JP6958139B2 - Flux-cored wire for gas shielded arc welding and welding joint manufacturing method - Google Patents

Description

The present invention relates to a flux-cored wire for gas shielded arc welding and a method for manufacturing a welded joint.

In recent years, the demand for safety of structural materials has become more and more stringent. The requirements include, for example, mechanical properties (tensile strength and toughness) and corrosion resistance. Highly corrosion resistant materials are suitable for structures exposed to harsh corrosive environments.

Welded structural steel with excellent strength and weldability is used in oil tanks for transporting or storing crude oil, such as oil tanks for crude oil tankers that transport crude oil and above-ground or underground crude oil tanks for storing crude oil. The steel oil tank is exposed to a corrosive environment due to the water, salt and corrosive gas components contained in the crude oil. In particular, the inner surface of a crude oil tanker oil tank becomes a unique corrosive environment due to volatile components in crude oil, mixed seawater, salt in oil field salt water, and dew condensation due to temperature fluctuations during the day and night, and the steel plate and welded parts are corroded and thinned. The most effective way to prevent total or local corrosion is to apply a heavy coat to the surface to protect it from the corrosive environment. However, in the painting work, the area to be applied is enormous, and repainting is required due to the deterioration of the coating film, so that a huge cost is incurred for inspection and painting.

Further, when the strength of the steel sheet is increased, there is a problem that low temperature cracks occur in the weld metal. Low-temperature cracking is a general term for cracks that occur in a welded portion after the temperature of the welded portion drops to around room temperature after welding, and cracks under the bead, cracks at the toe, and the like belong to these cracks. Cold cracking is one of the most serious welding defects because its shape is generally a sharp notch. The occurrence of low-temperature cracks can be suppressed by preheating the welded portion during welding, but the preheating process greatly increases the cost and period of welding.

Patent Documents 1 to 3 disclose a technique for improving the corrosion resistance of a welded portion by controlling the ratio of Cu, Mo or W in the weld metal and the steel sheet. As the welding method, a shielded metal arc welding method and a submerged arc welding method have been proposed. However, in the welding of crude oil tankers, horizontal fillet welding of reinforcing materials called longe, vertical fillet welding, vertical downward fillet welding, and upward fillet welding are performed, and beads in each welding posture are performed. There is a strong demand for flux-cored wires for gas shielded arc welding, which have excellent bead shape including metal sagging resistance in appearance, standing and upward posture, and excellent slag peeling property.

Patent Documents 4 to 5 propose flux-cored wires for gas shielded arc welding having excellent corrosion resistance. However, in the gas shielded arc welding proposed in Patent Document 4 and Patent Document 5, there is no mention of measures against low temperature cracking.

For the reasons described above, in the industrial world, it is possible to manufacture weld metal having excellent mechanical properties (tensile strength and toughness) and corrosion resistance, all-attitude welding (particularly upright welding) is possible, and There is a long-awaited welding material and welding method (welding joint manufacturing method) capable of suppressing the occurrence of low-temperature cracks without performing preheating work or only by simple preheating work.

Japanese Unexamined Patent Publication No. 2005-21981 Japanese Unexamined Patent Publication No. 2005-23421 Japanese Unexamined Patent Publication No. 2012-1810 Japanese Unexamined Patent Publication No. 2013-226757 Japanese Unexamined Patent Publication No. 2013-226578

In order to fully exert the effect of the corrosion-resistant steel, it is necessary to ensure the corrosion resistance even in the welded portion of the corrosion-resistant steel. On the other hand, in the welding material, in addition to ensuring the corrosion resistance of the welded part, ensuring the mechanical properties (tensile strength and toughness) of the welded part, suppressing low temperature cracking, ensuring the weldability, and ensuring the all-posture weldability. It is preferable that the characteristics are also provided. However, welding materials having these properties have not been provided in the prior art.

In view of the above-mentioned problems of the background technology, the present invention can improve the corrosion resistance of the welded portion while imparting high mechanical properties (tensile strength and toughness) to the welded portion, and is excellent in low temperature crack resistance. It is an object of the present invention to provide a flux-cored wire for gas shielded arc welding, which has high welding workability and is capable of full-position welding, and a method for manufacturing a welded joint.

The gist of the present invention is as follows.

(1) The flux-containing wire for gas shielded arc welding according to one aspect of the present invention includes a steel outer skin and a flux filled inside the steel outer skin, and the flux is the flux-containing wire of the flux-containing wire. 1 selected from the group consisting of _{CaF 2} , MgF ₂ , LiF, NaF, K ₂ ZrF ₆ , K ₂ SiF ₆ , and Na ₃ AlF ₆ , with a total mass% of total mass of 0.10 to 3.00%. Seeds or fluorides of two or more, _{Ti oxide having a TiO 2} conversion value of 4.00 to 7.50% with respect to the total mass of the flux-filled wire, and FeO with respect to the total mass of the flux-filled wire. , Na ₂ O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ and K ₂ O, totaling 0.05 to 2.00% of Fe oxide, Na oxide, Si One or more oxides selected from the group consisting of oxides, Zr oxides, Mg oxides, Al oxides, Mn oxides, and K oxides, and the total mass of the flux-filled wire. One or two selected from the group consisting of _{MgCO 3} , Na ₂ CO ₃ , LiCO ₃ , CaCO ₃ , K ₂ CO ₃ , FeCO ₃ , and MnCO ₃ , with a total of 0 to 0.60% by mass. The CaF ₂ content is 0 to 2.00% by mass with respect to the total mass of the flux-filled wire, and the Ca oxide content in terms of CaO is , 0% or more and less than 0.20% in mass% with respect to the total mass of the flux-filled wire, and the fluoride, the oxide, the Ti oxide, the Ca oxide, and the said of the flux-filled wire. The chemical components excluding carbonate are C: 0.003 to 0.150%, Si: 0.35 to 1.00%, Mn: 1.00 to 5 in mass% with respect to the total mass of the flux-filled wire. .00% or less, P: 0.030% or less, S: 0.020% or less, Cu: 0 to 1.50%, Cr: 0 to 5.00%, Mo: 0 to 1.50%, W: 0 to 1.50%, Sn: 0 to 1.00%, Sb: 0 to 1.00%, Al: 0.001 to 0.500%, Ni: 0 to 5.00%, Mg: 0 to 0 .90%, Ti: 0 to 0.10%, B: 0 to 0.0200%, Nb: 0 to 0.20%, V: 0 to 0.20%, Bi: 0 to 0.030%, Ca : 0 to 0.50%, and REM: 0 to 0.010% The balance is composed of Fe and impurities, the Ceq calculated by the formula 1 is 0.53 to 1.00%, and the formula 2 is further satisfied.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14: Equation 1
0.05 ≤ [Cr] + [Mo] + [Cu] + [W] + [Sn] + [Sb] ≤ 5.00: Equation 2
The element symbol enclosed in square brackets in Formulas 1 and 2 excludes the fluoride, the oxide, the Ti oxide, the Ca oxide, and the carbonate of the flux-filled wire, the chemistry. It is the content of the element corresponding to each element symbol in the component in mass% with respect to the total mass of the flux-filled wire.
(2) In the flux-cored wire for gas shielded arc welding described in (1) above, the X value calculated by Equation 3 may be 2.00% or less.
X = 0.7 × ([Na ₃ AlF ₆ ] + [NaF] + [MgF ₂ ]) + 0.8 × ([K ₂ SiF ₆ ] + [K ₂ ZrF ₆ ]) + 0.9 × ([LiF] ) +3.5 × ([CaF ₂ ]): Equation 3
The chemical formula enclosed in square brackets in the formula 3 is the content of the compound corresponding to each of the chemical formulas in mass% with respect to the total mass of the flux-cored wire.
(3) In the flux-cored wire for gas shielded arc welding according to (1) or (2) above, the Y value calculated by Equation 4 may be 5.0 or more and 27.0 or less.
Y = ([TiO ₂ ] + 1.2 × [SiO ₂ ] + 1.4 × [Al ₂ O ₃ ] + 1.5 × [ZrO ₂ ]) / (F) ^1/2 : Equation 4
Regarding the chemical formula enclosed in square brackets in Equation 4 , [TiO ₂ ] is the TiO ₂ conversion value of Ti oxide, [SiO ₂ ] is the SiO ₂ conversion value of Si oxide, and [Al ₂ O ₃ ] is Al oxidation. terms _{of Al} 2 _{O 3} value of the object, [ZrO _2] is in terms of ZrO ₂ value of Zr oxide, a containing chromatic said amount against the total mass of the flux cored wire, F in the formula 4, wherein It is the total content of the fluoride in F conversion value.
(4) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (3) above, the flux is 0% or more in mass% with respect to the total mass of the flux-welded wire. It may further contain less than 0% iron powder.
(5) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (4) above, the steel outer skin may have a seamless shape.
(6) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (4) above, the steel outer skin may have a slit-shaped gap.
(7) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (6) above, the flux-cored wire further applies perfluoropolyether oil to the surface of the flux-cored wire. You may prepare.
(8) A method for manufacturing a welded joint according to another aspect of the present invention includes a step of gas shielded arc welding of a base steel plate, and is a welding material for forming the outermost layer of weld metal on one side or both sides of the welded joint. Is the flux-containing wire for gas shielded arc welding according to any one of (1) to (7) above.

The flux-cored wire according to the present invention is excellent in tensile strength, toughness, corrosion resistance and low temperature cracking resistance, and a welded portion having a good bead shape can be obtained. Further, when welding is performed using the flux-cored wire according to the present invention, the welding workability is high. The flux-cored wire according to the present invention can obtain the above-mentioned effects even when combined with any kind of shield gas. Further, the method for manufacturing a welded joint according to the present invention can be applied to all-position welding, and preheating work for preventing cracking of the weld metal becomes unnecessary, or preheating work can be significantly reduced. ..

It is the schematic which shows the sampling position of the 2mm V notch Charpy impact test piece and the round bar tension test piece. It is a figure explaining the test apparatus used for the total corrosion test. It is a figure explaining the test apparatus used for the pitting corrosion test.

In order to impart corrosion resistance to the welded portion, the present inventors include one or more elements selected from the group consisting of Cr, Mo, Cu, W, Sn, and Sb in the flux-cored wire as an alloy component. I found that it was effective. However, these elements are also elements that can impair the toughness of the weld metal. The present inventors limit the content of these elements to a predetermined range, and further include a strength-improving element in the flux-filled wire to increase the tensile strength and toughness of the weld metal without impairing the corrosion resistance of the weld metal. We found that it was possible to secure it.

Further, the present inventors have found that it is effective to contain a flux in a flux-cored wire to reduce the amount of diffusible hydrogen in the weld metal in order to secure the low temperature crack resistance. On the other hand, fluoride may increase spatter, deteriorate welding workability, and cause bead shape defects. The present inventors have found that both low-temperature crack resistance and welding workability can be ensured by imposing certain restrictions on the type of fluoride and further setting the content within a predetermined range. Furthermore, the present inventors have found that the omnidirectional weldability can be ensured by adding Ti oxide and other oxides to the flux-cored wire to increase the amount of slag.

The flux-cored wire according to the present embodiment obtained based on the above findings includes a steel outer skin and a flux filled inside the steel outer skin. Hereinafter, the reasons for limiting the requirements for forming the flux-cored wire according to the present embodiment will be described.

First, the components contained in the flux of the flux-cored wire according to the present embodiment will be described.
The flux of the flux-cored wire according to the present embodiment contains a fluoride, a Ti oxide, and an oxide (excluding Ti oxide and Ca oxide), and preferably further contains a carbonate. Further, the flux of the flux-cored wire according to the present embodiment may further contain Ca oxide and iron powder, but the Ca oxide and iron powder solve the problem of the flux-cored wire according to the present embodiment. It is not necessary for this. Hereinafter, these components will be described in detail. In the following description, "%" means "mass% with respect to the total mass of the flux-cored wire" unless otherwise specified.

_{(Tio 2} conversion value of Ti oxide: 4.00 to 7.50% by mass with respect to the total mass of the flux-cored wire)
The flux of the flux-cored wire according to the present embodiment contains 4.0 to 7.5% of Ti oxide in mass% with respect to the total mass of the flux-filled wire in terms of _{TiO 2.} The TIO ₂ conversion value of the Ti oxide means the content of _{TIO 2} when it is assumed that all the oxides of Ti are TIO _2. Hereinafter, the " _{content of Ti oxide in terms of TiO 2} " may be abbreviated as "content of Ti oxide". The TiO ₂ conversion value is obtained by analyzing the mass of Ti existing as an oxide contained in the flux-filled wire using an analytical instrument such as EPMA and calculating based on the mass of Ti as this oxide. The same applies to the Ca oxide and the like described below as described above with respect to the Ti oxide.

Ti oxide mainly acts as a slag forming agent. When performing upright welding using a flux-cored wire having a Ti oxide content of less than 4.00%, it is not possible to secure a sufficient amount of slag to support the molten metal so that it does not drip. Therefore, vertical weldability cannot be ensured. Therefore, the lower limit of the content of Ti oxide is set to 4.00%. The lower limit of the content of Ti oxide is more preferably 4.20%. In order to improve the vertical weldability, the lower limit of the content of Ti oxide may be 4.40%, 4.60%, 4.80%, or 5.30%.

On the other hand, a Ti oxide exceeding 7.50% excessively increases the amount of slag, and thus increases the defects of slag entrainment. Therefore, the upper limit of the content of Ti oxide is set to 7.50%. The upper limit of the content of Ti oxide is more preferably 7.00%. If necessary, the upper limit of the content of Ti oxide may be 6.70%, 6.40%, 6.20%, 6.00%, 5.90%, or 5.80%. ..

(Total content of fluoride in mass% based on total mass of flux-cored wire: 0.10 to 3.00%)
The flux of the flux-cored wire according to the present embodiment contains a total of 0.10 to 3.00% of fluoride in mass% with respect to the total mass of the flux-cored wire. The flux in the flux has a function of reducing the amount of diffusible hydrogen in the weld metal and remarkably improving the low temperature crack resistance of the weld metal. The reason for this is not clear, but it is presumed that F and hydrogen (H) in the fluoride are combined during welding to form hydrogen fluoride (HF), and this HF is released to the outside of the weld metal. NS. However, when the total amount of fluoride in the flux is less than 0.10%, the amount of diffusible hydrogen in the weld metal is not sufficiently reduced, so that the low temperature crack resistance of the weld metal becomes insufficient. Therefore, the flux of the flux-cored wire according to the present embodiment is required to contain a total of 0.10% or more of fluoride. In order to further reduce the amount of diffusible hydrogen in the weld metal, the lower limit of the total amount of fluoride may be 0.15%, 0.20%, or 0.25%.

On the other hand, if the fluoride content is excessive, the amount of spatter during welding increases. Therefore, the total content of fluoride in mass% with respect to the total mass of the flux-cored wire is 3.00% or less. If you want to prioritize the reduction of the amount of spatter generated over the reduction of the amount of diffusible hydrogen, the upper limit of the total amount of fluoride is 2.50%, 2.00%, 1.50%, 1.00%, or , 0.50% may be used.

(Types of fluoride: one or more selected from the group consisting of _{CaF 2} , MgF ₂ , LiF, NaF, K ₂ ZrF ₆ , K ₂ SiF ₆ , and Na ₃ AlF ₆₎
The fluoride of the flux-cored wire according to the present embodiment is one or two selected from the group consisting of _{CaF 2} , MgF ₂ , LiF, NaF, K ₂ ZrF ₆ , K ₂ SiF ₆ , and Na ₃ AlF _6. That is all. Ca, Mg, Li, Na, K, Zr, Si, and Al generated by ionization of these fluorides act as deoxidizing elements that combine with oxygen to reduce the amount of oxygen in the weld metal. The lower limit of the content of these various fluorides is not particularly limited as long as the total of fluorides is 0.10% or more.

As long as the total content of the fluoride described above and _{the content of CaF 2} described later are within the specified range, the type and composition of the fluoride are not limited. However, since K ₂ ZrF ₆ and K ₂ SiF ₆ also function as arc stabilizers, the fluoride of the flux-cored wire according to the present embodiment preferably contains _{K 2} ZrF ₆ and K ₂ SiF _6. Further, from the viewpoint of arc stability, it is preferable that a plurality of types of fluorides are contained in the flux so that the content of a single type of fluoride is 2.0% or less. Further, the fluoride preferably contains any one of _{Na 3} AlF ₆ , NaF, and MgF ₂ , which does not easily increase the spatter generation index X described later. _{Therefore, the total content of Na 3} AlF ₆ , NaF, and MgF ₂ in% by mass of the total mass of the fluxed wire is 50% of the total content of fluoride in% by mass of the fluxed wire. It is more preferably 60% or more, 80% or more, 90% or more, or 100%.

(Spatter generation index X (X value): preferably 2.00% or less)
If the fluoride content is too large, the amount of spatter generated during welding becomes excessive and the weldability deteriorates. The present inventors have studied a method for increasing the amount of fluoride as much as possible and reducing the amount of spatter within an acceptable range. As a result, we found that Na ₃ AlF ₆ , NaF, and MgF ₂ are less likely to increase the amount of spatter than other types of fluoride _{, and CaF 2} is more difficult to increase the amount of spatter than other types of fluoride. I found it easy to make it. As a result of further studies, the present inventors have found that there is a good correlation between the spatter generation index X (X value) calculated by the following equation 3 and the spatter amount.
X = 0.7 × ([Na ₃ AlF ₆ ] + [NaF] + [MgF ₂ ]) + 0.8 × ([K ₂ SiF ₆ ] + [K ₂ ZrF ₆ ]) + 0.9 × ([LiF] ) +3.5 × ([CaF ₂ ]): Equation 3
For the additive-free fluoride, zero shall be substituted into the above equation. In the above formula 3, the chemical formula enclosed in square brackets is the content of the fluoride corresponding to each chemical formula in mass% with respect to the total mass of the flux-cored wire.

The present inventors investigated the relationship between the amount of various fluorides added and the amount of spatter generated, and obtained a regression equation to clarify the effect of each fluoride on the amount of spatter generated. There is a good correlation between the X value obtained by the above regression equation and the spatter amount, and in order to reduce the spatter amount to 3.5 g / min or less under the above welding conditions, the X value should be 2.00% or less. The present inventors have found that it is preferable to do so. Therefore, in the flux-cored wire according to the present embodiment, it is preferable to control the fluoride content so that the X value is 2.00% or less. The spatter amount can be controlled by controlling the mere total value of the fluoride content as described above, but controlling the fluoride content using the X value suppresses the spatter amount and the weld metal. It is preferable because it is easy to achieve both reduction of the amount of hydrogen in the above. The preferable upper limit of the X value is 1.80%. If you want to further reduce the amount of spatter generated, set the upper limit of the X value to 1.60%, 1.40%, 1.20%, 1.00%, 0.90%, 0.80%, or 0. It may be 70%.

It is not necessary to limit the lower limit of the X value. However, since the total amount of fluoride needs to be 0.10% or more, the minimum value of the X value that can satisfy the regulation of the amount of fluoride may be set as the lower limit of the X value. That is, the X value is the minimum when the total amount of fluoride is the lowest value and the fluoride is composed of any of _{Na 3} AlF ₆ , NaF, and MgF _2. Therefore, there is no possibility that the lower limit of the X value is less than 0.07% (= 0.7 × 0.10). Therefore, the lower limit of the X value may be 0.07%. When further reducing the amount of diffusible hydrogen, the lower limit of the X value may be 0.09% or 0.11%. The X value is preferably as small as long as the total amount of fluoride is equal to or greater than the above-mentioned lower limit value.

( _{Content of CaF 2} : 0 to 2.00% by mass with respect to the total mass of the flux-cored wire)
CaF ₂ is a fluoride that tends to increase the amount of spatter. The present inventors have found that CaF ₂ exceeding 2.00% generates a large amount of sputtering and deteriorates welding workability. Therefore, in the flux-cored wire according to the present embodiment, the CaF ₂ content needs to be 2.00% or less. The preferable upper limit of the CaF _{2 content is 1.50%.} If necessary, the CaF ₂ content may be 1.00% or less, 0.50% or less, or 0.05% or less. Further, the flux-cored wire according to the present embodiment is therefore not essential CaF _2, the lower limit of the content of CaF ₂ is 0%.

(Total content of oxides excluding Ti oxide and Ca oxide: 0.05 to 2.00% by mass with respect to the total mass of the flux-cored wire)
(Types of oxides excluding Ti oxides and Ca oxides: Fe oxides, Na oxides, Si oxides, Zr oxides, Mg oxides, Al oxides, Mn oxides, and K oxides. One or more selected from)
The flux of the flux-cored wire according to the present embodiment contains Ti oxide as described above. Further, as described later, in the flux of the flux-cored wire according to the present embodiment, the Ca oxide content (CaO conversion value) is 0.10% or less. The flux of the flux-cored wire according to the present embodiment also includes oxides other than these Ti oxides and Ca oxides as slag forming agents. In the flux-containing wire according to the present embodiment, the oxides as the slag forming agent are Fe oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxide. One or more selected from the group consisting of objects. Hereinafter, when simply referred to as "oxide", the term means the above-mentioned oxide group and does not include Ti oxide and Ca oxide.
Similar to the above-mentioned Ti oxide content controlled by TiO ₂ conversion value, Fe oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K. The oxide content is controlled by a value converted into each of the contents of _{FeO, Na 2} O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ and K _{2 O.} Hereinafter, one or more oxidations selected from the group consisting of Fe oxides, Na oxides, Si oxides, Zr oxides, Mg oxides, Al oxides, Mn oxides, and K oxides. The "total value of the contents of FeO, Na ₂ O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ or K ₂ O at each conversion value" is simply "the total amount of oxides". Is abbreviated.

The oxide has an effect of maintaining a good weld bead shape and an effect of improving vertical weldability. Na oxide, K oxide, Mg oxide, Fe oxide and the like also have the effect of stabilizing the arc. In order to obtain the effect, the oxide content needs to be 0.05% or more. In order to exert these effects more, the lower limit of the oxide content may be 0.10%, 0.15%, or 0.20%. However, if the oxide content exceeds 2.00%, slag entrainment may occur. The preferred upper limit of the oxide is 1.50%, 1.00%, or 0.50%.

It is not necessary to specify the oxide content for each type of oxide, but for example, Si oxide: 0.08% or more and 0.95% or less, Zr oxide: 0.80% or less, Al oxide. : A composition of 0.50% or less is preferable.

(Y value: preferably 5.0 to 27.0)
In the flux wire according to the present embodiment, the Y value calculated by the following equation 4 is preferably 5.0 or more and 27.0 or less.
Y = ([TiO ₂ ] + 1.2 × [SiO ₂ ] + 1.4 × [Al ₂ O ₃ ] + 1.5 × [ZrO ₂ ]) / (F) ^1/2 : Equation 4
For additive-free oxides, zero shall be substituted into the above equation.
The compound corresponding to each chemical formula enclosed in square brackets in the above formula 4 indicates the content of each compound in mass% with respect to the total mass of the flux-cored wire, and corresponds to each oxide as described above. The content in the converted value is shown. “F” in the formula 4 is the total content of fluoride in terms of F, and is represented by the following formula A. The F conversion value is substantially the same as the value of fluorine contained in the flux-cored wire in mass% with respect to the total mass of the flux-cored wire.
0.487 x [CaF ₂ ] +0.610 x [MgF ₂ ] +0.732 x [LiF] +0.452 x [NaF] +0.402 x [K ₂ ZrF ₆ ] + 0.517 x [K ₂ SiF ₆ ] +0.543 × [Na ₃ AlF ₆ ]: Formula A
For additive-free fluoride, zero shall be substituted into the above equation.
The chemical formula of the fluoride enclosed in square brackets in the above formula A indicates the mass% of the fluoride corresponding to each chemical formula with respect to the total mass of the flux-cored wire.

Among the oxides, the present inventors have Ti oxide (TiO ₂ conversion value), Si oxide (SiO ₂ conversion value), Al oxide (Al ₂ O ₃ conversion value), and Zr oxide (ZrO ₂ conversion value). It was found that it is preferable to keep the relationship between the amount of (value) and the amount of fluoride (F conversion value) within an appropriate range. When welding is performed using a flux-cored wire in which the amount of Ti oxide, Si oxide, Al oxide, and Zr oxide is too large with respect to the amount of fluoride, that is, the Y value is more than 27.0. The present inventors have found that slag entrainment is likely to occur because the amount of oxide-based slag having a high melting point increases. On the other hand, welding is performed using a flux-cored wire in which the amounts of Ti oxide, Si oxide, Al oxide, and Zr oxide are too small with respect to the amount of fluoride, that is, the Y value is less than 5.0. In this case, the present inventors have found that the arc force is increased by the flux, the molten metal is compressed, and the bead shape is likely to be deteriorated and the vertical weldability is likely to be deteriorated. Therefore, the Y value of the flux-cored wire according to the present embodiment is preferably 5.0 to 27.0. The lower limit of the Y value is more preferably 7.0, 9.0, 10.0, 11.0, or 12.0. The upper limit of the Y value is more preferably 25.0, 22.5, 20.0, 18.0, 16.0 or 15.0.

(Total carbonate content: 0-0.60% by mass of flux-cored wire)
The flux of the flux-cored wire according to the present embodiment does not need to contain a carbonate. Therefore, in the flux-cored wire according to the present embodiment, the lower limit of the carbonate content is 0%. However, carbonates are ionized by the arc to generate _{CO 2 gas.} The CO ₂ gas lowers the partial pressure of hydrogen in the welding atmosphere and reduces the amount of diffusible hydrogen in the weld metal. In order to obtain this effect, the flux of the flux-cored wire according to the present embodiment may contain a carbonate.

On the other hand, an amount of carbonate exceeding 0.60% may cause the welding bead to sag and deteriorate the welding workability. Therefore, the upper limit of the carbonate contained in the flux of the flux-cored wire according to the present embodiment needs to be set to 0.60%. The preferable upper limit of the carbonate content is 0.40%. If necessary, the upper limit of the carbonate content may be 0.30%, 0.20%, 0.10%, 0.06%, or 0.03%.

(Type of carbonate: One or more selected from the group consisting of _{MgCO 3} , Na ₂ CO ₃ , LiCO ₃ , CaCO ₃ , K ₂ CO ₃ , FeCO ₃ , and MnCO ₃₎
Types of carbonate contained in the flux of the flux cored wire according to the present embodiment _is selected from _{MgCO 3, Na 2 CO 3,} LiCO 3, CaCO 3, K 2 CO 3, FeCO 3, and the group consisting of MnCO ₃ 1 type or 2 or more types. As long as the carbonate content is within the above range, the type and composition of the carbonate are not limited.

(Ca oxide: 0% or more and less than 0.20% in terms of CaO, which is the mass% of the total mass of the flux-cored wire)
Ca oxide may be contained in the flux of the flux-cored wire according to the present embodiment. However, in the flux-cored wire according to the present embodiment, the content of Ca oxide in the flux needs to be less than 0.20% (CaO conversion). Ca oxide may increase spatter and deteriorate weldability. The preferred upper limit of the Ca oxide content is 0.15%, 0.10%, 0.05%, 0.02%, or 0.01%. Since it is preferable that Ca oxide is not contained, the lower limit of the Ca oxide content is 0%. Since Ca oxide may be contained in a normal flux material in an amount of 0.20% or more as an impurity, a material that does not contain Ca oxide is selected when producing the flux-cored wire according to the present embodiment. There is a need to.

(Iron powder: preferably 0% or more and less than 15.0% by mass with respect to the total mass of the flux-cored wire)
As described above, iron powder may be contained in the flux of the flux-cored wire according to the present embodiment. Iron powder may be contained as necessary for adjusting the flux filling rate in the flux-cored wire or for improving the welding efficiency.
The iron powder content is not particularly specified. However, the oxygen adhering to the surface layer of the iron powder may increase the amount of oxygen in the weld metal and reduce the toughness. Therefore, in the flux-cored wire according to the present embodiment, the iron powder content is preferably less than 15.0% or less than 10.0%. If necessary, the upper limit of the iron powder content may be limited to 8.0%, 6.0%, 4.0%, 2.0%, or 1.0%. Since iron powder is not required to solve the problem of the flux-containing wire according to the present embodiment, the lower limit of the iron powder content in the flux-containing wire according to the present embodiment is 0%.

The flux of the flux-cored wire according to the present embodiment may contain components other than those described above. For example, the chemical component of the weld metal and the alloy component for controlling Ceq and the like may be contained in the flux in a state other than a fluoride, an oxide, or a carbonate (for example, a state of a metal powder or an alloy powder). .. The metal powder and the alloy powder melt at the time of welding in the same manner as the steel outer skin, and affect the weld metal. Therefore, the alloy component described later has the same effect whether it is contained in the flux-filled wire in the form of metal powder or alloy powder, or in the flux-filled wire in the form of a steel outer skin. Further, the flux-cored wire according to the present embodiment may contain fluorides, oxides, carbonates and the like other than the above-mentioned components as long as the characteristics are not impaired. In this case, the contents of fluorides, oxides, and carbonates other than the above-mentioned components shall not be included in the contents of the above-mentioned fluorides, oxides, and carbonates. Further, the contents of elements constituting fluoride, oxide, and carbonate other than the above-mentioned components shall not be included in the alloy components described later.

Next, the chemical components of the flux-containing wire according to the present embodiment, excluding fluorides, oxides (excluding Ti oxides and Ca oxides), Ti oxides, Ca oxides, and carbonates, will be described. In the following description, unless otherwise specified, "%" means "% by mass with respect to the total mass of the flux-cored wire". The chemical composition described below may be contained in the steel outer skin, may be contained in the flux as described above, or may be contained in the plating on the outer surface of the steel outer skin. In the following description, "chemical components excluding fluorides, oxides, Ti oxides, Ca oxides, and carbonates" may be simply referred to as "chemical components" or "alloy components".

(C: 0.003 to 0.150%)
C is an important element for ensuring the proof stress and tensile strength of the weld metal by solid solution strengthening. If the C content of the chemical component of the flux-containing wire is less than 0.003%, the proof stress and tensile strength of the weld metal cannot be ensured. On the other hand, when the C content of the chemical component of the flux-containing wire exceeds 0.150%, the C content in the weld metal becomes excessive, the toughness and tensile strength of the weld metal excessively increase, and the weld metal The toughness of the metal decreases. In order to stably secure all of the toughness, proof stress, and tensile strength of the weld metal, it is preferable to set the lower limit of the C content of the chemical component of the flux-cored wire to 0.003%, and the flux-cored wire. The upper limit of the C content of the chemical component of is preferably 0.080%. If necessary, the lower limit of the C content may be 0.010%, 0.020%, 0.030%, 0.040%, 0.050%, or 0.060%. Similarly, the upper limit of the C content may be 0.120%, 0.100%, 0.090%, 0.080%, or 0.070%.

(Si: 0.35-1.00%)
Si is a deoxidizing element and has a function of reducing the amount of oxygen in the weld metal and improving the cleanliness of the weld metal. Furthermore, the present inventors have found that Si contained in the flux-filled wire increases the viscosity of the weld metal, prevents the weld metal from sagging during vertical welding, and improves the vertical weldability. When the shield gas was Ar-20% CO ₂ , the Si content of the flux-cored wire was 0.35% or more, so that the upper limit current value of sagging increased remarkably. Based on the above findings, the present inventors have defined the lower limit of the Si content of the flux-cored wire according to the present embodiment as 0.35%. However, when the Si content of the chemical component of the flux-filled wire exceeds 1.00%, Si deteriorates the toughness of the weld metal. In order to stably secure the toughness of the weld metal, the upper limit of the Si content of the chemical component of the flux-filled wire may be 0.90%, 0.80%, 0.70% or 0.60%. If necessary, the lower limit of the Si content may be 0.40%, 0.45%, 0.50%, or 0.60%.

(Mn: 1.00 to 5.00% or less)
Mn is an element necessary for ensuring the hardenability of the weld metal and increasing the strength of the weld metal. In order to surely obtain the effect, it is necessary to set the Mn content of the chemical component of the flux-cored wire to 1.00%. In order to further increase the strength of the weld metal, the lower limit of the Mn content of the chemical component of the flux-cored wire may be 1.25%, 1.50%, or 2.00%. On the other hand, when the Mn content of the chemical component of the flux-containing wire exceeds 5.00%, the grain boundary embrittlement sensitivity of the weld metal increases and the toughness of the weld metal deteriorates. Therefore, the upper limit of the Mn content is set to 5.00%. Preferably, the upper limit of the Mn content is 4.50%, 4.00%, 3.00%, or 3.50%.

(P: 0.030% or less)
Since P is an impurity element and reduces the toughness of the weld metal, it is necessary to reduce the P content in the flux-cored wire as much as possible. Therefore, the lower limit of the P content of the chemical component of the flux-cored wire is 0%. Further, when the P content of the chemical component of the flux-cored wire is 0.030% or less, the adverse effect on the toughness of P is within an acceptable range. In order to prevent solidification cracking of the weld metal, the P content of the chemical component of the flux-filled wire is more preferably 0.020% or less, 0.015% or less, or 0.010% or less.

(S: 0.020% or less)
S is also an impurity element, and if it is excessively present in the weld metal, both the toughness and ductility of the weld metal are deteriorated. Therefore, it is preferable to reduce the S content in the flux-filled wire as much as possible. Therefore, the lower limit of the S content of the chemical component of the flux-cored wire is 0%. Further, when the S content of the chemical component of the flux-cored wire is 0.020% or less, the adverse effect of S on the toughness and ductility of the weld metal is within an acceptable range. The S content of the chemical component of the flux-cored wire is more preferably 0.010% or less, 0.008% or less, 0.006% or less, or 0.005% or less.

As will be described later, in the flux-containing wire according to the present embodiment, the total amount of Cr, Mo, Cu, W, Sn, and Sb is 0.05 to 5.00% by mass with respect to the total mass of the flux-containing wire. There is a need to. Therefore, the flux-cored wire according to the present embodiment needs to contain one or more elements selected from the group consisting of Cr, Mo, Cu, W, Sn, and Sb as an alloy component. However, the content of Cr, Mo, Cu, W, Sn, or Sb may be 0% as long as the above-mentioned total amount regulation is satisfied. Hereinafter, each of Cr, Mo, Cu, W, Sn, and Sb will be described.

(Cr: 0-5.00%)
Cr has the effect of improving the corrosion resistance of the weld metal. In order to obtain this effect, the Cr content is preferably 0.50% or more, 1.00% or more, or 2.00% or more. However, the Cr content may be 0% as long as the formula 2 described later is satisfied. On the other hand, if Cr is contained in an amount of more than 5.00%, the weld metal may be excessively hardened and the low temperature crack resistance and toughness of the welded portion may be lowered. Therefore, the upper limit of the Cr content is set to 5.00%. The upper limit of the Cr content may be 4.00%, 3.00%, or 2.00%.

(Mo: 0 to 1.50%)
(W: 0 to 1.50%)
Mo and W are important elements for corrosion resistance in both crude oil and ballast environments. Mo and W have almost the same effect, and even if both are contained in excess of 1.50%, not only their effects are almost saturated, but also adverse effects such as deterioration of the toughness of the weld metal become apparent. Therefore, in the present invention, the upper limit is 1.50%. In order to obtain the corrosion resistance effect, the lower limit values of Mo and W, respectively, may be 0.01%, 0.05% or 0.10%. However, the Mo content and the W content may be set to 0% as long as the formula 2 described later is satisfied. Further, in order to secure the toughness of the weld metal, the upper limits of Mo and W may be set to 1.30%, 1.00% or 0.50%, respectively.

(Cu: 0 to 1.50%)
Cu is effective in improving corrosion resistance in both crude oil environment and ballast environment. Further, Cu has the effect of improving the strength and toughness of the weld metal. In order to obtain the effect sufficiently, it is preferable that the Cu content of the chemical component of the flux-cored wire is 0.01% or more. However, the Cu content may be 0% as long as the formula 2 described later is satisfied. Cu may be included in the plating on the surface of the steel outer skin of the flux-cored wire, and may be included in the flux as a simple substance or as an alloy. Cu plating also has the effect of improving rust prevention, electrical conductivity, and chip wear resistance. Therefore, the Cu content of the chemical component of the flux-containing wire is the total amount of the Cu contained in the steel outer skin and the flux and the Cu contained in the plating on the wire surface. On the other hand, if the Cu content of the chemical component of the flux-cored wire exceeds 1.50%, the toughness of the weld metal decreases. The upper limit of the Cu content of the chemical component of the flux-cored wire is preferably 1.30%, 1.00%, or 0.70%.

(Sn: 0 to 1.00%)
(Sb: 0 to 1.00%)
By containing 0.01% or more of Sn and Sb in the flux-cored wire, it has an effect of suppressing corrosion resistance, particularly the progress of local corrosion in the liquid phase portion. Therefore, Sn and Sb are contained in the flux-cored wire as necessary. Is also good. In order to obtain this effect stably, the lower limit of each of the Sn content and the Sb content may be set to 0.01%. However, the Sn content and the Sb content may be set to 0% as long as the formula 2 described later is satisfied. Further, even if Sn and Sb are contained in excess of more than 1.0%, not only the effect is saturated, but also there is a concern that the toughness of the weld metal deteriorates due to temper embrittlement. Therefore, the upper limit of each of the Sn content and the Sb content is set to 1.00%. The upper limit of each of Sn and Sb may be 0.80% or 0.50%.

(Al: 0.001 to 0.500%)
Al is a deoxidizing element, and like Si, it reduces the amount of oxygen in the weld metal and has the effect of improving the cleanliness of the weld metal. If the Al content of the chemical component of the flux-containing wire is less than 0.001%, the amount of oxygen in the weld metal becomes high, and toughness cannot be ensured. When the Al content of the chemical component of the flux-containing wire exceeds 0.500%, Al forms nitrides, oxides and the like to reduce the toughness of the weld metal, and Al also increases spatter. Therefore, the upper limit of the Al content of the chemical component of the flux-cored wire is set to 0.500%. The upper limit of the Al content of the chemical component of the flux-cored wire is preferably 0.400%, 0.300%, 0.200%, 0.100% or 0.099%. The lower limit of the Al content of the chemical component of the flux-cored wire is preferably 0.005%, 0.010%, 0.050%, 0.100%, 0.150% or 0.200%.

(Ni: 0-5.00%)
The solid solution toughness of Ni improves the toughness of the weld metal. In order to obtain this effect, the Ni content is preferably 0.30% or more, 0.50% or more, or 1.00% or more. However, the flux-cored wire according to the present embodiment improves the toughness of the welded portion even by another alloying element, so that the above effect of Ni is not essential. Therefore, even if the Ni content is set to 0%, the flux-cored wire according to the present embodiment can solve the problem. Further, if Ni is added in excess of 5.00%, the high temperature crack resistance and toughness of the weld metal are lowered, so the upper limit of the Ni content is set to 5.00%. The upper limit of the Ni content may be 4.50%, 4.00%, or 3.50%.

The chemical composition of the flux-cored wire according to the present embodiment may contain the following optional components, if necessary, in addition to the above basic components. However, since the flux-cored wire according to the present embodiment can solve the problem without containing any component, the lower limit of the content of each of the optional components is 0%.

(Mg: 0 to 0.90%)
Since Mg is not an essential component, the lower limit of the Mg content of the chemical component of the flux-cored wire is 0%. On the other hand, Mg is a deoxidizer and is an element that reduces the amount of oxygen in the weld metal and thereby improves the toughness of the weld metal. In order to obtain the effect sufficiently, the Mg content of the chemical component of the flux-cored wire may be 0.10% or more. On the other hand, when the Mg content of the chemical component of the flux-cored wire exceeds 0.90%, Mg and oxygen react violently in the arc, and the amount of spatter and fume generated increases. Therefore, the Mg content is set to 0.90% or less. The more preferable lower limit of the Mg content of the chemical component of the flux-cored wire is 0.15%, 0.20%, 0.25%, or 0.30%. The preferred upper limit of the Mg content of the chemical component of the flux-cored wire is 0.70%, 0.55%, 0.45%, or 0.35%.

(Ti: 0 to 0.10%)
Since Ti is not an essential component, the lower limit of the Ti content of the chemical component of the flux-cored wire is 0%. On the other hand, Ti is a deoxidizing element and has an effect of reducing the amount of oxygen in the weld metal. Further, Ti contained in the chemical component of the flux-containing wire remains slightly in the weld metal to fix the solid solution N, and thus has an effect of alleviating the adverse effect of the solid solution N on the toughness of the weld metal. Therefore, the chemical composition of the flux-cored wire may contain 0.01% or more of Ti. However, if the Ti content of the chemical component of the flux-cored wire exceeds 0.10%, the toughness of the weld metal may deteriorate due to the formation of excessive precipitates. When Ti is contained in the chemical component of the flux-cored wire, ferrotitanium (an alloy of iron and titanium) is generally contained in the flux. The upper limit of the Ti content of the chemical component of the flux-cored wire is preferably 0.08%, 0.06%, 0.04%, or 0.02%.

(B: 0-0.0200%)
Since B is not an essential component, the lower limit of the B content of the chemical component of the flux-cored wire is 0%. On the other hand, since B is combined with the solid solution N in the weld metal to form a BN, it has an effect of reducing the adverse effect of the solid solution N on the toughness of the weld metal. Further, B has an effect of improving the strength of the weld metal because it enhances the hardenability of the weld metal. Therefore, the chemical composition of the flux-cored wire may contain 0.0005% or more of B. However, when the B content of the chemical component of the flux-filled wire exceeds 0.0200%, B in the weld metal becomes excessive, forming coarse BN and B compounds such as _{Fe 23} (C, B) _6. It is not preferable because it deteriorates the toughness of the weld metal. The upper limit of the B content of the chemical component of the flux-filled wire is preferably 0.0150%, 0.0100%, 0.0050%, 0.0030%, or 0.0010%.

(Nb: 0 to 0.20%)
Since Nb is not an essential component, the lower limit of the Nb content of the chemical component of the flux-cored wire is 0%. On the other hand, Nb forms fine carbides in the weld metal, and the fine carbides cause precipitation strengthening in the weld metal, so that Nb improves the tensile strength of the weld metal. In order to obtain the effect sufficiently, it is preferable that the Nb content of the chemical component of the flux-cored wire is 0.005% or more. However, it is not preferable that the Nb content of the chemical component of the flux-filled wire exceeds 0.20% because Nb forms coarse precipitates in the weld metal and deteriorates the toughness of the weld metal. The upper limit of the Nb content of the chemical component of the flux-cored wire is preferably 0.08%, 0.06%, 0.04%, or 0.02%.

(V: 0-0.20%)
Since V is not an essential component, the lower limit of the V content of the chemical component of the flux-cored wire is 0%. On the other hand, V is an element effective for increasing the strength of the weld metal because it improves the hardenability of the weld metal. In order to obtain the effect sufficiently, it is preferable that the V content of the chemical component of the flux-cored wire is 0.01% or more. When the V content of the chemical component of the flux-containing wire exceeds 0.20%, the amount of V-carbide deposited in the weld metal becomes excessive, the weld metal is excessively hardened, and the toughness of the weld metal is deteriorated. The upper limit of the V content of the chemical component of the flux-cored wire is preferably 0.16%, 0.12%, 0.08%, 0.04%, or 0.02%.

(Bi: 0 to 0.030%)
Since Bi is not an essential component, the lower limit of the Bi content of the chemical component of the flux-cored wire is 0%. On the other hand, Bi is an element that improves the peelability of slag. In order to sufficiently obtain the effect, the Bi content of the chemical component of the flux-cored wire is preferably 0.005% or more, 0.010% or more, or 0.012% or more. On the other hand, when the Bi content of the chemical component of the flux-filled wire exceeds 0.030%, solidification cracks are likely to occur in the weld metal, so the upper limit of the Bi content of the chemical component of the flux-filled wire is 0.030. %. The upper limit of the Bi content of the chemical component of the flux-cored wire is preferably 0.025%, 0.020%, 0.017%, or 0.015%.

(Ca: 0 to 0.50%)
(REM: 0 to 0.010%)
Since Ca and REM are not essential components, the lower limit of the Ca content and the REM content of the chemical component of the flux-cored wire is 0%. On the other hand, both Ca and REM have a function of changing the structure of the sulfide in the weld metal and reducing the size of the sulfide and the oxide, thereby improving the ductility and toughness of the weld metal. .. Therefore, the Ca content of the chemical component of the flux-filled wire may be 0.002% or more, and the REM content of the chemical component of the flux-filled wire may be 0.0002% or more. On the other hand, when the Ca content and the REM content of the chemical components of the flux-cored wire are excessive, the spatter amount increases and the weldability is impaired. Therefore, the upper limit of the Ca content of the chemical component of the flux-filled wire is 0.50%, and the upper limit of the REM content of the chemical component of the flux-filled wire is 0.010%.

(Remaining: Fe and impurities)
The above is the reason for limiting the chemical components of the flux-filled wire of the present embodiment except for fluorides, oxides, Ti oxides, Ca oxides, and carbonates, but the other remaining components include Fe and impurities. The remaining Fe is, for example, Fe contained in the steel outer skin, Fe in the alloy powder added to the flux, and the like. Impurities are components derived from raw materials or mixed due to various factors in the manufacturing process when the flux-cored wire is industrially manufactured, and do not adversely affect the flux-cored wire according to the present embodiment. Means what is acceptable in the range.

(Ceq: 0.25 to 1.00%)
The Ceq of the flux-cored wire according to the present embodiment is an index (carbon equivalent) indicating hardenability calculated by the following formula 1.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14: Equation 1
For additive-free elements, zero shall be substituted into the above equation.
The element symbols enclosed in square brackets in Formula 1 are the elements corresponding to each element symbol in the chemical composition, except for fluorides, oxides, Ti oxides, Ca oxides, and carbonates, of the flux-filled wire. , The content in mass% with respect to the total mass of the flux-filled wire. That is, the Ceq (Ceq of the flux-cored wire) calculated from the chemical composition of the flux-cored wire of the present embodiment is converted into the flux-cored wire in the state of a flux, an oxide, a Ti oxide, a Ca oxide, or a carbonate. It is calculated without considering the content of the contained elements. Elements contained in the fluxed wire in the form of fluorides, oxides, Ti oxides, Ca oxides, or carbonates are substantially discharged to the outside of the weld metal as slag during welding. Does not affect the hardenability of weld metal.

The Ceq of the flux-cored wire affects the hardenability of the weld metal. When the Ceq of the flux-cored wire is high, the weld metal is hardened, so that the tensile strength of the weld metal is improved, but on the other hand, the toughness of the weld metal is lowered. In the flux-containing wire according to the present embodiment, it is necessary to control the chemical composition excluding fluoride, oxide, Ti oxide, Ca oxide, and carbonate so that the Ceq is 0.20% or more. .. When the Ceq of the flux-cored wire is less than 0.20%, the Ceq of the weld metal is also insufficient, so that the tensile strength of the weld metal is insufficient. In order to increase the tensile strength of the weld metal, the lower limit of Ceq of the flux-cored wire may be set to 0.22%, 0.25%, 0.30% or 0.32%. On the other hand, when the Ceq of the flux-cored wire exceeds 1.00%, the Ceq of the weld metal becomes excessive, so that the toughness of the weld metal is insufficient. In order to increase the toughness of the weld metal, the upper limit of Ceq of the flux-cored wire may be 0.90%, 0.80%, 0.70%, 0.60%, 0.50%.

(0.05 ≦ [Cr] ＋ [Mo] ＋ [Cu] ＋ [W] ＋ [Sn] ＋ [Sb] ≦ 5.00)
In the flux-cored wire according to the present embodiment, the contents of Mo, Cu, W, Sn and Sb are defined as described above, and the total content of each element is in the range of 0.05 to 5.00%. It is said to be inside. That is, the flux-cored wire according to the present embodiment satisfies the following equation 2.
0.05 ≤ [Cr] + [Mo] + [Cu] + [W] + [Sn] + [Sb] ≤ 5.00: Equation 2
The element symbols enclosed in square brackets in Formula 2 are the elements corresponding to each element symbol in the chemical composition, excluding fluorides, oxides, Ti oxides, Ca oxides, and carbonates of flaked wires. It is the content in mass% with respect to the total mass of the flux-filled wire.

When the total content of Cr, Mo, Cu, W, Sn and Sb is less than 0.05%, the corrosion resistance of the weld metal cannot be ensured. Further, when the total content of Cr, Mo, Cu, W, Sn and Sb exceeds 5.00%, the crack resistance and toughness of the welded portion may deteriorate. Therefore, the total content of Cr, Mo, Cu, W, Sn and Sb needs to be 5.00% or less. The preferable lower limit of the total content of Cr, Mo, Cu, W, Sn and Sb is 0.10%, 0.15%, or 0.20%. The preferred upper limit of the total content of Cr, Mo, Cu, W, Sn and Sb is 4.00%, 3.00%, or 2.00%. If the total content of Cr, Mo, Cu, W, Sn and Sb is 0.05 to 5.00%, as described above, in the flux-cored wire according to the present embodiment, Cr, Mo, Cu , W, Sn and Sb may be set to 0%.

As long as the above-mentioned matters are satisfied, the steel outer skin of the flux-filled wire according to the present embodiment is not particularly limited, and this is, for example, a mild steel outer skin having a chemical composition of C: 0 to 0.1%. Si: 0 to 0.10%, Mn: 0 to 3.00%, P: 0.030% or less, S: 0.020% or less, Al: 0 to 0.1%, and N: 0 to 0. It may contain 030% and the balance may contain iron and impurities.

Next, the shape of the flux-cored wire according to the present embodiment will be described.
Usually, in a flux-cored wire, since the seam of the steel outer skin is welded, the wire having a shape without a slit-shaped gap (seamless shape) (sometimes called a seamless wire) and the seam of the steel outer skin are welded. Since it is not welded, it is distinguished from a wire having a shape including a slit-shaped gap.

Any shape can be adopted for the flux-cored wire according to the present embodiment. However, in order to suppress the occurrence of low-temperature cracking of the weld metal, it is preferable that the steel outer skin does not have a slit-shaped gap. H (hydrogen) that invades the welded portion during welding diffuses into the weld metal and the material to be welded and accumulates in the stress concentration portion, causing low-temperature cracking. There are various sources of H, but when welding is performed with the cleanliness of the weld and the conditions of the gas shield strictly controlled, the water content (H ₂ O) contained in the wire is the main component. It becomes a source of H, and the amount of this water strongly affects the amount of diffusible hydrogen in the welded joint. If the steel crust has seams, atmospheric moisture can easily penetrate into the flux through the seams. For this reason, it is desirable to remove the seams of the steel outer skin to prevent moisture in the atmosphere from entering the flux through the steel outer skin between the time the wire is manufactured and the time the wire is used. If the steel crust has seams and the period from wire production to wire use is long, vacuum package the entire flux-cored wire to prevent the ingress of H sources such as moisture. It is desirable to store the flux-cored wire in a container that can be kept dry.

The amount of hydrogen contained in the flux-filled wire according to the present embodiment is not particularly specified, but in order to reduce the amount of diffusible hydrogen in the weld metal, it is preferably 12 ppm or less with respect to the total mass of the flux-filled wire. The amount of hydrogen in the flux-cored wire may increase due to the ingress of moisture into the flux-cored wire during storage of the flux-cored wire. Therefore, when the period from wire production to wire use is long, it is desirable to prevent the ingress of moisture by the above-mentioned means.

The diameter of the flux-cored wire according to the present embodiment is not particularly specified, but is, for example, φ1.0 to φ2.0 mm. The diameter of a general flux-cored wire is φ1.2 to φ1.6 mm. The filling rate of the flux-cored wire according to the present embodiment is not particularly limited as long as the above-mentioned conditions are satisfied. In view of the general packing rate of the flux-cored wire, the lower limit of the packing rate of the flux-cored wire according to the present embodiment may be set to, for example, 10% or 12%. Further, the upper limit of the filling rate of the flux-cored wire according to the present embodiment may be set to, for example, 20% or 17%.

The flux-cored wire according to the present embodiment may further include a lubricant applied to the wire surface. The lubricant applied to the surface of the wire has the effect of improving the feedability of the wire during welding. Various types of lubricants for welding wires (for example, vegetable oils such as palm oil) can be used, but in order to suppress low temperature cracking of the weld metal, H-free perfluoropolyether oil (PFPE) is used. Oil) is preferred. Further, as described above, the flux-cored wire according to the present embodiment may further include plating formed on the wire surface. In this case, the lubricant is applied to the surface of the plating.

Next, a method for manufacturing the flux-cored wire according to the present embodiment will be described.
The flux-cored wire of the present embodiment can be manufactured by a normal flux-cored wire manufacturing process. An example of the manufacturing method will be described below.

The method for manufacturing a wire containing flux having a seamless shape includes a process of preparing flux, a process of forming a U-shaped open tube by forming a steel strip in the longitudinal direction using a forming roll, and an open tube. A process of supplying flux into the open pipe through the opening, a process of butt-welding the opposing edges of the opening of the open pipe to obtain a seamless pipe, and a process of drawing the seamless pipe and containing a flux having a predetermined wire diameter. The process includes a step of obtaining the wire and a step of quenching the flux-containing wire during or after the process of drawing the wire. The flux is prepared so that the amount of fluoride, the amount of oxide, the amount of carbonate, the chemical component, and the like of the flux-containing wire are within the above-mentioned predetermined ranges. The flux filling rate, which is determined by the width and thickness of the steel strip, which is the material of the steel outer skin, and the flux filling amount, is also the amount of flux, oxide amount, carbonate amount, and chemistry of the flux-cored wire. It should be noted that it affects the ingredients and the like. Butt welding is performed by electric stitch welding, laser welding, TIG welding, or the like. Further, the flux-cored wire is annealed in order to remove the moisture in the flux-cored wire during the wire drawing step or after the wire drawing step is completed. In order to make the H content of the flux-cored wire 12 ppm or less, it is necessary that the annealing temperature is 650 ° C. or higher and the annealing time is 4 hours or longer. The annealing temperature needs to be 900 ° C. or lower in order to prevent deterioration of the flux.

In the method of manufacturing a flux-containing wire having a slit-shaped gap, instead of the process of butt-welding the ends of the open pipes to obtain a seamless pipe, an open pipe is formed and the ends of the open pipes are butt-butted to form a slit-shaped wire. It is the same as the method for manufacturing a flux-containing wire having a seamless shape, except that it has a step of obtaining a tube with a gap. The method for producing a flux-cored wire having a slit-shaped gap may further include a step of crimping the end portion of the abutted open tube. In the method for manufacturing a flux-cored wire having a slit-shaped gap, a pipe having a slit-shaped gap is drawn.

If the cross section of the butt-seam welded, flux-filled wire having no slit-shaped gap is polished and etched, a weld mark is observed, but if it is not etched, no weld mark is observed. Therefore, it is sometimes called seamless as described above. For example, "Introduction to Welding and Joining Technology" (2008), edited by the Welding Society, Sanpo Publishing, p. In 111, a flux-cored wire that is butt-seam welded and has no slit-shaped gap is described as a seamless type wire. Even if the gaps in the steel outer skin of the flux-cored wire are brazed, a flux-cored wire having no slit-shaped gaps can be obtained.

The flux-cored wire of the present embodiment described above can be applied to welding of all kinds of steel materials, and the flux-cored wire according to the present embodiment cracks at a low temperature without preheating or at a preheating temperature of 50 ° C. or less. Can be prevented.

Next, a method (welding method) for manufacturing a welded joint according to the present embodiment will be described below. The method for manufacturing a welded joint according to the present embodiment includes a step of gas shielded arc welding of a base steel plate, and the welding material for forming the outermost layer of the weld metal is the flux for gas shielded arc welding according to the present embodiment. It is said to be an incoming wire. When welding is performed in only one pass, the flux-cored wire for gas shielded arc welding according to the present embodiment is used in that one pass. When the groove shape is V-shaped or the like, the flux-cored wire for gas shielded arc welding according to the present embodiment is used when forming at least one of the front bead and the back bead. When corrosion resistance is required on only one side of the welded joint, only the outermost layer of the weld metal (only the front bead or the back bead) on one side of the welded joint is formed with the flux-containing wire for gas shielded arc welding according to the present embodiment. You just have to. On the other hand, when corrosion resistance is required on both sides of the welded joint, the outermost layer of the weld metal (both the front bead and the back bead) on both sides of the welded joint is formed of the flux-containing wire for gas shielded arc welding according to the present embodiment. do it. As a matter of course, it is not hindered to use the flux-cored wire for gas shielded arc welding according to the present embodiment when forming a portion other than the outermost layer of the weld metal.

The type of base steel sheet (base material) used in the method for manufacturing a welded joint according to the present embodiment is not particularly limited. When the method for manufacturing a welded joint according to the present embodiment is applied to welding of corrosion-resistant steel, a welded joint in which corrosion resistance is ensured in both the base metal and the welded portion can be obtained, which is considered to be particularly suitable.

The polarity of the flux-cored wire used in the method for manufacturing a welded joint according to the present embodiment is either positive or negative because the influence on the amount of diffusible hydrogen and the amount of spatter generated of the weld metal is so small that it can be ignored. It may be good, but it is preferably positive.

The type of shield gas used in the method for manufacturing a welded joint according to the present embodiment is not particularly limited. The method for manufacturing a welded joint according to the present embodiment can obtain a welded joint exhibiting excellent welding workability and having high strength, high toughness, and high corrosion resistance regardless of the type of shield gas. However, it is preferable that 100 vol% carbon dioxide gas, which is generally used frequently, and _{a mixed gas of Ar and 3 to 30 vol% CO 2} are shield gases in the method for manufacturing a welded joint according to the present embodiment. Further, the shield gas at the time of welding using the flux-cored wire according to the present embodiment may _{contain O 2} gas of 5 Vol% or less. Since these gases are inexpensive, welding using these gases is advantageous for industrial use. Usually, when these gases are used in combination with rutile-based FCW, a large amount of spatter is generated and the welding workability is deteriorated. However, since the method for manufacturing a welded joint according to the present embodiment uses the flux-cored wire according to the present embodiment that can sufficiently suppress the amount of spatter, good welding workability is achieved even when these gases are shield gases. Can be demonstrated.

The welding posture in the welding joint manufacturing method according to the present embodiment is not particularly limited. The method for manufacturing a welded joint according to the present embodiment uses a flux-cored wire according to the present embodiment, which can sufficiently suppress the amount of spatter and sufficiently increase the viscosity of the molten metal, so that the welding posture is a downward posture. Good welding workability can be exhibited in any of the lateral posture, the vertical posture, and the upward posture.

The welded joint obtained by the method for manufacturing a welded joint according to the present embodiment includes a base metal plate (base material) and a welded portion composed of a weld metal and a weld heat-affected zone. Since it is manufactured using the flux-cored wire according to the present embodiment in which the total amount of Cr, Mo, Cu, W, Sn, and Sb, the amount of Ceq, the fluoride, the amount of the slag forming agent, and the like are preferably controlled. This welded joint comprises a weld metal having high strength, high toughness, and high corrosion resistance, having a diffusible hydrogen content of the weld metal of 1.0 ml / 100 g or less, and having a good bead shape. The base material of the welded joint is not particularly limited, but is preferably corrosion-resistant steel.

Since the flux-cored wire according to the present embodiment has the above-mentioned characteristics, it is possible to obtain a welded portion having excellent corrosion resistance, low temperature cracking resistance, strength, and toughness, and the amount of spatter generated during welding is significantly reduced. It can be applied to all-position welding.

Next, the feasibility and effect of the present invention will be described in more detail by way of examples. Are all within the technical scope of the present invention.

The flux-cored wires of the invention examples and the comparative examples were manufactured by the methods described below. First, while feeding the steel strip in the longitudinal direction, it was molded using a forming roll to obtain a U-shaped open pipe. Flux was supplied into the open pipe through the opening of the open pipe, and the opposing edges of the opening of the open pipe were butt-welded to obtain a seamless pipe. This seamless tube was drawn to obtain a flux-cored wire having no slit-shaped gap. However, for some samples, a slit-shaped tube with a gap that was not seam welded was used, and the tube was drawn. In this way, a flux-cored wire having a final wire diameter of φ1.2 mm was prototyped. In the middle of the wire drawing work of these flux-cored wires, the flux-cored wires were annealed in a temperature range of 650 to 950 ° C. for 4 hours or more. After the trial production, a lubricant was applied to the wire surface. The configuration of these flux-cored wires is shown in the table.

The content of each fluoride disclosed in Table 1, the content of each oxide and the total amount of oxides (excluding Ti oxide and Ca oxide), the content of each carbonate and the total amount of carbonate, The unit of iron powder content and chemical components (content of each element contained as alloy components) excluding fluorides, oxides, Ti oxides, Ca oxides, and carbonates is based on the total mass of the fluxed wire. It is mass%. In the table, "mass% with respect to the total mass of the flux-filled wire" is abbreviated as "mass%", and "chemical components excluding fluorides, oxides, Ti oxides, Ca oxides, and carbonates" are "alloy components". I abbreviated. _{The total amount of oxides disclosed in the table is FeO, Na 2 of} Fe oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxide. It is the total value of the converted values of O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ and K ₂ O, and does not include the contents of Ti oxide and Ca oxide. The X value (spatter generation index X) and Y value of the flux-cored wire disclosed in the table are the values obtained by the above-mentioned formulas A, 3 and 4, respectively. The Ceq disclosed in the table is the value obtained by the above formula 1. For _{carbonates other than CaCO 3} and Na ₂ CO ₃ , the total content is listed in the "Other" column.

The rest of the flux-cored wire disclosed in the table (ie, components other than each component disclosed in the table) was iron and impurities. The flux-cored wires disclosed in the table had a seamless shape unless otherwise specified in the "Wire structure" column, and palm oil was applied as a lubricant unless otherwise specified in the "Remarks" column. The flux-cored wire described as "with gap" in the "wire structure" column is a wire having a seam-like gap, and the wire described as "PTFE" in the "remarks" column is coated with PTFE oil. It was a wire. Each element contained as an alloy component in the flux-cored wire disclosed in the table was in the form of a steel hull or metal powder. In the table, numerical values outside the range specified in the present invention are underlined. In addition, a blank in the table relating to the content of the chemical component or compound means that the chemical component or compound is not intentionally added. These chemical components and compounds may be unavoidably mixed or produced.

The flux-cored wires of the invention and comparative examples were evaluated by the methods described below. However, since the evaluation could not be performed on the sample in which the weld metal had high temperature cracks, it was described as "unevaluated due to the occurrence of high temperature cracks" in the evaluation result column. At the time of evaluation, all welding currents were direct current, and all wire polarities were positive.

(Evaluation of tensile strength and toughness of weld metal)
In order to evaluate the mechanical properties (tensile strength and toughness) and the amount of diffusible hydrogen of the weld metal obtained by using the flux-cored wire, the flux-cored wire is used to use a base metal having a plate thickness of 20 mm, a root gap of 16 mm and a root gap of 16 mm. The joints for evaluation shown in FIG. 1 were obtained by butt welding at a groove angle of 20 degrees and using a backing metal to perform downward welding under welding condition 1 shown in Table 6. The base metal 1 and the backing metal 2 were SM490A. The groove surface of the base metal 1 and the surface of the backing metal 2 were buttered with two or more layers and an extra height of 3 mm or more using a flux-cored wire to be tested. The strength of the weld metal 3 thus obtained was evaluated by a tensile test, and the toughness was evaluated by a Charpy impact test at 0 ° C. From the weld metal 3 obtained in the downward welding test, as shown in FIG. 1, A1 tensile test piece (round bar) 5 and No. 4 Charpy test piece (2 mm V notch) 4 conforming to JIS Z3111 (2005). And were collected and subjected to a tensile test and a Charpy impact test. A flux-cored wire having a tensile strength of the weld metal of 490 MPa or more was accepted as a pass in terms of tensile strength. A flux-cored wire having a charpy absorption energy of 47 J or more at 0 ° C. of the weld metal was accepted for low temperature toughness.

(Evaluation of diffusible hydrogen content in weld metal)
The welding conditions for evaluating the amount of diffusible hydrogen in the weld metal obtained by using the invention example and the comparative example were set to condition 4 shown in Table 6. The amount of diffusible hydrogen in the weld metal was measured by a gas chromatograph method based on JIS Z 3118 (method for measuring the amount of hydrogen in steel welds). A flux-cored wire having a diffusible hydrogen content of the weld metal of 1.0 ml / 100 g or less was accepted for the diffusible hydrogen content.

(Evaluation of welding workability (spatter generation amount, vertical weldability, bead shape, and slag entrainment))
Further, in order to evaluate the welding workability of vertical welding using a flux-cored wire, vertical improvement fillet welding and vertical improvement bead-on plate welding were performed on the above-mentioned base material. The welding conditions were the welding condition 2 shown in Table 6 when evaluating the spatter amount, and the welding condition 3 shown in Table 6 when evaluating the vertical weldability, the bead shape, and the slag entrainment. The workability of vertical welding was evaluated based on the presence or absence of metal sagging, the amount of spatter generated, the slag peelability, and the results of visual inspection of the bead shape. Then, the presence or absence of slag entanglement defects was visually investigated in the cross sections of the five welded portions obtained by the above method. The presence or absence of metal sagging, the evaluation of slag peelability, and the evaluation of the bead shape were performed by both the vertical improvement fillet welding and the vertical improvement bead-on plate welding. The presence or absence of slag entanglement defects was determined only by vertical fillet welding.

Regarding the vertical weldability, the case where the molten metal drips occurred was rejected, and the case where the molten metal drips did not occur was rejected. Regarding the peelability of slag, those that did not peel off by brushing with a steel brush were rejected, and those that peeled off were accepted. Regarding the appearance evaluation of the bead shape, the case where the undercut and the convex bead occurred was rejected, and the case where these defects did not occur was rejected. Regarding the determination of the presence or absence of slag entrainment defects, if there was slag entrainment in even one of the five cross sections, it was rejected, and if there was no slag entrainment in all five cross sections, it was accepted. The amount of spatter generated was evaluated by the amount of spatter generated per minute of arc time obtained by dividing the weight of spatter generated during welding by the welding time. A flux-cored wire having a spatter generation amount of 3.5 g / min or less was accepted as a spatter generation amount.

(Evaluation of low temperature crack resistance)
The low temperature crack resistance was evaluated by welding to a tensile strength 780 MPa class steel having a plate thickness of 20 mm under a constant atmosphere control of a temperature of 5 ° C. and a humidity of 60% under the welding condition 5 in Table 6. The welded joint was tested in accordance with JIS Z 3157 (U-shaped weld crack test method) and JIS Z 3158 (y-type weld crack test method). A flux-cored wire applied to a welded joint in which cracks did not occur in both the U-shaped weld crack test and the y-type weld crack test was accepted for low-temperature crack resistance.

(Evaluation of corrosion resistance of weld metal)
(1) Full-scale corrosion test In order to evaluate the full-scale corrosion resistance of the back surface of the upper deck of the tanker, a small rectangular piece (corrosion resistance test piece 6) having a width of 25 mm, a length of 60 mm, and a thickness of 5 mm was formed so that only weld metal was used. It was cut out from the evaluation joint of FIG. 1 manufactured under the welding condition 1 of Table 6, and the surface thereof was polished with 600 count emery paper. The back surface and the end surface were sealed with tape so as not to be corroded, and a full-scale corrosion test was performed using the corrosion test apparatus shown in FIG.

This corrosion test apparatus is composed of a corrosion test tank 12 and a temperature control plate 13, and water 16 whose temperature is maintained at 36 ° C. is injected into the corrosion test tank 12, and the water 16 is filled with water 16. A mixed gas (introduced gas 4) consisting of 4 vol% O ₂ , 13 _{vol% CO 2} , 0.01 vol% SO ₂ , 0.05 _{vol% H 2} S, and the balance N _{2 was introduced into the corrosion test tank 12.} It is filled with supersaturated water vapor and reproduces the corrosive environment behind the upper deck of the crude oil tank. Then, the corrosion test piece 11 set on the upper and lower surfaces of the test tank is subjected to a temperature change of 180 ° C. × 3 hours + 50 ° C. × 21 hours as one cycle via a temperature control plate 13 having a built-in heater and cooling device. It was repeatedly applied for a day to cause dew condensation water on the surface of the test piece 11 to cause total corrosion. In FIG. 2, 15 shows the exhaust gas from the test tank.

After the above test, the rust on the surface of each test piece was removed, and the amount of mass reduction due to corrosion was determined from the mass change before and after the test, and this value was converted into the plate thickness reduction per year (corrosion rate on one side). As a result, when the corrosion rate was 0.10 mm / y or less and no local corrosion was observed, the total corrosion resistance was evaluated as good.

(2) Local corrosion (pitting corrosion) test In order to evaluate the corrosion resistance of the bottom plate of the tanker oil tank to pitting corrosion, a small rectangular piece (corrosion resistance test piece) with a width of 25 mm, a length of 60 mm, and a thickness of 5 mm is used so that only weld metal is used. 6) was cut out from the evaluation joint of FIG. 1 manufactured under the welding condition 1 of Table 6, and the entire surface thereof was polished with 600-count emery paper.

Next, a test solution prepared by preparing a 10 mass% NaCl aqueous solution to a Cl ion concentration of 10 mass% and a pH of 0.85 using concentrated hydrochloric acid was prepared, and the test solution was hung through a 3 mmφ hole opened at the top of the test piece through a Tegs. A corrosion test was conducted in which the mixture was immersed in 2 L of the test solution for 168 hours. The test solution was preheated and maintained at 30 ° C., and replaced with a new test solution every 24 hours.

The apparatus used for the corrosion test is shown in FIG. This corrosion test device is a dual type device of a corrosion test tank 18 and a constant temperature bath 19. The test solution 20 is put in the corrosion test tank 18, and the test piece 17 is suspended by a fishing line 21 and immersed in the test solution 20. ing. The temperature of the test solution 20 is maintained by adjusting the temperature of the water 22 placed in the constant temperature bath 19.

After the above corrosion test, after removing the rust generated on the surface of the test piece, the mass difference before and after the test was calculated, and this difference was rebated by the total surface area to obtain the amount of decrease in plate thickness per year (corrosion rate on both sides). rice field. As a result, when the corrosion rate was 0.50 mm / y or less, the local corrosion resistance was evaluated as good.

The test results obtained by the above method are shown in the table. When welding is performed using the flux-cored wire of the invention example, the temperature of the welding environment is 5 ° C, which is considered to be a very low temperature condition in view of common technical knowledge, and the steel material is not preheated. In all the cross sections of the y-shaped weld crack test and the U-shaped weld crack test, there was no cross-section crack (no cross-section crack occurred). Therefore, it was proved that the flux-cored wire of the invention example has extremely high low temperature crack resistance. Further, as shown in the test results in the table, the flux-cored wire of the invention example is subjected to spatter generation amount evaluation, vertical weldability evaluation, bead shape evaluation, and slag even when subjected to vertical improvement welding. All of the entrainment evaluations passed, showing good welding workability. In addition, the flux-containing wire of the invention example has passed the evaluation items of the tensile strength of the weld metal, the toughness of the weld metal, the amount of diffusible hydrogen in the weld metal, and the corrosion resistance, and has excellent properties. Was able to be manufactured.

On the other hand, the comparative example did not satisfy any of the requirements specified in the present invention, and therefore failed in one or more evaluation items.

1 Base material 2 Backing metal 3 Welded metal No. 4 Charpy test piece (2 mm V notch)
5 A1 Tensile Test Piece (Round Bar)
6 Corrosion resistance test pieces 11, 17 Test pieces 12, 18 Corrosion test tank 13 Temperature control plate 14 Introduced gas 15 Exhaust gas 16, 22 Water 19 Constant temperature tank 20 Test liquid 21 Tegus

Claims (8)

With a steel outer skin,
The flux filled inside the steel outer skin and
Is a flux-cored wire
The flux is
_{A group consisting of CaF 2} , MgF ₂ , LiF, NaF, K ₂ ZrF ₆ , K ₂ SiF ₆ , and Na ₃ AlF ₆ , with a total mass% of 0.10 to 3.00% of the total mass of the flux-cored wire. One or more fluorides selected from
_{A Ti oxide having a TIO 2} conversion value of 4.00 to 7.50% with respect to the total mass of the flux-cored wire.
A total of 0.05 to 2.00% of the total mass of the flux-containing wire _{in terms of FeO, Na 2} O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ and K _{2 O.} One or more of oxidations selected from the group consisting of Fe oxides, Na oxides, Si oxides, Zr oxides, Mg oxides, Al oxides, Mn oxides, and K oxides. Things and
_{From the group consisting of MgCO 3} , Na ₂ CO ₃ , LiCO ₃ , CaCO ₃ , K ₂ CO ₃ , FeCO ₃ and MnCO ₃ in total of 0 to 0.60% by mass of the flux-filled wire with respect to the total mass. With one or more carbonates selected
Including
The content of CaF ₂ is 0 to 2.00% by mass with respect to the total mass of the flux-cored wire.
The Ca oxide content in terms of CaO is 0% or more and less than 0.20% in mass% with respect to the total mass of the flux-cored wire.
The chemical composition of the flux-filled wire, excluding the fluoride, the oxide, the Ti oxide, the Ca oxide, and the carbonate, is by mass% of the total mass of the flux-filled wire.
C: 0.003 to 0.150%,
Si: 0.35-1.00%,
Mn: 1.00 to 5.00% or less,
P: 0.030% or less,
S: 0.020% or less,
Cu: 0 to 1.50%,
Cr: 0-5.00%,
Mo: 0 to 1.50%,
W: 0 to 1.50%,
Sn: 0 to 1.00%,
Sb: 0-1.00%,
Al: 0.001 to 0.500%,
Ni: 0-5.00%,
Mg: 0 to 0.90%,
Ti: 0 to 0.10%,
B: 0-0.0200%,
Nb: 0 to 0.20%,
V: 0-0.20%,
Bi: 0-0.030%,
Ca: 0 to 0.50%, and REM: 0 to 0.010%,
The rest consists of Fe and impurities
The Ceq calculated by Equation 1 is 0.53 to 1.00%.
Further, a flux-cored wire for gas shielded arc welding, which is characterized in that Equation 2 is satisfied.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14: Equation 1
0.05 ≤ [Cr] + [Mo] + [Cu] + [W] + [Sn] + [Sb] ≤ 5.00: Equation 2
The element symbol enclosed in square brackets in Formulas 1 and 2 excludes the fluoride, the oxide, the Ti oxide, the Ca oxide, and the carbonate of the flux-filled wire, the chemistry. It is the content of the element corresponding to each element symbol in the component in mass% with respect to the total mass of the flux-filled wire. The flux-cored wire for gas shielded arc welding according to claim 1, wherein the X value calculated by the formula 3 is 2.00% or less.
X = 0.7 × ([Na ₃ AlF ₆ ] + [NaF] + [MgF ₂ ]) + 0.8 × ([K ₂ SiF ₆ ] + [K ₂ ZrF ₆ ]) + 0.9 × ([LiF] ) +3.5 × ([CaF ₂ ]): Equation 3
The chemical formula enclosed in square brackets in the formula 3 is the content of the compound corresponding to each of the chemical formulas in mass% with respect to the total mass of the flux-cored wire. The flux-cored wire for gas shielded arc welding according to claim 1 or 2, wherein the Y value calculated by the formula 4 is 5.0 or more and 27.0 or less.
Y = ([TiO ₂ ] + 1.2 × [SiO ₂ ] + 1.4 × [Al ₂ O ₃ ] + 1.5 × [ZrO ₂ ]) / (F) ^1/2 : Equation 4
Regarding the chemical formula enclosed in square brackets in Equation 4 , [TiO ₂ ] is the TiO ₂ conversion value of Ti oxide, [SiO ₂ ] is the SiO ₂ conversion value of Si oxide, and [Al ₂ O ₃ ] is Al oxidation. terms _{of Al} 2 _{O 3} value of the object, [ZrO _2] is in terms of ZrO ₂ value of Zr oxide, a containing chromatic said amount against the total mass of the flux cored wire, F in the formula 4, wherein It is the total content of the fluoride in F conversion value. The gas shield according to any one of claims 1 to 3, wherein the flux further contains iron powder of 0% or more and less than 15.0% in mass% with respect to the total mass of the flux-cored wire. Flux-filled wire for arc welding. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 4, wherein the steel outer skin has a seamless shape. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 4, wherein the steel outer skin has a slit-shaped gap. The flux-cored wire for gas shielded arc welding according to any one of claims 1 to 6, wherein the flux-cored wire further comprises perfluoropolyether oil on the surface of the flux-cored wire. Equipped with a process of gas shielded arc welding of the base steel plate
A welded joint characterized in that the welding material for forming the outermost layer of the weld metal on one side or both sides of the welded joint is the flux-cored wire for gas shielded arc welding according to any one of claims 1 to 7. Manufacturing method.

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