Submerged arc welding flux

Abstract

Provided is a flux for submerged arc welding of a welded metal, which is excellent in weldability and enables stable production of a welded metal having excellent mechanical properties. A flux for submerged arc welding of a Cr-Mo steel sheet contains, relative to the total mass of the flux, Mn: 0.01 mass% or more and 5.00 mass% or less, Al: 0.50 mass% or more and 3.00 mass% or less, N: more than 0 mass% and 0.50 mass% or less, MgO: 5.0 mass% or more and 40.0 mass% or less, F: 5.0 mass% or more and 12.0 mass% or less, Ca: 9.5 mass% or more and 21.5 mass% or less, Al2O3: 11.0 mass% or more and 23.0 mass% or less, Si and a SiO2 conversion value of a Si compound: 7.0 mass% or more and 20.0 mass% or less, CO2: 3.0 mass% or more and 10.0 mass% or less, C: 1.00 mass% or less, and Ni: 1.00 mass% or less.

Description

Technical Field

[0001] This invention relates to fluxes for submerged arc welding. Background Technology

[0002] Historically, high-strength materials with excellent high-temperature properties, such as 1.25%Cr-0.5%Mo steel or 2.25%Cr-1.0%Mo steel, have been used in reactors (hereinafter also referred to as "reactors") operating under high temperature and high pressure conditions, such as those located in oil refineries. Furthermore, in the manufacture of reactors, multi-layer surfacing welding based on submerged arc welding combining solid welding wire and bonding flux is generally used. Considering the operation of such reactors in cold regions and brittle fracture during operation shutdowns, in addition to the aforementioned high strength and high-temperature properties, excellent toughness in low-temperature environments is also required.

[0003] For example, Patent Document 1 discloses a welding method aimed at improving the low-temperature toughness and high-temperature strength of the weld metal by including Al and N in the welding wire or flux.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 58-58982 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] However, as disclosed in Patent Document 1, when the welding wire contains Al and N, there is a problem of wire breakage during the manufacturing process, which increases manufacturing costs.

[0009] On the other hand, if the Al and N content in the welding wire is reduced, and a flux containing Al and N is used within the range described in Patent Document 1, the compositional inhomogeneity of the weld metal increases, and the required toughness and mechanical properties cannot be fully obtained. In particular, when welding at high currents with the aim of improving operational efficiency, the performance of the weld metal becomes unstable. Therefore, not only are excellent high-temperature properties and low-temperature toughness required, but the requirements for excellent weld operability are also increasing.

[0010] The present invention was made in view of the above-mentioned problems, and its purpose is to provide a submerged arc welding flux for Cr-Mo steel plates that has excellent welding operability and can stably produce weld metal with excellent mechanical properties.

[0011] means for solving problems

[0012] Through numerous in-depth studies, the inventors have discovered that by including more Al in the flux used for submerged arc welding than before, and by controlling the content of other components such as oxides, it is possible to improve operational efficiency and obtain weld metal with excellent mechanical properties even when welding under high current.

[0013] In other words, the above-mentioned objective of the present invention is achieved by the composition of the flux for submerged arc welding as described below [1].

[0014] [1] A flux for submerged arc welding, characterized in that it is a flux for submerged arc welding of Cr-Mo series steel plates, and contains, relative to the total mass of the flux:

[0015] Mn: ≥0.01% by mass and ≤5.00% by mass

[0016] Al: ≥0.50% by mass and ≤3.00% by mass

[0017] N: greater than 0% by mass and less than 0.50% by mass

[0018] MgO: ≥5.0% by mass and ≤40.0% by mass

[0019] F: 5.0% by mass or more and 12.0% by mass or less

[0020] Ca: ≥9.5% by mass and ≤21.5% by mass

[0021] Al2O3: ≥11.0% by mass and ≤23.0% by mass

[0022] Si and Si compounds: SiO2 conversion values: 7.0% by mass and 20.0% by mass; CO2: 3.0% by mass and 10.0% by mass.

[0023] C: Less than 1.00% by mass

[0024] Ni: less than 1.00% by mass.

[0025] In addition, the preferred embodiments of the flux for submerged arc welding involved in this invention are as follows [2] or [3].

[0026] [2] The flux for submerged arc welding as described in [1] is characterized in that it further contains at least one of Na, K and Li, and the total content of Na, K and Li relative to the total mass of the flux is 0.01% by mass or more and 1.00% by mass or less.

[0027] [3] The flux for submerged arc welding as described in [1] or [2] is characterized in that, relative to the total mass of the flux, it contains Fe: 0.10% by mass or more and 5.00% by mass or less.

[0028] Invention Effects

[0029] The flux for submerged arc welding according to the present invention has excellent welding operability and can stably produce weld metal with excellent mechanical properties. Detailed Implementation

[0030] The present invention will now be described in detail in terms of the methods used to implement it. However, the present invention is not limited to the embodiments described below.

[0031] [1. Flux for submerged arc welding]

[0032] The submerged arc welding flux of this embodiment (hereinafter, it may also be referred to simply as "flux") is a submerged arc welding flux used for submerged arc welding of Cr-Mo series steel plates, and contains specified amounts of Mn or Mn compounds, Al, N, MgO, F, Ca, Al2O3, Si or Si compounds, CO2, C, and Ni.

[0033] The reasons for limiting the composition of the flux in this embodiment will be explained below.

[0034] <Mn: ≥0.01% by mass and ≤5.00% by mass>

[0035] Mn is a component included to ensure the room temperature strength of the weld metal, and especially to improve its toughness. Additionally, Mn also has a deoxidizing effect on the weld metal. If the Mn content in the flux is less than 0.01% by mass, the above-mentioned effect cannot be obtained, resulting in a coarser weld metal structure and decreased toughness. Therefore, the Mn content in the flux is preferably 0.01% by mass or more, more preferably 0.5% by mass or more, and more preferably 1.0% by mass or more, relative to the total mass of the flux.

[0036] On the other hand, if the Mn content in the flux is greater than 5.00% by mass, the creep rupture strength of the weld metal deteriorates, and the temper embrittlement characteristics also deteriorate. Therefore, the Mn content in the flux is preferably 4.00% by mass or less, and more preferably 3.00% by mass or less, relative to the total mass of the flux.

[0037] Furthermore, Mn is contained in the flux in the form of elemental Mn, Mn alloys, or Mn compounds.

[0038] <Al: 0.50% by mass or more and 3.00% by mass or less>

[0039] Al is a component that improves the toughness of weld metal by enhancing its hardenability and refining its microstructure. If the Al content in the flux is less than 0.50% by mass, the above-mentioned effect cannot be achieved. Therefore, the Al content in the flux is 0.50% by mass or more relative to the total mass of the flux, preferably 0.6% by mass or more, more preferably 0.8% by mass or more, further preferably 1.0% by mass or more, and most preferably 1.2% by mass or more.

[0040] On the other hand, if the Al content in the flux is greater than 3.00% by mass, the microstructure becomes coarser and the toughness of the weld metal decreases. Therefore, the Al content in the flux is preferably 2.5% by mass or less, more preferably 2.0% by mass or less, even more preferably 1.8% by mass or less, and most preferably 1.6% by mass or less, relative to the total mass of the flux.

[0041] Furthermore, Al refers to the total amount of acid-soluble Al contained in the flux, either in the form of elemental Al or Al alloys such as Fe-Al. Additionally, the Al content does not include compounds such as Al₂O₃, as shown below.

[0042] <N: greater than 0% by mass and less than 0.50% by mass>

[0043] Nitrogen (N) is a solid solution strengthening element and a component that can improve the strength of weld metal. Specifically, in this embodiment, by containing appropriate amounts of Al and N in the flux, AlN precipitates in the weld metal, thereby increasing the tensile strength of the weld metal. Even trace amounts of N in the flux can achieve the above-mentioned effect. Therefore, the N content in the flux is greater than 0% by mass relative to the total mass of the flux, preferably 0.05% by mass or more, more preferably 0.10% by mass or more, further preferably 0.12% by mass or more, and most preferably 0.15% by mass or more.

[0044] On the other hand, if the nitrogen content in the flux is greater than 0.50% by mass, the yield strength and tensile strength of the weld metal will increase significantly due to solid solution strengthening, resulting in a decrease in the toughness of the weld metal. Therefore, the nitrogen content in the flux is preferably 0.30% by mass or less relative to the total mass of the flux, more preferably 0.25% by mass or less, even more preferably 0.22% by mass or less, and most preferably 0.20% by mass or less.

[0045] Furthermore, N is contained in the flux as nitrogen compounds such as MnN, AlN, and CrN. In this embodiment, N is defined as the total amount of these nitrides converted to N.

[0046] <MgO: ≥5.0% by mass and ≤40.0% by mass>

[0047] MgO, with its high melting point, promotes slag solidification and helps adjust the weld bead shape. It also controls the oxygen content in the weld metal. If the MgO content in the flux is less than 5% by mass, the deoxidation effect during welding decreases, leading to an increase in oxides in the weld metal and consequently, a decrease in toughness. Therefore, the MgO content in the flux is preferably 5.0% by mass or more, more preferably 10.0% by mass or more, and even more preferably 20.0% by mass or more, relative to the total mass of the flux.

[0048] On the other hand, if the MgO content in the flux is greater than 40.0% by mass, the weld bead shape deteriorates, resulting in decreased slag peelability. Therefore, the MgO content in the flux is preferably 38.0% by mass or less, and more preferably 35.0% by mass or less, relative to the total mass of the flux.

[0049] <F: 5.0% by mass or more and 12.0% by mass or less>

[0050] Flame (F), present in flux as compounds such as CaF, improves the electrical conductivity and fluidity of the slag, and is a component that influences the high-temperature viscosity of the slag. If the F content in the flux is less than 5.0% by mass, the slag will solidify immediately, hindering gas escape or causing slag sticking. Therefore, the F content in the flux is 5.0% by mass or more relative to the total mass of the flux, preferably 6.0% by mass or more, and more preferably 7.0% by mass or more.

[0051] On the other hand, if the F content in the flux is greater than 12.0% by mass, the weld bead becomes coarser and the weld appearance deteriorates. Therefore, the F content in the flux is preferably 11.5% by mass or less, and more preferably 11.0% by mass or less, relative to the total mass of the flux.

[0052] <Ca: ≥9.5% by mass and ≤21.5% by mass>

[0053] Ca, present as CaO and fluorides, increases the basicity of the slag, thereby improving the cleanliness of the weld metal, and also affects the flowability of the slag. If the Ca content in the flux is less than 9.5% by mass, the cleanliness of the weld metal decreases, and its toughness declines. Therefore, the Ca content in the flux is 9.5% by mass or more relative to the total mass of the flux, preferably 11.0% by mass or more, and more preferably 15.0% by mass or more.

[0054] On the other hand, if the Ca content in the flux is greater than 21.5% by mass, the fluidity of the molten slag becomes too high, and the appearance and shape of the weld bead deteriorate. Therefore, the CaO content in the flux is preferably 21.0% by mass or less, and more preferably 20.0% by mass or less, relative to the total mass of the flux.

[0055] <Al2O3: ≥11.0% by mass and ≤23.0% by mass>

[0056] Al2O3 improves the fluidity of slag and controls the oxygen content of the weld metal. If the Al2O3 content in the flux is less than 11.0% by mass, the fusion between the weld bead and the base metal deteriorates, and slag entrapment is more likely. Therefore, the Al2O3 content in the flux is 11.0% by mass or more relative to the total mass of the flux, preferably 13.0% by mass or more, and more preferably 15.0% by mass or more.

[0057] On the other hand, if the Al2O3 content in the flux is greater than 23.0% by mass, the weld bead becomes coarser and the weld appearance deteriorates. Therefore, the Al2O3 content in the flux is preferably 22.0% by mass or less, and more preferably 20.0% by mass or less, relative to the total mass of the flux.

[0058] Furthermore, the Al2O3 content is the Al2O3 conversion value of the Al contained in the Al compound of the Al alloy.

[0059] <Si and Si compounds SiO2 conversion value: 7.0% by mass or more and 20.0% by mass or less>

[0060] >

[0061] Si and Si compounds are components that improve the fluidity of molten slag. If the SiO2 conversion value of Si and Si compounds in the flux is less than 7.0% by mass, the fusion between the weld bead and the base metal becomes poor, and slag entrapment is more likely to occur. Therefore, the SiO2 conversion value in the flux is 7.0% by mass or more, preferably 8.0% by mass or more, and more preferably 9.0% by mass or more, relative to the total mass of the flux.

[0062] On the other hand, if the SiO2 conversion value in the flux is greater than 20.0% by mass, the oxide content in the weld metal increases due to the increased oxygen content, resulting in a decrease in toughness. Therefore, the SiO2 conversion value in the flux is preferably 18.0% by mass or less, and more preferably 15.0% by mass or less, relative to the total mass of the flux.

[0063] Furthermore, Si is contained in the flux in the form of elemental Si, Si alloys, or Si compounds. In this embodiment, the SiO2 conversion value is defined as the total Si content, including all Si and Si contained in Si compounds, converted into the SiO2 value.

[0064] <CO2: 3.0% by mass or more and 10.0% by mass or less>

[0065] CO2 is a component that controls the amount of diffusible hydrogen in the welding metal. If the CO2 content in the flux is less than 3.0% by mass, the amount of diffusible hydrogen in the welding metal increases, making low-temperature cracking more likely. Therefore, the CO2 content in the flux is 3.0% by mass or more relative to the total mass of the flux, preferably 4.0% by mass or more, and more preferably 5.0% by mass or more.

[0066] On the other hand, if the CO2 content in the flux is greater than 10.0% by mass, the oxygen content in the weld metal increases and the toughness decreases. Therefore, the CO2 content in the flux is preferably 9.0% by mass or less, and more preferably 8.0% by mass or less, relative to the total mass of the flux.

[0067] Furthermore, CO2 is contained in the flux in the form of metal carbonates such as CaCO3. In this embodiment, CO2 is defined as the value of all metal carbonates converted to CO2.

[0068] <C: Less than 1.00% by mass (including 0% by mass)>

[0069] C is a component contained in the flux to ensure the room temperature strength, creep rupture strength, and toughness of the weld metal. C is not necessarily contained in the flux; other components can also be used to improve the room temperature strength, creep rupture strength, and toughness of the weld metal. However, the C content in the flux is preferably 0.05% by mass or more, and more preferably 0.10% by mass or more, relative to the total mass of the flux.

[0070] On the other hand, if the carbon content in the flux is greater than 1.00% by mass, the toughness of the weld metal decreases. Therefore, the carbon content in the flux is preferably 0.80% by mass or less, and more preferably 0.50% by mass or less, relative to the total mass of the flux.

[0071] Furthermore, C can be contained in flux in the form of elemental C, alloys of C, or C compounds.

[0072] <Ni: 1.00% by mass or less (including 0% by mass)>

[0073] Ni is an effective element for improving the toughness of weld metal, but it is also a component that significantly reduces creep rupture strength. Ni does not necessarily have to be present in the flux; other components can also be used to improve toughness. However, the Ni content in the flux is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.05% by mass or more, relative to the total mass of the flux.

[0074] On the other hand, if the Ni content in the flux is greater than 1.00% by mass relative to the total mass of the flux, the creep rupture strength of the weld metal decreases. Therefore, the Ni content in the flux is preferably 0.80% by mass or less, and more preferably 0.50% by mass or less, relative to the total mass of the flux.

[0075] Furthermore, Ni can be contained in the flux in the form of elemental Ni or Ni alloys such as Fe-Ni.

[0076] <Total content of Na, K, and Li: ≥0.01% by mass and ≤1.00% by mass>

[0077] Alkali metals such as Na, K, and Li are components that improve arc stability, so these alkali metals do not necessarily need to be added to the flux. In this embodiment, the flux preferably contains at least one of Na, K, and Li.

[0078] The above-mentioned effect can be obtained if the total content of Na, K and Li in the flux is 0.01% by mass or more. Therefore, when the flux contains at least one of Na, K and Li, the total content of Na, K and Li in the flux is preferably 0.01% by mass or more, and more preferably 0.05% by mass or more, relative to the total mass of the flux.

[0079] On the other hand, if the total content of Na, K, and Li in the flux is 1.00% by mass or less, it can prevent the slag melting point from decreasing and obtain an excellent weld bead shape. Therefore, when the flux contains at least one of Na, K, and Li, the total content of Na, K, and Li in the flux is preferably 1.00% by mass or less, more preferably 0.5% by mass or less, relative to the total mass of the flux.

[0080] Furthermore, Na, K, and Li can be added to the flux as fluorides and complex oxides. In this embodiment, compounds containing Na, K, and Li are specified by their values ​​converted to Na, K, and Li, respectively.

[0081] <Fe: 0.10% by mass or more and 5.00% by mass or less>

[0082] Fe is a component that prevents slag from sticking together. Fe does not necessarily have to be present in the flux, but if the Fe content in the flux is 0.10% by mass or more, the above-mentioned effect can be obtained. Therefore, the Fe content in the flux is preferably 0.10% by mass or more, and more preferably 0.30% by mass or more, relative to the total mass of the flux.

[0083] On the other hand, if the Fe content in the flux is 5.00% by mass or less, the solidification temperature of the slag can be adjusted, and the deterioration of the weld appearance, weld shape, and slag peeling can be prevented. Therefore, the Fe content in the flux is preferably 5.00% by mass or less, and more preferably 3.00% by mass or less.

[0084] Furthermore, Fe is defined as the total amount of all Fe, including elemental Fe, Fe alloys, and Fe oxides.

[0085] The flux of this embodiment preferably contains 85% by mass or more of Mn, Al, N, MgO, F, Ca, Si, and the SiO2 equivalent of Si compounds, CO2, C, and Ni, more preferably 90% by mass or more, even more preferably 93% by mass or more, and particularly preferably 95% by mass or more.

[0086] In addition to the components mentioned above, it contains unavoidable impurities. Furthermore, depending on the required characteristics of the weld metal, it may contain various components such as Sr compounds and Ba compounds.

[0087] [2. Manufacturing method of flux for submerged arc welding]

[0088] When manufacturing the flux according to this embodiment, for example, raw material powder is prepared in the manner described above, mixed with a binder, granulated, and calcined. At this time, sodium silicate can be used as a binder (adhesive). Furthermore, the granulation method is not particularly limited, but methods such as roller granulators and extrusion granulators are preferred.

[0089] The calcination after granulation can be carried out using a rotary kiln, a stationary box furnace, or a belt kiln. From the viewpoint of changing the binder to be non-water-soluble, the calcination temperature is preferably 350°C or higher, more preferably 450°C or higher. There is no particular upper limit, but it is generally below 1200°C.

[0090] Example

[0091] The following examples illustrate this embodiment in more detail, but the present invention is not limited to these examples. Modifications can be made to the implementation within the scope that conforms to the spirit of the present invention, and all of these are included within the technical scope of the present invention.

[0092] [1. Chemical composition of welding wire]

[0093] First, the chemical composition of the welding wire used in the embodiments is shown in Table 1, and the chemical composition of the flux is shown in Table 2. Furthermore, as shown in Table 1, welding wire marked W1 is a welding wire for 2.25% Cr-1.0% Mo steel, and welding wire marked W2 is a welding wire for 1.25% Cr-0.5% Mo steel.

[0094] Table 1

[0095] Table 1

[0096]

[0097] Table 2

[0098] Table 2

[0099]

[0100] ※“-” indicates that it was not added during manufacturing, or that it was below the detection limit.

[0101] [2. Submerged arc welding]

[0102] Using welding wire with a diameter of 4.0 mm and the composition shown in Table 1 above, and flux as shown in Table 2, submerged arc welding was performed on the bevel of the base metal as specified in ASTM A387-Gr22, and the weld operability was evaluated. The base metal was 25 mm thick, 120 mm wide, and 600 mm long. Other welding conditions and post-weld heat treatment conditions are shown below.

[0103] (a) Welding conditions

[0104] (Welding Condition A)

[0105] Welding current: 525A

[0106] Welding voltage: 28V

[0107] Welding speed: approximately 40cm / minute

[0108] Polarity: DCEP (Direct Current Electrode Positive)

[0109] Welding posture: Downward posture

[0110] Welding wire protrusion length: 30mm

[0111] Preheating interlayer temperature: 190-220℃

[0112] (Welding condition B: Tandem welding)

[0113] Welding current of the leading electrode: 580A

[0114] Soldering voltage for the leading electrode: 30V

[0115] Welding speed of the leading electrode: 60 cm / min

[0116] Polarity of the preceding pole: DCEP

[0117] Welding current for the rear electrode: 600A

[0118] Welding voltage for the rear electrode: 32V

[0119] Welding speed of the rear electrode: 60cm / minute

[0120] Polarity of the moving pole: AC (Alternating Current)

[0121] (b) Post-Weld Heat Treatment (PWHT) Conditions

[0122] PWHT Condition A: 1 hour at 690°C

[0123] PWHT Condition B: 8 hours at 685°C

[0124] PWHT condition C: 670℃ for 6 hours

[0125] In addition, the evaluation criteria include weld operability, arc stability, anti-pitting properties, weld shape, slag peeling properties, weld fusion, and weld neatness. A score of ○ (good) indicates all items are rated as good, while a score of × (poor) indicates any item is rated as bad.

[0126] Subsequently, the obtained weld metal was subjected to a tensile test according to JIS Z2241:2011 to determine the 0.2% yield strength and tensile strength. A 0.2% yield strength of 310 MPa or higher was considered good, and a tensile strength of 515 MPa or higher was also considered good.

[0127] In addition, the low-temperature toughness of the metallic materials was evaluated by performing a pendulum impact test according to JIS Z2242:2018. For the evaluation of low-temperature toughness, two pendulum impact tests were conducted at -30℃, and the average value of the two pendulum impact values ​​was 80 J / cm². 2 The lowest value measured above is 60 J / cm³. 2 The above are rated ◎ (excellent), and the average value of the two tests is 54 J / cm. 2 The lowest value measured above is 47 J / cm³. 2 Above and below 60 J / cm 2 The result is ○ (good), and the average of the two tests is less than 54 J / cm. 2 Or, the lowest value measured is less than 47 J / cm³. 2 The one marked as × (bad).

[0128] Furthermore, for comparative examples No. 27–30, tensile tests and pendulum impact tests were not performed.

[0129] The welding wire, flux, welding conditions, post-weld heat treatment conditions, and evaluation results of each test are shown in Table 3 below.

[0130] Table 3

[0131] Table 3

[0132]

[0133] When using fluxes F1 to F12 as examples of the invention in Table 2 above, as shown in Examples No. 1 to 22 of the invention in Table 3, excellent welding operability can be maintained even when welding under high current, and weld metal with excellent mechanical properties can be obtained.

[0134] On the other hand, when fluxes F13 to F16 were used as comparative examples, the mechanical properties decreased compared to the examples of the present invention because the Al content was outside the scope of the present invention, as shown in Comparative Examples No. 23 to 26, 31 to 34.

[0135] Furthermore, when fluxes F17 to F20 were used as comparative examples, the soldering operability was poor, as shown in Comparative Examples No. 27 to 30, since most of the components in the flux were outside the scope of this invention. Therefore, post-weld heat treatment was not performed.

[0136] The above description describes various embodiments, but the present invention is not limited to these examples. Those skilled in the art will obviously be able to conceive of various modifications or alterations within the scope of the patent claims, and these should also be understood to fall within the technical scope of the present invention. Furthermore, the constituent elements in the above embodiments can be arbitrarily combined without departing from the spirit of the present invention.

[0137] Furthermore, this application is based on Japanese Patent Application No. 2020-213838, filed on December 23, 2020, the contents of which are incorporated herein by reference.

Claims

1. A flux for submerged arc welding, characterized in that, This is a submerged arc welding flux used for submerged arc welding of Cr-Mo series steel plates, wherein, relative to the total mass of the flux, it contains: Mn: ≥0.01% by mass and ≤5.00% by mass Al: ≥0.60% by mass and ≤3.00% by mass N: greater than 0% by mass and less than 0.50% by mass MgO: ≥5.0% by mass and ≤40.0% by mass F: 5.0% by mass or more and 12.0% by mass or less Ca: ≥9.5% by mass and ≤21.5% by mass Al2O3: ≥11.0% by mass and ≤23.0% by mass Si and Si compounds SiO2 conversion values: 7.0% by mass or more and 20.0% by mass or less. CO2: 3.0% by mass or more and 10.0% by mass or less, and, C: Less than 1.00% by mass Ni: less than 1.00% by mass The CO2 content is the amount of all metal carbonates converted into CO2.

2. The flux for submerged arc welding according to claim 1, characterized in that, It also contains at least one selected from Na, K and Li, wherein the total content of Na, K and Li relative to the total mass of the flux is more than 0.01% by mass and less than 1.00% by mass.

3. The flux for submerged arc welding according to claim 1 or 2, characterized in that, Relative to the total mass of flux, it also contains Fe: more than 0.10% by mass and less than 5.00% by mass.

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