JP7160734B2 - flux cored wire - Google Patents

Description

The present invention relates to flux cored wires for gas shielded arc welding.

In shipyards, the welding work, which occupies about 30% of the process, is being developed for automation and efficiency improvement in order to promote labor saving and efficiency improvement. Especially for downward butt welding and horizontal fillet welding, welding robots, line welders, etc. have been introduced, and a large number of dedicated welding materials have been developed.
On the other hand, the rising welding position, which is mainly used for block joints in shipbuilding, is automated because the welding position is narrow and the structure cannot be turned over. is difficult.

As a flux-cored wire suitable for all-position welding using a welding robot, for example, Patent Document 1 discloses that by appropriately controlling the Al content and the Mg content, Flux-cored wires have been proposed that are excellent in welding workability, slag removability, weld metal impact resistance, and the like.

Japanese Patent No. 3824973

However, in all-position welding using a welding robot, not only the dripping of molten metal, the amount of spatter, the dripping of slag, and the welding workability of arc stability, but also all performances including bead shape and slag peelability , must be well-balanced. Therefore, there is a demand for the development of a flux-cored wire that is even more excellent in these properties and is suitable for all-position welding.

The present invention has been made in view of the above-mentioned situation, and all the performances of molten metal dripping, spatter generation, slag dripping and arc stability welding workability, bead shape and slag peelability are improved. To provide a well-balanced flux-cored wire for gas-shielded arc welding suitable for all-position welding.

The flux-cored wire of the present invention is a flux-cored wire for gas-shielded arc welding in which a steel sheath is filled with flux, and TiO ₂ is 5.0% by mass or more and 10.0% by mass based on the total mass of the wire. Below, Al ₂ O ₃ : 0.05% by mass or more and 0.50% by mass or less, metal Al: less than 0.10% by mass, SiO ₂ conversion value of metal Si and Si oxide: 1.0% by mass or more 3 .5% by mass or less, ZrO2 conversion value of metal Zr and Zr oxide: 0.05% by mass or _more and 0.50% by mass or less, MgO conversion value of metal Mg and Mg oxide: 0.5% by mass or more 2.2% by mass or less, fluoride: 0.05% by mass or more and 0.30% by mass or less, C: 0.01% by mass or more and 0.08% by mass or less, Mn: 2.0% by mass or more and 4.0% by mass % or less, and the Al ₂ O ₃ conversion value, ZrO ₂ conversion value, MgO conversion value, and SiO ₂ conversion value of Al and Al ₂ O ₃ are (Al ₂ O ₃ conversion value + ZrO ₂ conversion value + MgO converted value)/SiO ₂ converted value: 0.35 or more and 1.50 or less.

The flux-cored wire further contains at least one selected from Na, Na oxides, K and K oxides, and the sum of the Na ₂ O conversion value and the K ₂ O conversion value per total weight of the wire: 0 It is preferable to satisfy 0.01% by mass or more and 0.30% by mass or less.

According to the present invention, all performances such as dripping of molten metal, amount of spatter, slag dripping and welding workability such as arc stability, and bead shape and slag peelability are well-balanced and suitable for all-position welding. It is possible to provide a flux-cored wire for gas-shielded arc welding .

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the embodiments described below, and can be arbitrarily modified without departing from the gist of the present invention.

In order to obtain a flux-cored wire for gas-shielded arc welding that has excellent welding workability and good bead shape and slag releasability, the present inventors have investigated the inclusion of various components in the flux-cored wire. Considered quantity. As a result, TiO ₂ , Al ₂ O ₃ , metal Al, SiO ₂ conversion values for metal Si and Si oxides, ZrO ₂ conversion values for metal Zr and Zr oxides, and MgO conversion values for metal Mg and Mg oxides value, fluoride, C, and Mn component amounts, and the Al ₂ O ₃ equivalent value of Al and Al ₂ O ₃ with respect to the SiO ₂ equivalent value,
We have found that it is effective to appropriately adjust the sum of the _ZrO2 equivalent value and the MgO equivalent value.

The flux-cored wire (hereinafter also simply referred to as wire) according to the present embodiment contains TiO ₂ : 5.0% by mass or more and 10.0% by mass or less, and Al ₂ O ₃ : 0.05% by mass or more, based on the total mass of the wire. 0.50% by mass or less, metal Al: less than 0.10% by mass, _SiO2 conversion value of metal Si and Si oxide: 1.0% by mass or more and 3.5% by mass or less, metal Zr and Zr oxide ZrO2 conversion value of: 0.05 mass% or _more and 0.50 mass% or less, MgO conversion value of metal Mg and Mg oxide: 0.5 mass% or more and 2.2 mass% or less, fluoride: 0.05 % by mass or more and 0.30% by mass or less, C: 0.01% by mass or more and 0.08% by mass or less, Mn: 2.0% by mass or more and 4.0% by mass or less, and Al and Al ₂ O ₃ The Al ₂ O ₃ conversion value, ZrO ₂ conversion value, MgO conversion value, and SiO ₂ conversion value are (Al ₂ O ₃ conversion value + ZrO ₂ conversion value + MgO conversion value) / SiO ₂ conversion value: 0.35 or more 1.50 or less is satisfied.

The flux-cored wire of this embodiment has a steel sheath filled with flux. Specifically, the flux-cored wire according to the present embodiment is composed of a tubular steel outer sheath and flux filled inside (inside) the outer sheath. Note that the flux-cored wire may be of either a seamless type with a seamless outer sheath or a seam type with a seamless outer sheath. Moreover, the flux-cored wire may or may not be plated with Cu or the like on the wire surface (outside of the sheath). Moreover, the flux-cored wire according to the present embodiment is a so-called mild steel wire.

Although the wire diameter (diameter) of the flux-cored wire according to the present embodiment is not particularly limited, it is preferably 1.2 to 4.0 mm, more preferably 1.2 to 4.0 mm, from the viewpoint of wire feeding stability. is 1.2 to 2.4 mm.

In the flux-cored wire according to the present embodiment, each component has a predetermined content with respect to the total mass of the wire, and the content of some components satisfies a predetermined relational expression. In the following, the composition of the flux-cored wire according to the present embodiment will be described with respect to the reasons for adding the components and the reasons for limiting the composition.

In the following description, unless otherwise specified, the amount of each component in the flux-cored wire is defined as the content per total weight of the wire (the total amount of the outer coat and the flux in the outer coat).

In this embodiment, TiO ₂ is included as a typical Ti oxide as the Ti oxide. Ti oxides may include other oxides, but in the present embodiment, TiO ₂ includes these other oxides. Other oxide components such as SiO ₂ , ZrO ₂ , Al ₂ O ₃ and the like are the same for oxide components.

Further, for example, "metal Al" means one or more of "pure metal Al" and "alloy Al", that is, the sum of Al contained in a single metal or an alloy. The same applies to other elements such as “metal Si” and “metal Mg”. That is, as a metal, it means that it is not an oxide.
Further, "oxide" means one or more of "single oxide" and "composite oxide". The term “single oxide” refers to, for example, an oxide of Si alone (SiO ₂ ) in the case of Si, and the term “composite oxide” refers to an aggregate of a plurality of types of these single oxides, together with, for example, Zr , Si, and Mg, and oxides containing a plurality of metal components.

<TiO ₂ : 5.0% by mass or more and 10.0% by mass or less>
_TiO2 generally acts as a slag former and arc stabilizer. In the present embodiment, TiO ₂ is defined as TiO ₂ converted from Ti in metal Ti and all Ti oxides contained in the entire composition including the flux and the outer coating.
If TiO ₂ is less _than 5.0% by mass, the amount of slag sufficient to support the molten metal cannot be secured, and the molten metal drips. 6.0% by mass or more.
_On the other hand, if TiO ₂ exceeds 10.0% by mass, the arc becomes unstable and the generation of spatters increases. .

<Al ₂ O ₃ : 0.05% by mass or more and 0.50% by mass or less>
Al ₂ O ₃ has the effect of raising the slag solidification point. Here, Al ₂ O ₃ is the Al ₂ O ₃ conversion value of Al oxide.
If the content of Al ₂ O ₃ is less than 0.05% by mass, the effect of raising the slag freezing point cannot be obtained, and the slag drips, so the content of Al ₂ O ₃ is 0.05 mass%. % or more, preferably 0.07 mass % or more.
On the other hand, if the content of Al ₂ O ₃ exceeds 0.50% by mass, the bead shape deteriorates, so the content of Al ₂ O ₃ is 0.50% by mass or less, preferably 0.40% by mass. Below.

<Metal Al: less than 0.10% by mass>
Metallic Al is a component that affects the toughness of the metal of the welded portion and also acts as a slag forming agent.
If the metal Al content is 0.10% by mass or more, the bead shape deteriorates and the toughness of the welded portion also decreases. Therefore, the Al content is less than 0.10% by mass, preferably less than 0.08% by mass.

< _SiO2 conversion value: 1.0% by mass or more and 3.5% by mass or less>
Metallic Si and Si oxides act as slag formers and arc stabilizers. In the present embodiment, Si in metal Si and all Si oxides contained in the entire composition including the flux and the crust is defined as a SiO ₂ conversion value converted to SiO ₂ .
If the _SiO2 conversion value is less _than 1.0% by mass, the arc becomes unstable and the generation of spatters increases. and
_On the other hand, if the _SiO2 conversion value exceeds 3.5% by mass, the slag becomes hard and the slag removability decreases. and
The content of SiO ₂ (Si oxide converted to SiO ₂ ) is preferably 0.10% by mass or more, more preferably 0.20% by mass or more, and preferably 1.00% by mass or less. Preferably, it is 0.80% by mass or less.
In addition, the content of metal Si is preferably 0.4% by mass or more, more preferably 0.5% by mass or more, and preferably 1.5% by mass or less, more preferably 1.3% by mass or less. .

<ZrO ₂ conversion value: 0.05% by mass or more and 0.50% by mass or less>
Metal Zr and Zr oxides raise the slag solidification point and act as an arc stabilizer. In this embodiment, metal Zr contained in the entire composition including the flux and the crust and Zr in all Zr oxides are defined as ZrO ₂ conversion values converted to ZrO ₂ .
If the ZrO ₂ conversion value is less than 0.05% by mass, the effect of raising the slag solidification point cannot be obtained, the slag will drip, and the effect as an arc stabilizer cannot be obtained. ₂ conversion value is 0.05% by mass or more, preferably 0.08% by mass or more.
_On the other hand, if the _ZrO2 conversion value exceeds 0.50% by mass, the arc tends to become unstable and the occurrence of spatters increases. 40% by mass or less.

<MgO conversion value: 0.5% by mass or more and 2.2% by mass or less>
Metal Mg and Mg oxide raise the slag freezing point and act as an arc stabilizer. In this embodiment, metal Mg contained in all components including flux and outer coating and Mg in all Mg oxides are defined as MgO conversion values converted to MgO.
If the MgO conversion value is less than 0.5% by mass, the effect of raising the slag freezing point cannot be obtained, the slag will drip, and the effect as an arc stabilizer cannot be obtained. The value should be 0.5% by mass or more, preferably 0.7% by mass or more.
On the other hand, if the MgO conversion value exceeds 2.2 mass %, the bead shape deteriorates, so the MgO conversion value is 2.2 mass % or less, preferably 2.0 mass % or less.
The content of MgO (MgO conversion value of Mg oxide) is preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and preferably 0.50% by mass or less, more preferably It is 0.40% by mass or less.
The content of metal Mg is preferably 0.2% by mass or more, more preferably 0.25% by mass or more, and preferably 1.0% by mass or less, more preferably 0.8% by mass or less. .

<Fluoride: 0.05% by mass or more and 0.30% by mass or less>
Fluoride acts as an arc stabilizer.
If the total content of fluoride contained in the entire composition including the flux and the outer coating is less than 0.05% by mass, the effect as an arc stabilizer cannot be obtained, so the fluoride content is 0.05%. It should be at least 0.06% by mass, preferably at least 0.06% by mass.
On the other hand, if the total fluoride content exceeds 0.30% by mass, the slag tends to drip, so the fluoride content is 0.30% by mass or less, preferably 0.26% by mass. % or less.
Specific fluorides include K ₂ SiF ₆ , NaF, CaF ₂ and the like.

<C: 0.01% by mass or more and 0.08% by mass or less>
C has the effect of improving the hardenability and toughness of the weld metal.
If the C content is less than 0.01% by mass, the weld metal is insufficiently quenched and sufficient toughness cannot be obtained. % or more.
On the other hand, if the C content exceeds 0.08% by mass, the arc blowing becomes strong and the amount of spatter generation increases. 07% by mass or less.

<Mn: 2.0% by mass or more and 4.0% by mass or less>
Mn acts as a deoxidizing agent and also has the effect of improving the strength and toughness of the weld metal.
If the Mn content is less than 2.0% by mass, the deoxidation is insufficient, and welding defects such as blowholes may occur in the weld zone, or the strength and toughness may decrease. 0% by mass or more, preferably 2.2% by mass or more.
On the other hand, if the Mn content exceeds 4.0% by mass, the strength of the weld metal becomes too high and hot cracks are likely to occur. .8% by mass or less.
Here, Mn means total Mn contained in metallic Mn and Mn oxides.

<(Al ₂ O ₃ conversion value + ZrO ₂ conversion value + MgO conversion value)/SiO ₂ conversion value: 0.35 or more and 1.50 or less>
In this embodiment, the sum of the Al ₂ O ₃ equivalent value, the ZrO ₂ equivalent value, and the MgO equivalent value for the SiO ₂ equivalent value is limited, but the Al ₂ O ₃ equivalent value used in the above formula is the flux and the crust. Metal Al contained in all constituents and Al in all Al oxides are converted to Al ₂ O ₃ . Also, the ZrO ₂ equivalent value, the MgO equivalent value and the SiO ₂ equivalent value are as described above.
If the sum of the Al ₂ O ₃ equivalent value, the ZrO ₂ equivalent value and the MgO equivalent value with respect to the SiO ₂ equivalent value is less than 0.35, the bead shape deteriorates and the slag removability decreases. is set to 0.35 or more, preferably 0.45 or more.
On the other hand, when the sum of the Al ₂ O ₃ equivalent value, the ZrO ₂ equivalent value and the MgO equivalent value with respect to the SiO ₂ equivalent value exceeds 1.50, the arc becomes unstable and the bead shape deteriorates. The value of the above relational expression should be 1.50 or less, preferably 1.30 or less.

<Total of Na ₂ O conversion value and K ₂ O conversion value: 0.01% by mass or more and 0.30% by mass or less>
The flux-cored wire according to the present embodiment preferably further contains at least one selected from Na, Na oxides, K and K oxides as an optional component. By appropriately adjusting these oxide conversion values, it is possible to obtain a flux-cored wire that is more suitable for all-position welding.
Na ₂ O and K ₂ O act as arc stabilizers, but if they are too large, they act in the direction of lowering the viscosity of the slag, making it easier for the slag to drip.
If the total of the Na ₂ O conversion value and the K ₂ O conversion value contained in the entire composition including the flux and the outer coating is less than 0.01% by mass, the effect as an arc stabilizer cannot be obtained. The value should be 0.01% by mass or more, preferably 0.05% by mass or more.
On the other hand, if the total of the Na ₂ O conversion value and the K ₂ O conversion value exceeds 0.30% by mass, the slag tends to drip, so the total value is preferably 0.30% by mass or less. is 0.25% by mass or less.
The above Na ₂ O conversion value is a value obtained by converting Na in metal Na and all Na oxides contained in the entire composition including the flux and the crust into Na ₂ O. Further, the K ₂ O conversion value is a value obtained by converting metal K and K in all K oxides contained in the entire composition including the flux and the crust into K ₂ O.

<Fe: 80 to 93% by mass>
Fe is the main component of flux-cored wires. The Fe content is preferably 80 to 93% by mass, more preferably 82 to 92% by mass, based on the total mass of the wire in view of the deposition amount and other component compositions.
Here, the flux-cored wire according to the present embodiment contains the aforementioned Fe, TiO ₂ , Al ₂ O ₃ , metal Al, SiO ₂ equivalent value, ZrO ₂ equivalent value, MgO equivalent value, fluoride, C, and Mn. In total, it contains 95% or more. This sum is preferably 98% or more.

<Remainder>
The remainder of the flux-cored wire according to this embodiment contains unavoidable impurities. In the flux-cored wire according to the present embodiment, in addition to the above-described wire components, a small amount of Cr, Mo, Cu, or the like is added to the flux as a further hardening agent for the weld metal within a range that does not impair the effect. good too. For example, it may contain less than 0.1% by mass of each of Cr, Mo, Cu, etc., and less than 0.5% by mass of each of V ₂ O ₅ . Moreover, P, S, Sn, V, etc. may each be contained in an amount of 0.030% by mass or less.

<Others: Flux filling rate>
The flux filling rate (=flux mass/total wire mass×100) of the flux-cored wire according to this embodiment is not particularly limited.
However, when the flux filling rate is less than 10% by mass, the stability of the arc deteriorates, the amount of spatter generation increases, and the welding workability decreases. More preferably, it is 14% by mass or more.
On the other hand, if the flux filling rate exceeds 25% by mass, wire breakage may occur, and powder may spill out during flux filling, resulting in reduced productivity. Therefore, the flux filling rate is preferably 25% by mass. or less, more preferably 20% by mass or less.

Next, a method for manufacturing a flux-cored wire according to this embodiment will be described.
[Wire manufacturing method]
The method for manufacturing the flux-cored wire according to this embodiment is not particularly limited, but for example, it can be manufactured by the method shown below.
First, a steel strip constituting the steel outer skin is prepared, and the steel strip is formed by forming rolls while being fed in the longitudinal direction to form a U-shaped open pipe. Next, the steel sheath is filled with a flux containing various raw materials so as to have a predetermined composition, and then processed to have a circular cross section. Thereafter, the wire is drawn by cold working to form a flux-cored wire having a wire diameter of, for example, 1.2 to 2.4 mm.
Annealing may be performed during cold working. In addition, it is possible to employ either a seamless wire in which the joints of the steel outer skin formed during the manufacturing process are welded, or a wire in which the joints are not welded and are left as gaps.

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to invention examples and comparative examples, but the present invention is not limited to these.

Table 1 shows the component contents of the flux-cored wires of the invention examples and comparative examples. The main component of the remainder other than the components in Table 1 is Fe, and P, S, N, Cu and the like are included as unavoidable impurities. "-" in Table 1 indicates that the corresponding component was not actively added.

Test No. shown in Table 1 above. 1 to 9 (invention examples) and test No. 10 to 23 (comparative example) flux-cored wires are used, JIS G 3106, SM490A steel plates are used as the materials to be welded, and 100% by mass CO ₂ is supplied as the shielding gas at a flow rate of 25 liters / minute, and the following Welding tests (1) to (3) were carried out to evaluate the weldability.

(1) Evaluation of dripping properties of weld metal and slag by vertical upward welding Vertical upward welding was performed by the method shown in Table 2 below, and the dripping properties of weld metal and slag were evaluated. Evaluation criteria are as follows.
(1-1) Evaluation of dripping of weld metal Weld metal dripping did not occur and was good: 〇 Weld metal dripping occurred: ×
(1-2) Evaluation of slag dripping Good with no slag dripping: 〇 Some slag dripping occurred but no problem in practice: △
Slag dripping occurred: ×

(2) Evaluation of amount of spatter, arc stability, slag exfoliation, and bead shape Sensory evaluation of the amount of spatter, sensory evaluation of arc stability, and evaluation of slag exfoliation by performing rising fillet welding. did Moreover, sensory evaluation was performed also about the bead shape. Evaluation criteria are as follows.
(2-1) Evaluation of amount of spatter generated Small amount of spatter generated (amount of spatter generated: less than 1.5 g/min): ○
Slightly large amount of spatter (amount of spatter: 1.5 g/min or more): ×
(2-2) Evaluation of arc stability Good arc concentration: ○
Poor arc convergence and fluttering of the arc: ×
(2-3) Evaluation of slag peelability Good slag peelability (slag natural peeling rate (= slag natural peeling length / weld length): 25% or more): ○
Poor slag peelability (slag natural peeling rate (= slag natural peeling length / weld length): less than 25%): ×
(2-4) Evaluation of bead shape Good bead shape: ○ Poor bead shape: ×

(3) Evaluation of mechanical performance Hot cracking, toughness and strength of metal pieces obtained by welding were evaluated.
(3-1) Evaluation of hot cracks Hot cracks did not occur: ○
High temperature cracking occurred: ×
The hot cracks were detected by an X-ray transmission test.
(3-2) Evaluation of Toughness A test steel plate corresponding to JIS G 3106 (SM490A) was used and welded according to the test method for all deposited metals specified in JIS Z 3313. Evaluation criteria are as follows.
Absorbed energy by Charpy impact test of 60 J or more and less than 90 J: ○
Absorbed energy in the Charpy impact test of less than 60 J: ×
(3-3) Evaluation of strength The conditions were the same as those in the above evaluation of toughness. Evaluation criteria are as follows.
Those with a tensile strength of 500 to 640 MPa: 〇 Those with a tensile strength outside the above range: ×
The evaluation results of each welding test described above are shown in Table 3 below.

As shown in the results of Tables 1 and 3, Test No. 1, which is a comparative example, No. 10 has a poor bead shape because the content of metal Al exceeds the upper limit of the range of the present invention. In addition, the toughness evaluation results are lower than those of the invention examples.
Test No. which is a comparative example. In No. 11, since the content of TiO ₂ is less than the lower limit of the range of the present invention, dripping of the weld metal occurs.
Test No. which is a comparative example. In No. 12, since the content of Al ₂ O ₃ is less than the lower limit of the range of the present invention, slag dripping occurs.
Test No. which is a comparative example. In No. 13, the content of Al ₂ O ₃ exceeds the upper limit of the range of the present invention, so the bead shape is defective.
Test No. which is a comparative example. In No. 14, the SiO ₂ conversion value is less than the lower limit of the range of the present invention, so the arc becomes unstable and the amount of spatter generation increases.
Test No. which is a comparative example. In No. 15, the SiO ₂ conversion value exceeds the upper limit of the range of the present invention, so the slag removability is lowered.

Test No. which is a comparative example. In No. 16, since the ZrO ₂ conversion value is less than the lower limit of the range of the present invention, the arc becomes unstable and slag drips.
Test No. which is a comparative example. In No. 17, the ZrO ₂ conversion value exceeds the upper limit of the range of the present invention, so the amount of spatter generation increases.
Test No. which is a comparative example. In No. 18, the MgO conversion value is less than the lower limit of the range of the present invention, so the arc becomes unstable and slag drips.
Test No. which is a comparative example. In No. 19, the MgO conversion value exceeds the upper limit of the range of the present invention, so the bead shape is defective.
Test No. which is a comparative example. In No. 20, the arc is unstable because the fluoride content is less than the lower limit of the range of the present invention.
Test No. which is a comparative example. In No. 21, since the content of fluoride exceeds the upper limit of the range of the present invention, slag dripping occurs.
Test No. which is a comparative example. In No. 22, the value obtained by the formula of (Al ₂ O ₃ conversion value + ZrO ₂ conversion value + MgO conversion value) / SiO ₂ conversion value is less than the lower limit of the range of the present invention, so the bead shape is poor and the slag removability is poor. is also declining.
Test No. which is a comparative example. In No. 23, the value obtained by the above formula exceeds the upper limit of the range of the present invention, so the arc becomes unstable and the bead shape is defective.

On the other hand, Test No. which is an invention example. All of 1 to 9 satisfy the specified range of the present invention, so the dripping of molten metal, the amount of spatter, the dripping of slag, the welding workability of arc stability, and the bead shape and slag peelability are good. good results have been obtained. In addition, good results are obtained in all of hot cracking, toughness and strength, which relate to mechanical performance.
In particular, test no. Since 1 to 8 satisfy the preferred numerical range for the sum of Na ₂ O converted value and K ₂ O converted value, excellent results were obtained for all evaluations including slag dripping.

Welding workability in downward and horizontal fillet welding was also confirmed by the same test, and all of the invention examples were good.

As described in detail above, according to the present invention, molten metal dripping, spatter generation, slag dripping, arc stability welding workability, bead shape and slag peelability are all well-balanced. A flux-cored wire for arc welding that is suitable for welding can be obtained.

Claims (2)

A flux-cored wire for gas-shielded arc welding, wherein the steel sheath is filled with flux,
per total wire mass,
TiO ₂ : 5.7 % by mass or more and 9.3 % by mass or less,
Al ₂ O ₃ : 0.10 % by mass or more and 0.43 % by mass or less,
Metal Al: 0.09 % by mass or less ,
_SiO2 conversion value of metal Si and Si oxide: 1.3 % by mass or more and 3.5% by mass or less,
ZrO2 conversion value of metal Zr and Zr oxide: 0.06 % by mass or _more and 0.36 % by mass or less,
MgO conversion value of metal Mg and Mg oxide: 0.7 % by mass or more and 1.9 % by mass or less,
Fluoride: 0.08 % by mass or more and 0.22 % by mass or less,
C: 0.01% by mass or more and 0.08% by mass or less,
Mn: 2.0% by mass or more and 4.0% by mass or less ,
Fe: 80 to 93% by mass
and
The TiO ₂ , the Al ₂ O ₃ , the metal Al, the SiO ₂ conversion value, the ZrO ₂ conversion value, the MgO conversion value, the fluoride, the C, the Mn and the Fe are 95% by mass in total. contains more than
The Al ₂ O ₃ equivalent value, the ZrO ₂ equivalent value, the MgO equivalent value, and the SiO ₂ equivalent value of the Al and the Al ₂ O ₃ are
(Al ₂ O ₃ conversion value + ZrO ₂ conversion value + MgO conversion value)/SiO ₂ conversion value: A flux-cored wire characterized by satisfying 0.50 or more and 1.12 or less. Furthermore, containing at least one selected from Na, Na oxide, K and K oxide,
per total weight of wire,
2. Sum of the Na ₂ O conversion value of the Na and the Na oxide and the K ₂ O conversion value of the K and the K oxide : 0.05 % by mass or more and 0.25 % by mass or less. flux-cored wire as described in .