JP6692200B2 - Method for manufacturing mechanical clinch joint parts - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a mechanical clinch joint component and a method for manufacturing the same. In particular, it relates to a high-strength mechanical clinch joint component and a method for producing the component favorably without defects such as cracks.

  In order to achieve both collision safety and weight reduction of automobiles, the application of ultra-high strength steel sheets to body skeletons is increasing. In order to suppress the deformation of steel parts for automobiles to a certain level or less when subjected to the impact of a collision, at present, reinforcing members are joined by spot welding to the main members that make up the above steel parts, and partially thickened. We are reinforcing. However, in such a construction method, since the main member and the reinforcing member are respectively molded and then they are assembled by spot welding, there is a problem of increased cost.

  On the other hand, a joining method called mechanical clinch joining is known as a joining method for cold spot joining instead of the spot welding. This joining method is a kind of caulking joining in which metals are mechanically joined. Table 1 shows the types of caulking and the characteristics of each type. As shown in Table 1, there are several kinds of caulking joints. Among them, mechanical clinch bonding is a method of simultaneously pressing two or more metal plates with a convex punch and a concave die. As shown in Table 1, this mechanical clinch joining does not require pretreatment or joining auxiliary material and can be joined at the same time as press forming. Also, if it is applied to hot forming, it is cooled by a die to quench the joint. Is also possible.

  This mechanical clinch joint can realize low cost and high productivity as compared with spot welding. For example, Patent Document 1 discloses that caulking bonding called TOX (registered trademark) is performed at the same time as pressing that is presumed to be cold. However, the target of this joining method is a side outer panel, and the strength of the base metal of the component is low, and it is considered that even an ultrahigh-strength crimped component has not been realized.

  When mechanical clinch joining is performed in the cold state, if the strength of the steel sheets used increases, cracks occur during joining, and high strength steel parts cannot be obtained. On the other hand, in Patent Document 2, a relatively low temperature press in a state in which the burring portion of the bracket portion member that is not heated is fitted in the engagement hole of the beam body portion member that is at a high temperature of 850 ° C. or higher. It is shown that the beam main body is shaped and hardened by pressing using a mold, and the beam main body and the bracket are simultaneously caulked by bending or crushing the burring portion.

  However, this method requires a bracket part preparation step in advance for forming a bracket part member having a cylindrical flange-shaped burring part that can be fitted into the engagement hole of the beam body part member. That is, when processing into a complicated shape, a step different from the pressing step is required, which leads to an increase in cost. Further, it is not premised on using an ultra-high-strength steel plate, and it is conceivable that cracks may occur or a sufficiently high peel strength may not be exhibited even when heated and caulked.

  Therefore, in particular, a part obtained by using an ultra-high strength steel sheet having a tensile strength of 1180 MPa or more and having an ultra-high strength and a sufficiently high peel strength can be mechanically treated without an extra step other than the mechanical clinch joining step. It is required that the clinching is performed well without defects such as cracks.

International publication 2013/008515 pamphlet JP 2006-32405 A

  The present invention has been made by paying attention to the circumstances as described above, and an object thereof is to provide a mechanical clinch-bonding component having an ultrahigh strength and a sufficiently high peel strength with an extra step different from the mechanical clinch-bonding step. It is to realize a method for favorably manufacturing mechanical clinch joints without any troubles such as cracks.

  A mechanical clinch joint part of the present invention which can solve the above problems is a mechanical clinch joint part composed of two or more steel plates, and has at least one joint part having a peel strength of 0.200 kN / mm or more, and The hardness is Hv 360 or more.

In addition, the method of manufacturing the mechanical clinch joint component of the present invention that has solved the above problems is
Heating two or more steel plates to an Ac ₃ point or higher; and
A step of performing mechanical clinch joining so that the carbon equivalent Ceq of the steel sheet, the bottom dead center holding time t during mechanical clinch joining, and the joining start temperature T satisfy the following equations (1) and (2);
Is characterized by including in this order.
Ceq × (0.00209 × t + 0.000731 × T−0.0365) ≧ 0.200
... (1)
Ceq ≧ −0.00071 × T + 0.993 (2)
In the above formulas (1) and (2), Ceq is the carbon equivalent (mass%) of the steel plate obtained by the following formula (3), t is the bottom dead center holding time (seconds), and T is the joining start temperature (° C). ) Is shown. If the two or more steel plates have different Ceqs, the lowest Ceq is used.
Ceq = C + (1/6) × Mn + (1/24) × Si + (1/40) × Ni + (1/5) × Cr + (1/4) × Mo + (1/14) × V ... (3 )
In the above formula (3), each element represents the content in the steel sheet in mass%, and the elements not included are zero.

As for the two or more steel plates used in the manufacturing method, each has a composition of mass%,
C: 0.15-0.4%,
Si: more than 0% and 2% or less, and
At least one of Mn and Cr: 1.0-5.0% in total, and
Ti: 0% to 0.10%, B: 0% to 0.005%, Al: 0% to 0.5%, Mo: 0% to 1%, Cu: 0% to 0.5 % Or less, Ni: 0% or more and 0.5% or less, Nb: 0% or more and 0.10% or less, V: 0% or more and 0.10% or less, and Zr: 0% or more and 0.10% or less. May be used.

  In the method of manufacturing a mechanical clinch-bonded component, hot press molding may be performed together with the step of performing the mechanical clinch-bonding.

  Further, in the method of manufacturing the mechanical clinch-bonded component, the step of performing the mechanical clinch-bonding may be performed a plurality of times.

  According to the present invention, it is possible to provide a mechanical clinch-bonded component exhibiting ultrahigh strength and sufficiently high peel strength, and cracking the component by mechanical clinch bonding without providing an extra step different from the mechanical clinch-bonding step. It is possible to provide a good manufacturing method without problems such as the above.

FIG. 1 is a schematic diagram showing an embodiment of the present invention. FIG. 2 is a schematic diagram showing another embodiment of the present invention. FIG. 3 shows a mold to which a mechanical clinch tool is attached, which is used for manufacturing the test material in the examples. FIG. 4 is a diagram for explaining how to obtain d / D. FIG. 5 shows No. 1 in the embodiment. 5 (a) is an overall photograph of the component cross section, FIG. 5 (b) is a partial photograph of the component cross section, and FIG. 5 (c) is the ellipse of FIG. 5 (b). It is an enlarged photograph of a part. FIG. 6 is a diagram showing the relationship between the value on the left side of Expression (1) and the value of CTS / L.

The present inventors have conducted extensive studies to solve the above problems. First, in order to reconfirm the limit of the tensile strength at which cracking occurs in cold joining, a mechanical clinch tool used in Examples described later is attached to a steel sheet having a tensile strength of 270 to 1470 MPa and a plate thickness of 1.4 mm. Using a die, cold forming was performed to join in a cross shape. As a result, as shown in Table 2 below,
It was confirmed that when the tensile strength of the steel sheet was 780 MPa or more, cracking occurred during joining, and mechanical clinch joining could not be performed. In addition, below, "mechanical clinch joining" may be called "joining", and "mechanical clinch joining parts " may be called "joining parts."

As described above, the inventors of the present invention, as an ultra-high-strength steel sheet that has been required to be applied in recent years, have a tensile strength of 1180 MPa or more, that is, in the results shown in Table 2 above, it is clear that cracking occurs in cold joining. On the premise of using high-strength steel plates, we have conducted intensive studies to achieve good mechanical clinch bonding. In detail, earnest research was repeated to achieve all of the following (A) to (D).
(A) The component exhibits ultra-high strength, specifically, the hardness of the component is Vickers hardness Hv 360 or more, that is, a tensile strength of 1180 MPa or more, preferably Hv 450 or more, that is, a tensile strength of 1470 MPa or more. Showing;
(B) The peel strength of the component is high, specifically, the cross tensile strength per unit circumferential length of the joint portion, that is, the peel strength, which is obtained by the method described below, is 0.200 kN / mm or more;
(C) Being able to join without cracking when manufacturing parts;
(D) It is possible to omit the preliminary process before the press working and the post process after the press working, and to manufacture at low cost.

  Then, in the present invention, the carbon equivalent Ceq of the steel sheet, and the relationship between the bottom dead center holding time t and the joining start temperature T during the mechanical clinch joining in the joining step after the heating step of heating the steel sheet to a certain degree or more will be described later. It was found that the formulas (1) and (2) should be satisfied. Hereinafter, each step will be described in detail.

[Heating process]
In the present invention, at the time of performing the above-mentioned joining, first, two or more steel plates are heated to an Ac ₃ point or more. By this heating, the later-described joining can be facilitated and a joined part having desired characteristics can be obtained. The heating temperature is preferably (Ac ₃ points + 10) ° C. or higher. If the heating temperature is too high, the microstructure may become coarse, which may cause deterioration of ductility and bendability. Therefore, the upper limit of the heating temperature is preferably (Ac ₃ points + 180) ° C., more preferably Is about (Ac ₃ points + 150) ° C.

The Ac ₃ point can be determined by using the following formula described in “Leslie Steel Materials Science” (Maruzen Co., Ltd., issued May 31, 1985, p. 273). In the following formula, [element] indicates the content of each element in steel in mass%. In the formula below, the elements not included may be calculated as zero.
Ac ₃ transformation point (℃) = 910-203 × [C ] 0.5 -15.2 × [Ni] + 44.7 × [Si] + 104 × [V] + 31.5 × [Mo] + 13.1 × [W] -30x [Mn] -11x [Cr] -20x [Cu] + 700x [P] + 400x [Al] +400 [Ti]

The heating and holding time at the above heating temperature is preferably 1 minute or more. From the viewpoint of suppressing grain growth of austenite and the like, it is preferable that the heating and holding time is 15 minutes or less. The heating rate up to the Ac ₃ transformation point is not particularly limited. Furnace heating, electric current heating, induction heating or the like can be adopted as the heating method.

[Joining process]
In particular, the conditions in this joining process were examined in order to increase the peel strength of the joined portion of the joined component. First, in the present invention, since the cross tensile strength CTS depends on the line length L of the joint portion, CTS / L obtained by dividing CTS by L is taken as the peel strength. This allows the peel strength to be evaluated regardless of the size of the joint. In the embodiment described later, the joint portion is circular, and L corresponds to the circumference of this circle.

  Then, in the present invention, particularly, in order to achieve a component in which the hardness of the component and the peel strength are not less than a certain level, and particularly the peel strength CTS / L is not less than 0.200 kN / mm, the joining conditions were examined. Specifically, as shown in Examples described later, when the components of the steel sheet, the bottom dead center holding time and the joining start temperature were changed to produce a mechanical clinch joined part, the hardness and the peel strength of the above parts were not less than a certain level. It has been found that there are joining conditions that allow parts to be molded without cracking.

Therefore, further studies were conducted to find the above-mentioned joining conditions. First, the peel strength is considered to be influenced by the base metal hardness of the part after hot stamping, and the base metal hardness depends on the hardenability of the steel sheet and the quenching start temperature and the bottom dead center holding time t. Further, since the quenching start temperature corresponds to the joining start temperature T of the present invention, the peel strength CTS / L is first determined by the carbon equivalent Ceq, which is an index of the hardenability of the steel sheet, and the bottom dead center retention. The time t and the joining start temperature T are used to express as in the following equation (4). In the following formula (4), Ceq (mass%) is a value obtained from the following formula (3) defined by JIS G0203, and a, b and c are coefficients.
CTS / L = Ceq × (a × t + b × T + c) (4)
Ceq = C + (1/6) × Mn + (1/24) × Si + (1/40) × Ni + (1/5) × Cr + (1/4) × Mo + (1/14) × V ... (3 )
In the above formula (3), each element represents the content in the steel sheet in mass%, and the elements not included are zero.

The inventors of the present invention, as shown in Examples described later, change the components of the steel sheet, the bottom dead center holding time and the joining start temperature to manufacture mechanical clinch joined parts, and measure the peel strength of the obtained parts. I went. Then, in order to obtain an expression for achieving a peel strength of 0.200 kN / mm or more, the coefficients a, b and c in the above expression (4) are determined by performing multiple regression analysis on the above experimental results, and the following expression ( 1) was obtained.
Ceq × (0.00209 × t + 0.000731 × T−0.0365) ≧ 0.200
... (1)
In the above formula (1), Ceq is the carbon equivalent (mass%) of the steel sheet obtained by the following formula (3), t is the bottom dead center holding time (seconds), and T is the joining start temperature (° C). If the two or more steel plates have different Ceqs, the lowest Ceq is used.
Ceq = C + (1/6) × Mn + (1/24) × Si + (1/40) × Ni + (1/5) × Cr + (1/4) × Mo + (1/14) × V ... (3 )

  By satisfying the above expression (1), it is considered that the ratio d / D between the joint diameter d and the die diameter D of the product can be reduced, and the peel strength can be increased.

Further, in the present invention, it is necessary to satisfy the following formula (2). The following formula (2) is set in view of the fact that the joining start temperature is affected by Ceq among the composition of the steel sheet. This formula (2) is also derived by conducting an experiment in which mechanical clinch bonded parts are manufactured by changing the components of the steel sheet and the bonding start temperature and the peel strength of the resulting parts is measured.
Ceq ≧ −0.00071 × T + 0.993 (2)
In the above formula (2), Ceq represents the carbon equivalent (mass%) of the steel sheet obtained by the above formula (3), and T represents the joining start temperature (° C).

  Two or more steel sheets used for the mechanical clinch joining of the present invention may have different component compositions, that is, Ceq may differ. In such a case, the lowest Ceq is substituted into the above formula (1) or the above formula (2).

  All of the above (A) to (D) can be achieved by performing the bonding under the conditions that satisfy the above formulas (1) and (2). That is, a mechanical clinch bonded component having (A) component strength Hv ≧ 360 and (B) peel strength CTS / L ≧ 0.200 kN / mm can be obtained at low cost without adding a preliminary process or a post-process. .. Further, imparting a shape to a component by mechanical clinch bonding is the same as imparting a shape to a component by pressing, and is considered to contribute to improving the rigidity of the component.

  In the present invention, it suffices that the manufacturing method of the joined component satisfies the above conditions, and other conditions are not particularly limited. The bonding start temperature is preferably 400 ° C. or higher from the viewpoint of suppressing an increase in molding load and a decrease in moldability. Further, a longer bottom dead center retention time is preferable from the viewpoint of improving peel strength, but when importance is attached to productivity or the multi-step described below is carried out, the bottom dead center retention time in one joining is 3 seconds or less. It is preferable that

  In the present invention, hot press molding may also be performed in the step of performing mechanical clinch bonding. The conditions of this hot press molding are not particularly limited, and a commonly used method can be adopted. From the viewpoint of satisfactorily performing hot press forming, it is preferable that the start of press forming, that is, the time when the die reaches the position in contact with the steel plate is about 400 ° C. or higher.

  The method for manufacturing a joined component of the present invention may include the above-described heating step and joining step in this order, and the joining step may be performed only once or twice or more. Further, between the heating of the steel sheet and the end of forming, as a step other than the above-mentioned joining step, for example, a step of working the steel sheet may be included as shown in the first step of the following second embodiment. In the present invention, since it is not necessary to provide a separate process other than the heating-molding process, the bonded component can be manufactured with high productivity and at a low cost.

  As a specific aspect of the manufacturing method of the present invention, when joining is performed simultaneously with hot press forming, for example, the following Embodiment 1 and Embodiment 2 can be mentioned. However, the present invention is not limited to this. In the examples described below, the shape of the clinch portion is a round point bond, but other shapes such as a point bond such as a square or a line bond along the length of the component may be included.

[Embodiment 1: Single step]
For example, it can be molded using the apparatus shown in FIG. More specifically, the heated steel plate 1 and another steel plate 2 corresponding to the reinforcing member are superposed on each other, placed on the support base 3, and then air-cooled to the welding start temperature, and then the press provided inside the welding punch 6 is installed. The punch 11 is lowered to perform press forming and joining. FIG. 1 shows a state where bottom dead center is reached. In the first embodiment, as shown in FIG. 1, the press die 8, the pad 9 and the press punch 11 are used for press forming, and the pad 9 is also joined by the joining die 4 and the joining punch 6 provided therein. ..

[Embodiment 2: Multi-step]
For example, it can be molded as shown in FIG. In FIG. 2, after heating the steel sheet, the first step shown in FIG. 2A, the second step shown in FIG. 2B, and the third step shown in FIG. 2C are continuously performed. Each step will be described. First, in the first step, after the heated steel plate 1 is placed on the support base 3, the excess wire length imparting punch 10 is lowered, and the excess wire length is added to the steel plate 1 forming the outer wall of the component as shown in FIG. Is given. Next, in the second step, another steel plate 2 is placed on the steel plate 1 after the surplus line length is given, and the bonding punch 6 is lowered, and as shown in FIG. The press die 8 is joined to the press die 8 at two places by using the joining die 4 to obtain joint portions 12A and 12B.

  Then, in the third step, which is the final step, joining is performed simultaneously with hot press forming. In detail, the press punch 11 provided inside the joining punch 6 is lowered to perform press forming and joining. FIG.2 (c) has shown the state which reached the bottom dead center. In the third step, as shown in FIG. 2C, the press die 8, the pad 9 and the punch 11 for press are used for press molding, and the die 9 and the punch 6 for bonding provided inside the pad 9 are used. The joined portion 12C is formed by joining. According to this step, the joint portions 12A and 12B can be provided on the vertical wall portion 13 of the component.

  In the case of steel parts for automobiles, for example, the steel plate 1 can be applied as an outer and the other steel plate 2 can be applied as an inner. Although not in the above-described embodiment, the same portion may be joined a plurality of times as shown in Example 2 described later.

  The components of the steel plates used for the joining are not particularly limited. For example, the two or more steel plates may satisfy the following component composition. As the type of steel sheet, a hot-rolled steel sheet, a cold-rolled steel sheet, a galvanized steel sheet such as a galvanized steel sheet obtained by plating these, or an alloyed hot-dip galvanized steel sheet obtained by further alloying treatment may be used. it can. Further, it can be applied not only to join steel plates to each other but also to join dissimilar materials such as steel plates to aluminum (multi-material).

  The following composition is mentioned as a component composition of the steel plate which comprises the component of this invention, ie, a component composition of the steel plate used for joining.

[C: 0.15-0.4%]
In order to easily achieve the hardness Hv of 360 or more, the C content is preferably 0.15% or more. The C content is more preferably 0.17% or more, still more preferably 0.20% or more. On the other hand, considering the weldability of the obtained member, the upper limit of the C content is preferably 0.4% or less, more preferably 0.30% or less, and further preferably 0.26% or less.

[Si: more than 0% and less than 2%]
Si is an element effective for enhancing the hardenability of the steel plate for hot pressing and for stably securing the strength of the hot press formed part. From this viewpoint, it is preferably 0.05% or more, and more preferably 0.15% or more. However, if the Si content is too high, it becomes difficult to soften the steel plate for hot pressing, and the Ac ₃ point remarkably increases, and ferrite remains in the heating stage during hot pressing to obtain high strength. It's hard to be caught. Therefore, the Si amount is preferably 2% or less, more preferably 1.65% or less, and further preferably 1.45% or less.

[At least one of Mn and Cr: 1.0 to 5.0% in total]
Mn and Cr are elements useful for improving the hardenability of the steel sheet and obtaining a high-strength member. These elements may be used alone or in combination of two kinds. From the above viewpoint, it is preferable that at least one of Mn and Cr is contained in a total amount of 1.0% or more, more preferably 1.5% or more in total, and further preferably 1.8% or more in total. It is preferably 2.0% or more in total. However, even if these elements are excessively contained, the effect is saturated, which causes a cost increase. Therefore, in the present invention, the total content of at least one of Mn and Cr is preferably 5.0% or less. It is more preferably 3.5% or less in total, and even more preferably 2.8% or less in total.

  Examples of the component composition include those containing the above components and the balance being iron and inevitable impurities. Examples of the unavoidable impurities include P, S, and N as shown below.

  Since P deteriorates the ductility, the P amount is preferably suppressed to 0.05% or less, more preferably 0.045% or less, and further preferably 0.040% or less. Since it is difficult to set the P content to 0%, the lower limit of the P content is more than 0%.

  Since S also deteriorates the ductility like P, the S amount is preferably suppressed to 0.05% or less, more preferably 0.045% or less, and further preferably 0.040% or less. Since it is difficult to manufacture the S amount to 0%, the lower limit of the S amount is more than 0%.

  By fixing B as BN, N reduces the hardenability improving effect. Further, N forms coarse Ti-containing precipitates such as TiN, and these precipitates act as a starting point of fracture, and reduce the ductility of the steel sheet. Therefore, the N content is preferably 0.01% or less, more preferably 0.008% or less, and further preferably 0.006% or less. Since it is difficult to manufacture the N content at 0%, the lower limit of the N content is more than 0%.

  Further, in addition to the above-mentioned elements, by further containing an appropriate amount of a selective element such as Ti shown below, it is possible to obtain effects such as easily ensuring high strength. When at least one of the following Ti, B, Al, Mo, Cu, Ni, Nb, V, and Zr is included, these elements may be used alone or in combination of two or more. Good. Hereinafter, these elements will be described in detail.

[Ti: 0% to 0.10%]
Ti is an element effective for fixing N as TiN and allowing B to exist in a solid solution state to ensure hardenability. When the effect of Ti is exhibited, the Ti content is preferably more than 0%, more preferably 0.015% or more, still more preferably 0.020% or more. On the other hand, when the amount of Ti is excessive, the strength of the steel sheet to be processed is increased more than necessary, the life of the cutting / punching tool is shortened, and as a result, the cost is increased. Therefore, the Ti amount is preferably 0.10% or less, more preferably 0.06% or less, still more preferably 0.04% or less.

[B: 0% or more and 0.005% or less]
B is an element useful for improving the hardenability of steel materials and achieving high strength even in slow cooling. When the effect of B is exerted, the B content is preferably more than 0%, more preferably 0.0003% or more, still more preferably 0.0015% or more, still more preferably 0.0020% or more. is there. On the other hand, when B is contained excessively, BN is excessively generated and the toughness is deteriorated. Therefore, the B content is preferably 0.005% or less, more preferably 0.0040% or less, and further preferably 0.0035% or less.

[Al: 0% or more and 0.5% or less]
Al is an element used for deoxidation. In order to exert this effect, the amount of Al is preferably more than 0%, more preferably 0.01% or more. On the other hand, when the amount of Al increases, the effect of increasing the Ac ₃ point becomes large, and as a result, it is necessary to raise the heating temperature during hot pressing, resulting in poor production efficiency. Therefore, the Al amount is preferably 0.5% or less, more preferably 0.20% or less, still more preferably 0.10% or less, still more preferably 0.050% or less.

[Mo: 0% to 1%]
Mo is an element effective for improving the hardenability of the steel sheet, and by containing this element, it is expected to reduce the hardness variation in the molded product. When the effect of Mo is exerted, the amount of Mo is preferably more than 0%, more preferably 0.01% or more, still more preferably 0.1% or more. However, when the amount of Mo becomes excessive, the effect is saturated and causes a cost increase. Therefore, the amount of Mo is preferably 1% or less, more preferably 0.8% or less, further preferably 0.5%. % Or less.

[Cu: 0% or more and 0.5% or less]
Cu is an element effective for improving hardenability. It is also an element useful for improving delayed fracture resistance and oxidation resistance of molded products. When the effect of Cu is exerted, the amount of Cu is preferably more than 0%, more preferably 0.01% or more, still more preferably 0.1% or more. However, if the amount of Cu is excessive, it may cause surface defects during the production of steel sheet. As a result, the pickling property is deteriorated and the productivity is deteriorated. Therefore, the Cu content is preferably 0.5% or less, more preferably 0.3% or less.

[Ni: 0% or more and 0.5% or less]
Ni is an element effective for improving hardenability. It is also an element useful for improving delayed fracture resistance and oxidation resistance of molded products. When the effect of Ni is exerted, the amount of Ni is preferably more than 0%, more preferably 0.01% or more, still more preferably 0.1% or more. However, when the amount of Ni becomes excessive, it becomes a cause of generation of surface flaws during the production of steel sheet. As a result, the pickling property is deteriorated and the productivity is deteriorated. Therefore, the Ni content is preferably 0.5% or less, more preferably 0.3% or less.

[Nb: 0% or more and 0.10% or less]
Nb has the effect of refining the structure and is an element that contributes to the improvement of toughness. Therefore, when Nb is contained, the amount of Nb is preferably more than 0%, more preferably 0.005% or more, still more preferably 0.010% or more. On the other hand, when the amount of Nb becomes excessive, the strength of the steel sheet becomes high, and as a result, the tool life in the blanking step of cutting the steel sheet into a predetermined shape before hot press forming is shortened and the cost is increased. Therefore, the Nb content is preferably 0.10% or less, and more preferably 0.05% or less.

[V: 0% or more and 0.10% or less]
V has the effect of refining the structure and is an element that contributes to the improvement of toughness. Therefore, when V is contained, the V content is preferably more than 0%, more preferably 0.005% or more, still more preferably 0.010% or more. On the other hand, when the amount of V becomes excessive, the strength of the steel plate becomes high as in the case of Nb, and as a result, the tool life in the blanking process is shortened and the cost is increased. Therefore, the V amount is preferably 0.10% or less, and more preferably 0.05% or less.

[Zr: 0% or more and 0.10% or less]
Zr is an element that has the effect of refining the structure and contributes to the improvement of toughness. Therefore, when Zr is contained, the Zr content is preferably more than 0%, more preferably 0.005% or more, still more preferably 0.010% or more. On the other hand, when the amount of Zr is excessive, the strength of the steel sheet becomes high as in the case of Nb and V, and as a result, the tool life in the blanking process is shortened and the cost is increased. Therefore, the Zr content is preferably 0.10% or less, more preferably 0.05% or less.

  Further, the method for manufacturing the above steel sheet is not limited. By a usual method, casting, heating, hot rolling, if necessary, cold rolling after pickling, and further if necessary annealing may be performed. Further, the obtained hot-rolled steel sheet or cold-rolled steel sheet can be subjected to a plating treatment such as zinc-containing plating by a usual method, if necessary, and an alloying treatment, if necessary.

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples and can be carried out by making changes within a range compatible with the gist of the preceding and the following. Yes, all of them are included in the technical scope of the present invention.

[Example 1]
For steel plate A and steel plate B satisfying the component composition shown in Table 3, two test pieces each having a size of 150 mm x 50 mm x a plate thickness of 1.4 mm were prepared, and mechanical clinch bonding was performed using the apparatus shown in Fig. 3. .. Specifically, referring to FIG. 3, a steel plate 1 and another steel plate 2 heated at 930 ° C. for 4 minutes are superposed in a cross shape and installed on a bonding punch 6 installed on a bonding punch holder 7 and a bonding die holder 5. After arranging it on the support base 3 between the joined die 4 and the joined die 4, it is air-cooled to the following joining start temperature, and then the joining die 4 is lowered to perform mechanical clinch joining under the following conditions to form a component. Corresponding test materials were obtained.
(Joining condition)
Holder pressure: 3 tonf
Punch diameter: Dp = 10.0 mm
Die diameter: D = 14.0mm
Molding speed: 20 spm
Joining start temperature: Steel plate A as shown in Table 4 and steel plate B as shown in Table 5 Bottom dead center retention time: Steel plate A as shown in Table 4 and steel plate B as shown in Table 5

  The hardness and peel strength of the obtained test material were measured as follows.

(Measurement of hardness of test material)
The Vickers hardness Hv as the hardness of the test material, the site excluding the joint portion, i.e., at the holder portion of the component, a 1/4 position of the sheet thickness of the steel sheets composing the parts, several per sheet steel It was measured under the conditions of a point and a load of 1 kgf. Then , for example, the average value of three points of each steel plate was obtained, and the hardness of the test material was obtained by setting the lowest average value of the plurality of steel plates as the hardness of the component, and evaluated according to the following criteria.
(Hardness evaluation criteria)
⊚: Hv ≧ 450
◯: 450> Hv ≧ 360
×: 360> Hv

(Measurement of peel strength of test material)
The cross tensile strength CTS (kN) of the test material was measured according to JIS Z3137, and this CTS was divided by the peripheral length L (mm) of the joint to obtain the cross tensile strength CTS / L (per unit peripheral length of the joint). kN / mm) was obtained as the peel strength. When the CTS / L was 0.200 kN / mm or more, the peel strength was evaluated as high.

  FIG. 4 is a view showing a cross section of the die used and the obtained joined component. As shown in FIG. 4 (b), the joint diameter d of the joint component is measured, and the value of d / D obtained by dividing the joint diameter d by the die diameter D shown in FIG. 4 (a) is also for reference. I asked. A smaller d / D means stronger bonding, and is preferably 1.029 or less.

  Table 4 shows the results when the steel plate A was used, and Table 5 shows the results when the steel plate B was used.

  First, Table 4 shows the following regarding the case of using the steel plate A. No. 1 to 8 are the mechanical equivalents of the carbon equivalent Ceq of the used steel plate, and the mechanical clinch so that the bottom dead center holding time t and the joining start temperature T during the mechanical clinch joining satisfy the relations of the stipulated formulas (1) and (2). This is an example of joining. In these examples, good joining can be achieved without cracking, the obtained parts have a high hardness Hv, equivalent to or higher than 1180 MPa, and the peel strength CTS / L is equal to or higher than 0.200 kN / mm. It was Especially No. As shown in 4 and 8, when the bottom dead center retention time was 10 seconds, sufficient hardness was obtained. Especially No. As shown in 4, when the joining start temperature was 800 ° C. and the bottom dead center retention time was 10 seconds, a sufficiently high peel strength could be secured.

  On the other hand, No. In No. 9, the joining start temperature did not satisfy the formula (2) and the soft phase was precipitated, so cracking did not occur, but the hardness was low and the peel strength was also low.

  Next, with respect to the case of using the steel plate B, the following can be seen from Table 5. No. Nos. 1 to 12 are mechanical equivalents of the carbon equivalent Ceq of the used steel plate, and the mechanical clinch so that the bottom dead center holding time t and the joining start temperature T during the mechanical clinch joining satisfy the relations of the stipulated formulas (1) and (2). This is an example of joining. In these examples, good joining can be achieved without cracking, the obtained parts have a high hardness Hv, equivalent to or higher than 1180 MPa, and the peel strength CTS / L is equal to or higher than 0.200 kN / mm. It was Especially at 500 ° C. or higher, Hv ≧ 450 and CTS / L ≧ 0.200 kN / mm could be achieved even if the bottom dead center holding was omitted.

  In particular, No. As shown in FIG. 5, when the joining start temperature was 800 ° C. and the bottom dead center holding time was 10 seconds, a sufficiently high peel strength was obtained. This No. 5, the cross section of the component was confirmed as shown in FIG. 5 (a), and as shown in FIG. 5 (b), and further as shown in FIG. 5 (c) in which the elliptical portion of FIG. It can be seen that, at the interface where they contact each other, surface pressure is applied during mechanical clinch to promote mutual diffusion, resulting in diffusion bonding. No. In No. 5, it is considered that a higher peel strength was obtained by this diffusion bonding.

  As shown in Table 5, in the case of using the steel plate B, it is possible to join at 500 to 600 ° C., and the bottom dead center can be shortened or omitted. Therefore, joining can be performed in multiple steps, and joining to the vertical wall portion as shown in FIG. 2 described above is also possible.

  On the other hand, especially at the joining start temperature of 400 ° C. As shown in 13, when the bottom dead center retention was omitted, cracking did not occur, but it was not crimped and joining was not possible. In addition, No. As shown in Nos. 14 and 15, even when the holding time was 2.5 seconds and 5 seconds, Hv ≧ 360 was satisfied, but the peel strength was insufficient.

  In addition, No. As shown in 16, when the joining start temperature was 300 ° C., cracking occurred during joining.

  From FIG. 6 created based on the results of Tables 4 and 5 above, it can be seen that the value on the left side of the above equation (1) and the value of CTS / L are substantially the same.

[Example 2]
In this example, the characteristics when the steel plate B was used to join the same site a plurality of times were evaluated. In detail, it carried out as follows about each example of Table 6.
・ No. 1: Heating to 930 ° C → Air cooling to a joining start temperature of 800 ° C → Mechanical clinch joining → Evaluation of characteristics ・ No. 2: Heating to 930 ° C. → Air cooling to a joining start temperature of 800 ° C. → First mechanical clinch bonding → Second mechanical clinch bonding → Characteristic evaluation / No. 3: Heating to 930 ° C → Air-cooling to a joining start temperature of 800 ° C → 1st mechanical clinch joining → 2nd mechanical clinch joining → 3rd mechanical clinch joining → Characteristic evaluation

  The mechanical clinch bonding was performed under the conditions shown in Table 6 using the device shown in FIG. Further, the characteristics of the obtained test material, that is, hardness, peel strength and d / D were measured in the same manner as in Example 1. The results are shown in Table 6.

  From Table 6, it can be seen that the peeling strength CTS / L is increased by increasing the number of joinings. This is because the bottom dead center retention time was zero by pressing the same part continuously, but the total number of contact times between the steel plate and the tool increased, and the total contact time increased, and d / D decreased. it is conceivable that.

1 Steel Plate 2 Other Steel Plate, Steel Plate for Reinforcement Member 3 Supporting Base 4 Bonding Die 5 Bonding Die Holder 6 Bonding Punch 7 Bonding Punch Holder 8 Pressing Die 9 Pad 10 Excessive Line Length Giving Punch 11 Pressing Punch 12A , 12B, 12C Joint part 13 Vertical wall part

Claims (4)

A method for producing a mechanical clinch-bonded component comprising two or more steel plates, having at least one joint having a peel strength of 0.200 kN / mm or more, and having a hardness of Hv360 or more ,
Heating two or more steel plates to an Ac ₃ point or higher; and
A step of performing mechanical clinch joining so that the carbon equivalent Ceq of the steel sheet, the bottom dead center holding time t during mechanical clinch joining, and the joining start temperature T satisfy the following equations (1) and (2);
A method for manufacturing a mechanical clinch joint part, which comprises:
Ceq × (0.00209 × t + 0.000731 × T−0.0365) ≧ 0.200
... (1)
Ceq ≧ −0.00071 × T + 0.993 (2)
In the above formulas (1) and (2), Ceq is the carbon equivalent (mass%) of the steel plate obtained by the following formula (3), t is the bottom dead center holding time (seconds), and T is the joining start temperature (° C). ) Is shown. If the two or more steel plates have different Ceqs, the lowest Ceq is used.
Ceq = C + (1/6) × Mn + (1/24) × Si + (1/40) × Ni + (1/5) × Cr + (1/4) × Mo + (1/14) × V ... (3 )
In the above formula (3), each element represents the content in the steel sheet in mass%, and the elements not included are zero. The composition of each of the two or more steel plates is% by mass,
C: 0.15-0.4%,
Si: more than 0% and 2% or less, and
At least one of Mn and Cr: 1.0-5.0% in total, and
Ti: 0% to 0.10%, B: 0% to 0.005%, Al: 0% to 0.5%, Mo: 0% to 1%, Cu: 0% to 0.5 % Or less, Ni: 0% or more and 0.5% or less, Nb: 0% or more and 0.10% or less, V: 0% or more and 0.10% or less, and Zr: 0% or more and 0.10% or less. Item 2. A method for manufacturing a mechanical clinch joint component according to Item 1 . The method for producing a mechanical clinch-bonded component according to claim 1 or 2 , wherein hot press molding is also performed in the step of performing the mechanical clinch bonding. Method for manufacturing a mechanical clinch joint component according to any of the mechanical clinch joining claims 1 to 3, step a plurality of times to perform.