Single-sided submerged arc welding method and welded joint

Abstract

Provided are: a single-sided submerged arc welding method which has excellent mechanical properties and high productivity in high-heat input welding of thick steel plates, particularly in the shipbuilding field, the construction field, or the like; and a welded joint produced using the welding method. In a single-surface submerged arc welding method for welding two steel plates by abutting, the thickness of the steel plates is 9-40 mm, a truncated edge greater than 0 mm and not greater than 5 mm is formed at the bottom of an abutting groove of the steel plates, a two-stage angle is provided in the groove portion, the first-stage groove angle on the surface side is 50-70 DEG, and the second-stage groove angle on the surface side is 50-70 DEG. The welding is performed in one pass from the front surface side, with the angle of the second-stage groove in contact with the truncated edge being 20-45 DEG, the depth of the second-stage groove being 2-5 mm, and the welding heat input being 15-200 kJ / cm, within the established range of formula (1). (t-10) * 5lt; hlt; (t-4) * 6... (1) H is the welding heat input amount (kJ / cm), and t is the plate thickness (mm) of the steel plate.

Description

Technical Field

[0001] The present invention relates to a single-sided submerged arc welding method capable of efficiently obtaining excellent weld joint properties using a submerged arc welding method, and a weld joint produced by the welding method. Background Art

[0002] In the fields of shipbuilding and construction, submerged arc welding (hereinafter also referred to as "SAW") is used for the joint welding of huge plates. Such welding is difficult to perform flipping operations after welding, and in many cases a single-sided welding method that does not require flipping operations is used. In the single-sided welding method, a V-groove or a Y-groove can be used as the butt groove of the steel plate to be welded. For these grooves, if the groove angle is set to be constant, the groove depth and groove width will 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. When the cross-sectional area of ​​the groove increases, the deposited metal increases, resulting in an increase in welding man-hours.

[0003] To address this problem, for example, Patent Document 1 discloses the following: by using a single-sided single-layer submerged arc welding method, the number of electrodes is increased and welding is performed at a high heat input, thereby significantly increasing the amount of deposition per unit time and performing welding construction in a single layer.

[0004] In addition, Patent Document 2 discloses the following: In order to increase the plate thickness limit and improve the efficiency of single-pass single-sided welding construction based on single-sided submerged arc welding of thick steel plates, a multi-level groove is formed with the groove angle expanding in at least two stages under the limitation of a specific flux.

[0005] In addition, Patent Document 3 discloses the following: As a submerged arc welding method suitable for seam welding of large-diameter steel pipes, it is set to have three or more electrodes, and under the limitations of the wire diameter and current density of the first electrode, a secondary groove is set in which the groove angle on the bottom side is smaller than the groove angle on the surface side.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2017-213569

[0009] Patent Document 2: Japanese Patent Application Laid-Open No. 02-258191

[0010] Patent Document 3: International Publication No. 2013 / 080523

[0011] Summary of the Invention

[0012] Technical problem to be solved by the invention

[0013] In conventional single-sided welding technology, as plate thickness increases, the cross-sectional area of ​​the groove increases significantly, significantly increasing welding time. To reduce welding time, the welding heat input (hereinafter referred to as "heat input") must be increased. As a result, the excessive heat input significantly reduces the low-temperature toughness of the weld heat-affected zone (hereinafter also referred to as "HAZ").

[0014] The technique described in Patent Document 1 requires a high welding current to supply the required amount of weld metal per layer from the welding wire, increasing the heat input per unit weld length. Increasing the welding heat input significantly reduces the cooling rate after welding. This leads to prolonged exposure to high temperatures due to the weld heat, resulting in coarsening of the metal's microstructure and deterioration of mechanical properties.

[0015] The technology described in Patent Document 2 shows an example of using a two-stage groove during high-heat-input welding to reduce heat input by reducing the groove's cross-sectional area. However, since the groove angle at the bottom side of the groove is not significantly different from the groove angle at the surface side, the effect of reducing the cross-sectional area cannot be fully achieved.

[0016] The technique described in Patent Document 3 shows a welding method using a two-stage groove. However, the bottom groove angle is not sufficiently narrow compared to conventional groove shapes. Therefore, in order to increase the weld bead width, the top groove angle is excessively widened, resulting in a lower reduction in groove cross-sectional area than in conventional welding using a Y-groove. Consequently, a significant heat input reduction effect, which affects the metal microstructure, is not achieved.

[0017] The present invention has been completed in view of the above-mentioned circumstances, and its purpose is to provide a submerged arc welding method with excellent mechanical properties and high productivity in high heat input welding of thick steel plates, particularly in the shipbuilding field, the construction field, etc., and a welded joint produced using this welding method.

[0018] Solutions to the Problem

[0019] The conventional groove shape suitable for single-sided welding is as follows Figure 2The Y-shaped groove shown. The Y-shaped groove is formed by blunt edges 3a, 3b for matching the lower surface sides of the steel plates 1a, 1b and tapered portions 2a, 2b processed with a given groove angle (θ1) on the upper part of the steel plates. In this Y-shaped groove, if the depth (r) of the blunt edge is set to be constant, the groove depth (depth of the tapered portion) (h1) and the width of the groove 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 welding wire. If the welding speed is kept constant in order to maintain productivity, the welding current is sometimes increased or the number of electrodes is increased in order to increase the supply speed of the welding wire.

[0020] However, increasing the welding current or the number of electrodes increases heat input and slows the cooling rate after welding. This slow cooling rate prolongs the exposure of the heat-affected zone to high temperatures. This results in coarsening of the grains and a significant deterioration in mechanical properties. Furthermore, depending on the set current and number of electrodes, additional welding power supplies may be required, increasing equipment costs and posing challenges in securing installation space.

[0021] On the other hand, when reducing the cross-sectional area (S) of the groove by narrowing the groove angle (θ1), the arc is generated in the upper portion of the groove when the groove angle (θ1) is narrowed, resulting in insufficient penetration of the root edge. Furthermore, increasing the root edge depth (r) to shallow the groove prevents the entire root edge from being melted by the arc during welding, making it impossible to form the desired penetration bead (penetration bead) in single-sided welding.

[0022] To achieve the above-mentioned objectives, the inventors conducted extensive research on the appropriate groove shape for reducing the amount of deposited metal. They discovered that by setting the groove angle to two levels, adding a shallow, specific, small-angle second-level groove at the bottom of the first-level groove to assist penetration, the cross-sectional area of ​​the groove can be minimized.

[0023] The present invention has been completed as a result of further research based on this finding, and the gist of the present invention is as follows.

[0024] [1] A single-sided submerged arc welding method, which is a single-sided submerged arc welding method for butting two steel plates together, wherein:

[0025] The thickness t of the steel plate is set in the range of 9 to 40 mm.

[0026] A blunt edge with a depth of greater than 0 mm and less than 5 mm is formed at the bottom of the butt groove of the steel plate, and two angles are set at the groove portion. The first groove angle on the surface side is set to a range of 50-70 degrees, and the second groove angle connected to the blunt edge is set to a range of 20-45 degrees. The depth of the second groove is set to a range of 2-5 mm.

[0027] The welding heat input H is set to the range of 15~200kJ / cm,

[0028] Furthermore, the welding heat input H (kJ / cm) satisfies the following formula 1 relative to the thickness t (mm) of the steel plate:

[0029] [Formula 1]

[0030] (t-10)×5 <H<(t-4)×6

[0031] Welding is performed in one pass from the surface side.

[0032] [2] The single-sided submerged arc welding method according to [1] above, wherein welding is performed by selecting any one of the following methods, or a combination of two or more of the following methods:

[0033] Set the welding speed to 50~120cm / min.

[0034] Use more than one electrode, and

[0035] The welding current of the first electrode was set in the range of 700 to 1600A.

[0036] [3] The single-sided submerged arc welding method according to [1] or [2] above, wherein:

[0037] Use flux in the pad.

[0038] [4] A welded joint made by the single-sided submerged arc welding method described in [1] to [3] above.

[0039] [5] The welded joint according to [4] above, wherein:

[0040] The Charpy absorbed energy of the weld heat affected zone at -60°C is 27 J or more.

[0041] Effects of the Invention

[0042] According to the present invention, a welding method capable of efficiently obtaining a welded joint having a weld heat-affected zone excellent in low-temperature toughness can be provided, which can exert a significant industrial effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1This is a schematic cross-sectional view showing an example of a groove shape suitable for the welding method according to the embodiment of the present invention.

[0044] Figure 2 This is a schematic cross-sectional view showing the shape of a Y-groove in a conventional welding method.

[0045] Figure 3 This is a graph showing a preferred range of welding heat input relative to plate thickness in the welding method according to the above embodiment.

[0046] Figure 4 It is a schematic cross-sectional view showing the sampling position of the test piece in the Charpy impact test.

[0047] Figure 5 This is a graph comparing the relationship between the plate thickness of the steel plate and the welding heat input in the inventive example and the conventional example.

[0048] Explanation of symbols

[0049] 1a, 1b steel plates

[0050] 2a, 2b tapered portion (first stage)

[0051] 3a, 3b blunt edges

[0052] 4a, 4b tapered portion (second stage)

[0053] 5 Weld Metal

[0054] 6. Heat-Affected Zone (HAZ)

[0055] 7 test pieces

[0056] 7a V-notch

[0057] 8 Full penetration welds

[0058] t Plate thickness (thickness)

[0059] h The first level groove depth

[0060] h1 (conventional) groove depth

[0061] k The second level groove depth

[0062] r Depth of blunt edge

[0063] S is the cross-sectional area of ​​the groove

[0064] θ The first level groove angle

[0065] θ1 (conventional) groove angle

[0066] δ The second level groove angle DETAILED DESCRIPTION

[0067] Hereinafter, embodiments of the present invention will be described in detail.

[0068] [Single-sided single-layer submerged arc welding]

[0069] This embodiment uses a single-sided submerged arc welding method for butting two steel plates. To achieve efficient welding, this method uses a single pass from the front side. Specifically, full penetration welding (penetration bead welding) is achieved using single-sided, single-layer submerged arc welding.

[0070] It should be noted that submerged arc welding (SAW) is generally a welding method in which an electrode formed by a welding wire (hereinafter also referred to as "welding wire") is continuously supplied to a powdery flux pre-spread on a base material, and an arc is generated between the front end of the welding wire and the base material. SAW has the advantage of being able to efficiently perform welding by increasing the melting speed of the welding wire using a large current. In this embodiment, as described below, single-electrode or multi-electrode welding can be applied. In multi-electrode welding, 2 to 4 electrodes are arranged in series according to the thickness and groove shape of the steel plate to improve welding efficiency. In addition, when welding with a single side and a single layer, in order to optimize the shape of the penetration weld, a flux copper backing plate method can be used in which a backing plate flux is spread on a copper plate and pressed from the back side of the weld portion by the pressure of an air hose.

[0071] [Bevel shape]

[0072] In this embodiment, a secondary groove is used as the groove shape. In the secondary groove, Figure 1 As shown, blunt edges 3a and 3b of depth r are formed at the bottom of the butt groove of the steel plates 1a and 1b. In addition, two angles are set in the groove portion. That is, a first-level groove angle θ formed by the tapered portions 2a and 2b of depth h formed on the surface side, and a second-level groove angle δ formed by the tapered portions 4a and 4b of depth k formed in contact with the blunt edges 3a and 3b are set. The depth h is the depth of the first-level groove, and the depth k is the depth of the second-level groove. δ needs to be set to be smaller than θ. The depth r of the blunt edge and the depths h and k of the groove are measured along the thickness direction of the steel plate, and their total is consistent with the thickness t of the steel plate.

[0073] (i) Blunt edge

[0074] The root edges 3a and 3b are provided on the back side to facilitate butting the plates together. Their depth, r, is set to a range of greater than 0 mm and less than 5 mm. If r exceeds 5 mm, the root edges will remain molten, resulting in an uneven weld bead shape. Note that r greater than 0 mm refers to the minimum root edge, which is a linear, continuous weld. A range of 3 to 4 mm is preferred.

[0075] (ii) First-level groove angle

[0076] The first-stage groove angle θ is set in the range of 50-70°. If θ is less than 50°, the groove width is narrow, causing arcing near the surface and preventing deep penetration. Furthermore, if θ exceeds 70°, the amount of deposited metal is excessive. The preferred range for θ is 50-60°.

[0077] (iii) Second level groove angle

[0078] The second-stage groove angle δ is set to a range of 20 to 45°. If δ is less than 20°, the arc generation position becomes shallow, resulting in insufficient penetration. Furthermore, if δ is greater than 45°, the desired effect of reducing the cross-sectional area of ​​the groove cannot be achieved. δ is preferably within the range of 25 to 40°. δ is preferably smaller than θ by 10 to 20°.

[0079] (iv) Depth of the second-level groove

[0080] The depth k of the second-stage 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 necessary minimum is essentially unattainable. Furthermore, if k exceeds 5 mm, a blunt edge will remain after melting, resulting in an uneven penetration bead shape. The preferred range for k is 3 to 4 mm.

[0081] It is preferable that the depth r of the blunt edge is smaller than the sum of the depth h of the first-stage groove and the depth k of the second-stage groove, and the depth k of the second-stage groove is smaller than the depth h of the first-stage groove.

[0082] By setting the groove shape as described above, the welding heat input amount can be further reduced compared to the case of the conventional Y-shaped groove.

[0083] [Steel Plate]

[0084] (i) Thickness of steel plate

[0085] The thickness of the steel plate serving as the base material, i.e., the plate thickness t, is set to a range of 9 to 40 mm. This is because when t is less than 9 mm, sufficient single-pass welding can be achieved using conventional single-electrode submerged arc welding with a Y-groove. On the other hand, when t is greater than 40 mm, it becomes difficult to achieve a good single-pass weld using four electrodes. The preferred range for t is 12 to 25 mm.

[0086] It should be noted that for steel plates with a thickness t greater than 40 mm, two or more passes of welding may be applicable. By adopting the groove shape within the range of this embodiment in the first pass of welding, a significant improvement in construction efficiency can be expected.

[0087] (ii) Steel grade of the steel plate

[0088] In this embodiment, in order to make the HAZ have excellent mechanical properties, especially excellent low-temperature toughness, the steel plate as the base material is preferably a steel plate having a tensile strength of 440 MPa or more and a Charpy absorption energy at -60°C (hereinafter also referred to as " V E -60 ”) is a steel grade with a J value of 70J or more. Examples of such steel grades include SLA325A specified in JIS G 3126.

[0089] [Welding conditions]

[0090] (i) Welding heat input

[0091] In this embodiment, the welding heat input H is set to a range of 15 to 200 kJ / cm. In the case of multiple electrodes, the heat input H refers to the total heat input of each electrode. For groove shapes 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 will decrease. On the other hand, if the heat input H is less than 15 kJ / cm, welding defects are likely to occur.

[0092] Furthermore, from the perspective of achieving both a good weld shape and excellent HAZ low-temperature toughness in the weld joint, the welding heat input H (kJ / cm) needs to satisfy the following formula 1 relative to the thickness t (mm) of the steel plate.

[0093] [Formula 1]

[0094] (t-10)×5 <H<(t-4)×6

[0095] Therefore, the suitable range of welding heat input relative to plate thickness is Figure 3 It should be noted that, for the boundary of the shaded area, the portion included in the area is represented by a solid line, and the portion not included is represented by a dotted line.

[0096] (ii) Welding speed

[0097] In this embodiment, the welding speed is preferably in the range of 50 to 120 cm / min. A welding speed of less than 50 cm / min reduces productivity. On the other hand, a welding speed exceeding 120 cm / min is susceptible to interference caused by machining errors in the groove shape and welding distortion. A welding speed of 60 to 90 cm / min is more preferred.

[0098] (iii) Electrodes

[0099] In this embodiment, it is preferred to use one or more electrodes. This is because even with a single electrode (single electrode), efficient welding can sometimes be achieved. It should be noted that using five or more electrodes complicates welding conditions, so four or fewer electrodes is more preferred. When using multiple electrodes, they are referred to as the first electrode, the second electrode, etc., starting from the first electrode.

[0100] It should be noted that when using three electrodes, the preferred range for the wire diameter used is 4.0-4.8 mm φ for the first electrode, and 4.8-6.4 mm φ for the second and third electrodes. The wire diameters of the second and third electrodes are larger than those of the first electrode to increase the penetration width. Furthermore, the wire spacing between the first and second electrodes is preferably 30-50 mm. If the first and second electrodes are too close together, arc interference may result in an unstable weld bead. If they are too far apart, the penetration depth may be unstable, resulting in poor weld bead formation. The preferred range for the distance between the second and third electrodes is 120-180 mm. If the second and third electrodes are too close together, cracks may occur, while if they are too far apart, slag inclusion may occur.

[0101] (iv) Welding current / voltage of the first electrode

[0102] In this embodiment, the welding current (AC) of the first electrode (this electrode in the case of a single electrode) is preferably set to a range of 700 to 1600 A. If the welding current of the first electrode is less than 700 A, the blunt edge may not be melted, resulting in poor penetration. On the other hand, if the welding current of the first electrode is greater than 1600 A, the blunt edge may be excessively melted, resulting in burn-through. More preferably, the welding current of the first electrode is in the range of 800 to 1500 A. A preferred welding voltage for 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.

[0103] (v) Welding current / voltage of the second and third electrodes

[0104] When the number of electrodes is three, the preferred welding current (AC) for the second electrode is in the range of 800 to 1400 A. More preferably, the welding current for the second electrode is in the range of 900 to 1300 A. Furthermore, the preferred welding voltage for the second electrode is in the range of 30 to 45 V. More preferably, the welding voltage for the second electrode is in the range of 32 to 40 V.

[0105] The 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. The 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.

[0106] Thus, by setting the welding current higher and the welding voltage lower for the front electrode compared to the rear electrode, the root edge can be melted deeply and stably. On the other hand, by setting the welding voltage higher for the rear electrode compared to the front electrode, the weld bead width becomes wider, achieving a stable weld bead shape on the surface.

[0107] [Welding materials]

[0108] (i) Backing material

[0109] In this embodiment, the backing material can be preferably any material, such as copper, ceramic, or flux, with flux being particularly preferred. The aforementioned flux copper backing method can be used as a backing material. This further stabilizes the weld bead shape, achieving an appropriate shape.

[0110] An example of a backing flux used in the flux copper backing method is the following composition. Its composition, in mass %, includes 8-47% BaO, 5-28% SiO₂, 10-21% MgO, 0-7% CaO, 12-24% CaF₂, 5-15% Al₂O₃, 0-10% TiO₂, 0-5% ZrO₂, and 0-9% CO₂. The remainder is metal powder serving as a deoxidizer or alloying agent.

[0111] In this embodiment, after the steel plates are butted and the backing plate is applied, welding flux is spread into the grooves on the back side (second stage) and the front side (first stage), and then single-sided, single-layer welding is performed in a flat welding position without preheating. In this case, the following examples of welding wire and welding flux suitable for this embodiment can be given.

[0112] (ii) Welding wire

[0113] Examples of welding wire suitable for this embodiment include solid wire made of low-temperature steel. An example composition includes, by mass%, 0.05-0.15% C, 0.02-0.05% Si, 1.3-2.0% Mn, 1.6-2.9% Ni, and 0.3-0.8% Mo, with the remainder consisting of Fe and unavoidable impurities. However, in this embodiment, the welding wire is not limited to this composition.

[0114] (iii) Soldering flux

[0115] As the soldering flux, any of the known molten flux and adhesive flux can be used. For example, as an example of an adhesive flux, there can be cited a flux containing SiO2: 10-30%, CaO: 10-50%, MgO: 20-50%, Al2O3: 10-30%, CaF2: 5-20%, CaCO3: 2-15%, etc. in mass%. However, in the present invention, the soldering flux is not limited to this. It should be noted that when using an adhesive flux, it is preferably dried at a temperature in the range of 200-300°C for 1-2 hours before soldering, as in the conventional SAW method.

[0116] [Welded joints]

[0117] A welded joint according to another embodiment of the present invention is produced by the welding method according to the above embodiment and has excellent low-temperature toughness of the HAZ.

[0118] [Low-temperature toughness of HAZ]

[0119] The welded joint of this embodiment preferably has a Charpy absorbed energy of -60°C of the HAZ, i.e. V E -60 More than 27J. V E -60 When the stress is ≥27J, it has the advantage that brittle fracture is less likely to occur.

[0120] Example

[0121] The present invention will be described in more detail below with reference to Examples, but the present invention is not limited to the scope described in the Examples.

[0122] [Steel Plate]

[0123] The steel plate used as the base material is an aluminum-killed steel plate for low-temperature use in shipbuilding. Its composition, by mass%, consists of 0.07% C, 0.28% Si, 1.37% Mn, 0.007% P, and 0.002% S, with the remainder consisting of Fe and unavoidable impurities. The plate thickness ranges from 12 to 40 mm. The tensile strength of the steel plate is 500 MPa. V E -60 It is 70 J. It should be noted that the tensile strength of the steel plate is obtained by a tensile test in accordance with the provisions of JIS Z 2241:2011. V E -60 The strength was determined by a Charpy impact test in accordance with JIS Z 2242:2018.

[0124] [Welding materials / Welding conditions]

[0125] The flux-copper backing method was used, where a copper plate coated with backing flux was pressed against the backside of a 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 consisted of metal powder as a deoxidizer or alloying agent.

[0126] The welding flux applied to the groove used a bonding flux containing, by mass%, 20% SiO₂, 5% CaO, 25% MgO, 10% Al₂O₃, 5% CaF₂, and 5% CaCO₃. This bonding flux was dried at 300°C for one hour before application.

[0127] Solid wire (4.8 mm and 6.4 mm diameter) was used for welding. Single-sided, single-layer submerged arc welding was performed in the flat welding position without preheating using one to four electrodes under the various welding conditions shown in Table 1. This solid wire is for low-temperature steel and has a composition containing, by mass%, 0.10% C, 0.03% Si, 1.65% Mn, 2.40% Ni, and 0.50% Mo, with the remainder consisting of Fe and inevitable impurities.

[0128] [Mechanical properties of welded joints]

[0129] According to JIS Z 2242 (Charpy impact test method for metallic materials), Figure 4 At the test piece collection positions shown, Charpy impact test pieces (V-notch) were collected from the butt-welded joint portion obtained by the above-mentioned single-sided single-layer SAW, and an impact test was performed.

[0130] The result of performing single-sided single-layer SAW on the steel plates 1a and 1b is as follows: Figure 4 As shown, weld metal 5 is formed in the groove on the front side, a full penetration weld bead 8 is formed in the groove on the back side, and a weld heat-affected zone 6 is formed between the weld metal 5 and the steel plate. A Charpy V-notch test piece 7 having a V-notch 7a formed therein is collected from the weld heat-affected zone 6 at a depth of 1 / 2t of the plate thickness (t) of the steel plate in accordance with JIS Z 3128 (Impact testing method for welded joints).

[0131] The Charpy impact test was carried out by preparing three test pieces 7 obtained above. V E-60 The average value is taken as the low-temperature toughness value of the heat-affected zone of each weld joint.

[0132] [Evaluation of weld shape]

[0133] The weld shape was evaluated visually or by dimensional measurement based on the shape of the penetration bead and the appearance of the surface bead. For the evaluation of the penetration bead shape, a penetration bead 8 with a bead width of 5.0 mm or greater, a bead height of 1.0 to 2.5 mm, and no undercut was evaluated as good (○), while all other evaluations were evaluated as poor (×). For the appearance of the bead, a uniform and good bead height and width were evaluated as good (○). Other evaluations, such as uneven shape, undercut, or both, were evaluated as poor (×).

[0134] The evaluation results are shown in Table 2. In Table 2, joints No. A to I are examples of the present invention. In the examples of the present invention, all of them have both the desired weld shape (good weld bead appearance and good penetration weld bead shape) and the HAZ. V E -60 The welded joint has excellent low-temperature toughness of 27 J or more. Regarding the welded joint strength, a joint tensile test was conducted in accordance with JIS Z 3121:2013, and the tensile strength was confirmed to be high, ranging from 440 to 560 MPa.

[0135] On the other hand, in the comparative examples (joints No. J to V) that are outside the scope of the present invention, the weld bead appearance or the formation of the penetration weld bead is insufficient, and the low-temperature toughness of the HAZ is insufficient ( V E ~60 Less than 27J) or both. That is, in the comparative examples, it is not possible to obtain a weld joint having both a good weld shape and excellent low-temperature toughness of the HAZ. The following describes each comparative example.

[0136] Joint No. J is a Y-groove. For a plate thickness of 12 mm, the heat input required to obtain a good weld shape is too large for the low-temperature toughness of the HAZ, and the low-temperature toughness of the HAZ is reduced. V E -60 =9J<27J).

[0137] Joint No. K has a Y-groove. Since the root edge is set too deep (r = 6 mm), the root edge has insufficient penetration, making it impossible to form a full penetration weld bead and to collect a Charpy test piece.

[0138] Joint No. L is a Y-groove. For a plate thickness of 16 mm, the heat input required to obtain a good weld shape is too large for the low-temperature toughness of the HAZ, which reduces the low-temperature toughness of the HAZ. V E -60 =15J<27J).

[0139] Joint No. M had a Y-groove and was welded at a heat input that did not reduce the low-temperature toughness of the HAZ. However, the wire supply was insufficient relative to the groove area, and the height of the weld bead did not reach the surface of the steel plate, resulting in poor weld bead appearance.

[0140] Joint No. N is a secondary groove. The heat input exceeds the appropriate range for a 16mm plate thickness, so the low-temperature toughness of the HAZ decreases ( V E -60 =20J<27J). In addition, the welding wire was supplied in excess relative to the cross-sectional area of ​​the groove, causing the weld bead width and reinforcement to become uneven.

[0141] Joint No.O is a secondary groove, and the second-level groove angle δ is 55°, which is out of the scope of the present invention and cannot fully achieve the effect of reducing the cross-sectional area of ​​the groove. Therefore, the height of the weld cannot fill the surface of the steel plate, and the weld appearance is poor.

[0142] Joint No. P is a secondary groove with a second groove angle δ of 10°, which is outside the scope of the present invention and cannot fully achieve the effect of deepening the penetration of the blunt edge. Therefore, the blunt edge penetration is insufficient and a full penetration weld cannot be formed.

[0143] The joint No. Q is a Y-groove. For a plate thickness of 25 mm, the heat input required to obtain a good weld shape is too large for the low-temperature toughness of the HAZ, and the low-temperature toughness of the HAZ is reduced. V E -60 =12J<27J).

[0144] Joint No. R had a Y-groove and was welded at 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 height of the weld bead did not reach the surface of the steel plate.

[0145] Joint No. S has a Y-groove, and since the blunt edge is set deep (r = 7mm), the blunt edge has insufficient penetration and cannot form a full penetration weld bead. In addition, the heat input required to achieve full penetration of the blunt edge is too high for the low-temperature toughness of the HAZ, which reduces the low-temperature toughness of the HAZ ( V E -60 =19J<27J).

[0146] The joint No. T is a Y-groove. For a plate thickness of 40 mm, the heat input for obtaining a good weld shape is greater than 200 kJ / cm, which is out of the scope of the present invention. The low-temperature toughness of the HAZ is reduced. V E -60 =10J<27J).

[0147] Joint No. U had a Y-groove and was welded at 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 height of the weld bead did not reach the surface of the steel plate.

[0148] Joint No. V is a secondary groove with a heat input greater than 200 kJ / cm, which is out of the scope of the present invention. Therefore, the low-temperature toughness of the HAZ is reduced ( V E -60 =24J<27J). In addition, the welding wire was supplied in excess relative to the cross-sectional area of ​​the groove, causing the weld bead width and height to become uneven.

[0149]

[0150]

[0151] Note that, the conditions No. 1, 3, 5, and 7 in Table 1 adopted in the inventive examples in Table 2 are plotted as curve B (● mark, solid line), and the conditions No. 2, 4, 6, and 8 in Table 1 adopted in the comparative examples in Table 2 with good weld shape are plotted as curve A (▲ mark, dotted line). The relationship between the welding heat input and the plate thickness for obtaining a good weld shape is shown in FIG. Figure 5 This graph shows that the inventive example can reduce the welding heat input compared to the conventional example. It is generally known that for steel plates of the same thickness, toughness increases when the heat input is reduced. It is believed that the use of the present invention can prevent the degradation of the low-temperature toughness of the HAZ caused by excessive heat input.

Claims

1. A single-sided submerged arc welding method, which is a single-sided submerged arc welding method for butting two steel plates together, wherein: The thickness t of the steel plate is set in the range of 9 to 40 mm. A blunt edge with a depth of greater than 0 mm and less than 5 mm is formed at the bottom of the butt groove of the steel plate, and two angles are set at the groove portion. The first groove angle on the surface side is set to a range of 50-70 degrees, and the second groove angle connected to the blunt edge is set to a range of 20-45 degrees. The depth of the second groove is set to a range of 2-5 mm. The welding heat input H is set to the range of 15~200kJ / cm, Furthermore, the welding heat input H (kJ / cm) satisfies the following formula 1 relative to the thickness t (mm) of the steel plate: [Formula 1] (t-10)×5 <H<(t-4)×6 Welding is performed in one pass from the surface side.

2. The single-sided submerged arc welding method according to claim 1, wherein welding is performed by any one of the following methods, or a combination of two or more methods: Set the welding speed to 50~120cm / min. Use more than one electrode, and The welding current of the first electrode was set in the range of 700 to 1600A.

3. The single-sided submerged arc welding method according to claim 1 or 2, wherein: Use flux in the pad.

4. A welded joint, made by the single-sided submerged arc welding method according to claim 1 or 2.

5. A welded joint made by the single-sided submerged arc welding method according to claim 3.

6. The weld joint according to claim 4, wherein: The Charpy absorbed energy of the weld heat affected zone at -60°C is 27 J or more.

7. The weld joint according to claim 5, wherein: The Charpy absorbed energy of the weld heat affected zone at -60°C is 27 J or more.

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