JP7540976B2 - One-sided welding method and manufacturing method for welded joint - Google Patents

Description

The present invention relates to a one-sided welding method and a method for manufacturing a welded joint in which flux is placed from the underside of the groove as a backing material, the groove is filled with a groove filler, and the groove surface is gas-shielded arc-welded using two or more electrodes.

The one-sided welding method involves pressing a fire-resistant backing material against the back side of the groove of the butt joint, which is the material to be welded (hereinafter also referred to as the base material or work), and welding is performed from the front side of the groove, forming a back bead on the back side of the groove as well. This makes it possible to obtain complete penetration by welding from only one side without having to flip the butt joint, improving the efficiency of the welding work.

In this single-sided welding method, the formation of the back bead is important. For example, Patent Document 1 discloses a multi-electrode gas-shielded arc single-sided welding method in which the formation of the back bead is very good and impact performance is also excellent. The single-sided welding method described in Patent Document 1 includes a leading electrode and a trailing electrode, the leading electrode has an opposite polarity and uses a flux-cored wire or solid wire, and the trailing electrode has a positive polarity and uses a flux-cored wire.

The leading electrode has a wire extension length (EL) of 15-35 mm, a welding current (IL) of 350-550 A, and a wire feed rate (WL) of 5.0-14.0 m/min, satisfying the relationship 130≦(IL×WL/EL)≦450. The trailing electrode, a flux-cored wire, contains 1.5-3.5 mass% metallic Al and 0.2-1.0 mass% Mg, satisfying the relationships 2.0 mass%≦(metallic Al+Mg)≦4.0 mass% and 2.0≦(metallic Al/Mg)≦10.0.

JP 2019-13980 A

As described above, one-sided gas-shielded arc welding uses a refractory backing material on the back side of the groove, and generally uses a solid ceramic backing material. This ceramic backing material is mainly attached to the back side of the groove with an adhesive, but since this attachment is done manually by the worker, the longer the target weld length, the longer the work time becomes.
For example, if submerged arc welding is applied to a weld with a long weld length (hereinafter also referred to as a long-length weld) and a flux backing method using flux (hereinafter also referred to as backing flux) as a backing material can be applied, the effort of placing flux on the back side of the groove will be unnecessary, and it is thought that the work time can be shortened.

Submerged arc welding has high welding efficiency and is good for linear and monotonous welding, such as welding large plates together on thick plate panel lines in the shipbuilding industry. However, submerged arc welding requires large equipment configurations, and there are some welding locations where it is difficult to apply, such as block joints and welding of curved outer plates. On the other hand, one-sided welding in gas shielded arc welding requires relatively low equipment costs, can be applied to many locations, and is highly versatile.

In this way, it would be nice if the flux backing method could be applied to gas-shielded arc welding, which has different application areas from submerged arc welding; however, gas-shielded arc welding has the characteristic that the current density is higher than that of submerged arc welding, and heat is more likely to concentrate due to constriction. Therefore, when welding the surface of a groove with gas-shielded arc welding, the effect of the arc is more pronounced than with submerged arc welding, making it difficult to achieve both a good back bead shape and the prevention of welding defects.

In particular, when the welding current is increased to ensure an appropriate deposition rate and a good back bead shape, the thermal energy of the arc becomes excessive, causing the backing flux to heat up more than necessary, which results in a large amount of metal vapor being generated from the backing flux, which causes a welding defect called a blowhole defect.
On the other hand, if the welding current is weakened in order to suppress the effect on the backing flux, the filler and base material will not melt sufficiently, resulting in reduced welding efficiency and the inability to obtain a good back bead shape.

The present invention was made in consideration of these problems, and aims to provide a one-sided welding method and a manufacturing method for a welded joint that uses flux as a backing material and uses multiple electrodes to perform gas-shielded arc welding, which can obtain an appropriate deposition amount and a good back bead shape, and can prevent porosity defects in the back bead.

The above object of the present invention is achieved by the following configuration [1] relating to a one-sided welding method.

[1] A one-sided welding method in which a pair of steel plates are butted together substantially horizontally to form a groove, a backing flux is placed from the lower side of the groove, a groove filler is filled in the groove, and gas-shielded arc welding is performed from the upper side of the groove using a plurality of electrodes arranged in the direction of the weld line,
The filling height of the groove filler is 4 mm or more,
The pressing pressure for pressing the backing flux against the groove side is set to 0.05 Pa or more,
The average welding current of the most leading electrode is 440 A or more,
A single-sided welding method, characterized in that, when an average welding current of the leading electrode is expressed as I _L (av) and an average arc voltage of the leading electrode is expressed as V _L (av), I _L (av)/V _L (av) is 12.0 or more and 14.0 or less.

Furthermore, preferred embodiments of the present invention relating to a one-sided welding method relate to the following [2] to [11].
[2] The groove filler is at least one of a powder filler and a cut wire,
The one-sided welding method according to [1], characterized in that the groove filler contains 95 mass% or more of Fe with respect to the total mass of the groove filler.

[3] The one-sided welding method described in [1] or [2], characterized in that the pressing pressure is 0.07 MPa or more and 0.15 MPa or less.

[4] The leading electrode is a solid wire,
The single-sided welding method according to any one of [1] to [3], characterized in that at least one of the electrodes, excluding the leading electrode, among the plurality of electrodes is a flux-cored wire.

[5] The plurality of electrodes are constituted by two electrodes, the leading electrode and a trailing electrode following the leading electrode,
The one-sided welding method according to any one of [1] to [4], characterized in that the polarities of the leading electrode and the trailing electrode are both DCEP.

[6] The one-sided welding method described in [5], characterized in that the electrode distance between the leading electrode and the trailing electrode is 40 mm or more and 65 mm or less.

[7] The angle of the torch of the leading electrode is set to 45° or more and 110° or less with respect to the welding direction,
The single-sided welding method according to [5] or [6], characterized in that the angle of the torch of the trailing electrode is 90° or more and 135° or less with respect to the welding direction.

[8] The welding current of the trailing electrode is 250 A or more and 400 A or less,
The single-sided welding method according to any one of [5] to [7], characterized in that the average arc voltage of the trailing electrode is 28 V or more.

[9] A one-sided welding method according to any one of [5] to [8], characterized in that at least one of the leading electrode and the trailing electrode is weaved in the width direction relative to the welding advance direction.

[10] The backing flux is
Contains at least one of a metal powder and a slag former,
The one-sided welding method according to any one of [1] to [9], characterized in that the remainder is unavoidable impurities.

[11] The backing flux further comprises:
The single-sided welding method according to [10], characterized in that the powder contains at least one of a non-metallic powder and a non-metallic compound powder excluding a slag former.

The above object of the present invention also relates to the following item [12], which relates to a method for manufacturing a welded joint.
[12] A method for manufacturing a welded joint, comprising: manufacturing a welded joint using the one-sided welding method according to any one of [1] to [11].

The present invention provides a one-sided welding method and a method for manufacturing a welded joint that can obtain an appropriate deposition amount and a good back bead shape, while preventing porosity defects in the back bead.

FIG. 1 is a schematic diagram showing the state of a filler before welding in a one-sided welding method according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a weld metal after welding in a single-sided welding method according to an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing the position of the wire and the state of the filler during welding along the welding line direction.

The inventors conducted various studies to determine the conditions under which a good back bead shape and prevention of welding defects can both be achieved when performing one-sided welding using multiple electrodes with gas-shielded arc welding. As a result, they discovered that by controlling the filling height of the groove filler, the groove filler can be made to act as a buffer that buffers excessive arc pressure during gas-shielded arc welding.

The following describes in detail an embodiment of the present invention. Note that the present invention is not limited to the embodiment described below, and can be modified as desired without departing from the spirit of the present invention.

[1. One-sided welding method]
The one-sided welding method according to this embodiment is a method in which a pair of steel plates are butted together approximately horizontally to form a groove, backing flux is placed from the lower side of the groove, i.e., the back side, and the groove is filled with a groove filler. Gas-shielded arc welding is then performed from the upper side of the groove, i.e., the front side, using multiple electrodes arranged in the direction of the weld line.

Below, an example of the single-sided welding method according to this embodiment will be specifically described with reference to the drawings. FIG. 1 is a schematic diagram showing the state of the filler before welding in the single-sided welding method according to this embodiment. FIG. 2 is a schematic diagram showing the weld metal after welding in the single-sided welding method according to this embodiment. FIG. 3 is a schematic cross-sectional view showing the position of the wire and the state of the filler along the weld line direction during welding. In this embodiment, welding is performed using two electrodes, a leading electrode and a trailing electrode that follows the leading electrode.

As shown in FIG. 1, a pair of steel plates 1a and 1b are butted together at an arbitrary groove width G (hereinafter also referred to as gap width) and horizontally arranged to form a groove 2, and a backing flux 11 is arranged under the groove 2. The backing flux 11 is pressed toward the groove side by the gas pressure (hereinafter referred to as pressing pressure P) in an air hose 13 through an underlay flux 12. The backing flux 11, the underlay flux 12, and the air hose 13 are stored in a U-shaped metal case 15. Furthermore, the metal case 15 is lifted by the gas pressure (hereinafter referred to as trough pressing pressure P _T ) in an air hose 14 arranged below it and is brought close to the groove, thereby ensuring the pressing of the backing flux 11 by the air hose 13. In this way, the backing flux 11 is held in a predetermined position.

Next, the groove filler 6 is sprayed into the groove 2. The amount of the groove filler 6 to be sprayed is determined by a predetermined filling height h, a groove angle, and a groove width G in the one-sided welding method according to the embodiment of the present invention.
Thereafter, as shown in FIGS. 2 and 3 , an arc welding torch 7 having a solid wire 7a as a consumable electrode is placed above the groove 2 as a leading electrode, and an arc welding torch 8 having a flux-cored wire 8a as a consumable electrode is placed as a trailing electrode so that the distance in the weld line direction (hereinafter also referred to as the electrode distance) is within an arbitrary range.

Thereafter, the welding conditions are set based on the amount of the groove filler 6, and the pressing pressure P is set. Then, in the leading electrode and the trailing electrode, arcs 7b and 8b are generated while flowing shielding gases 9 and 10, respectively, and these are moved relatively along the groove 2 of the pair of steel plates 1a and 1b.
At this time, the backing flux 11 of the leading electrode is not excessively heated, while the groove filler 6 is set to a condition that allows it to be sufficiently melted, so that a good buried arc state is maintained. Note that a buried arc refers to a state in which the arc length is kept short and the wire is plunged into the molten pool dug by the arc pressure.
In addition, the trailing electrode plays an auxiliary role to the leading electrode, and by appropriately controlling the current, voltage, etc. of the trailing electrode, the shape of the molten pool can be made even better.

In this way, the surfaces of the steel plates 1a and 1b at the groove 2 melt to form molten metal 16, which is then cooled to form weld metal 3 with an excellent bead shape coated with slag 4 and 5 on the front and back sides of the groove 2, respectively, and the steel plates 1a and 1b are joined together. Hereinafter, the bead on the front side is referred to as the "front bead" and the bead on the back side is referred to as the "back bead."

In the above-described embodiment shown in Figures 1 to 3, the arc welding torch 7 holding the solid wire 7a is the leading electrode, and the arc welding torch 8 holding the flux-cored wire 8a is the trailing electrode that follows the leading electrode, but the present invention is not limited to this. For example, two or more electrodes may be used as the heat source. When multiple electrodes are used, by controlling the welding current of the most leading leading electrode and the ratio of the average welding current and average arc voltage of this leading electrode, it is possible to form weld metal with excellent bead shapes on both the front and back sides of the groove, as described above.

The following provides a detailed explanation of the type of groove filler, filling height, backing flux pressing pressure, welding conditions, and welding materials used in the one-sided welding method according to this embodiment.

<Grove filling agent>
(Type of groove filler)
In this embodiment, the groove filler is not particularly limited, but since it is easy to melt, it is preferable to use at least one of a powder filler containing metal powder and a cut wire. The composition of the groove filler is also not particularly limited, but for example, it is preferable that the groove filler contains 95 mass% or more of Fe with respect to the total mass of the groove filler, or has the same composition as the solid wire described later, and specifically, it is preferable that it is an alloy in which a small amount of Mn is added to pure iron or Fe.

(Filling height of groove filler h: 4 mm or more)
In addition to the conventional effect of ensuring the deposition amount and improving the welding efficiency, in this embodiment, the groove filler has the effect of buffering the excessive arc pressure in gas shielded arc welding. When considering the buffering of the arc pressure, the depth of the molten metal is important, so the height at which the filler is added (hereinafter also referred to as the filling height h) is an important guideline, not the amount of filler. That is, after determining the filling height h, the amount of filler to be filled is determined based on the groove shape, groove angle, and groove width.

If the filling height h of the groove filler is less than 4 mm, the molten metal is dug down by the arc pressure, the backing flux is exposed, and the backing flux is excessively heated by the heat of the arc, causing a large amount of metal vapor to be generated and causing pore defects. Therefore, the filling height h of the groove filler is set to 4 mm or more, and preferably 4.5 mm or more.
There is no particular upper limit to the filling height h of the groove filler, but it is preferably 7 mm or less because this results in a better back bead shape, and more preferably 6.5 mm or less.

<Backing flux pressing pressure P: 0.05 MPa or more>
The pressing pressure P of the backing flux affects the cohesiveness of the backing flux. When the pressure P increases and the backing flux is compressed, the cohesiveness increases. The higher the cohesiveness, the more the molten metal is prevented from dripping and the better the shape of the back bead can be maintained. In addition, the higher the cohesiveness of the backing flux, the more difficult it is for metal vapor to escape from inside the backing flux, and the more pore defects can be prevented.

If the pressing pressure P is less than 0.05 MPa, pore defects occur and the back bead shape tends to be convex. Therefore, the pressing pressure P of the backing flux is set to 0.05 MPa or more, and in order to obtain a better back bead, the pressing pressure P is preferably set to 0.06 MPa or more, and more preferably set to 0.07 MPa or more.
On the other hand, there is no particular upper limit to the pressing pressure P, but if it is excessively high, the back bead shape tends to become somewhat flat. Therefore, in order to obtain a good back bead shape, the pressing pressure P is preferably 0.15 MPa or less, and more preferably 0.14 MPa or less.

The method for controlling the pressing pressure P can be selected arbitrarily depending on the method for placing the backing flux. For example, when pressing the backing flux 11 toward the groove 2 using the method shown in Figures 1 and 2, the pressing pressure P can be controlled by adjusting the gas pressure in the air hose 13.

<Leading pole>
(Average welding current _IL (av) of leading electrode: 440A or more)
In this embodiment, since gas-shielded arc welding is performed using multiple electrodes, a good buried arc state can be maintained by controlling the average welding current _IL (av) and average arc voltage _VL (av) of the most leading electrode, as described above. As a result, weld metal with excellent bead shapes can be formed on the front and back sides of the groove.
Specifically, by adjusting the average welding current I _L (av) of the leading electrode, it is possible to obtain a deposition amount with good welding efficiency and to form a good back bead.

If the average welding current I _L (av) of the leading electrode is less than 440 A, a good back bead is not formed under conditions of high welding efficiency with a filler provided. Therefore, the average welding current I _L (av) of the leading electrode is set to 440 A or more, preferably 445 A or more, and more preferably 450 A or more.
On the other hand, in this embodiment, the upper limit of the average welding current _IL (av) of the leading electrode is not particularly limited, but considering the use of a general-purpose 500 A power source, it is preferable to set it to 500 A or less from the viewpoint of equipment.

(average welding current _IL (av) of leading electrode/average arc voltage _VL (av) of leading electrode: 12.0 or more and 14.0 or less)
In this embodiment, the groove filler is used as a buffer by controlling the filling height h of the groove filler, but this buffer effect is high, and it is difficult to form a back bead by simply increasing the welding current. Therefore, by considering the ratio of the average welding current and the average arc voltage of the leading electrode, a good buried arc state can be maintained. As mentioned above, the buried arc refers to a state in which the wire is plunged into the molten pool.

If the average welding current of the leading electrode is expressed as _IL (av) and the average arc voltage of the leading electrode is expressed as _VL (av), the buried arc state can be expressed by the formula _IL (av)/ _VL (av). That is, if the value of _IL (av)/ _VL (av) is less than 12.0, the arc pressure is weak and the excavated molten pool is shallow for the filler conditions that can ensure the deposition amount, so that the back bead shape is not formed. Therefore, the value obtained by _IL (av)/ _VL (av) is 12.0 or more, and preferably 12.7 or more.
On the other hand, if the value of I _L (av)/V _L (av) exceeds 14.0, the arc pressure becomes excessively high, and the excavated molten pool becomes deeper than necessary, exposing the backing flux. As a result, the backing flux is excessively heated by the heat of the arc, generating a large amount of metal vapor and causing porosity defects. Therefore, the value obtained by I _L (av)/V _L (av) should be 14.0 or less, and preferably 13.8 or less.

(Average arc voltage _VL (av) of the leading electrode: 31.5 V or more and 40 V or less)
In this embodiment, the average arc voltage V _L (av) of the leading electrode is not particularly limited, but from the viewpoint of arc stability, it is preferably 31.5 V or more, and more preferably 32 V or more.
From the viewpoint of arc stability, the average arc voltage V _L (av) of the leading electrode is preferably 40V or less, and more preferably 38V or less.

(Wire feed rate of leading electrode: 5.0 m/min to 15.0 m/min)
In this embodiment, the wire feed rate of the leading electrode is not particularly limited, but from the viewpoint of facilitating the formation of the back bead, the wire feed rate is preferably 5.0 m/min or more, more preferably 5.5 m/min or more, and even more preferably 6.0 m/min or more.
On the other hand, if the wire feed rate of the leading electrode is set to 15.0 m/min or less, the stability of the back bead is improved and melt-through can be prevented, which is preferable. Therefore, the wire feed rate of the leading electrode is more preferably set to 15.0 m/min or less, and even more preferably set to 13.0 m/min or less.

(Weaving width of leading pole: 0 mm to 7 mm)
In this embodiment, it is preferable that at least one of the leading electrode and the trailing electrode is weaved in the width direction relative to the welding direction. The weaving of the leading electrode may be performed as necessary, and it is not necessary to weave the leading electrode. In addition, the weaving width of the leading electrode is not particularly limited, but from the viewpoint of improving the formation state of the back bead, it is preferable to set it to 0 mm or more, and more preferably to set it to 1 mm or more.
On the other hand, from the viewpoint of improving the formation state of the back bead, the weaving width of the leading electrode is preferably 7 mm or less, and more preferably 5 mm or less.

(Polarity of leading electrode: DCEP)
The polarity of the leading electrode is preferably DCEP (Direct Current Electrode Positive) from the viewpoint of increasing the arc pressure for forming a back bead.

(Wire type of leading electrode: Flux-cored wire or solid wire)
In this embodiment, the type and composition of the wire of the leading electrode are not particularly limited, but for example, a flux-cored wire or a solid wire (hereinafter sometimes referred to as a welding wire) may be used. In addition, it is more preferable to select a solid wire as the leading electrode, since the arc pressure for forming a back bead can be increased.

Flux-cored wire is a wire in which flux is filled inside a tubular steel sheath. Either a seamless wire (where the seams of the steel sheath are welded) or a seam-free wire (where the seams are not welded but left as gaps) can be used. The outside of the sheath may also be copper-plated.

(Torch angle of the leading electrode: 45° to 110° with respect to the welding direction)
In this embodiment, the angle of the torch of the leading electrode is not particularly limited, but is preferably set within a range that does not interfere with the electrode following the leading electrode, and is preferably set to 45° to 110° with respect to the welding direction, i.e., a retreat angle of 0° to 45° or a advance angle of 0° to 20°. The angle of the torch of the leading electrode is more preferably 85° to 95°, and even more preferably 90°, which is perpendicular to the welding direction.

(Wire diameter of leading electrode: 1.0 mm or more and 2.0 mm or less)
In this embodiment, the wire diameter of the flux-cored wire or solid wire used as the leading electrode is not particularly limited, but from the viewpoint of welding workability, the wire diameter of the leading electrode is preferably 1.0 mm or more, more preferably 1.2 mm or more. Also, from the viewpoint of welding workability, the wire diameter of the leading electrode is preferably 2.0 mm or less, more preferably 1.6 mm or less.

(Shielding gas when welding with the leading electrode)
In this embodiment, the shielding gas used during welding with the leading electrode is not particularly limited, but may be, for example, Ar gas, carbon dioxide gas, a mixed gas of Ar gas and carbon dioxide gas, or a mixed gas of Ar gas and oxygen gas. The flow rate of the gas is also not particularly limited, but may be, for example, 15 L/min to 30 L/min.

(Wire extension length of leading electrode: 15 mm to 35 mm)
In this embodiment, the wire extension length of the leading electrode is not particularly limited, but is preferably 15 mm or more because it improves the stability of the back bead and prevents burn-through. The wire extension length of the leading electrode is more preferably 17 mm or more, and even more preferably 19 mm or more.
Furthermore, it is preferable to set the wire extension length of the leading electrode to 35 mm or less, since this facilitates the formation of a back bead. It is more preferable to set the wire extension length of the leading electrode to 33 mm or less, and even more preferable to set it to 31 mm or less.

<Backward pole>
As described above, the trailing electrode plays a supporting role to the leading electrode. In this specification, even when a one-sided welding method uses three or more electrodes, at least one of the electrodes excluding the leading electrode is referred to as a trailing electrode, as in the case of two electrodes.

(Average welding current I _F (av) of trailing electrode: 250 A or more and 400 A or less)
By appropriately controlling the average welding current I _F (av) of the trailing electrode, a better front bead shape can be ensured. In the present embodiment, the average welding current I _F (av) of the trailing electrode is not particularly limited, but from the viewpoint of ensuring a good front bead, the average welding current I _F (av) of the trailing electrode is preferably 250 A or more, and more preferably 280 A or more.
On the other hand, from the viewpoint of improving welding workability, the average welding current I _F (av) of the trailing electrode is preferably 400 A or less, more preferably 380 A or less, even more preferably 350 A or less, and particularly preferably 320 A or less.

(Average arc voltage _VF (av) of trailing electrode: 28V or more and 40V or less)
In this embodiment, the average arc voltage V _F (av) of the trailing electrode is not particularly limited, but from the viewpoint of arc stability, it is preferably 28 V or more, and more preferably 30 V or more.
From the viewpoint of arc stability, the average arc voltage V _F (av) of the trailing electrode is preferably 40V or less, and more preferably 38V or less.

(Wire feed rate of trailing electrode: 5.0 m/min or more and 14.0 m/min or less)
In this embodiment, the wire feed rate of the trailing electrode is not particularly limited, but is preferably 5.0 m/min or more, since the arc force is sufficient and welding defects such as insufficient fusion do not occur. The wire feed rate of the trailing electrode is more preferably 8.0 m/min or more, and even more preferably 12.0 m/min or more.
In addition, when the wire feed rate of the trailing electrode is set to 14.0 m/min or less, the arc force becomes sufficient to prevent welding defects such as incomplete fusion, and the arc becomes stable, so that the amount of spatter generated can be reduced. The wire feed rate of the trailing electrode is more preferably set to 13.5 m/min or less, and even more preferably set to 13.0 m/min or less.

(Weaving width of trailing pole: 0 mm to 10 mm)
As described above, in this embodiment, it is preferable that at least one of the leading electrode and the trailing electrode is weaved in the width direction relative to the welding progress direction. As with the leading electrode, the trailing electrode may be weaved as necessary, and may not be weaved at all. There are no particular restrictions on the weaving width of the trailing electrode, but it is preferable that it be 0 mm or more from the viewpoint of improving the formation state of the front bead.
On the other hand, from the viewpoint of improving the state of formation of the surface bead, the weaving width of the trailing electrode is preferably 10 mm or less, and more preferably 8 mm or less.
Since the weaving of the trailing electrode contributes to the shape of the front bead, it is preferable to weave at least the trailing electrode.

(Polarity of trailing pole: DCEP)
The polarity of the trailing electrode is preferably DCEP from the viewpoint of maintaining a good surface bead shape.

(Wire type of trailing electrode: flux-cored wire)
In this embodiment, the type and composition of the wire of the trailing electrode are not particularly limited, but it is preferable to select a flux-cored wire as the trailing electrode because this allows the shape of the front bead to be improved.

(Torch angle of trailing electrode: 90° to 135° with respect to the welding direction)
In this embodiment, the angle of the torch of the trailing electrode is not particularly limited, but it is preferable to set it within a range that does not interfere with the leading electrode, and from the viewpoint of improving the bead appearance, it is preferable that the trailing electrode has a forward angle. Therefore, the angle of the torch of the trailing electrode is preferably 90° or more and 135° or less with respect to the welding direction, that is, the forward angle is preferably 0° or more and 45° or less, and more preferably 90° or more and 110° or less.

(Wire diameter of trailing electrode: 1.0 mm or more and 2.0 mm or less)
In this embodiment, the wire diameter of the flux-cored wire used as the trailing electrode is not particularly limited, but from the viewpoint of welding workability, the wire diameter of the trailing electrode is preferably 1.0 mm or more, more preferably 1.2 mm or more, and from the viewpoint of welding workability, the wire diameter of the trailing electrode is preferably 2.0 mm or less, more preferably 1.6 mm or less.

(Shielding gas when welding with trailing electrode)
In this embodiment, the shielding gas used during welding with the trailing electrode is not particularly limited, but may be, for example, Ar gas, carbon dioxide gas, a mixed gas of Ar gas and carbon dioxide gas, or a mixed gas of Ar gas and oxygen gas. The flow rate of the gas is also not particularly limited, but may be, for example, 15 L/min to 30 L/min.

(Wire extension length of trailing electrode: 15 mm to 35 mm)
In this embodiment, the wire extension length of the trailing electrode is not particularly limited, but is preferably 15 mm or more because the arc force is sufficient and ghost lines indicating the segregation of impurities can be completely eliminated. The wire extension length of the trailing electrode is more preferably 17 mm or more, and even more preferably 19 mm or more.
Furthermore, when the wire extension length of the trailing electrode is 35 mm or less, the arc force becomes sufficient to completely eliminate ghost lines, and the arc is stabilized, so that the amount of spatter generated can be reduced. The wire extension length of the trailing electrode is more preferably 33 mm or less, and even more preferably 31 mm or less.

<Welding conditions>
(Distance D between leading and trailing electrodes: 40 mm or more and 65 mm or less)
In this embodiment, the electrode distance D between the leading electrode and the trailing electrode is not particularly limited, but when the electrode distance D is set within an optimal range, the molten pool can be kept at an appropriate size, strain in the weld metal can be reduced, and the occurrence of hot cracking can be prevented. Furthermore, when the electrode distance D is an appropriate distance, the occurrence of slag in the front bead can be further suppressed. From the viewpoint of maintaining the size of the molten pool within an appropriate range and obtaining excellent hot cracking resistance, and from the viewpoint of suppressing slag in the front bead, the electrode distance D between the leading electrode and the trailing electrode is preferably 40 mm or more, and more preferably 50 mm or more.
From the viewpoint of obtaining excellent hot cracking resistance, the inter-electrode distance D between the leading electrode and the trailing electrode is preferably 65 mm or less, and more preferably 60 mm or less.

(Group width G: 0 mm or more and 3 mm or less)
In this embodiment, the root gap, i.e., the groove width G, is not particularly limited, but it is preferable that the groove width G is in the range of 0 mm or more and 3 mm or less, since this allows both an excellent back bead shape and arc stability to be achieved.

(Welding speed: 400 mm/min to 700 mm/min)
In this embodiment, the welding speed is not particularly limited, but is preferably 400 mm/min or more and 700 mm/min or less. By setting the welding speed at 400 mm/min or more, an appropriate heat input can be obtained, so that a good back bead shape can be obtained and the occurrence of defects such as peeling of the backing material can be suppressed. The welding speed is more preferably 450 mm/min or more, and even more preferably 500 mm/min or more.
Furthermore, by setting the welding speed at 700 mm/min or less, the cooling rate of the weld metal does not become too fast, and the occurrence of hot cracks can be further suppressed. The welding speed is more preferably set at 680 mm/min or less, and even more preferably set at 650 mm/min or less.

(Thickness of plate: 40mm or less)
In this embodiment, the thickness of the plate material to be welded is not particularly limited, but if the thickness is 40 mm or less, the occurrence of angular distortion due to welding heat input can be suppressed and the occurrence of hot cracks can be further prevented. Therefore, the thickness of the plate material is preferably 40 mm or less, and more preferably 35 mm or less.
In addition, in this embodiment, since the filling height h of the groove filler is set, it is preferable that the plate thickness of the plate material be thicker than the filling height h, and it is more preferable that the plate thickness be at least twice the filling height.
In this embodiment, the plate material is a steel plate.

(Groove shape, groove angle)
In this embodiment, the shape of the groove formed between the pair of plate materials is not particularly limited, and various shapes of grooves such as V-shape, I-shape, L-shape, U-shape, X-shape, H-shape, etc. may be used. In contrast, the one-sided welding method according to the present embodiment can be used. It is preferable that the groove shape is a V-shaped groove because a good back bead shape can be obtained. In addition, the groove angle is 25 When the angle is 35° or more, the occurrence of hot cracks can be further prevented, which is preferable, and when the angle is 35° or more, it is more preferable.

<Welding Wire Composition>
In the welding method according to the present embodiment, the components of the flux-cored wire or solid wire are not particularly limited and may be appropriately adjusted depending on the application. Suitable applications for this embodiment include welding of mild steel, high-tensile steel, low-temperature steel, or weathering steel. Therefore, it is preferable that the optional components of the flux-cored wire or solid wire are in the same range as the chemical composition range of the deposited metal specified in JIS Z 3313:2009, JIS Z 3312:2009 for mild steel, high-tensile steel, or low-temperature steel, or JIS Z 3320:2012 for weathering steel. In addition, components other than the elements specified in JIS Z 3313:2009 for mild steel, high tensile steel or low temperature steel, JIS Z 3312:2009, or JIS Z 3320:2012 for weathering steel may be further added to the flux-cored wire within the scope of common technical common knowledge according to any application, thereby adjusting mechanical properties and improving welding workability.

In addition, suitable compositions for the alloy components of solid wires used for mild steel, high tensile steel, low temperature steel, weathering steel, etc., and flux-cored wires excluding the slag formers described below, are, for example, in mass % relative to the total mass of the wire, C: 0.5 mass % or less, Si: 2.0 mass % or less, Mn: 3.0 mass % or less, Ni: 5.0 mass % or less, Mo: 3.0 mass % or less, W: 3.0 mass % or less, Nb: 3. It is preferable that the contents of these elements are 0 mass% or less, V: 3.0 mass% or less, Cr: 5.0 mass% or less, Ti: 3.0 mass% or less, Al: 3.0 mass% or less, Mg: 3.0 mass% or less, N: 0.05 mass% or less, S: 0.05 mass% or less, P: 0.05 mass% or less, B: 0.005 mass% or less, Cu: 2.0 mass% or less, Ta: 3.0 mass% or less, REM: 0.1 mass% or less, and alkali metals: 3 mass% or less.
In addition, unless otherwise specified, these elements are also included in the amount of 0 mass %. Furthermore, flux-cored wires generally used for mild steel, high-tensile steel, low-temperature steel, weathering steel, etc. have an outer sheath made of an Fe-based alloy.

The alloy components of the solid wire or flux-cored wire that can be used in this embodiment will be described in more detail below, along with the reasons for their limitations. The content of each component is expressed as mass% relative to the total mass of the solid wire or flux-cored wire, unless otherwise specified. In addition, in the flux-cored wire, the non-metallic components such as C, P, and S and metallic components specified below are based on the metal powder contained in the hoop (metal band) and flux of the flux-cored wire, compounds excluding slag formers, etc.

(C: 0.5% by mass or less)
C is an element that affects the strength of the weld metal, and the higher the content, the higher the strength. It satisfies the strength range required for commonly used steel types such as mild steel, high tensile steel, and low temperature steel. For this reason, the C content in the wire is preferably 0.5 mass % or less, and more preferably 0.2 mass % or less. , preferably 0.001 mass % or more.

(Mn: 3.0% by mass or less)
Mn is an element that affects the strength and toughness of the weld metal. In order to satisfy the mechanical properties required for commonly used steel types such as mild steel, high tensile steel, and low temperature steel, Mn is added to the wire. The Mn content is preferably 3.0 mass% or less, and more preferably 2.5 mass% or less, while the Mn content is preferably 0.5 mass% or more. .

(Si: 2.0% by mass or less)
Silicon acts as a deoxidizer for the weld metal, reducing the oxygen content in the weld metal and contributing to improving toughness. In order to satisfy the mechanical properties required for the steel type used, the Si content in the wire is preferably 2.0 mass% or less, more preferably 1.2 mass% or less, and more preferably 1.0 mass% or less. It is more preferable that the Si content is 0.0 mass% or less. On the other hand, the Si content is preferably 0.1 mass% or more.

(Ni: 5.0% by mass or less)
Ni is a component that stabilizes the austenitic structure of the weld metal and improves the toughness at low temperatures, and is also a component that can adjust the amount of crystallization of the ferrite structure. The Ni content is preferably 0% by mass or less, and more preferably 3.0% by mass or less. On the other hand, when used for welding low-temperature steels, the Ni content is 0.20% by mass or more. It is preferable.

(Mo: 3.0% by mass or less)
Mo is an element that improves high-temperature strength and pitting corrosion resistance. In order to satisfy the mechanical properties required for commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, Mo in the wire is The content of Mo is preferably 3.0 mass% or less, and more preferably 2.0 mass% or less. On the other hand, when used for welding high tensile steel, heat resistant steel, etc., the content of Mo is The amount is preferably 0.10% by weight or more.

(W: 3.0% by mass or less)
W is an ingredient that improves high-temperature strength and pitting corrosion resistance. In order to satisfy the mechanical properties required for commonly used steel types such as mild steel, high-tensile steel, and low-temperature steel, the W content in the wire is The content is preferably 3.0 mass % or less, and more preferably 2.0 mass % or less.

(Nb: 3.0% by mass or less)
Nb is an element that affects mechanical properties such as strength. In order to satisfy the mechanical properties required for commonly used steel types such as mild steel, high tensile steel, and low temperature steel, Nb is added to the wire. The Nb content is preferably 3.0 mass % or less, and more preferably 2.0 mass % or less.

(V: 3.0% by mass or less)
V has the effect of improving the strength of the weld metal, but at the same time, it reduces the toughness and crack resistance. Therefore, the V content in the wire is preferably 3.0 mass% or less, and 2.0 mass% or less. It is more preferable that the content is 0.0 mass % or less.

(Cr: 5.0% by mass or less)
Cr is an element that affects the mechanical properties of the weld metal, such as its strength. In order to satisfy the mechanical properties required for commonly used steel types, such as mild steel, high-tensile steel, and low-temperature steel, The Cr content in the wire is preferably 5.0 mass% or less, and more preferably 3.0 mass% or less. When used in heat-resistant steel, the Cr content is It is preferably 0.10 mass % or more.

(Ti: 3.0% by mass or less)
Ti combines with C and N to refine the crystal grains and is a component that mainly improves the toughness of the weld metal. It is commonly used in steel types such as mild steel, high-tensile steel, and low-temperature steel. In the case where Ti is contained in the wire for the purpose of improving toughness, the Ti content in the wire is preferably 3.0 mass% or less, and more preferably 1.0 mass% or less. The Ti content is preferably 0.01 mass % or more.

(Al: 3.0% by mass or less)
Al is a deoxidizing component that reduces the amount of dissolved oxygen in the weld metal and reduces the occurrence of porosity defects. In the case where Al is contained in the wire for the purpose of improving toughness, the content of Al in the wire is preferably 3.0 mass % or less, and more preferably 1.0 mass % or less. The Al content is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and more preferably 0.10% by mass or more. It is more preferably at least % by mass.

(Mg: 3.0% by mass or less)
Mg, like Al, is a deoxidizing component and has the effect of reducing the amount of dissolved oxygen in the weld metal and decreasing the occurrence of porosity defects.
In this embodiment, the Mg content in the wire may be 0 mass %. However, in commonly used steel types such as mild steel, high tensile steel, and low temperature steel, the wire may be made of 0 mass % Mg in order to improve toughness. When Mg is contained in the wire, the content of Mg in the wire is preferably 3.0 mass% or less, more preferably 1.0 mass% or less, and more preferably 0.5 mass% or less. The Mg content is preferably 0.01 mass% or more, and more preferably 0.10 mass% or more, and even more preferably 0.20 mass% or more, based on the total mass of the wire. More preferably, it is equal to or greater than this.

(N: 0.05% by mass or less)
N is an element that improves strength by dissolving in the crystal structure as an interstitial solid solution. On the other hand, N can also cause porosity defects such as blowholes and pits in the weld metal, so it is used in areas where strength is particularly required. Therefore, the N content in the wire is preferably 0.05 mass% or less, and more preferably 0.03 mass% or less. The N content is preferably 0.0010 mass % or more.

(S: 0.05% by mass or less)
S reduces the viscosity and surface tension of the droplets when the wire melts, facilitating droplet transfer, reducing the size of spatter and improving welding workability. S is an element that reduces cracking resistance. Therefore, the content of S in the wire is preferably 0.05 mass% or less, and more preferably 0.03 mass% or less. The amount is preferably at least 0.0005% by weight.

(P: 0.05% by mass or less)
Since P is an element that reduces the crack resistance and mechanical properties of the weld metal, the P content in the wire is preferably suppressed to 0.05 mass% or less, and more preferably 0.03 mass% or less. It is more preferable to do so.

(B: 0.005% by mass or less)
B is an element that prevents the deterioration of toughness due to nitrogen in the weld metal, but at the same time reduces crack resistance. Therefore, the content of B in the wire is preferably 0.005 mass% or less. In the case where B is contained in the wire for the purpose of ensuring toughness, the B content is preferably 0.0005% by mass or more.

(Cu: 2.0% by mass or less)
Cu is an element that contributes to improving the strength and weather resistance of the weld metal. It satisfies the strength and weather resistance required for commonly used steel types such as mild steel, high tensile steel, and low temperature steel. In order to secure the strength and weather resistance of the weld metal, the Cu content in the wire is preferably 2.0 mass % or less, and more preferably 1.0 mass % or less. When Cu is contained in the wire for this purpose, the Cu content is preferably 0.01 mass % or more.

(Ta: 3.0% by mass or less)
Ta is an element that affects mechanical properties such as strength. In order to satisfy the mechanical properties required for commonly used steel types such as mild steel, high tensile steel, and low temperature steel, the Ta content in the wire is The content is preferably 3.0 mass % or less, and more preferably 2.0 mass % or less.

(REM total: 0.1% by mass or less)
REM (Rare Earth Metals) refers to rare earth elements, such as Ce and La. REM has a high affinity with S, and is effective in suppressing grain boundary segregation of S and suppressing high-temperature cracking caused by S. On the other hand, since the arc stability is better as the amount of REM added is smaller, in order to satisfy the required crack resistance and arc stability, the total content of REM in the wire is 0.1 mass% or less. It is preferable to set the content to 0.05 mass % or less, and more preferable to set the content to 0.05 mass % or less.

(Total of alkali metals: 3% by mass or less)
The alkali metal element acts as an arc stabilizer. The alkali metal in this embodiment is based on metal powder and compounds containing one or more alkali metal elements. Examples of the alkali metal element include K, Li, and Na. The total content of alkali metals in the wire refers to the total content of alkali metals in the wire calculated from metal powder and compounds composed of alkali metal elements. The total content of alkali metals in the wire is preferably 3 mass% or less, and more preferably 2 mass% or less, based on the total mass of the wire, from the viewpoint of making it easier to adjust the melt properties to be favorable for improving the bead shape.

(Remainder: Fe and inevitable impurities)
In the present embodiment, when a solid wire is used as the leading electrode or the trailing electrode, the remainder other than the above elements is preferably Fe and unavoidable impurities. When using the above-mentioned elements and the slag forming agent, the balance is preferably Fe and unavoidable impurities.
The content of Fe, which is the balance, is preferably 80 mass % or more and 98 mass % or less. Impurities refer to elements that are not intentionally added, and elements other than those mentioned above are Examples of the impurities include Sn, Co, Sb, As, etc. When the above elements are contained as oxides, O is also contained in the balance. The total content of impurities in the wire is 0. It is preferably 5% by mass or less, and more preferably 0.3% by mass or less.

The flux-cored wire that can be used in this embodiment has an outer sheath filled with flux, and it is preferable that the outer sheath is formed from a cold-rolled steel strip from the standpoint of availability and economy. As the cold-rolled steel strip, it is preferable to use steel strips with the symbols SPCC, SPCD, SPCE, SPCF, SPCG, etc., of the types described in JIS G 3141:2017.

In addition, the flux-cored wire that can be used in this embodiment preferably contains a slag former in an amount of 2.5 mass % to 18.0 mass % based on the total mass of the wire. This range allows for better formation of a surface bead. The slag former preferably contains a metal oxide and a metal fluoride, with the remainder being unavoidable impurities.
The content of the slag former relative to the total mass of the wire is more preferably 3.0 mass% or more, and even more preferably 3.4 mass% or more, while the content of the slag former relative to the total mass of the wire is more preferably 15.0 mass% or less, even more preferably 13.0 mass% or less, and particularly preferably 10.5 mass% or less.

Examples of metal oxides that can be contained in _{the slag former include TiO2, SiO2, ZrO2, MnO, Al2O3 , Na2O , K2O , and Li2O} . Examples of metal fluorides that can be contained in the slag former include _K2SiF6 , NaF, _KF , _{CeF3 , Na3AlF6 , Na2SiF6 , AlF3} , _{MgF2 ,} and _K2ZrF6 . When these are added, it is preferable to adjust the melt properties of the molten slag within the following ranges, in mass % relative to the total mass of the flux-cored wire: _TiO2 : 1% or more and 10% or less, _SiO2 : 1% or more and 10% or less, _ZrO2 : 1% or more and 10% or less, _{Al2O3 :} 1 _% or more _and 10% or less, the total of _Na2O , _K2O and _Li2O : 0.5% or less, and the total of _K2SiF6 , _NaF , KF, _CeF3 , _{Na3AlF6 , Na2SiF6 , AlF3} , _MgF2 and _K2ZrF6 : 0.5% or less, which allows a good back bead shape to be obtained.

<Composition of backing flux>
In this embodiment, the backing flux may contain at least one of a metal powder and a slag former, with the remainder being unavoidable impurities. The backing flux may further contain at least one of a nonmetal powder and a nonmetal compound powder excluding the slag former. Examples of the metal powder include Fe powder, Si powder, Fe-Si powder, Fe-Mn powder, Fe-Al powder, and mixtures thereof. Examples of the nonmetal powder include graphite, and examples of the nonmetal compound powder excluding the slag former include carbides, nitrides, and sulfides excluding the slag former.

Backing flux includes metal type fluxes that contain 90% by mass or more of metal powder based on the total mass of the backing flux, and slag-positively-added fluxes that contain more than 10% by mass of a slag-forming agent based on the total mass of the backing flux, and these can be used appropriately depending on the application. Note that since metal type fluxes have the effect of reducing oxygen in the weld metal, if the mechanical performance of the weld metal is important, metal type fluxes should be selected, and if the back bead shape and slag removability are important, slag-positively-added fluxes should be selected.
Below, we will explain about metal type flux and slag positively added flux.

<Metal type flux>
The remaining 10% by mass or less of the metal powder contained in the metal type flux may be optionally added with a slag former, nonmetallic powder, or nonmetallic compound powder other than the slag former, and the remainder other than these may be impurities. If the slag removability is to be improved, the amount of the slag former, which will be described in detail later, may be adjusted to less than 10% by mass, and if the mechanical performance is to be improved, the amount of the nonmetallic powder and nonmetallic compound powder other than the slag former may be adjusted to a total amount of 5% by mass or less. In other words, the slag former, nonmetallic powder, and nonmetallic compound powder other than the slag former are not essential, and may be metal powder and the remaining impurities. The main elements constituting the nonmetallic powder and nonmetallic compound powder other than the slag former include C, N, S, etc., and more preferably, the total amount of C, N, and S may be adjusted to a range of 5% by mass or less.

The elements contained in the metal powder preferably include Si, more preferably include Mn and Fe, and even more preferably are composed of only Si, Mn, and Fe. Next, the Si, Mn, and Fe contained in the metal powder will be described in detail.

(Si in backing flux: 0.3 mass% or more and 50 mass% or less)
When the backing flux contains Si, the shape of the back bead can be stabilized, and the appearance can be made smooth. When the content of Si based on the Si powder and the Fe-Si powder contained as metal powder in the backing flux is 0.3 mass% or more with respect to the total mass of the backing flux, the appearance of the back bead can be improved. Therefore, the content of Si in the backing flux is preferably 0.3 mass% or more, more preferably 0.5 mass% or more with respect to the total mass of the backing flux.

On the other hand, if the content of Si based on the Si powder and Fe-Si powder contained as metal powder in the backing flux is 50 mass% or less relative to the total mass of the backing flux, it is possible to reduce surface cracks that occur due to an excessive amount of Si contained in the back bead. Therefore, the content of Si in the backing flux is preferably 50 mass% or less relative to the total mass of the backing flux, more preferably 25 mass% or less, and even more preferably 10 mass% or less.

(Mn in backing flux: 50% by mass or less)
Mn has the effect of improving hardenability and is an effective component for improving mechanical performance. Therefore, in the backing flux according to the present embodiment, Mn may be added as necessary to adjust the mechanical performance, and there is no particular restriction on the lower limit. In addition, in consideration of the adjustment of the mechanical performance assumed for application to mild steel, high tensile steel, or low temperature steel, it is preferable to adjust the range to 50 mass% or less. Note that Mn can be added to the flux in the form of an alloy such as Fe-Mn, in addition to Mn alone.

(Fe in backing flux: 99.5 mass% or less)
Since Fe can increase the apparent density of the flux, when dust generation resistance is required, Fe may be added as necessary, and there is no particular lower limit. Since Fe can also reduce the alloy cost of the weld metal, the remaining metal powder except for the above-mentioned Si and Mn may be Fe from the viewpoint of cost. As described above, when Si is 0.3 mass% or more, the appearance of the back bead can be improved, so from the viewpoint of the appearance of the back bead, it can be said that it is preferable that Fe is at least 99.7 mass% or less.
Incidentally, Fe can be added to the backing flux in the form of an alloy such as Fe--Mn or Fe--Si, in addition to simple Fe.

In addition, in this embodiment, the backing flux may contain a slag former in addition to the metal powder. When the backing flux contains a slag former, the back bead is protected by the slag, and after the slag is peeled off, a glossy and good appearance can be obtained. It is preferable that the slag former contains a metal oxide and a metal fluoride, with the remainder being unavoidable impurities.

Examples of metal oxides that can be contained in the slag former include _TiO2 , MgO, _SiO2 , _ZrO2 , _MnO2 , _Al2O3 , _Na2O , _K2O , and _{Li2O .} Examples of metal fluorides that can be contained in the slag former include _K2SiF6 , _NaF , _KF , _CeF3 , _Na3AlF6 , _{Na2SiF6 , AlF3} , _MgF2 , _{and K2ZrF6} . In addition, when a slag positively added flux described later is used, the mass % relative to the total mass of the backing flux is as follows: TiO ₂ : 2.00% or more and 16.00% or less, MgO: 2.00% or more and 16% or less, MnO ₂ : 0.10% or more and 1.00% or less, SiO ₂ : 5.00% or more and 25.00% or less, ZrO ₂ : 3.00% or more and 9.00% or less, Al ₂ O ₃ : 0.50% or more and 9.00% or less, the sum of Na ₂ O, K ₂ O and Li ₂ O: 3.00% or less, K ₂ SiF ₆ , NaF, KF, CeF ₃ , Na ₃ AlF ₆ , Na ₂ SiF ₆ , AlF ₃ , MgF ₂ and K ₂ ZrF The total amount of metal fluorides such as ₆ , etc. is preferably 35.00% or less.

<Flux with active addition of slag>
The higher the content of the slag former in the backing flux, the better the slag removability. Therefore, when a slag-positively-added flux is used as the backing flux, the content of the slag former in the backing flux is preferably more than 10 mass% with respect to the total mass of the backing flux, and more preferably 14.0 mass% or more. There is no particular upper limit to the content of the slag former, but as components other than the slag former, metal powder, nonmetallic elements, and nonmetallic compound powders other than the slag former may be added as necessary. For example, as described above, it is preferable from the viewpoint of stabilizing the back bead shape that the content of Si contained in the metal powder is 0.3 mass% or more with respect to the total mass of the backing flux, so if both slag removability and stabilization of the back bead shape are desired, the content of the slag former should be 99.7 mass% or less. Details of the elements contained in the metal powder, the slag former, and the like are the same as those described in detail in the above-mentioned metal-based flux, and the effects are the same.

Furthermore, in the present embodiment, when the backing flux contains the above-mentioned slag forming agent, the backing flux is preferably made by kneading the raw material with water glass, forming it into granules, and then sintering it. Fine powder-like backing flux may scatter and deteriorate the working environment, and may also segregate due to vibration, causing bias in the welding result.
On the other hand, backing flux obtained by forming into granules and then sintering is less likely to scatter and segregate, and therefore can be preferably used.

[2. Manufacturing method of welded joint]
The method for manufacturing a welded joint according to this embodiment is a method for manufacturing a welded joint using the welding method described above in [1. One-sided welding method].
The filling height h of the groove filler, the pressing pressure of the backing flux, the welding current of the leading electrode, and the ratio of the average welding current to the average arc voltage, as well as the type and composition of the wire used, the composition of the backing flux, and the welding conditions are as described in [1. One-sided welding method] above.

The present invention will be described in detail below with examples and comparative examples, but the present invention is not limited to these.

[1. One-sided welding]
(1-1. Preparation of the welded material, wire and backing flux)
Two SM490A steel plates were prepared as materials to be welded.
A solid wire having a wire diameter of 1.4 mm was prepared as the wire of the leading electrode, and a flux-cored wire having a wire diameter of 1.4 mm was prepared as the wire of the trailing electrode. Furthermore, a backing flux and a groove filler were prepared. The type of solid wire as the leading electrode is shown in Table 1 below, and the composition of the flux-cored wire as the trailing electrode is shown in Table 2 below. The composition of the backing flux is shown in Table 3 below. In this example, a powder filler containing 99.1 mass% Fe, 0.85 mass% Mn, and the remainder being impurities, etc. was used as the groove filler.

In addition, in Table 3, in addition to Mn and Si, Fe is also contained in the range of 99.5 mass% or less as components other than the slag forming agent, but this is not listed in the table. In addition to the components listed in the table, the components of the backing flux also contain unavoidable impurities.
A steel strip corresponding to the symbol SPCG of the type described in JIS G 3141:2017 was used as the outer sheath of the flux-cored wire shown in Table 2. The contents of the components contained in the SPCG steel strip are C: 0.02 mass% or less, Mn: 0.25 mass% or less, P: 0.020 mass% or less, and S: 0.020 mass% or less.

(1-2. One-sided welding)
As shown in Figures 1 to 3, a V-groove with a groove angle of 40° was formed in a pair of steel plates 1a and 1b, and the plates were horizontally butted together with a groove width G of 0 mm. Next, backing flux 11 was placed under the groove 2, and the backing flux 11 was pressed toward the back side of the groove 2 with a pressing pressure P by an air hose 13. In addition, the groove 2 was filled with a groove filler 6.
Then, a solid wire 7a was used as the leading electrode, and a flux-cored wire 8a was used as the trailing electrode following the leading electrode, and the leading and trailing electrodes were moved simultaneously in the welding direction while maintaining a predetermined distance. At this time, the polarity of the leading and trailing electrodes was DCEP, and the shielding gas was 100% _CO2 gas. The torch angle of the leading electrode was 90°, the weaving width was 1 mm, and the torch angle of the trailing electrode was 80°, and the weaving width was 5 mm.
In this manner, the weld metal 3 was formed in the groove 2, and the steel plates 1a and 1b were joined together.

The conditions for the leading and trailing electrodes are shown in Table 4 below, and other welding conditions are shown in Table 5 below. Note that the "amount of filler sprayed" in Table 5 refers to the area occupied by the groove filler on a plane perpendicular to the weld line direction.

2. Evaluation
The front surface (welded surface) and back surface of the joint after the above-mentioned one-side welding were observed, and the appearance of the joint was evaluated in terms of the various items shown below.

(2-1. Back bead shape)
The bead shape on the back surface of the joint was visually observed.
The evaluation criteria were as follows: "A" (excellent) was obtained when a convex back bead was obtained and the height of the bead protruding from the back side of the welded material was 0.5 mm or more and less than 5 mm, "B" (good) was obtained when the height of the bead was 0 mm or more and less than 0.5 mm, and "C" (poor) was obtained when a convex back bead was not obtained and the height of the bead was 5 mm or more.

(2-2. Pore defects on the back side)
The back surface of the joint was visually observed to evaluate the presence or absence of pore defects.
The evaluation criteria were as follows: "absent" (good) when no pore defects were observed on the back side, and "present" (bad) when pore defects were observed. In the "presence or absence of pore defects on the back side" column in Table 5, "-" indicates that evaluation was not possible because a back bead was not formed.
The results of each evaluation are shown in Table 5 below.

As shown in Tables 4 and 5, in the invention examples Nos. 1 to 9, the filling height h of the groove filler, the pressing pressure P of the backing flux, the average welding current of the leading electrode, and the ratio of the average welding current of the leading electrode to the average arc voltage (I _L (av)/V _L (av)) were within the numerical ranges specified in the present invention, so the evaluation results of the back bead shape were excellent or good, and no porosity defects were observed.

In particular, in Nos. 1, 3 and 5 to 9, the filling height h of the groove filler and (I _L (av)/V _L (av)) were all within the preferred ranges defined in the present invention, so the evaluation results for the back bead shape were excellent. In addition, in Nos. 1 to 8, the electrode distance was within the preferred range of the present invention, so the amount of slag on the surface of the front bead was appropriate.

On the other hand, in the comparative examples Nos. 10 to 20, at least one of the filling height h of the groove filler, the pressing pressure P of the backing flux, the average welding current of the leading electrode, and the ratio of the average welding current of the leading electrode to the average arc voltage (I _L (av)/V _L (av)) was outside the range specified in the present invention. Therefore, in some of the comparative examples, a back bead was not formed, and the evaluation result of the back bead shape was poor. Furthermore, even in the cases where a back bead was formed, porosity defects occurred.

In this way, it can be seen that the one-sided welding method according to the present invention and the method for manufacturing a welded joint according to the present invention can obtain an appropriate deposition amount and a good back bead shape, and can prevent porosity defects in the back bead.

1a, 1b Steel plate 2 Groove 3 Weld metal 4, 5 Slag 6 Groove filler 7a Solid wire 8a Flux-cored wire 9, 10 Shielding gas 11 Backing flux

Claims (12)

A one-sided welding method comprising the steps of: butting a pair of steel plates substantially horizontally to form a groove; disposing a backing flux from a lower side of the groove; filling the groove with a groove filler; and performing gas-shielded arc welding from an upper side of the groove using a plurality of electrodes arranged in a weld line direction,
The filling height of the groove filler is 4 mm or more and 6.5 mm or less ,
The pressing pressure for pressing the backing flux against the groove side is set to 0.05 Pa or more,
The average welding current of the most leading electrode is set to 440 A or more,
A single-sided welding method, characterized in that, when an average welding current of the leading electrode is expressed as I _L (av) and an average arc voltage of the leading electrode is expressed as V _L (av), I _L (av)/V _L (av) is 12.7 or more and 14.0 or less. The groove filler is at least one of a powder filler and a cut wire,
The one-sided welding method according to claim 1, characterized in that the groove filler contains 95 mass% or more of Fe with respect to the total mass of the groove filler. The one-sided welding method according to claim 1 or 2, characterized in that the pressing pressure is 0.07 MPa or more and 0.15 MPa or less. The leading electrode is a solid wire,
4. The one-sided welding method according to claim 1, wherein at least one of the electrodes, excluding the leading electrode, among the plurality of electrodes is a flux-cored wire. The plurality of electrodes are configured by two electrodes, the leading electrode and a trailing electrode following the leading electrode,
The one-sided welding method according to any one of claims 1 to 4, characterized in that the polarities of the leading electrode and the trailing electrode are both DCEP. The one-sided welding method according to claim 5, characterized in that the electrode distance between the leading electrode and the trailing electrode is 40 mm or more and 65 mm or less. The torch angle of the leading electrode is set to 45° or more and 110° or less with respect to the welding direction,
7. The method according to claim 5, wherein the angle of the torch of the trailing electrode is set to be 90° or more and 135° or less with respect to the welding proceeding direction. The welding current of the trailing electrode is set to 250 A or more and 400 A or less,
The one-sided welding method according to any one of claims 5 to 7, characterized in that the average arc voltage of the trailing electrode is 28 V or more. The one-sided welding method according to any one of claims 5 to 8, characterized in that at least one of the leading electrode and the trailing electrode is weaved in the width direction relative to the welding progress direction. The backing flux is
Contains at least one of a metal powder and a slag former,
The one-sided welding method according to any one of claims 1 to 9, characterized in that the balance is unavoidable impurities. The backing flux further comprises:
The method for one-sided welding according to claim 10, further comprising the step of: adding at least one of a non-metallic powder and a non-metallic compound powder excluding a slag former. A method for manufacturing a welded joint, characterized in that the welded joint is manufactured using the one-sided welding method described in any one of claims 1 to 11.

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