JP2012206165A - Method and equipment line for producing press-formed steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress generation of scales by increasing a sealing degree of a heating device to maintain an inert gas atmosphere inside the heating device.SOLUTION: The method for producing a press-formed steel plate includes processes of: rewinding a steel plate coil; and performing press forming on a carrier line of a rewound steel plate. In the method for the press-formed steel plate, a process of heating the rewound steel plate under the inert gas atmosphere is performed.

Description

  The present invention relates to a method of manufacturing a press-formed steel sheet, which is heated to a predetermined temperature and then press-formed into a predetermined shape, and a manufacturing equipment row thereof.

  2. Description of the Related Art Conventionally, members used in automobiles and the like are manufactured by press forming a steel plate having a predetermined strength. In recent years, high-strength steel sheets have been increasingly used as structural members of automobile bodies in order to achieve both weight reduction and collision safety performance of automobiles. On the other hand, when the strength of the steel plate is increased, the workability deteriorates and it tends to be difficult to process into a predetermined part shape. In particular, when high-strength steel sheets are cold-formed, spring backs that are elastically deformed and lose their shape are easily generated when the product is removed from the press mold, and it is difficult to improve dimensional accuracy.

  Focusing on this point, a press molding method as disclosed in Patent Document 1 is disclosed. In the method of Patent Document 1, a metal plate is punched from a metal roll material by a punching press, the metal plate is heated to a temperature of 850 ° C. or higher and lower than the melting point, and immediately after the heating, the metal plate is conveyed to a forming press. A metal plate kept at a high temperature of ℃ or higher is pressed using a normal temperature press die to give a desired shape. This method is generally called hot pressing or die quenching, which is a method in which a steel sheet whose formability is improved by heating is pressed and strength is given by quenching by contact with a press die.

  However, in this hot press, scale is generated on the surface of the steel sheet when the steel sheet is heated. If scale exists, the weldability and surface properties of the steel sheet deteriorate, so to prevent this, it is necessary to remove the scale generated during heating after press forming. The scale is removed by shot blasting, but it is difficult to completely remove the complicated part shape. Moreover, in a steel plate having a plate thickness of 2 mm or less, deformation of a molded part is likely to occur due to shot blasting, which is a technical problem. Patent Document 1 describes that the inside of the heating apparatus is set to an inert gas atmosphere, but since a general-purpose electric furnace is used, it is not possible to completely prevent oxidation of the atmosphere during heating when the steel sheet is loaded and unloaded. .

  Further, in Patent Document 2, for a hot-rolled steel sheet having a specific chemical composition, the scale is removed by shot blasting after die quenching by reducing the thickness of the scale generated during die quenching to 8 μm or less. A technology that can be easily performed and that does not deform parts during shot blasting is disclosed.

JP 2002-102980 A JP 2008-214650 A

However, in the methods of Patent Documents 1 and 2, since heating is performed using a general-purpose heating device, it is necessary to open the heating device when the metal plate is taken in and out of the heating device, and oxygen is contained in the heating device. It is difficult to maintain a sufficient inert gas atmosphere. In particular, in the technique of Patent Document 1, the scale generated on the surface of the steel plate being heated becomes thick, causing problems in the surface properties and dimensional accuracy of the press-formed product.
An object of this invention is to maintain the inert gas atmosphere in a heating apparatus by suppressing the sealing degree of a heating apparatus, and to suppress the production | generation of a scale.

  As a result of diligent research, the inventors of the present invention have increased the sealing degree of the heating device in a method in which the coil that has been sequentially rewound from the coil is directly passed through the heating device and heated, and then pressed and cut. The inventors have found a method for suppressing the generation of scale during heating by maintaining an inert gas atmosphere in the heating apparatus, and have completed the following present invention.

(1) A method for producing a press-formed steel sheet, comprising a step of rewinding a steel sheet coil and a step of press-forming on a rewinding steel sheet conveying line,
A method for producing a press-formed steel sheet, comprising performing a step of heating the unrolled steel sheet in an inert gas atmosphere before performing the press-forming process.

  (2) The method for producing a press-formed steel sheet according to (1), further comprising the step of cooling the press-formed steel sheet after performing the process of press-forming the steel sheet.

  (3) Further, after the step of rewinding the coil of the steel plate, the step of cutting the steel plate, the step of joining the cut steel plate, and the sheet passing speed of the steel plate are adjusted with a looper device. The method for producing a press-formed steel sheet according to (1) or (2), wherein the steps are performed in this order.

  (4) Further, following the step of heating the steel plate in an inert gas atmosphere, a step of cutting the heated steel plate is performed. The press-formed steel plate according to (1) or (2) Production method.

  (5) A press-formed steel plate manufacturing facility line arranged on a downstream conveying line of a coil unwinding device for a steel plate, the device for heating the steel plate having an inert gas supply device, and a press-forming device, A press-formed steel plate manufacturing equipment line, comprising a formed product cutting device in this order, wherein the heating device has pinch rollers arranged on the entry side and the exit side, respectively.

  (6) The press-formed steel sheet according to (5), further comprising a device for cooling the formed product after pressing on the downstream side of the press-forming device and upstream of the cutting device for the formed product. Manufacturing equipment column.

  (7) On the downstream side of the rewinding device, on the upstream side of the heating device, the steel plate cutting device, a joining device for the cut steel plate, and a looper device for passing the joined steel plate. (5) or (6), the press forming equipment row of steel sheets according to (5) or (6), which is provided in this order.

  (8) The apparatus has the steel plate cutting device and the steel plate transfer device in this order downstream of the heating device and upstream of the press forming device (5) or (6) A manufacturing equipment column for press-formed steel sheets according to 1.

  According to the present invention, the inside of the heating device is maintained in an inert gas atmosphere, and the generation of oxide scale on the surface of the steel sheet during heating and loading / unloading is suppressed, so that a press-formed product having excellent weldability and surface properties can be obtained. Can be manufactured. Moreover, since the airtightness in a heating apparatus is maintained, the improvement of heating efficiency and the improvement of productivity by continuation can also be achieved.

It is the schematic which shows the equipment row | line before and behind the press molding apparatus which is one embodiment of this invention. It is a schematic side view which shows the heating furnace used for the press molding apparatus which is one embodiment of this invention. It is a schematic side view which shows the example which applied the pinch roller to the press molding apparatus which is one embodiment of this invention. It is a schematic top view which shows the example which applied the pinch roller to the press molding apparatus. It is an AA arrow figure which shows the example which applied the pinch roller to the press molding apparatus. It is a schematic side view which shows the press molding apparatus of 2nd Embodiment which is one embodiment of this invention. It is a schematic side view which shows the press molding equipment row | line | column of one Embodiment of this invention. It is a schematic side view which shows the press molding apparatus of a prior art. It is a schematic side view which shows the press molding equipment row | line | column of one Embodiment of this invention.

The form for implementing this invention is demonstrated below.
First, the present invention will be described with reference to FIG. 1 showing an equipment row before and after the press molding apparatus of the present invention and FIG. 2 which is a schematic diagram of a heating apparatus 4.

  As shown in FIG. 1, the coil of the steel plate 1 used as a blank is rewound by the rewinding device 3, and is sequentially inserted into the heating device 4 from the tip on the rewinding steel sheet conveying line, and the steel plate 1 is continuously formed. Heat to a predetermined temperature in an inert gas atmosphere. The steel plate 1 exiting the heating device 4 is press-formed while maintaining a high temperature by the press-forming device 5 on the transport line, sent to the molded product cutting device 7b, and cut into individual molded products 2 at predetermined locations. , Sent to the next process.

  As shown in FIG. 2, the heating device 4 of the present invention has an inert gas supply device 9, includes a pinch roller 8 at the inlet and outlet of the steel plate 1, and has a structure in which outside air does not enter the heating device 4 as much as possible. It has become. The steel plate 1 is continuously conveyed by the pinch roller 8 and the conveyance roller 10 and heated to a predetermined temperature. The inside of the heating device 4 is maintained at a positive pressure in an inert atmosphere such as nitrogen gas, and the entrainment of the external air during the loading and unloading of the steel plate 1 can be prevented, and scale formation on the surface of the steel plate 1 is suppressed. As for the heating method, any type such as an electric furnace, current heating, induction heating, radiant tube, etc. can be used as long as it does not generate an oxidizing gas such as an open flame burner in the heating device 4. . Although heating temperature changes with steel plate materials used as object, the range of 900-1060 degreeC is preferable.

  In addition, by keeping the inert gas pressure in the heating device 4 at or above the ambient atmospheric pressure, it is possible to further suppress the penetration of ambient air into the heating device 4. In addition, a ventilator or an oxygen sensor may be installed around the heating device 4 to appropriately require technical technical means for safety from protecting the worker from lack of oxygen.

  Between the outlet of the heating device 4 and the press molding device 5, it can be covered as much as possible with a heat retaining cover or the like (not shown) in order to avoid a temperature drop.

  Although it is possible to apply a normal cold press device as the press molding device 5, a structure in which the inside of the press mold is water-cooled is used in order to perform the press in a hot state where the steel plate is heated. In addition, a cooling device 6 may be additionally provided to quench the press-formed product 2. FIG. 9 shows a schematic side view of the apparatus of the present invention in which the press molding apparatus 5 and the cooling apparatus 6 are provided.

  The press-formed steel sheet 1 after the press forming is transferred using a transfer means such as a transfer table on the transfer line. In order to apply a traction force, a pinch roller 8 can be used as appropriate (FIG. 4). When the pinch roller 8 is used, the pinch roller 8 is in contact with only the die face portion 12 while avoiding the molding portion. Details of the application of the pinch roller 8 after molding are shown in FIGS. In the case where the pinch roller 8 and the transport roller 10 are installed between the heating device 4 and the press molding device 5, in order to minimize heat removal due to contact with the roller before press molding, as shown in FIGS. As in the pinch roller 8, it is preferable that only the portion corresponding to the die face of the coil is in contact with the roller.

  In the method of the present invention, it is necessary to let the tip of one coil of steel plate pass through the apparatus before starting operation. Since it takes time to pass the plate, it is desirable to reduce the plate passing work as much as possible. Therefore, as shown in FIG. 6, the inventors installed a plurality of rewinding devices 3, and joined a plurality of steel plate coils by joining the rear end of the preceding steel plate coil and the front end of the subsequent steel plate coil. A method for continuous operation was devised. After the leading end of the preceding steel plate 1 coil and the defective shape portion of the steel plate 1 called the tongue or fishtail at the leading end of the following steel plate coil are cut with the steel plate cutting device 7a, and the shape of the end is adjusted, The joining device 14 joins the rear end of the preceding steel plate coil and the front end of the subsequent steel plate coil.

  For example, shear cutting can be used as the cutting method, and various welding methods can be used as the joining method. In order to ensure the time for cutting and joining the front and rear ends of the steel sheet coil, it is preferable to provide a looper device 13 (hereinafter also simply referred to as “looper”) in the vicinity of the steel sheet cutting device 7 a and the joining device 14. Prior to cutting / joining, a part of the steel plate is stored in the looper 13, and during the cutting / joining operation, the steel plate is discharged from the looper 13 so that the operation can be continued without stopping the processes after heating. it can. By using the looper 13, it is possible to cope with temporary interruptions due to troubles without stopping the operation. Therefore, the looper 13 can be attached to a facility having only one rewinding device 3 as shown in FIG. 1. Installation is technically significant.

  In the embodiment of FIG. 1, the press-formed steel sheet is sent to a molded product cutting device 7 b and cut into a press-formed product 2 at a predetermined location. As a cutting method, various cutting means such as shear cutting and laser cutting can be used. In the case of high-tensile steel whose tensile strength becomes 1500 MPa by quenching during press molding, cutting is performed by shear cutting. However, it is preferable to employ laser cutting because the working efficiency is excellent.

  On the other hand, the arrangement of the steel plate cutting device 7a may be between the heating device 4 and the press forming device 5 as shown in FIG. In this case, since the steel plate to be cut is immediately after heating, it is soft and has an advantage that it can be easily cut with a shear. The cut plate after cutting is mounted on the press molding device 5 by a transfer device 15 such as a robot and press-molded. When the installation distance between the steel plate cutting device 7a and the press forming device 5 is large, it is predicted that the steel plate 1 falls below a predetermined temperature before press forming, and the space between the steel plate cutting device 7a and the press forming device 5 is predicted. And a temperature measuring means (not shown) and an auxiliary heating device (not shown), and when the temperature measured by the temperature measuring means is lower than a predetermined temperature, the auxiliary heating device is operated to a required temperature. It is desirable to raise the temperature. As the temperature measuring means, a non-contact method such as a radiation thermometer is preferable in order to avoid a temperature drop, and as the auxiliary heating means, an electric heating method or an induction heating method capable of rapid heating is preferable.

  As described above, according to the press forming method and the press forming apparatus 5 according to the present invention described above, the inside of the heating apparatus 4 is maintained in an inert gas atmosphere, and generation of oxide scale on the surface of the steel sheet 1 during heating is suppressed. And a press-formed product 2 having excellent surface properties can be produced. Further, as a secondary effect, since the hermeticity in the heating device 4 is maintained, improvement in heating efficiency and improvement in productivity due to continuation can be expected.

  In addition, this invention is not necessarily applicable only to a steel plate, It can apply to arbitrary metal plates and metal alloy plates, such as aluminum and an aluminum alloy.

  In addition, the atmosphere in the heating device 4 is not limited to the inert gas atmosphere, and the oxide film can be more actively removed as a reducing atmosphere. Examples of the inert gas include a mixed gas of nitrogen and argon. Examples of the reducing atmosphere gas include a mixed gas of hydrogen and an inert gas.

  Cooling the steel sheet after press forming is preferable for preventing the generation of oxide on the steel sheet surface. As a cooling method, for example, nitrogen gas is rapidly blown from a nozzle.

After heating the steel sheet at 950 ° C. to form austenite, press forming was started at a temperature of Ar ₃ temperature or higher, and quenching was performed by heat removal from the contact with the press mold to completely martensite. High tensile strength of 1480 MPa class A simulated tensile steel center pillar was experimentally produced using a pilot plant.

  An outline of a pilot plant according to the prior art is shown in FIG. A hot coil having a thickness of 1.2 mm and a width of 900 mm pickled after hot rolling was rewound and cut to a length of 600 mm to obtain a blank. Using the transfer device 15 (robot) provided on the inlet side of the heating device 4 one by one, the blanks stored in the temporary storage place 16 are inserted into the inlet side of the heating device 4 (opening width 1200 mm, high And is inserted into the heating device 4. The heating device 4 is an electric furnace, and nitrogen is supplied from a nitrogen supply device in order to keep the inside in a nitrogen atmosphere. After setting the temperature of the heating device 4 to 950 ° C. and heating the blank for 3 minutes, the transfer device 15 (robot) provided on the outlet side of the heating device 4 causes a carry-out port on the outlet side of the heating device 4 (width of the opening 1200 mm, (Height 300 mm) was opened, the heated blank was taken out, set in the press molding apparatus 5 and press molded.

  In the test operation by the pilot plant based on the prior art, the defect rate due to the shape defect caused by shot blasting and the surface defect considered to be caused by the remaining scale reached about 5%. Note that after the press-formed product 2 was cooled to room temperature, a sample for cross-sectional observation was taken from the die face part 12, the cut surface was observed with an SEM, and the generated scale thickness was measured. The average scale thickness was about 10 μm. Met.

  On the other hand, the outline of the pilot plant according to the present invention is shown in FIG. The heating device 4 is an electric furnace, and nitrogen is supplied from a nitrogen supply device in order to keep the inside in a nitrogen atmosphere. As shown in FIG. 2, the inlet and outlet of the heating device 4 have a structure in which the hot coil is sandwiched between two rollers, and the structure prevents the air from entering and keeps the nitrogen atmosphere in the heating device 4. . A hot coil having a thickness of 1.2 mm and a width of 900, pickled after hot rolling, is loaded into the rewinding device 3, and the leading end of the hot coil is passed through the heating device 4 and the press molding device 5, and the exit side of the press molding device 5. The pinch roller 8 was bitten and the test operation was started. The press-molded portion of the hot coil was sent to the molded product cutting device 7b on the conveyance table, and sheared to obtain a molded product 2.

  In the operation based on the present invention, the defective rate due to the shape defect caused by shot blasting and the surface defect considered to be caused by the remaining scale was about 2% or less, and good results were obtained. Note that after the press-formed product 2 was cooled to room temperature, a sample for cross-sectional observation was taken from the die face portion 12, the cut surface was observed with an SEM, and the generated scale thickness was measured. The average scale thickness was about 7 μm. Met.

  Compared to the results of the pilot plant test operation according to the prior art and the pilot plant test operation according to the present invention described above, the present invention suppresses the generation of scale on the surface of the steel sheet and improves the surface properties and shape accuracy of the press-formed product. It is clear that this was done.

INDUSTRIAL APPLICABILITY The present invention can be used for press forming of a steel plate, particularly a high-tensile steel plate, and can produce a press-formed product having excellent surface properties.

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Press molded product 3 Rewinding device 4 Heating device 5 Press molding device 6 Cooling device 7a Steel plate cutting device 7b Molded product cutting device 8 Pinch roller 9 Inert gas supply device 10 Conveying roller 11 Press molding unit 12 Die face unit 13 Looper 14 Joiner 15 Transfer device 16 Temporary storage location

Claims (8)

A method for producing a press-formed steel sheet, comprising a step of rewinding a steel sheet coil and a step of press-forming on a rewinding steel sheet conveying line,
A method for producing a press-formed steel sheet, comprising performing a step of heating the unrolled steel sheet in an inert gas atmosphere before performing the press-forming process.   The method for manufacturing a press-formed steel sheet according to claim 1, further comprising a step of cooling the press-formed steel sheet after performing the process of press-forming the steel sheet.   Furthermore, after performing the step of rewinding the coil of the steel plate, the step of cutting the steel plate, the step of joining the cut steel plate, and the step of adjusting the sheet passing speed of the steel plate with a looper device The method for producing a press-formed steel sheet according to claim 1 or 2, wherein the method is performed in this order.   Furthermore, following the process of heating the said steel plate in inert gas atmosphere, the process of cut | disconnecting the said heated steel plate is performed, The manufacturing method of the press-formed steel plate of Claim 1 or 2 characterized by the above-mentioned.   A manufacturing equipment row of press-formed steel plates arranged on a downstream conveying line of a coil rewinding device for steel plates, a device for heating the steel plates having an inert gas supply device, a press-forming device, and a molded product The apparatus for manufacturing press-formed steel sheets is characterized in that a cutting device is provided in this order, and the heating device is provided with pinch rollers on the entry side and the exit side, respectively.   The apparatus for manufacturing a press-formed steel sheet according to claim 5, further comprising a device for cooling the formed product after pressing on the downstream side of the press-forming device and upstream of the cutting device for the formed product. .   The steel plate cutting device, the cut steel plate joining device, and the looper device for passing the joined steel plates are provided in this order on the downstream side of the rewinding device and upstream of the heating device. The press forming equipment row | line | column of the steel plate of Claim 5 or 6 characterized by the above-mentioned.   The press forming according to claim 5 or 6, wherein the steel plate cutting device and the steel plate transfer device are provided in this order on the downstream side of the heating device and on the upstream side of the press forming device. Steel plate manufacturing equipment line.

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