Fused Flux for Submerged Arc Welding

Abstract

To provide a melting type flux for submerged arc welding, which is superior in welding workability such as arc stability, slag releasability and bead shape, and in which powdering is less likely to occur despite that flux is recovered after welding and repeatedly used.SOLUTION: A melting type flux for submerged arc welding contains, in mass% to the total flux mass, 30-55% of SiO2, 6-20% of Al2O3, 5-20% of MgO, and 0.5-5% of FeO, and an average area ratio occupied by an olivine type crystalline phase is 0.01-20% on a surface of flux particles.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a molten flux for submerged arc welding used when welding steel structures.

Background Art

[0002] Submerged arc welding is a method in which granular flux is previously sprayed along the welding part, a welding wire is continuously supplied into the flux, and an arc is generated between the material to be welded and the tip of the welding wire while being covered with the flux to perform welding. After welding, the flux is generally recovered except for the slagified one, and is repeatedly used while replenishing fresh flux. For this reason, the flux exhibits a pulverization phenomenon in which the particles are broken into fine powder due to the collision and friction between the flux particles by repeated recovery.

[0003] The particle size of the flux is designed so that the particle size is controlled within a certain range so as to appropriately release the gas generated during welding. However, when the fine powder increases, the gas escape deteriorates, resulting in appearance defects (pop marks) where the bead surface sinks, and depending on the atmospheric conditions, it may absorb moisture in the air and cause welding defects such as blowholes and welding cracks. In particular, the foaming type molten flux has excellent welding workability such as stable arc, good slag detachability, and good bead appearance. However, the particles are porous and have a large specific surface area, making them prone to pulverization. Not only are the characteristics of the foaming type molten flux lost, but on the contrary, the welding workability deteriorates.

[0004] In response to such problems, for example, Patent Document 1 proposes a technique for improving the anti-pulverization strength of the flux by mixing a glassy molten flux and a pumiceous molten flux in a weight ratio range of 10 to 90% and 90 to 10%, respectively.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when manufacturing the molten flux disclosed in Patent Document 1, the manufacturing methods of the glassy molten flux and the pumiceous molten flux are different, and furthermore, since a particle size adjustment and a weighing / mixing process are required, the productivity of the flux is poor and the manufacturing cost is high. In addition, since the pulverization strength of the pumiceous molten flux has not been improved, when the weight ratio of the pumiceous molten flux is large, the effect of suppressing pulverization is not sufficient.

[0007] Therefore, the present disclosure has been devised in view of the above-described problems, and an object thereof is to provide a submerged arc welding molten flux that is excellent in welding workability such as arc stability, slag detachability, and bead shape, and is less likely to be pulverized even when the flux is recovered and reused after welding.

Means for Solving the Problems

[0008] The gist of the present disclosure for solving the above problems is as follows. <1> In terms of mass% with respect to the total mass of the flux, SiO2: 30 to 55%, Al2O3: 6 to 20%, MgO: 5 to 20%, and FeO: 0.5 to 5% are contained, The average area ratio occupied by the olivine-type crystal phase on the surface of the flux particles is 0.01 to 20%, A submerged arc welding molten flux. <2> The submerged arc welding molten flux according to <1>, wherein 90 mass% or more of the flux particles have a particle size in the range of more than 0.3 to 1.4 mm with respect to the total mass of the flux. <3> The bulk density is 0.6 to 1.3 g / cm 3The molten flux for submerged arc welding according to <1> or <2>.

Advantages of the Invention

[0009] According to the present disclosure, there is provided a molten flux for submerged arc welding that is excellent in welding workability such as arc stability, slag detachability, and bead shape, and is not easily powdered even when the flux is recovered and reused after welding.

Brief Description of the Drawings

[0010]

Figure 1

Modes for Carrying Out the Invention

[0011] Hereinafter, an embodiment which is an example of the molten flux for submerged arc welding according to the present disclosure (in the present disclosure, it may be referred to as "molten flux" or simply "flux") 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, a numerical range represented by "~" means a range including these numerical values as the lower limit value and the upper limit value when "more than" or "less than" is not attached to the numerical values described before and after "~". Further, a numerical range in which "more than" or "less than" is attached to the numerical values described before and after "~" means a range not including these numerical values as the lower limit value or the upper limit value. In the numerical ranges described step by step in this specification, the upper limit value of a certain stepwise numerical range may be replaced with the upper limit value of the numerical range described in other stepwise descriptions, or may be replaced with the value shown in the examples. Also, the lower limit value of a certain stepwise numerical range may be replaced with the lower limit value of the numerical range described in other stepwise descriptions, or may be replaced with the value shown in the examples. Regarding the content, "% " means "% by mass" unless otherwise specified. In addition, when only the upper limit is defined as "~% or less" without defining the lower limit for the content (%), it means that it can be included within the range of more than 0% to the upper limit.

[0012] In order to solve the above problems, the inventors of the present invention have intensively studied the influence of the particle size, bulk density, crystal structure, and chemical composition of flux particles on the powdering of the flux and the welding workability. As a result, it has been found that it is extremely effective to contain a predetermined amount of olivine-type crystal phase in the flux after limiting the flux components and particle size.

[0013] <Submerged arc welding flux for melting type> The submerged arc welding flux for melting type according to the present disclosure is In mass% based on the total mass of the flux, SiO2: 30 to 55%, Al2O3: 6 to 20%, MgO: 5 to 20%, and FeO: 0.5 to 5% is contained, The average area ratio occupied by the olivine-type crystal phase on the surface of the flux particles is 0.01 to 20%.

[0014] [Component composition] The reasons for limiting the component composition of the submerged arc welding flux for melting type of the present disclosure are described below. The content of each component composition in the present disclosure is mass% based on the total mass of the flux, and is simply described as %. The submerged arc welding flux for melting type according to the present disclosure contains SiO 2、 Al2O3, MgO, and FeO as essential components.

[0015] [SiO2: 30 to 55%] SiO2, which uses silica sand, wollastonite, etc. as raw materials, adjusts the viscosity of the molten slag to improve the bead shape. If SiO2 is less than 30%, the viscosity of the molten slag is insufficient, and welding defects such as undercut and slag entrainment are likely to occur. On the other hand, if SiO2 exceeds 55%, the viscosity of the slag becomes too high, and the bead shape becomes poor. Therefore, SiO2 should be 30 - 55%. Preferably, it is 35 - 50%.

[0016] [Al2O3: 6 - 20%] Al2O3, which uses alumina, etc. as raw materials, is an effective component for adjusting the viscosity of the molten slag. If Al2O3 is less than 6%, the viscosity of the molten slag becomes low, and undercut is likely to occur. On the other hand, if Al2O3 exceeds 20%, the viscosity of the molten slag becomes too high, and the bead becomes convex. Therefore, Al2O3 should be 6 - 20%. Preferably, it is 6 - 15%.

[0017] [MgO: 5 - 20%] MgO, which uses magnesia clinker, magnesium oxide, etc. as raw materials, adjusts the viscosity of the molten slag to improve the bead shape. If MgO is less than 5%, the viscosity of the molten slag is insufficient, and bead meandering and undercut occur. On the other hand, if MgO exceeds 20%, the spread of the bead width becomes discontinuous. Therefore, MgO should be 5 - 20%. Preferably, it is 10 - 20%.

[0018] [FeO: 0.5 - 5%] FeO, which uses mill scale, etc. as raw materials, adjusts the viscosity and melting point of the molten slag to improve the bead shape. It also has the effect of enhancing the pockmark resistance. If FeO is less than 0.5%, bead meandering and pockmarks are likely to occur. On the other hand, if FeO exceeds 5%, the slag adheres and the slag peeling property deteriorates. Therefore, FeO should be 0.5 - 5%, preferably 1 - 4%.

[0019] In addition to the above essential components, the flux of the present disclosure can optionally contain, for example, the following components as needed.

[0020] [MnO: 18~28%] MnO, which is made from manganese oxide, roasted manganese, etc., is an effective ingredient for adjusting the viscosity of molten slag and slag detachability. In order to obtain this effect, it is contained at 18% or more. On the other hand, excessive content of MnO deteriorates the bead shape, so the upper limit is set at 28%. Preferably it is 20~26%.

[0021] [TiO2: 2~6%] TiO2, which is made from rutile, titanium oxide, etc., is effective for obtaining the smoothness of the bead surface. In order to obtain this effect, it is contained at 2% or more. On the other hand, excessive content of TiO2 deteriorates the slag detachability, so the upper limit is set at 6%. Preferably it is 3~5%.

[0022] [CaF2: 5~9%] CaF2, which is made from fluorite, etc., has the effect of adjusting the fluidity of molten slag and improving the slag detachability. In order to obtain this effect, it is contained at 5% or more. On the other hand, excessive content of CaF2 increases the gas component and causes pockmarks, so the upper limit is set at 9%. Preferably it is 5~8%.

[0023] [Total of one or both of Na2O and K2O: 0.5~2.0%] Na2O and K2O, which are made from sodium carbonate, potassium carbonate, etc., have the effect of improving the stability of the arc. In order to obtain this effect, the total of one or both of Na2O and K2O is contained at 0.5% or more. On the other hand, excessive content of Na2O and / or K2O deteriorates the bead shape, so the upper limit of the total of one or both of Na2O and K2O is set at 2.0%, and 1.8% is also acceptable.

[0024] [Bi2O3: 0.05% or less] Bi2O3, which uses bismuth oxide etc. as a raw material, has the effect of improving slag detachability. 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 although Bi2O3 has the effect of improving slag detachability with a small amount of addition, it is preferably 0.001% or more in order to obtain that effect.

[0025] [B2O3: 1.5% or less] B2O3, which uses boron oxide etc. as a raw material, has the effect of suppressing the growth of primary ferrite formed at the austenite grain boundaries of the weld metal and improving toughness. If B2O3 is 1.5% or less, deterioration of hot cracking of the weld metal is suppressed. Therefore, it is preferable that B2O3 be 1.5% or less. Note that although B2O3 has the effect of improving the toughness of the weld metal with a small amount of addition, it is preferably 0.01% or more in order to obtain that effect.

[0026] [CaO: 5.0% or less] CaO, which uses calcium oxide etc. as a raw material, has the effect of improving the toughness of the weld metal. If CaO is 5.0% or less, deterioration of the bead shape is suppressed. Therefore, it is preferable that CaO be 5.0% or less. Note that CaO has the effect of improving the toughness of the weld metal with a small amount of addition, but it is preferably 0.01% or more in order to obtain that effect.

[0027] [BaO: 5.0% or less] BaO, which uses barium oxide etc. as a raw material, 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 BaO has the effect of improving the toughness of the weld metal with a small amount of addition, but it is preferably 0.01% or more in order to obtain that effect.

[0028] The remainder of the flux of the present disclosure is impurities such as P and S contained in trace amounts in the raw materials.

[0029] [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 in mass% with respect to the total mass of the fusion-type flux according to the present disclosure, and is simply described as %.

[0030] Flux particles with a particle size exceeding 0.3 mm to 1.4 mm are important particles for forming a stable bead shape. Also, such flux particles have the effect of improving slag detachability. If the flux particles with a particle size exceeding 0.3 mm to 1.4 mm are 90% or more, the bead shape is suppressed from becoming a convex shape, the gas escape is suppressed from deteriorating, and pop marks are less likely to occur. Also, the flux is less likely to be pulverized. Therefore, it is preferable that the total mass of the flux particles with a particle size exceeding 0.3 mm to 1.4 mm in the flux according to the present disclosure is 90% or more. Preferably it is 95% or more. In addition, 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 exceeding 1.4 mm, the more preferable.

[0031] The particle size of the flux particles is measured in accordance with "6.3 Particle Size Test of Flux" in JIS Z3352:2017 Flux for Submerged Arc Welding and Electro-Slag Welding. Sieves with corresponding nominal mesh openings (300 μm and 1.4 mm) in JIS Z8801-1:2019 "Test Sieves - Part 1: Wire Mesh Sieves for Metals" are used, and the sieving time is 4 minutes. Mechanical sieving in JIS Z8815:1994 "General Rules for Sieving Test Methods" is performed, and a rotary tap type sieve shaker is used as the measuring instrument. The flux used in the test is 200 g. In such a particle size test of the flux, the flux particles that pass through the sieve with a nominal mesh opening of 1.4 mm and do not pass through the sieve with a nominal mesh opening of 300 μm are the flux particles with a particle size exceeding 0.3 mm to 1.4 mm.

[0032] [Average area ratio of olivine-type crystal phase] Next, the average area ratio occupied by olivine-type crystals on the surface of the flux particles will be described. Olivine is the English name for kanranite, generally represented 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 formed in the molten flux, it is presumed that the effect of reinforcement by the glassy part is obtained and the pulverization is suppressed. However, this effect cannot be obtained if the average area ratio of the olivine-type crystals is less than 0.01%. On the other hand, since the melting point of olivine is as high as 1557°C, slag entrainment occurs when the average area ratio of the olivine-type crystals exceeds 20%. Therefore, in the molten flux for submerged arc welding according to the present disclosure, the average area ratio of the olivine-type crystal phase in the flux particles is set to 0.01 to 20%. Preferably, it is 1 to 15%.

[0033] The olivine-type crystal phase has the structure of (Mg·Fe)2·SiO4 and can be easily discriminated because its components are different from those of the surrounding glassy material. The area ratio occupied by the olivine-type crystal phase in the flux particles is measured as follows.

[0034] Among the flux particles, an arbitrary particle is selected, embedded in resin, mirror-polished, and after C is deposited to ensure conductivity, a WD / ED combine Electron Probe Microanalyzer (EPMA) JXA 8230 manufactured by JEOL Ltd. is used with an acceleration voltage of 15 kV and an irradiation current of 2×10 -8 A is used to analyze the specified field of view (magnification: 3000 times, field of view: 30 μm × 30 μm, total number of analysis regions: 65536). Then, for one field of view, the number of analysis regions in which the concentrations of Mg, Si, Fe, and O, which are the olivine constituent elements, are detected above their respective averages among the total 65536 analysis regions is calculated. By dividing the calculated number of analysis regions by the total 65536 analysis regions, the area ratio occupied by the olivine-type crystal phase can be calculated. Perform such analysis on 10 flux particles, and calculate the area ratio occupied by the olivine-type crystal phase in each particle. Then, determine the average value of the area ratio occupied by the olivine-type crystal phase as the average area ratio of the olivine-type crystal phase in the flux particles constituting the flux.

[0035] [Bulk density] The bulk density of the flux acts on the shielding property of the molten pool from the atmosphere during welding and the spread of the weld bead. If the bulk density of the flux is 0.6 g / cm 3 or more, the flux blowing phenomenon is less likely to occur, and insufficient shielding is suppressed, preventing the occurrence of pop marks. On the other hand, if the bulk density of the flux is 1.3 g / cm 3 or less, the bead is less likely to spread, suppressing the occurrence of undercut. Therefore, the bulk density of the flux according to the present disclosure is preferably 0.6 to 1.3 g / cm 3 . A more preferable range is 0.6 to 1.2 g / cm 3 . The measurement of the bulk density of the flux can be carried out in accordance with JIS K5101-12-1:2004. Bulk density (g / cm 3 ) = (mass of the receiver containing the sample (g) - mass of the receiver (g)) / internal volume of the receiver (cm 3 )

[0036] <Manufacturing method of submerged arc welding molten flux> Next, the manufacturing method of the submerged arc welding molten flux according to the present disclosure will be described. When manufacturing the molten flux according to the present disclosure, the manufacturing method is not particularly limited as long as the components, particle size, and average area ratio of the olivine-type crystal phase are within the ranges of the present disclosure described above. For example, the raw materials can be blended to contain the components described above, melted by heating in an electric furnace or the like, cooled with water, and then pulverized for manufacturing.

[0037] The average area ratio of the olivine-type crystal phase in the flux particles depends on manufacturing conditions such as raw materials and cooling rate. For example, the average area ratio of the olivine-type crystal phase can be adjusted by melting a raw material with a composition containing relatively reducible oxides such as Mn and Si together with a reducing agent (such as C and Al) at a high temperature (for example, 1300 to 1700 °C).

[0038] In addition, as a method for adjusting the particle size of the flux, for example, a method of directly impinging jet water on the melt can be mentioned. By controlling the water pressure, water volume, and the amount of the molten flux and then performing granulation and sieving, the particle size of the flux can be adjusted.

[0039] In addition, as a method for adjusting the bulk density of the flux, after mixing various raw materials of the flux and melting them in an electric furnace, the molten flux is cooled in warm water to slow down the cooling rate and foam the flux, or the molten flux is cooled in jet water cooling to obtain a flux in which acicular, antler-shaped, spherical, and scaly particles are mixed, thereby adjusting the bulk density of the flux.

Examples

[0040] Hereinafter, the effects of the present disclosure will be described in more detail with reference to examples, but the present disclosure is not limited to the following examples.

[0041] [Manufacture of submerged arc welding molten flux] Prototype molten fluxes with various components, particle sizes, and bulk densities shown in Table 1 were produced. The molten fluxes shown in Table 1 were obtained by melting various mineral raw materials, pulverizing them into powder form after cooling, and then sizing them to a particle size of 300 μm to 1.4 mm. The remainder in the flux components are P, S, etc. that are unavoidably mixed in from the raw materials. In Table 1, the underlines indicate that it is outside the scope of the present disclosure. Also, "0", "0.0", or "0.00" means that the component is not included (not added).

[0042] (Manufacture of molten flux F1) The raw materials were blended and mixed to form the components shown by the flux symbol F1 in Table 1, heated to 1350 °C in an electric furnace to obtain a molten flux (melt), and then poured into a large amount of water for cooling. 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 pulverization and sieving.

[0043] (Production of molten fluxes F2 to F20) Except for changing the blending of the raw materials so as to become the components shown in Table 1 respectively, the molten fluxes F2 to F20 were produced by the same method as the molten flux Fl.

[0044] (Production of molten fluxes F21 to F28) Except for changing the blending of the raw materials so as to become the components shown in Table 1 respectively, the molten fluxes F21 to F28 were produced by the same method as the molten flux F1.

[0045] (Production of molten flux F29) Except for changing the blending of the raw materials so as to become the components shown in Table 1 respectively, it was heated to 1200 °C in an electric furnace to obtain a molten flux (melt), and then poured into a large amount of water for cooling. The other operations were the same as those for the molten flux F1 to produce the molten flux F29.

[0046] (Production of molten flux F30) Except for changing the blending of the raw materials so as to become the components shown in Table 1 respectively, it was heated to 1800 °C in an electric furnace to obtain a molten flux (melt), and then poured into a large amount of water for cooling. The other operations were the same as those for the molten flux F1 to produce the molten flux F30.

[0047]

Table 1

[0048] [Measurement] The average area ratio, particle size, and bulk density of the olivine-type crystal phase of each flux produced as described above were measured by the methods described above, respectively.

[0049] (Average area ratio of olivine-type crystal phase) Ten arbitrary particles were selected from each flux, and for each particle, an arbitrary field of view of 30 μm × 30 μm was subjected to EPMA elemental mapping analysis to measure the average area ratio occupied by the olivine-type crystal phase with respect to the total area of the observation field. It was denoted as "Olivine area ratio" in Table 1.

[0050] (Particle size) For each flux, using a rotary tap type sieve shaker (manufactured by Ito Seisakusho Co., Ltd., product name: Rotary tap type sieve shaker S type), in accordance with the method compliant with JIS Z8815:1994 "General rules for sieve analysis test methods", the mass ratio (%) of flux particles with a particle size exceeding 0.3 mm to 1.4 mm was measured.

[0051] (Bulk density) The bulk density of each flux was measured by the method compliant with JIS K5101-12-1:2004 described above.

[0052] [Evaluation] Submerged arc welding was performed using the trial-produced molten-type flux. Specifically, bead-on-plate welding workability evaluation was carried out using a solid wire with a wire diameter of 4.8 mm of JIS Z3351 YS-S6:2012 shown in Table 4 under the welding conditions shown in Table 2, and a steel plate with a thickness of 16 mm of JIS G3136:2012 SN490B shown in Table 3. Note that except for the components shown in Tables 3 and 4, the rest are Fe and impurities. In addition, to evaluate the powdering status of the flux, the flux remaining after welding was recovered using a flux recovery device (VC-661 type, AC200V) manufactured by Daihen Corporation, and welding was repeated 10 times using the recovered flux by the method shown in Figure 1, and then the particle size of the 10th flux was measured.

[0053]

Table 2

[0054] [Table 3]

[0055] [Table 4]

[0056] (Weldability) For the evaluation of weldability, the arc stability, slag detachability, bead shape (presence or absence of undercut, pits, pockmarks, irregularities on the bead surface), and presence or absence of blowholes were investigated. The arc stability was regarded as "stable" if the welding voltage fluctuation during welding was within ±5V. Regarding slag detachability, since the slag after welding peels off naturally, the slag was removed with a brush, the area of the remaining slag that could be visually confirmed was estimated, and a slag detachment rate of 95% or more was considered "good", and 98% or more was considered "very good". Regarding the irregularities on the bead surface, within a range of 150 mm in welding length, if the difference between the minimum and maximum values of the bead width was 7 mm or less, it was considered "good", and 5 mm or less was considered "very good". If the difference between the minimum and maximum values of the bead width exceeded 7 mm, it was considered "bad", and if there were defects in the bead shape, the defects were described. For blowholes, tests were conducted based on the radiographic test method for steel welded joints shown in JIS Z3104:1995, and it was considered defect-free if no flaws occurred.

[0057] (Flux pulverization) For the evaluation of flux pulverization measurement, after repeating the flux recovery and welding 10 times, it was considered qualified if the particles with a particle size of less than 300 μm in the flux were within 3 mass%. The mass ratio of particles with a particle size less than 300 μm was measured in accordance with "6.3 Particle Size Test of Flux" in JIS Z3352:2017 Flux for Submerged Arc Welding and Electro-Slag Welding. A sieve with a corresponding nominal mesh size (300 μm) in JIS Z8801-1:2019 "Test Sieves - Part 1: Wire Mesh Sieves for Metals" was used, and the sieving time was set to 4 minutes. Mechanical sieving was performed in accordance with JIS Z8815:1994 "General Rules for Sieving Test Methods", and a rotary tap type sieve shaker was used as the measuring instrument. The flux used in the test was 200 g. In such a particle size test of the flux, the flux particles that passed through the sieve with a nominal mesh size of 300 μm were judged as particles less than 300 μm, and their mass ratio (%) was measured.

[0058] The results are summarized in Table 5.

[0059]

Table 5

[0060] In Table 5, the flux symbols F1 to F20 are the examples of the present invention, and the flux symbols F21 to F30 are the comparative examples. For the flux symbols F1 to F20 which are examples of the present invention, since the amounts of SiO2, Al2O3, MgO, and FeO are appropriate, and the particle size of the flux and the average area ratio occupied by the olivine-type crystal phase are also appropriate, in bead-on-plate welding, the arc is stable, no undercut or the like occurs, the bead shape is good, the slag detachability is also good, no pits or blowholes occur, and the welding workability is good.

[0061] In the comparative example, for the flux symbol F21, since the amount of SiO2 is small, undercut and slag entrainment occurred. For the flux symbol F22, since the amount of SiO2 is large, the bead shape became defective. For the flux symbol F23, since the amount of Al2O3 is large, undercut occurred. For the flux symbol F24, since the amount of Al2O3 is small, the bead shape became defective. Since the flux symbol F25 has little MgO, the bead shape is defective and undercut also occurred. Since the flux symbol F26 has a large amount of MgO, the bead shape became defective. Also, since the bulk density of the flux is high, the effect of improving the bead shape could not be obtained. Since the flux symbol F27 has little FeO, the bead shape is defective and pockmarks also occurred. Also, since the bulk density of the flux is low, the effect of enhancing the shielding property could not be obtained. Since the flux symbol F28 has a large amount of FeO, the slag detachability was poor. Also, since the particle size of the flux is small, the effect of improving the slag detachability could not be obtained. Since the average area ratio occupied by the olivine-type crystal phase in the flux symbol F29 is small, it is prone to powdering, and the particle size of the flux after 10 repetitions was 3% or more below 300 μm. Since the average area ratio occupied by the olivine-type crystal phase in the flux symbol F30 is large, slag entrainment occurred.

Explanation of symbols

[0062] 1 Flux

Claims

1. In terms of mass% based on the total mass of the flux, SiO ２ : 34 - 55%, Al ２ O ３ : 6 to 20%, MgO: 5 to 20%, and FeO: contains 1 to 5%, CaO: 5.0% or less, and MnO: 28% or less, The average area ratio occupied by the olivine-type crystal phase on the surface of the flux particles is 0.01 to 20%, A submerged arc welding flux of the melting type.

2. The submerged arc welding flux of the melting type according to claim 1, wherein 90% by mass or more of the flux particles have a particle size in the range exceeding 0.3 to 1.4 mm with respect to the total mass of the flux.

3. The bulk density is 0.6 to 1.3 g / cm ３ The flux for submerged arc welding according to claim 1 or claim 2, which has the above property.

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