Narrow groove two-electrode large heat input submerged arc welding method

Abstract

To provide a highly efficient narrow groove two-electrode large heat input submerged arc welding method which can obtain a sound weld part having no high-temperature cracking and weld defects, prevents generation of a pop mark and a projection, and can obtain excellent welding workability and excellent mechanical properties of weld metal.SOLUTION: A narrow groove two-electrode large heat input submerged arc welding method of single pass per layer brings a backing material into contact with a rear face of a narrow groove having plate thickness of 60 mm or more, a chevron type or a V shape, a groove angle of 16 to 20°, and a root gap of 4 to 10 mm, and then performs submerged arc welding of single pass per layer so that the total of heat inputs of a preceding electrode and a succeeding electrode for each path is 200 to 490 kJ / cm, using a sintered type flux containing the total of SiO2 and CaO conversion values and the total of MgO of 30 to 40%, 4 to 10% TiO2, 16 to 26% Al2O3, 1 to 5% ZrO2, the total of CaF2, B2O3, Si and Al of 1.5 to 5.5%, the total of an Li2O conversion value of 0.5 to 2.0%, 15 to 25% Fe, and the total of Mn, Ni and Mo of 3.5 to 7.5%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a narrow-gap, two-electrode, large-heat-input submerged-arc welding method for high-tensile, extra-thick steel plates with a plate thickness of 60 mm or more, which can produce sound welds free from hot cracking or welding defects, provide good welding workability such as good bead shape and slag removability, and produce weld metal with excellent mechanical properties. [Background technology]

[0002] In order to prevent brittle fracture of structures during earthquakes, there has been a great social demand in recent years for higher toughness in weld metals for building structures. Meanwhile, as building structures become taller, thick box columns with plate thicknesses of 60 mm or more are being manufactured, and high-heat-input submerged arc welding is advantageous in terms of efficiency for welding box column corner joints. Furthermore, in recent years, the number of high-rise building structures has increased in line with demand for urban redevelopment, and the strength of box columns in building structures has also increased, resulting in a demand for even higher efficiency and toughness in high-heat-input submerged arc welding.

[0003] Various studies have been conducted on improving the efficiency and toughness of high-heat-input submerged arc welding for such extra-thick steel, and Patent Document 1 discloses a method of using two or more electrodes and increasing the heat input of each electrode to increase the deposition amount during welding, thereby reducing the number of welding passes and improving welding efficiency. However, while the high-heat-input submerged arc welding with multiple electrodes disclosed in Patent Document 1 significantly improves welding efficiency, it has problems such as poor welding workability, poor slag removability and bead formation, and is prone to welding defects such as poor fusion, making it difficult to ensure sufficient resistance to welding defects.

[0004] On the other hand, narrow-gap submerged arc welding, which has a small groove angle, allows for a reduced number of welding passes even in multi-layer welding because the cross-sectional area of ​​the groove is narrow. As disclosed in Patent Document 2, this welding method enables high efficiency in submerged arc welding of extra-thick steel. However, because the groove is narrow, this welding method is prone to poor penetration, leading to welding defects such as hot cracking, blowholes, and insufficient fusion. Furthermore, there are problems with slag removal, which is very time-consuming and results in poor bead shape.

[0005] Various methods have been considered to improve the problems of narrow-gap submerged arc welding in extra-thick steel. Patent Document 3 discloses a narrow-gap submerged arc welding method that provides good welding workability, such as by using a high-melting-point molten flux to improve slag removability. However, because the narrow-gap submerged arc welding method described in Patent Document 3 involves welding within a narrow groove, penetration at the bottom of the groove tends to be shallow, which may require back-chasing. Back-chasing is performed using methods such as mechanical cutting or arc air gouging, but when the structure is long, the processing time is long, which poses a problem of significantly reduced work efficiency.

[0006] Patent Document 4 also discloses narrow-gap, two-electrode, high-heat-input submerged arc welding for extra-thick steel plates 60 mm or thicker, in which a backing material is placed on the backside of the groove, iron particles are scattered within the groove, and then a single-layer, single-pass welding is performed. This type of two-electrode submerged arc welding allows for single-side, single-layer, single-pass welding without back-chasing using arc air gouging or other techniques, significantly improving welding efficiency. However, the narrow-gap, two-electrode, high-heat-input submerged arc welding described in Patent Document 4 requires precise groove accuracy during assembly of the steel plates, which takes time to perform. Furthermore, if the amount of iron particles scattered within the groove is uneven, stable penetration cannot be achieved, resulting in a poor weld metal. Furthermore, the flux described in Patent Document 4 has the following problems: it does not provide the required weld metal strength for 590 MPa-class high-tensile steel, and because it does not adjust the intragranular structure of the weld metal, it does not provide the required weld metal toughness. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 4-210874 [Patent Document 2] Japanese Patent Application Publication No. 55-120488 [Patent Document 3] Japanese Patent Application Publication No. 55-84280 [Patent Document 4] Japanese Patent Publication No. 2021-126696 Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention has been devised in view of the above-mentioned problems, and has as its object to provide a highly efficient narrow-gap, two-electrode, large-heat-input submerged arc welding method that can produce a sound weld free of welding defects such as hot cracking, blowholes, poor penetration, and poor fusion in narrow-gap submerged arc welding of high-tensile strength 590 MPa-class extra-thick steel plates having a plate thickness of 60 mm or more, that does not produce pop marks or protrusions on the bead surface, that ensures welding workability such as good slag removability and bead shape, and that produces weld metal with excellent mechanical properties. [Means for solving the problem]

[0009] The gist of the present invention is (1) a narrow-gap two-electrode, large-heat-input submerged arc welding method for high-tension, extra-thick steel, in which the plate thickness is 60 mm or more, the groove shape is a square or V-shaped groove, the groove angle is 16 to 20°, and the root gap is 4 to 10 mm. After a backing metal is abutted against the back side of the narrow groove, the flux is mixed with a mixture of SiO2, the total of CaO equivalents and the total of MgO: 30 to 40%, TiO2: 4 to 10%, Al2O3: 16 to 26%, ZrO2: 1% by mass. The welding method is characterized by using a sintered flux containing 0.5% to 5% of CaF2, 0.5% to 5% of B2O3, 0.5% to 2.0 ...

[0010] (2) A narrow gap two-electrode high heat input submerged arc welding method according to (1), characterized in that multi-layer welding is performed with one pass per layer under the following welding conditions: in the first layer welding, the welding current of the leading electrode is 1500 to 1900 A, the arc voltage of the leading electrode is 38 to 44 V, the welding current of the trailing electrode is 1200 to 1600 A, the arc voltage of the trailing electrode is 40 to 48 V, and the total heat input of the leading and trailing electrodes is 200 to 450 kJ / cm; and in the second and subsequent layers welding, the welding current of the leading electrode is 1600 to 2000 A, the arc voltage of the leading electrode is 35 to 44 V, the welding current of the trailing electrode is 1200 to 1800 A, the arc voltage of the trailing electrode is 42 to 52 V, and the total heat input of the leading and trailing electrodes is 270 to 490 kJ / cm. [Effects of the Invention]

[0011] According to the narrow-gap two-electrode, large-heat-input submerged-arc welding method of the present invention, in narrow-gap two-electrode, large-heat-input submerged-arc welding of 590 MPa-class high-tensile steel and extra-thick steel of 60 mm or more, a sound weld can be obtained that is free of welding defects such as hot cracking, blowholes, poor penetration, and poor fusion, and that does not produce pop marks or protrusions on the bead surface, and that provides excellent welding workability such as good slag removability and bead shape.This method enables highly efficient narrow-gap submerged-arc welding, and weld metal with excellent mechanical properties can be obtained highly efficiently. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing a groove shape used in narrow-gap, two-electrode, large-heat-input submerged arc welding with one layer and one pass to which the present invention is applied. [Figure 2] FIG. 2 is a diagram showing a groove shape used in narrow-gap, two-electrode, large-heat-input submerged arc welding of a V-groove, one layer, one pass, to which the present invention is applied. DETAILED DESCRIPTION OF THE INVENTION

[0013] In order to solve the above-mentioned problems, the present inventors have investigated welding conditions and fluxes to achieve a narrow-gap, two-electrode, large-heat-input submerged arc welding method for high-tensile, extra-thick steel, which can provide excellent welding workability, such as good slag removability and bead shape, while ensuring excellent mechanical properties of the weld metal, and can also efficiently produce sound welds free from welding defects such as hot cracking, insufficient penetration, and insufficient fusion.

[0014] First, we conducted various studies on narrow-gap, two-electrode, large-heat-input submerged arc welding, which involves multi-pass welding in one layer with high strength (590 MPa) and extra-thick steel (60 mm or thicker). Figure 1 shows a cross-sectional view of a square groove 1 used in the narrow-gap, two-electrode, large-heat-input submerged arc welding method of the present invention, which involves multi-pass welding in one layer. Figure 2 shows a cross-sectional view of a V-groove 2 used in the narrow-gap, two-electrode, large-heat-input submerged arc welding method of the present invention, which involves multi-pass welding in one layer with one pass. Welding is performed by abutting a backing material 3 on the backside of each square groove 1 and V-groove 2. Narrow-gap, two-electrode, high-heat-input submerged arc welding (SAW) with one layer and one pass typically uses a square groove (see Figure 1) or a V-groove (see Figure 2). Various studies using SAW or V-groove (see Figure 2) on 590 MPa-class high-tensile steel with thicknesses of 60 mm or more revealed that narrow-gap SAW welding is prone to poor penetration within the groove due to the narrow gap, and welding defects such as blowholes and insufficient fusion are likely to occur in the weld when multiple passes are performed. Furthermore, slag generated at the bead toe can become embedded, resulting in poor slag removability and bead shape, requiring significant slag removal and other labor-intensive tasks, resulting in poor welding efficiency. Furthermore, narrow-gap SAW welding requires a large penetration depth. If the penetration depth is too deep compared to the bead width, the welding may be unable to withstand shrinkage strain due to solidification during cooling, leading to hot cracking in the weld.

[0015] Therefore, we found that by specifying the groove angle and root gap for narrow-gap, two-electrode, large-heat-input submerged arc welding using multi-pass, single-layer welding with 590 MPa-class high-strength steel and extra-thickness steel of 60 mm or more, and by specifying the heat input for each pass of two-electrode submerged arc welding, we can prevent welding defects such as poor penetration and fusion and obtain a sound weld.We also found that by eliminating slag entrapment at the toe of the bead, we can improve welding workability such as bead shape and slag removability, and reduce the time required for slag removal, thereby significantly improving welding efficiency.We also found that by optimizing the ratio of penetration depth to bead width, we can improve hot cracking resistance.

[0016] Next, various fluxes were investigated for use in narrow-gap, two-electrode, large-heat-input, multi-pass, single-layer welding of 590 MPa-class, extra-thick steel sheets with thicknesses of 60 mm or more. Sintered fluxes, which offer excellent welding workability and allow the addition of alloying elements, are commonly used for narrow-gap, two-electrode, large-heat-input, multi-pass welding of 590 MPa-class, extra-thick steel sheets with thicknesses of 60 mm or more. Various investigations were conducted using sintered fluxes for narrow-gap, two-electrode, large-heat-input, multi-pass welding of 590 MPa-class, extra-thick steel sheets with thicknesses of 60 mm or more. Results indicated that such narrow-gap, large-heat-input, submerged-arc welding did not achieve the required strength in the weld metal, tended to coarsen grain boundaries in the weld metal structure, resulting in reduced toughness. Furthermore, protrusions and pop marks were formed on the bead surface, and welding workability was adversely affected, including poor bead toe conformance and poor slag removability.

[0017] As a result of extensive research into the various components of sintered flux, it was found that by using a sintered flux with an appropriate total content of SiO2, calcium compounds, and MgO, an appropriate TiO2 content, an appropriate Al2O3 content, an appropriate ZrO2 content, an appropriate total content of CaF2, B2O3, Si, and Al, and an appropriate total content of lithium compounds, Fe content, and an appropriate total content of Mn, Ni, and Mo, it is possible to obtain excellent welding workability, such as obtaining the necessary strength and toughness of the weld metal, good conformity of the bead toe, no blowholes in the weld, no protrusions or pop marks on the bead surface, good slag removability, and good bead shape.

[0018] The reasons for each limitation of the narrow-gap two-electrode, large-heat-input submerged arc welding method of the present invention will be explained in detail below.

[0019] [Plate thickness: 60mm or more] In narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tensile, extra-thick steel in one-layer, one-pass multi-pass welding, the steel plate thickness is set to 60 mm or more in order to improve welding efficiency.

[0020] In order to prevent the welding equipment from becoming too large and to ensure excellent mechanical properties of the weld metal, the plate thickness is preferably 100 mm or less.

[0021] [Bevel shape: V-shaped or R-shaped groove] In single-pass, multi-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel, the groove shape is either a square groove or a V-groove. As shown in Figure 1, a square groove 1 is formed by cutting only one of the steel plates 5 sandwiching the groove at an angle so that the weld in the steel plate 5 is square, and as shown in Figure 2, a V-groove 2 is formed by cutting both sides of the steel plates 5 sandwiching the groove at an angle so that the weld in the steel plate 5 is V-shaped.

[0022] In narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel in single-layer, single-pass multi-pass welding, if the groove shape is a square groove, the torch angles of the leading and trailing electrodes may be tilted 2 to 5 degrees outward from the square groove in order to sufficiently melt the root gap and prevent welding defects such as poor penetration.

[0023] [Bevel angle: 16~20°] In a single-layer, single-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding method for high-tension, extra-thick steel, setting the groove angle of the extra-thick steel to 16-20° improves slag removability and hot cracking resistance. If the groove angle is less than 16°, the generated slag will get caught in the bead toe in the groove, reducing slag removability and making the weld more susceptible to hot cracking. On the other hand, if the groove angle exceeds 20°, the number of required welding passes increases, welding efficiency decreases, and welding defects such as insufficient fusion become more likely. Therefore, the groove angle of the steel plate in single-layer, single-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding for high-tension, extra-thick steel is set to 16-20°.

[0024] [Root gap: 4~10mm] In single-pass, multi-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel, a root gap of 4 to 10 mm ensures a sufficient groove width for narrow-gap, two-electrode, large-heat-input submerged arc welding, stabilizes the arc, ensures sufficient weld penetration, prevents poor penetration, and improves hot cracking resistance. A root gap of 4 to 10 mm also improves slag removability, enabling highly efficient welding. A root gap of less than 4 mm prevents the welding tip from penetrating the groove, increasing the wire extension length and resulting in an unstable arc. A root gap of less than 4 mm also results in insufficient penetration, making poor penetration more likely, and increasing the likelihood of hot cracking in the weld. Furthermore, a root gap of less than 4 mm results in poor slag removability due to slag entrapment, increasing the time required for slag removal and reducing welding efficiency. On the other hand, a root gap of more than 10 mm increases the cross-sectional area of ​​the groove, reducing welding efficiency. Therefore, the root gap for narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel in one-pass, one-layer multi-layer welding should be 4 to 10 mm.

[0025] [Total heat input of leading and trailing electrodes for each pass: 200-490 kJ / cm] In narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel in a single-layer, single-pass process, setting the total heat input of the leading and trailing electrodes in each pass to 200 to 490 kJ / cm ensures excellent mechanical properties of the weld metal, prevents welding defects such as insufficient penetration and fusion, and reduces the number of required welding passes, enabling highly efficient welding. If the total heat input of the leading and trailing electrodes in each pass is less than 200 kJ / cm, the number of required welding passes increases, welding efficiency decreases, and welding defects such as insufficient penetration and fusion become more likely to occur. On the other hand, if the total heat input of the leading and trailing electrodes in each pass exceeds 490 kJ / cm, the penetration depth becomes too large, and coarse pro-eutectoid ferrite is likely to form at the austenite grain boundaries during the cooling process, resulting in insufficient strength and toughness of the weld metal. Therefore, the total heat input of the leading and trailing electrodes in each pass of narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel in one-layer, one-pass multi-pass welding is 200 to 490 kJ / cm.

[0026] In narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel in one-layer, one-pass multi-pass welding, the first layer welding has a particularly narrow groove width, making the weld prone to hot cracking. In addition, slag can burn, making slag removal difficult and resulting in poor bead shape, and making highly efficient welding impossible. Therefore, by setting the total heat input of the leading and trailing electrodes in the first layer welding, the welding current and arc voltage of the leading and trailing electrodes as follows, it is possible to achieve more pronounced effects.

[0027] [Total heat input of leading and trailing electrodes in first layer welding: 200~450kJ / cm] In the first layer of narrow-gap, two-electrode, high-heat-input submerged arc welding of high-tension, extra-thick steel in single-layer, single-pass multi-pass welding, the total heat input of the leading and trailing electrodes significantly affects deposition rate, weld bead width, and penetration depth. Therefore, it is an important factor for preventing weld defects such as poor penetration in the first layer and for further improving the mechanical performance and welding efficiency of the weld metal. By setting the total heat input of the leading and trailing electrodes at 200 kJ / cm or more, we can effectively prevent weld defects such as poor penetration and reduce the number of required welding passes, enabling more efficient welding. Furthermore, by setting the total heat input of the leading and trailing electrodes at 450 kJ / cm or less, the formation of coarse pro-eutectoid ferrite during cooling can be suppressed, further improving the mechanical performance of the weld metal.

[0028] [Welding current of the leading electrode in the first layer welding: 1500~1900A] In the first layer of high-tension, single-pass, narrow-gap, two-electrode, high-heat-input submerged arc welding of extra-thick steel, the welding current of the leading electrode directly contributes to deposition volume and penetration depth, and also significantly affects heat input. Therefore, it is an important factor in further improving resistance to weld defects such as poor penetration and hot cracking in the first layer. Setting the welding current of the leading electrode for the first layer to 1500A or higher enables sufficient melting within the groove of the extra-thick steel, thereby better preventing weld defects such as poor penetration. Furthermore, setting the welding current for the leading electrode for the first layer to 1900A or less ensures an appropriate ratio between penetration depth and weld bead width, further improving hot cracking resistance.

[0029] [Arc voltage of leading electrode in first layer welding: 38-44V] In the first layer of narrow-gap, two-electrode, high-heat-input submerged arc welding of high-tension, extra-thick steel in single-layer, single-pass multi-pass welding, the arc voltage of the leading electrode contributes to the penetration depth and arc width during welding and also affects the heat input, making it an important factor for further improving resistance to weld defects such as poor penetration and hot cracking in the first layer. Setting the arc voltage of the leading electrode in the first layer to 38 V or higher makes it possible to more appropriately adjust the arc width and penetration depth, further improving hot cracking resistance. Setting the arc voltage of the leading electrode in the first layer to 44 V or lower further prevents weld defects such as poor penetration in the first layer.

[0030] [Welding current of trailing electrode in first layer welding: 1200~1600A] In the first layer of narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tensile, extra-thick steel in single-layer, single-pass multi-pass welding, the welding current of the trailing electrode contributes to the amount of deposition and also affects the heat input, making it an important factor in further improving hot cracking resistance. By setting the welding current of the trailing electrode in the first layer welding to 1200A or more and 1600A or less, the ratio of penetration depth to weld bead width becomes appropriate, further improving hot cracking resistance.

[0031] [Arc voltage of trailing electrode in first layer welding: 40-48V] In the first layer of narrow-gap, two-electrode, high-heat-input submerged arc welding of high-tension, extra-thick steel in single-layer, single-pass multi-pass welding, the arc voltage of the trailing electrode contributes to the arc height and width during welding and also affects the heat input, making it an important factor for further improving the bead shape, slag removability, and hot cracking resistance in the first layer. Setting the arc voltage of the leading electrode in the first layer welding to 40 V or higher makes it possible to more appropriately adjust the arc height and arc width, thereby smoothing the weld bead surface and further improving the bead shape and hot cracking resistance. Setting the arc voltage of the leading electrode in the first layer welding to 48 V or lower further improves slag removability.

[0032] Furthermore, in narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel in one-layer, one-pass multi-pass welding, although the groove width is wider in the second and subsequent layers than in the first layer welding, the narrow groove may result in poor hot cracking resistance, slag removability, bead shape, and welding efficiency. Therefore, by setting the total heat input of the leading and trailing electrodes, the welding current and arc voltage of the leading and trailing electrodes as follows for the second and subsequent layers as well, it is possible to obtain more pronounced effects.

[0033] [Total heat input of the leading and trailing electrodes in welding from the second layer onwards: 270-490kJ / cm] In single-pass, multi-pass, narrow-gap, two-electrode, high-heat-input submerged arc welding of high-tension, extra-thick steel, the total heat input of the leading and trailing electrodes affects deposition volume, weld bead width, and penetration depth. Therefore, it is an important factor for preventing welding defects such as incomplete fusion in the second and subsequent layers, ensuring the mechanical properties of the weld metal, and further improving welding efficiency. By maintaining a total heat input of 270 kJ / cm or more, we can effectively prevent welding defects such as incomplete fusion in the second and subsequent layers and reduce the number of required welding passes, enabling more efficient welding. Furthermore, by maintaining a total heat input of 490 kJ / cm or less, the formation of coarse pro-eutectoid ferrite during cooling can be suppressed, ensuring the mechanical properties of the weld metal.

[0034] [Welding current of the leading electrode for the second and subsequent layers: 1600-2000A] In the second and subsequent layers of narrow-gap, two-electrode, high-heat-input submerged arc welding of high-tension, extra-thick steel in single-layer, single-pass multi-pass welding, the welding current of the leading electrode directly contributes to the amount of deposition, better prevents weld defects such as incomplete fusion, and significantly affects the heat input, making it an important factor for further improving hot cracking resistance in the second and subsequent layers. Increasing the welding current of the leading electrode in the second and subsequent layers to 1600 A or more effectively prevents weld defects such as incomplete fusion and further improves hot cracking resistance. Furthermore, keeping the welding current of the leading electrode in the second and subsequent layers to 2000 A or less optimizes the ratio of penetration depth to weld bead width, further improving hot cracking resistance.

[0035] [Arc voltage of the leading electrode for welding from the second layer onwards: 35-44V] In the second and subsequent layers of narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel in single-layer, single-pass multi-pass welding, the arc voltage of the leading electrode contributes to the arc width during welding and also affects the heat input, making it an important factor in further improving hot cracking resistance in the second and subsequent layers.By setting the arc voltage of the leading electrode for the second and subsequent layers to 35V or higher and 44V, the ratio between penetration depth and weld bead width becomes appropriate, further improving hot cracking resistance in the second and subsequent layers.

[0036] [Welding current of trailing electrode for second layer and subsequent layers: 1200-1800A] In the second and subsequent layers of narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel in single-layer, single-pass multi-pass welding, the welding current of the trailing electrode contributes to the amount of deposition and also affects the heat input, making it an important factor in further improving hot cracking resistance. By setting the welding current of the trailing electrode in the second and subsequent layers to 1200A or higher and 1800A or lower, the ratio of penetration depth to weld bead width becomes appropriate, further improving hot cracking resistance.

[0037] [Arc voltage of trailing electrode for second and subsequent layers: 42-52V] In single-layer, single-pass, multi-pass welding of high-tension, extra-thick steel in narrow-gap, two-electrode, high-heat-input submerged arc welding from the second layer onward, the arc voltage of the trailing electrode contributes to the arc height and width during welding and also affects the heat input. Therefore, it is an important factor for further improving the bead shape, slag removability, and hot cracking resistance in the second and subsequent layers. By setting the arc voltage of the trailing electrode to 42 V or higher in the second and subsequent layers, it is possible to more appropriately adjust the arc height and width, thereby smoothing the weld bead surface and further improving the bead shape and hot cracking resistance. Furthermore, by setting the arc voltage of the trailing electrode to 52 V or lower in the second and subsequent layers, it is possible to further improve the slag removability.

[0038] Next, the flux applied to the present invention is a sintered flux that has excellent welding workability in high heat input submerged arc welding and to which alloying elements can be added. The chemical components of the sintered flux to which the present invention is applied are described below. Note that the content of the following elements represents mass % relative to the total mass of the flux, and the description of mass % is simply written as %.

[0039] [SiO2, total CaO equivalent, total MgO in sintered flux: 30-40%] In narrow-gap, two-electrode, high-heat-input submerged arc welding of high-tension, extra-thick steel in a single-layer, single-pass, multi-pass welding process, the SiO2, calcium compounds, and MgO in the sintered flux significantly affect the slag melting point, slag fluidity, and slag refractoriness, resulting in a good bead shape. In narrow-gap, two-electrode, high-heat-input submerged arc welding in a single-layer, single-pass, multi-pass welding process, if the total SiO2, CaO equivalent, and MgO in the sintered flux is less than 30%, the slag refractoriness at the bead toe also deteriorates, resulting in poor adhesion and poor bead shape. On the other hand, if the total SiO2, CaO equivalent, and MgO in the sintered flux exceeds 40%, the slag melting point decreases, slag fluidity deteriorates, bead height becomes uneven, and protrusions tend to form on the bead surface. Therefore, in single-layer, single-pass, multi-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel, the total amount of SiO2, CaO equivalents, and MgO in the sintered flux should be 30-40%. SiO2 can be added from silica sand, feldspar, nickel slag, sodium silicate, and potassium silicate, calcium compounds from wollastonite, calcium carbonate, etc., and MgO from magnesia clinker, nickel slag, etc.

[0040] [TiO2 in sintered flux: 4-10%] In single-layer, single-pass, high-tension, narrow-gap, two-electrode, large-heat-input submerged arc welding of extra-thick steel, TiO2 in sintered flux improves bead smoothness, improves bead shape, and improves weld metal toughness. In single-layer, single-pass, high-tension, narrow-gap, two-electrode, large-heat-input submerged arc welding of extra-thick steel, TiO2 in sintered flux less than 4% improves bead smoothness and weld metal toughness, resulting in poor bead shape and reduced weld metal toughness. On the other hand, TiO2 in sintered flux exceeding 10% results in a steep bead toe angle and a convex bead. Therefore, the TiO2 content in sintered flux for single-layer, single-pass, high-tension, narrow-gap, two-electrode, large-heat-input submerged arc welding of extra-thick steel should be 4-10%. TiO2 can be added from rutile, titanium slag, titanium oxide, etc.

[0041] [Al2O3 in sintered flux: 16-26%] In single-layer, single-pass, multi-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel, the Al2O3 in the sintered flux improves slag removability. In single-layer, single-pass, multi-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel, if the Al2O3 content in the sintered flux is less than 16%, the effect of improving slag removability is not obtained. On the other hand, if the Al2O3 content in the sintered flux exceeds 26%, the bead becomes convex. Therefore, in single-layer, single-pass, multi-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel, the Al2O3 content in the sintered flux should be 16-26%. Note that Al2O3 can be added from alumina, etc.

[0042] [ZrO2 in sintered flux: 1-5%] In single-layer, single-pass, multi-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel, ZrO2 in sintered flux has a high slag melting point, improving slag refractoriness, slag removability, and bead shape. In single-layer, single-pass, multi-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel, if the ZrO2 content in the sintered flux is less than 1%, the slag refractoriness improvement effect is not achieved, and slag removability and bead shape deteriorate. On the other hand, if the ZrO2 content in the sintered flux exceeds 5%, slag will be burned at the bead toe, resulting in poor bead shape. Therefore, the ZrO2 content in the sintered flux for single-layer, single-pass, high-tension, narrow-gap, two-electrode, large-heat-input submerged arc welding of extra-thick steel should be 1-5%. ZrO2 can be added from zirconium sand, etc.

[0043] [Total of CaF2, B2O3, Si and Al in sintered flux: 1.5 to 5.5%] In single-layer, single-pass, high-tension, narrow-gap, two-electrode, large-heat-input submerged arc welding of extra-thick steel, the CaF2, B2O3, Si, and Al in the sintered flux improve the toughness of the weld metal. In single-layer, single-pass, high-tension, narrow-gap, two-electrode, large-heat-input submerged arc welding of extra-thick steel, if the total amount of CaF2, B2O3, Si, and Al in the sintered flux is less than 1.5%, the effect of improving the toughness of the weld metal is insufficient. On the other hand, if the total amount of CaF2, B2O3, Si, and Al in the sintered flux exceeds 5.5%, the slag melting point is low, resulting in poor slag fluidity, poor bead smoothness, poor bead shape, and excessive hardness of the weld metal, deteriorating the toughness of the weld metal. Therefore, in single-layer, single-pass, multi-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel, the total amount of CaF2, B2O3, Si, and Al in the sintered flux should be 1.5 to 5.5%. CaF2 can be added from fluorite, B2O3 from comarenite, Si from metallic Si, Fe-Si, Fe-Si-Mn, and Al from metallic Al, Fe-Al, and so on.

[0044] [Total Li2O equivalent value in sintered flux: 0.5 to 2.0%] In single-layer, single-pass, high-tension, narrow-gap, two-electrode, large-heat-input submerged arc welding of extra-thick steel, lithium compounds in sintered fluxes gasify with welding heat, improving shielding in the arc atmosphere and stabilizing the arc. In single-layer, single-pass, high-tension, narrow-gap, two-electrode, large-heat-input submerged arc welding of extra-thick steel, if the total Li2O equivalent in the sintered flux is less than 0.5%, the shielding effect is insufficient, the arc becomes unstable, and blowholes are more likely to occur in the weld metal. On the other hand, if the total Li2O equivalent in the sintered flux exceeds 2.0%, the arc becomes unstable and pockmarks are more likely to occur on the bead surface. Therefore, the total Li2O equivalent in the sintered flux in single-layer, single-pass, high-tension, narrow-gap, two-electrode, large-heat-input submerged arc welding of extra-thick steel should be 0.5-2.0%. Lithium compounds can be added from sources such as lithium carbonate.

[0045] [Fe in sintered flux: 15-25%] In single-layer, single-pass, multi-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel, the iron in the sintered flux reduces heat input and improves welding efficiency. In single-layer, single-pass, multi-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel, if the iron content in the sintered flux is less than 15%, the effect of reducing heat input and improving welding efficiency is not fully achieved, resulting in poor welding efficiency. On the other hand, if the iron content in the sintered flux exceeds 25%, protrusions are likely to form on the bead surface. Therefore, the iron content in the sintered flux for single-layer, single-pass, narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel should be 15-25%. Iron can be added from iron powder or other sources.

[0046] [Total of Mn, Ni, and Mo in sintered flux: 3.5 to 7.5%] In single-layer, single-pass, high-tension, narrow-gap, two-electrode, large-heat-input submerged arc welding of extra-thick steel, Mn, Ni, and Mo in the sintered flux improve the strength of the weld metal and also improve the hardenability of the weld metal, thereby significantly improving the toughness of the weld metal. In single-layer, single-pass, high-tension, narrow-gap, two-electrode, large-heat-input submerged arc welding of extra-thick steel, if the total content of Mn, Ni, and Mo in the sintered flux is less than 3.5%, the effects of improving the strength and toughness of the weld metal are insufficient. On the other hand, if the total content of Mn, Ni, and Mo in the sintered flux exceeds 7.5%, the strength of the weld metal becomes excessively high, the grain boundaries in the weld metal structure become coarse, and the toughness of the weld metal deteriorates. Therefore, in single-layer, single-pass, high-tension, narrow-gap, two-electrode, large-heat-input submerged arc welding of extra-thick steel, the total content of Mn, Ni, and Mo in the sintered flux should be 3.5 to 7.5%. Mn can be added from metallic Mn, Fe-Mn, Fe-Si-Mn, etc., Ni can be added from metallic Ni, Fe-Ni, etc., and Mo can be added from metallic Mo, Fe-Mo, etc.

[0047] In addition, FeO, NaO, KO, etc. may be added to the sintered slacks of the present invention from the viewpoint of improving welding workability. Inevitable impurities such as P and S form compounds with low melting points and reduce the toughness of the weld metal, so it is preferable that the content be as low as possible.

[0048] Furthermore, the electrode gap between two electrodes in narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel in one-layer, one-pass multi-pass welding is not particularly limited, but is preferably 70 to 90 mm from the viewpoint of ensuring the welding current of the leading and trailing electrodes and obtaining a good bead shape.

[0049] Furthermore, there are no particular limitations on the lead angle and retraction angle of the leading and trailing electrodes for each pass in narrow-gap, two-electrode, large-heat-input submerged arc welding of high-tension, extra-thick steel in one-layer, one-pass multi-pass welding, but from the perspective of ensuring sufficient penetration depth, the leading electrode may have a retraction angle of 2 to 5°, and from the perspective of improving the bead shape, the trailing electrode may have a lead angle of 2 to 5°.

[0050] Furthermore, from the viewpoint of ensuring excellent mechanical properties of the weld metal and good welding workability, the components of the submerged arc solid wire are preferably, in mass % relative to the total mass of the wire, C 0.02 to 0.18%, Si 0.05 to 0.50%, Mn 1.2 to 2.3%, Mo 0.1 to 0.8%, Ti 0.005 to 0.050%, Ni 0.1% or less, Al 0.05% or less, N 0.007% or less, P 0.02% or less, and S 0.01% or less.

[0051] The backing material that contacts the bottom of the groove is not particularly limited, but it is preferable to use a steel material conforming to JIS G 3138, which is used for building structures. [Example]

[0052] The effects of the present invention will be specifically described below with reference to examples.

[0053] Sintered fluxes with the various components shown in Table 1 were prototyped and evaluated for welding workability in narrow-gap two-electrode large heat input submerged arc welding and mechanical performance in weld metal tests.

[0054] For the weld metal tests, steel plates with the various compositions shown in Table 2 were used, and the prototype sintered flux and welding wire with the various compositions shown in Table 3 were used to assemble the steel plates processed to the thickness and groove shape shown in Tables 4 and 5. A backing material with a composition conforming to JIS G 3138 SNR490B was attached to the bottom of the groove, and then narrow-gap two-electrode large-heat-input submerged arc welding was performed under the welding conditions shown in Tables 4 and 5. The length of the test specimen was 1000 mm.

[0055] The welding workability was evaluated during the above-mentioned weld metal test, and the arc condition, slag removability, bead shape, and hot cracking were examined. The welding workability was evaluated by visually inspecting the arc condition, and a good condition was determined if the arc voltage remained constant with little fluctuation during welding. The slag removability was determined to be good if the slag covering the bead surface after welding peeled off naturally or could be removed by lightly tapping with a chipping hammer. The bead shape conformed to the "Guidelines for Measuring Steel Frame Accuracy" of the Architectural Institute of Japan, and was evaluated as good if the reinforcement height and bead width were consistent, the bead surface was uniform, and there were no pockmarks or protrusions. The hot cracking was evaluated as good if the bead surface after welding was visually inspected and there were no cracks.

[0056] For weld defects, all welds were inspected using ultrasonic testing in accordance with the Architectural Institute of Japan's "Standards and Commentary for Ultrasonic Inspection of Welded Joints in Steel Structure Buildings" 2018, and welds with good penetration and fusion and no significant harmful defects such as poor penetration or fusion or large blowholes were deemed to be good.

[0057] To investigate the mechanical properties of the weld metal, Charpy impact test pieces (JIS Z 2242 V-notch) and tensile test pieces (JIS Z 3111 A1) were taken from the weld metal after the above weld metal test, centered 7 mm below the steel plate surface, and mechanical tests were performed on each. Strength was evaluated by conducting a tensile test, with a 0.2% proof stress of 440 to 570 MPa and a tensile strength of 590 to 720 MPa being considered good. Toughness was evaluated by conducting a Charpy impact test at 0°C, with an average value of 70 J or more for three repetitions being considered good. The results are shown in Table 6.

[0058] [Table 1]

[0059] [Table 2]

[0060] [Table 3]

[0061] [Table 4]

[0062] [Table 5]

[0063] [Table 6]

[0064] In Tables 4-6, Test Nos. S1 to S14 are examples of the present invention, and Test Nos. S15 to S29 are comparative examples. In Test Nos. S1 to S14, which are examples of the present invention, a backing material was applied to the backside of the groove. The plate thickness, groove shape, groove angle, and root gap were appropriate. The sintered flux contained appropriate amounts of SiO, the total CaO equivalent value, the total MgO, TiO, Al, ZrO, CaF, B, O, the total Si and Al, the total Li, O equivalent value, and the total Fe, Mn, Ni, and Mo. This enabled stable submerged arc welding, resulting in sound welds with few blowholes and no significant defects such as hot cracking, poor penetration, or poor fusion, or large blowholes. The bead surface was free of pockmarks or protrusions, and the slag removability and bead shape were good. Furthermore, submerged arc welding with easy slag removal and high welding efficiency was possible. Furthermore, the 0.2% yield strength, tensile strength and absorbed energy of the weld metal were also satisfactory.

[0065] In S1, S2, S4, and S6, the welding current and arc voltage of the leading electrode, the welding current and arc voltage of the trailing electrode, and the total heat input of the leading and trailing electrodes during the first layer welding were appropriate, and the welding current and arc voltage of the leading electrode, the welding current and arc voltage of the trailing electrode, and the total heat input of the leading and trailing electrodes during the second layer welding and beyond were appropriate, so resistance to hot cracking and weld defects was particularly improved, with no hot cracking or weld defects, and the bead shape, slag removability, and welding efficiency were particularly excellent, making more efficient submerged arc welding possible.In addition, the 0.2% proof stress, tensile strength, and absorbed energy of the weld metal were extremely good.

[0066] In the comparative example, Test No. S15, the root gap was small, resulting in an unstable arc state. Furthermore, slag removability was poor, resulting in poor welding efficiency. Furthermore, poor penetration occurred in the weld. Furthermore, the welding current of the leading electrode in the first layer welding was low, so the effect of improving weld defect resistance was not obtained. Furthermore, hot cracking occurred in the weld. Furthermore, the arc voltage of the leading electrode in the first layer welding was low, so the effect of improving hot cracking resistance was not obtained. Furthermore, the bead shape was poor because the combined sintered flux contained a small amount of SiO2, the total CaO equivalent value, and the total MgO.

[0067] In Test No. S16, the root gap was small, resulting in an unstable arc state. Furthermore, slag removability was poor, resulting in poor welding efficiency. Furthermore, poor penetration occurred in the weld. Furthermore, the arc voltage of the leading electrode in the first layer welding was high, which prevented the improvement of weld defect resistance. Furthermore, hot cracking occurred in the weld. Furthermore, the welding current of the leading electrode in the first layer welding was high, which prevented the improvement of hot cracking resistance. Furthermore, the combined sintered flux contained a large amount of ZrO2, resulting in a poor bead shape. Furthermore, the total heat input of the leading and trailing electrodes in the first layer welding was high, which resulted in low 0.2% yield strength, tensile strength, and absorbed energy of the weld metal.

[0068] Test No. S17 had poor slag removability due to the narrow groove angle. Hot cracking also occurred in the weld. The low welding current of the leading electrode in the second and subsequent welding layers prevented improved hot cracking resistance. The low combined heat input of the leading and trailing electrodes in the second and subsequent welding layers prevented poor fusion in the weld. The low welding current of the leading electrode in the second and subsequent welding layers prevented improved resistance to welding defects such as poor fusion. The combined sintered flux contained high amounts of SiO2, CaO equivalent, and MgO, resulting in uneven bead height and protrusions on the bead surface. The combined sintered flux contained low amounts of CaF2, B2O3, Si, and Al, resulting in low absorbed energy in the weld metal.

[0069] Test No. S18 had poor slag removability due to the narrow groove angle. Hot cracking also occurred in the weld. Furthermore, the welding current of the leading electrode was high in the second and subsequent welding layers, which prevented the improvement of hot cracking resistance. Furthermore, the root gap was large, resulting in poor welding efficiency. Furthermore, the combined sintered flux contained a large amount of Al2O3, resulting in a convex bead. Furthermore, the total heat input of the leading and trailing electrodes in the second and subsequent welding layers was high, resulting in low 0.2% yield strength, tensile strength, and absorbed energy of the weld metal.

[0070] In Test No. S19 of the comparative examples, the root gap was small, resulting in an unstable arc state. Also, slag removability was poor. Furthermore, poor penetration occurred in the weld. Also, welding efficiency was poor. Also, hot cracking occurred in the weld. Furthermore, because the welding current of the trailing electrode in the first layer welding was low, the effect of improving hot cracking resistance was not obtained. Furthermore, because the combined sintered flux contained a small amount of Mn, Ni, and Mo, the 0.2% proof stress, tensile strength, and absorbed energy of the weld metal were low.

[0071] In the comparative example, Test No. S20, the root gap was small, resulting in an unstable arc state. Furthermore, slag removability was poor. Furthermore, the arc voltage of the trailing electrode during the first layer welding was high, which prevented the improvement of slag removability. Furthermore, the welding efficiency was poor. Furthermore, poor penetration and hot cracking occurred in the weld. Furthermore, the welding current of the trailing electrode during the first layer welding was high, which prevented the improvement of hot cracking resistance. Furthermore, the combined sintered flux contained a large amount of TiO2, which resulted in poor conformity at the bead toe and a convex bead. Furthermore, the total heat input of the leading and trailing electrodes during the first layer welding was high, which resulted in low 0.2% proof stress, tensile strength, and absorbed energy of the weld metal.

[0072] In the comparative example, Test No. S21, the groove angle was narrow, resulting in poor slag removability. Hot cracking also occurred in the weld. Furthermore, the arc voltage of the trailing electrode was high in the second and subsequent welding layers, so the effect of improving slag removability was not achieved. Furthermore, the welding current of the trailing electrode was high in the second and subsequent welding layers, so the effect of improving hot cracking resistance was not achieved. Furthermore, the combined sintered flux contained a large amount of CaF2, B2O3, Si, and Al, resulting in poor bead smoothness and a poor bead shape. Furthermore, the absorbed energy of the weld metal was low.

[0073] In Comparative Example Test No. S22, the root gap was small, resulting in an unstable arc state. Also, slag removability was poor. Furthermore, poor penetration occurred in the weld. Also, welding efficiency was poor. Also, hot cracking occurred in the weld. Furthermore, the welding current of the trailing electrode in the second and subsequent welding layers was low, so the effect of improving hot cracking resistance was not achieved. Furthermore, the combined sintered flux contained a large amount of Mn, Ni, and Mo, so the 0.2% proof stress and tensile strength of the weld metal were excessively high, and the absorbed energy was low.

[0074] In the comparative example, Test No. S23, the groove angle was narrow, resulting in poor slag removability. Hot cracking also occurred in the weld. The arc voltage of the leading electrode was low in the second and subsequent welding layers, preventing improvement in hot cracking resistance. The total heat input of the leading and trailing electrodes in the second and subsequent welding layers was low, resulting in poor welding efficiency. Insufficient fusion also occurred in the weld. The TiO2 content of the combined sintered flux was low, resulting in poor bead smoothness and a poor bead shape. The absorbed energy of the weld metal was also low.

[0075] In the comparative example, Test No. S24, the groove angle was narrow, resulting in poor slag removability. Hot cracking also occurred in the weld. Furthermore, the arc voltage of the leading electrode was high in the second and subsequent welding layers, preventing improvement in hot cracking resistance. Furthermore, the total Li2O equivalent value of the combined sintered flux was low, resulting in an unstable arc state. Large blowholes also occurred in the weld. Furthermore, the low Fe content resulted in poor welding efficiency.

[0076] In the comparative example, Test No. S25, the root gap was small, resulting in an unstable arc state. Furthermore, slag removability was poor. Furthermore, poor penetration occurred in the weld. Furthermore, welding efficiency was poor. Furthermore, hot cracking occurred in the weld. Furthermore, the arc voltage of the trailing electrode in the first layer welding was low, so no improvement in hot cracking resistance was achieved. Furthermore, the combined sintered flux contained a large amount of TiO2, so the bead toe did not conform well, resulting in a convex bead. Furthermore, the arc voltage of the trailing electrode in the first layer welding was low, so no improvement in bead shape was achieved.

[0077] In the comparative example, Test No. S26, the root gap was small, resulting in an unstable arc state. Furthermore, slag removability was poor. Furthermore, poor penetration occurred in the weld. Furthermore, welding efficiency was poor. Furthermore, hot cracking occurred in the weld. Furthermore, the arc voltage of the trailing electrode was low in the second and subsequent welding layers, so no improvement in hot cracking resistance was achieved. Furthermore, the amount of Al2O3 in the combined sintered flux was high, resulting in a convex bead. Furthermore, the arc voltage of the trailing electrode was low in the second and subsequent welding layers, so no improvement in bead shape was achieved.

[0078] In the comparative example, Test No. S27, the steel plate thickness was small, resulting in poor welding efficiency. Also, the sintered flux used contained a small amount of Al2O3, resulting in poor slag removability. Furthermore, the high Fe content resulted in the formation of protrusions on the bead surface.

[0079] Test No. S28, one of the comparative examples, had poor welding efficiency due to a wide groove angle. Furthermore, the total heat input of the leading and trailing electrodes in welding from the second layer onward was somewhat low, so the effect of improving welding efficiency was not achieved. Furthermore, poor fusion occurred in the weld. Furthermore, the total heat input of the leading and trailing electrodes in welding from the second layer onward was somewhat low, so the effect of improving welding defect resistance was not achieved. Furthermore, the combined sintered flux contained a small amount of ZrO2, so slag removability was poor. Furthermore, the bead shape was poor.

[0080] In Comparative Example Test No. S29, the total LiO2 equivalent value of the combined sintered flux was high, so the arc state was unstable and pockmarks occurred on the bead surface.

[0081] In Comparative Example Test No. S30, the combined sintered flux contained a small amount of Mn, Ni, and Mo, so the 0.2% proof stress, tensile strength, and absorbed energy of the weld metal were low. In addition, the total heat input of the leading electrode and trailing electrode in the first layer welding was somewhat large, so the effect of improving the strength and toughness of the weld metal was not obtained. [Explanation of symbols]

[0082] 1. R-type groove 2 V-shaped bevel 3 Backing material 5 steel plate

Claims

1. In a narrow gap two-electrode large heat input submerged arc welding method for high-tension, extra-thick steel, After the backing material is applied to the back side of the narrow groove with a plate thickness of 60 mm or more, a groove shape of V-shape, a groove angle of 16 to 20 degrees, and a root gap of 4 to 10 mm, SiO in mass% relative to the total mass of the flux 2 , total of CaO equivalent value and total of MgO: 30 to 40%, TiO 2 : 4 to 10%, Al 2 O 3 :16-26%, ZrO 2 : 1-5%, CaF 2 , B 2 O 3 , the sum of Si and Al: 1.5 to 5.5%, Li 2 The total of O equivalents: 0.5 to 2.0%, Fe: 15 to 25%, the total of Mn, Ni and Mo: 3.5 to 7.5%, and the rest are FeO, Na 2 O.K. 2 A narrow-gap, two-electrode, large-heat-input submerged arc welding method characterized by performing multi-layer welding with one layer and one pass under welding conditions in which the total heat input of the leading electrode and the trailing electrode for each pass is 200 to 490 kJ / cm using a sintered flux containing O and inevitable impurities.

2. The welding current of the leading electrode in the first layer welding is 1500 to 1900 A, the arc voltage of the leading electrode is 38 to 44 V, the welding current of the trailing electrode is 1200 to 1600 A, the arc voltage of the trailing electrode is 40 to 48 V, and the total heat input of the leading electrode and the trailing electrode is 200 to 450 kJ / cm, 2. The narrow-groove two-electrode, large-heat-input submerged arc welding method according to claim 1, wherein multi-layer welding is performed with one pass per layer under the following welding conditions: welding current of the leading electrode in the second and subsequent layers: 1600 to 2000 A, arc voltage of the leading electrode: 35 to 44 V, welding current of the trailing electrode: 1200 to 1800 A, arc voltage of the trailing electrode: 42 to 52 V, and a total heat input of the leading and trailing electrodes of 270 to 490 kJ / cm.

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