JP6583657B1 - Lap laser welded joint, manufacturing method thereof, and structural member for automobile body - Google Patents

Abstract

A laser beam is intermittently applied to one surface of a steel plate in which a plurality of steel plates are overlapped, and a linear first joint portion and a linear subsequent joint portion are arranged in a row following the first joint portion. When forming the welded portion, at least the total gap G between the steel plates constituting the welded portion is set within a range of 0 to 15% of the total thickness T of the steel plates constituting the welded portion, and the laser beam is irradiated. By reversing the moving direction of the welding head and the scanning direction of the laser beam, the welding start end of the first joint and the welding end of the subsequent joint adjacent to the first joint face each other, and Formation of a welded portion so that the welding start end portion and the welding end portion of the subsequent joining portions face each other, and by controlling various dimensions of the above-described joining portion within an appropriate range, occurrence of cracks in the welding end portion of the joint portion No overlap laser with excellent peel strength Suggest contact joint and its manufacturing method, and automobile body structural member having the welded joint.

Description

  The present invention relates to a lap laser welded joint, a manufacturing method thereof, and a structural member for an automobile body having the lap laser welded joint.

  Resistance spot welding is generally used for welding a structural member (strength member) of an automobile body having a flange portion. However, in resistance spot welding, welding takes time, the heat generation amount decreases due to the diversion, the welding pitch cannot be narrowed, and a certain amount of space is required to set the welding gun. There is a problem. In order to solve these problems, in recent years, it has been studied and put into practical use that lap laser welding is used instead of conventional resistance spot welding. Here, the lap laser welding refers to a welding method in which one surface of a plurality of stacked steel plates is irradiated with a laser beam to melt and join the steel plates.

  Conventionally, lap laser welded joints irradiate laser beams intermittently on the surface of a plurality of stacked steel plates, melt and solidify the steel plates of the laser beam irradiated portions, and form a short length of linear joint A plurality of steel plates were joined by forming a welded portion in which the portions were continuously arranged in a row. However, the overlap laser beam welding has a problem that cracks are likely to occur in the final solidified portion on the welding end portion side of the linear joint portion. When cracking occurs, it propagates over the entire length of the linear joint, so that not only the static strength such as the shear strength and peel strength of the welded joint portion is reduced, but also the fatigue strength is significantly reduced. In recent years, structural members (strength members) that serve as skeleton members for automobile bodies have been increasingly used for high-strength steel sheets in order to improve the strength and rigidity of the vehicle body. Decrease in the static strength and fatigue strength of welded joints due to cracking becomes a serious problem.

  Therefore, various methods for preventing cracks at the welding end portion of the joint portion produced when laser beams are welded to the stacked steel plates have been studied. For example, Patent Literature 1 discloses a technique for preventing weld cracking by protruding a lower steel plate of lap welding and setting a welding start position away from the flange end. Patent Document 2 discloses a technique for preventing welding cracks by irradiating an end portion of a stacked surface with a laser beam obliquely. Patent Documents 3 and 4 disclose a technique for preventing welding cracks by reheating or welding a portion once welded and the periphery of the welded portion. Patent Document 5 discloses a technique for preventing the occurrence of weld cracks by welding the overlapping surfaces into an elliptical shape. Furthermore, Patent Document 6 discloses a technique for preventing the occurrence of weld cracking by optimizing the steel plate components and optimizing the ratio of the weld bead width to the bead thickness.

JP 2007-229740 A JP 2008-296236 A JP 2012-240083 A JP2012-240086A JP 2017-113781 A JP-A-2018-001197

  However, in the method described in Patent Document 1, since the lower steel plate of the lap weld is protruded, there is a problem that a part to be protruded becomes extra and the part design is restricted. In addition, in the method described in Patent Document 2, since laser irradiation is performed obliquely, when a gap is formed in the overlapped plates, the melted portion is not formed well on the overlapped surface, resulting in insufficient penetration. There is a problem that it is difficult to ensure strength. In addition, the methods described in Patent Documents 3 and 4 have a problem that the welding time becomes long because it is necessary to reheat or weld the welded portion or the periphery of the welded portion. In addition, the method described in Patent Document 5 welds the overlapped surface in an elliptical shape, and cannot be applied to prevent cracks at the welding end portion of the linear joint portion. Furthermore, in the method described in Patent Document 6, since stress tends to concentrate on the welding end portion, there is a problem that it is impossible to prevent the occurrence of cracks in the welding end portion of the linear joint having a short length. .

  The present invention has been made in view of the above-described problems of the prior art, and the purpose thereof is welding in which short-length joints (welding points) are formed in rows by intermittently irradiating a laser beam. The present invention provides a lap laser welded joint that has no weld cracking at the weld end of the joint and is excellent in the peel strength of the weld. An object of the present invention is to provide a structural member for an automobile body having a laser weld joint.

  In order to solve the above-mentioned problems, the inventors have formed a linear joint portion (hereinafter referred to as “first joint portion”) that forms a weld portion of a lap laser welded joint, and subsequently, Intensive study has been conducted focusing on the relationship with one or more linear joints (hereinafter referred to as “subsequent joints”) to be formed. In the present invention, the “first joint” and the “subsequent joint” are collectively referred to simply as “joint”.

  As a result, in order to prevent cracks occurring at the weld end portion of the joint portion, the shape of the first joint portion is made J-shaped, and the welding start end portion of the first joint portion and the subsequent portion adjacent thereto Forming the welded portion so that the weld end portion of the joint portion faces and the welding start end portion of the subsequent joint portion and the weld end portion of the subsequent joint portion formed adjacent thereto are opposed to each other, that is, It is important to form the welded portion so that the weld start end portion and the weld end portion of the joint portions face each other, and further, the crack of the weld end portion of the joint portion can be more reliably prevented, and sufficient In order to ensure the strength of the welded part, in addition to satisfying the above requirements, it has been found that it is effective to control the various dimensions of the first joint and the subsequent joint within an appropriate range. Invented the invention.

The present invention based on the above knowledge is that in a lap laser welded joint having a welded portion formed by overlapping a plurality of steel plates, the total gap G between the steel plates constituting the welded portion is the total thickness T of the steel plates constituting the welded portion. The welded portion is composed of a linear first joint portion and a linear subsequent joint portion arranged in a row following the first joint portion. The welding start end portion of the joining portion and the welding end portion of the subsequent joining portion adjacent thereto are opposed, and the welding start end portion and the welding end portion of the succeeding joining portions are opposed to each other, and the first joining is performed. The portion has a J-shape consisting of a linear joint and an arcuate or circular curvilinear joint connected to the welding end of the linear joint, and the weld is Formulas (1) to (4);
15.0 ≦ L ₁ ≦ 30.0 (1)
8.0 ≦ L ₂ ≦ 20.0 (2)
1/8 ≦ w / b ≦ 1/2 (3)
1/4 ≦ a / (L ₁ + L ₂ ) ≦ 1/2 or 1/2 ≦ a / L ₂ ≦ 1 (4)
Here, L ₁ : length of the first joint (mm)
L ₂ : Length of subsequent joint (mm)
b: Minimum thickness (mm) of molten metal at the joint
w: width of molten metal at joint (mm)
a: Shortest distance between joints (mm)
It is a lap laser welding joint characterized by satisfying all of the above.

In the lap laser welded joint of the present invention, the first joint portion is composed of only a linear joint portion, and instead of the above formula (1), the following formula (1 ′);
30.0 <L _{1 ′} ≦ 40.0 (1 ′)
Here, L _{1 ′} : length of the linear joint (mm)
It is characterized by satisfying.

  In the lap laser welded joint according to the present invention, at least one of the steel plates has C: 0.07 to 0.4 mass%, Si: 0.2 to 3.5 mass%, Mn: 1.8 to 5. 5 mass%, P + S: 0.03 mass% or less, Al: 0.08 mass% or less, and N: 0.010 mass% or less, with the balance being a component composition of Fe and inevitable impurities.

Moreover, in addition to the said component composition, the said steel plate in the overlap laser welding joint of this invention is further the following A group and B group;
Group A; Ti: 0.0005 to 0.01 mass% and Nb: 0.005 to 0.050 mass%, or one selected from the group B Group; Cr: 1.0 mass% or less, Mo: 0 It contains at least one group of components selected from one or two or more selected from .50 mass% or less and B: 0.10 mass% or less.

  In the lap laser welded joint according to the present invention, at least one of the steel plates is a high-tensile steel plate having a tensile strength of 980 MPa or more.

In the present invention, a plurality of steel plates are stacked one above the other, and one surface of the stacked steel plates is intermittently irradiated with a laser beam, followed by the linear first joint and the first joint. When forming the welded portion in which the linear subsequent joint portions are arranged in a row, the total gap G between the steel plates constituting the welded portion is set to 0 to 15% of the total thickness T of the steel plates constituting the welded portion. Within the range, the moving direction of the welding head for irradiating the laser beam and the scanning direction of the laser beam are reversed, so that the welding start end of the first joint and the subsequent joint adjacent to the first joint are The welding end portion is opposed to each other, and the welding start end portion and the welding end portion of the subsequent joining portions are opposed to each other, and the shape of the first joining portion is changed to a linear joining portion and its linear shape. Arc-shaped or circular curvilinear joints connected to the weld end of the joint And J-shaped and made of a further, the weld, the following equation (1) to (4);
15.0 ≦ L ₁ ≦ 30.0 (1)
8.0 ≦ L ₂ ≦ 20.0 (2)
1/8 ≦ w / b ≦ 1/2 (3)
1/4 ≦ a / (L ₁ + L ₂ ) ≦ 1/2 or 1/2 ≦ a / L ₂ ≦ 1 (4)
Here, L ₁ : length of the first joint (mm)
L ₂ : Length of subsequent joint (mm)
b: Minimum thickness (mm) of molten metal at the joint
w: width of molten metal at joint (mm)
a: Shortest distance between joints (mm)
In order to satisfy all of the above, a method of manufacturing a lap laser welded joint characterized by controlling at least one of laser output, focal position, welding speed and beam diameter is proposed.

In the method for producing a lap laser welded joint according to the present invention, the first joint is composed of only a linear joint, and instead of the above formula (1), the following formula (1 ′);
30.0 <L _{1 ′} ≦ 40.0 (1 ′)
Here, L _{1 ′} : length of the linear joint (mm)
It is characterized by controlling at least one of the laser output, the focal position, the welding speed, and the beam diameter so as to satisfy the above.

  Moreover, this invention is a structural member for motor vehicle bodies which has the overlap laser welding joint in any one of said.

  According to the present invention, it is possible not only to reliably suppress the occurrence of cracks in the weld end portion of the joint portion constituting the weld portion of the lap laser weld joint obtained by laser beam welding a plurality of stacked steel plates, It is possible to produce a lap laser welded joint having excellent peel strength. In addition, since the lap laser welded joint of the present invention can shorten the length of the joint portion, it increases the degree of freedom in component design, and enables development of a lighter, higher rigidity, and higher strength member. Therefore, the lap laser welding joint of the present invention can be preferably applied to a structural member (strength member) that becomes a skeleton of an automobile body.

It is a perspective view which shows an example of the conventional overlap laser welding joint. It is the schematic explaining the welding part of the conventional lap laser welding joint, (a) is a top view, (b) is AA sectional drawing of (a). It is the schematic explaining the welding part of the lap laser welding joint of this invention, (a) is a top view, (b) is BB sectional drawing of (a). It is a perspective view which shows an example of the overlap laser welding joint of this invention. It is a perspective view explaining the welding method of the overlap laser welding joint of this invention. It is a figure explaining the welding position of the overlap laser welding joint of this invention, (a) is a top view, (b) is CC sectional drawing of (a). It is a perspective view explaining the peeling test piece which has the overlap laser welding joint used for the Example of this invention.

Hereinafter, the lap laser welded joint of the present invention, the manufacturing method thereof, and the structural member for an automobile body having the lap laser welded joint will be described.
<Laminated laser welded joint>
FIG. 1 is a perspective view showing an example of a conventional lap laser welding joint. The lap laser welded joint 1 is obtained by superposing at least two steel plates, and in the example shown in FIG. 1, a cross-sectional shape having a vertical wall portion 2a and a flange portion 2b extending outward from the tip of the vertical wall portion 2a. The two steel plates of the substantially hat-shaped steel plate 2 and the flat panel-shaped steel plate 3 are overlapped so that the flange portion 2b and the steel plate 3 face each other to form a joint surface, and the flange portion 2b The surface of the flange portion 2b is irradiated with a laser beam from above to form a molten portion (molten metal portion) penetrating at least the steel plate 2, and solidified to form a joint portion (welding point). ing. In addition, although the heat affected zone (HAZ) exists around the melted portion, the joint portion of the present invention refers only to the melted portion excluding the heat affected zone.

  The welded portion of the lap laser welded joint 1 moves the laser beam from the flange portion 2b while moving the welding head WH, which is a laser beam source, along the longitudinal direction of the vertical wall portion 2a (the arrow direction in FIG. 1). It is formed by intermittently irradiating the surface. As a result, on the joining surface of the steel plate 2, as shown in FIG. 1, a short straight first joining portion 4 and a subsequent joining portion 5 are continuously formed. When the length of the flange portion is short, there may be only one subsequent joining portion 5, but when it is long, a plurality of the subsequent joining portions 5 are formed in a row along the length direction of the flange portion. As described above, in the present invention, the “first joint” and the “subsequent joint” are collectively referred to as “joint”.

  2 is a schematic view showing a conventional welded portion formed on the flange portion 2b of the lap laser welded joint shown in FIG. 1, and (a) shows the first joint portion 14 constituting the welded portion and the first welded portion 14b. The top view which looked at the adjacent joining part 15 from the upper part of the flange part 2b, (b) is sectional drawing which shows the AA cross section shown by the succeeding joining part 15 in said (a).

  In conventional laser beam welding, as shown in FIG. 2, when forming a welded portion composed of a linear first joint portion 14 and a subsequent joint portion 15 having a short length, the welding direction (running direction of the welding head) is used. ) And the welding direction (laser beam scanning direction) of the first joint portion 14 and the subsequent joint portion 15 are the same direction. For this reason, the center portions 14a and 15a of the welding end portion E (final solidified portion) of the first joint portion 14 and the subsequent joint portion 15 are crater-like and have a minimum plate thickness. Tensile stress (force in the direction of arrow Fa shown in FIG. 2A) is applied in a concentrated manner. Therefore, in the conventional lap laser welded joint, the crack 8 occurs in the welding end portion E of the first joint portion 14 and the subsequent joint portion 15, and then propagates from the welding end portion E to the welding start end portion S. There is a problem that the peel strength and fatigue strength are significantly impaired. The cracks that occur at the end of the weld can be prevented by making the lengths of the first joint 14 and the subsequent joint 15 sufficiently long. There is another problem that causes a decline in sex.

  In addition, the crack of the said welding termination part generate | occur | produces from the surface to the back surface at the welding termination part (final solidification part) of the 1st junction part 14 or the subsequent junction part 15, and the presence or absence of the occurrence should also be confirmed visually. However, in order to make a more reliable determination, cut the welding end of the joint after welding in the width direction, and determine by observing the cut surface with an optical microscope, for example, magnified about 10 times. Is preferred.

  Therefore, the inventors focused on the stress concentration generated at the weld end of the joint constituting the weld formed by the conventional laser beam welding method, and reduced this to reduce the weld end of the joint. We have made extensive studies on measures to prevent cracks that occur. As a result, it has been found that by adopting the welded portion shown in FIG. 3 instead of the welded portion shown in FIG. 2, it is possible to prevent cracks occurring at the weld end portion of the joint portion. Here, FIG. 3 is a schematic view showing the welded portion of the present invention formed on the flange portion 2b of the same lap laser welded joint as shown in FIG. 2, and (a) constitutes the welded portion. The top view which looked at the 1st junction part 4 and the succeeding junction part 5 adjacent to it from the upper part of the flange part 2b, (b) shows the BB cross section shown by the subsequent junction part 5 in said (a). It is sectional drawing.

  As can be seen from FIG. 3, the feature of the welded portion of the present invention is that the welding start end portion of the first joint portion 4 and the welding end portion of the subsequent joint portion 5 adjacent to the first joint portion 4 face each other, and That is, the welding start end portion and the welding end portion of the subsequent joint portion 5 adjacent thereto are opposed to each other, that is, the welding start end portion and the welding end portion of the adjacent joining portions are facing each other. By welding so that the welding start part of the preceding joining part and the welding terminal part of the succeeding joining part face each other as described above, it is possible to prevent the welding end part of the joining part from cracking. The reason is that at the time when the welding end portion of the subsequent joining portion has completed welding, the steel plate in the vicinity of the welding end portion is constrained by the preceding joining portion, so that the central portion (5a) of the final solidified portion. This is because the tensile stress (force in the direction of the arrow Fb shown in FIG. 3A) from the outer peripheral portion of the melted portion to the outside is reduced.

  Thereby, when a welding part is formed like the said FIG. 3, the crack of the welding termination | terminus part of a subsequent junction part can be prevented. However, since the steel plate around the welding end portion of the first joint portion is not restrained and is in a free state, it is not possible to prevent cracking at the welding end portion E of the first joint portion.

  Therefore, the inventors have further studied a method for suppressing cracking of the welding end portion of the first joint portion. As a result, as shown on the left side of FIG. 3A, the shape of the first joint portion is an arc shape or a circular shape formed by connecting the linear joint portion to the end portion side of the joint portion. It has been found that it is effective to form a J-shape comprising a curved joint. By adopting this shape, since the steel plate around the welding end portion side of the first joint portion, that is, the welding end portion of the curved joint portion, is already restrained by the linear weld portion, the center of the final solidified portion Tensile stress (force in the direction of arrow Fc shown in FIG. 3A) from the outer peripheral portion of the melted portion applied to the portion (4a) to the outside is reduced, and cracking at the welding end portion of the first joint portion can be prevented. .

  As shown in FIG. 3 above, the welding start end portion of the first joint portion 4 and the welding end portion of the subsequent joint portion 5 adjacent thereto are opposed to each other, and the welding start end portion of the subsequent joint portion 5 is adjacent thereto. In addition to forming the welded portion so that the welded end portion of the subsequent joined portion 5 faces the welded end portion, the first joined portion and the welded end of the subsequent joined portion are formed in a J-shape. The crack in a part can be prevented. For reference, FIG. 4 shows an example in which the welded portion of the present invention shown in FIG. 3 is applied to the lap laser weld joint shown in FIG.

However, according to further research by the inventors, as shown in FIG. 3 in order to more reliably prevent cracks occurring at the weld end of the joint and to give sufficient peel strength to the weld. In addition to forming the welded portion, the total gap G between the steel plates constituting the welded portion is in the range of 0 to 15% of the total thickness T of the steel plates constituting the welded portion, and the welded portion is formed. Part, that is, the first joint and the subsequent joint constituting the welded part are the following formulas (1) to (4);
15.0 ≦ L ₁ ≦ 30.0 (1)
8.0 ≦ L ₂ ≦ 20.0 (2)
1/8 ≦ w / b ≦ 1/2 (3)
1/4 ≦ a / (L ₁ + L ₂ ) ≦ 1/2 or 1/2 ≦ a / L ₂ ≦ 1 (4)
Here, L ₁ : length of the first joint (mm)
L ₂ : Length of subsequent joint (mm)
b: Minimum thickness (mm) of molten metal at the joint
w: width of molten metal at joint (mm)
a: Shortest distance (mm) between joints
I found it necessary to meet all of the above.
This will be specifically described below.

0 ≦ G / T ≦ 0.15
In the overlap laser beam welded joint of the present invention, the ratio (G / T) of the total gap G between the steel plates constituting the welded portion to the total thickness T of the steel plates constituting the welded portion is 0 to 0.15, that is, the welded portion. It is necessary that the ratio of the total gap G between the steel plates constituting the welded portion to the total thickness T of the steel plates constituting the steel sheet is in the range of 0 to 15%. This is because if the ratio of G to T exceeds 15%, the depth of the crater at the end of welding becomes deeper and stress is more likely to concentrate. Preferably it is 0 to 10% of range.

15.0 mm ≦ L ₁ ≦ 30.0 mm
As described above, the lap laser welded joint of the present invention has a shape of the first joint portion and the arc shape in order to prevent cracking of the weld end portion of the first joint portion constituting the weld portion. Or, it is important to have a J-shape consisting of a circular curved joint, but in order to more reliably prevent cracking at the end of the weld and ensure a sufficient peel strength, the length _{L 1} of the first joint portion needs to be a range of 15.0～30.0Mm. The length L ₁ of the J-shaped first joint is the total length of the linear joint and the curved joint as shown in FIG. When L ₁ is shorter than 15.0 mm, cracking occurs in the welded end portion of the first joint. Preferably it is 20.0 mm or more. On the other hand, the upper limit of L ₁ is not limited from the viewpoint of preventing cracking, but is set to 30.0 mm or less from the viewpoint of shortening the welding time. Preferably it is 25.0 mm or less.

8.0 mm ≦ L ₂ ≦ 20.0 mm
Further, lap laser weld joint of the present invention is required to be a length L ₂ of the scope of 8.0~20.0mm subsequent joining portion constituting the weld. If L ₂ is shorter than 8.0 mm, ensuring a welding starting end of the preceding junction, also it is opposite the welded end portion of the joint portion of the trailing, the welding area of only relieving stress on the weld end portion Since this is not possible, cracking at the weld end cannot be reliably prevented. Preferably it is 10.0 mm or more. On the other hand, the upper limit of L ₂ is not limited from the viewpoint of preventing cracking, from the viewpoint of shortening the welding time, or less 20.0 mm. Preferably it is 15.0 mm or less.

1/8 ≦ w / b ≦ 1/2
Further, in the lap laser welded joint of the present invention, the ratio (w / b) of the width w of the molten metal of the joint to the minimum thickness b generated at the weld end (final solidified part) of the joint constituting the weld is 1. It needs to be in the range of / 8 to 1/2. If the ratio (w / b) is greater than 1/2, the tensile stress toward the outside from the outer peripheral portion of the melted portion applied to the final solidified portion of the weld termination portion of the first joint portion or the subsequent joint portion increases, The occurrence cannot be suppressed. On the other hand, if the ratio (w / b) is smaller than 1/8, the strength of the joint cannot be sufficiently secured. That is, in addition to making the welding start end portion of the preceding joining portion and the welding end portion of the succeeding joining portion face each other, the ratio (w / b) at the joining portion is set to a range of 1/8 to 1/2. Thereby, the crack in the welding terminal part of a junction part can be prevented more reliably, and the peeling strength of a weld part can be made into sufficient intensity | strength. A preferred ratio (w / b) is in the range of 1/6 to 1/3.

1/4 ≦ a / (L ₁ + L ₂ ) ≦ 1/2 or 1/2 ≦ a / L ₂ ≦ 1
In the lap laser welded joint of the present invention, the shortest distance a between the joints is (the length of the first joint L ₁ + the length of the subsequent joint) when the first joint is adjacent to the subsequent joint. In the case where the ratio of the above a to (L ₂ ) (a / (L ₁ + L ₂ )) is in the range of ¼ to ½, and between adjacent subsequent joints, the length L _{2 of the} subsequent joints The ratio of a to (a / L ₂ ) needs to be in the range of 1/2 to 1. If the ratio (a / (L ₁ + L ₂ )) is greater than ½, or if the ratio (a / L ₂ ) is greater than 1, then the subsequent junction is from the previous junction of that junction. The effect of suppressing the deformation of the steel plate around the joint portion cannot be sufficiently obtained, and cracking of the welding end portion cannot be prevented. The lower limit of the a is not limited from the viewpoint of preventing cracking, but from the viewpoint of shortening the welding time, the ratio (a / (L ₁ + L ₂ )) is 1/4 or more, and the ratio ( a / L ₂ ) is ½ or more. A preferred ratio (a / (L ₁ + L ₂ )) is in the range of 1/3 to 2/5, and a preferred ratio (a / L ₂ ) is in the range of 3/5 to 9/10.

In the description of the present invention described above, the technique for preventing cracks occurring at the welding end portion of the first joint portion by setting the shape of the first joint portion to a J shape has been described. However, as described above, it is possible to prevent the weld end portion of the joint from cracking by increasing the length of the linear joint. In that case, the length L _{1 ′} of the first joint portion is replaced by the following equation (1 ′) instead of the above-described equation (1);
30.0 <L _{1 ′} ≦ 40.0 (1 ′)
Here, L _{1 ′} : length of the linear joint (mm)
It is necessary to satisfy. When length L1 _' in case a 1st junction part consists only of a linear junction part is 30.0 mm or less, a crack generate | occur | produces in the terminal part of a 1st junction part. Preferably it is 32.0 mm or more. On the other hand, the upper limit of L _{1 ′} is not limited from the viewpoint of preventing cracking, but is 40.0 mm or less from the viewpoint of shortening the welding time. Preferably it is 38.0 mm or less.

Next, the steel plate constituting the lap laser weld joint of the present invention will be described.
1 to 4 show an example in which two steel plates are overlapped to form a laser welded joint. Of course, three or more steel plates may be overlapped to form a welded joint. is there.

Steel plate thickness The steel plates constituting the lap laser welded joint of the present invention each have a thickness of 0.5 to 3.2 mm, which is generally used as an outer plate or structural member (strength member) of an automobile body. There is no particular limitation as long as it is within the range. Further, the plurality of steel plates may all have the same thickness or may have different thicknesses. For example, in the case of the lap laser welding joint 1 having the shape shown in FIG. 4, the plate thickness t ₂ of the upper steel plate ₂ is 0.6 to 1.8 mm, and the plate thickness t ₃ of the lower steel plate ₃ is 1. may be used as the range of 0～2.5Mm, may the thickness _{t 3} of the thickness _{t 2} and the lower of the steel plate 3 of the upper steel plate 2 as the thickness of the same 0.5 to 3.2 mm.

The component composition of the plurality of steel plates constituting the lap laser welded joint of the present invention is not particularly limited, but at least one steel plate is C: 0.07-0. Contains 4 mass%, Si: 0.2-3.5 mass%, Mn: 1.8-5.5 mass%, P + S: 0.03 mass% or less, Al: 0.08 mass% or less, and N: 0.010 mass% or less And it is preferable that the remainder has a composition composed of Fe and inevitable impurities.

C: 0.07 to 0.4 mass%
C is an element effective for improving the strength of steel, and by containing 0.07 mass% or more, the effect of precipitation strengthening and transformation strengthening can be obtained. Moreover, desired intensity | strength and workability can be ensured, without causing precipitation of a coarse carbide | carbonized_material by making C content into 0.4 mass% or less. Therefore, the C content is preferably in the range of 0.07 to 0.4 mass%. More preferably, it is the range of 0.15-0.3 mass%.

Si: 0.2-3.5 mass%
Si is an element excellent in solid solution strengthening ability, and the strength of steel can be increased by containing 0.2 mass% or more. Moreover, by making Si content into 3.5 mass% or less, the excessive hardening of a welding heat affected zone can be suppressed and deterioration of the toughness and cold cracking resistance of a weld heat affected zone can be prevented. Therefore, the Si content is preferably in the range of 0.2 to 3.5 mass%. More preferably, it is the range of 1.0-2.5 mass%.

Mn: 1.8 to 5.5 mass%
Mn is an element effective in improving hardenability and suppressing precipitation of coarse carbides, and is preferably contained in an amount of 1.8 mass% or more. Moreover, by making Mn content 5.5 mass% or less, the raise of a grain-boundary embrittlement sensitivity can be suppressed and deterioration of toughness and low temperature cracking resistance can be prevented. Therefore, the Mn content is preferably in the range of 1.8 to 5.5 mass%. More preferably, it is in the range of 2.0 to 3.5 mass%.

P + S: 0.03 mass% or less P and S are harmful elements that adversely affect the ductility and toughness of steel. By making the total content of P and S 0.03 mass% or less, ductility and toughness are reduced. And desired strength and workability can be ensured. Therefore, the total content of P and S is preferably 0.03 mass% or less. More preferably, it is 0.02 mass% or less.

Al: 0.08 mass% or less Al is an element added as a deoxidizer in the steelmaking stage, and is generally added in an amount of 0.01 mass% or more. However, when the Al content exceeds 0.08 mass%, inclusions such as alumina increase, and an adverse effect on fatigue resistance becomes apparent. Therefore, the Al content is 0.08 mass% or less. Preferably it is the range of 0.02-0.07 mass%.

N: 0.010 mass% or less N is an element that greatly deteriorates the aging resistance of steel, and is preferably reduced as much as possible. In particular, when N exceeds 0.010 mass%, deterioration of aging resistance becomes remarkable, so the N content is set to 0.010 mass% or less. In addition, although the minimum of N is not specifically limited, From a viewpoint of preventing the raise of manufacturing cost, it is preferable to set it as about 0.001 mass%.

  In addition to at least one steel plate constituting the welded joint of the present invention, in addition to the above-described component composition, for the purpose of further improving the steel plate strength and the peel strength of the welded portion, the following groups A and B: It is preferable to contain at least one group of components.

Group A: Ti: 0.0005 to 0.01 mass% and Nb: one or two selected from 0.005 to 0.050 mass% Ti and Nb both form carbides and nitrides and precipitate In addition, there is an effect of suppressing the austenite coarsening during annealing during the production of the steel sheet. In order to acquire the said effect, it is preferable to contain 1 type or 2 types chosen from Ti and Nb, 0.0005 mass% or more of Ti and 0.005 mass% or more of Nb. However, even if Ti and Nb are contained excessively, the above effect is saturated and only the raw material cost is increased. Moreover, since the recrystallization temperature is raised, the metal structure after annealing at the time of manufacturing the steel sheet becomes non-uniform, and the stretch flangeability may be impaired. Further, the precipitation amount of carbide or nitride is increased, the yield ratio is increased, and the shape freezing property may be deteriorated. Therefore, when Ti and / or Nb are contained, Ti is preferably 0.01 mass% or less, and Nb is preferably 0.050 mass% or less. More preferable contents are Ti: 0.0006 to 0.0080 mass% and Nb: 0.010 to 0.040 mass%.

Group B: Cr: 1.0 mass% or less, Mo: 0.50 mass% or less, and B: 0.10 mass% or less selected from one or two or more Cr, Mo, and B improve the hardenability of steel. It is an element effective for improving, and in order to obtain the above-described effect, it contains at least one of Cr: 0.01 mass% or more, Mo: 0.004 mass% or more, and B: 0.0001 mass% or more. It is preferable. However, even if these elements are contained excessively, the above effect is saturated and only the cost of raw materials is increased. Therefore, when Cr, Mo and B are contained, it is preferable to add Cr: 1.0 mass% or less, Mo: 0.50 mass% or less, and B: 0.10 mass% or less. More preferably, the ranges are Cr: 0.02-0.50 mass%, Mo: 0.01-0.10 mass%, and B: 0.001-0.03 mass%.

  In at least one steel plate constituting the welded joint of the present invention, the balance other than the above components is Fe and inevitable impurities.

Moreover, it is preferable that at least one steel plate is a high-tensile steel plate having a tensile strength TS of 980 MPa or more among a plurality of steel plates constituting the lap laser welding joint of the present invention. If at least one steel plate is a high-strength steel plate as described above, the lap laser welded joint can obtain high joint strength, and even in the case where weld cracking occurs in the conventional welding method, Occurrence of weld cracks can be prevented by the effect of suppressing deformation of the steel plate around the joint due to. Therefore, for example, it is preferable that at least one of the plurality of steel plates has the above-described component composition and has a tensile strength TS of 980 MPa or more. The plurality of steel plates constituting the lap laser beam welded joint of the present invention may be steel plates having the same component and the same strength, or may be steel plates having different components and different strengths.

<Method for producing lap laser welded joint>
Next, the manufacturing method of the lap laser welding joint of this invention is demonstrated.
FIG. 5 is a diagram for explaining an example of a welding method used for manufacturing the lap laser welding joint of the present invention. In the lap laser welded joint 1 of the present invention, first, a plurality of steel plates are superposed one on the other, and a laser beam is intermittently irradiated to the uppermost steel plate surface among the superposed steel plates to form a first joint portion. 4 and a plurality of subsequent joining portions 5 that follow, and a welded portion is formed and manufactured.

As described above, in the present invention, one-side welding is performed on a plurality of stacked steel plates. By employing single-side welding, the work space required for welding can be reduced.
In one-side welding, it is preferable to irradiate a laser beam from the steel plate side with the larger plate thickness among a plurality of superposed steel plates from the viewpoint of preventing melting during welding. On the other hand, from the viewpoint of preventing unbonding due to non-penetration, it is preferable to irradiate the laser beam from the thinner plate. In addition, when the plate | board thickness of a steel plate is the same, you may irradiate a laser beam from which steel plate side.

  In the lap laser welding joint 1 shown in FIG. 5, two steel plates 2 and 3 are overlapped to form a joint surface, and a laser beam is intermittently irradiated on the joint surface to form a J-shaped first. A joint 4 and a plurality of linear subsequent joints 5 are formed subsequently to the joint 4.

  Here, what is important in the present invention is that the lap laser beam welded joint of the present invention has a ratio (G / T) of the total gap G between the steel plates constituting the welded portion to the total thickness T of the steel plates constituting the welded portion. Is 0 to 0.15, that is, the ratio of the total gap G between the steel plates constituting the welded portion to the total thickness T of the steel plates constituting the welded portion is set within a range of 0 to 15%. This is because if the ratio of G to T exceeds 15%, the depth of the crater at the end of welding becomes deeper and stress is more likely to concentrate. Preferably it is 0 to 10% of range.

  Further, in the present invention, what is important is that the laser beam LB is irradiated when the surface of the steel plate is irradiated with the laser beam LB while moving the welding head WH for irradiating the laser beam in the welding direction (arrow direction indicated by D in FIG. 5). Is the direction opposite to the moving direction of the welding head WH (the direction opposite to the arrow indicated by D in FIG. 5). By making the moving direction of the welding head WH and the scanning direction of the laser beam LB reverse as described above, the welding start end portion of the first joint portion 4 and the welding end portion of the subsequent joint portion 5 adjacent thereto are obtained. The welding start end of the subsequent joint 4 and the welding end of the subsequent joining 4 adjacent to each other are opposed to each other, that is, the welding start and welding end of the adjacent joint are opposed. Since the welded portion can be formed as described above, it is possible to prevent the weld end portion of the joint from cracking.

  Further, in the present invention, as shown in FIG. 5, the shape of the first joint portion 4 is an arc shape or a circular shape connected to the linear joint portion and the welding end portion side of the linear joint portion. It is important to have a J-shape consisting of curved joints. Thereby, the crack which generate | occur | produces in the welding termination | terminus part of a 1st junction part can be prevented.

Furthermore, what is important in the present invention is that the welded portion (first joint and subsequent joint) formed as described above has the following formulas (1) to (4):
15.0 ≦ L ₁ ≦ 30.0 (1)
8.0 ≦ L ₂ ≦ 20.0 (2)
1/8 ≦ w / b ≦ 1/2 (3)
1/4 ≦ a / (L ₁ + L ₂ ) ≦ 1/2 or 1/2 ≦ a / L ₂ ≦ 1 (4)
Here, L ₁ : length of the first joint (mm)
L ₂ : Length of subsequent joint (mm)
b: Minimum thickness (mm) of molten metal at the joint
w: width of molten metal at joint (mm)
a: Shortest distance between joints (mm)
It is important to control at least one of laser beam welding conditions, specifically, laser power, focal position, welding speed, and beam diameter so that all of the above are satisfied.

  Here, as the type of laser beam used in the laser beam welding according to the present invention, for example, a fiber laser, a disk laser, or the like can be used. Further, in order to satisfy the above equations (1) to (4), the laser beam irradiation is performed with an output of 2.0 to 6.0 kW, a focal position: a steel plate surface irradiated with the laser beam to a steel plate surface +30 mm, a beam. The diameter is preferably 0.4 to 1.0 mm and the scanning speed of the laser beam is preferably 2.0 to 5.0 m / min. More preferably, laser output: 2.5 to 5.0 kW, focal position: steel plate surface to which the laser beam is irradiated to steel plate surface + 20 mm, beam diameter: 0.5 to 0.8 mm, and laser beam scanning speed: 2.5 It is the range of -4.5 m / min.

In the welding method of the welded joint according to the present invention, the shape of the first joint portion 4 may be a shape composed of only a straight joint portion instead of a J shape. The length L _{1 ′ of the part} is replaced with the following formula (1 ′) instead of the formula (1);
30.0 ≦ L _{1 ′} ≦ 40.0 (1 ′)
Here, L _{1 ′} : length of the linear joint (mm)
It is important to control so as to satisfy. Thereby, even if it is not J-shaped, the crack which generate | occur | produces in the welding termination | terminus part of a 1st junction part can be prevented.

<Structural members for automobile bodies>
Next, the structural member for an automobile body of the present invention will be described.
As an example in which the lap laser welding joint of the present invention can be preferably used, there is a structural member (strength member) that becomes a skeleton part of an automobile body. The member shown in FIG. 1 (FIG. 4) described above is composed of a steel plate 2 that is a frame component having a substantially hat-shaped cross section and a steel plate 3 that is a panel component, and a flange portion 2b of the steel plate 2 and the flange portion. The steel plate 3 disposed opposite to 2b is joined by a welded portion made up of the first joint 4 and the subsequent joint 5 formed by the laser beam welding described above to constitute a closed cross section. In order to apply a member having such a shape to a strength member of an automobile body, it is important that the strength of the welded portion is excellent from the viewpoint of ensuring collision safety. Since the joint has no crack at the weld end portion of the joint and has sufficient peel strength, it can be suitably used, for example, for a structural member such as a center pillar or roof rail of an automobile body.

  Here, when manufacturing a structural member or the like for an automobile body by applying the lap laser beam welding joint of the present invention, L having flange portions 2b and 3b as shown in FIG. A case where two steel plates 2 and 3 having a letter-shaped cross section are overlapped so that the flange portions face each other and laser beam welding is performed from one side will be described as an example. FIG. 6A is a plan view of the overlapped flange portion as viewed from above. The flange portion includes a J-shaped first joint portion and a plurality of subsequent joint portions subsequent thereto. FIG. 6B is a cross-sectional view taken along the line C-C shown in FIG. 6A. FIG. 6B shows that a weld is formed.

In FIG. 6, the preferred position for forming the welded portion is that the center line of the plate thickness of the steel plates 2 and 3 is the base point (0 point), and from there to the center of the width of the joint 5 (4) formed in the flange portion. Is defined as a welding position X, the welding position X is expressed by the following formula (5):
5t ≦ X ≦ 8t (5)
Here, t: the thickness (mm) of the thickest steel plate among the steel plates constituting the welded portion
It is preferable to satisfy. For example, when the thickness t of the thickest steel plate is 2 mm, the welding position X is preferably in the range of 10 to 16 mm.

  If the welding position X is smaller than 5t, the weld metal part is more likely to break during the peel test, and the peel strength may be reduced. On the other hand, if the welding position X is larger than 8 t, the moment applied to the first joint 4 and the subsequent joint 5 in the peel test becomes too large, and the peel strength is also lowered. A more preferable range of X is a range of 6t ≦ X ≦ 7t. By forming the welded portion at the above position, the peel strength of the two-layer welded joint having a total steel plate thickness of 2 to 5 mm can be set to 3.0 kN or more.

  The equation (5) related to the welding position X is limited to a T-shaped overlap laser beam welded joint in which two steel plates having an L-shaped cross section are overlapped as shown in FIG. For example, the present invention is also applied to a lap laser welding joint obtained by laser beam welding a frame part (steel plate 2) and a panel part (steel plate 3) having a substantially hat-shaped cross section as shown in FIGS. In this case, the base point (0 point) of the welding position X may be the center of the thickness of the vertical wall portion 2a of the frame part having a substantially hat-shaped cross section.

  From the high-tensile steel plate having the composition of A to J shown in Table 1, the plate thickness is any of 1.2 mm, 1.6 mm and 2.0 mm, and the tensile strength TS is 590 to 1180 MPa class, A sample having a width of 100 mm and a length of 150 mm was taken and bent into an L shape having a long side of 120 mm and a short side of 30 mm to obtain an L-shaped steel plate. Here, the long side of the L-shaped steel plate corresponds to the vertical wall 2a in FIG. 1 (FIG. 4), and the short side corresponds to the flange portion 2b in FIG. 1 (FIG. 4). Next, as shown in FIG. 7, after superimposing the short sides of the two L-shaped steel plates 7 so as to face each other, a laser beam is irradiated in the atmosphere to perform the first joining. A welded portion composed of the portion 4 and a plurality of subsequent joined portions 5 was formed, and a T-shaped peel test piece 9 was produced.

When performing the above laser beam welding, a fiber laser having a beam diameter of 0.6 mmφ at the focal position is used as the laser beam, and the focal position is the upper surface of the superposed steel plates (the upper steel plate 7 shown in FIG. 7). As shown in Table 2, the gap G between the two steel plates, the output of the laser beam to be irradiated, and the scanning speed are variously changed to change the J-shaped first joint portion as shown in Table 2. The length L ₁ , the length L ₂ of the subsequent joint, the shortest distance a between the adjacent joints adjacent to the first joint and between the subsequent joints, the minimum thickness b of the molten metal part of the joint, and the The width w of the molten metal was variously changed as shown in Table 2. At this time, the welding position X for forming the welded portion was set to 6.5 times (constant) the thickest plate thickness t.

Further, the first joint portion, the J-shaped instead of the first joint portion, also produced in the same manner for welds employing the first junction of the length L _{1 'is} long straight, T-shaped A mold peel test piece 9 was prepared.

With respect to the T-shaped peel test piece thus obtained, the presence or absence of cracks in the welded portion, in particular, the welded end portion of the first joint portion and the subsequent joint portion, was determined by visual inspection and penetration testing.
Next, a tensile test in which the length direction of the long side of the two L-shaped steel plates was pulled was performed at a speed of 10 mm / min, and the peel strength (maximum load) was measured for the T-shaped peel test piece. . In this example, the case where the peel strength was 3.0 kN or more was determined as “pass”.

The determination results of the presence or absence of weld cracks and the measurement results of peel strength are also shown in Table 2.
From these results, the test pieces (Nos. 1, 8, 15, 22, 29, 36, 43, 50, 57 and 64) which were welded by laser beam welding under the conditions suitable for the present invention were all weld end points of the joints. There were no cracks in the part, and the peel strength was 3.0 kN or more.
In contrast, no. In the test pieces of 2, 9, 16, 23, 30, 37, 44, 51, 58 and 65, since the gap G of the welded portion was larger than 15% of the total thickness T of the steel plate, all of them were welded at the end of the welded portion. Cracks occurred in the part, and the peel strength was less than 3.0 kN.
No. In the test pieces of 3, 10, 17, 24, 31, 38, 45, 52, 59 and 66, the width w of the molten metal at the joint was larger than ½ of the minimum thickness b of the molten metal at the joint. A weld crack occurred. On the other hand, no. Since the test pieces of 4, 11, 18, 25, 32, 39, 46, 53, 60 and 67 had the width w of the molten metal at the joint portion smaller than 1/8 of the minimum thickness b of the molten metal at the joint portion, Although there was no occurrence of weld cracking, the peel strength was less than 3.0 kN.
No. It specimens 5,12,19,26,33,40,47,54,61 and 68, the length of the first joint portion _{L 1} is shorter than 15.0 mm, weld cracking occurs.
No. It specimens 6,13,20,27,34,41,48,55,62 and 69, the length _{L 2} of the trailing junction shorter than 8.0 mm, weld cracking occurs.
No. The test pieces of 7, 14, 21, 28, 35, 42, 49, 56, 63, and 70 have a distance a between the subsequent joints adjacent to the first joint and between the subsequent joints. for longer than _{L 2,} weld cracking occurs, peel strength was less than 3.0 kN.
No. 71 and 72 are the results showing the test results for the test pieces obtained by laminating two steel plates having different strength levels under the conditions suitable for the present invention and laser beam welding, and in the combination of the 590 MPa class and the 980 MPa class, The component composition of steel is within the preferred range of the present invention. No. 71 has no weld cracking and an excellent peel strength, but the component composition of steel is outside the preferred range of the present invention. No. 72 was weld cracked and had a peel strength of less than 3.0 kN.
No. 73 is a test piece adopting a linear joint having a long length L1 ′ as the first joint, and it is welded without being cracked by performing laser beam welding under conditions suitable for the present invention. It was found that a peel strength equivalent to that of the first joint was obtained.
As described above, in the present invention examples in which the lap laser beam welding was performed according to the present invention, good lap laser beam welded joints having the characteristics intended by the present invention were obtained, whereas In the comparative example out of the condition, a good lap laser beam welded joint could not be obtained.

  Since the technique of the present invention can be welded at high speed and with low distortion, it can be preferably applied to an automobile structural member having a flange portion.

1: Laminated laser beam welded joint 2, 3: Steel plate 2a: Vertical wall portion 2b: Flange portion 4, 14: First joint portion 4a, 14a: Center portion of welding end portion of first joint portion 5, 15: Subsequent joint Part 5a, 15a: Center part of welding end part of subsequent joining part 6: Welding part 7: L-shaped steel sheet 7a: Long side of L-shaped steel sheet 7b: Width of L-shaped steel sheet 8: Crack at welding terminal part of joining part 9 : Peeling test piece WH: welding head LB: laser beam D: moving direction of welding head d: laser beam scanning direction L ₁ , L _{1 ′} : length of the first joint L ₂ : length of the subsequent joint a : Minimum distance between adjacent joints b: Minimum thickness of molten metal at joints w: Width of molten metal at joints G: Gaps between steel plates S: Welding end of joints E: Welding end of joints Part Fa: Stress applied to the welding end part of the conventional joint part Fb: Initial stage of the subsequent joint part Stress Fc exerted on contact termination: stress exerted on the weld end of the first joined section 0: reference point welding position X

Claims (8)

In a lap laser welding joint having a welded portion formed by stacking a plurality of steel plates,
The total gap G between the steel plates constituting the weld zone is in the range of 0 to 15% of the total thickness T of the steel plates constituting the weld zone;
The welded portion is composed of a linear first joint portion and a linear subsequent joint portion arranged in a row following the first joint portion,
The welding start end portion of the first joint portion and the welding end portion of the subsequent joint portion adjacent to the first welding portion are opposed to each other, and the welding start end portion and the welding end portion of the subsequent joint portions are opposed to each other,
The first joint portion has a J-shape consisting of a linear joint portion and an arc-shaped or circular curved joint portion connected to the welding end portion side of the linear joint portion,
Further, the welded portion satisfies all of the following formulas (1) to (4), and is a lap laser welded joint.
15.0 ≦ L ₁ ≦ 30.0 (1)
8.0 ≦ L ₂ ≦ 20.0 (2)
1/8 ≦ w / b ≦ 1/2 (3)
1/4 ≦ a / (L ₁ + L ₂ ) ≦ 1/2 or 1/2 ≦ a / L ₂ ≦ 1 (4)
Here, L ₁ : length of the first joint (mm)
L ₂ : Length of subsequent joint (mm)
b: Minimum thickness (mm) of molten metal at the joint
w: width of molten metal at joint (mm)
a: Shortest distance between joints (mm) The lap laser welded joint according to claim 1, wherein the first joint portion includes only a linear joint portion and satisfies the following expression (1 ′) instead of the expression (1).
30.0 <L _{1 ′} ≦ 40.0 (1 ′)
Here, L _{1 ′} : length of the linear joint (mm) At least one of the steel plates is C: 0.07 to 0.4 mass%, Si: 0.2 to 3.5 mass%, Mn: 1.8 to 5.5 mass%, P + S: 0.03 mass% or less, The lap laser beam welded joint according to claim 1 or 2, wherein Al: 0.08 mass% or less and N: 0.010 mass% or less are contained, and the balance has a composition composed of Fe and inevitable impurities. . The lap laser welding joint according to claim 3, wherein the steel sheet further contains at least one component of the following group A and group B in addition to the component composition.
-Group A; Ti: 0.0005-0.01 mass% and Nb: One or two selected from 0.005-0.050 mass%-Group B: Cr: 1.0 mass% or less, Mo: One or more selected from 0.50 mass% or less and B: 0.10 mass% or less The lap laser weld joint according to any one of claims 1 to 4, wherein at least one of the steel plates is a high-tensile steel plate having a tensile strength of 980 MPa or more. A plurality of steel plates are stacked one above the other, and a laser beam is intermittently irradiated on one side surface of the stacked steel plates to form a linear first joint portion and a linear subsequent joint portion following the first joint portion. When forming welds arranged in a row,
The total gap G between the steel plates constituting the weld zone is within a range of 0 to 15% of the total thickness T of the steel plates constituting the weld zone,
By reversing the moving direction of the welding head for irradiating the laser beam and the scanning direction of the laser beam, a welding start end portion of the first joint portion and a welding end portion of a subsequent joint portion adjacent to the first joint portion are provided. And the welding start end portion and the welding end portion of the subsequent joint portions face each other,
The shape of the first joint portion is a J-shape consisting of a linear joint portion and an arcuate or circular curved joint portion connected to the welding end portion side of the linear joint portion,
Furthermore, the laser beam, the focal position, the welding speed, and the beam diameter are controlled so that the welded part satisfies all of the following formulas (1) to (4). A method for manufacturing a welded joint.
15.0 ≦ L ₁ ≦ 30.0 (1)
8.0 ≦ L ₂ ≦ 20.0 (2)
1/8 ≦ w / b ≦ 1/2 (3)
1/4 ≦ a / (L ₁ + L ₂ ) ≦ 1/2 or 1/2 ≦ a / L ₂ ≦ 1 (4)
Here, L ₁ : length of the first joint (mm)
L ₂ : Length of subsequent joint (mm)
b: Minimum thickness (mm) of molten metal at the joint
w: width of molten metal at joint (mm)
a: Shortest distance between joints (mm) At least one of the laser output, the focal position, the welding speed, and the beam diameter satisfying the following expression (1 ′) instead of the above expression (1), wherein the first joining part is composed of only a linear joining part. One method is controlled, The manufacturing method of the lap laser welding joint of Claim 6 characterized by the above-mentioned.
30.0 <L _{1 ′} ≦ 40.0 (1 ′)
Here, L _{1 ′} : length of the linear joint (mm) A structural member for an automobile body having the lap laser weld joint according to any one of claims 1 to 5.

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