WO2021200695A1 - Method for manufacturing rivet joint, rivet joint, and automotive part - Google Patents

Abstract

A method for manufacturing a rivet joint according to one embodiment of the present invention includes: passing the shaft of a steel rivet through the through-holes of a plurality of overlapping sheet members; sandwiching the rivet between a pair of electrodes in the axial direction of the rivet; applying pressure and energizing the rivet via the pair of electrodes to compress the tip of the shaft of the rivet; and cooling the rivet, and imparting a prescribed Vickers hardness to the center in the axial direction and the center in the radial direction of the shaft of the cooled rivet of 130 HV to less than 300 HV.

Description

How to manufacture rivet fittings, rivet fittings, and automobile parts

The present invention relates to a method for manufacturing a rivet joint, a rivet joint, and an automobile part.
The present application claims priority based on Japanese Patent Application No. 2020-060160 filed in Japan on March 30, 2020, the contents of which are incorporated herein by reference.

The application of high-strength steel sheets is recommended for the purpose of reducing the weight of automobiles and improving collision safety. However, the spot welded joint made of a high-strength steel plate has a problem that the cross tension strength (CTS) decreases when the tensile strength of the base steel plate exceeds 780 MPa.

If the strength of the spot welded joint is reduced, the welded part may break when the member is deformed due to a collision under extremely severe conditions. Therefore, even if the strength of the steel sheet is improved, the load capacity of the member as a whole may be insufficient. Therefore, there is a demand for a joining method for improving the strength of a joint made of high-strength steel plate.

The present inventors focused on rivet joining as one of the means for improving the cross tensile strength of the joint. In rivet joining, a through hole is formed in a steel sheet, a rivet having a head and a shaft portion is passed through the through hole, the tip of the shaft portion of the rivet is plastically deformed at room temperature, and the head and plastic deformation of the rivet are formed. This is a joining method in which a steel plate is crimped depending on the part. The present inventors have found that the cross tensile strength of a joint (rivet joint) obtained by rivet-joining a high-strength steel plate is significantly higher than that of a spot-welded joint. According to the rivet joining in which the steel plates are mechanically joined, the joint portion is not embrittled, so that it is considered that the CTS of the joined joint made of the high-strength steel plate can be held high.

On the other hand, according to the experiments by the present inventors, when the joint structure was manufactured using the steel rivet, the plate materials were in a state where they could rotate with each other around the rivet. It was considered that this was because the fastening force (axial force) between the head of the rivet and the deformed portion was insufficient. If rivet joining is performed at two or more locations, the plate material will not rotate. However, the present inventors have considered that if the axial force at the joint is insufficient, rattling may occur at the joint and the rigidity of the entire joint may decrease.

By the way, regarding the manufacturing method of the rivet joint, for example, the following technology is disclosed.

Patent Document 1 describes a method in which two or more constituent members are connected to each other by a fastener. Each constituent member is provided with a hole, and the constituent member has the holes overlapped with each other to form the fastener. The fasteners are arranged to be received in the holes, and the fasteners arranged in the holes are mechanically pressurized and heated to deform the fasteners so that the components are coupled to each other. In the above method, the fasteners are essentially heated only during the deformation stage of the fasteners to minimize heat transfer from the fasteners to the components to be coupled so that the fasteners are coupled. Disclosed is a method characterized in that both and the constituent members are made of the same or similar alloy contained in the material of the intermetallic alloy group.

In Patent Document 2, in a method in which a head portion and a tip portion of a rivet are sandwiched between a pair of electrodes, energized heating is performed, and the rivet is pressed and riveted, the back surface of the head surface of the rivet and the material to be rivet are separated. A spacer having a small cross-sectional area and a height such that the shaft portion of the rivet is sufficiently closely filled in the rivet hole, or after that, the back surface of the head and the rivet material come into contact with each other is provided. A riveting method characterized by riveting is disclosed.

Patent Document 3 describes in a method of fastening a rivet in which a rivet is sandwiched between electrodes and heated by resistance heat through electricity to perform pressure molding. A method of fastening a rivet is disclosed, which comprises heating the rivet.

In Patent Document 4, at least a part of a rivet hole formed through at least two members to be joined is formed as a tapered hole, the rivet is fitted into the rivet hole, and the shaft portion of the rivet is subjected to energization caulking. Is bulged and deformed into a shape along the tapered hole, and the shaft portion of the rivet and the tapered hole are brought into close contact with each other by heat shrinkage of the rivet after energization caulking, and the member is joined by energization caulking of the rivet. The binding method is disclosed. Here, the rivet temperature at the time of energization caulking is said to be 700 to 900 ° C.

Patent Document 5 is a rivet tightening method in which a plurality of workpieces are joined by using rivets, in which the rivets inserted through the plurality of workpieces are sandwiched between a pair of electrodes and energized in a pressurized state, and the energization is performed. A rivet tightening method characterized in that the rivet is softened by the resistance heat generation of the rivet itself and the end portion of the rivet is crimped is disclosed.

However, in any of Patent Documents 1 to 5, the cross tensile strength and axial force of the rivet joint have not been examined at all, and the configuration for improving these has not been sufficiently examined.

Japan Special Table 2006-507128 Japanese Patent Application Laid-Open No. 55-27456 Japanese Patent Application Laid-Open No. 53-78486 Japanese Patent Application Laid-Open No. 61-165247 Japanese Patent Application Laid-Open No. 10-205510

The present invention provides a method for manufacturing a rivet joint capable of manufacturing a joint having a high cross tensile strength (CTS) and an axial force, and a rivet joint and an automobile part having a joint having a high cross tensile strength and an axial force. The task is to do.

The gist of the present invention is as follows.
(1) The method for manufacturing a rivet joint according to one aspect of the present invention is to pass a shaft portion of a steel rivet through through holes of a plurality of stacked plate materials, and pair the rivets in the axial direction of the rivet. To sandwich the rivet between the electrodes, pressurize and energize the rivet with the pair of the electrodes to crush the tip of the shaft portion of the rivet, and cool the rivet to cool the rivet. The rivets hardness of the axial center and the radial center of the shaft portion is set to 130 HV or more and less than 300 HV.
(2) The method for manufacturing a rivet joint according to (1) above further includes joining a plurality of the plate members by one or more welding methods selected from the group consisting of spot welding, laser welding, and arc welding. You may.
(3) In the method for manufacturing a rivet joint according to the above (1) or (2), an adhesive is applied between a plurality of the plate materials at least around the through hole, and then the plurality of the plate materials are laminated. You may have more of that.
(4) In the method for manufacturing a rivet joint according to any one of (1) to (3) above, the difference in diameter of the through holes in the plurality of adjacent plate materials is within the range of 0.3 mm to 3 mm. It may be.
(5) In the method for manufacturing a rivet joint according to any one of (1) to (4) above, the maximum temperature of the shaft portion of the rivet may be set to exceed 900 ° C. by the energization.
(6) In the method for manufacturing a rivet joint according to any one of (1) to (5) above, the carbon equivalent Ceq calculated by the formula 1 of the rivet is 0.025 to 0.215% by mass. May be good.
Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 <Equation 1>
Here, the mass% of the component contained in the rivet is substituted for the element symbol included in the formula 1, and zero is substituted for the element not contained.
(7) The rivet joint according to another aspect of the present invention includes a plurality of stacked plate materials each having a through hole, and a rivet in which a shaft portion penetrates the through hole and crimps the plurality of plate materials. The Vickers hardness of the axial center and the radial center of the shaft portion of the rivet is 130 HV or more and less than 300 HV.
(8) The rivet joint according to (7) above may further have one or more welds selected from the group consisting of spot welds, laser welds, and arc welds.
(9) The rivet joint according to (7) or (8) above may further have an adhesive arranged between the plurality of plate materials, at least around the through hole.
(10) In the rivet joint according to any one of (7) to (9) above, the difference in diameter of the through holes in the plurality of adjacent plate materials is within the range of 0.3 mm to 3 mm. May be good.
(11) In the rivet joint according to any one of (7) to (10) above, even if the carbon equivalent Ceq calculated by the formula 1 of the rivet is 0.025 to 0.215% by mass. good.
Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14 <Equation 1>
Here, the mass% of the component contained in the rivet is substituted for the element symbol included in the formula 1, and zero is substituted for the element not contained.
(12) The automobile part according to another aspect of the present invention includes the rivet joint according to any one of (7) to (11) above.

According to the present invention, a method for manufacturing a rivet joint capable of manufacturing a joint having a high cross tensile strength (CTS) and an axial force, and a rivet joint and an automobile part having a joint having a high cross tensile strength and an axial force. Can be provided.

It is a figure which shows the manufacturing method of the rivet joint which concerns on this embodiment. It is a figure which shows the manufacturing method of the rivet joint which concerns on this embodiment. It is a figure which shows the manufacturing method of the rivet joint which concerns on this embodiment. It is a figure which shows the manufacturing method of the rivet joint which concerns on this embodiment. It is sectional drawing which shows an example of the rivet joint which concerns on this embodiment. It is sectional drawing which shows an example of the rivet joint which the size of a through hole is different for each plate material. It is sectional drawing which shows the rivet joint which further has an adhesive arranged around the through hole. It is a perspective view of the bumper which used the rivet joint and other joining means together. It is sectional drawing which shows an example of the means for preventing the interference between a rivet and other parts. It is sectional drawing which shows an example of the means for preventing the interference between a rivet and other parts. It is sectional drawing which shows an example of the means for preventing the interference between a rivet and other parts. It is sectional drawing of the B pillar which is an example of the automobile parts which concerns on this embodiment. It is sectional drawing of the bumper which is an example of the automobile parts which concerns on this embodiment.

The present inventors have further studied a method for producing a joint having high cross tensile strength (CTS) and axial force. As a result, it was found that the axial force can be increased by lowering the hardness of the steel rivet.

The reason why the axial force is increased by lowering the hardness of the rivet is not clear, but the present inventors presume that the martensite generated in the microstructure of the rivet has an effect.

The rivet joining of the plate material is performed by heating the rivet, deforming the tip of the rivet, and then cooling the rivet. If the heating temperature of the rivet is sufficiently high and the cooling rate of the rivet is sufficiently high, the rivet is hardened when the rivet is cooled, and the hardness of the rivet is increased. The increase in hardness is thought to be caused by martensitic transformation.

Here, the martensitic transformation of steel has the function of expanding the volume of steel. When martensitic transformation occurs in the rivet after deforming the tip of the rivet, the length of the shaft of the rivet increases, the distance between the head of the rivet and the deformed part of the tip of the rivet increases, and the axial force is impaired. The present inventors presume that this is the case.

The method for manufacturing a rivet joint according to one aspect of the present invention (hereinafter, may be abbreviated as a rivet joining method) obtained based on the above findings is a steel rivet as shown in FIGS. 1A to 1D. The shaft portion 121 of the 12 is passed through the through holes 111 of the plurality of stacked plate members 11, the rivet 12 is sandwiched between the pair of electrodes A in the axial direction of the rivet 12, and the rivet 12 is formed by the pair of electrodes A. Pressurize and energize to crush the tip of the shaft portion 121 of the rivet 12, and cool the rivet 12 at the axial center and radial center of the shaft portion 121 of the rivet 12 after cooling. The rivets hardness is set to 130 HV or more and less than 300 HV. In other words, the method for manufacturing the rivet 12 joint according to one aspect of the present invention includes a step of inserting the steel rivet 12 into the through holes 111 of the plurality of stacked plate members 11 and the rivet 12 of the pair of electrodes A. It includes a step of sandwiching the rivet 12, a step of pressurizing and energizing the rivet 12 via a pair of electrodes A to cause deformation of the tip of the shaft portion 121 of the rivet 12, and a step of cooling the rivet 12. The average Vickers hardness of the shaft portion 121 of the rivet 12 after cooling is set to 130 HV or more and less than 300 HV. Hereinafter, this manufacturing method will be described in detail.

First, the shaft portion 121 of the rivet 12 is passed through the through holes 111 of the plurality of stacked plate materials, and sandwiched between the pair of electrodes A in the axial direction of the rivet. The plate material 11 serves as a base material for the rivet joint 1. The rivet 12 usually has a shaft portion 121 and a head portion 122, and the tip of the shaft portion 121 is plastically deformed by riveting to form a deformed portion 123. The head portion 122 has a function of sandwiching (caulking) the plate member 11 together with the deformed portion 123. Even if the rivet 12 having no head portion 122 is passed through the through hole 111 and both ends of the shaft portion 121 are plastically deformed, the plate material 11 can be crimped. In this case, one of the two deformed portions 123 can be regarded as the head 122.

The configuration of the plate material 11 is not particularly limited. For example, when the plate material 11 is a steel plate, particularly a high-strength steel plate (for example, a steel plate having a tensile strength TS of about 590 MPa or more), the strength of the rivet joint 1 can be improved, which is preferable. Further, since the rivet joining method according to the present embodiment does not cause embrittlement causing a decrease in CTS in the high-strength steel sheet, the rivet joint 1 having a high CTS when applied to joining the high-strength steel sheet is provided. Can be done. When the tensile strength of the high-strength steel sheet is 980 MPa or more, the superiority of the rivet joint according to the present embodiment becomes more remarkable with respect to CTS over spot welding. More preferably, the tensile strength is 1180 MPa class or more, and more preferably 1500 MPa or more. The upper limit of the tensile strength is not particularly limited, but may be, for example, 2700 MPa or less. Further, the plate material 11 may be an aluminum plate, a CFRP plate, a titanium plate, or the like. Unlike the joining by welding, in the rivet joining according to the present embodiment, the material of the plate material 11 may be different. For example, a combination of a steel plate and an aluminum plate, or a combination of a steel plate and a CFRP plate may be used. The arrangement of the plate materials is not particularly specified, but in the case of plate materials of different materials, a plate material having a low melting point may be arranged on the head 122 side of the rivet 12. Various surface treatments may be applied to the plate material 11. For example, the plate material 11 is alloyed with the base metal by GA plating, GI plating, EG plating, Zn-Mg plating, Zn-Al plating, Zn-Ni plating, Zn-Al-Mg plating, Al plating, painting, and hot stamping. It may have a modified Zn-based plating (Zn—Fe, Zn—Ni—Fe), Al-based plating (Al—Fe—Si), and the like.

The plate thickness of the plate material 11 is not particularly limited, and may be, for example, 0.5 mm to 3.6 mm. The thickness of the plate material 11 may be different. The number of plate materials 11 is also not particularly limited. In the description of the rivet joining according to the present embodiment, it is assumed that the number of plate members 11 is two, but it is not hindered that the number of plate members is three or more. As a suitable combination, for example, a plate material having a plate thickness of about 1.6 mm and a plate material having a plate thickness of about 2.3 mm are laminated, or a plate material having a plate thickness of 0.75 mm, a plate material having a thickness of 1.8 mm, and a plate material having a thickness of 1.2 mm. Three layers with a plate material can be mentioned. As a range of suitable combinations of plate materials, for example, two plates having a plate thickness of about 0.6 mm to 2.9 mm and a plate material having a plate thickness of 0.6 mm to 2.9 mm are stacked, or a plate thickness is 0.6 mm to 1.6 mm. Examples thereof include three layers of a plate material, a plate material of 0.6 mm to 2.9 mm, and a plate material of 0.6 mm to 2.9 mm. The plate material may be a molded product obtained by cold or hot press molding, cold roll molding, hydrofoam molding, or hot blow molding. Further, the plate material may be formed in a pipe shape.

The shape of the through hole 111 can be, for example, a circular shape. On the other hand, the shape of the through hole 111 may be a polygon such as a quadrangle, a pentagon, a hexagon, or an octagon. The corners of these polygons may have curvature. Further, the shape of the through hole 111 may be an ellipse or a shape having a convex portion or a concave portion in a part of the circle. By making the through hole 111 into a shape other than the circular shape, it is possible to prevent the plate material joined by rivets from rotating around the rivet of the through hole and to reduce the rattling of the joint portion. More desirable.

The through hole 111 for passing the rivet 12 can be formed by any means such as laser cutting, punching using a die, and drilling using a drill. When the plate material 11 is a hot stamped steel plate, it is desirable to form the through hole 111 by hot stamping of a die or laser cutting.

The size of the through hole 111 may be constant in the depth direction of the plate material 11. On the other hand, a stepped shape or a tapered shape in which the size of the through hole 111 differs in the depth direction may be applied to the through hole 111. Further, the central axes of the through holes 111 between the plurality of materials to be joined do not have to be the same.

The diameters of the through holes 111 (in the case where the through holes 111 are not circular, the equivalent circle diameters) in the plurality of plate materials 11 may be the same as shown in FIG. 2, while they are different as shown in FIG. You may be doing it. In normal rivet joining, it is considered preferable to make the diameter of the through hole 111 constant from the viewpoint of reducing the gap between the joints. On the other hand, in the method for manufacturing a rivet joint according to the present embodiment, since the rivet 12 is heated and softened, the gap can be sufficiently reduced even if the diameter of the through hole 111 is not the same for each plate material 11. As a result, the shaft diameter in the joined state can be increased, which contributes to the improvement of TSS. Further, by providing a difference in the size of the through hole 111, a stress relaxation effect and an improvement in the efficiency of the work of passing the rivet 12 can be expected. The degree of difference in diameter of the through hole 111 is not particularly limited, but for example, the difference in diameter of the through hole 111 in the adjacent plate member 11 is preferably in the range of 0.3 mm to 3 mm. From the viewpoint of facilitating the work of passing the rivet 12, it is preferable to increase the diameter of the through hole of the plate material on the side opposite to the side that becomes the entrance of the rivet 12 (the side where the rivet head is located). As a result, it is possible to prevent the tip of the rivet 12 from being clogged in the through hole 111.

Further, it is desirable that the minimum value of the diameter of the through hole 111 is 0.1 mm to 5 mm larger than the maximum value of the diameter of the shaft portion of the rivet passing through the through hole 111. If the difference between the two is smaller than 0.1 mm, it becomes difficult to pass the rivet. On the other hand, if the difference between the two is larger than 5 mm, it becomes difficult to sufficiently fill the gap of the through hole 111. More preferably, the difference between the minimum value of the diameter of the through hole 111 and the maximum value of the diameter of the shaft portion of the rivet passing through the through hole 111 is in the range of 0.3 mm to 3 mm, and optimally 0.3 mm to 3 mm. The range is 1.5 mm. Further, the deviation of the central axis of the holes 111 between the plurality of materials to be joined is preferably 1.5 mm or less, and more preferably 0.75 mm or less.

As will be described later, the rivet 12 needs to be configured so that the hardness of the axial center and the radial center portion of the shaft portion 121 is 130 HV or more and less than 300 HV after the completion of the rivet joint. However, as long as this requirement is satisfied, the aspect of the rivet 12 is not particularly limited.

For example, the shape of the rivet 12 is not particularly limited, and can be appropriately selected depending on the thickness and mechanical properties of the plate material 11 as the base material, the size of the through hole 111, and the like. For example, the diameter of the shaft portion 121 of the rivet 12 (when the cross section of the shaft portion 121 is not circular, the diameter corresponding to the circle of the shaft portion 121) may be 3 mm or more from the viewpoint of ensuring the joint strength. Further, if the diameter of the shaft portion 121 is too large, the current density decreases and it becomes difficult to form the deformed portion. Therefore, the upper limit of the diameter of the shaft portion 121 may be 12 mm or less. The length of the shaft portion 121 (the value obtained by subtracting the thickness of the head 122 from the length of the rivet 12) needs to be larger than the total plate thickness of the plate members 11, and in the case of a rivet having a head, it is preferable. , Within the following range.
Total plate thickness + shaft diameter x 0.3 ≤ shaft length ≤ total plate thickness + shaft diameter x 2.0

By making the length of the shaft portion 121 of the rivet 12 larger than the total plate thickness of the plate material 11 + the diameter of the shaft portion 121 × 0.3, the crimped portion (deformed portion 123) after the tip of the shaft portion 121 is deformed. ) Can be secured and the joint strength can be further increased. By setting the length of the shaft portion 121 to the total plate thickness of the plate material 11 + the diameter of the shaft portion 121 × 2.0 or less, the manufacturing efficiency can be improved.

Further, in the case of a rivet without a head, the length of the shaft portion 121 (that is, the length of the rivet 12) is preferably within the following range.
Total plate thickness + shaft diameter x 0.6 ≤ shaft length ≤ total plate thickness + shaft diameter x 4.0
When joining using rivets without a head, it is necessary to deform both ends of the rivet. Therefore, it is preferable that the length of the shaft portion 121 of the rivet without the head is larger than that of the rivet with the head.

The diameter of the shaft portion 121 may be constant. On the other hand, the rivet 12 may have a shape (so-called taper shape) in which the diameter of the shaft portion 121 decreases toward the tip of the shaft portion 121. The tapered portion may be formed over the entire shaft portion 121, or may be formed only near the tip of the shaft portion 121. The tapered rivet 12 is preferable because it can easily pass through the through hole 111.

The shape of the head 122 of the rivet 12 may be a general flange shape. For example, the shape of the head 122 can be hemispherical (so-called round head), disk-shaped (so-called flat head), or a shape with a flat surface side and a conical root (so-called countersunk head). The shape of the head 122 in a plan view can be a polygon such as a circle, a quadrangle, or a hexagon. A recess for positioning may be provided at the center of the head 122 on the electrode side. Further, the seat portion (the surface in contact with the material to be joined) of the head portion 122 may be provided with a recess (so-called seat portion undercut) surrounding the shaft portion 121. Such recesses impart elasticity to the head 122, thereby further increasing the caulking force of the rivet 12. Further, one or more protrusions may be provided on the seat portion (the surface in contact with the material to be joined) of the head 122. Such a protrusion further increases the caulking force of the rivet 12 by sinking into the material to be joined during riveting or forming the material to be joined and the joint. Examples of the shape of the protrusion include a circular shape, a polygonal shape, and a ring shape surrounding the shaft portion.

The rivet 12 crimps the plate material 11 using its head 122. Therefore, it is preferable that the diameter of the head 122 is 1.5 mm or more larger than the diameter of the through hole 111. The thickness of the head 122 is preferably 0.8 mm to 5 mm. If the thickness of the head 122 is less than 0.8 mm, sufficient joint strength cannot be obtained. On the other hand, if the thickness of the head 122 is more than 5 mm, the head is too large and interference with other parts is likely to occur. In the case of the rivet 12 without the head 122, the diameter of the deformed rivet end (that is, the deformed portion 123) after the rivet joining is preferably 1.5 mm or more larger than the diameter of the through hole 111. The thickness of the deformed rivet end is preferably 0.8 mm to 5 mm.

The rivet is manufactured, for example, by cutting a coil wire and cutting it or cold forging it. From the viewpoint of productivity, the rivet processing method is preferably cold forging. The rivet may be used as it is processed, or may be heat-treated after processing and then used for joining.

The rivet 12 may be one that has not been surface-treated. On the other hand, if the joint structure 1 is required to have corrosion resistance, the rivet 12 may be surface-treated. For example, the rivet 12 may be subjected to zinc-based plating, aluminum-based plating, chrome-based plating, nickel-based plating, chromate treatment, or the like.

Next, the pair of electrodes A pressurizes and energizes the rivet 12 to crush the tip of the shaft portion 121 of the rivet 12 (so-called riveting). The energization of the rivet 12 causes the rivet 12 to generate heat of resistance and softens the rivet 12, thereby facilitating the deformation of the tip.

In the rivet joining according to the present embodiment, it is preferable to pressurize the rivet 12 using the electrode A and then energize the rivet 12. When energization is started in a pressurized state, the shaft portion 121 is softened and the tip of the shaft portion 121 is deformed. In this case, the joining is performed by sandwiching the rivet 12 between the electrodes A, pressurizing the rivet 12, energizing the rivet 12, and cooling the rivet 12. However, the timing of the start of heating to the rivet 12 and the timing of the start of pressurization of the rivet 12 are not limited to the above-mentioned preferable examples.

The rivet 12 is inserted into the through hole 111 by, for example, a rivet supply device after the plate members 11 are overlapped with each other. Then, for example, using a spot welder, the rivet is energized and heated while pressurizing the rivet. The pressurizing condition and energizing condition (current value, voltage value, energizing time, etc.) of the rivet 12 are not particularly limited, and can be appropriately selected depending on the shape and material of the rivet 12. Therefore, a person skilled in the art can examine the optimum pressurizing and energizing conditions according to the shape and material of the rivet 12 by performing the pressurizing and energizing the rivet 12 under various conditions.

As the pressing force and energizing conditions of the rivet 12, for example, the following can be exemplified. In the table below, the description of the voltage value is omitted. This is because the voltage value is determined according to the rivet 12 and the current value. When the diameter of the shaft portion 121 of the rivet 12 is increased, one or both of the current value and the energization time may be increased to increase the amount of heat input.
-Rivet shaft diameter: 4 mm to 10 mm
-Rivet shaft length: 5 mm to 12 mm
・ Current value: 4kA to 16kA
-Pressure: 250 kgf-600 kgf
・ Energization time: 0.2 to 1.0 seconds ・ Holding time: 0.1 to 1.0 seconds

Pressurization and energization of the rivet 12 is performed using a pair of electrodes A. The configuration of the pair of electrodes A is not particularly limited. For example, since the electrode for spot welding can be pressurized and energized, the rivet joint according to the present embodiment may be performed using this. The shape of the electrode A can be appropriately selected according to the shape of the rivet 12. For example, the electrode A may be a flat type electrode, a single R type, a CF type, a DR type, or the like. Examples of the material of the electrode A include chrome copper, alumina-dispersed copper, and chrome zirconium copper having excellent conductivity.

Examples of power sources for welding machines include single-phase AC, DC inverters, AC inverters, and the like. Examples of the type of gun include stationary type, C type, X type and the like. The pressing force applied to the rivet by the electrode A is, for example, 150 kgf to 1000 kgf. The pressing force is preferably 250 kgf to 600 kgf. The set value of the pressing force may be a constant value, but the pressing force may be changed as needed. The pressure direction of the rivet by the electrode is preferably an angle of 10 ° or less with respect to the direction in which the axis of the rivet extends, from the viewpoint of obtaining a good joint. More preferably, the angle formed by the pressurizing direction of the rivet and the axial direction of the rivet is 4 ° or less. Further, the pressing force may be changed during the holding time after the end of energization. The energizing time is, for example, 0.15 seconds to 2 seconds. The energizing time is preferably 0.2 seconds to 1 second. The number of times of energization may be one (so-called single energization), but if necessary, two-stage energization, three-stage or more multi-stage energization, or tempering temper energization by adjusting the current may be performed. Further, pulse energization, an upslope that gradually increases the current, and a downslope that gradually decreases the current may be energized.

The heating conditions for energization heating are not particularly limited, but for example, the maximum temperature reached at the shaft of the rivet may be over 900 ° C. By setting the maximum temperature of the shaft portion of the rivet to more than 900 ° C., the softening of the rivet can be promoted and the gap between the rivet 12 and the through hole 111 of the plate material 11 can be reduced. As a result, the joint strength is further improved. The upper limit of the maximum temperature reached at the shaft of the rivet is not specified. For example, melting may occur in a part of the rivet.

The softened rivet 12 is pressurized, the tip of the shaft portion 121 thereof is deformed, and then the rivet 12 is cooled. As a result, the plurality of plate members 11 are crimped and joined by the rivets 12. Specifically, the plurality of plate members 11 are crimped by the head 122 of the rivet 12 and the crushed tip (that is, the deformed portion 123) of the shaft portion 121 of the rivet 12.

In the method for manufacturing a rivet joint according to the present embodiment, the Vickers hardness of the shaft portion 121 of the rivet 12 after cooling at the center in the axial direction and the center in the radial direction needs to be 130 HV or more and less than 300 HV. Hereinafter, "the Vickers hardness of the shaft portion 121 at the center in the axial direction and the center in the radial direction" is simply referred to as the Vickers hardness of the shaft portion 121.
According to the experiments by the present inventors, the cross tensile strength (CTS) of the joint structure 1 can be ensured by setting the Vickers hardness of the shaft portion 121 of the rivet 12 to 130 HV or more. On the other hand, by setting the Vickers hardness of the shaft portion 121 of the rivet 12 to less than 300 HV, the axial force of the rivet 12 can be secured. The reason why there is a correlation between the hardness of the shaft portion 121 of the rivet 12 and the axial force of the rivet 12 is not clear at this time, but the present inventors have a function of improving the hardness of the shaft portion 121 of the rivet 12. It is presumed that the martensite having the above increases the length of the shaft portion 121 of the rivet 12 and decreases the axial force of the rivet 12. In order to secure both the cross tensile strength and the axial force, the Vickers hardness of the shaft portion 121 of the rivet 12 needs to be within the range of 130 HV or more and less than 300 HV. The Vickers hardness of the shaft portion 121 of the rivet 12 may be 150 HV or more, 180 HV or more, or 200 HV or more. The Vickers hardness of the shaft portion 121 of the rivet 12 may be 280 HV or less, 250 HV or less, or 220 HV or less.

The Vickers hardness of the shaft portion 121 of the rivet 12 at the axial center and the radial center is measured by the following procedure. The rivet 12 is cut along the central axis of the rivet 12 and the cross section is appropriately prepared. Next, the surface where the head portion 122 of the rivet 12 (in the middle of the two deformed portions when a rivet without a head is used) and the plate member 11 are in contact with each other at the center of the shaft portion 121 of the rivet 12 in the longitudinal direction. And, the Vickers hardness is measured at three places (a place in the middle of the surface where the deformed part 123 of the rivet 12 and the plate material 11 come into contact with each other). If a shrinkage nest is formed inside the rivet 12, the Vickers hardness is measured at a place where there is no shrinkage nest (a position 0.2 mm or more away from the shrinkage nest). The load in the hardness measurement is 0.5 kg. The average value of the measured hardness values is the Vickers hardness of the shaft portion 121 of the rivet 12 at the center in the axial direction and the center in the radial direction.

The method for keeping the Vickers hardness of the shaft portion 121 of the rivet 12 within the above range is not particularly limited. Factors that affect the hardness of the steel rivet 12 are, for example, carbon equivalent Ceq, heat treatment conditions, and the like. The Vickers hardness of the shaft portion 121 of the rivet 12 may be controlled by appropriately combining these elements.

For example, the carbon equivalent Ceq of the rivet 12 may be 0.025 to 0.215% by mass. Ceq is a value obtained by the following formula 1.
Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
<Equation 1>
Here, the mass% of the component contained in the rivet is substituted for the element symbol included in the formula 1, and zero is substituted for the element not contained. Ceq is a hardenability index of steel, and the larger it is, the greater the hardness after quenching. By setting Ceq in the range of 0.025 to 0.215% by mass, it becomes easy to set the average Vickers hardness of the shaft portion of the rivet after cooling to 130 HV or more and less than 300 HV.

Further, the higher the cooling rate of the rivet 12, the greater the Vickers hardness of the shaft portion 121 of the rivet 12. Therefore, if the Ceq of the rivet 12 and the cooling rate are appropriately controlled, the Vickers hardness of the shaft portion 121 of the rivet 12 after cooling can be set to 130 HV or more and less than 300 HV. The cooling method of the rivet 12 is not particularly limited. When the Ceq of the rivet 12 is high, the rivet 12 may be naturally cooled by leaving the rivet joint 1 in the atmosphere after the energization is completed. There is a slight time lag between the end of energization of the rivet 12 and the release of the rivet 12 from the electrode A, and heat transfer from the rivet 12 to the electrode A often occurs during this time. Further, when the Ceq of the rivet 12 is low, the rivet 12 may be accelerated and cooled by bringing the electrode A through which the refrigerant is circulated inside into contact with the rivet 12. Accelerated cooling may be performed using a holding time, which is the time from when the energization of the rivet 12 is completed until the rivet 12 is released from the electrode A. From the viewpoint of improving productivity, the holding time is preferably 3 seconds or less. The holding time is more preferably 0.01 seconds or more and 1.0 seconds or less. The holding time is optimally 0.1 seconds or more and 0.8 seconds or less.

Further, as described above, the temper energization may be performed on the rivet 12. As a result, the rivet 12 can be softened. Further, after cooling the rivet 12, additional heat treatment may be performed. For example, the joint structure 1 may be tempered in a furnace. That is, since the rivet 12 is heated at the time of riveting and subsequently cooled, it is preferable to control the hardness of the shaft portion 121 of the rivet 12 by using this, but other heat treatment is performed. May be good.

In the method for manufacturing a rivet joint according to the present embodiment, it is not hindered to use other joining means together. By combining two or more different types of joining means, the joining strength of the rivet joint can be further increased.

For example, the rivet welding method according to the present embodiment may be one or more welding methods selected from the group consisting of spot welding, laser welding, and arc welding such as MAG welding, MIG welding, CO _{2 welding, and plasma welding.} It may further have a step of joining a plurality of plate members 11. Welding may be performed before or after riveting. From the viewpoint of ensuring the assembly accuracy of the parts, it is desirable to perform rivet joining after welding because the plurality of plate members 11 are fixed at the time of welding, so that the variation in the assembly accuracy of the parts to be joined becomes small. In the case of spot welding, it is more desirable to perform rivet welding after spot welding, or to perform temporary fixing by spot welding to perform rivet welding, and then to perform additional striking by spot welding.

Further, the rivet joining method according to the present embodiment may further include a step of applying the adhesive 13 between the plurality of plate materials 11 at least around the through holes 111, and then stacking the plurality of plate materials 11. .. As a result, as shown in FIG. 4, the plate material 11 is adhered. The adhesive 13 needs to be applied before the plurality of plate materials 11 are stacked and the rivet 12 is passed through the plate material 11. In the case of a thermosetting adhesive, the adhesive may be cured by heating in a baking step on an electrodeposition coating line after riveting. In the case of a reaction-curing adhesive, the adhesive is cured by a lapse of time after the rivet bonding. In spot welding of the plate material 11, it may be necessary to separate the application portion of the adhesive 13 from the spot welded portion in order to prevent explosion. However, the rivet joining method according to the present embodiment has an advantage that the application location of the adhesive 13 is not limited because the explosion does not occur. By using the rivet 12 and the adhesive 13 together, there is an advantage that the rigidity of the joint can be further improved. Further, by using the rivet 12 and the adhesive 13 in combination, it is possible to prevent contact corrosion of the overlapping surfaces in joining dissimilar metals or joining a metal and CFRP. In addition to the adhesive 13, a sealer may be applied between the plate materials 11. The sealer enhances the water resistance and corrosion resistance of the rivet joint 1. Further, as the adhesive layer, a resin adhesive tape such as ionomer may be used. Further, the sealer may be applied so as to cover the rivet head. This makes it possible to prevent water from entering through the gap between the rivet head and the steel plate. Further, in the case of joining dissimilar metals or joining a metal and CFRP, at least one metal plate may be subjected to chemical conversion treatment and coating before rivet joining. As a result, contact corrosion between dissimilar materials can be further suppressed and corrosion resistance can be improved.

FIG. 5 shows an example (bumper) of the rivet joint 1 in which the rivet 12 and other joining means are used in combination. As shown in FIG. 5, the rivet joint 1 (black circle portion in FIG. 5) according to the present embodiment is applied to a portion where the stress applied at the time of collision is expected to be high, and another joining means is applied at other portions. (For example, a spot welded portion 2 formed by inexpensive spot welding) (white circle portion in FIG. 5) may be adopted.

In the joint structure 1 according to the present embodiment, as shown in FIG. 6, in a cross-sectional view parallel to the axis of the shaft portion 121 of the rivet 12, the top surface of the head portion 122 and / or the deformed portion 123 is the shaft portion 121. The shaft portion 121 may be located closer to the shaft portion 121 than a position 0.6 mm away from the surface 112 of the plate member 11 in the vicinity of the rivet 12 in the direction along the axis of the shaft portion 121 toward the side away from the shaft portion 121. Here, the surface 112 (outer surface) of the plate material 11 means a surface of the plate material 11 that is not in contact with other plate materials. As a result, the head 122 and / or the deformed portion 123 is suppressed from protruding from the plate material 11 (or the height of the protruding portion is suppressed within 0.6 mm), and the head 122 and / or the deformed portion 123 and , Interference with other parts can be suppressed.
In the examples of FIGS. 6 and 8, the top surface of the deformed portion 123 of the rivet 12 is closer to the shaft portion 121 than the surface 112 (outer surface) of the plate member 11 in the vicinity of the rivet 12. In the example of FIG. 7, the top surfaces of both the head portion 122 and the deformed portion 123 of the rivet 12 have a shaft portion 121 rather than the surface 112 (outer surface) of the plate material 11 for each of the plate materials 11 in the vicinity of the rivet 12. On the side. In FIGS. 6 to 8, the top surface of the head 122 and / or the deformed portion 123 is closer to the shaft portion 121 than the surface 112 (outer surface) of the plate material in the vicinity of the rivet 12, but the head 122 and / or The top surface of the deformed portion 123 may protrude from the outer surface by a maximum of 0.6 mm. That is, in FIGS. 6 to 8, even if the top surface of the head portion 122 and / or the deformed portion 123 protrudes by 0.6 mm from the broken line, the effect of suppressing interference with other parts can be obtained. The broken line shown in FIGS. 6 to 8 indicates a surface corresponding to the surface 112 of the plate material.

By press-molding the plate material 11 before or after joining the plate material 11 by the method described above, the head surface 122 and / or the top surface of the deformed portion 123 is oriented along the axis of the shaft portion 121. The shaft portion 121 may be located closer to the shaft portion 121 than the position 0.6 mm away from the surface 112 of the plate member 11 in the vicinity of the rivet 12. In the example of FIG. 6, of the two plate materials, the one on the deformed portion 123 side is deformed to the deformed portion 123 side in the vicinity of the rivet 12. In the example of FIG. 7, the two plate materials on the head 122 side are deformed to the head 122 side in the vicinity of the rivet 12, and the two plate materials on the deformed portion 123 side are rivets. In the vicinity of 12, it is deformed toward the deformed portion 123. In the example of FIG. 8, the two plate materials on the deformed portion 123 side are deformed to the deformed portion 123 side in the vicinity of the rivet 12, and the two plate materials on the head 122 side are rivets. In the vicinity of 12, it is deformed corresponding to the other plate material.

Next, the rivet joint according to another embodiment of the present invention will be described. As shown in FIG. 2, the rivet joint 1 according to the present embodiment has a plurality of stacked plate members 11 each having a through hole 111, and a shaft portion 121 penetrating the through hole 111, and the plurality of plate members 11 The Vickers hardness of the axial center and the radial center of the shaft portion 121 of the rivet 12 is 130 HV or more and less than 300 HV. In other words, the rivet joint 1 according to the present embodiment has a plurality of stacked plate members 11 having through holes 111, a shaft portion 121 inserted through the through holes 111 of the plurality of plate materials 11, and both ends of the shaft portion 121. A steel rivet 12 having a head portion 122 and a deformed portion 123 arranged on the rivet 12, and a plurality of plate members 11 are crimped by the head portion 122 and the deformed portion 123, and the average Vickers of the shaft portion 121 of the rivet 12 is provided. The hardness is 130 HV or more and less than 300 HV.

The configuration of the plurality of plate materials 11 is not particularly limited. Further, the configuration of the through hole 111 formed in the plate material 11 through which the rivet 12 is inserted is not particularly limited. These specific examples are as described in detail in the description of the method for manufacturing the rivet joint according to the present embodiment.

The diameters of the through holes 111 in the plurality of plate materials 11 (if the through holes 111 are not circular, the diameter equivalent to a circle) may be the same or different. In a normal rivet joint, it is considered preferable to make the diameter of the through hole 111 constant from the viewpoint of reducing the gap between the joints. On the other hand, in the rivet joint 1 according to the present embodiment, since the rivet 12 is heated and softened, the gap can be sufficiently reduced even if the diameter of the through hole 111 is not the same for each plate material 11. Therefore, in the rivet joint 1 according to the present embodiment, even if the diameters of the through holes 111 are different, the outer wall of the shaft portion 121 of the rivet 12 has a shape along the inner wall of the through holes 111. Further, by providing a difference in the size of the through hole 111, a stress relaxation effect and an improvement in the efficiency of the work of passing the rivet 12 can be expected. The degree of difference in diameter of the through hole 111 is not particularly limited, but for example, the difference in diameter of the through hole 111 in the adjacent plate member 11 is preferably in the range of 0.3 mm to 3 mm.

The rivet 12 includes a shaft portion 121, a head portion 122 provided at both ends of the shaft portion 121, and a deformed portion 123. The shaft portion 121 penetrates through holes 111 of the plurality of plate members 11, and the head portion 122 and the deformed portion 123 sandwich the plurality of plate members 11, whereby the shaft portion 121 crimps and joins the plurality of plate members 11. The deformed portion 123 is formed by crushing the tip of the shaft portion 121. Specific examples of the configuration (shape, material, surface treatment, etc.) of the rivet 12 are as described in detail in the description of the method for manufacturing the rivet joint according to the present embodiment.

The Vickers hardness of the axial center and the radial center of the shaft portion 121 of the rivet 12 (hereinafter, "the Vickers hardness of the axial center and the radial center portion of the shaft portion 121" is referred to as the shaft portion. The Vickers hardness of 121) is 130 HV or more and less than 300 HV. As a result, the axial force of the joint structure 1 is increased. The cause is unknown, but it is presumed that the martensitic transformation that increases the length of the shaft portion 121 of the rivet 12 is suppressed. The Vickers hardness of the shaft portion 121 of the rivet 12 may be 150 HV or more, 180 HV or more, or 200 HV or more. The Vickers hardness of the shaft portion 121 of the rivet 12 may be 280 HV or less, 250 HV or less, or 220 HV or less.

The chemical composition of the rivet 12 is not particularly limited. For example, the rivet 12 may have a chemical component such that the carbon equivalent Ceq calculated by the formula 1 is 0.025 to 0.215% by mass.
Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
<Equation 1>
Here, the mass% of the component contained in the rivet 12 is substituted for the element symbol included in the formula 1, and zero is substituted for the element not contained. Ceq is a hardenability index of steel, and the larger it is, the greater the hardness after quenching. By setting Ceq in the range of 0.025 to 0.215% by mass, it becomes easy to set the Vickers hardness of the shaft portion of the rivet after cooling to 130 HV or more and less than 300 HV. However, even if the rivet 12 has a Ceq outside the above range, the Vickers hardness of the shaft portion can be set to 130 HV or more and less than 300 HV by appropriately selecting the heat treatment conditions.

Further, the rivet joint 1 may further have one or more welded portions selected from the group consisting of a spot welded portion, a laser welded portion, and an arc welded portion. As described above, the joint strength of the rivet joint 1 can be further increased by combining a plurality of joining means. The rivet joint 1 may further have an adhesive arranged around a through hole 111 between at least a plurality of plate members 11. Further, the rivet joint 1 may further have a sealer arranged between the plurality of plate members 11. As a result, the water resistance and corrosion resistance of the rivet joint 1 are enhanced.

An automobile part according to another aspect of the present invention has a rivet joint according to the present embodiment. As a result, the automobile parts according to the present embodiment have high joint strength. The automobile parts according to the present embodiment are, for example, bumpers and B-pillars, which are important members for ensuring collision safety. FIG. 9 shows a cross-sectional view of a B-pillar which is an example of an automobile part according to the present embodiment. FIG. 10 shows a cross-sectional view of a bumper which is an example of an automobile part according to the present embodiment. In addition, A pillars, side sills, floor members, front side members, rear side members, front suspension towers, tunnel reinforcements, dash panels, torque boxes, seat frames, seat rails, battery case frames, and joints between these pillars ( The joint portion between the B-pillar and the side sill, the joint portion between the B-pillar and the roof rail, and the joint portion between the roof cross member and the roof rail) may be used as the automobile parts according to the present embodiment.

Steel rivets having various configurations are passed through through holes of two stacked steel plates, sandwiched between a pair of electrodes, and pressurized and energized using these to deform the tip of the shaft of the rivet. And further cooling the rivets to create various rivet joints. Here, the joining was carried out at only one place. Therefore, when the axial force is insufficient, the plate members rotate with the joint as the rotation axis. The two steel sheets were hot stamped steel sheets having a tensile strength of 2000 MPa class. The thickness of the two steel plates is 1.4 mm, and the chemical composition of the two steel plates is 0.34% C-0.2% Si-1.2% Mn-0.2% Cr-0.02% Ti. -0.0015% B (unit: mass%, balance iron and impurities).

The shape of the rivet was as shown in Table 1. Table 1 also shows the hole diameters of the plate materials. The rivet was pressurized and energized using a spot welder. The conditions for pressurization and energization were as shown in Table 2. It was confirmed that the maximum temperature reached at the shaft of the rivet was 900 ° C. or higher.

Then, the axial force and cross tensile strength (CTS) of the joint structure and the Vickers hardness of the rivet shaft were evaluated by the following methods. The evaluation results are shown in Table 3. Values outside the scope of the invention and values that do not meet the pass / fail criteria are underlined.

(Axial force)
A torque of 5 Nm was applied to the plate material. At this time, the sample in which the plate material was rotated was determined to be the sample in which the axial force was insufficient.

(Cross tensile strength (CTS))
Measured according to JIS Z 3137: 1999. A sample having a CTS of less than 10.0 kN was determined to be a sample lacking CTS.

(Vickers hardness of rivet shaft (shaft hardness))
The rivet was cut along the central axis of the rivet and the cross section was appropriately prepared. Next, the Vickers hardness was measured at three locations corresponding to the center of the shaft portion of the rivet in the longitudinal direction. If there was a shrinkage inside the rivet, the Vickers hardness was measured at the place where there was no shrinkage. The load in the hardness measurement was 0.5 kgf. The average value of the measured hardness was regarded as the Vickers hardness of the shaft of the rivet.

Samples B to J are joint structures obtained by a manufacturing method in which the Vickers hardness of the shaft portion of the rivet after cooling is 130 HV or more and less than 300 HV. In these samples, the axial force was secured, and the CTS of 10.0 kN or more was secured. Therefore, it can be said that these samples B to J were rivet joints having joints having high cross tensile strength and axial force.

On the other hand, in sample A, CTS was insufficient. It is presumed that this is because the Vickers hardness of the shaft of the rivet was insufficient.
Axial force was insufficient in samples K and L. It is presumed that this is because the Vickers hardness of the shaft portion of the rivet is excessive and the rivet length is increased. In addition, CTS was also insufficient in sample L. It is presumed that this is because the shaft hardness was too high and embrittlement occurred.

According to the present invention, there is provided a method for manufacturing a rivet joint capable of manufacturing a joint having a high cross tensile strength (CTS) and an axial force, and a rivet joint having a joint having a high cross tensile strength and an axial force. be able to. Since the automobile parts according to the present invention have high cross tensile strength and axial force, various contributions such as improvement of collision safety of automobiles can be expected. Therefore, the present invention has high industrial applicability.

1 Rivet joint 11 Plate material 111 Through hole 112 Plate material surface 12 Rivet 121 Shaft portion 122 Head 123 Deformation portion 13 Adhesive 2 Spot welded portion A Electrode

Claims (12)

1. Passing the shaft of a steel rivet through the through holes of multiple stacked plates,
   The rivet is sandwiched between a pair of electrodes in the axial direction of the rivet.
   The pair of electrodes pressurizes and energizes the rivet to crush the tip of the shaft portion of the rivet, and
   The Vickers hardness of the axial center and the radial center of the shaft portion of the rivet after cooling is set to 130 HV or more and less than 300 HV.
   A method of manufacturing a rivet joint comprising.
2. The method for manufacturing a rivet joint according to claim 1, further comprising joining a plurality of the plate members by one or more welding methods selected from the group consisting of spot welding, laser welding, and arc welding.
3. The production of the rivet joint according to claim 1 or 2, further comprising applying an adhesive between the plurality of plate materials, at least around the through holes, and then superimposing the plurality of the plate materials. Method.
4. The method for manufacturing a rivet joint according to any one of claims 1 to 3, wherein the difference in diameter of the through holes between the plurality of adjacent plate materials is within the range of 0.3 mm to 3 mm.
5. The method for manufacturing a rivet joint according to any one of claims 1 to 4, wherein the maximum temperature of the shaft portion of the rivet is raised to more than 900 ° C. by the energization.
6. The method for manufacturing a rivet joint according to any one of claims 1 to 5, wherein the carbon equivalent Ceq calculated by the formula 1 of the rivet is 0.025 to 0.215% by mass.
   Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
   <Equation 1>
   Here, the mass% of the component contained in the rivet is substituted for the element symbol included in the formula 1, and zero is substituted for the element not contained.
7. Multiple stacked boards, each with a through hole,
   A rivet in which a shaft portion penetrates the through hole and crimps the plurality of plate materials is provided.
   A rivet joint having a Vickers hardness of 130 HV or more and less than 300 HV at the axial center and the radial center of the shaft portion of the rivet.
8. The rivet joint according to claim 7, further comprising one or more welds selected from the group consisting of a spot weld, a laser weld, and an arc weld.
9. The rivet joint according to claim 7 or 8, further comprising an adhesive arranged at least around the through hole between the plurality of the plate materials.
10. The rivet joint according to any one of claims 7 to 9, wherein the difference in diameter of the through holes in the plurality of adjacent plate materials is within the range of 0.3 mm to 3 mm.
11. The rivet joint according to any one of claims 7 to 10, wherein the carbon equivalent Ceq calculated by the formula 1 of the rivet is 0.025 to 0.215% by mass.
    Ceq = C + Si / 24 + Mn / 6 + Ni / 40 + Cr / 5 + Mo / 4 + V / 14
    <Equation 1>
    Here, the mass% of the component contained in the rivet is substituted for the element symbol included in the formula 1, and zero is substituted for the element not contained.
12. An automobile part provided with the rivet joint according to any one of claims 7 to 11.

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