Lap welded joint, structural member for automobile, and method for manufacturing a lap welded joint.

Abstract

To provide a lap welding joint, an automobile skeleton member, and a manufacturing method of the lap welding joint that are constituted of a plurality of steel sheets including a high strength steel sheet and that have a high strength of joint.SOLUTION: A lap welding joint comprises: a plurality of steel sheets; laser welding metal for bonding overlapping parts of two or more steel sheets; and arc welding metal formed on one or more steel sheets. In the lap welding joint, one or more sheets out of the steel sheets bonded according to the laser welding metal is a high strength steel sheet with a tensile strength of 780 MPa or higher. A maximum value H1 of Vickers hardness in a region of 0.7 mm or less from the laser welding metal to a side of the arc welding metal is lower than a maximum value H2 of Vickers hardness in a region of 0.7 mm or less from the laser welding metal to the opposite side of the arc welding metal, and a difference between the maximum value H1 and the maximum value H2 is 25 HV or more.SELECTED DRAWING: Figure 1B

Description

Technical Field

[0001] The present invention relates to an overlap welded joint, a skeletal member for an automobile, and a method for manufacturing an overlap welded joint.

Background Art

[0002] For the purpose of reducing the weight of automobiles and improving collision safety, the application of high-strength steel sheets to automobile parts has been promoted. However, welded joints made of high-strength steel sheets have a problem that the joint strength is likely to decrease. Specifically, when the tensile strength of the base metal steel sheet is 780 MPa or more, the joint strength decreases.

[0003] Various techniques for improving the joint strength of welded joints made of high-strength steel sheets have been provided so far.

[0004] Patent Document 1 discloses a method for manufacturing a laser welded structural member, characterized in that one steel sheet having a bent portion and a flange following the bent portion is overlapped with another one or more steel sheets at the flange, a first laser welding is performed on the overlapping portion to form a first laser welded portion, and after the temperature of the first laser welded portion drops below the Mf point, a second laser welding is performed on a region near the first laser welded portion on the opposite side of the bent portion with respect to the formed first laser welded portion to form a second laser welded portion, and the heat affected zone of the first laser welded portion is tempered by the second laser welding so that the hardness of the heat affected zone is 90% or less of the hardness of the heat affected zone of the second laser welded portion.

[0005] Patent Document 2 discloses a welding method for an overlapping portion in which a plurality of steel plate members are joined at an overlapping portion, wherein at least one of the plurality of steel plate members contains a martensitic structure, comprising: a spot welding step of forming a spot weld portion having a nugget at the overlapping portion; and a molten solidification portion forming step of irradiating a laser beam to form a molten solidification portion that crosses the edge of the nugget between the nugget and a position 3 mm or more outward from the edge of the nugget, wherein the depth of the molten solidification portion is formed at a position 1 mm outward from the edge of the nugget in the steel plate member containing the martensitic structure to be 50% or more of the thickness of each plate.

[0006] Patent Document 3 discloses a spot welding method for high-strength thin steel plates, in which two or more overlapping high-strength thin steel plates are sandwiched between a pair of electrodes and spot welded while applying pressure, characterized in that after welding the first point, the position of the electrodes is moved, and after the first weld has cooled to a temperature below the Mf point, a second weld is performed so as to partially overlap the first weld.

[0007] Patent Document 4 discloses a welding method for joining multiple high-tensile steel plates by laser screw welding, comprising: a nugget forming step in which a laser is irradiated from an irradiation device onto the overlapping high-tensile steel plates to melt the high-tensile steel plates and form a nugget; and a tempering step in which a laser with a larger spot diameter at the irradiation point and a lower power than the laser used in the nugget forming step is irradiated from the irradiation device onto the heat-affected zone in an intermediate joint in which the nugget and the heat-affected zone formed around the nugget are formed.

[0008] Patent Document 5 discloses a method for manufacturing a laser-welded joint of high-strength steel plates by laser welding the overlapping portion of two high-strength steel plates having a tensile strength of 780 MPa or more. The method is characterized by first creating two parallel weld beads along the plate width direction in the overlapping portion by laser welding, with a joint width L of 1.5 to 10.0 mm, and then creating a third weld bead, or a third and fourth weld bead, parallel to these two weld beads, such that the distances d1 and d2 between the centers of the first two weld beads and the adjacent weld beads are both 0.2 to 2.0 mm. Here, the joint width L refers to the distance between the outer end faces of the first two weld beads at the joint surface of the two steel plates.

[0009] Patent Document 6 discloses a laser-welded joint with excellent joint strength, characterized in that it is formed by stacking multiple steel plates satisfying the following conditions: P content [P] and S content [S] are [P] + 5 [S] ≥ 0.026 mass%, and joining them with a laser, and having an average bead width W and a closed loop or closed loop main bead, a closed loop or closed loop temper bead with an inner toe positioned at a distance of more than W and 2.2W or less from the outer toe of the main bead, and an outer toe positioned at a distance of more than 1.5W and 4.0W or less from the outer toe of the main bead. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2010-12504 [Patent Document 2] International Publication No. 2014 / 024997 [Patent Document 3] Japanese Patent Publication No. 2010-172945 [Patent Document 4] Japanese Patent Publication No. 2017-87263 [Patent Document 5] Japanese Patent Publication No. 2015-136705 [Patent Document 6] Japanese Patent Publication No. 2012-240086 [Overview of the project] [Problems that the invention aims to solve]

[0011] However, in recent years, the demand for joint strength in welded joints has been increasing. There is a strong desire for further improvement in the joint strength of welded joints by means other than those described in Patent Documents 1-6.

[0012] The present invention aims to provide a lap-welded joint composed of multiple steel plates, including a high-strength steel plate, having high joint strength, an automotive frame member, and a method for manufacturing a lap-welded joint. [Means for solving the problem]

[0013] The gist of this invention is as follows:

[0014] (1) An overlap welded joint according to one aspect of the present invention comprises a plurality of steel plates that are partially or entirely overlapped, a laser weld metal that joins the overlapping portions of two or more of the steel plates, and an arc weld metal formed on one or more of the steel plates, wherein one or more of the steel plates joined by the laser weld metal is a high-strength steel plate with a tensile strength of 780 MPa or more, and when viewed in plan from the thickness direction of the overlap welded joint, the point on the edge of the laser weld metal closest to the arc weld metal and the point on the edge of the arc weld metal closest to the laser weld metal are connected. When the Vickers hardness is continuously measured along the overlapping surface of the high-strength steel plates joined by the laser weld metal, in a cross section that includes a straight line and is perpendicular to the overlapping portion of the steel plates, at a depth of 1 / 4 of the plate thickness of the high-strength steel plates, the maximum value H1 of the Vickers hardness in the region within 0.7 mm from the laser weld metal towards the arc weld metal is lower than the maximum value H2 of the Vickers hardness in the region within 0.7 mm from the laser weld metal towards the side opposite the arc weld metal, and the difference between the maximum value H1 and the maximum value H2 is 25 HV or more. (2) In the lap weld joint described in (1) above, preferably the laser weld metal is laser screw weld metal. (3) In the lap welded joint described in (1) or (2) above, preferably, the difference between the maximum value H1 and the maximum value H2 in the cross-section is 40HV or more. (4) In the lap welded joint described in any of (1) to (3) above, preferably, two or more of the steel plates are joined by both the laser weld metal and the arc weld metal. (5) In the lap welded joint described in any of (1) to (4) above, preferably, when viewed in plan from the thickness direction of the lap welded joint, the shortest distance between the edge of the laser weld metal and the edge of the arc weld metal is 3.0 mm or more and 17.0 mm or less. (6) In the lap welded joint described in any of (1) to (5) above, preferably, when viewed in plan from the thickness direction of the lap welded joint, the distance between the edge of the laser weld metal and the edge of the arc weld metal is greater than 0.7 mm. (7) In the lap weld joint described in any of (1) to (6) above, the width of the arc weld metal is preferably 3.0 mm or more. (8) In the lap welded joint described in any of (1) to (7) above, preferably, the number of steel plates is three or more, one or more of the steel plates are outside the laser weld metal, and the steel plate outside the laser weld metal and the steel plate joined by the laser weld metal are joined by the arc weld metal. (9) In the lap welded joint described in any of (1) to (8) above, the tensile strength of the high-strength steel plate is preferably 1700 MPa or more.

[0015] (10) An automotive frame member according to another aspect of the present invention has an overlapping welded joint as described in any one of the above items (1) to (9).

[0016] (11) A method for manufacturing an lap welded joint according to another aspect of the present invention comprises the steps of overlapping a part or all of a plurality of steel plates, laser welding the overlapping portion of the steel plates to form laser weld metal, and arc welding one or more of the steel plates to form arc weld metal, wherein one or more of the steel plates to be laser welded are high-strength steel plates with a tensile strength of 780 MPa or more, and the laser weld metal and its surrounding area are tempered by the welding heat of the arc welding. (12) In the method for manufacturing the lap welded joint described in (11) above, the laser welding is preferably laser screw welding. (13) In the method for manufacturing an lap welded joint described in (11) or (12) above, preferably, when viewed in plan from the thickness direction of the lap welded joint, the distance between the edge of the laser weld metal and the edge of the arc weld metal is greater than 0.7 mm. (14) In the method for manufacturing the overlap welding joint according to any one of (11) to (13) above, preferably, the heat input of the arc welding is 1000 J / cm or more, and when viewed in plan from the thickness direction of the overlap welding joint, the shortest distance between the edge of the laser welded metal and the edge of the arc welded metal is 3.0 mm or more and 17.0 mm or less. (15) In the method for manufacturing the overlap welding joint according to any one of (11) to (14) above, preferably, the method for manufacturing the overlap welding joint further includes a step of adding one or more steel plates to the two or more steel plates that have been laser welded before the arc welding, and joining the two or more steel plates that have been laser welded and the steel plates that have not been laser welded by the arc welding. (16) In the method for manufacturing the overlap welding joint according to any one of (11) to (15) above, preferably, the tensile strength of the high-strength steel plate is 1700 MPa or more.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide an overlap welding joint composed of a plurality of steel plates including high-strength steel plates and having high joint strength, a skeletal member for an automobile, and a method for manufacturing an overlap welding joint.

Brief Description of the Drawings

[0018] [Figure 1A] It is a plan view when viewed in plan from the thickness direction of the overlapping portion of the overlap welding joint according to an embodiment of the present invention. [Figure 1B] It is a cross-sectional view taken along the line IB-IB of the overlapping portion of the overlap welding joint of FIG. 1A. [Figure 1C] It is an example of a hardness curve of a laser welded metal and its peripheral region. [Figure 2A] It is a plan view when viewed in plan from the thickness direction of the overlapping portion of the overlap welding joint according to another embodiment of the present invention. [Figure 2B] It is a cross-sectional view taken along the line IIB-IIB of the overlapping portion of the overlap welding joint of FIG. A. [Figure 3] It is a cross-sectional view of an arc welded metal obtained by fillet welding a bent portion of a steel plate. [Figure 4] This is a cross-sectional view of arc weld metal obtained by welding the end faces of steel plates. [Figure 5A] This is a plan view of arc weld metal obtained by overlapping fillet welding the inner end faces of holes made in a steel plate. [Figure 5B] Figure 5A is a VB-VB cross-sectional view of the arc weld metal. [Figure 6] This is a cross-sectional view of an overlapping welded joint using a segiri structure. [Figure 7] This is a cross-sectional view of a lap welded joint to which a different slitting structure is applied. [Figure 8A] This is a plan view of the arc spot weld metal. [Figure 8B] Figure 8A is a cross-sectional view of the arc spot weld metal along the VIIIB-VIIIB line. [Figure 9] This is a plan view of an overlap welded joint having multiple arc weld metals. [Figure 10] This is a plan view of an overlapping welded joint in which the edges of a steel plate have irregularities, and the arc weld metal is placed on the protruding parts. [Figure 11] This is a plan view of an overlapping welded joint in which the edges of the steel plates have irregularities, and the arc weld metal is placed in the recesses. [Figure 12] This is a cross-sectional view of an lap welded joint consisting of three steel plates, where arc weld metal forms a fillet weld between two of the steel plates. [Figure 13] This is a cross-sectional view of an lap welded joint consisting of three steel plates, where the arc weld metal forms a fillet weld between the three steel plates. [Figure 14] This is a cross-sectional view of an overlapping welded joint consisting of three steel plates, with two overlapping arc fillet welds on two of the steel plates. [Figure 15] This is a cross-sectional view of an overlapping welded joint consisting of three steel plates, one of which has a hole for fillet welding, and two overlapping arc fillet welds formed by two of the steel plates. [Figure 16A] This is a plan view of an overlapping welded joint in which three steel plates are joined together by a single laser welding metal, and holes are used for arc welding of the three steel plates. [Figure 16B] Figure 16A is an XVIB-XVIB cross-sectional view of the arc weld metal. [Figure 17A] This is a plan view of an overlapping welded joint in which three steel plates are joined together by a single laser welding metal, and holes are used for arc welding of the three steel plates. [Figure 17B] Figure 17A is a cross-sectional view of the arc weld metal along the line XVIIB-XVIIB. [Figure 17C] Figure 17A is an XVIIC-XVIIC cross-sectional view of the arc weld metal. [Figure 18] This is a cross-sectional view of an overlapping welded joint where only two of the three steel plates were laser-welded, and the remaining steel plate was fillet-welded using an arc weld. [Figure 19] This is a cross-sectional view of an overlapping welded joint where only two of the three steel plates were laser-welded, and the remaining steel plate was arc-welded using a T-fillet weld. [Figure 20] This is a cross-sectional view of an overlapping welded joint in which only two of three steel plates were laser-welded, and the remaining steel plate was fillet-welded using an arc at the inner end face of a hole provided in the steel plate. [Figure 21] This is a cross-sectional view of an overlapping welded joint in which only two of three steel plates were laser-welded, and the remaining steel plate was arc-spot-welded through holes provided in the steel plate. [Figure 22] This is a cross-sectional view of an lap welded joint where only two of the three steel plates were laser welded, and the remaining steel plate was arc T fillet welded. [Figure 23A] This is a perspective view of a bumper reinforcement, an example of a structural component used in automobiles. [Figure 23B] Figure 23A is a cross-sectional view of the bumper reinforcement from XXIIIB to XXIIIB. [Figure 23C] Figure 23A is a cross-sectional view of the bumper reinforcement at XXIIIC-XXIIIC. [Figure 24A] This is a plan view of a floor member, which is an example of a structural component for an automobile. [Figure 24B] Figure 24A is a cross-sectional view of the floor member from XXIVB to XXIVB. [Figure 25A]This is a perspective view of a front side member, which is an example of a structural component for an automobile. [Figure 25B] This is a magnified view of the left side of the area enclosed by the dashed line in Figure 25A, showing the front side member. [Figure 25C] This is a magnified view of the right side of the area enclosed by the dashed line in Figure 25A, showing the front side member. [Figure 26A] This is a perspective view of the joint between a B-pillar reinforcement and a side sill reinforcement, which are examples of structural components for automobiles. [Figure 26B] This is a magnified view of the area indicated by the arrow in Figure 26A, which is the joint. [Figure 27] This is a perspective view of the joint between the front side member and side sill of an electric vehicle. [Figure 28A] This is a flowchart of a method for manufacturing a lap welded joint according to one aspect of the present invention. [Figure 28B] This is a flowchart of a method for manufacturing a lap welded joint according to another aspect of the present invention. [Figure 29A] Table 1 shows a plan view and a cross-sectional view of one of the invention examples in which laser weld metal is replaced with laser screw weld metal, and arc weld metal is provided only on the upper plate. [Figure 29B] Table 1 shows a plan view and a cross-sectional view of an example of the invention in which the laser weld metal is replaced with laser screw weld metal, and arc weld metal is provided to join the upper and lower plates. [Figure 29C] Table 1 shows a plan view and a cross-sectional view of an example of the invention in which the laser weld metal is linear in shape and arc weld metal is provided to join the upper and lower plates. [Figure 29D] Table 1 shows a plan view and a cross-sectional view of one of the invention examples in which the laser-welded metal has a zigzag shape and an arc-welded metal is provided to join the upper and lower plates. [Figure 29E] Table 1 shows a plan view and a cross-sectional view of one of the invention examples in which the laser weld metal is circumferentially shaped and arc weld metal is provided to join the upper and lower plates. [Figure 30] This is a perspective view of the hat member of Example 4. [Figure 31]These are the displacement-load curves obtained by bending tests of the hat members of the inventive example and comparative example. [Figure 32A] This is a photograph of the hat-shaped component of the invention after a bending test. [Figure 32B] This is a photograph of the hat-shaped member of the comparative example after the bending test. [Modes for carrying out the invention]

[0019] The lap welded joint 1 according to the first embodiment of the present invention, as shown in Figures 1A to 1C, for example, comprises a plurality of steel plates 11 that are partially or entirely overlapped, a laser welding metal 12 that joins the overlapping portions 111 of two or more steel plates 11, and an arc welding metal 13 formed on one or more steel plates 11, wherein one or more of the steel plates 11 joined by the laser welding metal 12 are high-strength steel plates 11H with a tensile strength of 780 MPa or more, and when viewed in plan from the thickness direction of the lap welded joint 1, the point Q closest to the arc welding metal on the edge of the laser welding metal and the point P closest to the laser welding metal on the edge of the arc welding metal are In a cross-section that includes the connecting line and is perpendicular to the overlapping portion 111 of the steel plate 11, when the Vickers hardness is continuously measured along the overlapping surface 11HS of the high-strength steel plate 11H joined by the laser weld metal 12 at a depth L of 1 / 4 of the plate thickness t of the high-strength steel plate, the maximum value H1 (maximum hardness in region A1) of the Vickers hardness in region A1 within 0.7 mm from the laser weld metal towards the arc weld metal is lower than the maximum value H2 (maximum hardness in region A2) of the Vickers hardness in region A2 within 0.7 mm from the laser weld metal towards the side opposite the arc weld metal, and the difference ΔH between the maximum value H1 and the maximum value H2 is 25 HV or more. The overlapping welded joint 1 according to this embodiment will be described in detail below.

[0020] The lap welded joint 1 according to this embodiment has a plurality of steel plates 11. Two or more of the plurality of steel plates 11 are overlapped in part or in whole, and the overlapping portion 111 is joined by laser weld metal 12. In the configuration illustrated in Figure 1B, the upper plate is a press-formed member having a flange portion, and the flange portion, which is part of the upper plate, is overlapped with the lower plate, and the overlapping portion 111 is joined by laser weld metal 12. On the other hand, both the upper plate and the lower plate may have a flat plate shape, and their entirety may be lap-welded. Laser welding is preferred because it can be applied to locations where it is difficult to place a spot welding machine.

[0021] In the lap welded joint according to this embodiment, at least one of the steel plates to be joined by laser weld metal is a steel plate with a tensile strength of 780 MPa or higher. This makes it possible to improve the strength of the machine part to which the lap welded joint 1 according to this embodiment is applied. With such high-strength steel plates, a problem arises in the strength reduction of the welded joint manufactured using them. However, in the lap welded joint 1 according to this embodiment, this problem is addressed by tempering the laser weld metal 12 and its surrounding area using the arc weld metal 13 described later.

[0022] The type of high-strength steel sheet is not particularly limited. Examples of high-strength steel sheets include DP steel sheets, TRIP steel sheets, composite structure steel sheets, martensitic steel sheets, and hot-stamped steel sheets. The greater the tensile strength of the steel sheet, the lower the joint strength in a normal welded joint. Therefore, the greater the tensile strength of the steel sheet, the more superior the effect of the lap welded joint according to this embodiment becomes compared to a normal welded joint. The tensile strength of the high-strength steel sheet is preferably 980 MPa or higher, more preferably 1300 MPa or higher, or 1700 MPa or higher. The high-strength steel sheet may be cold-rolled or hot-rolled. In the lap welded joint 1 illustrated in Figures 1A and 1B, a high-strength steel sheet 11H and a low-strength steel sheet 11 with a tensile strength of less than 780 MPa are joined by laser weld metal 12. Alternatively, two or more high-strength steel sheets 11H may be joined by laser weld metal 12.

[0023] The steel sheet may be plated steel sheet, unplated steel sheet, or a combination of these. Examples of plated steel sheets include GI plated steel sheet, GA plated steel sheet, EG plated steel sheet, Zn-Ni plated steel sheet, Zn-Al plated steel sheet, Zn-Mg plated steel sheet, and Zn-Mg-Al plated steel sheet. When a zinc-based hot-stamped steel sheet is included in the lap welded joint 1, zinc oxide may be included in the surface layer of the Fe-Zn or Fe-Zn-Ni solid solution phase. When an aluminum-based hot-stamped steel sheet is included in the lap welded joint 1, 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. When an unplated hot-stamped steel sheet is included in the lap welded joint 1, a shot-blasted version may be used to remove the scale generated during the hot-stamping process. When the steel sheet has a zinc-based plating, a gap may be provided on the overlapping surface of the steel sheet to remove zinc vapor generated during laser welding from the weld metal.

[0024] There are no particular restrictions on the thickness of the high-strength steel plate 11H. Generally, the thickness of steel plates used in automobile parts or car bodies is 0.6 to 3.2 mm. This thickness may be applied to the high-strength steel plate 11H of the overlapping welded joint 1 according to this embodiment. Furthermore, the number of overlapping steel plates 11 included in the overlapping portion 111 joined by the laser weld metal 12 is preferably in the range of, for example, 2 to 4 plates. The steel plate 11 that is laser-welded with the high-strength steel plate 11H may be a low-strength steel plate or a high-strength steel plate.

[0025] The composition of the laser weld metal 12 is not particularly limited and can be appropriately changed depending on the type of steel plate 11. For example, the shape of the laser weld metal 12 in plan view may be linear or dotted. Linear laser weld metal 12 may have a straight, C-shaped, circular, elliptical, or zigzag shape. Dotted laser weld metal 12 is obtained by laser welding multiple circles of different diameters and is generally referred to as laser screw weld metal.

[0026] In the lap welded joint according to this embodiment, it is preferable that the laser weld metal 12 be laser screw weld metal. This makes it possible to avoid burn-through during laser welding even when there is a gap in the overlapping surface of the steel plates. In addition, the laser weld metal can easily replace the nugget of resistance spot welding.

[0027] Furthermore, it is difficult to create resistance spot welds continuously at narrow intervals. This is because the nugget formed by the preceding resistance spot weld becomes a current path during subsequent resistance spot welds, hindering the subsequent welding. Laser screw weld metal, however, can be created continuously at narrow intervals.

[0028] The diameter of the laser screw weld metal is not particularly limited, but it is preferably in the range of 3.5√t to 9.0√t. Here, "t" is the thickness of the thinner of the two steel plates 11 placed on the surface of the overlapping portion 111 joined by the laser weld metal 12. The diameter of the laser screw weld metal is the diameter of the laser screw weld metal on the overlapping surface of the thinner of the two steel plates 11 placed on the surface. If the thicknesses of the two steel plates 11 placed on the surface are equal, the average value of the diameters of the laser screw weld metals of both is taken as the diameter of the laser screw weld metal.

[0029] Laser weld metal obtained by laser welding high-strength steel plates has the problem of low joint strength. This is thought to be because the laser weld metal becomes brittle due to the large amount of carbon contained in the high-strength steel plate. Therefore, the inventors of the present invention arranged arc weld metal 13 in the overlapping weld joint 1 so as to temper the laser weld metal 12 and its surrounding area with arc weld metal 13.

[0030] Arc weld metal 13 is formed by arc welding. Arc welding has a larger heat input than laser welding. Therefore, deformation of the steel plate 11 may occur around the arc weld metal 13. In addition, a heat-affected zone is formed over a wide area around the arc weld metal 13. This heat-affected zone may reduce the strength of the steel plate 11. Furthermore, the work efficiency of arc welding is lower than that of laser welding. For these reasons, laser welding is exclusively used for joining high-strength steel plates 11H in the manufacture of automobile bodies.

[0031] However, the inventors have found that by arranging the arc welding metal 13 so as to temper the laser welding metal 12 and its surrounding region, the joint strength of the lap welded joint 1 is dramatically improved. When the inventors examined the laser welding metal 12 with improved joint strength in detail, they found that the laser welding metal 12 and its surrounding region were tempered and softened by the heat input during arc welding. Generally, the surrounding region of the laser welding metal 12 is often a heat-affected zone (HAZ) with low toughness. The inventors believe that the softening of the laser welding metal 12 improved the brittleness of the laser welding metal 12 and its surrounding region, thereby improving the joint strength. For these reasons, the lap welded joint 1 according to this embodiment has arc welding metal 13 arranged so as to temper the laser welding metal 12 and its surrounding region.

[0032] Generally, "weld metal" refers to the molten and solidified portion that joins two or more materials. However, as shown in Figures 1A and 1B, in the lap welded joint 1 according to this embodiment, the arc weld metal 13 does not necessarily need to join two or more steel plates 11. The main function of the arc weld metal 13 is to temper and soften the laser weld metal 12 and its surrounding area. The arc weld metal 13 can improve the joint strength of the lap welded joint 1 without joining two or more steel plates 11.

[0033] On the other hand, as shown in Figures 2A and 2B, the arc weld metal 13 may join two or more steel plates 11. That is, two or more of the multiple steel plates 11 included in the lap weld joint 1 may be joined by both the laser weld metal 12 and the arc weld metal 13. In this case, the arc weld metal 13 improves the joint strength of the laser weld metal 12 by improving the toughness of the laser weld metal 12 and its surrounding region, and also improves the joint strength of the lap weld joint 1 itself.

[0034] As described above, in the lap weld joint 1 according to this embodiment, the hardness of the peripheral region of the laser weld metal 12 is reduced by the arc weld metal 13. The hardness of the peripheral region of the laser weld metal 12 is evaluated by the following procedure. (1) Identify the edge of the laser weld metal 12. The edge of the laser weld metal 12 is the boundary between the surface of the steel plate and the surface of the laser weld metal, and can be easily identified by viewing the overlapping weld joint in plan view. If another steel plate 11 or the like is provided to cover the surface of the laser weld metal 12, as illustrated in Figures 20 and 21 described later, it is sufficient to remove it and then observe the surface of the laser weld metal 12. (2) Identify the edge of the arc weld metal 13. The edge of the arc weld metal is the boundary between the surface of the steel plate and the surface of the arc weld metal, and can be easily identified by viewing the overlap weld joint in plan view. (3) Identify the point P closest to the laser weld metal on the edge of the arc weld metal 13, and the point Q closest to the arc weld metal on the edge of the laser weld metal 12. The distance between point P and point Q is the shortest distance between the arc weld metal 13 and the laser weld metal 12. (4) Draw a straight line connecting point P and point Q. For example, the dashed line IB-IB in Figure 1A and the dashed line IIB-IIB in Figure 2A are such straight lines. However, if the length of the straight line differs on the front and back of the overlapping welded joint 1, select the shorter of the two straight lines. (5) The overlapping portion 111 of the steel plate 11 is cut along the straight line. That is, the closest point between the laser weld metal and the arc weld metal is cut. This forms a cross section that includes the straight line and is perpendicular to the overlapping portion 111 of the steel plate 11. For example, the IB-IB cross section in Figure 1B and the IIB-IIB cross section in Figure 2B are such cross sections. If necessary, the cross section may be polished to a degree that allows for hardness measurement. (6) The hardness of the portion of the laser weld metal 12 contained in the cross-section that is contained in the high-strength steel plate 11H is measured. Specifically, the Vickers hardness is measured continuously along the overlapping surface 11HS of the laser weld metal of the high-strength steel plate 11H at a depth of 1 / 4 of the plate thickness t of the high-strength steel plate. The line L shown in Figures 1B and 2B is the hardness measurement position L. The hardness of the surrounding area of ​​the laser weld metal 12 is also measured at this time. The overlapping surface 11HS of the laser weld metal is the surface of the high-strength steel plate 11H that is joined to the other steel plate 11 by the laser weld metal 12. The hardness measurement conditions can be a measurement load of 500gf or 1000gf. Since almost the same value is obtained under either condition, the measurement conditions can be appropriately adopted according to the shape of the measurement area, etc.

[0035] Furthermore, if the shapes of the laser weld metal and the arc weld metal are parallel lines, points P and Q cannot be identified. In this case, a cross-section for hardness measurement can be formed by cutting perpendicularly to the laser weld metal and the arc weld metal at any point in the closest proximity of the laser weld metal and the arc weld metal. However, the start and end ends of linear arc weld metal and linear laser weld metal should be excluded from the cross-section for hardness evaluation.

[0036] Furthermore, depending on the combination of steel plates 11 in the overlapping section 111, there may be two or more overlapping surfaces 11HS of the laser-welded metal of the high-strength steel plate 11H. For example, if three steel plates 11 are laser-welded in the overlapping section 111, and the high-strength steel plate 11H is located in the center of the plate assembly, then in the overlapping welded joint 1, there will be two overlapping surfaces 11HS of the laser-welded metal of the high-strength steel plate 11H. In such a case, two or more hardness measurement positions L can be set based on each of the two or more overlapping surfaces 11HS of the laser-welded metal, and hardness measurements can be performed at each of them using the procedure described above. If the requirements described later are met at at least one of the multiple hardness measurement positions L, it is considered to be the overlapping welded joint 1 according to this embodiment. It is also preferable that the requirements described later are met at all of the multiple hardness measurement positions L.

[0037] When the hardness of the laser weld metal 12 and its surrounding area is measured according to the above procedures (1) to (6), a hardness curve like the one shown in Figure 1C is obtained. In the hardness curve of the laser weld metal 12 and its surrounding area according to this embodiment in which the arc weld metal 13 is placed, the hardness decreases the closer it is to the arc weld metal 13. This is because the closer it is to the arc weld metal 13, the higher the maximum temperature reached during arc welding, and therefore the higher the tempering temperature, and the greater the degree of softening due to tempering.

[0038] Based on the hardness curve described above, the hardness of the peripheral region of the laser weld metal 12 can be evaluated. Specifically, based on the hardness curve described above, the maximum Vickers hardness H1 in region A1 within 0.7 mm from the laser weld metal 12 toward the arc weld metal 13, and the maximum Vickers hardness H2 in region A2 within 0.7 mm from the laser weld metal toward the opposite side of the arc weld metal can be identified. Hereinafter, the maximum Vickers hardness H1 in region A1 will be referred to as "maximum hardness H1 in region A1," and the maximum Vickers hardness H2 in region A2 will be referred to as "maximum hardness H2 in region A2." In the lap welded joint according to this embodiment, H1 is lower than H2. Furthermore, in the lap welded joint according to this embodiment, the difference ΔH between the maximum hardness H1 in region A1 and the maximum hardness H2 in region A2 is 25HV or more.

[0039] When the laser weld metal 12 and its surrounding area are tempered by conventional heating means such as high-frequency heating or furnace heating, the laser weld metal 12 and its surrounding area are uniformly tempered. With tempering using conventional heating means, H1 and H2 become approximately the same, and the difference ΔH between H1 and H2 is 25HV or less.

[0040] On the other hand, in the lap welded joint according to this embodiment, the laser weld metal 12 and its surrounding region are tempered by the heat input of arc welding when forming the arc weld metal 13. Therefore, the tempering temperature is higher in areas closer to the arc weld metal 13. As a result, the laser weld metal 12 and its surrounding region are tempered unevenly. Consequently, in the lap welded joint according to this embodiment, H1 becomes lower than H2, and the difference ΔH between H1 and H2 becomes 25HV or more.

[0041] The difference ΔH between H1 and H2 is preferably large, for example, 30HV or more, 35HV or more, 40HV or more, or 50HV or more. There is no particular upper limit for the difference ΔH between H1 and H2, but for example, it may be 270HV or less, 220HV or less, or 170HV or less.

[0042] As long as H1 and H2 satisfy the above requirements, the distance between the laser weld metal 12 and the arc weld metal 13 is not particularly limited. According to the results of our experiments, for example, when viewed from the thickness direction of the overlap welded joint 1 in a plan view, if the shortest distance between the edge of the laser weld metal 12 and the edge of the arc weld metal 13 is 17 mm or less, 15 mm or less, or 13 mm or less, it is possible to sufficiently temper the laser weld metal 12 and its surrounding area to further increase ΔH. However, by increasing the heat input during arc welding, it was possible to make the difference ΔH between H1 and H2 25 HV or more even if the shortest distance between the edge of the laser weld metal 12 and the edge of the arc weld metal 13 was more than 17 mm.

[0043] Furthermore, arc welding involves a large heat input, and even if the distance between the laser weld metal 12 and the arc weld metal 13 is large, it is possible to make the difference ΔH between H1 and H2 25HV or more. Therefore, for example, when viewed from the thickness direction of the lap welded joint, the distance between the edge of the laser weld metal 12 and the edge of the arc weld metal 13 may be greater than 0.7 mm, 3.0 mm or more, 4.0 mm or more, or 5.0 mm or more.

[0044] There are no particular limitations on the size of the arc weld metal 13. However, according to the inventors' experimental results, it is preferable that the width of the arc weld metal 13 be 3.0 mm or more. The larger the width of the arc weld metal 13, the greater the amount of heat input during arc welding, and the more effectively the laser weld metal 12 and its surrounding area can be tempered. The width of the arc weld metal 13 may be 4.0 mm or more, 5.0 mm or more, or 6.0 mm or more. There is no need to specify an upper limit for the width of the arc weld metal 13, but for example, the width of the arc weld metal 13 may be 15.0 mm or less.

[0045] As described above, the number of steel plates 11 in the lap welded joint 1 according to this embodiment is not limited. Furthermore, the shape of the steel plates 11 is not particularly limited. Therefore, the lap welded joint 1 according to this embodiment can have various shapes. A preferred example is described below. In the examples listed below, any of the multiple steel plates 11 may be high-strength steel plates 11H. Therefore, in the figures corresponding to the examples listed below, for convenience, all steel plates 11 are denoted as "11".

[0046] The arc weld metal 13 shown in Figure 2B is a fillet weld metal that joins the surface of one steel plate 11 to the end face of the other steel plate 11. Alternatively, as shown in Figure 3, one of the multiple steel plates 11 may have a bent portion, and the arc weld metal 13 may join the surface of one steel plate 11 to the surface of the bent portion of the other steel plate 11 in a flare joint structure. Alternatively, as shown in Figure 4, the end faces of two steel plates 11, which are arranged on substantially the same plane, may be joined by the arc weld metal 13 in a helical joint structure.

[0047] Holes for arc welding may be provided in the steel plate 11. For example, as shown in the plan view of Figure 5A and the cross-sectional view of Figure 5B, holes may be provided in the steel plate 11, and the surface of the steel plate 11 in contact with the steel plate 11 and the inner end surface of the hole in the steel plate 11 may be overlapped and fillet-welded to obtain the weld metal obtained, which may be used as the arc weld metal 13 of the overlap-welded joint 1 according to this embodiment.

[0048] A joggled lap joint structure may be applied to the arc weld metal 13. A joggled lap joint, as described in JIS Z 3001-1:2018, is a welded joint in which a step is added to one of the members of a lap joint so that the base material surfaces are almost flush. Figures 6 and 7 show examples of cross-sections of arc weld metal 13 to which a joggled structure is applied. In the joggled structure shown in Figure 6, there is a gap between the arc weld metal 13 and the step provided on the steel plate 11. In the joggled structure shown in Figure 7, there is no gap between the arc weld metal 13 and the step provided on the steel plate 11. That is, in the joggled structure shown in Figure 7, the step on the steel plate 11 and the end face of the steel plate 11 overlapping this steel plate 11 are joined. In either case, the effect of straightening the stress flow can be obtained. This results in the advantages of improved energy transfer efficiency during collisions and improved static strength and fatigue strength of the joint.

[0049] The arc weld metal 13 may be replaced with arc spot weld metal 13. Arc spot weld metal 13 refers to weld metal obtained by spot welding using arc welding. An example of arc spot weld metal 13 is shown in the plan view of Figure 8A and the cross-sectional view of Figure 8B. Although the arc spot weld metal 13 exemplified in Figures 8A and 8B does not join two steel plates 11, it is possible to improve the joint strength by tempering the laser weld metal 12 and its surrounding area. Alternatively, arc spot weld metal 13 that joins two steel plates 11 may be formed by first drilling a hole in one of the steel plates 11 and then performing arc welding to transfer filler material into this hole.

[0050] In the example of the lap welded joint 1 described above, the direction in which the laser weld metal 12 and the arc weld metal 13 were aligned was perpendicular to the extending direction of the edge of the steel plate 11. However, naturally, the angle between the direction in which the laser weld metal 12 and the arc weld metal 13 are aligned and the extending direction of the edge of the steel plate 11 is not limited. Furthermore, one laser weld metal 12 and its surrounding area may be tempered by two or more arc weld metals 13. An example of such a combination of configurations is the lap welded joint 1 shown in Figure 9, in which arc weld metal 13 is placed between multiple laser weld metals 12. Even with the arrangement shown in Figure 9, the laser weld metal 12 and its surrounding area are tempered during arc welding, and the difference ΔH between H1 and H2 can be made 25HV or more.

[0051] Furthermore, when one laser weld metal 12 and its surrounding area are tempered by multiple arc weld metals 13, the cross-section for measuring the hardness of the laser weld metal 12 should be formed along a straight line connecting the point Q closest to the multiple arc weld metals on the edge of the laser weld metal and the point P closest to the laser weld metal on the edge of the multiple arc weld metals.

[0052] A method for measuring hardness when multiple arc weld metals 13 are arranged adjacent to a laser weld metal will be explained using the lower of the two laser weld metals 12 in Figure 9 as an example. Two arc weld metals 13A and 13B are arranged adjacent to the upper left and lower left sides of this laser weld metal 12, respectively. In the upper arc weld metal 13A, point P1 closest to the edge of the laser weld metal 12 is located to the lower right of arc weld metal 13A. In the lower arc weld metal 13B, point P2 closest to the edge of the laser weld metal 12 is located to the upper right of arc weld metal 13B. Within the edge of the laser weld metal 12, point Q1 closest to arc weld metal 13A is located to the upper left of the laser weld metal 12. Within the edge of the laser weld metal 12, point Q2 closest to arc weld metal 13B is located to the lower left of the laser weld metal 12. The distance between P1 and Q1 is smaller than the distance between P2 and Q2. In this case, the overlapping portion 111 can be cut along the straight line connecting P1 and Q1, and the hardness of the laser-welded metal 12 can be measured.

[0053] In the example of the lap welded joint 1 described above, the end of the steel plate 11 extended in a straight line. However, the shape of the end of the steel plate 11 can be changed in various ways. One example of the end shape is corrugated. Figures 10 and 11 show examples of plan views of the lap welded joint 1 in which the end of the steel plate 11 is corrugated. In both the lap welded joint 1 in Figure 10 and Figure 11, the end of the steel plate 11 is corrugated, consisting of convex and concave portions, and the laser weld metal 12 is placed inside the convex portions. In the lap welded joint 1 in Figure 10, the arc weld metal 13 is provided along the end of the convex portion, and in the lap welded joint 1 in Figure 11, the arc weld metal 13 is provided along the end of the concave portion. In either configuration, the weight of the steel plate 11 can be reduced. In addition, in either configuration, an improvement in joint strength can be obtained.

[0054] In the example of the lap welded joint 1 described above, there were two steel plates 11. However, the number of steel plates 11 may be three or more. Below, an example of a lap welded joint 1 having three or more steel plates 11 will be described.

[0055] Figure 12 shows an example in which the overlapping portion 111 of three steel plates 11 is joined by a single laser weld metal 12, and further, two steel plates 11 are joined by a single overlapping fillet arc weld metal 13. In this example, the steel plates 11 that are not joined by the arc weld metal 13 are firmly joined to the adjacent steel plates 11 by the laser weld metal 12 that has been tempered by the arc weld metal 13.

[0056] Figure 13 shows an example in which the overlapping portion 111 of three steel plates 11 is joined by a single laser weld metal 12, and the three steel plates 11 are further joined by a single overlapping fillet arc weld metal 13. In this example, all the steel plates 11 are firmly joined by two types of weld metals.

[0057] Figure 14 shows an example in which the overlapping portion 111 of three steel plates 11 is joined by one laser weld metal 12, and the three steel plates 11 are further joined using two overlapping fillet arc weld metals 13. Specifically, in this example, the steel plate 11 on one surface of the overlapping weld joint 1 and the central steel plate 11 are joined using one of the two arc weld metals 13, and the steel plate 11 on the other surface of the overlapping weld joint 1 and the central steel plate 11 are joined using the other of the two arc weld metals 13. In this example, all the steel plates 11 are firmly joined using three weld metals. In this example as well, the cross-section for hardness evaluation of the laser weld metal 12 is formed based on the arc weld metal 13 that is closer to the laser weld metal 12.

[0058] Figure 15 shows an example in which the hole illustrated in Figure 5B is applied to a single steel plate 11 in the example shown in Figure 14. In this example, a hole for arc welding is provided in the central of the three stacked steel plates 11. The overlapping fillet arc weld metal 13 is then placed on the inner end face of the hole.

[0059] Figures 16A and 16B also show an example in which the overlapping portion 111 of three steel plates 11 is joined by a single laser welding metal 12, and holes are used for arc welding of the three steel plates 11. Figure 16A is a plan view of the overlapping welded joint 1, and Figure 16B is a cross-sectional view along the dashed line XVIB-XVIB shown in Figure 16A. In the example shown in Figures 16A and 16B, elongated holes are provided in one of the three steel plates 11 that faces one surface of the overlapping welded joint 1 and in the center, and these elongated holes are overlapped. No holes are provided in the other of the three steel plates 11 that faces the other surface of the overlapping welded joint 1. The arc welding metal 13 is arranged so as to move the filler material throughout the interior of the two overlapping elongated holes. The laser welding metal 12 is aligned with the arc welding metal 13 along the extending direction of the elongated holes.

[0060] Figures 17A, 17B, and 17C also show examples in which the overlapping portion 111 of three steel plates 11 is joined by a single laser welding metal 12, and holes are used for arc welding of the three steel plates 11. Figure 17A is a plan view of the overlapping welded joint 1, Figure 17B is a cross-sectional view along the dashed line XVIIB-XVIIB shown in Figure 17A, and Figure 17C is a cross-sectional view along the dashed line XVIIC-XVIIC shown in Figure 17A. In this example, the laser welding metal 12 is aligned with the arc welding metal 13 along a direction perpendicular to the extending direction of the elongated hole. Also, in this example, the arc welding metal 13 is provided only in a part of the elongated hole. The rest of the configuration is the same as in Figures 16A and 16B.

[0061] In the examples shown in Figures 12 to 17C, all of the multiple steel plates 11 included in the lap welded joint 1 were overlapped in part and joined by laser welding metal 12. However, only a portion of the steel plates 11 included in the lap welded joint 1 may be joined by laser welding metal 12. In this case, the steel plates 11 outside of the laser welding metal 12 that are not joined by it may be joined using arc welding metal 13.

[0062] Figure 18 shows an example in which only two of the three steel plates 11 are laser welded. The un-laser-welded steel plate 11 and the laser-welded steel plate 11 are joined by overlapping fillet arc weld metal 13.

[0063] Figure 19 also shows an example where only two of the three steel plates 11 are laser-welded. The un-laser-welded steel plate 11 and the laser-welded steel plate 11 are joined by a T-shaped fillet arc weld metal 13. Here, the end face of the un-laser-welded steel plate 11 is abutted against the surface of the laser-welded steel plate 11.

[0064] Figure 20 also shows an example in which only two of the three steel plates 11 are laser-welded. Holes are made in the steel plates 11 that are not laser-welded, and the inner end faces of the holes in the steel plates 11 that are not laser-welded and the surface of the laser-welded steel plates 11 are joined by overlapping fillet arc weld metal 13.

[0065] Figure 21 also shows an example where only two of the three steel plates 11 are laser-welded. Holes are provided in the steel plate 11 that is not laser-welded, and the un-laser-welded steel plate 11 and the laser-welded steel plate 11 are joined by the arc spot weld metal 13 shown in Figures 8A and 8B. In an automobile body, the joint structures in Figures 18, 19, 20, and 21 can be used, for example, as a joint structure for a bumper and crash box assembled by laser welding.

[0066] In the examples shown in Figures 20 and 21, the laser weld metal 12 is covered by the arc-welded steel plate 11. However, when evaluating the hardness of the laser weld metal 12, the location where a cross-section for hardness measurement should be created can be identified by removing the arc-welded steel plate 11.

[0067] Figure 22 also shows an example in which only two of the three steel plates 11 are laser-welded. The un-laser-welded steel plate 11 and the laser-welded steel plate 11 are joined by a T-shaped fillet arc weld metal 13. However, unlike the example in Figure 19, in the example in Figure 22, the end face of the laser-welded steel plate 11 is abutted against the surface of the un-laser-welded steel plate 11.

[0068] Note that the example in Figure 22 includes three laser weld metals 12. Of these, the rightmost laser weld metal 12 and the central laser weld metal 12 are located near the arc weld metal 13, but the distance between them is large. In this case, the rightmost laser weld metal 12, the central laser weld metal 12, and their surrounding areas may not be sufficiently tempered during arc welding and may not meet the hardness requirements described above. However, even in such cases, if the leftmost laser weld metal 12 meets the hardness requirements described above, the example shown in Figure 22 can be considered an lap welded joint 1 according to this embodiment. When multiple laser weld metals 12 are provided in an lap welded joint 1, it is not necessary for all of them to meet the hardness requirements described above. If the hardness requirements described above are met only in the areas of the lap welded joint 1 where joint strength is particularly required, sufficient joint strength can be provided to the lap welded joint 1.

[0069] Although various embodiments of the lap welded joint 1 according to this embodiment have been described above, the present invention is not limited to these examples. It is also possible to combine the above-described examples as appropriate, and it is also possible to apply well-known joint structures not described above to the lap welded joint 1 according to this embodiment. For example, the lap welded joint according to this embodiment may have weld metal other than laser weld metal and arc weld metal. Weld metal other than laser weld metal and arc weld metal is, for example, the weld metal of projection welds of nuggets, nuts and bolts included in resistance spot welds, or the weld metal of arc stud welding.

[0070] Next, a frame member for automobiles according to a second embodiment of the present invention will be described. The frame member for automobiles according to this embodiment has a lap weld joint 1 according to the first embodiment. The lap weld joint 1 according to the first embodiment may be applied to only a part of the joint of the frame member for automobiles, or it may be applied to the entire joint. The part to which the lap weld joint 1 according to the first embodiment is applied has high joint strength. That is, the frame member for automobiles according to this embodiment has high joint strength despite containing high-strength steel plate 11H, which is prone to reduced joint strength at the joint.

[0071] Examples of automotive structural components include bumper reinforcements, crash boxes, A-pillars, B-pillars, side sills, roof rails, floor members connected to front side members, front side members, front side member kick sections, rear side members, front suspension towers, tunnel reinforcements, dash panels, torque boxes, seat frames, seat rails, and battery case frames. Any of these automotive structural components can exhibit excellent joint strength by applying the overlapping weld joint 1 according to this embodiment to part or all of them.

[0072] Even when the overlapping weld joint 1 according to this embodiment is applied to the joint between these automotive structural members and the pillars, they are also considered automotive structural members according to this embodiment. The joints between automotive structural members and pillars include, for example, the joint between the B-pillar reinforcement and the side sill, the joint between the front side member and the side sill of an electric vehicle, the joint between the B-pillar and the roof rail, the joint between the roof cross member and the roof rail, the joint between the side sill and the A-pillar, the joint between the dash panel and the tunnel, the base of the front side member, and the joint between the bumper and the crash box.

[0073] Figure 23A shows a perspective view of the bumper reinforcement 21. Figure 23B shows a cross-sectional view of the bumper reinforcement XXIIIB-XXIIIB of Figure 23A, and Figure 23C shows a cross-sectional view of the bumper reinforcement XXIIIC-XXIIIC of Figure 23A. The cross-sectional structure of Figure 23B, which is composed of three steel plates and has high strength, may be applied to the central part of the bumper reinforcement 21, which is the part that collides with an obstacle. On the other hand, the cross-sectional structure of Figure 23C, which is composed of two steel plates and is lightweight, may be applied to the parts other than the central part. In either cross-sectional structure, one or more flange portions can be bent, and arc weld metal can be provided at this bent portion. By arc welding, the laser weld metal can be softened, improving the joint strength. This makes it possible to prevent a decrease in energy transfer due to fracture of the joint of the bumper reinforcement 21 during a frontal collision of an automobile.

[0074] Figure 24A shows a plan view of the floor member 22 joined to the floor. Figure 24B shows a cross-sectional view XXIVB-XXIVB of the floor member in Figure 24A. In Figure 24B, the floor 24 is joined so that it is sandwiched between the lower member, the front side member 23, and the upper member, the floor member 22. The floor member 22 receives load from the front side member 23 during a frontal collision. By softening the laser weld metal through arc welding and improving the joint strength of the joint, it is possible to prevent fracture of the joint even when load is transmitted from the front side member 23.

[0075] Figure 25A shows a perspective view of the front side member 23. Figure 25B shows an enlarged view of the left side of the area enclosed by the two dashed lines in Figure 25A, and Figure 25C shows an enlarged view of the right side of the area enclosed by the two dashed lines in Figure 25A. In the joint shown in Figure 25B, the arc weld metal is formed in the recess of the flange of the upper plate as shown in Figure 11. As a result, the joint shown in Figure 25B is lap fillet welded and has high joint strength. In addition, in the joint shown in Figure 25B, since the arc weld metal is housed in the recess, interference with other members can be prevented and subsequent processes after welding can be avoided.

[0076] In the joint shown in Figure 25C, the arc weld metal is formed on the flange protrusion of the lower plate. As a result, the joint shown in Figure 25C is lap fillet welded and has high joint strength. The flange protrusion of the lower plate may also have holes for fastening bolts and nuts for joining to other members.

[0077] Figure 26A shows a perspective view of the joint between the B-pillar reinforcement 25 and the side sill reinforcement 26. The horizontal member shown at the bottom of Figure 26A is the side sill reinforcement 26, and the vertical member shown at the top of Figure 26A is the B-pillar reinforcement 25. Laser welding and arc welding are used in combination at the joint between the two.

[0078] Figure 26B shows an enlarged view of the area indicated by the arrow in Figure 26A. The joint between the B-pillar reinforcement 25 and the side sill reinforcement 26 is a point that is prone to fracture during a side collision of an automobile. By providing arc weld metal at this point, fracture can be further prevented. Furthermore, in the joint shown in Figure 26B, the arc weld metal is formed in the recess of the flange of the upper plate as shown in Figure 11. As a result, the joint shown in Figure 26B is lap fillet welded and has high joint strength.

[0079] Figure 27 shows a perspective view of the joint between the front side member 23 and the side sill 27 of an electric vehicle. The member on the left is the front side member 23, and the member on the right is the side sill 27. The front side member 23 and the side sill 27 are joined by a central connecting member 28. In electric vehicles, a large space is provided on the floor for placing the batteries. Therefore, in the event of a frontal collision in an electric vehicle, the load applied from the front side member 23 needs to be transmitted to the side sill 27. For this reason, the offset of the shape of this member needs to be large. As the offset of the shape increases, the moment increases, making the laser welded metal at the joint more prone to fracture. Therefore, it is preferable to use both laser welded metal and arc welded metal at the joint between the front side member 23 and the side sill 27.

[0080] Next, a method for manufacturing the lap welded joint 1 according to a third embodiment of the present invention will be described. As shown in Figure 28A, the method for manufacturing the lap welded joint 1 according to this embodiment includes the steps of: step S1 overlapping part or all of a plurality of steel plates 11; step S2 laser welding the overlapping portion 111 of the steel plates 11 to form laser weld metal 12; and step S3 arc welding one or more steel plates 11 to form arc weld metal 13 such that the laser weld metal 12 and its surrounding area are tempered. Here, one or more of the steel plates 11 to be laser welded are high-strength steel plates 11H with a tensile strength of 780 MPa or more. Furthermore, the laser weld metal 12 and its surrounding area are tempered by the welding heat of the arc welding.

[0081] The manufacturing method of the lap welded joint 1 according to the third embodiment will now be described. Naturally, the various preferred examples given in the description of the lap welded joint 1 according to the first embodiment can also be applied to the manufacturing method of the lap welded joint 1 according to the third embodiment.

[0082] In step S1, where steel plates 11 are overlapped, multiple steel plates 11 are overlapped. In S1, all areas of the steel plates 11 may be overlapped, or only parts of them may be overlapped. Furthermore, in S1, it is not necessary to overlap all the steel plates 11 that constitute the overlapped welded joint 1; only the steel plates 11 that are to be laser-welded need to be overlapped. At this time, gaps may occur in the overlapped surfaces, but from the viewpoint of ensuring laser welding quality, it is desirable that the gaps be 1.0 mm or less, and more preferably 0.8 mm or less.

[0083] Here, one or more of the steel plates 11 to be laser-welded are high-strength steel plates 11H with a tensile strength of 780 MPa or more. Preferred embodiments of the high-strength steel plates 11H are those illustrated in the description of the first embodiment. The number, shape, and positional relationship of the steel plates 11 can also be appropriately applied to the embodiments illustrated in the description of the first embodiment. For example, the tensile strength of the high-strength steel plates 11H may be 1700 MPa or more.

[0084] In the subsequent laser welding process S2, the overlapping portion 111 of the steel plates 11 is laser-welded. This forms a laser weld metal 12 that joins the overlapping portion 111 of the steel plates 11. The laser welding conditions and laser welding apparatus are not particularly limited, and known conditions and apparatus can be used as appropriate. A preferred example of laser welding is shown below.

[0085] Laser welding is performed by overlapping steel plates and irradiating the overlapping surfaces with a laser beam. The shape of the laser-welded metal can be linear, C-shaped, circular, elliptical, or zigzag. Preferably, the laser-welded metal is laser screw weld metal obtained by laser screw welding (LSW), which involves irradiating the metal with a laser in a spiral pattern to melt it in a circular pattern. Laser screw welding is preferable because it can join plate assemblies with large gaps between the steel plates. Alternatively, resistance spot welding may be performed on the plate assemblies to eliminate the gaps between the steel plates before laser welding.

[0086] Laser welding can be performed using, for example, fiber lasers, disk lasers, and semiconductor lasers. The beam diameter is not particularly limited, but may be in the range of, for example, 0.10 mm to 1.2 mm. The laser output is not particularly limited, but may be in the range of, for example, 1.0 kW to 20 kW. Laser welding may also be performed using a remote welding device in which the welding torch has a galvanometer scanner. When laser welding is performed as laser screw welding, the diameter of the laser weld metal may be 3.5√t or more and 9.0√t or less. t is the thickness of the thinner of the two steel plates 11 placed on the surface of the overlapping portion 111 joined by the laser weld metal 12.

[0087] Furthermore, when welding a plate assembly that includes zinc-plated steel sheets (e.g., alloyed hot-dip galvanized steel sheets, hot-dip galvanized steel sheets, etc.), there is a risk that the zinc on the overlapping surfaces may evaporate due to the welding heat. Zinc vapor may cause defects such as pits in the weld metal. When manufacturing parts with a structure that makes it difficult for gaps to form between the steel sheets constituting the plate assembly, there is a risk that defects such as pits may occur in the weld metal. To prevent defects caused by zinc vapor, it is possible to create small gaps on the overlapping surfaces of the steel sheets near the weld metal by creating embossing by press forming or by creating protrusions on the steel sheets by raising the molten area by laser pre-irradiation. The size of the gaps in the steel sheets is preferably in the range of, for example, 0.03 mm to 0.8 mm.

[0088] Then, in the subsequent arc welding process S3, arc welding is performed using the welding heat from the arc welding to temper the laser weld metal 12 and its surrounding area. This arc welding does not necessarily have to join two or more non-welded materials. This is because arc welding is performed to temper the laser weld metal 12 and its surrounding area by the heat input of the arc. Therefore, arc welding may be performed on only one steel plate 11 to form the arc weld metal 13 shown in Figure 1B. Alternatively, arc welding may be performed on two or more steel plates 11 to form the arc weld metal 13 shown in Figure 2B.

[0089] As long as the laser weld metal 12 and its surrounding area are tempered, the location and conditions for performing arc welding are not particularly limited. Generally, the smaller the distance between the laser weld metal 12 and the arc weld metal 13, the higher the maximum heating temperature of the laser weld metal 12 during arc welding. Also, the larger the heat input during arc welding, the higher the maximum heating temperature of the laser weld metal 12 during arc welding. The higher the maximum heating temperature, the greater the amount of tempering and softening of the laser weld metal 12 and its surrounding area. However, if the maximum heating temperature is too high, re-hardening of the laser weld metal 12 will occur, causing the laser weld metal 12 to harden. The location and heat input during arc welding should be appropriately selected while considering these factors.

[0090] A suitable example of arc welding is to set the heat input of the arc welding to 1000 J / cm or more, and to determine the arc welding position such that, when viewed from the thickness direction of the overlap welding joint 1 in a plan view, the shortest distance between the edge of the laser weld metal 12 and the edge of the arc weld metal 13 is between 3.0 mm and 17.0 mm.

[0091] Alternatively, the arc welding position may be determined so that the laser weld metal 12 and the arc weld metal 13 overlap. In this case, the gap between the edge of the laser weld metal 12 and the edge of the arc weld metal 13 is defined as 0 mm. From the viewpoint of sufficiently avoiding re-hardening of the laser weld metal 12, it is preferable to determine the arc welding position so that the gap between the edge of the laser weld metal 12 and the edge of the arc weld metal 13 is greater than 0.7 mm. The heat input for arc welding may be 1500 J / cm or more. The heat input for arc welding is the energy per unit length of the weld bead of the arc. The heat input H can be calculated using the following formula with the arc voltage E (V), arc current I (A), and welding speed ν (cm / min). H=60EI / ν

[0092] Examples of other suitable conditions for arc welding are described below. The arc welding may be, for example, gas-shielded arc welding using a consumable electrode with iron welding wire, or MIG brazing using a Cu alloy wire, but other types of arc welding may also be used. If the arc welding is MAG welding, for example, Ar+CO2 gas, Ar+CO2+O2 gas, and Ar+O2 gas may be used as shielding gas. If the arc welding is carbon dioxide welding, CO2 gas may be used as shielding gas. The welding wire for arc welding may be a welding wire from YGW12 to YGW17. If high joint strength is required, a high-strength wire with a weld metal hardness of approximately 280 to 480 may be used. Also, if blowholes in GA-plated steel sheets are a problem, a wire compatible with galvanized steel sheets may be used. Furthermore, if cracks due to hydrogen embrittlement occur around the weld metal, austenitic stainless steel wire such as SUS309 or duplex stainless steel wire may be used. By forming an austenite structure with high diffusive hydrogen absorption capacity in the weld metal, cracking due to hydrogen embrittlement is suppressed. Furthermore, any of the following arc welding methods are acceptable: pulse welding, short arc welding, or CMT welding. CMT welding is preferable because it produces less spatter in the weld. Synchro-feed welding and super-active wire welding are also acceptable. Although these welding methods have different names depending on the manufacturer, they are essentially the same welding method as CMT.

[0093] When arc welding is MIG brazing, a shielding gas such as Ar gas or a gas containing a small amount of oxidizing gas in addition to Ar can be used. The wire used in MIG brazing can be, for example, Cu-Al wire or Cu-Si wire. If it is necessary to further improve the joint strength with the arc weld metal 13, it is preferable to perform arc welding using a Cu-Al wire.

[0094] This makes it possible to set the maximum hardness H1 in region A1, within 0.7 mm of the laser weld metal on the side of the arc weld metal, to a value smaller than the maximum hardness H2 in region A2, within 0.7 mm of the laser weld metal on the side opposite the arc weld metal. Furthermore, the difference ΔH between the maximum hardness H1 in region A1 and the maximum hardness H2 in region A2 can be set to 25 HV or more. Preferably, the difference ΔH between H1 and H2 is 40 HV or more. In this way, by using the heat of arc welding to impart a hardness difference to the laser weld metal, the toughness of the laser weld metal is improved, which suppresses fracture, especially at the joint interface, and improves the joint strength.

[0095] An example of the positional relationship between arc welding and laser welding is similar to the positional relationship between the arc weld metal 13 and the laser weld metal 12 in the lap welded joint 1 described above. That is, the positional relationship between arc welding and laser welding should be set appropriately so that various forms illustrated in Figure 1A, etc., can be realized.

[0096] Furthermore, in the manufacturing method of the lap welded joint 1 according to this embodiment, all of the multiple steel plates 11 included in the lap welded joint 1 may be laser-welded by overlapping a portion of them. Alternatively, only a portion of the steel plates 11 included in the lap welded joint 1 may be laser-welded. In this case, the steel plates 11 that were not subjected to laser welding can be arc-welded to the laser-welded steel plates 11.

[0097] Accordingly, as shown in Figure 28B, the manufacturing method of the lap welded joint 1 according to this embodiment may further include a step S4 in which one or more steel plates 11 are added to two or more laser-welded steel plates 11 before the arc welding step S3. Then, the two or more laser-welded steel plates 11 and the steel plates 11 that have not been laser-welded may be joined by the arc welding step S3. The arc welding may be lap arc welding to obtain the lap welded joint 1 as illustrated in Figure 18, or butt arc welding to obtain a composite structure of a lap joint and a T-joint as illustrated in Figure 19. Accordingly, in the step S4 in which the steel plates 11 are added, the steel plates 11 to be arc-welded may be overlapped with the laser-welded steel plates 11 or butt-welded. Depending on the shape of the member and the structure of the manufacturing line, the step S4 in which the steel plates 11 are added may be provided before the laser welding step S2. However, even in this case, the arc welding step S3 must be performed after the laser welding step S2.

[0098] In the case of plate assemblies including galvanized steel sheets (alloyed hot-dip galvanized steel sheets, hot-dip galvanized steel sheets), the zinc on the overlapping surfaces may vaporize due to the heat of arc welding, causing defects such as pits in the arc weld metal. In this process, thermal deformation during laser welding creates tiny gaps between the overlapping steel sheets, allowing zinc vapor to escape. Therefore, defects such as pits are less likely to occur during arc welding. However, in the manufacture of parts with structures that make it difficult to form gaps, cases where defects such as pits are likely to occur can be anticipated. In such cases, a press forming process may be carried out in advance to create tiny protrusions on at least one steel sheet near the arc weld metal, so that small gaps (0.03 mm to 1.0 mm) are formed on the overlapping surfaces of the steel sheets. [Examples]

[0099] 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.

[0100] (Example 1) Two identical high-strength steel plates were overlapped and laser-welded. Then, these two high-strength steel plates were arc-welded. Details of the steel plates and welding conditions are as follows. • Thickness of high-strength steel plate: 1.6 mm • Tensile strength of high-strength steel plate: As shown in Table 1. • Laser shape in laser welding: Circular shape with a diameter of 6.0 mm • Shape of laser weld metal: As shown in Table 1. "LSW" refers to the laser screw weld metal shown in Figures 29A and 29B, "linear" refers to the linear laser weld metal shown in Figure 29C, "zigzag" refers to the zigzag laser weld metal shown in Figure 29D, and "circumferential" refers to the hollow circular laser weld metal shown in Figure 29E. • Arc welding current: 80A • Arc welding voltage: 15.6V Arc welding speed: 30 cm / min • Arc welding wire: YM-24T • Shielding gas for arc welding: Ar + 20% CO2 • Position of arc weld metal: As shown in Table 1. "Arc welding on the upper plate" means that the arc weld metal is placed only on the upper plate, as shown in Figure 29A, and "Arc welding on the overlapping surface" means that the arc weld metal is placed on both the upper and lower plates, as shown in Figures 29B to 29E.

[0101] The hardness of the laser weld metal of the lap welded joint obtained using the procedure described above was measured using the method described above. The maximum hardness H1 in region A1, within 0.7 mm from the laser weld metal towards the arc weld metal, and the maximum hardness H2 in region A2, within 0.7 mm from the laser weld metal towards the arc weld metal, were compared. The difference ΔH between the maximum hardness H1 in region A1 and the maximum hardness H2 in region A2 is also recorded in the table.

[0102] Furthermore, chisel tests were performed on the laser weld metal of various lap welded joints obtained in this way. The chisel tests were conducted in accordance with JIS Z 3144:2013 "Field Test Methods for Laser and Projection Welds," and the fracture mode was classified as either plug fracture or interfacial fracture. Lap welded joints that exhibited plug fracture were judged to have superior joint strength. The chisel test results are shown in Table 1.

[0103] [Table 1]

[0104] In lap welded joints where the difference ΔH between the maximum hardness H1 in region A1 and the maximum hardness H2 in region A2 was 25HV or more, the fracture mode observed in the chisel test was plug fracture. These lap welded joints are presumed to have excellent joint strength. On the other hand, in lap welded joints where ΔH was less than 25, the strength of the laser weld metal was low, and interfacial fracture occurred.

[0105] (Example 2) Two identical hot-stamped steel plates were stacked and laser-screw-welded together. These two hot-stamped steel plates were then arc-welded. Details of the steel plates and welding conditions are as follows. • Thickness of hot-stamped steel sheet: 1.6mm • Tensile strength of hot-stamped steel sheet: 2350 MPa • Chemical composition of hot-stamped steel sheet: 0.45C-0.2Si-0.6Mn-0.008P-0.002S-Cr,Nb,Ti,B • Laser screw weld metal diameter: approximately 6mm • Arc welding current: 80A • Arc welding voltage: 15.6V Arc welding speed: 30 cm / min • Arc welding wire: YM-24T • Shielding gas for arc welding: Ar + 20% CO2 • Positional relationship between laser weld metal and arc weld metal: As shown in Table 2.

[0106] The hardness of the laser weld metal of the lap welded joint obtained using the procedure described above was measured using the method described above. Furthermore, the chisel test described above was performed on the laser weld metal. The evaluation results are shown in Table 2.

[0107] [Table 2]

[0108] In lap welded joints where the difference ΔH between the maximum hardness H1 in region A1 and the maximum hardness H2 in region A2 was 25HV or more, the fracture mode observed in the chisel test was plug fracture. These lap welded joints are presumed to have excellent joint strength. On the other hand, in lap welded joints where ΔH was less than 25, the strength of the laser weld metal was low, and interfacial fracture occurred.

[0109] (Example 3) Two identical hot-stamped steel plates were stacked and laser-screw-welded together. These two hot-stamped steel plates were then arc-welded. Details of the steel plates and welding conditions are as follows. • Thickness of hot-stamped steel sheet: 1.6mm • Tensile strength of hot-stamped steel sheet: 1780 MPa Chemical composition of hot-stamped steel sheet: 0.29C-0.2Si-1.8Mn-0.012P-0.003S-Cr,Nb,Cu,Ni,Ti,B • Laser screw weld metal diameter: approximately 6mm • Arc welding current: 80A • Arc welding voltage: 15.6V Arc welding speed: 30 cm / min • Arc welding wire: YM-24T, φ1.2mm • Shielding gas for arc welding: Ar + 20% CO2 • Positional relationship between laser weld metal and arc weld metal: As shown in Table 3.

[0110] The hardness of the laser weld metal of the lap welded joint obtained using the procedure described above was measured using the method described above. Furthermore, the chisel test described above was performed on the laser weld metal. The evaluation results are shown in Table 3.

[0111] [Table 3]

[0112] In lap welded joints where the difference ΔH between the maximum hardness H1 in region A1 and the maximum hardness H2 in region A2 was 25HV or more, the fracture mode observed in the chisel test was plug fracture. These lap welded joints are presumed to have excellent joint strength. On the other hand, in lap welded joints where ΔH was less than 25HV, the strength of the laser weld metal was low, and interfacial fracture occurred.

[0113] (Example 4) A hat-shaped member, as shown in Figure 30, was manufactured using two identical hot-stamped steel plates. The flange portion of the hat-shaped member was laser-screw welded. In this invention, arc weld metal was formed such that the laser-screw weld metal and its surrounding area were tempered. Details of the steel plates and welding conditions are as follows. • Thickness of hot-stamped steel sheet: 1.6mm • Tensile strength of hot-stamped steel sheet: 2000 MPa • Chemical composition of hot-stamped steel sheet: 0.34C-0.2Si-1.3Mn-0.008P-0.001S-Cr,Nb,Ti,B • Laser screw weld metal diameter: approximately 5.5 mm • Laser screw weld metal center spacing: 50mm

[0114] In the hat member of the example invention, arc welding was performed such that the distance between the edge of the laser-welded metal and the edge of the arc-welded metal was 5.0 mm. The length of the arc-welded metal was 30 mm, and arc welding was performed at 8 locations. On the other hand, in the hat member of the comparative example, only laser welding was performed. Furthermore, these hat members were heated to 170°C and held for 20 minutes. This corresponds to the thermal history during electrodeposition coating baking performed on automotive frame members. Then, a three-point bending test was performed on these hat members. The locations indicated by the downward arrows in Figure 30 are where the bending load was applied. When applying the bending load, both ends of the hat member were supported using support members.

[0115] Figure 31 shows the displacement-load curve, which is the result of the bending test. The lower curve represents the test result of the comparative example in which only laser welding was performed. In this comparative example, as shown in the photograph in Figure 32B, fracture of the laser-welded metal occurred during the bending test. In the curve, fracture of the laser-welded metal occurred at the point where the load drops sharply. On the other hand, the upper curve represents the test result of the inventive example in which arc-welded metal was formed so as to temper the laser-welded metal and its surrounding area. In this inventive example, as shown in the photograph in Figure 32A, no fracture of the laser-welded metal occurred, and high member performance was obtained. [Explanation of symbols]

[0116] 1. Overlap welded joint 11 Steel plate 11H high strength steel plate Laser welding of 11HS high-strength steel plate, overlapping metal surface 111 Overlapping section 12 Laser-welded metals 13 Arc Weld Metal 21 Bumper Reinforcement 22 Floor Members 23 Front side member 24 floors 25 B-pillar reinforcement 26 Side sil reinforcement 27 Side sill 28 Connecting member P: The point at the edge of the arc weld metal closest to the laser weld metal. Q: The point closest to the arc weld metal at the edge of the laser weld metal. L Hardness measurement position t Thickness of high-strength steel plate A1 Area within 0.7 mm of the laser weld metal towards the arc weld metal. A2 Area within 0.7 mm from the laser weld metal to the side opposite the arc weld metal. Maximum hardness in region A1 of H1 Maximum hardness in region A2 of H2 ΔH is the difference between H1 and H2.

Claims

1. Multiple steel plates, some or all of which are overlapped, A laser welding metal used to join the overlapping portions of two or more steel plates, Arc weld metal formed on one or more of the aforementioned steel plates, A lap welded joint comprising, One or more of the steel plates joined by the laser-welded metal are high-strength steel plates with a tensile strength of 780 MPa or more. When viewed in plan from the thickness direction of the overlap welded joint, the Vickers hardness is measured continuously along the overlap surface in a cross section perpendicular to the overlapping portion of the steel plate, including a straight line connecting the point on the edge of the laser weld metal closest to the arc weld metal and the point on the edge of the arc weld metal closest to the laser weld metal, at a depth of 1 / 4 of the plate thickness of the high-strength steel plate from the overlapping surface of the high-strength steel plate joined by the laser weld metal, The maximum Vickers hardness H1 in the region within 0.7 mm from the laser weld metal toward the arc weld metal is lower than the maximum Vickers hardness H2 in the region within 0.7 mm from the laser weld metal toward the arc weld metal opposite to the arc weld metal. The difference between the aforementioned maximum value H1 and the aforementioned maximum value H2 is 25 HV or more. Overlap welded joint.

2. The lap weld joint according to claim 1, characterized in that the laser weld metal is laser screw weld metal.

3. The lap welded joint according to claim 1, characterized in that the difference between the maximum value H1 and the maximum value H2 in the cross-section is 40 HV or more.

4. The lap welded joint according to claim 1, characterized in that two or more of the steel plates are joined by both the laser weld metal and the arc weld metal.

5. The lap welded joint according to claim 1, characterized in that, when viewed in plan from the thickness direction of the lap welded joint, the shortest distance between the edge of the laser welded metal and the edge of the arc welded metal is 3.0 mm or more and 17.0 mm or less.

6. The lap welded joint according to claim 1, characterized in that, when viewed in plan from the thickness direction of the lap welded joint, the distance between the edge of the laser welded metal and the edge of the arc welded metal is greater than 0.7 mm.

7. The overlap welding joint according to claim 1, characterized in that the width of the arc welding metal is 3.0 mm or more.

8. The number of steel plates is three or more. One or more of the steel plates are located outside the laser-welded metal. The steel plate located outside the laser weld metal and the steel plate joined by the laser weld metal are joined by the arc weld metal. The lap welded joint according to feature 1.

9. The lap welded joint according to claim 1, characterized in that the tensile strength of the high-strength steel plate is 1700 MPa or more.

10. An automotive frame member having an overlapping welded joint according to any one of claims 1 to 9.

11. A process of overlapping some or all of multiple steel plates, The process involves laser welding the overlapping portion of the steel plates to form laser-welded metal, A step of forming arc weld metal by arc welding one or more of the aforementioned steel plates, A method for manufacturing an overlap welding joint comprising: One or more of the steel plates to be laser-welded are high-strength steel plates with a tensile strength of 780 MPa or more. The welding heat from the arc welding process tempers the laser weld metal and its surrounding area. A method for manufacturing an lap welded joint according to claim 1.

12. The method for manufacturing an overlap welding joint according to claim 11, characterized in that the laser welding is performed by laser screw welding.

13. When viewed from above in the thickness direction of the lap welded joint, the distance between the edge of the laser weld metal and the edge of the arc weld metal is greater than 0.7 mm. The method for manufacturing an lap welded joint according to claim 11.

14. The heat input for the aforementioned arc welding is set to 1000 J / cm or more. When viewed from above in the thickness direction of the lap welded joint, the shortest distance between the edge of the laser weld metal and the edge of the arc weld metal shall be 3.0 mm or more and 17.0 mm or less. The method for manufacturing an lap welded joint according to claim 11.

15. The method for manufacturing the lap welded joint is, before the arc welding, The process of adding one or more steel plates to the two or more laser-welded steel plates. Furthermore, The arc welding described above joins the two or more laser-welded steel plates with the steel plate that has not been laser-welded. The method for manufacturing an lap welded joint according to claim 11.

16. The tensile strength of the aforementioned high-strength steel plate is set to 1700 MPa or higher. A method for manufacturing an lap welded joint according to any one of claims 11 to 15.

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