Bonding flux for submerged arc welding of low-temperature steel

Abstract

The present invention addresses the problem of providing a bond flux for submerged arc welding of low-temperature steel, the bond flux having good welding workability, low diffusible hydrogen content in the welded metal, no welding defects, and being capable of obtaining a welded metal having stable low-temperature toughness. The bond flux for submerged arc welding of low-temperature steel is characterized in that: the amount of the bond flux is less than 1% by mass relative to the total mass of the bond flux; the present invention is characterized by containing 10 to 20% of SiO2, 6 to 15% of CaO, 25 to 40% of MgO, 10 to 25% of Al2O3, 0 to 0.05% of Bi2O3, 0.01 to 0.5% of the total of B alloy and B oxide in terms of B, 15 to 25% of the total of one or more metal fluorides, 1 to 8% of the total of one or more metal carbonates in terms of CO2, 0.1 to 2.0% of Si, 0.1 to 2.0% of Mn, 0.2 to 1.5% of Ti, and more than 0 to 8.00% of one or both of Na2O and K2O.

Description

Technical Field

[0001] The present invention relates to a bonded flux for submerged arc welding of low-temperature steel, and relates to a bonded flux for submerged arc welding of low-temperature steel that can obtain low-temperature crack resistance and low-temperature toughness of stable weld metal, has low diffusible hydrogen in the weld metal, has no welding defects, and has good welding workability. Background Art

[0002] In recent years, due to the depletion of fossil fuels, unstable supply, etc., the prices of fossil fuels have been continuously rising. Along with this, in the shipbuilding industry, in order to reduce ship costs, the enlargement of ships has been promoted, and the thickening of steel plates used and the high-strengthening using low-temperature steel have been continuously developed. In addition, in order to utilize natural energy to cope with the rise of fossil fuels, the construction of offshore wind power generation and pumped-storage hydroelectric power plants has been actively carried out.

[0003] In the welding of thick steel plates used in them, it is known that low-temperature cracks occur after welding. Generally, as a construction method for preventing low-temperature cracks, the following method is implemented: preheating the base metal to be welded, increasing the interpass temperature during welding, and performing post-weld heat treatment. In this construction method, the temperature difference between the welded part and the base metal is reduced to slow down the cooling rate of the welded part, thereby having the effects of suppressing the growth of the hard structure of the welded part caused by rapid cooling and at the same time promoting the release of diffusible hydrogen in the welded part, which is the cause of low-temperature cracks, and the effect of alleviating the generation of residual stress. However, the operations of preheating and post-heating thick steel plates require a large amount of time and labor, which will lead to a decrease in productivity, an increase in construction costs, etc.

[0004] Therefore, there is a great demand for the development of a submerged arc welding material that can reduce the preheating / interpass temperature during welding, omit post-weld heat treatment, can perform welding efficiently, and obtain the low-temperature toughness of weld metal.

[0005] For example, Patent Document 1 discloses a technique of a bonded flux for submerged arc welding of low-temperature steel with excellent welding workability and capable of obtaining weld metal with excellent low-temperature toughness. However, since the content of CaO contained in the flux is not within an appropriate range, there is a problem that weld metal with low-temperature toughness can be obtained at -74°C. In addition, the bulk density of the bonded flux is not specified, and there is still room for further research from the aspect of welding workability.

[0006] Prior Art Documents

[0007] Patent Documents

[0008] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2021-28075 Summary of the Invention

[0009] Problems to be Solved by the Invention

[0010] Accordingly, the present invention has been made in view of the above problems, and an object thereof is to provide a bonded flux for submerged arc welding of low-temperature steel, which has excellent welding workability, can obtain a weld metal having good mechanical properties, particularly excellent low-temperature toughness, and has a small amount of diffusible hydrogen.

[0011] Means for Solving the Problem

[0012] The gist of the present invention is a bonded flux for submerged arc welding of low-temperature steel, which is characterized in that, based on mass% of the total mass of the bonded flux, it contains SiO2: 10 to 20%, CaO: 6 to 15%, MgO: 25 to 40%, Al2O3: 10 to 25%, Bi2O3: 0 to 0.05%, the total of the B conversion values of B alloy and B oxide: 0.01 to 0.5%, the total of one or more metal fluorides: 15 to 25%, the total of the CO2 conversion values of one or more metal carbonates: 1 to 8%, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Ti: 0.2 to 1.5%, the total of one or two of Na2O and K2O in Na oxide and K oxide: more than 0 to 8.00%, and the balance is composed of Fe components from ferroalloy powder and inevitable impurities.

[0013] In addition, the bonded flux for submerged arc welding of low-temperature steel is further characterized in that in the composition of the bonded flux, the bulk density is 1.2 g / cm 3 as follows.

[0014] Effects of the Invention

[0015] According to the bonded flux for submerged arc welding of low-temperature steel to which the present invention is applied, the welding workability is excellent, a weld metal having good mechanical properties, particularly excellent low-temperature toughness, can be obtained, and a high-quality welded portion with a low amount of diffusible hydrogen and no welding defects can be provided efficiently. Detailed Embodiments

[0016] The present inventors have conducted various studies on the composition of a bonded flux for submerged arc welding that has good welding workability, a low amount of diffusible hydrogen in the weld metal, no welding defects, and can obtain a weld metal with stable low-temperature crack resistance and low-temperature toughness in the submerged arc welding method for low-temperature steel.

[0017] As a result, it was found that by making the total of the B conversion values of CaO, MgO, B alloy and B oxide, the total of one or more metal fluorides, Si, Mn and Ti appropriate, a weld metal having excellent strength and low-temperature toughness can be obtained. And it was found that by making the total of the CO2 conversion values of metal carbonates appropriate, the amount of diffusible hydrogen can be reduced.

[0018] Furthermore, it is found that the arc stability becomes good by adding appropriate amounts of Al2O3, Na2O, and K2O, the slag detachability and bead shape become good by adding appropriate amounts of SiO2 and Al2O3, and the bead shape becomes better by making the bulk density of the welding flux an appropriate value.

[0019] The reasons for limiting the component composition of the bonded welding flux for submerged arc welding of the low-temperature steel to which the present invention is applied will be described below. It should be noted that for each component composition, the mass % relative to the total mass of the bonded welding flux is shown, and when indicating the mass %, it is simply denoted as % for representation.

[0020] [SiO2: 10 - 20%]

[0021] SiO2 using silica sand, wollastonite, water glass (sodium silicate, potassium silicate), etc. as raw materials acts as a slag former, and has good slag detachability and the effect of adjusting the bead shape. However, if SiO2 is less than 10%, this effect cannot be obtained, and the slag detachability and bead shape are poor. On the other hand, if SiO2 exceeds 20%, the oxygen content in the weld metal increases and the low-temperature toughness decreases. Therefore, SiO2 is 10 - 20%.

[0022] [CaO: 6 - 15%]

[0023] CaO using wollastonite, calcium carbonate, etc. as raw materials has the effects of increasing the basicity of the slag, reducing the oxygen content in the weld metal, and improving the low-temperature toughness. If CaO is less than 6%, this effect cannot be obtained and the low-temperature toughness decreases. On the other hand, if CaO is higher than 15%, the basicity of the slag becomes too high, the arc becomes unstable, and the slag detachability and bead shape are poor. Therefore, CaO is 6 - 15%.

[0024] [MgO: 25 - 40%]

[0025] MgO using magnesite, magnesium carbonate, etc. as raw materials has the effects of increasing the basicity of the slag, reducing the oxygen content in the weld metal, and improving the low-temperature toughness. If MgO is less than 25%, this effect cannot be obtained and the low-temperature toughness decreases. On the other hand, if MgO is higher than 40%, the melting point of the slag increases and the slag detachability is poor. In addition, if MgO is higher than 40%, welding defects such as slag inclusions are likely to occur in the weld metal. Therefore, MgO is 25 - 40%.

[0026] [Al2O3: 10 - 25%]

[0027] Al2O3, which uses alumina as the main raw material, has the function of stabilizing the arc, improving slag detachability, and thus adjusting the bead appearance. However, if the Al2O3 content is less than 10%, the arc is unstable, and the slag detachability and bead shape are poor. On the other hand, if the Al2O3 content is higher than 25%, the slag detachability is poor, and welding defects such as slag inclusions are likely to occur in the welded metal. Therefore, the Al2O3 content is 10 - 25%.

[0028] [Bi2O3: 0 - 0.05%]

[0029] To improve slag detachability, Bi2O3, which uses bismuth oxide as the main raw material, can be contained. However, if the Bi2O3 content is higher than 0.05%, the low-temperature toughness of the welded metal decreases. In addition, if the Bi2O3 content is higher than 0.05%, cracks are likely to occur in the welded part. Therefore, the upper limit of Bi2O3 is 0.05% or less. It should be noted that Bi2O3 is not an essential component, and its content can be 0%.

[0030] [Total B conversion value of B alloy and B oxide: 0.01 - 0.5%]

[0031] B alloy and B oxide, which use borax and boron oxide as raw materials, have the effect of inhibiting the growth of proeutectoid ferrite formed at the austenite grain boundaries of the welded metal and improving low-temperature toughness. However, if the total B conversion value of the B alloy and B oxide is less than 0.01%, this effect cannot be obtained, and the low-temperature toughness decreases. On the other hand, if the total B conversion value of the B alloy and B oxide is higher than 0.5%, the strength of the welded metal is excessive, and the low-temperature toughness decreases. Therefore, the total B conversion value of the B alloy and B oxide is 0.01 - 0.5%.

[0032] [Total of one or more metal fluorides: 15 - 25%]

[0033] Metal fluorides, which use fluorite, aluminum fluoride, barium fluoride, magnesium fluoride, sodium fluoride, etc. as raw materials, have the effect of increasing the basicity of the slag, reducing the oxygen content of the welded metal, and improving low-temperature toughness. However, if the total of one or more metal fluorides is less than 15%, this effect cannot be obtained, and the low-temperature toughness decreases. On the other hand, if the total of one or more metal fluorides is higher than 25%, the arc becomes unstable, and the slag detachability and bead shape are poor. In addition, if the total of one or more metal fluorides is higher than 25%, pitting is likely to occur on the bead surface. Therefore, the total of one or more metal fluorides is 15 - 25%.

[0034] [Total CO2 conversion value of one or more metal carbonates: 1 - 8%]

[0035] The CO2 conversion value from metal carbonates such as calcium carbonate, magnesium carbonate, lithium carbonate, and barium carbonate has the effect of reducing the hydrogen partial pressure in the arc atmosphere and thus reducing the diffusible hydrogen content in the weld metal. However, if the total CO2 conversion value of one or more metal carbonates is less than 1%, this effect cannot be obtained, and the diffusible hydrogen content in the weld metal increases. On the other hand, if the total CO2 conversion value of one or more metal carbonates is higher than 8%, the bead shape and slag detachability are poor. In addition, if the total CO2 conversion value of one or more metal carbonates is higher than 8%, pitting is likely to occur on the bead surface. Therefore, the total CO2 conversion value of one or more metal carbonates is 1 - 8%.

[0036] [Si: 0.1 - 2.0%]

[0037] Si using metal Si, Fe - Si, Fe - Si - Mn, etc. as raw materials is a deoxidizing material and has the effect of improving the low - temperature toughness by reducing the oxygen content in the weld metal. However, if Si is less than 0.1%, this effect cannot be obtained, and the low - temperature toughness decreases. On the other hand, if Si is higher than 2.0%, the strength of the weld metal becomes too high and the low - temperature toughness decreases. Therefore, Si is 0.1 - 2.0%.

[0038] [Mn: 0.1 - 2.0%]

[0039] Mn using metal Mn, Fe - Mn, Fe - Si - Mn, etc. as raw materials has the effect of increasing the hardenability of the weld metal and generating intragranular ferrite to improve the low - temperature toughness. However, if Mn is less than 0.1%, this effect cannot be obtained, and the low - temperature toughness decreases. On the other hand, if Mn is higher than 2.0%, the strength of the weld metal becomes too high and the low - temperature toughness decreases. Therefore, Mn is 0.1 - 2.0%.

[0040] [Ti: 0.2 - 1.5%]

[0041] Ti using metal Ti, Fe - Ti, etc. as raw materials 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 is higher than 1.5%, the dissolved Ti in the weld metal increases and the low - temperature toughness decreases. Therefore, Ti is 0.2 - 1.5%.

[0042] [Total of one or two of Na2O and K2O in Na oxide and K oxide: higher than 0 - 8.00%]

[0043] Na oxides and K oxides such as sodium silicate (sodium metasilicate, potassium silicate) and potassium feldspar as main raw materials have the effect of stabilizing the arc. However, if the total of one or both of Na2O and K2O is higher than 8.00%, undercut will occur at the weld toe, resulting in poor bead shape. Therefore, the total of one or both of Na2O and K2O is 8.00% or less. On the other hand, for the lower limit, when it is higher than 0%, the effect of stabilizing the arc can be obtained, and it is preferably 0.01% or more.

[0044] [Flux bulk density: 1.2 g / cm 3 or less]

[0045] The bulk density of the flux plays a role in shielding the molten pool from the atmosphere during welding and the expansion of the welded bead. By making the bulk density 1.2 g / cm 3 or less, the effect of adjusting the bead shape can be obtained.

[0046] The measurement of the bulk density of the flux can be carried out according to JIS K5101-12-1:2004.

[0047] Bulk density (g / cm 3 ) = (mass of the receiver with the sample (g) - mass of the receiver (g)) / internal volume of the receiver (cm 3 )

[0048] The balance of the bonded flux for submerged arc welding of the low-temperature steel of the present invention is the Fe component from ferroalloy powders such as Fe-Si, Fe-Mn, Fe-Si-Mn, Fe-Ti, and inevitable impurities such as P and S. Both P and S form low-melting compounds, reducing the toughness of the welded metal. Therefore, it is preferably as low as possible.

[0049] In addition, the bonded flux of the present invention is combined with a welding wire for use in submerged arc welding. The welding wire is not particularly limited as long as it can be used for welding low-temperature steel. For example, a welding wire containing C: 0.05 - 0.20%, Si: 0.5% or less, Mn: 1.2 - 3.0%, Ni: 0 - 3%, Cr: 0 - 1%, Mo: 0 - 1%, Al: 0.1% or less, P: 0.030% or less, S: 0.015% or less, and the balance being Fe and impurities by total mass of the welding wire can be used. It should be noted that the welding wire can also be copper-plated.

[0050] Examples

[0051] The effects of the present invention will be further described in detail below through examples.

[0052] Prepare the bonded flux of various components shown in the trial production table 1, combine the 5 types of welding wires shown in table 2, process the steel plate with a thickness of 25 mm and a chemical composition shown in table 3 into a groove shape with a groove angle of 30° and a root gap of 13 mm, apply a backing plate, and perform a multi-layer and multi-pass welding test under the welding conditions shown in table 4.

[0053] It should be noted that for the bonded flux shown in table 1, after mixing and blending various mineral raw materials, granulation is carried out using water glass as a fixing agent, and then fired at 450 - 550 °C for 2 hours and sized to 1.4 × 0.15 mm. In addition, among the welding wires shown in table 2, the original wire is reduced in diameter, annealed, and coated to make a blank wire, and these blank wires are drawn to 4.0 mm for use.

[0054] [Table 1]

[0055]

[0056] Remarks *1: Ca in metal fluoride represents CaF2, and Na represents NaF.

[0057] *2: In the CO2 conversion value, Li represents Li2CO3, and Ca represents CaCO 3、 Mg represents MgCO3.

[0058] *3: In addition, as the balance, it is the Fe component from ferroalloys such as Fe - Si and Fe - Mn and inevitable impurities

[0059] [Table 2]

[0060]

[0061] [Table 3]

[0062]

[0063] [Table 4]

[0064]

[0065] Regarding the mechanical property evaluation of the weld metal, mechanical tests are carried out on the tensile test pieces and impact test pieces according to AWS.5.23. In the evaluation of the tensile test, a tensile strength of 540 - 720 MPa is regarded as good. In the evaluation of the impact test, a Charpy impact test at -74 °C is carried out, and the average value of the absorbed energy of 3 repeated specimens being 100 J or more is regarded as good. The measurement of the diffusible hydrogen content in the weld metal is carried out according to JIS Z3118. A diffusible hydrogen content in the weld metal of 5 ml / 100 g or less is regarded as good.

[0066] Regarding weldability, after investigating the arc stability, slag detachability, and bead shape during multi-layer and multi-pass welding except for the first layer, the presence of welding defects was investigated through X-ray penetration testing.

[0067] (Arc stability)

[0068] Regarding arc stability, if the welding voltage variation during welding is within ±5 V, it is considered "stable".

[0069] (Slag detachability)

[0070] Regarding slag detachability, the case where the solidified slag peels off naturally or can be easily removed by lightly tapping the solidified slag with a chisel hammer is considered "good".

[0071] (Bead shape)

[0072] Regarding bead shape, visually confirm the bead after welding. The case where there are no pits or undercuts and the difference between the minimum and maximum values of the bead width is 7 mm or less is considered "good", and 4 mm or less is considered "very good".

[0073] (Welding defects)

[0074] In the X-ray penetration test, the test was conducted based on the radiation energy penetration test of steel welded joints shown in JIS Z3104:1995. The case where no slag inclusions, cracks, etc. are generated in the welded part is considered "defect-free". The summary of these investigation results is shown in Table 5.

[0075] [Table 5]

[0076]

[0077] In Tables 1 and 5, the flux numbers F1 to F25 are examples of the present invention, and the flux numbers F26 to F39 are comparative examples. Among the flux numbers F1 to F25 as examples of the present invention, the total of the B conversion values of SiO2, CaO, MgO, Al2O3, B alloy, and B oxide in the flux, the total of one or more metal fluorides, the total of the CO2 conversion values of one or more metal carbonates, and the total of one or two of Si, Mn, Ti, Na2O, and K2O are appropriate. Therefore, good tensile strength and absorbed energy of the weld metal are obtained, the diffusible hydrogen content of the weld metal is also low, the arc is stable, the slag detachability and bead shape are good, which is a satisfactory result.

[0078] In addition, among the flux numbers F1, F2, F3, F4, F8, F9, F10, F12, F14, F17, F18, F19, F22, F23, and F24, the bulk density of the flux is appropriate. Therefore, the bead shape is very good, which is a very satisfactory result.

[0079] In the comparative examples, in the case of the welding flux grade F26, since the amount of SiO2 is small, the slag detachability and bead shape are poor. In addition, since the amount of Mn is large, the strength of the weld metal is excessive and the absorbed energy is low.

[0080] In the case of the welding flux grade F27, since the amount of CaO is small, the absorbed energy of the weld metal is low. It should be noted that since the bulk density of the welding flux is appropriate, the bead shape is very good.

[0081] In the case of the welding flux grade F28, since the amount of SiO2 is large, the absorbed energy of the weld metal is low. In addition, since the total amount of one or more metal fluorides is large, the arc is unstable and the slag detachability is poor. In addition, since the total amount of one or more metal fluorides is large, pitting occurs and the bead shape is poor.

[0082] In the case of the welding flux grade F29, since the amount of Ti is large, the absorbed energy of the weld metal is low. In addition, since the amount of CaO is large, the arc is unstable and the slag detachability and bead shape are poor.

[0083] In the case of the welding flux grade F30, since the amount of MgO is small, the absorbed energy of the weld metal is low.

[0084] In the case of the welding flux grade F31, since the amount of Ti is small, the absorbed energy of the weld metal is low. In addition, since the amount of MgO is large, the slag detachability is poor and slag inclusions are generated in the weld metal.

[0085] In the case of the welding flux grade F32, since the amount of Al2O3 is small, the arc is unstable and the slag detachability and bead shape are poor. In addition, since the amount of Mn is small, the absorbed energy of the weld metal is low.

[0086] In the case of the welding flux grade F33, since the amount of Al2O3 is large, the slag detachability is poor and slag inclusions are generated in the weld metal. In addition, since the amount of Si is large, the strength of the weld metal is excessive and the absorbed energy is low.

[0087] In the case of the welding flux grade F34, since the total B-converted value of the B alloy and B oxide is small, the absorbed energy of the weld metal is low. It should be noted that since the bulk density of the welding flux is appropriate, the bead shape is very good.

[0088] In the case of the welding flux grade F35, since the total B-converted value of the B alloy and B oxide is large, the strength of the weld metal is excessive and the absorbed energy is low. In addition, since the total CO2-converted value of one or more metal carbonates is large, pitting occurs, the bead shape is poor, and the slag detachability is also poor. It should be noted that the bulk density of the welding flux is appropriate, but the effect of adjusting the bead shape is not obtained.

[0089] In the case of the welding flux label F36, since the amount of Si is small, the absorbed energy of the weld metal is low.

[0090] In the case of the welding flux label F37, since the amount of Bi2O3 is large, the absorbed energy of the weld metal is low, and cracks are generated in the welded part. In addition, since the total CO2 conversion value of one or more metal carbonates is small, the diffusible hydrogen content in the weld metal is large. Further, since the total of one or both of Na2O and K2O is large, undercutting is generated at the weld toe, and the bead shape is poor.

[0091] In the case of the welding flux label F38, since the total of one or more metal fluorides is small, the absorbed energy of the weld metal is low. It should be noted that since the bulk density of the welding flux is appropriate, the bead shape is very good.

[0092] In the case of the welding flux label F39, since the amount of Mn is large, the strength of the weld metal is excessive and the absorbed energy is low. It should be noted that since the bulk density of the welding flux is appropriate, the bead shape is very good.

Claims

1. A bonded flux for submerged arc welding of low-temperature steel, characterized in that, Containing, in mass % relative to the total mass of the bonding flux: SiO2: 10% to 20%, CaO: 6% to 15%, MgO: 25% to 40%, Al2O3: 10% to 25%, Bi2O3: 0% to 0.05%, Total of the B conversion values of B alloy and B oxide: 0.01% to 0.5%, Total of one or more metal fluorides: 15% to 25%, Total of the CO2 conversion values of one or more metal carbonates: 1% to 8%, Si: 0.1% to 2.0%, Mn: 0.1% to 2.0%, Ti: 0.2% to 1.5%, Total of one or two of Na2O and K2O of Na oxide and K oxide: higher than 0 to 8.00%, and the balance consists of the Fe component from ferroalloy powder and inevitable impurities.

2. The bonding flux for submerged arc welding of the low-temperature steel according to claim 1, characterized in that, The bulk density of the flux is 1.2 g / cm 3 or less.

Images