JP2022146842A - Fusion type flux for fillet submerged arc welding - Google Patents

Abstract

To provide a fusion type flux for fillet submerged arc welding, capable of obtaining a stable arc, and a weld metal having favorable bead shape, slag peeling ability and toughness when fillet submerged arc welding is performed.SOLUTION: A fusion type flux for fillet submerged arc welding includes in mass% based on total mass of flux: SiO2 of 35-45%, MnO of 18-28%, Al2O3 of 6-20%, MgO of 11-16%, TiO2 of 2-6%, FeO of 0.5-4%, CaF2 of 5-9%, either one or total of Na2O and K2O of 0.5-1.0% and the balance of impurity. The basicity A of the flux obtained from the formula (1): A=([CaF2]+[MgO]+0.5([MnO]+[FeO]))/([SiO2]+0.5([Al2O3]+[TiO2]))...(1) is in the range of 0.50 to 1.00, and the bulk density of the flux is in the range of 0.8-1.3 g/cm3.SELECTED DRAWING: None

Description

The present disclosure relates to a molten flux for fillet submerged arc welding, and in particular, when columns and beams made of built H-shaped steel, which are often used for construction and bridges, are used for fillet welding with a large heat input, the arc is stabilized. The present invention relates to a molten flux for fillet submerged arc welding, which is capable of obtaining a weld metal having good bead shape and slag releasability and good toughness.

BACKGROUND ART In recent years, steel plates used for steel structures such as buildings and bridges tend to be thicker, and submerged arc welding with a large heat input is used for efficient welding. In addition, in order to ensure the safety of steel structures based on the lessons learned from earthquakes and other failures, stable weld metal properties are required even when welding with a large heat input.

Welded joints formed by fillet submerged arc welding are required to have good penetration depth, leg length, bead shape smoothness, and good compatibility between the weld metal and the base metal. In addition, in recent years, due to the increase in the size of steel structures damaged by earthquake disasters, good mechanical performance is required for fillet weld metal.

Conventionally, when the weld metal formed by fillet submerged arc welding is required to have a predetermined mechanical performance, a sintered flux capable of adding alloys to the flux is used, as disclosed in Patent Document 1, for example. It is However, since sintered flux has a high melting point, when welding is performed at a relatively high speed, the shape of the bead becomes poor, such as poor conformability of the bead waveform and bead toe, and welding efficiency cannot be improved.

On the other hand, a molten flux for fillet submerged arc welding is disclosed in Patent Document 2 and Patent Document 3, for example. The techniques disclosed in these Patent Documents 2 and 3 are intended to improve slag releasability and bead appearance and shape during high-speed fillet welding. is not obtained.

Further, Patent Document 4 discloses a molten flux for fillet submerged arc welding capable of obtaining good toughness of the weld metal of fillet welds. However, the molten flux described in Patent Document 4 contains less SiO ₂ and more Al ₂ O ₃ and TiO ₂ , so when fillet welding is performed with a large heat input, the bead shape is convex and slag seizure occurs. However, there was a problem that the slag removability was poor.

JP 2010-125508 A JP-A-53-133543 JP-A-61-154791 JP-A-62-183996

Therefore, the present disclosure has been devised in view of the above problems, and when performing fillet submerged arc welding, the arc is stable, the bead shape and slag exfoliation are good, and the weld has good toughness. It is an object of the present invention to provide a molten flux for fillet submerged arc welding capable of obtaining metal.

The gist of the present disclosure for solving the above problems is as follows.
<1> % by mass with respect to the total mass of flux,
_SiO2 : 35-45%,
MnO: 18-28%,
Al ₂ O ₃ : 6-20%,
MgO: 11-16%,
_TiO2 : 2-6%,
FeO: 0.5-4%,
CaF ₂ : 5 to 9%, and one or two of Na ₂ O and K ₂ O combined: 0.5 to 1.0%
and having a flux component in which the balance is impurities,
The basicity A determined from the following formula (1) is 0.50 to 1.00,
The flux has a bulk density of 0.8 to 1.3 g/cm ³ ,
Hot-melt flux for fillet submerged arc welding.
A=([ _CaF2 ]+[MgO]+0.5([MnO]+[FeO]))/([ _SiO2 ]+0.5 ₍ [ _Al2O3 ]+[ _TiO2 ]))...(1 ) where [ ] indicates the mass % of each component relative to the total mass of the flux.
<2> The molten flux for fillet submerged arc welding according to <1>, wherein flux particles having a particle size in the range of more than 0.3 mm to 1.4 mm account for 90% or more in mass% of the total mass of the flux. .
<3> Instead of a part of the flux component, mass % with respect to the total mass of the flux,
Bi ₂ O ₃ : The molten flux for fillet submerged arc welding according to <1> or <2>, containing 0.05% or less.
<4> Instead of a part of the flux component, mass % with respect to the total mass of the flux,
B ₂ O ₃ : The molten flux for fillet submerged arc welding according to any one of <1> to <3>, containing 1.5% or less.
<5> Instead of a part of the flux component, mass % with respect to the total mass of the flux,
The molten flux for fillet submerged arc welding according to any one of <1> to <4>, containing one or both of CaO: 5.0% or less and BaO: 5.0% or less.

According to the present disclosure, when performing fillet submerged arc welding, the arc is stable, the bead shape and slag releasability are good, and a weld metal with good toughness can be obtained. Flux is provided.

FIG. 1(a) is a schematic diagram showing the shape of a welding test plate with groove processing used in an example of the present disclosure, and FIG. 1(b) is a welding test plate used in an example of the present disclosure. is a schematic diagram showing a shape without groove processing. FIG. 2 is a schematic diagram showing the sampling positions of the Charpy impact test piece of the example of the present disclosure.

The present inventors have found that in high heat input submerged arc welding with and without a groove of H-shaped steel, the arc is stable, the slag exfoliation property and bead shape are good, and the toughness of the weld metal is good. The chemical composition of molten flux for submerged arc welding was investigated in detail.

As a result, arc stability is controlled by adjusting the sum of one or two of Na ₂ O and K ₂ O, and slag removability is controlled by controlling MnO, TiO ₂ , FeO and CaF ₂ in appropriate amounts. The geometry limits the bulk density of the flux with appropriate amounts of _SiO2 , MnO, _{Al2O3 ,} MgO, _TiO2 , FeO, _CaF2 , and the sum of one or _two of _Na2O and K2O I found out that it would be better.

In addition, in order to improve the toughness of the weld metal of the fillet weld by high heat input welding, it can be achieved by optimizing the amount of SiO ₂ , MgO and TiO ₂ and the basicity and bulk density of the flux. I found

Furthermore, by including an appropriate amount of Bi ₂ O ₃ instead of some of the above components _, the slag _removability can be further improved. It has been found that the weld metal toughness of the fillet weld by heat welding can be better.

Hereinafter, the components (flux components) of the molten flux for fillet submerged arc welding of the present disclosure (sometimes referred to as "molten flux" or simply "flux" in the present disclosure) and the reasons for limiting the composition etc. explain. The content of each component composition is represented by mass % with respect to the total mass of the flux, and the mass % is simply described as %.
In addition, when only the upper limit is limited to "~% or less" without limiting the lower limit of the content, the component may not be included, that is, 0%, or the range of more than 0% to the upper limit means that it may be contained within

[SiO ₂ : 35-45%]
SiO ₂ made from silica sand, wollastonite, etc. adjusts the viscosity of the molten slag to improve the bead shape. If the SiO ₂ content is less than 35%, the viscosity of the molten slag is insufficient, causing meandering and undercut of the bead, resulting in a poor bead shape. On the other hand, if _SiO2 exceeds 45%, the oxygen content of the weld metal increases and the toughness decreases. Therefore, SiO ₂ should be 35-45%.

[MnO: 18-28%]
MnO, which is made from manganese oxide, roasted manganese, etc., is an effective component for adjusting the viscosity of molten slag and the slag releasability. However, if the MnO content is less than 18%, the molten slag becomes highly viscous and sticks to the beads, resulting in poor slag releasability. On the other hand, when MnO exceeds 28%, the molten slag becomes less viscous, causing overlap and undercut. Therefore, MnO should be 18-28%.

[Al ₂ O ₃ : 6 to 20%]
Al ₂ O ₃ made from alumina or the like is an effective component for adjusting the viscosity of molten slag. If the Al ₂ O ₃ content is less than 6%, the viscosity of the molten slag becomes low and undercuts are likely to occur. On the other hand, if Al ₂ O ₃ exceeds 20%, the molten slag becomes too viscous and the bead becomes convex. Therefore, Al ₂ O ₃ should be 6 to 20%.

[MgO: 11-16%]
MgO made from magnesia clinker or the like adjusts the viscosity of the molten slag to improve the bead shape. MgO also reduces the amount of oxygen in the weld metal and improves toughness. If the MgO content is less than 11%, the viscosity of the molten slag becomes insufficient, causing meandering and undercutting of the beads. On the other hand, if the MgO content is less than 11%, the amount of oxygen in the weld metal increases and the toughness decreases. On the other hand, if the MgO content exceeds 16%, the bead width becomes narrow and hot cracks are likely to occur. Therefore, MgO should be 11 to 16%.

[ _TiO2 : 2 to 6%]
TiO ₂ made from rutile, titanium oxide, etc. is effective in obtaining smoothness of the bead surface. Moreover, TiO ₂ is a very effective component for improving the toughness by acting as nuclei for acicular ferrite in the weld metal and promoting refinement of the weld metal structure. Below 2% TiO ₂ the bead toe spread is discontinuous. Also, if TiO ₂ is less than 2%, the toughness of the weld metal decreases. On the other hand, if _TiO2 exceeds 6%, the slag is seized and the slag removability deteriorates. Therefore, TiO ₂ should be 2-6%.

[FeO: 0.5 to 4%]
FeO, which is made from mill scale or the like, adjusts the viscosity and melting point of the molten slag, improves the conformability of the bead toe, and improves the bead shape. If the FeO content is less than 0.5%, the bead toe will not conform well and the bead shape will be poor. On the other hand, if FeO exceeds 4%, the slag is seized and the slag removability deteriorates. Therefore, FeO should be 0.5 to 4%.

[ _CaF2 : 5-9%]
_CaF2 , which is made from fluorite or the like, has the effect of adjusting the fluidity of molten slag and improving the slag releasability. If the _CaF2 content is less than 5%, the slag is seized to the bead, resulting in poor slag removability. On the other hand, if the _CaF2 content exceeds 9%, the fluidity of the slag increases, causing overlaps and undercuts, as well as an increase in the gas component to generate pockmarks. Further, when CaF ₂ exceeds 9%, fillet welding at a high current and a high speed results in a convex bead, which is likely to cause hot cracks. Therefore, CaF ₂ should be 5-9%.

[Total of one or two of Na ₂ O and K ₂ O: 0.5 to 1.0%]
Na ₂ O and K ₂ O, which are made from sodium carbonate, potassium carbonate, etc., are effective components for improving the arc stability, making the bead finer, and improving the bead appearance. If the total content of one or two of Na ₂ O and K ₂ O is less than 0.5%, the arc becomes unstable and the bead becomes rough and poor in appearance. On the other hand, when the total content of one or two of Na ₂ O and K ₂ O exceeds 1.0%, undercuts tend to occur. Therefore, the total content of one or two of Na ₂ O and K ₂ O should be 0.5 to 1.0%.

[Basicity A: 0.50 to 1.00]
The basicity A obtained from the following formula (1) for each component adjusts the viscosity of the molten slag. Also, the amount of oxygen in the weld metal is reduced to improve the toughness. If the basicity A is less than 0.50, the amount of oxygen in the weld metal increases and the toughness decreases. On the other hand, when the basicity A exceeds 1.00, the viscosity of the slag becomes high and the slag removability deteriorates. Therefore, the basicity A determined from the following formula (1) should be 0.50 to 1.00.
A=([ _CaF2 ]+[MgO]+0.5([MnO]+[FeO]))/([ _SiO2 ]+0.5 ₍ [ _Al2O3 ]+[ _TiO2 ]))...(1 ) where [ ] indicates mass % of each component with respect to the total mass of the flux.

[Bulk density of flux: 0.8 to 1.3 g/cm ³ ]
The bulk density of the flux measured according to JIS K-6720 affects the shielding properties of the molten pool from the atmosphere and the spread of the weld bead during welding. If the bulk density of the flux is less than 0.8 g/cm ³ , shielding during welding becomes insufficient, nitrogen and oxygen in the weld metal increase, and toughness decreases. On the other hand, when the bulk density of the flux exceeds 1.3 g/cm ³ , the bead does not spread and undercut occurs. Therefore, the density of the flux should be 0.8 to 1.3 g/cm ³ .

The manufacturing method for adjusting the bulk density of the flux includes cooling the molten flux in hot water in the flux manufacturing process and foaming the flux by slowing the cooling rate, and cooling the molten flux in a jet water stream. The bulk density of the flux can be adjusted by forming a flux in which acicular, deer-antler, spherical and scaly particles are mixed.

The bulk density of flux is measured according to JIS K6720.
Bulk density (g/cm ³ ) = (mass of receiver containing sample (g) - mass of receiver (g))/inner volume of receiver (cm ³ )

Moreover, as a method of adjusting the particle size of the flux, for example, there is a method of directly applying jet water to the molten flux (melt). The particle size of the flux can be adjusted by controlling the water pressure, the amount of water, and the amount of the flux in the molten state to granulate and siev the flux.

[ _Bi2O3 : _0.05 % or less]
Bi ₂ O ₃ made from bismuth oxide or the like has the effect of improving the slag removability. However, when Bi ₂ O ₃ exceeds 0.05%, the toughness of the weld metal deteriorates. Therefore, Bi ₂ O ₃ should be 0.05% or less. Incidentally, although the addition of a very small amount of Bi ₂ O ₃ has the effect of improving the slag removability, it is preferable to make the content 0.001% or more in order to obtain the effect.

The remainder of the molten flux for fillet submerged arc welding of the present disclosure is impurities such as CaO, BaO, P and S, which are contained in trace amounts in the raw material, and the total content of these can be 3% or less.
Note that the molten flux for fillet submerged arc welding of the present disclosure may contain predetermined amounts of B ₂ O ₃ , CaO, and/or BaO instead of some of the flux components described above.

[B ₂ O ₃ : 1.5% or less]
B ₂ O ₃ whose raw material is boron oxide or the like has the effect of improving the toughness of the weld metal. However, when B ₂ O ₃ exceeds 1.5%, the toughness of the weld metal deteriorates. Therefore, when B ₂ O ₃ is included, it is made 1.5% or less. B ₂ O ₃ has the effect of improving the toughness of the weld metal, and in order to obtain the effect, it is preferably 0.01% or more.

[CaO: 5.0% or less]
CaO, which is made from calcium oxide or the like, has the effect of improving the toughness of the weld metal. However, above 5.0% CaO, the beads become convex. Therefore, when CaO is included, it is made 5.0% or less. In addition, CaO has the effect of improving the toughness of the weld metal, and in order to obtain the effect, it is preferably 0.01% or more.

[BaO: 5.0% or less]
BaO made from barium oxide or the like has the effect of improving the toughness of the weld metal. However, when BaO exceeds 5.0%, the beads become convex. Therefore, when BaO is included, it is made 5.0% or less. BaO has the effect of improving the toughness of the weld metal, and in order to obtain the effect, it is preferably 0.01% or more.

Although the particle size of the flux is not particularly limited, it is preferable that 90% or more of the flux particles have a particle size in the range of more than 0.3 mm to 1.4 mm. The particle size of the flux is measured by the method described later as an example.

Hereinafter, the effects of the molten flux according to the present disclosure will be specifically described with reference to examples.

<Example 1>
A molten flux having each component composition, basicity A, and bulk density shown in Table 1 was experimentally produced, and under the two-electrode submerged arc welding conditions shown in Table 2, a wire diameter of 4.8 mm of JIS Z3351 YS-S6 shown in Table 4. Welding tests were performed using steel plates of JIS G3136 SN490B having a plate thickness of 25 mm and 16 mm shown in Table 3.
As for the groove shape, for a steel plate with a thickness of 25 mm, as shown in FIG. A test piece 10 was produced by welding both sides by downward fillet submerged arc welding with the prototype flux. For a steel plate with a thickness of 16 mm, as shown in FIG. A test piece 11 was produced by welding both sides by arc welding.

The particle size of the flux was regulated through a 0.3 mm sieve mesh and a 1.4 mm sieve mesh.

The remainder of the flux component composition in Table 1 is CaO, BaO, P, S, etc. mixed as impurities from the raw material. In addition, underlines in the table indicate that they are outside the scope of the present disclosure.

Welding workability was evaluated by examining arc stability, bead shape (bead meandering, undercut, overlap, bead spread, etc.), slag exfoliation, and hot cracking.

Arc stability was judged to be good if the welding voltage fluctuation during welding was within ±5V.

For the bead shape, measure the bead width at 10 points from the weld bead sound part, and if the difference between the minimum value and the maximum value is within 8 mm and there are no weld defects (bead meandering, undercut, overlap, etc.), it is considered good. did.

Slag removability was determined by removing the slag with a brush because the slag naturally detached after welding, estimating the area of residual slag that could be visually confirmed, and determining a slag detachment rate of 98% or more as good. In addition, the area of residual slag that can be visually confirmed in the range of 30 cm of the sound bead portion was estimated, and the slag peeling rate of 100% was regarded as extremely good.

As shown in FIG. 2, the mechanical properties were measured from the welded test piece 12 consisting of the web steel plate 1 and the flange steel plate 2 having a steel plate thickness of 25 mm, from the center part of the fillet weld metal 20 to the Charpy impact test piece 3 (JIS Z2202 No. 4). was collected and evaluated. The Charpy impact test was repeated three times at a test temperature of 0° C., and an average value of absorbed energy of 50 J or more was considered good. These results are summarized in Table 5. In Table 5, regarding the test specimens shown in FIG. 1, the plate thickness of 25 mm shown in FIG. is "b".

In Tables 1 and 5, flux symbols F1 to F10 are examples of the present invention, and flux symbols F11 to F22 are comparative examples. Flux symbols F1 to F10, which are examples of the present invention, are appropriate amounts of one or two of SiO ₂ , MnO, Al ₂ O ₃ , MgO, TiO ₂ , FeO, CaF ₂ , Na ₂ O and K ₂ O. , Since the basicity A and the bulk density of the flux are appropriate, in downward fillet welding with a plate thickness of 25 mm and without groove processing with a plate thickness of 16 mm, the arc is stable and the bead meanders and undercuts. The bead shape was good with no overlap, convex bead, etc., the slag releasability was good, hot cracks did not occur, and the absorbed energy of the weld metal was high. Flux symbols F2, F3, F6, F8 and F10 containing an appropriate amount of Bi ₂ O ₃ exhibited extremely good slag removability.

Flux symbol F11 in the comparative example had a small amount of SiO ₂ , so that the bead meandered and undercut occurred both with and without groove processing. Also, since the amount of CaF ₂ was small, slag was seized and the slag removability was poor.

Flux symbol F12 had a large amount of _SiO2 , so the absorbed energy of the weld metal was low. In addition, since the FeO content was low, the bead toe did not conform well and the bead shape was poor.

Flux F13 had a small amount of MnO, so the slag seized and the slag removability was poor. In addition, since the total amount of one or two of Na ₂ O and K ₂ O was small, the arc was unstable and the bead had rough wavy lines, resulting in poor appearance.

Flux symbol F14 was rich in MnO, so overlap and undercut occurred. In addition, since the FeO content was large, the slag seized and the slag removability was poor.

Flux symbol F15 had less Al ₂ O ₃ and therefore undercut. In addition, since TiO ₂ was large, slag was seized and the slag removability was poor.

Flux symbol F16 had a large amount of Al ₂ O ₃ and therefore had a convex bead. Also, since the basicity A was low, the absorbed energy of the weld metal was low.

Flux symbol F17 had a small amount of MgO, so the bead meandered and undercut occurred both with and without groove processing. Also, since the amount of MgO was small, the absorbed energy of the weld metal was low.

Since the flux symbol F18 contained a large amount of MgO, the bead width was narrow and crater cracks occurred. Also, since the bulk density of the flux is small, the absorbed energy of the weld metal is low.

Flux symbol F19 had less _TiO2 , so the bead toe spread was discontinuous. Also, since the TiO ₂ content was low, the absorbed energy of the weld metal was low. Furthermore, since the basicity A was high, the slag removability was poor.

Since the flux symbol F20 has a large amount of _CaF2 , overlaps, undercuts and pockmarks occurred, and the bead became convex and crater cracks occurred. Also, since the amount of Bi ₂ O ₃ was large, the absorbed energy of the weld metal was low.

Flux symbol F21 had a high content of one or two of Na ₂ O and K ₂ O, resulting in an undercut.

For the flux symbol F22, since the bulk density of the flux was high, the bead width was narrow and undercut occurred both with and without groove processing.

<Example 2>
A molten flux having the component composition, basicity A, bulk density, and particle size (mass ratio of particle size exceeding 0.3 mm to 1.4 mm) shown in Table 6 was experimentally produced.
The remainder of the flux component composition in Table 6 is P, S, etc. mixed as impurities from the raw material.

The particle size of the flux is regulated on a 0.3 mm sieve mesh under a 1.4 mm sieve mesh, and then JIS Z3352: 2017 "6.3 Flux particle size test" in flux for submerged arc welding and electroslag welding. Measured according to A sieve with a nominal opening (300 μm and 1.4 mm) corresponding to JIS Z 8801-1:2019 “Test sieve-Part 1: Metal mesh sieve” is used, and the sieving time is 4 minutes. Perform mechanical sieving according to JIS Z8815:1994 "General rules for sieving test methods", and use a low-tap sieve shaker as a measuring instrument. 200 g of flux is used for the test. In such a flux particle size test, the flux that passes through a sieve with a nominal opening of 1.4 mm and does not pass through a sieve with a nominal opening of 300 μm is a flux with a particle size of more than 0.3 mm to 1.4 mm.

The flux symbols F31 and F32 used the same raw material and the same flux component, but the particle size and bulk density were adjusted by changing the pulverization conditions and sieving time when the flux was prototyped.

In the same manner as in Example 1 except that the flux symbols F31 to F38 were used, a test piece 10 was welded on both sides by downward fillet submerged arc welding as shown in FIG. Mechanical properties were evaluated. Table 7 shows the results.

Flux symbols F31 to F38, which are examples of the present invention, all contain one or two of SiO ₂ , MnO, Al ₂ O ₃ , MgO, TiO ₂ , FeO, CaF ₂ , Na ₂ O and K ₂ O. Since it is an appropriate amount, the basicity A and the bulk density of the flux are also appropriate, in downward fillet welding with groove processing with a plate thickness of 25 mm, the arc is stable and bead meandering, undercut, overlap and convex bead A good bead shape was obtained without any slag peelability, no hot cracking occurred, and a high absorbed energy of the weld metal was obtained.

Although the flux symbols F31 and F32 have the same components, the flux symbol F31, in which 90% or more of the flux particles have a particle size in the range of more than 0.3 mm to 1.4 mm, has better slag removability. The energy absorption of the weld metal was high, and the toughness was excellent.
Flux codes F33 to F38 contain an appropriate amount of at least one of B ₂ O ₃ , CaO and BaO in addition to the above components, and the absorbed energy of the weld metal is higher than when flux code F31 is used. The toughness was even better.

1 web steel plate 2 flange steel plate 3 Charpy impact test piece 10, 11 test piece 12 welding test piece 20 fillet weld metal

Claims (5)

% by mass of the total mass of the flux,
_SiO2 : 35-45%,
MnO: 18-28%,
Al ₂ O ₃ : 6-20%,
MgO: 11-16%,
_TiO2 : 2-6%,
FeO: 0.5-4%,
CaF ₂ : 5 to 9%, and one or two of Na ₂ O and K ₂ O combined: 0.5 to 1.0%
and having a flux component in which the balance is impurities,
The basicity A determined from the following formula (1) is 0.50 to 1.00,
The flux has a bulk density of 0.8 to 1.3 g/cm ³ ,
Hot-melt flux for fillet submerged arc welding.
A=([ _CaF2 ]+[MgO]+0.5([MnO]+[FeO]))/([ _SiO2 ]+0.5 ₍ [ _Al2O3 ]+[ _TiO2 ]))...(1 ) where [ ] indicates mass % of each component with respect to the total mass of the flux. 2. The hot-melt flux for fillet submerged arc welding according to claim 1, wherein 90% or more of the flux particles have a particle size in the range of more than 0.3 mm to 1.4 mm in mass % with respect to the total mass of the flux. Instead of a part of the flux component, in mass% with respect to the total mass of the flux,
Bi ₂ O ₃ : The molten flux for fillet submerged arc welding according to claim 1 or 2, containing 0.05% or less. Instead of a part of the flux component, in mass% with respect to the total mass of the flux,
B ₂ O ₃ : The molten flux for fillet submerged arc welding according to any one of claims 1 to 3, containing 1.5% or less. Instead of a part of the flux component, in mass% with respect to the total mass of the flux,
The molten flux for fillet submerged arc welding according to any one of claims 1 to 4, containing one or both of CaO: 5.0% or less and BaO: 5.0% or less.

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