Plastic forming flux, method for manufacturing a submerged arc welding joint, and submerged arc welding joint

Abstract

A plastic forming flux according to one embodiment of the present invention contains, in mass%, metal Al: 0.50 to 10.00%, TiO2: 0 to 12.00%, CaCO3: 2.00 to 30.00%, CaF2: 5.00 to 18.00%, CaO: 0 to 50.00%, Al2O3: 10.00 to 30.00%, MgO: 3.00 to 35.00%, B2O3: 0 to 1.00%, SiO2: 0 to 30.00%, MnO: 0 to 10.00%, and metal Cr: 0 to 10.00%, with the remainder being impurities. A method for manufacturing a welded joint according to another embodiment of the present invention comprises a process of submerged arc welding a steel material using the plastic forming flux above.

Description

Technology Field

[0001] The present invention relates to a bonded flux, a method for manufacturing a submerged arc welded joint, and a submerged arc welded joint. Background Technology

[0002] Submerged arc welding is one of the welding methods for manufacturing welded joints. Submerged arc welding is a welding method that uses arc heat generated from an arc between the welding wire and the base material in a flux.

[0003] In recent years, there has been an increasing demand for high toughness in the weld metal of weld joints obtained by submerged arc welding. One means to improve the toughness of the weld metal is to reduce the oxygen content of the weld metal.

[0004] As an example of a conventional technology for reducing the oxygen content of a weld metal, Patent Document 1 discloses a submerged arc welding flux characterized by adding one or more of Al, Al-Mg, Mg, and Ca-Si in a weight ratio of 0.5 to 80% to a metal or intermetallic compound in the submerged arc welding flux. Prior art literature

[0005] Japanese Patent Publication No. 60-61197 The problem to be solved

[0006] However, the oxygen content of the weld metal obtained using the flux disclosed in Patent Document 1 is at most about 0.01 mass%. In order to meet the demand for high toughness in recent years, it is necessary to further reduce the oxygen content of the weld metal.

[0007] The present invention aims to provide a plastic flux capable of reducing the oxygen content of a weld metal, and a method for manufacturing a welded joint capable of reducing the oxygen content of a weld metal. means of solving the problem

[0008] The gist of the present invention is as follows.

[0009] (1) A sintering flux according to one embodiment of the present invention contains, in mass%, metal Al: 0.50 to 10.00%, TiO2: 0 to 12.00%, CaCO3: 2.00 to 30.00%, CaF2: 5.00 to 18.00%, CaO: 0 to 50.00%, Al2O3: 10.00 to 30.00%, MgO: 3.00 to 35.00%, B2O3: 0 to 1.00%, SiO2: 0 to 30.00%, MnO: 0 to 10.00%, and metal Cr: 0 to 10.00%, with the remainder being impurities.

[0010] (2) In the sintering flux described in (1) above, the content of MnO is preferably 1.00 mass% or more.

[0011] (3) In the sintering flux described in (1) or (2) above, the content of SiO2 is preferably less than 5.00 mass%.

[0012] (4) In the sintering flux described in any one of (1) to (3) above, the content of B2O3 is preferably 0.30 mass% or less.

[0013] (5) A method for manufacturing a submerged arc welded joint according to another aspect of the present invention comprises a process of submerged arc welding a steel material using a plastic forming flux described in any one of claims (1) to (4).

[0014] (6) In the method for manufacturing a submerged arc welded joint described in (5) above, preferably, the oxygen content of the weld metal obtained by the submerged arc welding is 0.0250 mass% or less.

[0015] (7) In the method for manufacturing a submerged arc welded joint described in (5) above, preferably, the Al content of the steel is 0.100 mass% or less.

[0016] (8) In the method for manufacturing a submerged arc welded joint described in (5) or (6) above, the basicity of the molten pool is preferably 1.0 or higher.

[0017] (9) A submerged arc welded joint according to another aspect of the present invention comprises two or more steel materials and a weld metal that joins the steel materials, wherein the Al content of the steel materials is 0.100 mass% or less and the oxygen content of the weld metal is 0.0250 mass% or less.

[0018] (10) In the submerged arc welded joint described in (9) above, preferably, the chemical composition of the steel is, in unit mass%, C: 0.030 to 0.200%, Si: 0.500% or less, Mn: 0.30 to 2.50%, P: 0.020% or less, S: 0.005% or less, N: 0.0080% or less, O: 0.0050% or less, Ti: 0 to 0.030%, Nb: 0 to 0.100%, Cr: 0 to 1.00%, Mo: 0 to 1.00%, W: 0 to 1.00%, Ni: 0 to 1.00%, Cu: 0 to 1.00%, V: 0 to 0.10%, Ca: 0 to 0.0050%, Mg: 0 to 0.0100%, and REM: 0 to 0.0100%, with the remainder being iron and impurities. Effects of the invention

[0019] According to the present invention, a plastic flux capable of reducing the oxygen content of a weld metal and a method for manufacturing a welded joint capable of reducing the oxygen content of a weld metal can be provided. Brief explanation of the drawing

[0020] Figure 1 is a schematic diagram of submerged arc welding. Figure 2 is a scatter plot showing the Al concentration and O concentration in the weld metal of the examples and comparative examples shown in Table 6. Specific details for implementing the invention

[0021] As illustrated in FIG. 1, in submerged arc welding, flux (1) is first spread over the base material (8), and a welding wire (2) is fed into the flux (1). Subsequently, voltage is applied between the welding wire (2) and the base material (8) to generate an arc, thereby forming a space called an arc cavity (5). Molten volume (9) is transferred from the tip of the welding wire (2) onto the base material (8). The arc temperature is approximately 25,000 K.

[0022] By the arc, a portion of the flux (1) components, the welding wire (2), and the base material (8) are melted, and a molten pool (6) is formed. If the base material (8) is steel, the temperature of the molten pool (6) becomes approximately 2500K. In addition, a portion of the flux (1), the welding wire (2), and the base material (8) components becomes molten slag (3) and is discharged outside the molten pool (6).

[0023] Then, with the arc generated, the welding wire (2) is moved toward the welding direction. After the welding wire (2) moves, the molten pool (6) solidifies to become the welding metal (7) that joins the base material (8), and the molten slag (3) solidifies to become the slag (4). By this, a welded joint having the base material (8) and the welding metal (7) that joins it is manufactured.

[0024] The inventors have incorporated 0.50 to 10.00 mass% of metallic Al into the plastic flux as a means of reducing the amount of oxygen in the weld metal formed by submerged arc welding.

[0025] Here, "metallic Al" refers to Al included in the flux in the form of a metal, an alloy, or an intermetallic compound. For example, Al that forms part of a compound with non-metallic elements, such as Al constituting aluminum oxide, is not included in "metallic Al." An intermetallic compound of Al refers to a compound formed by Al and one or more other metallic elements, such as Fe-Al compounds, Al-Si compounds, and Al-Mg compounds. However, as for metallic Al, it is preferable that it be included in the flux in a form other than an intermetallic compound, that is, in the form of a metal or an alloy.

[0026] In addition, the "metallic Cr" described below is also Cr included in the flux in the form of a metal, alloy, or intermetallic compound. For example, Cr that forms part of a compound with non-metallic elements, such as Cr constituting chromium oxide, is not included in "metallic Cr." However, it is preferable that the metallic Cr be included in the flux in a form other than an intermetallic compound, that is, in the form of a metal or alloy.

[0027] Metallic Al exerts a deoxidizing effect by forming Al oxides. However, it has not been clear until now how metallic Al affects the oxygen content of the weld metal in submerged arc welding. If Al oxides are expelled to the outside of the weld metal as slag, metallic Al reduces the oxygen content of the weld metal. On the other hand, if Al oxides are introduced into the interior of the weld metal, metallic Al increases the oxygen content of the weld metal. During submerged arc welding, it has not been clear until now whether Al oxides remain inside the weld metal or are expelled to the outside.

[0028] As a result of repeated examinations regarding this matter, the inventors discovered that Al present as an alloying element in the base metal increases the oxygen content of the weld metal, whereas metallic Al included in the plastic forming flux decreases the oxygen content of the weld metal. Although the reason for this is not clear, the inventors analyzed the atmosphere within the arc cavity and found that metallic Al in the plastic forming flux [causes] P within the arc cavity CO2 / P CO It was observed that it reduces P in the arc cavity. Meanwhile, Al in the base metal reduces P in the arc cavity. CO2 / P CO It was not changed. It is presumed that metallic Al in the plastic forming flux reduces the oxygen partial pressure in the arc cavity and thereby reduces the oxygen content of the weld metal, whereas Al in the base metal does not have this effect. Furthermore, it is presumed that Al in the base metal increases the oxygen content of the weld metal by forming Al oxides and being incorporated into the weld metal. Based on this finding, the inventors decided to include a predetermined amount of metallic Al in the plastic forming flux.

[0029] CaCO3 is sometimes included in plastic forming fluxes because it improves the shape of the weld bead. However, during submerged arc welding, CaCO3 decomposes into CaO and CO2, increasing the partial pressure of CO2 in the arc. Furthermore, it is well known that CO2 in the welding environment increases the oxygen content of the weld metal. For example, in gas shielded arc welding, reducing the partial pressure of CO2 in the shielding gas reduces the oxygen content of the weld metal. Therefore, since CaCO3 is a component that increases the oxygen content of the weld metal, it has been customary not to use it in situations where the oxygen content of the weld metal needs to be reduced.

[0030] However, the inventors discovered that when CaCO3 is additionally included in a sintering flux containing a predetermined amount of metallic Al, the oxygen content of the weld metal obtained using this sintering flux does not increase. Furthermore, CaCO3 has the effect of improving the shape of the weld bead and also serves to prevent the intrusion of nitrogen or hydrogen. Therefore, the sintering flux according to the present embodiment contains CaCO3.

[0031] A sintering flux according to one embodiment of the present invention, obtained based on the above findings, contains, in mass%, metal Al: 0.50 to 10.00%, TiO2: 0 to 12.00%, CaCO3: 2.00 to 30.00%, CaF2: 5.00 to 18.00%, CaO: 0 to 50.00%, Al2O3: 10.00 to 30.00%, MgO: 3.00 to 35.00%, B2O3: 0 to 1.00%, SiO2: 0 to 30.00%, MnO: 0 to 10.00%, and metal Cr: 0 to 10.00%, with the remainder consisting of impurities. Details thereof will be described below. Unless otherwise noted, the unit “%” for the content of each component of the sintering flux means mass%.

[0032] The method for measuring the components of the sintering flux is as follows.

[0033] (Procedure 1) Dissolve the flux using acid and alkali solvents.

[0034] (Procedure 2) Measure the content (mass%) of the target element using ICP emission spectroscopic analysis.

[0035] (Procedure 3) In principle, all elements subject to measurement are assumed to form oxides, and the above-mentioned content is converted into an oxide content (mass%).

[0036] However, the Ca included in the calcination flux may take the form of not only oxide (CaO), but also fluoride (CaF2) and carbonate (CaCO3). Therefore, regarding CaO, CaF2, and CaCO3, Ca and F are analyzed individually using ICP (Inductively Coupled Plasma) emission spectroscopy, and C is analyzed using combustion infrared absorption spectroscopy. The amount of CaF2 estimated from the analysis value of F and the amount of CaCO3 estimated from the analysis value of C are calculated, and the remaining Ca is considered to form CaO, thereby calculating the amount of CaO.

[0037] In addition, the amount of Al included in the calcination flux is calculated as the amount of metallic Al from the molten portion by dissolving it with acid in (Procedure 1) and filtering it, and the amount calculated in (Procedure 3) from the amount of Al analyzed from the remaining molten portion is defined as the amount of Al2O3. In addition, the amount of metallic Cr is calculated in the same way as metallic Al by dissolving it with acid in (Procedure 1), filtering it, and performing ICP emission spectroscopic analysis on the molten portion.

[0038] (Type of flux: Plastic forming flux)

[0039] Fluxes used in submerged arc welding are broadly classified into plastic fluxes and molten fluxes. A molten flux is a flux in which raw materials are melted in an electric furnace or similar device, then ground, and the particle size is uniformly adjusted by sieving. A plastic flux is a flux in which a liquid binder is mixed with powdered raw materials to form a paste, granulated and dried using a kiln or similar device, and then the particle size is uniformly adjusted by sieving. The inventors have designated the flux in this embodiment as a plastic flux. This is because a plastic flux can contain metallic Al, which functions as a deoxidizer. Unless otherwise specified, "flux" refers to a plastic flux.

[0040] (Metal Al: 0.50 to 10.00%)

[0041] Metallic Al forms Al oxides during submerged arc welding. Metallic Al contained in the plastic forming flux is discharged as slag to the outside of the weld metal. As a result, the metallic Al contained in the plastic forming flux has the effect of reducing the oxygen content of the weld metal. To obtain the above-mentioned effect, the metallic Al content of the plastic forming flux is set to 0.50% or more. On the other hand, if the metallic Al content in the plastic forming flux is excessive, the Al content of the weld metal increases, and there is a risk that its toughness may be damaged. Therefore, the metallic Al content of the plastic forming flux is set to 10.00% or less. The metallic Al content of the plastic forming flux may be 1.00% or more, 1.50% or more, 2.00% or more, or 3.00% or more. The Al content of the plastic forming flux may be 9.00% or less, 8.00% or less, 6.00% or less, or 5.00% or less.

[0042] (TiO2: 0 to 12.00%)

[0043] As is known to those skilled in the art, TiO2 is not an essential component from the perspective of reducing the oxygen content of the weld metal. This is because TiO2 is discharged to the outside of the weld metal as slag during welding. Therefore, the TiO2 content may be 0%. On the other hand, TiO2 improves the fluidity of the slag, allowing for a better bead shape. Therefore, TiO2 may be included in the sintering flux (i.e., the TiO2 content may exceed 0%), and the TiO2 content may be 1.00% or more. However, if the TiO2 content of the sintering flux exceeds 12.00%, the above-described effect becomes saturated. Therefore, the TiO2 content of the sintering flux is 12.00% or less. The TiO2 content of the calcination flux may be 2.00% or more, 3.00% or more, 5.00% or more, 8.00% or more, or 10.00% or more. The TiO2 content of the calcination flux may be 11.60% or less, 11.10% or less, 11.00% or less, 10.00% or less, 8.00% or less, or 6.00% or less.

[0044] (CaCO3: 2.00 to 30.00%)

[0045] CaCO3 is generally used for purposes such as forming the shape of the weld bead or reducing the amount of diffusible hydrogen in the weld metal. To achieve this effect, the CaCO3 content of the plastic forming flux is set to 2.00% or more. On the other hand, if the amount of CaCO3 is excessive, there is a risk that the welding arc will become unstable. Therefore, the CaCO3 content of the plastic forming flux is set to 30.00% or less. The CaCO3 content of the plastic forming flux may be 3.00% or more, 5.00% or more, 6.00% or more, or 10.00% or more. The CaCO3 content of the plastic forming flux may be 28.00% or less, 25.00% or less, 20.00% or less, 10.00% or less, or 7.00% or less.

[0046] (CaF2: 5.00 to 18.00%)

[0047] CaF2 has the effect of ensuring the fluidity of the slag. In addition, CaF2 has the effect of reducing the oxygen content of the weld metal, although not as significantly as that of metallic Al. To obtain the above-mentioned effect, the CaF2 content of the sintering flux is set to 5.00% or more. On the other hand, if the amount of CaF2 is excessive, the above-mentioned effect becomes saturated. Therefore, the CaF2 content of the sintering flux is set to 18.00% or less. The CaF2 content of the sintering flux may be 6.00% or more, 7.00% or more, 8.00% or more, 10.00% or more, 11.00% or more, or 12.00% or more. The CaF2 content of the sintering flux may be 16.00% or less, 15.00% or less, 14.00% or less, or 13.00% or less.

[0048] (CaO: 0 to 50.00%)

[0049] As is known to those skilled in the art, CaO is not an essential component from the perspective of reducing the oxygen content of the weld metal. Therefore, the CaO content may be 0%. On the other hand, CaO has the effect of favorably changing the basicity of the molten pool. To obtain the above-mentioned effect, CaO may be included in the sintering flux (i.e., the CaO content may exceed 0%), and the CaO content may be 4.00% or more. On the other hand, if the amount of CaO is excessive, there is a risk that welding workability will be impaired. Therefore, the CaO content of the sintering flux shall be 50.00% or less. The CaO content of the sintering flux may be 6.00% or more, 7.00% or more, 8.00% or more, or 10.00% or more. The CaO content of the calcination flux may be 48.00% or less, 40.00% or less, 35.00% or less, 30.00% or less, 20.00% or less, 15.00% or less, 12.00% or less, or 11.00% or less.

[0050] (Al2O3: 10.00 to 30.00%)

[0051] As is known to those skilled in the art, Al2O3 is not an essential component from the perspective of reducing the oxygen content of the weld metal. On the other hand, Al2O3 has the effect of preferably controlling the viscosity and melting point of the sintering flux and further enhancing welding workability. To obtain the above-mentioned effect, the Al2O3 content of the sintering flux is set to 10.00% or more. On the other hand, if the amount of Al2O3 is excessive, the above-mentioned effect becomes saturated. Therefore, the Al2O3 content of the sintering flux is set to 30.00% or less. The Al2O3 content of the sintering flux may be 12.00% or more, 15.00% or more, 18.00% or more, 20.00% or more, 24.00% or more, or 24.50% or more. The Al2O3 content of the calcination flux may be 29.00% or less, 28.00% or less, 27.00% or less, or 26.00% or less.

[0052] (MgO: 3.00 to 35.00%)

[0053] As is known to those skilled in the art, MgO is not an essential component in terms of reducing the oxygen content of the weld metal. On the other hand, MgO has the effect of favorably changing the basicity of the molten pool. To obtain the above-mentioned effect, the MgO content of the sintering flux is set to 3.00% or more. On the other hand, if the amount of MgO is excessive, there is a risk that welding workability will be impaired. Therefore, the MgO content of the sintering flux is set to 35.00% or less. The MgO content of the sintering flux may be 5.00% or more, 8.00% or more, 12.00% or more, 15.00% or more, 20.00% or more, 23.00% or more, or 27.00% or more. The MgO content of the sintering flux may be 34.00% or less, 32.00% or less, 30.00% or less, or 29.00% or less.

[0054] (B2O3: 0 to 1.00%)

[0055] As is known to those skilled in the art, B2O3 is not an essential component from the perspective of reducing the oxygen content of the weld metal. Therefore, the B2O3 content may be 0%. On the other hand, since B2O3 combines with dissolved nitrogen in the weld metal to form BN, it has the effect of reducing the adverse effect of dissolved nitrogen on the low-temperature toughness of the weld metal. In addition, the boron generated from B2O3 increases the quenchability of the weld metal, thereby having the effect of improving the strength of the weld metal. To obtain the above-mentioned effects, B2O3 may be included in the plastic forming flux (i.e., the B2O3 content may exceed 0%), or the B2O3 content may be 0.01% or more. On the other hand, if the amount of B2O3 is excessive, the boron in the weld metal becomes excessive, resulting in coarse BN and Fe 23 (C, B)6 There are cases where B compounds are formed, which degrade the low-temperature toughness of the weld metal. For this reason, the B2O3 content of the sintering flux is 1.00% or less. The B2O3 content of the sintering flux may be 0.05% or more, 0.10% or more, 0.20% or more, or 0.25% or more. The B2O3 content of the sintering flux may be 0.90% or less, 0.70% or less, 0.50% or less, 0.30% or less, 0.28% or less, or 0.25% or less.

[0056] (SiO2: 0 to 30.00%)

[0057] As is known to those skilled in the art, SiO2 is not an essential component from the perspective of reducing the oxygen content of the weld metal. Therefore, the SiO2 content may be 0%. On the other hand, SiO2 has the effect of promoting the vitrification of the sintering flux. To obtain the above-mentioned effect, SiO2 may be included in the sintering flux (i.e., the SiO2 content may be greater than 0%), and the SiO2 content may be 3.00% or more. On the other hand, by making the amount of SiO2 30.00% or less, the basicity of the molten pool can be kept within a desirable range. Therefore, the SiO2 content of the sintering flux is 30.00% or less. The SiO2 content of the sintering flux may be 4.00% or more, 6.00% or more, 7.00% or more, or 8.00% or more. The SiO2 content of the sintering flux may be 28.00% or less, 25.00% or less, 20.00% or less, less than 5.00 mass%, 4.80 mass% or less, or 4.50 mass% or less.

[0058] (MnO: 0 to 10.00%)

[0059] As is known to those skilled in the art, MnO is not an essential component from the perspective of reducing the oxygen content of the weld metal. Therefore, the MnO content may be 0%. On the other hand, MnO has the effect of increasing the fluidity of the slag and further improving the bead appearance. To obtain the above-mentioned effect, MnO may be included in the sintering flux (i.e., the MnO content may exceed 0%), and the MnO content may be 1.00% or more. On the other hand, if the amount of MnO is excessive, the above-mentioned effect becomes saturated. Therefore, the MnO content of the sintering flux is 10.00% or less. The MnO content of the sintering flux may be 2.00% or more, 3.00% or more, 4.50% or more, or 5.00% or more. The MnO content of the sintering flux may be 9.00% or less, 8.00% or less, 7.00% or less, or 5.00% or less.

[0060] (Metal Cr: 0 to 10.00%)

[0061] As is known to those skilled in the art, metallic Cr is not an essential component from the perspective of reducing the oxygen content of the weld metal. Therefore, the content of metallic Cr may be 0%. On the other hand, metallic Cr has the effect of increasing the strength of the weld metal by ensuring the quenchability of the weld metal. To obtain the above-mentioned effect, metallic Cr may be included in the plastic forming flux (i.e., the metallic Cr content may exceed 0%), and the metallic Cr content may be 1.00% or more. On the other hand, if the amount of metallic Cr is excessive, the low-temperature toughness of the weld metal may deteriorate. Therefore, the metallic Cr content of the plastic forming flux shall be 10.00% or less. The metallic Cr content of the plastic forming flux may be 2.00% or more, 3.00% or more, or 5.00% or more. The metallic Cr content of the plastic forming flux may be 9.00% or less, 8.00% or less, or 7.00% or less.

[0062] (Residue: Impurities)

[0063] The components of the sintering flux according to the present embodiment may contain impurities as a remainder other than those exemplified above. Impurities refer to components that are incorporated due to raw materials, such as ore, or various factors of the manufacturing process when the sintering flux is manufactured industrially, and are permitted within a range that does not adversely affect the properties of the sintering flux.

[0064] Examples of impurities include FeO, Na2O, K2O, MnO, P, and S. Additionally, the sintering flux according to the present embodiment may further contain various alloying elements present as metallic components (e.g., Fe present as a metallic component) as impurities. Furthermore, the sintering flux may contain carbon as an impurity. This carbon refers to carbon in a form that does not constitute a compound such as graphite. These components are considered to be impurities or equivalents included in the sintering flux, provided they fall within the ranges mentioned below, for example.

[0065] Na2O: 0 to 1.3%

[0066] K2O: 0 to 0.8%

[0067] FeO: 0 to 1.3%

[0068] MnO: 0 to 0.3%

[0069] P: 0 to 0.005%

[0070] S: 0 to 0.005%

[0071] C: 0 to 0.01%

[0072] Next, a method for manufacturing a welded joint according to another aspect of the present invention will be described. The method for manufacturing a welded joint according to this embodiment comprises a process of submerged arc welding a base material using the plastic forming flux according to this embodiment described above. The plastic forming flux according to this embodiment contains metallic Al and CaCO3, and these components have the effect of reducing the oxygen content of the weld metal. Therefore, according to the method for manufacturing a welded joint according to this embodiment, a welded joint having a weld metal with low oxygen content and high toughness can be manufactured.

[0073] In the method for manufacturing a welded joint according to the present embodiment, specific welding conditions are not particularly limited, but suitable examples are given below.

[0074] The oxygen content of the weld metal obtained by submerged arc welding may be 0.0250 mass% or less. By doing so, the toughness of the weld metal can be improved. For example, the oxygen content of the weld metal can be reduced by including 0.50 to 10.00 mass% of metallic Al and 2.00 to 30.00 mass% of CaCO3 in the plastic flux. The oxygen content of the weld metal may be 0.0220 mass% or less, 0.0200 mass% or less, 0.0150 mass% or less, 0.0100 mass% or less, or 0.0800 mass% or less.

[0075] While metallic Al included in the plastic forming flux reduces the oxygen content of the weld metal, Al present as an alloying element of the base metal may increase the oxygen content of the weld metal. Therefore, the Al content of the steel used as the weld base material may be 0.100 mass% or less. This further reduces the oxygen content of the weld metal. The Al content of the steel may be 0.080 mass% or less, 0.060 mass% or less, or 0.040 mass% or less. The lower limit of the Al content of the steel is not specifically limited, but, for example, it may be 0.001 mass% or more, 0.005 mass% or more, or 0.010 mass% or more.

[0076] The basicity of the molten pool may be 1.0 or higher. By keeping the basicity of the molten pool within a desirable range, the oxygen content of the weld metal is further reduced. The basicity of the molten pool is preferably 1.1 or higher, 1.2 or higher, or 1.4 or higher. The upper limit of the basicity is not particularly limited, but is, for example, 3.0 or lower, 2.5 or lower, or 2.0 or lower. The basicity of the molten pool can be controlled through the components of the plastic forming flux.

[0077] Next, a submerged arc welding joint according to another aspect of the present invention will be described. The submerged arc welding joint according to this embodiment comprises two or more steel materials and a welding metal that joins the steel materials, wherein the Al content of the steel materials is 0.100 mass% or less and the oxygen content of the welding metal is 0.0250 mass% or less.

[0078] (Al content of steel)

[0079] While metallic Al included in the plastic forming flux reduces the oxygen content of the weld metal, Al present as an alloying element of the base metal may increase the oxygen content of the weld metal. Therefore, the Al content of the steel used as the weld base material may be 0.100 mass% or less. This further reduces the oxygen content of the weld metal. The Al content of the steel may be 0.080 mass% or less, 0.060 mass% or less, or 0.040 mass% or less. The lower limit of the Al content of the steel is not specifically limited, but, for example, it may be 0.001 mass% or more, 0.005 mass% or more, or 0.010 mass% or more.

[0080] (Oxygen content of weld metal)

[0081] The oxygen content of the weld metal may be 0.0250 mass% or less. By doing so, the toughness of the weld metal can be improved. The oxygen content of the weld metal can be reduced through the composition of the plastic forming flux. The oxygen content of the weld metal may be 0.0220 mass% or less, 0.0200 mass% or less, 0.0150 mass% or less, 0.0100 mass% or less, or 0.0800 mass% or less.

[0082] In the submerged arc welding joint according to the present embodiment, the chemical composition of steel other than Al is not particularly limited. The main characteristic of the submerged arc welding joint according to the present embodiment is the oxygen content of the weld metal. The oxygen content of the weld metal is mainly influenced by the composition of the plastic forming flux used during manufacturing and the Al content of the steel. On the other hand, the influence of the chemical composition of steel other than Al on the oxygen content of the weld metal is very minor compared to the composition of the plastic forming flux and the Al content of the steel. However, the chemical composition of steel other than Al may be limited for the purpose of improving the mechanical properties of the submerged arc welding joint. Examples of suitable steel compositions are shown below. The unit "%" of the content of elements included in the steel means mass%.

[0083] (C: e.g. 0.030 to 0.200%)

[0084] C is an element that improves the strength of steel. If the C content of the steel is 0.030% or higher, a sufficient strength improvement effect is obtained. Therefore, it is desirable to have a C content of 0.030% or higher in the steel.

[0085] Meanwhile, by reducing the carbon content of the steel to 0.200% or less, weldability can be improved and low-temperature cracking can be suppressed more effectively. In addition, by reducing the carbon content of the steel to 0.200% or less, the hardness of the weld heat-affected zone can be reduced. Therefore, it is desirable to reduce the carbon content of the steel to 0.200% or less.

[0086] (Si: e.g., 0.500% or less)

[0087] By keeping the Si content of the steel at 0.500% or less, the toughness of the weldment can be improved. For this reason, it is desirable to keep the Si content of the steel at 0.500% or less. The Si content of the steel is preferably 0.350% or less, and more preferably 0.300% or less.

[0088] The lower limit of the Si content of the steel may be 0%. Meanwhile, to improve refining costs, the lower limit of the Si content of the steel may be 0.010%. In addition, Si may be included in the steel for deoxidation. In this case, the lower limit of the Si content of the steel may be 0.100%.

[0089] (Mn: e.g. 0.30 to 2.50%)

[0090] Mn forms MnS in steel, thereby neutralizing dissolved sulfur. Additionally, Mn increases the quenchability of steel, thereby improving the strength and toughness of the steel. These effects are sufficiently obtained when the Mn content of the steel is 0.30% or higher. Therefore, it is desirable to have a Mn content of 0.30% or higher in the steel.

[0091] Meanwhile, by keeping the Mn content of the steel at 2.50% or less, the weldability of the steel can be further improved. Therefore, the Mn content of the steel may be 2.50% or less.

[0092] (P: e.g., 0.020% or less)

[0093] P is an element that may be contained as an impurity in steel. By reducing the P content of the steel to 0.020% or less, the low-temperature toughness of the steel and the weldment can be increased. Therefore, the P content of the steel may be reduced to 0.020% or less. The P content of the steel is preferably 0.015% or less.

[0094] It is preferable for the P content of the steel to be low, and the lower limit is 0%. However, if the P content of the steel is reduced to less than 0.001%, the manufacturing cost of the steel increases significantly. Therefore, the P content of the steel may be 0.001% or more.

[0095] (S: e.g., 0.005% or less)

[0096] S is an element that may be contained as an impurity in steel. During hot rolling of steel, S forms MnS that elongates in the rolling direction, which may reduce the low-temperature toughness and ductility of the steel. By reducing the S content of the steel to 0.005% or less, the low-temperature toughness of the steel can be improved. Preferably, the S content of the steel is 0.003% or less.

[0097] The lower limit of the S content of steel is 0%. However, if the S content of steel is reduced to less than 0.0001%, the manufacturing cost of steel increases significantly. Therefore, the S content of steel may be 0.0001% or more.

[0098] (N: e.g., 0.0080% or less)

[0099] N is an element that can be contained as an impurity in steel. By reducing the N content of the steel to 0.0080% or less, the low-temperature toughness and ductility of the steel are improved. Therefore, the N content of the steel may be reduced to 0.0080% or less.

[0100] The lower limit of the N content of steel is 0%. However, if the N content of steel is reduced to less than 0.0010%, the manufacturing cost of the steel increases significantly. In addition, if at least one of Ti and Nb is contained in the steel, N combines with these elements to form nitrides. Nitrides contribute to the refinement of the austenite grain size of the steel. Therefore, the N content of the steel may be 0.0010% or more.

[0101] (O: For example, 0.0050% or less)

[0102] O is an element that may be contained as an impurity in steel. By reducing the O content of the steel to 0.0050% or less, the amount of oxides in the steel can be reduced, and the low-temperature toughness and ductility of the steel can be improved. For this reason, the O content of the steel may be reduced to 0.0050% or less. In order to further improve the toughness of the steel plate and the toughness of the weldment, the O content of the steel is more preferably 0.0040% or less, and more preferably 0.0030% or less.

[0103] It is desirable for the O content of the steel to be low. Therefore, the lower limit for the O content of the steel is 0%. However, if the O content of the steel is reduced to less than 0.0001%, the manufacturing cost of the steel increases significantly. For this reason, the O content of the steel may be 0.0001% or higher. In terms of further improving manufacturing costs, it is even more desirable for the O content of the steel to be 0.0005% or higher.

[0104] (Ti: e.g., 0 to 0.030%)

[0105] Ti forms carbonitrides, contributing to the fineness of the crystal grains in the steel. In addition, Ti forms fine oxides, contributing to the refinement of the crystal grains and the formation of transformation ferrite within the grains. The Ti content of the steel may be 0%, but if it is 0.001% or more, the above-described effects are sufficiently obtained.

[0106] In addition, if the Ti content of the steel is reduced to 0.030% or less, the amount of carbonitrides can be kept within an appropriate range, thereby further improving the low-temperature toughness and ductility of the steel. For this reason, the Ti content of the steel may be reduced to 0.030% or less. The Ti content of the steel is preferably 0.025% or less, and more preferably 0.020% or less.

[0107] (Nb: e.g. 0 to 0.100%)

[0108] Nb forms carbides and / or nitrides and contributes to the improvement of the strength of the steel. In addition, when the steel is subjected to controlled rolling, Nb also exhibits the effect of suppressing recrystallization. The Nb content of the steel may be 0%, but if the Nb content of the steel is 0.006% or more, the above-mentioned effect is sufficiently obtained.

[0109] In addition, if the Nb content of the steel is reduced to 0.100% or less, the low-temperature toughness and ductility of the steel can be further improved. For this reason, the Nb content of the steel may be reduced to 0.100% or less. The Nb content of the steel is preferably 0.080% or less, and more preferably 0.060% or less. In addition, for example, to improve the toughness of the weldment (weld heat-affected zone and weld metal), the Nb content of the steel may be reduced to 0.040% or less, 0.035% or less, or 0.033% or less.

[0110] (Cr: e.g. 0 to 1.00%)

[0111] (Mo: e.g., 0 to 1.00%)

[0112] (W: e.g., 0 to 1.00%)

[0113] (Ni: e.g. 0 to 1.00%)

[0114] (Cu: e.g. 0 to 1.00%)

[0115] (V: e.g., 0 to 0.10%)

[0116] Cr, Mo, W, Ni, Cu, and V are elements that increase the quenching properties of steel. Therefore, steel may contain one or more selected from Cr, Mo, W, Ni, Cu, and V. To obtain the above effect, it is preferable for the steel to contain one or more selected from Cr: 0.10% or more, Mo: 0.03% or more, W: 0.03% or more, Ni: 0.10% or more, Cu: 0.10% or more, and V: 0.005% or more. More preferably, it is preferable for the steel to contain one or more selected from Cr: 0.10% or more, Mo: 0.03% or more, W: 0.03% or more, Ni: 0.10% or more, Cu: 0.10% or more, and V: 0.005% or more.

[0117] In addition, by keeping the content of Cr, Mo, W, Ni, and Cu at 1.00% or less each, and the V content at 0.10% or less, an excessive increase in the hardness of the steel can be suppressed and the low-temperature toughness of the steel can be increased. For this reason, it is desirable to keep the content of Cr, Mo, W, Ni, and Cu at 1.00% or less each, and the V content at 0.10% or less. Preferably, Cr: 0.50% or less, Mo: 0.40% or less, W: 0.40% or less, Ni: 0.50% or less, Cu: 0.50% or less, and V: 0.06% or less.

[0118] (Ca: e.g. 0 to 0.0050%)

[0119] Ca suppresses the formation of MnS that elongates in the rolling direction by forming CaS in the steel. As a result, Ca contributes to the improvement of the steel's low-temperature toughness and resistance to welding cracking. The Ca content of the steel may be 0%, but the above effect can be sufficiently obtained by making the Ca content of the steel 0.0005% or more.

[0120] By keeping the Ca content of the steel at 0.0050% or less, the accumulation of oxides in the steel can be suppressed, and the low-temperature toughness and weld crack resistance of the steel can be further enhanced. For this reason, the Ca content of the steel may be kept at 0.0050% or less. The Ca content of the steel is preferably 0.0045% or less, and more preferably 0.0040% or less.

[0121] (Mg: e.g. 0 to 0.0100%)

[0122] (REM: e.g. 0 to 0.0100%)

[0123] REM is a collective term for 16 elements that are rare earth elements and consist of Sc and lanthanoids. REM content refers to the total content of the 16 elements consisting of Sc and lanthanoids.

[0124] Mg and REM are elements that control the form of sulfides. In addition, Mg and REM form fine oxides and contribute to the refinement of grains or the formation of transformation ferrite within the grains. Although the Mg content and REM content of the steel may be 0%, in order to obtain the above effects, it is preferable that the steel contains one or two types selected from Mg: 0.001% or more and REM: 0.001% or more.

[0125] In addition, when the Mg content and REM content of the steel are each 0.0100%, coarsening of sulfides can be prevented. Therefore, it is desirable to keep the Mg content and REM content of the steel both 0.0100% or less. The Mg content and REM content of the steel are preferably 0.0050% or less.

[0126] The remainder of the chemical composition of the steel includes Fe and impurities. Here, "impurities" refers to components that are incorporated due to raw materials such as ore and scrap, or various factors of the manufacturing process when steel is manufactured industrially, and are permitted within a range that does not adversely affect the present invention.

[0127] Examples of impurities include Sb, Sn, Co, As, Pb, Bi, H, Zr, Ta, B, Nd, Y, Hf, and Re. When these elements are included in steel, it is desirable to control the content of each to the range described below.

[0128] (Sb: e.g., 0.10% or less)

[0129] (Sn: e.g. 0.10% or less)

[0130] (Co: e.g. 0.10% or less)

[0131] (As: For example, 0.10% or less)

[0132] (Pb: e.g. 0.005% or less)

[0133] (Bi: e.g. 0.005% or less)

[0134] (H: e.g., 0.0005% or less)

[0135] Sb, Sn, Co, As, Pb, Bi, and H may be incorporated into the steel as impurities, but if they are within the above ranges, they do not impair the properties of the welded joint according to the present embodiment. Therefore, it is desirable to limit the content of these elements in the steel to the above ranges. In addition, for example, it is desirable to limit the total content of these elements to 0.10% or less.

[0136] Zr, Ta, B, Nd, Y, Hf, and Re: Total 0.10% or less

[0137] These elements may be incorporated into the steel as impurities, but if the total content is within the range of 0.10% or less, they do not impair the characteristics of the welded joint according to the present embodiment. Therefore, the total content of these elements in the steel may be limited to 0.10% or less.

[0138] Examples

[0139] The effects of one embodiment of the present invention are explained in more detail by way of examples. However, the conditions in the examples are merely examples of conditions adopted to verify the feasibility and effects of the present invention. The present invention is not limited to these examples of conditions. The present invention may adopt various conditions as long as the objectives of the present invention are achieved without departing from the gist of the present invention.

[0140] Submerged arc welding was performed on steel having the components shown in Table 1, welding wire having the components shown in Table 2, and plastic flux having the components shown in Table 3. In addition, the units of the steel components shown in Table 1 and the wire components shown in Table 2 are mass%, and the remainder of the components were iron and impurities. The units of the plastic flux components shown in Table 3 are also mass%, and represent the content relative to the amount excluding impurities from the total flux.

[0141] In addition, the plate thickness of all steel materials shown in Table 1 was set to 35 mm. The number of welding passes for submerged arc welding was set to one. The impurity content of all plastic forming fluxes shown in Table 3 was 1 mass% or less relative to the total flux. In addition, the particle size of all plastic forming fluxes shown in Table 3 was set to 12×150 mesh (0.1 mm to 1.75 mm).

[0142] "t-Al" in Tables 1 and 2 refers to the total amount of Al existing in an alloy state and Al oxide. The underlined values ​​in Table 3 are outside the range of the sintering flux for the present embodiment.

[0143] The conditions for manufacturing plastic flux and the welding conditions for submerged arc welding are as described in Table 4. In addition, the combination of steel, wire, and plastic flux is as described in Table 5.

[0144] The composition of various weld metals obtained by this was measured, and the results are listed in Table 6. The units of the weld metal composition in Table 6 are mass%. Weld metals with an oxygen content of less than 0.0250 mass% were judged to have sufficiently reduced oxygen content. Oxygen content that did not meet this acceptance criterion was underlined.

[0145]

[0146]

[0147]

[0148]

[0149]

[0150]

[0151] The weld metals of Comparative Examples A to D were manufactured using a conventional plastic flux a that does not contain metallic Al. The oxygen content of these weld metals was 0.03% or more.

[0152] Meanwhile, the oxygen content of the weld metals of Examples E to N, manufactured using the plastic forming flux according to the present embodiment, was reduced dramatically compared to Comparative Examples A to D. Therefore, the weld metals of Examples E to M are thought to have higher toughness than the weld metals of Comparative Examples A to D.

[0153] Figure 2 is a scatter plot showing the Al concentration and O concentration in the weld metal of the examples and comparative examples shown in Table 6. In the comparative example, where the plastic flux did not contain Al and thus the Al source of the weld metal was Al in the steel, a tendency was observed for the O content of the weld metal to increase along with the increase in the Al content of the weld metal. On the other hand, in the example where the plastic flux contained metallic Al, a tendency was observed for the O content of the weld metal to decrease along with the increase in the Al content of the weld metal. The scatter plot in Figure 2 suggests that the behavior of metallic Al in submerged arc welding is completely different depending on whether its source is the plastic flux or the base material. Explanation of the symbols

[0154] 1: Flux (molding flux) 2: Welding wire 3: Molten slag 4: Slag 5: Ark Joint 6: Molten pool 7: Welding metal 8: Base material 9: Volume

Claims

Claim 1 A sintering flux comprising, in mass%, metallic Al: 0.50 to 10.00%, TiO2: 1.00 to 12.00%, CaCO3: 2.00 to 30.00%, CaF2: 5.00 to 18.00%, CaO: 4.00 to 50.00%, Al2O3: 10.00 to 30.00%, MgO: 3.00 to 35.00%, B2O3: 0 to 1.00%, SiO2: 0 to 30.00%, MnO: 0 to 10.00%, and metallic Cr: 0 to 10.00%, with the remainder being impurities. Claim 2 A sintering flux according to claim 1, characterized in that the content of the MnO is 1.00 mass% or more. Claim 3 A sintering flux according to claim 1, characterized in that the content of SiO2 is less than 5.00 mass%. Claim 4 A sintering flux according to claim 1, characterized in that the content of B2O3 is 0.30 mass% or less. Claim 5 A method for manufacturing a submerged arc welded joint comprising a process of submerged arc welding a steel material using a plastic forming flux described in any one of claims 1 to 4. Claim 6 A method for manufacturing a submerged arc welded joint according to claim 5, characterized in that the oxygen content of the weld metal obtained by the submerged arc welding is 0.0250 mass% or less. Claim 7 A method for manufacturing a submerged arc welded joint according to claim 5, characterized in that the Al content of the steel is 0.100 mass% or less. Claim 8 delete Claim 9 delete Claim 10 delete

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