JP7043485B2 - Welding method and welded joint - Google Patents

Description

The present invention relates to a welding method and a welded joint.

Welding techniques such as the gas shield metal arc welding method are known as techniques for joining two steel plates to each other. In the gas shield metal arc welding method, an arc is generated between the wire and the two steel plates, and this arc becomes a heat source, the wire and the steel plates are melted, and the steel plates are welded to each other. Further, at this time, since the shield gas is supplied around the arc, welding can be performed in a state where the welded portion is isolated from the external environment.

Japanese Unexamined Patent Publication No. 6-79485

In the above welding technique, when an oxide film called black skin is present at the welded portion of the steel sheet, there may often be a problem that welding defects occur in the weld layer. In particular, when arc welding is performed with a large current, there is a high possibility that large defects such as pipe-shaped defects will occur.

Therefore, in order to prevent such welding defects, a process of removing the oxide film is usually carried out before the welding process (for example, Patent Document 1).

However, such a process of removing the oxide film is a factor that reduces the work efficiency of welding. Therefore, there is a demand for a technique capable of performing sound welding by an efficient method.

The present invention has been made in view of such a background, and an object of the present invention is to provide a welding method capable of suppressing large pipe-shaped defects without lowering work efficiency. Another object of the present invention is to provide a welded joint in which large pipe-shaped defects are significantly suppressed.

In the present invention, it is a welding method.
(1) A step of forming a first welding layer between a first member, a second member, and a backing plate by a first welding pass.
The first member has a first surface, the second member has a second surface, and the backing plate has an upper surface.
The first member and the second member are arranged so that the first surface and the second surface face or contact the upper surface of the backing plate.
The first weld layer is viewed from a cross section perpendicular to the extending direction of the first weld layer.
On the side of the first member, the intersection P1 with the _first surface of the first member, and on the side of the second member, the intersection P with the second surface of the second member. The process formed so as to intersect in ₂ and
(2) A step of forming a second welding layer on the first welding layer by the second welding pass, and
Have,
_{When a} straight line L passing through the intersection P1 and the intersection P2 is drawn,
The second weld layer is arranged so that the tip in the depth direction is introduced into the backing plate beyond the straight line L.
The second weld layer intersects the straight line L at intersections _Q1 and _Q2 , and the intersection _Q1 is closer to the first member than the intersection _Q2 .
The intersection _Q1 is inside the _first weld layer or coincides with the intersection P1.
A welding method is provided in which the intersection _Q2 is inside the _first weld layer or coincides with the intersection P2.

Further, in the present invention, it is a welded joint in which the first member, the second member and the backing plate are joined to each other by a welded portion.
The first member has a first surface and has a first surface.
The second member has a second surface and has a second surface.
The first member and the second member are arranged so that the first surface and the second surface face or contact the upper surface of the backing plate.
The weld has a first weld layer and a second weld layer from the side closer to the backing plate in the depth direction.
When the welded portion is viewed from a cross section perpendicular to the extending direction of the welded portion,
The first weld layer intersects the first surface of the _first member at an intersection P1 on the side of the first member, and on the side of the second member, of the second member. It intersects with the _second surface at the intersection P2,
_{When a} straight line L passing through the intersection P1 and the intersection P2 is drawn,
The second weld layer is arranged so that the tip in the depth direction is introduced into the backing plate beyond the straight line L.
The second weld layer intersects the straight line L at intersections _Q1 and _Q2 , and the intersection _Q1 is closer to the first member than the intersection _Q2 .
The intersection _Q1 is inside the _first weld layer or coincides with the intersection P1.
A welded joint is provided in which the intersection _Q2 is inside the _first weld layer or coincides with the intersection P2.

INDUSTRIAL APPLICABILITY The present invention can provide a welding method capable of suppressing large pipe-shaped defects without lowering work efficiency. Further, the present invention can provide a welded joint in which large pipe-shaped defects are significantly suppressed.

It is a figure which showed the example of the conventional welding method schematically. It is a schematic perspective view of the welded joint by one Embodiment of this invention. It is a schematic cross-sectional view along the line AA of the welded joint shown in FIG. It is a figure which showed schematically the cross section of the 1st weld layer and its vicinity. It is sectional drawing which shows typically one aspect of the unsuitable welded part in a welded joint. It is sectional drawing which shows typically one aspect of the unsuitable welded part in a welded joint. It is sectional drawing which shows typically one aspect of the appropriate welded part in a welded joint. It is a figure which showed typically the flow of the welding method by one Embodiment of this invention. It is a figure which showed roughly one step of the welding method by one Embodiment of this invention. It is a figure which showed roughly one step of the welding method by one Embodiment of this invention. It is a figure which showed roughly one step of the welding method by one Embodiment of this invention. In Example 1, it is a photograph which showed an example of the cross section of the part to be welded after the first welding pass. In Example 1, it is a photograph which showed an example of the cross section of the welded part after the second welding pass. It is a photograph which showed an example of the cross section of the welded part obtained in Example 2. It is a photograph obtained by cutting the welded portion obtained in Example 2 along the vicinity of the weld bead and taking a transmitted X-ray photograph from the side surface of the bead.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

(Problems with conventional welding methods)
In order to better understand the features of the present invention, first, the problems of the conventional welding method will be briefly described with reference to FIG.

FIG. 1 schematically shows an example of a conventional welding method.

When carrying out the conventional welding method, first, as shown in FIG. 1A, a first steel plate 20, a second steel plate 30, and a backing plate 40 are prepared. Further, these members are arranged in a predetermined relationship.

The first steel plate 20 has an inclined end face 26, and the second steel plate 30 has an inclined end face 36. The first steel plate 20 and the second steel plate 30 are arranged on the backing plate 40 so that the inclined end faces 26 and 36 face each other.

Next, in such an arrangement state, the first welding pass is performed between the inclined end face 26 and the inclined end face 36. As a result, the weld layer 50 as shown in FIG. 1 (b) is formed.

Here, if an oxide film is present at or near the welded portion of the first steel plate 20, the second steel plate 30, and the backing plate 40, defects may often occur in the weld layer 50.

In particular, when the heat input energy during welding is large, for example, when arc welding is performed with a large current exceeding 500 A, a worm hole as shown in FIG. 1 (b) is formed inside the weld layer 50. A so-called pipe-shaped defect 70 can occur. Here, the "pipe-shaped defect" means an elongated tubular cavity defect generated in the weld metal due to outgassing.

Such a pipe-shaped defect 70 may adversely affect the characteristics of the welded layer 50. Therefore, usually, before the welding treatment, a treatment for removing the oxide film existing on the first steel plate 20, the second steel plate 30, and the backing plate 40 is performed.

However, such a treatment for removing the oxide film has a problem that it becomes a factor of lowering the work efficiency of welding.

(Welded joint according to one embodiment of the present invention)
Next, a welded joint according to an embodiment of the present invention will be described with reference to FIGS. 2 and 3. FIG. 2 shows a schematic perspective view of a welded joint (hereinafter referred to as “first welded joint”) according to an embodiment of the present invention. Further, FIG. 3 shows a schematic cross-sectional view taken along the line AA of the first welded joint shown in FIG.

As shown in FIG. 2, the first welded joint 100 includes a first member 120, a second member 130, a backing plate 140, and a welded portion 150 between the first member 120 and the second member 130. Has.

The first member 120 has a first surface 122 and a second surface 124 facing each other, and an end surface 126 connecting both surfaces. Further, the second member 130 has a third surface 132 and a fourth surface 134 facing each other, and an end surface 136 connecting both surfaces.

In the example shown in FIG. 2, the welded portion 150 is not formed on the entire surface of the end face 126 and the end face 136, and as a result, a part of the end face 126 and the end face 136 is visually recognized.

However, unlike this, the weld 150 may be formed to cover the entire surface of the end face 126 and the end face 136. In this case, the end face 126 and the end face 136 cannot be visually recognized.

In the first welded joint 100, the first member 120 and the second member 130 are arranged so that both end faces 126 and 136 face each other. Further, the first member 120 and the second member 130 are arranged so that the first surface 122 and the third surface 132 are oriented in the same direction (upward).

The backing plate 140 has an upper surface 142. The backing plate 140 is arranged below the welded portion 150 so that the upper surface 142 faces or contacts the second surface 124 of the first member 120 and the fourth surface 134 of the second member 130. Weld.

In the first welded joint 100, the first member 120, the second member 130, and the backing plate 140 are joined to each other by the welded portion 150.

As shown in FIG. 3, the weld 150 has a first weld layer 151 and a second weld layer 152 from the side closer to the backing plate 140 in the depth direction (Z direction in FIG. 3). The first welded layer 151 extends in the depth direction beyond the upper surface 142 of the backing plate 140 and to the inside of the backing plate 140. Similarly, the second weld layer 152 extends in the depth direction beyond the upper surface 142 of the backing plate 140 and into the inside of the backing plate 140.

Here, in order to facilitate the following description, the names of the welded portions 150 in the first welded joint 100, particularly the names of the respective portions of the first welded layer 151 will be described with reference to FIG.

FIG. 4 schematically shows a cross section of the first weld layer 151 and its vicinity.

In addition, in FIG. 4, the first welding layer 151 is schematically shown as a state before forming the second welding layer 152, and therefore, the first welding layer 151 is shown in FIG. It has a cross-sectional shape different from that of the welding layer 151 of 1. Further, in FIG. 4, the broken line in the first welding layer 151 shows the approximate contour lines of the first member 120, the second member 130, and the backing plate 140 before welding. There is.

In FIG. 4, the horizontal direction (X direction) is referred to as "width direction (of the weld layer)", and the vertical direction (Z direction) is referred to as "depth direction (of the weld layer)". The width direction is positive for the right direction, and the depth direction is positive for the downward direction.

As shown in FIG. 4, the first weld layer 151 is formed so as to join the respective members of the first member 120, the second member 130, and the backing plate 140.

As a result, the first welding layer 151 intersects the second surface 124 of the first member ₁₂₀ at the intersection P1 on the side of the first member 120 (left side in FIG. 4), and the upper surface of the backing plate 140 It intersects 142 at the intersection _P3 .

Further, the first welding layer 151 intersects with the fourth surface 134 of the _second member 130 at the intersection P2 on the side of the second member 130 (on the right side in FIG. 4), and the upper surface 142 of the backing plate 140 And at the intersection _P4 .

In the example shown in FIG. 4, between the second surface 124 of the first member 120 and the upper surface 142 of the backing plate 140, and between the fourth surface 134 and the backing plate 140 of the second member 130. There is a gap between the upper surface 142 and the upper surface 142. However, as another embodiment, the second surface 124 of the first member 120 and the upper surface 142 of the backing plate 140, and the fourth surface 134 of the second member 130 and the upper surface 142 of the backing plate 140 come into contact with each other. It may be. In that case, the intersection P ₃ = the intersection P ₁ and the intersection P ₄ = the intersection P ₂ .

In the _first weld layer 151, the region from the intersection P1 to the intersection P3 is referred to as the " _first intersection region (160)", and the region from the intersection P2 to the intersection P4 is referred to as the " _second intersection region ₍ 160)". 162) ”. Further, in the first welding layer 151, the maximum position in the depth direction (Z direction) is referred to as "tip (164)".

When the intersection point P ₃ = the intersection point P ₁ , the first intersection region 160 becomes a dot shape when viewed from a cross section as shown in FIG. However, even in that case, the first intersection region 160 extends in the depth direction (direction perpendicular to the paper surface). The same applies to the case of intersection P ₄ = intersection P ₂ .

The pipe-shaped defect 70 as shown in FIG. 1 (b) above tends to occur starting from the first intersection region 160 and / or the second intersection region 162.

Here, the first welded joint 100 has the following characteristics when the welded portion 150 is viewed from a cross section (XZ plane in FIG. 4) perpendicular to the extending direction of the welded portion:
( ₁ ) When a straight line L passing through the intersection P1 and the intersection P2 is drawn, the tip of the _second weld layer 152 in the depth direction is introduced into the backing plate 140 beyond the straight line L. And (2) the second weld layer 152 intersects the straight line L at the intersection _Q1 and the intersection _Q2 , and the intersection _Q1 is closer to the first member than the intersection _Q2 . Yes, the intersection _Q1 is inside the _first weld layer 151 or coincides with the intersection P1, and the intersection _Q2 is inside the _first weld layer 151 or coincides with the intersection P2.

Hereinafter, the effects of these features will be described with reference to FIGS. 5 to 7.

5 to 7 show a cross section of the first weld layer that can be formed by the first weld pass and a cross section of the second weld layer that can be formed by the second weld pass in an overlapping manner.

In reality, since a part of the first welding layer is melted by the second welding pass, the shape of the first welding layer changes after the second welding pass. Therefore, FIGS. 5 to 7 schematically show a cross section of the first weld layer before performing the second weld pass.

In particular, FIGS. 5 and 6 show inappropriate weld morphologies, and FIG. 7 shows suitable weld morphologies.

Further, in FIGS. 5 to 7, in order to avoid complicating the drawings, the first member 120 and the backing plate 140, and the second member 130 and the backing plate 140 are in contact with each other (in order to avoid complications). That is, it is shown with no gap).

First, referring to FIG. 5, the first weld layer 151 has a first crossing region 160 and a second crossing region 162. Since FIG. 5 is a cross-sectional view, these intersection regions ₁₆₀ and 162 _are shown as intersection points P1 and intersection points P2, respectively.

As mentioned above, pipe-like defects tend to occur starting from the first intersection region 160 and / or the second intersection region 162. Therefore, FIG. 5 schematically shows the pipe-shaped defect 170 extending from the first crossing region 160 and the second crossing region 162.

The second welding layer 152A is formed by carrying out the second welding pass after the formation of the first welding layer 151 by the first welding pass. The second weld layer 152A has a tip 168A.

Here, in the example shown in FIG. 5, when _a straight line L passing through the intersection P1 and the intersection P2 is drawn, the tip 168A of the _second weld layer 152A does not reach the straight line L. That is, the above-mentioned feature (1) is not satisfied.

When the second weld layer 152A is formed in such an embodiment, the pipe-shaped defects 170 contained in the first weld layer 151 remain as they are or are hardly shortened even after the second welding pass. It is more likely to remain. As a result, there is a high possibility that large pipe-shaped defects 170 will remain after the welding process is completed.

Next, referring to FIG. 6, in this example, after the formation of the first welding layer 151, the second welding layer 152B is formed by the second welding path.

As described above, the first weld layer 151 has an intersection P1 and an intersection P2 corresponding to the _first intersection 160 and the _second intersection 162, respectively.

The second weld layer 152B has a tip 168B. Further, the second weld layer 152B is in contact with the second surface 124 of the first member 120 at the intersection _Q1 in the width (X) direction, and is in contact with the fourth surface 134 of the _second member 130 at the intersection Q2. It is formed so as to touch with.

In the example shown in FIG. 6, when a straight line L passing through the intersection P1 and the intersection P2 of the _first welding layer 151 is drawn, the tip 168B of the _second welding layer 152B has a straight line L in the depth direction. It is formed so as to exceed and be introduced into the backing plate 140.

That is, the second weld layer 152B satisfies the above-mentioned feature (1).

When the second weld layer 152B is formed in this way, at least a part of the pipe-shaped defects 170 existing in the first weld layer 151 can be remelted during the second welding pass. Therefore, after the second weld pass, the pipe-like defects 170 in the first weld layer 151 are shortened, and as a result, there is a high possibility that the pipe-like defects 170 can be removed or reduced.

However, in the _second weld layer 152B, the intersection _Q1 with the straight line L is on the left _side (-X direction) of the intersection P1, and the intersection _Q2 with the straight line L is on the right side of the intersection P2 (in the −X direction). It is formed so as to be in the + X direction).

That is, in the second welding layer 152B, the intersection _Q1 and the intersection _Q2 are both outside the first welding layer 151, and the above-mentioned feature (2) is not satisfied.

In such an embodiment, at the time of the second welding pass, the intersection _Q1 becomes a new intersection region 180B, and the intersection _Q2 becomes a new intersection region 182B. That is, there is a high possibility that a new pipe-shaped defect 171 will occur in the second weld layer 152B starting from the new intersection regions 180B and 182B.

On the other hand, referring to FIG. 7, in this example, after the formation of the first welding layer 151, the second welding layer 152C is formed by the second welding path.

As described above, the first weld layer 151 has an intersection P1 and an intersection P2 corresponding to the _first intersection 160 and the _second intersection 162, respectively.

The second weld layer 152C has a tip 168C.

Here, in the example shown in FIG. 7, when _a straight line L passing through the intersection P1 and the intersection P2 is drawn as described above, the tip 168C of the _second weld layer 152C forms a straight line L in the depth direction. It is formed so as to exceed and be introduced into the backing plate 140.

That is, the second weld layer 152C satisfies the above-mentioned feature (1).

In this case, at least a part of the pipe-shaped defect 170 existing in the first welding layer 151 can be remelted during the second welding pass. Therefore, after the second weld pass, the pipe-like defects 170 in the first weld layer 151 are shortened, and as a result, there is a high possibility that the pipe-like defects 170 can be removed or reduced.

Further, in the example shown in FIG. 7, in the second welding layer 152C, the intersection _Q1 with the straight line L is on the right _side (+ X direction) of the intersection P1, and the intersection _Q2 with the straight line L is. It is formed so as to be on the left _side (-X direction) of the intersection P2.

That is, in the second welding layer 152C, the intersection _Q1 and the intersection _Q2 are both inside the first welding layer 151, and the above-mentioned feature (2) is satisfied.

In such an embodiment, it is possible to prevent the intersection _Q1 and the intersection Q2 from creating a new intersection region in the _second weld layer 152C during the second welding pass. When the intersection _Q1 and the intersection _Q2 are formed inside the first weld layer 151, the second weld layer 152C has the first member 120, the second member 130, and the backing plate on the straight line L. This is because it does not come into contact with any of 140.

Therefore, in the embodiment shown in FIG. 7, it is unlikely that a new pipe-shaped defect starting from a new intersection region will occur in the second weld layer 152C.

As described above, when the second weld layer 152C is formed so as to satisfy both the above-mentioned features (1) and (2), the pipe-shaped defect 170 existing in the first weld layer 151 is shortened. The pipe-shaped defect 170 can be significantly removed or reduced. Further, it is possible to avoid the occurrence of a new crossing region due to the formation of the second weld layer 152C.

Therefore, in the first welded joint 100 having both the above-mentioned features (1) and (2), it is possible to significantly suppress large pipe-shaped defects.

(Each member included in the welded joint according to the embodiment of the present invention)
Next, the features and configurations of each member included in the welded joint according to the embodiment of the present invention will be described in more detail.

Here, for the sake of clarification, the reference numerals shown in FIGS. 2 to 4 and 7 are used to represent each member.

(First member 120 and second member 130)
The shape of the first member 120 is not particularly limited as long as it is plate-shaped. For example, in the first member 120, the first surface 122 and the second surface 124 may have curved surfaces. The thickness of the first member 120 may be, for example, in the range of 6 mm to 60 mm.

The material of the first member 120 is not particularly limited, but may be, for example, a steel material such as carbon steel.

The same can be said for the second member 130. The first member 120 and the second member 130 may be made of the same material or different materials.

(Back plate 140)
The backing plate 140 may be made of, for example, the same material as the first member 120 or the second member 130.

The backing plate 140 may have a thickness of, for example, 6 mm to 22 mm.

(Welded portion 150)
The weld 150 is composed of a plurality of weld layers. The number of layers is not particularly limited as long as it is 2 or more.

The first weld layer 151 exists at the bottom of the weld 150 and forms an interface with each member of the first member 120, the second member 130, and the backing plate 140.

More specifically, when the welded portion 150 is viewed from a cross section perpendicular to the extending direction, the first weld layer 151 is on the side of the first member 120 as shown in FIG. 4 above. , It intersects with the second surface 124 of the _first member ₁₂₀ at the intersection P1 and intersects with the upper surface 142 of the backing plate 140 at the intersection P3. Further, the first weld layer 151 intersects with the _fourth surface 134 of the second member 130 at the intersection P2 on the side of the _second member 130, and intersects with the upper surface 142 of the backing plate 140 at the intersection P4. ..

The width W ₁ (see FIGS. 4 and 7) between the intersection P ₁ and the intersection P ₂ in the first weld layer 151 may be in the range of 3 mm to 20 mm.

Further, regarding the second welding layer 152, as described above, when _a straight line L passing through the intersection P1 and the intersection P2 is drawn, the _second welding layer 152 has the intersection _Q1 and the intersection Q with the straight line L. ₂ are all formed so as to be contained inside the first weld layer 151.

Here, the distance between the intersection P1 and the intersection _Q1 is preferably 2 mm or less, and more preferably ₁ mm or less. Similarly, the distance between the intersection P ₂ and the intersection Q ₂ is preferably 2 mm or less, and more preferably 1 mm or less.

Further, the width W ₂ (see FIG. 7) between the intersection Q ₁ and the intersection Q ₂ may be in the range of 2 mm to 20 mm. In particular, the ratio of the width W ₂ to the width W ₁ is preferably 70% or more, and more preferably 80% or more.

Such a welded portion 150 can be formed, for example, by the method shown below.

(Welding method according to one embodiment of the present invention)
Next, a welding method according to an embodiment of the present invention will be described with reference to FIGS. 8 to 11.

FIG. 8 schematically shows the flow of the welding method according to the embodiment of the present invention. Further, FIGS. 9 to 11 schematically show one step of the welding method according to the embodiment of the present invention.

As shown in FIG. 8, the welding method according to the embodiment of the present invention (hereinafter referred to as “first welding method”) is
(A) A step of arranging the first member, the second member, and the backing plate at predetermined positions (step S110).
(B) A step of forming a first welding layer between the first member, the second member, and the backing plate by the first welding pass (step S120).
(C) A step of forming a second welding layer on the first welding layer by the second welding pass (step S130).
Have.

Hereinafter, each step will be described with reference to FIGS. 9 to 11.

Here, as an example, a welding method in the case of manufacturing the first welded joint 100 as described above will be described. Therefore, when representing each member, the reference numerals used in FIGS. 2 to 4 and 7 described above are used.

(Step S110)
First, the first member 120, the second member 130, and the backing plate 140 are prepared, and the three members are arranged at appropriate relative positions.

FIG. 9 schematically shows how the three members are arranged at appropriate positions.

As shown in FIG. 9, the first member 120 has a first surface 122 and a second surface 124 facing each other, and an end surface 126 connecting both surfaces. Further, the second member 130 has a third surface 132 and a fourth surface 134 facing each other, and an end surface 136 connecting both surfaces. The backing plate 140 has an upper surface 142.

The first member 120 and the second member 130 are arranged on the backing plate 140 so that both end faces 126 and 136 face each other. At this time, the first member 120 and the second member 130 are arranged so that the first surface 122 and the third surface 132 are oriented in the same direction (upward). In other words, the first member 120 and the second member 130 are arranged so that the second surface 124 and the fourth surface 134 face or contact the upper surface 142 of the backing plate 140.

In the example shown in FIG. 3, the end surface 126 of the first member 120 and the end surface 136 of the second member 130 are inclined at a predetermined angle. Therefore, when the first member 120 and the second member 130 are properly arranged with respect to each other, a V-shaped groove shape having an angle θ is formed by the end faces 126 and 136 of both. The angle θ is usually in the range of 30 ° to 90 °.

However, this is only an example, and the inclination angles of the end face 126 and the end face 136 are not particularly limited. For example, at least one or at least a part of the end face 126 of the first member 120 and the end face 136 of the second member 130 has no inclination and is parallel to the thickness direction of the respective members 120 and 130, respectively. good. Further, the end face 126 and the end face 136 may have different inclination angles.

Further, the minimum distance D (see FIG. 9) between the first member 120 and the second member 130 is, for example, in the range of 0 mm to 20 mm.

As described above, the first surface 122 and the second surface 124 of the first member 120 do not necessarily have to be flat, and they may have curved surfaces. The same applies to the third surface 132 and the fourth surface 134 of the second member 130.

(Step S120)
Next, arc welding using a filler material such as a wire is carried out. As a result, the first welding layer 151 is formed between the first member 120, the second member 130, and the backing plate 140 by the first welding pass.

FIG. 10 schematically shows how the first welding layer 151 is formed by the first welding pass.

As shown in FIG. 10, the first weld layer 151 is formed at the bottom between the end face 126 of the first member 120 and the end face 136 of the second member 130. Further, the first welding layer 151 is formed so that the tip 164 penetrates into the inside of the backing plate 140.

As described above, in the cross section of the first weld layer 151, the intersection point where the first weld layer 151 intersects the second surface 124 of the first member 120 on the side of the first member ₁₂₀ is defined as P1. The intersection of the second member 130 with the fourth surface 134 on the side of the _second member 130 is defined as P2.

The first welding pass may be carried out by applying a large current exceeding 500 A between the electrode wire and each of the members 120 and 130, or by applying a smaller current. May be.

(Step S130)
Next, as shown in FIG. 11, the second welding layer 152 is formed on the first welding layer 151 by the second welding pass.

Usually, the second welding pass is carried out by applying a large current exceeding 500 A between the electrode wire and each of the members 120 and 130.

Here, the second weld layer 152 has the above-mentioned characteristics.

That is, when _a straight line L passing through the intersection P1 and the intersection P2 is drawn, the tip 168 in the depth direction of the _second weld layer 152 is introduced into the backing plate 140 beyond the straight line L. Is formed like this.

Further, in the second weld layer 152, the intersection _Q1 is inside the _first weld layer 151 or coincides with the intersection P1, and the intersection _Q2 is inside the first weld layer 151, or the intersection. It is formed so as to coincide with P ₂ .

As described above, the intersection _Q1 and the intersection Q2 are defined as the intersections where the _second weld layer 152 intersects the straight line L in the cross section of the second weld layer 152. Here, the intersection _Q1 is defined as the intersection on the side closer to the first member 120 than the intersection _Q2 .

If necessary, the third, fourth ... Welding layers may be installed on the second welding layer 152.

By the above steps, the welded portion 150 is formed. Further, it is possible to obtain a first welded joint 100 in which the first member 120, the second member 130, and the backing plate 140 are joined to each other via the welded portion 150.

In such a first welding method, at least a part of the pipe-shaped defect 170 that may be present in the first welding layer 151 can be remelted during the second welding pass in (step S130). Therefore, after the second welding pass, the pipe-shaped defect 170 in the first welding layer 151 can be removed or reduced.

Further, in the first welding method, when the second welding layer 152 is formed by the second welding path, it is possible to avoid the occurrence of new intersecting regions at the intersections _Q1 and _Q2 .

Therefore, in the first welding method, even if an oxide film is present at the welded portion of the first member 120, the second member 130, and / or the backing plate 140, a large pipe-like defect is significant. It is possible to suppress it.

Further, in the first welding method, it is not necessary to carry out a step of removing the oxide film existing on the first member 120, the second member 130, and the backing plate 140, and the work efficiency can be improved. It will be possible.

The first welding method may be carried out by using any welding technique as long as the above-mentioned characteristics can be obtained.

For example, the first welding method is gas shielded metal arc welding (GMAW) technology, shielded metal arc welding (FCAW) technology, or submerged arc welding (SAW) technology using a mixed gas of Ar and CO ₂ or CO ₂ gas. It may be carried out by using the arc welding method such as.

Next, examples of the present invention will be described.

(Example 1)
Using the first welding method described above, two steel plates and a backing plate were welded to each other to manufacture a welded joint.

SM490 (rolled steel material for welded structure) having a thickness of about 12 mm was used for the two steel plates. The V-shaped groove angle θ composed of the end faces of both steel plates was about 50 °, and the minimum distance D between both steel plates was about 5 mm (see FIG. 9).

For the backing plate, the same material as the steel plate was used.

The two steel plates and the backing plate were not particularly treated to remove the oxide film.

A gas shield metal arc welder was used for welding. The shield gas was a mixed gas of Ar and CO ₂ , and the wire used was a solid wire having a diameter of 1.4 mm and equivalent to YGW15 (JIS standard).

The number of welding passes was two, and a welded portion composed of two weld layers was formed. In the first welding pass, a current of less than 500 A was applied between the electrodes. On the other hand, in the second welding pass, a current exceeding 500 A was applied between the electrodes.

When the obtained welded joint was inspected, it was confirmed that the welded portion was in a sound state and that the two steel plates and the backing plate were properly joined. No pipe-like defects were found in the welded part.

FIG. 12 shows an example of a cross section of a portion to be welded after the first welding pass. Further, FIG. 13 shows an example of a cross section of a portion to be welded after the second welding pass.

From FIG. 12, it can be seen that the first weld layer extends from the side of the two steel plates to the inside of the backing plate. Similarly, from FIG. 13, it can be seen that the tip of the second weld layer reaches the inside of the backing plate in the depth direction.

From FIG. 13, the intersection P ₁ , the intersection P ₂ , the intersection Q ₁ , and the intersection Q ₂ were obtained according to the above definition. As a result, it was found that _both the intersection _Q1 and the intersection Q2 exist inside the first weld layer.

The distance between the intersection P1 and the intersection _Q1 was about _{1 mm} , and the distance between the intersection P2 and the intersection _Q2 was about 0.5 mm. The ratio of the width W ₂ between the intersection Q ₁ and the intersection Q ₂ to the width W ₁ between the intersection P ₁ and the intersection P ₂ was about 70%.

(Example 2)
A welded joint was manufactured by welding two steel plates and a backing plate to each other using a conventional welding method.

The same as in Example 1 was used for the two steel plates and the backing plate. A gas shield metal arc welder was used for welding. The shield gas was CO ₂ , and the same wire as in Example 1 was used.

In Example 2, a large current exceeding 500 A was applied between the electrode wire and the steel plate to form a welded portion in one welding pass. Therefore, the weld has a single weld layer.

14 and 15 show an example of the obtained welded portion.

FIG. 14 is a photograph of a cross section of the welded portion observed (photographed) from a direction perpendicular to the stretching direction. Further, FIG. 15 is a photograph obtained by cutting the welded portion along the weld bead and taking a transmitted X-ray from the side surface. In FIG. 15, the upper portion corresponds to two steel plates, and the lower portion corresponds to a backing plate.

From FIG. 14, it can be seen that a pipe-shaped defect has occurred in the intersection region on the left side of the weld layer. Further, from FIG. 15, it can be seen that a large number of pipe-shaped defects starting from the intersection region occur in the welded portion.

As described above, in Example 2, it was found that a large number of pipe-shaped defects were contained in the welded portion.

From the above, by forming the second weld layer on the first weld layer so as to satisfy the above-mentioned characteristics (1) and (2), pipe-shaped defects that may occur in the welded portion are formed. , It was confirmed that it can be significantly suppressed.

This application claims priority based on Japanese Patent Application No. 2017-050152 filed on March 15, 2017, and the entire contents of the Japanese application are incorporated herein by reference.

20 First steel plate 26 Inclined end face 30 Second steel plate 36 Inclined end surface 40 Backing plate 50 Welding layer 70 Pipe-like defect 100 First welded joint 120 First member 122 First surface 124 Second surface 126 End surface 130 Second member 132 Third surface 134 Fourth surface 136 End surface 140 Backing plate 142 Top surface 150 Welded part 151 First weld layer 152, 152A, 152B, 152C Second weld layer 160 First intersection region 162 Second Welding Layer Tip 164 First Welding Layer Tip 168, 168A, 168B, 168C Second Welding Layer Tip 170 Pipe Defect 171 New Pipe Defect 180B New Crossing Area 182B New Crossing Area

Claims (6)

It ’s a welding method.
(1) A step of forming a first welding layer between a first member, a second member, and a backing plate by a first welding pass.
The first member has a first surface, the second member has a second surface, and the backing plate has an upper surface.
The first member and the second member are arranged so that the first surface and the second surface face or contact the upper surface of the backing plate.
The first weld layer is viewed from a cross section perpendicular to the extending direction of the first weld layer.
On the side of the first member, it intersects with the first surface of the first member at an intersection P ₁ and intersects with the upper surface of the backing plate at an intersection P ₃ (provided that P ₁ = P ₃ ). Yes), on the side of the second member, it intersects with the _second surface of the second member at an intersection P2, and intersects with the upper surface of the backing plate at an intersection P4 ₍ however, P ₂ = The process formed as ₍ may be P4 ) and
(2) A step of forming a second welding layer on the first welding layer by the second welding pass, and
Have,
_{When a} straight line L passing through the intersection P1 and the intersection P2 is drawn,
The second weld layer is arranged so that the tip in the depth direction is introduced into the backing plate beyond the straight line L.
The second weld layer intersects the straight line L at intersections _Q1 and _Q2 , and the intersection _Q1 is closer to the first member than the intersection _Q2 .
The intersection _Q1 is inside the _first weld layer or coincides with the intersection P1.
The intersection _Q2 is inside the _first weld layer or coincides with the intersection P2.
The second weld layer is a region surrounded by the intersection P ₁ , the intersection P ₂ , the intersection P ₄ , and the intersection P ₃ in the depth range from the straight line L to the upper surface of the backing plate. A welding method that is configured to fit in . The welding method according to claim ₁ , wherein the distance between the intersection P1 and the intersection _Q1 is ₂ mm or less, and / or the distance between the intersection P2 and the intersection Q2 is ₂ mm or less. The welding method according to claim 1, wherein the ratio of the width W ₂ (W ₂ / W ₁ ) from the intersection Q ₁ to the intersection Q ₂ to the width W ₁ from the intersection P ₁ to the intersection P ₂ is 70% or more. A welded joint in which a first member, a second member, and a backing plate are joined to each other by a welded portion.
The first member has a first surface and has a first surface.
The second member has a second surface and has a second surface.
The first member and the second member are arranged so that the first surface and the second surface face or contact the upper surface of the backing plate.
The weld has a first weld layer and a second weld layer from the side closer to the backing plate in the depth direction.
When the welded portion is viewed from a cross section perpendicular to the extending direction of the welded portion,
The first weld layer intersects the first surface of the _first member at an intersection P1 and intersects with the upper surface of the backing plate at an intersection P3 _on the side of the first member ( provided that the first weld layer intersects the first surface of the first member at an intersection P1). , P ₁ = P ₃ ), on the side of the second member, intersects the second surface of the _second member at the intersection P2 , and intersects the upper surface of the backing plate at the intersection P4 _. Fellowship (however, P ₂ = P ₄ in some cases),
_{When a} straight line L passing through the intersection P1 and the intersection P2 is drawn,
The second weld layer is arranged so that the tip in the depth direction is introduced into the backing plate beyond the straight line L.
The second weld layer intersects the straight line L at intersections _Q1 and _Q2 , and the intersection _Q1 is closer to the first member than the intersection _Q2 .
The intersection _Q1 is inside the _first weld layer or coincides with the intersection P1.
The intersection _Q2 is inside the _first weld layer or coincides with the intersection P2.
The second weld layer is a region surrounded by the intersection P ₁ , the intersection P ₂ , the intersection P ₃ , and the intersection P ₄ in the depth range from the straight line L to the upper surface of the backing plate. A welded joint that is configured to fit in . The welded joint according to claim ₄ , wherein the distance between the intersection P1 and the intersection _Q1 is ₂ mm or less, and / or the distance between the intersection P2 and the intersection Q2 is ₂ mm or less. The welded joint according to claim 4, wherein the ratio of the width W ₂ (W ₂ / W ₁ ) from the intersection Q ₁ to the intersection Q ₂ to the width W ₁ from the intersection P ₁ to the intersection P ₂ is 70% or more.

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