JP7790953B2 - Basic flux-cored wire, deposited metal obtained by using basic flux-cored wire, welding method, and method for manufacturing welded joint - Google Patents

Description

The present invention relates to a basic flux-cored wire that enables welding in all positions and has an excellent balance of strength and toughness, a weld metal obtained using the basic flux-cored wire, and a welding method and weld joint using the basic flux-cored wire.

Flux-cored wires are classified into rutile, basic, and metal types depending on the type of flux they contain. These are used for different purposes, but basic flux-cored wires have the advantage of being able to keep the oxygen content of the weld metal low, thereby achieving excellent toughness. However, basic flux-cored wires also have the disadvantage of being less easy to weld, making them particularly difficult to use in difficult welding positions such as vertical, horizontal, and overhead welding.

Patent Document 1 discloses a technology for overcoming the above-mentioned drawbacks of basic flux-cored wires. Specifically, Patent Document 1 describes that all-position welding is possible when the flux contains a strongly deoxidizing metal element containing Mg and Al and a fluorine compound powder, the strongly deoxidizing metal powder and the fluorine compound powder related to the strongly deoxidizing metal element have specific particle sizes, the flux rate is 10 to 30 mass%, and the specific composition is satisfied, including Al: 1.0 to 3.5 mass%, Mg _(wire) : 0.3 to 0.9 mass%, the total fluorine equivalent value F of the fluorine compounds: 0.30 to 1.20 mass%, the total of the strongly deoxidizing metal elements: 2.2 mass% or more, the strongly deoxidizing metal element: 15 to 35 mass%, and the fluorine compound powder: 10 to 45 mass%.

Japanese Patent Application Laid-Open No. 2021-000646

The flux-cored wire described in Patent Document 1 contains a strong deoxidizing element to enable all-position welding. The strong deoxidizing element has an excellent deoxidizing effect during welding, and some elements are slag-out and others remain as inclusions in the weld metal.
However, the inclusions remaining in the weld metal adversely affect mechanical properties, particularly toughness. In other words, although Patent Document 1 overcomes the drawback of basic flux-cored wires that enable all-position welding, it is not possible to make the most of the advantage of basic flux-cored wires, namely, excellent toughness.

Furthermore, while toughness depends on the strength value, there is also the issue that the balance between strength and toughness varies depending on the target strength. For example, if a high strength is designed, toughness may be good, but if the target strength is lowered and the design is redesigned, toughness may become extremely poor. This is because the elements added change depending on the target strength, affecting the deposited metal structure or weld metal structure.

The present invention was made in consideration of these problems, and aims to provide a basic flux-cored wire and welding method that enables welding in all positions and produces a deposited metal and weld metal (hereinafter also referred to as a "weld joint") that has an excellent balance of strength and toughness, as well as a deposited metal and weld joint that has an excellent balance of strength and toughness.

The above object of the present invention is achieved by the following configuration [1] relating to a basic flux-cored wire.

[1] A basic flux-cored wire containing a strong deoxidizing element,
The total amount of the strong deoxidizing elements is 1.50 mass% or more and 4.00 mass% or less with respect to the total mass of the wire,
REM: 0.030% by mass or more and 0.120% by mass or less,
Fe: 85.0% by mass or more,
Contains
C: 0.050% by mass or less,
Si: 0.60% by mass or less,
Mn: 2.00% by mass or less,
P: 0.0150% by mass or less,
S: 0.0150% by mass or less,
Cr: 1.00% by mass or less,
Mo: 1.00% by mass or less,
Al: 3.00% by mass or less,
Mg: 3.00% by mass or less,
Zr: 3.000% by mass or less,
Ti: 3.000% by mass or less,
Ca: 3.00% by mass or less,
Ni: 5.00% by mass or less,
B: 0.0200% by mass or less,
Ba: 4.00% by mass or less,
F: 2.00% by mass or less,
and
A value calculated by the following formula (1): 48.0 or less,
A value calculated by the following formula (2): 48.0 or less,
A value calculated by the following formula (3): 0.09 or more,
A value calculated by the following formula (4): 0.14 or more,
A basic flux-cored wire characterized by:
Formula (1):
32.1×[Si]-40.6×[Mn]-20.1×[Ni]-19.7×[Mo]-172.6×[C]-408.2×[REM]-5824.4×[B]-38.4×[Cr]-9960×[P]+43793×[S]
Formula (2):
33.9×[Si]-47.0×[Mn]-22.2×[Ni]-11.9×[Mo]-203.9×[C]-443.5×[REM]-4482.2×[B]-36.1×[Cr]-15281×[P]+47868×[S]
Formula (3):
0.001×[Fe]-0.71×[Si]+0.08×[Mn]-0.08×[Al]+0.69×[Zr]+0.03×[Ni]+0.01×[Mo]+0.32×[C]+2.27×[REM]+9.57×[B]+0.11×[Cr]
Formula (4):
0.003×[Fe]-0.35×[Si]+0.09×[Mn]-0.13×[Al]+0.22×[Zr]+0.02×[Ni]-0.02×[Mo]-0.11×[C]+1.17×[REM]+4.30×[B]+0.09×[Cr]
In the formulas (1) to (4), [REM], [Fe], [C], [Si], [Mn], [P], [S], [Cr], [Mo], [Al], [Zr], [Ni], and [B] respectively represent the contents of the REM, Fe, C, Si, Mn, P, S, Cr, Mo, Al, Zr, Ni, and B, expressed as mass% with respect to the total mass of the wire.

Furthermore, preferred embodiments of the present invention relating to basic flux-cored wire relate to the following [2] to [11].

[2] With respect to the total mass of the wire,
Furthermore, for the total mass of the wire,
Nb: 0.50% by mass or less,
Cu: 2.00% by mass or less,
W: 1.00% by mass or less,
Ta: 1.00% by mass or less,
V: 1.00% by mass or less,
Sr: 4.00% by mass or less, and
Total alkali metal elements: 3.00 mass% or less,
Contains at least one selected from
The basic flux-cored wire according to [1], characterized in that the balance is O, N, and impurities.

[3] The basic flux-cored wire according to [1] or [2], characterized in that the B content is 0.0020 mass% or more and 0.0150 mass% or less, based on the total mass of the wire.

[4] The content of B includes the B-equivalent value of B oxide,
When the B-equivalent value of the B oxide relative to the total mass of the wire is expressed as [B oxide] in mass%,
The basic flux-cored wire according to any one of [1] to [3], characterized in that a value calculated by formula (5): [B oxide]/[B] is 0.5 or more.

[5] Ba: 4.00% by mass or less,
Contains at least one selected from Ca: 3.00% by mass or less, and Sr: 4.00% by mass or less,
The flux contains at least one selected from BaF ₂ , CaF ₂ and SrF ₂ , which are fluorides of Ba, Ca and Sr,
The Ba content includes the Ba equivalent value of the _BaF2 ,
The Ca content includes the Ca equivalent value of the _CaF2 ,
The Sr content includes the Sr-equivalent value of the _SrF2 ,
The basic flux-cored wire according to any one of [1] to [4], characterized in that the content of F includes the F-equivalent values of BaF ₂ , CaF ₂ and SrF ₂ .

[6] The basic flux-cored wire according to [5], wherein the F content is equal to the F-equivalent value of all fluorides contained in the flux.

[7] A basic flux-cored wire according to any one of [1] to [6], characterized in that the oxide content in the flux is 0.005 mass% or more and 0.100 mass% or less relative to the total mass of the wire.

[8] The Cr content is 0.20 mass% or more and 0.90 mass% or less with respect to the total mass of the wire,
The content of Mo is 0.50 mass% or less with respect to the total mass of the wire,
The basic flux-cored wire according to any one of [1] to [7], characterized in that a value calculated by equation (6): [Cr]/([Cr]+[Mo]) is 0.20 or more.

[9] The Cr content is 0.90 mass% or less with respect to the total mass of the wire,
The content of Mo is 0.10 mass% or more and 0.80 mass% or less with respect to the total mass of the wire,
The basic flux-cored wire according to any one of [1] to [7], characterized in that a value calculated by formula (7): [Mo]/([Cr]+[Mo]) is 0.10 or more.

[10] The wire contains, as the strong deoxidizing element, 1.00 mass% or more and 2.50 mass% or less of Al relative to the total mass of the wire,
The Mg content is 1.00% by mass or less,
When the content of Mg in the wire is expressed as [Mg] in mass% relative to the total mass of the wire,
The basic flux-cored wire according to any one of [1] to [9], characterized in that a value calculated by formula (8): [Al]/([Al]+[Mg]) is 0.5 or more and 1.0 or less.

[11] A basic flux-cored wire according to any one of [1] to [10], characterized in that the REM consists of La and Ce.

The above object of the present invention also relates to the following [12] regarding the deposited metal.
[12] Based on the total mass of the deposited metal,
C: 0.020% by mass or more and 0.100% by mass or less,
Si: 0.05% by mass or more and 0.50% by mass or less,
Mn: 0.20% by mass or more and 1.80% by mass or less,
Al: 0.30% by mass or more and 1.50% by mass or less,
Ce: 0.002 mass% or more and 0.010 mass% or less,
Fe: 85.0% by mass or more,
Contains
La: 0.008% by mass or less,
P: 0.0200% by mass or less,
S: 0.0200% by mass or less,
Cr: 1.00% by mass or less,
Mo: 1.00% by mass or less,
Mg: 0.50% by mass or less,
Zr: 0.50% by mass or less,
Ti: 0.05% by mass or less,
Ca: 0.50% by mass or less,
Ni: 3.00% by mass or less,
B: 0.0090% by mass or less,
Ba: 1.00% by mass or less,
Nb: 0.001% by mass or less,
Cu: 0.1% by mass or less,
V: 0.001% by mass or less,
W: 0.1% by mass or less,
Ta: 0.1% by mass or less,
Sr: 1.00% by mass or less,
Total alkali metal elements: 0.05% by mass or less,
O: 0.0250% by mass or less,
N: 0.0100% by mass or less;
The remainder of the deposited metal is impurities.

Furthermore, the above object of the present invention relates to the following [13], which relates to basic flux-cored wire.

[13] A basic flux-cored wire characterized by producing the deposited metal described in [12].

Furthermore, the above object of the present invention relates to the following welding method [14].

[14] A welding method characterized by gas-shielded arc welding using the basic flux-cored wire described in any one of [1] to [11] and [13].

Furthermore, the above object of the present invention relates to the following [15] regarding welded joints.

[15] A welded joint manufactured using the welding method described in [14].

The present invention provides a basic flux-cored wire and welding method that enables welding in all positions and produces deposited metal and weld metal with an excellent balance of strength and toughness, as well as deposited metal and weld joints with an excellent balance of strength and toughness.

In this embodiment, by incorporating an appropriate amount of strong deoxidizing elements into the basic flux-cored wire, welding workability is improved and welding in difficult positions becomes possible. However, depending on the elements used to adjust the strength, there is a risk that the balance between strength and toughness of the deposited metal or weld metal may not be achieved.

The inventors therefore further derived a parameter equation from the relationship between composition and mechanical performance, designed within the strength range used industrially. Specifically, they summarized the relationship between the composition of this embodiment and mechanical performance, namely strength, toughness, and brittle fracture rate, using a multiple regression equation, and discovered that by satisfying the four equations described below, it is possible to derive a wire composition with an excellent balance of strength and toughness.

Embodiments of the present invention are described in detail below. Note that the present invention is not limited to the embodiments described below, and can be modified and implemented as desired without departing from the spirit and scope of the present invention.

[1. Basic Flux-Cored Wire]
The basic flux-cored wire according to this embodiment (hereinafter sometimes simply referred to as "wire") includes a flux core and a hoop sheath. The following specifically describes the components contained in the basic flux-cored wire according to this embodiment, their contents, and the preferred ranges and reasons for limiting the components.

In the present specification, the word "to" is used to mean that the numerical values before and after it are included as the lower and upper limits. In addition, in the present specification, when "(Wire)" is added immediately after an element, it means that the element is contained in a wire.
Similarly, when "(Metal)" is added immediately after an element, it indicates that the element is contained in the deposited metal.

Here, let us take Mn as an example of an element. The metal Mn _(Wire) of the entire wire includes the Mn contained in the hoop and the Mn metal powder contained in the flux, while the Mn equivalent value _(Wire) of the Mn compounds of the entire wire includes the Mn equivalent value of Mn oxides, etc. The content of Mn _(Wire) is the total amount of the metal Mn _(Wire) of the entire wire and the Mn equivalent value _(Wire) of the compounds related to Mn, expressed as the Mn content of the entire wire in mass % relative to the total mass of the wire. Note that either the metal Mn _(Wire) of the entire wire or the Mn equivalent value _(Wire) of the Mn compounds of the entire wire may be 0.

<Total Amount of Strong Deoxidizing Elements: 1.50% by Mass or More and 4.00% by Mass or Less>
The basic flux-cored wire according to this embodiment (hereinafter, sometimes simply referred to as "wire") includes a core (flux) and an outer sheath (hoop). In this embodiment, adding an appropriate amount of a strong deoxidizing element can improve welding operability and enable welding in difficult positions. Examples of strong deoxidizing elements include Al, Mg, Ti, Ca, and Zr, and are defined as the total amount. This total amount is expressed in mass% relative to the total mass of the wire. For example, when the wire contains Al, Mg, Ti, Ca, and Zr, it is the total amount of these elements. If the total amount of strong deoxidizing elements is less than 1.50 mass%, application to difficult positions becomes difficult. Therefore, the total amount of strong deoxidizing elements is set to 1.50 mass% or more, and preferably 2.00 mass% or more.
On the other hand, if the total amount of strong deoxidizing elements exceeds 4.00 mass%, the number of inclusions in the weld metal increases excessively, resulting in a decrease in toughness. Therefore, the basic flux-cored wire according to this embodiment has a composition range that satisfies the formulas (1) to (4) described below, and the total amount of strong deoxidizing elements is preferably 4.00 mass% or less and 3.20 mass% or less. As will be described later, it is preferable that Al and Mg are contained as strong deoxidizing elements.

<REM _(Wire) : 0.030% by mass or more and 0.120% by mass or less>
REM (Rare Earth Metals) refers to rare earth elements, such as Ce and La. As described above, by including a strong deoxidizing element in the wire, welding in difficult positions can be achieved. However, if the content of the strong deoxidizing element in the wire is excessive, inclusions remain in the weld metal, deteriorating toughness. The present inventors have found that, based on the relationship between the number density of inclusions in the weld metal and toughness, toughness can be improved by reducing this number density. Furthermore, the present inventors have found that the number density can be reduced by including REM _(Wire) in the wire within a predetermined content range.

Specifically, by adding 0.030 or more REM _(Wire) , the REM acts as a binder that aggregates the oxides of the added strong deoxidizing elements. For example, when observing the structure of the weld metal made using wire to which Al, Mg, and REM are added, it was confirmed that a composite oxide of REM, Al, and Mg was formed and the number density of inclusions in the weld metal was reduced.

If the content of REM _(Wire) is less than 0.030% by mass, the above-mentioned oxide aggregation effect cannot be exerted. Therefore, the content of REM _(Wire) is set to 0.030% by mass or more, and preferably 0.040% by mass or more, based on the total mass of the wire.
On the other hand, if the content of REM _(Wire) exceeds 0.120 mass%, the inclusions may become coarse due to aggregation, which may adversely affect mechanical performance or cause unacceptable welding defects. Therefore, the content of REM _(Wire) is set to 0.120 mass% or less, and preferably 0.110 mass% or less, relative to the total mass of the wire.

It is preferable that REM is contained in the flux. The form of addition is not particularly limited, and may be any form such as metallic REM, an alloy containing REM, or a compound of REM. When REM is contained in the flux in the form of a compound of REM, the content of REM _(Wire) includes the REM equivalent value of the compound related to REM. It is preferable that REM is contained in the flux in the form of an alloy containing REM, and it is more preferable that all REM added in the wire is contained in the flux in the form of an alloy containing REM. It is preferable that the REM contained in the basic flux-cored wire according to this embodiment is La and Ce.

In this embodiment, in order to achieve the object of the present invention, a plurality of parameters are generated using the contents of specific elements, and the values of these parameters are specified. In this specification, the content of a certain component relative to the total mass of the wire is represented as [(component name)]. Specifically, [REM], [Fe], [C], [Si], [Mn], [P], [S], [Cr], [Mo], [Al], [Zr], [Ni], [B], and [Mg] respectively represent the contents of REM _(Wire) , Fe _(Wire) , C _(Wire) , Si _(Wire) , Mn _(Wire) , P _(Wire) , S _(Wire) , Cr _(Wire) , Mo _(Wire) , Al _(Wire) , Zr _{( Wire} ), Ni (Wire), B _(Wire) , and Mg _(Wire) in the wire, expressed as mass% relative to the total mass of the wire.

<Value calculated by the following formula (1): 48.0 or less>
Equation (1) is used to adjust mechanical properties such as strength and toughness, and is a formula obtained by parameterizing the relationship between elements related to carbon equivalent and cold cracking susceptibility and the brittle fracture rate at -46°C using multiple regression analysis. When the value calculated by the following formula (1) based on the content of each element is 48.0 or less, the wire composition is a combination of elements that have a low brittle fracture rate at cryogenic temperatures, and therefore can be said to have excellent toughness at cryogenic temperatures. On the other hand, when the value calculated by the following formula (1) exceeds 48.0, the wire composition is a combination of elements that have a high brittle fracture rate, fail to ensure sufficient toughness, and may cause variations in toughness depending on the welded portion. Therefore, the value calculated by the following formula (1) is preferably 48.0 or less, and more preferably 47.0 or less.

Formula (1):
32.1×[Si]-40.6×[Mn]-20.1×[Ni]-19.7×[Mo]-172.6×[C]-408.2×[REM]-5824.4×[B]-38.4×[Cr]-9960×[P]+43793×[S]

<Value calculated by the following formula (2): 48.0 or less>
Equation (2) is used to adjust mechanical properties such as strength and toughness, and is a formula obtained by parameterizing the relationship between elements related to carbon equivalent and low-temperature cracking susceptibility and the brittle fracture rate at -20°C using multiple regression analysis. When the value calculated by the following formula (2) based on the content of each element is 48.0 or less, the wire composition is a combination of elements that have a high brittle fracture rate at low temperatures, and therefore can be said to have excellent low-temperature toughness. On the other hand, when the value calculated by the following formula (2) exceeds 48.0, the wire composition is a combination of elements that have a high brittle fracture rate, cannot ensure sufficient toughness, and may cause variations in toughness depending on the welded portion. Therefore, the value calculated by the following formula (2) is preferably 48.0 or less, and more preferably 40.0 or less.

Formula (2):
33.9×[Si]-47.0×[Mn]-22.2×[Ni]-11.9×[Mo]-203.9×[C]-443.5×[REM]-4482.2×[B]-36.1×[Cr]-15281×[P]+47868×[S]

<Value calculated by the following formula (3): 0.09 or more>
Equation (3) is used to adjust mechanical properties such as strength and toughness, and is an equation obtained by parameterizing the relationship between elements related to carbon equivalent and cold cracking susceptibility and the "balance between strength and toughness at -46 ° C" (parameter CVN (-46 ° C) / TS) using multiple regression analysis. Here, CVN refers to Charpy absorbed energy (J), and TS refers to tensile strength (MPa). When the value calculated by the following equation (3) based on the content of each element is 0.09 or more, the wire composition is a combination of elements that provide a good balance between strength and toughness. On the other hand, when the value calculated by the following equation (3) is less than 0.09, the wire composition is a combination of elements that provide a poor balance between strength and toughness. Therefore, the value calculated by the following equation (3) is preferably 0.09 or more, and more preferably 0.10 or more.

Formula (3):
0.001×[Fe]-0.71×[Si]+0.08×[Mn]-0.08×[Al]+0.69×[Zr]+0.03×[Ni]+0.01×[Mo]+0.32×[C]+2.27×[REM]+9.57×[B]+0.11×[Cr]

<Value calculated by the following formula (4): 0.14 or more>
Equation (4) is used to adjust mechanical properties such as strength and toughness, and is an equation obtained by parameterizing the relationship between elements related to carbon equivalent and cold cracking susceptibility and the "balance between strength and toughness at -20°C" (parameter CVN(-20°C)/TS) by multiple regression analysis. Here, CVN refers to Charpy absorbed energy (J), and TS refers to tensile strength (MPa). When the value calculated by the following equation (4) based on the content of each element is 0.14 or more, the wire composition is a combination of elements that provides a good balance between strength and toughness. On the other hand, when the value calculated by the following equation (4) is less than 0.14, the wire composition is a combination of elements that provides a poor balance between strength and toughness.

Formula (4):
0.003×[Fe]-0.35×[Si]+0.09×[Mn]-0.13×[Al]+0.22×[Zr]+0.02×[Ni]-0.02×[Mo]-0.11×[C]+1.17×[REM]+4.30×[B]+0.09×[Cr]

Next, we will explain the individual elements that are included for purposes such as improving workability and adjusting mechanical performance. If the elements described below satisfy the above formulas (1) to (4), a good balance between strength and toughness can be achieved. However, common technical knowledge dictates that excessive addition of any element, except for Fe, can lead to weld cracking and other problems, and therefore an upper limit has been set for each element. Furthermore, because the elements are intended to improve workability and adjust mechanical performance, and may be included as needed, the following definitions of elements with no lower limit set include 0% by mass.

<Fe _(Wire) : 85.0% by mass or more>
In commonly used steels such as mild steel, high-tensile steel, and low-temperature steel, Fe is the main element contained in order to satisfy the required mechanical performance. If the Fe _(Wire) content is less than 85 mass%, the influence of the remaining elements may be significant, resulting in a risk of deterioration of mechanical performance. Therefore, the Fe _(Wire) content is set to 85 mass% or more, and preferably 87.0 mass% or more, based on the total mass of the wire. Examples of Fe sources in the wire include Fe metal powder added to the flux, Fe alloy metal powder, Fe compounds, and Fe contained in the hoop. When Fe is contained in the flux, it is preferably contained in the form of Fe metal powder or Fe alloy metal powder, from the viewpoint of improving the deposition amount.

<C _(Wire) : 0.050% by mass or less>
C is a component that affects the strength of the weld metal and the deposited metal, and increasing the C content in the weld metal increases the strength. In commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, it is preferable to include C in the wire in order to satisfy the required strength range. However, if the C _(Wire) content increases, carbides are more likely to precipitate in the weld metal and the deposited metal, which may reduce the toughness relative to the target strength and result in an imbalance between strength and toughness. Therefore, the C _(Wire) content is set to 0.050 mass% or less, and preferably 0.040 mass% or less, based on the total mass of the wire.
On the other hand, in order to adjust the strength, the content of C _(Wire) is preferably 0.001 mass% or more with respect to the total mass of the wire. Examples of C sources in the wire include graphite or carbides added to the flux, and C contained in the hoop. However, from the viewpoint of suppressing carbides, the lower the C _(Wire) content, the better, and it is more preferable that the flux does not contain C.

<Si _(Wire) : 0.60% by mass or less>
Si is a component that affects the strength and toughness of the weld metal. In commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, it is preferable to include Si in the wire in order to satisfy the required mechanical performance. Si has a deoxidizing effect, and if Si is contained in the wire in excess, inclusions may increase, causing an imbalance between strength and toughness. Therefore, the content of Si _(Wire) is set to 0.60 mass% or less, and preferably 0.50 mass% or less, based on the total mass of the wire.
On the other hand, in order to adjust the strength, the content of Si _(Wire) is preferably 0.01 mass% or more with respect to the total mass of the wire. Examples of Si sources in the wire include metal powder of Si added to the flux, metal powder of an alloy related to Si, a compound related to Si, and Si contained in the hoop. When Si is contained in the flux for the purpose of suppressing inclusions, it is preferably contained in the form of metal powder of Si or metal powder of an alloy related to Si.

<B _(Wire) : 0.0200% by mass or less>
B is an element that prevents a decrease in the toughness of the deposited metal and the weld metal while increasing their crack resistance. Therefore, the content of B _(Wire) is set to 0.0200 mass% or less, and preferably 0.0150 mass% or less, relative to the total mass of the wire. It has also been confirmed that the inclusion of B in the wire according to this embodiment reduces the brittle fracture rate. This is because the inclusion of B in the wire can suppress the formation of coarse ferrite or bainite phases at grain boundaries. Therefore, from the viewpoint of reducing the brittle fracture rate, the content of B _(Wire) is preferably 0.0020 mass% or more, relative to the total mass of the wire. Furthermore, the balance between strength and toughness changes depending on the content of Zr _(Wire) and the content of B _{( Wire} ), and therefore the preferred range of the content of B _(Wire) changes depending on the content of Zr (Wire). That is, if the content of Zr _(Wire) is 0.045% by mass or less, as described above, the content of B _(Wire) is preferably set to 0.0150% by mass or less, but if the content of Zr _(Wire) exceeds 0.045% by mass, it is more preferable that the content of B _(Wire) be set to 0.0045% by mass or less.
The source of B in the wire may be metal powder of B added to the flux, metal powder of an alloy related to B, a compound related to B, or B contained in the hoop.

In addition, if B is contained in the flux in the form of an oxide, the B oxide is more likely to be mixed uniformly in the flux, which is advantageous from the viewpoint of manufacturing. Therefore, it is preferable to contain B in the flux in the form of an oxide rather than in the form of a metal powder. In this case, the content of B _(Wire) includes the B-equivalent value of B oxide, and the value calculated by the following formula (5) is preferably 0.5 or more, more preferably 0.7 or more, and even more preferably 1.0. When the value calculated by the following formula (5) is 1.0, the content of B _(Wire) represents the B-equivalent value of B oxide. In other words, when B is contained in the wire, it is preferable to contain all of it in the flux in the form of B oxide.

Formula (5): [B oxide]/[B]
In the above formula (5), [B oxide] represents the B equivalent value _(Wire) of B oxide relative to the total mass of the wire, expressed as mass % relative to the total mass of the wire.

<Mn _(Wire) : 2.00% by mass or less>
Mn, like Si, is a component that affects the strength and toughness of the weld metal. It is preferable to include Mn in the wire in commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel in order to satisfy the required mechanical performance. Mn has a deoxidizing effect, and if excessive Mn is included in the wire, inclusions increase, which may cause an imbalance between strength and toughness. Therefore, the content of Mn _(Wire) is set to 2.00 mass% or less, and preferably 1.80 mass% or less, based on the total mass of the wire.
On the other hand, in order to adjust the strength, the content of Mn _(Wire) is preferably 0.01 mass% or more with respect to the total mass of the wire. Examples of Mn sources in the wire include metal powder of Mn added to the flux, metal powder of an alloy related to Mn, a compound related to Mn, and Mn contained in the hoop. When Mn is contained in the flux for the purpose of suppressing inclusions, it is preferable to contain it in the form of metal powder of Mn or metal powder of an alloy related to Mn.

<P _(Wire) : 0.0150% by mass or less>
P is an element that reduces the cracking resistance and mechanical properties of the weld metal. Therefore, the content of P _(Wire) is controlled to 0.0150 mass% or less, and preferably 0.0100 mass% or less, based on the total mass of the wire. It is preferable that P is not forcibly added to the wire.

<S _(Wire) : 0.0150% by mass or less>
S is an element that reduces crack resistance, and therefore the content of S _(Wire) is set to 0.0150 mass % or less, and preferably 0.010 mass % or less, with respect to the total mass of the wire.
On the other hand, S _(Wire) has the effect of reducing the viscosity and surface tension of droplets when the wire is melted, smoothing droplet transfer, thereby reducing the size of spatter and improving welding workability. Therefore, from the viewpoint of welding workability, the content of S _(Wire) is preferably 0.0005 mass% or more with respect to the total mass of the wire. The S source in the wire is not particularly limited, and may be contained in the flux or in the hoop in the form of S powder or an S compound, but it is more preferable not to forcibly add S to the wire.

<Cr _(Wire) : 1.00% by mass or less>
Cr is a component that affects the strength and toughness of the deposited metal and weld metal. It is preferable to include Cr in the wire in order to satisfy the required mechanical performance in commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel. If Cr is included in the wire in excess, it tends to precipitate as carbides at grain boundaries, which may cause an imbalance between strength and toughness. Therefore, the Cr _(Wire) content is set to 1.00 mass% or less, and preferably 0.90 mass% or less, based on the total mass of the wire.
On the other hand, in order to adjust the strength, the content of Cr _(Wire) is preferably 0.20 mass% or more with respect to the total mass of the wire. Examples of Cr sources in the wire include Cr metal powder added to the flux, Cr alloy metal powder, Cr compounds, and Cr contained in the hoop. When Cr is contained in the flux, it is preferably contained in the flux in the form of Cr metal powder or Cr alloy metal powder.

<Mo _(Wire) : 1.00% by mass or less>
Mo is a component that improves high-temperature strength. In commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, it is preferable to include Mo in the wire in order to satisfy the required mechanical performance. If Mo is contained in the wire in excess, the strength may increase excessively, and the balance between strength and toughness may be lost. Therefore, the content of Mo _(Wire) is set to 1.00 mass% or less, and preferably 0.90 mass% or less, with respect to the total mass of the wire.
On the other hand, in order to adjust the strength, the content of Mo _(Wire) is preferably 0.10 mass% or more with respect to the total mass of the wire. Examples of Mo sources in the wire include Mo metal powder, Mo alloy metal powder, Mo compounds, and Mo contained in the hoop, which are added to the flux. When Mo is contained in the flux, it is preferably contained in the flux in the form of Mo metal powder or Mo alloy metal powder.

In addition, when combining Cr, which contributes to strength and toughness, with Mo, a commonly used element for improving high-temperature strength, it is preferable to determine the content according to the application in order to strike a balance between strength and toughness, as shown below.

(Design to improve toughness)
For example, when it is desired to further improve toughness, it is preferable to make the content of Cr, which contributes to strength and toughness, higher than the content of Mo. That is, the content of Cr _(Wire) is set to 0.20 mass% or more and 0.90 mass% or less with respect to the total mass of the wire, and the content of Mo _(Wire) is set to 0.50 mass% or less with respect to the total mass of the wire, and the value calculated by the following formula (6) is preferably 0.20 or more, more preferably 0.50 or more, even more preferably 0.75 or more, and most preferably 1.00.

Formula (6): [Cr]/([Cr]+[Mo])

(Designed to improve high-temperature strength)
On the other hand, when it is desired to use it in heat-resistant steel applications, it is preferable to make the content of Mo, which is a general-purpose element that improves high-temperature strength, higher than the content of Cr. In other words, the content of Cr _(Wire) is set to 0.90 mass% or less with respect to the total mass of the wire, and the content of Mo _(Wire) is set to 0.10 mass% or more and 0.80 mass% or less with respect to the total mass of the wire, and the value calculated by the following formula (7) is preferably 0.10 or more, more preferably 0.45 or more, even more preferably 0.70 or more, and most preferably 1.00.

Formula (7): [Mo]/([Cr]+[Mo])

<Al _(Wire) : 3.00% by mass or less>
Al is a strong deoxidizing element, and by causing an oxidation reaction in the weld metal, it forms oxides (hereinafter also referred to as "slag") on the molten pool, which makes it possible to improve the bead shape and burn-through resistance in all welding positions, including difficult positions such as vertical welding and overhead welding. If the wire contains excessive Al, the amount of inclusions remaining in the weld metal increases, adversely affecting toughness. Therefore, the content of Al _(Wire) is set to 3.00 mass% or less, preferably 2.50 mass% or less, and more preferably 1.70 mass% or less, based on the total mass of the wire.
On the other hand, the content of Al _(Wire) is preferably 0.50 mass% or more, and more preferably 1.00 mass% or more, relative to the total mass of the wire. Examples of Al sources in the wire include Al metal powder, Al alloy metal powder, Al compounds, and Al contained in the hoop, added to the flux. When Al is contained in the flux in order to further reduce the amount of oxygen in the weld metal, it is preferable to contain it in the form of Al metal powder or Al alloy metal powder.

<Mg _(Wire) : 3.00% by mass or less>
Like Al, Mg is a strong deoxidizing element, and by causing an oxidation reaction in the weld metal, it forms slag on the molten pool, making it possible to improve burn-through resistance in all welding positions, including difficult positions such as vertical welding and overhead welding. If the wire contains excessive Mg, the amount of inclusions remaining in the weld metal increases, adversely affecting toughness. Therefore, the content of Mg _(Wire) is set to 3.0 mass% or less, preferably 1.50 mass% or less, and more preferably 1.00 mass% or less, based on the total mass of the wire.
On the other hand, the content of Mg _(Wire) is preferably 0.30 mass% or more, and more preferably 0.50 mass% or more, based on the total mass of the wire. Examples of Mg sources in the wire include Mg metal powder, Mg alloy metal powder, Mg compounds, and Mg contained in the hoop, added to the flux. When Mg is contained in the flux in order to further reduce the amount of oxygen in the weld metal, it is preferable to contain it in the form of Mg metal powder or Mg alloy metal powder.

<Zr _(Wire) : 3.000% by mass or less>
Like Al, Zr is a strong deoxidizing element, and by causing an oxidation reaction in the weld metal, it forms slag on the molten pool, making it possible to improve burn-through resistance in all welding positions, including difficult positions such as vertical welding and overhead welding. If the wire contains excessive Zr, the amount of inclusions remaining in the weld metal increases, adversely affecting toughness. Therefore, the content of Zr _(Wire) is set to 3.000 mass% or less, preferably 0.500 mass% or less, based on the total mass of the wire, and more preferably 0.045 mass% or less, taking into account the content of B _(Wire) .
On the other hand, there is no particular meaning in specifying a lower limit value for Zr _(Wire) . Furthermore, when Mg and Al are mainly contained in the wire as strong deoxidizing elements, it is preferable that the content of Zr _(Wire) be zero. Examples of Zr sources in the wire include metal powder of Zr, metal powder of an alloy related to Zr, a compound related to Zr, and Ti contained in the hoop, which are added to the flux. When Zr is contained in the flux for the purpose of further reducing the amount of oxygen in the weld metal, it is preferable that Zr be contained in the flux in the form of metal powder of Zr or metal powder of an alloy related to Zr.

<Ti _(Wire) : 3.000% by mass or less>
Like Al, Ti is a strong deoxidizing element, and by causing an oxidation reaction in the weld metal, it forms oxides (slag) on the molten pool, making it possible to improve burn-through resistance in all welding positions, including difficult positions such as vertical welding and overhead welding. If the wire contains excessive Ti, the amount of inclusions remaining in the weld metal increases, adversely affecting toughness. Therefore, the content of Ti _(Wire) is set to 3.000 mass% or less, preferably 0.500 mass% or less, and more preferably 0.010 mass% or less, based on the total mass of the wire.
On the other hand, Ti has a smaller effect as a deoxidizing component than Mg and Al, and there is a risk of forming precipitates such as TiC, which deteriorates toughness. Therefore, there is no particular meaning in specifying a lower limit for Ti _(Wire) , and when Mg and Al are mainly contained in the wire, it is preferable that the content of Ti _(Wire) be zero. Examples of Ti sources in the wire include metal powder of Ti, metal powder of an alloy related to Ti, compounds related to Ti, and Ti contained in the hoop, added to the flux. When Ti is contained in the flux for the purpose of further reducing the amount of oxygen in the weld metal, it is preferable that it be contained in the flux in the form of metal powder of Ti or metal powder of an alloy related to Ti.

<Ca _(Wire) : 3.00% by mass or less>
Like Al, Ca is a strong deoxidizing element that causes an oxidation reaction in the weld metal, forming oxides (slag) on the molten pool, making it possible to improve burn-through resistance in all welding positions, including difficult positions such as vertical welding and overhead welding. However, if the wire contains excessive Ca, the amount of inclusions remaining in the weld metal increases, adversely affecting toughness. Therefore, the content of Ca _(Wire) is set to 3.0 mass% or less, preferably 1.00 mass% or less, and more preferably 0.30 mass% or less, based on the total mass of the wire.
On the other hand, Ca, when contained in the flux as the fluoride _CaF2 , contributes to the deoxidation of the weld metal and improvement of welding workability. The content of Ca _(Wire) above includes the Ca-equivalent value of _CaF2 in the flux, but the fluoride in the flux is not limited to _CaF2 and, for example, fluorides such as _BaF2 and _SrF2 can be used, so there is no need to set a lower limit for the Ca content. Furthermore, when Mg and Al are mainly added to the wire as strong deoxidizing components, it is preferable that the content of Ca _(Wire) be 0 mass%.

Examples of Ca sources in the wire include Ca metal powder added to the flux, Ca-based alloy metal powder, Ca-based compounds, and Ca contained in the hoop. In this embodiment, when Ca is contained in the wire, if this Ca is contained in the flux, the amount of oxygen in the weld metal can be further reduced. Therefore, it is preferable that all Ca contained in the wire be contained in the flux in the form of fluoride powder, i.e., in the form of _CaF2 .

It should be noted that there are various elements called strong deoxidizing elements other than the above-listed Al, Mg, Zr, Ti, and Ca. However, in this embodiment, it is preferable that the above-listed five elements, which are generally contained in wires mainly in the form of metal powder, are used as strong deoxidizing elements as elements to be contained in basic flux-cored wires.
Among these five elements, Al and Mg are particularly useful for achieving difficult welding positions using basic flux-cored wires because they tend to form slag quickly and over the entire surface of the molten pool. On the other hand, Zr, Ti, and Ca tend to disperse slag, and slag formation tends to concentrate at the edges of the molten pool due to the flow of the molten pool, making them less effective than Al and Mg.

Therefore, it is preferable to contain at least one strong deoxidizing element selected from Al, Mg, Ti, Ca, and Zr in the wire. The contents of these elements are as follows: Al _(wire) 1.00% by mass to 2.50% by mass, Mg _(wire) 0.30% by mass to 0.50% by mass, Ti _(wire) 0.10% by mass or less (including 0% by mass), Zr _(wire) 0.20% by mass or less (including 0% by mass), and Ca _(wire) 0.10% by mass or less (including 0% by mass), with the total amount of the strong deoxidizing elements contained in the wire being 1.50% by mass to 4.00% by mass.

Furthermore, in this embodiment, it is more preferable to contain at least one of Al and Mg, and even more preferable to contain at least Al. In this case, it is particularly preferable that the content of Al _(Wire) is 1.00 mass% or more and 2.50 mass% or less, and the content of Mg _(Wire) is 1.00 mass% or less, relative to the total mass of the wire, and the value calculated by the following formula (8) is 0.5 or more and 1.0 or less.

Formula (8): [Al]/([Al]+[Mg])

<Ni _(Wire) : 5.00% by mass or less>
Ni is a component that stabilizes the austenite structure of the weld metal and improves toughness at low temperatures, and is also a component that can adjust the amount of crystallization of the ferrite composition. In commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, it is preferable to include Ni in the wire in order to satisfy the required mechanical performance. If an excessive amount of Ni is included in the wire, the strength may increase excessively, and the balance between strength and toughness may be lost. Therefore, the content of Ni _(Wire) is set to 5.0 mass% or less, and preferably 3.0 mass% or less, based on the total mass of the wire.
On the other hand, when used for welding low-temperature steels, etc., the content of Ni _(Wire) is preferably 0.20 mass% or more relative to the total mass of the wire. Examples of Ni sources in the wire include Ni metal powder, Ni alloy metal powder, Ni compounds, and Ni contained in the hoop, added to the flux. When Ni is contained in the flux for the purpose of further reducing the amount of oxygen in the weld metal, it is preferable to contain it in the form of Ni metal powder or Ni alloy metal powder.

<Ba _(Wire) : 4.00% by mass or less>
Ba, contained in the flux mainly in the form of the fluoride _BaF2 , contributes to the deoxidation of the weld metal and improvement of welding workability. Fluorides are generally added as flux for basic flux-cored wires, and among various fluorides, _BaF2 is frequently used. However, if the wire contains excessive Ba, arc deflection may occur, which may deteriorate welding workability. Therefore, the content of Ba _(Wire) is set to 4.00 mass% or less, and preferably 3.00 mass% or less.

The Ba _(Wire) content includes the Ba-equivalent value of _BaF2 in the flux. However, the fluoride in the flux is not limited to _BaF2 , and fluorides such as _CaF2 and _SrF2 can also be used. Therefore, there is no need to set a lower limit for the Ba content. However, when a Ba compound such as _BaF2 or _BaCO3 is contained in the flux, the Ba _(Wire) content relative to the total mass of the wire is preferably 1.75 mass% or more. Examples of Ba sources in the wire include Ba metal powder added to the flux, Ba alloy metal powder, Ba compounds, and Ba contained in the hoop. In this embodiment, when Ba is contained in the wire, it is preferable that all Ba be contained in the flux in the form of _BaF2 , which is a fluoride.

<F _(Wire) : 2.00% by mass or less>
F _(Wire) is mainly derived from fluorides. It is contained in the flux of the flux-cored wire in the form of fluorides of Ca, Ba, Sr, etc. as described above. Fluorides are commonly added to basic flux-cored wires and contribute to improving welding workability. However, if the F _(Wire) content exceeds 2.00 mass% relative to the total mass of the wire, excessive vaporization of F may occur inside the wire, increasing the amount of spatter generated and potentially deteriorating welding workability. Therefore, the Ba _(Wire) content is set to 2.00 mass% or less, preferably 1.00 mass% or less, and more preferably 0.80 mass% or less, relative to the total mass of the wire.

On the other hand, when F is contained in the wire for the purpose of improving welding workability, the content of F _(Wire) is preferably 0.40 mass% or more with respect to the total mass of the wire. It is preferable that all F sources in the wire are derived from fluorides, and examples thereof include BaF ₂ , SrF ₂ , Na ₃ AlF ₆ , NaF, CaF ₂ , AlF ₃ , MgF _{2 ,} etc., and the wire may contain one or more of these. Among these fluorides, it is preferable from the viewpoint of welding workability to contain at least one fluoride selected from the group consisting of BaF ₂ , SrF ₂ , and CaF ₂ in the wire so as to satisfy the contents described in the above section on Ba, Sr, and Ca. Furthermore, Ba has a low work function and has the effect of further stabilizing cathode spots, contributing to improving welding workability. Therefore, in this embodiment, it is more preferable that BaF ₂ , a fluoride of Ba, is mainly contained in the wire. In this embodiment, all Ba _(Wire) sources are preferably _BaF2 , and the remainder of the F _(Wire) content excluding the F converted value of _BaF2 in the F _(Wire) content is preferably a supply source of _CaF2 .

In addition, the following elements may be added in addition to or in place of the elements described above to commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, within the scope of general technology, for the purpose of adjusting mechanical properties, improving welding workability, etc. The following Nb, Cu, W, Ta, V, Sr, and alkali elements are not added in this embodiment, and their addition is not particularly necessary, but if various commonly known effects are desired, it is preferable to add them within the optimal ranges explained below.

<Nb _(Wire) : 0.50% by mass or less>
Nb is a component that affects mechanical properties such as strength. In commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, Nb may be contained in the wire to satisfy the required mechanical properties. In this case, the content of Nb _(Wire) is preferably 0.50 mass% or less, and more preferably 0.30 mass% or less, relative to the total mass of the wire. Examples of Nb sources in the wire include metal powder of Nb added to flux, metal powder of an Nb-based alloy, a Nb-based compound, and Nb contained in the hoop.

<Cu _(Wire) : 2.0% by mass or less>
Cu is an element that contributes to improving the strength and weather resistance of the weld metal. In commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, Cu may be contained in the wire to satisfy the required strength and weather resistance. In this case, the content of Cu _(Wire) is preferably 2.0 mass% or less, and more preferably 1.0 mass% or less, based on the total mass of the wire.
On the other hand, when Cu is contained in the wire for the purpose of ensuring the strength and weather resistance of the weld metal, the content of Cu _(Wire) is preferably 0.01 mass% or more with respect to the total mass of the wire. Note that the Cu source in the wire includes Cu metal powder added to the flux, Cu alloy metal powder, Cu compounds, Cu contained in the hoop, and also Cu plating on the wire surface.

<W _(Wire) : 1.00% by mass or less>
W is a component that improves high-temperature strength and pitting corrosion resistance. In commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, W may be contained in the wire to satisfy the required mechanical performance. In this case, the content of W _(Wire) is preferably 1.00 mass% or less, and more preferably 0.5 mass% or less, relative to the total mass of the wire. Examples of W sources in the wire include metal powder of W added to flux, metal powder of a W-related alloy, a W-related compound, and W contained in the hoop.

<Ta _(Wire) : 1.00% by mass or less>
Ta is an element that affects mechanical properties such as strength. Ta may be contained in wire to satisfy the required mechanical properties of commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel. In this case, the Ta _(Wire) content is preferably 1.00 mass% or less, and more preferably 0.50 mass% or less, based on the total mass of the wire. Examples of Ta sources in the wire include Ta metal powder added to flux, Ta alloy metal powder, Ta compounds, and Ta contained in the hoop.

<V _(Wire) : 1.00% by mass or less>
V is an element that improves the strength of the weld metal but also reduces the toughness and crack resistance. Therefore, the content of V _(Wire) in the wire is preferably 1.00 mass% or less, and more preferably 0.50 mass% or less, based on the total mass of the wire. Examples of V sources in the wire include V metal powder added to the flux, V alloy metal powder, V compounds, and V contained in the hoop.

<Sr _(Wire) : 4.00% by mass or less>
Sr, contained in the flux mainly as the fluoride _SrF2 , contributes to the deoxidation of the weld metal and the improvement of welding workability. However, if the Sr content in the wire is 4.00 mass% or less, arc deflection can be suppressed and good welding workability can be obtained. Therefore, the content of Sr _(Wire) is preferably 4.00 mass% or less, and more preferably 3.00 mass% or less, based on the total mass of the wire.
The Sr _(Wire) content includes the Sr-equivalent value of _SrF2 in the flux. However, the fluoride in the flux is not limited to _SrF2 . Fluorides such as _CaF2 and _BaF2 can also be used. Therefore, there is no need to set a lower limit for the Sr content. However, when a Sr compound such as _SrF2 or _SrCO3 is contained in the flux, the Sr _(Wire) content relative to the total mass of the wire is preferably 0.05 mass% or more. Examples of Sr sources in the wire include Sr metal powder added to the flux, Sr alloy metal powder, Sr compounds, and Sr contained in the hoop. In this embodiment, when Sr is contained in the wire, it is preferable that all Sr be contained in the flux in the form of _SrF2 , which is a fluoride.

As described above, the basic flux-cored wire according to this embodiment preferably contains at least one flux selected from _BaF2 , _CaF2 , and _SrF2 , which are fluorides of Ba, Ca, and Sr. In this case, the Ba content includes the Ba-equivalent value of _BaF2 , the Ca content includes the Ca-equivalent value of _CaF2 , the Sr content includes the Sr-equivalent value of _SrF2 , and the F content includes the F-equivalent values of _BaF2 , _CaF2 , and _SrF2 . In addition, it is preferable that all F sources in the wire are derived from fluorides, i.e., the F content in the wire is equal to the F-equivalent value of all fluorides contained in the flux.

<Total of alkali metals: 3.00 mass% or less>
The alkali metal element acts as an arc stabilizer. The alkali metal in this embodiment is based on metal powder and compounds containing one or more alkali metal elements. Examples of alkali metal elements include K, Li, Na, etc. The total content of alkali metals in the wire refers to the total content of alkali metals in the wire converted from metal powder and compounds composed of alkali metal elements. That is, it is the total amount of K _(Wire) , Li _(Wire) , Na _(Wire), etc. From the viewpoint of making it easier to adjust the melt properties to be favorable for improving the bead shape, the total content of alkali metals in the wire is preferably 3.00 mass% or less, and more preferably 2.00 mass% or less, relative to the total mass of the wire.

(Oxides in wire: 0.005% by mass or more and 0.100% by mass or less)
Since oxides become the basis for coarse inclusions and affect toughness, it is preferable to avoid adding them to the flux in the form of oxides as much as possible. Therefore, it is more preferable that the total amount of oxides of each element added to the flux be limited to 0.100 mass% or less in terms of mass% relative to the total mass of the wire. Furthermore, from the viewpoint of manufacturing, it is preferable that B and REM are added in the form of oxides, and it is even more preferable that the oxide content be 0.005 mass% or more.

(Remainder: O, N and inevitable impurities)
In this embodiment, the balance excluding the above elements is preferably O, N, and unavoidable impurities, and the total content of the balance is preferably 0.50 mass% or less. Impurities refer to elements that are not intentionally added, and examples of elements other than the above include Sn, Co, Sb, and As. The total content of impurities in the wire is preferably 0.45 mass% or less, and more preferably 0.30 mass% or less.
Furthermore, O and N when the above elements are contained in the flux in the form of oxides or nitrides or when they are solid-solved in the hoop are also included in the balance. Since O and N cannot be clearly analyzed in a flux-cored wire, they are referred to as the balance. However, in this embodiment, based on the amount of oxides added to the flux-cored wire or the amount of O and N added to the hoop, it can be estimated that the total amount of O and N is 0.05 mass% or less, in terms of mass% relative to the total mass of the wire. From the perspective of mechanical performance, it is technically impossible for O and N to exceed 0.05 mass% in a basic flux-cored wire.

〔hoop〕
The flux-cored wire according to the present embodiment has a hoop filled with flux, and the hoop is preferably formed of a cold-rolled steel strip from the viewpoints of availability and economy. As the cold-rolled steel strip, it is preferable to use a steel strip having the designation SPCC, SPCD, SPCE, SPCF, SPCG, or the like as described in JIS G 3141:2017.

Another embodiment of the basic flux-cored wire of the present invention is a wire that produces the following deposited metal. Since the deposited metal refers to the metal that has migrated from the filler metal to the weld, the wire can be limited by specifying the composition of the deposited metal produced under commonly used welding conditions. Commonly used welding conditions can be, for example, welding conditions that comply with the method for producing weld metal described in JIS Z3184. For example, conditions such as a welding current of 200 to 220 A, a welding voltage of 0 to 23 V, a shielding gas of 100% _CO2 , and a welding heat input of 0.8 to 1.1 kJ/mm can be used.

[2. Welded metal]
As described above, the basic flux-cored wire according to this embodiment contains strong deoxidizing elements and REM, which enables welding in difficult positions and achieves a good balance between strength and toughness. Similarly, the deposited metal according to this embodiment has an appropriately specified B _(metal) content and an appropriately specified La _(metal) and Ce _(metal) content as REM, which further enhances the above-mentioned effects. The composition of the deposited metal according to this embodiment and the reasons for the limitations will be specifically described below.

<C _(Metal) : 0.020% by mass or more and 0.100% by mass or less>
C is a component that affects the strength of the weld metal, and the strength increases as the C content in the weld metal increases. Therefore, the C _(Metal) content is set to 0.020 mass% or more, and preferably 0.040 mass% or more, based on the total mass of the weld metal.
On the other hand, if the C _(Metal) content increases, carbides tend to precipitate in the weld metal, which reduces toughness relative to the target strength, potentially resulting in an imbalance between strength and toughness. Therefore, the C _(Metal) content is set to 0.100 mass% or less, and preferably 0.095 mass% or less, based on the total mass of the weld metal.

<Si _(Metal) : 0.05% by mass or more and 0.50% by mass or less>
Silicon is a component that affects the strength and toughness of the weld metal, and by containing a certain amount of silicon in the weld metal, the required mechanical performance can be satisfied. Therefore, the Si _(Metal) content is preferably 0.05 mass% or more, and more preferably 0.10 mass% or more, based on the total mass of the weld metal.
On the other hand, Si has a deoxidizing effect, and if Si is contained in excess, it is likely that Si will remain as inclusions in the weld metal, which may cause an imbalance between strength and toughness. Therefore, the Si _(Metal) content is set to 0.50 mass% or less, and preferably 0.45 mass% or less, based on the total mass of the weld metal.

<Mn _(Metal) : 0.20% by mass or more and 1.80% by mass or less>
Mn, like Si, is a component that affects the strength and toughness of the weld metal, and by containing a certain amount of Mn in the weld metal, the required mechanical performance can be satisfied. Therefore, the Mn _(Metal) content is preferably 0.20 mass% or more, and more preferably 0.50 mass% or more, based on the total mass of the weld metal.
On the other hand, Mn has a deoxidizing effect, and if Mn is contained in excess, it is likely to remain in the deposited metal as inclusions, which may cause an imbalance between strength and toughness. Therefore, the Mn _(Metal) content is set to 1.80 mass% or less, and preferably 1.65 mass% or less, based on the total mass of the deposited metal.

<Al _(Metal) : 0.30% by mass or more and 1.50% by mass or less>
Al is a strong deoxidizing component that causes an oxidation reaction in the weld metal, forming oxides (slag) on the molten pool and improving burn-through resistance in all welding positions, including difficult positions such as vertical welding and overhead welding. Therefore, the content of Al _(Metal) is preferably 0.30 mass% or more, and more preferably 0.40 mass% or more, based on the total mass of the weld metal.
On the other hand, if Al is contained in excess, there is a high possibility that Al will remain in the deposited metal as inclusions, which will adversely affect toughness. Therefore, the Al _(Metal) content is set to 1.50 mass % or less, preferably 1.10 mass % or less, and more preferably 1.00 mass %, based on the total mass of the deposited metal.

<La _(Metal) : 0.008% by mass or less>
La is a type of REM contained in the wire and acts as a binder to aggregate oxides of strong deoxidizing elements in the weld metal. In this embodiment, there is no particular lower limit for the La content in the weld metal, but in order to obtain the above-mentioned effect, the La _(Metal) content is preferably 0.001 mass% or more relative to the total mass of the weld metal.
On the other hand, if the La _(Metal) content exceeds 0.008 mass%, the inclusions may become coarse due to aggregation, which may adversely affect mechanical performance or cause unacceptable welding defects. Therefore, the La _(Metal) content is set to 0.008 mass% or less, and preferably 0.006 mass% or less, based on the total mass of the deposited metal.

<Ce _(Metal) : 0.002% by mass or more and 0.010% by mass or less>
Like La, Ce is a type of REM contained in the wire and acts as a binder to aggregate oxides of strong deoxidizing elements in the weld metal. Therefore, the Ce _(Metal) content is set to 0.002 mass% or more, and preferably 0.003 mass% or more, based on the total mass of the weld metal.
On the other hand, if the Ce _(Metal) content exceeds 0.010 mass%, the inclusions may become coarse due to agglomeration, which may adversely affect mechanical performance or cause unacceptable welding defects. Therefore, the Ce _(Metal) content is set to 0.010 mass% or less, and preferably 0.009 mass% or less, based on the total mass of the deposited metal.

<Fe _(Metal) : 85.0% by mass or more>
In commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, Fe is the main element contained in order to satisfy the required mechanical performance. If the Fe _(Metal) content is less than 85 mass%, the influence of the remaining elements becomes large, and there is a risk of deterioration in mechanical performance. Therefore, the Fe _(Metal) content is set to 85 mass% or more, and preferably 87.0 mass% or more, based on the total mass of the deposited metal.

<P _(Metal) : 0.0200% by mass or less>
P is an element that reduces the crack resistance and mechanical properties of the weld metal, so the P _(Metal) content is set to 0.020 mass % or less, and preferably 0.0100 mass % or less, based on the total mass of the weld metal.

<S _(Metal) : 0.0200% by mass or less>
S is an element that reduces crack resistance, and therefore the S _(Metal) content is set to 0.0200 mass % or less, and preferably 0.0100 mass % or less, based on the total mass of the weld metal.

<Cr _(Metal) : 1.00% by mass or less>
Cr is a component that affects the strength and toughness of the weld metal, but if the weld metal contains an excessive amount of Cr, it tends to precipitate as carbides at grain boundaries, which may cause an imbalance between strength and toughness. Therefore, the Cr _(Metal) content is set to 1.00 mass% or less based on the total mass of the weld metal.

<Mo _(Metal) : 1.00% by mass or less>
Mo is an element that improves high-temperature strength, but if Mo is contained in excess in the weld metal, the strength may increase excessively, resulting in an imbalance between strength and toughness. Therefore, the Mo _(Metal) content is set to 1.00 mass% or less based on the total mass of the weld metal.

<Mg _(Metal) : 0.50% by mass or less>
Like Al, Mg is a strong deoxidizing element, and if Mg is contained in excess, it is likely to remain in the deposited metal as inclusions, adversely affecting toughness. Therefore, the Mg _(Metal) content is set to 0.50 mass% or less, preferably 0.30 mass% or less, and more preferably 0.20 mass% or less, based on the total mass of the deposited metal.

<Zr _(Metal) : 0.50% by mass or less>
Zr, like Al, is a strong deoxidizing element, and if Zr is contained in excess, it is likely to remain in the deposited metal as inclusions, adversely affecting toughness. Therefore, the Zr _(Metal) content is set to 0.50 mass% or less, and preferably 0.45 mass% or less, based on the total mass of the deposited metal.

<Ti _(Metal) : 0.05% by mass or less>
Like Al, Ti is a strong deoxidizing element, and if Ti is contained in excess, it is likely to remain in the deposited metal as inclusions, adversely affecting toughness. Therefore, the Ti _(Metal) content is set to 0.05 mass% or less, preferably 0.03 mass% or less, and more preferably 0.01 mass% or less, based on the total mass of the deposited metal.

<Ca _(Metal) : 0.50% by mass or less>
Like Al, Ca is a strong deoxidizing element, and if it is contained in excess, it is likely to remain in the deposited metal as inclusions, which will adversely affect toughness. Therefore, the Ca _(Metal) content is set to 0.50 mass% or less, and preferably 0.45 mass% or less, based on the total mass of the deposited metal.

<Ni _(Metal) : 3.00% by mass or less>
Ni is a component that stabilizes the austenite structure of the weld metal and improves its toughness at low temperatures, and also adjusts the amount of ferrite crystallized. However, if the weld metal contains an excessive amount of Ni, the strength may increase excessively, and the balance between strength and toughness may be lost. Therefore, the Ni _(Metal) content is set to 3.0 mass% or less, and preferably 2.5 mass% or less, based on the total mass of the weld metal.

<B _(Metal) : 0.0090% by mass or less>
B is an element that prevents a decrease in the toughness of the weld metal but also decreases its crack resistance. Therefore, the B _(Metal) content is set to 0.0090 mass% or less, and preferably 0.0050 mass% or less, based on the total mass of the weld metal. Furthermore, B has the effect of decreasing the brittle fracture rate, so the B content is preferably set to 0.0010 mass% or more, and more preferably 0.0020 mass% or more.

<Ba _(Metal) : 1.00% by mass or less>
Ba is an element that contributes to the deoxidation of the weld metal and the improvement of welding workability, but if the weld metal contains excessive Ba, arc deflection may occur and the welding workability may deteriorate. Therefore, the Ba _(Metal) content is set to 1.00 mass% or less, and preferably 0.90 mass% or less.

<Nb _(Metal) : 0.001% by mass or less>
Nb is a component that affects mechanical properties such as strength. In commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, Nb may be contained in the weld metal to satisfy the required mechanical properties. In this case, the Nb _(Metal) content is set to 0.001 mass% or less, and preferably 0.0008 mass% or less, based on the total mass of the weld metal.

<Cu _(Metal) : 0.1% by mass or less>
Cu is an element that contributes to improving the strength and weather resistance of the weld metal. In commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, Cu may be contained in the weld metal to satisfy the required strength and weather resistance. In this case, the Cu _(Metal) content is set to 0.1 mass% or less, and preferably 0.08 mass% or less, based on the total mass of the weld metal.

<V _(Metal) : 0.001% by mass or less>
V is an element that improves the strength of the weld metal but also reduces the toughness and crack resistance of the weld metal, so the V _(Metal) content in the weld metal is set to 0.001 mass % or less, and preferably 0.0006 mass % or less, based on the total mass of the weld metal.

<W _(Metal) : 0.1% by mass or less>
W is an element that improves high-temperature strength and pitting corrosion resistance. In commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, W may be contained in the weld metal to satisfy the required mechanical performance. In this case, the content of W _(Metal) is set to 0.1 mass% or less, and preferably 0.08 mass% or less, based on the total mass of the weld metal.

<Ta _(Metal) : 0.1% by mass or less>
Ta is an element that affects mechanical properties such as strength. In commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, Ta may be contained in the weld metal to satisfy the required mechanical properties. In this case, the Ta _(Metal) content is 0.1 mass% or less, and preferably 0.08 mass% or less, based on the total mass of the weld metal.

<Sr _(Metal) : 1.00% by mass or less>
Sr is an element that is preferably contained in the flux because it contributes to the deoxidation of the weld metal and the improvement of welding workability, and therefore Sr may be contained in the weld metal. In this case, the content of Sr _(Metal) is set to 1.00 mass% or less, and preferably 0.90 mass% or less, based on the total mass of the weld metal.

<O _(Metal) : 0.0250% by mass or less>
O exists in the weld metal as a solid solution or in the form of an oxide. If O is contained in excess, there is a high possibility that a large amount of oxide-based inclusions will remain in the weld metal, which will have an adverse effect on toughness. Therefore, the O _(Metal) content is set to 0.0250 mass% or less, and preferably 0.0200 mass% or less, based on the total mass of the weld metal.

<N _(Metal) : 0.0100% by mass or less>
N exists in the weld metal in the form of solid solution or nitrides. If N is contained in excess, the strength may increase excessively due to solid solution strengthening, and the balance between strength and toughness may be lost. Therefore, the N _(Metal) content is set to 0.0100 mass% or less, and preferably 0.0050 mass% or less, based on the total mass of the weld metal.

(Remainder: impurities)
In this embodiment, the remainder excluding the above elements is preferably impurities. Impurities refer to elements that are not intentionally added, and examples of elements other than the above include Sn, Co, Sb, and As. The total content of impurities in the deposited metal is preferably 0.010 mass% or less, and more preferably 0.005 mass% or less.

The deposited metal according to this embodiment can be produced, for example, by gas-shielded arc welding using the basic flux-cored wire described above.

[3. Welding Method]
The welding method according to this embodiment is a gas-shielded arc welding method using the basic flux-cored wire described above in [1. Basic Flux-Cored Wire].
Specifically, among various gas-shielded arc welding methods, it is preferable to employ gas-shielded arc welding using positive polarity, with the electrode side being negative (-) and the base metal side being positive (+). The type of gas used for welding is not particularly limited, but examples include 100% by volume Ar gas, 100% by volume _CO2 gas, 100% by volume _O2 gas, and mixtures of these. When using Ar gas, it is preferable to use a shielding gas containing 70% or more by volume of Ar. When using _CO2 gas, it is preferable to use a shielding gas containing 70% or more by volume of _CO2 , and it is more preferable to use 100% by volume of _CO2 gas (hereinafter also referred to as "carbon dioxide gas"). Furthermore, when using a mixed gas of Ar gas and _CO2 gas, a mixed gas of 80% by volume of Ar gas and 20% by volume of _CO2 gas is preferable. The gas flow rate is also not particularly limited, but can be, for example, approximately 15 to 30 L/min.

The welding current waveform may be linear or pulse-shaped. Note that linear here means that it does not have to be a special waveform. The welding current range is not particularly limited; for example, 200-300 A for flat welding, 150-250 A for vertical and horizontal welding, and a combination of these ranges can be used for circumferential welding of fixed pipes, etc. The arc voltage is also not particularly limited; for example, it can be 15-35 V. The welding speed is also not particularly limited; for example, it can be 10-50 cm/min. The wire extension length is also not particularly limited; for example, it can be set to 10-30 mm. However, all welding conditions are not limited to the above ranges and can be determined appropriately depending on the application.

[4. Welded joints]
The welded joint according to this embodiment is produced using the welding method described above in [3. Welding method]. In the welded joint according to this embodiment, the portion corresponding to the weld metal preferably has the composition described above in [2. Weld metal].

The present invention will be explained in more detail below using examples and comparative examples, but the present invention is not limited to these examples and can be implemented with modifications within the scope of the present invention, all of which are within the technical scope of the present invention. Furthermore, the welding conditions described here are merely examples, and the present embodiment is not limited to the following welding conditions.

Weld metals were prepared using wires with the various compositions shown in Tables 1 to 4 below under the welding conditions shown below. Tensile tests were conducted to measure strength (TS), and impact tests were conducted to measure Charpy absorbed energy (CVN) at -20°C and -46°C.

<Welding conditions>
Welding current: 210A
Arc voltage: 21V
Polarity: DCEN
Shielding gas: 100% CO2 by _volume
Lamination method: 7 layers, 14 passes Heat input: 0.8 to 1.0 kJ/mm

<Measurement method>
(Tensile test)
Tensile test pieces according to JIS Z 3111:2005 No. A1 were taken from the obtained weld metal, and the tensile strength (TS) and 0.2% proof stress (yield stress: PS) of the weld metal were measured by a tensile test in accordance with "Method for tensile and impact testing of weld metal" specified in JIS Z 3111:2005.

(Impact test)
A 2 mm V-notch impact test piece according to JIS Z 3111:2005 was taken from the obtained weld metal, and the absorbed energy (CVN) of the weld metal at -20°C and -46°C was measured at three points by an impact test in accordance with "Method for tensile and impact testing of weld metal" specified in JIS Z 3111:2005, and the average values were used as the values of CVN (-46°C) and CVN (-20°C).

<Evaluation method>
Next, the balance between strength and toughness and the brittle fracture rate were evaluated. Specifically, the values obtained by the following formulas (a) and (b) were calculated, and the balance between strength and toughness was evaluated.
Formula (a): CVN (-46°C)/TS
Formula (b): CVN (-20°C)/TS

The closer the values obtained by formula (a) and formula (b) are to 1, the better the balance between strength and toughness. Specifically, for formula (a), a value of 0.100 or higher is considered to indicate a good balance between strength and toughness, 0.150 or higher is considered to be even better, and 0.180 or higher is considered to be excellent, with values of good or better being considered to pass. For formula (b), a value of 0.150 or higher is considered to indicate a good balance between strength and toughness, 0.200 or higher is considered to be even better, and 0.220 or higher is considered to be excellent, with values of good or better being considered to pass.

The brittle fracture rate at -20°C and -46°C was also evaluated. The brittle fracture rate was calculated by observing the fracture surface of the test piece after the Charpy impact test and calculating the area ratio of the region exhibiting brittle fracture to the specified cross-sectional area before the test. A brittle fracture rate of 40% or less at -20°C and -46°C was considered good, and a brittle fracture rate of 30% or less was considered excellent, with good or better being considered acceptable. The composition of the obtained weld metal is shown in Tables 5 and 6 below, and the evaluation results are shown in Tables 7 and 8 below. In Tables 1, 3, 5, and 6 below, "-" indicates that the content was below the detection limit. In Table 4, "-" indicates that the content could not be calculated. The remainder of the wire composition shown in Tables 1 and 3 below is O, N, and impurities, and the remainder of the weld metal composition shown in Tables 5 and 6 below is Fe and impurities.

Furthermore, in Tables 2 and 4, formulas (1) to (8) represent the following formulas.
Formula (1):
32.1×[Si]-40.6×[Mn]-20.1×[Ni]-19.7×[Mo]-172.6×[C]-408.2×[REM]-5824.4×[B]-38.4×[Cr]-9960×[P]+43793×[S]

Formula (2):
33.9×[Si]-47.0×[Mn]-22.2×[Ni]-11.9×[Mo]-203.9×[C]-443.5×[REM]-4482.2×[B]-36.1×[Cr]-15281×[P]+47868×[S]

Formula (3):
0.001×[Fe]-0.71×[Si]+0.08×[Mn]-0.08×[Al]+0.69×[Zr]+0.03×[Ni]+0.01×[Mo]+0.32×[C]+2.27×[REM]+9.57×[B]+0.11×[Cr]

Formula (4):
0.003×[Fe]-0.35×[Si]+0.09×[Mn]-0.13×[Al]+0.22×[Zr]+0.02×[Ni]-0.02×[Mo]-0.11×[C]+1.17×[REM]+4.30×[B]+0.09×[Cr]

Formula (5): [B oxide]/[B]

Formula (6): [Cr]/([Cr]+[Mo])

Formula (7): [Mo]/([Cr]+[Mo])

Formula (8): [Al]/([Al]+[Mg])

Here, [REM], [Fe], [C], [Si], [Mn], [P], [S], [Cr], [Mo], [Al], [Zr], [Ni], [B], and [Mg] represent the contents of REM _(wire) , Fe _(wire) , C _(wire) , Si ( _wire ), Mn _(wire) , P _(wire) , S _{( wire} ), Cr _(wire) , Mo _(wire) , Al _(wire) , Zr _(wire) , Ni (wire), B _(wire) , and Mg _(wire) , respectively, expressed as mass% relative to the total mass of the wire. Also, [B oxide] represents the B equivalent value of B oxide in the wire, expressed as mass% relative to the total mass of the wire. In this example, only B was added in the form of an oxide. In other words, the amount of oxide in the wire of this embodiment is the B ₂ O ₃ equivalent value of the value of B _(Wire) .

As shown in Tables 1-4, 7, and 8, in Examples 1-16, the components contained in the basic flux-cored wire and the values obtained by formulas (1) to (8) were within the ranges specified by the present invention, thereby improving burn-through, enabling welding in all positions, and producing weld metal with an excellent balance of strength and toughness. Comparing Examples 5-7, when the Zr content in the wire was 0.045% by mass or less, the balance between strength and toughness improved with an increase in the B content. Comparing Examples 5, 11, and 14, when the B content was 0.0046-0.0055% by mass and the Zr content in the wire was increased beyond 0.045% by mass, a tendency was observed for at least one of formulas (a) and (b), which indicate the balance between strength and toughness, to decrease with an increase in Zr content. In other words, it was found that when both the B content and Zr content approach the upper limits of the ranges specified in the present invention, the balance between strength and toughness deteriorates.

In particular, Invention Examples Nos. 9, 10, 12, 13, 15, and 16 had wire Zr and B contents within the preferred ranges specified by the present invention, resulting in excellent results in both the brittle fracture rate and the balance between strength and toughness.

On the other hand, in Comparative Examples 1 to 19, at least one of the REM content, C content, and values obtained by Equations (1) to (4) in the wire was outside the range specified in the present invention, and therefore at least one of the brittle fracture rate and the balance between strength and toughness was poor.

Furthermore, as shown in Tables 5 to 8, in Invention Examples 1 to 16, the content of each component contained in the deposited metal was within the range specified in the present invention, resulting in a weld metal with an excellent balance between strength and toughness.

As such, the basic flux-cored wire, welding method, and weld joint manufacturing method of the present invention enable welding in all positions and produce weld metal and weld joints with an excellent balance of strength and toughness.

Claims (14)

It is obtained under welding conditions conforming to the method for producing weld metal described in JIS Z 3184,
For the total mass of deposited metal,
C: 0.020% by mass or more and 0.100% by mass or less,
Si: 0.05% by mass or more and 0.50% by mass or less,
Mn: 0.20% by mass or more and 1.80% by mass or less,
Al: 0.30% by mass or more and 1.50% by mass or less,
Ce: 0.002 mass% or more and 0.010 mass% or less,
Fe: 85.0% by mass or more,
Contains
La: 0.008% by mass or less,
P: 0.0200% by mass or less,
S: 0.0200% by mass or less,
Cr: 1.00% by mass or less,
Mo: 1.00% by mass or less,
Mg: 0.50% by mass or less,
Zr: 0.50% by mass or less,
Ti: 0.05% by mass or less,
Ca: 0.50% by mass or less,
Ni: 3.00% by mass or less,
B: 0.0010% by mass or more and 0.0090% by mass or less,
Ba: 1.00% by mass or less,
Nb: 0.001% by mass or less,
Cu: 0.1% by mass or less,
V: 0.001% by mass or less,
W: 0.1% by mass or less,
Ta: 0.1% by mass or less,
Sr: 1.00% by mass or less,
Total alkali metal elements: 0.05% by mass or less,
O: 0.0250% by mass or less,
N: 0.0100% by mass or less;
A basic flux-cored wire containing at least one strong deoxidizing element selected from Al, Mg, Ti, Ca, and Zr for obtaining a deposited metal with the balance being impurities,
The total amount of the strong deoxidizing elements is 1.50 mass% or more and 4.00 mass% or less with respect to the total mass of the wire,
REM: 0.030% by mass or more and 0.120% by mass or less,
Fe: 85.0% by mass or more,
Contains
C: 0.050% by mass or less,
Si: 0.60% by mass or less,
Mn: 2.00% by mass or less,
P: 0.0150% by mass or less,
S: 0.0150% by mass or less,
Cr: 1.00% by mass or less,
Mo: 1.00% by mass or less,
Al: 3.00% by mass or less,
Mg: 3.00% by mass or less,
Zr: 3.000% by mass or less,
Ti: 3.000% by mass or less,
Ca: 3.00% by mass or less,
Ni: 5.00% by mass or less,
B: 0.0200% by mass or less,
Ba: 4.00% by mass or less,
F: 2.00% by mass or less,
and
A value calculated by the following formula (1): 48.0 or less,
A value calculated by the following formula (2): 48.0 or less,
A value calculated by the following formula (3): 0.09 or more,
A value calculated by the following formula (4): 0.14 or more,
A basic flux-cored wire characterized by:
Formula (1):
32.1×[Si]-40.6×[Mn]-20.1×[Ni]-19.7×[Mo]-172.6×[C]-408.2×[REM]-5824.4×[B]-38.4×[Cr]-9960×[P]+43793×[S]
Formula (2):
33.9×[Si]-47.0×[Mn]-22.2×[Ni]-11.9×[Mo]-203.9×[C]-443.5×[REM]-4482.2×[B]-36.1×[Cr]-15281×[P]+47868×[S]
Formula (3):
0.001×[Fe]-0.71×[Si]+0.08×[Mn]-0.08×[Al]+0.69×[Zr]+0.03×[Ni]+0.01×[Mo]+0.32×[C]+2.27×[REM]+9.57×[B]+0.11×[Cr]
Formula (4):
0.003×[Fe]-0.35×[Si]+0.09×[Mn]-0.13×[Al]+0.22×[Zr]+0.02×[Ni]-0.02×[Mo]-0.11×[C]+1.17×[REM]+4.30×[B]+0.09×[Cr]
In the formulas (1) to (4), [REM], [Fe], [C], [Si], [Mn], [P], [S], [Cr], [Mo], [Al], [Zr], [Ni], and [B] respectively represent the contents of the REM, Fe, C, Si, Mn, P, S, Cr, Mo, Al, Zr, Ni, and B, expressed as mass% with respect to the total mass of the wire. Furthermore, for the total mass of the wire,
Nb: 0.50% by mass or less,
Cu: 2.00% by mass or less,
W: 1.00% by mass or less,
Ta: 1.00% by mass or less,
V: 1.00% by mass or less,
Sr: 4.00% by mass or less, and
Total alkali metal elements: 3.00 mass% or less,
Contains at least one selected from
2. The basic flux-cored wire according to claim 1, wherein the balance is O, N, and impurities. The basic flux-cored wire according to claim 1 or 2, characterized in that the B content is 0.0020 mass% or more and 0.0150 mass% or less relative to the total mass of the wire. The content of B includes the B-equivalent value of B oxide,
When the B-equivalent value of the B oxide relative to the total mass of the wire is expressed as [B oxide] in mass%,
4. The basic flux-cored wire according to claim 1, wherein a value calculated by formula (5): [B oxide]/[B] is 0.5 or more. Ba: 4.00% by mass or less,
Contains at least one selected from Ca: 3.00% by mass or less, and Sr: 4.00% by mass or less,
The flux contains at least one selected from BaF ₂ , CaF ₂ and SrF ₂ , which are fluorides of Ba, Ca and Sr,
The content of Ba includes the Ba equivalent value of _BaF2 ,
The Ca content includes the Ca equivalent value of the _CaF2 ,
The Sr content includes the Sr-equivalent value of the _SrF2 ,
5. The basic flux-cored wire according to claim 1, wherein the content of F includes the F-converted values of BaF ₂ , CaF ₂ and SrF ₂ . The basic flux-cored wire according to claim 5, wherein the F content is equal to the F-equivalent value of all fluorides contained in the flux. A basic flux-cored wire according to any one of claims 1 to 6, characterized in that the oxide content in the wire is 0.005 mass% or more and 0.100 mass% or less relative to the total mass of the wire. The Cr content is 0.20 mass% or more and 0.90 mass% or less with respect to the total mass of the wire,
The content of Mo is 0.50 mass% or less with respect to the total mass of the wire,
The basic flux-cored wire according to any one of claims 1 to 7, characterized in that a value calculated by equation (6): [Cr]/([Cr]+[Mo]) is 0.20 or more. The Cr content is 0.90 mass% or less with respect to the total mass of the wire,
The content of Mo is 0.10 mass% or more and 0.80 mass% or less with respect to the total mass of the wire,
The basic flux-cored wire according to any one of claims 1 to 7, characterized in that a value calculated by equation (7): [Mo]/([Cr]+[Mo]) is 0.10 or more. As the strong deoxidizing element, the Al is contained in an amount of 1.00 mass% or more and 2.50 mass% or less with respect to the total mass of the wire,
The Mg content is 1.00% by mass or less,
When the content of Mg in the wire is expressed as [Mg] in mass% relative to the total mass of the wire,
10. The basic flux-cored wire according to claim 1, wherein a value calculated by equation (8): [Al]/([Al]+[Mg]) is 0.5 or more and 1.0 or less. The basic flux-cored wire according to any one of claims 1 to 10, characterized in that the REM consists of La and Ce. For the total mass of deposited metal,
C: 0.020% by mass or more and 0.100% by mass or less,
Si: 0.05% by mass or more and 0.50% by mass or less,
Mn: 0.20% by mass or more and 1.80% by mass or less,
Al: 0.30% by mass or more and 1.50% by mass or less,
Ce: 0.002 mass% or more and 0.010 mass% or less,
Fe: 85.0% by mass or more,
Contains
La: 0.008% by mass or less,
P: 0.0200% by mass or less,
S: 0.0200% by mass or less,
Cr: 1.00% by mass or less,
Mo: 1.00% by mass or less,
Mg: 0.50% by mass or less,
Zr: 0.50% by mass or less,
Ti: 0.05% by mass or less,
Ca: 0.50% by mass or less,
Ni: 3.00% by mass or less,
B: 0.0010% by mass or more and 0.0090% by mass or less,
Ba: 1.00% by mass or less,
Nb: 0.001% by mass or less,
Cu: 0.1% by mass or less,
V: 0.001% by mass or less,
W: 0.1% by mass or less,
Ta: 0.1% by mass or less,
Sr: 1.00% by mass or less,
Total alkali metal elements: 0.05% by mass or less,
O: 0.0250% by mass or less,
N: 0.0100% by mass or less;
the remainder being impurities,
A value calculated by the following formula (a): 0.100 or more,
A value calculated by the following formula (b): 0.150 or more,
A weld metal characterized in that the brittle fracture rate at -20°C and -46°C is 40% or less in both cases .
Formula (a):
CVN (-46℃)/TS
Formula (b):
CVN (-20℃)/TS
In the formulas (a) and (b), [CVN (-20°C)] and [CVN (-46°C)] are the average values (J) of absorbed energy (CVN) of the weld metal at -20°C and -46°C measured at three points by an impact test in accordance with "Tensile and impact test methods for weld metals" specified in JIS Z3111:2005, and TS is the tensile strength (MPa). A welding method characterized by gas-shielded arc welding using the basic flux-cored wire described in any one of claims 1 to 11. A method for manufacturing a welded joint, characterized by using the welding method described in claim 13.