JP2011255385A - Flux-cored wire for carbon dioxide gas-shielded arc welding for high-tensile steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flux-cored wire for carbon dioxide gas-shielded arc welding for a high-tensile steel, used for welding a high-tensile steel having ≥690 MPa of strength using 100% carbon dioxide gas as a shielding gas, obtaining superior welding workability and obtaining a weld metal having excellent mechanical capability.SOLUTION: The wire contains, by mass% to the total mass of the wire, 0.03-0.10% C, 0.1-0.4% Si, 2.0-4.0% Mn, 1.0-3.5% Ni, 0.06-1.5% Al, 0.10-1.00% Mo, contains one or more kinds of 0.1-1.0% Cr, 0.01-0.05% Nb and 0.01-0.05 V, and contains 2.5-7.5% TiO, 0.1-0.5% SiO, 0.2-0.9% ZrO, 0.1-0.4% AlOand 0.01-0.4% one or more kinds of fluorine compound in total in terms of F value. In the wire, the total hydrogen amount of the wire is ≤15 ppm by mass ratio to the entire wire.

Description

  The present invention relates to a flux-cored wire for gas shielded arc welding that uses carbon dioxide gas as a shielding gas for welding high-strength steel having a proof stress of 690 MPa or more. The present invention relates to a flux-cored wire for carbon dioxide shielded arc welding for high-strength steel with good welding workability.

  For the welding of high-strength steel, which is mainly used in construction machinery and offshore structures, the coated arc welding method, the submerged arc welding method, and the gas shield arc welding method using solid wire, which are excellent in toughness, are applied. Among them, the covering arc welding method or the gas shielded arc welding method using a solid wire is generally applied to members that require posture welding such as vertical, upward, and horizontal.

  However, the covering arc welding method has low welding efficiency. Also, in the gas shielded arc welding method using a solid wire, it is difficult to perform highly efficient welding because posture welding requires welding at a low current to prevent metal dripping.

On the other hand, gas shield arc welding using a flux-cored wire is mostly applied to all-position welding of low strength steel having a yield strength of less than 690 MPa.
In gas shielded arc welding using flux-cored wire, the high melting point slag agent added to the wire at the time of welding solidifies and retains it before the weld metal. Therefore, it is possible to perform high-current welding with high current, that is, high welding.

However, gas shielded arc welding using flux-cored wire is generally difficult to obtain toughness as compared with other welding methods because the slag agent added to the flux-cored wire is mainly an oxide. In the case of using CO ₂ gas, it is more difficult to ensure toughness because the amount of oxygen in the weld metal increases than the mixed gas of Ar and CO ₂ . In addition, due to moisture contained in the flux raw material and moisture absorption during wire storage, the amount of diffusible hydrogen is higher than that of solid wire, so there is concern about cold cracking of the weld metal, making it difficult to apply it to high-strength steel welding. there were. Furthermore, in conventional welding of high strength steel, it is necessary to preheat the steel plate to 100 ° C. or higher in order to prevent cold cracking of the weld metal, which causes a reduction in efficiency.

  Various developments of flux-cored wire for welding high-strength steel have been made so far. For example, Japanese Patent Application Laid-Open No. 2006-198630 (Patent Document 1), Japanese Patent Application Laid-Open No. 2007-144516 (Patent Document 2), and Japanese Patent Application Laid-Open No. 2009-255169 (Patent Document 3) include a metal-based flux containing no slag agent. A wire is disclosed. These mainly focus on downward welding, and all-position welding requires welding at a low current in order to prevent metal dripping as in the gas shielded arc welding method using solid wire.

  JP-A-9-253886 (Patent Document 4) and JP-A-3-47695 (Patent Document 5) describe a slag agent mainly composed of rutile in a flux-cored wire for all postures for high-tensile steel. Although flux-cored wires are disclosed in which low-temperature toughness is improved by adding metal fluoride or basic oxide and reducing the oxygen content of the weld metal, these do not take into account the low-temperature crack resistance of the weld metal.

  Japanese Patent Laying-Open No. 2006-281223 (Patent Document 6) discloses a weld metal and a flux-cored wire that can obtain low temperature toughness by suppressing the generation of ferrite side plates at the old γ grain boundaries. However, the cold cracking resistance of the weld metal is not considered.

Furthermore, Japanese Patent Application Laid-Open No. 2008-87043 (Patent Document 7) describes low temperature toughness at about -60 ° C., welding workability and low temperature cracking resistance of weld metal with a flux cored wire for all orientations for high strength steel. An improved flux-cored wire is disclosed. However, although the slag agent added to the flux-cored wire contains TiO ₂ or TiO ₂ and MgO, there is a problem that the metal tends to sag particularly in the case of vertical welding.

JP 2006-198630 A JP 2007-144516 A JP 2009-255169 A JP-A-9-253886 Japanese Patent Laid-Open No. 3-47695 JP 2006-281223 A JP 2008-87043 A

The flux-cored wires described in Patent Documents 1 to 7 are designed on the assumption that welding is performed using Ar-based Ar—CO ₂ gas as a shielding gas. Since Ar gas is expensive, it is required to use 100% carbon dioxide as a shielding gas. However, if carbon dioxide shielded arc welding is performed using these flux-cored wires without using Ar gas, there is a problem that workability in all-position welding becomes poor and the toughness of the weld metal decreases.

  INDUSTRIAL APPLICABILITY The present invention is used for welding high-strength steel having a proof stress of 690 MPa or more. In a flux-cored wire using 100% carbon dioxide as a shielding gas, high-efficiency welding is possible in all positions, and low oxygen and low hydrogen An object of the present invention is to provide a flux-cored wire for carbon dioxide shielded arc welding for high-strength steel, from which a weld metal having excellent toughness and low-temperature cracking resistance can be obtained.

In the flux-cored wire for all-position welding using 100% carbon dioxide gas as the shielding gas, the present inventors have tensile strength, toughness including proof stress of 690 MPa or more as the mechanical performance of the weld metal of high-strength steel, Various studies have been conducted to obtain a wire component that can ensure low temperature cracking resistance and can provide excellent welding workability.
As a result, a chemical component including a slag component mainly composed of rutile (titanium oxide) and an optimum alloy component, and a weld metal having excellent welding workability in all-position welding and excellent mechanical performance can be obtained. The content of each component was found. Furthermore, it has been found that the cold cracking resistance of the weld metal can be improved by reducing the total hydrogen content in the wire to 15 ppm or less in terms of the mass ratio of the entire wire.

The gist of the present invention for solving the above problems is as follows.
(1) A flux-cored wire for high-strength steel, which is used for shield arc welding of high-strength steel with a yield strength of 690 MPa or more using 100% carbon dioxide as the shielding gas, and is formed by filling a steel outer shell with flux. In mass% with respect to mass, C: 0.03-0.10%, Si: 0.1-0.4%, Mn: 2.0-4.0%, Ni: 1.0-3.5%, Al: 0.06 to 1.5%, Mo: 0.10 to 1.00% are contained as essential elements, Cr: 0.1 to 1.0%, Nb: 0.01 to 0.05% V: 0.01 to 0.05%, or one or more elements selected from 0.01 to 0.05%, and TiO ₂ : 2.5 to 7.5%, SiO ₂ : 0.1 to 0. _{5%, ZrO 2: 0.2~0.9%} , Al 2 O 3: 0.1~0.4%, 1 kind of fluorine compound Or the total of 2 or more types of F conversion value: 0.01-0.4% is contained as a flux, the remainder consists of Fe, an arc stabilizer, and an unavoidable impurity, and the total hydrogen amount of a wire is the mass with respect to the whole wire. A flux-cored wire for carbon dioxide shielded arc welding for high-strength steel, characterized by a ratio of 15 ppm or less.

(2) Mass% with respect to the total mass of the wire, Ti: 0.1 to 1.0%, Mg: 0.01 to 0.9%, Ca: 0.01 to 0.5%, REM: 0.01 to The flux-cored wire for high-tensile steel carbon dioxide shielded arc welding as described in (1), containing one or more selected from 0.5%.
(3) The flux-cored wire for high-tensile steel welding according to the above (1) or (2), characterized by containing B: 0.001 to 0.015% in mass% with respect to the total mass of the wire.
(4) The flux-cored wire for carbon dioxide shielded arc welding for high-strength steel according to any one of (1) to (3), wherein the steel outer skin is seamless.

  According to the flux-cored wire for carbon dioxide shielded arc welding for high-strength steel of the present invention, in the welding of high-strength steel having a proof stress of 690 MPa or more, a coated arc welding method or a solid wire can be used without using Ar gas as a shielding gas. Compared to the gas shielded arc welding method used, high-efficiency welding is possible in all positions, and weld metal with good mechanical properties such as cold cracking resistance, toughness, proof stress, and tensile strength can be obtained. The quality of the part and the welding efficiency can be improved economically.

The flux-cored wire for carbon dioxide shielded arc welding for high-strength steel of the present invention "hereinafter may be abbreviated as wire" refers to shielded arc welding of high-strength steel with a yield strength of 690 MPa or more using 100% carbon dioxide as the shielding gas. The steel outer shell is filled with flux.
The reasons for limiting the chemical components of the wire will be described below. In the following description, “%” indicating the content of the chemical component of the wire is mass% with respect to the total mass of the wire. First, C, Si, Mn, Ni, Al, and Mo contained as essential elements of the wire will be described.

[C: 0.03-0.10 mass%]
C is an important element for ensuring the yield strength and tensile strength of the weld metal by solid solution strengthening. If the C content of the wire is less than 0.03%, the effect of ensuring the yield strength and tensile strength of the weld metal cannot be obtained. If it exceeds 0.10%, excess C is retained in the weld metal, and the yield strength and tensile strength of the weld metal are reduced. Strength increases excessively and toughness decreases. In addition, the preferable range of C content is 0.04 to 0.08%.

[Si: 0.1 to 0.4% by mass]
Si is an element contained for the purpose of improving the toughness of the weld metal. If the Si content of the wire is less than 0.1%, the effect of improving toughness cannot be obtained. On the other hand, if the Si content exceeds 0.4%, the amount of slag generated increases, and slag entrainment defects occur when multilayer welding is performed. In addition, the yield of Si in the weld metal becomes excessive, and the tensile strength of the weld metal increases excessively, so that the toughness decreases. In addition, the preferable range of Si content is 0.2 to 0.3%.

[Mn: 2.0 to 4.0% by mass]
Mn is an element contained for the purpose of ensuring the toughness of the weld metal and improving the tensile strength and proof stress. If the Mn content of the wire is less than 2.0%, the shielding gas is carbon dioxide, so that the yield in the weld metal is insufficient due to oxidation consumption, and the tensile strength of the weld metal is reduced. On the other hand, when the Mn content exceeds 4.0%, the amount of slag generated increases, and slag entrainment defects occur when multilayer welding is performed. On the other hand, if the Mn content exceeds 4.0%, the yield of Mn in the weld metal becomes excessive, and the tensile strength of the weld metal is excessively increased, so that the toughness is lowered. A preferable range of the Mn content for stably obtaining the tensile strength and proof stress of the weld metal is 2.6 to 4.0%.

[Ni: 1.0 to 3.5% by mass]
Ni is an element contained for the purpose of improving the tensile strength and toughness of the weld metal. If the Ni content of the wire is less than 1.0%, the effect is insufficient, and if it exceeds 3.5%, the tensile strength of the weld metal increases excessively and the toughness decreases. In addition, the preferable range of Ni content is 1.8 to 2.5%.

[Al: 0.06 to 1.5% by mass]
Al is an element that improves toughness because it has an effect as a deoxidizer that combines with dissolved oxygen in the molten pool, but it has a relatively low heat input in carbon dioxide shielded arc welding using a flux-cored wire. In the case of the conditions, the slag floating of the formed oxide tends to be insufficient, and it remains as a nonmetallic inclusion in the weld metal, resulting in a decrease in toughness. Therefore, the Al content is 0.06 to 1.5%. In addition, the preferable range of Al content is 0.06 to 0.8%.

[Mo: 0.10 to 1.00% by mass]
Mo is not oxidized and consumed even when the shielding gas is CO ₂ gas, and yields stably in the weld metal. Further, since Mo is a precipitation strengthening element, it is effective in improving the yield strength and tensile strength of the weld metal. If the Mo content is less than 0.10%, the effect of improving the tensile strength of the weld metal cannot be obtained. If it exceeds 1.00%, the tensile strength increases excessively and the toughness decreases. In addition, the range of preferable Mo content for obtaining the yield strength and tensile strength of a weld metal is more than 0.20 to 1.00%.

Next, Cr, Nb, and V contained as wire selection elements will be described.
[Cr: 0.1 to 1.0% by mass, Nb: 0.01 to 0.05% by mass, V: 0.01 to 0.05% by mass or two or more]
Cr, Nb and V are all elements contained for the purpose of improving the yield strength and tensile strength of the weld metal. These are elements contained in the wire by selecting one or more, but if the amount exceeds the specified amount, the tensile strength of the weld metal becomes excessive and the toughness decreases. On the other hand, the effect of improving the yield strength and tensile strength of the weld metal even if it contains one or more of less than 0.1% Cr, less than 0.01% Nb, and less than 0.01% V. Cannot be obtained.

Next, one or more of TiO ₂ , SiO ₂ , ZrO ₂ , Al ₂ O ₃ , and fluorine compound contained as the wire flux will be described.
[TiO ₂ : 2.5 to 7.5% by mass]
The flux TiO ₂ is an arc stabilizer and a main component of the slag agent. Encapsulates the weld metal during welding and shields it from the atmosphere, and keeps the bead shape of the weld metal properly due to its appropriate viscosity. Affect. If the content of TiO ₂ is less than 2.5%, metal dripping is likely to occur in the vertical improvement welding and it is difficult to perform all-position welding. On the other hand, when the content of TiO ₂ exceeds 7.5%, the amount of slag becomes excessive and slag entrainment occurs, non-metallic inclusions increase and toughness decreases. A preferable range of the TiO ₂ content is 4.5 to 6.5%.

[SiO ₂ : 0.1 to 0.5% by mass]
SiO ₂ in the flux improves the slag encapsulating increase the viscosity of the molten slag. If the content of SiO ₂ is less than 0.1%, the viscosity of the molten slag is insufficient, and the slag encapsulation is insufficient, and metal dripping occurs in the vertical improvement welding. On the other hand, when the content of SiO ₂ exceeds 0.5%, the viscosity of the molten slag becomes excessive, and the slag releasability and the bead shape become poor. A preferable range of SiO ₂ content is 0.2 to 0.4%.

[ZrO ₂ : 0.2 to 0.9% by mass]
The flux ZrO ₂ has the effect of adjusting the viscosity and solidification temperature of the molten slag and enhancing the slag encapsulation. If the content of ZrO ₂ is less than 0.2%, the effect is insufficient, and metal dripping occurs in vertical improvement welding. On the other hand, if the content of ZrO ₂ exceeds 0.9%, the bead shape becomes convex, and slag entrainment or poor fusion tends to occur. A preferable range of the content of ZrO ₂ is 0.3 to 0.6%.

[Al ₂ O ₃ : 0.1 to 0.4% by mass]
The flux Al ₂ O ₃ has the effect of adjusting the viscosity and solidification temperature of the molten slag and enhancing the slag encapsulation, like ZrO ₂ . If the content of Al ₂ O ₃ is less than 0.1%, the effect is insufficient, and metal dripping occurs in vertical improvement welding. On the other hand, when the content of Al ₂ O ₃ exceeds 0.4%, the bead shape becomes convex, and slag entrainment or poor fusion tends to occur.

[Total of F-converted values of one or more fluorine compounds: 0.01 to 0.4% by mass]
Fluorine compound of flux encapsulates the weld metal as a slag agent to improve the bead shape, promotes slag floating separation from the weld metal, and improves the toughness by reducing the oxygen content in the weld metal. Has the effect of obtaining a good mechanical performance. Metal fluorides as the fluorine compound, alkali metal fluorides, but using an alkaline-earth metal _{fluorides, CaF 2, BaF 2, MgF} 2, AlF 3, LiF, NaF, K 2 ZrF 6, K 2 SiF 6, Na ₃ AlF ₆ or the like is effective, and the arc stability is improved when an alkali metal fluoride is used.

  If the total content of one or two or more F-converted fluorine compounds in the flux is less than 0.01%, the effect is insufficient, and if it exceeds 0.4%, the slag fluidity becomes excessive. At the same time, the arc becomes unstable, and metal dripping occurs in the vertical improvement welding.

[Total hydrogen content of wire: 15 mass ppm or less]
The total amount of hydrogen in the wire can be measured by an inert gas melting thermal conductivity method or the like. Since hydrogen in the wire serves as a diffusible hydrogen source for the weld metal, it must be reduced as much as possible. When the amount of hydrogen in the wire exceeds 15 ppm in terms of the mass ratio of the entire wire, the amount of diffusible hydrogen increases and the sensitivity to cold cracking increases.
The total amount of hydrogen in the wire can be reduced by selecting a filling flux with a low hydrogen content and annealing the wire strand after filling the flux.

Moreover, you may contain 1 type, or 2 or more types chosen from Ti, Mg, Ca, and REM by the content shown below as a selection element of a wire.
[Ti: 0.1 to 1.0% by mass, Mg: 0.01 to 0.9% by mass, Ca: 0.01 to 0.5% by mass, REM: 0.01 to 0.5% by mass Species or 2 or more types]
The wire components Ti, Mg, Ca, and REM are all elements contained as deoxidizers for the purpose of reducing oxygen in the weld metal and improving toughness. These are elements contained in the wire by selecting one kind or two or more kinds. However, when the amount exceeds the specified amount, it reacts violently with oxygen in the arc and the generation of spatter and fumes increases.
On the other hand, even if it contains one or more of less than 0.1% Ti, less than 0.01% Mg, less than 0.01% Ca and less than 0.01% REM, a deoxidizer As a result, the effect of reducing the oxygen of the weld metal and improving the toughness cannot be obtained.

Moreover, you may contain B by the content shown below as a selection element of a wire.
[B: 0.001 to 0.015 mass%]
B of the wire component is an element that enhances the hardenability of the weld metal and improves the tensile strength and low-temperature toughness of the weld metal by adding a small amount. If the content of B is less than 0.001%, the effect is insufficient, and if it exceeds 0.015%, the tensile strength becomes excessive and the low temperature toughness deteriorates. In addition, since the effect by containing B can be exhibited by any of a metal simple substance, an alloy, or an oxide, the form when added to the flux is arbitrary.

[Seamless steel skin]
A flux-cored wire has a structure in which a steel outer shell is formed into a pipe shape and the inside is filled with flux, and welded with a seamless wire formed by welding a seam of the steel outer shell formed during the manufacturing process. It can be broadly divided into wires having gaps. Any cross-sectional structure can be adopted in the present invention, but a wire without a steel outer shell can be heat-treated for the purpose of reducing the total amount of hydrogen in the wire, and does not absorb moisture after production. Therefore, it is more desirable for the purpose of reducing the amount of diffusible hydrogen and improving cold cracking resistance.

In addition, the alloy component in a flux adjusts a compounding component in each limited range in consideration of the component and content of a steel outer shell. By adjusting the alloy components in the flux, it is possible to obtain flux-cored wires according to the components of various high-tensile steels (base materials).
Further, P and S contained in the wire both generate a low melting point compound, lower the tensile strength of the grain boundary, and lower the toughness of the weld metal. For this reason, P contained in the wire is preferably 0.0015% or less, and S is preferably 0.0010% or less, and is preferably as low as possible.
Furthermore, the iron powder can be used to adjust the flux filling rate to 10 to 20%. However, since oxygen is introduced, it is desirable that both the flux filling rate and the iron powder addition amount are low.

  In addition, as other components in the wire, the Fe content of the steel outer sheath, the Fe content in the alloy component added to the flux, the oxide of alkali metal or alkaline earth metal as an arc stabilizer is included. . Moreover, when Cu plating processing effective for rust prevention, electrical conductivity, and chip wear resistance is performed on the surface of the wire, Cu is contained as another component in the wire.

The wire diameter of the wire of the present invention is preferably 1.0 to 2.0 mm, and more preferably 1.2 to 1.6 mm, in which the current density during welding is increased to obtain a high welding rate.
Further, the shielding gas at the time of welding is limited to 100% carbon dioxide gas because it improves slag peelability and bead shape and is inexpensive.

Hereinafter, the effect of the present invention will be described in detail with reference to examples.
The seam is formed into a U shape in the process of forming the steel outer shell, filled with fluxes of various components in the steel outer shell, and further formed into a O shape after the steel outer shell is formed into a seam. A wire with a gap that is not welded and a wire with a gap that is not welded were piped and drawn to produce a flux-cored wire having a chemical component wire diameter of 1.2 mm shown in Tables 1 to 5 as a prototype.

  The prototype wire was measured by measuring the total amount of hydrogen using a hydrogen analyzer manufactured by HORIBA, Ltd .: EMGA-621, and then using a steel plate specified in JIS G3128 SHY685 to improve the welding workability by fillet welding. And mechanical properties were evaluated as a weld (welding) metal test. Furthermore, a weld cracking test was performed on the steel plates welded using the prototyped wires. These welding conditions are summarized in Table 6.

  Stand-up progress fillet welding was performed by semi-automatic welding, and as an evaluation of welding workability, the presence or absence of metal sag, spatter generation, slag peelability and bead shape were examined visually. Thereafter, five macro sections were sampled and examined for the presence of slag entrainment defects.

  For mechanical property evaluation, a tensile test piece (JIS Z3111 A1) and an impact test piece (JIS Z3111 No. 4) were each collected from the center of the plate thickness of the weld metal and subjected to the test, and the 0.2% proof stress was 690 MPa or more. Charpy absorbed energy at a test temperature of −40 ° C. was 47 J or more.

The weld crack test was performed in accordance with the U-shaped weld crack test method (JIS Z3157), and the preheating temperature of the test specimen was 75 ° C. About the test body which passed 48 hours after welding, the presence or absence of the generation | occurrence | production of a surface crack and a cross-section crack (5 cross sections) was investigated by the penetration test (JIS Z2343).
The results are summarized in Tables 7 to 11.

  In Tables 1 to 11, wire symbols A1 to A56 are examples of the present invention, and wire symbols B1 to B31 are comparative examples.

The wire symbols A1 to A56, which are examples of the present invention, are the content of each element of C, Si, Mn, Ni, Al, Mo, the content of one or more elements selected from Cr, Nb, V, TiO ₂ , SiO ₂ , ZrO ₂ , Al ₂ O ₃ , 1 type of fluorine compound or 2 or more types of F-converted values and appropriate amount of total hydrogen, 1 type selected from Ti, Mg, Ca, REM Or the content in the case of containing two or more, and the content in the case of containing B is also an appropriate amount, so that the welding workability is good and the proof stress, tensile strength and Charpy absorbed energy of the weld metal are also good. Furthermore, no cold cracking occurred and the result was very satisfactory.

  On the other hand, the wire symbols B1 to 31 as comparative examples have mechanical properties because the content of any chemical component of the wire (mass% with respect to the total mass of the wire) is excessive or insufficient compared to the scope of the present invention. Or the welding workability was inferior.

Claims (4)

This is a high-strength steel flux cored wire that is used for shield arc welding of high-strength steel with a yield strength of 690 MPa or more using 100% carbon dioxide as the shielding gas, and is made by filling the steel outer shell with flux, and the mass with respect to the total mass of the wire %so,
C: 0.03-0.10%,
Si: 0.1 to 0.4%,
Mn: 2.0 to 4.0%,
Ni: 1.0 to 3.5%
Al: 0.06 to 1.5%,
Mo: 0.10 to 1.00%
As an essential element,
Cr: 0.1 to 1.0%,
Nb: 0.01-0.05%
V: 0.01 to 0.05%
1 type or 2 types or more selected from as a selected element, and
TiO _2: 2.5~7.5%,
SiO ₂ : 0.1 to 0.5%,
ZrO ₂ : 0.2 to 0.9%,
Al ₂ O ₃ : 0.1 to 0.4%,
Total of one or more fluorine compounds in terms of F: 0.01 to 0.4%
The balance is made of Fe, an arc stabilizer, and inevitable impurities, and the total hydrogen content of the wire is 15 ppm or less by mass ratio with respect to the entire wire. Carbon dioxide shielded arc welding for high-strength steel Flux cored wire. % By mass relative to the total mass of the wire
Ti: 0.1 to 1.0%,
Mg: 0.01 to 0.9%
Ca: 0.01 to 0.5%,
REM: 0.01 to 0.5%
The flux-cored wire for carbon dioxide shielded arc welding for high-strength steel according to claim 1, comprising one or more selected from the group consisting of: % By mass relative to the total mass of the wire
B: 0.001 to 0.015%
The flux-cored wire for carbon dioxide shielded arc welding for high-strength steel according to claim 1 or 2, characterized by comprising:   The flux-cored wire for carbon dioxide shielded arc welding for high-strength steel according to any one of claims 1 to 3, wherein the steel outer skin is seamless.