TW202434375A - Single-sided submerged arc welding method and welding joint - Google Patents

Abstract

The present invention provides a single-sided submerged arc welding method having excellent mechanical properties and high productivity, particularly in the process of large heat input welding of thick steel plates in the shipbuilding field or the construction field, and a welded joint produced using the welding method. A single-sided submerged arc welding method is provided, wherein two steel plates are butt-welded, and in the single-sided submerged arc welding method, the thickness of the steel plate is set to 9 mm to 40 mm, a blunt edge greater than 0 mm and less than 5 mm is formed at the bottom of the butt groove of the steel plate, two angles are set at the groove portion, the first groove angle on the surface side is set to 50° to 70°, the second groove angle connected to the blunt edge is set to 20° to 45°, the depth of the second groove is set to 2 mm to 5 mm, the welding heat input is set to 15 kJ/cm to 200 kJ/cm and is within the range of formula (1), and single-pass welding is performed from the surface side. (t-10)×5＜H＜(t-4)×6    ···(1) H: welding heat input (kJ/cm), t: steel plate thickness (mm)

Description

Single-sided submerged arc welding method and welding joint

The present invention relates to a single-sided submerged arc welding method capable of efficiently obtaining excellent weld joint properties by using the submerged arc welding method and a weld joint manufactured by using the welding method.

Submerged arc welding (hereinafter also referred to as "SAW") is used for joint welding of huge plates in the fields of shipbuilding or construction. This type of welding is difficult to reverse after welding, and most of the time, a single-sided welding method that does not require a reversal operation is used. In the single-sided welding method, a V-shaped groove or a Y-shaped groove can be used for the butt groove of the steel plate as the welded material. For these grooves, if the groove angle is set to a certain value, 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. If the cross-sectional area of the groove increases, the deposited metal increases, resulting in an increase in welding man-hours.

In order to solve this problem, for example, Patent Document 1 discloses that by increasing the number of electrodes in a single-sided single-layer submerged arc welding method and performing welding with a large heat input, the amount of deposition per unit time is greatly increased, and single-layer welding construction is performed.

In addition, Patent Document 2 discloses that in order to utilize single-sided submerged arc welding of thick steel plates to achieve an increase in the plate thickness limit and high efficiency of single-pass single-sided welding construction, a multi-stage groove with a groove angle expanded in at least two stages is formed under the limitation of a specific welding agent.

In addition, Patent Document 3 discloses a submerged arc welding method suitable for seam welding of large diameter steel pipes, which includes: providing three or more electrodes and forming two grooves with a groove angle on the bottom side smaller than the groove angle on the surface side under the limitation of the wire diameter and current density of the first electrode. [Prior art document] [Patent document]

Patent document 1: Japanese Patent Publication No. 2017-213569 Patent document 2: Japanese Patent Publication No. 02-258191 Patent document 3: International Publication No. 2013/080523

[Problem to be solved by the invention] In the previous single-sided welding technology, as the plate thickness increases, the cross-sectional area of the groove increases, and the welding time increases significantly. In order to reduce the welding time, the welding heat input (hereinafter referred to as "heat input") has to be increased. As a result, there is a problem that the low-temperature toughness of the heat affected zone (hereinafter referred to as "HAZ") is significantly reduced due to excessive heat input.

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, the welding current needs to be set high, and the heat input per unit welding length becomes large. If the welding heat input is increased, the cooling rate after welding is extremely reduced, so there is a problem that the weld heat is exposed to high temperature for a long time, the crystal grains of the metal microstructure are coarsened, and the mechanical properties are deteriorated.

The technology described in Patent Document 2 shows an example in which a two-stage groove is used to reduce the heat input by reducing the cross-sectional area of the groove in high heat input welding. However, since the groove angle on the bottom side of the groove is not much different from the groove angle on the surface side, the effect of reducing the cross-sectional area cannot be fully obtained.

The technique described in Patent Document 3 shows a welding method using a two-stage groove. However, the groove angle on the bottom side is not too narrow compared to the previous groove shape. Therefore, the groove angle on the surface side is made too wide for the purpose of increasing the width of the weld bead, and the effect of reducing the cross-sectional area of the groove is low compared to welding using the previous Y-shaped groove. Therefore, a large heat input reduction effect such as an influence on the metal microstructure is not obtained.

The present invention is made in view of the above situation, and its purpose is to provide a submerged arc welding method with excellent mechanical properties and high productivity, especially in the process of large heat input welding of thick steel plates in the shipbuilding field or the construction field, and a welded joint produced using this welding method. [Means for solving the problem]

The groove shape previously used in single-sided welding is a Y-shaped groove as shown in Figure 2. The Y-shaped groove is formed by blunt edges 3a and 3b used for plate joining on the lower surface sides of steel plates 1a and 1b, and tapered portions 2a and 2b processed at a predetermined 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 constant, the groove depth (depth of the tapered portion) (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 supplied from the welding wire is required. If the welding speed is kept constant in order to maintain productivity, there is a case where the welding current is increased or the number of electrodes is increased in order to increase the feeding speed of the welding wire.

However, in the method of increasing the welding current or the method of increasing the number of electrodes, the heat input increases and the cooling rate after welding decreases. If the cooling rate decreases, the time that the weld heat-affected part is exposed to high temperature increases. As a result, there is a problem of coarsening of the grains and significant deterioration of the mechanical properties. In addition, there is a situation where additional welding power supply devices are required depending on the setting current or the number of electrodes, and the cost of the equipment increases or the securing of the installation space is also a problem.

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), if the groove angle (θ1) is narrowed, the arc is generated at the upper part of the groove, and the penetration of the blunt part becomes insufficient. In addition, if the blunt depth (r) is increased in order to form a shallow groove, the blunt cannot be completely melted by the arc during welding, and the required root cannot be formed in single-sided welding.

In order to achieve the above-mentioned purpose, the inventors have made great efforts to study the appropriate groove shape for reducing the amount of deposited metal. As a result, they found that the cross-sectional area of the groove can be set to the minimum required limit by setting the groove angle to two stages and adding a second groove with a specific small angle at the bottom of the first groove at a shallow depth for the purpose of assisting the penetration.

The present invention is completed based on the above-mentioned insights and further research, and its main purpose is as follows. [1] A single-sided submerged arc welding method, wherein two steel plates are butt-welded, and in the single-sided submerged arc welding method, the thickness t of the steel plate is set to a range of 9 mm to 40 mm, a blunt edge with a depth of more than 0 mm and less than 5 mm is formed at the bottom of the butt groove of the steel plate, two angles are set at the groove portion, the first groove angle on the surface side is set to a range of 50° to 70°, the second groove angle connected to the blunt edge is set to a range of 20° to 45°, the depth of the second groove is set to a range of 2 mm to 5 mm, the welding heat input H is set to a range of 15 kJ/cm to 200 kJ/cm, further, the welding heat input H (kJ/cm) satisfies the following formula 1 relative to the thickness t (mm) of the steel plate, Single-pass welding is performed from the surface side. [Formula 1] (t-10)×5＜H＜(t-4)×6 [2] A single-sided submerged arc welding method as described in [1], wherein welding is performed by selecting any one or a combination of two or more of the following: setting the welding speed to a range of 50 cm/min to 120 cm/min, using one or more electrodes, and setting the welding current of the first electrode to a range of 700 A to 1600 A. [3] A single-sided submerged arc welding method as described in [1] or [2], wherein a flux is used in the pad. [4] A welded joint, which is produced using a single-sided submerged arc welding method as described in any one of [1] to [3]. [5] A welded joint as described in [4], wherein the Charpy absorbed energy at -60°C of the weld heat affected portion is 27 J or more. [Effect of the invention]

The present invention can provide a welding method for a welding head that can efficiently obtain excellent low-temperature toughness of the welding heat-affected portion, which has a significant effect in the industry.

The following is a detailed description of the implementation form of the present invention. [Single-sided single-layer submerged arc welding] This implementation form is a single-sided submerged arc welding method for butt-welding two steel plates. In this method, single-pass welding is performed from the surface side for efficient welding. That is, full penetration welding (root welding) is performed by single-sided single-layer submerged arc welding.

Furthermore, submerged arc welding (SAW) is generally a welding method in which an electrode including a welding wire (hereinafter also referred to as "welding wire") is continuously supplied to a powdered flux pre-dispersed on a base material, and an arc is generated between the tip of the welding wire and the base material. SAW has the advantage of being able to weld efficiently by increasing the deposition speed of the welding wire by using a large current. In this embodiment, as described later, single-electrode welding or multi-electrode welding can be applied. In multi-electrode welding, two to four electrodes are arranged in series according to the thickness of the steel plate or the shape of the groove to improve the welding efficiency. In addition, when welding on one side and one layer, the following method can be used: in order to make the root shape appropriate, a pad flux is spread on the copper plate and pressed from the back side of the weld using the pressure of an air hose.

[Groove shape] In this embodiment, a two-stage groove is used as the groove shape. In the two-stage groove, as shown in FIG1, blunt edges 3a and 3b of depth r are formed at the bottom of the butt groove of steel plates 1a and 1b. Then, two angles are set in the groove part. That is, a first-stage groove angle θ formed by tapered portions 2a and 2b of depth h formed on the surface side and a second-stage groove angle δ formed by tapered portions 4a and 4b of depth k formed by connecting to the blunt edges 3a and 3b are set. 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 blunt edge and the depth h and depth k of the groove are set to the values measured in the thickness direction of the steel plate, and their total is consistent with the thickness t of the steel plate. (i) Blunt edge The blunt edge 3a and blunt edge 3b are set on the back side for plate bonding, and their depth r is set to a range of more than 0 mm and less than 5 mm. The reason is that if r exceeds 5 mm, the blunt edge will be melted and the root shape will become uneven. In addition, r exceeds 0 mm, which means that the blunt edge is the minimum value and is connected in a linear manner. It is better that r is 3 mm to 4 mm. (ii) First-stage groove angle The first-stage groove angle θ is set to a range of 50° to 70°. The reason is that if θ is less than 50°, the groove width is narrow, so the arc is generated near the surface and deep penetration cannot be obtained. In addition, if θ exceeds 70°, the amount of deposited metal becomes too large. It is better to have θ in the range of 50° to 60°. (iii) Second-stage groove angle The second-stage groove angle δ is set in the range of 20° to 45°. If δ is less than 20°, the arc generation position becomes shallow, resulting in the disadvantage of insufficient penetration. In addition, if δ exceeds 45°, the effect of reducing the cross-sectional area of the target groove cannot be obtained. It is better to have δ in the range of 25° to 40°. δ is preferably in the range of 10° to 20° smaller than θ. (iv) Depth of the second groove The depth k of the second groove is set in the range of 2 mm to 5 mm. The reason is that if k is less than 2 mm, it is basically impossible to achieve the effect of reducing the amount of deposited metal to the minimum required. In addition, if k exceeds 5 mm, blunt edge melting residues remain and the root shape becomes uneven. It is preferred that k is in the range of 3 mm to 4 mm. It is preferred that the depth r of the blunt edge is less than the sum of the depth h of the first groove and the depth k of the second groove, and the depth k of the second groove is less than the depth h of the first groove. By setting the groove shape as described above, the welding heat input can be reduced compared to the previous Y-shaped groove.

[Steel Plate] (i) Thickness of Steel Plate The thickness of the steel plate serving as the base material, i.e., the plate thickness t, is set in the range of 9 mm to 40 mm. The reason is that if t is less than 9 mm, sufficient single-sided single-pass welding can be performed using submerged arc welding using a single electrode in the conventional Y-shaped groove. On the other hand, if t exceeds 40 mm, it is difficult to perform single-pass welding soundly using four electrodes. Preferably, t is in the range of 12 mm to 25 mm. Furthermore, for steel plates having a plate thickness t exceeding 40 mm, more than two passes of welding can be applied. By adopting a groove shape within the range of this embodiment in the first pass of welding, a significant improvement in construction efficiency can be expected. (ii) Steel Type of Steel Plate In the present embodiment, in order to provide the HAZ with excellent mechanical properties, particularly excellent low temperature toughness, the steel plate as the base material is preferably a steel type having a tensile strength of 440 MPa or more and a Charpy absorbed energy at -60°C (hereinafter also referred to as " _VE - ₆₀ ") of 70 J or more. Examples of the steel type include SLA325A specified in Japanese Industrial Standards (JIS) G 3126.

[Welding conditions] (i) Welding heat input In the present embodiment, the welding heat input H is set to a range of 15 kJ/cm to 200 kJ/cm. In the case of multiple electrodes, the heat input H is the total of the heat inputs of each electrode. In the groove shape within the range of the present embodiment, if the heat input H exceeds 200 kJ/cm, the low-temperature toughness of the HAZ of the weld joint will be reduced. On the other hand, if the heat input H is less than 15 kJ/cm, welding defects are likely to occur. Furthermore, from the perspective of taking into account both a sound weld shape and excellent low-temperature toughness of the HAZ 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. [Formula 1] (t-10)×5＜H＜(t-4)×6 Therefore, the suitable range of welding heat input relative to the plate thickness is the area indicated by the hatching in Figure 3. Furthermore, regarding the boundary of the hatched area, the portion included in the area is indicated by a solid line, and the portion not included is indicated by a dotted line. (ii) Welding speed In this embodiment, the welding speed is preferably in the range of 50 cm/min to 120 cm/min. The reason is that if the welding speed is less than 50 cm/min, the productivity decreases. On the other hand, if the welding speed exceeds 120 cm/min, it is easily affected by interference caused by processing errors in the groove shape or welding deformation. A more preferred welding speed is in the range of 60 cm/min to 90 cm/min. (iii) Electrode In this embodiment, it is preferred to use more than one electrode. The reason for this is that even if there is only one electrode (single electrode), efficient welding can be performed. Furthermore, when there are five or more electrodes, welding conditions become complicated, so it is more preferred to use four or less electrodes. When multiple electrodes are used, they are sequentially referred to as the first electrode, the second electrode, etc. from the first electrode. Furthermore, in the case of three electrodes, the preferred range of the diameter of the welding wire used is 4.0 mm Φ to 4.8 mm Φ for the first electrode, and 4.8 mm Φ to 6.4 mm Φ for the second and third electrodes. The reason for making the welding wire diameter of the second and third electrodes larger than that of the first electrode is to expand the penetration width. In addition, the spacing between the welding wires is preferably 30 mm to 50 mm between the first electrode and the second electrode. If the distance between the first electrode and the second electrode is close, arc interference may occur, resulting in an unstable weld bead. If they are too far apart, the penetration depth may be unstable, resulting in poor root formation. The distance between the second electrode and the third electrode is preferably set to a range of 120 mm to 180 mm. If the second electrode and the third electrode are too close, cracks may occur. If they are too far apart, slag may be drawn in.

(iv) Welding current/voltage of the first electrode In the present embodiment, the welding current (alternating current (AC)) of the first electrode (in the case of a single electrode) is preferably set to a range of 700 A to 1600 A. If the welding current of the first electrode is less than 700 A, there is a problem that the blunt edge cannot be melted, resulting in poor penetration. On the other hand, if the welding current of the first electrode exceeds 1600 A, there is a problem that the root is over-melted and molten. It is more preferable that the welding current of the first electrode is in the range of 800 A to 1500 A. Furthermore, as a preferred welding voltage for the first electrode, a range of 25 V to 40 V can be listed. More preferably, the welding voltage for the first electrode is in the range of 28 V to 35 V. (v) Welding current/voltage for the second and third electrodes When there are three electrodes, a preferred welding current (AC) for the second electrode is in the range of 800 A to 1400 A. More preferably, the welding current for the second electrode is in the range of 900 A to 1300 A. Furthermore, as a preferred welding voltage for the second electrode, a range of 30 V to 45 V can be listed. More preferably, the welding voltage for the second electrode is in the range of 32 V to 40 V. In addition, as a preferred welding current (AC) of the third electrode, a range of 600 A to 1300 A can be cited. A more preferred range is a range of 800 A to 1200 A for the welding current of the third electrode. Furthermore, as a preferred welding voltage of the third electrode, a range of 30 V to 50 V can be cited. A more preferred range is a range of 35 V to 45 V for the welding voltage of the third electrode. As described above, in the preceding electrode, the welding current is increased and the welding voltage is decreased compared to the subsequent electrode, thereby making it possible to melt the blunt edge stably and deeply. On the other hand, the welding voltage is set higher in the subsequent electrode than in the preceding electrode, thereby increasing the width of the weld bead and obtaining a stable weld bead shape on the surface.

[Welding material] (i) Backing material In this embodiment, as a backing material, any one of copper plate, ceramic, solder, etc. can be preferably used, and solder is more preferably used. The backing method using solder can be listed as the solder copper backing method described above. Thereby, the root shape is further stabilized and becomes appropriate.

As the pad solder used in the solder copper pad method, for example, the following composition can be cited. The composition contains, by mass%, BaO: 8% to 47%, SiO ₂ : 5% to 28%, MgO: 10% to 21%, CaO: 0% to 7%, CaF ₂ : 12% to 24%, Al ₂ O ₃ : 5% to 15%, TiO ₂ : 0% to 10%, ZrO ₂ : 0% to 5%, and CO ₂ : 0% to 9%. The remainder is a deoxidizer or metal powder as an alloying agent.

In this embodiment, after the butting and padding of the steel plates, welding flux is spread in the grooves of the back side (second stage) and the front side (first stage), and then single-sided one-layer welding is performed in a downward posture without preheating. In this case, the following can be listed as welding wire and welding flux applied to this embodiment. (ii) Welding wire As the welding wire applied to this embodiment, a solid wire for low-temperature steel can be listed. An example of its composition is as follows: C: 0.05% to 0.15%, Si: 0.02% to 0.05%, Mn: 1.3% to 2.0%, Ni: 1.6% to 2.9%, and Mo: 0.3% to 0.8%, and the remainder includes Fe and inevitable impurities. However, in the present embodiment, the welding wire is not limited to this. (iii) Welding flux As the welding flux, any of a known melting flux and a bonding flux can be used. For example, as an example of the bonding flux, there can be cited a flux containing SiO ₂ : 10% to 30%, CaO: 10% to 50%, MgO: 20% to 50%, Al ₂ O ₃ : 10% to 30%, CaF ₂ : 5% to 20%, CaCO ₃ : 2% to 15%, etc. in terms of mass%. However, in the present invention, the welding flux is not limited to this. Furthermore, when the bonding flux is used, it is preferred to dry it at a temperature in the range of 200°C to 300°C for 1 hour to 2 hours before welding, similar to the method of use in the previous SAW.

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

[Low-temperature toughness of HAZ] The welded joint of this embodiment preferably has a HAZ with a Charpy absorbed energy at -60°C, i.e., _VE - _60, of 27 J or more. If _VE - ₆₀ ≧ 27 J, brittle failure is less likely to occur. [Example]

The present invention is described in more detail below with reference to the following embodiments, but the present invention is not limited to the scope described in the embodiments.

[Steel Plate] The steel plate used as the base material is a low-temperature aluminum-stabilized steel plate for shipbuilding, and the composition of the steel plate is: C: 0.07%, Si: 0.28%, Mn: 1.37%, P: 0.007% and S: 0.002% by mass%, and the remainder includes Fe and inevitable impurities. The thickness of the steel plate is 12 mm to 40 mm. The tensile strength of the steel plate is 500 MPa, and _{VE -60} is 70 J. The tensile strength of the steel plate is obtained by a tensile test in accordance with the provisions of JIS Z 2241:2011. In addition, _{VE -60} of the steel plate is obtained by a Charpy impact test in accordance with the provisions of JIS Z 2242:2018.

[Welding materials/welding conditions] As a welding method, a copper plate with backing flux is pressed against the back of a steel plate to perform welding. The backing flux contains BaO: 32%, SiO ₂ : 12%, MgO: 11%, CaO: 1%, CaF ₂ : 15%, Al ₂ O ₃ : 10%, TiO ₂ : 2%, ZrO ₂ : 4% and CO ₂ : 9% by mass. The remainder is a deoxidizing agent or metal powder as an alloying agent.

The welding flux to be spread in the groove used a bonding flux containing SiO ₂ : 20%, CaO: 5%, MgO: 25%, Al ₂ O ₃ : 10%, CaF ₂ : 5% and CaCO ₃ : 5% by mass. The bonding flux was dried at 300°C for 1 hour before being spread in the groove.

Solid wires (diameters 4.8 mm and 6.4 mm) were used as welding wires, and one electrode to four electrodes were used in a downward position without preheating, and single-sided single-layer submerged arc welding was performed according to various welding conditions shown in Table 1. The solid wires were solid wires for low-temperature steel and had the following composition: C: 0.10%, Si: 0.03%, Mn: 1.65%, Ni: 2.40%, and Mo: 0.50%, and the remainder contained Fe and inevitable impurities.

[Mechanical properties of welded joints] In accordance with the provisions of JIS Z 2242 (Charpy impact test method for metal materials), a Charpy impact test piece (V-shaped notch) was taken from the test piece taking position shown in FIG4 from the butt welded joint portion obtained by the above-mentioned single-sided single-layer SAW, and an impact test was performed. The steel plate 1a and the steel plate 1b were butt-jointed to perform single-sided single-layer SAW. As a result, as shown in FIG4, a weld metal 5 was formed in the groove on the front side, a root 8 was formed in the groove on the back side, and a weld heat affected portion 6 was formed between the weld metal 5 and the steel plate. Regarding the test piece 7, a Charpy V-notch test piece 7 having a V-notch 7a formed therein is taken from the position of the weld heat affected portion 6 located at a depth of 1/2t of the plate thickness (t) of the steel plate in accordance with JIS Z 3128 (impact test method for welded joints). In the Charpy impact test, three of the test pieces 7 taken are prepared, _{VE -60} is obtained, and the average value thereof is set as the value of the low temperature toughness of the weld heat affected portion of each welded joint.

[Evaluation of weld shape] Regarding weld shape, the root shape and the weld bead appearance on the surface were evaluated by visual observation or further dimensional measurement. Regarding the evaluation of the root shape, the weld bead width of the root 8 was 5.0 mm or more, the weld bead height was 1.0 mm to 2.5 mm, and no undercut was evaluated as good (○), and the situation other than the above was evaluated as poor (×). Regarding the weld bead appearance, the weld bead reinforcement height or width was uniform and good. The situation other than the above, such as the shape is uneven and the situation with undercut, or both, was evaluated as poor (×).

The obtained evaluation results are shown in Table 2. In Table 2, joints No. A to No. I are examples of the present invention. In the examples of the present invention, all of them are welded joints having both the desired weld shape (good weld bead appearance and good root shape) and excellent low-temperature toughness with _{VE -60} of HAZ being 27 J or more. In addition, regarding the strength of the welded joint, a joint tensile test was conducted in accordance with JIS Z 3121: 2013, and it was confirmed that the tensile strength was in the range of 440 MPa to 560 MPa, which is high strength.

On the other hand, in the comparative examples (joint No. J to joint No. V) that are out of the scope of the present invention, either or both of the weld bead appearance or the root formation is insufficient, and the low-temperature toughness of the HAZ is insufficient ( _{VE -60} is less than 27 J). That is, in the comparative examples, a welded joint that takes into account both a good weld shape and excellent low-temperature toughness of the HAZ cannot be obtained. The following is a description of each comparative example.

In joint No. J, the Y-groove is used. 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 decreases ( _{VE -60} = 9 J < 27 J).

In joint No.K, the Y-shaped groove was used and the blunt edge was set deep (r=6 mm). Therefore, the blunt edge had insufficient penetration, the root could not be formed, and the Charpy test piece could not be taken.

In joint No. L, the Y-groove is used. 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, and the low-temperature toughness of the HAZ decreases ( _{VE -60} = 15 J < 27 J).

In joint No. M, a Y-shaped groove was used for welding with a heat input that did not reduce the low-temperature toughness of the HAZ. However, the welding wire was not supplied sufficiently relative to the groove area, and the height of the weld bead could not fill the surface of the steel plate, resulting in a poor weld bead appearance.

In joint No. N, there are two grooves, and the heat input exceeds the appropriate range for the plate thickness of 16 mm, so the low-temperature toughness of the HAZ decreases ( _{VE -60} = 20 J < 27 J). In addition, the welding wire is oversupplied relative to the cross-sectional area of the groove, and the weld width and reinforcement height are uneven.

In joint No.O, there are two grooves, and the angle δ of the second groove is 55°, which is out of the scope of the present invention. The effect of reducing the cross-sectional area of the groove cannot be fully obtained, so the height of the weld cannot fill the surface of the steel plate, and the appearance of the weld is poor.

In joint No. P, there are two grooves, and the angle δ of the second groove is 10°, which is out of the scope of the present invention. The effect of deepening the penetration of the root cannot be fully obtained, so the penetration of the blunt edge is insufficient and the root cannot be formed.

In joint No. Q, the Y-groove is used. 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 decreases ( _{VE -60} = 12 J < 27 J).

In joint No. R, a Y-shaped groove was used for welding with a heat input that did not reduce the low-temperature toughness of the HAZ. However, the welding wire was not supplied sufficiently relative to the cross-sectional area of the groove, and the height of the weld bead could not fill the surface of the steel plate.

In joint No. S, the Y-groove was used and the blunt edge was set deep (r=7 mm), so the blunt edge was not melted enough and the root could not be formed. In addition, the heat input increased to melt the blunt edge was too large for the low-temperature toughness of the HAZ, and the low-temperature toughness of the HAZ decreased ( _{VE -60} =19 J＜27 J).

In joint No. T, the Y-groove is used. For a plate thickness of 40 mm, the heat input required to obtain a good weld shape exceeds 200 kJ/cm, which is beyond the scope of the present invention, and the low-temperature toughness of the HAZ decreases ( _{VE -60} = 10 J < 27 J).

In joint No.U, a Y-shaped groove was used for welding with a heat input that did not reduce the low-temperature toughness of the HAZ. However, the welding wire was not supplied sufficiently relative to the cross-sectional area of the groove, and the height of the weld did not reach the surface of the steel plate.

In joint No. V, the heat input exceeds 200 kJ/cm and is out of the scope of the present invention, so the low-temperature toughness of the HAZ is reduced ( _{VE -60} = 24 J < 27 J). In addition, the welding wire is oversupplied relative to the cross-sectional area of the groove, and the weld width and weld height are uneven.

[Table 1] Welding condition No. First electrode Second electrode Third electrode Fourth electrode Welding speed Heat input Wire diameter Current Voltage Wire diameter Current Voltage Wire diameter Current Voltage Wire diameter Current Voltage mm A V mm A V mm A V mm A V cm/min kJ/cm 1 4.8 950 35 - - - - - - - - - 75 26.6 2 4.8 950 35 6.4 700 44 - - - - - - 75 51.2 3 4.8 1150 30 6.4 1050 38 - - - - - - 70 63.8 4 4.8 1200 30 6.4 1100 35 6.4 900 40 - - - 70 94.7 5 4.8 1250 32 6.4 1200 38 - - - - - - 55 93.4 6 4.8 1300 32 6.4 1200 35 6.4 1100 45 - - - 55 145.2 7 4.8 1400 35 6.4 1300 40 6.4 1250 45 - - - 50 188.7 8 4.8 1600 35 6.4 1300 40 6.4 1200 45 6.4 1100 45 50 253.8 Note: The polarity of the electrodes used is all AC

[Table 2] Connector No. Plate thickness Welding condition No. Bevel shape Is the heat input adequate? Welding shape Low temperature toughness of HAZ _{VE -60} Remarks Paragraph 1 Paragraph 2 Blunt edge depth r Groove depth h Groove angle θ Groove depth k Groove angle δ Weld bead appearance Root shape mm mm ° mm ° mm J A 12 1 6 60 3 45 3 Suitable ○ ○ 77 Invention Example B 16 3 10 50 4 25 2 Suitable ○ ○ 80 Invention Example C 16 3 10 60 3 40 3 Suitable ○ ○ 71 Invention Example D 16 3 9 60 4 40 3 Suitable ○ ○ 68 Invention Example E 25 5 18 55 3 30 4 Suitable ○ ○ 55 Invention Example F 25 5 17 50 5 30 3 Suitable ○ ○ 60 Invention Example G 25 5 16 50 4 30 5 Suitable ○ ○ 86 Invention Example H 25 5 17 50 5 25 3 Suitable ○ ○ 87 Invention Example I 40 7 30 50 5 30 5 Suitable ○ ○ 70 Invention Example J 12 2 9 60 0 0 3 no ○ ○ 9 Comparison Example K 12 1 6 60 0 0 6 Suitable ○ × Unable to take test strips Comparison Example L 16 4 13 50 0 0 3 no ○ ○ 15 Comparison Example M 16 3 13 50 0 0 3 Suitable × ○ 69 Comparison Example N 16 4 10 60 3 40 3 no × ○ 20 Comparison Example O 16 3 9 60 4 55 3 Suitable × ○ 55 Comparison Example P 16 3 9 60 4 10 3 Suitable ○ × 72 Comparison Example Q 25 6 twenty one 45 0 0 4 no ○ ○ 12 Comparison Example R 25 5 twenty one 45 0 0 4 Suitable × ○ 65 Comparison Example S 25 6 18 50 0 0 7 no ○ × 19 Comparison Example T 40 8 34 45 0 0 6 no ○ ○ 10 Comparison Example U 40 7 34 45 0 0 6 Suitable × ○ 49 Comparison Example V 40 8 30 45 5 30 5 no × ○ twenty four Comparison Example Note 1: k=0 mm, δ=0° in the second paragraph refers to a Y-shaped groove. Note 2: "Suitable" for heat input means suitable for the present invention, and "No" means unsuitable. The suitable range of heat input is: when the plate thickness is t=12 mm, it is 15 kJ/cm or more and less than 48 kJ/cm; when the plate thickness is t=16 mm, it is more than 30 kJ/cm and less than 72 kJ/cm; when the plate thickness is t=25 mm, it is more than 75 kJ/cm and less than 126 kJ/cm; when the plate thickness is t=40 mm, it is more than 150 kJ/cm and less than 200 kJ/cm.

Furthermore, the conditions No. 1, No. 3, No. 5, and No. 7 of Table 1 adopted in the invention example of Table 2 are plotted as curve B (● mark, solid line), and the conditions No. 2, No. 4, No. 6, and No. 8 of Table 1 adopted in the comparative example of Table 2 with good weld shape are plotted as curve A (▲ mark, dotted line), and the relationship between the welding heat input and the plate thickness for obtaining a good weld shape is shown in FIG5. From this graph, it can be seen that the welding heat input can be reduced in the invention example compared with the previous example. It is generally known that if the heat input is reduced relative to a steel plate of the same plate thickness, the toughness is improved, and it can be said that by using the present invention, the deterioration of the low-temperature toughness of the HAZ caused by excessive heat input can be prevented.

1a, 1b: Steel plate 2a, 2b: Tapered part (first section) 3a, 3b: Blunt edge 4a, 4b: Tapered part (second section) 5: Weld metal 6: Heat affected zone (HAZ) 7: Test piece 7a: V-notch 8: Root h: Depth of first groove h1: (previous) groove depth/depth of taper H: Welding heat input/heat input k: Depth of second groove r: Depth of blunt edge S: Cross-sectional area of groove t: Plate thickness (thickness) θ: Angle of first groove θ1: (previous) groove angle δ: Angle of second groove A, B: Curves

FIG. 1 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. FIG. 2 is a schematic cross-sectional view showing a Y-shaped groove shape in a previous welding method. FIG. 3 is a graph showing a preferred range of welding heat input relative to plate thickness in the welding method according to the embodiment. FIG. 4 is a schematic cross-sectional view showing the location of the test piece for the Charpy impact test. FIG. 5 is a graph comparing the relationship between the plate thickness and the welding heat input of the steel plate using the invention example and the previous example.

1a, 1b: Steel plate

2a, 2b: Cone-shaped part (first section)

3a, 3b: blunt edge

4a, 4b: Cone-shaped part (second section)

h: Depth of the first slope section

k: Depth of the second slope

r: Depth of blunt edge

S: cross-sectional area of the groove

t: Plate thickness (thickness)

θ: Angle of the first groove

δ: The angle of the second groove

Claims (7)

A single-sided submerged arc welding method, wherein two steel plates are butt-welded, and in the single-sided submerged arc welding method, the thickness t of the steel plate is set to a range of 9 mm to 40 mm, a blunt edge with a depth of more than 0 mm and less than 5 mm is formed at the bottom of the butt groove of the steel plate, two angles are set at the groove portion, the first groove angle on the surface side is set to a range of 50° to 70°, the second groove angle connected to the blunt edge is set to a range of 20° to 45°, and the depth of the second groove is set to a range of 2 mm to 5 mm, the welding heat input H is set to a range of 15 kJ/cm to 200 kJ/cm, further, the welding heat input H (kJ/cm) satisfies the following formula 1 relative to the thickness t (mm) of the steel plate, Single pass welding from the surface side; [Formula 1] (t-10)×5＜H＜(t-4)×6. The single-sided submerged arc welding method as described in claim 1, wherein welding is performed by selecting any one or a combination of two or more of the following: Setting the welding speed to a range of 50 cm/min to 120 cm/min, Using more than one electrode, and Setting the welding current of the first electrode to a range of 700 A to 1600 A. A single-sided submerged arc welding method as described in claim 1 or 2, wherein a flux is used in a pad. A welding joint is made using the single-sided submerged arc welding method as described in claim 1 or 2. A welding joint is made using the single-sided submerged arc welding method as described in claim 3. The weld joint as described in claim 4, wherein the Charpy absorbed energy of the weld heat affected portion at -60°C is 27 J or more. The weld joint as described in claim 5, wherein the Charpy absorbed energy of the weld heat affected portion at -60°C is 27 J or more.