Overlap laser-welded joint, structural member for automobile body, and method for manufacturing an overlap laser-welded joint

Abstract

To provide a lap laser welding joint capable of preventing welding cracks, a structure member for an automobile body, and a method for manufacturing the lap laser welding joint.SOLUTION: This lap laser welding joint comprises a first bead for joining a plurality of metal plates, and a ratio of a total thickness value G of gaps among the metal plates to a total thickness value T of the metal plates is 0-17%. The lap laser welding joint further comprises a second bead. The first bead has a bent shape. The second bead has a bent shape. A gap between a deepest recess of a first crater and a deepest recess of a second crater is 5.0 mm or smaller. A part or a whole of a first terminal and a part or a whole of a second terminal are arranged adjacent to each other in a width direction.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a laser lap welding joint, a structural member for an automobile body, and a method for manufacturing a laser lap welding joint.

Background Art

[0002] A lap joint is a welded joint obtained by welding a plurality of overlapping metal plates. One of the welding means for manufacturing a lap joint is laser welding. Laser lap welding is a welding method in which a laser beam is irradiated onto one surface of a plurality of overlapping metal plates, and the metal plates are joined by melting and solidifying the metal plates.

[0003] Laser lap welding can join narrow regions such as the flange portion of a hat-shaped member at high speed. However, laser lap welding has a problem that cracks are likely to occur in the final solidification portion at the end of the weld bead.

[0004] In laser welding, a flow of molten metal occurs in the direction opposite to the direction of laser travel. Therefore, a depression called a crater occurs at the end of the bead formed by laser welding. Furthermore, after the laser welding is completed, a tensile stress is applied to the end of the bead. This is because after the laser welding is completed, the welded portion is rapidly cooled and shrinks due to heat extraction from the welded portion to its periphery. When a tensile stress is applied to the end of the bead where a crater is formed, the end of the bead may break so as to be torn perpendicularly to the extending direction of the bead. In this case, the breakage at the end may progress along the bead, and cracks may be formed over the entire bead.

[0005] In recent years, there has been an increasing trend towards using high-strength materials for mechanical structural components. For example, in automotive body components, particularly structural members that form the car's frame, high-strength steel sheets with a tensile strength of 980 MPa or higher are increasingly being used to improve the overall strength of the vehicle body. However, as the tensile strength of the metal sheet increases, the tensile stress applied to the bead end after laser welding increases, raising the risk of cracking at the bead end. If a crack occurs along the entire length of the bead, the static strength of the joint, such as shear strength and peel strength, decreases, and the fatigue strength also decreases significantly. For these reasons, there is a strong demand for technology to prevent cracking at the bead end in high-strength metal sheets.

[0006] Patent Document 1 discloses a lap laser welded joint, a method for manufacturing the same, and a structural member for an automobile body having the same welded joint, in which, when intermittently irradiating a laser beam onto one side surface of a steel plate made by overlapping multiple steel plates, a welded joint is formed in which a linear first joint and a linear subsequent joint following the first joint are arranged in a row, and at least the total gap G between the steel plates constituting the welded joint is within the range of 0 to 15% of the total thickness T of the steel plates constituting the welded joint, and the direction of movement of the welding head that irradiates the laser beam and the scanning direction of the laser beam are in opposite directions, so that the welding start end of the first joint and the welding end of the subsequent joint adjacent to the first joint face each other, and the welding start end and welding end of the subsequent joints face each other, and the various dimensions of the joint are controlled to an appropriate range, the welded joint is formed so that there is no cracking at the welding end of the joint and the peel strength is excellent.

[0007] Patent Document 2 discloses an impact-absorbing member that has excellent impact absorption characteristics during automobile collisions and can protect occupants by reliably and effectively absorbing collision energy. This impact-absorbing member consists of a cylindrical body having a laser-welded bead on the flange for joining a first member having a flange and a second member. The laser-welded bead is composed of a plurality of first regions and a plurality of second regions that are alternately formed spaced apart in the longitudinal direction of the flange, and the projected length in the width direction of the flange of the first regions is greater than the projected length in the width direction of the flange of the second regions.

[0008] Patent Document 3 discloses a welding structure with high joint strength that does not experience stress concentration in the weld bead, that is, does not cause continuous fracture of the heat-affected zone due to insufficient strength at the welding start and end points or welding defects. It also discloses a welding method and welding apparatus that can reduce the effects of welding defects that occur when welding with a high-energy beam. In this invention, in a welding structure in which two members are joined by overlap welding, at least one of the weld beads formed in a single pass, specifically the start end and the end end, is formed by bending laterally relative to the weld bead in the middle section. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2020 / 194669 [Patent Document 2] Japanese Patent Publication No. 2008-161911 [Patent Document 3] Japanese Patent Publication No. 2003-290951 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] However, even with these technologies, it is difficult to sufficiently suppress cracking, especially in laser welding of high-strength steel plates. In the technology of Patent Document 1, there is a risk of crack propagation along the curved joint having a J-shape. In the technology of Patent Document 2, the laser welded area is composed of a pair of first regions and a second region formed between them, and if the first region is formed as a point, or in the case of a U-shaped weld or a modified U-shaped weld, there is a risk of crack propagation to the second region. On the other hand, in the case of an I-shaped weld, it is thought that this suppresses cracking in the second region. However, in the first region, there is a risk of crack propagation along its extension direction. In the technology of Patent Document 3, the laser welded area is composed of a starting point, an intermediate part, and an ending part, and if these are U-shaped or roughly U-shaped, or if the additional weld bead is formed at a position offset from the welding end point of the weld bead, there is a risk of crack propagation or occurrence in the weld bead (intermediate part). On the other hand, in the case of I-shaped welding, it is thought that cracking in the middle section is suppressed. However, there is a risk that cracks may propagate along the direction of extension at the starting and ending points.

[0011] In view of the above circumstances, the object of the present invention is to provide a lap laser welded joint capable of preventing the occurrence of welding cracks, a structural member for an automobile body, and a method for manufacturing a lap laser welded joint. [Means for solving the problem]

[0012] The gist of this invention is as follows:

[0013] (1) An overlapping laser-welded joint according to the first embodiment of the present invention comprises a plurality of overlapping metal plates and a first bead which is a linearly extending laser-welded portion that joins the plurality of metal plates, wherein the ratio G / T of the total thickness G of the gap between the plurality of metal plates to the total thickness T of the plurality of metal plates is 0 to 17%, and the overlapping laser-welded joint further comprises a second bead which is a linearly extending laser-welded portion, and in a plan view along the thickness direction of the overlapping laser-welded joint, on at least one surface of the overlapping laser-welded joint, the first bead is a portion from the end up to 5.0 mm and consists of a first end portion in which a first crater is formed and a first main portion which is the portion other than the first end portion, and The second bead is the portion up to 5.0 mm from the end, and consists of a second end portion where a second crater is formed, and a second main portion which is the portion other than the second end portion. The first bead has a bent shape such that the deepest recess of the first crater is separated by 0.5 mm or more from the extension of the central axis of the first main portion of the first bead. The second bead has a bent shape such that the deepest recess of the second crater is separated by 0.5 mm or more from the extension of the central axis of the second main portion of the second bead. The distance between the deepest recess of the first crater and the deepest recess of the second crater is 5.0 mm or less, and part or all of the first end portion and part or all of the second end portion are arranged adjacent to each other in the width direction. (2) In the overlapping laser-welded joint described in (1) above, the central axis of the first terminal and the central axis of the second terminal may be parallel to each other in whole or in part. (3) In the overlapping laser welded joint described in (1) or (2) above, the area of ​​the second bead contained within a circle with a radius of 5 mm centered on the deepest recess of the first crater is 10.0 mm 2 The above is true, and the area of ​​the first bead contained within a circle with a radius of 5 mm centered on the deepest recess of the second crater is 10.0 mm². 2 That's fine too.

[0014] (4) An overlapping laser-welded joint according to a second embodiment of the present invention comprises a plurality of overlapping metal plates and a first bead which is a linearly extending laser-welded portion that joins the plurality of metal plates, wherein the ratio G / T of the total thickness G of the gap between the plurality of metal plates to the total thickness T of the plurality of metal plates is 0 to 17%, and the overlapping laser-welded joint further comprises a second bead which is a linearly extending laser-welded portion, and in a plan view along the thickness direction of the overlapping laser-welded joint, on at least one surface of the overlapping laser-welded joint, the first bead has a first end portion which is the portion from the end to 5.0 mm and the portion other than the first end portion The first bead consists of a first main part, which is a portion of the bead, and the second bead consists of a second end portion, which is a portion from the end to 5.0 mm, and a second main part, which is a portion other than the second end portion, the first end portion and the second end portion are connected, one crater is formed in either the first end portion or the second end portion, the first bead has a bent shape such that the deepest recess of the crater is separated by 0.5 mm or more from the extension of the central axis of the first main part of the first bead, and the second bead has a bent shape such that the deepest recess of the crater is separated by 0.5 mm or more from the extension of the central axis of the second main part of the second bead. (5) In the overlapping laser welding joint described in any one of the above items (1) to (4), the second bead may join a plurality of the metal plates. (6) In the overlapping laser-welded joint described in any one of the above paragraphs (1) to (5), the deepest recesses of all the craters may be located in the region between a virtual line perpendicular to the straight line connecting the center of the first main part and the center of the second main part and passing through the center of the first main part, and a virtual line perpendicular to the straight line connecting the center of the first main part and the center of the second main part and passing through the center of the second main part. (7) In the lap laser welded joint described in any one of the above paragraphs (1) to (6), part or all of the first terminal portion may be parallel to the longest straight portion of the first main portion, and part or all of the second terminal portion may be parallel to the longest straight portion of the second main portion. (8) In the overlapping laser welded joint described in any one of the above items (1) to (7), the first bead may be present only on one side of the overlapping laser welded joint. (9) In the lap laser welded joint described in any one of the above items (1) to (8), when the larger of the width W1 of the first bead and the width W2 of the second bead is defined as Wmax, the entirety of the first bead and the second bead may be included in the region between two parallel imaginary lines with a spacing of 2 × Wmax. (10) In the lap laser welded joint described in any one of the above items (1) to (9), the plurality of metal plates are a plurality of steel plates, and the chemical composition of one or more of the plurality of steel plates may contain 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. (11) In the lap laser welded joint described in any one of the above items (1) to (10), the plurality of metal plates may be a plurality of steel plates, and one or more of the plurality of steel plates may have a tensile strength of 980 MPa or more. (12) The lap laser welded joint described in any one of the above items (1) to (11) may be a lap fillet joint.

[0015] (13) A structural member for an automobile body according to the third embodiment of the present invention comprises an overlapping laser welding joint as described in any one of (1) to (12) above.

[0016] (14) A method for manufacturing a lap laser welded joint according to a fourth embodiment of the present invention comprises the steps of: overlapping a plurality of metal plates; and performing a first laser welding on the overlapped plurality of metal plates to form a first bead which is a linearly extending laser welded portion that joins the plurality of metal plates, wherein in the overlapping, the ratio G / T of the total thickness of the gap between the plurality of metal plates to the total thickness of the plurality of metal plates to be 0 to 17%, and the method for manufacturing a lap laser welded joint further comprises the step of performing a second laser welding on the metal plates on at least one surface of the lap laser welded joint to form a second bead which is a linearly extending laser welded portion, wherein in a plan view along the thickness direction of the lap laser welded joint, on the laser irradiation surface, the first bead is in a portion from the end to 5.0 mm, and the first crater is The first bead consists of a formed first end portion and a first main portion which is the portion other than the first end portion, the second bead consists of a second end portion which is the portion up to 5.0 mm from the end and in which a second crater is formed and a second main portion which is the portion other than the second end portion, the first bead has a bent shape such that the deepest recess of the first crater is separated by 0.5 mm or more from the extension of the central axis of the first main portion of the first bead, the second bead has a bent shape such that the deepest recess of the second crater is separated by 0.5 mm or more from the extension of the central axis of the second main portion of the second bead, the distance between the deepest recess of the first crater and the deepest recess of the second crater is 5.0 mm or less, and part or all of the first end portion and part or all of the second end portion are arranged adjacent to each other in the width direction.

[0017] (15) The manufacturing method of the overlapping laser welding joint according to the fifth embodiment of the present invention includes a step of overlapping a plurality of metal plates, and a step of performing a first laser welding on the plurality of overlapped metal plates so as to form a first bead which is a linearly extending laser welding part for joining the plurality of metal plates. The manufacturing method of the overlapping laser welding joint includes, in the overlapping, setting the ratio G / T of the total value G of the thicknesses of the gaps between the plurality of metal plates to the total value T of the thicknesses of the plurality of metal plates to be 0 to 17%. The manufacturing method of the overlapping laser welding joint further includes a step of performing a second laser welding on the metal plate on at least one surface of the overlapping laser welding joint so as to form a second bead which is a linearly extending laser welding part. In a plan view along the thickness direction of the overlapping laser welding joint, on the laser irradiation surface, the first bead is composed of a first terminal part which is a part from the terminal end to 5.0 mm and a first main part which is a part other than the first terminal part. The second bead is composed of a second terminal part which is a part from the terminal end to 5.0 mm and a second main part which is a part other than the second terminal part. The first terminal part and the second terminal part are connected, and one crater is formed in either the first terminal part or the second terminal part. The first bead has a bent shape such that the deepest part of the crater is separated from the extension line of the central axis of the first main part of the first bead by 0.5 mm or more. The second bead has a bent shape such that the deepest part of the crater is separated from the extension line of the central axis of the second main part of the second bead by 0.5 mm or more. (16) In the manufacturing method of the overlapping laser welding joint described in the above (14) or (15), the second laser welding may be performed after the first laser welding. (17) In the manufacturing method of the overlapping laser welding joint described in the above (14) or (15), the first laser welding may be performed after the second laser welding. (18) In the manufacturing method of the overlapping laser welding joint described in any one of the above (14) to (17), the overlapping laser welding joint may be an overlapping fillet joint.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide an overlapping laser welding joint capable of preventing the occurrence of welding cracks, a structural member for an automobile body, and a method for manufacturing the overlapping laser welding joint.

Brief Description of the Drawings

[0019] [Figure 1] It is a plan view of an example of an overlapping laser welding joint according to the first embodiment. [Figure 2] It is a plan view of an example of an overlapping laser welding joint according to the first embodiment. [Figure 3] It is a plan view of an example of an overlapping laser welding joint according to the first embodiment. [Figure 4A] It is a cross-sectional view perpendicular to the central axis of the first main part of the first bead in an overlapping laser welding joint in which the first bead is formed on both sides. [Figure 4B] It is an enlarged cross-sectional view perpendicular to the central axis of the first bead. [Figure 4C] It is a cross-sectional view perpendicular to the central axis of the first main part of the first bead in an overlapping laser welding joint in which the first bead is formed on only one side. [Figure 5] It is a plan view of an example of an overlapping laser welding joint according to the second embodiment. [Figure 6] It is a plan view of an overlapping laser welding joint in which the deepest part of the first crater and the deepest part of the second crater are located in the region between the virtual line VL2 and the virtual line VL3. [Figure 7] It is a plan view of an overlapping laser welding joint of a comparative example. [Figure 8A] It is the result of FEM analysis of the stress generated in a bead provided independently. [Figure 8B] It is a schematic diagram of the stress and welding crack generated in a bead provided independently. [Figure 8C] It is a schematic diagram of the stress generated in two beads whose end portions are provided adjacent to each other in the width direction. [Figure 9] It is a plan view of an overlapping fillet joint which is a modification of the present invention. [Figure 10] It is a plan view of an overlapping fillet joint which is a modification of the present invention. [Figure 11] This is a plan view of the overlapping laser-welded joint in the comparative example. [Figure 12] This is a photograph of the overlapping laser-welded joint in Example No. 5. [Figure 13] This is a photograph of the overlapping laser-welded joint in Example No. 7. [Figure 14A] This is a photograph of the overlapping laser-welded joint in example No. 17. [Figure 14B] This is a schematic plan view of the overlapping laser-welded joint in Example No. 17. [Figure 15] This is a photograph of the overlapping fillet joint in example No. 24. [Modes for carrying out the invention]

[0020] <Layer laser welded joint 1 according to the first embodiment> As shown in Figures 1 to 3, the overlapping laser-welded joint 1 of the present invention comprises a plurality of overlapping metal plates 10 and a first bead 11 which is a linearly extending laser-welded portion that joins the plurality of metal plates 10. Here, the ratio G / T of the total thickness G of the gaps between the plurality of metal plates 10 to the total thickness T of the plurality of metal plates 10 is 0 to 17%. The overlapping laser-welded joint 1 further comprises a second bead 12 which is a linearly extending laser-welded portion. In a plan view along the thickness direction of the overlapping laser welded joint 1, on at least one face of the overlapping laser welded joint 1, the first bead 11 is a portion up to 5.0 mm from the end and consists of a first end portion 111 in which a first crater 113 is formed and a first main portion 112 which is the portion other than the first end portion 111, the second bead 12 is a portion up to 5.0 mm from the end and consists of a second end portion 121 in which a second crater 123 is formed and a second main portion 122 which is the portion other than the second end portion 121, and the first bead 11 is the The first crater has a bent shape such that its deepest recess is at least 0.5 mm away from the extension of the central axis of the first main portion 112 of the first bead 11, and the second bead 12 has a bent shape such that its deepest recess is at least 0.5 mm away from the extension of the central axis of the second main portion 122 of the second bead 12, the distance between the deepest recess of the first crater and the deepest recess of the second crater is 5.0 mm or less, and part or all of the first end portion 111 and part or all of the second end portion 121 are arranged adjacent to each other in the width direction. The overlapping laser welded joint 1 according to the first embodiment will be described in detail below.

[0021] (Metal plate 10) Multiple metal plates 10 are the base material for the overlapping laser-welded joint 1. The type, thickness, and presence or absence of surface treatment of the metal plates 10 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 can be any number of two or more.

[0022] A suitable example of the multiple metal plates 10 is a plurality of steel plates, a plurality of Al plates, etc. Alternatively, a combination of steel plates and Al plates may be used to form the multiple metal plates 10. When the metal plates 10 are steel plates, the chemical composition of these steel plates is not particularly limited, and a suitable chemical composition can be applied depending on the application of the lap laser welded joint 1. For example, one or more of the multiple steel plates may contain a chemical composition of C: 0.05~0.5 mass%, Si: 0.1~3.5 mass%, Mn: 0.1~5.5 mass%, and P and S: total 0.03 mass% or less. In this case, the remainder of the chemical composition of the steel plates may include Fe and impurities. Since steel plates with such a chemical composition have high strength, they can provide excellent strength to the lap laser welded joint 1. However, when conventional lap laser welding is performed on steel plates with such a chemical composition, weld cracks are likely to occur at the end of the bead. However, in the overlapping laser-welded joint 1 according to the first embodiment, welding cracks are suppressed by specifying the bead shape and the positional relationship of the bead end portion, as will be described later.

[0023] Furthermore, from the viewpoint of increasing the strength of the overlapping laser-welded joint 1, it is preferable that the strength of the metal plates 10 is higher. For example, if the multiple metal plates 10 are multiple steel plates, the tensile strength of one or more of these steel plates may be 980 MPa or higher, 1000 MPa or higher, or 1100 MPa or higher. The higher the tensile strength of the steel plate, the greater the tensile stress on the end of the bead after welding. However, in the overlapping laser-welded joint 1 according to the first embodiment, welding cracks are suppressed by specifying the bead shape and the positional relationship of the bead end, as will be described later.

[0024] Furthermore, steel plates with a tensile strength of 980 MPa or higher, i.e., high-strength steel plates, may be placed on the outermost surface of the overlapping laser-welded joint 1, or on the inside. Generally, high-strength steel plates have a high carbon content, and if a high-strength steel plate is included somewhere in a plate assembly made up of overlapping steel plates to be welded, the carbon content of the welded area will be high, making welding cracks more likely to occur. However, in the overlapping laser-welded joint 1 according to the first embodiment, by specifying the bead shape and the positional relationship of the bead end portion, as will be described later, the effect of preventing welding cracks can be effectively exhibited even in plate assemblies that include high-strength steel plates. When the multiple metal plates 10 are multiple steel plates, and one or more of them are high-strength steel plates, it is preferable that both the first bead 11 and the second bead 12, described later, penetrate to the high-strength steel plate. Furthermore, it is even more preferable that the positional relationship between the first bead 11 and the second bead 12, described later, is satisfied in the high-strength steel plate. On the other hand, even if beads are formed only on steel plates with a tensile strength of less than 980 MPa that can be combined with high-strength steel plates, as long as the positional relationship between the first bead 11 and the second bead 12 described later is satisfied on at least one side of the overlapping laser welded joint 1, the effect of relieving tensile stress at the bead end and suppressing welding cracks in the high-strength steel plate can be sufficiently obtained.

[0025] The metal sheet 10 may be plated or unplated. Examples of plating include GI plating, GA plating, EG plating, Zn-Ni plating, Zn-Al plating, Zn-Mg plating, and Zn-Mg-Al plating. If the metal sheet 10 is a zinc-based hot-stamped steel sheet, zinc oxide may be included in the surface layer of the Fe-Zn or Fe-Zn-Ni solid solution phase. If the metal sheet 10 is an aluminum-based hot-stamped steel sheet, multiple Al-Fe-Si intermetallic compound layers may be formed, and furthermore, ZnO or a black coating may be formed on the intermetallic compound layers. If the metal sheet 10 is an unplated hot-stamped steel sheet, it may be shot-blasted to remove the scale generated in the hot-stamping process.

[0026] (G gap between multiple metal plates 10) In laser welding, a flow of weld metal occurs in the direction opposite to the direction of laser propagation. Therefore, a depression called a crater is generally formed at the end of the bead formed by laser welding. Craters can cause weld cracks, so it is preferable for them to be as small as possible. Here, the crater can be reduced by reducing the gap between multiple metal plates 10. For the above reasons, the ratio G / T of the total thickness of the gaps between multiple metal plates 10 to the total thickness of the multiple metal plates 10 is set to be within the range of 0 to 17%. G is the size of the gap between the two metal plates 10 when there are two metal plates 10, and the total thickness of the gaps between the metal plates 10 when there are three or more metal plates 10. For example, in the cross-sectional view of the overlapping laser-welded joint 1 illustrated in Figure 4A, G is the sum of gap g1 and gap g2, and T is the sum of plate thicknesses t1, t2, and t3. A smaller G / T ratio is preferable, and may be 15% or less, 12% or less, 10% or less, or 8% or less.

[0027] The size of the gap between the metal plates 10 is measured in the cross-section of the first bead 11. The cross-section passes through 5.0 mm from the end of the first bead 11, that is, through the boundary between the end portion 111 and the main portion 112 of the first bead 11. The cross-section is also perpendicular to the central axis 112X which is perpendicular to the width direction of the first main portion 112 at the aforementioned position. In this cross-section, the sum of the thicknesses of the gaps between the multiple metal plates 10, G, and the sum of the thicknesses of the multiple metal plates 10, T, are measured. Also, as shown in Figure 4B, the size of the gap is measured at both ends of the first main portion 112 of the first bead 11 in the cross-section. The average value of the gap size gl on the left side of the first main portion 112 and the gap size gr on the right side is considered to be the size of the gap between the metal plates 10.

[0028] (Laser welded section) In the overlapping laser-welded joint 1 according to the first embodiment, a plurality of metal plates 10 are joined together by a first bead 11 and a second bead 12 provided near the end of the first bead 11. Generally, "bead" refers to the raised portion created by welding, but in the first embodiment, a bead mark formed by removing the raised portion of the bead by polishing or the like is also considered a "bead". Even if the beads 11 and 12 are flattened, the effect of the overlapping laser-welded joint 1 according to the first embodiment is not impaired. By optimizing the spacing between the plurality of metal plates 10 and the shape and positional relationship of the beads 11 and 12, welding cracks at the end portions 111 and 121 of the beads 11 and 12 can be prevented. The shape and positional relationship of the beads 11 and 12 will be described below.

[0029] Note that the shapes of beads 11 and 12 do not necessarily coincide on the front and back surfaces of the overlapping laser-welded joint 1. If the shapes and positional relationships of beads 11 and 12 described below are satisfied on at least one surface of the overlapping laser-welded joint 1, the effect of suppressing welding cracks can be obtained. Therefore, a joint in which the shapes and positional relationships of beads 11 and 12 described below are within the range described later on at least one surface is considered to be the overlapping laser-welded joint 1 according to the first embodiment. The shapes and positional relationships of beads 11 and 12 described below may also be satisfied on both surfaces of the overlapping laser-welded joint 1. Also, unless otherwise specified, the shapes and positional relationships of beads 11 and 12 described below are as seen when the overlapping laser-welded joint 1 is viewed in plan along the thickness direction of the overlapping laser-welded joint 1.

[0030] In the overlapping laser-welded joint 1 according to the first embodiment, one or more pairs of beads 11 and 12 are provided. In the pair of beads 11 and 12, their end portions 111 and 121 are adjacent to each other while satisfying predetermined conditions. Hereinafter, for convenience, the pair of beads 11 and 12 will be referred to as the first bead 11 and the second bead 12. The difference between the first bead 11 and the second bead 12 is that the former always joins multiple metal plates 10, while the latter may not join multiple metal plates 10. However, in other respects, the two are equivalent. If both of the pair of beads 11 and 12 join multiple metal plates 10, either may be considered the first bead 11. Hereinafter, the description of the first bead 11 also applies to the second bead 12 unless otherwise specified.

[0031] (First bead 11) The first bead 11 is a linearly extending laser weld that joins multiple metal plates 10. The shape of the first bead 11 is not particularly limited as long as it is linear. The first bead 11 may be straight, curved, or even bent. For example, the first bead 11 may be C-shaped or L-shaped.

[0032] The portion of the first bead 11 up to 5.0 mm from its end is referred to as the first end portion 111. A crater is formed in the first end portion 111. The crater formed in the first end portion 111 is referred to as the first crater 113. The first end portion 111 is a portion that is subjected to large tensile stress during solidification and is prone to weld cracking. The portion of the first bead 11 other than the first end portion 111 is referred to as the first main portion 112.

[0033] Since the first bead 11 joins multiple metal plates 10, when viewed in cross-section, the first bead 11 usually extends in the thickness direction, spanning all the metal plates 10, as illustrated in Figure 4A. However, the first bead 11 does not need to penetrate all the metal plates 10. As illustrated in Figure 4C, the first bead 11 may be formed on only one side of the overlapping laser-welded joint 1. Furthermore, it is permissible for the first bead 11 to join only a portion of the multiple metal plates 10. For example, by providing beads that join only a portion of the multiple metal plates 10 on both sides of the overlapping laser-welded joint 1, all of the multiple metal plates 10 can be joined.

[0034] Furthermore, if the area of ​​the metal plate 10 to be welded is large, multiple first beads 11 may be provided in the overlapping laser-welded joint 1. In this case, the second end portion 121 of the second bead 12, described later, should be placed near each of the first end portions 111 of the multiple first beads 11. However, it is not necessary to place the second end portion 121 of the second bead 12 near the first end portion 111 of all the first beads 11 included in the overlapping laser-welded joint 1. The second end portion 121 of the second bead 12 may be placed only in areas where welding cracks are a particular concern.

[0035] (Second bead 12) The second bead 12 is also a laser weld extending in a linear manner. Since the first bead 11 is responsible for joining multiple metal plates 10, the second bead 12 does not need to join multiple metal plates 10. On the other hand, by having the second bead 12 join multiple metal plates 10, the joint strength of the overlapping laser welded joint 1 is further improved.

[0036] Except for this point, the second bead 12 has the same structure as the first bead 11. That is, the portion of the second bead 12 from its end to 5.0 mm is called the second end portion 121. The crater formed in the second end portion 121 is called the second crater 123. The portion of the second bead 12 other than the second end portion 121 is called the second main portion 122. In addition, the matters described above regarding the first bead 11 can also be applied to the second bead 12.

[0037] The pair of beads 11 and 12, consisting of a first bead 11 and a second bead 12, have the following shapes. (A) Both of the pair of beads 11 and 12 have a curved shape such that the deepest recess of the crater provided in each is separated by 0.5 mm or more from the extension of the central axis of the main part of each bead. (B) The distance between the deepest points of the two craters 113 and 123 is 5.0 mm or less. (C) Parts or all of the end portions 111, 121 of each pair of beads 11, 12 are arranged adjacent to each other in the width direction. By ensuring that the pair of beads 11 and 12 have a shape that satisfies all three of these requirements, welding cracks are suppressed very effectively in the overlapping laser-welded joint 1 according to the first embodiment.

[0038] (A) Bend shape of the bead The first bead 11 and the second bead 12 each have a bent shape, and as a result, the deepest part of the first crater 113 is separated by 0.5 mm or more from the extension of the central axis 112X of the first main part 112, and the deepest part of the second crater 123 is separated by 0.5 mm or more from the extension of the central axis 122X of the second main part 122. According to the inventors' experimental results, for example, in a pair of beads 11 and 12 that do not have a bent shape, as shown in Figure 7, the occurrence of welding cracks could not be sufficiently suppressed. On the other hand, by bending the beads 11 and 12 as shown in Figures 1 to 3, the occurrence of welding cracks could be suppressed. The reason for this is not clear, but it is presumed that the bent shape mitigates the effect of the tensile stress generated by the solidification of the main parts 112 and 122 on the end parts 111 and 121. In addition, by utilizing the bent shape, it may be possible to obtain the effect of reducing the area required to form a pair of beads 11 and 12. This provides various benefits, such as reducing the weight of the mechanical structural component by narrowing the width of the flange portion where the pair of beads 11 and 12 are formed.

[0039] Here, in each of the pair of beads 11 and 12, the deepest recess of the crater must be at least 0.5 mm away from the extension of the central axis of the main part. That is, the first bead 11 has a bent shape such that the deepest recess of the first crater 113 is at least 0.5 mm away from the extension of the central axis 112X of the first main part of the first bead 11, and the second bead 12 has a bent shape such that the deepest recess of the second crater 123 is at least 0.5 mm away from the extension of the central axis 122X of the second main part 122 of the second bead 12. If the distance between the deepest recess of the craters 113 and 123 and the extension of the central axis of the main parts 112 and 122 is less than 0.5 mm, the effect of suppressing the occurrence of welding cracks cannot be obtained. The distance between the deepest recess of the craters 113 and 123 and the extension of the central axis of the main parts 112 and 122 may be 0.8 mm or more, 1.0 mm or more, or 2.0 mm or more.

[0040] The "deepest point of the crater" refers to the deepest point of the crater, relative to the plane on which craters 113 and 123 are located. Since craters 113 and 123 are usually visible as small points to the naked eye, it may be acceptable to consider the entire crater as the deepest point of the crater. On the other hand, if necessary, the deepest points of craters 113 and 123 may be precisely determined by methods such as three-dimensional shape measurement.

[0041] Furthermore, "the central axis of the main part of the bead" refers to the central axis of the main part, along the longitudinal direction of the main part. "The extension of the central axis of the main part of the bead" means simply the straight line obtained by extending the central axis if the main part is linear in shape. On the other hand, if the main part is not linear in shape, "the extension of the central axis of the main part of the bead" means the straight line that is tangent to the central axis of the main part of the bead at the boundary between the main part and the end part.

[0042] (B) The distance between the deepest parts of the two craters 113 and 123 (C) Positional relationship of the two terminals 111 and 121 The distance between the deepest parts of craters 113 and 123 is set to 5.0 mm or less. In other words, as shown in Figures 1 to 3, the deepest part of the second crater 123 is located within a circle C1 with a radius of 5.0 mm centered on the deepest part of the first crater 113, and the deepest part of the first crater 113 is located within a circle C2 with a radius of 5.0 mm centered on the deepest part of the second crater 123. As a result, the end portions 111 and 121 where craters 113 and 123 are formed are located within a very close range. In addition, part or all of the end portions 111 and 121 of the pair of beads 11 and 12 are arranged adjacent to each other in the width direction. This makes it possible to cancel out the tensile stress generated during solidification of the end portions 111 and 121 of the pair of beads 11 and 12. This point will be explained with reference to Figures 8A to 8C.

[0043] Figure 8A shows the FEM analysis results of the stress applied to the tip of the first bead 11 when the second bead 12 is absent. Figure 8B is a conceptual diagram of the tensile stress, compressive stress, and weld cracking applied to the first bead 11 when the second bead 12 is absent. A first crater 113 is formed at the first end portion 111 of the first bead 11. In addition, tensile stress is applied to the side edge of the first end portion 111 due to the contraction of the base material heated by laser welding. Furthermore, as a result of the FEM analysis performed by the inventors, it was found that compressive stress is also applied to the tip of the first end portion 111, as shown in Figures 8A and 8B. The arrows in Figure 8B pointing away from the first bead 11 illustrate the tensile stress applied to the first end portion 111. Furthermore, the arrow in Figure 8B, pointing towards the first bead 11, illustrates the compressive stress applied to the tip of the first end portion 111. When the first end portion 111 is torn by this tensile stress, a weld crack C is generated. The weld crack C occurs along the extension direction of the first bead 11 and propagates and grows along the first bead 11. Currently, it is believed that if no other beads are provided around the end portion of the bead, the compressive stress applied to the tip of the end portion does not particularly affect the behavior of the crack at the end portion.

[0044] On the other hand, Figure 8C is a conceptual diagram of tensile and compressive stress when the second end portion 121 of the second bead 12 is formed adjacent to the first end portion 111 of the first bead 11. When part or all of the first end portion 111 and part or all of the second end portion 121 are arranged adjacent to each other in the width direction, welding cracks C are less likely to occur in the first end portion 111. This is presumed to be because the tensile stress generated on the side of the second end portion 121 relieves the tensile stress applied to the side edge of the first end portion 111. For the same reason, welding cracks C are also less likely to occur in the second end portion 121.

[0045] However, if the distance between the two craters 113 and 123 is too great, the tensile stresses will not cancel each other out, and the occurrence of weld cracks cannot be sufficiently suppressed. Also, even if the distance between the two craters 113 and 123 is small, as shown in Figure 7, if the two end portions 111 and 121 are adjacent to each other in the longitudinal direction and their tips are butted together, the tensile stresses will not cancel each other out. Furthermore, if the tip of one end portion is located to the side of the other end portion, the tensile stresses will not cancel each other out. This is because compressive stress is generated at the tip of the end portion, and this does not have the effect of canceling out the tensile stress applied to the side edge of the adjacent end portion. The positional relationship of the pair of beads 11 and 12 must be determined so that the tensile stress generation region on the side of one end portion and the tensile stress generation region of the other end portion overlap. For the reasons stated above, in the overlapping laser-welded joint 1 according to the first embodiment, (B) the distance between the deepest recess of the first crater and the deepest recess of the second crater is 5.0 mm or less, and (C) part or all of the first end portion 111 and part or all of the second end portion 121 are arranged adjacent to each other in the width direction.

[0046] Furthermore, the first end portion 111 and the second end portion 121 may be separated or touching, as long as they are adjacent to each other in the width direction. If the first end portion 111 and the second end portion 121 are separated, it is sufficient that the side edges of the first end portion 111 and the side edges of the second end portion 121 face each other. If the first end portion 111 and the second end portion 121 are touching, it is sufficient that the side of the first end portion 111 and the side of the second end portion 121 overlap. Since the two end portions 111 and 121 are placed very close together so that the distance between the two craters 113 and 123 is 5.0 mm or less, it is sufficient, for example, for about 50% of the side edge of one end portion to face the side edge of the other end portion, or for about 50% of the side of one end portion to overlap with the side of the other end portion. Furthermore, the central axes of the first end portion 111 and the second end portion 121 do not need to be parallel; they may be at a slight angle to each other. It is also possible to eliminate the first crater 113 or the second crater 123 by bringing the first end portion 111 and the second end portion 121 even closer together. Such an overlapping laser-welded joint corresponds to the overlapping laser-welded joint 2 according to the second embodiment described below.

[0047] <Layer-welded joint 2 according to the second embodiment> Next, a lap laser welded joint 2 according to the second embodiment will be described. As shown in Figure 5, the lap laser welded joint 2 according to the second embodiment comprises a plurality of overlapping metal plates 20 and a first bead 21 which is a linearly extending laser weld that joins the plurality of metal plates 20, wherein the ratio G / T of the total thickness G of the gap between the plurality of metal plates 20 to the total thickness T of the plurality of metal plates 20 is 0 to 17%, and the lap laser welded joint 2 further comprises a second bead 22 which is a linearly extending laser weld, and in a plan view along the thickness direction of the lap laser welded joint 2, on at least one surface of the lap laser welded joint 2, the first bead 21 is a first end portion 211 which is the portion up to 5.0 mm from the end, and a first main portion 212 which is the portion other than the first end portion 211. The second bead 22 consists of a second terminal portion 221, which is the portion up to 5.0 mm from the end, and a second main portion 222, which is the portion other than the second terminal portion 221. The first terminal portion 211 and the second terminal portion 221 are connected, and one crater 231 is formed in either the first terminal portion 211 or the second terminal portion 221. The first bead 21 has a bent shape such that the deepest recess of the crater 231 is separated by 0.5 mm or more from the extension of the central axis 212X of the first main portion 212 of the first bead 21. The second bead 22 has a bent shape such that the deepest recess of the crater 231 is separated by 0.5 mm or more from the extension of the central axis 222X of the second main portion 222 of the second bead 22. Here, if the end of the first bead 21 or the end of the second bead 22 is overwritten by the other bead and cannot be confirmed, the end of the bead whose end cannot be confirmed is considered to be the point closest to the starting end among the points where the central axis of the bead whose end cannot be confirmed intersects with the outer edges of the first bead 21 and the second bead 22.

[0048] The overlapping laser-welded joint 2 according to the second embodiment is the same as the overlapping laser-welded joint 1 according to the first embodiment in that the G / T is in the range of 0 to 17%, it has a first bead 21 and a second bead 22 consisting of a main part and an end part, these end parts 211 and 221 have a shape that is close together, and the first bead 21 and the second bead 22 each have a bent shape. The same configuration as in the first embodiment will be omitted from the description below.

[0049] On the other hand, the overlapping laser-welded joint 2 according to the second embodiment differs from the overlapping laser-welded joint 1 according to the first embodiment in that the two end portions 211 and 221 are closer together than in the overlapping laser-welded joint 1 according to the first embodiment, and the first end portion 211 and the second end portion 221 are connected, resulting in the disappearance of the first crater 113 or the second crater 123. It also differs from the overlapping laser-welded joint 1 according to the first embodiment in that the two end portions 211 and 221 are not necessarily adjacent in the width direction. The following describes the configuration specific to the overlapping laser-welded joint 2 according to the second embodiment.

[0050] In the overlapping laser-welded joint 2 according to the second embodiment, the first end portion 211 and the second end portion 221 are connected, and one crater 231 is formed on either the first end portion 211 or the second end portion 221. As long as there is only one crater 231, it may be provided on either the first end portion 211 or the second end portion 221. This is because, as described above, the first bead 21 and the second bead 22 are substantially equivalent.

[0051] After the first laser welding is completed, a second laser welding is performed to overlap the end of the first bead and form the end of the second bead, thereby connecting the first end 211 and the second end 221, and forming one crater 231 on either the first end 211 or the second end 221. Even if the first bead has solidified and a crater has formed when the end of the second bead is formed, the melting and solidification of the end of the second bead will cause the first crater to disappear. If the first bead has not solidified when the end of the second bead is formed, the end of the second bead will become the final solidified part of the pair of beads, and one crater will be formed. In either case, one crater 231 will be formed on either the first end 211 or the second end 221.

[0052] No crater is formed at the starting end of the bead. Therefore, in the overlapping laser-welded joint 2 according to the second embodiment, the number of craters in the entire pair of beads 21 and 22 is limited to only one. Furthermore, in the overlapping laser-welded joint 2, as described later, the first bead 21 has a bent shape such that the deepest recess of the crater 231 is separated by 0.5 mm or more from the extension of the central axis 212X of the first main part of the first bead 21, and the second bead 22 has a bent shape such that the deepest recess of the crater 231 is separated by 0.5 mm or more from the extension of the central axis 222X of the second main part 222 of the second bead 22. By forming a bent portion near the crater 231, the tensile stress generated during solidification of the end portions 211 and 221 of the pair of beads 21 and 22 can be canceled out, and welding cracks can be suppressed. Furthermore, according to the inventors' experimental results, in the overlapping laser-welded joint 2 according to the second embodiment, it is not essential to arrange the two end portions 211 and 221 adjacent to each other in the width direction. For example, even with beads 21 and 22 having the shape shown in Figure 5, the occurrence of welding cracks could be sufficiently suppressed.

[0053] As mentioned above, in the overlap laser welded joint 1 according to the first embodiment, the degree of bending of the first bead 11 is defined based on the first crater 113, and the degree of bending of the second bead 12 is defined based on the second crater 123. In the overlap laser welded joint 2 according to the second embodiment, the degree of bending of both the first bead 21 and the second bead 22 is defined based on one crater 231. That is, in the overlap laser welded joint 2 according to the second embodiment, the first bead 21 has a bent shape such that the deepest recess of the crater 231 is separated by 0.5 mm or more from the extension line of the central axis 212X of the first main part of the first bead 21, and the second bead 22 has a bent shape such that the deepest recess of the crater 231 is separated by 0.5 mm or more from the extension line of the central axis 222X of the second main part 222 of the second bead 22. This is because, when the two terminal sections 211 and 221 are welded together so that they overlap, the first crater and the second crater can be considered to have occurred in the same location.

[0054] As long as the above requirements are met, the overlapping laser-welded joint 1 according to the first embodiment and the overlapping laser-welded joint 2 according to the second embodiment can take various forms. More preferred embodiments of the overlapping laser-welded joints 1 and 2 will be described below. For convenience, the drawings and reference numerals used for explanation are those relating to the overlapping laser-welded joint 1 according to the first embodiment. However, unless otherwise specified, the embodiments described below are applicable to both the overlapping laser-welded joints 1 and 2 according to the first and second embodiments.

[0055] In the overlapping laser-welded joint 1 according to the first and second embodiments, as shown in Figure 6, the deepest recesses of all craters 113, 123 may be located in the region between a virtual line VL2 perpendicular to the straight line VL1 connecting the centers of the first main part 112 and the second main part 122 and passing through the center of the first main part 112, and a virtual line VL3 perpendicular to the straight line VL1 connecting the centers of the first main part 112 and the second main part 122 and passing through the center of the second main part 122. Here, "center of the main part" refers to a point on the central axis of the main part that is at a distance of 1 / 2 the length of the main part measured along the central axis of the main part from the tip of the main part. This makes it possible to increase the length of the weld line, which combines the first bead 11 and the second bead 12, thereby improving the joint strength of the overlapping laser-welded joint 1 and more efficiently preventing cracking at the two end parts.

[0056] As described above, in the overlapping laser-welded joint 1, the central axis of the first end portion 111 and the central axis of the second end portion 121 may be at a slight angle. On the other hand, it is preferable that part or all of the first end portion 111 and the second end portion 121 are parallel to each other. This makes it possible to house the pair of beads 11 and 12 within a narrow area. For example, when providing a pair of beads 11 and 12 on the flange portion of a mechanical structural part, it is preferable to make part or all of the first end portion 111 and the second end portion 121 parallel to each other, as this can narrow the flange width.

[0057] Part or all of the first end portion 111 may be parallel to the longest straight portion of the first main portion 112, and part or all of the second end portion 121 may be parallel to the longest straight portion of the second main portion 122. This makes it possible to house the pair of beads 11 and 12 within a narrow area.

[0058] The first bead 11 may be present on only one side of the overlapping laser-welded joint 1. That is, the first bead 11 does not have to penetrate all of the multiple metal plates 10 included in the overlapping laser-welded joint 1. This prevents molten metal from flowing out onto the other side of the overlapping laser-welded joint 1 or into the gaps between the multiple metal plates, which can reduce the size of the crater and further mitigate its effects. On the other hand, the first bead 11 may be present on both sides of the overlapping laser-welded joint 1. The second bead 12 may also be present on only one side or on both sides of the overlapping laser-welded joint 1.

[0059] In the overlapping laser-welded joint 1, when viewing the plane in which the first bead 11 and the second bead 12 are arranged as described above, the area of ​​the second bead 12 that is contained within a circle C1 with a radius of 5.0 mm centered on the deepest recess of the first crater 113 is 10.0 mm². 2 Therefore, the area of ​​the first bead 11, which is contained within a circle C2 with a radius of 5.0 mm centered on the deepest part of the second crater 123, is 10.0 mm². 2 This may be greater than or equal to 12.0 mm each. Preferably, each is 12.0 mm. 2 That concludes the explanation. In other words, it is preferable to place as many of the other bead's beads as possible within 5.0 mm of the crater of the other bead. This further enhances the tensile stress relaxation effect that one bead exerts on the other bead.

[0060] When the maximum width of the bead measured along a direction perpendicular to the central axis of the bead is defined as the bead width, and the larger of the widths W1 of the first bead 11 and W2 of the second bead 12 is defined as Wmax, the entirety of the first bead 11 and the second bead 12 may be contained within the region between two parallel imaginary lines with a spacing of 2 × Wmax. This makes it possible to house a pair of beads 11 and 12 within a narrow area. For example, when a pair of beads 11 and 12 are provided on the flange portion of a mechanical structural part, it is preferable to be able to narrow the flange width.

[0061] <Structural component for automobile body according to the third embodiment> Next, a structural member for an automobile body according to another aspect of the present invention will be described. The structural member for an automobile body according to another aspect of the present invention includes the overlapping laser welding joint 1 according to the first embodiment and / or the overlapping laser welding joint 2 according to the second embodiment. Structural members for automobile bodies 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 overlapping laser welding joints 1 and 2 to the flange portions of these members, it is possible to obtain structural members for automobile bodies that have excellent productivity and suppress the occurrence of welding cracks.

[0062] <Method for manufacturing laser-welded joints according to the fourth and fifth embodiments> Next, a method for manufacturing the overlapping laser-welded joint 1 according to the fourth embodiment of the present invention and a method for manufacturing the overlapping laser-welded joint 2 according to the fifth embodiment will be described. According to this manufacturing method, the overlapping laser-welded joint 1 according to the first embodiment or the overlapping laser-welded joint 2 according to the second embodiment described above can be suitably manufactured. However, even if an overlapping laser-welded joint is obtained by a method other than the manufacturing method described below, it will be considered an overlapping laser-welded joint according to the first or second embodiment if it satisfies the above requirements.

[0063] Both the method for manufacturing the overlapping laser-welded joint 1 according to the fourth embodiment and the method for manufacturing the overlapping laser-welded joint 2 according to the fifth embodiment are, (S1) A process of stacking multiple metal plates, (S2) A step of performing first laser welding to form first beads 11, 21 which are linearly extending laser welded joints that join multiple metal plates, It is equipped with, and furthermore, (S3) A step of performing a second laser welding to form second beads 12 and 22, which are linearly extending laser welded areas. The device includes the following: In the overlapping process (S1), the ratio G / T of the total thickness of the gaps between the multiple metal plates G to the total thickness of the multiple metal plates T is set to 0-17%. These processes are described below.

[0064] First, (S1) multiple metal plates are stacked on top of each other. Next, (S2) a first laser welding is performed on the multiple metal plates to form first beads 11 and 21 that join the multiple metal plates. Then, (S3) a second laser welding is performed on the metal plate on at least one surface of the stacked laser-welded joint to form second beads 12 and 22. As described above, the first bead and the second bead are substantially equivalent, so the order of the first and second laser welding is not particularly limited. The second laser welding may be performed after the first laser welding, or vice versa. A stop time may be provided between the end of the first laser welding and the start of the second laser welding, but from the viewpoint of work efficiency, the stop time may be 60 seconds or less, 50 seconds or less, 30 seconds or less, or 10 seconds or less.

[0065] In the manufacturing method according to the fourth embodiment, in a plan view along the thickness direction of the overlapping laser-welded joint 1, the laser irradiation surface comprises a first bead 11 which is a first end portion 111 that extends 5.0 mm from the end and has a first crater 113 formed thereon, and a first main portion 112 which is the portion other than the first end portion 111, and a second bead 12 which comprises a second end portion 121 that extends 5.0 mm from the end and has a second crater 123 formed thereon, and a second main portion 122 which is the portion other than the second end portion 121, and the first bead 11 The first bead 11 has a bent shape such that the deepest recess of the first crater is separated by 0.5 mm or more from the extension of the central axis 112X of the first main part of the first bead 11, and the second bead 12 has a bent shape such that the deepest recess of the second crater is separated by 0.5 mm or more from the extension of the central axis of the second main part 122 of the second bead 12, the distance between the deepest recess of the first crater and the deepest recess of the second crater is 5.0 mm or less, and part or all of the first end portion 111 and part or all of the second end portion 121 are arranged adjacent to each other in the width direction. The shape and arrangement of the resulting pair of beads 11 and 12 are the same as those of the overlapping laser welded joint 1 according to the first embodiment described above. This effectively suppresses welding cracks that occur in the overlapping laser welded joint 1.

[0066] In the manufacturing method according to the fifth embodiment, in a plan view along the thickness direction of the overlapping laser-welded joint 2, the laser irradiation surface comprises the first bead 21 consisting of a first end portion 211 which is the portion up to 5.0 mm from the end and a first main portion 212 which is the portion other than the first end portion 211, and the second bead 22 consisting of a second end portion 221 which is the portion up to 5.0 mm from the end and a second main portion 222 which is the portion other than the second end portion 221, and the first end portion 211 and the second end The end portions 221 are connected, and a crater 231 is formed in either the first end portion 211 or the second end portion 221. The first bead 21 is bent so that the deepest recess of the crater 231 is at least 0.5 mm away from the extension of the central axis 112X of the first main portion of the first bead 21. The second bead 22 is bent so that the deepest recess of the crater 231 is at least 0.5 mm away from the extension of the central axis of the second main portion 222 of the second bead 22. The shape and arrangement of the resulting pair of beads 21 and 12 are the same as those of the overlapping laser-welded joint 2 according to the second embodiment described above. This effectively suppresses welding cracks that occur in the overlapping laser-welded joint 2. Here, if the end of the first bead 21 or the end of the second bead 22 is overwritten by the other bead and cannot be confirmed, the end of the bead whose end cannot be confirmed is considered to be the point closest to the starting end among the points where the central axis of the bead whose end cannot be confirmed intersects with the boundary between the first bead 21 and the second bead 22.

[0067] Preferred embodiments applicable to the overlapping laser-welded joints 1 and 2 according to the first and second embodiments can also be applied to the manufacturing methods according to the fourth and fifth embodiments.

[0068] Up to this point, we have described overlapping laser-welded joints, structural members for automobile bodies, and methods for manufacturing overlapping laser-welded joints with reference to 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 spirit of the present invention.

[0069] <Layer laser welded joint (layer fillet joint) 1A> For example, the lap laser welded joint according to this embodiment may be a lap fillet joint. In the lap fillet joint 1A, for example as shown in Figure 9, the end face of a first metal plate 10A, which is the outermost metal plate 10 among a plurality of metal plates 10, and the surface of a second metal plate 10B which is superimposed on the first metal plate 10A are joined by at least a first bead 11A.

[0070] The lap fillet joint 1A is basically the same as the lap laser welded joint 1 described above, except that at least the first bead 11A joins the end face of the first metal plate 10A and the surface of the second metal plate 10B. Therefore, the lap fillet joint 1A is a lap fillet joint comprising a plurality of overlapping metal plates 10 and a first bead 11A which is a linearly extending laser weld that joins the plurality of metal plates 10, wherein the ratio G / T of the total thickness G of the gap between the plurality of metal plates 10 to the total thickness T of the plurality of metal plates 10 is 0 to 17%, and the lap fillet joint 1A further comprises a second bead 12A which is a linearly extending laser weld, and in a plan view along the thickness direction of the lap fillet joint 1A, on at least one surface of the lap fillet joint 1A, the first bead 11A is a portion up to 5.0 mm from the end and consists of a first end portion 111A in which a first crater 113A is formed and a first main portion 112A which is the portion other than the first end portion 111A, and the second bead 12A is a portion up to 5.0 mm from the end The first bead 11A is a part consisting of a second terminal portion 121A on which a second crater 123A is formed, and a second main portion 122A which is a part other than the second terminal portion 121A. The first bead 11A has a bent shape such that the deepest recess of the first crater 113A is separated by 0.5 mm or more from the extension of the central axis 112AX of the first main portion 112A of the first bead 11A. The second bead 12A has a bent shape such that the deepest recess of the second crater 123A is separated by 0.5 mm or more from the extension of the central axis 122AX of the second main portion 122A of the second bead 12A. The distance between the deepest recess of the first crater 113A and the deepest recess of the second crater 123A is 5.0 mm or less, and part or all of the first terminal portion 111A and part or all of the second terminal portion 121A are arranged adjacent to each other in the width direction.

[0071] (First bead 11A) The first bead 11A is a fillet laser weld that extends linearly, formed by joining the end face of the first metal plate 10A and the surface of the second metal plate 10B, among the multiple metal plates 10. The shape of the first bead 11A is not particularly limited as long as it is linear. The main portion 112A of the first bead 11A is, for example, shaped along the end face of the first metal plate 10A. The first end portion 111A of the first bead 11A includes a portion that extends from the first main portion 112A and bends toward the first metal plate 10A, as shown in Figure 9. Since the first end portion 111A is the portion of the first bead 11A up to 5.0 mm from its end, the first end portion 111A may include a part of the portion of the first bead 11A that is along the end face of the first metal plate 10A. Furthermore, the first end portion 111A of the first bead 11A may be bent toward the second metal plate 10B, for example.

[0072] The first bead 11A joins at least the end face of the first metal plate 10A and the surface of the second metal plate 10B among the multiple metal plates 10, but it may extend in the thickness direction so as to span all of the multiple metal plates 10 in order to join the multiple metal plates 10. Furthermore, the first bead 11A does not need to penetrate all of the metal plates 10, and the first bead 11A may be formed on only one side of the overlapping laser welded joint.

[0073] (Second bead 12A) The second bead 12A, like the first bead 11A, is a fillet laser weld that extends linearly, formed by joining the end face of the first metal plate 10A and the surface of the second metal plate 10B among the multiple metal plates 10.

[0074] The pair of beads 11A and 12A, consisting of a first bead 11A and a second bead 12A, satisfy the requirements (A) to (C) described above, and thus welding cracks are suppressed very effectively.

[0075] (G gap between multiple metal plates 10) The size of the gap between the metal plates 10 in the overlapping fillet joint 1A is basically measured in the same way as described above. However, the size of the gap between the first metal plate 10A and the second metal plate 10B is measured at the end of the first bead 11A on the side where the first metal plate 10A and the second metal plate 10B overlap in the cross-section.

[0076] The manufacturing method for the overlapping fillet joint 1A differs from the manufacturing method for the overlapping laser-welded joint 1 in that, in the first laser welding step, at least the end face of the first metal plate 10A, which is positioned on the outermost surface of the plurality of metal plates 10, is joined to the surface of the second metal plate 10B, which is overlapped with the first metal plate 10A, and in the second laser welding step, the end face of the first metal plate 10A, which is positioned on the outermost surface of the plurality of metal plates 10, is joined to the surface of the second metal plate 10B, which is overlapped with the first metal plate 10A. However, the other steps are the same as those for the manufacturing method for the laser-welded joint 1. Therefore, the manufacturing method of the lap fillet joint 1A comprises the steps of overlapping a plurality of metal plates 10, and performing a first laser welding on the overlapping plurality of metal plates 10 to form a first bead 11A that joins the plurality of metal plates 10 by performing a first laser welding on the end face of the first metal plate 10A which is placed on the outermost surface of the plurality of overlapping metal plates 10 and the surface of the second metal plate 10B which is overlapped with the first metal plate 10A. In the above overlapping, the ratio G / T of the total thickness G of the gap between the plurality of metal plates 10 to the total thickness T of the plurality of metal plates 10 is set to 0 to 17%. The manufacturing method of the lap fillet joint 1A further comprises the step of performing a second laser welding on the end face of the first metal plate 10A which is placed on the outermost surface of the plurality of overlapping metal plates 10 and the surface of the second metal plate 10B which is overlapped with the first metal plate 10A.In a plan view along the thickness direction of the overlapping fillet joint 1A, on the laser irradiation surface, the first bead 11A is the portion up to 5.0 mm from the end, consisting of a first end portion 111A where the first crater 113A is formed, and a first main portion 112A which is the portion other than the first end portion 111A; the second bead 12A is the portion up to 5.0 mm from the end, consisting of a second end portion 121A where the second crater 123A is formed, and a second main portion 122A which is the portion other than the second end portion 121; and the first bead 11A is the portion where the deepest recess of the first crater 113A is the first bead The first main part 112A of the second bead 11A is bent so as to be at least 0.5 mm away from the extension of the central axis 112AX of the second main part 122A of the second bead 12A, and the second bead 12A is bent so as to be at least 0.5 mm away from the extension of the central axis 122AX of the second main part 122A of the second bead 12A, and the distance between the deepest part of the first crater 113A and the deepest part of the second crater 123A is at least 5.0 mm, and part or all of the first end part 111A and part or all of the second end part 121A are arranged adjacent to each other in the width direction.

[0077] <Layer laser welded joint (layer fillet joint) 2A> Furthermore, the modified lap fillet joint 2A may have the same configuration as the second embodiment described above. That is, as shown in Figure 10, the lap fillet joint 2A is a lap fillet joint comprising a plurality of overlapping metal plates 20 and a first bead 21A which is a linearly extending laser weld that joins the plurality of metal plates 20, wherein the ratio G / T of the total thickness G of the gap between the plurality of metal plates 20 to the total thickness T of the plurality of metal plates 20 is 0 to 17%, and the lap fillet joint 2A further comprises a second bead 22A which is a linearly extending laser weld, and in a plan view along the thickness direction of the lap fillet joint 2A, on at least one surface of the lap fillet joint 2A, the first bead 21A consists of a first end portion 211A which is the portion up to 5.0 mm from the end and a first main portion 212A which is the portion other than the first end portion 211A, and the second Bead 22A consists of a second terminal portion 221A, which is the portion up to 5.0 mm from the end, and a second main portion 222A, which is the portion other than the second terminal portion 221A. The first terminal portion 211A and the second terminal portion 221A are connected, and one crater 231A is formed in either the first terminal portion 211A or the second terminal portion 221A. The first bead 21A has a bent shape such that the deepest recess of the crater 231 is separated by 0.5 mm or more from the extension of the central axis 212AX of the first main portion 212A of the first bead 21A, and the second bead 22A has a bent shape such that the deepest recess of the crater 231 is separated by 0.5 mm or more from the extension of the central axis 222AX of the second main portion 222A of the second bead 22A.

[0078] The manufacturing method for the overlapping fillet joint 2A differs from the manufacturing method for the laser-welded joint 1 in that, in the first laser welding step, at least the end face of the first metal plate 20A, which is positioned on the outermost surface of the plurality of metal plates 20, is joined to the surface of the second metal plate 20B, which is overlapped with the first metal plate 20A, and in the second laser welding step, the end face of the first metal plate 20A, which is positioned on the outermost surface of the plurality of metal plates 20, is joined to the surface of the second metal plate 10B, which is overlapped with the first metal plate 20A. However, the other steps are the same as those for the manufacturing method for the overlapping laser-welded joint 2. Therefore, the method for manufacturing a lap fillet joint 2A comprises the steps of: overlapping a plurality of metal plates 20; and performing a first laser welding on the plurality of overlapped metal plates 20 to form a first bead 21A that joins the plurality of metal plates 20 by performing a first laser welding on the end face of a first metal plate 20A placed on the outermost surface of the plurality of overlapped metal plates 20 and the surface of a second metal plate 20B that is overlapped with the first metal plate 20A. In the above overlapping, the ratio G / T of the total thickness of the gap between the plurality of metal plates G to the total thickness of the plurality of metal plates 20 T is set to 0 to 17%, and the method for manufacturing a lap fillet joint 2A further comprises the step of performing a second laser welding on the end face of a first metal plate 20A placed on the outermost surface of the plurality of overlapped metal plates 20 and the surface of a second metal plate 20B that is overlapped with the first metal plate 20A.In a plan view along the thickness direction of the overlapping fillet joint 2A, on the laser irradiation surface, the first bead 21A consists of a first end portion 211A, which is the portion up to 5.0 mm from the end, and a first main portion 212A, which is the portion other than the first end portion 211A, and the second bead 22A consists of a second end portion 221A, which is the portion up to 5.0 mm from the end, and a second main portion 222A, which is the portion other than the second end portion 221A, and the first end portion 211A and the second end portion 221A are connected, and the first end A crater 231A is formed in either section 211A or the second terminal section 221A, the first bead 21A is bent so that the deepest recess of the crater 231A is at least 0.5 mm away from the extension of the central axis 212AX of the first main section 212A of the first bead 21A, and the second bead 22A is bent so that the deepest recess of the crater 231A is at least 0.5 mm away from the extension of the central axis 222AX of the second main section 222A of the second bead 22A. [Examples]

[0079] The effects of one aspect of the present invention will be further explained in detail by the examples. However, the conditions in the examples are merely examples of conditions adopted to confirm the feasibility and effects of the present invention. The present invention is not limited to these examples of conditions. The present invention can adopt various conditions as long as it does not depart from the spirit of the invention and achieves the objectives of the present invention.

[0080] [Example 1] Two steel plates shown in Table 1 were stacked and laser-welded under various conditions to produce a first and second weld bead. Chemical components other than those shown in Table 1 are Fe and impurities. During laser welding, 3 to 5 times the normal amount of oil was applied to the steel plates to facilitate crack evaluation. The oil acts as a hydrogen source, promoting hydrogen embrittlement cracking in the laser-welded joint. The presence or absence of weld cracks in the various lap laser-welded joints obtained was confirmed. The shape of the laser-welded joint and the evaluation results are shown in Table 2. In Nos. 1 to 19, the first and second main sections were straight. On the other hand, in Nos. A1 and A2, the first and second main sections were C-shaped.

[0081] The "Shape" column in Table 2 describes the shape of the bead. The drawing number that most closely matches the shape of each bead is indicated in that column. For reference, a photograph of Example No. 5 is shown in Figure 12, a photograph of Example No. 7 is shown in Figure 13, and a photograph of Example No. 17 is shown in Figure 14A. The shape of the end of the bead in No. 17 is as shown in Figure 14B, with one end of the bead having the shape shown in Figure 2 and the other end having the shape shown in Figure 3.

[0082] In Table 2, "Degree of bending of the first bead" refers to the distance between the deepest point of the first crater and the extension of the central axis of the first main part of the first bead. This value was measured on the side facing the laser irradiation.

[0083] In Table 2, "Degree of bending of the second bead" refers to the distance between the deepest point of the second crater and the extension of the central axis of the second main part of the second bead. This value was measured on the side facing the laser irradiation.

[0084] In Table 2, "distance to the deepest point" refers to the distance between the deepest point of the first crater and the deepest point of the second crater. This value was measured on the side facing the laser irradiation. Note that for Nos. 7, 8, 18, and 19, only one crater was formed, so "distance to the deepest point" is not recorded.

[0085] In Table 2, "Second bead area in C1" refers to the area of ​​the second bead contained within a circle C1 with a radius of 5.0 mm centered on the deepest part of the first crater, and "First bead area in C2" refers to the area of ​​the first bead contained within a circle C2 with a radius of 5.0 mm centered on the deepest part of the second crater. In Nos. 7, 8, 18, and 19, only one crater was formed, so "Second bead area in C1" and "First bead area in C2" were not recorded.

[0086] In Table 2, "G / T" refers to the value obtained by dividing the gap between the two steel plates by the sum of the thicknesses of the two steel plates, which is 3.2 mm.

[0087] In Table 2, "Penetration Degree" refers to the state of the first bead on the side opposite to the laser irradiation side. If the steel plates are joined by the first bead, but the first bead is not formed on the joint surface opposite to the laser irradiation side, "Partial" is written in this column. If the steel plates are joined by the first bead, and the first bead is also formed on the joint surface opposite to the laser irradiation side, "Complete" is written in this column.

[0088] The "Crack Evaluation Results" column in Table 2 shows the results of crack evaluation performed using the following method. Three test specimens were prepared under identical conditions, and the number of weld cracks that occurred in these specimens was determined. In Table 2, the number of test specimens that did not crack is listed as the numerator, and the number of test specimens "3" is listed as the denominator. For cases where cracks occurred in all test specimens, the weld crack resistance was evaluated as "×", for cases where no cracks occurred in any test specimens, the weld crack resistance was evaluated as "〇", and for cases where cracks occurred in some test specimens, the weld crack resistance was evaluated as "△". Cases evaluated as "〇" or "△" were evaluated as having excellent weld crack resistance.

[0089] [Table 1]

[0090] [Table 2]

[0091] The pair of beads, No. 1 and No. 2, had the curved shape shown in Figure 1, and the degree of curvature was appropriate. Also, as shown in Figure 1, the ends of the pair of beads were aligned adjacent to each other in the width direction. In addition, the thickness of the gap between the plates was within the appropriate range. However, the distance between the deepest part of the first crater and the deepest part of the second crater was too large, resulting in insufficient resistance to weld cracking.

[0092] The pair of beads No. 3 and No. 4 had an appropriate spacing between the deepest parts of the first and second craters. In addition, the thickness of the gap between the plates was within the appropriate range. However, these beads had a substantially straight shape as shown in Figure 7, and the ends of these beads were adjacent along the longitudinal direction, with their tips butted together. Therefore, the resistance to weld cracking was insufficient in No. 3 and No. 4.

[0093] In No. 15 and No. 16, the shape and arrangement of the pair of weld beads were appropriate, but the thickness of the gap between the plates was inappropriate. As a result, the resistance to weld cracking was insufficient in No. 15 and No. 16.

[0094] In No. 18 and No. 19, only one crater was formed at the connection point between the first and second terminal ends. However, these beads had a substantially straight shape as shown in Figure 11. Because the first and second beads were not bent, the resistance to weld cracking was insufficient in No. 18 and No. 19.

[0095] On the other hand, in the examples where the bead shape and arrangement, as well as the thickness of the plate gap, were all appropriate, the weld crack resistance evaluation results were good. As mentioned above, the laser-welded joints in these examples were laser-welded after applying 3 to 5 times the normal amount of oil. Therefore, the laser-welded joints in these examples were manufactured under conditions that made them extremely prone to cracking. It is believed that cracking would not occur if these examples were manufactured under normal conditions.

[0096] [Example 2] Two steel plates A to C, having the tensile strength, thickness, and composition described in Table 3, were stacked together. The end face of the first metal plate, placed on the outermost layer, and the surface of the second metal plate stacked on top of the first metal plate were laser-welded under various conditions to form the first weld bead. Chemical components other than those shown in Table 3 are Fe and impurities. To facilitate crack evaluation during laser welding, 3 to 5 times the normal amount of oil was applied to the steel plates. The presence or absence of weld cracks in the various overlapping laser-welded joints obtained was confirmed. The shape of the laser-welded joint and the evaluation results are shown in Table 4. In Nos. 22, 24 to 30, and 35, the first and second main parts were made into straight shapes.

[0097] The "Shape" column in Table 4 describes the shape of the weld bead. The drawing number that most closely matches the shape of each bead is indicated in that column. However, in all examples from No. 22 to 35, the first main part and the second main part are assumed to be welded to the end face of the first metal plate. In other words, the central axis of the first main part and the central axis of the second main part coincide with the end face of the first metal plate in a plan view. For reference, a photograph of Example No. 24 is shown in Figure 15.

[0098] Each item in Table 4 has the same meaning as each item in Example 1. In Nos. 31 and 34, only one crater was formed, so "distance to the deepest recess," "second bead area in C1," and "first bead area in C2" were not recorded.

[0099] The "degree of penetration" in Table 4 was described according to the same criteria as in Example 1. Furthermore, crack evaluation was performed according to the same criteria as in Example 1.

[0100] [Table 3]

[0101] [Table 4]

[0102] The pair of weld beads in No. 22 had the curved shape shown in Figure 1, and the degree of curvature was appropriate. Also, as shown in Figure 1, the ends of the pair of weld beads were aligned adjacent to each other in the width direction. In addition, the thickness of the gap between the plates was within the appropriate range. However, the distance between the deepest part of the first crater and the deepest part of the second crater was too large, resulting in insufficient resistance to weld cracking.

[0103] In No. 23, the pair of weld beads had an appropriate spacing between the deepest points of the first and second craters. In addition, the thickness of the gap between the plates was within the appropriate range. However, these beads had a substantially linear shape as shown in Figure 7, and the ends of these beads were adjacent along the longitudinal direction, with their tips butted together. Therefore, in No. 23, the resistance to weld cracking was insufficient.

[0104] In No. 30, the shape and arrangement of the pair of weld beads were appropriate, but the thickness of the gap between the plates was inappropriate. As a result, the resistance to weld cracking in No. 30 was insufficient.

[0105] In No. 34, only one crater was formed at the connection point between the first and second terminal ends. However, these beads had a substantially straight shape as shown in Figure 11. Because the first and second beads were not bent, No. 34 had insufficient resistance to weld cracking.

[0106] On the other hand, in the examples where the bead shape and arrangement, as well as the thickness of the plate gap, were all appropriate, the weld crack resistance evaluation results were good. As mentioned above, the laser-welded joints in these examples were laser-welded after applying 3 to 5 times the normal amount of oil. Therefore, the laser-welded joints in these examples were manufactured under conditions that made them extremely prone to cracking. It is believed that cracking would not occur if these examples were manufactured under normal conditions. [Explanation of symbols]

[0107] 1. Overlap laser-welded joint 1A Overlap laser welded joint (overlap fillet joint) 10, 10A, 10B metal plate 11, 11A First bead 111, 111A First Termination Section 112, 112A First Main Section 112X, 112AX Central axis of the first main body 113, 113A First Crater 12, 12A Second bead 121, 121A Second Termination Section 122, 122A Second Main Section 122X, 122AX: Central axis of the second main section 123, 123A Second Crater 2. Overlap laser welded joint 2A Overlap laser welded joint (overlap fillet joint) 20, 20A, 20B metal plate 21, 21A First bead 211, 211A First Termination Section 212, 212A First Main Section 212X, 212AX Central axis of the first main section 22, 22A Second bead 221, 221A Second Termination Section 222, 222A Second main section 222X, 222AX: Central axis of the second main section Craters 231 and 231A A circle with a radius of 5 mm centered on the deepest part of the first crater, C1. A circle with a radius of 5 mm centered on the deepest part of the second crater, C2.

Claims

1. Multiple metal plates stacked on top of each other, A lap laser welded joint comprising: a first bead which is a linearly extending laser welded portion that joins a plurality of the aforementioned metal plates, The ratio G / T of the total thickness G of the gaps between the multiple metal plates to the total thickness T of the multiple metal plates is between 0 and 17%. The aforementioned overlapping laser-welded joint further comprises a second bead, which is a linearly extending laser-welded portion. In a plan view along the thickness direction of the overlapping laser-welded joint, at least one surface of the overlapping laser-welded joint is: The first bead is the portion from the end to 5.0 mm, and consists of a first terminal portion where the first crater is formed, and a first main portion which is the portion other than the first terminal portion. The aforementioned second bead is the portion extending 5.0 mm from the end, and consists of a second terminal portion where a second crater is formed, and a second main portion which is the portion other than the second terminal portion. The first bead has a bent shape such that the deepest recess of the first crater is separated by 0.5 mm or more from the extension of the central axis of the first main part of the first bead. The second bead has a bent shape such that the deepest recess of the second crater is separated by 0.5 mm or more from the extension of the central axis of the second main part of the second bead. The distance between the deepest recess of the first crater and the deepest recess of the second crater is 5.0 mm or less. A part or all of the first end portion and a part or all of the second end portion are arranged adjacent to each other in the width direction. Overlap laser welded joint.

2. The overlapping laser-welded joint according to claim 1, characterized in that a part or all of the central axes of the first terminal portion and the central axes of the second terminal portion are parallel to each other.

3. The area of ​​the second bead, contained within a circle with a radius of 5 mm centered on the deepest recess of the first crater, is 10.0 mm². ２ That's all. The area of ​​the first bead, contained within a circle with a radius of 5 mm centered on the deepest recess of the second crater, is 10.0 mm². ２ That's all. The overlapping laser-welded joint according to claim 1 or 2.

4. Multiple metal plates stacked on top of each other, A lap laser welded joint comprising: a first bead which is a linearly extending laser welded portion that joins a plurality of the aforementioned metal plates, The ratio G / T of the total thickness G of the gaps between the multiple metal plates to the total thickness T of the multiple metal plates is between 0 and 17%. The aforementioned overlapping laser-welded joint further comprises a second bead, which is a linearly extending laser-welded portion. In a plan view along the thickness direction of the overlapping laser-welded joint, at least one surface of the overlapping laser-welded joint is: The first bead consists of a first terminal portion, which is the portion from the end to 5.0 mm, and a first main portion, which is the portion other than the first terminal portion. The aforementioned second bead consists of a second terminal portion, which is the portion from the end to 5.0 mm, and a second main portion, which is the portion other than the aforementioned second terminal portion. The first terminal and the second terminal are connected, A crater is formed at either the first or second terminal portion. The first bead has a bent shape such that the deepest recess of the crater is separated by 0.5 mm or more from the extension of the central axis of the first main part of the first bead. The second bead has a bent shape such that the deepest recess of the crater is separated by 0.5 mm or more from the extension of the central axis of the second main part of the second bead. Overlap laser welded joint.

5. The overlapping laser welding joint according to claim 1, 2, or 4, characterized in that the second bead joins a plurality of the metal plates.

6. The overlapping laser-welded joint according to claim 1, 2, or 4, characterized in that the deepest recesses of all the craters are located in the region between a virtual line perpendicular to the straight line connecting the center of the first main part and the center of the second main part and passing through the center of the first main part, and a virtual line perpendicular to the straight line connecting the center of the first main part and the center of the second main part and passing through the center of the second main part.

7. The overlapping laser-welded joint according to claim 1, 2, or 4, characterized in that a part or all of the first terminal portion is parallel to the longest straight portion of the first main portion, and a part or all of the second terminal portion is parallel to the longest straight portion of the second main portion.

8. The overlapping laser welded joint according to claim 1, 2, or 4, characterized in that the first bead is present only on one side of the overlapping laser welded joint.

9. When Wmax is defined as the larger of the width W1 of the first bead and the width W2 of the second bead, The entirety of the first bead and the second bead are contained within the region between two parallel imaginary lines with a spacing of 2 × Wmax. The overlapping laser-welded joint according to claim 1, 2, or 4.

10. The multiple metal plates are multiple steel plates, The chemical composition of one or more of the aforementioned 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: Total 0.03 mass% or less The overlapping laser welding joint according to claim 1, 2, or 4, characterized by containing the following:

11. The multiple metal plates are multiple steel plates, The overlapping laser-welded joint according to claim 1, 2, or 4, characterized in that one or more of the multiple steel plates have a tensile strength of 980 MPa or more.

12. The lap laser welded joint according to claim 1, 2, or 4, wherein the lap laser welded joint is a lap fillet joint.

13. A structural member for an automobile body comprising an overlapping laser-welded joint according to claim 1, 2, or 4.

14. The process of stacking multiple metal plates, A step of performing a first laser welding on a plurality of stacked metal plates so as to form a first bead, which is a linearly extending laser welding portion that joins the plurality of metal plates, A method for manufacturing an overlapping laser-welded joint comprising: In the aforementioned superposition, the ratio G / T of the total thickness of the gaps between the multiple metal plates G to the total thickness of the multiple metal plates T is set to 0 to 17%. The method for manufacturing the overlapping laser-welded joint further comprises the step of performing a second laser welding on the metal plate on at least one surface of the overlapping laser-welded joint so as to form a second bead which is a linearly extending laser-welded portion. In a plan view along the thickness direction of the aforementioned overlapping laser-welded joint, on the laser irradiation surface, The first bead consists of a first terminal portion, which is the portion from the end to 5.0 mm and in which the first crater is formed, and a first main portion, which is the portion other than the first terminal portion. The second bead is comprised of a second terminal portion, which is 5.0 mm from the end and in which a second crater is formed, and a second main portion, which is the portion other than the second terminal portion. The first bead is bent such that the deepest recess of the first crater is separated by 0.5 mm or more from the extension of the central axis of the first main part of the first bead. The second bead is bent such that the deepest recess of the second crater is separated by 0.5 mm or more from the extension of the central axis of the second main part of the second bead. The distance between the deepest recess of the first crater and the deepest recess of the second crater shall be 5.0 mm or less. A part or all of the first end portion and a part or all of the second end portion are arranged adjacent to each other in the width direction. A method for manufacturing overlapping laser-welded joints.

15. The process of stacking multiple metal plates, A step of performing a first laser welding on a plurality of stacked metal plates so as to form a first bead, which is a linearly extending laser welding portion that joins the plurality of metal plates, A method for manufacturing an overlapping laser-welded joint comprising: In the aforementioned superposition, the ratio G / T of the total thickness of the gaps between the multiple metal plates G to the total thickness of the multiple metal plates T is set to 0 to 17%. The method for manufacturing the overlapping laser-welded joint further comprises the step of performing a second laser welding on the metal plate on at least one surface of the overlapping laser-welded joint so as to form a second bead which is a linearly extending laser-welded portion. In a plan view along the thickness direction of the aforementioned overlapping laser-welded joint, on the laser irradiation surface, The first bead consists of a first end portion, which is the portion from the end to 5.0 mm, and a first main portion, which is the portion other than the first end portion. The second bead consists of a second terminal portion, which is the portion from the end to 5.0 mm, and a second main portion, which is the portion other than the second terminal portion. The first terminal and the second terminal are connected, A crater is formed at either the first or second terminal portion. A method for manufacturing an overlapping laser welded joint, wherein the first bead has a bent shape such that the deepest recess of the crater is separated by 0.5 mm or more from the extension of the central axis of the first main part of the first bead, and the second bead has a bent shape such that the deepest recess of the crater is separated by 0.5 mm or more from the extension of the central axis of the second main part of the second bead.

16. A method for manufacturing an overlapping laser-welded joint according to claim 14 or 15, characterized in that the second laser welding is performed after the first laser welding.

17. A method for manufacturing an overlapping laser-welded joint according to claim 14 or 15, characterized in that the first laser welding is performed after the second laser welding.

18. The method for manufacturing an overlapping laser-welded joint according to claim 14 or 15, wherein the overlapping laser-welded joint is an overlapping fillet joint.

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