JP2019042782A - Gas shield arc-welding flux-cored wire and manufacturing method of welding joint - Google Patents

Abstract

To provide a gas shield arc-welding flux-cored wire which can give high mechanical characteristics and corrosion resistance to a weld part, is excellent in low temperature cracking resistance, has high welding operability and permits all posture welding, and to provide a manufacturing method of welding joint.SOLUTION: A gas-shield arc welding flux-cored wire includes a steel shell and flux. Therein, the flux contains 0.10 to 3.00% of total fluorides, 4.00 to 7.50% of Ti oxide, 0.05 to 2.00% of total oxides and 0 to 0.60% of total carbonates, the content of CaFis 0 to 2.00%, the content of Ca oxide is 0% or more and less than 0.20%, an alloy component is within a predetermined range, Ceq is 0.20 to 1.00% and [Cr]+[Mo]+[Cu]+[W]+[Sn]+[Sb] is 0.05 to 5.00%.SELECTED DRAWING: Figure 1

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, demands for the safety of structural materials have become increasingly severe. The requirements include, for example, mechanical properties (tensile strength and toughness) and corrosion resistance. Materials with high corrosion resistance are suitable for structures that are exposed to severe corrosive environments.

  Steel tanks for transporting or storing crude oil, such as oil tanks for crude oil tankers that transport crude oil and ground or underground crude oil tanks that store crude oil, use welded structural steels that are excellent in strength and weldability. The steel oil tank is exposed to a corrosive environment due to moisture, salinity and corrosive gas components contained in the crude oil. In particular, on the inner surface of a crude oil tanker tank, a volatile component in crude oil, mixed seawater, salinity in oilfield salt water, and dew condensation caused by temperature fluctuations during the day and night become a unique corrosive environment, and the steel plates and welds are corroded. The most effective way to prevent general corrosion and local corrosion is to coat the surface with heavy coating to protect it from the corrosive environment. However, the painting work requires an enormous amount of area for application, and the paint film needs to be repainted due to the deterioration of the coating film.

  Furthermore, when the strength of the steel plate is increased, there is a problem that cold cracks occur in the weld metal. Cold cracking is a general term for cracks that occur in a welded part after the temperature of the welded part has dropped to around room temperature after welding, and cracks under the bead and toe cracks belong to this crack. Cold cracking is one of the most serious defects among welding defects because its shape is generally a sharp notch. The occurrence of cold cracking can be suppressed by preheating the welded part during welding construction, but the preheating process greatly increases the cost and construction period of the welding construction.

  Patent Documents 1 to 3 disclose a technique for improving the corrosion resistance of a welded part by controlling the ratio of Cu, Mo, or W in the weld metal and the steel plate. As the welding method, a covering arc welding method and a submerged arc welding have been proposed. However, in the welding of crude oil tankers, etc., horizontal fillet welding of the reinforcing material called Longi, vertical improvement fillet welding, vertical down fillet welding, and upward fillet welding are performed. There is a strong demand for a flux-cored wire for gas shield arc welding that is excellent in appearance, bead shape including metal sag resistance in a vertical or upward posture, and excellent in slag peelability.

  Patent Documents 4 to 5 propose a flux-cored wire for gas shielded arc welding excellent in corrosion resistance. However, in the gas shielded arc welding proposed in Patent Literature 4 and Patent Literature 5, no mention is made regarding measures against cold cracking.

  For the reasons described above, it is possible in the industry to produce weld metals with excellent mechanical properties (tensile strength and toughness) and corrosion resistance, and all-position welding (especially vertical improvement welding) is possible, and There is a need for a welding material and a welding method (a method for manufacturing a welded joint) that can suppress the occurrence of low-temperature cracking without performing a preheating operation or only with a simple preheating operation.

Japanese Patent Laid-Open No. 2005-21981 Japanese Patent Laid-Open No. 2005-23421 JP 2012-1810 A JP 2013-226577 A JP 2013-226578 A

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

  In view of the problems of the background art described above, 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 cold crack resistance, An object of the present invention is to provide a flux-cored wire for gas shielded arc welding that has high welding workability and can be welded in all positions, and a method for manufacturing a welded joint.

  The gist of the present invention is as follows.

(1) A flux-cored wire for gas shielded arc welding according to an aspect of the present invention includes a steel outer sheath and a flux filled in the steel outer sheath, wherein the flux is the flux cored 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 in a total mass of 0.10 to 3.00% by mass with respect to the total mass. Fluoride which is a seed or two or more types, 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, and FeO with respect to the total mass of the flux-cored wire _{, Na 2 O, SiO 2,} ZrO 2, MgO, Al 2 O 3, MnO total 0.05 to 2.00% in each of the corresponding value of ₂ and _{K 2} O, Fe oxide, a oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and oxide that is one or more selected from the group consisting of K oxide, and the flux wire the total from 0 to _0.60% by mass% relative to the total weight _of, 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 or 2 or more carbonates, and the content of the CaF ₂ is 0 to 2.00% by mass% with respect to the total mass of the flux-cored wire, and Ca oxidation in terms of CaO The content of the product is 0% or more and less than 0.20% by mass% with respect to the total mass of the flux-cored wire, and the fluoride, the oxide, the Ti oxide, The chemical components excluding the Ca oxide and the carbonate are mass% with respect to the total mass of the flux-cored wire, C: 0.003 to 0.150%, Si: 0.35 to 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 to 5.00%, Mo: 0 to 0 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 -0.030%, Ca: 0 to 0.50%, and REM: 0 to 0.010%, the balance consisting of Fe and impurities, C calculated by Formula 1 q is from 0.20 to 1.00%, further satisfying the expression 2.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14: Formula 1 0.05 ≦ [Cr] + [Mo] + [Cu] + [W] + [Sn] + [Sb] ≦ 5.00: Formula 2
The element symbols enclosed in square brackets in Formula 1 and Formula 2 are the chemicals of the flux-cored wire, excluding the fluoride, the oxide, the Ti oxide, the Ca oxide, and the carbonate. It is content in the mass% with respect to the said total mass of the said flux cored wire of the element corresponding to each said element symbol in a component.
(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 ]): Formula 3
The chemical formula enclosed in square brackets in Formula 3 is the content of the compound corresponding to each chemical formula in mass% with respect to the total mass of the flux-cored wire.
(3) In the flux-cored wire for gas shielded arc welding described in (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 : Formula 4
The chemical formula enclosed in square brackets in Formula 4 is the content of the compound corresponding to each chemical formula in the respective converted values with respect to the total mass of the flux-cored wire, and F in Formula 4 is This is the total content of the fluoride in terms of F.
(4) In the flux-cored wire for gas shielded arc welding according to any one of the above (1) to (3), the flux is 0% or more and 15.5% by mass with respect to the total mass of the flux-cored 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), the steel outer shell may have a seamless shape.
(6) In the flux-cored wire for gas shielded arc welding according to any one of (1) to (4), 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), the flux-cored wire further includes perfluoropolyether oil on 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-shield arc welding of a base steel plate, and a welding material for forming the outermost layer of the weld metal on one side or both sides of the welded joint. Is a flux-cored 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 cold cracking resistance, and can provide a weld having a good bead shape. Furthermore, when welding is performed using the flux-cored wire according to the present invention, welding workability is high. The flux-cored wire according to the present invention can obtain the above-described effects even when combined with any kind of shielding gas. Furthermore, the method for manufacturing a welded joint according to the present invention can be applied to all-position welding, and a preheating operation for preventing cracking of the weld metal is not required, or the preheating operation can be significantly reduced. .

It is the schematic which shows the collection position of a 2mmV notch Charpy impact test piece and a round bar tensile test piece. It is a figure explaining the test equipment used for the general 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 inventors include one or more elements selected from the group consisting of Cr, Mo, Cu, W, Sn, and Sb as an alloy component in the flux-cored wire. I found out 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 within a predetermined range, and further include a strength improving element in the flux-cored wire, thereby reducing the tensile strength and toughness of the weld metal without impairing the corrosion resistance of the weld metal. I found that it was possible to secure.

  In addition, the present inventors have found that it is effective to reduce the amount of diffusible hydrogen in the weld metal by adding fluoride to the flux-cored wire in order to ensure low temperature cracking resistance. On the other hand, fluoride increases spatter and deteriorates welding workability, and may cause a bead shape defect. The inventors of the present invention have found that it is possible to ensure both cold cracking resistance and welding workability by adding certain restrictions to the type of fluoride and further setting its content within a predetermined range. Furthermore, the present inventors have found that all-position weldability can be ensured by increasing the amount of slag by containing Ti oxide and other oxides in the flux-cored wire.

  The flux cored wire according to the present embodiment obtained based on the above knowledge includes a steel outer sheath and a flux filled in the steel outer sheath. Hereinafter, the reasons for limiting the requirements for configuring the flux-cored wire according to the present embodiment will be described.

First, 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 includes fluoride, Ti oxide, and oxide (excluding Ti oxide and Ca oxide), and preferably further includes carbonate. Further, the flux of the flux-cored wire according to the present embodiment may further include Ca oxide and iron powder, but the Ca oxide and the iron powder solve the problem of the flux-cored wire according to the present embodiment. This is unnecessary. 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.

(Ti oxide equivalent of TiO ₂ : 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 includes 4.0 to 7.5% of Ti oxide in terms of TiO _{2 in} terms of mass% with respect to the total mass of the flux cored wire. The TiO ₂ equivalent value of the Ti oxide means the content of TiO ₂ when it is assumed that all of the Ti oxide is TiO ₂ . Hereinafter, “content of Ti oxide in terms of TiO ₂ ” may be abbreviated as “content of Ti oxide”. The TiO ₂ equivalent value is obtained by analyzing the mass of Ti present as an oxide contained in the flux-cored wire using an analytical instrument such as EPMA and calculating based on the mass of Ti as the oxide. In addition, it is the same as that mentioned above regarding Ti oxide also about Ca oxide etc. which are demonstrated below.

  Ti oxide mainly acts as a slag forming agent. When standing up welding is performed using a flux-cored wire with a Ti oxide content of less than 4.00%, a sufficient amount of slag cannot be secured to support the molten metal so that it does not droop down. Therefore, vertical weldability cannot be ensured. Therefore, the lower limit value of the Ti oxide content is 4.00%. The lower limit value of the Ti oxide content is more preferably 4.20%. In order to improve vertical weldability, the lower limit value of the Ti oxide content may be 4.40%, 4.60%, 4.80%, or 5.30%.

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

(Total content of fluoride in mass% with respect to the total mass of the flux-cored wire: 0.10 to 3.00%)
The flux of the flux cored wire according to the present embodiment includes a total of 0.10 to 3.00% of fluoride in mass% with respect to the total mass of the flux cored wire. The fluoride in the flux has a function of significantly reducing the low temperature cracking resistance of the weld metal by reducing the amount of diffusible hydrogen in 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 out of the weld metal. The 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 cold crack resistance of the weld metal becomes insufficient. Therefore, the flux of the flux-cored wire according to this 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, when the content of fluoride is excessive, the amount of spatter during welding increases. Accordingly, the total content of fluoride in mass% with respect to the total mass of the flux-cored wire is set to 3.00% or less. If priority is given to reducing the amount of spatter generated over reducing 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% is acceptable.

(Fluoride _{type: CaF 2, MgF 2, LiF} , NaF, K 2 ZrF 6, K 2 SiF 6, and one or more members selected from the group consisting of _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's it. 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.

The type and composition of the fluoride are not limited as long as the total content of the fluorides described above and the content of CaF ₂ described later are within the specified range. However, since K ₂ ZrF ₆ and K ₂ SiF ₆ also function as an arc stabilizer, the fluoride of the flux-cored wire according to this embodiment preferably includes K ₂ ZrF ₆ and K ₂ SiF ₆ . From the viewpoint of arc stability, it is preferable that a plurality of types of fluorides are contained in the flux, whereby the content of a single type of fluoride is 2.0% or less. Further, the fluoride preferably contains any of Na ₃ AlF ₆ , NaF, and MgF ₂ that hardly increases the sputter generation index X described later. Therefore, the total content of Na ₃ AlF ₆ , NaF and MgF ₂ in mass% with respect to the total mass of the flux-cored wire is 50% with respect to the total content of fluoride in mass% with respect to the total mass of the flux-cored wire. More preferably, it is 60% or more, 80% or more, 90% or more, or 100%.

(Spatter generation index X (X value): preferably 2.00% or less)
When the content of fluoride is too large, the amount of spatter generated during welding becomes excessive and weldability deteriorates. The present inventors have studied a method for increasing the amount of fluoride as much as possible and reducing the amount of sputtering to within an allowable range. As a result, the inventors 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 increases the amount of spatter than other types of fluoride. I found that it was easy to make. 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 formula 3 and the amount of spatter.
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 ]): Formula 3
For the non-added fluoride, zero is substituted into the above equation. In the above-mentioned 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 each fluoride added and the amount of spatter generated, and obtained a regression equation that clarifies the effect of each fluoride on the amount of spatter generated. There is a good correlation between the X value obtained by the 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 this. 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 amount of spatter can also be controlled by managing the mere total value of the fluoride content as described above, but managing the fluoride content using the X value is effective in reducing the amount of spatter and welding metal. This is preferable because both of the reduction of the hydrogen amount can be easily achieved. A preferable upper limit of the X value is 1.80%. When it is desired to further reduce the amount of spatter generated, the upper limit value of the X value is 1.60%, 1.40%, 1.20%, 1.00%, 0.90%, 0.80%, or 0. It may be 70%.

There is no need 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 definition of the fluoride amount may be set as the lower limit value of the X value. That is, the X value is minimized when the total fluoride is the lowest and the fluoride is composed of Na ₃ AlF ₆ , NaF, or MgF ₂ . Therefore, there is no possibility that the lower limit value of the X value falls below 0.07% (= 0.7 × 0.10). For this reason, it is good also considering the lower limit of X value as 0.07%. In order to further reduce the amount of diffusible hydrogen, the lower limit value of the X value may be 0.09% or 0.11%. The X value is preferably smaller as long as the total fluoride is equal to or more than the lower limit value described above.

(CaF ₂ content: 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 sputtering. The present inventors have found that CaF ₂ exceeding 2.00% generates a large amount of spatter 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. Preferred upper limit of the content of CaF ₂ is 1.50%. If necessary, the content of CaF _2, 1.00% or less, 0.50% or less, or may be 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 amount 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 oxide and Ca oxide: Fe oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxide group 1 type or 2 types selected from
As described above, the flux of the flux-cored wire according to the present embodiment includes Ti oxide. Further, as will be described later, in the flux of the flux-cored wire according to the present embodiment, the Ca oxide content (CaO equivalent value) is 0.10% or less. The flux of the flux-cored wire according to the present embodiment includes oxides other than these Ti oxide and Ca oxide as a slag forming agent. In the flux-cored wire according to the present embodiment, the oxide as the slag forming agent is Fe oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxidation. It is 1 type (s) or 2 or more types selected from the group which consists of a thing. Hereinafter, when it is simply described as “oxide”, the term means the above-described oxide group and does not include Ti oxide and Ca oxide.
Fe oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K as well as the content of the above-mentioned Ti oxide managed by TiO ₂ equivalent value The content of the oxide is managed by a value converted into the content of each of FeO, Na ₂ O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ and K ₂ O. Hereinafter, "oxidation that is one or more selected from the group consisting of Fe oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxide" The total value of the content of each of the converted values of FeO, Na ₂ O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ or K ₂ O ”is simply“ the total amount of oxides ” Abbreviated.

  The oxide has an effect of maintaining a good weld bead shape and an effect of improving the vertical weldability. Na oxide, K oxide, Mg oxide, Fe oxide, and the like also have an effect of stabilizing the arc. In order to obtain the effect, the oxide content needs to be 0.05% or more. In order to exhibit 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 may be entrained. A preferable upper limit of the oxide is 1.50%, 1.00%, or 0.50%.

  The oxide content does not need to be specified for each type of oxide. For example, Si oxide: 0.08% to 0.95%, Zr oxide: 0.80% or less, Al oxide : The composition which is 0.50% or less is suitable.

(Y value: preferably 5.0 to 27.0)
In the flux wire according to the present embodiment, it is preferable that the Y value calculated by the following Expression 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 : Formula 4
For additive-free oxides, zero is 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 terms of converted values is shown. “F” in Formula 4 is the total content of fluoride in terms of F, and is represented by Formula A below. The F-converted value is substantially the same value as the mass% of fluorine contained in the flux-cored wire with respect to the total mass of the flux-cored wire.
0.487 × [CaF ₂ ] + 0.610 × [MgF ₂ ] + 0.732 × [LiF] + 0.452 × [NaF] + 0.402 × [K ₂ ZrF ₆ ] + 0.517 × [K ₂ SiF ₆ ] + 0.543 × [Na ₃ AlF ₆ ]: Formula A
For additive-free fluoride, zero is 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 include Ti oxide (TiO ₂ equivalent value), Si oxide (SiO ₂ equivalent value), Al oxide (Al ₂ O ₃ equivalent value), and Zr oxide (ZrO ₂ equivalent value). Value) and the amount of fluoride (F converted value) was found to be within an appropriate range. When the amount of Ti oxide, Si oxide, Al oxide, and Zr oxide is too much with respect to the amount of fluoride, that is, when welding is performed using a flux-cored wire having a Y value exceeding 27.0 The present inventors have found that since the amount of oxide-based slag having a high melting point increases, slag entrainment tends to occur. On the other hand, welding is performed using a flux-cored wire in which the amount of Ti oxide, Si oxide, Al oxide, and Zr oxide is too small relative 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 fluoride, the molten metal is pressed, and the bead shape and the vertical weldability are easily deteriorated. Therefore, the Y value of the flux-cored wire according to the present embodiment is preferably set to 5.0 to 27.0. The lower limit value 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 content of carbonate: 0 to 0.60% 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 does not need to contain carbonate. Therefore, in the flux cored wire according to the present embodiment, the lower limit value of the carbonate content is 0%. However, carbonate is ionized by the arc and generates CO ₂ gas. CO ₂ gas lowers the hydrogen partial pressure 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 this embodiment may include carbonate.

  On the other hand, an amount of carbonate exceeding 0.60% may cause welding bead sagging and deteriorate welding performance. Therefore, the upper limit of the carbonate contained in the flux of the flux-cored wire according to this embodiment needs to be 0.60%. A 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%.

(Types of carbonates: 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 types or more. As long as the carbonate content is within the above range, the type and composition of the carbonate are not limited.

(Ca oxide:% by mass with respect to the total mass of the flux-cored wire, 0% or more and less than 0.20% in terms of CaO)
Ca flux 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 Ca oxide content in the flux needs to be less than 0.20% (CaO equivalent). Ca oxide may increase spatter and deteriorate weldability. The upper limit with preferable content of Ca oxide is 0.15%, 0.10%, 0.05%, 0.02%, or 0.01%. Since it is preferable that no Ca oxide is contained, the lower limit of the content of Ca oxide is 0%. Since Ca oxide may be contained in an ordinary flux material by 0.20% or more as an impurity, a material that does not contain Ca oxide is selected when manufacturing the flux-cored wire according to this 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 included in the flux of the flux-cored wire according to the present embodiment. Iron powder may be included as necessary for adjusting the filling rate of the flux in the flux-cored wire or for improving the welding efficiency.
The iron powder content is not specified. However, oxygen attached to the surface layer of the iron powder may increase the oxygen content of the weld metal and reduce toughness. Therefore, in the flux-cored wire according to this embodiment, the iron powder content is preferably less than 15.0% or less than 10.0%. As needed, you may restrict | limit the upper limit of content of iron powder to 8.0%, 6.0%, 4.0%, 2.0%, or 1.0%. Since iron powder is unnecessary to solve the problem of the flux-cored wire according to the present embodiment, the lower limit value of the iron powder content is 0% in the flux-cored wire according to the present embodiment.

  The flux of the flux-cored wire according to the present embodiment may include a component other than the components 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 that is not fluoride, oxide, or carbonate (for example, in the state of metal powder or alloy powder). . The metal powder and the alloy powder melt in the same manner as the steel outer shell during welding, and affect the weld metal. Therefore, even if the alloy component described later is included in the flux-cored wire in the form of metal powder or alloy powder, or is included in the flux-cored wire in the form of a steel outer shell, the same effect can be obtained. In addition, the flux-cored wire according to the present embodiment may contain fluorides, oxides, carbonates, and the like other than the above-described components as long as the characteristics are not impaired. In this case, the contents of fluorides, oxides, and carbonates other than the components described above are not included in the contents of the fluorides, oxides, and carbonates described above. In addition, the contents of elements constituting fluorides, oxides, and carbonates other than the components described above are not included in the alloy components described later.

  Next, chemical components of the flux-cored wire according to the present embodiment excluding fluoride, oxide (excluding Ti oxide and Ca oxide), Ti oxide, Ca oxide, and carbonate will be described. In the following description, unless otherwise specified, “%” means “mass% with respect to the total mass of the flux-cored wire”. The chemical components described below may be included in the steel outer shell, may be included in the flux as described above, or may be included in the plating of the outer surface of the steel outer shell. In the following description, “a chemical component excluding fluoride, oxide, Ti oxide, Ca oxide, and carbonate” may be simply referred to as “chemical component” or “alloy component”.

(C: 0.003-0.150%)
C is an important element for securing the yield strength and tensile strength of the weld metal by solid solution strengthening. If the C content of the chemical component of the flux-cored wire is less than 0.003%, the yield strength and tensile strength of the weld metal cannot be ensured. On the other hand, if the C content of the chemical component of the flux-cored wire exceeds 0.150%, the C content in the weld metal becomes excessive, and the proof stress and tensile strength of the weld metal are excessively increased. The toughness of the steel 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%, The upper limit value of the C content of the chemical component 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 increasing the cleanliness of the weld metal by reducing the oxygen content of the weld metal. Furthermore, the present inventors have found that Si contained in the flux-cored wire increases the viscosity of the weld metal, prevents the weld metal from dripping during vertical welding, and improves vertical weldability. When the shielding gas was Ar-20% CO ₂ , the dripping upper limit current value significantly increased when the Si content of the flux-cored wire was 0.35% or more. Based on the above knowledge, the present inventors specified the lower limit value of the Si content of the flux-cored wire according to this embodiment as 0.35%. However, when the Si content of the chemical component of the flux-cored 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-cored 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 reliably 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 value of the Mn content of the chemical component of the flux-cored wire may be set to 1.25%, 1.50%, or 2.00%. On the other hand, when the Mn content of the chemical component of the flux-cored wire exceeds 5.00%, the grain boundary embrittlement susceptibility 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, if 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 falls within an allowable range. In order to prevent solidification cracking of the weld metal, the P content of the chemical component of the flux-cored wire is more preferably 0.020% or less, 0.015% or less, or 0.010% or less.

(S: 0.020% or less)
Since S is also an impurity element and 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-cored 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, if 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, the flux-cored wire according to this embodiment has a total amount of Cr, Mo, Cu, W, Sn, and Sb of 0.05 to 5.00% by mass% with respect to the total mass of the flux-cored 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 alloy components. However, the content of Cr, Mo, Cu, W, Sn, or Sb may be 0% as long as the above total amount regulation is satisfied. Hereinafter, each of Cr, Mo, Cu, W, Sn, and Sb will be described.

(Cr: 0 to 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 Equation 2 described below is satisfied. On the other hand, when Cr is contained more than 5.00%, the weld metal is excessively hardened, and the cold crack resistance and toughness of the welded portion may be deteriorated. Therefore, the upper limit of the Cr content is 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 and ballast environments. Mo and W have almost the same effect, and even if both of them are contained in excess of 1.50%, these effects are not only saturated but also the adverse effects such as deterioration of the toughness of the weld metal are also manifested. Therefore, in the present invention, the upper limit is made 1.50%. In order to obtain a corrosion resistance effect, the lower limit values of Mo and W may be 0.01%, 0.05%, or 0.10%. However, the Mo content and the W content may be 0% as long as Formula 2 described below is satisfied. Moreover, in order to ensure the toughness of a weld metal, it is good also considering each upper limit of Mo and W as 1.30%, 1.00%, or 0.50%.

(Cu: 0 to 1.50%)
Cu is effective in improving corrosion resistance in both crude oil environment and ballast environment. Furthermore, Cu has the effect of improving the strength and toughness of the weld metal. In order to sufficiently obtain the effect, 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 Formula 2 described below is satisfied. Cu may be included in the plating on the surface of the steel outer surface of the flux-cored wire, and may be included in the flux as a single substance or 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-cored wire is the total amount of Cu contained in the steel outer sheath and flux and 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%)
Sn and Sb have the effect of suppressing the progress of local corrosion in the liquid phase part by containing 0.01% or more in the flux cored wire, so that it is contained in the flux cored wire as necessary. Also good. In order to stably obtain this effect, the lower limits of the Sn content and the Sb content may be 0.01%. However, the Sn content and the Sb content may be 0% as long as Formula 2 described later is satisfied. Moreover, even if each of Sn and Sb is contained excessively exceeding 1.0%, the effect is not only saturated, but there is also 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%. It is good also considering each upper limit of Sn and Sb as 0.80% or 0.50%.

(Al: 0.001 to 0.500%)
Al is a deoxidizing element and, like Si, reduces the amount of oxygen in the weld metal and has an effect of improving the cleanliness of the weld metal. If the Al content of the chemical component of the flux-cored wire is less than 0.001%, the amount of oxygen in the weld metal increases, and toughness cannot be ensured. When the Al content of the chemical component of the flux-cored wire exceeds 0.500%, Al forms nitrides and oxides 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 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 value 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 to 5.00%)
The solid solution toughening 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 with another alloy element, so the above effect of Ni is not essential. Therefore, even if the Ni content is 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 hot cracking resistance and toughness of the weld metal are lowered, so the upper limit of the Ni content is 5.00%. The upper limit of the Ni content may be 4.50%, 4.00%, or 3.50%.

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

(Mg: 0-0.90%)
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 oxygen content of the weld metal and thereby improves the toughness of the weld metal. In order to sufficiently obtain the effect, 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 vigorously in the arc, increasing the amount of spatter and fumes generated. Therefore, the Mg content is set to 0.90% or less. In addition, the more preferable lower limit of Mg content of the chemical component of the flux-cored wire is 0.15%, 0.20%, 0.25%, or 0.30%. The upper limit with preferable Mg content of the chemical component of a 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-cored wire slightly remains in the weld metal to fix the solid solution N, and therefore has an effect of mitigating the adverse effect of the solid solution N on the toughness of the weld metal. Therefore, the chemical component 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%, there is a risk that toughness deterioration occurs due to the formation of excessive precipitates in the weld metal. 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, 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 toughness of the weld metal. B also has the effect of improving the strength of the weld metal because it enhances the hardenability of the weld metal. Therefore, the chemical component 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-cored wire exceeds 0.0200%, the B in the weld metal becomes excessive, forming coarse BN and B compounds such as Fe ₂₃ (C, B) _6. This 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-cored 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 carbide in the weld metal, and this fine carbide causes precipitation strengthening in the weld metal, so Nb improves the tensile strength of the weld metal. In order to sufficiently obtain the effect, the Nb content of the chemical component of the flux-cored wire is preferably set to 0.005% or more. However, it is not preferable that the Nb content of the chemical component of the flux-cored 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 to 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 improves the hardenability of the weld metal and is therefore an effective element for increasing the strength of the weld metal. In order to sufficiently obtain the effect, the V content of the chemical component of the flux-cored wire is preferably set to 0.01% or more. When the V content of the chemical component of the flux-cored wire exceeds 0.20%, the precipitation amount of V carbide 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: 0-0.030%)
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 slag peelability. 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-cored wire exceeds 0.030%, solidification cracking is likely to occur in the weld metal, so the upper limit of the Bi content of the chemical component of the flux-cored 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: 0-0.010%)
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 sulfides in the weld metal and reducing the size of sulfides and oxides, thereby improving the ductility and toughness of the weld metal. . Therefore, the Ca content of the chemical component of the flux-cored wire may be 0.002% or more, and the REM content of the chemical component of the flux-cored wire may be 0.0002% or more. On the other hand, when the Ca content and the REM content of the chemical component of the flux-cored wire are excessive, the amount of sputtering increases and the weldability is impaired. Therefore, the upper limit value of the Ca content of the chemical component of the flux cored wire is 0.50%, and the upper limit value of the REM content of the chemical component of the flux cored wire is 0.010%.

(Balance: Fe and impurities)
The above is the reason for limiting the chemical components of the flux-cored wire of this embodiment except for fluoride, oxide, Ti oxide, Ca oxide, and carbonate, but the other remaining components contain Fe and impurities. The remaining Fe is, for example, Fe contained in the steel outer shell, Fe in alloy powder added to the flux, or the like. Impurities are components derived from raw materials or mixed due to various factors in the manufacturing process when industrially manufacturing a flux-cored wire, and do not adversely affect the flux-cored wire according to the present embodiment. It means what is allowed in the range.

(Ceq: 0.20 to 1.00%)
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: Formula 1
For non-added 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 fluoride, oxide, Ti oxide, Ca oxide, and carbonate of the flux-cored wire. , The content in mass% relative to the total mass of the flux-cored wire. That is, Ceq (Ceq of the flux-cored wire) calculated from the chemical composition of the flux-cored wire of this embodiment is converted into the flux-cored wire in the state of fluoride, oxide, Ti oxide, Ca oxide, or carbonate. It is calculated without considering the content of the contained elements. Elements contained in the flux-cored wire in the state of fluoride, oxide, Ti oxide, Ca oxide, or carbonate are substantially discharged outside the weld metal as slag during welding. Does not affect the hardenability of the weld metal.

  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 the toughness of the weld metal is lowered. In the flux-cored wire according to the present embodiment, it is necessary to control chemical components other than 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 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 toughness of the weld metal is insufficient because the Ceq of the weld metal becomes excessive. In order to increase the toughness of the weld metal, the upper limit value of Ceq of the flux-cored wire may be 0.90%, 0.80%, 0.70%, 0.60%, and 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 each defined as described above, and the total content of each element is in the range of 0.05 to 5.00%. It is assumed that That is, the flux cored wire according to the present embodiment satisfies the following Expression 2.
0.05 ≦ [Cr] + [Mo] + [Cu] + [W] + [Sn] + [Sb] ≦ 5.00: Formula 2
The element symbols enclosed in square brackets in Formula 2 are the elements corresponding to each element symbol in the chemical composition, excluding fluoride, oxide, Ti oxide, Ca oxide, and carbonate of the flux-cored wire. It is content in mass% with respect to the total mass of the flux-cored 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. Moreover, when the total content of Cr, Mo, Cu, W, Sn, and Sb is more than 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 upper limit with preferable 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 content may be 0%.

  As long as the above-mentioned matter is satisfied, the steel outer sheath of the flux-cored wire according to the present embodiment is not particularly limited, but this is, for example, a mild steel outer shell, the chemical component of which is 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 0.0. It may include 030%, and the balance may include iron and impurities.

Next, the shape of the flux cored wire according to the present embodiment will be described.
Normally, the flux-cored wire is welded at the seam of the steel outer shell, which has a shape (seamless shape) that has no slit-like gaps because the seam of the steel outer shell is welded. Since it is not made, it can be distinguished from either a wire having a shape including a slit-like gap.

Any shape can be adopted in the flux-cored wire according to the present embodiment. However, in order to suppress the occurrence of cold cracks in the weld metal, it is preferable that the steel outer shell has no slit-like gap. H (hydrogen) that penetrates into the welded part during welding diffuses into the weld metal and the material to be welded, accumulates in the stress concentration part, and causes cold cracking. Although the supply source of H is various, when welding is performed in a state in which the cleanliness of the weld and the gas shield conditions are strictly controlled, moisture (H ₂ O) contained in the wire is mainly used. It becomes a supply source of H, and the amount of moisture strongly affects the amount of diffusible hydrogen in the welded joint. When the steel outer shell has a seam, moisture in the atmosphere tends to enter the flux through the seam. For this reason, it is desirable to suppress the intrusion of moisture in the atmosphere into the flux through the steel outer shell by removing the seam of the steel outer shell after the wire is manufactured until the wire is used. If the steel sheath has a seam and the period from wire manufacture to wire use is long, in order to prevent the supply of H such as moisture from entering, vacuum-wrap the entire flux-cored wire, 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-cored wire according to the present embodiment is not particularly defined, but is preferably 12 ppm or less with respect to the total mass of the flux-cored wire in order to reduce the amount of diffusible hydrogen in the weld metal. The amount of hydrogen in the flux-cored wire may increase due to moisture entering the flux-cored wire during storage of the flux-cored wire. Therefore, when the period from wire manufacture to wire use is long, it is desirable to prevent moisture from entering by the above-described means.

  The diameter of the flux-cored wire according to the present embodiment is not particularly defined, 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-described conditions are satisfied. In view of the filling rate of a general flux cored wire, the lower limit value of the filling rate of the flux cored wire according to the present embodiment may be set to, for example, 10% or 12%. Moreover, it is good also considering the upper limit of the filling rate of the flux cored wire which concerns on this embodiment as 20% or 17%, for example.

  The flux cored wire according to this 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 wire feedability during welding. Various types of lubricants for welding wires (for example, vegetable oils such as palm oil) can be used. In order to suppress low temperature cracking of the weld metal, perfluoropolyether oil (PFPE) that does not contain H is used. Oil) is preferably used. Moreover, 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 plating surface.

Next, the manufacturing method of the flux cored wire which concerns on this embodiment is demonstrated.
The flux cored wire of the present embodiment can be manufactured by a normal flux cored wire manufacturing process. Below, an example of a manufacturing method is demonstrated.

  A method of manufacturing a flux-cored wire having a seamless shape includes a step of preparing a flux, a step of forming a U-shaped open tube by forming a steel strip while feeding a steel strip in the longitudinal direction, Supplying flux into the open pipe through the opening, butt welding the opposite edges of the opening of the open pipe to obtain a seamless pipe, and flux containing a predetermined wire diameter by drawing the seamless pipe A step of obtaining a wire, and a step of annealing the flux-cored wire during or after the drawing step. The flux is prepared so that the fluoride content, oxide content, carbonate content, chemical composition, etc. of the flux-cored wire are within the predetermined ranges described above. Note that the flux filling rate determined by the width and thickness of the steel strip that is the material of the steel outer sheath and the flux filling amount, etc. is also the fluoride content, oxide content, carbonate content, and chemical content of the flux-cored wire. It should be noted that it affects the ingredients. The butt welding is performed by electric seam welding, laser welding, TIG welding, or the like. Moreover, in order to remove the water | moisture content in a flux cored wire in the middle of a wire drawing process or after completion of a wire drawing process, a flux cored wire is annealed. In order to set the H content of the flux-cored wire to 12 ppm or less, it is necessary that the annealing temperature is 650 ° C. or more and the annealing time is 4 hours or more. In order to prevent flux alteration, the annealing temperature needs to be 900 ° C. or lower.

  The manufacturing method of the flux-cored wire having the slit-shaped gap is not the step of butt welding the end of the open tube to obtain a seamless tube, but forming the open tube and butting the end of the open tube Except for having a step of obtaining a tube with a gap, it is the same as the method of manufacturing a flux-cored wire having a seamless shape. The manufacturing method of the flux-cored wire having the slit-shaped gap may further include a step of caulking the end portion of the opened open tube. In a method for manufacturing a flux-cored wire having a slit-like gap, a tube having a slit-like gap is drawn.

  The cross-section of the flux-cored wire that is butt seam welded and has no slit-like gaps is polished and etched to observe the weld trace, but otherwise the weld trace is not observed. Therefore, it may be called seamless as described above. For example, “New Edition Introduction to Welding and Joining Technology” edited by the Japan Welding Society (2008); In 111, a butt seam welded flux-cored wire with no slit-like gap is described as a seamless type wire. Even if the gap between the steel outer sheaths of the flux-cored wire is brazed, a flux-cored wire having no slit-like gap can be obtained.

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

  Next, the manufacturing method (welding method) of the 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 performing gas shield arc welding of a base steel plate, and the welding material used to form the outermost layer of the weld metal is the gas shielded arc welding flux according to the present embodiment. It is assumed to be a corrugated wire. When welding is performed only in one pass, the flux-cored wire for gas shield arc welding according to the present embodiment is used in that one pass. When the groove shape is a V shape, the flux-cored wire for gas shield 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-cored wire for gas shield arc welding according to this embodiment. That's fine. On the other hand, when corrosion resistance is required on both sides of the welded joint, the outermost layer (both front and back beads) of the weld metal on both sides of the welded joint is formed with the flux-cored wire for gas shield arc welding according to this embodiment. do it. As a matter of course, the use of the flux-cored wire for gas shielded arc welding according to this embodiment when forming a portion other than the outermost layer of the weld metal is not hindered.

  The kind of base material steel plate (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 that ensures corrosion resistance in both the base material and the welded portion can be obtained, which is considered particularly suitable.

  The polarity of the flux-cored wire used in the method for manufacturing a welded joint according to this embodiment is so small that the influence on the amount of diffusible hydrogen and the amount of spatter generated in the weld metal is negligible. However, it is preferably positive.

The kind 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 provide a welded joint that exhibits excellent welding workability and has 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 and a mixed gas of Ar and 3 to 30 vol% CO ₂ or the like that are commonly used are shield gases for the welded joint manufacturing method according to the present embodiment. Moreover, the shield gas at the time of welding using the flux-cored wire according to the present embodiment may include 5 Vol% or less O ₂ gas. Since these gases are inexpensive, welding using these gases is advantageous for industrial use. Usually, when these gases are used in combination with a rutile FCW, a large amount of spatter is generated to deteriorate welding workability. 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 can be achieved even when these gases are shield gases. Can be demonstrated.

  The welding posture in the method for manufacturing a welded joint according to the present embodiment is not particularly limited. 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 and can sufficiently increase the viscosity of the molten metal, the welding posture is a downward posture. In any of the horizontal posture, the vertical posture, and the upward posture, good welding workability can be exhibited.

  A welded joint obtained by the method for manufacturing a welded joint according to the present embodiment includes a base steel plate (base material), and a welded portion composed of a weld metal and a weld heat affected zone. Since the total amount of Cr, Mo, Cu, W, Sn, and Sb, the amount of Ceq, the amount of fluoride, the amount of the slag forming agent, and the like are manufactured preferably using the flux-cored wire according to this embodiment. The weld joint includes a weld metal having high strength, high toughness, and high corrosion resistance, a diffusible hydrogen content of the weld metal of 1.0 ml / 100 g or less, and 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-described characteristics, it is possible to obtain a welded portion having excellent corrosion resistance, cold cracking resistance, strength, and toughness, and greatly reduce the amount of spatter generated during welding. It can be applied to all position welding.

  Next, the feasibility and effects of the present invention will be described in more detail by way of examples. However, the following examples are not of a nature that limits the present invention, and the design changes are made thoroughly to the purpose described above and below. These are all included in the technical scope of the present invention.

  The flux-cored wires of the inventive example and the comparative example were manufactured by the method described below. First, while feeding the steel strip in the longitudinal direction, it was formed using a forming roll to obtain a U-shaped open tube. A flux was supplied into the open pipe through the opening of the open pipe, and the opposite edge portions of the opening of the open pipe were butt welded to obtain a seamless pipe. The seamless tube was drawn to obtain a flux-cored wire having no slit-like gap. However, some of the samples were slit-like tubes with no seam welding and were drawn. In this manner, a flux-cored wire having a final wire diameter of φ1.2 mm was made as a prototype. In addition, the flux-cored wire was annealed for 4 hours or more in the temperature range of 650-950 degreeC in the middle of the wire drawing operation | work of these flux-cored wires. After the trial production, a lubricant was applied to the wire surface. The composition 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 the content of iron powder and chemical components (content of each element contained as an alloy component) excluding fluoride, oxide, Ti oxide, Ca oxide, and carbonate is based on the total mass of the flux-cored wire. % By mass. In the table, “mass% with respect to the total mass of the flux-cored wire” is abbreviated as “mass%”, and “chemical components excluding fluoride, oxide, Ti oxide, Ca oxide, and carbonate” are “alloy components” Abbreviated. The total oxide amount disclosed in the table means FeO, Na _{2 of} Fe oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxide. This 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 values obtained by the above-described formula A, formula 3 and formula 4, respectively. Ceq disclosed in the table is a value obtained by Equation 1 above. For carbonates other than CaCO ₃ and Na ₂ CO ₃ , the total content is listed in the “Other” column.

  The balance of the flux-cored wires disclosed in the table (that is, components other than the components 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 shell or metal powder. In the table, numerical values outside the range defined by the present invention are underlined. Moreover, the blank in the table | surface concerning content, such as a chemical component and a compound, means that the chemical component, a compound, etc. are not added intentionally. These chemical components and compounds may be inevitably mixed in or generated.

  The flux-cored wires of the inventive examples and comparative examples were evaluated by the method described below. However, since it was not possible to evaluate a sample in which hot cracking occurred in the weld metal, it was described as “Not evaluated due to occurrence of hot cracking” in the evaluation result column. In the evaluation, all the welding currents were DC, and all the polarities of the wires 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 using the flux-cored wire, a base material having a plate thickness of 20 mm, a root gap of 16 mm and The joints for the evaluation shown in FIG. 1 were obtained by butt-welding at a groove angle of 20 degrees and downward welding using a backing metal under welding conditions 1 shown in Table 6. Base material 1 and backing metal 2 were SM490A. The groove surface of the base material 1 and the surface of the backing metal 2 were subjected to buttering with two or more layers and an extra height of 3 mm or more using the 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 mmV notch) 4 conforming to JIS Z3111 (2005) 4 Were collected and subjected to a tensile test and a Charpy impact test. A flux-cored wire in which the tensile strength of the weld metal is 490 MPa or more was determined to be acceptable with respect to the tensile strength. A flux-cored wire in which the Charpy absorbed energy at 0 ° C. of the weld metal is 47 J or more was determined to be acceptable with respect to low-temperature toughness.

(Evaluation of diffusible hydrogen content in weld metal)
The welding conditions for evaluating the diffusible hydrogen content of the weld metal obtained using the inventive examples and the comparative examples were the conditions 4 shown in Table 6. The diffusible hydrogen content of the weld metal was measured by a gas chromatograph method in accordance with JIS Z 3118 (Method for measuring the hydrogen content of steel welds). A flux-cored wire in which the diffusible hydrogen content of the weld metal was 1.0 ml / 100 g or less was determined to be acceptable with respect to 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-described base material. The welding conditions were welding conditions 2 shown in Table 6 when evaluating the amount of spatter, and welding conditions 3 shown in Table 6 when evaluating vertical weldability, bead shape, and slag entrainment. The workability of vertical welding was evaluated based on the results of visual inspection of the presence or absence of metal sag, spatter generation, slag peelability and bead shape. Thereafter, the presence or absence of slag entrainment defects was visually inspected in the cross sections of the five welds obtained by the above method. In addition, determination of the presence or absence of metal sagging, evaluation of slag peelability, and evaluation of bead shape were performed by both standing-up advance fillet welding and stand-up advance bead-on-plate welding. The determination of the presence or absence of slag entrainment defects was made only by vertical improvement fillet welding.

  Regarding vertical weldability, the case where the dripping of the molten metal occurred was rejected, and the case where no dripping of the molten metal occurred was accepted. Regarding the slag removability, 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 an undercut or a convex bead was generated was rejected, and the case where these defects were not generated was determined to be acceptable. About the judgment of the presence or absence of a slag entrainment defect, when there was slag entanglement even in one section in 5 sections, it was rejected, and the thing without slag engulfment in all 5 sections was considered acceptable. 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 with a sputter generation amount of 3.5 g / min or less was accepted with respect to the sputter generation amount.

(Evaluation of cold cracking resistance)
Evaluation of cold cracking resistance was obtained by welding to a 780 MPa class steel having a tensile strength of 780 MPa with a plate thickness of 20 mm under a constant atmosphere control at a temperature of 5 ° C. and a humidity of 60%. The welded joint obtained was subjected to a test based on JIS Z 3157 (U-shaped weld crack test method) and JIS Z 3158 (y-type weld crack test method). The flux cored wire applied to the welded joint in which no crack was generated in both the U-shaped weld crack test and the y-shaped weld crack test was regarded as acceptable in terms of low-temperature crack resistance.

(Evaluation of corrosion resistance of weld metal)
(1) Overall corrosion test In order to evaluate the corrosion resistance against the overall corrosion on the back of the tanker upper deck, a rectangular piece (corrosion resistance test piece 6) having a width of 25 mm, a length of 60 mm and a thickness of 5 mm so as to be only a weld metal, It cut out from the joint for evaluation of FIG. 1 manufactured by the welding conditions 1 of Table 6, and the surface was grind | polished with the 600th emery paper. The back surface and the end surface were sealed with tape so as not to corrode, and a full surface 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 having a temperature of 36 ° C. is injected into the corrosion test tank 12. 4 vol% O ₂ , 13 vol% CO ₂ , 0.01 vol% SO ₂ , 0.05 vol% H ₂ S and the balance N ₂ are introduced into the corrosion test tank 12 by introducing a mixed gas (introduction gas 4). It is filled with supersaturated water vapor and reproduces the corrosive environment behind the upper deck of a crude oil tank. Then, a temperature change with a cycle of 25 ° C. × 3 hours + 50 ° C. × 21 hours is applied to the corrosion test pieces 11 set on the upper and rear surfaces of the test tank via a temperature control plate 13 incorporating a heater and a cooling device. It is repeatedly applied for one day, and condensed water is generated on the surface of the test piece 11 to cause overall corrosion. In FIG. 2, 15 indicates exhaust gas from the test tank.

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

(2) Local corrosion (pitting corrosion test) In order to evaluate the corrosion resistance against pitting corrosion in the tanker tank bottom plate, a rectangular small piece (corrosion resistance test piece 25 mm wide x 60 mm long x 5 mm thick) so as to be only a weld metal. 6) was cut out from the joint for evaluation of FIG. 1 manufactured under welding conditions 1 in Table 6, and the entire surface was polished with 600th emery paper.

  Next, a 10 mass% NaCl aqueous solution was prepared using concentrated hydrochloric acid to prepare a test solution having a Cl ion concentration of 10 mass% and a pH of 0.85. A corrosion test was conducted by immersing in 2 L of 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 apparatus is a double type apparatus of a corrosion test tank 18 and a constant temperature bath 19. The test solution 20 is placed in the corrosion test tank 18, and the test piece 17 is suspended and immersed in the tegs 21 therein. ing. The temperature of the test solution 20 is maintained by adjusting the temperature of the water 22 put in the thermostat 19.

  After removing the rust generated on the surface of the test piece after the corrosion test, the mass difference before and after the test is calculated, the difference is divided by the total surface area, and the reduction in thickness (corrosion rate on both sides) per year is calculated. It was. As a result, local corrosion resistance was evaluated as good when the corrosion rate was 0.50 mm / y or less.

  The test results obtained by the above method are shown in the table. When welding is performed using the flux-cored wire of the inventive example, the temperature of the welding environment is 5 ° C. considered to be a very low temperature condition in view of technical common sense, and the steel material is not preheated. Also, no cross-section cracks (no cross-section cracks occurred) in all cross sections of the y-type weld crack test and the U-type weld crack test. Therefore, it was proved that the flux-cored wire of the invention example has extremely high cold cracking resistance. Furthermore, as shown in the test results of the table, the flux-cored wire of the invention example is evaluated for spatter generation, vertical weldability evaluation, bead shape evaluation, and slag even when subjected to vertical improvement welding. All the evaluations of the entrainment were acceptable and showed good welding workability. In addition, the flux-cored wire of the inventive example is a weld metal having excellent characteristics that passes the evaluation items of tensile strength of weld metal, toughness of weld metal, amount of diffusible hydrogen in weld metal, and corrosion resistance. Could be manufactured.

  On the other hand, since the comparative example did not satisfy any of the requirements defined in the present invention, it failed in one or more evaluation items.

1 Base material 2 Back metal 3 Weld metal 4 No. 4 Charpy test piece (2mmV notch)
5 A1 tensile test piece (round bar)
6 Corrosion resistance test piece 11, 17 Test piece 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 Tegs

Claims (8)

A steel hull,
A flux filled in the steel outer shell,
A flux-cored wire comprising:
The flux is
Total 0.10 to 3.00% by mass% relative to the total weight of the flux-cored _{wire, CaF 2, MgF 2, LiF} , NaF, the group consisting of _{K 2 ZrF 6, K 2 SiF} 6, and _Na 3 AlF ₆ One or more fluorides selected from:
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,
Total of 0.05 to 2.00% in terms of converted values of FeO, Na ₂ O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ and K ₂ O with respect to the total mass of the flux-cored wire. The oxidation is one or more selected from the group consisting of Fe oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, and K oxide Things,
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 a total mass of 0 to 0.60% by mass% with respect to the total mass of the flux-cored wire. Carbonates that are one or more selected, and
Including
The CaF ₂ content is 0 to 2.00% by mass% with respect to the total mass of the flux-cored wire,
The content of Ca oxide in terms of CaO is 0% or more and less than 0.20% by mass% with respect to the total mass of the flux-cored wire,
Chemical components of the flux-cored wire excluding the fluoride, the oxide, the Ti oxide, the Ca oxide, and the carbonate are in mass% with respect to the total mass of the flux-cored 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 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 consists of Fe and impurities,
Ceq calculated by Equation 1 is 0.20 to 1.00%,
Further, the flux-cored wire for gas shielded arc welding, wherein the formula 2 is satisfied.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14: Formula 1
0.05 ≦ [Cr] + [Mo] + [Cu] + [W] + [Sn] + [Sb] ≦ 5.00: Formula 2
The element symbols enclosed in square brackets in Formula 1 and Formula 2 are the chemicals of the flux-cored wire, excluding the fluoride, the oxide, the Ti oxide, the Ca oxide, and the carbonate. It is content in the mass% with respect to the said total mass of the said flux cored wire of the element corresponding to each said element symbol in a component. 2. The flux-cored wire for gas shielded arc welding according to claim 1, wherein the X value calculated by Equation 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 ]): Formula 3
The chemical formula enclosed in square brackets in Formula 3 is the content of the compound corresponding to each chemical formula in mass% with respect to the total mass of the flux-cored wire. 3. The flux-cored wire for gas shielded arc welding according to claim 1, wherein the Y value calculated by Equation 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 : Formula 4
The chemical formula enclosed in square brackets in Formula 4 is the content of the compound corresponding to each chemical formula in the respective converted values with respect to the total mass of the flux-cored wire, and F in Formula 4 is This is the total content of the fluoride in terms of F.   The gas shield according to any one of claims 1 to 3, wherein the flux further includes iron powder of 0% or more and less than 15.0% by mass% with respect to the total mass of the flux-cored wire. Flux-cored 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 shell 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 shell 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 a surface of the flux-cored wire. It has a process of gas shield arc welding of the base steel plate,
The welded 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.

Images