JP2021171774A - Joint member, welded joint, method for manufacturing welded joint, and method for manufacturing joint member - Google Patents

Abstract

To provide a joint member which enables joining of high-strength steel materials by friction welding, a welded joint of a high-strength steel material obtained by friction welding, and a method for manufacturing them.SOLUTION: A joint member that joins a first steel material and a second steel material superposed on the first steel material and is made of steel includes a shaft part, and a head part that is provided at a first end of the shaft part and overhangs outside outer periphery of the shaft part in plan view vertical to an axial direction of the shaft part. A diameter of the shaft part is 2.5-10.0 mm, the shaft part has a pointed end provided at a second end of the shaft part, the pointed end is composed of an oblique surface forming an angle to the axial line of 45-75° in a plane including the axial line of the shaft part, Vickers hardness at a depth of 1.25 mm from the surface of the shaft part is 180-550 HV, and Vickers hardness at a depth of 0.05 mm from the surface of the shaft part is 600 HV or harder.SELECTED DRAWING: Figure 1

Description

The present invention relates to a joining member, a joining joint, a method for manufacturing a joining joint, and a method for manufacturing a joining member.

Friction welding is known as one of the methods for joining members to manufacture a joined joint. Friction welding is a technique for solid-phase joining members by applying pressure while rubbing the members. Friction between the members is performed, for example, by forming the pressure contact surface of one member into a rotationally symmetric shape (for example, a circular shape or a polygonal shape) and rotating the pressure contact surface at high speed.

One of the features of friction welding is that the members do not melt or stir at the joint. Welding is a joining method in which a joint is formed by melting and resolidifying a member. Friction stir welding is a joining method in which a press-fit member is rotated at high speed to stir the contact portions between the members to form a joint portion. Therefore, the members are mixed at the joint portion of the joint joint formed by welding or friction stir welding. On the other hand, in the joint joint formed by friction welding, the region where the members are mixed does not exist or is extremely small. By observing the cross section of the joint portion of the joint formed by friction welding, it is possible to determine how the members are separated through the friction welding surface.

As a technique related to friction welding, for example, Patent Document 1 describes, in terms of mass%, C: 0.1 to 0.8%, Si: 0.05 to 2.5%, Mn: 0.2 to 3%, Al: A member made of a steel material containing 0.005 to 0.1% and N: 0.001 to 0.02%, the balance of which is composed of Fe and unavoidable impurities, and a tensile strength of 600 MPa or more is friction-welded. Disclosed is a friction welding component having excellent fatigue resistance, characterized in that the compressive residual stress on the surface of the friction welding portion is 50 to 90% of the tensile strength of the steel material. ing.

Patent Document 2 describes a method of friction welding of a propeller shaft in which a thin-walled pipe and a thick-walled pipe are coaxially arranged, and both end faces are pressed against each other by frictional heat generated by abutting the end faces thereof and rotating relative to each other. A method of friction welding of a propeller shaft is disclosed, which comprises making the inner diameter of the pipe smaller than the inner diameter of a thick pipe.

In friction welding, there is an upper limit to the size of the joint surface (friction welding surface). Therefore, a rivet-shaped joining member is used when friction welding a large non-bonding material. Specifically, (1) first, while rotating the joining member at high speed, the shaft portion is pressed against the upper plate to allow the shaft portion to penetrate the upper plate, and (2) then the tip portion of the joining member is lowered. Friction welding to the plate. As a result, the upper plate is crimped by the head of the joining member, and the upper plate and the lower plate are joined. In this case, it is the joining member and the lower plate that are friction-welded, and the upper plate and the lower plate are mechanically joined by the rivet-shaped joining member. However, for the sake of simplification of the description, such a joining in which a mechanical joining and a friction welding are combined is also referred to as "friction welding" below.

Japanese Unexamined Patent Publication No. 2006-297398 Japanese Unexamined Patent Publication No. 2004-141933

The present inventors have studied applying such friction welding to joining high-strength steel materials. In recent years, application of high-strength steel materials (for example, steel sheets having a tensile strength of 780 MPa or more) to mechanical parts (for example, automobile parts) has been promoted. In this process, a decrease in the joint strength of the spot welded portion of the high-strength steel material has become a problem. Generally, the higher the strength of the steel material, the higher the strength of the spot welded portion thereof. However, when the strength of the steel material exceeds about 780 MPa, the higher the strength of the steel material, the lower the strength of the spot welded portion (particularly, the cross tensile strength CTS). It is presumed that this is because the alloying elements contained in the steel material in order to improve the strength of the steel material embrittle the spot welded portion.

When joining high-strength steel materials by the above-mentioned friction welding, the steel materials are mechanically joined. Therefore, according to friction welding, embrittlement of the high-strength steel material does not occur. The present inventors considered that friction welding is promising as a means for joining high-strength steel materials. However, when friction welding is applied to joining high-strength steel materials, the problems described below have been found.

As described above, in order to join steel materials by friction welding, (1) a step of penetrating the shaft portion of the joining member through one steel material (hereinafter, the member penetrated by the joining member is referred to as a second steel material). And (2) a step of friction welding the tip of the joining member to the other steel material (hereinafter, the member with which the joining member is friction-welded is referred to as a first steel material) is required. However, when the second steel material is a high-strength steel material, the tip portion of the shaft portion of the joining member is deformed before penetrating the second steel material, and the second steel material cannot be penetrated.

On the other hand, the present inventors have found that if the hardness of the shaft portion is increased to facilitate penetration, it becomes difficult to friction-weld the tip portion of the joining member to the first steel material. As a result of various experiments, the present inventors have found that the joint strength (force to withstand tension in the peeling direction) of the joint cannot be sufficiently secured depending on the joint member in which the hardness of the shaft portion is increased. As a result of detailed investigation of such a joint, the joint member of the joint with insufficient joint strength has a smaller amount of plastic deformation at the tip than the joint with sufficient joint strength, and friction. It was found that the area of the pressure welding surface was also small.

At the time of friction welding, the tip of the joining member is crushed and plastically deformed so as to spread away from the axis. This plastic deformation increases the area of the friction welding surface. It is presumed that there is a strong correlation between the area of the friction welding surface and the joint strength of the friction welding surface. In other words, if the plastic deformation of the tip of the joining member is small, it is presumed that the area of the friction welding surface cannot be secured and the joining strength is insufficient.

As described above, the joining member for friction welding a high-strength steel material is required to have both a function of penetrating the second member and a function of friction welding with the first member. It is not easy to enhance both of these features. In the prior art, there are almost no examples of attempting friction welding of high-strength steel materials, and means for solving the above-mentioned problems have not been studied in the prior art.

In view of the above circumstances, the present invention provides a joining member capable of joining high-strength steel materials by friction welding, a joint joint of high-strength steel materials obtained by friction welding, and a method for manufacturing these. Make it an issue.

The gist of the present invention is as follows.
(1) The joining member according to one aspect of the present invention is a steel joining member for joining a first steel material and a second steel material superposed on the first steel material, and is a shaft portion and the above. It is provided at the first end of the shaft portion, and has a head projecting outward from the outer periphery of the shaft portion in a plan view perpendicular to the axis direction of the shaft portion, and the diameter of the shaft portion is 2.5. ~ 10.0 mm, the shaft portion has a tip portion provided at the second end of the shaft portion, and the tip portion is 45 with respect to the axis in a plane including the axis of the shaft portion. It is composed of slopes forming an angle of ~ 75 °, and the Vickers hardness of the shaft portion at a depth of 1.25 mm from the surface is 180 to 550 HV, and the shaft portion has a depth of 0.05 mm from the surface. Vickers hardness in is 600 HV or more.
(2) In the joining member according to (1) above, the chemical composition in the shaft core of the shaft portion is C: 0.10 to 0.50% and Si: 0.02 to 3.00% in mass%. , Mn: 0.05 to 3.00%, Cr: 0.02 to 1.50%, P: 0.030% or less, S: 0.030% or less, Al: 0.100% or less, N: 0 It may contain .001 to 0.05%, and the balance may be Fe and impurities.
(3) The joining member according to (1) or (2) may have a carburized layer on the surfaces of the shaft portion and the tip portion.
(4) The joining member according to (1) or (2) may have a nitriding layer on the surfaces of the shaft portion and the tip portion.
(5) The joint joint according to another aspect of the present invention is provided at the first steel material, the second steel material superposed on the first steel material, the shaft portion, and the first end of the shaft portion. A joint member having a head for crimping the second steel material is provided, the shaft portion of the joint member penetrates the second steel material, and the second end of the shaft portion becomes the first steel material. Friction welding is performed, the second steel material is crimped by the head portion, and the Vickers hardness of the shaft portion at a depth of 1.25 mm from the surface is 150 to 550 HV. The Vickers hardness at a depth of 0.05 mm from the surface is 350 HV or more.
(6) In the joint according to (5) above, even if the tensile strength of the second steel material is 150 to 2100 MPa and the thickness of the second steel material is 0.3 to 2.5 mm. good.
(7) The method for manufacturing a joint joint according to another aspect of the present invention includes a step of superimposing a first steel material and a second steel material and the joining according to any one of (1) to (4) above. The step of pressing the member against the second steel material while rotating the member to penetrate the shaft portion of the joining member with respect to the second steel material, and pressing the joining member against the first steel material while rotating the member. A step of friction welding the tip of the shaft portion to the first steel material is provided.
(8) The method for manufacturing a joining member according to another aspect of the present invention is the method for manufacturing a joining member according to any one of (1) to (4) above, wherein a steel material is molded and joined. The process includes a step of obtaining the member and a step of heat-treating the shaft portion and the tip portion of the joint member to harden the surface thereof.
(9) In the method for producing a joining member according to (8) above, the heat treatment may be a carburizing treatment, a nitriding treatment, a carburizing nitriding treatment, or a soft nitriding treatment.

According to the present invention, it is possible to provide a joining member capable of joining high-strength steel materials by friction welding, a joint joint of high-strength steel materials obtained by friction welding, and a method for producing these.

It is sectional drawing in the plane including the axis of an example of a joining member. It is sectional drawing in the plane including the axis of an example of a joint. It is the schematic which shows an example of the manufacturing method of a joined joint. It is the schematic of the surface hardening treatment condition (1). It is the schematic of the surface hardening treatment condition (2). It is the schematic of the surface hardening treatment condition (3). It is the schematic of the surface hardening treatment condition (4). It is the schematic of the surface hardening treatment condition (5). It is the schematic of the surface hardening treatment condition (6).

The joining member for friction welding the high-strength steel material easily penetrates one steel material (hereinafter, the member penetrated by the joining member is referred to as a second steel material), and the other steel material (hereinafter, the joining member) The member that is friction-welded is referred to as the first steel material) and must be easily friction-welded. The present inventors have diligently studied a joining member that satisfies both of these conditions. As a result, the present inventor found that the penetrating ability of the tip of the shaft largely depends on the hardness of the surface layer of the shaft, while the deformation ability of the tip greatly depends on the hardness of the inside of the shaft. bottom. According to this finding, even if only the surface hardness of the shaft portion is increased, the ability to penetrate the second steel material can be enhanced. Further, even when the hardness of the surface layer of the shaft portion is increased, if the inside of the shaft portion is made soft, the area of the friction welding surface can be secured and the joint strength can be increased.

As shown in FIG. 1, the joining member 1 according to one aspect of the present invention obtained by the above findings joins the first steel material 21 and the second steel material 22 superposed on the first steel material 21. A steel joint member 1 provided at the shaft portion 11 and the first end of the shaft portion 11 and outward from the outer circumference of the shaft portion 11 in a plan view perpendicular to the axis A direction of the shaft portion 11. The shaft portion 11 has a diameter of 2.5 to 10.0 mm, and the shaft portion 11 has a tip portion 111 provided at the second end of the shaft portion 11. The portion 111 is composed of a slope 1111 forming an angle of 45 to 75 ° with respect to the axis A in a plane including the axis A of the shaft portion 11, and the Vickers hardness of the shaft portion 11 at a depth of 1.25 mm from the surface. The Vickers hardness of the shaft portion 11 at a depth of 0.05 mm from the surface is 600 HV or more. Hereinafter, the joining member 1 according to the present embodiment will be described in detail.

The joining member 1 has a shaft portion 11 and a head portion 12 provided at one end of the shaft portion 11 (hereinafter, referred to as a first end for convenience). Further, the shaft portion 11 has a tip portion 111 at the other end portion (hereinafter, referred to as a second end for convenience).

(Head 12)
The head portion 12 has a role of sandwiching the second steel material 22 after the tip portion 111 of the joining member 1 is joined to the first steel material 21. Therefore, the diameter of the head portion 12 is made larger than the diameter of the hole formed by the shaft portion 11 penetrating the second steel material 22. Since the diameter of the hole formed in the second steel material 22 and the diameter of the shaft portion 11 are substantially the same, the head portion 12 has a shape protruding outward from the outer circumference of the shaft portion 11. ..

The specific size of the head portion 12 is not particularly specified, and the second steel material 22 may be mechanically joined to the first steel material 21. For example, the diameter of the head portion 12 may be defined as 1.1 times or more, 1.2 times or more, or 1.5 times or more the diameter of the shaft portion 11. Here, the diameter of the head portion 12 and the diameter of the shaft portion 11 mean the diameters of these cross sections if the shape in the C cross section (cross section perpendicular to the axis A of the shaft portion 11) is a circle. If the shape in the C cross section of is a shape other than a circle (for example, a polygon), it means the longest width of the cross section. In many cases, the longest width of the cross section is the diameter of the smallest inclusion circle in the cross section.

(Shaft 11)
The shaft portion 11 has a so-called tapered shape in which the tip thereof becomes thinner as it approaches the second end of the shaft portion 11. Hereinafter, the tip of the shaft portion 11 is referred to as a tip portion 111. The tip portion 111 plays a role of promoting the penetration of the second steel material 22 by the joining member 1.

The diameter of the shaft portion 11 is 2.5 to 10.0 mm. The diameter of the shaft portion 11 is the longest width of the shaft portion 11 (excluding the portion designated as the tip portion 111) if the shaft portion shape in the C cross section is a shape other than a circle (for example, a polygon). If the shape of the shaft portion in this C cross section is a circle, it means the diameter thereof. When the diameter of the shaft portion 11 is less than 2.5 mm, it becomes difficult to secure the joint strength of the joint joint 2. On the other hand, when the diameter of the shaft portion 11 exceeds 10.0 mm, it becomes difficult for the shaft portion 11 to penetrate the second steel material 22.

In FIG. 1, the diameter of the shaft portion 11 is constant along the longitudinal direction thereof. On the other hand, the shaft portion 11 may have a tapered shape, and its diameter may be gradually narrowed toward the tip. In this case, the diameter of the shaft portion 11 may be 2.5 to 10.0 mm over the entire longitudinal direction (excluding the portion designated as the tip portion 111).

The length of the shaft portion 11 (distance along the axis A between the boundary between the shaft portion 11 and the head portion 12 and the boundary between the shaft portion 11 and the tip portion 111) is such that the joining member 1 is the second steel material 22. Can be appropriately selected within the range in which the first steel material 21 can be reached through the plate thickness direction. That is, the length of the shaft portion 11 may be selected according to the thickness of the second steel material 22. Therefore, in the joining member 1 according to the present embodiment, the length of the shaft portion 11 is not particularly limited. In view of the preferable thickness of the second steel material 22 described later, the length of the shaft portion 11 may be 3.0 mm or more and 9.0 mm or less.

The tip portion 111 is composed of a slope forming an angle of 45 to 75 ° with respect to the axis A in a plane including the axis A of the shaft portion 11. In other words, when the joining member 1 is cut on the plane including the axis A of the shaft portion 11, the angle of the portion marked with the reference numeral θ shown in FIG. 1 must be 45 to 75 °. When θ is more than 75 °, it becomes difficult for the shaft portion 11 to penetrate the second steel material 22. On the other hand, when θ is less than 45 °, the tip portion 111 is deformed and blunted in the early stage of the drilling process, and the shaft portion 11 penetrates the second steel material 22 as in the case where θ is more than 75 °. It becomes difficult to do. θ may be 48 ° or more, 50 ° or more, or 52 ° or more. θ may be 70 ° or less, 60 ° or less, 58 ° or less, 55 ° or less, or 53 ° or less.

Further, in the shaft portion 11, the Vickers hardness at a position (inside) at a depth of 1.25 mm from the surface is 180 to 550 HV, and the Vickers hardness at a position (surface layer) at a depth of 0.05 mm from the surface is set. Is 600 HV or more.

By setting the hardness of the surface layer of the shaft portion 11 to 600 HV or more, the penetration ability of the joining member 1 can be enhanced, and for example, a steel material having a tensile strength of 150 MPa or more can be penetrated. The hardness of the surface layer of the shaft portion 11 may be 620 HV or more, 650 HV or more, or 700 HV or more.

It is not necessary to set an upper limit on the hardness of the surface layer of the shaft portion 11. As long as the hardness inside the shaft portion 11 described later is appropriate, the hardness of the surface layer of the shaft portion 11 is preferably larger. On the other hand, the hardness of the surface layer of the shaft portion 11 may be 1000 HV or less, 900 HV or less, or 800 HV or less in consideration of the capacity of the manufacturing equipment.

Further, by setting the internal hardness of the shaft portion 11 to 550 HV or less, the deformation ability of the tip portion 111 can be enhanced, the friction welding surface can be expanded, and the joint strength can be improved. The hardness inside the shaft portion 11 may be 500 HV or less, 450 HV or less, or 400 HV or less.

However, if the internal hardness of the shaft portion 11 is too low, the penetration ability and joining strength of the joining member 1 may be insufficient. Therefore, the hardness inside the shaft portion 11 is set to 180 HV or more. The hardness inside the shaft portion 11 may be 200 HV or more, 250 HV or more, or 300 HV or more.
The hardness of the tip portion 111 is not particularly specified. Normally, when the hardness of the surface layer of the shaft portion 11 is increased as described above, the hardness of the surface layer of the tip portion 111 tends to be slightly higher than that of the shaft portion 11 (for example, more than 0% and 15% or less). Is. Such a phenomenon has been reported in, for example, Toshiyuki Morita and Yasushi Matsumura, "Effects of Alloy Components on Excessive Carburizing of Edges in Vacuum Carburizing" (Electrical Steelmaking, Vol. 81, No. 2, 2010, pp. 109-p116). The surface layer of the tip portion 111 has a higher carbon concentration after carburizing than the surface layer of the shaft portion 11. Therefore, the tip portion 111 usually has a higher hardness than the shaft portion 11. On the other hand, the hardness of the inside of the tip portion 111 is the same as that of the inside of the shaft portion 11 at a portion where the influence of surface treatment such as carburizing is small. Therefore, if the hardness of the shaft portion 11 is defined as described above, it is considered that the penetration performance of the joining member 1 is ensured. This is supported by the experimental results of the inventors.

The hardness of the surface layer of the shaft portion 11 is such that the resin-embedded joining member 1 is cut on a surface substantially including the axis A of the shaft portion 11, the cut surface is polished, and the depth is 0.05 mm from the surface. It is obtained by performing a Vickers hardness test 5 times with a load of 0.3 kgf and averaging the measured values. The hardness of the inside of the shaft portion 11 is obtained by making the above-mentioned measurement at a depth of 1.25 mm from the surface.

The chemical composition of the joining member 1 can be appropriately selected so that the hardness of the shaft portion 11 is within the above range. A suitable example of the chemical composition will be described below. However, the following chemical composition is only an example, and the chemical composition of each part of the joining member 1 is not limited as long as the above requirements are satisfied.

The chemical composition in the shaft core of the shaft portion 11 is, for example, C: 0.10 to 0.50%, Si: 0.02 to 3.00%, Mn: 0.05 to 3.00%, Cr. : 0.02 to 1.50%, P: 0.030% or less, S: 0.030% or less, Al: 0.100% or less, and N: 0.001 to 0.05%, and the balance Are Fe and impurities. Hereinafter, the chemical composition in the shaft core of the shaft portion 11 of the joining member may be simply referred to as the chemical composition of the joining member 1.

(C: preferably 0.10 to 0.50%)
C is an essential element for ensuring the strength of steel. By setting the C content of the joining member 1 to 0.10% or more, the strength of the joining member 1 can be further increased, and the penetrating ability and the joining strength can be secured. On the other hand, by setting the C content of the joining member 1 to 0.50% or less, the deformability of the tip portion 111 can be secured and the area of the friction welding surface can be further increased.

(Si: preferably 0.02 to 3.00%)
Si is an element that enhances the hardenability of steel and increases the temper softening resistance. By setting the Si content of the joining member 1 to 0.02% or more, the strength of the joining member 1 can be further increased, and the penetration ability and the joining strength can be secured. On the other hand, by setting the Si content of the joining member 1 to 3.00% or less, the deformability of the tip portion 111 can be secured and the area of the friction welding surface can be further increased.

(Mn: preferably 0.05 to 3.00%)
Mn is an element that enhances the hardenability of steel. By setting the Mn content of the joining member 1 to 0.05% or more, the strength of the joining member 1 can be further increased, and the penetration ability and the joining strength can be secured. On the other hand, by setting the Mn content of the joining member 1 to 3.00% or less, the deformability of the tip portion 111 can be secured and the area of the friction welding surface can be further increased.

(Cr: preferably 0.02 to 1.50%)
Cr is an element that enhances the hardenability of steel. By setting the Cr content of the joining member 1 to 0.02% or more, the strength of the joining member 1 can be further increased, and the penetration ability and the joining strength can be secured. On the other hand, by setting the Cr content of the joining member 1 to 1.50% or less, the deformability of the tip portion 111 can be secured and the area of the friction welding surface can be further increased.

(P: preferably 0.030% or less)
P is an element that segregates at the grain boundaries and lowers the grain boundary strength. By setting the P content of the joining member 1 to 0.030% or less, it is possible to prevent grain boundary cracking of the joining member 1 and further increase the joining strength. The P content may be 0%. However, the lower limit of the P content may be 0.001% or more, 0.002% or more, or 0.005% or more in consideration of the capacity of the manufacturing equipment and the manufacturing cost.

(S: preferably 0.030% or less)
S is an element that reduces the hot ductility of steel. Therefore, by setting the S content of the joining member 1 to 0.030% or less, the production of the joining member 1 can be further facilitated. The S content may be 0%. However, the lower limit of the S content may be 0.001% or more, 0.002% or more, or 0.005% or more in consideration of the capacity of the manufacturing equipment and the manufacturing cost.

(Al: preferably 0.100% or less)
Al has a deoxidizing action and can increase the toughness of the joining member 1. On the other hand, when the Al content exceeds 0.100%, the above-mentioned effect is saturated. Therefore, it is preferable that the Al content of the joining member 1 is 0.100% or less. The Al content may be 0%. However, the lower limit of the Al content may be 0.001% or more, 0.002% or more, or 0.005% or more in consideration of the capacity of the manufacturing equipment and the manufacturing cost.

(N: preferably 0.001 to 0.05%)
N is an element that forms a nitride and enhances the strength of steel by precipitation strengthening. By setting the N content of the joining member 1 to 0.02% or more, the strength of the joining member 1 can be further increased, and the penetrating ability and the joining strength can be secured. On the other hand, by setting the N content of the joining member 1 to 0.05% or less, the deformability of the tip portion 111 can be secured and the area of the friction welding surface can be further increased.

The balance of the chemical components of the joining member 1 can be, for example, iron and impurities. Impurities are components that are mixed in by raw materials such as ore or scrap, or various factors in the manufacturing process, for example, when steel materials are industrially manufactured, and have an adverse effect on the joining member 1 according to the present embodiment. It means what is allowed within the range not given.
The above-mentioned chemical composition is a measured value at the shaft core of the shaft portion 11. The measurement is carried out by a high-frequency combustion method using chips collected from the shaft core of the shaft portion 11. Specifically, chips are collected from a region having a diameter of 100 μm centered on the shaft core of the shaft portion 11, the C and S contents are determined by a high frequency inductive heating combustion method, and the N content is an inert gas melting. -The thermal conductivity method is used to determine the content of other elements by inductively coupled plasma emission spectrometry (ICP-OES).

The hardness of the surface layer of the shaft portion 11 needs to be larger than that of the inside. The means for controlling the hardness is not particularly limited, and for example, the hardness of the surface layer of the shaft portion 11 may be increased by various heat treatments. For example, a carburizing treatment layer or a nitriding treatment layer may be provided on the surface of the shaft portion, whereby the Vickers hardness at a depth of 0.05 mm from the surfaces of the shaft portion and the tip portion may be 600 HV or more. Further, an induction hardening layer may be provided on the surface of the shaft portion. When a surface treatment layer such as a carburizing treatment layer, a nitriding treatment layer, and an induction hardening layer is provided on the surface of the shaft portion 11, these surface treatment layers are also formed on the tip portion 111, the head portion 12, and the like. Is normal.

Next, the joint joint 2 according to another aspect of the present invention will be described. As shown in FIG. 2, the joint joint 2 according to another aspect of the present invention includes a first steel material 21, a second steel material 22 superposed on the first steel material 21, a shaft portion 11, and a shaft. It is provided with a joining member 1 provided at the first end of the portion 11 and having a head portion 12 for crimping the second steel material 22, and the shaft portion 11 of the joining member 1 penetrates the second steel material 22 and has a shaft portion. The second end of 11 is friction-welded to the first steel 21, the second steel 22 is crimped by the head 12, and the Vickers hardness of the shaft 11 at a depth of 1.25 mm from the surface. Is 150 to 550 HV, and the Vickers hardness of the shaft portion 11 at a depth of 0.05 mm from the surface is 350 HV or more.

The first steel material 21 of the joint 2 is a steel material to which the joint member 1 is friction-welded. In the first steel material 21, it is desirable that the surface to which the joining member 1 is pressure-contacted is larger than the shaft portion 11 of the joining member 1. In the first steel material 21, when the surface to which the joining member 1 is pressure-welded is smaller than the shaft portion 11 of the joining member 1, the first steel material 21 bites into the inside of the shaft portion 11 of the joining member 1, which is normal. This is because friction welding becomes difficult.

However, in other words, in the joint joint 2 in which the second end of the shaft portion 11 of the joining member 1 is friction-welded to the first steel material 21, the first steel material 21 satisfies the above-mentioned requirements. Is normal. Therefore, in the joint joint 2 according to the present embodiment, the first steel material 21 is not particularly limited. The strength, chemical composition, etc. are not particularly limited. This is because, unlike welding, friction welding can join dissimilar metals. For example, the tensile strength of the first steel material 21 may be 150 to 2100 MPa.

The second steel material 22 is a steel material through which the joining member 1 has penetrated, and is mechanically joined to the first steel material 21 by being crimped by a head portion 12 arranged at the first end of the joining member 1. In the joint joint 2 according to the present embodiment, the second steel material 22 is not particularly limited. The strength, chemical composition, etc. are not particularly limited. This is because, unlike welding, the second steel material 22 of the joint joint 2 according to the present embodiment is mechanically joined to the first steel material 21. Further, in the joint joint 2 according to the present embodiment, since the joint member 1 has a high penetration ability, even if the second steel material 22 is a high-strength steel material, the joint member 1 can be penetrated.

A preferred embodiment of the second steel material 22 is as follows. The tensile strength of the second steel material 22 may be, for example, 150 to 2100 MPa. By setting the tensile strength of the second steel material 22 to 150 MPa or more, the strength of the joint joint 2 can be further increased. Further, by setting the tensile strength of the second steel material 22 to 2100 MPa or less, the occurrence of joint defects can be further suppressed. The tensile strength of the second steel material 22 may be 250 MPa or more, 550 MPa or more, or 950 MPa or more. The tensile strength of the second steel material 22 may be 1900 MPa or less, 1700 MPa or less, or 1500 MPa or less.

The thickness of the second steel material 22 may be, for example, 0.3 mm to 2.5 mm. By setting the thickness of the second steel material 22 to 0.3 mm or more, the strength of the joint joint 2 can be further increased. Further, by setting the thickness of the second steel material 22 to 2.5 mm or less, the occurrence of joint defects can be further suppressed. The thickness of the second steel material 22 may be 0.5 mm or more, 0.7 mm or more, or 0.9 mm or more. The thickness of the second steel material 22 may be 2.2 mm or less, 2.0 mm or less, or 1.8 mm or less.

The joining member 1 is provided at the shaft portion 11 and the first end of the shaft portion 11, and the head portion 12 projecting outward from the outer circumference of the shaft portion 11 in a plan view perpendicular to the axis A direction of the shaft portion 11. And have. Further, the shaft portion 11 of the joining member 1 penetrates the second steel material 22, and the second end of the shaft portion 11 of the joining member 1 is friction-welded to the first steel material 21. With these configurations, the joining member 1 sandwiches the second steel material 22 between the second end joined to the first steel material 21 and the head portion 12, and the first steel material 21 and the second steel material 22 And mechanically join.

However, in the joint joint 2 according to the present embodiment, it is usual that no trace of the tip portion 111 of the joint member 1 can be confirmed. This is because, as shown in FIG. 2, the tip portion 111 of the joining member 1 is significantly plastically deformed during friction welding. Therefore, in the joint joint 2 according to the present embodiment, the tip portion 111 is not particularly specified.

Further, in the joining member 1, the Vickers hardness of the shaft portion 11 at a depth of 1.25 mm from the surface (inside) is 150 to 550 HV, and the Vickers hardness is set to a depth of 0.05 mm from the surface (surface layer). The Vickers hardness in the above is 350 HV or more. Since the hardness of the surface layer of the joining member 1 is appropriately controlled, in the joining joint 2 according to the present embodiment, the shaft portion 11 can be easily penetrated through the second steel material 22. Further, since the internal hardness of the joining member 1 is appropriately controlled, in the joining joint 2 according to the present embodiment, the shaft portion 11 is largely plastically deformed to secure the area of the friction welding surface and join. The joint strength between the member 1 and the first steel material 21 can be increased. According to the experimental results of the present inventors, the hardness of the joining member 1 after friction welding tends to be lower than that before friction welding, especially in the surface layer portion. The Vickers hardness of the shaft portion 11 at a depth of 1.25 mm from the surface may be 160 HV or more, 180 HV or more, or 200 HV or more. The Vickers hardness of the shaft portion 11 at a depth of 1.25 mm from the surface may be 520 HV or less, 500 HV or less, or 450 HV or less. The Vickers hardness of the shaft portion 11 at a depth of 0.05 mm from the surface may be 380 HV or more, 400 HV or more, or 420 HV or more.

In the joint joint 2, the hardness of the surface layer of the shaft portion 11 of the joint member 1 is such that the resin-embedded joint joint 2 is cut on a surface substantially including the axis A of the shaft portion 11 and the cut surface is polished. , The Vickers hardness test is performed 5 times at a depth of 0.05 mm from the surface of the shaft portion 11 of the joint member 1 with a load of 0.3 kgf, and the measured values are averaged. The hardness of the inside of the shaft portion 11 is obtained by making the above-mentioned measurement at a depth of 1.25 mm from the surface.

In principle, the above-mentioned measurement is performed at a portion of the shaft portion 11 that is not substantially plastically deformed. When the second end of the shaft portion 11 is significantly deformed and all parts of the shaft portion 11 are severely plastically deformed, the above measurement may be performed on the head portion 12. Usually, in the joining member 1 before friction welding, the surface layer hardness and the internal hardness are uniform as a whole. Therefore, when the surface hardness and the internal hardness of the head portion 12 are within the above ranges after friction welding, the surface hardness and the internal hardness of the shaft portion 11 can also be considered to be within the above ranges.

Other requirements of the joining member 1 in the joining joint 2 are not particularly limited. The preferable chemical composition and preferable surface structure of the joining member 1 are the same as those of the joining member 1 before friction welding described above.

Next, a method for manufacturing the joint joint 2 according to another aspect of the present invention will be described. As shown in FIG. 3, the method for manufacturing the joint joint 2 according to another aspect of the present invention includes the step S1 in which the first steel material 21 and the second steel material 22 are overlapped, and the joint member 1 according to the present embodiment. S2 in which the shaft portion 11 of the joining member 1 is penetrated through the second steel material 22 by pressing the joint member 1 against the second steel material 22 while rotating the joint member 1 and pressing against the first steel material 21 while rotating the joining member 1. A step S3 of friction welding the tip portion 111 of the shaft portion 11 to the first steel material 21.

In the method for manufacturing the joint joint 2, the Vickers hardness of the shaft portion 11 of the joint member 1 at a depth of 0.05 mm from the surface (surface layer) is set to 600 HV or more. Therefore, even if the second steel material 22 is a high-strength steel material, the shaft portion 11 of the joining member 1 can be easily penetrated through the second steel material 22. Further, in the method of manufacturing the joint joint 2, the Vickers hardness of the shaft portion 11 of the joint member 1 at a depth of 1.25 mm from the surface (inside) is set to 180 to 550 HV. Therefore, the tip portion 111 of the joining member 1 can be easily friction-welded to the first steel material 21.

As long as the joining member 1 is as described above, other conditions are not particularly specified in the method for manufacturing the joining joint 2. A preferred embodiment of the first steel material 21 and the second steel material 22 conforms to the embodiment described in the joint joint 2 according to the present embodiment described above. The rotation speed, pressing force, pressurizing time, etc. of the joining member 1 at the time of friction welding shall be appropriately selected according to various aspects of the joining member 1, the first steel material 21, and the second steel material 22. Can be done. For example, the rotation speed of the joining member 1 may be 1000 to 8000 rpm, and the pressing force of the joining member may be 3 to 9 kN, but the present invention is not limited to this.

Next, a method for manufacturing the joining member 1 according to another aspect of the present invention will be described. The method for manufacturing the joining member 1 according to another aspect of the present invention includes a step of forming a steel material to obtain the joining member 1 and a step of heat-treating the shaft portion 11 of the joining member 1 to harden the surface thereof. ..

The means for forming the steel material is not particularly limited, and examples thereof include cutting, hot working, and cold working. The joining member 1 obtained by molding a steel material has the above-mentioned shape.

Next, at least the shaft portion 11 of the joining member 1 is heat-treated to cure its surface. As a matter of course, the entire joining member 1 including the head portion 12 may be heat-treated to cause curing over the entire surface of the joining member 1. The type of heat treatment is not particularly limited, and examples thereof include carburizing treatment, nitriding treatment, carburizing nitriding treatment, and soft nitriding treatment. The surface layer of the shaft portion 11 may be hardened by induction hardening. A plurality of heat treatments may be combined. However, heat treatment (for example, quenching and tempering by heating in a furnace) that cures the inside of the joining member 1 is not preferable.

The specific heat treatment conditions are not particularly limited. As long as the surface hardness and internal hardness of the shaft portion 11 of the finally obtained joint member 1 are within the above ranges, various conditions can be adopted according to the chemical composition and shape of the joint member 1. ..

The effects of one aspect of the present invention will be described more specifically by way of examples. However, the conditions in the examples are only one condition example adopted for confirming the feasibility and effect of the present invention. The present invention is not limited to this one-condition example. The present invention may adopt various conditions as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

Various steel materials having the chemical components shown in Table 1 were molded to prepare a joining member. The shape of the joining member is as follows.
-Cross-sectional shape of the shaft: circular-Shaft diameter: 4.5 mm in diameter
-Head diameter: 9.0 mm in diameter
-Angle θ: 70 ° between the slopes that make up the tip and the axis

Next, various heat treatments were performed on the joint members. The heat treatment conditions are shown in FIGS. 4-1 to 4-6. In these figures, "Cp" means carbon potential, and _{the value of "C 2} H ₂ " is the flow rate of acetylene gas used for vacuum carburizing, and "NH ₃ " and "N". _{The values of "2} " and "CO ₂ " are the flow rates of the gas components used for various nitriding treatments. A plurality of joining members were prepared for each condition, a part of which was subjected to hardness measurement, and a part of which was subjected to friction welding. Further, none of these heat treatment conditions affect the chemical composition in the shaft core of the joining member of this embodiment. The chemical composition shown in Table 1 is the chemical composition of the steel material, which is presumed to be equal to the chemical composition in the shaft core of the shaft portion.

The manufactured joining members are embedded in resin, these joining members are cut on a surface substantially including the axis of the shaft, the cut surface is polished, and a load of 0.3 kgf is applied at a depth of 1.25 mm from the surface. The Vickers hardness test was carried out 5 times, and the measured values were averaged to obtain the hardness inside the shaft and the tip. Further, at a depth of 0.05 mm from the surface of the shaft portion of this cut surface, a Vickers hardness test was performed 5 times with a load of 0.3 kgf, and the measured values were averaged to obtain the shaft portion and the tip portion. The hardness of the surface layer was obtained. Table 2 shows the hardness of the shaft portion of each joining member.

Then, after the first steel material and the second steel material are overlapped with each other, the various joint members described above are rotated and pressed against the second steel material to penetrate the shaft portion of the joint member with respect to the second steel material. I let you. Further, the joining member was pressed against the first steel material while rotating, and the tip end portion of the shaft portion was friction-welded to the first steel material. In all the examples, the thickness of the first steel material was 1.6 mm, and the tensile strength of the first steel material was 980 MPa. The thickness of the second steel material was in the range of 1.0 to 1.4 mm, and the tensile strength of the second steel material was 590 MPa or 980 MPa. At the time of friction welding, the rotation speed of the joining member was set to 8000 rpm, and the pressing force of the joining member was set to 9 kN. Table 2 shows the components of the joining member, the heat treatment conditions of the joining member, and the tensile strength and thickness of the second steel material in each embodiment.

The joint strength of the various joint members thus obtained was evaluated by applying the chisel test specified in JIS Z 3144: 2013 mutatis mutandis. Specifically, a chisel was applied to the interface between the first steel material and the second steel material at an appropriate position near the friction welding portion, and press-fitting was performed. The joining member that did not break after the test was judged to have excellent joining strength. The judgment results are shown in Table 2.

Manufacturing No. In the comparative example of 17, the internal hardness of the joining member was excessive. Therefore, the production No. In the comparative example of 17, the tip portion of the joining member was not sufficiently deformed, the area of the friction welding surface was insufficient, and the result of the chisel test was unacceptable.

Manufacturing No. 18 and No. A comparative example of 19 is an example in which a high carbon steel material is subjected to normal quenching and uniformly hardened from the surface layer to the inside. Manufacturing No. 18 and No. In the 19th comparative example, the internal hardness of the joining member was excessive. Therefore, the production No. 18 and No. In the comparative example of 19, the tip portion of the joining member was not sufficiently deformed, the area of the friction welding surface was insufficient, and the result of the chisel test was unacceptable.

Manufacturing No. In the comparative example of 20, the surface hardness of the joining member was insufficient. Therefore, the production No. In the comparative example of 20, the joining member could not penetrate the second steel material, and the joining member could not be manufactured. Therefore, "x" is described in the test results.

On the other hand, the production No. in which the surface hardness and the internal hardness of the joining member were appropriate. In the examples of the inventions 1 to 15, the result of the chisel test was passed. That is, the production No. Examples of the inventions 1 to 15 were joining members capable of joining high-strength steel materials by friction welding.

According to the present invention, it is possible to provide a joining member capable of joining high-strength steel materials by friction welding, a joint joint of high-strength steel materials obtained by friction welding, and a method for producing these. When the present invention is applied to joining a high-strength steel plate having a tensile strength of 780 MPa or more, for example, it is possible to prevent embrittlement of the joint and manufacture a joint having a higher joint strength than a conventional spot welded joint. .. Therefore, the present invention has high industrial applicability.

1 Joining member 11 Shaft part 111 Pointed end part 1111 Slope 12 Head 2 Joining joint 21 First steel material 22 Second steel material A Axial line

Claims (9)

A steel joining member for joining a first steel material and a second steel material superposed on the first steel material.
Shaft and
A head provided at the first end of the shaft portion and projecting outward from the outer circumference of the shaft portion in a plan view perpendicular to the axial direction of the shaft portion is provided.
The diameter of the shaft portion is 2.5 to 10.0 mm, and the shaft portion has a diameter of 2.5 to 10.0 mm.
The shaft portion has a tip portion provided at the second end of the shaft portion, and has a tip portion.
The tip portion is composed of a slope forming an angle of 45 to 75 ° with respect to the axis in a plane including the axis of the shaft.
The Vickers hardness of the shaft portion at a depth of 1.25 mm from the surface is 180 to 550 HV.
A joining member having a Vickers hardness of 600 HV or more at a depth of 0.05 mm from the surface of the shaft portion. The chemical composition in the shaft core of the shaft portion is mass%.
C: 0.10 to 0.50%,
Si: 0.02 to 3.00%,
Mn: 0.05 to 3.00%,
Cr: 0.02 to 1.50%,
P: 0.030% or less,
S: 0.030% or less,
Al: 0.100% or less,
N: 0.001 to 0.05%,
The joining member according to claim 1, wherein the joining member contains Fe and impurities in the balance. The joining member according to claim 1 or 2, wherein the surface of the shaft portion and the tip portion has a carburized layer. The joining member according to claim 1 or 2, wherein the surface of the shaft portion and the tip portion has a nitriding treatment layer. The first steel material and
With the second steel material superimposed on the first steel material,
A joint member having a shaft portion and a head portion provided at the first end of the shaft portion and crimping the second steel material is provided.
The shaft portion of the joining member penetrates the second steel material,
The second end of the shaft portion is friction-welded to the first steel material.
The second steel material is crimped by the head.
The Vickers hardness of the shaft portion at a depth of 1.25 mm from the surface is 150 to 550 HV.
A joint joint having a Vickers hardness of 350 HV or more at a depth of 0.05 mm from the surface of the shaft portion. The tensile strength of the second steel material is 150 to 2100 MPa, and the tensile strength is 150 to 2100 MPa.
The joint according to claim 5, wherein the thickness of the second steel material is 0.3 to 2.5 mm. The process of superimposing the first steel material and the second steel material,
A step of pressing the joining member according to any one of claims 1 to 4 against the second steel material while rotating the joint member to penetrate the shaft portion of the joining member through the second steel material.
A step of friction-welding the tip of the shaft portion to the first steel material by pressing the joint member against the first steel material while rotating the joint member.
A method of manufacturing a joint joint comprising. The process of forming a steel material to obtain a joint member,
The method for manufacturing a joint member according to any one of claims 1 to 4, further comprising a step of heat-treating a shaft portion and a tip portion of the joint member to harden the surface thereof. The method for manufacturing a joining member according to claim 8, wherein the heat treatment is a carburizing treatment, a nitriding treatment, a carburizing nitriding treatment, or a soft nitriding treatment.

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