JP7787658B2 - 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 with flux.
Various studies have been conducted to improve the welding workability in submerged arc welding. For example, Patent Documents 1 to 3 disclose that by foaming flux particles to form porous particles and reducing the bulk density, welding workability such as slag removability and bead appearance can be improved.

Japanese Unexamined Patent Publication No. 2-268997 Japanese Unexamined Patent Publication No. 183996/1983 Special Publication No. 51-046653

However, the welding phenomenon in submerged arc welding is not steady, and gas within the arc cavity may sequentially bubble up with a certain probability, blowing away the flux (a phenomenon known as blow-up). When this phenomenon occurs, there is concern that the thickness of the flux spread may be insufficient with conventional foamable molten flux. If the flux is not spread thick enough, the arc becomes directly visible, and it becomes impossible to obtain sound weld metal that is free from the effects of the atmosphere. The reason for this is that when part of the arc is exposed to the atmosphere, the nitrogen content in the weld metal increases, causing defects such as pits, blowholes, and pockmarks.

The present disclosure was devised in consideration of the above-mentioned problems, and aims to provide a molten flux for submerged arc welding that prevents insufficient spray thickness even when the flux blow-up phenomenon occurs during submerged arc welding, and that has excellent welding workability, such as arc stability, slag removability, and bead shape.

The gist of the present disclosure for solving the above problems is as follows.
<1> A molten flux for submerged arc welding, which satisfies the following formula (1), when a mass ratio of foamed flux particles is X% and a mass ratio of flux particles other than the foamed flux particles is Y% relative to a total mass of the flux:

<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 mm 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 prevents insufficient spray thickness even when flux blow-up occurs during submerged arc welding, and that offers excellent welding workability, including arc stability, slag removability, and bead shape.

FIG. 10 is a diagram showing an example of the results of image analysis used to determine whether a particle of a flux used in an example of the present disclosure is foamed or not.

Hereinafter, an embodiment that is an example of a molten flux for submerged arc welding according to the present disclosure (sometimes referred to as a "molten flux" or simply as a "flux" in the present disclosure) will be described.
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.

As a result of intensive research conducted by the inventors to solve the above-mentioned problems, they discovered that controlling the mass ratio of foamed flux particles to flux particles other than foamed flux particles (in this disclosure, flux particles other than foamed flux particles may be referred to as "non-foamed flux particles") within a certain range in the molten flux used in submerged arc welding is extremely effective in improving the aforementioned welding workability. While the reason why specifying the mass ratio between the two is effective in improving welding workability is not entirely clear, the inventors presume that it is because foamed flux particles and non-foamed flux particles interfere with each other and provide resistance to blow-up.

Embodiments of the fusible flux for submerged arc welding according to the present disclosure are described in detail below. Note that the fusible flux for submerged arc welding according to the present disclosure is not limited to the embodiments described below.

<Fused flux for submerged arc welding>
The molten flux for submerged arc welding according to the present disclosure is configured to satisfy the following formula (1), where the mass ratio of foamed flux particles is X% and the mass ratio of flux particles other than foamed flux particles (non-foamed flux particles) is Y% relative to the total mass of the flux.

By performing submerged arc welding using a molten flux in which the mass ratio X% of foamed flux particles and the mass ratio Y% of non-foamed flux particles satisfy formula (1), that is, the mass ratio of foamed flux particles is in the range of 1 to 40% relative to the total mass of the flux, the effect of suppressing the blow-up phenomenon can be obtained, and exposure of the arc to the atmosphere (open arc) can be suppressed.
If the mass ratio of foamable flux particles (X/(X+Y)) is less than 0.01, the flux as a whole will be insufficiently foamed, making it impossible to form a stable arc cavity, and therefore, a poor bead shape is likely to result. On the other hand, if the mass ratio of foamable flux particles exceeds 0.40, the arc will not be able to resist the blow-up phenomenon, resulting in an open arc. Furthermore, the amount of N in the weld metal will increase due to contamination from the atmosphere, making it more likely that porosity defects such as pits and blowholes will occur. Therefore, the mass ratio of foamable flux particles in the molten flux according to the present disclosure is set to 0.01 to 0.40, and preferably 0.01 to 0.30.

In the molten flux for submerged arc welding according to the present disclosure, foamed flux particles and flux particles other than foamed flux particles (non-foamed flux particles) are distinguished using image analysis software. Specifically, 50 g of flux is randomly sampled, and a photograph of the flux (magnification: 30x) is taken using a Keyence digital microscope (VHX-900). The photograph is then binarized using image analysis software (JTrim) to represent 1300 x 1200 pixels (1,560,000 pixels), with white particles identified as foamed particles and black particles identified as non-foamed particles. The threshold value for binarization is set to 150. Particles containing both white and black regions, i.e., particles containing both foamed and non-foamed regions, are considered to be flux particles other than foamed flux particles (non-foamed flux particles).

The present inventors have verified the accuracy of determining whether a flux particle is foamed or non-foamed by image analysis using an enlarged photograph of the flux, by measuring the bulk density.
A mixture of foamed and non-foamed flux particles was sorted based on the particle appearance using a magnifying glass capable of magnifying 5 to 30 times. The flux used was Example F5 in Table 1 of the Examples section described later. Specifically, the particles were sorted into three types: Particle A, which was whitish or yellowish overall, pumice-like particle B, which was blackish overall, and Particle C, which was a mixture of whitish or yellowish and blackish parts.
The bulk densities of particles A, B, and C thus separated based on appearance using a magnifying glass were measured according to JIS K5101, yielding values of approximately 0.5 g/ ^cm3 for particles A, approximately 1.5 g/ ^cm3 for particles B, and approximately 1.0 g/ ^cm3 for particles C. From these results, it can be considered that whitish to yellowish particles A contain bubbles throughout and therefore have a low bulk density, that blackish particles B contain no bubbles throughout and therefore have a high bulk density, and that particles C, which are a mixture of whitish to yellowish and blackish parts, contain bubbles partially and therefore have a bulk density approximately intermediate between those of particles A and B.

On the other hand, when the separated flux particles A, B, and C were subjected to image analysis of enlarged photographs using the method described above, particle A was identified as a white particle, particle B as a black particle, and particle C as a particle containing a mixture of white and black.
From these results, the presence or absence of foaming of the flux particles can be accurately determined by the image analysis described above. That is, in the molten flux for submerged arc welding according to the present disclosure, in the image binarization process described above, white particles are classified as foaming flux particles, and black particles and particles containing both black and white are classified as non-foaming flux particles.
Then, 50 g of flux is randomly collected, and the white particles are separated from other particles (black particles and particles containing a mixture of black and white particles) by the binarization process described above. The total mass of the white particles is measured, and the mass ratio X% of the foamed flux particles and the mass ratio Y% of the non-foamed flux particles can be calculated.

The components constituting the molten flux for submerged arc welding according to the present disclosure are not particularly limited, but preferred components are described below.

[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 30% or more, the molten slag will not have sufficient viscosity, making welding defects such as undercuts and slag inclusion less likely to occur. On the other hand, if the _SiO2 content is 55% or less, the slag viscosity will not be too high, making it easier to achieve a good bead shape. Therefore, the _SiO2 content is preferably 30 to 55%, and more preferably 35 to 50%.

[Al ₂ O ₃ : 6-20%]
Al ₂ O ₃ , derived from alumina or other raw materials, is an effective component for adjusting the viscosity of the molten slag. If the _{Al 2} O ₃ content is 6% or more, the viscosity of the molten slag is prevented from decreasing, making undercut less likely to occur. On the other hand, if the Al ₂ O ₃ content is 20% or less, the viscosity of the molten slag does not become too high, preventing the bead from becoming convex. Therefore, the Al ₂ O ₃ content is preferably 6 to 20%, and more 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. When the MgO content is 5% or more, the molten slag is prevented from becoming insufficiently viscous, making it less likely for meandering or undercutting of the bead to occur. On the other hand, when the MgO content is 20% or less, discontinuous bead width expansion is less likely to occur. Therefore, the MgO content is preferably 5 to 20%, and more 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. When FeO is 0.5% or more, meandering of the bead and the occurrence of pockmarks are reduced. On the other hand, when FeO is 5% or less, slag seizure, which deteriorates slag removability, is suppressed. A more preferable range is 1 to 4%.

[MnO: 18-28%]
MnO, derived from manganese oxide, roasted manganese, etc., is an effective component for adjusting the viscosity and slag removability of the molten slag. To achieve this effect, it is preferable to include 18% or more of MnO. However, since excessive addition of MnO deteriorates the bead shape, the upper limit is preferably set to 28%, and more preferably 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, it is preferable to include 2% or more of _TiO2 . However, since excessive addition of _TiO2 deteriorates slag removability, the upper limit is preferably set at 6%, and more preferably 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, it is preferable to include 5% or more. However, excessive addition of _CaF2 increases the gas content and causes pockmarks, so the upper limit is preferably set at 9%. A more preferable range 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, it is preferable to add 0.5% or more. However, since excessive addition of Na ₂ O and/or K ₂ O deteriorates the bead shape, it is preferable to set the upper limit of the total amount of one or both of Na ₂ O and K ₂ O to 2.0%.

[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 according to the present disclosure 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. Therefore, it is preferable that the flux disclosed herein has a total mass of flux particles with a particle size of more than 0.3 mm to 1.4 mm of 90% or more. 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.

[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 fusible flux for submerged arc welding according to the present disclosure will be described. The method for producing the fusible flux according to the present disclosure is not particularly limited as long as the foamed flux particles and non-foamed flux particles are contained so as to satisfy formula (1). For example, multiple types of fluxes having different mass ratios of foamed flux particles and non-foamed flux particles may be produced and blended so that the mass ratio (X/(X+Y)) of the foamed flux particles to the non-foamed flux particles satisfies formula (1). From the viewpoint of ease of production, a method for producing a flux by adjusting raw materials and production conditions so that the foamed flux particles and non-foamed flux particles are formed in a mass ratio that satisfies formula (1) is preferred.

The molten flux for submerged arc welding according to the present disclosure can be produced, for example, by blending raw materials to contain the aforementioned components, melting the flux by heating, and then cooling the resulting flux with water. When producing the flux by cooling the molten flux with water in this way, the mass ratio of foamed flux particles in the resulting flux depends on the raw materials, cooling rate, and other production conditions. For example, the proportion of foamed flux particles tends to increase when raw materials containing relatively easily reduced oxides of elements such as Mn and Si are melted together with a reducing agent (C, Al, etc.) at high temperatures (e.g., 1300-1700°C).

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.

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.

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]
Molten fluxes were prepared with the component compositions, mass ratios, and bulk densities shown in Table 1. In Table 1, underlines indicate values outside the scope of the present disclosure. Also, "0,""0.0," or "0.00" means that the component is not included (not added).

(Production of molten 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.

(Production of molten fluxes F2 to F17)
Melt fluxes F2 to F17 were produced in the same manner as melt flux F1, except that the blending of the raw materials was changed so as to have the components shown in Table 1.

(Production of molten fluxes F21 to F22)
Molten fluxes F21 and F22 were produced in the same manner as for molten flux F1, except that the blending of the raw materials was changed so as to have the components shown in Table 1.

[measurement]
50 g of each flux produced as described above was randomly sampled and separated into foamed flux particles and other particles (non-foamed flux particles) by the image analysis described above, and the mass ratios (%) X and Y of each particle were measured.
The bulk density of each flux was measured by the method in accordance with JIS K5101-12-1:2004.
Furthermore, regarding the particle size of 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 the above-mentioned JIS Z8815:1994 "General rules for sieving test methods."

[evaluation]
Submerged arc welding was performed using the prototype molten flux. Specifically, bead-on-plate welding was performed using a 4.8 mm diameter solid wire conforming to JIS Z3351:2012 YS-S6 shown in Table 4 and a 16 mm thick steel plate conforming to JIS G3136:2012 SN490B shown in Table 3 under the welding conditions shown in Table 2. Note that components other than those shown in Tables 3 and 4 consist of Fe and impurities.

The welding workability was evaluated by examining arc stability, slag removability, bead shape (presence or absence of undercuts, pits, irregularities on the bead surface), and 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, if the difference between the minimum and maximum bead widths within a 150 mm weld length 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.
The evaluation results are summarized in Table 5.

In Tables 1, 5, and 6, flux symbols F1 to F17 are examples of the present invention, and flux symbols F21 and F22 are comparative examples.
The fluxes designated F1 to F17, which are examples of the present invention, have a mass ratio of foamed flux particles within the range of the present disclosure. In bead-on-plate welding using these fluxes, the arc was stable, no undercuts or pits occurred, the bead shape was good, the slag removability was good, and no pits or blowholes occurred, resulting in good welding workability.

In the comparative example, flux symbol F21 had a small mass ratio of foamed flux particles, so the arc was unstable and undercut occurred.
The comparative flux F22 had a large mass ratio of foamed flux particles, which resulted in an open arc, an unstable arc, a poor bead shape, and pits and blowholes.

1. Foaming flux particles (foamed flux particles)
2. Non-foamed flux particles (non-foamed flux particles)

Claims (3)

The flux contains, based on the total mass, SiO ₂ : 32 to 55%, Al ₂ O ₃ : 6 to 20%, and MgO: 5 to 20%, and CaO: 0.0 to 5.0%;
A molten flux for submerged arc welding that satisfies the following formula (1), where the mass ratio of foamed flux particles is X% and the mass ratio of flux particles other than the foamed flux particles is Y% relative to the total mass of the flux:

The molten flux for submerged arc welding according to claim 1, wherein flux particles with particle sizes in the range of greater than 0.3 mm 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 .