JP2010158717A - Laser welded lap joint made of high-strength steel sheets and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser welded lap joint made of high-strength steel sheets and a method for manufacturing the same, which prevents a break even in a weld metal with narrow beads formed with a small heat input and provides stable strength, in the case of manufacturing the laser welded lap joint made of the high-strength steel sheets by laser beam welding. <P>SOLUTION: The laser welded lap joint is manufactured by the laser beam welding of high-strength steel sheets 1 and 2 having a tensile strength of 440 MPa or more. The ratio (Lb/Ws) of the weld length (Lb) of the laser beam welded part 4 to the width (Ws) of the sheets 1 and 2 to be welded is 0.6 or more. The ratio of the weld width of the laser beam welded part 4 to the thickness of the sheets 1 and 2 is 0.8 or more and 2 or less. Openings 9 piercing through the sheet thickness whose length along a direction perpendicular to the longitudinal direction of the laser beam welded part 4 is 80% or more of the weld width around the laser beam welded part 4 are provided in both areas adjoining the initiating portion and the terminating portion of the laser beam welded part 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a laser lap weld joint for a high-strength thin steel sheet and a method for producing the same.

  In recent years, high strength steel sheets with a tensile strength of 440 MPa or higher are often used for automobile bodies in order to meet the demands of improving the fuel efficiency and safety of automobiles, using laser welding. Therefore, it is required to weld these steel plates. Furthermore, in a method of superposing and welding high-strength thin steel sheets, a laser welding method that can obtain stable joint strength is desired.

  Since laser welding uses laser light as a heat source, control of the heat input is more reliable and easier than arc welding such as TIG welding (Tungsten Inert Gas arc welding) and MIG welding (Metal Inert Gas arc welding). For this reason, the thermal deformation can be reduced by appropriately setting the welding conditions such as the welding speed, the laser beam irradiation output, and the shielding gas flow rate. Laser welding is suitable for assembly welding of complicated members such as a car body because it can be welded from one side.

In fact, laser welding is widely used for welding members formed by processing thin steel sheets in the automobile manufacturing industry, electrical equipment manufacturing industry, and other fields. In connection with this, many laser welding methods for lap joints having excellent weld joint strength have been proposed.
For example, in Patent Document 1, in a method of laser welding a lap joint of a member to be welded, in order to obtain a good joint strength, the laser is determined by the ratio Lb / Ws of the weld length Lb of the laser weld to the width Ws of the member to be welded. An invention is disclosed in which the ratio Wb / t of the weld width Wb of the weld to the plate thickness t is defined.

  Further, Patent Document 2 includes a step of irradiating a YAG laser to a planned welding location in a lap joint welding of thin steel plates, and a step of performing gas metal arc welding thereafter, and a width W of the weld bead is a predetermined formula. A lap welding process is disclosed that adjusts laser power, arc current, and welding speed to satisfy.

  By the way, from the viewpoint of suppressing the production cost, when welding only the minimum welding length necessary to obtain the required strength without welding over the entire width of the member to be welded, and depending on the fixing method of the joining member, This is sufficient when the weld length must be smaller than the width of the member to be welded. However, according to the experiments by the present inventors, it has been found that, in a laser lap weld joint of a high-strength thin steel sheet, when the weld length is less than the full width, the joint strength improvement proportional to the weld length is not necessarily achieved. .

  Specifically, when laser welding is performed on a high-strength steel sheet (member to be welded) having a tensile strength of 440 MPa or more, and the welding strength is measured by a tensile test, the weld length of the laser welded portion with respect to the width Ws of the member to be welded When the Lb ratio Lb / Ws was 0.6, the welding strength varied. As the form of fracture at this time, there were two kinds of forms, that is, the case of shear fracture with a weld metal and the case of fracture at a steel plate heat-affected zone. Moreover, in the range where Lb / Ws is more than 0.6 and less than 0.8, the welding strength per unit weld length is lower than that in the case where Lb / Ws is 0.6 or less.

Japanese Patent Laid-Open No. 2002-079387 JP 2002-144063 A

  When the present inventors investigated the cause of variation in weld strength and the cause of decrease in weld strength per unit weld length, stress (or strain) was concentrated at the start and end of the weld bead due to tensile stress. It has been found that this stress (or strain) causes a shear fracture of the weld metal, resulting in a variation in weld strength and a decrease in weld strength.

In view of the above findings by the present inventors, in order to prevent the shear fracture in the weld metal and increase the joint strength, according to the invention described in Patent Document 1, the heat input is increased by slowing the welding speed or the like. If the welding width is widened, distortion does not concentrate at the start and end portions of the weld bead, and a good joint can be obtained. However, in this case, there is a problem that not only the thermal deformation of the thin steel plate is increased and the advantages of laser welding are impaired, but also the welding time is increased and the production cost is increased.
Further, in the welding method for obtaining a necessary welding width using the laser and arc described in Patent Document 2, since the absolute amount of heat input is increased as compared with the case of laser single welding, thermal deformation is applied to the thin steel plate. There was a problem of getting bigger.

  Therefore, the present invention advantageously solves the conventional problems and prevents the weld metal from breaking even with a thin bead with a small heat input when a lap joint of a high-strength thin steel plate is produced by laser welding. An object of the present invention is to provide a laser lap weld joint of a high-strength thin steel sheet and a method for producing the same.

The gist of the present invention is as follows.
A laser lap weld joint formed by laser welding a high strength thin steel sheet having a tensile strength of 440 MPa or more, and a ratio of a weld length (Lb) of a laser weld to a width (Ws) of a member to be welded (Lb / Ws) is 0.6 or more, the ratio (Wb / t) of the welding width (Wb) of the laser welded part to the plate thickness (t) is 0.8 or more and 2 or less, and the start end of the laser welded part The plate thickness in which the opening length along the direction perpendicular to the longitudinal direction of the laser welded portion is 80% or more of the weld width centering on the laser welded portion in both the adjacent region and the adjacent region of the terminal portion. A laser lap weld joint for high-strength thin steel sheets, characterized in that a through opening is provided. However, the weld width (Wb) is a weld width on the overlapping surface of the high-strength thin steel sheets, and the adjacent region is a rectangular region in plan view surrounded by one side and the other side orthogonal to the one side. The one side extends along the longitudinal direction of the laser welded portion from the R stop of the laser welded portion to a position protruding from the endmost portion of the laser welded portion by the plate thickness (t). The other side has a length of 80% of the welding width around the laser welded portion along a direction orthogonal to the longitudinal direction of the laser welded portion.
The laser welded portion is composed of one continuous weld bead, the adjacent region is provided in each of the start end and the end of the weld bead, and the plate thickness through opening is provided in each adjacent region. The laser lap weld joint of the high-strength thin steel sheet according to (1), wherein However, the adjacent region is a rectangular region in plan view surrounded by one side and the other side orthogonal to the one side, and the one side is an R stop of the weld bead along the longitudinal direction of the weld bead. Extending from the outermost end of the weld bead to a position protruding by the plate thickness (t), and the other side is along the direction orthogonal to the longitudinal direction of the weld bead, The welding bead has a length that is 80% of the welding width.
The laser weld portion is composed of a plurality of weld beads formed intermittently along the width direction of the member to be welded, and the total bead length of each weld bead is the weld length (Lb), The adjacent region is provided in a part or all of each start end and each end of each of the plurality of weld beads, and the plate thickness through opening is provided in each of the adjacent regions. A laser lap weld joint of the high-strength thin steel sheet according to 1). However, the adjacent region is a rectangular region in plan view surrounded by one side and the other side orthogonal to the one side, and the one side extends along the longitudinal direction of each welding bead. It extends from the R stop of the bead to a position protruding from the outermost end of each weld bead by the thickness (t), and the other side is the longitudinal direction of each weld bead. Along the orthogonal direction, the weld width is 80% of the length of the weld bead.
The laser weld portion is composed of a plurality of weld beads formed intermittently along the width direction of the member to be welded, and the total bead length of each weld bead is the weld length (Lb), Among the plurality of weld beads, the adjacent region is provided at a position corresponding to the start end portion and the terminal end portion of the laser welded portion, and the plate thickness through opening is provided in each of the adjacent regions. The laser lap weld joint of the high-strength thin steel sheet according to (1). However, the adjacent region is a rectangular region in plan view surrounded by one side and the other side orthogonal to the one side, and the one side extends along the longitudinal direction of each welding bead. It extends from the R stop of the bead to a position protruding from the outermost end of each weld bead by the thickness (t), and the other side is the longitudinal direction of each weld bead. Along the orthogonal direction, the weld width is 80% of the length of the weld bead.
(1) to (4) is a method for producing a laser lap weld joint of the high-strength thin steel sheet according to any one of the above, and prior to the formation of the laser welded portion, at a position corresponding to the adjacent region, A step of providing a plate-thickness through-opening in which the opening length along the direction orthogonal to the longitudinal direction of the laser welded portion is 80% or more of the weld width centering on the laser welded portion, and the width of the member to be welded ( The ratio (Lb / Ws) of the weld length (Lb) of the laser welded part to Ws) is 0.6 or more, and the ratio (Wb / t) of the weld width (Wb) of the laser welded part to the plate thickness (t) is And a step of forming the laser weld so as to be 0.8 or more and 2 or less, and a method for producing a laser lap weld joint of a high strength thin steel sheet. However, the weld width (Wb) is a weld width on the overlapping surface of the high-strength thin steel sheet, and the adjacent region is a rectangular region surrounded by one side and the other side orthogonal to the one side, The one side extends along the longitudinal direction of the laser welded portion from the R stop of the laser welded portion to a position protruding from the endmost portion of the laser welded portion by the plate thickness (t). The other side has a length of 80% of the welding width around the laser welded portion along a direction orthogonal to the longitudinal direction of the laser welded portion.
(1) It is a method for manufacturing a laser lap weld joint of a high-strength thin steel sheet according to any one of (4), wherein a weld length (Lb) of a laser weld portion with respect to a width (Ws) of a member to be welded ) Ratio (Lb / Ws) is 0.6 or more, and the ratio (Wb / t) of the welding width (Wb) of the laser welded portion to the plate thickness (t) is 0.8 or more and 2 or less. An opening length along a direction orthogonal to the longitudinal direction of the laser welded portion is formed in both the step of forming the laser welded portion and the adjacent region of the start end portion and the adjacent end portion of the laser welded portion. And a step of providing a plate-thickness through opening having a length equal to or greater than 80% of the weld width centering on the center, and a method for producing a laser lap weld joint of a high-strength thin steel sheet. However, the weld width (Wb) is a weld width on the overlapping surface of the high-strength thin steel sheet, and the adjacent region is a rectangular region surrounded by one side and the other side orthogonal to the one side, The one side extends along the longitudinal direction of the laser welded portion from the R stop of the laser welded portion to a position protruding from the endmost portion of the laser welded portion by the plate thickness (t). The other side has a length of 80% of the welding width around the laser welded portion along a direction orthogonal to the longitudinal direction of the laser welded portion.

  According to the present invention, even with a thin bead with a small heat input, by providing a plate thickness through opening in the adjacent region of the start and end portions, the fracture mode can be reduced from the shear fracture of the weld metal and the welding heat is less likely to cause a decrease in strength. It is possible to shift to the rupture of the affected part, to prevent a shear rupture of the weld metal, and to provide a lap weld joint excellent in welding strength.

FIG. 1 is a schematic plan view showing a laser lap weld joint according to the present invention. FIG. 2 is a graph showing the relationship between the weld length Lb of the welded portion and the joint strength in a conventional laser lap weld joint. FIG. 3A is an enlarged schematic plan view showing a starting end portion or a terminal end portion of a weld bead surface in a conventional laser lap weld joint, and FIG. 3B is a cross section taken along line C1-C2 in FIG. It is a schematic diagram, and is a diagram for explaining the shape of the weld metal and the fracture location that occurs at the time of shear fracture with the weld metal. FIG. 4 (A-1) is an enlarged schematic plan view showing the start end or end portion of the weld bead surface in the laser lap weld joint before providing the plate thickness through opening, and FIG. 4 (A-2) is FIG. 4 is an enlarged schematic plan view showing the start end or end of the weld bead surface in the laser lap weld joint of the present invention, and FIG. 4B is a schematic cross-sectional view taken along line D1-D2 in FIG. It is a figure explaining the fracture location which arises at the time of the plug fracture in the shape of a weld metal, and a heat affected zone. FIGS. 5A and 5B are diagrams showing deformation during a tensile test of a conventional laser lap joint, where FIG. 5A is a diagram showing deformation that occurs on the extension of the weld bead, and FIG. 5B is a rotation around the weld bead. It is a figure which shows a deformation | transformation, (C) is a figure which shows the out-of-plane deformation | transformation which arises as a result of rotational deformation. FIG. 6 is a diagram showing a shear stress component parallel to the overlapping surface, which occurs in the weld metal between the steel plates during joint tension. FIG. 7 is a diagram showing a shear stress component in the plate thickness direction that is perpendicular to the overlapping surface and is generated during joint tension. FIG. 8 is a view for explaining adjacent regions in the laser lap weld joint of the present invention. FIG. 9 is a schematic plan view showing the laser lap weld joint according to the first embodiment of the present invention. FIG. 10 is a schematic cross-sectional view showing the vicinity of the laser welded portion of the laser lap weld joint according to the first embodiment of the present invention. FIG. 11 is a diagram for explaining a method for determining the start and end portions of a weld bead, wherein (A) is a schematic cross-sectional view of the weld bead, and (B) is a weld bead formed on the lower steel plate. It is a plane schematic diagram which shows. FIG. 12 is a diagram for explaining a method for determining the welding width of the weld bead, and is a schematic cross-sectional view showing the weld bead. FIG. 13 is a schematic plan view showing an example of the plate thickness through opening in the laser lap weld joint of the present invention. FIG. 14 is a schematic plan view showing another example of the plate thickness through opening in the laser lap weld joint of the present invention. FIG. 15 is a schematic plan view showing still another example of the plate thickness through opening in the laser lap weld joint of the present invention. FIG. 16 is a schematic plan view showing another example of the plate thickness through opening in the laser lap weld joint of the present invention. FIG. 17 is a schematic plan view showing still another example of the plate thickness through opening in the laser lap weld joint of the present invention. FIG. 18 is a schematic plan view showing another example of the plate thickness through opening in the laser lap weld joint of the present invention. FIG. 19 is a graph showing the relationship between the joint strength of the laser lap weld joint and the weld width / plate thickness (Wb / t). FIG. 20 is a schematic plan view showing an example of a laser lap weld joint according to the second embodiment of the present invention. FIG. 21 is a schematic plan view showing another example of a laser lap weld joint which is the second embodiment of the present invention. FIG. 22 is a schematic plan view showing a laser lap weld joint according to the third embodiment of the present invention. FIG. 23 is a schematic plan view for explaining the formation position of the through hole in the example. FIG. 24 is a schematic plan view for explaining the formation position of the through hole in the example.

  From the viewpoint of reducing production costs, welding is performed only when the minimum welding length is sufficient to obtain the required strength without welding over the entire width of the welded member, and depending on the method of fixing the joining member, welding is performed. In some cases, the length must be smaller than the width of the member to be welded. However, according to the experiments by the present inventors, in the laser lap weld joint of high-strength thin steel sheet, when the weld length is less than the full width of the member to be welded, improvement in joint strength proportional to the weld length is not necessarily achieved. Turned out not to be. Below, the said experiment of the present inventors is demonstrated.

  The investigated steel plate was an alloyed hot-dip galvanized steel plate having a tensile strength of 590 MPa, a plate thickness of 1.2 mm, a width of 60 mm, and a length of 185 mm. Two of these were overlapped at an overlap allowance of 60 mm, and the welding length Lb was 12 mm (20% of the width Ws of the welded member), 24 mm (40% of the same), with respect to the total width Ws of the test piece (width of the welded member). A test piece of a laser lap weld joint as shown in FIG. 1 was obtained by changing the welding to 36 mm (60%), 48 mm (80%), and 60 mm (100%). In FIG. 1, reference numerals 1 and 2 are alloyed hot-dip galvanized steel sheets having a tensile strength of 590 MPa, reference numeral 3 is an overlapping portion, and reference numeral 4 is a laser welded portion.

  The laser welding conditions were a weld bead width of 1.2 mm, a beam waist of 0.6 mm, a machining point output of 4 kW, a defocusing distance of 0 mm, a welding speed of 3 m / min, and a flow rate of 20 L / min as a shielding gas from a nozzle with a nozzle diameter of 5 mm. Ar gas was supplied through a coaxial center shield (no back shield). During welding, a metal foil having a thickness of 0.1 mm was inserted between the two steel plates 1 and 2 so as not to overlap the laser welded portion in order to release zinc vapor generated during welding of the galvannealed steel plate. .

  In order to evaluate the strength of the laser weld 4, as shown in FIG. 1, a tensile test is performed by pulling the weld bead in a direction perpendicular to the weld bead (direction of reference numeral 5), and the maximum load when the laser weld 4 is broken is examined. This was defined as joint strength (kN). The tensile speed was 10 mm / min, and the distance between chucks was 240 mm.

  As a result of the experiment, as shown in FIG. 2, it was found that when the welding length Lb is less than the full width Ws, the joint strength improvement proportional to the welding length Lb is not necessarily achieved. The dotted line in FIG. 2 is a straight line connecting plots when the welding length Lb is 20% and 40% of the width Ws of the welded member. The joint strength corresponding to this straight line is the joint strength proportional to the weld length Lb. As shown in FIG. 2, particularly when the welding length was 36 mm (60% of the width of the member to be welded), the joint strength varied greatly and the joint strength was lower than the dotted line in FIG. Therefore, when the fracture mode was investigated, the shear fracture at the weld metal at the steel plate interface parallel to the overlap surface (denoted as S in the figure) and the steel plate heat-affected zone perpendicular to the overlap surface. Two types of plug breakage (denoted as P in the figure) were observed. As shown in the schematic cross-sectional view (FIG. 3B) of the overlapped portion in FIG. 3, the shear fracture S is a fracture of the weld metal 4a at the steel plate interface at the line indicated by reference numeral 10, and the plug fracture P is 4, the heat-affected zone of the steel sheet 1 is broken at the line indicated by reference numeral 11 as shown in the schematic plan view (FIG. 4A-1) and the schematic cross-sectional view (FIG. 4B) of the overlapped portion in FIG. 4. It is a thing. Reference numeral 10 indicates a fracture location at the time of shear fracture, and 11 indicates a fracture location at the time of plug fracture.

  As shown in FIG. 2, in the case of the shear fracture S, the joint strength was lower than that of the plug fracture P in the steel plate heat-affected zone. Furthermore, when the weld length Lb was 48 mm (80% of the test piece width), the actual joint strength was significantly lower than the joint strength expected from the weld length Lb. As a result of investigation, it was found that all fracture forms were shear fractures S in weld metal.

  When the weld length Lb is as long as 60% and 80% of the width Ws of the member to be welded and the shear fracture S occurs, the main cause that the joint strength is lower than the strength expected from the weld length Lb; FIG. 5 shows the results of examining the deformation of the test piece during the tensile test in order to investigate the reason why it is divided into the shear fracture S and the plug fracture P.

  At the time of the tensile test, since the plate thickness centers of the loaded steel plates 1 and 2 are shifted on the left and right, a rotational moment occurs around the weld metal 4a, and the steel plates 1 and 2 as shown in FIG. Rotational deformation M1 occurs so that the plate thickness centers are aligned. However, at the same time, on the extension of the laser welded portion 4, since there is no weld metal 4 a serving as the center of the rotational deformation M 1, an out-of-plane bending deformation M 2 as shown in FIGS. 5A and 5C occurs. Arise. When the bending deformation M2 as described above proceeds, the start and end portions of the laser welded portion are parallel to the overlapping surface as shown in FIG. 6 due to the bending deformation M2 shown in FIG. The shear stress component 7 acts greatly on the weld metal 4a between the steel plates. In addition, such shear stress on the start and end portions becomes stress concentration, and becomes prominent because the joint strength and the accompanying deformation increase as the weld length Lb increases. Therefore, when the weld length Lb is as long as 60% or 80%, the weld metal 4a does not bear a load uniformly, so that it is considered that the result is that the expected strength is lowered.

  In addition, when the reason why the weld fracture Lb is divided into the shear fracture S and the plug fracture P when the weld length Lb is 60% is examined from the load-displacement curve (SS curve) during the tensile test, the two curve shapes are almost the same. Thus, it was found that the plug break P did not occur in the shear break S but occurred when the rotational deformation progressed as it was. That is, when the deformation progresses without causing the shear fracture S, as shown in FIG. 7, the shear stress component 8 in the plate thickness direction, which is perpendicular to the overlapping surface, increases, and the weld 4 is peeled off. It is thought that the plug breaks because the load acts in the direction.

  Further, as a factor that promotes the separation into the shear fracture S and the plug fracture P, it is considered that the test piece fixed to the tensile tester is not always pulled uniformly in the plate width direction. That is, when the load balance is biased to one of the weld beads, the stress concentration acting on either the start end portion or the end portion is increased, so that the shear fracture S occurs, and when the load is not biased, It is considered that the deformation has progressed sufficiently to result in a plug break P.

(First embodiment)
Based on the above knowledge, the first embodiment of the present invention relates to a laser lap welded joint for a high-strength thin steel sheet and a method for producing the same, and has a tensile strength of 440 MPa or higher and the width (Ws) of the member to be welded. The ratio (Lb / Ws) of the weld length (Lb) of the laser welded portion is 0.6 or more, and the ratio (Wb / t) of the weld width (Wb) of the laser welded portion to the plate thickness (t) is 0. When producing a lap welded joint of high strength thin steel sheets of .8 or more and 2 or less by laser welding, as shown in FIG. 8, the adjacent region A in the start end portion and the adjacent region A in the end portion of the laser welded portion 4 The thickness of the opening along the direction perpendicular to the longitudinal direction of the laser welded part 4 is 80% (0.8 Wb) or more of the weld width (Wb) centered on the laser welded part 4. A through opening is provided.

  As shown in FIG. 9, the laser welded portion 4 in the present embodiment is composed of one continuous weld bead 4 b from the start end to the end. Adjacent regions A are provided at the start and end portions of the weld bead 4b, respectively, and plate-thickness through openings 9 are provided in the adjacent regions A. The plate thickness through opening 9 is a through hole that penetrates the stacked steel plates 1 and 2.

  Here, the member width (Ws) and the weld length (Lb) of the laser welded portion 4 of the steel plates 1 and 2 having the plate thickness (t) are as shown in FIG. 9, and the weld width (Wb) is as shown in FIG. As shown in Fig. 4, the width of the welded and solidified weld metal on the overlapping surfaces of the steel plates 1 and 2 is the smaller one of the weld widths of the weld metal 4a between the steel plates 1 and 2. Further, as shown in FIG. 8, the adjacent region A is a rectangular region in a plan view surrounded by one side A1 and the other side A2 orthogonal to the one side A1 in the weld bead 4b having a shorter weld width between the steel plates. The one side A1 extends along the longitudinal direction of the laser weld 4 from the R stop (R-end) of the laser weld 4 (weld bead 4b) to the end of the laser weld 4 (weld bead 4b). The other side A2 extends to a position protruding beyond the thickness of 4c by the thickness (t), and the other side A2 is laser welded along a direction orthogonal to the longitudinal direction of the laser welded portion 4 (weld bead 4b). The length (0.8 Wb) is 80% of the welding width (Wb) with the portion 4 (weld bead 4b) as the center.

  The process of manufacturing the laser lap weld joint is composed of two processes, a process of providing the plate thickness through opening 9 and a process of manufacturing the laser weld 4 (weld bead 4b), and there is no particular limitation as to which one is performed first. . In the case of producing a joint in the order of producing the laser weld 4 (weld bead 4b) after providing the plate thickness through opening 9, after opening the plate thickness through opening 9 by, for example, press punching, What is necessary is just to form the laser welding part 4 (weld bead 4b) which connects between the center of the two plate | board thickness penetration opening parts 9 by laser welding.

  Further, as an order, after the laser welded portion 4 (weld bead 4b) is prepared, when the plate thickness through opening 9 is provided, drilling by laser is performed at both ends of the weld bead 4b formed on the surface of the steel plate 1. For example, the plate thickness through opening 9 may be provided.

  The means for providing the plate thickness through-opening 9 is not limited to press punching or laser drilling. In addition to drilling with a drill or milling machine that directly contacts and cuts, Examples thereof include water jet processing using water, drilling processing using high pressure water and a water jet induction laser using a laser, and the like.

  Regarding the output of the processing point and the welding speed when producing the weld bead 4b by laser welding, the size necessary for forming the weld bead 4b (laser weld 4) connecting the two thin steel plates 1 and 2 is large. That's fine.

  In addition, the shape of the plate thickness through-opening 9 and the surface roughness of the cut surface are not particularly limited, but when the plate thickness through-opening 9 is first prepared and then welded, In order to avoid blocking the plate thickness through opening 9 during welding, it is preferable to provide the plate thickness through opening 9 having a region equal to or larger than a circle whose diameter is the weld width Wb of the weld bead 4b. The upper limit of the plate thickness through opening 9 is not particularly limited, but a through hole that greatly reduces the member itself is not practical, and the strength of the structure is reduced when a structure is manufactured. Therefore, it is not preferable.

  Further, as shown in FIG. 11, the start and end portions (reference numerals i1 and i2 in FIG. 11) and the welding width Wb of the weld bead 4b necessary for determining the adjacent area A and the adjacent area A are the steel plate 1 The shape of the weld bead 4b on the superposed surfaces 2 and 2 is the original, but it is generally difficult to know this accurately from the appearance.

  However, when performing lap welding of the steel plates 1 and 2 with a laser, the welding width on the surface of the upper steel plate 1 or the back surface of the lower steel plate 2 when welding tends to be larger than the welding width between the steel plates 1 and 2. Is seen. Also, the start and end portions of the weld bead formed on the upper surface of the upper steel plate 1 or the lower surface of the lower steel plate 2 tend to spread outward from the start and end portions formed between the steel plates 1 and 2. It becomes.

Therefore, in order to relieve stress concentration reliably by providing the plate thickness through opening 9, as shown in FIG. 11 (A), it terminates from the start end i3 of the weld bead formed on the surface of the upper steel plate 1. Compare the length to the part i4 with the length from the starting end i5 to the terminal end i6 of the welding bead of the lower steel plate 2, and among the welding beads, the starting end part i5 of the shorter welding bead and What is necessary is just to make the position of the termination | terminus part i6 substitute for the exact start part position i1 and the termination | terminus part position i2. In addition, the arrow 12 of FIG. 11 has shown the welding direction.
As for the welding width Wb, as shown in FIG. 12, the larger one of the welding width (Wb-upper) of the surface of the upper steel plate 1 and the welding width (Wb-lower) of the lower steel plate 2 is used. Instead, the adjacent region A may be determined.

  When determined as described above, the positional deviation between the start end and the end can be minimized, but an error occurs in the weld width Wb and the adjacent region A. Therefore, the plate thickness through opening 9 is more preferable. Is preferably provided with a plate-thickness through-opening 9 in a direction perpendicular to the weld bead 4b and having a length (0.8 Wb) equal to or greater than the welding width determined as described above.

  First, the present inventors perform laser welding on all or part (Lb) of the member widths (Ws) of the steel plates having various plate thicknesses with various welding widths (Wb). Details of the relationship between welding conditions such as welding width (Wb) and welding length (Lb) and the strength and fracture mode of the joint when a tensile load is applied in the direction of arrow 5 shown in FIG. Examined.

  As a result, the tensile strength is 440 MPa class or more, the ratio (Lb / Ws) of the welding length (Lb) of the laser welded portion 4 to the width (Ws) of the member to be welded is 0.6 or more, and laser welding As shown in FIGS. 13 to 18, a lap weld joint of a high-strength thin steel sheet in which the ratio (Wb / t) of the weld width (Wb) of the portion 4 to the plate thickness (t) is 0.8 or more and 2 or less. In the adjacent area A, a plate-thickness through-opening 9 including a region that occupies 80% of the weld width (Wb) around the weld bead 4b in the direction perpendicular to the weld bead 4b is provided. In this case, it was found that the shear fracture at the weld metal 4a can be prevented and the plug fracture P can be achieved.

Here, FIGS. 13 to 18 will be described in detail.
The plate-thickness through opening 9 shown in FIG. 13 has a substantially rectangular shape in plan view, and the long side constituting the rectangle extends along a direction perpendicular to the longitudinal direction of the weld bead 4b. Four corners of the through opening 9 are curved in plan view. One long side that defines the plate-thickness through opening 9 is adjacent to the side A2 on the R-end side of the weld bead 4b in the other side A2 that defines the adjacent region A. 13 has a length along the direction orthogonal to the longitudinal direction of the weld bead 4b, which is 1.5 times the weld width Wb of the weld bead 4b (1.5Wb). It has become.

  Next, the plate-thickness through opening 9 shown in FIG. 14 has a substantially rectangular shape in plan view, and the long side constituting this rectangle extends along the direction orthogonal to the longitudinal direction of the weld bead 4b. One long side that defines the plate-thickness through opening 9 is adjacent to the side A2 on the opposite side to the side that contacts the R stop (R-end) of the weld bead 4b in the other side A2 constituting the adjacent region A. is doing. Further, in the plate thickness through opening 9 shown in FIG. 14, the length along the direction orthogonal to the longitudinal direction of the weld bead 4b is the same length (Wb) as the weld width Wb of the weld bead 4b.

  Next, the plate-thickness through opening 9 shown in FIG. 15 has a substantially circular shape in plan view, and is disposed in the approximate center of the adjacent region A. Further, the plate thickness through opening 9 shown in FIG. 15 has the same length (Wb) as the weld width Wb of the weld bead 4b along the length orthogonal to the longitudinal direction of the weld bead 4b. Since the plate thickness through opening 9 shown in FIG. 15 is substantially circular in plan view, the length along the direction orthogonal to the longitudinal direction of the weld bead 4 b corresponds to the diameter of the plate thickness through opening 9.

  Next, the plate-thickness through opening 9 shown in FIG. 16 has a substantially circular shape in plan view, and is disposed in the approximate center of the adjacent region A. Further, the plate thickness through opening 9 shown in FIG. 16 has a length along the direction orthogonal to the longitudinal direction of the weld bead 4b that is 0.8 times the weld width Wb of the weld bead 4b (0.8 Wb). It has become. Since the plate thickness through opening 9 shown in FIG. 16 is substantially circular in plan view, the length along the direction orthogonal to the longitudinal direction of the weld bead 4b is the diameter of the plate thickness through opening 9 as in FIG. Equivalent to.

  Next, the plate-thickness through opening 9 shown in FIG. 17 is substantially rectangular in plan view, and the long side constituting the rectangle is inclined with respect to the longitudinal direction of the weld bead 4b. Further, the plate-thickness through opening 9 is disposed substantially at the center of the adjacent region A. 17 has a length along the direction orthogonal to the longitudinal direction of the weld bead 4b, which is 1.3 times the weld width Wb of the weld bead 4b (1.3Wb). It has become.

  Next, the plate thickness through opening 9 shown in FIG. 18 is substantially rectangular in plan view, and the long side constituting the rectangle is inclined with respect to the longitudinal direction of the weld bead 4b. Further, the plate-thickness through opening 9 is arranged closer to the R stop (R-end) than the center of the adjacent region A. Further, in the plate thickness through opening 9 shown in FIG. 18, the length along the direction orthogonal to the longitudinal direction of the weld bead 4b is the same length (Wb) as the weld width Wb of the weld bead 4b.

  Thus, at least a part of the plate thickness penetrating portion 9 according to the present invention is disposed in the adjacent region A, and the opening length is 80% (0.8 Wb) of the welding width Wb with the laser welding portion 4 as the center. What has the above length should just be. As shown in FIGS. 13, 14, 15, 17, and 18, a part of the plate thickness penetrating portion 9 may protrude from the adjacent region A.

  As shown in FIG. 19, the ratio of the welding width Wb to the plate thickness T (Wb / t)) is taken on the horizontal axis, and the welded joint of the prior art and the welded joint of the present embodiment in which the plate-thickness through opening 9 is not produced. In comparison, it has been found that when the welding length Lb is constant, the same joint strength can be obtained with a bead thinner than the conventional welding bead, and the amount of heat input and thermal deformation can be kept low.

  However, the ratio (Lb / Ws) of the length (Lb) of the laser welded portion 4 to the width (Ws) of the members to be welded (steel plates 1 and 2) is less than 0.6, and the tensile test of the joint is performed. Even when the plate thickness through opening 9 was formed so as to satisfy the conditions described in the claims when the result was a shear fracture in the weld metal, the plug fracture did not proceed.

  Further, the ratio (Lb / Ws) of the weld length (Lb) of the laser welded portion 4 to the width (Ws) of the members to be welded (steel plates 1 and 2) is 0.6 or more, and the laser welded portion 4 When the ratio (Wb / t) of the welding width (Wb) to the plate thickness (t) is 0.8 or more and 2 or less, but the plate thickness through-opening 9 is produced without satisfying the conditions described in the claims However, it did not shift to plug rupture.

  The reason why the lower limit of the value of (Wb / t) is 0.8 and the upper limit is limited to 2 is the ratio of the length (Lb) of the laser welded portion to the width (Ws) of the members to be welded (steel plates 1 and 2). This is because even if (Lb / Ws) is 0.6 or more, if the value of (Wb / t) is less than 0.8, plug rupture does not occur, and shear rupture occurs from the overlapping surface. If the upper limit of 2 (Wb / t) is exceeded, the heat input is too large and welding deformation becomes large.

  Moreover, the reason which limited the tensile strength of the steel plates 1 and 2 to the 440 MPa class or more is that the welding length of the laser welded portion 4 with respect to the width (Ws) of the members to be welded (steel plates 1 and 2) ( This is because the joint strength of the joint produced by changing the ratio (Lb / Ws) of Lb) did not extremely decrease from the strength proportional to the weld length Lb. This is because the steel sheet below the 440 MPa class has a large elongation, so even if stress concentration occurs at the start and end portions of the weld bead 4b, local elongation occurs there, so the weld bead 4b. This is because the load is uniformly borne with respect to the stress, and as a result, the stress concentration at the start and end portions of the weld bead 4b is alleviated.

  Furthermore, the reason why the upper limit of the tensile strength of the steel plates 1 and 2 was not set is that even when the tensile strength is high, the plate thickness (t) is reduced, and the laser welded portion 4 with respect to the width (Ws) of the member to be welded. The ratio (Lb / Ws) of the welding length (Lb) is 0.6 or more, and the ratio (Wb / t) of the welding width (Wb) of the laser welded portion 4 to the plate thickness (t) is 0.8 or more. If it is 2 or less, the joint strength is extremely reduced from the strength proportional to the weld length.

  In the adjacent area A, the plate thickness through opening 9 is 80% of the welding width (Wb) in the direction perpendicular to the laser weld 4 (weld bead 4b) with the laser weld 4 (weld bead 4b) as the center. The reason for including the area occupying (0.8 Wb) and making it larger than that area, and the reason for making the adjacent area A up to the R stop (R-end) is the place where stress concentration occurs when the joint is pulled. Is the R stop (R-end) of the start end and the end of the laser weld 4 (weld bead 4b) shown in FIG. 8, and by providing the plate thickness through opening 9 at the position described above, R This is because the stress concentration in the direction of shearing fracture of the weld metal to the stop (R-end) can be relaxed. The reason for the stress concentration on the R-end is that the lap joint at the time of the tensile test is unloaded, and from the observation results of the crack origin and the state of occurrence, it is in the case of out-of-plane deformation that occurs simultaneously with rotational deformation. In addition, it is considered that the deformation progresses around the start and end portions of the weld bead 4b. Further, the reason why the stress concentration can be reduced by providing the plate thickness through opening 9 is that the start and end of the weld bead 4b is separated from the surrounding plates during the out-of-plane deformation that proceeds simultaneously with the rotational deformation. It turns out that the power of time is not transmitted.

  Further, one side A1 of the adjacent region A is moved in the direction of the laser welded portion 4 (weld bead 4b) from the R stop (R-end) of the laser welded portion 4 (welded bead 4b) to the outermost end portion 4c + plate thickness (t The reason for the above is that if the through opening 9 is provided at an outer position exceeding the extreme end 4c of the weld bead 4b + the thickness t, the distance between the extreme end 4c of the weld bead 4b and the through opening 9 is large. This is because the force is transmitted to the start and end of the weld bead 4b during the out-of-plane deformation that proceeds simultaneously with the rotational deformation, and the stress concentration mitigating effect is not seen.

As described above, according to the laser lap weld joint of this embodiment, as shown in FIGS. 13 to 18, since the plate thickness through openings 9 are provided at both ends of the weld bead 4 b, the deformation is out of plane. It is possible to alleviate the stress concentration occurring at the start and end portions of the weld bead 4b.
As a result, even a thin bead with a small heat input prevents a shear fracture S at the weld metal at the steel plate interface as shown in FIG. 3, and as shown in FIG. Lap joints with stable joint strength even when a non-uniform load is applied in the width direction of the plate, and the joint strength does not drop extremely from the strength proportional to the weld length. Can be realized. According to the present invention, the quality of the laser welded joint of the thin steel sheet forming member, which is frequently used in the automobile industry, the electrical equipment industry, and other fields, and the application range of the laser welded joint are expanded. Industrial effects are immeasurable.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the laser lap weld joint of the high-strength thin steel plate according to the present embodiment, the laser weld portion is composed of a plurality of weld beads, and a plate thickness through opening is provided at a part or all of both ends of each weld bead. . Note that, among the components of the present embodiment, the description of the same components as those described in the first embodiment is omitted.

  That is, as shown in FIG. 20, an example of the laser lap weld joint of this embodiment includes a plurality of laser welded portions 14 formed intermittently along the width direction of the members to be welded (steel plates 1 and 2). It consists of weld beads 14b, and a plurality of weld beads 14b are provided with adjacent regions at respective start end portions and part of respective end portions, and plate thickness through openings 9 are provided at the respective adjacent regions. . In the example shown in FIG. 20, the plate-thickness through openings 9 are always provided at both ends 14A and 14B of the laser welded portion 14 formed of a plurality of weld beads 14b.

  Moreover, in another example of the laser lap weld joint of this embodiment, as shown in FIG. 21, the laser welding part 14 was intermittently formed along the width direction of the members to be welded (steel plates 1 and 2). It consists of a plurality of weld beads 14b, adjacent regions are provided in all of the start and end portions of the plurality of weld beads 14b, and a plate thickness through opening 9 is provided in each adjacent region.

Steel plates 1 and 2 shown in FIGS. 20 and 21 are high-strength thin steel plates having a tensile strength of 440 MPa or more, as in the first embodiment.
20 and 21, the total bead length (Lb1 + Lb2) of each weld bead 14b is the weld length (Lb), and is relative to the width (Ws) of the members to be welded (steel plates 1 and 2). The ratio (Lb / Ws) of the weld length (Lb) is 0.6 or more, and the ratio (Wb / t) to the plate thickness (t) of the weld width (Wb) is 0.8 or more and 2 or less. ing. The reason for limiting these numerical ranges is the same as in the first embodiment.

  Further, the adjacent region provided in the start end portion and the end end portion is a rectangular region in plan view surrounded by one side and the other side orthogonal to the one side, as in the first embodiment, and the one side is welded Along the longitudinal direction of the bead 14b, it extends from the R stop of the weld bead 14b to a position protruding from the outermost end of the weld bead 14b by the plate thickness (t), and the other side is The weld bead 14b has a length of 80% of the weld width along the direction orthogonal to the longitudinal direction of the weld bead 14b.

  Further, similarly to the first embodiment, the plate thickness through opening 9 is a through hole that penetrates the stacked steel plates 1 and 2 and has an opening length along a direction orthogonal to the longitudinal direction of the weld bead 14b. What is necessary is just to have the length of 80% or more of the welding width centering on the weld bead 14b, and what was specifically shown in FIGS. 13-18 may be sufficient.

  Between the adjacent weld beads 14b, when the steel plates 1 and 2 are pulled, convex out-of-plane deformation such as a hump occurs, so as shown in FIGS. 20 and 21, both ends of each weld bead 14b. It is desirable to provide the plate-thickness penetrating portions 9 in several and all locations as necessary for each adjacent region existing in.

  By providing the plate-thickness through opening 9 in part or all of the start end and the end of each weld bead 14b, the stress caused by the out-of-plane deformation when the steel plates 1 and 2 are pulled is subjected to the start end of each weld bead 14b. There is no fear of concentrating on the part and the terminal part, the shear fracture S at the weld metal at the steel plate interface can be prevented, and the transition can be made to the fracture at the heat affected zone where the crack progresses in the thickness direction. As a result, the joint strength does not extremely decrease from the strength proportional to the weld length, and a lap joint with stable joint strength can be realized even when a non-uniform load is applied in the plate width direction.

(Third embodiment)
Next, a third embodiment of the present invention will be described. In the laser lap weld joint of the high-strength thin steel plate of this embodiment, the laser welded portion 24 is composed of a plurality of weld beads 24b. Moreover, an adjacent area | region is provided only in the position corresponded to the start end part and the terminal part of the laser welding part 24 among several welding beads 24b, and the plate | board thickness penetration opening part 9 is provided in each adjacent area | region. Note that, among the components of the present embodiment, the description of the same components as those described in the first embodiment is omitted.

  That is, as an example of the laser lap weld joint of this embodiment, as shown in FIG. 22, a plurality of laser welded portions 24 are intermittently formed along the width direction of the members to be welded (steel plates 1 and 2). An adjacent region is provided at a position corresponding to the start end portion 24A and the end portion 24B of the laser weld portion 24 among the plurality of weld beads 24b, and the plate thickness through opening 9 is provided in each adjacent region. Is provided.

The steel plates 1 and 2 shown in FIG. 22 are high-strength thin steel plates having a tensile strength of 440 MPa or more, as in the first embodiment.
In FIG. 22, the total bead length (Lb1 + Lb2) of each weld bead 24b is the weld length (Lb), and the weld length with respect to the width (Ws) of the members to be welded (steel plates 1 and 2). The ratio (Lb / Ws) of (Lb) is 0.6 or more, and the ratio (Wb / t) of the welding width (Wb) to the plate thickness (t) is 0.8 or more and 2 or less. The reason for limiting these numerical ranges is the same as in the first embodiment.

  Also, the adjacent region is a rectangular region in plan view surrounded by one side and the other side orthogonal to the one side, as in the first embodiment, and the one side extends along the longitudinal direction of the weld bead 24b. Extending from the R stop of the weld bead 24b to a position protruding from the outermost end of the weld bead 24b by a thickness (t), and the other side is the longitudinal direction of the weld bead 24b. Along the orthogonal direction, the weld bead 24b is the center, and the length is 80% of the weld width.

  Further, as in the first embodiment, the plate thickness through opening 9 is a through hole that penetrates the stacked steel plates 1 and 2 and has an opening length along a direction orthogonal to the longitudinal direction of the weld bead 24b. What is necessary is just to have the length of 80% or more of the welding width centering on the weld bead 24b, and what was specifically shown in FIGS. 13-18 may be sufficient.

  By providing the plate thickness through opening 9 at a position corresponding to the start end portion 24A and the end end portion 24B of the laser welded portion 24, the stress caused by the out-of-plane deformation when the steel plates 1 and 2 are pulled is applied to each weld bead 24b. There is no fear of concentrating on the start and end portions, shear fracture S at the weld metal at the steel plate interface can be prevented, and transition to fracture at the heat affected zone where the crack progresses in the plate thickness direction can be achieved. As a result, the joint strength does not extremely decrease from the strength proportional to the weld length, and a lap joint with stable joint strength can be realized even when a non-uniform load is applied in the plate width direction.

Hereinafter, the present invention will be described in more detail with reference to examples.
Three types of alloyed hot-dip galvanized steel sheets with a tensile strength of 590 MPa and plate thicknesses of 0.8 mm, 1.2 mm, and 2.0 mm were prepared, and these were superposed to perform laser welding, as shown in FIG. Such a lap joint was manufactured. In FIG. 9, reference numerals 1 and 2 are alloyed hot-dip galvanized steel sheets having a tensile strength of 590 MPa, reference numeral 3 is an overlapping portion, and reference numeral 4 is a laser welded portion. The specimen width Ws was 60 mm, and the specimen length was 185 mm.

  The welding sequence includes the step of forming the weld bead 4b after first providing the plate thickness through opening 9 (through hole) (cutting destination), and the step of forming the through hole 9 after previously forming the weld bead 4b (welding). The above two types were used. As shown in FIG. 23, through-holes 9 having different sizes from 1 mm to 5 mm in diameter were provided. The center position of the through hole 9 was adjusted so that the length Lb of the weld bead was kept constant regardless of the size of the through hole 9 with respect to the entire width of the test piece.

  In addition, during laser welding, two steel plates are overlapped at a stacking allowance of 60 mm, and zinc vapor generated during welding of the alloyed hot-dip galvanized steel plate is released between the two plates. The steel plate was inserted so as not to overlap the laser weld.

  For laser welding, a YAG laser was used, the processing point output was 4 kW, the defocusing distance was 0 mm, the beam waist was 0.6 mm, and the welding width between the steel plates 1 and 2 was adjusted by changing the welding speed. At this time, the ratio (Wb / t) of the welding width Wb to the plate thickness t is 0.6 to 1.4, and the ratio (Lb / Ws) of the welding length Lb to the specimen width Ws is 0.6 to 0. .8. Regarding the shielding gas, Ar gas having a flow rate of 20 L / min was supplied from a nozzle having a nozzle diameter of φ5 mm through a coaxial center shield (no back shield).

  In order to confirm the strength and soundness of the laser welded part 4, a tensile test was performed on the members to be welded (steel plates 1 and 2) at a tensile speed of 10 mm / min and a distance between chucks of 240 mm in a shear direction parallel to the overlapping surface. And the fracture form of the welded joint was examined. The results are shown in Table 1.

As shown in Table 1, when the weld length Lb is 36 mm and no through holes are provided at the start and end of the weld bead, shear fracture occurs in the weld metal, resulting in variations in joint strength, In some cases, the strength corresponding to the length Lb could not be obtained. On the other hand, the joints according to the examples of the present invention were always fractured at the weld heat affected zone regardless of the diameter of the through-hole, and the joint strength corresponding to the weld length Lb was obtained.
In addition, when the weld length Lb is 48 mm, the strength of the joint according to the present invention exceeds all the strengths of the joints of the comparative examples in which no through holes are provided, and there is no case where the joint strength becomes extremely low. Invariably, breakage occurred at the heat affected zone.

  Since the structure of the lap joint of the present invention enables relaxation of stress concentration by providing through holes at both ends of the weld bead, the welding bead and the through hole are manufactured in the reverse order, that is, welded. It was found that the same effect as in the example can be obtained when a through hole is opened later.

  Next, after producing a weld bead 4b as shown in FIG. 9 using the same steel plate and welding conditions as described above, tensile test pieces were produced in the order in which the through holes 9 were provided.

When the through-hole 9 is opened, as shown in FIG. 24, the position deviated from the outermost end 4c of the weld bead 4b by the plate thickness is defined as the origin O, and the diameter d is taken along the X axis in the longitudinal direction of the weld bead 4b. The center M of the through-hole 9 of 1 mm was taken at various positions. FIG. 24 is a diagram illustrating a relative positional relationship between the weld bead 4b and the through hole 9. 24A shows a case where the center M of the through hole 9 is located dmm closer to the weld bead 4b than the origin O (denoted as −dmm), and FIG. 24B shows that the center M of the through hole 9 is the origin O. 24C (shown as 0 mm), FIG. 24C shows that the center M of the through-hole 9 is shifted by d / 2 mm from the origin O in a direction away from the weld bead 4 b (shown as d / 2 mm). It is.
Table 2 shows the results of conducting a tensile test on such a welded joint and examining the fracture form of the welded joint.

  From Table 2, even when the weld length Lb is 36 mm and 48 mm, the center M of the through hole 9 is at the positions of -dmm, -d / 2 mm, and 0 mm, and the through hole 9 exists at a position within the range of the present invention. In all cases, fractures always occurred in the weld heat-affected zone, and joint strength corresponding to the weld length was obtained.

  However, when the center M of the through hole 9 is at a position of d / 2 mm, the ratio (Wb / t) of the welding width Wb to the plate thickness t is 0.9 to 1.4, and the welding length Lb Even if the ratio (Lb / Ws) of the specimen width Ws is 0.6 to 0.8, the position of the through hole 9 is not within the scope of the present invention, so that shear fracture occurs in the weld metal, and the weld length The strength corresponding to was not obtained.

  Furthermore, in Table 3, as shown in FIG. 22, the test piece provided with the laser welded portion composed of two weld beads has through holes only at positions corresponding to the start end portion and the end end portion of the laser welded portion. Tensile tests for cases (Table 3: through holes only at both ends), cases where through holes are provided at both ends of each weld bead (Table 3: all through holes), and cases where no through holes are provided (no through holes) The result of having performed is shown.

As shown in Table 3, it is within the scope of the present invention, and has a through hole only at a position corresponding to the start end and the end of the laser welded part, and a case having a through hole at both ends of each weld bead. In this case, the weld heat affected zone was always broken, and the joint strength corresponding to the weld length was obtained.
On the other hand, in the comparative examples having no through-holes at all, fractures in the metal always occurred, and the joint strength corresponding to the weld length could not be obtained.

Furthermore, a large specimen with a specimen width Ws of 500 mm and a specimen length of 1520 mm is prepared with an alloyed hot-dip galvanized steel sheet having a tensile strength of 590 MPa and 980 MPa, and two steel sheets are overlapped at a stacking allowance of 30 mm and welded. A lap joint having a laser welded portion having 5 or more beads was produced. At this time, the ratio (Wb / t) of the melt width Wb to the plate thickness t is 0.8 to 1.4, and the ratio of the total weld length ΣLb to the specimen width Ws (ΣLb / Ws) is 0.6 to 0.00. It was set to 8.
Table 4 shows tensile strength when through holes of the same form as in FIG. 21 are provided at all ends of each weld bead (Table 4: all through holes) and when no through holes are provided (Table 4: no holes). The result of the test is shown. In Table 4, each bead length (Lb1, Lb2,...) Is a weld length per weld bead, and the total weld length ΣLb is a total length of each bead length (Lb1 + Lb2 +...).

  As shown in Table 4, it is within the scope of the present invention, and when there are through-holes at both ends of each weld bead, the weld heat-affected zone always breaks, but has no through-holes at all. In the comparative example, the fracture always occurred in the metal, and the joint strength was lower than the fracture at the weld heat affected zone.

  DESCRIPTION OF SYMBOLS 1, 2 ... Steel plate (high-strength thin steel plate (member to be welded)), 3 ... Overlapping part, 4, 14, 24 ... Laser welding part, 4a ... Weld metal, 4b, 14b, 24b ... Weld bead, 9 ... Plate Thickness through opening, A ... adjacent region, A1 ... one side, A2 other side, Lb ... weld length, Lb1, Lb2 ... weld length of weld bead, R-end ... R stop at the start or end, t ... plate thickness , Wb: welding width, Ws: width of a member to be welded.

Claims (6)

A laser lap weld joint obtained by laser welding a high strength thin steel sheet having a tensile strength of 440 MPa or more,
The ratio (Lb / Ws) of the weld length (Lb) of the laser weld to the width (Ws) of the member to be welded is 0.6 or more,
The ratio (Wb / t) of the welding width (Wb) of the laser welded portion to the plate thickness (t) is 0.8 or more and 2 or less,
The opening length along the direction orthogonal to the longitudinal direction of the laser welded portion is 80% or more of the welding width centering on the laser welded portion in both the adjacent region of the starting end portion and the adjacent region of the terminal end portion of the laser welded portion. A high-strength thin steel plate laser lap weld joint, characterized in that a plate-thickness through opening having a length of 1 mm is provided.
However, the weld width (Wb) is a weld width on the overlapping surface of the high-strength thin steel sheets, and the adjacent region is a rectangular region in plan view surrounded by one side and the other side orthogonal to the one side. The one side extends along the longitudinal direction of the laser welded portion from the R stop of the laser welded portion to a position protruding from the endmost portion of the laser welded portion by the plate thickness (t). The other side has a length of 80% of the welding width around the laser welded portion along a direction orthogonal to the longitudinal direction of the laser welded portion. The laser welded portion is composed of one continuous weld bead, the adjacent region is provided in each of the start end and the end of the weld bead, and the plate thickness through opening is provided in each adjacent region. The laser lap weld joint of the high-strength thin steel sheet according to claim 1.
However, the adjacent region is a rectangular region in plan view surrounded by one side and the other side orthogonal to the one side, and the one side is an R stop of the weld bead along the longitudinal direction of the weld bead. Extending from the outermost end of the weld bead to a position protruding by the plate thickness (t), and the other side is along the direction orthogonal to the longitudinal direction of the weld bead, The welding bead has a length that is 80% of the welding width. The laser weld portion is composed of a plurality of weld beads formed intermittently along the width direction of the member to be welded, and the total bead length of each weld bead is the weld length (Lb), The adjacent region is provided in a part or all of each start end and each terminal end of the plurality of weld beads, and the plate thickness through opening is provided in each adjacent region. Item 2. A laser lap weld joint of the high-strength thin steel sheet according to item 1.
However, the adjacent region is a rectangular region in plan view surrounded by one side and the other side orthogonal to the one side, and the one side extends along the longitudinal direction of each welding bead. It extends from the R stop of the bead to a position protruding from the outermost end of each weld bead by the thickness (t), and the other side is the longitudinal direction of each weld bead. Along the orthogonal direction, the weld width is 80% of the length of the weld bead. The laser weld portion is composed of a plurality of weld beads formed intermittently along the width direction of the member to be welded, and the total bead length of each weld bead is the weld length (Lb), Among the plurality of weld beads, the adjacent region is provided at a position corresponding to the start end portion and the terminal end portion of the laser welded portion, and the plate thickness through opening is provided in each of the adjacent regions. The laser lap weld joint of the high strength thin steel sheet according to claim 1.
However, the adjacent region is a rectangular region in plan view surrounded by one side and the other side orthogonal to the one side, and the one side extends along the longitudinal direction of each welding bead. It extends from the R stop of the bead to a position protruding from the outermost end of each weld bead by the thickness (t), and the other side is the longitudinal direction of each weld bead. Along the orthogonal direction, the weld width is 80% of the length of the weld bead. A method for producing a laser lap weld joint of the high-strength thin steel sheet according to any one of claims 1 to 4,
Prior to the formation of the laser welded portion, the opening length along the direction orthogonal to the longitudinal direction of the laser welded portion is 80% or more of the weld width centering on the laser welded portion at a position corresponding to the adjacent region. Providing a plate-thickness through opening having:
The ratio (Lb / Ws) of the welding length (Lb) of the laser welded part to the width (Ws) of the member to be welded is 0.6 or more, and the ratio of the welding width (Wb) of the laser welded part to the plate thickness (t) And a step of forming the laser weld so that (Wb / t) is 0.8 or more and 2 or less, and a method for producing a laser lap weld joint of a high strength thin steel sheet.
However, the weld width (Wb) is a weld width on the overlapping surface of the high-strength thin steel sheet, and the adjacent region is a rectangular region surrounded by one side and the other side orthogonal to the one side, The one side extends along the longitudinal direction of the laser welded portion from the R stop of the laser welded portion to a position protruding from the endmost portion of the laser welded portion by the plate thickness (t). The other side has a length of 80% of the welding width around the laser welded portion along a direction orthogonal to the longitudinal direction of the laser welded portion. A method for producing a laser lap weld joint of the high-strength thin steel sheet according to any one of claims 1 to 4,
The ratio (Lb / Ws) of the welding length (Lb) of the laser welded part to the width (Ws) of the member to be welded is 0.6 or more, and the ratio of the welding width (Wb) of the laser welded part to the plate thickness (t) A step of forming the laser weld so that (Wb / t) is 0.8 or more and 2 or less;
The opening length along the direction orthogonal to the longitudinal direction of the laser welded portion is 80% or more of the welding width centering on the laser welded portion in both the adjacent region of the starting end portion and the adjacent region of the terminal end portion of the laser welded portion. And a step of providing a plate-thickness through-opening portion having the length of: a method of manufacturing a laser lap weld joint of a high-strength thin steel sheet, comprising:
However, the weld width (Wb) is a weld width on the overlapping surface of the high-strength thin steel sheet, and the adjacent region is a rectangular region surrounded by one side and the other side orthogonal to the one side, The one side extends along the longitudinal direction of the laser welded portion from the R stop of the laser welded portion to a position protruding from the endmost portion of the laser welded portion by the plate thickness (t). The other side has a length of 80% of the welding width around the laser welded portion along a direction orthogonal to the longitudinal direction of the laser welded portion.

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