Bonding flux for submerged arc welding

Abstract

To provide a bond flux for submerged arc welding that offers good weldability, low diffusible hydrogen content in the weld metal, no welding defects, and yields weld metal with the required strength and stable low-temperature toughness. [Solution] In a bond flux for submerged arc welding, the following components are present in mass % of the total mass of the bond flux: SiO2: 5-20%, CaO: 5-20%, MgO: 25-35%, Al2O3: 10-20%, CaF2: 23-35%, total CO2 equivalent values ​​of one or two types of CaCO3 and MgCO3: 2-7%, total Na2O and two types of K2O: 1-5%, Si: 0.3-2.0%, Mn: 0.1-0.8%, Ni: 0.1-1.5%, Mo: 0.05-0.3%, Al: 0-0.8%, total Mn oxide equivalent value: 0-0.5%, total Fe oxide equivalent value: 0-0.2%, and total Ti oxide equivalent value: 0-0.1%.

Description

Technical Field

[0001] The present invention relates to a bonding flux for submerged arc welding of 780 MPa grade high-tensile steel, which can obtain the required strength of the weld metal and stable low-temperature toughness of the weld metal, and has a low diffusible hydrogen content in the weld metal, no welding defects, and good welding workability.

Background Art

[0002] Submerged arc welding has high efficiency and good welding workability, and can obtain a weld metal with excellent mechanical properties. Therefore, it is applied in a wide range of fields such as shipbuilding, steel structures, pipe manufacturing, bridges, and vehicles. In recent years, with the development of the energy industry, the increase in the strength and toughness of steel materials, and the increase in the plate thickness due to the enlargement of structures, the application ratio of submerged arc welding has been increasing year by year from the aspects of quality and productivity. In the submerged arc welding of such high-tensile steel, further quality improvement is required to improve productivity, ensure safety and durability in welding construction. In order to obtain the strength and low-temperature toughness of the weld metal suitable for the steel material properties, reduce the diffusible hydrogen content of the weld metal to prevent low-temperature cracking, and ensure good welding workability, a bonding flux that can freely adjust the chemical composition is applied, and various technical developments have been carried out conventionally.

[0003] For example, Patent Documents 1 and 2 disclose a bonding flux, wire, weld metal, and welding method for submerged arc welding that can obtain a weld metal having excellent low-temperature toughness even at -60°C by making the components of the bonding flux and wire appropriate. However, since the bonding flux described in Patent Documents 1 and 2 has little CaF2, stable low-temperature toughness cannot be obtained. Furthermore, since metallic Ca and metallic Ti are added, the arc becomes unstable and the slag detachment property is also poor.

[0004] Furthermore, Patent Document 3 discloses a submerged arc welding flux that exhibits good welding workability regardless of whether the welding current is AC or DC, and that reduces the amount of moisture absorbed by the flux and the amount of diffusible hydrogen in the weld metal. However, the sintered flux described in Patent Document 3 addresses the toughness of the obtained weld metal at low temperatures down to approximately -40°C in Charpy impact tests, and does not improve toughness at lower temperatures. Moreover, it does not offer any indication regarding tensile strength. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2013-39604 [Patent Document 2] Japanese Patent Publication No. 2013-141681 [Patent Document 3] Japanese Patent Publication No. 2016-140889 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Therefore, the present invention was devised in view of the above-mentioned problems, and aims to provide a bond flux for submerged arc welding of 780 MPa class high-tensile steel that has good welding workability, low diffusible hydrogen content in the weld metal, no welding defects, and yields a weld metal with the required strength and stable low-temperature toughness. [Means for solving the problem]

[0007] The gist of the present invention is a bond flux for submerged arc welding, in which the mass percentage of the total mass of the bond flux is as follows: SiO2: 5-20%, CaO: 5-20%, MgO: 25-35%, Al2O3: 10-20%, CaF2: 23-35%, total CO2 equivalent values ​​of one or two types of CaCO3 and MgCO3: 2-7%, total Na2O and two types of K2O: 1- It is characterized by containing 5% of the following: Si: 0.3-2.0%, Mn: 0.1-0.8%, Ni: 0.1-1.5%, Mo: 0.05-0.3%, Al: 0-0.8%, total Mn oxide equivalent value: 0-0.5%, total Fe oxide equivalent value: 0-0.2%, total Ti oxide equivalent value: 0-0.1%, with the remainder consisting of Fe from the iron alloy and unavoidable impurities. [Effects of the Invention]

[0008] The bond flux for submerged arc welding to which the present invention is applied makes it possible to provide high-efficiency, high-quality weld metal in submerged arc welding of 780 MPa class high-tensile steel, with good welding workability, low diffusible hydrogen content in the weld metal, no welding defects, and the required weld metal strength and stable low-temperature toughness. [Modes for carrying out the invention]

[0009] The inventors of the present invention conducted various studies on the component composition of bond flux for submerged arc welding in order to obtain a weld metal with good weldability, low diffusible hydrogen content in the weld metal, no welding defects, and stable low-temperature toughness in a submerged arc welding method for 780 MPa class high-tensile steel.

[0010] As a result, we found that by adding appropriate amounts of CaO, MgO, and CaF2 to the flux to increase the basicity of the slag, and by adding appropriate amounts of the deoxidizing elements Si and Mn, we could optimize the strength and oxygen content of the weld metal and obtain stable low-temperature toughness. Furthermore, regarding the chemical composition of the weld metal, Ni and Mo are often added to the wire to ensure a stable yield of alloying elements. However, excessive addition of Ni and Mo results in excessive tensile strength and hardness of the wire, which deteriorates the wire's flexibility and feeding properties during welding, and leads to unstable arcs, posing challenges to welding workability. Therefore, we found that by adding Ni and Mo to the wire in amounts that do not impair welding workability, and also adding Ni and Mo to the flux, it is possible to achieve both improved welding workability and the necessary strength and stable low-temperature toughness of the weld metal.

[0011] Furthermore, we found that the amount of diffusible hydrogen in the weld metal can be reduced by adding appropriate amounts of CaCO3 and MgCO3.

[0012] Furthermore, we found that adding appropriate amounts of SiO2 and Al2O3 improves slag detachability and bead shape, and adding appropriate amounts of Na2O, K2O, and Al2O3 improves arc stability, thereby improving the welding workability.

[0013] The following explains the reasons for limiting the component composition of the bond flux for submerged arc welding according to the present invention. Note that the component composition is expressed as a mass percentage relative to the total mass of the bond flux, and when expressing the mass percentage, it is simply written as %.

[0014] [SiO2: 5~20%] SiO2 acts as a slag-forming agent and is an important component for obtaining good slag release properties and bead shape. If the SiO2 content is less than 5%, this effect is not obtained, resulting in poor slag release properties and bead shape. On the other hand, if the SiO2 content exceeds 20%, the amount of oxygen in the weld metal increases, reducing toughness. Therefore, the SiO2 content should be between 5% and 20%. SiO2 can be added as a raw material, for example, from silica sand or water glass.

[0015] [CaO: 5-20%] CaO has the effect of increasing the basicity of the slag and reducing the oxygen content of the weld metal. If the CaO content is less than 5%, this effect is not achieved, and the low-temperature toughness of the weld metal decreases. On the other hand, if the CaO content exceeds 20%, the basicity of the slag increases, the arc becomes unstable, and the slag detachability deteriorates. Therefore, the CaO content should be between 5% and 20%. CaO can be added as a raw material, for example, from wollastonite or calcium oxide.

[0016] [MgO: 25-35%] MgO has the effect of increasing the basicity of the slag and reducing the oxygen content of the weld metal. If the MgO content is less than 25%, this effect is not obtained, and the low-temperature toughness of the weld metal decreases. On the other hand, if the MgO content exceeds 35%, the melting point of the slag increases, and the slag detachability and bead shape deteriorate. Also, if the MgO content exceeds 35%, welding defects such as slag inclusion are more likely to occur. Therefore, the MgO content should be between 25% and 35%. MgO can be added from raw materials such as magnesia clinker.

[0017] [Al2O3: 10-20%] Al2O3 acts as a slag-forming agent. It also improves arc stability. Below 10% Al2O3, the arc becomes unstable, and slag detachability and bead shape deteriorate. Conversely, above 20% Al2O3, the oxygen content of the weld metal increases, reducing its low-temperature toughness. Therefore, the Al2O3 content should be between 10% and 20%. Al2O3 can be added as a raw material, for example, from alumina.

[0018] [CaF2: 23-35%] CaF2 has the effect of increasing the basicity of the slag and reducing the oxygen content of the weld metal. If the CaF2 content is less than 23%, this effect is not obtained, and the low-temperature toughness of the weld metal decreases. On the other hand, if the CaF2 content exceeds 35%, the arc becomes unstable, and the slag detachability and bead shape deteriorate. Therefore, the CaF2 content should be between 23% and 35%. CaF2 can be added as a raw material, for example, from fluorite.

[0019] [Total CO2 equivalent value of one or both of CaCO3 and MgCO3: 2 - 7%] The total CO2 equivalent value from CaCO3 and MgCO3 is an important component for reducing the amount of diffusible hydrogen in the weld metal. During welding, CaCO3 and MgCO3 decompose to release CO or CO2 gas, which reduces the hydrogen partial pressure in the arc atmosphere and has the effect of reducing the amount of diffusible hydrogen in the weld metal. If the total CO2 equivalent value of one or both of CaCO3 and MgCO3 is less than 2%, the effect of reducing the amount of diffusible hydrogen cannot be obtained. On the other hand, if the total CO2 equivalent value of one or both of CaCO3 and MgCO3 exceeds 7%, pop marks are likely to occur, the bead shape deteriorates, the oxygen content of the weld metal increases, and the low-temperature toughness of the weld metal decreases. Therefore, the total CO2 equivalent value of one or both of CaCO3 and MgCO3 should be 2 - 7%. Note that CaCO3 can be added as a raw material from, for example, calcium carbonate, etc., and MgCO3 can be added as a raw material from, for example, magnesium carbonate, etc.

[0020] [Total of one or both of Na2O and K2O: 1 - 5%] Na2O and K2O improve the stability of the arc. If the total of one or both of Na2O and K2O is less than 1%, this effect cannot be obtained and the arc becomes unstable. If the total of one or both of Na2O and K2O exceeds 5%, pop marks are likely to occur, the bead shape deteriorates, and the amount of diffusible hydrogen in the weld metal also increases. Therefore, the total of one or both of Na2O and K2O should be 1 - 5%. Note that Na2O and K2O can be added as raw materials from, for example, sodium silicate and potassium silicate in water glass, etc.

[0021] [Si: 0.3 - 2.0%] Si is a deoxidizing element and has the effect of reducing the oxygen content of the weld metal. If Si is less than 0.3%, the deoxidizing effect cannot be obtained and pop marks are likely to occur. On the other hand, if Si exceeds 2.0%, the strength of the weld metal increases and the low-temperature toughness decreases. Therefore, Si should be 0.3 - 2.0%. Note that Si can be added as a raw material from, for example, metallic Si, Fe - Si, and Fe - Si - Mn, etc.

[0022] [Mn: 0.1 - 0.8%] Mn is added as a major deoxidizing element similar to Si. Also, Mn has the effect of improving the strength of the weld metal. If Mn is less than 0.1%, the deoxidizing effect cannot be obtained and pockmarks are likely to occur. On the other hand, if Mn exceeds 0.8%, the strength of the weld metal becomes high and the low-temperature toughness decreases. Therefore, Mn should be 0.1 - 0.8%. Note that Mn can be added from, for example, metallic Mn, Fe-Mn, and Fe-Si-Mn as raw materials.

[0023] [Ni: 0.1 - 1.5%] Ni has the effect of lowering the transformation temperature and refining the structure, and at the same time, dissolving in the weld metal to increase the strength without decreasing the toughness. Also, Ni has the effect of improving the low-temperature toughness of the weld metal. If Ni is less than 0.1%, the effect of preventing the decrease in toughness cannot be obtained and the low-temperature toughness decreases. On the other hand, if Ni exceeds 1.5%, hot cracking is likely to occur. Therefore, Ni should be 0.1 - 1.5%, preferably 0.1 - 0.7%. Note that Ni can be added from, for example, metallic Ni, Fe-Ni, etc. as raw materials.

[0024] [Mo: 0.05 - 0.3%] Mo, similar to Ni, has the effect of lowering the transformation temperature, refining the structure, and improving the low-temperature toughness and strength of the weld metal. If Mo is less than 0.05%, that effect cannot be obtained and the low-temperature toughness and strength of the weld metal decrease. On the other hand, if Mo exceeds 0.3%, the strength of the weld metal becomes excessively high and the low-temperature toughness decreases. Therefore, Mo should be 0.05 - 0.3%, preferably 0.05 - 0.2%. Note that Mo can be added from, for example, metallic Mo, Fe-Mo, etc. as raw materials.

[0025] The total MnO conversion value of Al and Mn oxides, the total FeO conversion value of Fe oxides, and the total TiO2 conversion value of Ti oxides are not essential components, but one or more of these components may be simultaneously contained as required. The effects and upper limit values obtained by containing each component will be described. Note that the lower limit when not containing these components is 0%.

[0026] [Al: 0~0.8%] Al acts as a deoxidizing agent, reducing the oxygen content of the weld metal and improving its toughness. To achieve this effect, it is preferable to set the lower limit of Al to 0.01% or higher. On the other hand, if Al exceeds 0.8%, low-melting-point compounds are formed, reducing low-temperature toughness. Therefore, the upper limit of Al should be 0.8% or less. Al can be added as a raw material, for example, from metallic Al, Fe-Al, etc.

[0027] [Total Mn oxide equivalent value: 0-0.5%] The total MnO equivalent value of Mn oxide has the effect of improving the bead shape by adjusting the viscosity, fluidity, and melting point of the slag. To obtain this effect, it is preferable to set the lower limit of the total MnO equivalent value of Mn oxide to 0.01% or more. On the other hand, if the total MnO equivalent value of Mn oxide exceeds 0.5%, the amount of oxygen in the weld metal increases, and the toughness of the weld metal decreases. Therefore, the upper limit of the total MnO equivalent value of Mn oxide should be 0.5% or less. Mn oxide can be added as a raw material from manganese oxide, manganese dioxide, etc.

[0028] [Total FeO equivalent value of Fe oxides: 0-0.2%] The total FeO equivalent value of Fe oxide has the effect of adjusting the viscosity and melting point of the molten slag, thereby improving the bead shape. To obtain this effect, it is preferable to set the lower limit of the total FeO equivalent value of Fe oxide to 0.01% or more. On the other hand, if the total FeO equivalent value of Fe oxide exceeds 0.2%, the bead shape and slag detachability will be poor. Therefore, the upper limit of the total FeO equivalent value of Fe oxide should be 0.2% or less. Fe oxide can be added as a raw material from mill scale, etc.

[0029] [Total Ti oxide equivalent value: 0-0.1%] The total TiO2 equivalent value of Ti oxide has the effect of refining the weld metal structure and improving low-temperature toughness. To obtain this effect, it is preferable to set the lower limit of the total TiO2 equivalent value of Ti oxide to 0.01% or more. On the other hand, if the total TiO2 equivalent value of Ti oxide exceeds 0.1%, burning occurs on the bead surface and the slag detachability deteriorates. Therefore, the total TiO2 equivalent value of Ti oxide should be 0.1% or less. Ti oxide can be added as a raw material, for example, from rutile, titanium oxide, titanium slag, etc.

[0030] The remainder of the components described above consists of Fe from iron alloys and unavoidable impurities. While Fe from iron alloys is inevitably present as Fe from iron alloys such as Fe-Si, Fe-Mn, Fe-Si-Mn, Fe-Ni, and Fe-Mo, it is preferable that the amount of Fe from iron alloys be 3% or less from the viewpoint of ensuring good bead shape and slag detachability. Elements detected as unavoidable impurities include P and S. Since both P and S form low-melting-point compounds that reduce the toughness of the weld metal, it is preferable to keep their levels as low as possible. Other components, such as B2O3, may also be present. B2O3 is present incidentally with other components.

[0031] Furthermore, other components and the remainder are inevitably present due to other components, and if present in excess, there is a concern that they may inhibit the effects of the various components of the bond flux that have been intentionally added. Therefore, it is preferable to keep the amount of other components and the remainder as small as possible.

[0032] Furthermore, in submerged arc welding, the chemical composition of the welding wire is preferably such that, from the viewpoint of achieving both weldability, the required strength of the weld metal, and stable low-temperature toughness, the total mass of the wire contains C: 0.05-0.15%, Si: 0.6% or less, Mn: 1.5-2.5%, Ni: 2-3%, Cr: 1% or less, Mo: 1% or less, Ti: 0.1% or less, and further contains Al: 0.1% or less, P: 0.015% or less, S: 0.015% or less, with the remainder being Fe, Cu from the copper plating on the wire surface, and unavoidable impurities. [Examples]

[0033] The effects of the present invention will be described in more detail below with reference to examples.

[0034] Bond fluxes with various components shown in Table 1 were prototyped, and combined with the five types of solid wires shown in Table 2, 20 mm thick, 780 MPa class steel plates with the chemical components shown in Table 3 were processed to a groove shape with a groove angle of 20° and a root gap of 16 mm. Multilayer welding tests were performed with a backing plate and the welding conditions shown in Table 4. In addition, the diffusible hydrogen content of the weld metal was measured for combinations of bond fluxes from Table 1 and solid wires from Table 2.

[0035] The bond flux shown in Table 1 was prepared by blending and mixing various mineral raw materials, granulating with water glass as a binder, and then firing at 500-550°C for 2 hours to achieve a uniform particle size of 0.15 × 1.4 mm. Components that were not added are left blank in Table 1. The solid wire shown in Table 2 was prepared by reducing the diameter of the original wire, annealing it, and plating it to obtain individual strands, which were then drawn to a length of 4.0 mm.

[0036] [Table 1]

[0037] [Table 2]

[0038] [Table 3]

[0039] [Table 4]

[0040] Each test was evaluated by investigating arc stability, slag detachability, bead shape and appearance, and the presence or absence of welding defects using X-ray transmission testing during multi-layer welding, as well as the mechanical properties of the weld metal.

[0041] (arc stability) A welding arc voltage fluctuation of within ±5V was considered "stable."

[0042] (Slag detachability) After welding, any naturally detached or solidified slag was struck with a chipping hammer, then the slag was removed with a brush. The area of ​​remaining slag that could be visually confirmed was estimated, and a slag detachment rate of 95% or higher was considered "good."

[0043] (Bead shape / appearance) The weld bead shape and appearance were considered "good" if the difference between the minimum and maximum bead widths was 7 mm or less within a 150 mm weld length. Conversely, if the difference between the minimum and maximum bead widths exceeded 7 mm, or if undercuts or pockmarks occurred, the weld was considered "poor."

[0044] (Presence or absence of welding defects) The presence or absence of welding defects was investigated based on the radiographic testing method for steel welded joints specified in JIS Z3104:1995. If slag inclusion or other defects occurred, it was recorded as "present," and if slag inclusion or other defects did not occur, it was recorded as "absent."

[0045] (High-temperature cracking) The presence or absence of high-temperature cracking was determined by visually inspecting the bead surface during welding. Crater cracks or similar issues were considered present, while the absence of such issues was considered absent.

[0046] (Machine performance evaluation) The mechanical performance of the weld metal was evaluated by taking tensile test specimens (NK U1A) and impact test specimens (NK U4) from the center of the weld metal in the thickness direction and performing mechanical tests. For the tensile test, a tensile strength of 800-940 MPa was considered good. For the impact test, a Charpy impact test was performed at -60°C, and an average absorbed energy of 80 J or higher over three repeated tests was considered good.

[0047] (Diffusible hydrogen content of weld metal) The diffusible hydrogen content of the weld metal was investigated based on the method for measuring diffusible hydrogen content in steel welds specified in JIS Z 3118:2022. A diffusible hydrogen content of 5 ml / 100g or less was considered good. These investigation results are summarized in Table 5.

[0048] [Table 5]

[0049] In Tables 1 and 5, flux symbols F1 to F25 represent examples of the present invention, and flux symbols F26 to F40 represent comparative examples. Flux symbols F1 to F25, which are examples of the present invention, contain the sum of the CO2 equivalent values ​​of one or two types of bond fluxes SiO2, CaO, MgO, Al2O3, CaF2, CaCO3, and MgCO3, the sum of one or two types of Na2O and K2O, and appropriate amounts of Si, Mn, Ni, and Mo. As a result, good tensile strength and absorbed energy of the weld metal were obtained, the diffusible hydrogen content of the weld metal was low, the arc was stable, and the slag detachability and bead appearance and shape were good, resulting in extremely satisfactory results.

[0050] In the comparative example, flux symbol F26 had poor slag detachability and poor bead shape and appearance due to the low amount of SiO2 in the flux. Furthermore, the low amount of Mo in the flux resulted in low tensile strength and low absorbed energy in the weld metal. Additionally, the low total CO2 equivalent value of one or both CaCO3 and MgCO3 resulted in a high amount of diffusible hydrogen in the weld metal.

[0051] Flux symbol F27 indicates a high SiO2 content, resulting in low energy absorption by the weld metal. However, the low Mn content of the flux leads to pockmarks on the bead surface, resulting in poor bead shape and appearance.

[0052] Flux symbol F28 indicates a low CaO content in the flux, resulting in low absorbed energy of the weld metal. Additionally, the low Si content of the flux led to pockmarks on the bead surface, resulting in poor bead shape and appearance. Furthermore, the high total Ti oxide content (in TiO2 equivalent) of the flux resulted in poor slag release properties.

[0053] Flux symbol F29 indicates a high CaO content, resulting in an unstable arc and poor slag detachability. Additionally, the high Mo content of the flux resulted in high tensile strength of the weld metal and low absorbed energy.

[0054] Flux symbol F30 indicates a low amount of MgO in the flux, resulting in a low absorbed energy in the weld metal. Furthermore, the high total amount of one or two types of Na2O and K2O in the flux led to pockmarks on the bead surface, resulting in poor bead shape and appearance, and a high amount of diffusible hydrogen in the weld metal.

[0055] Flux symbol F31 indicates a high MgO content, resulting in poor slag detachability, bead shape, and appearance, as well as slag inclusion in the weld metal. Additionally, the high Mn content of the flux resulted in high tensile strength of the weld metal and low absorbed energy.

[0056] Flux symbol 32 indicates that the low amount of Al2O3 in the flux resulted in an unstable arc, poor slag detachability, and poor bead shape and appearance. Furthermore, the high amount of Si in the flux resulted in high tensile strength of the weld metal and low absorbed energy.

[0057] Flux symbol F33 indicates a high concentration of Al2O3 in the flux, resulting in low absorbed energy of the weld metal. Additionally, the low total amount of one or two types of Na2O and K2O in the flux led to an unstable arc. Furthermore, the high concentration of Ni in the flux resulted in crater-like cracking on the weld bead surface.

[0058] Flux symbol F34 indicates a low CaF2 content in the flux, resulting in a low absorbed energy in the weld metal. Furthermore, the combined CO2 equivalent values ​​of one or both CaCO3 and MgCO3 in the flux are low, leading to a high diffusible hydrogen content in the weld metal.

[0059] Flux symbol F35 indicates a high CaF2 content, resulting in an unstable arc, poor slag detachability, and poor bead shape and appearance. Additionally, the low Ni content of the flux resulted in low absorbed energy in the weld metal.

[0060] Flux symbol F36 indicates that the combined CO2 equivalent values ​​of one or both CaCO3 and MgCO3 in the flux are high, resulting in low energy absorption in the weld metal, the formation of pockmarks on the bead surface, and poor bead shape and appearance.

[0061] Flux symbol F37 indicates a low SiO2 content, resulting in poor slag release properties and poor bead shape and appearance. Additionally, the high Al content of the flux resulted in low absorbed energy in the weld metal.

[0062] Flux symbol F38 indicates a high CaO content in the flux, resulting in an unstable arc and poor slag detachability. Additionally, the high total Mn oxide content (MnO equivalent) in the flux led to a low absorbed energy in the weld metal.

[0063] Flux symbol F39 indicates a low CaF2 content in the flux, resulting in low absorbed energy of the weld metal. Furthermore, the high total FeO equivalent value of the Fe oxide in the flux led to poor slag detachability and poor bead shape and appearance.

[0064] Flux symbol F40 indicates a low total CO2 equivalent value of one or both CaCO3 and MgCO3 in the flux, resulting in a high diffusible hydrogen content in the weld metal. Additionally, the high Al content of the flux resulted in a low absorbed energy in the weld metal. Furthermore, the high total FeO equivalent value of Fe oxides in the flux led to poor slag detachability and poor bead shape and appearance.

Claims

[Claim 1] In terms of mass % relative to the total mass of bond flux, Yes 2 :5~20%、 CaO: 5-20%, MgO: 25-35%, Al 2 O 3 : 10-200 CaF 2 :23~35%、 CaCO 3 and MgCO 3 One or two types of CO 2 Total converted value: 2-7%, Na 2 O and K 2 Total of one or two of O: 1 - 5%, Si: 0.3-2.0%, Mn: 0.1 to 0.8%, Ni: 0.1 to 1.5%, Mo: 0.05-0.3%, Al: 0-0.8%, Total Mn oxide equivalent value: 0-0.5% Total FeO equivalent value of Fe oxides: 0-0.2% Ti oxide TiO 2 Total converted value: Contains 0-0.1%, A bond flux for submerged arc welding, characterized in that the remainder consists of Fe content from an iron alloy and unavoidable impurities.

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