Bond flux for submerged arc welding of steel for low temperature use

Abstract

To provide a bond flux for submerged arc welding of steel for low temperature use which has good welding workability, is low in diffusible hydrogen of weld metal, has no defect, and enables manufacture of weld metal having stable low temperature toughness.SOLUTION: A bond flux for submerged arc welding of steel for low temperature use contains, in mass% to the total mass of a bond flux, 10 to 20% SiO2, 6 to 15% CaO, 25 to 40% MgO, 10 to 25% Al2O3, 0 to 0.05% Bi2O3, 0.01 to 0.5% of the total of a B conversion value of B alloy and B oxide, 15 to 25% of the total of one or more kinds of metal fluoride, 1 to 8% of the total of a CO2 conversion value of one or more metal carbonates, 0.1 to 2.0% Si, 0.1 to 2.0% Mn, 0.2 to 1.5% Ti, and more than 0 to 8.00% of the total of one or more kinds of Na2O and K2O.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a bond flux for submerged arc welding of low-temperature steel, which provides stable cold cracking resistance and low-temperature toughness in the weld metal, has low diffusible hydrogen in the weld metal, is free of welding defects, and has good welding workability. [Background technology]

[0002] In recent years, the price of fossil fuels has continued to rise due to factors such as their depletion and unstable supply. In response to this, the shipbuilding industry has been promoting the use of larger ships, thicker steel plates, and high-strength steel plates for low temperatures in order to reduce ship costs. Furthermore, in response to the rising prices of fossil fuels, the construction of offshore wind power plants and pumped-storage hydroelectric power plants has been actively promoted in order to utilize natural energy.

[0003] It is known that cold cracking occurs after welding of the thick steel plates used in these applications. A common method for preventing cold cracking is to preheat the base metal to be welded, increase the interpass temperature during welding, and perform post-weld heat treatment. This method reduces the temperature difference between the weld and the base metal and slows the cooling rate of the weld, thereby suppressing the growth of hard structures in the weld that occur due to rapid cooling. At the same time, it promotes the release of diffusible hydrogen from the weld, which causes cold cracking, and reduces the generation of residual stress. However, the process of preheating and post-heating thick steel plates requires a great deal of time and effort, resulting in reduced productivity and increased construction costs.

[0004] Therefore, there is a strong demand for the development of submerged arc welding materials that can eliminate the need for lowering the preheating and interpass temperatures during welding and post-weld heat treatment, enable highly efficient welding, and provide low-temperature toughness to the weld metal.

[0005] For example, Patent Document 1 discloses a technology for a bond flux for submerged arc welding of low-temperature steel that provides excellent welding workability and weld metal with excellent low-temperature toughness, but the flux does not contain CaO in an appropriate range, which causes a problem that weld metal with excellent low-temperature toughness at −74° C. is not obtained. Furthermore, the bulk density of the bond flux is not specified, leaving room for further consideration from the perspective of welding workability. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-28075 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been devised in view of the above-mentioned problems, and an object of the present invention is to provide a bond flux for submerged arc welding of low-temperature steel, which provides a weld metal having excellent welding workability, good mechanical properties, and particularly excellent low-temperature toughness, and which also has a small amount of diffusible hydrogen. [Means for solving the problem]

[0008] The gist of the present invention is a bond flux for submerged arc welding of low-temperature steel, characterized in that it contains, in mass % relative to the total mass of the bond flux, 10 to 20% SiO2, 6 to 15% CaO, 25 to 40% MgO, 10 to 25% Al2O3, 0 to 0.05% Bi2O3, a sum of B alloys and B oxides in terms of B: 0.01 to 0.5%, a sum of one or more metal fluorides: 15 to 25%, a sum of one or more metal carbonates in terms of CO2: 1 to 8%, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Ti: 0.2 to 1.5%, a sum of one or two of Na oxides and K oxides, Na2O and KO: more than 0 to 8.00%, and the remainder consisting of Fe from the iron alloy powder and unavoidable impurities.

[0009] In addition, the bulk density of the bond flux is 1.2 g / cm 3 The bond flux for submerged arc welding of low-temperature steel is also characterized by the following: [Effects of the Invention]

[0010] The bond flux for submerged arc welding of low-temperature steel to which the present invention is applied can provide a weld metal with excellent welding workability and good mechanical properties, particularly low-temperature toughness, and can also efficiently provide high-quality welds with a low amount of diffusible hydrogen and no welding defects. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present inventors have conducted extensive research into the component composition of a bond flux for submerged arc welding that is capable of producing a weld metal that has good welding workability, a low amount of diffusible hydrogen in the weld metal, is free of welding defects, and has stable cold cracking resistance and low temperature toughness in a submerged arc welding method for low temperature steels.

[0012] As a result, it was found that weld metal with excellent strength and low-temperature toughness can be obtained by adjusting the total B equivalent of CaO, MgO, B alloy and B oxide, the total of one or more metal fluorides, Si, Mn and Ti to appropriate amounts. It was also found that the amount of diffusible hydrogen can be reduced by adjusting the total CO2 equivalent of metal carbonates.

[0013] Furthermore, it was found that the arc stability can be improved by adding appropriate amounts of Al2O3, Na2O, and K2O, and that the slag removability and bead shape can be improved by adding appropriate amounts of SiO2 and Al2O3, and that the bead shape can be further improved by adjusting the flux bulk density to an appropriate value.

[0014] The reasons for limiting the chemical composition of the bonded flux for submerged arc welding using the low-temperature steel of the present invention will be explained below. Note that the chemical composition of each component is shown in mass % relative to the total mass of the bonded flux, and when expressing mass %, it is simply written as %.

[0015] [SiO2: 10-20%] SiO2, derived from silica sand, wollastonite, water glass (sodium silicate, potassium silicate), etc., acts as a slag former, improving slag removability and bead shape. However, if the SiO2 content is less than 10%, this effect is not achieved, resulting in poor slag removability and bead shape. On the other hand, if the SiO2 content exceeds 20%, the amount of oxygen in the weld metal increases, reducing low-temperature toughness. Therefore, the SiO2 content is set to 10-20%.

[0016] [CaO: 6-15%] CaO, derived from wollastonite, calcium carbonate, etc., increases the basicity of the slag, reduces the oxygen content of the weld metal, and improves low-temperature toughness. If the CaO content is less than 6%, this effect is not obtained and low-temperature toughness decreases. On the other hand, if the CaO content exceeds 15%, the slag basicity becomes excessively high, causing the arc to become unstable, resulting in poor slag removability and poor bead shape. Therefore, the CaO content is set to 6-15%.

[0017] [MgO: 25-40%] MgO, derived from magnesia clinker, magnesium carbonate, etc., increases the basicity of the slag, reduces the oxygen content of the weld metal, and improves low-temperature toughness. If the MgO content is less than 25%, this effect is not obtained and low-temperature toughness decreases. On the other hand, if the MgO content exceeds 40%, the melting point of the slag increases, resulting in poor slag removability. Furthermore, if the MgO content exceeds 40%, welding defects such as slag entrapment in the weld metal become more likely to occur. Therefore, the MgO content is set to 25-40%.

[0018] [Al2O3; 10-25%] Al2O3, whose main ingredient is alumina, stabilizes the arc, improves slag removability, and also improves the bead appearance. However, if the Al2O3 content is less than 10%, the arc becomes unstable, resulting in poor slag removability and poor bead shape. On the other hand, if the Al2O3 content exceeds 25%, slag removability becomes poor and welding defects such as slag entrapment in the weld metal become more likely to occur. Therefore, the Al2O3 content is set to 10-25%.

[0019] [Bi2O3: 0~0.05%] Bi2O3, whose main ingredient is bismuth oxide, may be added to improve slag removability, but if Bi2O3 exceeds 0.05%, the low-temperature toughness of the weld metal decreases. Furthermore, if Bi2O3 exceeds 0.05%, cracks are more likely to occur in the weld. Therefore, the upper limit of Bi2O3 is set to 0.05%. Note that Bi2O3 is not an essential component, and the content may be 0%.

[0020] [Total B-equivalent value of B alloy and B oxide: 0.01-0.5%] B alloy and B oxide, which are made from borax and boron oxide, have the effect of suppressing the growth of pro-eutectoid ferrite that forms at the austenite grain boundaries of the weld metal, thereby improving low-temperature toughness. However, if the total B equivalent of B alloy and B oxide is less than 0.01%, this effect is not obtained and low-temperature toughness decreases. On the other hand, if the total B equivalent of B alloy and B oxide exceeds 0.5%, the strength of the weld metal becomes excessive and low-temperature toughness decreases. Therefore, the total B equivalent of B alloy and B oxide is set to 0.01 to 0.5%.

[0021] [Total of one or more metal fluorides: 15-25%] Metal fluorides made from raw materials such as fluorite, aluminum fluoride, barium fluoride, magnesium fluoride, and sodium fluoride increase the basicity of the slag, reduce the oxygen content of the weld metal, and improve low-temperature toughness. However, if the total content of one or more metal fluorides is less than 15%, this effect is not obtained and low-temperature toughness decreases. On the other hand, if the total content of one or more metal fluorides exceeds 25%, the arc becomes unstable, resulting in poor slag removability and bead shape. Furthermore, if the total content of one or more metal fluorides exceeds 25%, pockmarks are likely to occur on the bead surface. Therefore, the total content of one or more metal fluorides is set to 15-25%.

[0022] [Total CO2 equivalent value of one or more metal carbonates: 1-8%] The CO2 equivalent values from metal carbonates such as calcium carbonate, magnesium carbonate, lithium carbonate, and barium carbonate have the effect of lowering the hydrogen partial pressure in the arc atmosphere and reducing the amount of diffusible hydrogen in the weld metal. However, if the total CO2 equivalent values of one or more metal carbonates is less than 1%, this effect is not obtained and the amount of diffusible hydrogen in the weld metal increases. On the other hand, if the total CO2 equivalent values of one or more metal carbonates exceeds 8%, the bead shape and slag removability become poor. Furthermore, if the total CO2 equivalent values of one or more metal carbonates exceeds 8%, pockmarks are likely to occur on the bead surface. Therefore, the total CO2 equivalent values of one or more metal carbonates should be 1-8%.

[0023] [Si: 0.1-2.0%] Silicon, derived from metallic Si, Fe-Si, Fe-Si-Mn, etc., is a deoxidizing agent that reduces the oxygen content in the weld metal, thereby improving low-temperature toughness. However, if the Si content is less than 0.1%, this effect is not obtained and low-temperature toughness decreases. On the other hand, if the Si content exceeds 2.0%, the strength of the weld metal becomes excessively high and low-temperature toughness decreases. Therefore, the Si content is set to 0.1 to 2.0%.

[0024] [Mn: 0.1-2.0%] Mn, derived from raw materials such as metallic Mn, Fe-Mn, and Fe-Si-Mn, improves the hardenability of weld metal and improves low-temperature toughness by forming intragranular ferrite. However, if the Mn content is less than 0.1%, this effect is not obtained and low-temperature toughness decreases. On the other hand, if the Mn content exceeds 2.0%, the strength of the weld metal becomes excessively high and low-temperature toughness decreases. Therefore, the Mn content is set to 0.1 to 2.0%.

[0025] [Ti: 0.2~1.5%] Ti, derived from metallic Ti, Fe-Ti, etc., has the effect of improving the low-temperature toughness of the weld metal. However, if Ti is less than 0.2%, the low-temperature toughness of the weld metal decreases. On the other hand, if Ti exceeds 1.5%, the amount of solid-solubilized Ti in the weld metal increases, reducing the low-temperature toughness. Therefore, the Ti content is set to 0.2 to 1.5%.

[0026] [Total of one or both of sodium oxides and potassium oxides, Na2O and K2O: over 0 to 8.00%] NaO and KO, sodium oxides and potassium oxides made primarily from water glass (sodium silicate, potassium silicate) and potassium feldspar, have the effect of stabilizing the arc. However, if the total content of one or both of NaO and KO exceeds 8.00%, undercutting occurs at the toe of the bead, resulting in a poor bead shape. Therefore, the total content of one or both of NaO and KO should be 8.00% or less. On the other hand, although the arc stabilizing effect can be obtained at a content above 0%, the lower limit is preferably 0.01% or more.

[0027] [Flux bulk density: 1.2 g / cm 3 below] The bulk density of the flux affects the shielding of the molten pool from the atmosphere during welding and the spreading of the weld bead. 3 The bead shape can be adjusted by doing the following:

[0028] The bulk density of the flux can be measured in accordance with JIS K5101-12-1:2004.

[0029] 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 )

[0030] The balance of the bond flux for submerged arc welding of low-temperature steel according to the present invention is composed of Fe from iron alloy powder such as Fe-Si, Fe-Mn, Fe-Si-Mn, and Fe-Ti, and unavoidable impurities such as P and S. Both P and S form compounds with low melting points and reduce the toughness of the weld metal, so it is preferable that their contents are as low as possible.

[0031] The bond flux of the present invention is used in combination with a welding wire for submerged arc welding. The welding wire is not particularly limited as long as it can be used for welding low-temperature steels. For example, a welding wire containing, by mass %, C: 0.05 to 0.20%, Si: 0.5% or less, Mn: 1.2 to 3.0%, Ni: 0 to 3%, Cr: 0 to 1%, Mo: 0 to 1%, Al: 0.1% or less, P: 0.030% or less, S: 0.015% or less, with the balance being Fe and impurities can be used. This welding wire may be copper-plated. [Example]

[0032] The effects of the present invention will be described in more detail below with reference to examples.

[0033] Bond fluxes with various compositions shown in Table 1 were prototyped and combined with the five types of wire shown in Table 2. Steel plates with a thickness of 25 mm and made of the chemical compositions shown in Table 3 were processed into groove shapes with a groove angle of 30° and root spacing of 13 mm. Backing metal was then applied and multi-pass welding tests were carried out under the welding conditions shown in Table 4.

[0034] The bond flux shown in Table 1 was prepared by compounding and mixing various mineral raw materials, granulating them with water glass as a binder, and then firing them at 450-550°C for 2 hours to granulate them to 1.4 x 0.15 mm. The wires shown in Table 2 were prepared by reducing, annealing, and plating the raw wires to form strands, which were then drawn to 4.0 mm.

[0035] [Table 1]

[0036] [Table 2]

[0037] [Table 3]

[0038] [Table 4]

[0039] To evaluate the mechanical performance of the weld metal, tensile test pieces and impact test pieces were taken in accordance with AWS.5.23 and mechanical tests were conducted. In the tensile test, a tensile strength of 540 to 720 MPa was considered good. In the impact test, a Charpy impact test was conducted at -74°C, and an average absorbed energy of 100 J or more after three repeated tests was considered good. The diffusible hydrogen content of the weld metal was measured in accordance with JIS Z3118. A diffusible hydrogen content of 5 ml / 100 g or less was considered good.

[0040] The welding workability was investigated by investigating the arc stability, slag removability, and bead shape during multi-layer welding (excluding the first layer), and then X-ray examination was carried out to check for the presence or absence of welding defects.

[0041] (Arc stability) Arc stability was considered "stable" if the welding voltage fluctuation during welding was within ±5V.

[0042] (Slag removability) The slag removability was rated as "good" if the solidified slag peeled off naturally or could be easily removed by lightly hitting it with a chipping hammer.

[0043] (Bead shape) The bead shape was visually inspected after welding to ensure there were no pockmarks or undercuts, and the difference between the minimum and maximum bead widths was rated as "good" if it was 7 mm or less, and "very good" if it was 4 mm or less.

[0044] (welding defects) The X-ray examination was conducted based on the radioactivity penetration test for steel welded joints specified in JIS Z3104:1995, and the weld was deemed "free" if no slag inclusions or cracks were found in the weld. The results of these examinations are summarized in Table 5.

[0045] [Table 5]

[0046] In Tables 1 and 5, fluxes designated F1 to F25 are examples of the present invention, and fluxes designated F26 to F39 are comparative examples. The fluxes designated F1 to F25, which are examples of the present invention, have appropriate amounts of SiO2, CaO, MgO, Al2O3, the sum of the B-equivalent values of the B alloy and B oxide, the sum of one or more metal fluorides, the sum of the CO2-equivalent values of one or more metal carbonates, and the sum of one or two of Si, Mn, Ti, Na2O, and KO, so that the weld metal had good tensile strength and absorbed energy, the amount of diffusible hydrogen in the weld metal was low, the arc was stable, and the slag removability and bead shape were good, resulting in satisfactory results.

[0047] In addition, the flux codes F1, F2, F3, F4, F8, F9, F10, F12, F14, F17, F18, F19, F22, F23, and F24 had appropriate bulk densities, resulting in extremely good bead shapes and very satisfactory results.

[0048] The flux F26 in the comparative examples had poor slag removability and bead shape due to its low SiO2 content, and had a high Mn content, which resulted in excessive weld metal strength and low absorbed energy.

[0049] Flux F27 has a low CaO content, so the absorbed energy of the weld metal was low. In addition, the bulk density of the flux was appropriate, so the bead shape was extremely good.

[0050] Flux F28 contained a large amount of SiO2, resulting in low absorbed energy in the weld metal. It also contained a large amount of one or more metal fluorides, which resulted in an unstable arc and poor slag removability. It also contained a large amount of one or more metal fluorides, which resulted in pockmarks and poor bead shape.

[0051] Flux F29 contained a large amount of Ti, which resulted in low absorbed energy in the weld metal. Also, because it contained a large amount of CaO, the arc became unstable, resulting in poor slag removability and bead shape.

[0052] Flux code F30 has a low MgO content, so the absorbed energy of the weld metal was low.

[0053] Flux F31 had a low Ti content, resulting in low absorbed energy in the weld metal. Also, because it contained a large amount of MgO, slag removability was poor, resulting in slag inclusion in the weld metal.

[0054] Flux F32 contained a small amount of Al2O3, which resulted in an unstable arc, poor slag removability, and poor bead shape. Also, because it contained a small amount of Mn, the absorbed energy of the weld metal was low.

[0055] Flux F33 contained a large amount of Al2O3, which resulted in poor slag removal and slag inclusion in the weld metal. Also, because it contained a large amount of Si, the weld metal was too strong and the absorbed energy was low.

[0056] Flux code F34 had a low total B-equivalent value of B alloy and B oxide, so the absorbed energy of the weld metal was low. In addition, the bulk density of the flux was appropriate, so the bead shape was extremely good.

[0057] Flux F35 had a high total B-equivalent value for B alloys and B oxides, resulting in excessive weld metal strength and low absorbed energy. Also, because the total CO2-equivalent value of one or more metal carbonates was high, pockmarks occurred, the bead shape was poor, and slag removability was poor. Although the bulk density of the flux was appropriate, it did not have the effect of shaping the bead.

[0058] Flux code F36 has a low Si content, so the absorbed energy of the weld metal was low.

[0059] Flux F37 contained a large amount of Bi2O3, which resulted in low absorbed energy in the weld metal, causing cracks in the weld. Also, the total CO2 equivalent value of one or more metal carbonates was low, resulting in a high amount of diffusible hydrogen in the weld metal. Furthermore, the total amount of Na2O and one or two types of K2O was high, resulting in undercut at the toe of the bead, resulting in a poor bead shape.

[0060] Flux F38 had a low total content of one or more metal fluorides, resulting in a low absorbed energy value for the weld metal. Furthermore, the flux had an appropriate bulk density, resulting in an extremely good bead shape.

[0061] Flux code F39 contained a large amount of Mn, which resulted in excessive strength of the weld metal and low absorbed energy. In addition, the bulk density of the flux was appropriate, resulting in an extremely good bead shape.

Claims

1. In mass % of the total mass of the bond flux, Yes 2 :10~20%、 CaO: 6-15%, MgO: 25-40%, <h2 style=";text-align:left;direction:ltr">Al<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> O<h2 style=";text-align:left;direction:ltr"> 3 <h2 style=";text-align:left;direction:ltr"> :15~25%、 Yes 2 Oh 3 :0~0.05%, The total of B alloy and B oxide converted into B: 0.01 to 0.5%; Total of one or more metal fluorides: 15 to 25%, One or more metal carbonates 2 Total conversion value: 1-8% Si: 0.1-2.0%, Mn: 0.1 to 2.0%, Ti: 0.2 to 1.5%, Na in Na oxide and K oxide 2 O and K 2 The total content of one or two of O: more than 0 to 8.00%, A bond flux for submerged arc welding of low-temperature steel, the balance of which consists of Fe from the iron alloy powder and unavoidable impurities.

2. Flux bulk density: 1.2 g / cm 3 2. The bond flux for submerged arc welding of low-temperature steel according to claim 1, wherein:

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