JP7795067B2 - Flux-cored wire and method for manufacturing welded joint - Google Patents

Description

This disclosure relates to a flux-cored wire for gas-shielded arc welding and a method for manufacturing a weld joint.

In recent years, there has been an increasing demand for larger and lighter construction and industrial machinery, and as a result, ultra-high tensile steel plates such as 780 MPa and 980 MPa class steel are being used. These ultra-high tensile steel plates are being used because they make products lighter and reduce the amount of steel used, thereby reducing steel and transportation costs. Furthermore, thinner steel means less weight per unit, making it easier to handle and requiring less welding, which is expected to shorten manufacturing times and reduce construction costs.

For example, Patent Document 1 describes a Ni-based alloy flux-cored wire having an outer sheath made of a Ni-based alloy, in which the filling rate of the flux contained therein is 10 to 33 wt % relative to the total weight of the wire, and the flux composition contains, relative to the total weight of the wire, 2 to 10 wt % of TiO ₂ , 0.1 to 3 wt % of SiO ₂ , 0.01 to 2 wt % of Al ₂ O ₃ , 0.4 to 3 wt % of ZrO ₂ , at least one compound selected from the group consisting of Li, Na, and K compounds: 0.01 to 0.4 wt % in total in terms of Li, Na, and K, 1 to 25 wt % in total of metal components, and 4 to 15 wt % in total of slag components.
The Ni-based alloy flux-cored wire of Patent Document 1 is described as having excellent welding workability, few welding defects, and excellent resistance to hot cracking in MAG welding of Ni-containing steel and Ni-based alloy.

Patent Document 2 also describes a Ni-based alloy flux-cored wire having an outer sheath made of a Ni-based alloy containing Nb and/or Mn, characterized in that the filling rate of the flux contained therein is 15 to 36 wt % relative to the total weight of the wire, and the flux composition contains, relative to the total weight of the wire, 2 to 10 wt % of TiO ₂ , 0.1 to 3 wt % of SiO ₂ , 0.4 to 4 wt % of ZrO ₂ , at least one kind selected from the group consisting of Li, Na and K compounds: 0.01 to 0.4 wt % in total converted into Li, Na and K, 1 to 25 wt % in total of metal components, and 4 to 15 wt % in total of slag components, and is substantially free of Al ₂ O ₃ , carbonates, Fe oxides and Mn oxides.
The Ni-based alloy flux-cored wire of Patent Document 2 is described as being free from slag seizure and having excellent resistance to hot cracking when welding Ni steel or Ni-based alloys, and as being excellent in welding workability in all positions and in bead shape.

Flux-cored wires are also disclosed in Patent Documents 3 to 9.

Japanese Patent Application Laid-Open No. 2000-117488 Japanese Patent Application Laid-Open No. 2000-343276 International Publication No. 2019/102932 JP 2011-125875 A International Publication No. 2017/188275 Special table 2016-515942 publication Japanese Unexamined Patent Publication No. 169196/1986 International Publication No. 2017/154725 Japanese Patent Application Publication No. 06-106382

For example, when welding high-strength, extra-thick steel plates, preheating is performed to prevent cold cracking. Reducing diffusible hydrogen during welding is effective in preventing cold cracking and eliminating or simplifying preheating. Inventions that incorporate fluorides into flux and welding wire to reduce the amount of diffusible hydrogen have been reported. The mechanism is thought to be that fluorides in the welding material are dissociated by the arc, and the hydrogen partial pressure in the arc atmosphere is reduced by the fluorine material, thereby reducing the amount of hydrogen dissolved in the molten pool. However, the inclusion of fluorides makes the molten pool more susceptible to sagging, reducing welding workability (especially vertical welding). Furthermore, resistance to hot cracking is sometimes required when welding high-tensile steel plates.
The flux-cored wires disclosed in Patent Documents 1 to 9 have room for further improvement in terms of improving welding workability and suppressing hot cracking of the weld metal in gas-shielded arc welding.

The purpose of this disclosure is to provide a flux-cored wire and a method for manufacturing a welded joint that provides high welding workability and suppresses hot cracking of the weld metal in gas-shielded arc welding.

The gist of the present disclosure is as follows.
<1> A flux-cored wire for gas-shielded arc welding, comprising a steel sheath having a Ni content of 50% by mass or less and flux filled inside the steel sheath, wherein the flux-cored wire contains 0.01 to 20.00% in total of rare earth oxides, in mass% relative to the total mass of the flux-cored wire, and in a chemical composition excluding fluorides, nitrides, oxides, and metal carbonates, the Cr content, in mass% relative to the total mass of the flux-cored wire, is 0 to less than 22.00%.
<2> The flux-cored wire according to <1>, which contains a fluoride and has an F content of 0.003 to 30.000% by mass relative to the total mass of the flux-cored wire.
<3> The flux-cored wire according to <1> or <2>, which contains nitrides and has an N content of 0.003 to 15.00% by mass relative to the total mass of the flux-cored wire.
<4> The chemical composition excluding fluorides, nitrides, oxides, and metal carbonates is, in mass% with respect to the total mass of the flux-cored wire,
C: 0.003-0.500%,
Si: 0 to 3.50%,
Mn: 0 to 10.00%,
P: 0 to 0.030%,
S: 0-0.030%,
Cu: 0 to 10.00%,
Ni: 0 to 50.00%,
Cr: 0-10.00%
Mo: 0 to 50.00%,
Nb: 0 to 0.500%,
V: 0-0.500%,
W: 0-10.00%,
Sn: 0-10.00%,
Sb: 0 to 10.00%,
Ti: 0 to 0.500%,
Al: 0-1.000%,
B: 0-1.000%,
Mg: 0-2.000%,
Ca: 0-2.000%,
REM: 0-0.5000%,
<1><2> The flux-cored wire according to any one of <1> to <2>, wherein the flux-cored wire contains 0 to 0.300% Bi, and the balance is Fe and impurities.
<5> The flux-cored wire according to any one of <1> to <4>, which contains one or more specific oxides selected from the group consisting of Ti oxide, Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide and Ca _oxide , and the total content of the specific oxides is 10.00% or less, expressed in mass% relative to the total mass of the flux-cored wire, and in terms of each of the specific oxides as TiO ₂ , FeO, BaO, Na ₂ O, SiO ₂ , ZrO 2 , MgO, Al ₂ O ₃ , MnO ₂ , K ₂ O or CaO.
<6> The flux _- cored wire according to any one of <1> to <5>, _{which contains one or more specific metal carbonates selected from the group consisting of MgCO3, Na2CO3, LiCO3, CaCO3, K2CO3 , BaCO3 , FeCO3 , MnCO3 , and SrCO3} , and the total content of the specific metal carbonates is 10.00% or less in mass% relative to the total mass of the flux-cored wire.
<7> The flux-cored wire according to any one of <1> to <6>, wherein the surface is coated with one or both of polytetrafluoroethylene oil and perfluoropolyether oil.
<8> The flux-cored wire according to any one of <1> to <7>, wherein the rare earth oxides are contained in an amount of more than 0.20% in total, in terms of mass% relative to the total mass of the flux-cored wire.
<9> The flux-cored wire according to any one of <1> to <8>, wherein the Cr content in the chemical composition excluding fluorides, nitrides, oxides, and metal carbonates is 0 to less than 10.00%.
<10> A method for manufacturing a welded joint, comprising a step of gas-shielded arc welding steel materials using the flux-cored wire according to any one of <1> to <9>.
<11> The method for manufacturing a welded joint according to <10>, wherein in the gas-shielded arc welding step, welding is performed using a torch that does not have a suction nozzle.

This disclosure provides a flux-cored wire and a method for manufacturing a welded joint that provides high welding workability and suppresses hot cracking in the weld metal in gas-shielded arc welding.

An embodiment that is an example of the present disclosure will be described.
In this specification, when a numerical range expressed using "to" is not preceded or followed by "greater than" or "less than," it means a range that includes these numerical values as the lower and upper limits. When "to" is preceded or followed by "greater than" or "less than," it means a range that does not include these numerical values as the lower or upper limit.
In the present specification, the upper limit of a numerical range may be replaced by the upper limit of another numerical range, or may be replaced by a value shown in an example. Furthermore, the lower limit of a numerical range may be replaced by the lower limit of another numerical range, or may be replaced by a value shown in an example.
Furthermore, with regard to the content, "%" means "% by mass".
The content (%) of "0 or more" means that the component is an optional component and may not be contained.

<Flux-cored wire>
The flux-cored wire according to the present disclosure includes a steel sheath having a Ni content of 50 mass % or less and flux filled inside the steel sheath.
The flux-cored wire according to the present disclosure is a flux-cored wire for gas-shielded arc welding, which contains, in mass% relative to the total mass of the flux-cored wire, 0.01 to 20.00% in total of rare earth oxides, and in a chemical composition excluding fluorides, nitrides, oxides, and metal carbonates, the Cr content, in mass% relative to the total mass of the flux-cored wire, is 0 to less than 22.00%.
The reasons for limiting the requirements (including optional requirements) for the flux-cored wire according to the present disclosure will be specifically described below.

The flux-cored wire according to the present disclosure contains 0.01 to 20.00% in total of rare earth oxides.
In the following description, "%" means "mass % with respect to the total mass of the flux-cored wire" unless otherwise specified.

(Rare earth oxides)
The flux-cored wire according to the present disclosure contains 0.01 to 20.00% in total of rare earth oxides (hereinafter also referred to as "REM oxides"), thereby improving welding workability in gas-shielded arc welding. Although the reason for this is not clear, it is thought that the inclusion of rare earth oxides in the flux-cored wire increases the solidification temperature of slag, thereby suppressing dripping from the molten pool and improving welding workability (particularly vertical welding workability).
It is presumed that if REM is contained in a flux-cored wire simply as an alloy rather than as an oxide, the REM tends to oxidize, and the amount of REM in the alloy becomes unstable, making it difficult to control the composition. In response to this, the inventors have discovered that by adding REM, an oxide-forming element, as an REM oxide, the amount of REM in the oxide becomes constant, making it easier to control the amount of REM in the wire, and further finding that it is possible to suppress an increase in spatter and a decrease in mechanical properties.

In gas-shielded arc welding, from the perspective of improving welding workability, the lower limit of the rare earth oxide content is preferably 0.05% or more, 0.10% or more, 0.15% or more, or more than 0.20%. Furthermore, the upper limit of the rare earth oxide content is set to 20.00% or less, as the effect of adding rare earth oxides reaches saturation. If necessary, the upper limit of the rare earth oxide content may be set to 15.00% or less, 10.00% or less, 5.00% or less, 1.00% or less, or 0.50% or less.

Here, the rare earth oxide refers to an oxide of a rare earth element, and the flux-cored wire according to the present disclosure contains one or more oxides selected from the group consisting of Sc oxide, Y oxide, La oxide, Ce oxide, Pr oxide, Nd oxide, Pm oxide, Sm oxide, Eu oxide, Gd oxide, Tb oxide, Dy oxide, Ho oxide, Er oxide, Tm oxide, Yb oxide, and Lu oxide.
Among these, the rare earth oxide contained in the flux-cored wire according to the present disclosure is preferably one or more oxides selected from the group consisting of Y oxide, La oxide, and Ce oxide, from the viewpoint of improving welding workability.

(Cr content: 0 to less than 22.00%)
Since Cr is not an essential component, the lower limit of the Cr content in the chemical composition of the flux-cored wire, excluding fluorides, nitrides, oxides, and metal carbonates, is 0%.
On the other hand, if the Cr content is 22.00% or more, spattering increases and workability tends to decrease, so the Cr content is set to less than 22.00%. The Cr content will be described in detail later.
Here, the "oxides" excluded from the above chemical composition include the rare earth oxides (REM oxides).

(F content: 0.003-30.000%)
The flux-cored wire according to the present disclosure does not need to contain fluoride, and therefore, in the flux-cored wire according to the present disclosure, the lower limit of the fluoride content is 0%.
On the other hand, fluorides have the effect of reducing the amount of diffusible hydrogen in the weld metal and significantly improving the cold cracking resistance of the weld metal. This is presumably because, when welding is performed with a flux-cored wire, fluorine (F ^- ) in the flux combines with hydrogen (H ⁺ ) to form hydrogen fluoride (HF), which is then released outside the weld metal. To achieve this effect, the total F content is preferably 0.003% or more.
On the other hand, fluorides cause the generation of fumes during welding. Therefore, when the flux-cored wire according to the present disclosure contains fluoride, it is preferable that it further contains nitride so that the N content falls within the range described below. It has been found that the flux-cored wire according to the present disclosure contains nitride, thereby suppressing the generation of fumes during welding even when it contains fluoride. Although the reason for this is not clear, it is presumed that because nitrogen has a lower boiling point than hydrogen fluoride (HF) (N ₂ : −196°C, hydrogen fluoride (HF) : +20°C), nitrides are decomposed by the arc to generate nitrogen (N), which then combines as nitrogen molecules (N ₂ ). This lowers the arc temperature, reducing the amount of high-temperature vapor in the arc, thereby suppressing the generation of fumes.

When the flux _{-cored wire according to the present disclosure contains a fluoride, the type of fluoride is not limited, but preferably the flux contains one or more fluorides selected from the group consisting of CaF2, MgF2, LiF, NaF, K2ZrF6, K2SiF6 , and Na3AlF6 . These fluorides} ionize to produce Ca, Mg, Li, Na, _K , Zr, Si, and Al, which all bond with oxygen to reduce the oxygen content in the weld metal and act as deoxidizing elements. This is advantageous in terms of improving the toughness and elongation of the weld metal.
When the flux-cored wire according to the present disclosure contains 0.003% or more of fluoride, the lower limit of the content of each fluoride is not particularly limited as long as the total mass percentage of the fluorides contained in the flux-cored wire (preferably flux) according to the present disclosure is 0.003% or more in terms of F. Furthermore, since the F content indicates the amount of fluorine (F) contained in the fluoride in terms of mass % relative to the total mass of the flux-cored wire, when the type of fluoride is the above-mentioned preferred example fluoride, the F content is calculated by the following formula B.
Formula B: 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
Here, the chemical formula of the fluoride in formula B indicates the mass % of the fluoride corresponding to each chemical formula with respect to the total mass of the flux-cored wire. The coefficient of each chemical formula of the fluoride is calculated from the chemical formula weight of each fluoride.
When a fluoride other than the above-mentioned preferred examples is contained, the F content is calculated from the chemical formula weight of each fluoride in accordance with the above formula B.
The lower limit of the F content is preferably 0.003% by mass relative to the total mass of the flux-cored wire, and more preferably 0.005%, 0.010%, 0.015%, 0.020%, 0.025%, or 0.030%.
From the viewpoint of suppressing generation of fumes during welding, the preferred upper limit of the F content is 30.000%, 20.000%, 10.000%, 3.000%, 2.000%, 1.000%, 0.500%, 0.100%, or 0.050% by mass relative to the total mass of the flux-cored wire.
The F content in the flux-cored wire according to the present disclosure is measured by fluorescent X-ray analysis.

(N content: 0.003-15.00%)
The flux-cored wire according to the present disclosure does not need to contain nitrides, and therefore, in the flux-cored wire according to the present disclosure, the lower limit of the nitride content is 0%.
On the other hand, nitrides have the function of reducing the amount of diffusible hydrogen in the weld metal and significantly improving the cold cracking resistance of the weld metal. Although the reason for this is not clear, it is speculated that one of the reasons is that N in the nitrides combines with hydrogen (H) during welding to form ammonia (NH ₃ ), and this NH ₃ is released outside the weld metal. The flux-cored wire according to the present disclosure may contain nitrides in the steel sheath, but from the viewpoint of easily controlling the N content relative to the total mass of the wire within the range described below, it is preferable that nitrides be contained at least in the flux.

Examples of nitrides that can be contained in the flux-cored wire according to the present disclosure include AlN, _BN , _Ca3N2 , CeN, CrN, Cu3N, _Fe4N , _{Fe3N , Fe2N} , _Mg3N , _Mo2N , _NbN , _Si3N4 , TiN, VN, ZrN, _Mn2N , and _Mn4N . When the flux-cored wire according to the present disclosure contains one or more of these nitrides and does not contain any other nitrides, the N content is represented by the following formula A.
Formula A: N content = 0.342 x AlN + 0.564 x BN + 0.189 x Ca ₃ N ₂ + 0.091 x CeN + 0.212 x CrN + 0.068 x Cu ₃ N + 0.059 x Fe ₄ N + 0.077 x Fe ₃ N + 0.111 x Fe ₂ N+0.161×Mg ₃ N+0.068×Mo ₂ N+0.131×NbN+0.399×Si ₃ N ₄ +0.226×TiN+0.216×VN+0.133×ZrN+0.113×Mn ₂ N+0.06×Mn ₄ N
Here, the chemical formula of the nitride in Formula A indicates the mass % of the nitride corresponding to each chemical formula with respect to the total mass of the flux-cored wire. The coefficients of the chemical formula of each nitride are calculated from the chemical formula weight of each nitride.
When nitrides other than those listed above are contained, the N content is calculated from the chemical formula weight of each nitride in accordance with the above formula A.

The flux-cored wire according to the present disclosure preferably contains 0.003% or more of N based on the total mass of the flux-cored wire.

The amount of nitrogen contained in the flux-cored wire is measured by analysis using JIS G1228:1997.
If the total N content in the entire flux-cored wire is 0.003% or more, the amount of diffusible hydrogen in the weld metal is sufficiently reduced, and the cold cracking resistance of the weld metal is improved.
In order to further reduce the amount of diffusible hydrogen in the weld metal, the lower limit of the N content may be set to 0.005%, 0.008%, 0.010%, 0.015%, 0.020%, or 0.022%.
In the flux-cored wire of the present disclosure, the upper limit of the N content is not particularly limited from the viewpoint of reducing the amount of diffusible hydrogen, but considering that the interior of the steel sheath is filled with flux, the upper limit of the N content is 15.00%, and may be 10.00%, 8.00%, or 5.00%.
The proportion of N contained in the steel sheath relative to the entire wire is small, and the N content in the flux-cored wire according to the present disclosure can be adjusted mainly by the type and content of nitrides contained in the flux.

In addition, in the flux-cored wire according to the present disclosure, the N content of nitrogen contained as nitrides in the flux is preferably 0.002% or more relative to the total mass of the flux-cored wire. Furthermore, in order to further reduce the amount of diffusible hydrogen in the weld metal, the lower limit of the N content of nitrogen contained as nitrides in the flux may be set to 0.005%, 0.008%, 0.010%, 0.015%, 0.020%, or 0.022% relative to the total mass of the flux-cored wire. Furthermore, considering that the interior of the steel sheath is filled with flux, the upper limit of the N content of nitrogen contained as nitrides in the flux is preferably 15.00% relative to the total mass of the flux-cored wire, and may be 10.00%, 8.00%, or 5.00%.

Next, the chemical composition of the flux-cored wire according to the present disclosure, excluding fluorides, nitrides, oxides, and metal carbonates, will be described.
The chemical components constituting the chemical composition described below may be contained in the steel sheath or in the flux. Furthermore, when the flux-cored wire according to the present disclosure has a plating layer on the outer surface of the steel sheath, the chemical components may be contained in the plating layer. In the following description, the "chemical composition excluding fluorides, nitrides, oxides, and metal carbonates" may be simply referred to as the "chemical composition."
The chemical composition of the flux-cored wire according to the present disclosure, excluding fluorides, nitrides, oxides, and metal carbonates, is as follows:
C: 0.003 to 0.500%,
Si: 0 to 3.50%,
Mn: 0 to 10.00%,
P: 0 to 0.030%,
S: 0-0.030%,
Cu: 0 to 10.00%,
Ni: 0 to 50.00%,
Cr: 0-10.00%
Mo: 0 to 50.00%,
Nb: 0 to 0.500%,
V: 0 to 0.500%,
W: 0-10.00%,
Sn: 0-10.00%,
Sb: 0 to 10.00%,
Ti: 0 to 0.500%,
Al: 0-1.000%,
B: 0-1.000%,
Mg: 0-2.000%,
Ca: 0-2.000%,
REM: 0-0.5000%,
It is preferable that the alloy contains 0 to 0.300% Bi, and the balance is Fe and impurities.

(C: 0.003-0.500%)
C is an important element for ensuring the yield strength and tensile strength of the weld metal through solid solution strengthening. When the C content in the chemical composition of the flux-cored wire is 0.003% or more, the yield strength and tensile strength of the weld metal can be sufficiently ensured.
On the other hand, by setting the C content in the chemical composition of the flux-cored wire to 0.500% or less, the C content in the weld metal is maintained at an appropriate amount, an excessive increase in the proof stress and tensile strength of the weld metal is suppressed, and a decrease in the toughness of the weld metal can be suppressed.
Therefore, in order to stably ensure all of the toughness, yield strength, and tensile strength of the weld metal, the lower limit of the C content in the chemical composition of the flux-cored wire is preferably set to 0.003%, and the upper limit of the C content in the chemical composition of the flux-cored wire is preferably set to 0.500%. If necessary, the lower limit of the C content may be set to 0.010%, 0.020%, 0.030%, 0.040%, 0.050%, or 0.060%. Similarly, the upper limit of the C content may be set to 0.450%, 0.400%, 0.350%, 0.300%, or 0.250%.

(Si: 0-3.50%)
Since Si is not an essential component, the lower limit of the Si content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Si is a deoxidizing element and has the function of reducing the oxygen content in the weld metal and increasing the cleanliness of the weld metal. However, since a Si content of 3.50% or less can suppress a decrease in the toughness of the weld metal, this is preferably set as the upper limit. Furthermore, to stably ensure the toughness of the weld metal, the upper limit of Si may be 3.00%, 2.00%, or 1.00%. To obtain the above effect, the lower limit of the Si content may be 0.40%, 0.45%, 0.50%, or 0.60%.

(Mn: 0-10.00%)
Since Mn is not an essential component, the lower limit of the Mn content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Mn is an element effective for ensuring the hardenability of the weld metal and increasing its strength. When the Mn content in the chemical composition of the flux-cored wire is 10.00% or less, the susceptibility of the weld metal to intergranular embrittlement is reduced, and a decrease in the toughness of the weld metal can be suppressed. Therefore, it is preferable to set the upper limit of the Mn content to 10.00%. More preferably, the upper limit of the Mn content is 9.50%, 9.00%, 8.00%, or 6.00%. To achieve the above effect, the lower limit of the Mn content may be set to 0.40%, 0.45%, 0.50%, or 0.60%.

(P: 0-0.030%)
P is an impurity element, and from the viewpoint of suppressing a decrease in the toughness of the weld metal, it is preferable to reduce the P content in the flux-cored wire as much as possible. Therefore, the lower limit of the P content in the chemical composition of the flux-cored wire is 0%. Furthermore, if the P content in the chemical composition of the flux-cored wire is 0.030% or less, a decrease in the toughness of the weld metal can be suppressed. In order to effectively suppress solidification cracking of the weld metal, the P content in the chemical composition of the flux-cored wire is more preferably 0.020% or less, 0.015% or less, or 0.010% or less.
However, since an extreme reduction in the P content leads to an increase in manufacturing costs, from the viewpoint of reducing the cost of dephosphorization, the P content is preferably 0.003% or more.

(S: 0-0.030%)
S is also an impurity element, and from the viewpoint of suppressing a decrease in the toughness and ductility of the weld metal, it is preferable to reduce the S content in the flux-cored wire as much as possible. Therefore, the lower limit of the S content in the chemical composition of the flux-cored wire is 0%. Furthermore, if the S content in the chemical composition of the flux-cored wire is 0.030% or less, it is possible to suppress a decrease in the toughness and ductility of the weld metal. The S content in the chemical composition of the flux-cored wire is more preferably 0.020% or less, 0.010% or less, 0.008% or less, 0.006% or less, or 0.005% or less.
However, since an extreme reduction in the S content leads to an increase in manufacturing costs, from the viewpoint of reducing desulfurization costs, the S content is preferably 0.003% or more.

(Cu: 0-10.00%)
Since Cu is not an essential component, the lower limit of the Cu content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Cu has the effect of improving the strength and toughness of the weld metal. To fully obtain this effect, it is preferable that the Cu content in the chemical composition of the flux-cored wire be 0.01% or more. Cu may be contained in the plating on the surface of the steel sheath of the flux-cored wire, or may be contained in the flux as a single element or as an alloy. Cu plating also has the effect of improving rust resistance, electrical conductivity, and tip wear resistance.
Therefore, the Cu content in the chemical composition of the flux-cored wire is the total amount of Cu contained in the steel sheath and flux, and Cu contained in the plating on the wire surface.
On the other hand, when the Cu content in the chemical composition of the flux-cored wire is 10.00% or less, a decrease in the toughness of the weld metal can be suppressed. Therefore, it is preferable that the Cu content be 10.00% or less. The upper limit of the Cu content in the chemical composition of the flux-cored wire is preferably 9.00%, 8.00%, 7.00%, 6.00%, 5.00%, 4.00%, 3.00%, or 2.00%.

(Ni: 0-50.00%)
Since Ni is not an essential component, the lower limit of the Ni content in the chemical composition of the flux-cored wire is 0%.
Ni improves the toughness of the weld metal by increasing the solid solution toughness of Ni. To achieve this effect, the Ni content is preferably set to 0.30% or more, 0.50% or more, or 1.00% or more. On the other hand, a Ni content of 50.00% or less can suppress a decrease in the hot cracking resistance of the weld metal. Therefore, the upper limit of the Ni content in the chemical composition of the flux-cored wire is preferably set to 50.00% or less. The upper limit of the Ni content may also be set to 45.00%, 40.00%, or 35.00%.

(Cr: 0-10.00%)
Since Cr is not an essential component, the lower limit of the Cr content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Cr is an element effective for ensuring the hardenability of the weld metal and increasing its strength. As described above, Cr may be contained in an amount less than 22.00%. However, by setting the Cr content in the chemical composition of the flux-cored wire to 10.00% or less, a decrease in the toughness of the weld metal can be suppressed. Therefore, the upper limit of the Cr content in the chemical composition of the flux-cored wire is preferably set to 10.00% or less, and more preferably to less than 10.00%. More preferably, the upper limit of the Cr content is 9.50%, 9.00%, 8.00%, or 6.00%. If necessary, the lower limit of the Cr content may be set to 0.01%, 0.05%, 0.10%, or 0.20%.

(Mo: 0-50.00%)
Since Mo is not an essential component, the lower limit of the Mo content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Mo has the effect of improving the hardenability of the weld metal, and is therefore an element effective in increasing the strength of the weld metal. To achieve this effect, the lower limit of the Mo content in the chemical composition of the flux-cored wire is preferably set to 0.01%, 0.05%, 0.10%, or 0.15%. On the other hand, by setting the Mo content in the chemical composition of the flux-cored wire to 50.00% or less, a decrease in the toughness of the weld metal can be suppressed. Therefore, the Mo content in the chemical composition of the flux-cored wire is preferably set to 50.00% or less. The upper limit of the Mo content in the chemical composition of the flux-cored wire is preferably 48.00%, 45.00%, 40.00%, 30.00%, or 10.00%.

(Nb: 0-0.500%)
Since Nb is not an essential component, the lower limit of the Nb content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Nb forms fine carbides in the weld metal, and these fine carbides cause precipitation strengthening in the weld metal, so Nb improves the tensile strength of the weld metal. To fully obtain this effect, it is preferable that the lower limit of the Nb content in the chemical composition of the flux-cored wire be 0.005%, 0.010%, 0.015%, or 0.020%.
On the other hand, when the Nb content in the chemical composition of the flux-cored wire is 0.500% or less, the formation of coarse precipitates in the weld metal due to Nb is suppressed, and a decrease in the toughness of the weld metal can be suppressed. Therefore, the upper limit of the Nb content in the chemical composition of the flux-cored wire is preferably 0.500%, and more preferably 0.450%, 0.400%, 0.300%, or 0.200%.

(V: 0-0.500%)
Since V is not an essential component, the lower limit of the V content in the chemical composition of the flux-cored wire is 0%.
On the other hand, V improves the hardenability of the weld metal and is therefore an element effective in increasing the strength of the weld metal. To fully obtain this effect, it is preferable that the lower limit of the V content in the chemical composition of the flux-cored wire be 0.001%, 0.010%, 0.030%, or 0.050%.
On the other hand, when the V content in the chemical composition of the flux-cored wire is 0.500% or less, the amount of V carbide precipitated in the weld metal does not increase too much, excessive hardening of the weld metal is suppressed, and a decrease in the toughness of the weld metal can be suppressed. Therefore, the upper limit of the V content in the chemical composition of the flux-cored wire is preferably 0.500%, and more preferably 0.400%, 0.300%, 0.200%, 0.100%, or 0.080%.

(W: 0-10.00%)
Although W is an element effective for improving the corrosion resistance of the weld metal, W is not an essential component. Therefore, the lower limit of the W content in the chemical composition of the flux-cored wire is 0%. On the other hand, when the W content in the chemical composition of the flux-cored wire is 10.00% or less, the occurrence of cracks in the weld metal can be suppressed. Therefore, it is preferable that the upper limit of the W content in the chemical composition of the flux-cored wire is 10.00%. More preferably, the upper limit of the W content is 9.50%, 9.00%, 8.00%, or 6.00%. If necessary, the lower limit of the W content may be 0.01%, 0.03%, 0.50%, or 0.60%.

(Sn: 0-10.00%)
Although Sn is an effective element for improving the corrosion resistance of the weld metal, Sn is not an essential component. Therefore, the lower limit of the Sn content in the chemical composition of the flux-cored wire is 0%. On the other hand, when the Sn content in the chemical composition of the flux-cored wire is 10.00% or less, the occurrence of cracks in the weld metal can be suppressed. Therefore, it is preferable that the upper limit of the Sn content in the chemical composition of the flux-cored wire is 10.00%. More preferably, the upper limit of the Sn content is 9.50%, 9.00%, 8.00%, or 6.00%. If necessary, the lower limit of the Sn content may be 0.01%, 0.03%, 0.50%, or 0.60%.

(Sb: 0-10.00%)
Although Sb is an effective element for improving the corrosion resistance of the weld metal, Sb is not an essential component. Therefore, the lower limit of the Sb content in the chemical composition of the flux-cored wire is 0%. On the other hand, when the Sb content in the chemical composition of the flux-cored wire is 10.00% or less, the occurrence of cracks in the weld metal can be suppressed. Therefore, it is preferable that the upper limit of the Sb content in the chemical composition of the flux-cored wire is 10.00%. More preferably, the upper limit of the Sb content is 9.50%, 9.00%, 8.00%, or 6.00%. If necessary, the lower limit of the Sb content may be 0.01%, 0.03%, 0.50%, or 0.60%.

(Ti: 0-0.500%)
Since Ti is not an essential component, the lower limit of the Ti content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Ti is a deoxidizing element and has the effect of reducing the amount of oxygen in the weld metal. Furthermore, Ti contained in the chemical composition of the flux-cored wire remains in small amounts in the weld metal and fixes solute N, thereby mitigating the adverse effect of solute N on the toughness of the weld metal. Therefore, the chemical composition of the flux-cored wire may contain 0.001% or more, 0.010% or more, 0.030% or more, or 0.050% or more of Ti.
On the other hand, when the Ti content in the chemical composition of the flux-cored wire is 0.500% or less, the formation of excessive precipitates in the weld metal is suppressed, thereby suppressing a decrease in toughness. When Ti is contained in the chemical composition 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 in the chemical composition of the flux-cored wire is preferably 0.500%, and more preferably 0.400%, 0.300%, 0.200%, 0.100%, or 0.080%.
In addition, when the flux-cored wire according to the present disclosure contains Ti oxide, the above Ti content is the content of components other than Ti that constitute the Ti oxide.

(Al: 0-1.000%)
Since Al is not an essential component, the lower limit of the Al content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Al is a deoxidizing element and, like Si, reduces the amount of oxygen in the weld metal and has the effect of improving the cleanliness of the weld metal. However, an Al content of 1.000% or less can suppress a decrease in the toughness of the weld metal. Therefore, it is preferable that the Al content in the chemical composition of the flux-cored wire be 1.000% or less. Furthermore, to stably ensure the toughness of the weld metal, the upper limit of the Al content may be 0.950%, 0.900%, 0.850%, or 0.800%. If necessary, the lower limit of the Al content may be 0.005%, 0.010%, 0.050%, 0.100%, 0.150%, or 0.200%.

(B: 0-1.000%)
Since B is not an essential component, the lower limit of the B content in the chemical composition of the flux-cored wire is 0%.
On the other hand, B combines with solute N in the weld metal to form BN, thereby reducing the adverse effect of solute N on the toughness of the weld metal. Furthermore, B also enhances the hardenability of the weld metal, thereby improving the strength of the weld metal. Therefore, the chemical composition of the flux-cored wire may contain 0.0005% or more of B.
On the other hand, by setting the B content in the chemical composition of the flux-cored wire to 1.000% or less, the B content in the weld metal does not increase too much, the formation of coarse BN and B compounds such as _Fe23 (C,B) ₆ is suppressed, and a decrease in the toughness of the weld metal can be suppressed. Therefore, the upper limit of the B content in the chemical composition of the flux-cored wire is preferably 1.000%, and more preferably 0.900%, 0.800%, or 0.700%.

(Mg: 0-2.000%)
Since Mg is not an essential component, the lower limit of the Mg content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Mg is a deoxidizing element and, like Al, reduces the amount of oxygen in the weld metal and improves the cleanliness of the weld metal. However, by setting the Mg content in the chemical composition of the flux-cored wire to 2.000% or less, the amount of spatter and fumes generated by the violent reaction between Mg and oxygen in the arc can be suppressed. Therefore, it is preferable that the Mg content in the chemical composition of the flux-cored wire be 2.000% or less. The preferred lower limit of the Mg content in the chemical composition of the flux-cored wire is 0.150%, 0.200%, 0.250%, or 0.300%. The preferred upper limit of the Mg content in the chemical composition of the flux-cored wire is 1.700%, 1.600%, 1.500%, 1.400%, 1.000%, or 0.900%.

(Ca: 0-2.000%)
(REM: 0-0.5000%)
Since Ca and REM are not essential components, the lower limit values of the Ca content and the REM content in the chemical composition of the flux-cored wire are both 0%.
On the other hand, both Ca and REM change the structure of sulfides in the weld metal and also reduce the size of sulfides and oxides, thereby improving the ductility and toughness of the weld metal. Therefore, the Ca content in the chemical composition of the flux-cored wire may be set to 0.002% or more, and the REM content in the chemical composition of the flux-cored wire may be set to 0.0002% or more.
On the other hand, by reducing the Ca content and REM content in the chemical composition of the flux-cored wire, the amount of spatter can be suppressed and weldability can be improved. Therefore, the upper limit of the Ca content in the chemical composition of the flux-cored wire is preferably 2.000%, and the upper limit of the REM content in the chemical composition of the flux-cored wire is preferably 0.5000%.
In the present disclosure, "REM" contained in the chemical composition excluding fluorides, nitrides, oxides, and metal carbonates refers to an alloy that does not contain at least the aforementioned "rare earth oxides."
Here, REM is a collective term for Sc, Y, and lanthanides, a total of 17 elements, and the REM content refers to the total REM content. Furthermore, REM is generally contained in misch metal. Therefore, for example, misch metal may be added to the alloy to adjust the REM content to the above range.

(Bi: 0-0.300%)
Since Bi is not an essential component, the lower limit of the Bi content in the chemical composition of the flux-cored wire is 0%.
On the other hand, Bi is an element that improves slag removability. To fully obtain this effect, the Bi content in the chemical composition 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 in the chemical composition of the flux-cored wire is 0.300% or less, the occurrence of solidification cracking in the weld metal can be suppressed. Therefore, the upper limit of the Bi content in the chemical composition of the flux-cored wire is preferably 0.300%. The upper limit of the Bi content in the chemical composition of the flux-cored wire may also be preferably 0.250%, 0.200%, or 0.100%.

(balance: Fe and impurities)
The remaining components in the flux-cored wire according to the present disclosure are Fe and impurities, such as Fe contained in the steel sheath and Fe in the alloy powder contained in the flux.
Further, the term "impurities" refers to components that are introduced into the flux-cored wire during industrial production due to the raw materials or various factors in the production process, and are acceptable within a range that does not adversely affect the flux-cored wire according to the present disclosure.

(Total content of specific oxides: 0 to 10.00%)
The flux-cored wire according to the present disclosure may contain one or more specific oxides selected from the group consisting of Ti oxide, Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide, and Ca oxide, and the total content of the specific oxides is preferably 10.00% or less. In the present disclosure, oxides included in the group consisting of Ti oxide, Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide, and Ca oxide may be simply referred to as "specific oxides." Furthermore, the total content of each of the specific oxides may be abbreviated as "total content of specific oxides." Note that the specific oxides do not include the previously described "rare earth oxides."
The total content of _{the specific oxides is calculated by converting each of the specific oxides into TiO2, FeO, BaO, Na2O, SiO2, ZrO2, MgO, Al2O3, MnO2 , K2O or CaO and calculating the} total amount thereof. In other words, the total content of specific oxides represents the sum of the total Ti oxide content in terms of _TiO2 , the total Fe oxide content in terms of FeO, the total Ba oxide content in terms of BaO, the total Na oxide content in terms of _Na2O , the total Si oxide content in terms of _SiO2 , the total Zr oxide content in terms of _ZrO2 , the total Mg oxide content in terms of _MgO , the total Al oxide content in terms of _Al2O3 , the total Mn oxide content in terms of _MnO2 , the total K oxide content in terms of _K2O , and the total Ca oxide content in terms of CaO.
For example, when the flux-cored wire according to the present disclosure contains _{only one} or more of TiO2, FeO, _BaO , _Na2O , _SiO2 , ZrO2, _MgO , _Al2O3 , _MnO2 , _K2O and CaO as the specific oxides, the total content of the specific oxides is calculated as the sum of the contents of _TiO2 , FeO, BaO, _Na2O , _SiO2 , _ZrO2 , _{MgO, Al2O3, MnO2, K2O and CaO .}
Since the specific oxides are not essential components of the flux-cored wire according to the present disclosure, the lower limit of the total amount of the specific oxides in the flux-cored wire is 0%.
On the other hand, the specific oxides have the effect of maintaining a good weld bead shape and improving vertical weldability. Furthermore, Na oxide, K oxide, Mg oxide, Fe oxide, and the like also have the effect of stabilizing the arc. To achieve such effects, the total content of the specific oxides is preferably 0.05% or more. To further enhance these effects, the lower limit of the total content of the specific oxides may be 0.10%, 0.15%, or 0.20%. On the other hand, by keeping the total content of the specific oxides 10.00% or less, the occurrence of slag entrapment can be suppressed. Therefore, the upper limit of the total content of the specific oxides is preferably 10.00%, and may be 9.00%, 8.00%, 7.00%, 6.00%, 3.00%, 2.00%, 1.00%, or 0.50%.

The content of the above-mentioned specific oxides in the flux-cored wire according to the present disclosure does not need to be limited to each type of specific oxide, but from the viewpoint of suppressing deterioration in toughness due to an excessive increase in the oxygen content in the weld metal, a composition containing, for example, Si oxide: 0.08% or more and 0.95% or less, Zr oxide: 0.80% or less, and Al oxide: 0.50% or less is preferred.

Here, the measurement of the content of each specific oxide and the total content of the specific oxides in the flux-cored wire according to the present disclosure will be described.
First, the content of Ti oxides is analyzed using an X-ray fluorescence analyzer to analyze the mass of Ti present as a specific oxide in the flux-cored wire. Specifically, the wire is polished to expose a longitudinal cross section (a cross section parallel to the longitudinal direction of the wire: _L cross section) at a position half the wire diameter φ, and the cross section is analyzed. For example, if _TiO2 , _Ti2O3 , _{and Ti3O5} are detected by analysis, the mass percentages of each Ti oxide are expressed as [ _TiO2 ], [ _{Ti2O3 ]} , and [ _Ti3O5 ], and the total _TiO2- equivalent value of the Ti oxides is expressed as [equivalent _TiO2 ], and the total TiO2 _- equivalent value is calculated using the following formula C1.
[Converted TiO ₂ ]=(0.60×[TiO ₂ ]+0.67×[Ti ₂ O ₃ ]+0.64×[Ti ₃ O ₅ ])×1.67...Formula C1
The coefficients (0.60, 0.67, 0.64) in formula C1 are coefficients for calculating the amount of Ti contained in each oxide, and the multiplier (1.67) at the end is a multiplier for calculating the _TiO2 equivalent value from the total amount of Ti present as an oxide in the wire.

Here, a method for determining the coefficient will be explained. If oxides of M _x O _y (for example, TiO ₂ , Ti ₂ O ₃ , Ti ₃ O ₅ ) are detected, the coefficient for M _x O _y is calculated using the following formula C2.
[Atomic weight of M element] x / ([Atomic weight of M element] x x + [Atomic weight of oxygen] x y) ... Formula C2
The coefficients 0.60, 0.67, and 0.64 in formula C1 correspond to the coefficients calculated in formula C2 above.
Next, a method for determining a multiplier for calculating a converted value will be described. The multiplier for converting to _{M a} O _b (for example, TiO ₂ ) is calculated using the following formula C3.
([atomic weight of M element] × a + [atomic weight of oxygen] × b) / [atomic weight of M element × a] Formula C3
The 1.67 in formula C1 corresponds to the multiplier calculated in formula C3 above.
The oxide may be a compound formed by bonding two metal elements. In this case, the coefficient is calculated using the following formula ^C4 , assuming that _MxOyM2z (e.g., _TiO3.Fe , i.e., an _oxide where M= _Ti , ^M2 =Fe, x=1, y=3, and z=1) is detected.
[Atomic weight of M element] × x / ([Atomic weight of M element] × x + [Atomic weight of oxygen] × y + [Atomic weight of ^M2 element] × z) ... Formula C4
The content of specific oxides other than Ti oxide is also measured by fluorescent X-ray analysis in the same manner as the content of Ti oxide described above.

(Total content of specific metal carbonates: 0 to 10.00%)
The flux-cored wire according to the present disclosure does not need to contain metal carbonate, and therefore, in the flux-cored wire according to the present disclosure, the lower limit of the metal carbonate content is 0%.
On the other hand, metal carbonates are ionized by the arc to generate _CO2 gas. _CO2 gas reduces the hydrogen partial pressure in the welding atmosphere and reduces the amount of diffusible hydrogen in the weld metal. To achieve this effect, the flux-cored wire according to the present disclosure may contain metal carbonate. In particular, it is preferable that the flux of the flux-cored wire contains metal carbonate.
The type and composition of the metal carbonate contained in the flux-cored wire according to the present disclosure are not limited, but the type of metal carbonate contained in the flux-cored wire is preferably one or more selected from the group consisting of MgCO ₃ , Na ₂ CO ₃ , LiCO ₃ , CaCO ₃ , K ₂ CO ₃ , BaCO ₃ , FeCO _{3 ,} MnCO 3 and SrCO ₃ (hereinafter, the metal carbonates contained in this group may be abbreviated as “specific metal carbonates”).
In order to obtain the above-mentioned effects, it is preferable to contain the specific metal carbonates, that is, it is preferable that the total content of the specific metal carbonates is greater than 0%. In order to further exert these effects, the lower limit of the total content of the specific metal carbonates may be set to 0.05%.
On the other hand, when the content of the specific metal carbonate is 10.00% or less, the occurrence of sagging of the weld bead can be suppressed, thereby improving welding workability. Therefore, when the flux-cored wire according to the present disclosure contains the specific metal carbonate, the upper limit of the total content of the specific metal carbonate is preferably 10.00%. If necessary, the upper limit of the content of the specific metal carbonate may be 9.00%, 8.00%, 7.00%, 6.00%, 3.00%, 2.00%, 1.00%, or 0.50%.
The content of each specific metal carbonate and the total content of the specific metal carbonates in the flux-cored wire according to the present disclosure are measured by using fluorescent X-ray analysis, similar to the content of Ti oxide described above.

The flux-cored wire according to the present disclosure may further include a lubricant applied to the surface. The lubricant applied to the surface of the wire has the effect of improving the wire feedability during welding. Various types of lubricants can be used for welding wire (e.g., vegetable oils such as palm oil), but to suppress cold cracking of the weld metal, it is preferable to use one or both of H-free polytetrafluoroethylene oil (PTFE oil) and perfluoropolyether oil (PFPE oil). Furthermore, as described above, the flux-cored wire according to the present disclosure may further include a plating formed on the wire surface. In this case, the lubricant is applied to the surface of the plating.

The amount of hydrogen contained in the flux-cored wire according to the present disclosure is not particularly limited, but in order to reduce the amount of diffusible hydrogen in the weld metal, it is preferable that the amount be 12 ppm or less relative to the total mass of the flux-cored wire. The amount of hydrogen in the flux-cored wire may increase if moisture penetrates into the flux-cored wire during storage. Therefore, if there is a long period between the wire's manufacture and its use, it is desirable to prevent moisture penetration using the measures described below.

(steel shell)
The steel sheath of the flux-cored wire according to the present disclosure has a Ni content of 50% by mass or less. If the Ni content exceeds 50% by mass, hot cracking of the weld metal becomes more likely to occur. Therefore, the Ni content in the steel sheath is set to 50% by mass or less. The Ni content in the steel sheath is preferably 40% by mass or less, and more preferably 20% by mass or less.
Furthermore, as long as the above-mentioned conditions are satisfied, the steel sheath of the flux-cored wire according to the present disclosure is not particularly limited. For example, the steel sheath may be a mild steel sheath having a chemical composition including Ni: 0-50%, C: 0-0.1%, Si: 0-0.10%, Mn: 0-3.00%, P: 0-0.030%, S: 0-0.020%, Al: 0-0.1%, and N: 0-0.030%, with the balance being iron and impurities.

Although the steel sheath also normally contains N as an impurity, N contained in the flux as nitrides is more effective at reducing the amount of diffusible hydrogen in the weld metal than N contained in the steel sheath. The detailed mechanism behind this is unknown, but it is presumed that this is because the steel sheath is in contact with the shielding gas and is therefore at a lower temperature than the flux, so although the N in the steel sheath diffuses into the droplets, it is difficult for it to dissociate into the arc.
From the above viewpoints, it is preferable that the N content of nitrogen contained as nitride in the flux of the flux-cored wire according to the present disclosure is 0.002% or more with respect to the total mass of the flux-cored wire. Furthermore, if the steel sheath contains a large amount of nitrogen, it may be difficult to draw the wire and may cause breakage. Therefore, it is generally preferable that the N content (%) in the steel sheath is low.

(wire shape)
Next, the shape (wire structure) of the flux-cored wire according to the present disclosure will be described.
Flux-cored wires are usually classified into two types: wires having a shape without slit-like gaps (seamless shape) because the seams of the steel outer sheath are welded (sometimes called seamless wires), and wires having a shape including slit-like gaps because the seams of the steel outer sheath are not welded.

Any of these shapes can be adopted for the flux-cored wire according to the present disclosure. However, in order to suppress the occurrence of cold cracking in the weld metal, it is preferable that the steel sheath does not have slit-shaped gaps. H (hydrogen) that penetrates the weld during welding diffuses into the weld metal and the material to be welded, and accumulates in areas where stress is concentrated, causing cold cracking. There are various sources of H, but when welding is performed under strict control of the cleanliness of the weld and the gas shielding conditions, moisture (H ₂ O) contained in the wire is the main source of H, and the amount of this moisture strongly affects the amount of diffusible hydrogen in the weld joint.
When the steel sheath has a seam, moisture in the atmosphere is likely to penetrate into the flux through the seam. Therefore, it is desirable to prevent moisture in the atmosphere from penetrating into the flux through the steel sheath during the period from wire production to use by removing the seam of the steel sheath. When the steel sheath has a seam and the period from wire production to use is long, it is desirable to vacuum-pack the entire flux-cored wire or store the flux-cored wire in a container that can keep it dry in order to prevent the penetration of sources of H, such as moisture.

(wire diameter)
The diameter of the flux-cored wire according to the present disclosure is not particularly limited, but is, for example, 1.0 to 2.0 mm. Note that the diameter of a typical flux-cored wire is 1.2 to 1.6 mm.

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

<Method for manufacturing flux-cored wire>
Next, a method for manufacturing a flux-cored wire according to the present disclosure will be described.
The manufacturing method described below is an example, and the method for manufacturing the flux-cored wire according to the present disclosure is not limited to the following method.

(In the case of seamless flux-cored wire)
The method for manufacturing a flux-cored wire having a seamless shape includes the steps of preparing flux, forming a steel strip using a forming roll while feeding it in the longitudinal direction to obtain a U-shaped open tube, supplying flux into the open tube through the opening of the open tube, butt-welding opposing edge portions (both circumferential ends) of the opening of the open tube to obtain a seamless tube, drawing the seamless tube to obtain a flux-cored wire having a predetermined wire diameter, and annealing the flux-cored wire during or after the drawing step.
The flux is prepared so that the amount of rare earth oxides in the flux-cored wire, and further the amount of nitrides, fluorides, specific oxides, specific metal carbonates, and chemical composition, which are contained as needed, fall within the above-mentioned ranges. Note that the flux filling rate, which is determined by the width and thickness of the steel strip that is the material of the steel sheath, and the amount of flux filling, also affect the amount of nitrides, fluorides, specific oxides, specific metal carbonates, and chemical composition of the flux-cored wire.

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

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

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

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

The gas-shielded arc welding process does not require the use of a special torch, such as a torch with a suction nozzle, and welding can be performed using a normal torch.

In the method for manufacturing a welded joint according to the present disclosure, gas-shielded arc welding is used as the welding method.
In the method for manufacturing a welded joint according to the present disclosure, the type of steel material (workpiece) that serves as the base material of the welded joint is not particularly limited. For example, a high-strength steel plate having a tensile strength of 590 MPa or more and 1700 MPa or less and a plate thickness of 20 mm or more can be suitably used.

The method for manufacturing a welded joint according to the present disclosure uses the welding wire according to the present disclosure, which has high welding workability and can suppress hot cracking in the weld metal. Therefore, even when steel materials with high hot cracking sensitivity are welded using the method for manufacturing a welded joint according to the present disclosure, the welding work can be performed easily and the occurrence of hot cracking in the weld metal can be suppressed. Furthermore, the joint obtained by the method for manufacturing a welded joint according to the present disclosure may be an undermatched joint, in which the tensile strength of the weld metal is lower than the tensile strength of the steel plate base material.

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

The type of shielding gas used in the method for manufacturing a welded joint according to the present disclosure is not particularly limited. The method for manufacturing a welded joint according to the present disclosure exhibits excellent welding operability regardless of the type of shielding gas, and can produce a welded joint with high strength, high toughness, and high fatigue strength. Commonly used shielding gases such as 100% carbon dioxide and a mixed gas of Ar and 3 to 30% _CO2 by volume can be preferably used as the shielding gas in the method for manufacturing a welded joint according to the present disclosure. Furthermore, the shielding gas used in welding using the flux-cored wire according to the present disclosure may contain 5% or less _O2 by volume. Because these gases are inexpensive, welding using these gases is advantageous for industrial use.
Normally, when these gases are used in combination with a rutile-based flux-cored wire, they generate a large amount of spatter, deteriorating welding workability. However, the method for manufacturing a welded joint according to the present disclosure uses the flux-cored wire according to the present disclosure, which can sufficiently suppress the amount of spatter, and therefore, even when these gases are used as shielding gases, good welding workability can be achieved.

The welding position in the method for manufacturing a welded joint according to the present disclosure is not particularly limited. The method for manufacturing a welded joint according to the present disclosure can achieve good welding workability regardless of the welding position: flat, horizontal, vertical, or overhead.

The welded joint obtained by the welded joint manufacturing method according to the present disclosure comprises a base steel plate (base material) and a welded joint composed of a weld metal and a weld heat-affected zone. There are no particular limitations on the base material of the welded joint. The welded joint according to the present disclosure is manufactured using the flux-cored wire according to the present disclosure, in which the amount of rare earth oxides, etc., is preferably controlled, thereby suppressing hot cracking of the welded metal.

By using the flux-cored wire disclosed herein for gas-shielded arc welding, it is possible to obtain a weld with excellent resistance to hot cracking.

Next, the feasibility and effects of the present disclosure will be explained in more detail using examples and comparative examples. However, the following examples do not limit the scope of the present disclosure, and all design modifications that adhere to the spirit described above and below are within the technical scope of the present disclosure.

(Flux-cored wire manufacturing)
The flux-cored wires of the examples and comparative examples were produced by the method described below.
First, a steel strip was fed in the longitudinal direction and formed using forming rolls to obtain a U-shaped open tube. Flux was supplied into the open tube through the opening, and opposing edges of the opening of the open tube were butt-welded to obtain a seamless tube.
The seamless tube was drawn to obtain a flux-cored wire without slit-like gaps, although some samples were drawn to tubes with slit-like gaps without seam welding.
In this way, flux-cored wires with a final wire diameter of 1.2 mm were produced as prototypes. During the drawing process, the flux-cored wires were annealed at a temperature range of 650 to 950°C for 4 hours or more. After the prototypes were produced, a lubricant was applied to the wire surface. The configurations of these flux-cored wires are shown in the table below.

Tables 1A to 1E show the rare earth oxide content, Cr content, fluoride content, F content, nitride content, N content, chemical composition (i.e., the content of each element contained as a chemical component excluding fluorides, nitrides, oxides, and metal carbonates), specific oxide content, specific fluoride content, specific metal carbonate content, and iron powder content in the wire. The units of these contents shown in Tables 1A to 1E are mass% relative to the total mass of the flux-cored wire, except for the "Ni content in the sheath" shown in Table 1A. In the tables, "mass% relative to the total mass of the flux-cored wire" is abbreviated to "mass%," and "chemical composition excluding nitrides, oxides, fluorides, and metal carbonates" is abbreviated to "chemical composition." The unit of "Ni content in the sheath" shown in Table 1A is mass% relative to the total mass of the steel sheath.

The F content shown in Table 1A indicates the amount of fluorine (F) contained in fluorides in the flux in mass % relative to the total mass of the flux-cored wire, and is a value (F equivalent value) calculated by the above-mentioned formula B.
The N content of the flux-cored wire shown in Table 1B indicates the amount of nitrogen (N) contained in nitrides in the flux in mass % relative to the total mass of the flux-cored wire, and is a value (N equivalent value) calculated by the above-mentioned formula A.
The units of the amount of Ni shown in Table 1C (Ni in the flux, Ni in the sheath, total Ni) are all mass % relative to the total mass of the flux-cored wire.
The total of specific oxides shown in Table 1D is the total value of the content of each of Ti oxide, Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide and Ca oxide, converted into TiO ₂ , FeO, BaO, Na ₂ O, SiO ₂ , ZrO ₂ , MgO, Al ₂ O ₃ , MnO ₂ , K ₂ O or CaO.

The remainder of the flux-cored wire shown in the table (i.e., components other than those shown in the table) is iron and impurities.
Among the flux-cored wires shown in the table, those marked "seamless" in the "wire structure" column have a seamless shape, and unless otherwise specified in the "remarks" column, are wires coated with palm oil as a lubricant. Furthermore, those marked "with slit-like gaps" in the "wire structure" column are wires with slit-like gaps, and those marked "coated with perfluoropolyether" in the "remarks" column are wires coated with perfluoropolyether (PFPE) oil on the surface.
The elements listed in the chemical composition of the wires in Table 1A and the flux-cored wires in Table 1C are in the form of a steel sheath or metal powder, and values outside the ranges specified in this disclosure are underlined in the tables.
Furthermore, in Tables 1A to 1E, blank columns in the tables relating to the chemical composition or content of compounds, etc., mean that the chemical composition, compound, etc. is not intentionally contained. These chemical compositions, compounds, etc. may be unavoidably mixed in or generated.

[evaluation]
The flux-cored wires of the examples and comparative examples were used to carry out gas-shielded arc welding and evaluation. Specifically, the evaluation was carried out by the method described below.
The steel plates to be welded were 50 mm thick and had a tensile strength of 780 MPa, and the welding gas used in the evaluation was Ar-20% _CO2 . The welding current used in the evaluation was DC, and the wire polarity was positive.
The welding conditions for the evaluation were as shown in Tables 2, 3 and 4. The voltage was changed within a range of ±3 V depending on the arc state, and when the voltage was changed from the standard conditions (conditions shown in the tables), the speed was adjusted to achieve the desired heat input.

(Evaluation of slag entrapment)
The evaluation of slag inclusion was performed by performing horizontal fillet welding on the above-mentioned steel plates under welding condition E shown in Table 4. A flux-cored wire that had no slag inclusion on any of the cross sections of the five welds was rated as "pass."

(Evaluation of workability)
Bead-on welding was performed on 10 mm thick SM490 material under welding conditions A, B, and C shown in Table 2. The welding current was DC, and the type of welding gas and wire polarity were as described above. Cases where welding was possible under welding condition A were rated as excellent (◎), cases where welding was possible under B were rated as good (○), and cases where welding was possible or not possible under C were rated as poor (×).

(Evaluation of spatter amount)
Flat bead-on-plate welding was performed on 10 mm thick SM490 material under welding condition D shown in Table 3. The spatter generated during welding was collected in a copper collection box placed around the welding site and its mass was measured to determine the amount of spatter generated per unit time (g/min). The welding current was DC, and the type of welding gas and wire polarity were as described above. A spatter generation rate of less than 3.0 g/min was rated as excellent (◎), 3.0 g/min to less than 3.5 g/min was rated as good (◯), and 3.5 g/min or more was rated as poor (×).

(Evaluation of Hot Cracking Resistance) T-Weld Cracking Test Hot cracking resistance was evaluated by welding a 50 mm thick steel plate having a tensile strength of 780 MPa under welding condition E shown in Table 4 in a constant atmosphere controlled at a temperature of 20°C and a humidity of 60%, and then subjecting the welded joint thus obtained to a test in accordance with JIS Z 3153-1993 (T-Weld Cracking Test Method). The welding current was DC, and the type of welding gas and the polarity of the wire were as described above.
The flux-cored wires in the welded joints that did not develop cracks in the T-weld cracking test were rated as "pass" in terms of hot cracking resistance.

The test results obtained using the above method are shown in Table 5. If all evaluation items were passed, the overall evaluation was deemed to be a pass; if even one item was not passed, the overall evaluation was deemed to be a fail.

It can be seen that when welding is performed using the flux-cored wires of the examples, welding workability (particularly vertical welding ability) is high in gas shielded arc welding, and hot cracking of the weld metal can be suppressed.
Furthermore, as shown in the test results in Table 5, the flux-cored wires of the examples were also evaluated favorably in terms of the amount of spatter and slag inclusion, and showed good welding workability.
On the other hand, the comparative examples did not satisfy any of the requirements defined in this disclosure and therefore failed in one or more evaluation items.

Claims (9)

A flux-cored wire for gas-shielded arc welding, comprising a steel sheath having a Ni content of 50% by mass or less and flux filled inside the steel sheath,
The flux-cored wire contains a fluoride, and the F content is 0.003 to 30.000% by mass relative to the total mass of the flux-cored wire;
The flux-cored wire contains nitrides, and the N content is 0.003 to 15.00% by mass relative to the total mass of the flux-cored wire;
The flux-cored wire contains rare earth oxides in a total amount of 0.01 to 20.00% by mass relative to the total mass of the flux-cored wire, and the chemical composition excluding fluorides, nitrides, oxides, and metal carbonates is, in mass%, relative to the total mass of the flux-cored wire,
C: 0.003 to 0.500%,
Si: 0 to 3.50%,
Mn: 0 to 10.00%,
P: 0 to 0.030%,
S: 0-0.030%,
Cu: 0 to 10.00%,
Ni: 0 to 50.00%,
Cr: 0-10.00%,
Mo: 0 to 50.00%,
Nb: 0 to 0.500%,
V: 0 to 0.500%,
W: 0-10.00%,
Sn: 0-10.00%,
Sb: 0 to 10.00%,
Ti: 0 to 0.500%,
Al: 0-1.000%,
B: 0-1.000%,
Mg: 0-2.000%,
Ca: 0-2.000%,
REM: 0-0.5000%,
Bi: 0 to 0.300%, and
The balance is Fe and impurities . The Ni content in the steel outer skin is 1.0% or more in mass% relative to the total mass of the steel outer skin, and
the Cr content in a chemical composition of the flux-cored wire excluding fluorides, nitrides, oxides, and metal carbonates is 0.01% or more in mass% with respect to the total mass of the flux-cored wire;
2. The flux-cored wire according to claim 1, wherein either one or both of the above is satisfied . 3. The flux-cored wire according to claim 1 or 2, comprising one or more specific oxides selected from the group consisting of Ti oxide, Fe oxide, Ba oxide, Na oxide, Si oxide, Zr oxide, Mg oxide, Al oxide, Mn oxide, K oxide and Ca _oxide , and the total content of the specific oxides is 10.00% or less, in terms of mass% relative to _the total mass of the flux-cored wire , and each of the specific oxides is expressed as a converted value of _TiO2 , FeO, BaO, _Na2O , _SiO2 , _ZrO2 , MgO, _Al2O3 , _MnO2 , K2O or CaO. The flux _{-cored wire according to any one of claims 1 to 3, comprising one or more specific metal carbonates selected from the group consisting of MgCO3, Na2CO3, LiCO3, CaCO3, K2CO3 , BaCO3 , FeCO3 , MnCO3 and SrCO3 , and} the total content of the specific metal carbonates is 10.00% or less in mass% relative to the total mass of the flux-cored wire. 5. The flux-cored wire according to claim 1 , wherein the surface is coated with one or both of polytetrafluoroethylene oil and perfluoropolyether oil. The flux-cored wire according to any one of claims 1 to 5 , wherein the rare earth oxides are contained in a total amount of more than 0.20% by mass, in terms of mass% relative to the total mass of the flux-cored wire. The flux-cored wire according to any one of claims 1 to 6, wherein in a chemical composition excluding fluorides, nitrides, oxides, and metal carbonates, the Cr content is 0 to less than 10.00% in mass% with respect to the total mass of the flux-cored wire. A method for manufacturing a welded joint, comprising a step of gas-shielded arc welding steel materials using the flux-cored wire according to any one of claims 1 to 7 . The method for manufacturing a welded joint according to claim 8 , wherein the gas-shielded arc welding step uses a torch that does not have a suction nozzle.