JP7295487B2 - Rivet joint manufacturing method, rivet joint, automobile part, and electric heating rivet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a riveted joint manufacturing method, a riveted joint, an automobile part, and an electric heating rivet.
This application claims priority based on Japanese Patent Application No. 2020-060158 filed in Japan on March 30, 2020, the content of which is incorporated herein.

The application of high-strength steel sheets is being promoted for the purpose of reducing the weight of automobiles and improving collision safety. However, spot-welded joints made of high-strength steel sheets have a problem that cross tension strength (CTS) decreases when the tensile strength of the base steel sheet exceeds 780 MPa. Moreover, when the tensile strength of the steel sheet exceeds 1500 MPa, not only the cross tensile strength but also the tensile shear strength (TSS) tends to decrease.

If the strength of the spot-welded joint is reduced, there is a risk that the weld will break when the member is deformed, such as by a collision under very severe conditions. Therefore, even if the strength of the steel plate is improved, the load resistance of the entire member may be insufficient. Therefore, there is a demand for a joining method that improves the strength of joints made of high-strength steel plates.

The present inventors focused on riveting as one means of improving the cross tensile strength of joints. Riveting involves forming a through hole in a steel plate, inserting a rivet having a head and a shank into the through hole, plastically deforming the tip of the rivet shank at room temperature to crush it, and then and a joining method in which steel plates are crimped by plastically deformed parts. A joint obtained by riveting is called a riveted joint.

For example, the following techniques have been disclosed with respect to methods of manufacturing riveted joints.

U.S. Patent No. 5,200,402 discloses a method of joining two or more components together with a fastener, each component having a hole, and the components having the holes overlapping each other to connect the fastener to the fastener. The fastener disposed within the bore is mechanically pressurized and heated to deform the fastener and thereby cause the components to join together. wherein the fastener is heated essentially only during the deformation stage of the fastener to minimize heat transfer from the fastener to the components to be bonded, and bonding is achieved by and said component are made of the same or similar alloys included in the intermetallic alloy group of materials.

Patent Document 2 describes a method of riveting by sandwiching the head and tip of a rivet between a pair of electrodes, heating them with electricity, and pressing them. A spacer is provided which has a small cross-sectional area and has a height such that the rivet shaft is sufficiently tightly filled in the rivet hole, or that the back surface of the head and the material to be riveted come into contact after that. A riveting method is disclosed, characterized in that riveting is performed by

Patent Document 3 describes a rivet fastening method in which a rivet is sandwiched between electrodes, heated by resistance heat through electricity, and pressure-molded. A method of setting a rivet is disclosed, characterized in that the heat is applied to the rivet.

In Patent Document 4, a rivet hole formed through at least two members to be joined is formed at least partially in a tapered hole, a rivet is fitted into the rivet hole, and the shaft portion of the rivet is crimped by an electric current. is expanded and deformed into a shape along the tapered hole, and the shaft of the rivet and the tapered hole are joined without a gap by thermal contraction of the rivet after electric crimping. A bonding method is disclosed. Here, the rivet temperature at the time of electric crimping is said to be 700 to 900.degree.

Patent Document 5 discloses a riveting method for joining a plurality of works using rivets, in which a rivet inserted into a plurality of works is sandwiched between a pair of electrodes and energized while being pressurized, and the rivet by energization A riveting method is disclosed in which the rivet is softened by its own resistance heating and the end of the rivet is crimped.

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

The present inventors could not confirm an example in which riveting is applied to high-strength plate materials (in particular, high-strength metal plates or steel plates). Manufacturing a rivet from a high-strength material that matches the strength of the high-strength plate requires processing costs. In addition, joining plate materials using rivets increases the number of parts and the manufacturing cost of the joint. On the other hand, the merits of riveting high-strength plate materials were not known. For the above reasons, welding (particularly spot welding) has been the only means of joining high-strength plate materials, and there have been no examples of application of riveting. For example, in any of Patent Documents 1 to 5, the object to be joined is a low-strength material.

However, the inventors have found that the cross tensile strength of joints obtained by riveting high-strength steel sheets (riveted joints) is significantly higher than that of spot-welded joints. Riveting, which mechanically joins steel plates, does not cause embrittlement of the joint, so it was considered possible to maintain a high CTS of a welded joint composed of high-strength steel plates.

On the other hand, the present inventors also found that the tensile shear strength of riveted joints is inferior to that of spot welded joints. It was thought that the reason for the lower tensile shear strength of the rivet shank was that the rivet shank had a lower hardness than the spot weld. In addition, since there is a gap between the rivet and the plate material, the cross-sectional area of the area where the shear stress is applied in the riveted joint is smaller than that of the spot welded joint. was taken.

For example, none of Patent Documents 1 to 5 discuss means for improving TSS. Further, the present inventors have studied and found that the joint strength (TSS, CTS, etc.) of riveted joints obtained by applying these techniques to high-strength steel sheets is not sufficient.

In view of the above circumstances, the present invention provides a method for manufacturing a riveted joint capable of manufacturing a joint having high cross tensile strength (CTS) and tensile shear strength (TSS), and a joint having high CTS and TSS. An object of the present invention is to provide a rivet joint and an automobile part having Another object of the present invention is to provide a rivet for electric heating that can produce joints with high CTS and TSS.

The gist of the present invention is as follows.
(1) A method for manufacturing a riveted joint according to one aspect of the present invention includes: inserting the shaft of a steel rivet through a through-hole of a plurality of stacked plate materials; pressing and energizing the rivet with the pair of electrodes to crush the tip of the shank; and cooling the rivet, and the shank of the rivet after cooling and setting the Vickers hardness of the center in the axial direction and the center in the radial direction to 300 HV or more and 600 HV or less.
(2) In the method for manufacturing a riveted joint described in (1) above, one or more of the plurality of plate materials may be a high-strength steel plate having a tensile strength of 980 MPa or more.
(3) The method for manufacturing a riveted joint according to (1) or (2) above joins the plurality of plate materials by one or more welding methods selected from the group consisting of spot welding, laser welding, and arc welding. You may also have:
(4) The method for manufacturing a rivet joint according to any one of (1) to (3) above, wherein an adhesive is applied at least around the through holes between the plurality of plate materials, and then a plurality of and stacking the planks.
(5) In the method for manufacturing a rivet joint according to any one of (1) to (4) 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
(6) In the method for manufacturing a riveted joint according to any one of (1) to (5) above, the maximum temperature at the point at the center in the axial direction and the center in the radial direction of the shaft portion exceeds 900°C. may be
(7) In the method for manufacturing a riveted joint according to any one of (1) to (6) above, the carbon content of the rivet is 0.08 to 0.32% by mass, and the carbon equivalent of the rivet is 0. 0.22 to 0.45% by mass.
(8) The method for manufacturing a riveted joint according to any one of (1) to (7) above may further comprise heating the rivet before passing the shaft portion through the through hole. .
(9) A riveted joint according to another aspect of the present invention includes a plurality of stacked plate members each having a through hole, a rivet having a shaft penetrating the through hole and crimping the plurality of plate members, and the Vickers hardness of the axial center and radial center of the shaft portion of the rivet is 300 HV or more and 600 HV or less.
(10) In the riveted joint described in (9) above, at least one of the plurality of plate materials may be a high-strength steel plate having a tensile strength of 980 MPa or more.
(11) The riveted joint described in (9) or (10) above may further have one or more welds selected from the group consisting of spot welds, laser welds, and arc welds.
(12) The rivet joint according to any one of (9) to (11) above may further include an adhesive disposed between the plurality of plate materials and at least around the through holes. .
(13) In the rivet joint according to any one of (9) to (12) above, the difference in diameter of the through holes in the plurality of adjacent plate members is within the range of 0.3 mm to 3 mm. good too.
(14) In the riveted joint according to any one of (9) to (13) above, the rivet has a carbon content of 0.08 to 0.32% by mass and a carbon equivalent of 0.22. It may be up to 0.45% by mass.
(15) In the rivet joint according to any one of (9) to (14) above, the rivet has a head and a deformed portion arranged at both ends of the shaft, and the shaft of the rivet In a cross-sectional view parallel to the axis of the portion, the top surface of the head and/or the deformed portion extends from the surface of the plate near the rivet in the direction along the axis of the shaft. It may be located on the shaft side of the position 0.6 mm away from the .
(16) An automobile part according to another aspect of the present invention comprises the riveted joint according to any one of (9) to (15) above.
(17) The automobile component described in (16) above may be a bumper or a B-pillar.
(18) An electrically heating rivet according to another aspect of the present invention is made of steel having a shaft that is passed through a through-hole of a plurality of stacked plate materials, is quenched at the center, and is crushed at the tip. The rivet for electric heating has a carbon content of 0.08 to 0.32% by mass and a carbon equivalent of 0.22 to 0.45% by mass.

The present invention provides a method for producing riveted joints capable of producing joints with high cross tensile strength (CTS) and tensile shear strength (TSS), and riveted joints and automotive parts having joints with high CTS and TSS. can provide. In addition, the present invention can provide a rivet for electric heating that can produce joints with high CTS and TSS.

It is a figure which shows the manufacturing method of the riveted joint which concerns on this embodiment. It is a figure which shows the manufacturing method of the riveted joint which concerns on this embodiment. It is a figure which shows the manufacturing method of the riveted joint which concerns on this embodiment. It is a figure which shows the manufacturing method of the riveted joint which concerns on this embodiment. It is a sectional view showing an example of a riveted joint concerning this embodiment. FIG. 4 is a cross-sectional view showing an example of a rivet joint in which the size of the through-hole is different for each plate material. FIG. 4 is a cross-sectional view showing a riveted joint further having adhesive disposed around the perimeter of the through-hole; FIG. 4 is a perspective view of a bumper using a riveted joint and other joining means; FIG. 4 is a cross-sectional view showing an example of means for preventing interference between the rivet and other parts; FIG. 4 is a cross-sectional view showing an example of means for preventing interference between the rivet and other parts; FIG. 4 is a cross-sectional view showing an example of means for preventing interference between the rivet and other parts; It is a sectional view of B pillar which is an example of the automobile parts concerning this embodiment. 1 is a cross-sectional view of a bumper that is an example of an automobile component according to an embodiment; FIG.

The present inventors have extensively studied a joining method capable of producing a joint with high joint strength (cross tensile strength (CTS) and tensile shear strength (TSS)). As a result, the inventors have found that the cross tensile strength of a joint obtained by riveting high-strength steel sheets (riveted joint) is significantly higher than that of a spot-welded joint. Riveting, which mechanically joins steel plates, does not cause embrittlement of the joint, so it was considered possible to maintain a high CTS of a welded joint composed of high-strength steel plates. On the other hand, the inventors also found that the TSS of riveted joints is inferior to that of spot-welded joints.

The present inventors have made further studies on how to increase the TSS of the rivet joint. As a result, the material of the rivet is steel, and a quenched portion is formed at the center of the shaft in the axial direction and the center in the radial direction (hereinafter sometimes referred to as "the center of the shaft"). , the TSS of the riveted joint was found to be dramatically increased. The rivet shank is a portion having a certain diameter, including the central portion of the rivet in the axial direction.

A typical riveting method includes passing a rivet shank through a plurality of base plate materials, applying pressure to the rivet to cause deformation, and thereby crimping and joining the plate members. Here, it is said that the rivet may be heated. This is because, by heating and softening the rivet, the resistance to deformation of the rivet is reduced, making it easier to perform caulking. It has also been reported that heating and softening the rivet can also reduce the gap between the rivet and the base material. However, the heating temperature was much lower than the austenite transformation point ( _A3 transformation point) of the steel forming the rivet.

Quenching of steel is a heat treatment in which the steel is heated to produce austenite in its metallographic structure and then rapidly cooled to transform the austenite into martensite. For full quenching, it is desirable to heat the steel to a temperature above the _A3 transformation point where it transforms completely to the austenitic phase. In the prior art, a hardened portion was not formed in the center of the rivet shank. It is presumed that this is because when the rivet is heated excessively, unnecessary heat history is given to the plate material, and the metal structure may change in quality. For example, U.S. Pat. No. 6,300,009 states that heat transfer from fasteners to components should be minimized. On the other hand, no advantage of overheating the rivet has been found.

However, the present inventors have found that by heating the rivet to a temperature range higher than the normal range during riveting and forming a hardened portion inside it, the resistance of the rivet to shear stress is increased, and the riveting It was found that the TSS of the part is much higher than the conventional one. It has also been found that heating for hardening the rivet does not adversely affect the mechanical properties of the base material, and therefore does not cause embrittlement that would lower the CTS.

A method for manufacturing a riveted joint according to one aspect of the present invention obtained based on the above knowledge (hereinafter sometimes abbreviated as a riveted joint method) is as shown in FIGS. 1A to 1D.
(S1) passing the shaft portion 121 of the steel rivet 12 (rivet for electric heating) through the through hole 111 of the plurality of stacked plate members 11;
(S2) sandwiching the rivet 12 between the pair of electrodes in the axial direction of the rivet 12;
(S3) pressurizing and energizing the rivet 12 with a pair of electrodes to crush the tip of the shaft portion 121;
(S4) cooling the rivet 12 and setting the Vickers hardness of the axial center and radial center of the rivet 12 after cooling to 300 HV or more and 600 HV or less;
Prepare. This manufacturing method will be described in detail below.

First, as shown in FIG. 1A, the shaft portion 121 of the steel rivet 12 is passed through the through-holes 111 of the stacked plate members. Next, as shown in FIG. 1B, the rivet 12 is sandwiched between a pair of electrodes in the axial direction of the rivet 12 . The plate material 11 becomes the base material of the rivet joint 1 . The rivet 12 normally 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 deformation portion 123 . The head portion 122 has a function of sandwiching (caulking) the plate member 11 together with the deformation portion 123 . Even if the rivet 12 without the head portion 122 is inserted into 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 deformation portions 123 can be regarded as the head portion 122 .

The configuration of the plate material 11 is not particularly limited. For example, if 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 riveted joint 1 can be improved, which is preferable. In addition, the riveting method according to the present embodiment does not cause embrittlement that leads to a decrease in CTS in the high-strength steel sheet. Therefore, the riveting method according to the present embodiment can provide a riveted joint 1 having a high CTS when applied to joining high-strength steel plates. When the tensile strength of the high-strength steel sheet is 980 MPa or more, the superiority of the riveted joint according to the present embodiment with respect to CTS becomes even more pronounced over spot welding. More preferably, the strength level of the plate material 11 is a tensile strength of 1180 MPa or higher, and most preferably 1500 MPa or higher. Although the upper limit of the tensile strength of the plate material 11 is not particularly limited, it may be 2700 MPa or less, for example.
Also, the plate member 11 may be an aluminum plate, a CFRP plate, a titanium plate, or the like. Unlike joining by welding, in riveting according to the present embodiment, the material of the plate members 11 may be changed. 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. Although there are no particular restrictions on the arrangement of the plate members, in the case of plate members made of different materials, it is desirable to arrange the plate member with the lower melting point on the rivet head side from the viewpoint of avoiding melting of the plate member with the lower melting point. Various surface treatments may be applied to the plate member 11 . For example, a combination of a steel plate and an aluminum plate, a combination of a steel plate and a CFRP plate, or the like may be used. For example, the plate material 11 is alloyed with the base metal by GA plating, GI plating, EG plating, Zn-Al plating, Zn-Mg plating, Zn-Ni plating, Zn-Al-Mg plating, Al plating, and hot stamping. Zn-based plating (Zn--Fe, Zn--Ni--Fe) and Al-based plating (Al--Fe--Si) may also be used.

The plate thickness of the plate member 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 varied. The number of plates 11 is also not particularly limited. In the description of the riveting according to this embodiment, it is assumed that the number of plates 11 is two, but the number of plates may be three or more. As a suitable combination, for example, a plate with a thickness of about 1.6 mm and a plate with a thickness of about 2.3 mm are stacked, or a plate with a thickness of 0.75 mm, a plate with a thickness of 1.8 mm, and a plate with a thickness of 1.2 mm are stacked. A three-ply stack with a plate material can be mentioned. As a suitable combination range of the plate materials, for example, a plate material having a thickness of about 0.6 mm to 2.9 mm and a plate material having a thickness of about 0.6 mm to 2.9 mm are stacked, or a thickness of 0.6 mm to 1.0 mm. A three-ply stack of a 6 mm plate, a 0.6 mm to 2.9 mm plate, and a 0.6 mm to 2.9 mm plate can be used. The sheet material may be a cold or hot pressed, cold roll formed, or hydroformed molding. Also, the plate material may be shaped like a pipe.

The configuration of the through hole (through hole) 111 through which the rivet 12 is inserted is also not particularly limited. From the viewpoint of smoothly passing the rivet 12 through the through-hole 111 , the diameter of the through-hole 111 is preferably larger than the diameter of the shaft portion of the rivet 12 .

The shape of the through hole 111 can be circular, for example. On the other hand, the shape of the through hole 111 may be a polygon such as a quadrangle, a pentagon, a hexagon, and an octagon. The corners of these polygons may have curvature. Also, the shape of the through-hole 111 may be an ellipse, or a circular shape with a convex portion or a concave portion. By forming the through hole 111 to have a shape other than a circular shape, it is possible to prevent the riveted plate material from rotating around the rivet of the through hole and to reduce rattling at the joint. Even more desirable.

The through hole 111 through which the rivet 12 is passed can be formed by any means such as laser cutting, punching using a mold, or drilling using a drill. When the plate material 11 is a hot-stamped steel plate, it is desirable to form the through holes 111 by hot die punching or laser cutting.

The size of the through hole 111 may be constant in the depth direction of the plate member 11 . On the other hand, a stepped shape or a tapered shape in which the sizes of the through holes 111 are different in the depth direction may be applied to the through holes 111 . Also, the central axes of the through holes 111 between the plurality of joined members do not have to match.

The diameters of the through holes 111 in the plurality of plate members 11 (when the through holes 111 are not circular, the equivalent circle diameter) may be the same as shown in FIG. 2, or may be different as shown in FIG. You may By providing a difference in the sizes of the through holes 111, a stress relaxation effect and an improvement in the efficiency of the operation of inserting the rivet 12 can be expected. Although the degree of difference in diameter of through-holes 111 is not particularly limited, for example, the difference in diameter of through-holes 111 between adjacent plate members 11 is preferably within the range of 0.3 mm to 3 mm. From the viewpoint of facilitating the operation of passing the rivet 12, it is preferable to increase the diameter of the through hole of the plate on the side opposite to the rivet entrance side (the side where the rivet head is located). This can prevent the tip of the rivet 12 from clogging the through hole 111 .

Also, the minimum diameter of the through-hole 111 is preferably 0.1 mm to 5 mm larger than the maximum diameter of the shaft of the rivet to be inserted. This is because if the thickness is smaller than 0.1 mm, the insertability is deteriorated, and if the thickness is larger than 5 mm, it becomes difficult to sufficiently fill the clearance of the through hole 111 . More preferably, it is in the range of 0.3 mm to 3 mm, optimally in the range of 0.3 mm to 1.5 mm. Further, the deviation of the central axes of the through-holes 111 between the plurality of members to be joined is preferably 1.5 mm or less, more preferably 0.75 mm or less.

The rivet 12 must be made of steel in order to form a hardened portion at its axial center and radial center (the center of the shank). For example, by setting the carbon content of the rivet 12 to 0.08 to 0.32% by mass and the carbon equivalent of the rivet 12 to 0.22 to 0.45% by mass, it is easier to form the hardened portion 124. becomes. Incidentally, the carbon equivalent is a value obtained by the following formula, and indicates the hardenability of the steel material in consideration of alloying elements other than carbon.
Carbon equivalent = C + Si/24 + Mn/6 + Ni/40 + Cr/5 + Mo/4 + V/14
Here, the content % by mass is substituted for the above element name. If not, substitute zero.

Other configurations of the rivet 12 are not particularly limited, and can be appropriately selected according to 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 (diameter) of the shaft portion 121 of the rivet 12 (when the cross section of the shaft portion 121 is not circular, the circle equivalent diameter of the shaft portion 121) may be 3 mm or more from the viewpoint of ensuring joint strength. On the other hand, if the diameter of the shaft portion 121 is too large, the current density will decrease and the rivet will be difficult to soften. Therefore, the upper limit of the diameter of the shaft portion 121 may be 12 mm or less. The length of the shank 121 (the length of the rivet 12 minus the thickness of the head 122) must be greater than the total thickness of the plate 11. If the rivet 12 has the head 122, Preferably, it should be within the following range.
Total plate thickness of plate material + shaft diameter x 0.3 ≤ shaft length ≤ total plate thickness of plate + shaft diameter x 2.0
By setting the length of the shaft portion 121 of the rivet 12 to be larger than the total plate thickness of the plate material 11 + the diameter of the shaft portion 121 × 0.3, the crimped portion (the deformed portion 123 ) can be secured, and joint strength can be further increased. By setting the length of the shaft portion 121 to be equal to or less than the total plate thickness of the plate material 11 + the diameter of the shaft portion 121 x 2.0, manufacturing efficiency can be enhanced.

Moreover, 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 of plate + diameter of shaft x 0.6 ≤ length of shaft ≤ total thickness of plate + diameter of shaft x 4.0
When joining with headless rivets, it is necessary to deform the ends of the rivets. Therefore, the length of the shank 121 of the headless rivet is preferably greater than that of the headless rivet.

Note that the diameter of the shaft portion 121 may be constant. On the other hand, the rivet 12 may have a shape in which the diameter of the shaft portion 121 decreases toward the tip of the shaft portion 121 (so-called tapered shape). 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 . A rivet 12 having a tapered shape is preferable because it can be easily inserted into the through hole 111 . Also, the tip of the shaft portion 121 may be flat or hemispherical. It is preferable to make the tip of the shaft portion 121 semispherical because it is easy to insert the shaft portion 121 into 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 flat on the surface side and conical at the base (so-called countersunk head). The shape of the head 122 in plan view can be, for example, a circle, a square, or a polygon such as a hexagon. A recess for positioning may be provided in the central portion of the head 122 on the electrode side. A recess (so-called seat undercut) surrounding the shaft 121 may be provided in the seat of the head 122 (the surface that comes into contact with the material to be joined). Such a recess imparts elasticity to the head 122, thereby further increasing the crimping force of the rivet 12. FIG. Also, one or more projections may be provided on the seat of the head 122 (the surface that comes into contact with the material to be joined). Such protrusions further increase the crimping force of the rivet 12 by sinking into the material to be joined during riveting or by forming a joint with the material to be joined. The shape of the projection may be circular, polygonal, or ring-shaped surrounding the shaft.

The rivet 12 crimps the plate material 11 using its head. Therefore, it is preferable that the diameter of the head be larger than the diameter of the through hole 111 by 1.5 mm or more. Also, the thickness of the head portion 122 is preferably 0.8 mm to 5 mm. If the thickness of the head portion 122 is less than 0.8 mm, sufficient joint strength cannot be obtained. On the other hand, when the thickness of the head portion 122 exceeds 5 mm, the head portion is too large, and interference with other parts is likely to occur. For a headless rivet, the diameter of the deformed rivet end (ie deformed portion 123) after riveting is preferably 1.5 mm or more greater than the diameter of the through hole 111. FIG. Also, the thickness of the deformed rivet end is preferably 0.8 mm to 5 mm.

A rivet may be manufactured, for example, by cutting a coil wire and subjecting it to cutting or cold forging. From the viewpoint of productivity, cold forging is desirable as a method for processing cut coils. The rivet may be used as processed, but if joint strength is particularly required, the rivet after cutting or cold forging may be quenched and tempered. By increasing the hardness of the entire rivet including the rivet head by this heat treatment, the joint strength is further improved.

The rivet may be one that is not surface-treated, but may be surface-treated if corrosion resistance is required. For example, the rivet may be subjected to zinc-based plating, aluminum-based plating, chromium-based plating, nickel-based plating, chromate treatment, and the like.

Next, as shown in FIG. 1C, the rivet 12 is pressurized and energized via a pair of electrodes. As a result, resistance heat is generated in the rivet 12, the rivet 12 is softened, and the tip of the shaft portion 121 of the rivet 12 is crushed (so-called riveting).

In the rivet joining according to the present embodiment, it is preferable that the rivet 12 is energized after the electrode A is used to apply pressure to 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. At this time, a melted portion may occur inside the rivet 12 . In this case, the rivet 12 is sandwiched between the electrodes A, the rivet 12 is pressurized, the rivet 12 is energized, and the rivet 12 is cooled. However, the timing to start heating the rivet 12 and the timing to start pressurizing the rivet 12 are not limited to the preferred examples described above.

Further, in normal riveting, it is allowed to heat and soften the rivet 12 before the shaft portion 121 of the rivet 12 is inserted into the through hole 111 of the plate member 11 . Also in the method of manufacturing a riveted joint according to the present embodiment, the rivet 12 may be heated and then the shaft portion 121 of the rivet 12 may be passed through the through-hole of the plate material 11 . After the insertion, the pair of electrodes is energized to generate resistance heat in the rivet 12, soften the rivet 12, deform the tip of the rivet shank, cool the rivet, and form a hardened portion in the center of the rivet shank. form. Before insertion, if the diameter of the rivet shaft is large or if the rivet is hard, it may be preferable to soften the rivet before insertion.

The rivet 12 is cooled and quenched following pressurization and energization. Therefore, the rivet 12 must be energized to the extent that it can be quenched. However, the temperature required for quenching differs depending on the components of the rivet 12 (eg, carbon content, carbon equivalent, etc.). Therefore, the heating temperature may be appropriately selected according to the components of the rivet 12 . For example, if the highest temperature reached at the shaft portion 121 of the rivet 12 exceeds 900° C., it is possible to form the hardened portion 124 in the steel rivet 12 . However, if the _A3 point of the rivet 12 is low, the maximum temperature of the shaft portion may be less than 900°C. Further, the rivet head 122 does not need to be quenched, so the maximum temperature may be 900°C or higher or lower than 900°C. The maximum temperature reached by the rivet shank can be estimated by observing the metal structure of the cross section of the rivet shank 121 . For example, if the material of the rivet is an iron alloy and the martensite structure is generated in the shaft portion, it can be estimated that the maximum temperature reached at the shaft portion of the rivet was approximately 900° C. or higher. Further, if the material of the rivet is an iron alloy and a melt-solidified portion is formed in the shaft portion, it can be estimated that the maximum temperature reached at the shaft portion of the rivet was 1530° C. or higher.

The rivets 12 are inserted into the through-holes 111 by, for example, a rivet feeder after the plate materials 11 are superimposed. Then, for example, using a spot welder, the rivet is electrically heated while being pressurized. Specific energization conditions (current value, voltage value, energization time, etc.) for heating the rivet 12 to the temperature required for quenching and pressurization conditions for the rivet 12 are not particularly limited, and the shape of the rivet 12 And it can be appropriately selected according to the material. The presence of the hardened portion 124 of the rivet 12 can be confirmed by cutting the rivet 12 and measuring the Vickers hardness of the cut surface. Therefore, a person skilled in the art can examine the optimum pressurizing conditions and energizing conditions according to the shape and material of the rivets 12 by applying pressure and energizing to the rivets 12 under various conditions. .

It is preferable that the rivet 12 is pressurized and energized using a pair of electrodes. The configuration of the pair of electrodes is not particularly limited. For example, since an electrode for spot welding can apply pressure and electricity, it may be used to perform riveting according to the present embodiment. The shape of the electrode can be appropriately selected according to the shape of the rivet 12 . For example, the electrodes may be flat type electrodes, single R type, CF type, DR type, and the like. Examples of materials for the electrodes include chromium copper, alumina-dispersed copper, chromium zirconium copper, and the like, which are excellent in conductivity. It is desirable that one side of the pair of electrodes has a mechanism for holding the head of the rivet until joining by means of a magnet, a mechanical holding mechanism, or a vacuum. Examples of materials for the electrodes include chromium copper, alumina-dispersed copper, chromium zirconium copper, and the like, which are excellent in conductivity. Also, the pair of electrodes may have different shapes and materials.

Examples of power sources for welding machines include single-phase AC, DC inverters, AC inverters, and the like. Examples of gun types include stationary or C-type, or X-type. The pressure applied to the rivet by the electrode is, for example, 150 kgf to 1000 kgf. The applied pressure is preferably 250 kgf to 600 kgf. The set value of the applied pressure may be a constant value, but the applied pressure may be changed during energization as necessary. The direction in which the electrode presses the rivet is preferably at 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 desirably, the angle between the pressing direction and the axial direction of the rivet is 4° or less.

The energization time is, for example, 0.15 seconds to 2 seconds. The energization time is preferably 0.2 seconds to 1 second. The number of times of energization may be one (so-called single energization), but two-stage energization or three-stage multi-stage energization may be performed as necessary. Also, pulse energization, up-slope energization that gradually increases the current, or down-slope energization that gradually decreases the current may be used. Alternatively, a high current may be supplied in the first half of the energization to rapidly heat the rivet, and the current may be lowered in the second half to deform the rivet. On the other hand, as described above, the rivet 12 may be heated by means other than resistance heating, and in this case, the means for applying pressure to the rivet 12 for riveting is not limited to a pair of electrodes.

After pressurizing the softened rivet 12 to deform the tip of the shaft portion 121, 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 . Furthermore, cooling the rivet 12 transforms the austenite generated in the metal structure of the rivet 12 when the rivet 12 is heated into martensite. As a result, a quenched portion 124 is formed in the center of the shaft portion 121, and the Vickers hardness of the center of the rivet 12 after cooling in the axial direction and the center in the radial direction (the center of the shaft portion 121) is 300 HV or more and 600 HV. You can:

The present inventors evaluated the strength of various riveted joints manufactured by heating the rivet 12 to a temperature higher than usual and observed the cross section of the joint. As a result, it was found that the CTS and TSS of a rivet joint in which a quenched portion is formed inside the rivet 12 and the Vickers hardness at the center of the shaft portion 121 is within the above range is significantly higher than that of a normal rivet joint. rice field. Based on the above experimental results, in the riveting according to the present embodiment, the center of the shaft portion 121 of the rivet 12 is quenched to generate resistance heat so that the hardness can be set to 300 HV or more and 600 HV or less. I decided to Even in a riveted joint in which the mating surfaces of the plates do not coincide with the center of the shaft portion 121, the TSS can be increased if the Vickers hardness of the center of the shaft portion 121 is within the above range. In the rivet 12 in which the Vickers hardness at the center of the shaft portion 121 is within the above range, it is estimated that the Vickers hardness of substantially the entire region within the through hole 111 is 300 HV or more and 600 HV or less. This is because that. During heating, the shaft portion 121 of the rivet 12 is heated to a temperature higher than the _A3 transformation point. Since the diameter of the shaft portion 121 is small and there is almost no difference in the cooling rate within the cross section of the shaft portion 121, variations in hardness within the cross section of the shaft portion 121 are small. Therefore, when the hardness at the center of shaft portion 121 is 300 HV or more and 600 HV or less, the hardness of shaft portion 121 is estimated to be 300 HV or more and 600 HV or less.

Hardened portion 124 is formed inside shaft portion 121 of rivet 12 . The Vickers hardness of the axial center and radial center of the rivet 12 is set within the range of 300HV to 600HV. By setting the Vickers hardness of the axial center and radial center of the rivet 12 to 300 HV or more, the TSS can be further increased. On the other hand, by setting the Vickers hardness of the axial center and radial center of the rivet 12 to 600 HV or less, embrittlement of the rivet 12 due to excessive hardening can be further suppressed. More preferably, the lower limit of the Vickers hardness at the axial center and radial center of the rivet 12 is 380 HV, and the upper limit is 560 HV.

A method of measuring the hardness of the rivet 12 is as follows. First, the rivet 12 is cut along a plane parallel to the axis of the shaft portion 121 of the rivet 12 and passing through the axis of the shaft portion 121 . Next, on the cut surface of the rivet 12, the hardness measurement is continuously performed along the axial center of the shaft portion 121 of the rivet. Then, the average value of the hardness at three locations near the center in the radial direction of the shaft portion 121 of the rivet 12 is defined as the Vickers hardness at the location at the center in the axial direction and the center in the radial direction of the shaft portion 121 of the rivet 12. I reckon. The Vickers hardness measurement load is 0.5 kgf, and the measurement interval in continuous hardness measurement is 500 μm. However, if there is a defect such as a crack, blowhole, etc. at the Vickers hardness measurement position, the measurement shall be performed at a position near the defect at least 0.2 mm away.

The overlapping surfaces of the plate members 11 are places where a shearing stress is applied to the shaft portion 121 of the rivet. The hardness of the region of the shaft portion 121 along the overlapping surfaces of the plate members 11 is closely related to the TSS. As described above, when the rivet 12 is heated, the entire shaft portion 121 of the rivet 12 is heated to a temperature higher than the _A3 transformation point. Moreover, there is not much difference in the cooling of the shaft portion 121 even if the position in the axial direction is different. Therefore, there is no substantial difference between the hardness of the region of the shank 121 along the overlapping surfaces of the plates 11 and the region of the rivet shank 121 along the cross section passing through the axial center of the rivet shank 121. None. That is, if the Vickers hardness of the axial center and radial center of the shaft portion is 300 HV or more and 600 HV or less, the hardness of the region of the shaft portion 121 along the overlapping surface of the plate members 11 is also 300 HV or more and 600 HV or less. is. The hardness of the rivet head 122 and deformed portion 123 in the vicinity of the contact surface with the electrode has little effect on the tensile shear strength, so it may be 300 HV or more but less than 300 HV.

Although the cooling conditions for the rivet 12 are not particularly limited, for example, the cooling rate of the rivet 12 between 800 and 500° C. is 50° C./second or more, more preferably 100° C./second or more, and optimally 150° C./second or more. may be specified. Thereby, martensite transformation can be reliably generated in the center of the shaft portion 121 of the rivet 12 .

The means for cooling the rivet 12 is also not particularly limited. Even if the rivet 12 is allowed to stand in the air after the energization is finished and allowed to cool naturally, it is presumed that a sufficient cooling rate will be ensured. This is because the resistive heat generated in the rivet 12 quickly moves to the surrounding plate material 11 . Also, after welding, it is desirable to accelerate cooling by extending the holding time of the electrode. A coolant flows inside the electrodes, and the rivets 12 can be acceleratedly cooled by bringing the electrodes into contact with the rivets 12 after energization. The accelerated cooling of the rivet 12 makes it possible to harden the rivet 12 and further increase the joining strength of the joint. However, if the contact state between the electrode and the rivet is maintained for accelerated cooling (retention time) is too long, the productivity is lowered. Therefore, it is desirable to set the holding time to 3 seconds or less after the completion of energization. The retention time is more desirably 0.01 seconds or more and 1.00 seconds or less. The retention time is optimally between 0.10 seconds and 0.80 seconds.

In the method of manufacturing a riveted joint according to this embodiment, it is possible to use other joining means in combination. By combining two or more different joining means, the joining strength of the riveted joint can be further increased.

For example, the rivet joining method according to the present embodiment is one or more welding methods selected from the group consisting of spot welding, laser welding, and arc welding (such as MAG welding, MIG welding, _CO2 welding, plasma welding, etc.). It may further comprise joining the plurality of plate members 11 by. Welding may be performed before or after riveting. From the viewpoint of improving assembly accuracy of parts, it is desirable to perform riveting after welding. When welding is spot welding, riveting may be performed after spot welding. Alternatively, after spot welding, riveting may be performed, and then spot welding may be performed.

In addition, the riveting method according to the present embodiment may further include applying the adhesive 13 at least around the through holes 111 between the plurality of plate members 11, and then stacking the plurality of plate members 11. . Thereby, as shown in FIG. 4, the plate material 11 is adhered. Although the thickness of the adhesive is not particularly specified, it may be 0.03 mm or more and 1.5 mm or less. If it is too thin, poor adhesion will occur, and if it is too thick, the adhesive strength will decrease. The adhesive 13 must be applied before the plurality of plate members 11 are stacked and the rivets 12 are passed through the plate members 11 . In the case of a thermosetting adhesive, curing of the adhesive 13 may be performed by heating for baking paint in an electrodeposition coating line after riveting. In the case of a reaction-curing adhesive, curing of the adhesive 13 takes place with the lapse of time after riveting. In the spot welding of the plate material 11, it may be necessary to separate the application location of the adhesive 13 from the spot welding location in order to prevent explosion. However, the rivet joining method according to the present embodiment has the advantage that the application location of the adhesive 13 is not limited because the explosion does not occur. The combined use of the rivet 12 and the adhesive 13 has the advantage of further improving the rigidity of the joint. Further, by using the rivet 12 and the adhesive 13 together, it is possible to prevent contact corrosion of overlapping surfaces in joining dissimilar metals or joining metal and CFRP. A sealer may be applied between the plate members 11 in addition to the adhesive 13 . The sealer increases the water resistance and corrosion resistance of the riveted joint 1 . Furthermore, in the case of joining dissimilar metals or joining metal and CFRP, at least one metal plate may be chemically treated and painted before riveting. As a result, contact corrosion between dissimilar materials can be suppressed more strongly, and corrosion resistance can be improved.

Next, a riveted joint according to another embodiment of the invention will be described. As shown in FIG. 2 , the rivet joint 1 according to the present embodiment includes a plurality of stacked plate members 11 each having a through hole 111 , and a shaft portion 121 passing through the through hole 111 and extending through the plurality of plate members 11 . and a Vickers hardness of 300 HV or more and 600 HV or less at the center in the axial direction and the center in the radial direction of the shaft portion 121 of the rivet 12 .

The configuration of the plurality of plate members 11 is not particularly limited. Also, the configuration of the through-hole 111 formed in the plate member 11 and 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 of manufacturing the riveted joint according to this embodiment.

The diameters of the through-holes 111 in the plurality of plate members 11 (when the through-holes 111 are not circular, the equivalent circle diameter) may be the same or different. By providing a difference in the sizes of the through holes 111, a stress relaxation effect and an improvement in the efficiency of the operation of inserting the rivet 12 can be expected. Although the degree of difference in diameter of through-holes 111 is not particularly limited, for example, the difference in diameter of through-holes 111 between adjacent plate members 11 is preferably within the range of 0.3 mm to 3 mm.

The rivet 12 is a member whose shaft portion 121 passes through the through hole 111 and crimps the plurality of plate members 11 . Therefore, for example, the rivet 12 may include a head portion 122 and a deformation portion 123 provided at both ends of the shaft portion 121 . The shaft portion 121 is inserted through the through holes 111 of the plurality of plate members 11 , and the plurality of plate members 11 are sandwiched between the head portion 122 and the deformation portion 123 , whereby the shaft portion 121 crimps and joins the plurality of plate members 11 . The deformation portion 123 is formed by crushing the tip of the shaft portion 121 . On the other hand, as described above, the rivet 12 has the shaft portion 121 and the two deformation portions 123 provided at both ends of the shaft portion 121, and these deformation portions 123 may sandwich the plurality of plate members 11. .
A specific example of the configuration (shape, material, surface treatment, etc.) of the rivet 12 is as described in detail in the description of the method of manufacturing the riveted joint according to this embodiment. That is, the carbon content of the rivet 12 is preferably 0.08-0.32% by mass, and the carbon equivalent of the rivet is preferably 0.22-0.45% by mass.

The rivet 12 further has a hardened portion 124 therein. As a result, the rivet 12 has a Vickers hardness of 300 HV or more and 600 HV or less at the center in the axial direction and the center in the radial direction. The rivet 12 having such a quenched portion 124 has a high resistance to shear stress, and therefore can dramatically increase the TSS of the riveted joint 1 .

A hardened portion 124 is formed at the shank of the rivet 12 . The Vickers hardness of the rivet 12 at the center in the axial direction and the center in the radial direction is set to 300 HV or more and 600 HV or less. The Vickers hardness of the rivet 12 at the center in the axial direction and the center in the radial direction is within the range of 300HV to 600HV. By setting the Vickers hardness of the central portion in the axial direction and the central portion in the radial direction to 300 HV or more, the TSS can be further increased. On the other hand, by setting the Vickers hardness of the central portion in the axial direction and the central portion in the radial direction to 600 HV or less, embrittlement of the rivet 12 due to excessive hardening can be further suppressed.

One or more of the plurality of plate members 11 may be steel plates. In particular, when the plate material 11 and the rivets 12 are made of high-strength steel (for example, steel having a tensile strength of 980 MPa or more), the strength of the riveted joint 1 can be dramatically increased. It should be noted that unlike spot welds, rivets 12 do not embrittle the steel and therefore do not cause CTS degradation. Also, unlike ordinary rivets, the rivets 12 of the riveted joint according to the present embodiment have a high TSS, so they are suitable for joining high-strength steel plates.

Moreover, the rivet joint 1 may further have an adhesive 13 arranged around the through hole 111 between at least the plurality of plate members 11 . The riveted joint 1 may further have one or more welds selected from the group consisting of spot welds, laser welds, and arc welds. As described above, the joint strength of the riveted joint 1 can be further increased by combining a plurality of joining means. The rivet joint 1 may further have a sealer arranged between the plate members 11 . This enhances the water resistance and corrosion resistance of the riveted joint 1 . Also, a resin adhesive tape such as an ionomer may be used as the adhesive layer. Also, a sealer may be applied to cover the rivet head and/or deformed portion. This can prevent water from entering through the gap between the rivet head and/or deformed portion and the metal or CFRP.

FIG. 5 shows an example of a riveted joint 1 (bumper) using both the rivet 12 and other joining means. As shown in FIG. 5, the rivets 12 according to the present embodiment (black circles in FIG. 5) are used to join parts where the stress applied during a collision is expected to be high. Joining means (for example, spot welds 2 formed by inexpensive spot welding) (white circles in FIG. 5) may be employed.

In the rivet joint 1 according to this embodiment, the rivet 12 may have a head portion 122 and a deformation portion 123 arranged at both ends of the shaft portion 121 . Here, as shown in FIGS. 6 to 8, 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 deformation portion 123 is aligned along the axis of the shaft portion 121. It may be located on the shaft portion 121 side of a position 0.6 mm away from the surface of the plate member 11 in the vicinity of the rivet 12 toward the side away from the shaft portion 121 in the direction. Here, the surface (outer surface) of the plate member 11 means a surface of the plate member 11 that is not in contact with other plate members. As a result, the head 122 and/or the deformation portion 123 are prevented from protruding from the plate member 11 (or the height of the protrusion is suppressed to within 0.6 mm), and the head 122 and/or the deformation portion 123 are , interference with other parts can be suppressed.

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 near 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 are positioned closer to the shaft portion 121 than the surface 112 (outer surface) of each of the plate members near the rivet 12 . be. Here, the surface 112 (outer surface) of the plate member means the surface of each plate member that is not in contact with another plate member. 6 to 8, the top surface of the head portion 122 and/or the deformation portion 123 is closer to the shaft portion 121 than the surface 112 (outer surface) of the plate near the rivet 12. Alternatively, the top surface of the deformed portion 123 may protrude from the surface 112 of the plate material by 0.6 mm at maximum. That is, in FIGS. 6 to 8, even if the top surface of the head portion 122 and/or the deformation portion 123 protrudes by 0.6 mm from the dotted line, the effect of suppressing interference with other parts can be obtained.

By press-molding the plate material 11 before or after joining the plate material 11 by the above-described method, the top surface of the head portion 122 and/or the deformation portion 123 is aligned in the direction along the axis of the shaft portion 121. , it may be located on the shaft portion 121 side of 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, one of the two plate members 11 disposed on the deformation portion 123 side is deformed toward the deformation portion 123 side in the vicinity of the rivet 12 . In the example of FIG. 7, one of the two plate members on the head 122 side is deformed toward the head 122 near the rivet 12, and one of the two plate members on the deformed portion 123 side is the rivet. 12 is deformed toward the deformation portion 123 side. In the example of FIG. 8 , the one of the two plate members 11 arranged on the deformed portion 123 side is deformed toward the deformed portion 123 side in the vicinity of the rivet 12 and the head portion 122 of the two plate members 11 is deformed toward the deformed portion 123 side. The one on the side is deformed in the vicinity of the rivet 12 so as to correspond to the other plate member 11 . 6 to 8, illustration of the quenched portion 124 described above is omitted. Also, dashed lines shown in FIGS. 6 to 8 indicate surfaces that coincide with the surface 112 of the plate material.

An automobile part according to another aspect of the invention has a riveted joint according to the present embodiment. Thereby, the automobile component according to the present embodiment has high bonding strength. 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 component according to this embodiment. FIG. 10 shows a cross-sectional view of a bumper, which is an example of an automobile component according to this embodiment. In addition, A pillar, side sill, floor member, front side member, rear side member, front suspension tower, tunnel reinforcement, dash panel, torque box, seat frame, seat rail, battery case frame, and connection between those pillars (B A pillar-side sill joint, a B-pillar-roof rail joint, a roof cross member-roof rail joint) may be the automobile part according to the present embodiment.

(Example 1)
Using a steel rivet having the shape shown in Table 1 and the composition (mass%) shown in Table 2, and a hot-stamped high-strength steel plate (thickness 1.6 mm) with a tensile strength of 2000 MPa class, the table Various riveted joints were produced under the conditions shown in 3 (the electrode material is a Cr--Cu alloy). In Table 1, the diameter of the through-hole of the steel plate (prepared hole diameter) is also listed. A rivet with a disk-shaped head was set so that the head was on the lower plate side.

Various evaluations were carried out on the various riveted joints thus obtained. Specifically, the Vickers hardness (axial hardness) at the center in the direction of the rivet and the center in the radial direction, the tensile shear strength TSS (JIS Z 3136) of the riveted joint, and the cross tensile strength CTS of the riveted joint (JIS Z 3137) was measured. The shaft hardness was measured by the method described above. The measurement methods of TSS and CTS conformed to the above-mentioned standards. A riveted joint having a TSS of 14.5 kN or more and a CTS of 11.0 kN or more was judged to be a riveted joint having cross tensile strength (CTS) and tensile shear strength (TSS) within the acceptable range.

The hardness of each riveted joint was also measured. The measurement results are shown in the table below. Matters outside the scope of the invention are underlined.

In the invention examples in which the Vickers hardness (axial hardness) of the rivet at the center in the axial direction and the center in the radial direction was set to 300 HV or more and 600 HV or less, a riveted joint with sufficiently high TSS and CTS could be obtained. On the other hand, in the riveted joints obtained by Comparative Examples B and F, which lacked shaft hardness, the CTS was equivalent to that of the other invention examples, but a sufficiently high TSS was not obtained. In Comparative Example D, in which the shaft hardness was excessive, the CTS was at a level lower than that of the Inventive Examples.

(Example 2)
Using a rivet having the shape shown in Table 5 and the composition (% by mass) shown in Table 2, and a hot-stamped high-strength steel plate (thickness 1.6 mm) with a tensile strength of 2000 MPa class, Various riveted joints were made under the specified conditions. Table 5 also shows the diameter of the through-hole of the steel plate (prepared hole diameter). The rivet had a disk-shaped head and was set so that the head was on the lower plate side. The rivet No. 10 was heat-treated before the insertion work. This preheat treatment consisted of heating the entire rivet to 950°C, quenching, and then tempering at 200°C. The hardness of the rivet before the insertion work was set to 440 to 465 HV. This cured the entire rivet, including the head.

Various riveted joints thus obtained were measured for tensile shear strength TSS (JIS Z 3136) and cross tensile strength CTS (JIS Z 3137). The measurement results are shown in the table below. In all riveted joints, the hardness (shaft hardness) at the center in the axial direction and the center in the radial direction was within the range of 300 HV or more and 600 HV or less.

As shown in Table 6, the TSS of the riveted joint with the quenched portion was dramatically increased compared to the TSS of the riveted joint without the quenched portion, regardless of the shape of the rivet.

The present invention provides a method for producing riveted joints capable of producing joints with high cross tensile strength (CTS) and tensile shear strength (TSS), and riveted joints and automotive parts having joints with high CTS and TSS. can be provided, it has high industrial applicability.

1 Rivet joint 11 Plate material 111 Through hole 112 Plate surface 12 Rivet 121 Shaft part 122 Head part 123 Deformed part 124 Hardened part 13 Adhesive 2 Spot welding part A Electrode

Claims (18)

passing the shank of a steel rivet through a through-hole of a plurality of stacked plate materials;
sandwiching the rivet between a pair of electrodes in the axial direction of the rivet;
pressing and energizing the rivet with the pair of electrodes to crush the tip of the shaft;
cooling the rivet, and setting the Vickers hardness of the axial center and the radial center of the shaft of the rivet after cooling to 300 HV or more and 600 HV or less;
A method of manufacturing a riveted joint comprising: 2. The method of manufacturing a riveted joint according to claim 1, wherein at least one of the plurality of plate materials is a high-strength steel plate having a tensile strength of 1180 MPa class or higher. 3. Manufacture of a riveted joint according to claim 1 or 2, further comprising joining the plurality of plate materials by one or more welding methods selected from the group consisting of spot welding, laser welding, and arc welding. Method. 4. The method according to any one of claims 1 to 3, further comprising: applying an adhesive between the plurality of plate materials, at least around the through holes, and then stacking the plurality of plate members. manufacturing method of riveted joints. The method for manufacturing a riveted joint according to any one of claims 1 to 4, characterized in that a difference in diameter of said through-holes in a plurality of adjacent plate materials is within a range of 0.3 mm to 3 mm. The method for manufacturing a riveted joint according to any one of claims 1 to 5, characterized in that the highest temperature reached at the point at the center in the axial direction and the center in the radial direction of the shaft portion is over 900°C. The carbon content of the rivet is 0.08 to 0.32% by mass,
The method for manufacturing a riveted joint according to any one of claims 1 to 6, wherein the carbon equivalent of the rivet is 0.22 to 0.45% by mass. The method for manufacturing a riveted joint according to any one of claims 1 to 7, further comprising heating the rivet before passing the shaft portion through the through hole. a plurality of stacked plates each having a through hole;
a rivet having a shaft penetrating through the through hole and crimping the plurality of plate members;
with
A rivet joint, wherein the Vickers hardness of the axial center and radial center of the shaft portion of the rivet is 300 HV or more and 600 HV or less. 10. The rivet joint according to claim 9, wherein at least one of the plurality of plate materials is a high-strength steel plate having a tensile strength of 1180 MPa class or higher. 11. A riveted joint according to claim 9 or 10, further comprising one or more welds selected from the group consisting of spot welds, laser welds and arc welds. The rivet joint according to any one of claims 9 to 11, further comprising an adhesive disposed between the plurality of plate members and around at least the through holes. The rivet joint according to any one of claims 9 to 12, characterized in that a difference in diameter of said through-holes in a plurality of adjacent plate members is within a range of 0.3 mm to 3 mm. The rivet has a carbon content of 0.08 to 0.32% by mass,
A riveted joint according to any one of claims 9 to 13, characterized in that the rivet has a carbon equivalent of 0.22 to 0.45 mass%. the rivet has a head portion and a deformed portion arranged at both ends of the shank;
In a cross-sectional view parallel to the axis of the shaft of the rivet, the top surface of the head and/or the deformed portion is the surface of the plate near the rivet in the direction along the axis of the shaft. 15. The rivet joint according to any one of claims 9 to 14, wherein the rivet joint according to any one of claims 9 to 14 is located on the shaft portion side of a position 0.6 mm away from the shaft portion. Automobile part comprising a riveted joint according to any one of claims 9-15. 17. Automobile part according to claim 16, characterized in that it is a bumper or a B-pillar. A rivet for electric heating made of steel and having a shaft portion that is passed through a through-hole of a plurality of stacked plate materials, is quenched at the center, and is crushed at the tip,
The carbon content is 0.08 to 0.32% by mass,
A rivet for electric heating, characterized by having a carbon equivalent of 0.22 to 0.45% by mass.

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