JP2019181523A - Tailored blank material and manufacturing method thereof - Google Patents

Abstract

To provide a tailored blank material for not locally abrading a metal mold even when cutting by using the metal mold in punching processing.SOLUTION: A tailored blank material possesses at least one place being an area of 1.5 mm or more along a welding line and 0.75 mm or more in the vertical direction to the welding line of including the welding line of a steel plate and the other steel plate being 980 MPa or more in tensile strength of at least one-sheet steel plate and 980 MPa or more in tensile strength and a softening area lower by 15% or more as compared with Vickers hardness of the other welding line in Vickers hardness by including the steel plate of butt-welding at least two sheets.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a tailored blank material and a manufacturing method thereof.

  The tailored blank method is used as a method for realizing weight reduction and high functionality of automobile parts. The tailored blank method is a blank material made by welding multiple materials (for example, steel plates) with different required material strengths and thicknesses. After cutting off the excess portion of the blank material welded in the punching process, it is molded with a press. Thus, this is a technique for producing a member having a portion having a different thickness or strength in one member. In the punching step, the tailored blank material 11 is cut along the cutting line 12 as illustrated in FIG. 1 using a mold to obtain a desired shape.

  Tailored blanks can change the thickness and strength of a single component by connecting dissimilar steel plates, so that the weight of the component can be reduced and its functionality can be increased. There is an advantage that an expensive mold can be reduced with respect to the added method.

  Patent Document 1 discloses a method of manufacturing a tailored blank material by butt welding using laser welding.

Japanese Patent Laid-Open No. 2005-21968 JP 2012-148345 A

  The weld line of the tailored blank material is harder than the base metal part due to rapid solidification during welding. Therefore, when the tailored blank material 11 is cut by punching, the welding line cutting position of the die that cuts the position where the cutting line 12 and the welding line 13 intersect is preferentially worn. This is particularly noticeable when at least one of the tailored blank materials is ultra high tensile steel (a steel plate having a tensile strength of 980 MPa or more).

  Therefore, heat treatment was applied to the welded part, and a study to improve the characteristics was started. Some similar examination examples have been disclosed so far.

  In Patent Document 2, the second welding is performed in the vicinity of the first welded portion approximately in parallel with the first welded portion, and the second welded portion is formed at the time of molding more than the first welded portion. A method is disclosed in which the first weld is tempered away from the location subject to deformation.

  However, in the method disclosed in Patent Document 2, since the second welded portion remains hard, it is effective in parts where the second welded portion is far from the place where the second welded portion is deformed. It has no effect on the wear of molds.

  This invention solves said subject and makes it a subject to provide the tailored blank material which does not produce preferential wear to a metal mold | die even if it cut | disconnects using a metal mold | die by a punching process.

  The present inventors diligently studied a method for preventing the welding line cutting position from being preferentially worn in the mold. As a result of examination, in tailored blank materials, it is possible to prevent preferential wear of the mold by lowering the hardness of the position cut by punching on the weld line compared to other positions on the weld line. I found it.

  The present invention has been made on the basis of the above findings, and the summary thereof is as follows.

  (1) Along with a weld line of a steel plate including at least two butt-welded steel plates, wherein at least one of the steel plates has a tensile strength of 980 MPa or more and a tensile strength of 980 MPa or more and other steel plates. 5 mm or more, 0.75 mm or more in the direction perpendicular to the weld line, including the weld line, Vickers hardness is 15% or more lower than Vickers hardness at other positions of the weld line A tailored blank material having at least one region.

  (2) At least one of the steel plates having a tensile strength of 980 MPa or more, but joining two steel plates, laser welding to form a weld line, 1.5 mm or more along the weld line including the weld line, The manufacturing method of the tailored blank material characterized by including the process of heat-processing the area | region more than 0.75 mm in a perpendicular direction.

  (3) The method for manufacturing a tailored blank material according to (2), wherein the heat treatment is performed by a laser.

  (4) The method for manufacturing a tailored blank material according to (2) or (3), wherein the heat treatment is performed by heating the region to 500 to 850 ° C.

  According to the present invention, in the tailored blank material, since the hardness of the weld line in the vicinity of the cutting line scheduled to be cut by punching is reduced, when cutting the tailored blank material, the welding line cutting position of the mold is There is no wear preferentially, the frequency of mold replacement is reduced, and the cost can be reduced.

It is a figure which shows the outline of a tailored blank material, a cutting line, and a welding line. It is a figure which shows the other outline of a tailored blank material, a cutting line, and a welding line, (a), (b) is an example in which a welding line is not linear shape, (c) is an example using three steel plates. It is a figure explaining the measurement position of Vickers hardness. It is a figure which shows the outline of the tailored blank material in an Example, a cutting line, a welding line, and the heat processing position.

  First, the tailored blank material of the present invention will be described.

  In the manufacture of parts using the tailored blank method, a tailored blank material prepared by joining a plurality of steel plates by butt welding to form a weld line is processed by press forming, thereby completing the part. Since the tailored blank material is punched during the press working, the portion where the steel plate is butt welded is also cut. Since the weld line of the tailored blank material is harder than the base metal part, the weld line cutting position of the mold is worn preferentially.

  The tailored blank material of the present invention includes at least two steel plates, and the tensile strength of at least one steel plate is 980 MPa or more. And it has the softening area | region where hardness is low compared with another area | region in the weld line formed between the steel plate of the tensile strength 980 Mpa or more, and another steel plate. Specifically, it is an area of 1.5 mm or more along the weld line and 0.75 mm or more in the direction perpendicular to the weld line, and the Vickers hardness is different from other positions different from the softened area of the weld line. And at least one softened region having a Vickers hardness of 15% or more.

  In general, a linear shape is often used as the shape of the weld line, but there is no problem with a shape obtained by combining two or more straight lines or a curved shape. Further, the number of steel plates included in the tailored blank material is not limited to two, and may be three or more (FIG. 2).

  In addition, the Vickers hardness in this invention is the value which averaged the Vickers hardness measured by the load of 200gf in the position of 1/4, 2/4, 3/4 of plate | board thickness from the steel plate surface in the vertical cross section containing a weld line. (Fig. 3).

  When cutting a tailored blank material by punching, if the position where the cutting line and the welding line intersect is a softened region, the load on the mold is reduced, so the welding line cutting position of the mold is It will not wear preferentially. In order to prevent preferential wear at the welding line cutting position of the mold, it is preferable that all the positions where the cutting line and the welding line intersect are in the softened region.

  If the size of the softened region is 1.5 mm or more along the weld line and 0.75 mm or more in the direction perpendicular to the weld line, the load on the mold is reduced by softening the area cut by punching. An effect is obtained. The range of the softened region may be widened in consideration of the effect of heat treatment and the shift of the cutting position. It is preferably 4.0 mm or more along the weld line and 2.0 mm or more in the direction perpendicular to the weld line. An upper limit is not particularly provided, but if the region becomes too wide, the strength of the tailored blank material itself decreases and the cost of the process for obtaining the softened region increases, so 20 mm × 20 mm or less is preferable. The shape of the softened region is not limited to a rectangle, and may be an elliptical shape, for example.

  By having the softening region as described above, the position where the weld line is cut in the die during the punching process is the softening region, thereby preventing preferential wear of the die, The number of usable times can be increased, and an effect of avoiding delayed cracking that occurs on the cut end face can be expected as compared to the case where the cut is performed on another weld line.

  Next, the manufacturing method of the tailored blank material of this invention is demonstrated.

  The tailored blank material of the present invention is obtained by heat-treating a part of the weld line between a steel plate having a tensile strength of 980 MPa or more and another steel plate constituting the tailored blank material. More specifically, a softened region with low Vickers hardness can be provided by heat-treating a region of 1.5 mm or more along the weld line and 0.75 mm or more in a direction perpendicular to the weld line.

For the heat treatment, for example, a laser can be used. The type of laser is not particularly limited, and a YAG laser, a CO ₂ laser, a fiber laser, a semiconductor laser, or the like can be used. The output of the laser is not particularly limited as long as the welding line can be heated, but can be, for example, 1.0 to 5.0 kW.

  In order to uniformly and efficiently heat the region along the weld line, it is preferable to use a rectangular laser beam having a uniform intensity. In order to obtain a rectangular beam, a laser oscillator that can emit a beam from a rectangular core fiber may be used, or the laser beam emitted from the laser oscillator may be rectangularized using a cylinder lens, a kaleidoscope, or the like. . In addition, a semiconductor laser that oscillates directly in a rectangular shape without using a transmission fiber may be used. When the beam is rectangularized using a cylinder lens, a kaleidoscope, or the like, the optical path may be divided between welding and heating with a mirror or the like using the same laser oscillator used for welding.

  The heat source is not limited to the laser because it is sufficient to heat and cool the front and back surfaces of the weld line. A method of using an arc, contacting a tool for friction stir welding from both sides, or contacting a heated metal may be used.

  The heat treatment is preferably performed so that the region of 1.5 mm or more along the weld line and 0.75 mm or more in the direction perpendicular to the weld line is 500 to 850 ° C. The heating temperature can be measured with a radiation thermometer.

  The size of the region subjected to the heat treatment may be widened in consideration of the effect of the heat treatment and the shift of the heating position. It is preferably 4.0 mm or more along the weld line and 2.0 mm or more in the direction perpendicular to the weld line. An upper limit is not particularly provided, but if the region to be heat-treated becomes too wide, the strength of the tailored blank material itself is lowered and the cost of heat treatment is increased, so 20 mm × 20 mm or less is preferable. The shape of the region to be heat-treated is not limited to a rectangle, but may be an elliptical shape, for example.

  The tailored blank material thus obtained is punched so that the heat-treated region becomes a cutting line, and then press-molded to reduce the load on the die used for punching. Thus, a press-molded product can be manufactured.

  Normally, in tailored blank construction, a large amount of the same type of tailored blank material is prepared and punched out with the same mold to mass-produce parts. Once the cutting position can be specified, other tailored blanks can be specified. It is easy to heat treat the same location of the material and provide a softened area.

  Two types of steel plates cut into 200 mm × 100 mm shown in Table 1 were welded using a laser with a wavelength of 1064 nm that had their long sides (200 mm) butted together and focused to φ0.6 mm to produce a tailored blank material. (FIG. 4). The butt welding conditions were a laser output of 3.5 kW and a welding speed of 5.5 m / min.

  The tailored blank material produced in this manner was subjected to laser treatment with a rectangular laser beam having a wavelength of 940 nm on the heat treatment region 14 near the intersection of the cutting line 12 and the welding line 13 of the tailored blank material 11 under the conditions described in Table 1. Heat treatment was performed with an output of 1.3 kW.

  Table 1 shows the Vickers hardness of the tailored blank material before and after heat treatment. The Vickers hardness in Table 1 is ¼, 2/4 of the plate thickness from the steel sheet surface in a vertical section including the weld line (the hardness after the heat treatment is the weld line in the heat-treated region), It is a value obtained by averaging Vickers hardness measured at a load of 200 gf at a position of 3/4.

  This tailored blank was punched with a mold and cut with a cutting line 12 so that the portion where the weld line was cut was the heat treatment region 14, and the number of times until the mold had to be replaced was examined. The results are shown in Table 1.

  In the tailored blank material manufactured using the method of the present invention, the number of times of cutting until the mold change increased compared to the tailored blank material that was not subjected to heat treatment. No. 2 in which heat treatment was performed within a preferable range. 2, no. No. 4 showed that the number of cuts until the mold replacement was greatly increased, and that the present invention was effective in preventing local wear of the mold.

11 Tailored Blank Material 12 Cutting Line 13 Welding Line 14 Heat Treatment Area

Claims (4)

Including at least two butt welded steel plates,
The tensile strength of at least one of the steel plates is 980 MPa or more,
Vickers hardness is an area including the weld line of 1.5 mm or more along a weld line of a steel sheet having a tensile strength of 980 MPa or more and another steel sheet and 0.75 mm or more in a direction perpendicular to the weld line. Has at least one softened region which is 15% or more lower than the Vickers hardness at other positions of the weld line. A process of forming a weld line by laser welding the two steel plates having a tensile strength of at least 980 MPa at least one of the steel plates;
A method for producing a tailored blank material, comprising a step of heat-treating a region of 1.5 mm or more along the weld line including the weld line and a region of 0.75 mm or more in a direction perpendicular to the weld line.   The method for manufacturing a tailored blank material according to claim 2, wherein the heat treatment is performed by a laser.   The said heat processing heats the said area | region to 500-850 degreeC, The manufacturing method of the tailored blank material of Claim 2 or 3 characterized by the above-mentioned.

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