JP2023087674A - Laser lap welding joint, method for manufacturing laser lap welding joint, and structure member for automobile body - Google Patents

Abstract

To provide a laser lap welding joint capable of suppressing welding cracks at a bead tail end, a method for manufacturing the same, and a structure member for an automobile body.SOLUTION: The laser lap welding joint comprises; a plurality of metal plates; and a first bead that is a linearly extending laser welding part. The ratio G/T of a total value G of sizes of gaps among the metal plates to a total value T of thicknesses of the metal plates is 0-18%. The length L1 of the first bead is 10-100 mm. The laser lap welding joint further comprises a second bead. The length L2 of the second bead is shorter than the length L1. In a tail end surrounding region, the length of a region of the second bead having a distance of 2 mm or shorter from the width end of the first bead is 2 mm or shorter along the center axis of the first bead. The second bead is isolated from the center axis of the first bead. The second bead is not included in a start end surrounding region.SELECTED DRAWING: Figure 1

Description

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

A lap joint is a welded joint obtained by welding together a plurality of metal plates that are placed on top of each other. Laser welding is one of the welding means for manufacturing lap joints. Lap laser welding is welding in which one side surface of a plurality of metal plates is irradiated with a laser beam to melt and solidify the metal plates to join the metal plates.

Lap laser welding is capable of joining narrow regions such as flanges of hat-shaped members at high speed. However, lap laser welding has the problem that cracks are likely to occur at the final solidified portion at the end of the weld bead.

In laser welding, molten metal flows in the direction opposite to the direction of travel of the laser. Therefore, a recess called a crater is formed at the terminal end of the bead formed by laser welding. In addition, tensile stress is applied to the end portion of the bead after laser welding is completed. This is because after the laser welding is completed, the welded portion is rapidly cooled by heat transfer from the welded portion to its surroundings and shrinks. By applying a tensile stress to the bead end portion in which the crater is formed, the bead end portion may break so as to be torn perpendicularly to the extending direction of the bead. In this case, the termination break may propagate along the bead and form a crack throughout the bead.

In recent years, there have been an increasing number of cases in which materials for mechanical structural parts are being strengthened. For example, high-strength steel sheets with a tensile strength of 980 MPa or more are being used in an increasing number of automobile body members, particularly structural members that serve as frame members of automobiles, for the purpose of improving the strength and rigidity of the car body. However, the greater the tensile strength of the metal plate, the greater the tensile stress applied to the end portion of the bead after the end of laser welding, increasing the risk of cracking at the end portion of the bead. When the bead is cracked along its entire length, the static strength such as the shear strength and peel strength of the joint is reduced, and the fatigue strength is also significantly reduced. Due to the above circumstances, there is a long-awaited technique for preventing cracks at the end portion of a bead in a high-strength metal plate.

In Patent Document 1, a laser beam is intermittently irradiated to one side surface of a steel plate in which a plurality of steel plates are superimposed, and a linear first joint portion and a linear subsequent joint portion following the first joint portion are formed. When forming a welded portion in which the are arranged in a row, at least the total gap G between the steel plates constituting the welded portion is within the range of 0 to 15% of the total thickness T of the steel plates constituting the welded portion, By reversing the moving direction of the welding head that irradiates the laser beam and the scanning direction of the laser beam, the welding starting end of the first joint and the welding end of the subsequent joint adjacent to the first joint are opposed to each other, and the welding starting end and the welding end of the subsequent joints are opposed to each other, and the various dimensions of the joints are controlled within appropriate ranges. Disclosed is a lap laser welded joint which is free from cracks at the weld end portion and has excellent peel strength, a method for manufacturing the same, and a structural member for an automobile body having the welded joint.

In Patent Document 2, a plurality of steel plates having a plate thickness of 0.5 to 3.0 mm, including at least one high-tensile steel plate having a tensile strength of 780 MPa or more, and having oil applied to the surface are superimposed. A laser welded joint that is laser-welded with a laser, wherein the overlapping portion in which the plurality of steel plates are superimposed has a weld bead penetrating from the surface of the steel plate in the uppermost stage to the back surface of the steel plate in the lowermost stage, The minimum Vickers hardness of the weld bead is 350 Hv or more, and the chemical composition of the weld metal in the weld bead is C: 0.05 to 0.35% and Si: 0.01 to 2.5% by mass%. , Mn: 0.5 to 5.0%, P: 0.05% or less, S: 0.01% or less, the balance being Fe and unavoidable impurities, and C + Si / 5 ≤ 0.4 and a front bead width WS and a back bead width WB of the weld bead satisfying WS+WB≦3.5.

In Patent Document 3, a plurality of steel plates are superimposed or butted, and the surface of the uppermost steel plate in the overlapped or butted portion is irradiated with a laser to melt even the back surface of the lowermost steel plate to form a weld. , After forming the welded part, within 10 minutes, a shielding gas with an absolute humidity of 2 g / m ³ or less is supplied to the welded part on the surface of the uppermost steel plate, and penetrates to the back surface of the lowermost steel plate that is in contact with the atmosphere. A steel structure is disclosed in which the weld metal is re-irradiated with a laser beam one or more times so as to prevent the weld metal from melting, and the weld metal is re-melted by the number of irradiation times.

In Patent Document 4, in a lap laser welding method in which welding is performed by scanning a laser beam along the edge of a multi-layered work, from a direction inclined from 45 to 90 degrees with respect to the beam scanning direction, with respect to the work plate surface A lap laser welding method is disclosed in which welding is performed by obliquely irradiating a laser beam, and a bead is inclined within a cross section perpendicular to the beam scanning direction.

Patent Document 5 discloses a laser welding method for welding a plurality of metal members by irradiating a laser beam to a portion in which a plurality of metal members are superimposed, wherein at least one metal member among the plurality of metal members is welded. The member is formed of a plated steel plate in which the base material is coated with a coating material having a melting point lower than that of the base material. A pretreatment step of processing a side surface to generate a protrusion that rises from the other side surface on the other side on the opposite side; a welding step of welding the plurality of metal members together by irradiating a laser beam to the overlapped portion of the plurality of the metal members while maintaining the position in the in-plane direction while overlapping the metal members; A laser welding method is disclosed having:

WO2020/194669 JP 2019-188407 A JP 2012-240083 A JP 2008-296236 A WO2014/126172

In the technique of Patent Literature 1, weld cracking is suppressed by making the end portion of the bead J-shaped. However, the technique of Patent Document 1 requires a J-shaped end portion of the bead, and cannot be applied to a member having a small width of the welded portion, for example, the width of the flange. Moreover, the length of the bead must be equal to or greater than a predetermined value, and it cannot be applied to short beads. In the techniques of Patent Documents 2 to 5, no consideration is given to relaxation of the tensile stress at the end of the bead. Moreover, the technique of Patent Document 3 has a problem that the welding time becomes long.

In view of the above circumstances, it is an object of the present invention to provide a lap laser welded joint capable of suppressing weld cracking at the end portion of a bead, a method for manufacturing the lap laser welded joint, and a structural member for an automobile body.

The gist of the present invention is as follows.

(1) A lap laser welded joint according to an aspect of the present invention includes a plurality of superimposed metal plates and a first bead that is a linearly extending laser welded portion that joins the plurality of metal plates. and wherein the ratio G/T between the total value G of the size of the gaps between the plurality of metal plates and the total value T of the thicknesses of the plurality of the metal plates is 0 to 18. %, and the length L1 of the first bead measured along the central axis along the extending direction of the first bead is 10 to 100 mm, and the lap laser welded joint is further 2 beads, and the length L2 of the second bead measured along the central axis along the extending direction of the second bead is smaller than the L1, and the lap laser welded joint A first imaginary line passing through the end of the first bead and perpendicular to the center axis of the first bead at the end, and the end of the first bead in plan view in the thickness direction through a first point 5 mm away along said central axis of said first bead from toward the beginning of said first bead and perpendicular to said central axis of said first bead at said first point In the end peripheral region, which is the region between the second virtual line, the length of the region in the second bead, the distance from the end in the width direction of the first bead is 2 mm or less, 2 mm or more along the central axis of the first bead, and the second bead is spaced apart from the central axis of the first bead, passing through the beginning of the first bead and at the beginning a third imaginary line perpendicular to the central axis of the first bead, and along the central axis of the first bead from the starting end of the first bead toward the terminal end of the first bead; A starting end peripheral region that is the region between a fourth imaginary line passing through a second point separated by (1/3) × L1 and perpendicular to the central axis of the first bead at the second point does not include the second bead.
(2) In the lap laser welded joint described in (1) above, in a plan view of the lap laser welded joint viewed from the thickness direction, the second bead is aligned with the central axis of the first bead. As a reference, it may be formed on both sides of the first bead.
(3) In the lap laser welded joint described in (1) or (2) above, the first From a fifth imaginary line passing through a third point 2 mm away along the central axis of the bead and perpendicular to the central axis of the first bead at the third point, the second bead They may be separated.
(4) In the lap laser welded joint according to any one of (1) to (3) above, the first bead may be formed only on one surface of the lap laser welded joint.
(5) In the lap laser welded joint according to any one of (1) to (4) above, the second bead is one of the metal plates disposed on the outermost layer of the lap laser welded joint. The penetration depth of the second bead may be 1/2 or more of the thickness of the metal plate on which the second bead is formed.
(6) In the lap laser welded joint according to any one of (1) to (5) above, the plurality of metal plates are a plurality of steel plates, and one or more of the plurality of steel plates The component composition contains C: 0.05 to 0.5 mass%, Si: 0.1 to 3.5 mass%, Mn: 0.1 to 5.5 mass%, and P and S: total 0.03 mass% or less. It's okay.
(7) In the lap laser welded joint according to any one of (1) to (6) above, the plurality of metal plates are a plurality of steel plates, and one or more of the plurality of steel plates has a tensile strength The strength may be 980 MPa or more.
(8) In the lap laser welded joint according to any one of (7) above, the steel plate on which the second bead is formed among the plurality of steel plates may have a tensile strength of 980 MPa or more.

(9) A method for manufacturing a lap laser welded joint according to another aspect of the present invention includes a step of overlapping a plurality of metal plates, and a linearly extending laser welded portion joining the plurality of metal plates. A method for manufacturing a lap laser welded joint, comprising: performing a first laser irradiation so as to form a first bead; and the total value T of the thickness of the metal plate, the ratio G/T being 0 to 18%, and measured along the central axis along the extending direction of the first bead. The bead length L1 is set to 10 to 100 mm, and the method for manufacturing a lap laser welded joint further includes a step of performing a second laser irradiation so as to form a second bead, and the extension of the second bead. The length L2 of the second bead, which is measured along the central axis along the existing direction, is made smaller than the L1, and in a plan view of the lap laser welded joint in the thickness direction, the first bead a first imaginary line passing through the end of the bead and perpendicular to the central axis of the first bead at the end; is the area between a second imaginary line passing through a first point 5 mm away along said central axis of one bead and perpendicular to said central axis of said first bead at said first point In the end peripheral region, the length of the region of the second bead that is 2 mm or less from the end of the width direction of the first bead is 2 mm along the central axis of the first bead As above, the second bead is separated from the central axis of the first bead, and a third bead passes through the beginning of the first bead and is perpendicular to the central axis of the first bead at the beginning. and a second point spaced apart (⅓)×L1 along the central axis of the first bead from the starting end of the first bead toward the terminating end of the first bead and a fourth imaginary line perpendicular to the central axis of the first bead at the second point does not include the second bead, and the first The second bead is formed before 10 seconds after the end of the laser irradiation.
(10) In the method for manufacturing a lap laser welded joint described in (9) above, the second laser irradiation may be performed after the first laser irradiation.
(11) In the method for manufacturing a lap laser welded joint described in (9) above, the first laser irradiation may be performed after the second laser irradiation.
(12) In the method for manufacturing a lap laser welded joint according to any one of (9) to (11) above, in a plan view of the lap laser welded joint in the thickness direction, the second bead may be formed on both sides of the first bead with respect to the central axis of the first bead.
(13) In the method for manufacturing a lap laser welded joint according to any one of (9) to (12) above, from the terminal end of the first bead, the direction opposite to the starting end of the first bead a fifth imaginary line passing through a third point 2 mm away along said central axis of said first bead and perpendicular to said central axis of said first bead at said third point toward may be spaced apart from the second bead.
(14) In the method for manufacturing a lap laser welded joint according to any one of (9) to (13) above, the first bead may be formed only on one side of the lap laser welded joint.
(15) In the method for manufacturing a lap laser welded joint according to any one of (9) to (14) above, the penetration depth of the second bead is set to the metal on which the second bead is formed. It may be 1/2 or more of the thickness of the plate.

(16) A structural member for an automobile body according to another aspect of the present invention comprises the lap laser welded joint according to any one of (1) to (8) above.

(17) A lap laser welded joint according to an aspect of the present invention includes a plurality of metal plates that are superimposed, and a first metal plate that is a metal plate arranged in the outermost layer among the plurality of metal plates. and the surface of the second metal plate superimposed on the first metal plate, and a linearly extending laser welded portion that joins a plurality of the metal plates. 1 bead, wherein the ratio G/T between the total value G of the size of the gaps between the plurality of metal plates and the total value T of the thicknesses of the plurality of metal plates is 0 to 18%, the length L1 of the first bead measured along the central axis along the extending direction of the first bead is 10 to 100 mm, and the lap laser welded joint is Furthermore, the length L2 of the second bead, which has a second bead on at least the surface of the second metal plate and is measured along the central axis along the extending direction of the second bead is smaller than L1, and passes through the terminal end of the first bead and the central axis of the first bead at the terminal end in the mating surface of the second metal plate that is overlapped with the first metal plate and a first point 5 mm away along the central axis of the first bead from the terminal end of the first bead toward the beginning of the first bead and the width of the first bead in the second bead in the end peripheral region, which is the region between the first point and a second imaginary line perpendicular to the central axis of the first bead The length of the region whose distance from the end of the direction is 2 mm or less is 2 mm or more along the central axis of the first bead, and the second bead is located at the center of the first bead. a third imaginary line spaced from the axis, passing through the beginning of said first bead and perpendicular to said central axis of said first bead at said beginning; said central axis of said first bead passing through a second point spaced (1/3)×L1 along said central axis of said first bead toward said terminal end of said bead and at said second point; The second bead is not included in the starting end peripheral region, which is the region between the fourth imaginary line perpendicular to the .
(18) In the lap laser welded joint described in (17) above, in the mating surface of the second metal plate that is overlapped with the first metal plate, the second bead is the first bead. It may be formed on both sides of the first bead with respect to the central axis.
(19) In the lap laser welded joint described in (17) or (18) above, from the terminal end of the first bead toward the direction opposite to the starting end of the first bead, From a fifth imaginary line passing through a third point 2 mm away along the central axis of the bead and perpendicular to the central axis of the first bead at the third point, the second bead They may be separated.
(20) In the lap laser welded joint according to any one of (17) to (19) above, the first bead may be formed only on one surface of the lap laser welded joint.
(21) In the lap laser welded joint according to any one of (17) to (20) above, the penetration depth of the second bead in the second metal plate is It may be 1/2 or more of the thickness.
(22) In the lap laser welded joint according to any one of (17) to (21) above, the plurality of metal plates are a plurality of steel plates, and one or more of the plurality of steel plates are The component composition contains C: 0.05 to 0.5 mass%, Si: 0.1 to 3.5 mass%, Mn: 0.1 to 5.5 mass%, and P and S: total 0.03 mass% or less. You can stay.
(23) In the lap laser welded joint according to any one of (17) to (22) above, the plurality of metal plates are a plurality of steel plates, and one or more of the plurality of steel plates has a tensile strength The strength may be 980 MPa or more.
(24) In the lap laser welded joint described in (23) above, the steel plate on which the second bead is formed among the plurality of steel plates may have a tensile strength of 980 MPa or more.

(25) A method for manufacturing a lap laser welded joint according to another aspect of the present invention includes a step of overlapping a plurality of metal plates, and a linearly extending laser welded portion joining the plurality of metal plates. a first laser irradiation to form a first bead, wherein in the first laser irradiation, at least the plurality of metals At least an end surface of a first metal plate disposed on the outermost surface of the plates and a surface of a second metal plate superimposed on the first metal plate are joined, and in the superposition, the metal The ratio G/T between the total value G of the size of the gap between the plates and the total value T of the thickness of the metal plate is set to 0 to 18%, and the central axis along the extending direction of the first bead The length L1 of the first bead, measured along the 2, wherein the length L2 of the second bead measured along the central axis along the extending direction of the second bead is smaller than the L1; A first imaginary line passing through the terminal end of the first bead and perpendicular to the central axis of the first bead at the terminal end on the mating surface of the second metal plate that overlaps the first metal plate and passing through a first point separated by 5 mm along the central axis of the first bead from the terminal end of the first bead to the starting end of the first bead and at the first point In the end peripheral region, which is the region between the second imaginary line perpendicular to the central axis of the first bead, the distance from the end of the first bead in the width direction in the second bead is The length of the region that is 2 mm or less is 2 mm or more along the central axis of the first bead, the second bead is separated from the central axis of the first bead, and the first bead a third imaginary line passing through the starting end of the bead and perpendicular to the center axis of the first bead at the starting end; a fourth imaginary line passing through a second point spaced (1/3)×L1 along the central axis of one bead and perpendicular to the central axis of the first bead at the second point; The second bead is formed before 10 seconds after the end of the first laser irradiation without including the second bead in the starting end peripheral region, which is the region between .
(26) In the method for manufacturing a lap laser welded joint described in (25) above, the second laser irradiation may be performed after the first laser irradiation.
(27) In the method for manufacturing a lap laser welded joint described in (25) above, the first laser irradiation may be performed after the second laser irradiation.
(28) In the method for manufacturing a lap laser welded joint according to any one of (25) to (27) above, in the mating surface of the second metal plate that is overlaid with the first metal plate, the A second bead may be formed on both sides of the first bead with respect to the central axis of the first bead.
(29) In the method for manufacturing a lap laser welded joint according to any one of (25) to (28) above, the direction opposite to the starting end of the first bead from the terminal end of the first bead a fifth imaginary line passing through a third point 2 mm away along said central axis of said first bead and perpendicular to said central axis of said first bead at said third point toward may be spaced apart from the second bead.
(30) In the method for manufacturing a lap laser welded joint according to any one of (25) to (29) above, the first bead may be formed only on one side of the lap laser welded joint.
(31) In the method for manufacturing a lap laser welded joint according to any one of (25) to (30) above, the penetration depth of the second bead in the second metal plate is set to the second The thickness may be 1/2 or more of the thickness of the metal plate.

(32) A structural member for an automobile body according to another aspect of the present invention comprises the lap laser welded joint according to any one of (17) to (24) above.

According to the present invention, it is possible to provide a lap laser welded joint capable of suppressing weld cracking at the end portion of a bead, a method for manufacturing the lap laser welded joint, and a structural member for an automobile body.

FIG. 2 is a schematic diagram of a lap laser welded joint when viewed from the thickness direction of the lap laser welded joint. FIG. 4B is an enlarged view of the stress relief region of the second bead; 1 is an enlarged cross-sectional view of a lap laser welded joint including a first bead and a second bead in the first embodiment; FIG. It is an enlarged sectional view of the lap laser welding joint containing the 1st bead and the 2nd bead in the same embodiment. It is an enlarged sectional view of the lap laser welding joint containing the 1st bead in the same embodiment. 1 is a schematic diagram of tensile stress in a conventional lap laser welded joint without a second bead; FIG. FIG. 4 is a schematic representation of tensile stress in a lap laser welded joint with a second bead; FIG. 2 is a schematic diagram of a lap laser welded joint when viewed from the thickness direction of the lap laser welded joint. FIG. 4 is an enlarged cross-sectional view of a lap laser welded joint including first and second beads in a second embodiment; It is an enlarged sectional view of the lap laser welding joint containing the 1st bead and the 2nd bead in the same embodiment. It is an enlarged sectional view of the lap laser welding joint containing the 1st bead in the same embodiment. FIG. 4 is an enlarged cross-sectional view showing a modification of the lap laser welded joint according to one embodiment of the present invention; Condition no. 5 is a photograph of a lap laser welded joint of No. 5. FIG. Condition no. 8 is a photograph of a lap laser welded joint of No. 8. FIG. Condition no. 12 is a photograph of 12 lap laser welded joints. Condition no. 2 is a photograph of 20 lap laser welded joints. Condition no. 29 is a photograph of 29 lap laser welded joints. Condition no. 33 is a photograph of a lap laser welded joint. Condition no. 36 is a photograph of 36 lap laser welded joints.

[First embodiment]
<Lap laser welded joint 1>
Hereinafter, a lap laser welded joint according to a first embodiment of the present invention will be described with appropriate reference to the drawings. The lap laser welded joint 1 according to the present embodiment includes a plurality of superimposed metal plates 10, a first bead 11 that is a linearly extending laser welded portion that joins the plurality of metal plates 10, have
A ratio G/T between the total value G of the sizes of the gaps between the plurality of metal plates 10 and the total value T of the thicknesses of the plurality of metal plates 10 is 0 to 18%. The length L1 of the first bead 11 measured along the central axis 11X along the extending direction of the first bead 11 is 10-100 mm.
The lap laser welded joint 1 according to this embodiment further has a second bead 12 . The second bead 12 is spaced apart from the center axis 11X of the first bead 11 and at least part of it is arranged in an end peripheral area EA defined with reference to the end of the first bead 11 . Specifically, in the end peripheral region EA of the first bead 11, the length of the region of the second bead 12 that is 2 mm or less from the end of the width direction of the first bead 11 is It is 2 mm or more along the central axis 11X of one bead 11 . In addition, the second bead 12 is not included in the starting end peripheral area SA of the first bead 11 . The widthwise end of the first bead 11 means edges on both sides of the first bead 11 in the extending direction.
The terminal end of the first bead 11 corresponds to the intersection where the crater 111 exists, of the two intersections between the outer periphery of the first bead 11 and the central axis 11X. The terminal peripheral area EA and the starting edge peripheral area SA will be described later.

(Metal plate 10)
A plurality of metal plates 10 are base materials of the lap laser welded joint 1 . The type, thickness, and presence or absence of surface treatment of the metal plate are not particularly limited as long as they are suitable for laser welding. The number of metal plates 10 is also not particularly limited, and may be any number of two or more.

A suitable example of the plurality of metal plates 10 is a plurality of steel plates, a plurality of Al plates, and the like. When the metal plate 10 is a steel plate, the chemical composition of the steel plate is not particularly limited, and a suitable chemical composition according to the application of the lap laser welded joint can be applied. For example, the chemical composition of one or more of the plurality of steel plates is C: 0.05 to 0.5 mass%, Si: 0.1 to 3.5 mass%, Mn: 0.1 to 5.5 mass%, and P and S: 0.03 mass% or less in total, and the balance may include Fe and impurities. A steel sheet having such a chemical composition has high strength, and therefore can impart excellent strength to the lap laser welded joint 1 . If a steel plate having such a chemical composition is subjected to normal lap laser welding, weld cracks are likely to occur at the end portion of the bead. However, in the lap laser welded joint 1 according to the present embodiment, weld cracking is suppressed by the second bead 12, which will be described later.

Moreover, from the viewpoint of increasing the strength of the lap laser welded joint 1, it is preferable that the strength of the metal plate 10 is as high as possible. For example, when the plurality of metal plates 10 are a plurality of steel plates, one or more of these steel plates may have a tensile strength of 980 MPa or more, 1000 MPa or more, or 1100 MPa or more. The higher the tensile strength of the steel plate, the greater the tensile stress applied to the end portion of the bead after welding. In the lap laser welded joint 1 according to this embodiment, the second bead 12 described later reduces the tensile stress. It is Moreover, the steel plate having a tensile strength of 980 MPa or more, that is, the high-strength steel plate may be arranged on the outermost surface of the lap laser welded joint, or may be arranged on the inner side. In general, high-strength steel sheets have a high carbon content. Weld cracks are more likely to occur. However, in the lap laser welded joint 1 according to the present embodiment, by using a second bead 12 or the like, which will be described later, the effect of preventing weld cracks can be effectively exhibited even in a plate set including high-strength steel plates. can be done. In addition, when the plurality of metal plates 10 are a plurality of steel plates, and one or more of them are high-strength steel plates, it is preferable that the second beads 12 described later melt into the high-strength steel plates. Moreover, in the high-strength steel sheet, it is more preferable that the positional relationship between the first bead 11 and the second bead 12, which will be described later, is satisfied. On the other hand, even if the second bead 12 is formed only on the steel plate with a tensile strength of less than 980 MPa that is combined with the high-strength steel plate, the positional relationship between the first bead 11 and the second bead 12, which will be described later, is satisfied. As long as it is, the effect of alleviating the tensile stress at the end of the bead and suppressing weld cracking in the high-strength steel sheet can be sufficiently obtained.

(bead)
In the lap laser welded joint 1 according to this embodiment, a plurality of metal plates 10 are formed with first beads 11 and second beads 12 shorter than the first beads 11 . Note that the "bead" generally means a portion raised by welding, but in this embodiment, bead marks formed by removing the raised portion of the bead by polishing or the like are also regarded as "beads". . Even if the bead is flattened, the effect of the lap laser welded joint according to this embodiment is not impaired. By optimizing the intervals between the plurality of metal plates 10 and the shape and positional relationship of the beads, it is possible to prevent weld cracks at the end portions of the beads. The shape and positional relationship of the beads will be described below with reference to FIG. 1 and the like. Note that the shape of the bead on the front surface and the back surface of the lap laser welded joint 1 does not necessarily match. If the bead shape and positional relationship described below are satisfied on at least one surface of the lap laser welded joint 1, an effect of suppressing weld cracks can be obtained. Therefore, a joint in which the bead shape and positional relationship described below are within the range described below on at least one side is regarded as the lap laser welded joint 1 according to the present embodiment. Preferably, the bead shapes and relationships described below are satisfied on both sides of the lap laser welded joint 1 . Further, unless otherwise specified, the shapes and positional relationships of the beads described below are those when the lap laser welded joint 1 is viewed from the thickness direction of the lap laser welded joint 1 in plan view.

(First bead 11)
The first bead 11 is a linearly extending laser weld that joins the plurality of metal plates 10 . The shape of the first bead 11 is not particularly limited as long as it is linear, and may be straight, curved, or bent. For example, the first bead 11 may be C-shaped or L-shaped. Since the first bead 11 joins the plurality of metal plates 10, when the first bead 11 is viewed in cross section, as illustrated in FIGS. 10 and extends in the plate thickness direction. However, it is not necessary for the first bead 11 to penetrate all the metal plates 10 . As illustrated in FIG. 3B, the first bead 11 may be formed on only one side of the lap laser welded joint. Alternatively, a plurality of first beads 11 may join all metal plates 10 by joining several metal plates 10 respectively. When the first bead 11 is formed only on one side of the lap laser welded joint, the crater 111 of the first bead 11 becomes smaller, and weld cracking can be further suppressed.

(Gap G between multiple metal plates 10)
In laser welding, the weld metal flows in the direction opposite to the traveling direction of the laser. Therefore, a depression called a crater 111 is formed at the terminal end of the first bead 11 . Since the crater 111 causes weld cracking, the smaller the crater 111, the better. Here, the crater 111 can be made smaller by reducing the gap between the plurality of metal plates 10 . For the above reasons, the ratio G/T between the total value G of the size of the gaps between the plurality of metal plates 10 and the total value T of the thicknesses of the plurality of metal plates 10 is within the range of 0 to 18%. It is said that G is the size of the gap between the two metal plates when the number of the metal plates 10 is two, and the size of the gap between the metal plates when the number of the metal plates 10 is three or more. is the total value of For example, in the lap laser welded joint 1 illustrated in FIG. 3A, G is the sum of gap g1 and gap g2, and T is the sum of plate thicknesses t1, t2, and t3. G/T is preferably as small as possible, and may be 15% or less, 12% or less, or 10% or less.

The size of the gap between the metal plates 10 is measured on the cross section of the end portion of the first bead 11 . The cross section passes through a position 2.5 mm away from the terminal end 11E of the first bead 11 along the central axis 11X of the first bead 11 toward the starting end 11S. Also, the cross section is perpendicular to the central axis 11X of the first bead at the position. In this cross section, the total value G of the sizes of the gaps between the plurality of metal plates 10 and the total value T of the thicknesses of the plurality of metal plates 10 are measured. Also, as shown in FIG. 4, the size of the gap is measured at both ends of the first bead 11 in cross section. The average value of the size gl of the gap on the left side of the first bead 11 and the size gr of the gap on the right side of the first bead 11 is regarded as the size of the gap between the metal plates 10 .

(Length L1 of first bead 11)
The length L1 of the first bead 11 measured along the central axis 11X along the extending direction of the first bead 11 is 10 to 100 mm. When the length L1 of the first bead 11 is less than 10 mm, it becomes difficult to suppress weld cracking. From the viewpoint of further suppressing weld cracking, the length L1 of the first bead 11 may be 12 mm or more, 15 mm or more, or 20 mm or more. On the other hand, if the length L1 of the first bead 11 exceeds 100 mm, the time required for laser welding increases, which may impair productivity. The length L1 of the first bead 11 may be 90 mm or less, 80 mm or less, or 70 mm or less.

When the material to be welded is large, the lap laser welded joint 1 may be provided with a plurality of first beads 11 . In this case, a second bead 12, which will be described later, may be arranged in the vicinity of each end portion of the plurality of first beads 11. FIG. However, it is not necessary to arrange the second beads 12 at the end portions of all the first beads 11 included in the lap laser welded joint 1 . The second bead 12 may be formed only at locations where weld cracking is of particular concern.

(Second bead 12)
The lap laser welded joint 1 has a second bead 12 in addition to the first bead 11 . The second bead 12 is arranged near the end 11E of the first bead 11 . Also, the length L2 of the second bead 12 is shorter than the length L1 of the first bead 11 . The length L2 of the second bead 12 is the size of the second bead 12 measured along the central axis along the extending direction of the second bead 12 . When the second bead 12 is short and the direction in which the second bead extends cannot be specified, the major axis of the second bead 12 is regarded as the length L2 of the second bead 12 .

One of the causes of weld cracking at the end portion of a bead formed by laser welding is the tensile stress applied to the end portion of the bead after laser welding. Therefore, by reducing the tensile stress applied to the end portion of the bead, it is possible to suppress the occurrence of weld cracks in this region. This tensile stress is generated by contraction of the welded portion and its surroundings in the process of lowering the temperature of the welded portion after the end of laser welding. The present inventors diligently studied means for reducing this tensile stress. The present inventors have found that by forming another bead in the vicinity of the end portion of the bead before the temperature of the end portion of the bead drops, the tensile stress applied to the end portion can be dispersed and weld cracking can be suppressed. bottom.

FIG. 5A is a conceptual diagram of tensile stress applied to first bead 11 when second bead 12 is absent. A crater 111 is formed at the terminal end of the first bead 11 . Moreover, a tensile stress is applied to the end portion of the first bead 11 due to the contraction of the base material portion heated by the laser welding. The arrows shown in FIG. 5A illustrate the tensile stress applied to the termination. A weld crack C occurs when the end portion of the bead is torn by this tensile stress.

On the other hand, FIG. 5B is a conceptual diagram of tensile stress when the second bead 12 is formed near the end portion of the first bead 11 . Most of the tensile stress caused by contraction of the base material portion is applied to the second bead 12 . Moreover, the tensile stress is canceled between the first bead 11 and the second bead 12 . Therefore, the second bead 12 formed near the terminal end of the first bead 11 can significantly suppress the tensile stress applied to the terminal end of the first bead 11 .

For the reasons described above, in the lap laser welded joint 1 according to the present embodiment, the second bead 12 is used as a secondary bead in order to reduce the tensile stress applied to the end portion of the first bead 11 . However, if the size of the second bead 12 and the positional relationship between the first bead 11 and the second bead 12 are inappropriate, even if the second bead 12 is provided, welding Cracking cannot be sufficiently suppressed. The size and the like of the second bead 12 will be described in detail below.

Hereinafter, the terms terminating peripheral area EA of the first bead 11 and starting edge peripheral area SA of the first bead 11 are used to define the size and position of the second bead 12 .
The end peripheral area EA of the first bead 11 is an area between the first virtual line VL1 and the second virtual line VL2, as shown in FIG. The first virtual line VL1 is a virtual line passing through the terminal end 11E of the first bead 11 and perpendicular to the central axis 11X of the first bead 11 at the terminal end 11E. The second virtual line VL2 is a first point P1 which is 5 mm away from the terminal end 11E of the first bead 11 toward the starting end 11S of the first bead 11 along the central axis 11X of the first bead 11. It is an imaginary line that passes through and is perpendicular to the central axis 11X of the first bead 11 at the first point P1.
The start edge peripheral area SA of the first bead 11 is an area between the third virtual line VL3 and the fourth virtual line VL4, as shown in FIG. The third virtual line VL3 is a virtual line passing through the starting end 11S of the first bead 11 and perpendicular to the center axis 11X of the first bead 11 at the starting end 11S. The fourth imaginary line VL4 is (1/3)×L1 along the central axis 11X of the first bead 11 from the starting end 11S of the first bead 11 toward the terminal end 11E of the first bead 11. It is an imaginary line passing through the second point P2 and perpendicular to the central axis 11X of the first bead 11 at the second point P2.

(Positional relationship between second bead 12 and termination peripheral area EA)
First, at least a portion of the second bead 12 must be included in the terminal peripheral area EA. It is considered that the bead formed outside the terminal peripheral area EA does not exhibit the effect of alleviating the tensile stress at the terminal end of the first bead 11 .

(Length of stress relaxation region 121 of second bead 12)
Also, if the distance between the second bead 12 and the first bead 11 is too large, the second bead 12 cannot exhibit the tensile stress relaxation effect. Therefore, in the end peripheral region EA, the length of the region of the second bead 12 that is 2 mm or less from the end of the width direction of the first bead 11 is equal to the central axis 11X of the first bead 11. 2 mm or more. Here, the distance from the end of the first bead 11 in the width direction of the second bead 12 means the first is the distance between the widthwise end of the first bead and the widthwise end of the second bead on an imaginary line perpendicular to the center axis of the bead. However, if the widthwise end of the first bead and the widthwise end of the second bead are in contact with or overlap each other on an imaginary line perpendicular to the central axis of the first bead, In the second bead 12, the distance from the widthwise end of the first bead 11 to the widthwise end is zero. Hereinafter, for convenience of explanation, "the area in the second bead 12 in the end peripheral area EA where the distance from the widthwise end of the first bead 11 is 2 mm or less" will be referred to as the stress relaxation area 121. called. In other words, in the lap laser welded joint 1 according to the present embodiment, the length of the stress relaxation region 121 should be 2 mm or more along the central axis 11X of the first bead 11 . For reference, an enlarged view of the second bead 12 shown in FIG. 1 is shown in FIG. In FIG. 2 , the hatched area in the second bead 12 is the stress relaxation area 121 . Here, the method of measuring the length of the stress relaxation region 121 is 2 mm from the end in the width direction of the first bead 11 on a virtual line perpendicular to the central axis 11X of the first bead 11 in the terminal peripheral region EA. The maximum length of the existing second bead 12 along the central axis 11X of the first bead 11 is measured in the region sandwiched by the virtual lines . However, the stress relaxation region 121 may be continuous or discontinuous as long as the stress relaxation region 121 has a length of 2 mm or more along the central axis 11X of the first bead 11 .

It is considered that the beads arranged far from the first bead 11 do not exhibit the effect of alleviating the tensile stress. Therefore, of the second bead 12 , only the area within 2 mm from the first bead 11 is regarded as the area exhibiting the stress relaxation effect, that is, the stress relaxation area 121 . Also, if the stress relaxation region 121 is too small, it is considered that the effect of alleviating the tensile stress cannot be obtained. Therefore, the length of the stress relaxation region 121 is set to 2 mm or longer. The length of the stress relaxation region 121 is a value obtained by measuring the length of the stress relaxation region 121 along the central axis 11X of the first bead 11. FIG. The length of the stress relaxation region 121 may be 2.5 mm or longer, 3 mm or longer, or 4 mm or longer. Since the width of the termination peripheral area EA is 5 mm, the maximum length of the stress relaxation area 121 is 5 mm.

(Positional relationship between second bead 12 and central axis 11X of first bead 11)
The second bead 12 may be in contact with the first bead 11 . This is because even when the second bead 12 and the first bead 11 are in contact with each other, the tensile stress applied to the end portion of the first bead 11 is relaxed. However, if the area where the second bead 12 and the first bead 11 overlap is too large, the tensile stress may not be sufficiently relaxed. Therefore, the second bead 12 is separated from the central axis 11X of the first bead 11 . That is, the second bead 12 does not overlap the central axis 11X of the first bead 11. As shown in FIG.

(Positional relationship between second bead 12 and start edge peripheral area SA)
The second bead 12 is provided for the purpose of relieving tensile stress applied to the end portion of the first bead 11 . Further, even if the second bead 12 is extended to a location far away from the end portion of the first bead 11, the effect of alleviating the tensile stress cannot be obtained. For example, if the second bead 12 is extended toward the starting end 11S of the first bead 11 so that the second bead 12 overlaps with the starting end peripheral region SA, the manufacturing efficiency is impaired, but the tension is reduced. The effect of relieving stress is not improved. Therefore, in consideration of manufacturing efficiency, the second bead 12 is formed so as to be excluded from the starting end peripheral region SA. It should be noted that when the first bead 11 has a significantly curved shape such as a U shape, the starting end peripheral region SA may extend around the terminal end 11E of the first bead 11 . As described above, the periphery of the terminal end 11E is the region where the second bead 12 is to be arranged. It may be regarded as an area up to a point 7 mm away from the part.

Also, extending the second bead 12 toward the opposite side of the starting end 11S of the first bead 11 is not preferable in terms of manufacturing efficiency. Therefore, for example, from the terminal end 11E of the first bead 11, toward the direction opposite to the starting end 11S of the first bead 11, along the central axis 11X of the first bead 11, a third point P3 is located 2 mm away. and is perpendicular to the center axis 11X of the first bead 11 at the third point P3 is defined as a fifth virtual line VL5, the fifth virtual line VL to the second bead 12 are preferably spaced apart. Thereby, the manufacturing efficiency of the lap laser welded joint 1 can be further improved.

Also, the length L2 of the second bead 12 described above may be 7 mm or less, 6 mm or less, or 5 mm or less. As long as the length of the stress relaxation region 121 is 2 mm or more, it is preferable because the manufacturing efficiency of the lap laser welded joint 1 can be improved by shortening the length L2 of the second bead 12 .

Although the shape of the second bead 12 in plan view has been described above, the cross-sectional shape of the second bead 12 is not particularly limited. The first bead 11 needs to penetrate the metal plates 10 in order to join the plurality of metal plates 10 , but the second bead 12 does not need to penetrate the metal plates 10 . As shown in FIG. 3A, a second bead 12 may penetrate the metal plate 10 from one side of the lap laser welded joint 1 to the other side. On the other hand, as shown in FIG. 3B, the second bead 12 may be formed only on the metal plate 10 on the outermost surface of the lap laser welded joint 1 and may not reach the other metal plates 10 . Even in this case, the second bead 12 can exhibit the effect of relaxing the tensile stress. Weld cracks in the first bead 11 usually occur near the surface of the first bead 11 . Therefore, if the tensile stress is relieved on the surface of the first bead 11, weld cracking can be suppressed.

On the other hand, in order to further improve the tensile stress suppressing effect of the second bead 12, the lower limit of the penetration depth of the second bead 12 may be set. For example, the penetration depth of the second bead 12 is shallow, and as shown in FIG. 12 is provided, the depth of penetration of the second bead 12 is 1 of the thickness t of the metal plate 10a that is the outermost layer of the lap laser welded joint 1 and on which the second bead 12 is formed. /2 or more. In this case, the tensile stress can be sufficiently suppressed while shortening the manufacturing time of the second bead 12 .

In the configuration shown in FIG. 1, one second bead 12 is formed at the end of one first bead 11 . On the other hand, as shown in FIG. 6, two second beads 12 may be formed at the terminal end of one first bead 11 . Specifically, the second bead 12 may be provided on both sides of the first bead 11 with the central axis 11X of the first bead 11 as a reference. As a result, the tensile stress at the end portion of the first bead 11 is further relaxed, and weld cracking can be further suppressed. Also, two or more second beads 12 may be provided on one side of the central axis 11X, or three or more second beads 12 may be formed at the end of one first bead 11. may be In addition, as long as one or more second beads 12 are provided, a bead that does not satisfy the requirements for the second bead 12 described above may be formed near the end portion of the first bead 11. .

<Method for manufacturing lap laser welded joint>
Next, a method for manufacturing a lap laser welded joint according to this embodiment will be described. According to this manufacturing method, the lap laser welded joint 1 according to the present embodiment described above can be suitably manufactured. However, even a lap laser welded joint obtained by a method other than the manufacturing method described below can be regarded as the lap laser welded joint 1 according to the present embodiment as long as it satisfies the above requirements.

(Superposition and first laser irradiation)
The method for manufacturing a lap laser welded joint according to the present embodiment includes a step of overlapping a plurality of metal plates 10, and a first bead 11 that is a linearly extending laser welded portion that joins the plurality of metal plates 10. and performing a first laser irradiation so as to form Here, when the metal plates 10 are superimposed, the ratio G/T between the total value G of the size of the gaps between the metal plates 10 and the total value T of the thicknesses of the metal plates 10 is set to 0 to 18%. Thereby, the depth of the crater 111 formed at the end portion of the first bead 11 can be reduced. Also, the length L1 of the first bead 11 measured along the central axis 11X along the extending direction of the first bead 11 is set to 10 to 100 mm. By setting the upper limit of L1 to 100 mm, the manufacturing efficiency of the lap laser welded joint 1 can be improved, and by setting the lower limit of L1 to 10 mm, weld cracks can be suppressed. The preferred numerical ranges exemplified for the lap laser welded joint 1 according to the present embodiment described above can be appropriately applied to G/T and L1 in the manufacturing method according to the present embodiment. As for other configurations, the preferred aspects of the lap laser welded joint according to the present embodiment can be similarly applied to the manufacturing method according to the present embodiment.

(Second laser irradiation)
In the method for manufacturing a lap laser welded joint according to the present embodiment, the second laser irradiation is performed so as to form the second bead 12 shorter than the first bead 11 in the vicinity of the terminal end of the first bead 11. It further has a step.

In the second laser irradiation, a first virtual line VL1 passing through the end 11E of the first bead 11 and perpendicular to the center axis 11X of the first bead 11 at the end 11E, and the end of the first bead 11 11E to the starting end 11S of the first bead 11 along the central axis 11X of the first bead 11 passing through a first point P1 5 mm apart and the center of the first bead 11 at the first point P1 In the end peripheral area EA, which is the area between the second virtual line VL2 perpendicular to the axis 11X, the distance of the second bead 12 from the widthwise end of the first bead 11 is 2 mm or less. The length of the region should be 2 mm or more along the central axis 11X of the first bead 11 . Thereby, the tensile stress relaxation effect by the second bead 12 can be ensured.

Further, in the second laser irradiation, a third virtual line VL3 passing through the starting end 11S of the first bead 11 and perpendicular to the central axis 11X of the first bead 11 at the starting end 11S, and the first bead 11 along the central axis 11X of the first bead 11 from the starting end 11S of the first bead 11 toward the terminal end 11E of the first bead 11 passing through a second point P2 separated by (1/3) × L1 and passing through the second point P2 The second bead 12 must not be included in the starting edge peripheral area SA, which is the area between the fourth virtual line VL4 perpendicular to the central axis 11X of the first bead 11 in . Thereby, the manufacturing efficiency of the lap laser welded joint can be improved.

Furthermore, the second bead 12 should be spaced apart from the central axis 11X of the first bead 11 . Thereby, the tensile stress relaxation effect by the second bead 12 can be ensured.

In addition, it is necessary to form at least one or more second beads 12 before 10 seconds have passed since the end of the first laser irradiation. A weld crack at the terminal end of the first bead 11 occurs several tens of seconds after the end of the first laser irradiation. As a matter of course, even if the second bead 12 is formed after the occurrence of weld cracking, the effect of suppressing the weld cracking by the second bead 12 is not exhibited. According to the experimental results of the present inventors, no weld cracking occurs for at least 10 seconds after the end portion of the first bead 11 is formed. Based on this knowledge, the timing of the second laser irradiation was defined as described above.

Note that "forming the second bead 12" means forming the second bead 12 that satisfies the above requirements. For example, even if the second laser irradiation is started before 10 seconds have passed since the end of the first laser irradiation, the position where the laser irradiation is started is far from the terminal end of the first bead 11 and the second laser irradiation is started. If the formation of the second bead 12 having the above-described requirements is not completed 10 seconds after the end of the laser irradiation in step 1, the requirements for the second laser irradiation according to the present embodiment are satisfied. I can't say.

On the other hand, the timing of starting the second laser irradiation is not particularly limited as long as the second bead 12 can be formed before 10 seconds have passed since the end of the first laser irradiation.
The second laser irradiation may be performed before the first laser irradiation, and the second beads 12 may be formed in advance before the first beads 11 are formed. In this case, by ending the first laser irradiation in the vicinity of the pre-formed second bead 12, the second bead 12 can satisfy the above requirements. In particular, when using a metal plate subjected to surface treatment such as plating, it is preferable to form the second bead 12 in advance before the first laser irradiation step from the viewpoint of suppressing blowholes. By forming the second bead 12 in advance before the step of irradiating the first laser, in the step of overlapping the plurality of metal plates 10 before the step of irradiating the first laser, the metal plates 10 can be gaps can be formed, and the components of the surface treatment agent evaporated by the laser irradiation can be discharged from the gaps.
On the other hand, the second laser irradiation may be performed after the first laser irradiation. In particular, from the viewpoint of further suppressing weld cracking at the end portion of the bead, it is preferable to perform the second laser irradiation after the first laser irradiation. Since the second bead 12 can overwrite the tensile stress applied to the end portion of the first bead 11 by performing the second laser irradiation after the first laser irradiation, cracking is further suppressed. can.
When the second laser irradiation is performed twice or more to form two or more second beads 12, the second laser irradiation can be performed both before and after the first laser irradiation. When the second laser irradiation is performed twice, at least one second laser irradiation is performed so as to form the second bead 12 before 10 seconds after the end of the first laser irradiation. need to be Most preferably, all secondary laser irradiations are performed to meet this requirement.

In addition, in the manufacturing method according to this embodiment, a suitable configuration of the lap laser welded joint 1 according to this embodiment can be appropriately adopted. For example, the second beads 12 may be provided on both sides of the first bead 11 with the central axis 11X of the first bead 11 as a reference. From the terminal end 11E of the first bead 11 in the direction opposite to the starting end 11S of the first bead 11, passing through a third point P3 2 mm apart along the central axis 11X of the first bead 11, and The second bead 12 may be separated from the fifth imaginary line VL5 perpendicular to the central axis 11X of the first bead 11 at the third point P3. The first bead 11 may be formed on only one side of the lap laser welded joint 1 . The penetration depth of the second bead 12 may be 1/2 or more of the thickness of the metal plate 10 on which the second bead 12 is formed.

[Second embodiment]
<Lap laser welded joint 1A>
Hereinafter, a lap laser welded joint according to a second embodiment of the present invention will be described with appropriate reference to the drawings. In the laser welded joint 1 according to the first embodiment, the plurality of metal plates 10 are joined by the first bead 11 between the surfaces of the respective metal plates, but in the lap laser welded joint 1A according to the present embodiment, For example, as shown in FIG. 7A, the end face of the first metal plate 10b, which is the metal plate 10 arranged in the outermost layer among the plurality of metal plates 10, and the first metal plate 10b overlapped with the first metal plate 10b. 2 and the surface of the metal plate 10c are joined by a first bead 11A. That is, the laser welded joint 1A according to this embodiment is different from the laser welded joint 1 according to the first embodiment in that it is a lap fillet joint. In this embodiment, the configuration of the mating surface of the second metal plate 10c and the first metal plate 10b is the same as in FIG. Therefore, FIG. 1 is a schematic diagram of the lap laser welded joint 1A when the mating surfaces of the second metal plate 10c and the first metal plate 10b are viewed from the thickness direction of the lap laser welded joint 1A. It can be said that there is.
Therefore, the laser welded joint 1A according to the present embodiment includes a plurality of metal plates 10 that are overlapped, an end face of the first metal plate 10b among the plurality of metal plates 10, and a second metal plate 10c. and a first bead 11A that is a linearly extending laser welded portion that joins the surface and joins the plurality of metal plates.
In the laser welded joint 1A, the ratio G/T between the total value G of the gap sizes of the plurality of metal plates 10 and the total value T of the thicknesses of the plurality of metal plates 10 is 0 to 18%. The length L1 of the first bead 11A measured along the central axis along the extending direction of the first bead 11 is 10-100 mm.
The lap laser welded joint 1A further has a second bead 12 on at least the surface of the second metal plate 10c, and is measured along the central axis along the extending direction of the second bead 12. , the length L2 of the second bead 12 is less than L1. In the mating surface of the second metal plate 10c that is superimposed on the first metal plate 10b, a first Passing through a virtual line VL1 and a first point P1 which is 5 mm away along the central axis 11X of the first bead 11A from the terminal end 11E of the first bead 11A toward the starting end 11S of the first bead 11A and the first point P1. In the end peripheral area EA, which is the area between the second virtual line VL2 perpendicular to the central axis 11X of the first bead 11A at the point P1, the width direction of the first bead 11A in the second bead 12 The length of the region 121, which is 2 mm or less from the end of the bead 11A, is 2 mm or more along the central axis 11X of the first bead 11A.
The second bead 12 is separated from the central axis 11X of the first bead 11A.
Also, a third virtual line VL3 passing through the starting end 11S of the first bead 11A and perpendicular to the center axis 11X of the first bead 11A at the starting end 11S, and a line extending from the starting end 11S of the first bead 11A to the first bead 11A. A central axis 11X of the first bead 11A passes through a second point P2 separated by (1/3)×L1 along the central axis 11X of the first bead 11A toward the terminal end 11E of the The second bead 12 is not included in the starting edge peripheral area SA, which is the area between the fourth imaginary line VL4 perpendicular to . Each configuration of the laser welded joint 1A according to the present embodiment will be described below in more detail. Note that the positional relationship between the second bead 12 and the terminal peripheral area EA, the length of the stress relaxation area 121 of the second bead 12, and the distance between the second bead 12 and the central axis 11X of the first bead 11A Since the positional relationship is the same as in the first embodiment, detailed description is omitted here.

(First bead 11A)
The first bead 11A joins the end face of the first metal plate 10b and the surface of the second metal plate 10c among the plurality of metal plates 10, and joins the plurality of metal plates. , is a linearly extending fillet laser weld. The shape of the first bead 11A is not particularly limited as long as it is linear. The first bead 11A has, for example, a shape along the end surface of the first metal plate 10b. The first bead 11A joins at least the end face of the first metal plate 10b and the surface of the second metal plate 10c among the plurality of metal plates 10. 7A, the first bead 11A may extend in the plate thickness direction so as to straddle all the metal plates 10. . It is not necessary for the first bead 11A to penetrate all the metal plates 10, and as illustrated in FIG. 7B, the first bead 11A may be formed only on one side of the lap laser welded joint.

(Second bead 12)
As described above, the second bead 12 in the lap laser welded joint 1A according to this embodiment is the same as the second bead 12 in the laser welded joint 1 according to the first embodiment. The second bead 12 in this embodiment is formed by irradiating the first metal plate 10b with a laser to penetrate the first metal plate 10b and reach the second metal plate 10c. you can At this time, since the welded portion formed on the second metal plate 10c of the second bead 12 satisfies the above requirements, the tensile stress at the end portion of the first bead 11A can be relaxed. Alternatively, the second bead 12 may be formed by directly irradiating the second metal plate 10c with a laser.

In addition, on the mating surface of the second metal plate 10c that is overlaid with the first metal plate 10b, the second bead 12 is positioned on both sides of the first bead 11A with respect to the central axis 11X of the first bead 11A. may be provided in As a result, the tensile stress at the end portion of the first bead 11A is further relaxed, and weld cracking can be further suppressed.

Also, the penetration depth of the second bead 12 in the second metal plate 10c may be 1/2 or more of the thickness t of the second metal plate 10c. In this case, the tensile stress can be sufficiently suppressed while shortening the manufacturing time of the second bead 12 .

(Gap G between multiple metal plates 10)
The size of the gap between the metal plates 10 is basically measured in the same manner as in the first embodiment. However, the size of the gap between the first metal plate 10b and the second metal plate 10c, as shown in FIG. Measured at the end of the first bead 11A on the side.

<Method for manufacturing lap laser welded joint>
Next, a method for manufacturing a lap laser welded joint according to this embodiment will be described. According to this manufacturing method, the lap laser welded joint 1A according to the present embodiment described above can be suitably manufactured. However, even a lap laser welded joint obtained by a method other than the manufacturing method described below can be regarded as the lap laser welded joint 1 according to the present embodiment as long as it satisfies the above requirements.

In the method for manufacturing a lap laser welded joint according to the present embodiment, in the step of irradiating the first laser, at least the end surface of the first metal plate arranged on the outermost surface among the plurality of metal plates, and the This method differs from the lap laser welded joint manufacturing method according to the first embodiment in that at least the first metal plate and the surface of the second metal plate are joined.
Therefore, the method for manufacturing a lap laser welded joint according to the present embodiment includes a step of overlapping a plurality of metal plates 10, and a first laser welded portion that joins the plurality of metal plates 10 and extends linearly. and performing a first laser irradiation so as to form a bead 11A.
In the step of irradiating the first laser, at least the end face of the first metal plate 10b arranged on the outermost surface of the plurality of metal plates 10 and the second metal superimposed on the first metal plate 10b and the surface of the plate 10c are joined.
In this superposition, the ratio G/T between the total value G of the gap size of the metal plate 10 and the total value T of the thickness of the metal plate 10 is set to 0 to 18%, and the extension of the first bead 11A Let the length L1 of the first bead measured along the longitudinal central axis 11X be 10 to 100 mm.
The method for manufacturing a lap laser welded joint according to the present embodiment further includes the step of performing a second laser irradiation so as to form the second bead 12 on at least the second metal plate 10c. The length L2 of the second bead 12 measured along the central axis along the extending direction of the second bead 12 is made smaller than L1, and the first metal plate 10b in the second metal plate 10c A first virtual line VL1 passing through the end 11E of the first bead 11A and perpendicular to the central axis 11X of the first bead 11A at the end 11E, and the end 11E of the first bead 11A through a first point P1 5 mm away along the central axis 11X of the first bead 11A toward the starting end 11S of the first bead 11A and the central axis 11X of the first bead 11A at the first point P1 In the end peripheral area EA, which is the area between the second virtual line VL2 perpendicular to is 2 mm or more along the central axis 11X of the first bead 11A.
Also, the second bead 12 is spaced apart from the central axis 11X of the first bead 11A, and a third bead 12 passes through the starting end 11S of the first bead 11A and is perpendicular to the central axis 11X of the first bead 11A at the starting end 11S. and a second virtual line VL3 along the central axis 11X of the first bead 11A from the starting end 11S of the first bead 11A toward the terminal end 11E of the first bead 11A, which is separated from (1/3)×L1. The second bead 12 is not included in the starting edge peripheral area SA, which is the area between the fourth imaginary line VL4 passing through the point P2 and perpendicular to the central axis 11X of the first bead 11A at the second point P2. .
Also, the second bead 12 is formed before 10 seconds have passed since the end of the first laser irradiation.

In addition, in the manufacturing method according to the present embodiment, suitable conditions of the method for manufacturing the lap laser welded joint according to the first embodiment can be appropriately adopted.

<Structural members for automobile bodies>
A structural member for an automobile body according to another aspect of the present invention includes a lap laser welded joint according to the present embodiment. Automotive body structural members include, for example, A pillars, B pillars, roof rails, side sills, floor cross members, bumpers, crash boxes, instrument panel reinforcements, seat frames, and battery cases. By applying the lap laser welded joint according to the present embodiment to the flange portions of these members, it is possible to obtain a structural member for an automobile body that is excellent in productivity and suppresses the occurrence of weld cracks.

So far, the lap laser welded joint, the method for manufacturing the lap laser welded joint, and the structural member for an automobile body according to the present invention have been described with reference to the embodiments. However, the technical scope of the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

For example, in the second embodiment, laser fillet welding may be performed on both sides in the thickness direction of the lap laser welded joint 1A. That is, on both sides in the thickness direction of the lap laser welded joint 1A, the edge of the outermost layer metal plate and the surface of the metal plate adjacent to the metal plate in the thickness direction are fillet welded by laser. good too.

Also, the first bead 11 according to the first embodiment and the first bead 11A according to the second embodiment may be combined. For example, as shown in FIG. 9, a laser lap welded joint 1B includes three metal plates 10, and a first bead 11A, which is a fillet weld, is formed between the first metal plate 10b and the second metal plate. 10c, the first bead 11 is formed between the second metal plate 10c and the metal plate 10 arranged on the opposite side of the second metal plate 10c to the first metal plate 10b. , may be joined. In this case, the second bead 12 for relieving the tensile stress at the terminal end of the first bead 11 and the second bead 12 for relieving the tensile stress at the terminal end of the first bead 11A are arranged. be done.

The effect of one embodiment of the present invention will be described more specifically with reference to examples. However, the conditions in the examples are only one example of conditions adopted for confirming the feasibility and effects of the present invention. The present invention is not limited to this one conditional example. Various conditions can be adopted for the present invention as long as the object of the present invention is achieved without departing from the gist of the present invention.

[Example 1]
Two steel plates having the tensile strength, plate thickness, and chemical composition shown in Table 1 were superimposed and laser-welded under various conditions to form a first bead. Chemical components other than those shown in Table 1 are Fe and impurities. Also, in some examples, a second laser irradiation and a third laser irradiation were performed to form a second bead and a third bead near the end portion of the first bead. More specifically, a second bead and a third bead were formed so as to be positioned within the termination peripheral area EA. However, condition no. Condition No. 25 formed a second bead so as to extend from a position 2.6 mm from the terminal end of the first bead to the terminal end side of the first bead. 26 formed the second bead so as to extend from the end of the first bead to the end of the first bead from a position 7.0 mm from the end of the first bead to the start end. The presence or absence of weld cracks in various lap laser welded joints thus obtained was checked. Table 2 shows the order of the welding process, and Tables 3 and 4 show other welding conditions and evaluation results of the lap laser welded joints. Photographs of typical laser welded joints are shown in FIGS. 10 to 13. FIG.

In addition, both the second bead and the third bead correspond to the second bead of the lap laser welded joint according to the present embodiment described above. However, for the sake of convenience, the one of the two second beads that is formed later is referred to as the third bead. Similarly, when the second laser irradiation is performed twice, the later performed laser irradiation is referred to as the third laser irradiation.

The meanings of the symbols in the table are as follows.
- "L1", "L2", "L3": of the first, second or third bead measured along the central axis along the extending direction of the first, second or third bead length. If the bead is short and the extending direction of the second or third bead cannot be specified, the length of the bead.
- "W1", "W2", "W3": the width of the first, second or third bead measured along the direction perpendicular to the extending direction of the first, second or third bead . If the bead is short and the extension direction of the second or third bead cannot be specified, the short diameter of the bead.
- "H12S" and "H13S": the distance between the starting end of the second or third bead and the central axis of the first bead.
- "H12E" and "H13E": the distance between the end of the second or third bead and the central axis of the first bead.
"Output": laser output in the first to third laser irradiations.
・“Speed” is the moving speed of the laser irradiation position in the first to third laser irradiations.

Whether or not the second bead and the central axis of the first bead overlap can be determined from H12S, H12E, and W2. For example, condition no. In 5, the distance between the start and end of the second bead and the center axis of the first bead is sufficiently larger than 1/2 of the width of the second bead. It can be seen that the center axis of the bead 1 does not overlap. On the other hand, condition no. In 23, since the distance between the starting end of the second bead and the central axis of the first bead is smaller than 1/2 of the width of the second bead, the second bead and the first bead are aligned near the starting end. It can be seen that the central axis of

“The length of the stress relaxation region” is the length of the region of the second bead or the third bead in the end peripheral region EA, the distance from the end of the width direction of the first bead being 2 mm or less. It's about. If the second and third beads were not provided, a "0" was entered in this column. If only the second bead is provided, this column lists the length of the stress relief region of the second bead. When both the second and third beads are provided, the greater of the lengths of the stress relief regions of each bead is listed in the "Length of stress relief region" column. The length of the stress relaxation region was measured on the joint surface on the laser irradiation side.

The size of the gap between the steel plates was controlled by inserting a spacer between the steel plates. The “plate gap G” described in the table is a value measured in the cross section of the end portion of the first bead 11 . The measurement method was the method described above. Condition no. In the laser irradiation of 12-14, the control of the plate gap G used a spacer corresponding to the plate gap G. On the other hand, condition no. In the laser irradiation of No. 24, laser irradiation was performed without using a spacer. For reference, the table also shows the ratio between the size of the gap between the two steel plates and the total thickness of the two steel plates.

"Penetration degree" means the state of the first bead on the side opposite to the laser irradiation side. If the steel plate is joined by the first bead, but the first bead is not formed on the joint surface on the side opposite to the laser irradiation side, then "part" is written in this column and the steel plate is the first bead. and a first bead is formed on the joint surface opposite to the laser irradiation side, then "Complete" is entered in this column.

Weld crack resistance was evaluated by preparing three test pieces under the same conditions and determining the number of weld cracks that occurred in these test pieces. For examples in which cracks occurred in all test pieces, the weld crack resistance was evaluated as "×", and for examples in which no cracks occurred in all test pieces, the weld crack resistance was evaluated as "○". , Weld crack resistance was evaluated as "△" for examples in which cracks occurred in some test pieces. Examples evaluated as "O" or "Δ" were evaluated as excellent examples of weld crack resistance.

Condition no. In 1 to 4, no second bead was formed near the end of the first bead. These condition no. In 1 to 4, weld cracks occurred in all test pieces.
Condition no. In No. 7, the second bead was formed near the terminal end of the first bead, but the distance between the first bead and the second bead was 3 mm or more. That is, the second bead did not contain a stress relief region. Condition no. Also in No. 7, weld cracks occurred in all test pieces.
Condition no. 11, the second bead and the third bead are formed near the terminal end of the first bead, but the distance between the first bead and the second bead and the third bead is 3 mm or more. there were. That is, neither the second bead nor the third bead included a stress relief region. Condition no. Also in No. 11, weld cracks occurred in all test pieces.
Condition no. 14 had a G/T greater than 18%. Condition no. Also in No. 14, weld cracks occurred in all test pieces.
Condition no. 19 and condition no. At 20, a second bead and a third bead were formed near the terminal end of the first bead and partially sufficiently close to the first bead, but the stress relief areas of these beads were less than 2 mm. Condition no. 19 and condition no. Also in No. 20, weld cracks occurred in all test pieces.
Condition no. 22, the order of laser irradiation is set to the second laser irradiation, the third laser irradiation, and the first laser irradiation. This condition no. 22, the distance between the first bead and the second and third beads was 3 mm or more. That is, neither the second bead nor the third bead included a stress relief region. Condition no. Also in No. 22, weld cracks occurred in all test pieces.
Condition no. In 23, the second bead and the third bead were not spaced apart from the central axis of the first bead and did not exhibit a stress relieving effect. Therefore, condition no. Also in No. 23, weld cracks occurred in all test pieces.
In addition, condition no. 7, 11, 14, 19, 20, 22, and 23, the joint surface on the side opposite to the laser irradiation side was also evaluated. was not

On the other hand, condition no. In Nos. 5, 6, 8-10, 12, 13, 15-18, 21, and 24-26, at least the joint surface on the laser irradiation side satisfied the requirements of the present invention. In the lap laser welded joints obtained under these conditions, weld cracking at the end of the bead was suppressed. Moreover, condition no. 24, the order of laser irradiation was set to the second laser irradiation, the third laser irradiation, and the first laser irradiation. In addition, condition no. At 24, the second and third beads were formed prior to overlapping the steel sheets. As a result, condition no. In No. 24, an appropriate gap was generated without using a spacer.

[Example 2]
Two steel plates having the tensile strength, plate thickness, and chemical composition shown in Table 5 were superimposed and lap fillet welded by laser irradiation under various conditions to form a first bead. Specifically, the end face of one of the two steel plates (first metal plate) and the surface of the other metal plate (second metal plate) were joined by laser welding. Chemical compositions of each steel plate other than those shown in Table 5 are Fe and impurities. Also, in some examples, a second laser irradiation and a third laser irradiation were performed to form a second bead and a third bead near the end portion of the first bead. More specifically, a second bead and a third bead were formed on the second metal plate so as to be positioned within the termination peripheral area EA. The presence or absence of weld cracks in various lap laser welded joints thus obtained was checked. Table 6 shows the order of the welding process, and Tables 7 and 8 show other welding conditions and evaluation results of the lap laser welded joints. Photographs of typical laser welded joints are shown in FIGS. 14 to 16. FIG.

As in Example 1, both the second bead and the third bead correspond to the second bead of the lap laser welded joint according to the present embodiment described above. For the sake of convenience, the one of the two second beads formed later is referred to as the third bead. Similarly, when the second laser irradiation is performed twice, the later performed laser irradiation is referred to as the third laser irradiation.

The length of the stress relaxation region was measured on the surface of the second metal plate on the laser irradiation side. When the second laser irradiation is applied to the first metal plate, in the mating surface of the second metal plate formed by the second laser irradiation with the first metal plate, the stress relaxation region of the second bead length was measured. Specifically, the first metal plate was peeled off from the second metal plate, and the length of the stress relaxation region of the second bead was measured on the mating surface of the second metal plate with the first metal plate. .

The size of the gap between the steel plates was controlled by inserting a spacer between the steel plates. The “plate gap G” described in Table 8 is a value measured in the cross section of the end portion of the first bead 11 . The measurement method was the method described above. Condition no. In the laser irradiation of 39, 40, the control of the plate gap G used a spacer corresponding to the plate gap G. For reference, Table 8 also shows the ratio between the size of the gap between the two steel plates and the total thickness of the two steel plates.

"Degree of penetration" in Table 8 was described according to the same criteria as in Example 1. Evaluation of weld cracking resistance was performed according to the same criteria as in Example 1.

Condition no. In 27 and 28, the second bead was not formed near the end of the first bead on the second metal plate. These condition no. In Nos. 27 and 28, weld cracks occurred in all test pieces.
Condition no. 31, 44, 46 and 48, a second bead and a third bead were formed in the second metal plate near the terminal end of the first bead, but the first bead and the second bead Both the interval and the interval between the first bead and the third bead were 3 mm or more. That is, neither the second bead nor the third bead included a stress relief region. Condition no. Also in Nos. 31, 44, 46 and 48, weld cracks occurred in all test pieces.
Condition no. In 34, a second bead was formed near the end of the first bead on the second metal plate, but the distance between the first bead and the second bead was 3 mm or more. That is, the second bead did not contain a stress relief region. Condition no. Also in No. 34, weld cracks occurred in all test pieces.
Condition no. In 35, a second laser irradiation was performed on the first metal plate, but the output of the laser was small and the second bead was not formed on the second metal plate. Condition no. Also in No. 35, weld cracks occurred in all test pieces.
Condition no. At 38, a second laser irradiation was performed on the second metal plate and a second bead was formed in the second metal plate near the end of the first bead, but the first bead and the second bead was 3 mm or more. That is, the second bead did not contain a stress relief region. Condition no. Also in No. 38, weld cracks occurred in all test pieces.
Condition no. 40, the G/T was greater than 18%. Condition no. 40 also had weld cracks in all test pieces.

On the other hand, condition no. In Nos. 29, 30, 32, 33, 36, 37, 39, 41, 42, 43, 45, 47 and 49, the requirements of the present invention were satisfied at least on the joint surface on the laser irradiation side. In the lap laser welded joints obtained under these conditions, weld cracking at the end of the bead was suppressed.

1, 1A Lap laser welded joint 10, 10a Metal plate 10b First metal plate 10c Second metal plate 11, 11A First bead 11E End of first bead 11S Start of first bead 11X First bead Central axis 111 Crater 12 Second bead 121 Second bead stress relaxation area VL1 First virtual line VL2 Second virtual line EA Terminal peripheral area VL3 Third virtual line VL4 Fourth virtual line SA Beginning edge area Region VL5 Fifth virtual line P1 First point P2 Second point P3 Third point C Weld crack

Claims (32)

a plurality of superimposed metal plates;
a first bead that is a linearly extending laser welded portion that joins the plurality of metal plates;
A lap laser welded joint comprising:
A ratio G/T between the total value G of the size of the gaps between the plurality of metal plates and the total value T of the thicknesses of the plurality of metal plates is 0 to 18%,
The length L1 of the first bead measured along the central axis along the extending direction of the first bead is 10 to 100 mm,
the lap laser welded joint further having a second bead;
the length L2 of the second bead measured along the central axis along the extending direction of the second bead is smaller than the L1;
A first imaginary line passing through the terminal end of the first bead and perpendicular to the central axis of the first bead at the terminal end in a plan view viewed from the thickness direction of the lap laser welded joint; the first bead passing through a first point 5 mm apart along the central axis of the first bead from the terminal end of one bead to the beginning of the first bead and at the first point; The distance from the end of the first bead in the width direction in the second bead is 2 mm or less in the end peripheral region that is the region between the second imaginary line perpendicular to the central axis of The length of the region is 2 mm or more along the central axis of the first bead,
the second bead is spaced from the central axis of the first bead;
a third imaginary line passing through the starting end of the first bead and perpendicular to the center axis of the first bead at the starting end; A fourth point passing through a second point spaced (1/3)×L1 along the central axis of the first bead and perpendicular to the central axis of the first bead at the second point. Lap laser welded joint in which the second bead is not included in the starting end peripheral region, which is the region between the virtual line of . The second bead is formed on both sides of the first bead with respect to the central axis of the first bead in a plan view of the lap laser welded joint viewed from the thickness direction. A lap laser welded joint according to claim 1, characterized in that: From the terminal end of the first bead in a direction opposite to the starting end of the first bead, passing through a third point 2 mm away along the central axis of the first bead, and The lap laser welding according to claim 1 or 2, wherein the second bead is separated from a fifth imaginary line perpendicular to the central axis of the first bead at a third point. fittings. 3. The lap laser welded joint according to claim 1, wherein said first bead is formed only on one surface of said lap laser welded joint. the second bead is formed only on one of the metal plates disposed on the outermost layer of the lap laser welded joint;
The lap laser welding according to claim 1 or 2, wherein the penetration depth of the second bead is 1/2 or more of the thickness of the metal plate on which the second bead is formed. fittings. The plurality of metal plates are a plurality of steel plates,
The chemical composition of one or more steel sheets among the plurality of steel sheets is
C: 0.05 to 0.5 mass%,
Si: 0.1 to 3.5 mass%,
The lap laser welded joint according to claim 1 or 2, comprising Mn: 0.1 to 5.5 mass%, and P and S: 0.03 mass% or less in total. The plurality of metal plates are a plurality of steel plates,
3. The lap laser welded joint according to claim 1, wherein at least one of the plurality of steel plates has a tensile strength of 980 MPa or more. 8. The lap laser welded joint according to claim 7, wherein the steel plate on which the second bead is formed among the plurality of steel plates has a tensile strength of 980 MPa or more. a step of superimposing a plurality of metal plates;
A step of irradiating a first laser so as to form a first bead, which is a linearly extending laser welded portion that joins a plurality of the metal plates;
A method for manufacturing a lap laser welded joint comprising:
In the superposition, the ratio G/T between the total value G of the gap size of the metal plates and the total value T of the thicknesses of the metal plates is set to 0 to 18%,
The length L1 of the first bead measured along the central axis along the extending direction of the first bead is 10 to 100 mm,
The method for manufacturing a lap laser welded joint further comprises the step of applying a second laser so as to form a second bead,
making the length L2 of the second bead measured along the central axis along the extending direction of the second bead smaller than the L1;
A first imaginary line passing through the terminal end of the first bead and perpendicular to the central axis of the first bead at the terminal end in a plan view viewed from the thickness direction of the lap laser welded joint; the first bead passing through a first point 5 mm apart along the central axis of the first bead from the terminal end of one bead to the beginning of the first bead and at the first point; The distance from the end of the first bead in the width direction in the second bead is 2 mm or less in the end peripheral region that is the region between the second imaginary line perpendicular to the central axis of The length of the region is 2 mm or more along the central axis of the first bead,
spacing the second bead from the central axis of the first bead;
a third imaginary line passing through the starting end of the first bead and perpendicular to the center axis of the first bead at the starting end; A fourth point passing through a second point spaced (1/3)×L1 along the central axis of the first bead and perpendicular to the central axis of the first bead at the second point. Do not include the second bead in the starting end peripheral area, which is the area between the virtual line of
A method for manufacturing a lap laser welded joint in which the second bead is formed before 10 seconds have passed since the end of the first laser irradiation. 10. The method for manufacturing a lap laser welded joint according to claim 9, wherein the second laser irradiation is performed after the first laser irradiation. 10. The method of manufacturing a lap laser welded joint according to claim 9, wherein the first laser irradiation is performed after the second laser irradiation. The second bead is formed on both sides of the first bead with respect to the central axis of the first bead in a plan view of the lap laser welded joint viewed from the thickness direction. The method for manufacturing a lap laser welded joint according to any one of claims 9 to 11. From the terminal end of the first bead in a direction opposite to the starting end of the first bead, passing through a third point 2 mm away along the central axis of the first bead, and The second bead is spaced from a fifth imaginary line perpendicular to the central axis of the first bead at a third point, according to any one of claims 9 to 11. A method for manufacturing a lap laser welded joint. The method for manufacturing a lap laser welded joint according to any one of claims 9 to 11, wherein the first bead is formed only on one side of the lap laser welded joint. 12. The method according to any one of claims 9 to 11, wherein the penetration depth of the second bead is set to 1/2 or more of the thickness of the metal plate on which the second bead is formed. A method for manufacturing a lap laser welded joint of A structural member for an automobile body comprising the lap laser welded joint according to claim 1 or 2. a plurality of superimposed metal plates;
bonding the end face of the first metal plate, which is the outermost metal plate among the plurality of metal plates, to the surface of the second metal plate superimposed on the first metal plate; and a first bead that is a linearly extending laser welded portion that joins a plurality of the metal plates;
A lap laser welded joint comprising:
A ratio G/T between the total value G of the size of the gaps between the plurality of metal plates and the total value T of the thicknesses of the plurality of metal plates is 0 to 18%,
The length L1 of the first bead measured along the central axis along the extending direction of the first bead is 10 to 100 mm,
the lap laser welded joint further having a second bead on at least the surface of the second metal plate;
the length L2 of the second bead measured along the central axis along the extending direction of the second bead is smaller than the L1;
A first virtual plane passing through the terminal end of the first bead and perpendicular to the central axis of the first bead at the terminal end in the mating surface of the second metal plate that is superimposed with the first metal plate a line and a first point 5 mm apart along the central axis of the first bead from the terminal end of the first bead toward the beginning of the first bead and at the first point Distance from the end of the first bead in the width direction of the second bead in the end peripheral region that is the region between the first bead and a second imaginary line perpendicular to the central axis is 2 mm or less, the length of the region is 2 mm or more along the central axis of the first bead,
the second bead is spaced from the central axis of the first bead;
a third imaginary line passing through the starting end of the first bead and perpendicular to the center axis of the first bead at the starting end; A fourth point passing through a second point spaced (1/3)×L1 along the central axis of the first bead and perpendicular to the central axis of the first bead at the second point. Lap laser welded joint in which the second bead is not included in the starting end peripheral region, which is the region between the virtual line of . The second bead is formed on both sides of the first bead with respect to the central axis of the first bead on the mating surface of the second metal plate that is overlapped with the first metal plate. 18. The lap laser welded joint of claim 17, wherein the joint is lapped. From the terminal end of the first bead in a direction opposite to the starting end of the first bead, passing through a third point 2 mm away along the central axis of the first bead, and 19. Lap laser welding according to claim 17 or 18, wherein the second bead is spaced from a fifth imaginary line perpendicular to the central axis of the first bead at a third point. fittings. 19. The lap laser welded joint according to claim 17 or 18, wherein said first bead is formed only on one surface of said lap laser welded joint. The lap laser welding according to claim 17 or 18, wherein the penetration depth of the second bead in the second metal plate is 1/2 or more of the thickness of the second metal plate. fittings. The plurality of metal plates are a plurality of steel plates,
The chemical composition of one or more steel sheets among the plurality of steel sheets is
C: 0.05 to 0.5 mass%,
Si: 0.1 to 3.5 mass%,
The lap laser welded joint according to claim 17 or 18, comprising Mn: 0.1 to 5.5 mass%, and P and S: 0.03 mass% or less in total. The plurality of metal plates are a plurality of steel plates,
The lap laser welded joint according to claim 17 or 18, wherein the tensile strength of at least one of the plurality of steel plates is 980 MPa or more. 24. The lap laser welded joint according to claim 23, wherein the steel plate on which the second bead is formed among the plurality of steel plates has a tensile strength of 980 MPa or more. a step of superimposing a plurality of metal plates;
A step of irradiating a first laser so as to form a first bead, which is a linearly extending laser welded portion that joins a plurality of the metal plates;
A method for manufacturing a lap laser welded joint comprising:
In the step of irradiating the first laser, at least an end surface of a first metal plate disposed on the outermost surface of the plurality of metal plates and a second metal layer superimposed on the first metal plate joining at least the surface of the plate and
In the superposition, the ratio G/T between the total value G of the gap size of the metal plates and the total value T of the thicknesses of the metal plates is set to 0 to 18%,
The length L1 of the first bead measured along the central axis along the extending direction of the first bead is 10 to 100 mm,
The method for manufacturing the lap laser welded joint further comprises the step of applying a second laser so as to form a second bead on at least the second metal plate,
making the length L2 of the second bead measured along the central axis along the extending direction of the second bead smaller than the L1;
A first virtual plane passing through the terminal end of the first bead and perpendicular to the central axis of the first bead at the terminal end in the mating surface of the second metal plate that is superimposed with the first metal plate a line and a first point 5 mm apart along the central axis of the first bead from the terminal end of the first bead toward the beginning of the first bead and at the first point Distance from the end of the first bead in the width direction of the second bead in the end peripheral region that is the region between the first bead and a second imaginary line perpendicular to the central axis is 2 mm or less, the length of the region is 2 mm or more along the central axis of the first bead,
spacing the second bead from the central axis of the first bead;
a third imaginary line passing through the starting end of the first bead and perpendicular to the center axis of the first bead at the starting end; A fourth point passing through a second point spaced (1/3)×L1 along the central axis of the first bead and perpendicular to the central axis of the first bead at the second point. Do not include the second bead in the starting end peripheral area, which is the area between the virtual line of
A method for manufacturing a lap laser welded joint in which the second bead is formed before 10 seconds have passed since the end of the first laser irradiation. 26. The method of manufacturing a lap laser welded joint according to claim 25, wherein the second laser irradiation is performed after the first laser irradiation. 26. The method of manufacturing a lap laser welded joint according to claim 25, wherein the first laser irradiation is performed after the second laser irradiation. The second bead is formed on both sides of the first bead with respect to the central axis of the first bead on the mating surface of the second metal plate that is overlapped with the first metal plate. The method for manufacturing a lap laser welded joint according to any one of claims 25 to 27, characterized in that: From the terminal end of the first bead in a direction opposite to the starting end of the first bead, passing through a third point 2 mm away along the central axis of the first bead, and 28. The method of any one of claims 25-27, wherein the second bead is spaced from a fifth imaginary line perpendicular to the central axis of the first bead at a third point. A method for manufacturing a lap laser welded joint. The method for manufacturing a lap laser welded joint according to any one of claims 25 to 27, wherein the first bead is formed only on one side of the lap laser welded joint. According to any one of claims 25 to 27, characterized in that the penetration depth of the second bead in the second metal plate is set to 1/2 or more of the thickness of the second metal plate. A method of manufacturing the described lap laser welded joint. A structural member for an automobile body comprising the lap laser welded joint according to claim 17 or 18.

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