Sintered flux and submerged arc welding method for submerged arc welding of high-tensile steel

Abstract

To provide a flux and a welding method for securing weld metal having strength and tenacity comparable to those of a base material at a high heat input submerged arc joint of high strength steel.SOLUTION: A baked flux contains SiO2:15-25%, CaO:3-15%, MgO:25-45%, Al2O3:5-20%, CaF2:5-20%, a total of 0.5-10.0% of one or two kinds of Na2O and K2O, a total of 3-8% of the CO2 conversion values of one or two kinds of CaCO3 and MgCO3, Ni:3.00-7.20%, Cr:0.90-2.40%, Mo:0.50-1.30%, and a total of 0.080-0.220% of one or two kinds of V and Nb.SELECTED DRAWING: Figure 1

Description

[Technical Field] 【0001】 This invention relates to a sintered flux for submerged arc welding of high-tensile steel and a submerged arc welding method. In particular, it relates to a technology for welding extremely thick steel with a high strength of 780 MPa or more using multi-layer welding of 100 kJ / cm or more, while ensuring that the weld metal, which has a low diffusible hydrogen content, has strength and toughness equivalent to that of the base material. [Background technology] 【0002】 In recent years, with the increasing size of high-rise buildings and the expansion of column spans, box columns made of extremely thick, high-tensile steel have come into use. For welding box column corner joints, submerged arc welding, which allows for high-efficiency welding with high heat input, is widely used. 【0003】 Flux used in submerged arc welding is broadly classified into two types based on its manufacturing method: molten type and fired type. The former is a glassy flux produced by mixing raw materials to a predetermined composition, melting them in an arc furnace, and then grinding them after solidification to adjust the particle size to an appropriate level. The latter is produced by mixing raw material powder and alloying elements in a predetermined proportion, then granulating and firing the mixture with, for example, sodium silicate as a binder. 【0004】 In submerged arc welding of box column corner joints, it is common to use a relatively basic sintered flux to obtain a high-strength, high-toughness weld metal. Furthermore, when welding with a heat input (hereinafter simply referred to as "heat input") in the range of 300 to 600 kJ / cm, a sintered flux with added iron powder is used, while when performing single-sided multi-layer welding with a heat input of 300 kJ / cm or less, iron powder is often not added. 【0005】 In iron powder-added sintered fluxes, the sintering temperature must be relatively low to prevent oxidation of the iron powder during manufacturing, and the inability to sinter at high temperatures is a fundamental reason why the moisture content in the flux cannot be reduced. In particular, in welding extremely thick box columns, when single-pass welding is difficult due to the capacity of the welding machine and the joint characteristics, and multi-pass welding is applied, the cooling rate after welding is high, and there is no time for hydrogen in the weld metal to be released, resulting in residual hydrogen. On the other hand, when fluxes with a high moisture content are used, cracks caused by diffusive hydrogen are likely to occur in the heat-affected zone of the weld, and it is known that this tendency is even stronger in high-tensile steel with increased alloy additives. 【0006】 Iron powder-free sintered fluxes allow for higher firing temperatures compared to those with iron powder, thus enabling a reduction in moisture content. Furthermore, in submerged arc welding of high-tensile steel, sintered fluxes that allow for free adjustment of the weld metal composition are used to ensure the weld metal has strength and toughness equivalent to that of the base metal, and various technological developments have been carried out in this field. 【0007】 For example, Patent Document 1 specifies the composition of a sintered flux and welding wire for 80 kg-class high-tensile steel, V E -80 A technique for obtaining weld metal with a toughness of 3.5 kgf·m or higher is described. Here, V E -80 "℃" refers to the Charpy absorbed energy at the test temperature indicated by the subscript on the right (in this example, -80℃) (the same applies hereafter). The welding wire will also be simply referred to as "wire" hereafter. 【0008】 Patent Document 2 specifies the composition of a sintered flux and wire, with a tensile strength of 780 MPa or more. V E -60 This document describes a technique for obtaining weld metal with a toughness of 69 J or higher (℃). 【0009】 Patent Document 3 describes a sintered flux for high-strength steel that can produce weld metal with good toughness even at high strength of 780 MPa. 【0010】 Patent document 4 describes a technique that optimizes the composition of the weld metal by combining a solid wire and a sintered flux, thereby obtaining high strength and stable toughness in the weld metal, eliminating welding defects, and improving welding workability. 【0011】 Patent Document 5 describes a technique for obtaining a weld metal with high toughness and good strength by combining a sintered flux and wire for submerged arc welding of 780 MPa class high-tensile steel. 【0012】 Patent document 6 describes a submerged arc welding technique for 780 MPa class high-tensile steel, which involves welding using a sintered flux with a limited amount of alloying elements and optimized particle size, combined with a solid wire with a limited composition. The aim is to obtain a weld metal with a good bead shape free of welding defects, good weldability, and excellent mechanical performance. 【0013】 Patent Document 7 describes a technique for submerged arc welding of high-tensile steel, which involves applying a high-strength welding wire and incorporating appropriate amounts of Si and Mn in the flux. This ensures high strength while promoting deoxidation in the weld metal by incorporating appropriate amounts of Al, MgO, and CaF2, thereby improving toughness, reducing diffusible hydrogen content, stabilizing the arc, improving slag detachability, and improving the appearance and shape of the weld bead. [Prior art documents] [Patent Documents] 【0014】 [Patent Document 1] Japanese Patent Application Publication No. 3-52796 [Patent Document 2] Japanese Patent Publication No. 2013-39604 [Patent Document 3] Japanese Patent Application Publication No. 6-328291 [Patent Document 4] Japanese Patent Publication No. 2007-260696 [Patent Document 5] Japanese Patent Application Laid-Open No. 5-212583 [Patent Document 6] Japanese Patent Application Laid-Open No. 2015-120175 [Patent Document 7] Japanese Patent Application Laid-Open No. 2020-131221 [Summary of the Invention] [Problems to be Solved by the Invention] 【0015】 The prior arts described in Patent Documents 1 to 7 are intended to improve the mechanical properties of welded joints such as the strength and toughness of the weld metal obtained by submerged arc welding. However, the mechanical properties of the welded joints by these prior arts are the result of applying a heat input range of 24 to 36 kJ / cm (Examples of Patent Documents 1 to 7), which is a heat input lower than 100 kJ / cm. In the prior art, no consideration has been given to performing submerged arc welding with a large heat input of 100 kJ / cm or more on high-tensile steel of 780 MPa or more. 【0016】 The present invention has been made in view of the above problems, and has the following objectives. That is, to perform welding with a large heat input of 100 kJ / cm or more on a high-tensile steel base material having a tensile strength of 780 MPa or more, and to provide a sintered flux that can obtain a welded joint having sufficient strength and toughness equivalent to that of a base material with a low diffusible hydrogen content and no defects, with high efficiency under good workability. Another objective of the present invention is to provide a submerged arc welding method that combines the above sintered flux and a welding wire to ensure even better strength and toughness in the weld metal. [Means for Solving the Problems] 【0017】 The inventors of the present invention have conducted various studies on the chemical composition of the sintered flux for submerged arc welding that can solve the above problems and the chemical composition of the welding wire combined with these sintered fluxes. 【0018】 ​​As a result, by incorporating appropriate amounts of Ni, Cr, Mo, V, and Nb into the sintered flux, high strength of 780 MPa or more and V superior toughness with an E0℃ of 100 J or more were ensured in the weld metal of multi-layer welding with a heat input of 100 kJ / cm or more. 【0019】 Also, the amount of diffusible hydrogen in the weld metal was reduced by the synergistic effect of setting the CO2 equivalent value from CaCO3 and / or MgCO3 in the flux within an appropriate range. 【0020】 Furthermore, by appropriately controlling the amounts of Na2O and K2O for arc stability, the amounts of SiO2, Al2O3, and CaO for bead appearance and bead shape, and by containing appropriate amounts of Al2O3 and SiO2 for slag detachability, these welding workabilities were improved. 【0021】 Furthermore, it has been found that by combining specific high-strength welding wires, better strength and toughness can be obtained in the weld metal. 【0022】 The present invention has been further studied based on these findings, and the gist thereof is as follows. [1] A sintered flux for submerged arc welding of high-tensile steel, wherein the chemical composition of the sintered flux is, in mass%, SiO2: 15 - 25%, CaO: 3 - 15%, MgO: 25 - 45%, Al2O3: 5 - 20%, CaF2: 5 - 20%, The total of one or both of Na2O and K2O: 0.5 - 10.0%, The total of the CO2 equivalent values of one or both of CaCO3 and MgCO3: 3 - 8%, Ni: 3.00 - 7.20%, Cr: 0.90 - 2.40%, Mo: 0.50 - 1.30%, The total of one or both of V and Nb: 0.080 - 0.220%, and The remainder consists of Fe from the iron alloy and unavoidable impurities. A sintered flux for submerged arc welding of high-tensile steel, characterized by the following features. [2] In addition to the chemical composition of the calcination flux in [1] above, the flux further contains a total of 0.6 to 3.0% by mass of one or more elements selected from Si, Mn, Al, Ti, and Mg. A sintered flux for submerged arc welding of high-tensile steel, characterized by the following features. [3] The heat-sealed flux for submerged arc welding of high-tensile steel, characterized in that the high-tensile steel is high-tensile steel with a tensile strength of 780 MPa or more, as in [1] or [2] above. [4] A submerged arc welding method for high-tensile steel, comprising welding with a welding wire using the sintered flux described in [1] or [2] above, The chemical composition of the welding wire is, in mass%, C: 0.05~0.12%, Si: 0.01~0.35%, Mn: 1.30~2.10%, Cu: 0.01~0.25%, Ni: 0.70~3.20%, Mo: 0.40~0.90%, Total of one or two types of V and Nb: 0.001-0.070% P: 0.015% or less, Contains S: 0.015% or less, The Ceq shown in the following formula (1) is 0.40-0.80%, The remainder consists of Fe and unavoidable impurities. A submerged arc welding method for high-tensile steel, characterized by the following features. Ceq=C+Si / 24+Mn / 6+Ni / 40+Cr / 5+Mo / 4+V / 14...(1) Here, in equation (1), C, Si, Mn, Ni, Cr, Mo, and V represent the mass %) of each element, and the content of elements that are not present is set to 0 (zero). [5] In addition to the chemical composition of the welding wire in [4] above, in mass %, It contains one or more elements selected from Cr: 0.01-0.10%, Ti: 0.001-0.050%, and Al: 0.001-0.050%. A submerged arc welding method for high-tensile steel, characterized by the following features. [6] A submerged arc welding method for high-tensile steel, characterized in that the high-tensile steel is high-tensile steel having a tensile strength of 780 MPa or more, as in [4] or [5] above. [7] A submerged arc welding method for high-tensile steel, characterized in that, in any one of the above [4] to [6], the welding heat input is 100 kJ / cm or more. [8] A submerged arc welding method for high-tensile steel, characterized in that, in any one of [4] to [7] above, the welding method is performed by multi-layer welding. [Effects of the Invention] 【0023】 The sintered flux according to the present invention provides the following effects in submerged arc welding of high-tensile steel with a tensile strength of 780 MPa or higher. Specifically, it enables highly efficient and easy-to-work-with welds with low diffusible hydrogen content, no defects, and strength and toughness equivalent to the base material, achieved through multi-layer welding with a heat input of 100 kJ / cm or more. Furthermore, the submerged arc welding method according to the present invention also provides the effect of ensuring weld metal with high strength and high toughness. [Brief explanation of the drawing] 【0024】 [Figure 1] This is a schematic diagram showing the welding procedure for the welding test in the example. [Figure 2] This is a schematic diagram showing the electrode arrangement in the embodiment. [Figure 3] This is a schematic diagram showing the cross-section of a welded joint and the arrangement of vertical flaw detectors in the embodiment. [Figure 4] This is a schematic diagram showing the sampling locations for tensile test specimens of weld metal. [Figure 5] This is a schematic diagram showing the sampling locations for Charpy test specimens of weld metal. [Modes for carrying out the invention] 【0025】 Embodiments of the present invention will be described below. The present invention is applicable to submerged arc welding using high-tensile steel as the base material. 【0026】 [Base material] In particular, it is preferable that the base material have a tensile strength of 780 MPa or higher. If the tensile strength of the base material is 780 MPa or higher, it is possible to ensure strength and toughness equivalent to that of the base material in the weld metal of submerged arc welded joints in base material strength ranges and heat input ranges (100 kJ / cm or higher) that are not considered in conventional technology. On the other hand, if the tensile strength of the base material is less than 780 MPa, the strength and toughness of the weld metal can be ensured by conventional technology. 【0027】 To solve the aforementioned problems, the present invention limits the chemical composition of the sintered flux and further limits the chemical composition of the welding wire. Here, the content of each chemical composition of the sintered flux and welding wire is expressed in "mass%" and simply as "%". 【0028】 [Chemical composition of calcined flux] First, we will explain the chemical composition of the calcination-type flux according to the present invention and the reasons for setting its range. 【0029】 [SiO2: 15-25%] SiO2 is a slag-forming agent and is an important component for adjusting basicity and viscosity, thereby obtaining good weld metal toughness and weld bead formation. SiO2 also has the effect of making the slag glassy and easily breakable, improving slag release properties. If the SiO2 content is less than 15%, the slag viscosity decreases, resulting in poor bead shape. On the other hand, if the SiO2 content exceeds 25%, the oxygen content in the weld metal increases, reducing toughness and resulting in poor slag release properties. Therefore, the SiO2 content should be between 15% and 25%, preferably between 16% and 22%. 【0030】 [CaO: 3-15%] CaO is an important component for adjusting the basicity and softening point of slag. If the CaO content is less than 3%, lateral cracking hardly occurs in the solidified slag, and the slag's detachability deteriorates. On the other hand, if the CaO content exceeds 15%, the slag fluidity is poor, the bead height becomes uneven, and the bead shape and slag detachability are poor. Therefore, the CaO content should be between 3% and 15%, preferably between 5% and 13%. Note that CaO includes the CaO component of CaCO3. 【0031】 [MgO: 25-45%] MgO is an essential component for adjusting the basicity and softening point of the slag and ensuring its detachability. If the MgO content is less than 25%, the slag detachability within the groove deteriorates significantly, the bead becomes rougher, and pockmarks are more likely to occur. On the other hand, if the MgO content exceeds 45%, the bead shape becomes convex, the bead width narrows, and defects such as poor fusion and slag inclusion are more likely to occur. Therefore, the MgO content should be between 25% and 45%. Preferably, it is between 27% and 40%. Note that MgO includes the MgO portion of MgCO3. 【0032】 [Al2O3: 5-20%] Al2O3 is a necessary component for adjusting the softening point and viscosity of the slag, and it also has the effect of stabilizing the arc. If the Al2O3 content is less than 5%, the arc becomes unstable, the weld bead becomes rough, and the bead appearance and slag release properties become poor. On the other hand, if the Al2O3 content exceeds 20%, the bead becomes convex, resulting in a poor bead shape and poor slag release properties. Furthermore, if the Al2O3 content exceeds 20%, welding defects such as slag inclusion are more likely to occur. Therefore, the Al2O3 content should be between 5% and 20%. Preferably, it is between 7% and 18%. 【0033】 [CaF2: 5-20%] CaF2 is a component necessary for adjusting the basicity and viscosity of the slag. If the CaF2 content is less than 5%, the basicity will be low, the slag will lack fluidity, and the weld bead width will be narrow. On the other hand, if the CaF2 content exceeds 20%, the arc will become unstable, and welding defects will be more likely to occur. Therefore, the CaF2 content should be between 5% and 20%. Preferably, it should be between 7% and 18%. 【0034】 [Total of one or two types of Na2O and K2O: 0.5-10.0%] Na2O and K2O, primarily derived from water glass (sodium silicate, potassium silicate), have the effect of stabilizing the arc. If the total amount of one or both types of Na2O and K2O is less than 0.5%, the arc becomes unstable. On the other hand, if the total amount of one or both types of Na2O and K2O exceeds 10.0%, the fluidity of the slag becomes too high, the bead appearance deteriorates, and pock marks are more likely to occur. Therefore, the total amount of one or both types of Na2O and K2O should be between 0.5% and 10.0%. Preferably, it should be between 1.5% and 9.0%. 【0035】 [Total CO2 equivalent values ​​of one or two types of CaCO3 and MgCO3: 3-8%] CaCO3 and MgCO3 decompose during welding, generating CO or CO2 gas that lowers the nitrogen partial pressure in the arc atmosphere, reducing the nitrogen content in the weld metal and further reducing the diffusible hydrogen content. If the combined CO2 equivalent value of one or both CaCO3 and MgCO3 is less than 3%, the nitrogen content in the weld metal increases, reducing its toughness, and the diffusible hydrogen content increases, making it more susceptible to cold cracking. On the other hand, if the combined CO2 equivalent value of one or both CaCO3 and MgCO3 exceeds 8%, pock marks and pits are more likely to occur on the weld bead surface, resulting in a poor bead appearance, and the oxygen content in the weld metal increases, reducing toughness. Therefore, the combined CO2 equivalent value of one or both CaCO3 and MgCO3 should be between 3% and 8%. Preferably, it should be between 4% and 7%. Note that if only one of CaCO3 or MgCO3 is present, the CO2 equivalent value of that single element becomes the "total". 【0036】 [Ni: 3.00~7.20%] Ni is an element used to ensure the strength and toughness of the weld metal. If the Ni content is less than 3.00%, the strength and toughness of the weld metal will decrease. On the other hand, if the Ni content exceeds 7.20%, the austenite grain size of the weld metal will coarseen, reducing its toughness. Therefore, the Ni content should be between 3.00% and 7.20%. Preferably, it should be between 3.50% and 6.50%. As a raw material, for example, metallic Ni and Fe-Ni can be used. 【0037】 [Cr: 0.90~2.40%] Cr has the effect of ensuring the strength and stabilizing the toughness of the weld metal. If the Cr content is less than 0.90%, stable toughness cannot be obtained. On the other hand, if the Cr content exceeds 2.40%, the strength of the weld metal becomes excessive and the toughness deteriorates. Therefore, the Cr content should be between 0.90% and 2.40%. Preferably, it is between 1.10% and 2.00%. As raw materials, for example, metallic Cr and Fe-Cr can be used. 【0038】 [Mo: 0.50~1.30%] Mo is an element used to ensure the strength of the weld metal. If the Mo content is less than 0.50%, the strength of the weld metal will be low. On the other hand, if the Mo content exceeds 1.30%, the weld metal will harden significantly and its toughness will decrease. Therefore, the Mo content should be between 0.50 and 1.30%, preferably between 0.60 and 1.10%. As a raw material, for example, metallic Mo and Fe-Mo can be used. 【0039】 [Total of one or two types of V and Nb: 0.080~0.220%] V and Nb are elements used to ensure the strength of the weld metal. If the sum of one or both types of V and Nb is less than 0.080%, the strength will be insufficient. On the other hand, if the sum of one or both types of V and Nb exceeds 0.220%, the strength will be too high and the toughness will decrease. Therefore, the sum of one or both types of V and Nb should be between 0.080 and 0.220%. Preferably, it should be between 0.085 and 0.150%. As raw materials, one or both types of V and Nb can be metallic V, metallic Nb, Fe-V, Fe-Nb, Fe-V-Nb, etc. 【0040】 [Total of one or more of the following elements: Si, Mn, Al, Ti, Mg: 0.6-3.0%] Furthermore, it is preferable to add one or more elements selected from Si, Mn, Al, Ti, and Mg as needed. These elements have a deoxidizing effect. That is, an increase in the amount of oxygen in the weld metal degrades low-temperature toughness such as the Charpy impact value and CTOD value. Therefore, Si, Mn, Al, Ti, or Mg are necessary as deoxidizing agents. If the total amount of one or more elements selected from these is less than 0.6%, the deoxidizing effect is insufficient, and low-temperature toughness such as the Charpy impact value and CTOD value will be low. On the other hand, if it exceeds 3.0%, the amount of oxygen in the weld metal will be low, but if these elements are excessively present in the weld metal, it will lead to a decrease in low-temperature toughness such as the Charpy impact value and CTOD value. Therefore, it is preferable that the total amount of one or more elements selected from Si, Mn, Al, Ti, and Mg be between 0.6% and 3.0%. More preferably, it is between 0.9% and 2.8%. 【0041】 Furthermore, these elements can be added to the flux in the following forms: for Si, metallic Si, Fe-Si, Ca-Si, and other metal powders can be used. Similarly, for Mn, metallic Mn, Fe-Mn, for Al, metallic Al, Fe-Al, Al-Mg, for Ti, metallic Ti, and for Mg, Al-Mg, metallic Mg, and other metal powders can be used. 【0042】 [Remaining composition] The remainder of the aforementioned firing flux consists of Fe from iron alloys such as Fe-Mn, Fe-Al, Fe-Ni, Fe-Cr, Fe-Mo, Fe-V, Fe-Nb, and Fe-V-Nb, and unavoidable impurities. The unavoidable impurities include MnO, FeO, B2O3, C, P, S, etc., and among these, P and S both form low-melting-point compounds that reduce the toughness of the weld metal, so it is preferable to keep their levels as low as possible. The aforementioned firing flux does not contain iron powder. This allows the firing temperature to be set to 400-650°C, and enables a reduction in moisture content. 【0043】 [Method for manufacturing calcined flux] Next, a method for manufacturing the calcined flux will be described. Flux raw material powder is blended to achieve the chemical composition described above, kneaded with a binder, then granulated and fired. The granulation method is not particularly limited, but it is preferable to use a rolling granulator or an extrusion granulator. After granulation, it is desirable to perform sizing treatments such as dust removal and crushing of coarse particles to reduce the particle size to 2.5 mm or less. Suitable binders include aqueous solutions of polyvinyl alcohol and water glass. Among these, sodium silicate (water glass) with a molar ratio of SiO2 to Na2O of 1 to 5, which has been used conventionally, is sufficient. The amount of binder used is preferably about 100 to 300 cc per 1 kg of flux raw material. Furthermore, it is preferable to fire the material after granulation at a temperature of 400 to 650°C. This is because if the firing temperature is less than 400°C, the moisture introduced from the binder will not dry sufficiently, leading to an increase in diffusible hydrogen in the weld metal. On the other hand, if the firing temperature exceeds 650°C, the carbonates in the flux decompose, and the CO2 shielding effect is lost. Firing is carried out using rotary kilns, stationary batch furnaces, belt-type firing furnaces, etc. 【0044】 [Chemical composition of welding wire] Next, we will explain the chemical composition of the welding wire suitable for use in the submerged arc welding method of the present invention and the reasons for setting its range. 【0045】 [C:0.05~0.12%] Carbon (C) is an important element for ensuring the strength of the weld metal through solid solution strengthening, and it also reacts with oxygen in the arc to reduce the oxygen content in the arc atmosphere and the weld metal. If the C content is less than 0.05%, the deoxidation and strength-enhancing effects are insufficient, and toughness also decreases. On the other hand, if the C content exceeds 0.12%, the weld metal becomes primarily martensite-based, resulting in increased strength and decreased toughness. Furthermore, hot cracking becomes more likely. Therefore, the C content should be between 0.05 and 0.12%. Preferably, it is between 0.06 and 0.11%. 【0046】 [Si: 0.01~0.35%] Si is an important element for improving toughness because it has the effect of reducing the oxygen content of the weld metal. If the Si content is less than 0.01%, the toughness of the weld metal decreases. On the other hand, if the Si content exceeds 0.35%, it strengthens the matrix of the weld metal through solid solution, but it also coarses the ferrite crystal grains, resulting in a significant decrease in toughness. Therefore, the Si content should be between 0.01% and 0.35%, preferably between 0.02% and 0.30%. 【0047】 [Mn: 1.30~2.10%] Mn is an effective component for increasing the strength of weld metal. If the Mn content is less than 1.30%, the strength will be low. On the other hand, if the Mn content exceeds 2.10%, the strength of the weld metal will increase, but the toughness will deteriorate. Therefore, the Mn content should be between 1.30% and 2.10%. Preferably, it should be between 1.40% and 2.00%. 【0048】 [Cu: 0.01~0.25%] Submerged arc welding wires are often copper-plated to stabilize wire feeding and conductivity. Therefore, when copper-plated, the wire contains a certain amount of copper (Cu). On the other hand, if the Cu content is excessive, welding cracks are more likely to occur, so the Cu content should be 0.01 to 0.25%, preferably 0.05 to 0.20%. 【0049】 [Ni: 0.70~3.20%] Ni is an element used to ensure the strength and toughness of the weld metal. If the Ni content is less than 0.70%, the strength and toughness of the weld metal will decrease. On the other hand, if the Ni content exceeds 3.20%, it will coarse the austenite grain size of the weld metal, reducing its toughness. Therefore, the Ni content should be between 0.70% and 3.20%, preferably between 0.80% and 2.80%. 【0050】 [Mo: 0.40~0.90%] Mo is an element used to ensure the strength of the weld metal. If the Mo content is less than 0.40%, the strength of the weld metal will be low. On the other hand, if the Mo content exceeds 0.90%, the hardness of the wire increases significantly, hindering its drawability. Therefore, the Mo content should be between 0.40% and 0.90%. Preferably, it should be between 0.45% and 0.80%. 【0051】 [Total of one or two types of V and Nb: 0.001~0.070%] V and Nb are effective in improving the strength of the weld metal, and to achieve this effect, the total content of one or two of these elements should be 0.001% or more. On the other hand, excessive addition significantly increases the hardness of the wire and inhibits its drawability, so the total content of one or two of these elements should be 0.070% or less. Preferably, it is 0.003 to 0.060%. 【0052】 [P: 0.015% or less, S: 0.015% or less] Since both P and S form low-melting-point compounds that reduce toughness, it is desirable to keep their levels as low as possible, but a content of 0.015% or less for both is acceptable. 【0053】 [Ceq (carbon equivalent): 0.40~0.80%] The Ceq (carbon equivalent) of the wire according to the present invention is given by the following formula (1). Ceq=C+Si / 24+Mn / 6+Ni / 40+Cr / 5+Mo / 4+V / 14...(1) Here, in equation (1), C, Si, Mn, Ni, Cr, Mo, and V represent the mass %) of each element, and the content of elements that are not present is set to 0 (zero). 【0054】 The above Ceq needs to be in the range of 0.40 to 0.80% in order to ensure appropriate strength for 780 MPa steel and to avoid deterioration of wire drawability due to excessive hardening. If the Ceq is less than 0.40%, the target strength cannot be obtained. On the other hand, if the Ceq exceeds 0.80%, the wire becomes excessively hard, and the wire drawability deteriorates. Therefore, the wire's Ceq should be 0.40 to 0.80%. Preferably, it is 0.45 to 0.72%. 【0055】 [Optional composition of wire] In addition to the above composition, the welding wire according to the present invention may further contain, if necessary, one or more of the following optional compositions: Cr: 0.01-0.10%, Ti: 0.001-0.050%, and Al: 0.001-0.050%. 【0056】 [Cr: 0.01~0.10%] Cr has the effect of ensuring yield, strength, and stabilizing toughness in the weld metal, and is included as needed in this invention. When included, a content of 0.01% or more is preferable to obtain the aforementioned effects of Cr, but excessive addition significantly increases the hardness of the wire and inhibits drawability, so 0.10% or less is preferable. More preferably, it is 0.02 to 0.08%. 【0057】 [Ti: 0.001~0.050%] While a Ti content of 0.001% or more improves the toughness of weld metal in 580 MPa-grade steel, the toughness-improving effect is relatively small in the case of 780 MPa-grade steel weld metal; therefore, in this invention, the addition of Ti is optional. If added, 0.001% or more is preferred, but excessive content increases the solid-solution Ti in the weld metal, reducing toughness, so 0.050% or less is preferred. More preferably, it is 0.003 to 0.030%. 【0058】 [Al:0.001~0.050%] Al is used as a deoxidizing agent as needed and is present in the welding wire at a concentration of 0.001% or more. When present, it forms low-melting-point compounds that reduce toughness, but concentrations of 0.050% or less are acceptable, so 0.050% or less is preferred. More preferably, it is 0.001 to 0.030%. 【0059】 [Remaining composition] The remaining composition of the welding wire consists of Fe and unavoidable impurities. These unavoidable impurities include O (oxygen) and N, with O preferably at 0.004% or less and N preferably at 0.008% or less. 【0060】 [Wire diameter] Regarding wire diameter, wires smaller than 4.0 mm produce a thin arc, making it difficult to achieve a wide bead. Furthermore, the sharp shape of the penetration base increases the likelihood of defects such as slag inclusion. On the other hand, wires exceeding 6.4 mm become too rigid, placing excessive load on the welding machine's wire feeder. Therefore, a wire diameter of 4.0 to 6.4 mm is preferable. 【0061】 [Welding Method] [Heat input 100kJ / cm or more] In the submerged arc welding method according to the present invention, high efficiency is preferably achieved when the heat input is 100 kJ / cm or more. This range of heat input is a region that was not considered in conventional techniques, and the effects of the present invention can be realized here. Here, the heat input refers to the heat input per pass, and in the case of multiple electrodes, it is the sum of the heat inputs of each electrode per pass. However, excessive heat input may lead to problems such as severe blow-up of molten slag, so the heat input is preferably 300 kJ / cm or less. 【0062】 [Multilayer welding] For example, in cases where the base metal plate thickness exceeds the range in which welding can be completed in a single pass, such as in the welding of box column corner joints, the present invention preferably uses multi-layer welding with a heat input of 100 kJ / cm or more to ensure weld metal with strength and toughness equivalent to that of the base metal. The interpass temperature is preferably between 100 and 350°C. If the interpass temperature is below 100°C, hydrogen cracking is likely to occur, and if it exceeds 350°C, problems such as insufficient strength and toughness of the weld are likely to occur. 【0063】 [Base material thickness] The thickness of the base material is not particularly limited, but is preferably between 20 and 150 mm. 【0064】 [Group shape] Regarding the groove shape, the groove angle and root spacing are preferably as follows: If the groove angle is less than 25°, welding defects such as slag inclusion and poor fusion are likely to occur, and if it exceeds 50°, the number of welding passes increases and the construction time becomes excessive, so 25 to 50° is preferable. Also, if the root spacing exceeds 15 mm, insufficient penetration is likely to occur, so 15 mm or less is preferable. 【0065】 [Electrode arrangement] In the case of two electrodes, the following conditions are preferable for electrode placement within the groove. The electrode spacing (distance between the wire tips of the leading and trailing electrodes) is preferably 30 to 100 mm. This is because bead formation instability is likely to occur if the electrode spacing is less than 30 mm, and the molten pool is likely to become two separate pools if it exceeds 100 mm. 【0066】 Furthermore, the leading electrode extension is preferably 30-60 mm, and the trailing electrode extension is preferably 40-70 mm. This is because if the leading electrode extension is less than 30 mm, the electrode tip is more likely to melt, and if it exceeds 60 mm, the effect of misalignment due to wire bending becomes significant. Similarly, if the trailing electrode extension is less than 40 mm, the electrode tip is more likely to melt, and if it exceeds 70 mm, the effect of misalignment due to wire bending becomes significant. 【0067】 Furthermore, regarding the electrode tilt angle, it is preferable to set a receding angle of 3 to 15° for the leading electrode and an advancing angle of 3 to 20° for the trailing electrode. This is because it results in a weld with deep penetration and a good appearance. 【0068】 [Target diffusible hydrogen content, strength, and toughness] The present invention relates to the weld metal of a submerged arc welded joint with a base material of steel with a tensile strength of 780 MPa or higher and a heat input of 100 kJ / cm or higher, wherein the diffusible hydrogen content is 5.00 mL / 100 g or less, the tensile strength is 780 MPa or higher, and V The goal is to ensure E0℃:100J or higher. 【0069】 This is because if the diffusible hydrogen content in the weld metal is 5.00 mL / 100 g or less, defects such as cracks in the HAZ are less likely to occur. Preferably, it is 4.00 mL / 100 g or less. Also, if the tensile strength of the weld metal is 780 MPa or more and V the E0℃ is 100 J or more, the strength and toughness as a building structure can be ensured. Preferably, the 0.2% proof stress is 630 - 780 MPa and the tensile strength is 780 - 980 MPa. 【Examples】 【0070】 Hereinafter, the present invention will be described in more detail with reference to examples. 【0071】 Shaped fluxes with various chemical compositions shown in Table 1 were prototyped, combined with the 7 types of solid wires shown in Table 2, and using a 780 MPa grade high-tensile steel plate with a plate thickness t: 50 mm and the chemical composition shown in Table 3 as the base material, a welding test was carried out by two-electrode submerged arc welding. 【0072】 Note that the flux symbols F1 1st place and F15 shown in Table 1 are fluxes in which one or more of Si, Mn, Al, Ti, and Mg are added within the scope of the present invention to the same component systems as the flux symbols F 1st place and F5 above them. 【0073】 In this welding test, assuming the fillet welding of the box column shown in Fig. 1, one of the two base materials 1 was used as the flange plate 1F and the other as the web plate 1W. A groove shape with a groove angle θ: 42° and a root gap R: 2 mm was machined on these, and a backing 2 was applied for welding. As shown in Table 4, welding was carried out in 4 passes to fabricate a welded joint. 【0074】 Figure 2 shows the electrode arrangement with two electrodes in the groove. The electrode spacing D, which is the distance between the center positions of the tip of each welding wire 5 of the leading electrode (leading electrode E1) and the trailing electrode (trailing electrode E2), was set to 60 mm. The extension X1 of the leading electrode E1 was set to 40 mm, and the extension X2 of the trailing electrode E2 was set to 50 mm. In addition, the electrode tilt angles δ were set to a receding angle of 5° for the leading electrode E1 and an advancing angle of 10° for the trailing electrode E2. 【0075】 Figure 3 shows a schematic cross-section of the resulting welded joint. The weld metal 4 was welded in four passes. The preheating temperature for the first pass was 100°C, and the interpass temperature for the second and subsequent passes was 150°C. 【0076】 The combinations of sintered fluxes in Table 1 and welding wires in Table 2 are shown in Table 5. The sintered flux shown in Table 1 was prepared by blending and mixing various mineral raw materials, granulating them with water glass as a binder, sintering them at 450-500°C for 1 hour, and then sizing them to contain at least 70% of particles in the 12-200 mesh size range (12x200 mesh). The welding wire 5 shown in Table 2 was drawn to a wire diameter of 4.8 mm for use. 【0077】 Weldability was assessed by examining arc stability, slag detachability, and bead appearance and shape during multi-layer welding. Subsequently, to check for crack formation in the obtained weld metal 4, a vertical ultrasonic test was performed using a vertical flaw detector 3 from the flange plate 1F, as shown in Figure 3. For samples showing an echo height of 20% or more, defects in the weld metal 4 were observed by macroscopic cross-sectional inspection, and the causes of the defects, such as slag inclusion, were confirmed. 【0078】 Furthermore, as shown in Figure 4, the strength test of the weld metal 4 was performed at the center 4C of the weld metal at a distance L from the plate surface. T A 10mm tensile test specimen (Type A1 according to JIS Z 3111) was taken from sampling position 10, and the test was performed. 【0079】 The impact test of the weld metal 4 was performed at the center 4C of the weld metal at a distance L from the plate surface, as shown in Figure 5. SStandard specimens according to JIS Z 3128 were taken from Charpy test specimen sampling position 11 at a position of 2 mm and the test was performed. For tensile strength evaluation, a 0.2% yield strength of 630-780 MPa and a tensile strength of 780-980 MPa were considered good. For toughness evaluation, an impact test was performed at 0°C, and the absorbed energy ( V A good result was defined as an average of 100J or more (E0℃) across three samples. 【0080】 The diffusible hydrogen content of weld metal 4 was measured in accordance with JIS Z 3118. A diffusible hydrogen content of 4.00 mL / 100 g or less was considered good for weld metal 4. These investigation results are summarized in Table 5. 【0081】 In Table 5, Invention Examples 1 to 9 were carried out using fluxes within the scope of the present invention, in combination with their respective welding wires. Example 1 1 and 12 are inventions Example 5 And in contrast to 6, flux F For 15 and F11, welding wire ni W These were carried out by combining 3 and W7, respectively. Furthermore, Comparative Examples 1 to 5 were carried out in a similar manner, using fluxes outside the scope of the present invention and combined with their respective welding wires. 【0082】 In Invention Examples 1 to 9, all welding wires exhibited appropriate 0.2% yield strength and tensile strength of the weld metal, along with excellent toughness. Furthermore, the amount of diffusible hydrogen was low, the arc was stable, and the slag detachability, bead appearance and shape were good and defect-free, resulting in extremely satisfactory results. Among these, Invention Examples 1 to 5, in which the welding wires satisfied the conditions of the present invention, showed even more sufficient strength and toughness compared to Invention Examples 6 and 7 to 9. 【0083】 And, an example of an invention 11In step 12, the 0.2% yield strength and tensile strength of the weld metal were appropriate for all welding wires, and excellent toughness was obtained. Furthermore, the diffusible hydrogen content was low, the arc was stable, and the slag detachability, bead appearance and shape were good and defect-free, resulting in extremely satisfactory results. In particular, regarding the toughness of the weld metal, the invention Example 1 1 and 12 are inventions Example 5 The results showed an improvement of more than 20J compared to both and 6. 【0084】 In contrast to the above examples of inventions, in Comparative Example 1, the flux symbol F6 is outside the scope of the present invention, while the welding wire symbol W2 is within the scope of the present invention. Flux symbol F6 has a high MgO content, which caused protrusions to form on the bead surface, resulting in a poor bead appearance and slag inclusion. Furthermore, the sum of the CO2 equivalent values ​​of one or both CaCO3 and MgCO3 was low, resulting in a high amount of diffusible hydrogen in the weld metal. In addition, the high CaF2 content led to an unstable arc. Moreover, the low Mo content and the low sum of one or both V and Nb resulted in a low 0.2% yield strength of the weld metal. 【0085】 In Comparative Example 2, flux symbol F7 is outside the scope of the present invention, while welding wire symbol W3 is within the scope of the present invention. Flux symbol F7 has a low SiO2 content, resulting in poor bead toe adhesion, poor bead shape, and poor slag release properties. Furthermore, the low MgO content affects the deterioration of slag release properties, resulting in a coarse bead pattern, the occurrence of pock marks, and a poor bead appearance. In addition, the high total CO2 equivalent values ​​of one or two types of CaCO3 and MgCO3 contribute to the occurrence of pock marks, and the increased oxygen content in the weld metal reduces toughness. Moreover, the high Mo content and the high total V and Nb content resulted in an excessively high tensile strength of the weld metal. 【0086】 In Comparative Example 3, both flux symbol F8 and welding wire symbol W7 are outside the scope of the present invention. Flux symbol F8 had poor slag release properties because it contained little CaO. Also, because it contained a lot of Al2O3, it resulted in a convex bead and poor bead shape, which contributed to poor slag release properties. Furthermore, slag inclusion occurred in the weld metal. In addition, the arc became unstable because the total amount of Na2O and K2O was low. On the other hand, welding wire symbol W7 also contained little C, Ni, Mo, and Ceq, and the total amount of one or two types of V and Nb was low, resulting in low 0.2% yield strength and tensile strength of the weld metal. Furthermore, because it contained a lot of P and Ti, the Charpy absorption energy of the weld metal was low. 【0087】 In Comparative Example 4, flux symbol F9 is outside the scope of the present invention, while welding wire symbol W2 is within the scope of the present invention. Flux symbol F9 has a high CaO content, resulting in uneven bead height, poor bead shape, and poor slag detachability. Furthermore, the sum of the CO2 equivalent values ​​of one or both CaCO3 and MgCO3 is low, resulting in a high amount of diffusible hydrogen in the weld metal. In addition, the high Ni and Cr content led to an excessively high tensile strength of the weld metal. As the strength of the weld metal increased, the Charpy absorption energy also decreased. 【0088】 In Comparative Example 5, both flux symbol F10 and welding wire symbol W7 are outside the scope of the present invention. Flux symbol F10 has a high SiO2 content, resulting in poor slag release properties and an increased oxygen content in the weld metal, leading to a low Charpy absorption energy. Furthermore, the low CaF2 content resulted in a narrow bead width and poor bead shape. On the other hand, welding wire symbol W7 also has low levels of C, Ni, Mo, and Ceq, and a low total of one or two types of V and Nb, resulting in a low 0.2% yield strength of the weld metal. In addition, the high levels of P and Ti resulted in a low Charpy absorption energy of the weld metal. 【0089】 [Table 1] 【0090】 [Table 2] 【0091】 [Table 3] 【0092】 [Table 4] 【0093】 [Table 5] [Explanation of symbols] 【0094】 1 Base material 1F Flange Plate 1W Web board 2. Security deposit 3 Vertical flaw detector 4. Weld metal 4C Weld Metal Center 5 Welding wire 10. Sampling locations for tensile test specimens 11. Charpy test sample collection location t (base material) plate thickness R Root Interval θ Bevel angle δ (electrode) tilt angle D Electrode spacing E1 leading pole, E2 trailing pole X1 Leading pole extension, X2 Trailing pole extension L T Distance from the plate surface to the tensile test specimen sampling position in the center 4C of the weld metal L S Distance from the plate surface to the Charpy test specimen sampling position in the center 4C of the weld metal

Claims

[Claim 1] A sintered flux for submerged arc welding of high-tensile steel, The chemical composition of the calcination flux is, in mass%, Yes 2 :15~25%, CaO: 3-15%, MgO: 25-45%, Al 2 O 3 :5~20%、 CaF 2 :5~20%、 Na 2 O and K 2 Total of one or two types of O: 0.5-10.0% CaCO 3 and MgCO 3 The total conversion value of one or both of these CO 2 is 3-8%, Ni: 3.00-7.20%, Cr: 0.90-2.40%, Mo: 0.50-1.30%, Total of one or two types of V and Nb: 0.080–0.220% It contains, The remainder consists of Fe from the iron alloy and unavoidable impurities. A sintered flux for submerged arc welding of high-tensile steel, characterized by the following features. [Claim 2] In addition to the chemical composition of the aforementioned calcination flux, further, in mass%, Contains a total of 0.6-3.0% of one or more elements selected from Si, Mn, Al, Ti, and Mg. The sintered flux for submerged arc welding of high-tensile steel according to feature 1. [Claim 3] The high-tensile steel is a high-tensile steel having a tensile strength of 780 MPa or more, characterized in that it is a sintered flux for submerged arc welding of high-tensile steel according to claim 1 or 2. [Claim 4] A submerged arc welding method for high-tensile steel, comprising welding using a sintered flux according to claim 1 or 2 in combination with a welding wire, The chemical composition of the welding wire is, in mass%, C: 0.05-0.12%, Si: 0.01-0.35%, Mn: 1.30 to 2.10%, Cu: 0.01-0.25%, Ni: 0.70-3.20%, Mo: 0.40-0.90%, Total of one or two types of V and Nb: 0.001 to 0.070% P: 0.015% or less, Contains S: 0.015% or less, The Ceq shown in the following formula (1) is between 0.40% and 0.80%, The remainder consists of Fe and unavoidable impurities. A submerged arc welding method for high-tensile steel, characterized by the following features. Ceq=C+Si / 24+Mn / 6+Ni / 40+Cr / 5+Mo / 4+V / 14...(1) Here, in formula (1), C, Si, Mn, Ni, Cr, Mo, and V represent the mass percentage of each element, and the content of elements that are not present is set to 0 (zero). [Claim 5] In addition to the chemical composition of the welding wire, the following is further specified in mass %, It contains one or more elements selected from Cr: 0.01-0.10%, Ti: 0.001-0.050%, and Al: 0.001-0.050%. The submerged arc welding method for high-tensile steel according to feature 4. [Claim 6] The submerged arc welding method for high-tensile steel according to claim 4, characterized in that the high-tensile steel is high-tensile steel with a tensile strength of 780 MPa or more. [Claim 7] The submerged arc welding method for high-tensile steel according to claim 5, characterized in that the high-tensile steel is high-tensile steel with a tensile strength of 780 MPa or more. [Claim 8] The submerged arc welding method for high-tensile steel according to claim 4, characterized in that the welding heat input is 100 kJ / cm or more. [Claim 9] The submerged arc welding method for high-tensile steel according to claim 5, characterized in that the welding heat input is 100 kJ / cm or more. [Claim 10] The submerged arc welding method for high-tensile steel according to claim 4, characterized in that the welding method is performed by multi-layer welding. [Claim 11] The submerged arc welding method for high-tensile steel according to claim 5, characterized in that the welding method is performed by multi-layer welding.

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