JP7717509B2 - Fusible flux for submerged arc welding - Google Patents

Description

This disclosure relates to a molten flux for submerged arc welding used when welding steel structures.

Submerged arc welding is a welding method in which granular flux is spread along the weld in advance, a welding wire is continuously fed into the flux, and an arc is generated between the material to be welded and the tip of the welding wire while it is covered in flux. After welding, the flux is generally recovered, except for any slag that has formed, and is then repeatedly used by replenishing new flux. For this reason, repeated flux recovery can cause the particles to break down due to collisions and friction between the flux particles, resulting in a powdering phenomenon in which the particles turn into a fine powder.

The particle size of flux is designed to be controlled within a certain range so that gases generated during welding can escape properly. However, if the amount of fine powder increases, gas escape becomes poor, causing poor appearance (pockmarks) due to depressions on the bead surface, and depending on the atmospheric conditions, it can absorb moisture from the air and cause welding defects such as blowholes and weld cracks.
In particular, foamable molten flux has excellent welding workability, such as a stable arc, good slag removability, and good bead appearance. However, the particles are porous and have a large specific surface area, making them prone to powdering. This not only causes the flux to lose its properties but also degrades welding workability.

To address these issues, Patent Document 1, for example, proposes a technology that improves the resistance of flux to powdering by mixing a glass-based melting flux and a pumice-based melting flux in weight ratios of 10 to 90% and 90 to 10%, respectively.

Japanese Unexamined Patent Publication No. 56-165593

However, when producing the fusion-type flux disclosed in Patent Document 1, the manufacturing methods for the glassy fusion-type flux and the pumice-based fusion-type flux are different, and further particle size adjustment, measuring, and mixing processes are required, resulting in poor flux productivity and high manufacturing costs. Furthermore, the powdering resistance of the pumice-based fusion-type flux has not been improved, so when the weight ratio of the pumice-based fusion-type flux is high, the powdering suppression effect is insufficient.

The present disclosure was conceived in consideration of the above-mentioned problems, and aims to provide a molten flux for submerged arc welding that has excellent welding workability, such as arc stability, slag removability, and bead shape, and that is resistant to powdering even when the flux is recovered after welding and used repeatedly.

The gist of the present disclosure for solving the above problems is as follows.
<1> Mass% relative to the total mass of the flux
SiO ₂ :30-55%,
Al ₂ O ₃ : 6-20%,
Contains MgO: 5 to 20%, and FeO: 0.5 to 5%,
the average area ratio of the olivine-type crystal phase on the surface of the flux particles is 0.01 to 20%;
Fusible flux for submerged arc welding.
<2> The molten flux for submerged arc welding according to <1>, wherein flux particles having a particle size in the range of more than 0.3 to 1.4 mm account for 90 mass% or more of the total mass of the flux.
<3> The molten flux for submerged arc welding according to <1> or <2>, having a bulk density of 0.6 to 1.3 g/cm ³ .

This disclosure provides a molten flux for submerged arc welding that has excellent welding workability, including arc stability, slag removability, and bead shape, and that is resistant to powdering even when the flux is recovered after welding and used repeatedly.

FIG. 1 is a schematic diagram showing a dusting measurement test method used in the examples of the present disclosure.

Hereinafter, an embodiment that is an example of the molten flux for submerged arc welding according to the present disclosure (sometimes referred to as "molten flux" or simply "flux" in the present disclosure) will be described, but the molten flux for submerged arc welding according to the present disclosure is not limited to the embodiment described below.
In the present disclosure, when a numerical range expressed using "to" is not preceded or followed by "greater than" or "less than," it means a range that includes these numerical values as the lower and upper limits. When "to" is preceded or followed by "greater than" or "less than," it means a range that does not include these numerical values as the lower or upper limit.
In the present specification, the upper limit of a numerical range described in stages may be replaced by the upper limit of another numerical range described in stages or by a value shown in an example. Also, the lower limit of a numerical range may be replaced by the lower limit of another numerical range described in stages or by a value shown in an example.
With respect to the content, "%" means "% by mass" unless otherwise specified.
Furthermore, when the content (%) is specified with only an upper limit, such as "not more than ...", without specifying a lower limit, it means that the content may be in the range from more than 0% to the upper limit.

To solve the above-mentioned problems, the inventors conducted extensive research into the effects of flux particle size, bulk density, crystalline structure, and chemical components on flux pulverization and welding workability. As a result, they discovered that it is extremely effective to limit the flux components and particle size and include a specified amount of olivine-type crystalline phase in the flux.

<Fused flux for submerged arc welding>
The molten flux for submerged arc welding according to the present disclosure comprises:
In mass % relative to the total mass of the flux,
SiO ₂ :30-55%,
_Al2O3 : _6-20 %,
Contains MgO: 5 to 20%, and FeO: 0.5 to 5%,
The average area ratio of the olivine type crystal phase on the surface of the flux particles is 0.01 to 20%.

[Component composition]
The reasons for limiting the component composition of the molten flux for submerged arc welding according to the present disclosure will be explained below. Note that the content of each component in the present disclosure is expressed as mass% relative to the total mass of the flux, and is simply expressed as %.
The molten flux for submerged arc welding according to the present disclosure contains SiO _{2 ,} Al ₂ O ₃ , MgO, and FeO as essential components.

[SiO ₂ :30-55%]
_SiO2 , derived from silica sand, wollastonite, and other raw materials, adjusts the viscosity of the molten slag and improves the bead shape. If _{the SiO2} content is less than 30%, the molten slag will not have enough viscosity, making welding defects such as undercuts and slag inclusions more likely to occur. On the other hand, if the _SiO2 content exceeds 55%, the slag will have too high a viscosity, resulting in a poor bead shape. Therefore, the _SiO2 content is set to 30 to 55%, preferably 35 to 50%.

[Al ₂ O ₃ : 6-20%]
Al ₂ O ₃ , derived from alumina and other raw materials, is an effective component for adjusting the viscosity of the molten slag. If the Al ₂ O ₃ content is less than 6%, the viscosity of the molten slag will be low, making undercutting more likely to occur. On the other hand, if the Al ₂ O ₃ content exceeds 20%, the viscosity of the molten slag will be too high, causing the bead to become convex. Therefore, the Al ₂ O ₃ content should be 6 to 20%, preferably 6 to 15%.

[MgO: 5-20%]
MgO, derived from magnesia clinker, magnesia oxide, and other raw materials, adjusts the viscosity of the molten slag and improves the bead shape. If the MgO content is less than 5%, the molten slag will not have sufficient viscosity, resulting in meandering or undercutting of the bead. On the other hand, if the MgO content exceeds 20%, the bead width will become discontinuous. Therefore, the MgO content is set to 5 to 20%, preferably 10 to 20%.

[FeO: 0.5-5%]
FeO, derived from mill scale and other raw materials, improves the bead shape by adjusting the viscosity and melting point of the molten slag. It also has the effect of improving pockmark resistance. If FeO is less than 0.5%, the bead tends to meander and pockmarks tend to occur. On the other hand, if FeO exceeds 5%, the slag seizes and slag removability deteriorates. Therefore, the FeO content is set to 0.5 to 5%, preferably 1 to 4%.

In addition to the essential components described above, the flux disclosed herein may optionally contain, for example, the following components, as needed:

[MnO: 18-28%]
MnO, derived from manganese oxide, roasted manganese, etc., is an effective component for adjusting the viscosity and slag removability of molten slag. To achieve this effect, the content is set to 18% or more. However, excessive MnO content deteriorates the bead shape, so the upper limit is set to 28%. The preferred range is 20 to 26%.

[TiO ₂ :2-6%]
_TiO2 , derived from raw materials such as rutile and titanium oxide, is effective in achieving smoothness on the bead surface. To achieve this effect, 2% or more is added. However, excessive _TiO2 content deteriorates slag removability, so the upper limit is set at 6%. Preferably, it is 3 to 5%.

[ _CaF2 : 5-9%]
_CaF2 , derived from fluorite and other raw materials, has the effect of adjusting the fluidity of the molten slag and improving slag removability. To achieve this effect, 5% or more is added. However, excessive _CaF2 content increases the gas content and causes pockmarks, so the upper limit is set at 9%. Preferably, it is 5 to 8%.

[Total of one or both of Na ₂ O and K ₂ O: 0.5 to 2.0%]
Na ₂ O and K ₂ O, which are derived from sodium carbonate and potassium carbonate, have the effect of improving arc stability. To achieve this effect, one or both of Na ₂ O and K ₂ O are contained in a total amount of 0.5% or more. On the other hand, since an excessive content of Na ₂ O and/or K ₂ O deteriorates the bead shape, the upper limit of the total amount of one or both of Na ₂ O and K ₂ O is set to 2.0%, and may be 1.8%.

[Bi ₂ O ₃ : 0.05% or less]
_{Bi2O3 ,} derived from bismuth oxide and the like, has the effect of improving slag removability. If _Bi2O3 is 0.05% or less, deterioration of the toughness of the weld metal is suppressed. Therefore, it is preferable that _Bi2O3 be 0.05% or less. Note that even a small amount of _Bi2O3 can have the effect of improving slag removability, but to obtain this effect _, it is preferable that the _{Bi2O3 content} be 0.001% or more.

[B ₂ O ₃ : 1.5% or less]
_{B2O3 ,} derived from boron oxide or the like, has the effect of suppressing the growth of pro-eutectoid ferrite formed at the _austenite grain boundaries of the weld metal, thereby improving toughness. If _B2O3 is 1.5% or less, the deterioration of the weld metal due to hot cracking is suppressed. Therefore, it is preferable that _B2O3 be _1.5 % or less. Note that even a small amount of _{B2O3 can} have the effect of improving the toughness of the weld metal, but to obtain this effect, it is preferable that the amount be 0.01% or more.

[CaO: 5.0% or less]
CaO, derived from calcium oxide and the like, has the effect of improving the toughness of the weld metal. If the CaO content is 5.0% or less, deterioration of the bead shape is suppressed. Therefore, it is preferable that the CaO content be 5.0% or less. Note that even a small amount of CaO can have the effect of improving the toughness of the weld metal, but to obtain this effect, it is preferable that the CaO content be 0.01% or more.

[BaO: 5.0% or less]
BaO, derived from barium oxide and the like, has the effect of improving the toughness of the weld metal. If BaO is 5.0% or less, deterioration of the bead shape is suppressed. Therefore, it is preferable that BaO be 5.0% or less. Note that even a small amount of BaO can have the effect of improving the toughness of the weld metal, but to obtain this effect, it is preferable that the BaO content be 0.01% or more.

The remainder of the molten flux disclosed herein consists of impurities such as P and S contained in trace amounts in the raw materials.

[Particle size]
Next, the particle size of the flux will be described. The content of the flux based on the particle size is also expressed as mass % relative to the total mass of the fused flux according to the present disclosure, and is simply referred to as %.

Flux particles with a particle size of more than 0.3 mm to 1.4 mm are important for forming a stable bead shape. Furthermore, such flux particles are effective in improving slag removability. If 90% or more of the flux particles have a particle size of more than 0.3 mm to 1.4 mm, the bead shape is prevented from becoming convex, gas escape is prevented from becoming poor, and pockmarks are less likely to occur. Furthermore, the flux is less likely to pulverize. For this reason, the flux disclosed herein preferably contains flux particles with a particle size of more than 0.3 mm to 1.4 mm in total mass, with a total content of these particles being 90% or more. This is preferably 95% or more. The content of particles with a particle size of 0.3 mm or less is not particularly limited as long as it is 10% or less, but the lower the content of particles with a particle size of 0.3 mm or less and particles with a particle size of over 1.4 mm, the better.

The particle size of flux particles is measured in accordance with "6.3 Flux Particle Size Test" in JIS Z3352:2017 Fluxes for Submerged Arc Welding and Electroslag Welding. Sieves with nominal openings (300 μm and 1.4 mm) equivalent to those in JIS Z8801-1:2019 "Test Sieves - Part 1: Metallic Wire Sieves" are used, and the sieving time is 4 minutes. Mechanical sieving is performed in accordance with JIS Z8815:1994 "General Rules for Sieving Test Methods," using a low-tap sieve shaker as the measuring device. 200 g of flux is used for the test. In such flux particle size tests, flux particles that pass through a sieve with a nominal opening of 1.4 mm but do not pass through a sieve with a nominal opening of 300 μm are flux particles with a particle size of more than 0.3 mm to 1.4 mm.

[Average area ratio of olivine-type crystal phase]
Next, the average area ratio of the olivine crystals on the surface of the flux particles will be described.
Olivine is the English name for olivine, and is generally expressed by _{the chemical formula (Mg.Fe)2.SiO4 ,} and is a solid solution with forsterite ( _Mg2SiO4 ) and fayalite ( _Fe2SiO4 ) as _its end components. When an olivine-type crystal phase is generated in a molten flux, it is thought that the glassy portion provides a reinforcing effect and has the effect _of suppressing powdering.
However, if the average area fraction of the olivine crystals is less than 0.01%, this effect cannot be obtained. On the other hand, since the melting point of olivine is as high as 1557°C, if the average area fraction of the olivine crystals exceeds 20%, slag inclusion occurs. Therefore, in the molten flux for submerged arc welding according to the present disclosure, the average area fraction of the olivine crystal phase in the flux particles is set to 0.01 to 20%, preferably 1 to 15%.

The olivine-type crystal phase has a structure of (Mg.Fe) _{2.SiO4 and} is easily distinguishable from the surrounding glass because its composition is different. The area ratio of the olivine-type crystal phase in the flux particles is measured as follows.

Random particles were selected from the flux particles, embedded in resin, mirror-polished, and vapor-deposited with carbon to ensure conductivity. A JEOL Ltd. WD/ED Combined Electron Probe Microanalyzer (EPMA) JXA 8230 was then used to analyze a specified field of view at an acceleration voltage of 15 kV and a probe current of 2 × 10 ⁻⁸ A (magnification: 3000x, field of view: 30 μm × 30 μm, total number of analysis areas: 65,536). Then, for each field of view, the number of analysis areas in which the concentrations of the olivine constituent elements Mg, Si, Fe, and O were detected to be above their respective averages was calculated. The area ratio of the olivine-type crystalline phase was calculated by dividing the calculated number of analysis areas by the total number of analysis areas (65,536).
This analysis is performed on 10 flux particles, and the area ratio of the olivine-type crystalline phase in each particle is calculated. The average value of the area ratios of the olivine-type crystalline phase is then determined to be the average area ratio of the olivine-type crystalline phase in the flux particles that make up the flux.

[Bulk density]
The bulk density of the flux affects the shielding of the molten pool from the atmosphere and the spread of the weld bead during welding. If the bulk density of the flux is 0.6 g/ ^cm3 or higher, the flux blow-up phenomenon is less likely to occur, and the occurrence of pockmarks due to insufficient shielding is suppressed. On the other hand, if the bulk density of the flux is 1.3 g/ ^cm3 or lower, the bead is less likely to spread, and the occurrence of undercut is suppressed. Therefore, the bulk density of the flux according to the present disclosure is preferably 0.6 to 1.3 g/ ^cm3 . A more preferable range is 0.6 to 1.2 g/ ^cm3 .
The bulk density of the flux can be measured in accordance with JIS K5101-12-1:2004.
Bulk density (g/cm ³ )=(mass of receiver containing sample (g)−mass of receiver (g))/internal volume of receiver (cm ³ )

<Method for manufacturing fused flux for submerged arc welding>
Next, a method for producing the molten flux for submerged arc welding according to the present disclosure will be described.
The manufacturing method of the molten flux according to the present disclosure is not particularly limited as long as the components, particle size, and average area ratio of the olivine crystal phase are within the ranges of the present disclosure. For example, the flux can be manufactured by blending raw materials so as to contain the components described above, heating in an electric furnace or the like to melt the flux, cooling it with water, and then pulverizing it.

The average area ratio of the olivine crystal phase in flux particles depends on manufacturing conditions such as the raw materials and cooling rate. For example, the average area ratio of the olivine crystal phase can be adjusted by melting raw materials containing relatively easily reduced oxides of elements such as Mn and Si together with a reducing agent (C, Al, etc.) at high temperatures (e.g., 1300-1700°C).

Another method for adjusting the particle size of the flux is to impact the melt with a jet of water. The particle size of the flux can be adjusted by controlling the water pressure, water volume, and amount of molten flux to granulate it and then sieving it.

In addition, methods for adjusting the bulk density of the flux include mixing the various raw materials of the flux and melting them in an electric furnace, then cooling the molten flux in hot water to slow the cooling rate and foam the flux, or cooling the molten flux in a jet of water to create a flux containing a mixture of acicular, antler-shaped, spherical, and scale-shaped particles.

The effects of this disclosure will be explained in more detail below using examples, but this disclosure is not limited to the following examples.

[Production of fused flux for submerged arc welding]
Melt-type fluxes having the various components, particle sizes, and bulk densities shown in Table 1 were produced as prototypes.
The fused fluxes shown in Table 1 were prepared by melting various mineral raw materials, cooling them, pulverizing them into powder, and then sieving them to particle sizes of 300 μm to 1.4 mm. The remainder of the flux components are P, S, etc., which are inevitably mixed in from the raw materials. In Table 1, underlines indicate values outside the scope of this disclosure. "0,""0.0," or "0.00" means that the component is not included (not added).

(Production of fused flux F1)
The raw materials were blended and mixed to obtain the composition shown in Table 1 as flux symbol F1, and heated to 1350°C in an electric furnace to form a molten flux (melt), which was then poured into a large amount of water and cooled. The temperature of the cooling water before pouring the molten flux was set to 20°C. After water cooling, the particle size was adjusted by crushing and sieving.

(Production of fused fluxes F2 to F20)
Fusible fluxes F2 to F20 were produced in the same manner as for fusible flux F1, except that the blending of the raw materials was changed so as to have the components shown in Table 1.

(Production of fused fluxes F21 to F28)
Fusible fluxes F21 to F28 were produced in the same manner as for fusible flux F1, except that the blending of the raw materials was changed so as to have the components shown in Table 1.

(Production of fused flux F29)
The composition of the raw materials was changed to obtain the components shown in Table 1, and the flux was heated to 1200°C in an electric furnace to form a molten flux (melt), which was then poured into a large amount of water and cooled. Otherwise, fusion-type flux F29 was produced in the same manner as fusion-type flux F1.

(Production of fused flux F30)
The composition of the raw materials was changed to obtain the components shown in Table 1, and the flux was heated to 1800°C in an electric furnace to form a molten flux (melt), which was then poured into a large amount of water and cooled. Otherwise, fusion-type flux F30 was produced in the same manner as fusion-type flux F1.

[measurement]
The average area ratio, particle size, and bulk density of the olivine type crystal phase of each of the fluxes produced as described above were measured by the methods described above.

(Average area ratio of olivine-type crystal phase)
Ten particles were randomly selected from each flux, and a 30 μm × 30 μm field of view was randomly selected for each particle and subjected to EPMA elemental mapping analysis. The average area ratio of the olivine-type crystal phase to the total area of the observed field was measured. This is shown as the "olivine area ratio" in Table 1.

(particle size)
For each flux, a low-tap type sieve shaker (manufactured by Ito Seisakusho Co., Ltd., trade name: Low-tap type sieve shaker S type) was used to measure the mass ratio (%) of flux particles with particle sizes of more than 0.3 mm to 1.4 mm by a method in accordance with JIS Z8815:1994 "General rules for sieving test methods."

(Bulk density)
The bulk density of each flux was measured by the method in accordance with JIS K5101-12-1:2004.

[evaluation]
Submerged arc welding was performed using the prototype fused flux. Specifically, under the welding conditions shown in Table 2, a 4.8 mm diameter solid wire conforming to JIS Z3351 YS-S6:2012 shown in Table 4 and a 16 mm thick steel plate conforming to JIS G3136:2012 SN490B shown in Table 3 were used to evaluate the welding workability by bead-on-plate welding. Note that components other than those shown in Tables 3 and 4 are Fe and impurities.
In order to evaluate the state of powdering of the flux, the flux remaining after the completion of welding was collected using a flux collection device (VC-661 type, AC200V) manufactured by Daihen Corporation, and welding was repeated 10 times using the collected flux according to the method shown in Figure 1, after which the particle size of the flux after the 10th welding was measured.

(Welding workability)
The welding workability was evaluated by examining arc stability, slag removability, bead shape (presence or absence of undercuts, pits, pockmarks, irregularities on the bead surface), and the presence or absence of blowholes.
The arc stability was evaluated as "stable" if the welding voltage fluctuation during welding was within ±5V.
As the slag peels off naturally after welding, the slag was removed with a brush and the area of the remaining slag that could be visually confirmed was estimated. A slag peeling rate of 95% or more was rated as "good," and a rate of 98% or more was rated as "very good."
Regarding irregularities of the bead surface, within a weld length of 150 mm, if the difference between the minimum and maximum bead widths was 7 mm or less, it was rated as "good," and if it was 5 mm or less, it was rated as "very good." If the difference between the minimum and maximum bead widths exceeded 7 mm, it was rated as "poor," and if any defects in the bead shape occurred, they were noted.
The blowholes were tested based on the radiographic testing method for steel welded joints specified in JIS Z3104:1995, and the specimen was deemed defect-free when no flaws were found.

(Powdering of flux)
The evaluation of the powdering measurement of the flux was carried out by repeating the collection of the flux and welding 10 times, and if the flux particles having a particle size of less than 300 μm were within 3 mass %, the flux was judged to be acceptable.
The mass ratio of particles less than 300 μm in diameter was measured in accordance with "6.3 Flux Particle Size Test" in JIS Z3352:2017, "Flux for Submerged Arc Welding and Electroslag Welding." A sieve with a nominal mesh size (300 μm) equivalent to that of JIS Z8801-1:2019, "Test Sieves - Part 1: Metal Wire Sieves," was used, and the sieving time was 4 minutes. Mechanical sieving was performed according to JIS Z8815:1994, "General Rules for Sieving Test Methods," using a low-tap sieve shaker as the measuring instrument. 200 g of flux was used in the test. In this flux particle size test, flux particles that passed through a sieve with a nominal mesh size of 300 μm were considered to be particles less than 300 μm, and their mass ratio (%) was measured.

The results are summarized in Table 5.

In Table 5, flux symbols F1 to F20 are examples of the present invention, and flux symbols F21 to F30 are comparative examples.
The fluxes F1 to F20, which are examples of the present invention, contain appropriate amounts of SiO ₂ , Al ₂ O ₃ , MgO, and FeO, and the flux particle size and the average area ratio occupied by the olivine crystal phase are also appropriate, so in bead-on-plate welding, the arc is stable, no undercuts or the like occur, the bead shape is good, the slag removability is good, and no pits or blowholes occur, resulting in good welding workability.

In the comparative example, flux symbol F21 contained a small amount of _SiO2 , so undercut and slag inclusion occurred.
Flux symbol F22 contained a large amount of _SiO2 , resulting in a poor bead shape.
Flux symbol F23 contained a large amount of Al ₂ O ₃ , so undercut occurred.
Flux F24 contained a small amount of Al ₂ O ₃ , resulting in a poor bead shape.
Flux F25 contained a small amount of MgO, resulting in a poor bead shape and undercutting.
Flux F26 contained a large amount of MgO, resulting in a poor bead shape. In addition, the bulk density of the flux was high, so no effect of improving the bead shape was obtained.
Flux F27 had a low FeO content, which resulted in poor bead shape and the occurrence of pockmarks. In addition, the bulk density of the flux was low, so the effect of improving shielding properties was not obtained.
Flux F28 had poor slag removability due to its high FeO content. In addition, the particle size of the flux was small, so the effect of improving slag removability was not obtained.
Flux F29 had a small average area ratio occupied by the olivine type crystal phase, and was therefore prone to powdering, with 3% or more of the flux having a particle size of 300 μm or less after 10 repetitions.
Flux symbol F30 had a large average area ratio occupied by the olivine type crystal phase, so slag inclusion occurred.

1 Flux

Claims (3)

In mass % relative to the total mass of the flux,
SiO ₂ :34-55%,
_Al2O3 : _6-20 %,
Contains MgO: 5 to 20%, and FeO: 1 to 5%,
CaO: 5.0% or less , and
MnO: 28% or less ,
the average area ratio of the olivine-type crystal phase on the surface of the flux particles is 0.01 to 20%;
Fusible flux for submerged arc welding. The molten flux for submerged arc welding according to claim 1, wherein flux particles having a particle size in the range of greater than 0.3 to 1.4 mm account for 90 mass% or more of the total mass of the flux. 3. The molten flux for submerged arc welding according to claim 1, wherein the bulk density is 0.6 to 1.3 g/cm ³ .