CN113573838B - Overlap laser welded joint, method for producing same, and structural member for automobile body - Google Patents
Overlap laser welded joint, method for producing same, and structural member for automobile body Download PDFInfo
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- CN113573838B CN113573838B CN201980094061.XA CN201980094061A CN113573838B CN 113573838 B CN113573838 B CN 113573838B CN 201980094061 A CN201980094061 A CN 201980094061A CN 113573838 B CN113573838 B CN 113573838B
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 18
- 238000003466 welding Methods 0.000 claims abstract description 177
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- 238000000034 method Methods 0.000 claims description 28
- 239000002184 metal Substances 0.000 claims description 24
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/20—Bonding
- B23K26/21—Bonding by welding
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/20—Bonding
- B23K26/21—Bonding by welding
- B23K26/24—Seam welding
- B23K26/244—Overlap seam welding
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K26/00—Working by laser beam, e.g. welding, cutting or boring
- B23K26/20—Bonding
- B23K26/21—Bonding by welding
- B23K26/24—Seam welding
- B23K26/28—Seam welding of curved planar seams
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
- B23K35/24—Selection of soldering or welding materials proper
- B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550 degrees C
- B23K35/3053—Fe as the principal constituent
- B23K35/3073—Fe as the principal constituent with Mn as next major constituent
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2101/00—Articles made by soldering, welding or cutting
- B23K2101/006—Vehicles
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- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
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- Plasma & Fusion (AREA)
- Laser Beam Processing (AREA)
Abstract
There are proposed a lap laser welded joint, a method of manufacturing the same, and a structural member for an automobile body having the welded joint, wherein, when a laser beam is intermittently irradiated to a single-sided surface of a steel sheet in which a plurality of steel sheets are overlapped, and a welded portion is formed by arranging a 1 st joint portion and a subsequent joint portion in a straight line following the 1 st joint portion in a row, the welded portion is formed by controlling at least a total gap G between the steel sheets constituting the welded portion within a range of 0 to 15% of a total thickness T of the steel sheets constituting the welded portion, and a moving direction of the welded joint irradiated with the laser beam is reversed to a scanning direction of the laser beam, so that a welding start end portion of the 1 st joint portion and a welding end portion of a subsequent joint portion adjacent to the 1 st joint portion face each other, and the welding start end portion and the welding end portion of the subsequent joint portion face each other, and by controlling various dimensions of the joint portions within appropriate ranges, cracking does not occur at the welding end portion of the joint portion, and peel strength is excellent.
Description
Technical Field
The present invention relates to a lap laser welded joint, a method for manufacturing the lap laser welded joint, and a structural member for an automobile body having the lap laser welded joint.
Background
Resistance spot welding is generally used for welding structural members (strength members) of an automobile body having a flange portion. However, resistance spot welding has various problems such as a time-consuming welding, a reduced heat generation amount due to the split flow, a failure to reduce the welding pitch, and a certain amount of space required to install a welding gun. In order to solve these problems, in recent years, a lap laser welding technique has been studied and popularized instead of the conventional resistance spot welding. Here, the lap laser welding is a welding method in which laser beams are irradiated to one side surface of a plurality of overlapped steel plates to melt and join the steel plates.
Conventionally, in a lap laser welded joint, laser beams are intermittently irradiated onto surfaces of a plurality of steel sheets to be overlapped, and the steel sheets at the portions irradiated with the laser beams are melted and solidified, whereby welded portions having short linear joint portions and being continuously arranged in a row are formed, whereby the plurality of steel sheets are joined. However, in lap laser beam welding, there is a problem in that cracks are likely to occur in the final solidified portion located on the welding terminal portion side of the linear joint portion. When a crack is generated, the crack propagates over the entire length of the linear joint, and thus not only the static strength such as the shear strength and the peel strength of the welded joint is reduced, but also the fatigue strength is significantly reduced. In recent years, in parts for automobile bodies, particularly structural members (strength members) as skeleton members, high-tensile steel sheets have been often used to improve the strength and rigidity of the automobile bodies, and the reduction in static strength and fatigue strength of welded joints due to cracks generated in joints has become a serious problem.
Accordingly, various methods for preventing cracks from occurring at the welded terminal portion of the joint portion when laser beam welding is performed on the overlapped steel plates have been studied. For example, patent document 1 discloses preventing welding cracks by projecting a steel plate on the lower side of lap welding and making the welding start position be a position separated from the flange end. Patent document 2 discloses a technique of preventing weld cracking by irradiating laser light from an oblique direction to an end portion of a joint surface. Patent documents 3 and 4 disclose a technique of preventing weld cracking by reheating or welding the welded portion and the periphery of the welded portion. Further, patent document 5 discloses a technique of welding a lap surface in an elliptical shape to prevent occurrence of weld cracks. Further, patent document 6 discloses a technique of preventing occurrence of weld cracks by optimizing the composition of a steel sheet and optimizing the ratio of the weld width to the weld thickness.
Prior art literature
Patent literature
Patent document 1: japanese patent laid-open No. 2007-229740
Patent document 2: japanese patent laid-open No. 2008-296236
Patent document 3: japanese patent application laid-open No. 2012-240083
Patent document 4: japanese patent application laid-open No. 2012-240086
Patent document 5: japanese patent laid-open No. 2017-113781
Patent document 6: japanese patent laid-open publication No. 2018-001197
Disclosure of Invention
Problems to be solved by the invention
However, in the method described in patent document 1, since the lower steel sheet of the lap welding is protruded, the protruded portion becomes an unnecessary portion, and there is a problem that the design of parts is limited. In addition, in the method described in patent document 2, since laser light is irradiated from an oblique direction, when the overlapping plates are separated by a gap, a molten portion cannot be formed satisfactorily on the joint surface, and the penetration becomes insufficient, and there is a problem that it is difficult to secure sufficient strength. In addition, in the methods described in patent documents 3 and 4, there is a problem in that the welding time is long because the welded portion and the periphery of the welded portion need to be reheated or welded. In addition, the method described in patent document 5, in which the joint surface is welded in an elliptical shape, cannot be applied to prevention of cracking of the welded terminal portion of the linear joint portion. Further, in the method described in patent document 6, since stress tends to concentrate on the welding terminal portion, there is a problem that cracks cannot be prevented from occurring at the welding terminal portion of the straight joint portion having a short length.
The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a welded joint having a welded portion in which laser beams are intermittently irradiated so that short-length joint portions (welding spots) are formed in a row, a lap laser welded joint which does not cause cracking at a welded terminal portion of the joint portion and is excellent in peel strength of the welded portion, and a method for manufacturing the lap laser welded joint, and a structural member for an automobile body having the lap laser welded joint.
Means for solving the problems
In order to solve the above-described problems, the inventors of the present application have repeatedly studied focusing on the relationship between the first linear joint (hereinafter referred to as "1 st joint") formed to overlap the welded portion of the laser welded joint and 1 or more linear joints (hereinafter referred to as "subsequent joints") formed next to the first linear joint. In the present invention, the "1 st joint" and the "subsequent joint" are also collectively referred to simply as "joint".
As a result, it was found that, in order to prevent cracking from occurring at the welded terminal portion of the joint, it is important to form the welded portion in the following manner: forming the welding part in a J shape, wherein the welding start end part of the 1 st joint part is opposite to the welding end part of the adjacent subsequent joint part, and the welding start end part of the subsequent joint part is opposite to the welding end part of the adjacent subsequent joint part, namely, the welding parts are formed in a mode that the welding start end parts of the joint parts are opposite to the welding end parts; further, it has been found that it is effective to control the various dimensions of the 1 st joint and the subsequent joint to an appropriate range in order to more reliably prevent cracking of the welded terminal portion of the joint and to secure sufficient strength of the welded portion, in addition to satisfying the above requirements, and the present invention has been finally developed.
The present invention based on the above-described findings is a lap laser welded joint having a welded portion formed by lap-joining a plurality of steel plates, wherein a total gap G between the steel plates constituting the welded portion is in a range of 0 to 15% of a total thickness T of the steel plates constituting the welded portion, the welded portion includes a 1 st joint portion in a line shape and a subsequent joint portion in a line shape following the 1 st joint portion in a line shape, a welding start end portion of the 1 st joint portion is opposed to a welding end portion of a subsequent joint portion adjacent thereto, and the welding start end portions of the subsequent joint portions are opposed to the welding end portion, the 1 st joint portion has a J-shape formed by the linear joint portion and an arc-shaped or circular-shaped curved joint portion connected to a welding end portion side of the linear joint portion, and the welded portion satisfies all of the following formulas (1) to (4):
15.0≤L 1 ≤30.0 (1)，
8.0≤L 2 ≤20.0 (2)，
1/8≤w/b≤1/2 (3)，
1/4≤a/(L 1 +L 2 ) More than or equal to 1/2 or more than or equal to 1/2 less than or equal to a/L 2 ≤1 (4)，
Wherein L is 1 The length (mm) of the 1 st joint,
L 2 for the length (mm) of the subsequent joint,
b is the minimum thickness (mm) of the molten metal of the joint,
w is the width (mm) of the molten metal of the joint,
a is the shortest distance (mm) between the joint portions.
The lap laser welded joint of the present invention is characterized in that the 1 st joint portion includes only a linear joint portion, and satisfies the following formula (1') instead of the formula (1):
30.0＜L 1′ ≤40.0 (1′)，
wherein L is 1′ The length (mm) of the linear joint.
In the lap laser welded joint according to the present invention, the composition of at least 1 of the steel sheets contains C:0.07 to 0.4 mass% of Si:0.2 to 3.5 mass percent of Mn:1.8 to 5.5 mass percent, P+S:0.03 mass% or less, al:0.08 mass% or less and N: less than 0.010 mass percent, and the balance of Fe and unavoidable impurities.
The lap laser welded joint of the present invention is characterized in that the steel sheet contains, in addition to the above-mentioned composition, at least 1 component of the following groups a and B:
group a is from Ti:0.0005 to 0.01 mass% and Nb:0.005 to 0.050 mass% of 1 or 2 kinds selected from the group consisting of;
group B is a group consisting of Cr: less than 1.0 mass percent, mo:0.50 mass% or less and B:0.10 mass% or less of 1 or 2 or more selected from the group consisting of.
In the lap laser welded joint according to the present invention, at least 1 of the steel sheets is a high tensile steel sheet having a tensile strength of 980MPa or more.
Further, the present invention provides a method for manufacturing a lap laser welded joint, comprising, when a plurality of steel plates are vertically overlapped and intermittently irradiated with a laser beam to form a welded portion in which a 1 st joint portion and a subsequent joint portion in a line following the 1 st joint portion are arranged in a line, forming a total gap G between the steel plates constituting the welded portion in a range of 0 to 15% of a total thickness T of the steel plates constituting the welded portion, and further, controlling at least one of a laser power, a focal point position, a speed and a beam diameter to satisfy the following formula (1) by controlling at least one of a welding start end portion of the 1 st joint portion and a welding end portion of the subsequent joint portion adjacent to the 1 st joint portion to face each other and a welding end portion of the subsequent joint portion to form a J-shape formed by the linear joint portion and the curved or circular curved joint portion connected to the welding end portion side of the linear joint portion, and by controlling at least one of the laser power, focal point position, and beam diameter to satisfy the following formula (4):
15.0≤L 1 ≤30.0 (1)
8.0≤L 2 ≤20.0 (2)
1/8≤w/b≤1/2 (3)
1/4≤a/(L 1 +L 2 ) More than or equal to 1/2 or more than or equal to 1/2 less than or equal to a/L 2 ≤1 (4)
Wherein L is 1 The length (mm) of the 1 st joint,
L 2 for the length (mm) of the subsequent joint,
b is the minimum thickness (mm) of the molten metal of the joint,
w is the width (mm) of the molten metal of the joint,
a is the shortest distance (mm) between the joint portions.
The method for manufacturing a lap laser welded joint according to the present invention is characterized in that the 1 st joint portion includes only a linear joint portion, and at least 1 of laser power, focal position, welding speed, and beam diameter is controlled so as to satisfy the following formula (1') instead of the formula (1):
30.0＜L 1′ ≤40.0 (1′)，
wherein L is 1′ The length (mm) of the linear joint.
The present invention also provides a structural member for an automobile body, comprising the lap laser welded joint according to any one of the above.
ADVANTAGEOUS EFFECTS OF INVENTION
In accordance with the present invention,
a lap laser welded joint can be produced in which the occurrence of cracks at the welded terminal portion of the joint portion, which constitutes the welded portion of the lap laser welded joint obtained by laser beam welding a plurality of superimposed steel plates, can be reliably suppressed, and the peel strength of the welded portion is excellent. Further, since the lap laser welded joint of the present invention can shorten the length of the joint portion, the degree of freedom in designing the component can be increased, and development of a component having lighter weight, higher rigidity, and higher strength can be performed. Therefore, the lap laser welded joint of the present invention can be applied to a structural member (strength member) that becomes a skeleton of an automobile body.
Drawings
Fig. 1 is a perspective view showing an example of a conventional lap laser welded joint.
Fig. 2 is a schematic view illustrating a welded portion of a conventional lap laser welded joint, where (a) is a plan view, and (b) is a sectional view of (a) from A-A.
Fig. 3 is a schematic view illustrating a welded portion of a lap laser welded joint according to the present invention, (a) is a plan view, and (B) is a B-B cross-sectional view of (a).
Fig. 4 is a perspective view showing an example of the lap laser welded joint of the present invention.
Fig. 5 is a perspective view illustrating a welding method of the lap laser welding joint of the present invention.
Fig. 6 is a view illustrating a welding position of the lap laser welding joint according to the present invention, (a) is a plan view, and (b) is a C-C cross-sectional view of (a).
Fig. 7 is a perspective view illustrating a peel test piece having a lap laser welded joint used in the examples of the present invention.
Detailed Description
The lap laser welded joint, the method for producing the lap laser welded joint, and the structural member for automobile body having the lap laser welded joint according to the present invention will be described below.
< overlap laser welded joint >)
Fig. 1 is a perspective view showing an example of a conventional lap laser welded joint. The lap laser welded joint 1 is a structure in which at least 2 steel sheets are overlapped, and in the example shown in fig. 1, a steel sheet 2 having a vertical wall portion 2a and a flange portion 2b extending outward from the front end of the vertical wall portion 2a and having a substantially hat-shaped cross-sectional shape and a flat panel-shaped steel sheet 3 are overlapped so that the flange portion 2b faces the steel sheet 3 to form a joint surface, and a laser beam is irradiated from above the flange portion 2b to the surface of the flange portion 2b to form a molten portion (molten metal portion) penetrating at least the steel sheet 2 and solidified to form a joint portion (welding spot), whereby welding is performed. Although a Heat Affected Zone (HAZ) is present around the molten zone, the joint of the present invention refers only to a molten zone other than the heat affected zone.
The welded portion of the lap laser welded joint 1 is formed by intermittently irradiating the surface of the flange portion 2b with a laser beam while moving a welding head WH as a laser beam source along the longitudinal direction of the vertical wall portion 2a (the arrow direction in fig. 1). As a result, as shown in fig. 1, a short, linear 1 st joint 4 and a subsequent joint 5 formed continuously thereto are formed on the joint surface of the steel sheet 2. When the length of the flange portion is short, there is only one of the subsequent joining portions 5, and when the length of the flange portion is long, a plurality of subsequent joining portions 5 are formed in a row along the longitudinal direction of the flange portion. As described above, in the present invention, the "1 st joint" and the "subsequent joint" are also collectively referred to simply as "joint".
Fig. 2 is a schematic diagram showing a conventional welded portion formed on the flange portion 2b of the lap laser welding joint shown in fig. 1, (a) is a plan view of the 1 st joint portion 14 constituting the welded portion and the subsequent joint portion 15 adjacent thereto as seen from above the flange portion 2b, and (b) is a cross-sectional view showing A-A section shown at the subsequent joint portion 15 in (a) above.
In the conventional laser beam welding, as shown in fig. 2, when forming a welded portion including a 1 st joint 14 and a subsequent joint 15 having a short length in a straight line, the welding direction (the traveling direction of the welding head) and the welding direction (the scanning direction of the laser beam) of the 1 st joint 14 and the subsequent joint 15 are set to be the same. Therefore, the central portions 14a and 15a of the welding terminal portions E (final solidification portions) of the 1 st joint portion 14 and the subsequent joint portion 15 are in the form of an arc pit and have the smallest plate thickness, and therefore tensile stress (force in the arrow Fa direction shown in fig. 2 (a)) acts intensively on the portions from the outer peripheral portion of the molten portion to the outside. Therefore, in the conventional lap laser welded joint, there is a problem that cracks 8 occur in the weld terminal portion E of the 1 st joint portion 14 and the subsequent joint portion 15, and then the cracks propagate from the weld terminal portion E to the weld start portion S, so that the peel strength and fatigue strength of the welded portion are significantly reduced. By setting the lengths of the 1 st joint portion 14 and the subsequent joint portion 15 to be sufficient, cracking at the welding terminal portion can be prevented, but this method has another problem that the welding time is long and productivity is lowered.
It is to be noted that the cracks in the welded terminal portions are generated in the 1 st joint portion 14 and the welded terminal portion (final solidified portion) of the subsequent joint portion 15 so as to penetrate from the front surface to the rear surface, and whether or not the cracks are generated can be confirmed visually, but it is preferable to judge more reliably by cutting the welded terminal portion of the welded joint portion in the width direction and enlarging the cut surface to about 10 times by using an optical microscope, for example.
Accordingly, the inventors of the present application have paid attention to stress concentration occurring in a weld terminal portion of a joint portion constituting a weld portion formed by a conventional laser beam welding method, and have studied a countermeasure for preventing occurrence of cracks in the weld terminal portion of the joint portion by reducing the stress concentration. As a result, it was found that by using the welded portion shown in fig. 3 instead of the welded portion shown in fig. 2, cracks generated at the welded terminal portion of the joint portion can be prevented. Here, fig. 3 is a schematic view showing a welded portion of the present invention formed on a flange portion 2B of a lap laser welded joint having the same structure as that shown in fig. 2, (a) is a plan view of a 1 st joint portion 4 constituting the welded portion and a subsequent joint portion 5 adjacent thereto as seen from above the flange portion 2B, and (B) is a cross-sectional view showing a B-B section shown at the subsequent joint portion 5 in the above (a).
As is clear from fig. 3, the welded portion according to the present invention is characterized in that the welding start end portion of the 1 st joint portion 4 is opposed to the welding end portion of the subsequent joint portion 5 adjacent thereto, and the welding start end portion of the subsequent joint portion 5 is opposed to the welding end portion of the subsequent joint portion 5 adjacent thereto, that is, the welding start end portions of the adjacent joint portions are opposed to the welding end portions. As described above, by performing welding such that the welding start portion of the preceding joint portion and the welding end portion of the following joint portion face each other, cracking of the welding end portion of the joint portion can be prevented. The reason for this is that, at the point in time when the welding terminal portion of the subsequent joint portion is completed, the steel sheet in the vicinity of the welding terminal portion is restrained by the preceding joint portion, and therefore, the tensile stress (force in the arrow Fb direction shown in fig. 3 (a)) applied to the central portion (5 a) of the final solidified portion from the outer peripheral portion of the molten portion is reduced.
In this way, when the welded portion is formed as shown in fig. 3, cracking of the welded terminal portion of the subsequent joint portion can be prevented. However, since the steel sheet around the welding terminal portion of the 1 st joint is in an unconstrained free state, it is not possible to prevent cracking at the welding terminal portion E of the 1 st joint.
Accordingly, the inventors of the present application have further studied about a method of suppressing cracking of the welded terminal portion of the 1 st joint. As a result, it was found that it is effective to form the 1 st joint portion into a J-shape formed by a linear joint portion and an arc-shaped or circular curved joint portion connected to the terminal end side of the joint portion, as shown in the left side of fig. 3 (a). By forming this shape, the steel sheet on the welding terminal portion side of the 1 st joint portion, that is, around the welding terminal portion of the curved joint portion, is already restrained by the linear joint portion, and therefore the tensile stress (force in the arrow Fc direction shown in fig. 3 (a)) applied to the central portion (4 a) of the final solidified portion from the outer peripheral portion of the molten portion is reduced, and cracking at the welding terminal portion of the 1 st joint portion can be prevented.
As shown in fig. 3, the welding portion is formed such that the welding start end portion of the 1 st joint portion 4 faces the welding end portion of the subsequent joint portion 5 adjacent thereto, and the welding start end portion of the subsequent joint portion 5 faces the welding end portion of the subsequent joint portion 5 adjacent thereto, and the 1 st joint portion is formed in a J-shape, whereby cracking at the 1 st joint portion and the welding end portion of the subsequent joint portion can be prevented. For reference, fig. 4 shows an example in which the lap laser welding joint shown in fig. 1 is applied to the welded portion of the present invention shown in fig. 3.
However, according to further studies by the inventors of the present application, it is found that in order to more reliably prevent cracking from occurring at the welded terminal portion of the joint portion and to impart sufficient peel strength to the welded portion, it is necessary to form the welded portion shown in fig. 3 such that the total gap G between the steel plates constituting the welded portion is in the range of 0 to 15% of the total thickness T of the steel plates constituting the welded portion, and the welded portion, that is, the 1 st joint portion and the subsequent joint portion constituting the welded portion satisfy the following formulas (1) to (4):
15.0≤L 1 ≤30.0 (1)
8.0≤L 2 ≤20.0 (2)
1/8≤w/b≤1/2 (3)
1/4≤a/(L 1 +L 2 ) More than or equal to 1/2 or more than or equal to 1/2 less than or equal to a/L 2 ≤1 (4)
Wherein L is 1 : length (mm) of 1 st joint
L 2 : length (mm) of subsequent joint
b: minimum thickness (mm) of molten metal of the joint
w: width (mm) of molten metal of joint
a: shortest distance (mm) between the joint portions.
Hereinafter, the present invention will be specifically described.
0≤G/T≤0.15
In the lap laser welded joint of the present invention, the ratio (G/T) of the total gap G between the steel plates constituting the welded portion to the total thickness T of the steel plates constituting the welded portion is set to be 0 to 0.15, that is, the ratio of the total gap G between the steel plates constituting the welded portion to the total thickness T of the steel plates constituting the welded portion is set to be in the range of 0 to 15%. The reason for this is that if the ratio of G to T exceeds 15%, the depth of the arc pit at the welding terminal portion becomes deep, and the stress becomes more likely to concentrate. Preferably in the range of 0 to 10%.
15.0mm≤L 1 ≤30.0mm
As described above, in order to prevent cracking of the welded terminal portion of the 1 st joint portion constituting the welded portion, it is important for the lap laser welded joint of the present invention that the 1 st joint portion has a J-shape formed by a straight joint portion and an arcuate or circular curved joint portion, and in order to more reliably prevent cracking of the welded terminal portion and to secure a peel strength of sufficient strength, the length L of the 1 st joint portion 1 It is required to be 15.0 to 30.0 mm. As shown in fig. 3, the length L of the J-shaped 1 st joint portion 1 The total length of the linear joint and the curved joint is set. If L 1 If the length is less than 15.0mm, cracks may occur at the welding terminal portion of the 1 st joint portion. Preferably 20.0mm or more. On the other hand, for L 1 The upper limit of (2) is not limited from the viewpoint of preventing cracking, but is 30.0mm or less from the viewpoint of shortening the welding time. Preferably 25.0mm or less.
8.0mm≤L 2 ≤20.0mm
In addition, the lap laser welded joint of the present invention is required to be such that the length L of the subsequent joint portion constituting the welded portion 2 In the range of 8.0 to 20.0 mm. At L 2 If the welding diameter is smaller than 8.0mm, it is impossible to make the welding start end of the preceding joint portion face the welding end of the following joint portion Since a welding area for relaxing the stress applied to the welding terminal portion is secured, cracking of the welding terminal portion cannot be reliably prevented. Preferably 10.0mm or more. On the other hand, L 2 The upper limit of (2) is not limited from the viewpoint of preventing cracks, but is 20.0mm or less from the viewpoint of shortening the welding time. Preferably 15.0mm or less.
1/8≤w/b≤1/2
In addition, the lap laser welded joint of the present invention is required to have a ratio (w/b) of the width w of the molten metal of the joint portion to the minimum thickness b formed at the welding terminal portion (final solidified portion) of the joint portion constituting the welded portion in the range of 1/8 to 1/2. If the ratio (w/b) is greater than 1/2, the tensile stress applied to the final solidification portion of the welded terminal portion of the 1 st joint portion and the subsequent joint portion from the outer peripheral portion of the molten portion increases, and the occurrence of weld cracks cannot be suppressed. On the other hand, if the ratio (w/b) is less than 1/8, the strength of the joint portion cannot be sufficiently ensured. That is, by setting the ratio (w/b) at the joint to be in the range of 1/8 to 1/2, after the welding start end portion of the preceding joint is made to face the welding end portion of the following joint, cracking at the welding end portion of the joint can be prevented more reliably, and the peel strength of the welded portion can be made to be sufficient. The preferable ratio (w/b) is in the range of 1/6 to 1/3.
1/4≤a/(L 1 +L 2 ) More than or equal to 1/2 or more than or equal to 1/2 less than or equal to a/L 2 ≤1
In the lap laser welded joint according to the present invention, regarding the shortest distance a between joint portions, in the case between the 1 st joint portion and the adjacent subsequent joint portion, a is set to be equal to (the length L of the 1 st joint portion) 1 L+length of subsequent joint 2 ) Ratio (a/(L) 1 +L 2 ) In the case where adjacent subsequent joined portions are located between each other, the above-mentioned a is in the range of 1/4 to 1/2 with respect to the length L of the subsequent joined portions 2 Ratio (a/L) 2 ) It is required to be in the range of 1/2 to 1. At the above ratio (a/(L) 1 +L 2 ) In the case of more than 1/2 or in the above ratio (a/L) 2 ) If the ratio is greater than 1, the subsequent joint suppression slave cannot be sufficiently obtainedThe effect of the deformation of the steel plate around the joint portion, which is caused by the preceding joint portion of the joint portion, cannot prevent cracking of the welded terminal portion. The lower limit value of a is not limited from the viewpoint of preventing cracking, but from the viewpoint of shortening the welding time, the ratio (a/(L) 1 +L 2 ) More than 1/4 of the above ratio (a/L) 2 ) Is 1/2 or more. The preferred ratio (a/(L) 1 +L 2 ) In the range of 1/3 to 2/5, preferably the ratio (a/L) 2 ) In the range of 3/5 to 9/10.
In the description of the present invention described above, the technique of preventing the occurrence of cracks in the welding terminal portion of the 1 st joint portion by forming the 1 st joint portion in a J-shape is described. However, as described above, by increasing the length of the linear joint portion, cracking of the welding terminal portion of the joint portion can be prevented. In this case, the 1 st joint length L 1′ The following formula (1') is satisfied instead of the formula (1) described above:
30.0＜L 1′ ≤40.0 (1′)
wherein L is 1′ : the length (mm) of the linear joint.
Length L in the case where the 1 st joint portion includes only the linear joint portion 1′ If the thickness is 30.0mm or less, cracks are generated at the terminal end of the 1 st joint. Preferably 32.0mm or more. On the other hand, L 1′ The upper limit of (2) is not limited from the viewpoint of preventing cracks, but is 40.0mm or less from the viewpoint of shortening the welding time. Preferably 38.0mm or less.
Next, steel sheets constituting the lap laser welded joint of the present invention will be described.
Fig. 1 to 4 show examples in which 2 steel plates are joined to each other to form a joined laser welded joint, but it is needless to say that 3 or more steel plates may be joined to each other to form a welded joint.
Thickness of steel sheet
The thickness of each of the steel sheets constituting the lap laser welded joint of the present invention is not particularly limited, and is generally used as an outer panel and a structural member (strength member) of an automobile bodyIn the range of 0.5 to 3.2 mm. The plurality of steel sheets may have all the same sheet thickness or may have different sheet thicknesses. For example, in the case of the lap laser welded joint 1 having the shape shown in fig. 4, the plate thickness t of the upper steel plate 2 may be set to 2 The thickness t of the lower steel plate 3 is set to be 0.6-1.8 mm 3 In the range of 1.0 to 2.5mm, the thickness t of the upper steel sheet 2 may be set to 2 And the thickness t of the lower steel plate 3 3 The thickness is the same and is 0.5-3.2 mm.
Composition of steel sheet
In addition, the composition of the plurality of steel sheets constituting the lap laser welded joint of the present invention is not particularly limited, and it is preferable that at least 1 steel sheet has a composition as follows, and contains C:0.07 to 0.4 mass% of Si:0.2 to 3.5 mass percent of Mn:1.8 to 5.5 mass percent, P+S:0.03 mass% or less, al:0.08 mass% or less and N: less than 0.010 mass percent, and the balance of Fe and unavoidable impurities.
C:0.07 to 0.4 mass percent
C is an element contributing to the improvement of the strength of steel, and by containing 0.07 mass% or more, the effect of precipitation strengthening and phase change strengthening can be obtained. Further, by setting the C content to 0.4 mass% or less, coarse carbide precipitation can be avoided, and desired strength and workability can be ensured. Therefore, the C content is preferably in the range of 0.07 to 0.4 mass%. More preferably, the content is in the range of 0.15 to 0.3 mass%.
Si:0.2 to 3.5 mass%
Si is an element excellent in solid solution strengthening ability, and the strength of steel can be improved by containing 0.2 mass% or more. Further, by setting the Si content to 3.5 mass% or less, excessive curing of the welding heat affected zone can be suppressed, and deterioration of toughness and low-temperature crack resistance of the welding heat affected zone can be prevented. Therefore, the Si content is preferably in the range of 0.2 to 3.5 mass%. More preferably 1.0 to 2.5 mass%.
Mn:1.8 to 5.5 mass percent
Mn is an element effective for improving hardenability and suppressing coarse carbide precipitation, and is preferably contained in an amount of 1.8 mass% or more. In addition, when the Mn content is 5.5 mass% or less, the grain boundary embrittlement sensitivity can be suppressed from being improved, and deterioration of toughness and low-temperature cracking resistance can be prevented. Therefore, the Mn content is preferably in the range of 1.8 to 5.5 mass%. More preferably in the range of 2.0 to 3.5 mass%.
P+S:0.03 mass% or less
P and S are harmful elements that adversely affect ductility and toughness of the steel, and by setting the total content of P and S to 0.03 mass% or less, it is possible to prevent deterioration of ductility and toughness and secure desired strength and workability. Therefore, the total content of P and S is preferably 0.03 mass% or less. More preferably 0.02 mass% or less.
Al:0.08 mass% or less
Al is an element added as a deoxidizer at the stage of steel making, and is usually added in an amount of 0.01 mass% or more. However, if the Al content exceeds 0.08 mass%, inclusions such as alumina increase, and adverse effects on fatigue resistance become evident. Therefore, the Al content is 0.08 mass% or less. Preferably in the range of 0.02 to 0.07 mass%.
N:0.010 mass% or less
N is an element that significantly deteriorates the aging resistance of steel, and is preferably reduced as much as possible. In particular, when N exceeds 0.010 mass%, deterioration of aging resistance becomes remarkable, and thus the N content is 0.010 mass% or less. The lower limit of N is not particularly limited, but is preferably about 0.001 mass% from the viewpoint of preventing an increase in manufacturing cost.
In order to further improve the strength of the steel sheet and the peel strength of the welded portion, it is preferable that at least 1 steel sheet constituting the welded joint of the present invention contains at least 1 component of the following group a and group B in addition to the above-described component composition.
Group A: from Ti:0.0005 to 0.01 mass% and Nb:0.005 to 0.050 mass% of 1 or 2 kinds selected from the group consisting of
Both Ti and Nb have an effect of forming carbide and nitride and precipitating them to suppress austenite coarsening during annealing in the production of steel sheet. In order to obtain the above-mentioned effect, it is preferable to make 1 or 2 kinds selected from Ti and Nb contain 0.0005 mass% or more of Ti and 0.005 mass% or more of Nb. However, even if Ti and Nb are excessively contained, the above effects are saturated, and only the raw material cost increases. Further, since the recrystallization temperature is increased, there is a possibility that the annealed metal structure becomes uneven and stretch flangeability is impaired at the time of manufacturing the steel sheet. Further, there is a possibility that the yield ratio increases due to an increase in the amount of carbide or nitride deposited, and the shape freezing property deteriorates. Thus, when Ti and/or Nb are contained, ti is 0.01 mass% or less and Nb is 0.050 mass% or less. More preferred is Ti:0.0006 to 0.0080 mass%, nb:0.010 to 0.040 mass%.
Group B: from Cr: less than 1.0 mass percent, mo:0.50 mass% or less and B:0.10 mass% or less of 1 or 2 or more selected from
Cr, mo, and B are elements effective for improving the hardenability of steel, and preferably contain Cr in order to obtain the above effects: 0.01 mass% or more, mo:0.004 mass% or more and B: 0.0001% by mass or more of 1 or more. However, even if these elements are contained in an excessive amount, the above effects are saturated, and only the raw material cost increases. Thus, when Cr, mo, and B are contained, cr is preferably added: less than 1.0 mass percent, mo:0.50 mass% or less, B:0.10 mass% or less. More preferably Cr:0.02 to 0.50 mass% of Mo:0.01 to 0.10 mass percent, B:0.001 to 0.03 mass%.
The balance of at least 1 steel sheet constituting the welded joint of the present invention, excluding the above-mentioned components, is Fe and unavoidable impurities.
Tensile Strength of Steel sheet
Further, it is preferable that at least 1 steel sheet among the plurality of steel sheets constituting the lap laser welded joint of the present invention is a high tensile steel sheet having a tensile strength TS of 980MPa or more. When at least 1 steel sheet is the high-tensile steel sheet, the lap laser welded joint can obtain high joining strength, and even when welding cracks occur by the conventional welding method, the occurrence of welding cracks can be prevented by the effect of suppressing deformation of the steel sheet around the joined portion by the preceding joined portion in the present invention. Therefore, for example, it is preferable that at least 1 steel sheet of the plurality of steel sheets has the above-described composition and tensile strength TS is 980MPa or more. The plurality of steel plates constituting the lap laser welded joint of the present invention may be steel plates having the same composition and the same strength, or steel plates having different compositions and different strengths.
Method for manufacturing lap joint laser welded joint
Next, a method for manufacturing the lap laser welded joint according to the present invention will be described.
Fig. 5 is a diagram illustrating an example of a welding method used for manufacturing the lap laser welded joint according to the present invention. First, a plurality of steel sheets are stacked one on top of the other and laser beams are intermittently irradiated onto the uppermost steel sheet surface of the stacked plurality of steel sheets, and a 1 st joint 4 and a plurality of subsequent joints 5 following the 1 st joint are sequentially formed to form welded parts, thereby manufacturing the lap laser welded joint 1 of the present invention.
As described above, in the present invention, one-side welding is performed for a plurality of superimposed steel plates. By adopting the one-sided welding, the work space required for welding can be reduced.
In the one-side welding, it is preferable to irradiate a laser beam from the side of a steel sheet having a large sheet thickness out of the plurality of steel sheets stacked together, from the viewpoint of preventing burn-through during welding. On the other hand, from the viewpoint of preventing the non-joining due to the non-penetration, it is preferable to irradiate the laser beam from the steel plate side having a thin plate thickness. When the steel sheets have the same thickness, a laser beam may be irradiated from any of the steel sheet sides.
In the lap laser welded joint 1 shown in fig. 5, 2 steel sheets 2 and 3 are overlapped to form a joint surface, a laser beam is intermittently irradiated to the joint surface to form a J-shaped 1 st joint portion 4, and a plurality of linear subsequent joint portions 5 are formed next to the 1 st joint portion 4.
In the lap laser welded joint of the present invention, it is important that the ratio (G/T) of the total gap G between the steel plates constituting the welded portion to the total thickness T of the steel plates constituting the welded portion is 0 to 0.15, that is, the ratio of the total gap G between the steel plates constituting the welded portion to the total thickness T of the steel plates constituting the welded portion is in the range of 0 to 15%. This is because, if the ratio of G to T exceeds 15%, the depth of the arc pit at the welding terminal portion becomes deep, and the stress becomes more likely to concentrate. Preferably in the range of 0 to 10%.
It is important in the present invention that, when the laser beam LB is irradiated to the surface of the steel sheet while the welding head WH to which the laser beam is irradiated is moved in the welding direction (the arrow direction indicated by D in fig. 5), the scanning direction of the laser beam LB is set to be the direction opposite to the moving direction of the welding head WH (the direction opposite to the arrow indicated by D in fig. 5). As described above, by making the moving direction of the welding head WH opposite to the scanning direction of the laser beam LB, the welding end portion of the 1 st joint portion 4 and the welding end portion of the subsequent joint portion 5 adjacent thereto can be opposed to each other, and the welding end portion of the subsequent joint portion 5 adjacent thereto are opposed to each other, that is, the welding portion can be formed such that the welding end portion of the adjacent joint portion and the welding end portion are opposed to each other, and therefore, cracking of the welding end portion of the joint portion can be prevented.
In the present invention, as shown in fig. 5, it is important that the 1 st joint 4 has a J-shape formed by a linear joint and an arc-shaped or circular curved joint connected to the welding terminal portion side of the linear joint. This can prevent cracking from occurring in the welding terminal portion of the 1 st joint portion.
Further, in the present invention, it is important to control at least 1 of the welding conditions of the laser beam, specifically, the laser power, the focal position, the welding speed, and the beam diameter so that the welded portions (the 1 st joint and the subsequent joints) formed in the above manner satisfy all of the following formulas (1) to (4):
15.0≤L 1 ≤30.0 (1)
8.0≤L 2 ≤20.0 (2)
1/8≤w/b≤1/2 (3)
1/4≤a/(L 1 +L 2 ) More than or equal to 1/2 or more than or equal to 1/2 less than or equal to a/L 2 ≤1 (4)
Wherein L is 1 : length (mm) of 1 st joint
L 2 : length (mm) of subsequent joint
b: minimum thickness (mm) of molten metal of the joint
w: width (mm) of molten metal of joint
a: shortest distance (mm) between the joint portions.
Here, as the type of the laser beam used in the laser beam welding according to the present invention, for example, a fiber laser, a disk laser, or the like can be used. In order to satisfy the above formulas (1) to (4), it is preferable that the irradiation of the laser beam is performed at a power: 2.0-6.0 kW, focal position: steel plate surface irradiated with laser beam to +30mm+beam diameter: scanning speed of laser beam of 0.4-1.0 mm: 2.0 to 5.0 m/min. More preferably laser power: 2.5-5.0 kW, focal position: steel plate surface irradiated with laser beam to +20mm and beam diameter: scanning speed of laser beam of 0.5-0.8 mm: 2.5 to 4.5 m/min.
In the welding method of the welded joint according to the present invention, the 1 st joint portion 4 may be formed to include only a linear joint portion instead of the J-shape, and in this case, the length L of the linear joint portion may be controlled so as to be equal to 1′ It is important that the following formula (1') is satisfied instead of formula (1):
30.0≤L 1′ ≤40.0 (1′)
wherein L is 1′ : the length (mm) of the linear joint.
Thus, even if the welding terminal portion is not J-shaped, the welding terminal portion of the 1 st joint portion can be prevented from cracking.
Structural part for automotive body
Next, the structural member for an automobile body of the present invention will be described.
As an example of a lap laser welded joint that can be preferably used in the present invention, there is a structural member (strength member) that becomes a skeleton portion of an automobile body. The member shown in fig. 1 (fig. 4) is composed of a steel plate 2 as a frame component and a steel plate 3 as a panel component, each having a substantially hat-shaped cross section, and a flange portion 2b of the steel plate 2 and the steel plate 3 disposed opposite to the flange portion 2b are joined by a welded portion formed by the 1 st joint portion 4 and the subsequent joint portion 5 formed by the laser beam welding. In order to apply the member having such a shape to a strength member of an automobile body, it is important from the viewpoint of ensuring collision safety that the strength of the welded portion is excellent, but the lap laser welded joint of the present invention has no crack at the welded terminal portion of the joint portion and has sufficient peel strength, and thus, for example, is suitable for a structural member such as a center pillar, a roof rail, or the like of an automobile body.
Here, a description will be given of a preferred position for forming a welded portion when a lap laser welded joint according to the present invention is applied to manufacture a structural member for an automobile body, and the like, as shown in fig. 6, in which 2 steel plates 2, 3 having an L-shaped cross section with flange portions 2b, 3b are overlapped so that the flange portions face each other, and laser beam welding is performed from one side. Fig. 6 (a) is a plan view of the flange portion overlapping each other when viewed from above, and shows a welded portion including a J-shaped 1 st joint portion and a plurality of subsequent joint portions following the 1 st joint portion formed in the flange portion, and fig. 6 (b) is a cross-sectional view of the c—c section shown in (a) above.
In fig. 6, regarding a preferred position for forming the welded portion, when a distance from a center line of the plate thicknesses of the steel plates 2 and 3 to a widthwise central portion of the joint portion 5 (4) formed on the flange portion is defined as a welded position X, it is preferable that the welded position X satisfies the following formula (5):
5t≤X≤8t (5)
wherein t: the thickness (mm) of the thickest steel sheet among the steel sheets constituting the welded portion.
For example, when the thickness t of the thickest steel sheet is 2mm, the welding position X is preferably in the range of 10 to 16 mm.
This is because if the welding position X is less than 5t, the weld metal portion may be easily broken at the time of the peel test, and the peel strength may be lowered. On the other hand, if the welding position X is greater than 8t, the moment applied to the 1 st joint 4 and the subsequent joint 5 in the peel test becomes excessive, and the peel strength is still lowered. More preferably, X is in the range of 6 t.ltoreq.X.ltoreq.7t. By forming the welded portion at the above-described position, the peel strength of the 2 lap welded joint portion, in which the total sheet thickness of the steel sheet is 2 to 5mm, can be made to be 3.0kN or more.
The formula (5) for the welding position X is not limited to the overlap laser welding joint in which 2 steel plates having an L-shaped cross section overlap each other as shown in fig. 6, and may be applied to an overlap laser welding joint obtained by laser beam welding of a frame component (steel plate 2) and a panel component (steel plate 3) having a substantially hat-shaped cross section as shown in fig. 1 and 4, for example, in which the base point (0 point) of the welding position X is the center of the thickness of the vertical wall portion 2a of the frame component having a substantially hat-shaped cross section.
Examples
The width of the high tensile steel sheet having the composition of A to J shown in Table 1, the sheet thickness of 1.2mm, 1.6mm or 2.0mm, and the tensile strength TS of 590 to 1180MPa was collected from: 100mm, length: a150 mm sample was bent into an L-shape with a long side of 120mm and a short side of 30mm, and an L-shaped steel plate was produced. Here, the long side of the L-shaped steel plate corresponds to the vertical wall 2a in fig. 1 (fig. 4), and the short side corresponds to the flange 2b in fig. 1 (fig. 4). Next, as shown in fig. 7, after the 2L-shaped steel plates 7 were stacked with the short sides facing each other, a laser beam was irradiated to the stacked portion in the atmosphere to form a welded portion including the 1 st joint portion 4 and the plurality of subsequent joint portions 5, and a T-shaped peel test piece 9 was prepared.
In the lap joint laser beam welding, a fiber laser having a beam diameter of 0.6mm phi was used as the laser beam, the focal position was set to be the upper surface of the overlapped steel plate (the surface of the upper steel plate 7 shown in fig. 7), and the gap G between 2 steel plates, the power of the irradiated laser beam, and the scanning speed were varied to change the length L of the J-shaped 1 st joint portion as shown in table 2 1 Length of subsequent jointDegree L 2 The shortest distance a between the 1 st joint and the adjacent subsequent joint and between the subsequent joints, the minimum thickness b of the molten metal portion of the joint, and the width w of the molten metal of the joint were variously changed as shown in table 2. At this time, the welding position X at which the welded portion is formed is set to 6.5 times (fixed) the thickest plate thickness t.
Further, as the 1 st joint, a length L is used instead of the J-shaped 1 st joint 1′ A T-shaped peel test piece 9 was prepared in the same manner as the long linear weld portion of the 1 st joint portion.
With respect to the T-shaped peel test piece produced in the above manner, whether or not cracks were generated at the welded portion, particularly at the welded terminal portion of the 1 st joint portion and the subsequent joint portion, was determined by visual inspection and a penetration test.
Next, a tensile test was performed at a speed of 10mm/min on the T-shaped peel test piece with the longitudinal direction of the long side of 2L-shaped steel plates as the tensile direction, and the peel strength (maximum load) was measured. In this example, the peel strength was determined to be "acceptable" when it was 3.0kN or more.
TABLE 1]
[ Table 2-1]
[ Table 2-2]
Tables 2 to 3]
Table 2 shows the results of determining the presence or absence of the weld crack and the results of measuring the peel strength.
From the results, it was found that no crack was generated at the welded terminal portion of the joint portion and the peel strength was 3.0kN or more in the test pieces (nos. 1, 8, 15, 22, 29, 36, 43, 50, 57 and 64) after lap laser beam welding under the conditions suitable for the present invention.
In contrast, in the test pieces of nos. 2, 9, 16, 23, 30, 37, 44, 51, 58 and 65, since the gap G between the welded portions was greater than 15% of the total thickness T of the steel sheets, cracks were generated at the welded terminal portions of the joined portions, and the peel strength was also lower than 3.0kN.
In the test pieces of nos. 3, 10, 17, 24, 31, 38, 45, 52, 59, and 66, the width w of the molten metal at the joint was greater than 1/2 of the minimum thickness b of the molten metal at the joint, and therefore, weld cracks were generated. On the other hand, in the test pieces of Nos. 4, 11, 18, 25, 32, 39, 46, 53, 60 and 67, the width w of the molten metal at the joint was less than 1/8 of the minimum thickness b of the molten metal at the joint, so that no weld crack was generated, but the peel strength was less than 3.0kN.
In addition, the test pieces No.5, 12, 19, 26, 33, 40, 47, 54, 61 and 68 were each formed by the length L of the 1 st joint 1 Shorter than 15.0mm, and thus a weld crack is generated.
In addition, for the test pieces of No.6, 13, 20, 27, 34, 41, 48, 55, 62 and 69, the length L of the subsequent joint portion 2 Shorter than 8.0mm, and thus a weld crack is generated.
In addition, in the test pieces of No.7, 14, 21, 28, 35, 42, 49, 56, 63 and 70, the distance a between the 1 st joint and the adjacent subsequent joint and between the subsequent joints is longer than L of the length of the subsequent joints 2 Long, therefore, weld cracks are generated, and the peel strength is also lower than 3.0kN.
Further, as a result of the test pieces obtained by lap welding 2 steel plates having different strength levels under the conditions satisfying the present invention, it was shown that, although the combination of the strength levels was 590MPa and 980MPa, no weld crack was generated and excellent peel strength was obtained for No.71 having a steel composition within the preferred range of the present invention, and also the peel strength was lower than 3.0kN for No.72 having a steel composition outside the preferred range of the present invention.
In addition, no.73 is a length L used as the 1 st joint 1′ The long test piece of the linear joint was found to have no weld crack and to have a peel strength equivalent to that of the J-shaped 1 st joint by lap laser beam welding under the conditions satisfying the present invention.
As described above, in the examples of the present invention in which lap laser beam welding was performed according to the present invention, good lap laser welding joints having the characteristics desired in the present invention were obtained, but in the comparative examples in which the conditions of the present invention were not satisfied, good lap laser welding joints were not obtained.
Industrial applicability
The technique of the present invention can realize high-speed and low-strain welding, and therefore can be applied to structural members for automobiles having flange portions.
Description of the reference numerals
1: overlap joint laser welding joint
2. 3: steel plate
2a: longitudinal wall portion
2b: flange part
4. 14: 1 st joint
4a, 14a: center portion of welding terminal portion of 1 st joint portion
5. 15: subsequent joint
5a, 15a: center portion of welding terminal portion of subsequent joint portion
6: welded part
7: l-shaped steel plate
7a: long side of L-shaped steel plate
7b: width of L-shaped steel plate
8: cracking of welded terminal portion of joint
9: peeling test piece
WH: welding head
LB: laser beam
D: direction of movement of the welding head
d: scanning direction of laser beam
L 1 、L 1′ : length of 1 st joint
L 2 : length of subsequent joint
a: shortest distance between adjacent joint parts
b: minimum thickness of molten metal of joint
w: width of molten metal of joint
G: gap between steel plates
S: welding start end of joint
E: welded terminal part of joint
Fa: stress applied to a welded terminal portion of a conventional joint
Fb: stress to which the initial welded terminal portion of the subsequent joint is subjected
Fc: stress applied to the welding terminal portion of the 1 st joint portion
0: datum point of welding position X
Claims (10)
1. An overlap laser welded joint having a welded portion formed by overlapping a plurality of steel plates, the overlap laser welded joint being characterized in that,
the total gap G between the steel plates constituting the welded portion is in the range of 0 to 15% of the total thickness T of the steel plates constituting the welded portion,
the welding part comprises a linear 1 st joint part and a linear subsequent joint part which is arranged in a column shape by the 1 st joint part,
the welding start end of the 1 st joint is opposite to the welding end of the adjacent subsequent joint, the welding start ends of the subsequent joints are opposite to the welding end, and,
The 1 st joint part has a J-shape formed by a linear joint part and an arc-shaped or round curve joint part connected with the welding terminal part side of the linear joint part,
further, the welded portion satisfies all of the following formulas (1) to (4):
15.0≤L 1 ≤30.0 (1)，
8.0≤L 2 ≤20.0 (2)，
1/8≤w/b≤1/2 (3)，
1/4≤a/(L 1 +L 2 ) More than or equal to 1/2 or more than or equal to 1/2 less than or equal to a/L 2 ≤1 (4)，
Wherein L is 1 The length (mm) of the 1 st joint,
L 2 for the length (mm) of the subsequent joint,
b is the minimum thickness (mm) of the molten metal of the joint,
w is the width (mm) of the molten metal of the joint,
a is the shortest distance (mm) between the joint portions.
2. The lap laser weld joint according to claim 1, wherein the 1 st joint portion includes only a linear joint portion, and satisfies the following formula (1') instead of the above formula (1):
30.0＜L 1′ ≤40.0(1′)，
wherein L is 1′ The length (mm) of the linear joint.
3. The lap laser weld joint of claim 1, wherein the composition of at least 1 of the steel sheets contains C:0.07 to 0.4 mass% of Si:0.2 to 3.5 mass percent of Mn:1.8 to 5.5 mass percent, P+S:0.03 mass% or less, al:0.08 mass% or less and N: less than 0.010 mass percent, and the balance of Fe and unavoidable impurities.
4. The lap laser weld joint of claim 2, wherein the composition of at least 1 of the steel sheets contains C:0.07 to 0.4 mass% of Si:0.2 to 3.5 mass percent of Mn:1.8 to 5.5 mass percent, P+S:0.03 mass% or less, al:0.08 mass% or less and N: less than 0.010 mass percent, and the balance of Fe and unavoidable impurities.
5. The lap laser welded joint according to claim 3, wherein the steel sheet contains, in addition to the composition of the components, at least 1 of the following groups a and B:
group a is from Ti:0.0005 to 0.01 mass% and Nb:0.005 to 0.050 mass% of 1 or 2 kinds selected from the group consisting of;
group B is a group consisting of Cr: less than 1.0 mass percent, mo:0.50 mass% or less and B:0.10 mass% or less of 1 or 2 or more selected from the group consisting of.
6. The lap laser welded joint of claim 4, wherein said steel sheet contains, in addition to said composition of components, at least 1 of the following groups a and B:
group a is from Ti:0.0005 to 0.01 mass% and Nb:0.005 to 0.050 mass% of 1 or 2 kinds selected from the group consisting of;
group B is a group consisting of Cr: less than 1.0 mass percent, mo:0.50 mass% or less and B:0.10 mass% or less of 1 or 2 or more selected from the group consisting of.
7. The lap laser welded joint according to any one of claims 1 to 6, wherein at least 1 of the steel sheets is a high-tensile steel sheet having a tensile strength of 980MPa or more.
8. A method for manufacturing a lap laser welded joint, characterized in that, when a plurality of steel plates are overlapped vertically and laser beams are intermittently irradiated to one side surface of the overlapped steel plates to form a welded part formed by arranging a linear 1 st joint and a linear subsequent joint following the 1 st joint in a row,
The total gap G between the steel plates constituting the welded part is set to be in the range of 0 to 15% of the total thickness T of the steel plates constituting the welded part,
by reversing the direction of movement of the welding head that irradiates the laser beam and the scanning direction of the laser beam, the welding start end portion of the 1 st joint portion and the welding end portion of the subsequent joint portion adjacent to the 1 st joint portion are made to face each other, and the welding start end portions of the subsequent joint portions are made to face each other and the welding end portions are made to face each other,
the 1 st joint part is formed in a J-shape by a linear joint part and an arc-shaped or round curve joint part connected with the welding terminal part side of the linear joint part,
further, at least 1 of the laser power, the focal point position, the welding speed, and the beam diameter is controlled so that the welded portion satisfies all of the following formulas (1) to (4):
15.0≤L 1 ≤30.0 (1)，
8.0≤L 2 ≤20.0 (2)，
1/8≤w/b≤1/2 (3)，
1/4≤a/(L 1 +L 2 ) More than or equal to 1/2 or more than or equal to 1/2 less than or equal to a/L 2 ≤1 (4)，
Wherein L is 1 The length (mm) of the 1 st joint,
L 2 for the length (mm) of the subsequent joint,
b is the minimum thickness (mm) of the molten metal of the joint,
w is the width (mm) of the molten metal of the joint,
a is the shortest distance (mm) between the joint portions.
9. The method of manufacturing a lap laser welded joint according to claim 8, wherein the 1 st joint portion is made to include only a linear joint portion, and at least 1 of laser power, focal position, welding speed, and beam diameter is controlled so as to satisfy the following formula (1') instead of the above formula (1):
30.0＜L 1′ ≤40.0(1′)，
Wherein L is 1′ The length (mm) of the linear joint.
10. A structural member for an automobile body having the lap laser welded joint according to any one of claims 1 to 7.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/JP2019/013632 WO2020194669A1 (en) | 2019-03-28 | 2019-03-28 | Lap laser welding joint, method for manufacturing same, and automobile chassis structure member |
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| Publication Number | Publication Date |
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| CN113573838A CN113573838A (en) | 2021-10-29 |
| CN113573838B true CN113573838B (en) | 2023-06-02 |
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| JP (1) | JP6583657B1 (en) |
| KR (1) | KR102603852B1 (en) |
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| CN113199146A (en) * | 2021-03-24 | 2021-08-03 | 中车青岛四方机车车辆股份有限公司 | Side wall welding method and device, side wall, vehicle body and rail vehicle |
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| WO2020194669A1 (en) | 2020-10-01 |
| JP6583657B1 (en) | 2019-10-02 |
| JPWO2020194669A1 (en) | 2021-04-30 |
| KR20210116648A (en) | 2021-09-27 |
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| CN113573838A (en) | 2021-10-29 |
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