[Mo] / 4+[V] / 14...Formula B In formula B, the element symbols represent the content of each element in mass % relative to the total mass of the flux-cored wire. <4> The steel skin has welds at the seams of the steel skin. <1> ~ <3> 13. The flux-cored wire according to claim 12 . <5> The surface is coated with either or both of polytetrafluoroethylene oil and perfluoropolyether oil. <1> ~ <4> 13. The flux-cored wire according to claim 12 . <6> <1> ~ <5> 13. A method for manufacturing a welded joint, comprising: welding steel materials with the flux-cored wire according to claim 12. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide a flux-cored wire that can provide a weld metal that is excellent in low-temperature toughness and low-temperature cracking resistance as well as in welding workability (particularly vertical weldability), and a method for manufacturing a welded joint using the flux-cored wire. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] An embodiment that is an example of the present disclosure will be described. In this specification, a numerical range expressed using "~" means a range that includes the numerical values ​​as the lower and upper limits when the numerical values ​​before and after "~" are not followed by "more than" or "less than." In addition, when the numerical values ​​before and after "~" are followed by "more than" or "less than," the numerical range does not include the numerical values ​​as the lower and upper limits. In the present specification, the upper limit of a certain numerical range may be replaced by the upper limit of another numerical range, or may be replaced by a value shown in an example. The lower limit of a certain numerical range may be replaced by the lower limit of another numerical range, or may be replaced by a value shown in an example. In addition, with regard to the content, "%" means "mass %". The content (%) of "0 to" means that the component is an optional component and does not have to be contained.

[0013] <Flux-cored wire> The flux-cored wire according to the present disclosure includes a steel sheath and flux filled inside the steel sheath. The flux-cored wire according to the present disclosure has a predetermined composition of chemical components excluding oxides, fluorides, nitrides, and metal carbonates, contains predetermined amounts of Ti oxide, Si oxide, fluoride, Na-containing compound, and K-containing compound, and contains no Zr oxide and Al oxide or contains predetermined amounts of Al oxide. The X value calculated by the formula A described later is 0.10 to 160.00.

[0014] Hereinafter, the reasons for limiting the requirements (including optional requirements) for the flux-cored wire according to the present disclosure will be specifically described.

[0015] These components will be described in detail below. In the following description, "%" means "mass % with respect to the total mass of the flux-cored wire" unless otherwise specified.

[0016] The chemical components described below may be included in the steel sheath or in the flux. In addition, when the flux-cored wire according to the present disclosure has a plating layer on the outer surface of the steel sheath, the chemical components may be included in the plating layer. In the following description, the "chemical components excluding nitrides, oxides, fluorides, and metal carbonates" may be simply referred to as the "chemical components."

[0017] The chemical composition of the flux-cored wire according to the present disclosure, excluding oxides, fluorides, nitrides, and metal carbonates, is as follows: C: 0.020~0.100%, Si: 0.20 to 0.80%, Mn: 1.50-3.50%, P: 0 to 0.030%, S: 0~0.030%, Cu: 0.005 to 1.000%, Ni: 0.10-5.00%, Cr: 0~1.000% Mo: 0~1.000%, Cr+Mo: 0.005~1.000% Nb: 0 to 0.0150%, V: 0 to 0.0150%, Mg: 0-1.00%, Al: 0 to 0.100%, Ca: 0-0.100%, Ti: 0 to 0.100%, B: 0~0.0100%, REM: 0~0.100%, Bi: 0 to 0.050%, and The balance is Fe and impurities.

[0018] That is, in the flux-cored wire according to the present disclosure, the above-mentioned components are the contents of components contained other than oxides, fluorides, nitrides, and metal carbonates.

[0019] (C: 0.020~0.100%) C contributes to stabilizing the arc during welding and has the effect of improving the strength of the weld metal. However, if the C content is less than 0.020%, this effect is not sufficiently obtained, the arc becomes unstable, and the necessary weld metal strength is not obtained. On the other hand, if the C content exceeds 0.100%, C is excessively retained in the weld metal, so that the strength of the weld metal becomes excessively high and the low-temperature toughness decreases. Therefore, the C content is set to 0.020 to 0.100%. The lower limit of the C content is preferably 0.040%, 0.050%, or 0.060%. The upper limit of the C content is preferably 0.090%, 0.080%, or 0.070%.

[0020] (Si: 0.20~0.80%) Silicon improves the shape and appearance of the weld bead by forming a part of the weld slag during welding, and contributes to improving welding workability (especially vertical weldability). However, if the Si content is less than 0.20%, the effect of improving the shape and appearance of the weld bead cannot be sufficiently obtained. On the other hand, if the Si content exceeds 0.80%, excessive Si is retained in the weld metal, which reduces the low-temperature toughness of the weld metal. Therefore, the Si content is set to 0.20 to 0.80%. The lower limit of the Si content is preferably 0.25%, 0.30%, or 0.40%. The upper limit of the Si content is preferably 0.75%, 0.70%, or 0.60%.

[0021] (Mn: 1.50-3.50%) Mn has the effect of increasing the strength and low-temperature toughness of the weld metal by being retained in the weld metal. However, if the Mn content is less than 1.50%, these effects are not sufficiently obtained, and the necessary strength and low-temperature toughness of the weld metal cannot be obtained. On the other hand, if the Mn content exceeds 3.50%, Mn is excessively retained in the weld metal, the strength of the weld metal becomes excessively high, and the low-temperature toughness decreases. Therefore, the Mn content is set to 1.50 to 3.50%. The lower limit of the Mn content is preferably 1.55%, 1.60%, or 1.70%. The upper limit of the Mn content is preferably 3.45%, 3.30%, or 3.20%.

[0022] (P:0~0.030%) Since P is an impurity element and reduces the toughness of the weld metal, it is preferable to reduce the P content in the flux-cored wire as much as possible. Therefore, the lower limit of the P content in the chemical components of the flux-cored wire is 0%. Also, if the P content in the chemical components of the flux-cored wire is 0.030% or less, the adverse effect of P on the toughness is within an acceptable range. In order to effectively suppress solidification cracking of the weld metal, the P content is preferably 0.020% or less, 0.015% or less, or 0.010% or less. However, from the viewpoint of reducing the dephosphorization cost, the P content is preferably 0.003% or more.

[0023] (S:0~0.030%) S is also an impurity element, and if present in excess in the weld metal, it deteriorates both the toughness and ductility of the weld metal, so it is preferable to reduce the S content in the flux-cored wire as much as possible. Therefore, the lower limit of the S content in the chemical components of the flux-cored wire is 0%. Also, if the S content in the chemical components of the flux-cored wire is 0.030% or less, the adverse effect of S on the toughness and ductility of the weld metal falls within an acceptable range. The S content is preferably 0.020% or less, 0.010% or less, 0.008% or less, 0.006% or less, or 0.005% or less. However, from the viewpoint of reducing the cost of desulfurization, the S content is preferably 0.003% or more.

[0024] (Cu: 0.005 to 1.000%) Cu has the effect of improving the strength and low-temperature toughness of the weld metal. To fully obtain this effect, the Cu content is set to 0.005% or more. Cu may be contained in the plating on the surface of the steel sheath of the flux-cored wire, or may be contained in the flux as a single element or as an alloy. Cu plating also has the effect of improving rust resistance, electrical conductivity, and chip wear resistance. Therefore, the Cu content is the total amount of Cu contained in, for example, the steel sheath and the flux, and the Cu contained in the plating on the wire surface. On the other hand, if the Cu content exceeds 1.000%, the low-temperature toughness of the weld metal may decrease. Therefore, the Cu content is set to 0.005 to 1.000%. The lower limit of the Cu content is preferably 0.010%, 0.020%, or 0.030%. The upper limit of the Cu content is preferably 0.950%, 0.900%, or 0.800%.

[0025] (Ni: 0.10~5.00%) Ni contributes to improving the low-temperature toughness of the weld metal by increasing the solid solution toughness of Ni. To obtain this effect, the Ni content is set to 0.10% or more. On the other hand, if the Ni content exceeds 5.00%, the low-temperature toughness as well as the cold cracking resistance of the weld metal decreases. Therefore, the Ni content is set to 0.10 to 5.00%. The lower limit of the Ni content is preferably 0.20%, 0.40%, or 0.50%. The upper limit of the Ni content is preferably 4.90%, 4.70%, or 4.50%.

[0026] (Cr:0~1.000%) Cr is not an essential element, so the lower limit of the Cr content is 0%. However, when Mo is not contained, Cr is an essential element. On the other hand, Cr is an effective element for ensuring the hardenability of the weld metal and increasing the strength of the weld metal, but if the Cr content exceeds 1.000%, the low-temperature toughness of the weld metal may deteriorate. Therefore, the upper limit of the Cr content is set to 1.000%. The upper limit of the Cr content is preferably 0.900%, 0.800%, or 0.700%.

[0027] (Mo:0~1.000%) Mo is not an essential component, so the lower limit of the Mo content in the chemical composition of the flux-cored wire is 0%. However, if Cr is not contained, Mo is an essential component. On the other hand, Mo has the effect of improving the hardenability of the weld metal, and is therefore an effective element for increasing the strength of the weld metal, but if the Mo content exceeds 1.000%, the low-temperature toughness of the weld metal deteriorates. Therefore, the upper limit of the Mo content is set to 1.000%. The upper limit of the Mo content is preferably 0.900%, 0.800%, or 0.700%.

[0028] (Cr+Mo (total of Cr and Mo): 0.005 to 1.000%) If the total content of Cr and Mo is less than 0.005%, the hardenability becomes insufficient and the strength cannot be ensured. On the other hand, if the total content of Cr and Mo exceeds 1.000%, the hardenability becomes excessively high and low-temperature toughness cannot be ensured. Therefore, the total content of Cr and Mo is set to 0.005 to 1.000%. The lower limit of the combined content of Cr and Mo is preferably 0.010%, 0.020%, or 0.030%. The upper limit of the combined Cr and Mo content is preferably 0.900%, 0.800%, or 0.700%.

[0029] (Nb: 0~0.0150%) Since Nb is not an essential component, the lower limit of the Nb content is 0%. Nb forms fine carbides in the weld metal, and these fine carbides cause precipitation strengthening in the weld metal, so Nb improves the tensile strength of the weld metal. On the other hand, if the Nb content exceeds 0.0150%, Nb forms coarse precipitates in the weld metal, deteriorating the low-temperature toughness of the weld metal. Therefore, the Nb content is set to 0 to 0.0150%. The lower limit of the Nb content is preferably 0.0001%, 0.0005%, 0.0010%, or 0.0080%. The upper limit of the Nb content is preferably 0.0140%, 0.0130%, 0.0120%, or 0.0100%.

[0030] (V:0~0.0150%) Since V is not an essential component, the lower limit of the V content is 0%. V improves the hardenability of the weld metal, and is therefore an effective element for increasing the strength of the weld metal. On the other hand, if the V content exceeds 0.0150%, the amount of V carbides precipitated in the weld metal becomes excessive, which may cause the weld metal to become excessively hard and degrade the low-temperature toughness of the weld metal. Therefore, the V content is set to 0 to 0.0150%. The lower limit of the V content is preferably 0.0001%, 0.0005%, 0.0010%, or 0.0080%. The upper limit of the V content is preferably 0.0140%, 0.0130%, 0.0120%, or 0.0100%.

[0031] (Mg: 0-1.00%) Since Mg is not an essential component, the lower limit of the Mg content is 0%. On the other hand, Mg is a deoxidizing element, and like Al, it reduces the amount of oxygen in the weld metal and has the effect of improving welding workability (especially vertical weldability) as well as low-temperature toughness. However, if the Mg content exceeds 1.00%, Mg and oxygen react violently in the arc, and the amount of spatter and fume generation may increase. Therefore, the Mg content is set to 0 to 1.00%. The lower limit of the Mg content is preferably 0.05%, 0.10%, or 0.20%. The upper limit of the Mg content is preferably 0.90%, 0.80%, or 0.70%.

[0032] (Al: 0 to 0.100%) Since Al is not an essential component, the lower limit of the Al content is 0%. On the other hand, Al is a deoxidizing element, and like Mg, it reduces the amount of oxygen in the weld metal and has the effect of improving the low-temperature toughness as well as the welding workability (especially vertical weldability). However, if the Al content exceeds 0.100%, the low-temperature toughness of the weld metal is deteriorated. Therefore, the Al content is set to 0 to 0.100%. The lower limit of the Al content is preferably 0.010%, 0.020%, or 0.030%. The upper limit of the Al content is preferably 0.090%, 0.080%, or 0.070%.

[0033] (Ca: 0~0.100%) Since Ca is not an essential component, the lower limit of the Ca content is 0%. Ca has the effect of changing the structure of sulfides in the weld metal and of reducing the size of sulfides and oxides, thereby improving the low-temperature toughness of the weld metal. On the other hand, if the Ca content exceeds 0.100%, the amount of spatter increases, and welding workability (particularly vertical weldability) is impaired. Therefore, the Ca content is set to 0 to 0.100%. The lower limit of the Ca content is preferably 0.010%, 0.020%, or 0.030%. The upper limit of the Ca content is preferably 0.090%, 0.080%, or 0.070%.

[0034] (Ti: 0~0.100%) Since Ti is not an essential component, the lower limit of the Ti content is 0%. Ti is a deoxidizing element that reduces the amount of oxygen in the weld metal and has the effect of improving welding workability (especially vertical weldability) as well as low-temperature toughness. In addition, Ti remains in the weld metal in small amounts to fix solute N, so it has the effect of mitigating the adverse effects of solute N on the low-temperature toughness of the weld metal. On the other hand, if the Ti content exceeds 0.100%, the toughness of the weld metal deteriorates due to the formation of excessive precipitates. When Ti is included in the chemical composition of a flux-cored wire, ferrotitanium (an alloy of iron and titanium) is generally included in the flux. Therefore, the Ti content is set to 0 to 0.100%. The lower limit of the Ti content is preferably 0.010%, 0.020%, or 0.030%. The upper limit of the Ti content is preferably 0.090%, 0.080%, or 0.070%.

[0035] (B: 0~0.0100%) Since B is not an essential component, the lower limit of the B content is 0%. B combines with solute N in the weld metal to form BN, and therefore has the effect of reducing the adverse effect of solute N on the low-temperature toughness of the weld metal. In addition, B increases the hardenability of the weld metal, and therefore has the effect of improving the strength of the weld metal. On the other hand, if the B content exceeds 0.0100%, the B in the weld metal becomes excessive, and coarse BN and Fe 23 It may form B compounds such as (C, B)6, which may deteriorate the low temperature toughness of the weld metal. Therefore, the B content is set to 0 to 0.0100%. The lower limit of the B content is preferably 0.0010%, 0.0020%, or 0.0030%. The upper limit of the B content is preferably 0.0090%, 0.0080%, or 0.0070%.

[0036] (REM:0~0.100%) Since REM is not an essential component, the lower limit of the REM content is 0%. REM has the effect of changing the structure of sulfides in the weld metal and also of reducing the size of sulfides and oxides, thereby improving the low-temperature toughness of the weld metal. On the other hand, if the REM content exceeds 0.100%, the amount of spatter increases, and welding workability (particularly vertical welding ability) is impaired. Therefore, the REM content is set to 0 to 0.100%. The lower limit of the REM content is preferably 0.010%, 0.020%, or 0.030%. The upper limit of the REM content is preferably 0.090%, 0.080%, or 0.070%. In this specification, REM refers to a total of 17 elements, namely Sc, Y, and lanthanoids, and the REM content refers to the content of one type of REM when there is one type of REM, and refers to the total content of these elements when there are two or more types of REM.

[0037] (Bi: 0 to 0.050%) Since Bi is not an essential component, the lower limit of the Bi content is 0%. Bi is an element that improves the detachability of the slag. On the other hand, if the Bi content exceeds 0.050%, solidification cracking occurs in the weld metal. Therefore, the Bi content is set to 0 to 0.050%. The lower limit of the Bi content is preferably 0.005%, 0.010%, or 0.020%. The upper limit of the Bi content is preferably 0.045%, 0.040%, or 0.035%.

[0038] (balance: Fe and impurities) The remaining components in the chemical composition of the flux-cored wire according to the present disclosure are Fe and impurities, such as Fe contained in the steel sheath and Fe (e.g., iron powder) in the alloy powder contained in the flux. Further, impurities refer to components that are mixed in due to various factors in the manufacturing process or that originate from raw materials when industrially manufacturing a flux-cored wire, and are acceptable within a range that does not adversely affect the flux-cored wire according to the present disclosure.

[0039] (Total of Ti oxides converted into TiO2: 3.00-8.00% by mass) Ti oxide is a slag component that acts to uniformly cover the entire bead with slag. Ti oxide also has the effect of stabilizing the duration of the arc and reducing the amount of spatter generated. Therefore, the inclusion of Ti oxide improves welding workability (especially vertical welding).

[0040] If the total of Ti oxides in terms of TiO2 is less than 3.00%, the amount of slag generated is insufficient and the bead cannot be uniformly covered, so that the slag is burned onto the bead surface, resulting in poor bead appearance. Also, if the total of Ti oxides in terms of TiO2 is less than 3.00%, the effect of stabilizing the arc is lost and the amount of spatter increases. Also, welding workability (especially vertical welding) cannot be ensured. On the other hand, if the total of Ti oxides in terms of TiO2 exceeds 8.00%, the arc becomes more stable and the amount of spatter decreases, but the viscosity of the slag increases, making the slag thicker and causing the toe of the bead to bulge. Also, if the total of Ti oxides in terms of TiO2 exceeds 8.00%, pits become more likely to occur. Also, slag inclusion occurs. In addition, the oxygen content of the weld metal increases, making it difficult to ensure low-temperature toughness.

[0041] Therefore, the total value of Ti oxides converted into TiO2 is set to 3.00 to 8.00%. The lower limit of the total amount of Ti oxides calculated as TiO2 is preferably 3.50%, 4.00%, or 4.50%. The upper limit of the total amount of Ti oxides calculated as TiO2 is preferably 7.50%, 7.00%, or 6.50%.

[0042] Incidentally, Ti oxide may be present in the flux mainly as rutile, titanium oxide, titanium slag, ilmenite, sodium titanate, potassium titanate, etc. Therefore, the Ti oxide content in the flux can be adjusted to the above range mainly by controlling the Ti oxide content in the flux.

[0043] Here, the total TiO2-converted value of Ti oxides refers to the mass % of TiO2 relative to the total mass of the wire, when all Ti oxides contained in the wire (e.g., TiO, TiO2, Ti2O3, Ti3O5, etc., added as rutile, titanium oxide, titanium slag, ilmenite, sodium titanate, potassium titanate, etc.) are converted into TiO2. The total of the Ti oxides converted into TiO2 is calculated by analyzing the mass of Ti present in the wire as oxide using an X-ray fluorescence analyzer. Specifically, the wire is polished to expose a longitudinal cross section (cross section parallel to the longitudinal direction of the wire: L cross section) at a position half the wire diameter φ, and the cross section is analyzed. For example, if TiO2, Ti2O3, and Ti3O5 are detected by the analysis, the mass% of each Ti oxide is expressed as [TiO2], [Ti2O3], and [Ti3O5], and the total of the Ti oxides converted into TiO2 is expressed as [converted TiO2], and the calculation is performed using the following formula 1. [Converted TiO2]=(0.60×[TiO2]+0.67×[Ti2O3]+0.64×[Ti3O5])×1.67...Equation 1 The coefficients (0.60, 0.67, 0.64) in Equation 1 are used to calculate the amount of Ti contained in each oxide, and the multiplier (1.67) at the end is used to calculate the TiO2 equivalent value from the total amount of Ti present as oxide in the wire.

[0044] Here, we will explain how to calculate the coefficients. x O y If oxides (e.g. TiO2, Ti2O3, Ti3O5) are detected, M x O y The coefficient is calculated using the following formula 2. [Atomic weight of element M] × x / ([Atomic weight of element M] × x + [Atomic weight of oxygen] × y) Equation 2 The values ​​0.60, 0.67, and 0.64 in formula 1 correspond to the coefficients calculated in formula 2 above. We will also explain how to calculate the multiplier to calculate the conversion value. a O b The multiplier for conversion to (e.g. TiO2) is calculated using the following formula 3. ([atomic weight of M element] × a + [atomic weight of oxygen] × b) / [atomic weight of M element × a] Equation 3 The 1.67 in formula 1 corresponds to the multiplier calculated in formula 3 above. In addition, oxides may be compounds that combine two metal elements. In that case, the coefficient is calculated as follows: M x Oy M 2 z (Example: TiO3·Fe, that is, M=Ti, M 2 = oxide of Fe, x=1, y=3, z=1) is detected, the calculation is made using the following formula 4. [Atomic weight of M element] × x / ([Atomic weight of M element] × x + [Atomic weight of oxygen] × y + [M 2 atomic weight of element x z) Equation 4

[0045] The sum of the SiO2-equivalent values ​​of Si oxides, the sum of the ZrO2-equivalent values ​​of Zr oxides, the sum of the Al2O3-equivalent values ​​of Al oxides, the sum of the MgO-equivalent values ​​of Mg oxides, the sum of the Na2O-equivalent values ​​of Na oxides, the sum of the K2O-equivalent values ​​of K oxides, the sum of the CaO-equivalent values ​​of Ca oxides, the sum of the MnO2-equivalent values ​​of Mn oxides, and the sum of the FeO-equivalent values ​​of Ti oxides are also calculated in the same manner as the sum of the TiO2-equivalent values ​​of Ti oxides. That is, a longitudinal cross section at 1 / 2 the wire diameter φ is analyzed by a fluorescent X-ray analyzer, and coefficients and multipliers are calculated according to the various oxides detected in accordance with the above formulas 2, 3, and 4, and calculations are performed in the same manner as the above formula 1. Representative oxides detected by analysis are listed below. Silicon oxides; SiO, SiO2, Si2O3, Si2O4 Zr oxide; ZrO2 Aluminum oxides: AlO, Al2O3, Al3O5 Magnesium oxide; MgO, MgO2, Mg2O Na oxide; Na2O, Na2O2 K oxide; K2O, KO2 Calcium oxide; CaO, CaO2 Manganese oxide; MnO, Mn2O, MnO2 Fe oxides; FeO, Fe2O4, FeO3

[0046] (Total of silicon oxides converted into SiO2: 0.10 to 0.50% by mass) Silicon oxide is a slag component that increases the viscosity of molten slag and improves the removability of the slag. If the total amount of silicon oxides converted into SiO2 is less than 0.10%, the slag encapsulation state is poor, slag removability is poor, the bead shape and bead appearance are also poor, and welding workability (especially vertical welding) cannot be ensured. On the other hand, if the total of the Si oxides in terms of SiO2 exceeds 0.50%, the amount of spatter increases. Furthermore, if the total of the Si oxides in terms of SiO2 exceeds 0.50%, pits and gas grooves are likely to occur. Also, slag inclusion occurs. In addition, the amount of oxygen in the weld metal increases, making it difficult to ensure low-temperature toughness.

[0047] Therefore, the total of the SiO2 converted value of Si oxides is set to 0.10 to 0.50%. The lower limit of the total amount of silicon oxides converted into SiO2 is preferably 0.15%, 0.20%, or 0.25%. The upper limit of the total amount of silicon oxides calculated as SiO2 is preferably 0.45%, 0.40%, or 0.35%.

[0048] The Si oxides may be present in the flux mainly as silica sand, zircon sand, feldspar, sodium silicate, potassium silicate, etc. Therefore, the content of the Si oxides in the flux can be controlled mainly to fall within the above range.

[0049] (Total of Zr oxides converted into ZrO2: 0 to 0.80% by mass) Zr oxide increases the oxygen content in the weld metal and reduces low-temperature toughness. Therefore, it is better not to include Zr oxide, and the lower limit of the total Zr oxide converted to ZrO2 is set to 0%.

[0050] However, Zr oxide is a slag component and has the effect of increasing the slag coverage in horizontal fillet welding and smoothing the bead shape. On the other hand, if the total ZrO2 content of Zr oxide exceeds 0.80%, the bead shape tends to become convex, and slag inclusion occurs.

[0051] Therefore, the total value of Zr oxide converted into ZrO2 is set to 0 to 0.80%. The upper limit of the total amount of Zr oxide calculated as ZrO2 is preferably 0.60%, 0.20%, or 0.10%.

[0052] Zr oxide may be present mainly as zircon sand, zirconium oxide, etc. in the flux, and may also be contained in a small amount in Ti oxide. Therefore, the Zr oxide content in the flux can be controlled to fall within the above range.

[0053] (Total of Al oxides converted into Al2O3: 0 to 0.80% by mass) Aluminum oxides lower the solidification temperature of welding slag and deteriorate welding workability (especially vertical welding). Therefore, it is better not to include aluminum oxides, and the lower limit of the total Al2O3 converted value of aluminum oxides is set to 0%.

[0054] However, when aluminum oxide is used to form molten slag, it has the effect of preventing undercutting on the upper leg side of the fillet bead by improving the slag encapsulation. On the other hand, if the total Al2O3-equivalent value of aluminum oxide exceeds 0.80%, the bead toe on the lower leg side of the fillet bead will have a bulging bead shape. Also, slag inclusion will occur. Therefore, the total Al2O3 converted value of Al oxides is set to 0 to 0.80%. The upper limit of the total content of Al oxides calculated as Al2O3 is preferably 0.60%, 0.20%, or 0.10%.

[0055] Incidentally, Al oxide is often present mainly as a component of alumina, feldspar, etc. in the flux, and therefore the content of Al oxide can be adjusted to the above range mainly by controlling the content of Al oxide in the flux.

[0056] (Total fluoride: 0.10 to 2.00% by mass) In K2SiF6, K2ZrF6, NaF, Na3AlF6, CaF2, and MgF2 (hereinafter, these fluorides may be referred to as "specific fluorides"), the F decomposed during welding reduces the amount of diffusible hydrogen in the weld metal. This is because fluorine (F - ) is hydrogen (H + ) to become hydrogen fluoride (HF), which is then released outside the weld metal. If the total amount of specific fluorides is less than 0.10%, the effect of reducing the amount of diffusible hydrogen in the weld metal is small, and low-temperature cracking resistance cannot be ensured. On the other hand, if the total content of specific fluorides exceeds 2.00%, the solidification temperature of the welding slag becomes lower, and the welding workability (particularly vertical welding ability) deteriorates.

[0057] Therefore, the total content of one or more of the specific fluorides is set to 0.10 to 2.00%. The lower limit for the total of particular fluorides is preferably 0.20%, 0.30%, or 0.40%. The upper limit for the total of particular fluorides is preferably 1.90%, 1.80%, or 1.70%.

[0058] (Total of Na-containing compounds: 0.01 to 2.00% by mass) Na oxides, NaF, and Na3AlF6 (hereinafter, these Na-containing compounds may be referred to as "specific Na-containing compounds") decompose during welding, and the Na acts as a deoxidizer, reducing the oxygen content in the weld metal. If the total amount of the specific Na-containing compounds is less than 0.01%, the effect of reducing the oxygen content in the weld metal is small, and low-temperature toughness cannot be ensured. On the other hand, if the total content of the specific Na-containing compounds exceeds 2.00%, the solidification temperature of the welding slag becomes lower, and the welding workability (particularly vertical welding ability) deteriorates.

[0059] Therefore, at least one of the specific Na-containing compounds is contained in a total amount of 0.01 to 2.00%. The lower limit of the total amount of the specific Na-containing compounds is preferably 0.15%, 0.20%, or 0.30%. The upper limit of the total of the specific Na-containing compounds is preferably 1.90%, 1.80%, or 1.70%. The content of Na oxide means the total Na2O equivalent value of Na oxide.

[0060] (Total of K-containing compounds: 0.01 to 2.00% by mass) In potassium oxide, K2SiF6, and K2ZrF6 (hereinafter, these potassium-containing compounds may be referred to as "specific potassium-containing compounds"), the potassium that decomposes during welding acts as a deoxidizer and reduces the amount of oxygen in the weld metal. If the total amount of the specific K-containing compounds is less than 0.01%, the effect of reducing the oxygen content in the weld metal is small, and low-temperature toughness cannot be ensured. On the other hand, if the total content of the specific K-containing compounds exceeds 2.00%, the solidification temperature of the welding slag becomes lower, and the welding workability (particularly vertical welding ability) deteriorates.

[0061] Therefore, the total content of at least one of the specific K-containing compounds is set to 0.01 to 2.00%. The lower limit of the total amount of specific K-containing compounds is preferably 0.20%, 0.30%, or 0.40%. The upper limit of the total amount of specific K-containing compounds is preferably 1.95%, 1.90%, or 1.80%. The content of K oxide means the total K2O equivalent value of K oxide.

[0062] (Total of Mg-containing compounds: 0.01 to 2.00% by mass) The flux-cored wire according to the present embodiment may contain at least one Mg-containing compound, such as Mg oxide and MgF2, in addition to the specific Na-containing compound and the specific K-containing compound. Mg oxides and MgF2 (hereinafter, these Mg-containing compounds may be referred to as "specific Mg-containing compounds") decompose during welding, and the Mg acts as a deoxidizer, reducing the amount of oxygen in the weld metal. When the total content of the specific Mg-containing compounds is 0.01% or more, the effect of reducing the oxygen content in the weld metal is increased, and the low-temperature toughness is further improved. On the other hand, when the total amount of the specific Mg-containing compounds is 2.00% or less, the solidification temperature of the welding slag becomes high, and the welding workability (especially vertical welding ability) is improved.

[0063] Therefore, the total amount of the specific Mg-containing compounds may be 0 to 2.00%, and it is preferable that one or more of the specific Mg-containing compounds are contained and the total amount is 0.01 to 2.00%. The lower limit of the total amount of the specific Mg-containing compounds is more preferably 0.20%, 0.30%, or 0.40%. The upper limit for the total amount of the specific Mg-containing compounds is more preferably 1.90%, 1.80%, or 1.70%. The content of Mg oxide means the total Mg oxide content calculated as MgO.

[0064] (The significance of including specific Na-containing compounds and specific K-containing compounds in wire) Even if the amount of the specific Na-containing compound and the specific K-containing compound are each less than 0.01% and the amount of CaF2 containing Ca that functions as a deoxidizer is increased, spatter increases and welding workability deteriorates. Also, even if the amount of metallic Mg that functions as a deoxidizer is increased, metallic Mg increases the amount of diffusible hydrogen in the weld metal, deteriorating cold cracking resistance. Therefore, in order to obtain a weld metal that is excellent in low-temperature toughness and resistance to low-temperature cracking as well as in welding workability (particularly vertical weldability), it is necessary to make the wire contain the specific Na-containing compound and the specific K-containing compound within the above-mentioned ranges. From a similar viewpoint, it is also preferable that the wire contains the specific Mg-containing compound in an amount within the above range. The contents of the specific Mg-containing compound, the specific Na-containing compound, and the specific K-containing compound are expressed in mass % relative to the total mass of the flux-cored wire.

[0065] (X value calculated by formula A) In the flux-cored wire according to the present disclosure, the X value calculated by the following formula A is 0.10 to 160.00. X=(8×CaF2+5×MgF2+5×NaF+5×K2SiF6+5×K2ZrF6+Na3AlF6) / (SiO2+Al2O3+ZrO2+0.5×MgO+CaO+0.5×Na2O+0.5×K2O+MnO2+FeO)...Formula A In formula A, CaF2, MgF2, NaF, K2SiF6, K2ZrF6, and Na3AlF6 are the contents of the compounds represented by each chemical formula in mass% relative to the total mass of the flux-cored wire. SiO2 represents the total of the SiO2 equivalent value of Si oxide, Al2O3 represents the total of the Al2O3 equivalent value of Al oxide, ZrO2 represents the total of the ZrO2 equivalent value of Zr oxide, MgO represents the total of the MgO equivalent value of Mg oxide, CaO represents the total of the CaO equivalent value of Ca oxide, Na2O represents the total of the Na2O equivalent value of Na oxide, K2O represents the total of the K2O equivalent value of K oxide, MnO2 represents the total of the MnO2 equivalent value of Mn oxide, and FeO represents the total of the FeO equivalent value of Fe oxide. In addition, the SiO2 equivalent value, the Al2O3 equivalent value, the ZrO2 equivalent value, the MgO equivalent value, the CaO equivalent value, the Na2O equivalent value, the K2O equivalent value, the MnO2 equivalent value, and the FeO equivalent value in Formula A are expressed in mass% with respect to the total mass of the flux-cored wire.

[0066] In formula A, the numerator is an index of the amount of compounds that decompose during welding, function as deoxidizers, and reduce the amount of oxygen in the weld metal (Ca, Mg, Na, K, Si), and fluorine, which reduces the amount of diffusible hydrogen in the weld metal. On the other hand, the denominator is an index of the amount of compounds containing oxygen (O), which increases the oxygen content of the weld metal.

[0067] That is, if the X value is less than 0.10, the amount of compounds containing oxygen (O) that increase the oxygen content in the weld metal is too large, the effect of reducing the oxygen content in the weld metal is small, and low-temperature toughness cannot be ensured. On the other hand, if the X value exceeds 160.00, the amount of fluoride is too large, causing slag inclusion and making it impossible to produce a sound joint.

[0068] Therefore, the X value calculated by formula A is set to 0.10 to 160.00. The lower limit of the X value is preferably 1.00, 5.00, or 10.00. The upper limit of the X value is preferably 130.00, 100.00, 70.00, 50.00, or 20.00.

[0069] (Ceq calculated by formula B) In the flux-cored wire according to the present disclosure, Ceq calculated by formula B is preferably 0.300 to 0.750. Ceq=[C]+[Si] / 24+[Mn] / 6+[Ni] / 40+[Cr] / 5+[Mo] / 4+[V] / 14...Formula B In formula B, the element symbols represent the content, in mass %, of each element contained as a chemical component excluding oxides, fluorides, nitrides, and metal carbonates relative to the total mass of the flux-cored wire.

[0070] Ceq affects the hardenability of the weld metal. When Ceq is high, the weld metal hardens, improving its tensile strength, but reducing its low-temperature toughness. When Ceq is 0.300% or more, Ceq of the weld metal is also more likely to be satisfied, and the tensile strength of the weld metal tends to be sufficient. When Ceq is 0.750% or less, it becomes easier to prevent the Ceq of the weld metal from becoming excessive, the low-temperature toughness of the weld metal is sufficient, and low-temperature cracking tends to be suppressed. Therefore, Ceq is preferably 0.300 to 0.750. The lower limit of Ceq is preferably 0.350, 0.400, or 0.450. The upper limit of Ceq is preferably 0.700, 0.650, or 0.600.

[0071] -Total content of other oxides: 0~10.00%- In the flux-cored wire according to the present disclosure, when oxides selected from the group consisting of Fe oxide, Mg oxide, Na oxide, K oxide, Mn oxide, and Ca oxide are included as oxides other than Ti oxide, Si oxide, Zr oxide, and Al oxide, the total content thereof is preferably 10.00% or less. The oxides included in the group consisting of Fe oxide, Mg oxide, Na oxide, K oxide, Mn oxide, and Ca oxide may be simply abbreviated as "other oxides". Also, the total value of the content of each oxide in the other oxides may be simply abbreviated as "total content of other oxides".

[0072] In the case where the flux-cored wire according to the present disclosure contains one or more of the other oxides, the total content of the other oxides is calculated as the sum of Fe oxide (converted into FeO), Mg oxide (converted into MgO), Na oxide (converted into Na2O), K oxide (converted into KO), Mn oxide (converted into MnO2), and Ca oxide (converted into CaO).

[0073] In addition, in the flux-cored wire according to the present disclosure, the other oxides are not essential components, so the lower limit of the total content of the other oxides in the flux-cored wire is 0%. On the other hand, other oxides have the effect of maintaining the weld bead shape well and the effect of improving vertical weldability. In addition, Mg oxide, Fe oxide, etc. also have the effect of stabilizing the arc. In order to obtain such an effect, the total content of other oxides may be more than 0%. In order to further exert these effects, the lower limit of the total content of other oxides may be 0.05%, 0.10%, 0.15%, or 0.20%. However, if the total content of other oxides exceeds 10.00%, slag inclusion may occur, making it impossible to manufacture a sound joint. Therefore, the upper limit of the total content of other oxides is preferably 10.00%, and may be 9.00%, 8.00%, 7.00%, 6.00%, 3.00%, 2.00%, 1.00%, 0.50%, or 0.30%.

[0074] The content of other oxides in the flux-cored wire according to the present disclosure does not need to be limited to each type of oxide. The content of each of the other oxides and the total content of the other oxides are measured by using a combination of fluorescent X-ray analysis and an electron probe micro analyzer (EPMA), in the same manner as the above-mentioned content of Ti oxide.

[0075] (nitrides, metal carbonates) Nitrides (especially nitrides in flux) reduce the amount of diffusible hydrogen in the weld metal, significantly improving the cold cracking resistance of the weld metal. The reason for this is not clear, but it is speculated that one of the reasons is that the N in the nitrides combines with hydrogen (H) during welding to become ammonia (NH3), and this NH3 is released outside the weld metal. Therefore, the flux-cored wire according to the present disclosure may include nitrides.

[0076] The flux-cored wire according to the present disclosure may contain, as a nitride, one or more types selected from the group consisting of, for example, AlN, BN, Ca3N2, CeN, CrN, Cu3N, Fe4N, Fe3N, Fe2N, Mg3N, Mo2N, NbN, Si3N4, TiN, VN, ZrN, Mn2N, and Mn4N.

[0077] Metal carbonates are ionized by the arc and generate CO2 gas, which reduces the hydrogen partial pressure in the welding atmosphere and reduces the amount of diffusible hydrogen in the weld metal. Therefore, the flux-cored wire according to the present disclosure may contain metal carbonate in the flux.

[0078] The flux-cored wire according to the present disclosure may contain, as the metal carbonate, one or more selected from the group consisting of MgCO3, Na2CO3, LiCO3, CaCO3, K2CO3, BaCO3, FeCO3, MnCO3, and SrCO3. However, the type and composition of the metal carbonate are not limited.

[0079] The contents of nitrides and metal carbonates are measured by using a combination of fluorescent X-ray analysis and an electron probe micro analyzer (EPMA), in the same manner as the above-mentioned Ti oxide content.

[0080] The flux-cored wire according to the present disclosure may further include a lubricant applied to the wire surface. The lubricant applied to the wire surface has the effect of improving the wire feedability during welding. Various types of lubricants for welding wires (e.g., vegetable oils such as palm oil) can be used, but in order to suppress low-temperature cracking of the weld metal, it is preferable to use one or both of polytetrafluoroethylene oil (PTFE oil) and perfluoropolyether oil (PFPE oil) that do not contain H. In addition, as described above, the flux-cored wire according to the present disclosure may further include a plating formed on the wire surface. In this case, the lubricant is applied to the surface of the plating.

[0081] The amount of hydrogen contained in the flux-cored wire according to the present disclosure is not particularly limited, but in order to reduce the amount of diffusible hydrogen in the weld metal, it is preferable that the amount is 12 ppm or less relative to the total mass of the flux-cored wire. The amount of hydrogen in the flux-cored wire may increase due to the intrusion of moisture into the flux-cored wire during storage of the flux-cored wire. Therefore, if the period between the manufacture of the wire and its use is long, it is desirable to prevent the intrusion of moisture by the means described below.

[0082] (steel shell) The steel sheath of the flux-cored wire according to the present disclosure is not particularly limited, and may be, for example, a mild steel sheath having a chemical composition including C: 0-0.1%, Si: 0-0.10%, Mn: 0-3.00%, P: 0-0.030%, S: 0-0.020%, Al: 0-0.1%, and N: 0-0.030%, with the balance including at least iron and impurities.

[0083] (Wire shape) Next, the shape (wire structure) of the flux-cored wire according to the present disclosure will be described. Flux-cored wires are usually classified into two types: wires having a shape (seamless shape) in which the seams of the steel outer sheath are welded and therefore have no slit-like gaps (wires having a weld at the seam of the steel outer sheath, hereinafter sometimes referred to as seamless wires), and wires having a shape including slit-like gaps in which the seams of the steel outer sheath are not welded.

[0084] In the flux-cored wire according to the present disclosure, any of the shapes may be adopted. However, in order to suppress the occurrence of cold cracking in the weld metal, it is preferable that the steel sheath does not have slit-shaped gaps. H (hydrogen) that penetrates the weld during welding diffuses into the weld metal and the welded material, accumulates in the stress concentration area, and causes cold cracking. There are various sources of H, but when welding is performed under conditions where the cleanliness of the weld and the gas shielding conditions are strictly controlled, the moisture (H2O) contained in the wire is the main source of H, and the amount of this moisture strongly affects the amount of diffusible hydrogen in the welded joint.

[0085] If the steel sheath has a seam, moisture in the air is likely to penetrate into the flux through the seam. For this reason, it is desirable to prevent moisture in the air from penetrating into the flux through the steel sheath during the period from wire manufacture to use by removing the seam of the steel sheath. If the steel sheath has a seam and the period from wire manufacture to use is long, it is desirable to vacuum package the entire flux-cored wire or store the flux-cored wire in a container that can keep it dry in order to prevent the penetration of H sources such as moisture.

[0086] (Wire diameter) The diameter of the flux-cored wire according to the present disclosure is not particularly limited, but is, for example, φ1.0 to φ2.0 mm. Note that the diameter of a typical flux-cored wire is φ1.2 to φ1.6 mm.

[0087] (Filling rate) The filling rate of the flux-cored wire according to the present disclosure is not particularly limited as long as the above-mentioned conditions are satisfied. In consideration of the filling rate of a general flux-cored wire, the lower limit of the filling rate of the flux-cored wire according to the present disclosure may be, for example, 8%, 10%, or 12%. The upper limit of the filling rate of the flux-cored wire according to the present disclosure may be, for example, 28%, 25%, 22%, 20%, or 17%.

[0088] <Method of manufacturing flux-cored wire> Next, a method for producing the flux-cored wire according to the present disclosure will be described. It should be noted that the manufacturing method described below is merely an example, and the method for manufacturing the flux-cored wire according to the present disclosure is not limited to the method described below.

[0089] (In the case of seamless flux-cored wire) A method for manufacturing a flux-cored wire having a seamless shape includes a step of preparing flux, a step of forming a steel strip using a forming roll while feeding the steel strip in the longitudinal direction to obtain a U-shaped open tube, a step of supplying flux into the open tube through the opening of the open tube, a step of butt-welding opposing edge portions (both circumferential ends) of the opening of the open tube to obtain a seamless tube, a step of drawing the seamless tube to obtain a flux-cored wire having a predetermined wire diameter, and a step of annealing the flux-cored wire during or after the drawing step is completed. The flux is adjusted so that each component of the flux-cored wire falls within the above-mentioned range. Note that the width and thickness of the steel strip, which is the material of the steel sheath, and the flux filling rate, which is determined by the amount of flux filling, also affect the amount of each component of the flux-cored wire.

[0090] The butt welding is performed by electric resistance welding, laser welding, TIG welding, or the like. During or after the wire drawing process, the flux-cored wire is annealed to remove moisture from the flux-cored wire. In order to make the H content of the flux-cored wire 12 ppm or less, the annealing temperature is preferably 650° C. or more and the annealing time is preferably 4 hours or more. In order to prevent deterioration of the flux, the annealing temperature is preferably 900° C. or less.

[0091] If the cross section of a butt seam welded flux cored wire without slit-like gaps is polished and etched, the weld marks can be seen, but if it is not etched, the weld marks cannot be seen. Therefore, it is sometimes called seamless as mentioned above. For example, in "New Edition Introduction to Welding and Joining Technology" (2008) edited by the Japan Welding Society, Sanpo Publishing, p.111, it is described that a butt seam welded flux cored wire without slit-like gaps is a seamless type wire. A flux cored wire without slit-like gaps can be obtained by brazing the gaps in the steel sheath of the flux cored wire.

[0092] (In the case of flux-cored wire with slit-shaped gaps) The method for producing a flux-cored wire having a slit-shaped gap is the same as the method for producing a flux-cored wire having a seamless shape, except that, instead of a step of butt-welding both circumferential ends of an open tube to obtain a seamless tube, a step of forming an open tube and butting the ends of the open tube to obtain a tube with a slit-shaped gap is included. The method for producing a flux-cored wire having a slit-shaped gap may further include a step of crimping the butted ends of the open tube. In a method for producing a flux-cored wire having slit-like gaps, a tube having slit-like gaps is drawn.

[0093] <Method of manufacturing welded joints> Next, a method for producing a welded joint (welding method) according to the present disclosure will be described. A method for manufacturing a welded joint according to the present disclosure includes a step of welding steel materials using the flux-cored wire according to the present disclosure described above.

[0094] In the method for manufacturing a welded joint according to the present disclosure, the welding method is preferably gas-shielded arc welding. In the method for producing a welded joint according to the present disclosure, the type of steel material (welded material) that is the base material of the welded joint is not particularly limited. For example, CM Steel materials having high cold cracking susceptibility in which the (weld crack susceptibility composition) is 0.24% or more, particularly high-strength steel plates having a tensile strength of 590 MPa to 1700 MPa and a plate thickness of 20 mm or more, can be suitably used.

[0095] In the method for manufacturing a welded joint according to the present disclosure, it is preferable to include a step of welding a base steel sheet using a flux-cored wire according to the present disclosure in one or more of the first pass to the final pass. When the welding is performed in only one pass, the flux-cored wire according to the present disclosure is used in that one pass. The type of base steel sheet (base material) is not particularly limited. The polarity of the flux-cored wire may be either positive or negative, since the effect on the amount of diffusible hydrogen in the weld metal and the amount of spatter generation is negligibly small, but is preferably positive.

[0096] The type of shielding gas used in the method for producing a welded joint according to the present disclosure is not particularly limited. The method for producing a welded joint according to the present disclosure exhibits excellent welding workability regardless of the type of shielding gas, and can obtain a welded joint having high strength, high toughness, and high fatigue strength. As the shielding gas in the method for producing a welded joint according to the present disclosure, 100% by volume carbon dioxide gas, which is commonly used, and a mixed gas of Ar and 3 to 30% by volume CO2, etc., can be preferably used. In addition, the shielding gas used in welding using the flux-cored wire according to the present disclosure may contain 5% or less by volume O2 gas. Since these gases are inexpensive, welding using these gases is advantageous in industrial use. Normally, when these gases are used in combination with rutile-based flux-cored wires, they cause a large amount of spatter and deteriorate the welding workability. However, the manufacturing method for a welded joint according to the present disclosure uses the flux-cored wire according to the present disclosure, which can sufficiently suppress the amount of spatter, and therefore, even when these gases are used as shielding gases, good welding workability can be achieved.

[0097] The welding position in the method for producing a welded joint according to the present disclosure is not particularly limited. The method for producing a welded joint according to the present disclosure can exhibit good welding workability (especially vertical weldability) regardless of whether the welding position is a flat position, a horizontal position, a vertical position, or an overhead position.

[0098] The welded joint obtained by the method for manufacturing a welded joint according to the present disclosure includes a base steel plate (base material) and a welded joint composed of a weld metal and a weld heat affected zone. The base material of the welded joint is not particularly limited. The welded joint according to the present disclosure is manufactured using the flux-cored wire according to the present disclosure, and therefore includes a weld metal having a good bead shape. The tensile strength of the welded metal obtained is high, ranging from 590 to 1200 MPa. EXAMPLES

[0099] Next, the feasibility and effects of the present disclosure will be explained in more detail using examples and comparative examples. However, the following examples do not limit the present disclosure, and any design changes that thoroughly achieve the spirit described above and below are all included in the technical scope of the present disclosure.

[0100] (Manufacture of flux-cored wire) The flux-cored wires of the examples and comparative examples were produced by the method described below. First, a steel strip was fed in the longitudinal direction and formed using a forming roll to obtain a U-shaped open tube. Flux was supplied into the open tube through the opening, and the opposing edges of the opening of the open tube were butt-welded to obtain a seamless tube. The seamless pipe was drawn to obtain a flux-cored wire without slit-like gaps, although some samples were drawn to have slit-like gaps without seam welding. In this way, flux-cored wires with a final wire diameter of φ1.2 mm were produced as prototypes. In addition, during the wire drawing process, the flux-cored wires were annealed within a temperature range of 650 to 950°C for 4 hours or more. After the prototypes were produced, a lubricant was applied to the wire surface. The configurations of these flux-cored wires are shown in Tables 1A to 1H.

[0101] The units of the contents of chemical components, oxides, fluorides, Na-containing compounds, K-containing compounds, Mg-containing compounds, and iron powder shown in Tables 1A to 1H are mass% relative to the total mass of the flux-cored wire. In the tables, "mass% relative to the total mass of the flux-cored wire" is abbreviated to "mass%", and "chemical components excluding oxides, fluorides, nitrides, and metal carbonates" is abbreviated to "chemical components".

[0102] [Table 1A]

[0103] [Table 1B]

[0104] [Table 1C]

[0105] [Table 1D]

[0106] [Table 1E]

[0107] [Table 1F]

[0108] [Table 1G]

[0109] [Table 1H]

[0110] The balance of the flux-cored wires shown in Tables 1A to 1B and Tables 1E to 1F (ie, components other than the components shown in the tables) is iron and impurities. Among the flux-cored wires shown in the table, those marked "seamless" in the "wire structure" column have a seamless shape and are coated with palm oil as a lubricant unless otherwise specified in the "remarks" column. In addition, those marked "with slit-like gaps" in the "wire structure" column are wires with slit-like gaps, and those marked "PTFE coated" in the "remarks" column are wires coated with PTFE oil. The elements contained in the flux-cored wires shown in Tables 1A to 1D and 1E to 1H are in the form of a steel sheath or metal powder, and in the tables, values ​​outside the ranges specified in this disclosure are underlined. In addition, in Tables 1A to 1D and Tables 1E to 1H, the blanks in the tables relating to the content of chemical components, compounds, etc., mean that the chemical components, compounds, etc. are not intentionally included. These chemical components, compounds, etc. may be unavoidably mixed in or generated.

[0111] [evaluation] The flux-cored wires of the examples and the comparative examples were used to carry out evaluation by vertical upward gas-shielded arc welding. Specifically, the evaluation was carried out by the method described below. The steel plate to be welded was 780MPa tensile strength steel with a plate thickness of 50mm, and the welding gas used in the evaluation was Ar-20%CO2 gas. In addition, the welding current was all direct current, and the wire polarity was all positive. The welding conditions for the evaluation were as shown in Table 2.

[0112] [Table 2]

[0113] (Evaluation of oxygen content in weld metal) The oxygen content of the weld metal obtained by gas shielded arc welding using the flux-cored wires of the examples and comparative examples was evaluated. The oxygen content of the weld metal was measured by cutting an analytical sample pin for measuring the oxygen content of the weld metal from the center of the plate thickness and the center of the width of the weld metal in the longitudinal direction of the weld joint, and measuring it by an inert gas dissolution infrared absorption method. An oxygen content of 380 ppm or less was marked as ◎, between 380 ppm and 450 ppm as ○, and over 450 ppm as ×.

[0114] (Evaluation of slag entrapment) The evaluation of slag inclusion was performed by performing vertical upward fillet welding on the above-mentioned steel plates. The flux-cored wire that had no slag inclusion on all five cross sections of the weld was judged to be "passed."

[0115] (Evaluation of low temperature cracking resistance) The cold cracking resistance was evaluated by welding a 50mm thick steel plate with a tensile strength of 780MPa under the welding conditions in Table 2 in a constant atmosphere controlled at a temperature of 5℃ and humidity of 60%, and then conducting tests on the welded joints obtained in accordance with JIS Z 3157-1993 (U-shaped weld cracking test method) and JIS Z 3158:2016 (y-shaped weld cracking test method). The welded joints in the U-shaped weld cracking test and the y-shaped weld cracking test were judged as "no cracks" or "cracks present".

[0116] [Table 3A]

[0117] [Table 3B]

[0118] The flux-cored wires of the examples did not cause slag inclusion even in vertical upward welding, and were excellent in welding workability (especially vertical welding). It is found that the flux-cored wires of the examples have a low oxygen content in the weld metal and excellent low-temperature toughness. In addition, no cross-sectional cracks were found in all cross sections in the y-shaped weld cracking test and the U-shaped weld cracking test, and it is found that the weld metal has low temperature cracking resistance. On the other hand, the comparative examples did not meet any of the requirements stipulated in this disclosure and therefore failed in one or more evaluation items.

Claims

1. A flux-cored wire for welding comprising a steel sheath and flux filled inside the steel sheath, The chemical components, excluding oxides, fluorides, nitrides, and metal carbonates, are, in mass% relative to the total mass of the flux-cored wire, C: 0.020-0.100%, Si: 0.20-0.80%, Mn: 1.50-3.50%, P: 0 to 0.030%, S: 0 to 0.030%, Cu: 0.005-1.000%, Ni: 0.10-5.00%, Cr: 0-1.000%, Mo: 0-1.000%, Cr+Mo: 0.005-1.000%, Nb: 0 to 0.0150%, V: 0 to 0.0150%, Mg: 0-1.00%, Al: 0-0.100%, Ca: 0-0.100%, Ti: 0 to 0.100%, B: 0 to 0.0100%, REM: 0-0.100%, Bi: 0 to 0.050%, and The balance is Fe and impurities. Ti oxide TiO ２ The total conversion value is 3.00% to 8.00%; Silicon oxide SiO ２ The total of the converted values ​​is 0.10% to 0.50%; Zr oxide ZrO ２ The total of the conversion values ​​is 0 to 0.80%, Al oxide Al ２ O ３ The total conversion value is 0 to 0.80%. K ２ SiF ６ , K ２ ZrF ６ , NaF, Na ３ AlF ６ , CaF ２ , and MgF ２ The total amount of any one or more fluorides is 0.10 to 2.00%, Na oxide, NaF, and Na ３ AlF ６ Contains one or more of the following Na-containing compounds (excluding Na oxides) ２ O equivalent value) is 0.01 to 2.00%, K oxide, K ２ SiF ６ , and K ２ ZrF ６ Contains one or more K-containing compounds, the total of which (except for K oxides) ２ O equivalent value) is 0.01 to 2.00%, The flux-cored wire has an X value calculated by the following formula A of 0.10 to 160.

00. X = (8 × CaF ２ + 5 × MgF ２ + 5 × NaF + 5 × K ２ SiF ６ + 5 × K ２ ZrF ６ + Na ３ AlF ６ ) / (SiO ２ + Al ２ O ３ + ZrO ２ + 0.5 × MgO + CaO + 0.5 × Na ２ O + 0.5 × K ２ O + MnO ２ + FeO) ···· Formula A In formula A, CaF ２ , MgF ２ , NaF, K ２ SiF ６ , K ２ ZrF ６ , and Na ３ AlF ６ is the content of the compound represented by each chemical formula in mass% relative to the total mass of the flux-cored wire. ２ is Si oxide SiO ２ The sum of the converted values ​​is Al ２ O ３ is Al of Al oxide ２ O ３ The sum of the converted values ​​is ZrO ２ is Zr oxide ZrO ２ MgO represents the sum of MgO converted values ​​of Mg oxides, CaO represents the sum of CaO converted values ​​of Ca oxides, and Na ２ O is Na in Na oxide ２ The sum of the O conversion values ​​is shown, and K ２ O is K in K oxide ２ The total of MnO is shown. ２ is Mn oxide MnO ２ The SiO in formula A represents the sum of the FeO converted values, and FeO represents the sum of the FeO converted values ​​of Fe oxides. ２ Conversion value, Al ２ O ３ Conversion value, ZrO ２ the MgO equivalent value, the CaO equivalent value, the Na ２ O equivalent value, the above K ２ O equivalent value, MnO ２ The converted value and the FeO converted value are expressed as mass % with respect to the total mass of the flux-cored wire.

2. Mg oxide and MgF ２ 2. The flux-cored wire according to claim 1, further comprising one or more Mg-containing compounds, the total of which (wherein Mg oxide is calculated as MgO) is 0.01 to 2.00%.

3. The flux-cored wire according to claim 1 or 2, wherein Ceq calculated by the following formula B is 0.300 to 0.

750. Ceq=[C]+[Si] / 24+[Mn] / 6+[Ni] / 40+[Cr] / 5+[Mo] / 4+[V] / 14...Formula B In formula B, the element symbols represent the content, in mass %, of each element contained as a chemical component excluding oxides, fluorides, nitrides, and metal carbonates with respect to the total mass of the flux-cored wire.

4. The flux-cored wire according to any one of claims 1 to 3, wherein the steel sheath has a welded portion at a joint of the steel sheath.

5. 5. The flux-cored wire according to claim 1, wherein the surface of the wire is coated with one or both of polytetrafluoroethylene oil and perfluoropolyether oil.

6. A method for manufacturing a welded joint, comprising a step of welding steel materials using the flux-cored wire according to any one of claims 1 to 5.

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