One-sided submerged arc welding method and method for manufacturing welded joint

Abstract

Provided is a single-sided submerged arc welding method having excellent mechanical properties and high productivity, particularly in high heat input welding of thick steel plates in the fields of shipbuilding and construction, and a welded joint produced by the welding method. In the single-sided submerged arc welding method for butt welding two steel plates, the thickness of the steel plates is 9 to 40 mm, a root face exceeding 0 mm and not exceeding 5 mm is formed at the bottom of the butt groove of the steel plates, a two-stage angle is provided in the groove portion, the groove angle of the first stage on the surface side is 50 to 70°, the groove angle of the second stage in contact with the root face is 20 to 45°, the depth of the second stage groove is 2 to 5 mm, the welding heat input is 15 to 200 kJ / cm, and the formula (1) is satisfied, and welding is performed in one pass from the surface side. (t-10)×5

Description

[Technical field]

[0001] The present invention relates to a one-sided submerged arc welding method that can efficiently obtain excellent welded joint characteristics using a submerged arc welding method, and to a welded joint produced by this welding method. [Background technology]

[0002] Submerged arc welding (hereinafter referred to as "SAW") is used in the fields of shipbuilding and construction to weld large plate joints. This type of welding is difficult to reverse after welding, so one-sided welding methods that do not require reversing are often used. In one-sided welding methods, V-grooves and Y-grooves are used as the butt grooves for the steel plates to be welded. For these grooves, if the groove angle is constant, the groove depth and groove width become wider as the plate thickness increases. Therefore, the cross-sectional area of ​​the groove increases in proportion to the square of the groove depth. An increase in the cross-sectional area of ​​the groove increases the amount of deposited metal, resulting in an increase in welding labor hours.

[0003] To address these issues, for example, Patent Document 1 discloses a one-sided, single-layer submerged arc welding method in which the number of electrodes is increased to weld with a large heat input, thereby significantly increasing the amount of deposition per unit time and performing welding in a single layer.

[0004] Furthermore, Patent Document 2 discloses that in order to increase the plate thickness limit and improve the efficiency of one-pass, one-sided welding of thick steel plates by one-sided submerged arc welding, a multi-stage groove is formed in which the groove angle widens in at least two stages under the limitation of a specific flux.

[0005] Furthermore, Patent Document 3 discloses a submerged arc welding method suitable for seam welding of large diameter steel pipes, in which three or more electrodes are used, and a two-stage groove is formed in which the groove angle on the bottom side is smaller than that on the top side under restrictions on the wire diameter and current density of the first electrode. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2017-213569 A [Patent Document 2] Japanese Patent Application Publication No. 02-258191 [Patent Document 3] International Publication No. 2013 / 080523 Summary of the Invention [Problem to be solved by the invention]

[0007] In conventional one-sided welding technology, as plate thickness increases, the cross-sectional area of ​​the groove increases dramatically, and the number of welding steps increases significantly, so that in order to reduce the number of welding steps, it is necessary to increase the welding heat input (hereinafter, simply referred to as "heat input"). As a result, there was a problem that the low-temperature toughness of the weld heat-affected zone (hereinafter, also referred to as "HAZ") is significantly reduced due to the excessive heat input.

[0008] In the technology described in Patent Document 1, in order to supply the amount of weld metal required for one layer from the welding wire, it is necessary to set the welding current high, and the heat input per unit weld length becomes large. As the welding heat input is increased, the cooling rate after welding drops dramatically, so the weld heat affected zone is exposed to high temperatures for a long time, causing the crystal grains in the metal microstructure to coarsen, and there is a problem that the mechanical properties deteriorate.

[0009] The technology described in Patent Document 2 shows an example in which a two-stage groove is used in high heat input welding to reduce the heat input by reducing the cross-sectional area of ​​the groove. However, since there is not a large difference between the groove angle on the bottom side of the groove and the groove angle on the surface side, the effect of reducing the cross-sectional area cannot be fully obtained.

[0010] The technology described in Patent Document 3 shows a welding method using a two-stage groove. However, the groove angle on the bottom side is not so narrow compared to the conventional groove shape. Therefore, the groove angle on the surface side becomes excessively wide in order to widen the bead width, and the effect of reducing the cross-sectional area of ​​the groove is low compared to welding using a conventional Y-shaped groove. Therefore, a large heat input reduction effect that affects the metal microstructure is not obtained.

[0011] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide a submerged arc welding method that has excellent mechanical properties and high productivity, particularly in large heat input welding of thick steel plates in the shipbuilding and construction fields, and a welded joint produced using this welding method. [Means for solving the problem]

[0012] The conventional groove shape applied to one-sided welding is a Y-groove as shown in FIG. 2. The Y-groove is formed by root faces 3a, 3b for joining plates on the lower side of steel plates 1a, 1b, and tapered parts 2a, 2b machined with a predetermined groove angle (θ1) on the upper part of the steel plates. In this Y-groove, if the depth (r) of the root face is constant, the groove depth (depth of the tapered part) (h1) and the groove width increase as the plate thickness (t) increases. Therefore, the cross-sectional area (S) of the groove increases in proportion to the square of the groove depth (h1). As the cross-sectional area (S) of the groove increases, a large amount of welding material is required to be supplied from the wire, and if the welding speed is kept constant to maintain productivity, the welding current must be increased or the number of electrodes must be increased to increase the wire supply speed.

[0013] However, methods that increase the welding current or the number of electrodes increase the heat input and slow the cooling rate after welding. When the cooling rate slows down, the heat-affected zone of the weld is exposed to high temperatures for a long time. As a result, there are problems with the crystal grains becoming coarse and the mechanical properties deteriorating significantly. In addition, depending on the set current and number of electrodes, it may be necessary to add additional welding power supplies, which increases the cost of the equipment and makes it difficult to secure the installation space.

[0014] On the other hand, in the case of a method of reducing the cross-sectional area (S) of the groove by narrowing the groove angle (θ1), the arc occurs at the top of the groove, resulting in insufficient penetration of the root face. Also, if the depth (r) of the root face is increased to make the groove shallower, the arc during welding cannot melt the entire root face, and the necessary back bead cannot be formed with one-sided welding.

[0015] In order to achieve the above-mentioned object, the inventors have thoroughly studied the appropriate groove shape for reducing the amount of deposited metal. As a result, they have found that the cross-sectional area of ​​the groove can be minimized by forming a two-stage groove with a two-stage groove and adding a shallow second stage groove with a specific small angle to the bottom of the first stage groove in order to assist penetration.

[0016] The present invention was completed based on these findings and through further investigation, and the gist of the present invention is as follows. [1] A single-sided submerged arc welding method for butt welding two steel plates together, comprising the steps of: The thickness t of the steel plate is in the range of 9 to 40 mm, A root face having a depth in the range of more than 0 mm and not more than 5 mm is formed at the bottom of the butt groove of the steel plate, and a two-stage angle is provided in the groove portion, the groove angle of the first stage on the surface side is in the range of 50 to 70 °, the groove angle of the second stage in contact with the root face is in the range of 20 to 45 °, and the depth of the second stage groove is in the range of 2 to 5 mm, The welding heat input H is in the range of 15 to 200 kJ / cm. Furthermore, the welding heat input H (kJ / cm) satisfies the following formula 1 with respect to the thickness t (mm) of the steel plate, A one-sided submerged arc welding method in which welding is done in one pass from the surface side. [Formula 1] (t-10)×5 <H<(t-4)×6 [2] The welding speed should be in the range of 50 to 120 cm / min. Using one or more electrodes; and The single-sided submerged arc welding method according to [1] above, wherein welding is performed by any one selected from the range of a welding current of the first electrode being in the range of 700 to 1600 A, or by a combination of two or more of these. [3] The method of one-sided submerged arc welding according to [1] or [2] above, wherein flux is used as a backing. [4] A welded joint produced by the one-sided submerged welding method described in any one of [1] to [3] above. [5] The welded joint described in [4] above, wherein the Charpy absorbed energy of the welded heat affected zone at -60°C is 27 J or more. Effect of the Invention

[0017] According to the present invention, it is possible to provide a welding method capable of efficiently obtaining a welded joint having excellent low-temperature toughness in the weld heat affected zone, and this has a significant industrial effect. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a schematic cross-sectional view showing an example of a groove shape suitable for a welding method according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic cross-sectional view showing a Y-shaped groove shape in a conventional welding method. [Diagram 3] 4 is a graph showing a suitable range of welding heat input with respect to plate thickness in the welding method according to the embodiment. [Figure 4] FIG. 2 is a schematic cross-sectional view showing the positions at which test pieces were taken for a Charpy impact test. [Diagram 5] 1 is a graph comparing the relationship between the plate thickness of a steel plate and the amount of welding heat input between an example of the present invention and a conventional example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present invention will be described in detail. [One-sided, single-layer submerged arc welding] This embodiment is a single-sided submerged arc welding method for butt welding two steel plates together. In this method, welding is performed in one pass from the front side for highly efficient welding. In other words, full penetration welding (uranami welding) is performed by single-sided single-layer submerged arc welding.

[0020] Submerged arc welding (SAW) is a welding method in which an electrode made of a welding wire (hereinafter, simply referred to as "wire") is continuously fed into powder-like flux that has been spread on the base metal in advance, and an arc is generated between the tip of the wire and the base metal. SAW has the advantage that efficient welding can be achieved by adopting a large current to increase the wire deposition speed. In this embodiment, as described later, single-electrode or multi-electrode welding is applied. In multi-electrode welding, two to four electrodes are arranged in series depending on the thickness of the steel plate and the groove shape to improve welding efficiency. In addition, when welding in one layer on one side, a flux copper backing method can be used in which backing flux is spread on a copper plate to optimize the back wave shape, and the back side of the weld is pressed with the pressure of an air hose.

[0021] [Group shape] In this embodiment, a two-stage groove is adopted as the groove shape. In this two-stage groove, as shown in FIG. 1, root faces 3a and 3b with a depth r are formed at the bottom of the butt groove of the steel plates 1a and 1b. Then, two-stage angles are provided in the groove portion. That is, a first stage groove angle θ formed by the tapered parts 2a and 2b with a depth h formed on the front surface side and a second stage groove angle δ formed by the tapered parts 4a and 4b with a depth k formed in contact with the root faces 3a and 3b are provided. The depth h is the depth of the first stage groove, and the depth k is the depth of the second stage groove. δ needs to be smaller than θ. The depth r of the root face and the depths h and k of the groove are measured in the thickness direction of the steel plate, and their sum corresponds to the thickness t of the steel plate. (i) Root surface The root faces 3a and 3b are provided on the back side for plate joining, and their depth r is set to be in the range of more than 0 mm and not more than 5 mm. If r exceeds 5 mm, the root faces will remain unmelted and the back wave shape will become uneven. Note that r exceeding 0 mm means that the root faces are in contact with each other in a line shape as the minimum value, and preferably r is 3 to 4 mm. (ii) First groove angle The groove angle θ of the first step is in the range of 50 to 70°. If θ is less than 50°, the groove width is narrow, so the arc occurs near the surface and deep penetration cannot be obtained. Also, if θ exceeds 70°, the amount of deposited metal becomes excessive. Preferably, θ is in the range of 50 to 60°. (iii) Second groove angle The second groove angle δ is in the range of 20 to 45°. If δ is less than 20°, the arc generation position becomes shallow, resulting in a problem of insufficient penetration. If δ exceeds 45°, the intended effect of reducing the cross-sectional area of ​​the groove cannot be obtained. Preferably, δ is in the range of 25 to 40°. It is preferable that δ is smaller than θ by 10 to 20°. (iv) Depth of the second groove The depth k of the second groove is set to be in the range of 2 to 5 mm. If k is less than 2 mm, the effect of reducing the amount of deposited metal to the minimum required is hardly obtained. If k exceeds 5 mm, the root face remains unmelted, and the back groove shape becomes non-uniform. Preferably, k is in the range of 3 to 4 mm. It is preferable that the depth r of the root face is smaller than the sum of the depth h of the first groove and the depth k of the second groove, and that the depth k of the second groove is smaller than the depth h of the first groove. By setting the groove shape as described above, the amount of welding heat input can be reduced compared to the case of a conventional Y-shaped groove.

[0022] [Steel plate] (i) Thickness of the steel plate The thickness of the steel plate used as the base material, i.e., the plate thickness t, is set to a range of 9 to 40 mm. If t is less than 9 mm, sufficient one-sided one-pass welding is possible using conventional submerged arc welding with a single electrode in a Y-groove. On the other hand, if t exceeds 40 mm, it becomes difficult to perform sound welding in one pass with four electrodes. Preferably, t is set to a range of 12 to 25 mm. For steel plates with a plate thickness t of more than 40 mm, two or more passes of welding can be applied. By adopting a groove shape within the range of this embodiment for the first pass of welding, a significant improvement in construction efficiency can be expected. (ii) Steel type of steel plate In this embodiment, in order to provide the HAZ with excellent mechanical properties, particularly excellent low-temperature toughness, the base steel plate has a tensile strength of 440 MPa or more and a Charpy absorbed energy at -60°C (hereinafter referred to as V E -60 It is preferable that the steel be a steel type having a hardness of 70J or more. Examples of such steel types include SLA325A specified in JIS G 3126.

[0023] [Welding conditions] (i) Welding heat input In this embodiment, the welding heat input H is in the range of 15 to 200 kJ / cm. In the case of multiple electrodes, the heat input H is the total of the heat inputs for each electrode. In a groove shape within the range of this embodiment, if the heat input H exceeds 200 kJ / cm, the low temperature toughness of the HAZ of the welded joint decreases, while if the heat input H is less than 15 kJ / cm, welding defects are likely to occur. Furthermore, from the viewpoint of achieving both a sound weld shape and excellent low-temperature toughness of the HAZ in the welded joint, the welding heat input H (kJ / cm) needs to satisfy the following formula 1 relative to the steel plate thickness t (mm). [Formula 1] (t-10)×5 <H<(t-4)×6 Therefore, the range of the welding heat input amount suitable for the plate thickness is the hatched area in Fig. 3. Note that the boundary of this hatched area is shown by a solid line for the part included in the area and a dashed line for the part not included. (ii) Welding speed In this embodiment, the welding speed is preferably in the range of 50 to 120 cm / min. If the welding speed is less than 50 cm / min, the productivity is low. On the other hand, if the welding speed exceeds 120 cm / min, the welding speed is easily affected by disturbances such as processing errors in the groove shape and welding deformation. More preferably, the welding speed is in the range of 60 to 90 cm / min. (iii) Electrode In this embodiment, it is preferable to use one or more electrodes. The reason is that there are cases where highly efficient welding can be performed even with one electrode (single electrode). Note that, when five or more electrodes are used, the welding conditions become complicated, so it is more preferable to use four or less electrodes. When multiple electrodes are used, they are referred to in order from the leading electrode as the first electrode, the second electrode, ... In the case of three electrodes, the preferred range of wire diameter is 4.0 to 4.8 mmφ for the first electrode, and 4.8 to 6.4 mmφ for the second and third electrodes. The reason for making the wire diameter of the second and third electrodes larger than that of the first electrode is to widen the penetration width. Regarding the wire spacing, the distance between the first and second electrodes is preferably 30 to 50 mm. If the distance between the first and second electrodes is too close, the arc may interfere with each other, resulting in an unstable bead, and if the distance is too far, the penetration depth may be unstable and the formation of the back wave may be poor. The distance between the second and third electrodes is preferably 120 to 180 mm. If the second and third electrodes are too close, cracks may occur, and if the distance is too far, slag may be involved.

[0024] (iv) Welding current and voltage of the first electrode In this embodiment, the welding current (AC) of the first electrode (the electrode in the case of a single electrode) is preferably in the range of 700 to 1600 A. If the welding current of the first electrode is less than 700 A, the root face may not be melted, resulting in a defect of poor penetration. On the other hand, if the welding current of the first electrode is more than 1600 A, the root portion may be excessively melted, resulting in a defect of melting through. More preferably, the welding current of the first electrode is in the range of 800 to 1500 A. Incidentally, a preferred welding voltage of the first electrode is in the range of 25 to 40 V. More preferably, the welding voltage of the first electrode is in the range of 28 to 35 V. (v) Welding current and voltage of the second and third electrodes When the number of electrodes is three, the preferred welding current (AC) of the second electrode is in the range of 800 to 1400 A. More preferably, the welding current of the second electrode is in the range of 900 to 1300 A. Furthermore, the preferred welding voltage of the second electrode is in the range of 30 to 45 V. More preferably, the welding voltage of the second electrode is in the range of 32 to 40 V. A preferred welding current (AC) for the third electrode is in the range of 600 to 1300 A. More preferably, the welding current for the third electrode is in the range of 800 to 1200 A. A preferred welding voltage for the third electrode is in the range of 30 to 50 V. More preferably, the welding voltage for the third electrode is in the range of 35 to 45 V. In this way, the leading electrode can be made to have a higher welding current and lower welding voltage than the trailing electrode, thereby enabling deep and stable melting of the root surface. On the other hand, the trailing electrode can be made to have a higher welding voltage than the leading electrode, resulting in a wider bead width and a more stable bead shape on the surface.

[0025] [Welding materials] (i) Backing material In this embodiment, any of copper plate, ceramic, flux, etc. can be preferably used as the backing material, but it is more preferable to use flux. The backing method using flux includes the above-mentioned flux copper backing method. This makes the back wave shape more stable and appropriate.

[0026] The backing flux used in the flux copper backing method has the following composition, for example: In mass%, it contains BaO: 8-47%, SiO2: 5-28%, MgO: 10-21%, CaO: 0-7%, CaF2: 12-24%, Al2O3: 5-15%, TiO2: 0-10%, ZrO2: 0-5%, and CO2: 0-9%. The remainder is metal powder as a deoxidizer or alloying agent.

[0027] In this embodiment, after the steel plates are butted and backed, welding flux is spread in the groove on the back side (second stage) and the front side (first stage), and then one-sided, single-layer welding is performed in a downward position without preheating. In this case, the following welding wires and welding fluxes are applicable to this embodiment. (ii) Welding wire An example of the welding wire applied to this embodiment is a solid wire for low temperature steel. One example of the composition is, in mass%, C: 0.05-0.15%, Si: 0.02-0.05%, Mn: 1.3-2.0%, Ni: 1.6-2.9%, and Mo: 0.3-0.8%, with the balance being Fe and unavoidable impurities. However, in this embodiment, the welding wire is not limited to this. (iii) Welding flux As the welding flux, any of known molten fluxes and bonded fluxes can be used. For example, examples of bonded fluxes include fluxes containing, by mass%, SiO2: 10-30%, CaO: 10-50%, MgO: 20-50%, Al2O3: 10-30%, CaF2: 5-20%, and CaCO3: 2-15%. However, in the present invention, the welding flux is not limited to these. When using bonded flux, it is preferable to dry it for 1-2 hours at a temperature in the range of 200-300°C before welding, as in the conventional SAW method.

[0028] [Welded joint] A welded joint according to another embodiment of the present invention is produced by the welding method of the above embodiment, and has excellent low-temperature toughness of the HAZ.

[0029] [Low temperature toughness of HAZ] The welded joint according to this embodiment has a Charpy absorbed energy of the HAZ at −60° C., i.e. V E -60 It is preferable that the value is 27 J or more. V E -60 If it is ≧27J, there is an advantage that brittle fracture is less likely to occur. EXAMPLES

[0030] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the scope described in the examples.

[0031] [Steel plate] The base steel plate used was an aluminum-killed steel plate for low temperature use in shipbuilding, with a composition by mass of C: 0.07%, Si: 0.28%, Mn: 1.37%, P: 0.007%, and S: 0.002%, with the balance being Fe and unavoidable impurities. The thickness of the steel plate was 12 to 40 mm. The tensile strength of the steel plate was 500 MPa, V E -60 The tensile strength of the steel plate was determined by a tensile test in accordance with the provisions of JIS Z 2241:2011. V E -60 was determined by a Charpy impact test in accordance with the provisions of JIS Z 2242:2018.

[0032] [Welding materials and conditions] The welding method used was the flux copper backing method, in which a copper plate with backing flux spread over it is pressed against the back of the steel plate for welding. The backing flux contained, by mass%, 32% BaO, 12% SiO2, 11% MgO, 1% CaO, 15% CaF2, 10% Al2O3, 2% TiO2, 4% ZrO2, and 9% CO2. The remainder was metal powder as a deoxidizer or alloying agent.

[0033] The welding flux used in the groove contained, by mass%, SiO2: 20%, CaO: 5%, MgO: 25%, Al2O3: 10%, CaF2: 5%, and CaCO3: 5%. This flux was dried at 300℃ for 1 hour before being sprayed in the groove.

[0034] Using solid wire (diameters 4.8 mm and 6.4 mm) as the welding wire, one-sided, one-layer submerged arc welding was performed without preheating in a downward position using one to four electrodes under the various welding conditions shown in Table 1. This solid wire is a solid wire for low-temperature steel, and has a composition, by mass%, of C: 0.10%, Si: 0.03%, Mn: 1.65%, Ni: 2.40%, and Mo: 0.50%, with the balance being Fe and unavoidable impurities.

[0035] [Mechanical properties of welded joints] Charpy impact test specimens (V-notch) were taken from the butt welded joint obtained by the above-mentioned single-sided single-layer SAW, in accordance with the provisions of JIS Z 2242 (Charpy impact test method for metallic materials), at the test specimen taking position shown in Figure 4, and an impact test was performed. Steel plates 1a and 1b were butted together and a single-layer SAW was performed on one side, resulting in the formation of weld metal 5 in the groove on the front side, a back bead 8 in the groove on the back side, and a weld heat-affected zone 6 between the weld metal 5 and the steel plate, as shown in Figure 4. For the test piece 7, a Charpy V-notch test piece 7 with a V-notch 7a formed at the position of the weld heat-affected zone 6 at a depth of 1 / 2t of the plate thickness (t) of the steel plate was taken in accordance with JIS Z 3128 (Impact test method for welded joints). For the Charpy impact test, three of the test pieces 7 were prepared. V E -60 The average value was taken as the low temperature toughness value of the weld heat affected zone of each weld joint.

[0036] [Evaluation of weld shape] The weld shape was evaluated by visual observation and / or dimensional measurement, based on the back bead shape and surface bead appearance. The back bead shape was evaluated as good (○) when the back bead width was 5.0 mm or more, the bead height was 1.0 to 2.5 mm, and there was no undercut, and all other cases were evaluated as poor (×). The bead appearance was evaluated as good (○) when the bead height and width were uniform and in good condition, and as poor (×) when either or both of the other cases, such as the shape being uneven and / or the occurrence of undercut, were evaluated.

[0037] The obtained evaluation results are shown in Table 2. In Table 2, joints No. A to I are examples of the present invention. In all of the examples of the present invention, the desired weld shape (good bead appearance and good back wave shape) and the HAZ V E -60 The welded joint also had excellent low-temperature toughness, with a hardness of 27 J or more. Regarding the strength of the welded joint, a tensile test was conducted on the joint in accordance with JIS Z 3121:2013, and it was confirmed that the tensile strength was high, ranging from 440 to 560 MPa.

[0038] On the other hand, in the comparative examples (joints No. J to V) that are outside the scope of the present invention, the bead appearance or the formation of the back wave is insufficient, and the low temperature toughness of the HAZ is insufficient ( V E -60 In other words, in the comparative examples, welded joints that achieved both a good weld shape and excellent low-temperature toughness of the HAZ were not obtained. Each of the comparative examples will be described below.

[0039] For joint No. J, the heat input to obtain a good weld shape for a plate thickness of 12 mm was too large for the low-temperature toughness of the HAZ, and the low-temperature toughness of the HAZ decreased ( V E -60 =9J<27J).

[0040] For joint No. K, a Y-shaped groove was used and the root face was set deep (r = 6 mm), which resulted in insufficient penetration at the root face, making it impossible to form a back bead, and making it impossible to obtain a Charpy test specimen.

[0041] Joint No. L has a Y-shaped groove, and the heat input to obtain a good weld shape for a plate thickness of 16 mm is too large for the low-temperature toughness of the HAZ, resulting in a decrease in the low-temperature toughness of the HAZ ( V E -60 =15J<27J).

[0042] Joint No. M had a Y-shaped groove and was welded with a heat input that did not reduce the low-temperature toughness of the HAZ. However, the wire supply was insufficient for the groove area, the bead height did not reach the surface of the steel plate, and the bead appearance was poor.

[0043] Joint No. N has a two-stage groove, and the heat input exceeds the range for a plate thickness of 16 mm, so the low-temperature toughness of the HAZ decreases ( V E -60 =20J<27J). In addition, the wire was excessively supplied relative to the cross-sectional area of ​​the groove, resulting in uneven bead width and weld height.

[0044] Joint No. O had a two-stage groove, and the second-stage groove angle δ was 55°, which was outside the range of the present invention. As a result, the effect of reducing the cross-sectional area of ​​the groove was not fully achieved, and the bead height did not reach the surface of the steel plate, resulting in a poor bead appearance.

[0045] Joint No. P had a two-stage groove, with the second stage groove angle δ being 10°, which was outside the range of the present invention. As a result, the effect of deepening the penetration of the root was not fully achieved, and the root face was insufficiently penetrated, making it impossible to form a back bead.

[0046] For joint No.Q, the heat input required to obtain a good weld shape for a plate thickness of 25 mm was too large for the low-temperature toughness of the HAZ, resulting in a decrease in the low-temperature toughness of the HAZ ( V E -60 =12J<27J).

[0047] Joint No. R had a Y-shaped groove and was welded with a heat input that did not reduce the low-temperature toughness of the HAZ. However, the wire supply was insufficient relative to the cross-sectional area of ​​the groove, and the bead height did not reach the surface of the steel plate.

[0048] In joint No. S, the root face was set deep (r = 7mm) with a Y-shaped groove, so the root face did not penetrate sufficiently and the back bead could not be formed. In addition, the heat input, which was increased in an attempt to penetrate the root face, was too high for the low-temperature toughness of the HAZ, and the low-temperature toughness of the HAZ decreased ( V E -60 =19J<27J).

[0049] Joint No. T has a Y-shaped groove, and the heat input required to obtain a good weld shape for a plate thickness of 40 mm is more than 200 kJ / cm, which is outside the range of the present invention, and the low-temperature toughness of the HAZ is reduced ( V E -60 =10J<27J).

[0050] Joint No. U had a Y-shaped groove and was welded with a heat input that did not reduce the low-temperature toughness of the HAZ. However, the wire supply was insufficient relative to the cross-sectional area of ​​the groove, and the bead height did not reach the surface of the steel plate.

[0051] Joint No. V has a two-stage groove and the heat input exceeds 200 kJ / cm, which is outside the range of the present invention, so the low-temperature toughness of the HAZ decreases ( V E -60 =24J<27J). In addition, the wire was excessively supplied relative to the cross-sectional area of ​​the groove, resulting in uneven bead width and height.

[0052] [Table 1]

[0053] [Table 2]

[0054] FIG. 5 shows the relationship between the welding heat input and plate thickness at which good weld shapes can be obtained, with conditions Nos. 1, 3, 5, and 7 in Table 1, which were used in the invention examples in Table 2, as plot B (● marks, solid lines), and conditions Nos. 2, 4, 6, and 8 in Table 1, which were used in the comparative examples in Table 2, in which the weld shapes were good, as plot A (▲ marks, dashed lines). This graph shows that the welding heat input can be reduced in the invention examples compared to the conventional examples. It is generally known that toughness improves when the heat input is reduced for steel plates of the same plate thickness, and it can be said that the use of the present invention can prevent deterioration of the low-temperature toughness of the HAZ due to excessive heat input. [Explanation of symbols]

[0055] 1a, 1b steel plate 2a, 2b Tapered section (first stage) 3a, 3b Root surface 4a, 4b Tapered section (second stage) 5 Welding metal 6. Heat-affected zone (HAZ) 7 Test Pieces 7a V-notch 8. Back Wave t Plate thickness (thickness) h First groove depth h1 (conventional) groove depth k Second groove depth r Root face depth S Cross-sectional area of ​​groove θ First groove angle θ1 (conventional) groove angle δ Second step groove angle

Claims

1. A single-sided submerged arc welding method for butt welding two steel plates, comprising the steps of: The thickness t of the steel plate is in the range of 9 to 40 mm, A root surface having a depth in the range of more than 0 mm and not more than 5 mm is formed at the bottom of the butt groove of the steel plate, and a two-stage angle is provided in the groove portion, the groove angle of the first stage on the surface side is in the range of 50 to 70 °, the groove angle of the second stage in contact with the root surface is in the range of 20 to 45 °, and the depth of the second stage groove is in the range of 2 to 5 mm, The welding heat input H is in the range of 15 to 200 kJ / cm. Furthermore, the welding heat input H (kJ / cm) satisfies the following formula 1 with respect to the thickness t (mm) of the steel plate, A one-sided submerged arc welding method in which welding is performed in one pass from the surface side. [Formula 1] (t-10)×5<H<(t-4)×6

2. The welding speed is in the range of 50 to 120 cm / min. Using one or more electrodes; and 2. The single-sided submerged arc welding method according to claim 1, wherein welding is performed by any one selected from the range of a welding current of the first electrode being in the range of 700 to 1600 A, or by a combination of two or more of them.

3. 3. The method of one-sided submerged arc welding according to claim 1 or 2, wherein a flux is used as a backing.

4. A method for producing a welded joint by the one-sided submerged arc welding method according to claim 1 or 2.

5. A method for producing a welded joint by the one-sided submerged arc welding method according to claim 3.

6. The method for manufacturing a welded joint according to claim 4, wherein the Charpy absorbed energy of the welded heat affected zone at −60° C. is 27 J or more.

7. The method for manufacturing a welded joint according to claim 5, wherein the Charpy absorbed energy of the welded heat affected zone at −60° C. is 27 J or more.

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